GIÁO TRÌNH TIẾNG ANH TRONG KỸ THUẬT HÓA HỌC PGS.TS. BÙI THỊ LỆ THỦY - 2019

TIẾNG ANH TRONG KỸ THUẬT HÓA HỌC

Ths Nguyễn Thanh Tú eBook Collection

GIÁO TRÌNH TIẾNG ANH TRONG KỸ THUẬT HÓA HỌC PGS.TS. BÙI THỊ LỆ THỦY - 2019 WORD VERSION | 2021 EDITION ORDER NOW / CHUYỂN GIAO QUA EMAIL TAILIEUCHUANTHAMKHAO@GMAIL.COM

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PGS.TS. BÙI THỊ LỆ THỦY

GIÁO TRÌNH

TIẾNG ANH TRONG KỸ THUẬT HÓA HỌC

NHÀ XUẤT BẢN GIAO THÔNG VẬN TẢI HÀ NỘI - 2019

CONTENTS LỜI NÓI ĐẦU ................................................................................................................ 1 PART 1 THE BASIC UNITS......................................................................................... 6 I.1 TYPICAL UNITS............................................................................................. 7 UNIT 1 SOME CONCEPTS IN CHEMISTRY ........................................................ 7 UNIT 2 HYDROCARBONS ................................................................................... 10 UNIT 3 CHEMICAL KINETIC AND CATALYSIS.............................................. 14 UNIT 4 ANALYTICAL CHEMISTRY .................................................................. 16 UNIT 5 CHEMICAL THERMODYNAMICS ........................................................ 19 UNIT 6 EMULSIONS ............................................................................................. 23 UNIT 7 PLASTICS IN THE CHEMICAL AGE..................................................... 27 UNIT 8 ENZYMES ................................................................................................. 31 I.2 ADDITIONAL UNITS .................................................................................. 34 UNIT 9 PROPERTIES OF GELS............................................................................ 34 UNIT 10 SOLVENT PROPERTIES OF SURFACTANT SOLUTIONS. EMULTION POLYMERIZATION......................................................................... 37 UNIT 11 THE NATURE OF RUBBER - LIKE ELASTICITY ............................. 39 UNIT 12 THERMOPLASTIC ELASTOMERS. THERMOSETTING AND THERMOPLASTIC MATERIAL ........................................................................... 42 UNIT 13 THERMOPLASTIC ELASTOMERS ...................................................... 45 UNIT 14 ABS PLASTIC ......................................................................................... 49 UNIT 15 HAFNIUM ................................................................................................ 52 REFERENCES ............................................................................................................. 56 PART 2 THE CHEMICAL ENGINEERING UNITS ................................................. 57 UNIT 16 TYPES OF REACTORS .......................................................................... 58 UNIT 17 HEAT TRANSFER AND ITS APPLICATIONS .................................... 62 UNIT 18 EXTRACTION WITH SOLVENTS ........................................................ 67 UNIT 19 INTRODUCTION TO DISTILLATION AND ATMOSPHERIC DISTILATION ......................................................................................................... 72 UNIT 20 VACUUM DISTILLATION .................................................................... 77 3

UNIT 21 STEAM DISTILLATION ......................................................................... 81 UNIT 22 CRYSTALLIZATION .............................................................................. 86 UNIT 23 ADSORPTION .......................................................................................... 90 UNIT 24 EVAPORATION....................................................................................... 93 UNIT 25 CHROMATOGRAPHY ............................................................................ 97 UNIT 26 LIQUIS-SOLID CHROMATOGHRAPHY ........................................... 100 REFERENCES ............................................................................................................ 104 PART 3 THE PETROCHEMICAL INDUSTRY AND REFINERY UNITS ............ 105 III.1 TYPICAL UNITS ....................................................................................... 106 UNIT 27 ON OIL AND GAS INDUSTRY ............................................................ 106 UNIT 28 COMPOSITION OF PETROLEUM ...................................................... 108 UNIT 29 BASIC PHYSICO-CHEMICAL PROPERTIES OF PETROLEUM AND PETROLEUM PRODUCTS ................................................................................... 112 UNIT 30 BASIC PHYSICO-CHEMICAL PROPERTIES OF PETROLEUM AND PETROLEUM PRODUCTS (CONTINUED) ........................................................ 117 UNIT 31 DISTILLATION OF PETROLEUM ...................................................... 121 UNIT 32 THERMAL PROCESSES IN REFINERY ............................................. 126 THERMAL CRACKING ....................................................................................... 126 UNIT 33 CATALYTIC PROCESSES IN REFINERY ......................................... 131 III.2 ADDITIONAL UNITS ............................................................................... 136 UNIT 34 CATALYTIC CRACKING OF PETROLEUM ..................................... 136 UNIT 35 CATALYTIC REFORMING OF PETROLEUM................................... 142 REFERENCES ............................................................................................................ 147 PART 4 ACADEMIC WRITING ............................................................................... 148 UNIT 36 INTRODUCTION TO ACADEMIC WRITING .................................... 149 UNIT 37 TYPES AND STRUCTURE OF ACADEMIC WRITING .................... 153 UNIT 38 HOW TO WRITE A SUCCESSFUL...................................................... 157 SCIENTIFIC MANUSCRIPT ................................................................................ 157 REFERENCES ............................................................................................................ 161

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LỜI NÓI ĐẦU

Giáo trình này được biên soạn cho những sinh viên năm cuối của ngành Kỹ thuật Hoá học. Giáo trình nhằm bổ sung cho sinh viên các từ vựng, tổ hợp từ, thuật ngữ, cấu trúc ngữ pháp hay gặp trong những tài liệu khoa học kỹ thuật, giúp sinh viên làm quen với việc dịch Anh-Việt và ngược lại, viết một văn bản khoa học bằng tiếng Anh. Nội dung của giáo trình gồm 4 phần. Các bài học trong các phần được biên soạn tăng dần theo mức độ chuyên sâu trong lĩnh vực hoá học.

Trong phần một tác giả chọn các bài khoá liên quan đến những kiến thức cơ bản của Hoá học, những chuyên đề cơ bản của Hoá học. Mỗi bài khoá đều sắp xếp theo trật tự logic từ bài đọc hiểu, các bài tập để sinh viên ôn luyện, từ đó giúp sinh viên làm quen với những từ, tổ hợp từ và tập trung vào kỹ năng đọc hiểu, dịch từ tiếng Anh sang tiếng Việt và ngược lại.

Phần hai gồm những bài khoá liên quan đến lĩnh vực Kỹ thuật Hoá học như lò phản ứng, những kỹ thuật tách chất phổ biến và thông dụng nhất. Cấu trúc bài khoá ở phần này cũng tương tự như ở phần một. Các bài tập đi kèm làm cho bài khoá thêm sinh động và đưa vào những cấu trúc ngữ pháp hay gặp trong khoa học.

Phần ba là những bài khoá tập trung vào lĩnh vực Hoá dầu. Nội dung mỗi bài đều gắn với chuyên môn sâu của sinh viên. Sau mỗi bài đều có bài tập để sinh viên rèn luyện khả năng đọc, dịch và viết tiếng Anh. Trong phần cuối cùng tác giả biên soạn ba bài cơ bản về kỹ thuật viết một văn bản khoa học trong lĩnh vực Kỹ thuật Hoá học, giúp sinh viên nắm được những bước cơ bản và sườn của một bản thảo bài báo khoa học.

Tác giả xin trân trọng cảm ơn các đồng nghiệp đã đóng góp ý kiến để hoàn thành cuốn sách này. Xin chân thành cảm ơn sự quan tâm của độc giả và mong nhận được những ý kiến góp của các độc giả và các bạn đồng nghiệp để cuốn sách ngày một hoàn thiện hơn.

Tác giả

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PART 1 THE BASIC UNITS

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I.1 TYPICAL UNITS UNIT 1 SOME CONCEPTS IN CHEMISTRY Structure of Atoms. According to Dalton’s atomic theory, a chemical element is material composed of only one type of atom. Atoms are very small particles that cannot be separated into simpler substances and that singly or in combination constitute all matter.

All atoms are constructed from the three particles: the electron, proton, and neutron.

Both neutrons and protons occupy the nucleus, which is in the center of the atom. The electrons orbit around the nucleus. Each atom contains equal number of electrons and protons, therefore, atoms are neutral. An atom of one element is distinguished from an atom of another element by its number of protons. The number of proton in the atomic nucleus is called the atomic number Z of an element. For instance, carbon atoms contain six protons and six electrons; therefore, the atomic number of carbon is 6. The total mass of an atom is almost entirely by the number of protons and neutrons because the mass of electrons is so much smaller.

The atoms of almost element have the same proton number but different neutron number; therefore they have different mass number. These atoms are called isotopes. For example, helium exists as helium-3 or He-3 (its nucleus contains 2 protons but only 1 neutron) or as helium-4 or He-4 (2 protons and 2 neutrons). These two examples are called isotopes of helium.

The elements are arranged in the periodic table, the invention of which is generally attributed to the 19th century Russian chemist Dimini Mendeleev. In the standard periodic table, the elements are listed in order of increasing atomic number (the number of protons in the nucleus of an atom). A new row (period) is started when a new electron shell has its first electron. Elements containing the same number of electron layers are arranged in the same period while elements with the same number of electrons in a particular subshell fall into the same columns.

Molecules, substances, and chemical compounds. Molecules are composed of the atoms of one or more elements. Nitrogen exists as nitrogen molecules in atmosphere, each molecule contains two nitrogen atoms. Its symbolic representation is N2. Water molecule contains one oxygen atom and two hydrogen atoms. Compounds are composed of the atoms of one or more elements. N2 is an elementary substance and water is a compound but both of them are called substances.

Exercises 1.1 Read and translate into Vietnamese Concept, structure, atom, atomic, theory, element, material, compose, substance, particle, combination, constitute, matter, electron, proton, neutron, neutral, nucleus, orbit, distinguish, atomic number, mass number, helium, arrange, periodic table, attribute, electron shell, subshell, molecule, substance, elementary substance, compound.

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1.2 Answer the following questions 1. What is an element?

2. What is an atom?

3. How many kinds of particles are there in every atom? What are they?

4. What is the atomic number of an element?

5. How can we determine the mass of an atom?

6. What is a molecule?

7. Please distinguish an elementary substance and a compound.

1.3 Translate into Vietnamese paying attention to the words in bold type 1. The name ABS, based on the first letters of each of the monomeric components has been adopted for this family.

2. By introducing acrylonitrile monomer into a similar system, a significant improvement in all these properties is obtained, as well as outstanding toughness and resistance.

3. Various combinations of properties are possible, thus making these polymers most attractive for a larger number of current and newly developed applications.

4. ABS plastics are extremely useful and versatile, since ease of processing and forming allows them to be used for a great number of applications.

5. The strength of a fabricated item produced from ABS plastic is dependent on a number of variables.

1.4 Translate into English 1. Nguyên tử là phần tử nhỏ nhất của vật chất có thể tồn tại độc lập.

2. Nguyên tử được cấu tạo từ proton, electron và nơtron. Electron tích điện âm, ptoton tích điện dương còn nơtron không mang điện.

3. Trong một nguyên tử, số proton bằng với số electron nên nguyên tử luôn trung hòa về điện.

4. Vì khối lượng của eletron rất nhỏ so với khối lượng của nơtron và proton nên khối lượng nguyên tử được tính xấp xỉ là tổng khối lượng của proton và nơtron.

5. Phân tử chứa các nguyên tử của một hoặc nhiều nguyên tố.

6. Các hợp chất bao gồm các nguyên tử của hai hay nhiều nguyên tố.

7. Các hạt proton và neutron nằm ở trung tâm và tạo ra hạt nhân còn các electron chuyển động xung quanh hạt nhân tạo ra các lớp electron.

8. Đồng vị là các nguyên tử của cùng nguyên tố có số nơtron khác nhau.

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9. Các nguyên tố trong cùng một chu kỳ có cùng số lớp electron 10. Các nguyên tố trong cùng một nhóm có cùng số electron ở lớp ngoài cùng, do đó, chúng có tính chất tương tự nhau.

11. Các nguyên tố hóa học được sắp xếp vào bảng hệ thông tuần hoàn dựa vào cấu hình electron của chúng.

1.5 Write a short summary of the text

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UNIT 2 HYDROCARBONS Hydrocarbons are compounds containing only carbon and hydrogen atoms.

1. Paraffin hydrocarbons (alkanes) Their general formula is CnH2n+2, where n is the number of carbon atoms. Each next hydrocarbon can be obtained from the previous one by substituting a methyl group CH3 for the extreme hydrogen atom in the chain: CH4

C2H6

C3H8

methane

ethane

propane

C4H10 butane

The paraffin hydrocarbons are the most stable of the lot because all valence bonds are fully satisfied as indicated by the single linkage. Most reactions involve the replacement of hydrogen atoms with other atoms, the carbon linkage remains stable.

Under common conditions, the hydrocarbons from CH4 to C4H10 are gaseous, those from C5H12 to C15H32 are liquids (they enter the composition of gasoline, kerosene, and diesel- fuel fractions), and those from C16H34 are solid (paraffins).

Beginning from the fourth term in the series (butane C4H10), hydrocarbons may exist in two or more forms differing in the structure. For instance, butane may exist in two forms: n-butane and isobutane. Compounds which have the same chemical formula but different molecular structure are called isomers.

The number of isomers increases for each next hydrocarbon in the series.

Hydrocarbons of the formula C13H28 may have 802 isomers, those of the formula C14H30, 1858, and so on. Thus, the composition of petroleum is quite complicated. Isomers possess different physical and chemical properties. For instance, heptane of normal structure (nC7H16) has an octane number of zero, whereas isooctane (iso- C8H18) has an octane number of 100.

2. Naphthenic Hydrocarbons (Cycloalkanes) Their general formula is CnH2n. They were discovered by V.V. Markovnikov, a prominent Russian chemist, when studying petroleum of Caucasian deposits.

In their chemical properties; naphthenic hydrocarbons are similar to paraffins, but differ from the latter in having a cyclic structure.

Cyclopentane and cyclohexane derivatives are especially important for the quality of petroleum and petroleum products.

3. Benzene Hydrocarbons (Arenes) Arenes of the benzene series have the general formula CnH2n-6. The cyclic structure of arenes differs from that of naphthenes by the presence of double bonds on the aromatic ring.

If one or more atoms of hydrogen in the ring are replaced by a methyl (-CH3) or an ethyl (C2H5) group, other arenes (toluene, xylenes and ethylbezene) are formed. Arenes are valuable raw materials for chemical technology and the manufacture of antiknock gasoline.

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4. Unsaturated Hydrocarbons (Olefins) Hydrocarbons of the ethylene series have the general formula is CnH2n, are characterized by a double bond in the molecule (ethylene C2H4, propylene C3H6, butylenes C4H8, amylenes C5H10, etc.) and may be of either normal or isomeric structure.

They are not present in crude petroleum, but constitute an appreciable part of the products obtained in thermal and some catalytic processes of petroleum processing. These hydrocarbons have high reactivity and are used for the manufacture of some important products, such as polyethylene, polypropylene, ethylene and propylene oxides and their derivatives.

Along with olefins, some less saturated hydrocarbons, with two double bonds in the structure, such as diolefins, can form in petroleum processing. These are extremely unstable and for that reason should not be present in final petroleum products. Some of them (butadiene C4H6 and isoprene C5H8) are obtained intentionally from petroleum and used for the manufacture of synthetic rubber and like products.

Exercises 2.1 Read and translate into Vietnamese Paraffin, general formula, substitute, methane, ethane, propane, butane, stable, satisfy, linkage, single, double, triple, bond, gasoline, kerosene, gaseous, fuel, petroleum, diesel, fraction, solid, isomer, isomeric, heptane, isooctane, naphthene, naphthenic, cycloalkane, prominent, cyclopentane, cyclohexane, derivatives, arene, benzene, aromatic, toluene, xylene, ethylbenzene, antiknock, unsaturated, ethylene, acetylene, amylene, butylene, constitute, appreciable, petroleum processing, polyethylene, polypropylene, propylene oxides, diolefin, unstable, butadiene, synthesis, synthesize, synthetic, rubber.

2.2 Answer the following questions 1. What kinds of substances are hydrocarbons?

2. What is the general formula of alkanes?

3. What are isomers?

4. What can you say about the properties of isomers?

5. Which compounds are called cyclic compounds?

6. What are benzene hydrocarbons or arene?

7. What are the uses of benzene and benzene hydrocarbons?

8. What are properties of unsaturated hydrocarbons?

9. What are the uses of unsaturated hydrocarbon?

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2.3 Fill the following schemes with suitable expressions Funnel, filter paper, mixture, residue, glass rod, filtrate, beaker, and stand.

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Figure 1. Laboratory setup for filtration experiment

2.4 State the purpose of the system and describe its operation

Figure 2. Laboratory setup for vacuum filtration experiment

Moisten the filter paper with the solvent used in the crystallization process and apply suction before the filtration is started. The suspension of crystals is then poured onto the filter in such a way that a layer of uniform thickness is collected. If crystals adhere to the walls of the flask in which crystallization was carried out, they may be washed out with some of the filtrate.

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2.5 Fill the following schemes with suitable expressions Support stands, water in, water out, pot, thermometer, rubber tubing, adapter, receiver, thermometer adapter, condenser, clamp, boiling chips, distilling head, support ring, electric flask heater.

Figure 3. Laboratory setup for simple distillation experiment

2.6 Translate into English 1. Hydrocacbon là các hợp chất chỉ chứa cacbon và hydro.

2. Trong dầu mỏ chỉ chứa các hydrocacbon paraffin, naphten và aromatic vì chúng bền. Các hydrocacbon không no chỉ tạo ra trong quá trình chế biến dầu mỏ.

3. Các hydrocacbon không no có hoạt tính vì chúng có các liên kết bội không bền.

4. Các paraffin và naphten có hoạt tính hoá học thấp do phân tử của chúng chỉ chứa các liên kết đơn (bão hoà).

2.7 Write a short summary of the text

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UNIT 3 CHEMICAL KINETIC AND CATALYSIS

Chemical kinetics, also known as reaction kinetics, is an important part of chemistry. Chemical kinetics study of how experimental conditions can influence the speed and yield of a chemical reaction. Investigation of chemical kinetics can give us the information about the reaction's mechanism as well as the mathematical models that can describe the characteristics of a chemical reaction.

There are many factors that determine the rate of a reaction. Temperature is an important factor which affects the reaction. Almost the reactions need energy by raising the temperature. The higher temperature the higher the atoms, molecules, and ions move which leads to the frequency of collision increases. High frequency of collision helps the particle to overcome the activation barrier. High concentration of the reactants also increases the rate of a reaction. If the reactant molecules are closed the collisions become more frequent which makes the reaction more likely happens.

In addition, the rate depends also upon physical form of reactant, the intimacy of their mixture, the pressure and solvents, the special physical circumstances such as irradiation with visible light, ultraviolet light, X-rays, neutrons, and the presence of other substances which affect the reaction but are not changed by it (catalysts).

A catalyst can accelerate a chemical reaction because it let the reaction takes place by an alternative pathway with lower activation energy barrier. Catalyst reacts to form a temporary intermediate which then regenerates the original catalyst in a cyclic process. In the presence of a catalyst, less free energy is required to reach the transition state, but the total free energy from reactants to products does not change. Many kinds of catalysts are used up to now such as acid, base, transition metal, complex, enzyme… Depend on the state of the catalytic reaction system catalysts may be classified as either homogeneous or heterogeneous.

The molecules of a homogeneous catalyst are dispersed in the same phase (usually gaseous or liquid) as the reactant molecules. The molecules of a heterogeneous catalyst are not in the same phase as the reactants, which are typically gases or liquids that are adsorbed onto the surface of the solid catalyst. Enzymes and other biocatalysts are often considered as a third category.

The detailed mechanism of catalysis is complex. Kinetically, catalytic reactions are typical chemical reactions; i.e. the reaction rate depends on the frequency of contact of the reactants in the rate-determining step. Usually, the catalyst participates in this slowest step, and rates are limited by amount of catalyst and its "activity".

Rate equation for a chemical reaction is an equation that shows the relationship between reaction rates and the concentrations or pressures of the reactants and constant parameters. Depending on the rate equation we can distinguish the zero order, first order, second order reactions and so on.

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Exercises 3.1 Read and translate into Vietnamese Chemical kinetic, kinetic, kinetically, catalysis, catalyst, catalytic, mechanism, mathematical model, factor, frequency, collision, activation, reactant, intimacy, circumstance, irradiation, visible, light, ultraviolet light, X-rays, accelerate, alternative, pathway, regenerate, cyclic process, free energy, transition metal, homogeneous, heterogeneous, adsorb, rate determining step, rate equation, zero order.

3.2 Answer the following questions 1. What is catalysis?

2. What is a catalyst?

3. Compare the homogeneous and heterogeneous catalysts!

4. Which kinds of catalysts are there?

5. What is the role of a catalyst?

6. What are the inhibitors and poisons of a reaction?

7. What is the rate-determining step?

8. Do catalysts change during the reaction?

3.3 Translate the following sentences into Vietnamese 1. Lewis found water and air to be thermodynamically unstable with respect to the formation of nitric acid.

2. Metastable or unstable compounds can be treated by the methods of thermodynamics, provided that they have a lifetime sufficiently long for thermodynamic measurements to be made.

3. Scientists consider adsorption from solutions to be physical or chemical.

4. It is noteworthy that in the case of phosphate buffers, the increase of pH is accompanied by a drop of interface tension between the two phases.

3.4 Translate into English 1. Chất xúc tác là chất làm tăng tốc độ phản ứng nhưng bản thân nó không bị biến đổi sau phản ứng.

2. Vai trò của chất xúc tác là làm giảm năng lượng hoạt hóa của phản ứng.

3. Ở cùng điều kiện nhiệt độ và nồng độ chất phản ứng, khi năng lượng hoạt hóa của phản ứng giảm đi thì tốc độ phản ứng tăng lên.

4. Chất xúc tác thường tham gia vào giai đoạn quyết định tốc độ phản ứng hay là giai đoạn chậm chất của phản ứng.

3.5 Write a short summary of the text 15

UNIT 4 ANALYTICAL CHEMISTRY

One should keep in mind that industrial analysis is not necessarily a routine, boring occupation. It can be frustrating at times but it can also be fascinating, instructive, humorous, and even exciting. It is usually pleasant if one dedicates himself to learning about what goes on in chemical systems. The key for enjoying analytical work lies in knowing that the results will be useful and important.

Problem - solving in analytical chemistry An analytical chemist should know enough about existing methodologies to choose the best one for application to a given sample, perhaps modifying it if necessary to fit the particular situation, and that there is also an analytical science which seeks the improvement of analytical methodologies with regard to scientific problems. Nowadays, with more and more instrumental methods in vogue, the analysts and determinators are coming closer together.

To be a good chemist one must first be a good analytical chemist. We can teach instrumental analysis in industry, but we should not teach basic chemistry.

Mercury? Questions and answers Some of you may be interested in the question of mercury and its determination in the environment. This is a fascinating question with many aspects. It illustrates again the importance of analytical chemists looking at the whole picture.

Swedish scientists had developed a gas chromatographic method for the determination of alkyl and aryl mercuric compounds extracted from fish with benzene and dilute hydrochloric acid. They were interested in those compounds because of their use as slimicides, but it turned out that regardless of what compound was used, the mercury found in fish was present as a monomethylmercuric ion.

A number of questions about the behavior of mercury remain to be answered. Several theories have been proposed as to how mercury might have gone from inorganic form in water or bottom sediment, into a methylated form of a fish. One theory assumes anaerobic conversion in the mud to volatile dimethyl mercury which enters fish via the gills. Another assumes aerobic conversion to monomethyl mercury by bacteria, with subsequent transfer up to the food chain. Still another assumes that a fish itself can methylate mercury taken in either through the gills as elemental vapor, or via the stomach as inorganic ions, or in an adsorbed state in silt particles. Before all these questions can be answered, we need to develop highly sensitive methods for each individual form of mercury. At present the most sensitive methods can go down only to about 0.05-ppm inorganic mercury in water.

At the conference on environmental mercury contamination in 1970 in Ann Arbor, Michigan, USA a number of sources from which mercury may enter the environment were mentioned. Among them were the burning of fossil fuels, use of mercurial compounds for fungicides in agricultural seed treatments, use of elemental mercury in the electrical industry for manufacture of batteries and mercury vapour lamps, use of mercuric catalysts, and the 16

disposal of domestic sewage sludges. It will be up to analytical chemists to evaluate all of the sources and to provide the data on which proper action can be based. This will be true not only for mercury, but also for all environmental contaminants.

It is interesting that both Finish and Swedish chemists have found fairly high content in fish from certain lakes in northern parts of their countries, remote from any known source of pollution.

Another interesting fact is that mercury will be found in the hair of a person who has been exposed to it. The average person has about one or two ppm in his hair or even more.

Having analyzed sections of the hair of a long- haired person and having known its growth rate, one can approximate the time and intensity of exposure. Most of these analyses have been done by neutron activation, which is advantageous because very small samples can be employed. However, hair can be analyzed by the atomic absorbance method following the digestion procedure used for fish analysis. A 100-mg sample is sufficient for hair in the range of 1 to 10 ppm.

Exercises 4.1 Read and translate into Vietnamese Analysis, analytical, routine, occupation, frustrating, fascinating, instructive, humourous, pleasant, dedicate, methodology, modify, particular, vogue, determination, determinator, instrument, instrumental, mercury, mecuric, environment, fascinating, aspect, illustrate, chromatographic, dilute, alkyl, aryl, extract, benzene, slimicide, regard, regardless, monomethylmercuric, sediment, methylate, anaerobic, mud, aerobic, gill, assume, inorganic, organic, volatile, dimethyl mercury, subsequent, transfer, chain, stomach, sensitive, silt, individual, contaminate, contamination, contaminant, mention, fossil fuel, fungicide, agriculture, agricultural, battery, disposal, domestic, sewage, sludge, evaluate, source, remote, pollution, approximate, expose, exposure, intensity, absorbance, digestion, sufficient.

4.2 Answer the following questions 1. What is the key for enjoying analytical work?

2. How is industrial analysis?

3. What should an analytical chemist know?

4. Which compounds of mercury are present in fish?

5. How has mercury transferred from inorganic form to methylated form?

4.3 Translate into Vietnamese paying attention to the finite and non- finite forms of the verb 1. Having developed a gas chromatographic method for the determination of alkyl and aryl compounds the Swedish scientists got interested in those compounds.

2. Swedish scientists developed a gas chromatographic method for the determination of alkyl and aryl mercuric compounds extracted from fish.

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3. The chemists extracted fairly high mercury contents from fish.

4. The scientists found high mercury contents in fish from certain lakes, remote from any known source of pollution.

5. Mercury found in fish was present as a monomethylmercuric ion.

4.4 Translate into Vietnamese paying attention to the pronoun “one” 1. One should keep in mind that industrial analysis is not necessarily a boring occupation.

2. It is pleasant if one dedicates himself to learning about what goes on in chemical systems.

3. An analytical chemist should know enough about existing methodologies to choose the best one for application.

4. To be a good chemist one must be first of all a good analytical chemist.

4.5 Translate into Vietnamese paying attention to the Model Verbs + Perfect infinitive 1. It was realized that drying may have caused some denaturation, but whatever the change it should not have affected the amino acid composition of the proteins.

2. It goes without saying that any of the acid derivatives (amide, ester, etc.) might have been prepared either from benzoyl chloride or benzoic anhydride instead of from benzoic acid.

3. The mercaptans obtained could have been oxidized in alkaline solutions to disulfides.

4. Zincate solutions could have been prepared by dissolving ZnO in aqueous KOH. 4.6 Read the following model of a summary The article “The pains and pleasures of industrial analytical chemistry” discusses what an analytical chemist should know about existing methodologies and presents a gas chromatographic method for determination of alkyl and aryl mercuric compounds extracted from fish with benzene and dilute hydrochloric acid.

The paper provides examples of fairly high mercury content in fish from certain lakes of Sweden and Finland, which are remote from any known source of pollution and of finding mercury in the hair of a person exposed to it.

The article illustrates and describes the importance of an analytical chemist who should use the best methodology to a given sample modifying it to fit the particular situation.

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UNIT 5 CHEMICAL THERMODYNAMICS

The science of thermodynamics concerns the chemical and physical processes, which involve the interconversion of various forms of energy, and it is not confined to the relation between heat and mechanical energy. It is developed mathematically on the basis of a number of postulates, which have been supported by experiments.

Although its application to chemical processes quite general, thermodynamics is not at all concerned with either the rate of a process or the mechanism of it. Thermodynamics is based on two fundamental laws, called the first and second laws of thermodynamics. The two laws of thermodynamics constitute one of the most powerful tools of physical chemistry.

Of fundamental importance to thermodynamics is the concept of equilibrium state.

Thermodynamic equilibrium in the true sense refers to a condition in which the properties of a system are absolutely unchanging with time so that, if the system is disturbed slightly in some way, it will return to essentially the same condition after the disturbing force is removed. This latter criterion may differentiate between a true state of equilibrium and a metastable one. If a metastable equilibrium is disturbed, as, for example, by introduction of a catalyst or by local heating, it may spontaneously undergo a drastic change to some new state.

Consider a container filled with chlorine gas. Provided that the container is sealed and thermally insulated from its surroundings a state of true thermodynamic equilibrium will be established in which the temperature and pressure are uniform. If we disturb the system by shining a light on it, some of the chlorine molecules will absorb radiation and dissociate into atoms. When we turn off the light, the chlorine atoms recombine and the system, except for the addition of a small amount of energy from the light beam, returns to its original condition.

By way of contrast, a mixture of hydrogen and chlorine is metastable. Although chlorine and hydrogen react with one another at room temperature, the rate is so slow as to be virtually undetectable. Hence the system seems to behave in just the same way as the pure chlorine system, in which uniform temperature and pressure are established. However, if we direct a beam of light through this mixture, it explodes, forming hydrogen chloride and evolving a large amount of heat. After being disturbed in this way, the system can not revert spontaneously to its original condition. In fact, the change, which does occur (the explosion), is a state of true thermodynamic equilibrium.

Although thermodynamics cannot deal with the rate at which reactions occur, it does establish the direction in which reaction can proceed. Metastable or unstable compounds can be treated by the methods of thermodynamics, provided that they have a lifetime sufficiently long for thermodynamic measurements to be made. This requirement may vary, depending on the type of experiment, from a minute fraction of a second to hours, or even days. In this regard, one can make the distinction between substances, which exits by virtue of its thermodynamic stability, or by reason only of its slow rate of reaction or decomposition.

There is a wide range in degree of inertness of unstable system. Diamond, on the one hand, is inert to the extent that there is no observable conversion (under ordinary conditions) 19

to the stable state of graphite. At the other extreme are such unstable substances as a supercooled liquid, or a sensitive explosive. In either of these cases, only a slight perturbation is necessary to change these systems drastically. Lewis and Ranall in their classic treatment of thermodynamic found that water and air, although inert, are thermodynamically unstable with respect to the formation of nitric acid.

Those substances, which are quite inert chemically, can generally be treated by the methods of thermodynamics.

As an example, both NO and NO2 are unstable with respect to decomposition into their elements, yet we can not only consider the reaction: 2NO2 → 2NO + O2 but also study the equilibrium by a direct experiment.

Exercises 5.1 Read and translate into Vietnamese Thermodynamics, concerns, involve, interconversion, confine, mechanical, mathematical, postulate, application, general, fundamental, constitute, equilibrium, absolute, unchanging, distribute, essential, disturb, metastable, disturb, criterion, differentiate, spontaneously, drastic, provided that, thermally, insulated, disturb, shine, absorb, radiation, dissociate, chlorine, recombine, beam, original, constract, virtually, detect, undetectable, establish, explode, explosion, explosive, evolve, heat, revert, deal with, lifetime, measurement, vary, minute, distinction, decomposition, inert, inertness, degree, diamond, observable, graphite, extreme, supercool, sensitive, perturbation, treat.

5.2 Answer the following questions 1. What does the science of thermodynamics deal with?

2. What are the main laws of thermodynamics?

3. What is meant under thermodynamic equilibrium?

4. Thermodynamics establishes the direction, in which a reaction proceeds, doesn't it?

5. What mixtures are considered to be metastable?

6. What conclusions did Lewis and Ranall draw?

5.3 Translate the following sentences paying attention to the words in bold type 1. Water and air are thermodynamically unstable with respect to the formation of nitric acid.

2. The preparation of smokes has already been referred to in the scientific journal.

3. The inert dust presumably takes up in virtue of its heat capacity, which would otherwise be available for raising more coal dust to its ignition point.

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4. The amino acids are amphoteric, i.e., can act either as acids by virtue of the carboxyl, or as bases by virtue of the amino group.

5. With respect to catalytic activity, metals considerably exceed other catalysts for many reactions.

6. Oxide catalysts have provided interesting systems for the study of electronic factors in catalysis.

7. Provided the oxidation directly after chlorination is carried out at sufficiently high pH, little damage is done to the cellulose.

8. Synthetic rubbers possess a marked advantage over natural ones by reason of the diversity of properties they affect.

5.4 Translate the following derivatives into Vietnamese 1. Catalysant, catalysate, catalysis, catalyst, catalytic, catalytical, catalysator, catalyzed, catalyzer.

2. Stability, stabilization, stabilizator, stabilize, stabilizer, stabilizing, stable.

5.5 Form nouns from the following verb establish

behave

explode

combine

fill

convert

occur

differentiate

perturb

dissociate

provide

distinguish

require

disturb

surround

direct equilibrate

5.6 Translate the following sentences into Vietnamese paying attention to conditional sentences 1. If a molecule with a lone pair of electrons is adsorbed on a transition metal, it will donate a pair of electrons.

2. A stable of thermodynamic equilibrium will be established, provided that the container is sealed.

3. A mixture would explode if one directed a beam of light through it.

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4. Were gypsum heated to a much higher temperature than 120oC, it would lose all its water of crystallization.

5. Had we disturbed a system by shining a light on it, some of the chlorine molecules would have absorbed radiation and dissociated into atoms.

6. If the fatty acid does not react chemically with the surface, it is relatively ineffective as a lubricant.

7. It would be expected that the heat of adsorption would decrease with an increase of temperature if the thermodynamic state of the surface and adsorbed species remained the same.

5.7 Translate into English 1. Định luật thứ nhất của nhiệt động học được xem là định luật bảo toàn năng lượng.

2. Cân bằng nhiệt động có nghĩa là trạng thái mà ở đó tính chất của hệ không bị thay đổi theo thời gian.

3. Như đã biết nội năng của một chất phụ thuộc vào trạng thái của nó nghĩa là phụ thuộc vào nhiệt độ, áp suất, dạng tinh thể.

4. Theo định luật thứ hai của nhiệt động học thì cân bằng không phụ thuộc vào cách thức mà nó đạt tới.

5.8 Write a short summary of the text

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UNIT 6 EMULSIONS

An emulsion represents a disperse system in which the phases are immiscible or partly immiscible liquids.

In nearly all emulsions, one of the phases is aqueous and the other is oil. If the oil is disperse phase, the emulsion is termed an oil in water (o/w) one. If the aqueous medium is the disperse phase, the emulsion is termed a water in oil (w/o) one.

If one shakes vigorously a vessel containing two immiscible liquids, both liquids are broken up into the droplets whose size depends upon the viscosity of the liquid, surface, interfacial tensions and the vigor of the shaking. As soon as the mechanical dispersive action ceases, the droplets begin to coalesce in order that the total surface free energy may be reduced. Most often, particularly in the case of two pure liquids, the coalescence process is rapid, and within a very few minutes the system consists only of two liquid layers. In the presence of the small amounts of additional components, termed emulsifiers, the rate of coalescence of the droplets may be greatly reduced. Emulsions are intrinsically unstable, thus resembling lyophobic colloids. Three distinct kinds of instability are found to exist; each may be of great importance in industrial products.

Emulsions may “cream”, i. e. separate into layers of aqueous phase with a concentrated layer of oil droplets floating on the top, the rate depending primarily on the viscosity of the aqueous phase, the size of the droplets, and the density difference between the aqueous phase and the droplets. They may also flocculate as do other lyophobic colloids. The flocs, being larger than individual drops, have a higher creaming rate.

Finally, the drops may coalesce giving a separated bulk layer of the once emulsified liquid, in which case re-emulsification can be affected only by drastic mechanical action.

No satisfactory quantitative theory of the emulsion stability has yet been developed. It is nevertheless becoming apparent in the case of coalescence that it is the structure of the interfacial film, which is controlling the behaviour of the system. For flocculated o/w emulsions the rate of coalescence is linearly dependent on the concentration of the adsorbed emulsifier in the interfacial film, and appears to extrapolate to zero at complete coverage of the surface of droplets.

It might be thought that dilute emulsions would be ideal system on which to test theories of the flocculation of lyophobic colloids. Many industrially important emulsions are “stabilized” (given long life) by the use of solids as emulsifiers.

Exercises 6.1 Read and translate into Vietnamese Emulsion, represent, disperse, phase, immiscible, aqueous, term, shake, vigorously, droplet, viscosity, surface, interfacial, tension, vigor, mechanical, dispersive cease, coalesce, 23

coalescence, additional, component, emulsify, emulsifier, intrinsical, lyophobic, colloid, distinct, instability, cream, floating, floc, bulk, emulsify, re-emulsification, satisfactory, nevertheless, apparent, interfacial film, interfacial, extrapolate, coverage.

6.2 Answer the following questions 1. What is an emulsion?

2. What emulsions are widely known?

3. What emulsions phases do you know?

4. What happens if one shakes vigorously a vessel containing two immiscible liquids?

5. When is the coalescence process rapid?

6. In what way can industrially important emulsions be “stabilized” 6.3 Translate the following derivatives 1. disperse, dispersed, disperser, dispersing, dispersion, dispersity, dispersive.

2. emulsification, emulsifier, emulsify, emulsifying, emulsion.

3. miscibility, miscible, mix, mixer, mixed, mixing, mixture.

4. Polymer, polymeric, polymerize polymerization, polymerize, polymerized, polymerizing.

6.4 Translate the following sentences paying attention to the words in bold type 1. Water dispersible dye is a good example of an emulsion in which the pigment helps to control the emulsion stability.

2. Polyformaldehyde is used for the manufacture of many consumer goods.

3. Latex foam from Government Rubber Styrene (GRS) of the proper type is good in colour, pore structure, and ageing but rather lacking in strength.

4. Even with a high alkali reserve, the storage life of neoprene latex is not as good as many other latices.

5. Neoprene is very desirable for dipped goods where special service conditions are required.

6. Gum Arabic is a fairly goods dispersing agent and has one desirable feature - good ultraviolet resistance.

7. The extensive data obtained in emulsion polymerization of methyl methacrylate are in good agreement with the assumption that the rate of reaction at high conversion is governed only by the diffusion rate of the monomer and the radical end of the polymeric chains.

6.5 Translate the following sentences paying attention to the negative pronoun "no” 1. No satisfactory quantitative theory of emulsion stability has yet been developed.

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2. The difference between suspension and emulsion polymerization points to a process of formation of particle in the latter, whereas no such process occurs in suspension reactions.

3. No equipment embodying brass or bronze should be allowed to come into contact with latex or its compounding ingredients at any stages of the manufacture.

4. No synthetic high polymers are chemically pure substances in the strict sense.

6.6 Translate the following sentences and states the function of the pronounce “one” 1. In nearly all emulsions, one of the phases is aqueous and the other is an oil.

2. The colloidal state for a substance is one in which it exhibits colloidal properties.

3. If one shakes vigorously a vessel containing two immiscible liquids, both liquids are broken up into droplets.

4. If the oil is the disperse phase, the emulsion is termed an oil in water one, if the aqueous medium is the disperse phase, the emulsion is termed a water in oil one.

6.7 Translate the following sentences into Vietnamese paying attention to the use of verb “to do” 1. Emulsions may flocculate, as do other lyophobic colloids.

2. When polymerization does take place, average molecular weights in the thousands are obtained.

3. Reinforcing agents did not generally have the effect on latex rubber that they did on milled rubber.

4. The experiments conducted show that adhesion does increase for a time after curing, but that it comes to a stable value during the first 24 hours.

6.8 Translate into Vietnamese paying attention to the rule of Sequence of Tenses 1. Berzelius stated that rubber could be redispersed.

2. It was known that ultraviolet light had a harmful influence on a rubber surface and caused photochemical effects on antioxidants.

3. Dent assumed that in the alkali halides the positive and negative ions in the surface remained coplanar.

4. Willbourne assumed that the methyl absorptivity was constant regardless of the position of the methyl group in the molecule.

5. It might be thought that dilute emulsions would be ideal systems.

6. It was considered that stabilizers belonged to a class of substances, which had been known as “surface active agents”.

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7. In the early 1920’s it was reasoned in England that individual particles of latex would be vulcanized without breaking the emulsion.

6.9 Translate into English 1. Như đã biết, đặc tính riêng biệt của nhũ tương điển hình là dạng hình cầu của hạt keo.

2. Người ta đã biết rằng, đường kính của hạt nhũ tương phụ thuộc vào độ nhớt và sức căng bề mặt cũng như vào cường độ lắc.

3. Người ta cho rằng, khi thêm vào một lượng nhỏ chất nhũ hóa thì có thể tăng tính ổn định của nhũ tương.

4. Như đã biết, cho đến nay chưa có một lý thuyết định lượng phù hợp nào về độ bền của nhũ tương được đưa ra.

5. Ý nghĩa thực tiễn của nhũ tương trong thực tế cũng như trong kỹ thuật là rất lớn.

6. Những nhũ tương tổng hợp mà được điều chế từ những chất lỏng khác nhau có mặt chất nhũ hóa đặc biệt thì có ý nghĩa lớn.

6.10 Write a short summary of the text

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UNIT 7 PLASTICS IN THE CHEMICAL AGE

The plastics industry is typical of the industries that have developed in recent years as a result of chemical research. The chemist is a key man in the plastics industry, and it is from chemical laboratories that new plastics are appearing almost day by day.

Little more than twenty years ago, plastics were still widely regarded as cheap substitutes for traditional materials such as wood and porcelain. Today, plastics have established themselves as wonderful new materials in their own right. They have ousted older materials because they can do a better job, often at lower cost.

We find new plastics encroaching in the fields where metals have reigned supreme.

The development of new techniques, such as lamination, has shown how modern plastics may be used for many engineering and structural applications. We can make gears and bearings for heavy machinery from laminated plastics. We can build car bodies, and the hulls of boats, we can pump our water supplier through the plastic pipes, and support larger buildings on plastic beams.

In time we shall have seagoing ships with plastics used for almost everything from crockery on the tables to the hull itself. We shall fly at supersonic speeds in plastic aircraft, and motor in cars with plastic bodies. House and public buildings will be constructed from plastics panels supported by plastic beams. We shall find plastic spaceships carrying us to the moon.

As the demand for the plastics grows, the need for chemical raw materials will increase. Plastics are largely organic chemicals, in which the “backbone" of the molecule consists of carbon atoms. They are made from simpler organic chemicals in which the molecules contain fewer carbon atoms, which are manipulated by the plastics chemist into thread - like structures.

Today, we draw our supplies of simple organic chemicals very largely from coal and petroleum. These are the chemical residues of plants and animals that lived millions of years ago, and they contain a variety of different organic substances. We obtain simple chemical raw materials from coal by heating it in retorts, and from petroleum by refining and processing techniques. Coal and petroleum are capital assets; the world has a limited supply, and we cannot replace the materials we use. As the demand for organic chemicals increases, the stocks of coal and petroleum will diminish; and some day, they will be gone.

Before this happens, we shall have to seek new sources of organic chemical raw materials, and we shall find them in the carbon dioxide of the air. This is the gas from which the growing plant builds up the sugar and other substances as organic raw materials, without waiting for nature to turn them into coal and oil.

It seems likely that alcohol will become the most important chemical raw material of all as supplies of coal and petroleum dwindle. We can make alcohol by fermentation of the sugar produced by fast growing plants, and it will provide us with the raw materials for 27

plastics and other synthetic chemical industries. The tropical countries of the world will use their vast areas of land for the cultivation of sugar producing crops.

It is probable, too, that we shall in time discover the secrets of photosynthesis, by which the plant uses sunshine to convert carbon dioxide into sugars and we shall use some synthetic process of this sort to turn carbon dioxide from the air into simple organic chemicals without depending entirely upon the growing plant to do it for us.

The twentieth century is the time when man began to understand how to make all the new synthetic materials from simple chemicals; materials, such as fibers and rubbers, synthetic drugs and dyes, insecticide and weed killers, hormones and vitamins - and, of course plastics.

Exercises 7.1 Read and translate into Vietnamese Plastic, typical, recent, appear, substitute, traditional, wood, porcelain, ouster, encroaching, reign, supreme, lamination, gear, bearing, hull, boat, pump, supplier, pipe, seagoing, supersonic, panel, spaceship, backbone, manipulate, residue, animal, retort, asset, diminish, carbon dioxide, alcohol, dwindle, fermentation, cultivate, scops, secret, photosynthesis, entirely, fiber, rubber, drug, dye, insecticide, weed, killer, hormone, vitamin.

7.2 Answer the following questions 1. What have plastics ousted today?

2. What can we make from laminated plastics?

3. Which ships will carry us to the moon?

4. What does the backbone of the molecule in plastics consist of?

5. What do we draw our supplies of? (today) 6. What do we obtain simple chemical raw materials from?

7. Why do we have to seek for new sources of organic chemical raw materials?

8. Where shall we find them?

9. What will become the most important chemical raw materials?

7.3 Read and translate the following derivatives industry, industrial type, typical wood, wooden laminate, laminated, lamination apply, application machine, machinery increase, decrease 28

7.4 Translate into Vietnamese paying attention to the words in bold type a) 1. Plastics can do a better job, often at lower cost.

2. The development of lamination has shown how modern plastics may be used for many engineering and structural applications.

3. We are able to build car bodies and the hulls of the boats from plastics.

4. We shall have to seek new sources of organic chemical raw materials.

5. The twentieth century is the time when one has to understand how to make all the new synthetic materials from simple chemicals. b) 6. In some time we shall have seagoing ships with plastics used for almost everything from the crockery on the table to the hull itself.

7. We used plastics as cheap substitutes for traditional materials such as wood and porcelain.

8. House constructed with the use of plastic parts is rather cheap.

9. Houses and public buildings will be constructed from plastic panels supported by plastic beams.

10. He supported himself by working at a chemical plant.

11. We can make alcohol by fermentation of the sugar produced by fast - growing plants.

12. We produced a great variety of alcohol by fast - growing plants.

7.5 Write a summary of the text and retell the text 7.6 Translate into English 1. Việc chế hóa các chất dẻo dạng lớp đã chỉ ra rằng chất dẻo có thể được sử dụng trong nhiều ngành kỹ thuật và trong xây dựng.

2. Ngày nay chúng ta có thể làm máy bay bằng chất dẻo.

3. Ngày nay, nguyên liệu để sản xuất chất dẻo là những chất hữu cơ thông thường lấy từ than đá và dầu mỏ.

4. Vì chúng ta có trữ lượng than và dầu mỏ hữu hạn nên chúng ta cần phải tìm kiếm những nguồn năng lượng mới...

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5. Có thể rượu sẽ trở thành một trong những nguồn nguyên liệu hóa học quan trọng nhất.

6. Có thể chúng ta sẽ phát hiện được những bí mật của sự quang hợp để biến CO2 thành đường nhờ ánh sáng mặt trời.

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UNIT 8 ENZYMES The study of enzymes is a subject, which has a special interest because it lies just on the borderline where the biological and the physical sciences meet. On the other hand, enzymes are of supreme importance in biology. Life depends on a complex network of chemical reactions brought by specific enzymes, and any modification of the enzyme pattern may have far- reaching consequences for the living organism. On the other hand, enzymes, as catalyst, are receiving increasing attention from physical chemists.

Enzymology has become a large and rapidly developing subject, which has close connections with many sciences, especially biochemistry, physical chemistry, bacteriology and microbiology, genetics, botany and agriculture, pharmacology and toxicology, pathology, physiology, medicine, and chemical engineering. It has in addition important practical applications to activities as diverse as brewing and industrial fermentations, pest control, and chemical warfare.

It is sometimes difficult to realize that enzymology is a subject of comparatively recent growth; the beginning of the subject can be traced back to the early nineteenth century, but the great developments have come during the last forty years.

Scientists found that an alcohol precipitate of malt extract contained a thermolabile substance, which converted starch into sugar. This substance is now called “amylase".

The great increase in the knowledge of the enzymes of living matter has brought a greatly increased understanding of the mechanism of many of the most fundamental vital processes, especially of metabolic processes which lead to the production and utilization of energy, on which life depends.

The availability of enzymes in the pure state has made possible their quantitative study by physico - chemical methods.

The substance on which an enzyme acts is termed the “substrate” of the enzyme.

In many cases an additional substance besides the enzymes and substrate is required in order that the reaction may proceed. Such “coenzymes” are part of the catalytic mechanism, and are found unchanged at the end of the reaction. They are thus distinguished from substrates.

It is frequently found that the addition of substances, which do not take part in the reaction, diminishes its velocity. These substances are known as “inhibitors “. Many of these inhibitors act as poisons of particular enzymes, and in some cases in very small concentrations.

Only comparatively recently has it been possible to develop the study of enzymes and enzyme systems in relation to the living cell.

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Exercises 8.1 Read and translate into Vietnamese Enzyme, borderline, biological, supreme, modification, consequence, organism, attention, enzymology, biochemistry, bacteriology, genetic, botany, agriculture, pharmacology, toxicology, pathology, physiology, medicine, diverse, brew, fermentation, warfare, comparative, thermolabile, starch, amylase, vital metabolic, utilization, quantitative, substrate, act, coenzyme, distinguish, diminish, velocity, inhibitor, poison, living cell.

8.2 Answer the following questions 1. Why has the study of enzymes a special interest?

2. What does life depend on?

3. What has enzymology close connections with?

4. What substance is called “amylase"?

5. What is termed the “substrate"?

6. What is a “coenzyme"?

7. What is an inhibitor?

8.3 Give derivatives to Special

activity

Enzyme

industry

Chemical

precipitate

Modify

production

Rapidly

availability

Practical

pure

Physical 8.4 Translate into Vietnamese paying attention to the words in bold type 1. The study of the enzymes is a subject, which has a special interest.

2. The treatments to which enzymes can be subjected are limited by their instability.

3. The path of energy migration is the subject of considerable controversy.

4. When subjected to a deforming force rigid structure will often fracture.

5. Only a comparatively recent has it been possible to systematically develop the enzyme studies in relation to the living cell.

6. In many cases an additional substance besides the enzyme and substrate is required.

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7. Enzymology has in addition important practical applications in brewing and industrial fermentations, pest control and chemical warfare.

8. It is frequently found that the addition of substances, which do not take part in the reaction, diminishes its velocity.

8.5 Translate into English 1. Việc nghiên cứu các ezym rất thú vị vì nó ở vào giao điểm của hai ngành khoa học: hóa học và sinh học.

2. Sự sống phụ thuộc vào hàng loạt các phản ứng hóa học được thực hiện nhờ các ezym đặc biệt.

3. Enzym học đã trở thành một ngành khoa học đang phát triển rất nhanh.

4. Sự hiểu biết của chúng ta về enzym của cơ thể sống đã giúp chúng ta hiểu rõ hơn về cơ chế của nhiều quá trình cơ bản.

5. Việc tách được các enzym ở dạng tinh khiết làm cho việc nghiên cứu các tính chất của enzym trở nên có thể thực hiện được.

8.6 Speak of the importance of enzyme

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I.2 ADDITIONAL UNITS UNIT 9 PROPERTIES OF GELS

Structure. The structure of various xerogels and jellies has been thoroughly studied in the last decades by several methods, such as the X-ray method, observations in the ultramicroscope, studies with the electron microscope, and so on. From all these studies the important conclusion may be drawn that jellies which contain large amounts of liquid have a network structure in which the liquid is bound to the fibrous particles and is also mechanically immobilised between them. The less asymmetric are the colloidal particles, the higher must be their concentration to be able to form a jelly.

The shape of the colloidal particles, however, is not the only factor, which determines the ability to form stable jellies. For instance, a 4% solution of nitrocellulose in a mixture of ether and alcohol does not set, although the molecules of the nitrocellulose are very long and thin. Another important factor, which determines the gelation, is the possibility of entanglement of the fibres or rods. The rods and fibres must be linked if a network is desired.

Hence the structural elements of a jel need not have long fibrous macromolecules. The solid framework of a jelly may be composed also of plate or needle shaped crystals as micelles. In such instances the concentration of the solid is always relatively high, whereas with linear macromolecules the concentration may be lower. The framework of a jelly must be coherent.

If the particles do not stick together there is no gelation. For example, concentrated graphite dispersion does not conduct electricity in the fluid state, although it becomes a conductor after it sets, because countless contact points are formed throughout the network. All gels can be classified into three structural groups: 1) gels with unstable frameworks; 2) jellies with metastable frameworks, and 3) systems with stable networks. A very labile framework is encountered in ferric hydroxide, aluminum hydroxide, bentonite, graphite and many other gels in which the structural elements are not very asymmetric. The crystallites or particles are joined in such cases by very weak cohesive forces (van der Waals attraction). Such gels are often thixotropic, i.e. the framework is so weak that it is destroyed by shaking. To this group belong also the entanglement gels of linear macromolecules, such as unvulcanized or rubber polystyrene. The corresponding solids, e.g. polystyrene, when placed in liquid in which they can dissolve, will swell first and then slowly go into solution. In the instances of weak frameworks of linear macromolecules the gels swell without limit; if the instance structural elements are not joined by sufficiently strong forces, the solvent may in time destroy the framework by gradually disconnecting the building units. Metastable frameworks are encountered in most of the protein jellies, for in those of gelatin. Finally, there are gels with stable frameworks, for example the gels of relatively concentrated silicic acid. Such gels can be obtained upon addition of acid to a solution of sodium silicate. The resulting gel is rigid and stable, and it cannot be reversibly transformed into a liquid system.

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Exercises 9.1 Translate into Vietnamese Gel, xerogel, microscope, ultramicroscope, jelly, network, fibrous, mechanical, immobilise, asymmetric, colloidal, gelation, entanglement, rod, macromolecules, needle shaped, micelle, conductor, countless, metastable, labile, crystallite, cohesive, thixotropic, entanglement, unvulcanize, rubber, swell, silicate, reverse, reversible, rigid, sodium.

9.2 Answer the following questions 1. What methods has the structure of various xerogels and jellies been studied by?

2. What conclusion may be drawn from all these studies?

3. What factors determine the ability to form stable jellies?

4. What must be linked if a network is desired?

5. What may the solid framework of a jelly be composed of?

6. In what cases may the concentration be high and low?

7. Is there gelation when the particles do not stick together?

8. What groups can all gels be classified into?

9. What are metastable frameworks encountered in?

10. What examples of gels with stable frameworks can you give?

11. How can gels with stable frameworks be obtained?

9.3 Translate the following sentences paying attention to the words in bold type 1. The less asymmetric are the colloidal particles, the higher must be their concentration to be able to form a jelly.

2. The larger the viscosity, the larger will be the inefficient expenditure of energy.

3. The smaller the number of valence electrons, the more readily the atom yields them.

4. If the acid is nonvolatile, only the ammonia is driven off while the acid remains in the vessel.

5. The shape of the colloidal particles, is not the only factor, which determines the ability to form stable jellies.

6. Hence the structural elements of a jel need not have long fibrous macromolecules.

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9.4 Translate into Vietnamese paying attention to the Participles 1. Some adsorbents may contain sufficient acid or alkali to after the pH of the water being treated.

2. Having been compressed the air is to be cooled.

3. Having been composed of liquid particles emulsions disperse in other liquids.

4. Being used in different fields of chemistry, industry and medicine colloid chemistry becomes increasingly important.

5. When placed in a liquid, the corresponding solids will swell first and then slowly go into solution 9.5 Translate into English 1. Hạt keo có tính đối xứng càng thấp thì nồng độ của chúng phải càng cao.

2. Hình dạng của hạt keo không phải là yếu tố độc nhất quyết định khả năng tạo thành keo bền.

3. Nếu các hạt keo không dính vào nhau thì sự tạo gel không xảy ra.

4. Một số gel thu được khi thêm axit vào dung dịch natri silicat. Gel tạo thành như vậy thì rắn, bền vững và không thể chuyển thành trạng thái lỏng.

9.6 Write an outline of the text and retell it

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UNIT 10 SOLVENT PROPERTIES OF SURFACTANT SOLUTIONS. EMULTION POLYMERIZATION

The term “emulsion polymerization” is applied to a variety of processes which have in common that the main chemical reaction is a polymerization and that the end product is latex, i. e. a suspension of polymer particles of colloidal dimensions in an aqueous medium. Such a process is called emulsion polymerization as the initial mixture of reagents usually consists of an aqueous emulsion of monomer and small amounts of other chemicals. Polymerizations in which the monomer is initially dissolved in water producing a suspension of small particles of polymer are sometimes named emulsion polymerizations as well, though rather inappropriately.

If the product of a polymerization consists of a suspension of relatively large particles (dimensions ~ 1), the process is termed a suspension polymerization. The difference between suspension and emulsion polymerization points to a process of formation of particles in the latter, whereas no such process occurs in suspension polymerization. In fact, suspension polymerizations were found to show the characteristics of a polymerization reaction in bulk monomer, the aqueous phase playing only a minor role.

In 1926 German scientists succeeded in producing synthetic rubber latices by polymerizing monomer emulsions stabilized by various surf active agents. The addition of surfactants profoundly influences the course of polymerization. In 1938 Fikentscher was the first to express the view that in emulsion polymerization the monomer, dissolved in the aqueous phase polymerizes rather than the monomer present as emulsified droplets.

A great deal of knowledge has been gained since emulsion polymers were first produced on a large scale. Smith and Ewart have developed a quantitative theory of particle formation and treated the growth of the particles during polymerization. One of the growth mechanisms considered has been found to hold true in many polymerizations with small particles.

The chemical reactions of emulsion polymerization take place in heterogeneous systems in which polymer particles of colloidal dimensions are formed. Physical and chemical phenomena influence each other profoundly.

The extensive data obtained in emulsion polymerization of methyl methacrylate are in good agreement with the assumption that the rate of reaction at high conversion is governed only by the diffusion rate of the monomer and the radical end of the polymeric chains.

Exercises 10.1 Translate into Vietnamese Term, emulsion, polymerization, emulsion polymerization, latex, suspension, colloid, initial, inappropriate, suspension, suspension polymerization, characteristic, latice, stabilize,

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surfactive, surfactant, profound, express, polymerise, droplet, quantitative, phenomena, assumption, govern, diffusion, radical, chain.

10.2 Answer the following questions 1. What is meant under “emulsion polymerization”?

2. What is meant under “suspension polymerization”?

3. What is the difference between emulsion and suspension polymerization?

4. Who treated the problem of the particle growth during polymerization?

5. What are the dimensions of the particles formed during emulsion polymerization?

10.3 Give a summary of the text 10.4 Give Vietnamese equivalent to

bulk layer

once emulsified liquid

individual drops

radical end

initial mixture 10.5 Translate into English 1. Mủ (latex) là sản phẩm cuối cùng của sự polyme hoá nhũ tương.

2. Phản ứng hoá học của sự polyme hoá nhũ tương xảy ra trong hệ dị thể và được kết thúc bởi sự tạo thành những hạt polyme có kích thước hạt keo.

3.Khi nghiên cứu sự polyme hoá metyl metacrylat, các nhà khoa học đã thu được các dữ kiện đáng chú ý.

4. Người ta đã xác nhận rằng poly metyl metacrylat thu được bằng cách polyme hoá nhũ tương thì rất cứng.

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UNIT 11 THE NATURE OF RUBBER - LIKE ELASTICITY

The characteristic property of rubber, its extensibility and complete recovery after even very large deformations, is shown also by many other substances. Of these we may mention supercooled molten sulfur and selenium, gelatin, muscle fibrils, substances built from long chain molecules such as polyvinyl alcohol, etc... These substances are very different chemically, but their common feature is a long flexible molecule. There is a rubber- like state, which many substances made from long molecules, may assume under suitable conditions.

The two factors which are necessary if perfect rubber - like elasticity is to be obtained are, firstly, that whole molecules must not be able to slip past each other under the action of deforming forces, and, secondly, that these forces shall meet little resistance in straightening out the coiled molecular chains. In lightly vulcanized rubber, the long chains are connected across at certain points by the strong sulfur linkages. This presence of only a few such points of linkage is sufficient to prevent slipping of the whole molecules, which would result in plastic flow. The atoms of the molecule share in the general thermal motion at any temperature, so that the free molecules would be continually coiling, twisting, and changing its shape. There are many more ways in which such molecules can be arranged to give a crumpled chain.

The lengths of chain between sulfur crosslinks behave in essentially the same way as the free rubber molecule, so that the vast majority of them are in a contracted form, which changes momentarily with the thermal motion. This freedom comes from weakness of the Van der Waals forces between the chains, which are not strong enough to hold them permanently in position side by side.

When we apply a force to the rubber, the flexible chains are slightly straightened, but are always attempting to return to their folded condition. It is evident that, the more violent the thermal motion, the greater the tendency of the chains to return to their normal positions.

If a rubber band is stretched by means of a weight, it contracts on heating owing to the effect of the increased thermal motion. This is contrary to the behaviour of normal substances, which deform more easily at high temperatures.

The highly coiled and folded condition of the rubber chains permits their being extended up to seven times their original length. Long before this, however, some of the chains will have been pulled approximately parallel. When this occurs, the attractive forces between them become sufficiently strong to bind them together in a regular arrangement. Thus the rubber is crystallized by tension. This result was clearly demonstrated

by Katz using X - ray diffraction to detect the crystallinity. He showed that ordinary, unstretched rubber has a disordered structure, resembling that of a liquid. Sufficient stretching gives an X - ray diffraction picture similar to that shown by fibrous materials. If the rubber is cooled, while under tension, to a low temperature, it does not contract when the tension is removed, and still gives a crystalline X - ray diffraction pattern. On reheating, “melting “occurs and the rubber contracts. If the frozen stretched rubber is pulverized when cold, it splits up into fibrous pieces, owing to the parallel orientation of the chains.

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If unstretched rubber is cooled, a slow crystallization takes place, giving a harder and less extensible material. On warming, "melting” again occurs, but unlike that of ordinary crystalline substances, it takes place over a range of some 100C in temperature. These effects may be observed in crepe soles kept for some time exposed to very cold weather.

In an ideal rubber- like substance no energy is used in separating chains and in increasing their separation during the stretching. As a result there is no change in the total volume of the substance when extended. This condition is not fulfilled by most rubber - like substances, so that their properties only partially correspond to those of the ideal substances.

Commercial rubbers are very complex systems, in which variation of the proportions of the constituents can give an immense range of products.

Exercises 11.1 Translate into Vietnamese Rubber, extensibility, deformation, mention, supercool, molten, muscle, fibril, alcohol, flexible, assume, slip, resistance, straighten, coil, vulcanize, linkage, sufficient, prevent, twist, crumple, crosslink, majority, contract, momentarily, weakness, permanent, fold, extend, crystallize, unstretch, disorder, resembling, diffraction, tension, detect, fibrous, frozen, pulverize, split, orientation, crepe, expose, stretch, constituent, immense.

11.2 Answer the following questions 1. What substances are known to display the characteristic properties of rubber?

2. What factors is perfect rubber-like elasticity due to?

3. What happens if one applies a force to rubber?

4. In what way did Katz succeed in detecting crystallinity?

5. In what case does the process of slow crystallisation take place?

11.3 Fill in the blanks with prepositions 1. The lengths ... chain sulfur crosslinks behave ... essentially the same way as the free rubber molecule, which changes ... thermal motion.

2. The characteristic property ... rubber, its extensibility and complete recovery... even large deformations, is shown ... many substances.

3. The two factors which are necessary if perfect rubber- like elasticity is to be obtained are, firstly, that whole molecules must not be able to slip ... each other ... the action ... deforming forces, and, secondly, that these forces shall meet ... little resistance ... straightening ... the coiled molecular chains.

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11.4 Translate into English 1. Gần 25 năm sau một số nhà bác học đã đưa ra hàng loạt lý thuyết về tính đàn hồi của cao su.

2. Sự phát triển những lý thuyết chung về tính đàn hồi là một sự kiện quan trọng trong khoa học.

3. Các nhà khoa học đã xác định là các phân tử cao su bị biến dạng khi chuyển động nhiệt.

4. Cần nhớ rằng cao su chưa lưu hoá chứa nhiều phân tử hơn sau khi lưa hoá.

5. Theo thuyết Brown thì bất kỳ một mạch cao su nào cũng ở trạng thái chuyển động nhiệt liên tục.

11.5 Give a summary of the text

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UNIT 12 THERMOPLASTIC ELASTOMERS. THERMOSETTING AND THERMOPLASTIC MATERIAL

Physical properties and applications of thermoplastic elastomers The development of that part of the rubber industry concerned with the fabrication of rubber articles has been primarily concerned with two processes. First, in order that an article of a given shape can be made by some kind of molding process, the viscous properties of raw material must be utilized and possibly enhanced by mastication and degradation. Once the article is shaped, however, viscous flow becomes undesirable, and intermolecular motion must be prevented while retaining sufficient chain segment mobility to provide elastomeric properties.

The thermoplastic industry was the first concerned with rigid polymers, which displaced traditional materials partly because of the economic advantages of high automatic production rates made possible by easy flowing melts and rapid set up on cooling. In recent years, the thermoplastic industry has introduced flexible material such as plasticized PVC and ethylene - vinyl acetate copolymer. Though these materials have some rubbery character, they do not compare with conventional vulcanizates as regards rapid retraction with low set from high elongation, resilience, and other physical properties, or as regards versatility and aesthetic appeal in many applications.

There are many diverse materials which require chemical reaction (usually at elevated temperature) to make useful articles, and these are loosely classed as thermosetting materials.

They range from hard rigid products, through flexible materials to soft high elastic rubber.

Another loose classification can be termed thermoplastic. Representatives of these materials occur only in the first categories, however, the rigid and the flexible.

Rigid

Thermosetting

Thermoplastic

Epoxies

Polystyrene

Phenol- Formaldehyde

Poly- Vinyl Chloride

Urea- Formaldehydes

Polypropylene

Hard rubber Polyethylene Flexible

Highly Vulcanized Rubbers

Ethylene-Vinyl-Acetate Copolymer Plasticized PVC

Rubbery

Vulcanized

Thermoplastic Elastomers

Rubbers (NR, SBR, IR, etc,)

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Thermosetting and thermoplastic material. Description of new products The materials are block copolymers of styrene and butadiene. Their low viscous component results from long chain entanglements and van der Waal’s forces between polymer chains. No covalent or chemical crosslinking, that is, no vulcanization or cure reaction is involved in their use. At lower temperature the interchain forces are sufficiently strong and the sites sufficiently immobile to permit typical snappy rubbery behavior, tensile strength up to 5.000 psi, high resilience, etc.; yet, at elevated temperatures, they are labile with the result that these materials have melt viscosities very similar to conventional thermoplastics at normal processing temperatures.

The thermoplastic elastomers are somewhat superior to conventional natural rubber or SBR vulcanizates in retaining their elastomeric properties down to low temperatures. The flexible thermoplastics, on the other hand, lose their flexibility at much higher temperatures, and in fact can become unusable stiff under fairly mild climatic conditions. (to be continued) Exercises 12.1 Translate into Vietnamese Thermoplastic, thermosetting, fabrication, enhance, mastication, undesirable, intermolecular, motion, prevent, viscous, segment, mobility, provide, elastomeric, displace, automobile, automatic, production, rubbery, conventional, vulcanization, elongation, resilience, regard, versatility, aesthetic, diverse, loosely, class, representative, categories, entanglement, cure, interchain, force, site, immobile, snappy, rubbery, tensile strength, resilience, labile, viscosity, superior.

12.2 Answer the following questions 1. What processes are generally used in the fabrication of rubber articles?

2. What is influence of viscous flow on the shaping process?

3. Is viscous flow desirable when the article is shaped?

4. Why do thermoplastic elastomers flow at elevated temperatures?

5. Why did thermoplastic polymers replace traditional materials?

6. What flexible thermoplastics are widely known at present?

7. Why are thermoplastic elastomers superior to conventional natural rubber?

8. What are the main characteristics of thermosetting materials?

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12.3 Give a short summary of the text Translate the following sentences and state whether the ing- form is expressed by the gerund or by a participle 1. The thermoplastic elastomers are somewhat superior to conventional natural rubber in retaining their elastomeric properties down to low temperatures.

2. The novel products permit the manufacture of elastomeric articles by the use of high speed thermoplastic processing techniques.

3. The new materials can be modified to impart desirable properties without affecting the strength of the polymer network or the capability of obtaining desirable melt flow characteristics.

4. The thermoplastic elastomers are capable of modification in many directions to give special properties while retaining their basic dual elastomeric nature.

5. Stress- strain properties are essentially unaffected by repeated melting and recovery of solid polymer.

6. The latex rubber, having had no mastication, produces a tough, strong film with superior ageing properties.

7. If the latex or latex compound is mixed with a certain thickening agent the amount of compound which clings to the surface of the forms after being immersed is increased.

12.4 Translate the following sentences into English 1. Các đồ vật bằng nhựa có thể điều chế được từ hỗn hợp nhựa nóng chảy.

2. Người ta cho rằng tính chảy dẻo của hỗn hợp cần giảm đi khi các đồ vật vừa mới được hình thành.

3. Như đã biết, gần đây những chất dẻo, hoạt nhiệt và nhiệt dẻo đã thay thế các kim loại trong rất nhiều lĩnh vực kỹ thuật.

4. Các chất dẻo đàn hồi có nhiều tính chất giống với các vật liệu nhiệt dẻo cũng như cao su.

5. Một mặt ở nhiệt độ trung bình và thấp, nhựa đàn hồi giữ được các tính chất của nhựa, nhưng mặt khác ở nhiệt độ cao chúng có khả năng chảy nhớt.

6. Như đã biết, nhiều chất dẻo đàn hồi là copolyme của styrene và butadien.

7. Các nhà khoa học cho rằng nhựa đàn hồi không chứa liên kết cầu.

8. Người ta cho rằng, để chế biến nhựa đàn hồi có thể dùng các thiết bị bình thường của nhà máy sản xuất nhựa.

12.5 Give a summary of the text 44

UNIT 13 THERMOPLASTIC ELASTOMERS (Continued) Applications The basic properties of the materials bring the advantages of both rubbers and the thermoplastics together in the same product and introduce the potential of manufacture rubber articles by the use of modern, high speed, automatic thermoplastics processing techniques from materials in the price range close to that of other general purpose rubbers. They are available in nib form, and since they need no vulcanization, the mastication and mixing steps required with conventional rubbers are avoided.

Like those of other polymers, their properties such as solution and bulk viscosities, hardness, tensile strength, et cetera, can be varied by suitable changes in molecular weight and monomer ratio. The materials can be modified to impart hardness and abrasion resistance, softness, flexibility, improve flow and other desirable properties without unduly affecting the strength of the polymer network, its thermal lability, or the capability of obtaining desirable melt flow characteristics.

These materials contain no gel. In crumb form, as Kraton 101 or Kraton 102, they readily dissolve in conventional rubber solvents; the premastication and cutting needed with baled rubbers is thus avoided. These materials give cast films with tensile strengths 4,500 5,000 psi, and can be formulated with conventional resins to produce excellent pressure sensitive, hot melt, and contact adhesives.

The products, which have so far been designed around these materials, range from soft, transparent rubbers to hard, highly abrasion resistant materials.

Summary New styrene - butadiene copolymer without chemical vulcanization, exhibit true elastomeric properties, that is snappy return from high elongation, high resilience, good tensile strength, and low set, together with rubbery frictional properties and melt flow characteristic similar to those of conventional thermoplastics. The unique properties of these polymers are derived from the complete reversibility of the interchain forces, which constitute crosslinks at ambient temperatures but are not operative in a melt or in a solution. Stress-train properties are essentially unaffected by repeated melting (or dissolution) and recovery of solid polymer.

These novel products permit the manufacture of elastomeric articles by the use of high -speed thermoplastics processing techniques. No curing step is used; hence, lengthy mixing processes are avoided. Scrap can be recycled.

Like conventional natural rubber or SBR vulcanizates, the thermoplastic elastomers retain elastomeric properties down to low temperatures (- 700F). In this, the behavior contrasts 45

with conventional thermoplastics which lose flexibility at temperatures only slightly below ambient.

The polymers are soluble in conventional rubber solvents and are thus suitable for formulation of adhesives, sealants and coatings. The versatility of the materials is such that special properties, such as ozone resistance, can be introduced by the use of simple modifications.

Notes 1. general purpose rubbers: cao su đa dụng tổng hợp 2. in nib form: dạng ban đầu, nguyên thuỷ 3. can be formulated: có thể pha trộn được với Exercises 13.1 Translate into Vietnamese Basic, introduce, potential, manufacture, technique, general purpose rubber, nib form, mastication, abrasion, softness, flexibility, unduly, lability, capacity, crumb, premastication, bale, formulate, adhesive, transparent, abrasion, elastomeric, set, frictional, unique, derive, reversibility, interchain, constitute, ambient, operate, operative, stress-train property, unaffected, cure, curing, scrap, retain, sealant, coating, versibility, ozone resistance, modification.

13.2 Answer the following questions: 1.

What kinds of thermoplastic elastomers are known nowadays?

2.

What is the nature of polymeric chains of thermoplastic elastomers?

3.

How many monomers may be used to prepare thermoplastic elastomers?

4.

What properties of thermoplastic elastomers are truly elastomeric?

5.

What can you say about the behavior of thermoplastic elastomers at low temperatures?

6.

What articles may one produce from thermoplastic elastomers?

7.

Is it possible to recycle the scraps from the fabrication of elastomeric articles?

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13.3 Give Vietnamese equivalents to the following words article

processing

formulation

readily

novel

resin

13.4 State to what parts of speech the following words belong, paying attention to the suffixes a) ambient

rubbery

conventional

soluble

elastic

sufficient

elastomeric

suitable

flexible

superior

natural

thermoplastic

operative

transparent

potential b) abrasion

lability

advantage

resilience

dissolution

resistance

elongation

reversibility

entanglement

softness

flexibility

vulcanizate

c) constitute

modify

formulate

vulcanize

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d) loosely

unusably

unduly 13.5 State the key words in the word combinations and translate them into Vietnamese 1. abrasion resistance

8. processing temperature

2. interchain forces

9.

3. inter molecular motion

10. general purpose rubbers

4. melt viscosity

11. stress - train properties

5. molding process

12. styrene butadiene copolymers

6. ozone resistance

13. ethylene - vinyl acetate copolymer

abrasion resistance materials

7. processing technique 13.6 Translate the following sentences paying attention to the pronoun “no” 1. No covalent or chemical crosslinking, that is, no vulcanization or cure reaction is involved in the use of thermoplastic elastomers.

2. No new results have been presented for the stress relaxation of stocks containing black.

3. Thermoplastics contain no gel, and in crumb form, they readily dissolve in conventional rubber solvents.

4. No test can duplicate all the conditions that may occur during natural ageing.

13.7 Translate the following sentences into English 1. Như đã biết, ngày nay công nghiệp chế tạo ra nhiều loại nhựa đàn hồi.

2. Tính chất của nhựa đàn hồi phụ thuộc vào cả phân tử lượng của chúng cũng như tỉ lệ các monomer trong mạch polyme.

3. Người ta đã xác định được rằng, độ chịu ozon của nhựa đàn hồi lớn hơn nhiều so với các polyme no bình thường.

4. Từ nhựa đàn hồi có thể sản xuất các đồ vật khác nhau như: chất kết dính, sơn, chi tiết của giày, các chất làm bền...

5. Từ lâu người ta đã dự đoán rằng nhựa đàn hồi có thể được ứng dụng rộng rãi trong kỹ thuật.

13.8 Give a summary of the text 48

UNIT 14 ABS PLASTIC

ABS plastics are composed of three monomeric chemicals - acrylonitrile, butadiene and styrene. The name ABS, based on the first letters of each of the monomeric components has been adopted for this family. ABS plastics are composed of styrene acrylonitrile copolymer as the continuous phase and a dispersed phase of butadiene - acrynitrile rubber or a butadiene containing rubber onto which styrene – acrylonitrile copolymers are grafted.

Various combinations of properties are possible, thus making these polymers most attractive for a larger number of current and newly developed applications.

ABS polymers are true thermoplastics similar to polystyrene, polyvinyl chloride, polyolefins, nylon, etc. On application of heat are softened, and when pressure is applied they attain viscous flow.

Upon cooling they harden, and on reheating are resoftened. Thus, they can be remelted and reformed into various shapes with essentially no loss2 in properties. As a result, ABS plastics are extremely useful and versatile, since ease of processing and forming allows them to be used for a great number of applications. In their natural form ABS plastics are opaque, similar in this respect to the impact polystyrenes.

General properties of ABS plastics The excellent combination of properties which ABS plastics offer has spurred the growth of these plastics into many applications. No one single property, but rather the combination of properties of ABS plastics has made them outstanding. Some of the properties, which make these plastics extremely useful, are: 1. Moderate price.

2. Ease of fabrication.

3. Good combination of toughness, rigidity and mechanical properties.

4. Wide colorability.

5. Good dimensional stability.

6. Nontoxicity.

7. Good water resistance.

8. Excellent chemical resistance.

The strength of a fabricated item produced from an ABS plastic is dependent on a number of variables, namely, the fabrication conditions used, the design and shape of the finished piece, the method of stress application, and the environmental conditions encountered. It should be stressed that the conditions under which the plastic part is formed play a very important role on the subsequent mechanical properties of ABS plastics. This is true to all thermoplastics. When ABS polymers are heated and subjected to fabricating conditions, such as injection molding, sheet or profile or pipe extrusion, or thermoforming, 49

many of the long chain polymer molecules change their position and shape and become more aligned: in other words, they become oriented or stretched out, pointing in the direction of flow. Thus, most properties of ABS plastics are not only time and temperature - dependent but are also frequently direction - dependent (anisotropic). Therefore, in describing the properties of ABS plastics, it is important, if at all possible, to specify the properties in relation to the flow direction and the degree of orientation.

Note 1. based on the first letters: (Viết tắt) từ những chữ cái đầu 2. with essentially no loss: về cơ bản không mất Exercises 14.1 Translate into Vietnamese Unique, evolve, acrylonitrile, butadiene, styrene, adopt, soften, harden, reheat, resoften, remelt, reform, versatile, opaque, spur, toughness, rigidity, colorability, water resistance, variable, subsequent, injection, extrusion, thermoforming, align, orient, anisotropic.

14.2 Answer the following questions 1. What is the name ABS based on?

2. How is significant improvement in toughness over polystyrene attained?

3. What other properties of plastics do you know?

4. What are ABS polymers similar to?

5. What happens to ABS polymer upon cooling and heating?

6. Why are ABS plastics extremely useful?

7. What plays a very important role on the mechanical properties of ABS plastics?

14.3 Translate into English 1. Một nhóm lớn các chất dẻo mà thành phần của chúng có: acrylonitrin, butadien và styrene đã được tạo ra trong những năm gần đây.

2. Các polyme thuộc nhóm ABS là chất nhiệt dẻo và giống như các polystyren, polyninylclorua, polyolefin, nilông...

3. Khi gặp nhiệt thì chất nhiệt dẻo chảy mềm ra, khi gặp lạnh thì chúng rắn lại.

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4. Các chất nhựa thuộc nhóm ABS được sử dụng rộng rãi vì dễ sản xuất các monome từ chúng.

5. Cần phải nhấn mạnh rằng, điều kiện để sản xuất các đồ vật bằng nhựa có ảnh hưởng nhiều đến tính chất cơ học của nó.

14.4 Give a summary of the text

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UNIT 15 HAFNIUM Interest in hafnium has increased owing to improved methods for its separation from zirconium and the possible use of zirconium and hafnium in light- weight refractory materials for aircraft construction.

The chemistry of hafnium began about 75 years ago. Coster and Hevesy decided to look for element 72 in minerals containing quadrivalent zirconium. Accordingly, the residues remaining after Norwegian and Greenland zircons had been leached in boiling acids were placed on a copper anticathode and an X ray spectroscopic analysis undertaken. Coster and Hevesy announced the discovery of element 72, proposing the name hafnium in honour of the city in which the discovery was made. This name is generally accepted except in France.

Occurrence Hafnium occurs in nature in small to moderate amount associated with zirconium in all types of zirconium - bearing minerals. The ratio of hafnium to zirconium has been estimated to be about 0.02. Zircons from granite rocks are reported to have higher Hf/Zr ratios than minerals from alkalic ones. Zircons, which may contain up to 7% hafnium, may have their hafnium content determined by radioactivity measurements. Inasmuch as hafnium is isomorphous with uranium and thorium, a constant ratio between hafnium and these radioactive elements is obtained. It is estimated that there are 4 parts per million of hafnium in the earth’s crust water-cooled nuclear reactors. In addition, hafnium is known to be used for making special glasses. It has been applied as a filament in incandescent lights, as a cathode in X - ray tubes, and as an electrode in high pressure discharge tubes. Hafnium - titanium alloys may be used as getters in evacuated or gas filled devices such as lamps, radio tubes, and television tubes.

Extraction Hafnium and zirconium are always extracted together, and the separation of hafnium from zirconium is an important step in the production of reactor - grade zirconium. Thus any technique employed to separate the two elements necessarily must be fractional one.

Extraction of hafnium containing mineral is complicated by the fact that following the fusion of the mineral with ammonium hydrogen fluoride, the fused product may contain a considerable amount associated impurities and as a consequence is not easily dissolved. This necessitates repeated extractions, which result in the accumulation of a large volume in solution. The main problem in the production of hafnium is its separation from zirconium, inasmuch as no chemical reaction is known which is exhibited by one of these elements but not by the other. It is evident that any method used to open zirconium minerals will result in the inclusion of both zirconium and hafnium in the solution.

Physical, mechanical and chemical properties The atomic number of hafnium is 72, the boiling point is known to be 54000C. Metallic hafnium has a brilliant luster. It is harder and less easily worked than zirconium.

After melting in an arc furnace under argon1, hafnium is considered to be hot - rolled in air at 52

8400C. It can be cold - rolled into sheet, swaged or drawn into wire or rod. If the metal is cold reduced in thickness more than 30%, the sheet will fracture if bent. Cold - worked hafnium, if annealed in vacuum or in inert atmosphere, recrystalllizes between 7000 and 8000C. Hafnium has excellent mechanical properties and is extremely corrosion resistant. The machineability of hafnium resembles that of stainless steel. Being a gas sensitive metal, traces of gases ruin its malleability, increase its electrical resistance, and decrease its temperature coefficient of resistance; its electrical conductivity being, at best, 6% that of copper.

The chemical properties of hafnium resemble those exhibited by zirconium very closely.

Hafnium freshly prepared in vacuum is so reactive that no dioxidizers for it are known. The rate of penetration of oxygen into metallic hafnium is lower than that for zirconium.

Applications Hafnium had few commercial uses because of its limited supply and high price, which were due to the difficulty in obtaining it free from its ores.

In recent years, however, this metal has become somewhat more readily available as by-product of reactor-grade zirconium 2, and considerable interest has been aroused in its potential usefulness as a control material in water -cooled nuclear reactors. In addition, hafnium is known to be used for making special glasses. It has been applied as a filament in incandescent lights, as a cathode in X - ray tubes, and as an electrode in high pressure discharge tubes.

Hafnium - titanium alloys may be used as getters in evacuated or gas -filled devices such as lamps, radio tubes, and television tubes.

Notes 1. under argon: trong khí quyển argon 2. reaction-grade zirconium: lò làm sạch zirconi Exercises 15.1 Translate into Vietnamese Hafnium, zirconium, zircon, refractory, construction, aircraft, quadrivalent, leach, copper, cathode, anticathode, granite, inasmuch, isomophous, uranium, thorium, crust, filament, incandescent, discharge, tube, titanium, alloy, evacuate, extraction, fusion, fuse, impurity, accumulate, luster, arc, swage, wire, rod, fracture, anneal, inert, recrystallise, corrosion, machineability, stainless, ruin, malleability, coefficient.

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15.2 Answer the following questions 1. When did the chemistry of hafnium begin?

2. Who was the first to discover the hafnium?

3. What does the word “hafnium" mean?

4. What can you say about the physical properties of hafnium?

5. What are the chemical properties of hafnium?

6. Is hafnium widely used nowadays?

15.3 Describe the process of hafnium extraction 15.4 Translate the following sentences into Vietnamese paying attention to the words in underline type 1. Inasmuch as hafnium is isomorphous with uranium and thorium, a constant ratio between hafnium and these elements is obtained.

2. The main problem in the production of hafnium is its separation from zirconium, inasmuch as no chemical reaction is known which is exhibited by one of these elements.

3. Inasmuch as the color of any oil product is practically always improved by acid, the color is to a certain extent taken as a criterion of the degree of refining.

4. Inasmuch as the rare earth metal is very difficult to prepare in pure form, these has been a lack of data on their physical properties.

15.5 Translate the following sentences into Vietnamese paying attention to the words in bold type 1. It is known that elementary hafnium was first prepared by Hevesy by the reduction of potassium hexafluohafnate with sodium.

2. The rate of penetration of oxygen into metallic hafnium is lower than that for zirconium.

3. The machineability of hafnium resembles that of stainless steel.

4. The chemical properties of hafnium resemble those exhibited by zirconium very closely.

15.6 Replace subordinate clauses by complex subject Model: a) It is known that hafnium is used for making special glasses. b) Hafnium is known to be used for making special glasses.

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1. It was proved that the boiling point of hafnium was 54000C. 2. It is considered that hafnium is hot-roll in air at 8400C. 3. It is known that zircons from granite rocks have higher Hf/Zn ratios than minerals from alkalic rocks.

4. It has been estimated that the ratio of hafnium to zirconium is 0.02 5. It is reported that the main problem in the production of hafnium is its separation from zirconium.

15.7 Translate into English 1. Như đã biết trong tự nhiên hafni được tìm thấy hầu như trong tất cả các khoáng vật chứa zirconi.

2. Hafni giống như thép không rỉ về tính chất cơ học.

3. Người ta đã xác định được rằng hafni chịu được quá trình cán nóng cũng như cán lạnh.

4. Như đã biết, hafni vừa điều chế được trong chân không có khả năng phản ứng hoá học cao hơn bất kỳ một chất khử nào.

5. Một mặt vì những khó khăn trong việc điều chế hafni ở trạng thái tự do, mặt khác vì giá thành cao mà ngày nay việc sử dụng hafni rất hạn chế.

15.8 Give a summary of the text

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REFERENCES Bùi Thị Lệ Thủy, Giáo trình Anh văn chuyên ngành (dùng cho sinh viên ngành Lọc Hóa Dầu), Hà nội, Trường đại học Mỏ- Địa chất, 2003.

1.

Nguyễn Thị Hiền, Nguyễn Trọng Đàn và Lê Thị Lan Chi, The laguage of chemistry, food and biology technology in English, Đại học Bách khoa Hà Nội, 2009.

2.

Mgr. Božena Velebná. English for Chemists. Univerzita Pavla Jozefa Šafárika v Košiciach, Szech Republic.

3.

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PART 2 THE CHEMICAL ENGINEERING UNITS

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UNIT 16 TYPES OF REACTORS The two main types of reactor are termed batch and continuous Batch reactors The simplest type of reactor is a batch reactor. Batch reactors are used for most of the reactions carried out in a laboratory. The reactants are introduced into a test-tube, flask or tank. They are mixed together, often heated for the reaction to take place and are then cooled.

The products are withdrawn out and, if necessary, purified.

This procedure is also carried out in industry, the key difference being one of size of reactor and the quantities of reactants. Batch reactors are typically used in small-scale production and reactions with biological materials, such as in brewing, pulping, and production of enzymes. One example of a batch reactor is a pressure reactor.

Continuous reactors Continuous process is to feed the reactants continuously into the reactor at one point and to take place and withdraw the products at another point. The flow rate of reactants must be equal to that of products. There are several types of continuous reactors using in industry.

CSTR (continuous stirred-tank reactor) In a CSTR, one or more fluid reagents are introduced into a tank reactor. The reactor is typically stirred with an impeller to ensure proper mixing of the reagents while the reaction effluent is removed. Dividing the volume of the tank by the average volumetric flow rate through the tank gives the space time, or the time required to process one reactor volume of fluid. Using chemical kinetics, the reaction's expected percent completion can be calculated PFR (plug flow reactor) In a PFR, sometimes called continuous tubular reactor (CTR), fluids (gases and/or liquids) flow through it at high velocities. The chemical reaction proceeds as the reagents travel through the PFR. At these high velocities, the products are unable to diffuse back and there is little or no back mixing; at the inlet to the PFR the rate is very high, but as the concentrations of the reagents decrease and the concentration of the product(s) increases the reaction rate slows.

Semibatch reactor A semibatch reactor is operated with both continuous and batch inputs and outputs. A fermenter, for example, is loaded with a batch of medium and microbes which constantly produces carbon dioxide that must be removed continuously. Similarly, reaction of a gas with a liquid is usually difficult, because a large volume of gas is required to react with an equal mass of liquid. To overcome this problem, a continuous feed of gas can be bubbled through a batch of a liquid. In general, in semibatch operation, one chemical reactant is loaded into the reactor and a second chemical is added slowly (for instance, to prevent side reactions), or a product which results from a phase change is continuously removed, for example a gas formed by the reaction, a solid that precipitates out, or a hydrophobic product that forms in an aqueous solution.

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Exercises 16.1 Read and translate into Vietnamese Batch, batch reactor, continuous, test tube, flask, tank, pulping, withdraw, stirrer, stir, impeller, volumetric, plug, tubular, velocity, diffuse, microbes, fermenter, bubble, semibatch, hydrophobic.

16.2 Answer the following questions 1. Please describe a batch reactor?

2. What are the various kinds of continuous reactors?

3. What is a continuous stirred-tank reactor?

4. Please describe a plug flow reactor?

5. What is a semibatch reactor?

6. Tell something about a semibatch reactor?

16.3 Translate into Vietnamese paying attention to the infinitives 1. This is the gas from which the growing plant builds up sugar and other substances as organic raw materials, without waiting for nature to turn them into coal and oil.

2. In some time we shall discover the secrets of photosynthesis, by which the plant uses sunshine to convert carbon dioxide into sugars.

3. We shall use some synthetic process to turn carbon dioxide from the air into simple organic chemicals.

4. The twentieth century was the time when man began to understand how to make all the new synthetic materials from simple chemicals.

5. To make use of isotope instruments to supervise a number of chemical processes which formerly had been difficult to check properly is very important for chemical industry today.

6. Polymerization of monomer chloride proceeds more easily, than that of ethylene, an effect to be associated with the polar nature of the vinyl chloride molecule.

16.4 Translate the following sentences into Vietnamese paying attention to the words in bold type 1. Repeated washing of latex in a centrifuge, followed by drying, results in rubber suited for insulation purposes.

2. Homologs of aniline result from the reduction of their corresponding nitro compounds.

3. In the experiment conducted in the laboratory the resultant product is a vitreous solid that softens at 1000.

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4. The fatty acids resulting from the hydrolysis are neutralized by the use of sodium or potassium hydroxide.

6. It is accepted that storage hardening results from the presence of carbonyl groups in very small proportions.

16.5 Select attributes (from the list given below) to the following words and translate them into Vietnamese

Amount

atomic

Analysis

earth’s

Atmosphere

deep electrical

Conductivity

high

Crust

hot-rolled

Filament

incandescent

Number

inert

Tube

moderate

Vacuum

spectroscopic

Zirconium

X-ray

16.6 Give Vietnamese equivalents to the following words 1. extract, extraction, extractive, extractor; 2. oxide, oxidize, oxidizer, deoxidizer, deoxidate, deoxidation, deoxidization; 3. nuclear, nucleate, nucleated, nucleation, nuclei, nucleonic, nucleus; 16.7 State the key words in the following word combinations and translate them into Vietnamese

arc furnace

hafnium-containing minerals

cold-rolled hafnium

reactor-grade zirconium

gas-filled device

zircon-bearing minerals

gas-sensitive metal

water-cooled nuclear reactor 60

16.8 Translate into English 1. Thiết bị phản ứng dạng mẻ thường được dùng trong phòng thí nghiệm.

2. Các thiết bị phản ứng dưới áp suất cao phải có van an toàn và chịu được áp suất cao.

3. Thiết bị phản ứng liên tục thường được dùng trong công nghiệp.

4. Lò phản ứng liên tục vận hành với cả đầu vào đầu ra liên tục 16.9 Write a short summary of the text

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UNIT 17 HEAT TRANSFER AND ITS APPLICATIONS

Practically all the operations that are carried out by the chemical engineer involve the production or absorption of energy in the form of heat. The laws governing the transfer of heat and the types of apparatus that have for their main object the control of heat flow are therefore of great importance. This section of the book deals with heat transfer and its applications in process engineering.

NATURE OF HEAT FLOW. When two objects at different temperatures are brought into thermal contact, heat flows from the object at the higher temperature to that at the lower temperature. The net flow is always in the direction of the temperature decrease. The mechanisms by which the heat may flow are three: conduction, convection, and radiation.

Conduction. If a temperature gradient exists in a continuous substance, heat can flow unaccompanied by any observable motion of matter. Heat flow of this kind is called conduction. In metallic solids, thermal conduction results from the motion of unbound electrons, and there is close correspondence between thermal conductivity and electrical conductivity. In solids that are poor conductors of electricity and in most liquids, thermal conduction results from the transport of momentum of individual molecules along the temperature gradient. In gases conduction occurs by the random motion of molecules, so that heat is “diffused” from hotter regions to colder ones. The most common example of conduction is heat flow in opaque solids, as in the brick wall of a furnace or the metal wall of a tube.

Convection. When a current or macroscopic particle of fluid crosses a specific surface, such as the boundary of a control volume, it carries with it a definite quantity of enthalpy.

Such a flow of enthalpy is called a convective flow of heat or simply convection. Since convection is a macroscopic phenomenon, it can occur only when forces act on the particle or stream of fluid and maintain its motion against the forces of friction. Convection is closely associated with fluid mechanics. In fact, thermodynamically, convection is not considered as heat flow but as flux of enthalpy. The identification of convection with heat flow is a matter of convenience, because in practice it is difficult to separate convection from true conduction when both are lumped together under the name convection. Examples of convection are the transfer of enthalpy by the eddies of turbulent flow and by the current of warm air from a household furnace flowing across a room.

Natural and forced convection. The forces used to create convection currents in fluids are of two types. If the currents are the result of buoyancy forces generated by differences in density and the differences in density are in turn caused by temperature gradients in the fluid mass, the action is called natural convection. The flow of air across a heated radiator is an 62

example of natural convection. If the currents are set in motion by the action of a mechanical device such as a pump or agitator, the flow is independent of density gradients and is called forced convection. Heat flow to a fluid pumped through a heated pipe is an example of forced convection. The two kinds of force may be active simultaneously in the same fluid, and natural and forced convection then occur together.

Radiation. Radiation is a term given to the transfer of energy through space by electromagnetic waves. If radiation is passing through empty space, it is not transformed into heat or any other form of energy nor is it diverted from its path. If, however, matter appears in its path, the radiation will be transmitted, reflected, or absorbed. It is only the absorbed energy that appears as heat, and this transformation is quantitative. For example, fused quartz transmits practically all the radiation that strikes it; a polished opaque surface or mirror will reflect most of the radiation impinging on it; a black or matte surface will absorb most of the radiation received by it and will transform such absorbed energy quantitatively into heat.

Monatomic and most diatomic gases are transparent to thermal radiation, and it is quite common to find that heat is flowing through masses of such gases both by radiation and by conduction-convection. Examples are the loss of heat from a radiator or uninsulated steam pipe to the air of a room and heat transfer in furnaces and other high-temperature gas-heating equipment. The two mechanisms are mutually independent and occur in parallel, so that one type of heat flow can be controlled or varied independently of the other. Conductionconvection and radiation can be studied separately and their separate effects added together in cases where both are important. In very general terms, radiation becomes important at high temperatures and is independent of the circumstances of the flow of the fluid. Conductionconvection is sensitive to flow conditions and is relatively unaffected by temperature level.

Exercises 17.1. Read and translate into Vietnamese Operation, absorption, transfer, engineering, conduction, conductivity, convection, radiation, gradient, unccompany, matter, unbounded, correspondence, transport, individual, diffuse, oqaque, macroscopic, force, friction, associated, fluid, thermodynamic, enthalpy, identification, lump, eddy, turbulent, current, household, buoyancy, radiator, motion, mechanical, agitator, pump, simultaneous, simultaneously, electromagnetic, divert, transmit, reflect, fuse, quartz, stiker, polish, impinging, monatomic, diatomic, transparent, mutually.

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17.2 Group the following words into pairs of synonyms employed

provided

diluted

watered

presumably

totally

investigation

original

if

precisely

initial

procedure

utilized

exactly

entirely

search

probably

process

17.3 Group the following words into pairs of antonyms original

conventional

rapidly

in particular

start

above

insoluble

as slow as

as high as

soluble

final

unusual

slowly

below

complete

in general

17.4 Give Vietnamese equivalents as slow as 0.02

long enough

efficiency of grafting

on storage

in contrast with

refer to

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17.5 Give antonyms to the following words immobilised

low

asymmetric

fluid

unable

stable

short

destroy

thick

unvulcanized

unimportant

disconnect

undesirable

rigid

liquid

strong

17.6 Translate the following derivatives into Vietnamese structure, structural

solution, solvent, soluble, dissolve

vary, various

possible, impossible

conclude, conclusion, conclusive

line, linear

liquid, liquefy

coherence, coherent, cohesive

fibre, fibrous

gelation, gel

ability, able, unable

conduct, conductive, conduction

stable, unstable, stability

ferrous, ferric

17.7 Select attributes (from the list given below) to the following words and translate them into Vietnamese Amount

atomic

Analysis

earth’s

Atmosphere

deep electrical

Conductivity

high

Crust

hot-rolled

Filament

incandescent

Number

inert

Tube

moderate

Vacuum

spectroscopic

Zirconium

X-ray

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17.8 Give Vietnamese equivalents to the following words 4. extract, extraction, extractive, extractor; 5. oxide, oxidize, oxidizer, deoxidizer, deoxidate, deoxidation, deoxidization; 6. nuclear, nucleate, nucleated, nucleation, nuclei, nucleonic, nucleus; 17.9 State the key words in the following word combinations and translate them into Vietnamese arc furnace

hafnium-containing minerals

cold-rolled hafnium

reactor-grade zirconium

gas-filled device

zircon-bearing minerals

gas-sensitive metal

water-cooled nuclear reactor

17.10 Write a short summary of the text

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UNIT 18 EXTRACTION WITH SOLVENTS Extraction of Solids Examples of extractions of solid mixtures are the extraction of alkaloids from leaves and bark, flavoring extracts from seeds, perfume essence from flowers, and sugar from sugar cane. Solvents commonly used for this purpose are ether, dichloromethane, chloroform, acetone, various alcohols, and water. Brewing coffee is an example of liquid-solid extraction.

In the laboratory, a common form of apparatus for continuous extraction of solids by means of volatile solvents is the Soxhlet extractor, shown in Figure 4.

(a)

(b)

Figure 4. Soxhlet extraction (a) and separatory funnel (b)

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Vapors from the solvent boiling in the pot rise through the vertical tube at the left into the condenser at the top. The liquid condensate drips into the filter paper thimble in the center, which contains the solid sample to be extracted. The extract seeps through the pores of the thimble and eventually fills the siphon tube at the left, where it can flow back down into the pot. If the sample being extracted is not volatile it gradually accumulates in the pot. With the apparatus shown, the siphoning action is intermittent. No liquid will flow through the siphon until the liquid level in the thimble reaches the top of the siphon tube. At that point almost all of the liquid in the siphon and the thimble drain out and the cycle of filling and draining starts again.

Extraction of Solutions A more common application of extraction is in “liquid-liquid” extraction, which is used to isolate a substance dissolved in one solvent by shaking (mixing) the solution another solvent, immiscible with the first, in a separatory funnel (see Figure 4.b). In the ideal situation, the substance is extracted into the second solvent, the impurities are left behind, and after the two layers are separated, the substance is isolated by removal of the solvent.

The general physical principle underlying this process is known as the distribution law. In dilute solutions a substance distributes itself between two immiscible solvents so that the ratio of the concentration in one solvent to the concentration in the second solvent always remains constant (at constant temperature). This constant ratio of concentrations for the distribution of a solute between two particular solvents is called the distribution coefficient or the partition coefficient for the substance between the two solvents.

K = CA/CB where: K is distribution coefficient between solvents A and B, CA is concentration (g/ml) of S in A, CB: Concentration (g/ml) of S in B. It is important to observe the manner in which the ratio is expressed; e.g., at 20°C the distribution coefficient of butanoic acid between ether and water is approximately 5 (concn in ether/concn in water = 5), but if the ratio is expressed as the distribution between water and ether the value is 0.2 (concn in water/concn in ether = 1/5).

In actuality, no two solvents are totally immiscible (insoluble in each other); there is always some solubility, small though it may be. In practice the most common application of the distribution law is to the extraction of dissolved substances from aqueous solutions by almost water-insoluble solvents such as ether, hexane, and dichloromethane. Ether, which is used frequently as an extraction solvent because so many neutral organic compounds are soluble in it, is somewhat more soluble in water than other common solvents; e.g., at 30°C diethyl ether is soluble to the extent of 1 g in 18.8 g of water (and water is soluble to the extent of 1 g in 73 g of ether). Ether, unfortunately, is highly flammable and presents a serious fire hazard. Dichloromethane (bp 40°C) is less soluble in water (about 2 g/100 mL at 20°C) and has the important advantage over ether that it is not flammable under ordinary conditions; the drawback of dichloromethane is that prolonged exposure to its vapors is hazardous, so that it must be used in a well-ventilated area. Hexane is for all practical purposes insoluble in water, but it also suffers from the disadvantage of being highly flammable, although not as severe as diethyl ether.

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The actual distribution coefficient is determined by bringing the solvents and solute into equilibrium at a given temperature and measuring the concentration of solute per unit volume of each separate phase. A rough approximation to the distribution coefficient can be made by determining the solubility of the solute in each pure solvent independently, since the distribution coefficient is approximately the ratio of the solubilities in the two solvents. The values obtained in this way are subject to several errors but are usually good enough for simple laboratory calculations.

For application of the distribution law to laboratory extractions a convenient formula is shown in equation (1), which gives the fraction of compound S remaining in volume VA of solvent A after extraction with volume VB of solvent B.

fraction remaining in A 

C final Cinitial



1 V 1 B VA K

(1)

where Cfinal is the final concentration of S in A, Cinitial is the initial concentration of S in A, and K is the distribution coefficient (concentration of S in A divided by the concentration of S in B).

Example. Let us apply equation (1) to the situation where the distribution coefficient of the compound S between hexane and water (K hexane/ water) is 1/3 at 25°. If a hexane solution containing 8 g of S in 100 mL of hexane is extracted at 25°C with 100 mL of water, the fraction of S remaining in the hexane is from which it follows that the weight of S in the hexane layer is 2.0 g (i.e., a reduction by 1.0-0.25, or three fourths) and the amount in the aqueous layer is 6.0 g.

1 100mL 1 100mL  1

 0.25 3

If the hexane layer is separated and extracted with a fresh 100-mL portion of water, the amount of S will again be reduced by three fourths to give only 0.5 g remaining in the hexane layer. The second aqueous extract contains 1.5 g of S, which, when added to the 6.0 g of S in the first aqueous extract, gives a total of 7.5 g of S in the combined aqueous layers.

Exercises 18.1 Read and translate into Vietnamese Extraction, extract, extractor, isolation, isolate, arise, alkaloid, bark, common, commonly, Soxhlet, vertical, tube, drip , thimble, seep, gradually, accumulate, siphon, intermittent, drain, shake, miscible, immiscible, funnel, separatory funnel, impurity, distribution law, dilute, hazard, prolong, exposure, ventilate, to be subject, error.

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18.2 Answer the following questions 1. What is the purpose of extraction process in chemical engineering?

2. Give some examples of extraction of solids?

3. Which solvents are used in extraction and why?

4. What is the principle of liquid – liquid extraction?

5. How can people choose the solvents for extraction?

6. What are the advantages and disadvantages of ether as solvent for extraction?

7. The same questions for dichloromethane and hexane?

18.3 Translate the following sentences paying attention to the words in bold type 1. A great deal of knowledge has been gained since emulsion polymers were first produced on a large scale.

2. The term “emulsion polymerization” is applied to processes which have in common that the main chemical reaction is a polymerization and that the end product is a latex.

3. Most often, particularly in the case of two pure liquids, the coalescence process is rapid.

4. Polymerizations in which the monomer is initially dissolved in water producing a suspension of small particles of polymer are sometimes named emulsion polymerizations as well.

5. Ultra-violet light is known to have a harmful influence on a rubber surface, as well as causing photochemical effects on antioxidants.

6. The chemical reactions of emulsion polymerization take place in heterogeneous system in which polymer particles of colloidal dimensions are formed.

7. One of the growth mechanisms has been found to hold true in many polymerizations with small particles.

8. In 1926 German scientists succeeded in producing synthetic rubber latices by polymerizing monomer emulsions stabilized by various surfactive agents.

9. In 1938 Fikentscher was the first to express the view that in emulsion polymerizations the monomer, dissolved in the aqueous phase polymerizes rather than the monomer present as emulsified droplets.

18.4 Put question to the words in bold type 1. The Hardness of rubber is measured either by Mooney viscosity or Williams plasticity.

2. The generation of oxygenated groups in some secondary reaction is consistent with our present knowledge of polyisoprene biosynthesis.

3. The infra-red spectrum is closely similar to that of natural rubber.

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4. The stress produced by shearing is very low compared with that of natural rubber.

18.5 Translate the following sentences paying attention to the function of the verb to do 1. Monosaccharides do not hydrolize to simpler substances.

2. An organic chemist has much to do with different reactions.

3. It is known that most fibers when suspended in an alkaline aqueous medium have a negative charge as do the particles in alkaline latex.

4. Upon what structural arrangement does the colour of an organic compound depend?

5. Some grades of synthetic material have lower cis- content than does natural rubber.

6. The results of the experiment show that adhesion does increase for a time after curing, at least when measured at room temperature.

7. On the basis of oxidizability, the zinc salt had the effect, as did mercaptobenzimidazole itself.

18.6 Translate into English 1. Phương pháp chiết dùng để tách các hợp chất ra khỏi hỗn hợp rắn hoặc lỏng của chúng.

2. Các hợp chất tự nhiên được phân lập ra khỏi lá, vỏ cây, hạt… bằng phương pháp chiết rắnlỏng.

3. Phương pháp chiết lỏng – lỏng thường dùng để tinh chế các chất ra khỏi tạp chất.

4. Trong phòng thí nghiệm, thiết bị chiết Soxhlet được dùng để chiết rắn-lỏng.

5. Phễu chiết được dùng để chiết lỏng – lỏng 6. Nguyên tắc vật lý của quá trình chiết lỏng – lỏng là sự khác nhau về độ tan của chất cần tách và tạp chất trong các dung môi.

18.7 Write a short summary of the text

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UNIT 19 INTRODUCTION TO DISTILLATION AND ATMOSPHERIC DISTILATION

Distillation consists of boiling a liquid or a solid and condensing the vapor in such a manner that the condensate (distillate) is collected in a separate container. A simple apparatus assembly for this operation consists of a distillation flask fitted with a thermometer and appropriate condenser. The common use of the term fractional distillation refers to a distillation operation in which a fractionating column has been inserted between the boiler and the vapor take off to the condenser. The effect of this column is to increase the separation efficiency of the system.

Fractionating Columns. The easiest way to understand the principles by which fractionating columns give their superior separations is to consider first a rather special type of column known as a bubble plate column. The essential features of a bubble plate column, illustrated in Figure 5 consist of (1) a series of horizontal plates, A, which support a layer of distillate; (2) capped risers, B, through which the distilling vapors ascend; and (3) overflow pipes, C, which return any excess distillate to the next lower plate. At the beginning of a distillation, the vapors coming up from the boiler pass through the first riser and are deflected downward by the cap onto the first plate, where they are condensed. As simple vaporization and condensation continue, the rising vapors are forced to bubble through the liquid on the plate. The liquid level rises to the top of the overflow tube and then flows downward to the boiler. The liquid on the first plate corresponds to the first fraction in a simple distillation, it is enriched in the lower-boiling component. It follows that the temperature of the vapor bubbling through the liquid is above the boiling point of the liquid on the plate; through heat exchange, the liquid is brought to its boiling point and its vapor rises to the second plate where the same processes are repeated. As the distillation continues, each plate becomes filled with a layer of liquid whose composition is that of the vapor rising from the next lower plate.

Under ideal circumstances, each plate achieves an increment of separation equivalent to one simple distillation.

Figure 5. Bubble Plate Column

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The overflow tubes serve a more important function than just acting as returns for excess condensate. Since the vapor leaving any plate is richer in the lower-boiling component than the vapor entering the plate, the higher-boiling materials tend to accumulate on the plate.

The overflow returns this higher- boiling material to the lower plate, so that an equilibrium balance of low-boiling to high-boiling components is maintained. In effect, vapor and condensate are passing in opposite directions through the column; the more volatile component ascends the column in the vapor stream, while the less volatile components descend in the condensate stream. The counterflow is essential for effective separation in a fractionating column.

The separation process can be understood more clearly by reference to a liquid-vapor composition diagram such as that shown in Figure 6 for carbon tetrachloride (bp 77°C) and toluene (bp 111°C). A liquid mixture containing 50 mol percent carbon tetrachloride (point A on the liquid line) is in equilibrium with vapor containing 71mole percent carbon tetrachloride (point A' on the vapor curve). If liquid with composition A is partially vaporized and the vapor with composition A' condensed completely on the first bubble plate, the condensate is represented by B (on the liquid line). Repetition of the vaporization- condensation process with liquid B yields a new distillate, C, containing 85% carbon tetrachloride, which condenses on the second bubble plate. Each successive bubble plate achieves an additional increment of separation.

Figure 6. Boiling point diagram: Tetracarbon-Toluene

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Bubble plate columns have the drawback of requiring large samples for effective operation, and a substantial portion of material is condensed on the plates (holdup). To overcome these disadvantages, small-scale laboratory fractionations are usually done with cylindrical columns packed with materials having large surface area (glass beads or helices, small sections of twisted metal, Carborundum chips, and the like). The principles of operation of packed columns are quite similar to those of the bubble plate column. The layers of packing material, like the bubble plates, serve as support for films of condensate; vapor passing through the layers is enriched in the lower-boiling component, and the higher-boiling components drip downward to lower layers. The packing material provides the thorough mixing of vapor and condensate that is essential for fractionating efficiency.

Exercises 19.1 Read and translate into Vietnamese Collect, fractional distillation, simple distillation, fractionating column, principle, bubble, feature, illustrate, horizontal plate, cap, riser, ascend, overflow pipe, deflect, flow, enrich, correspond, circumstance, increment, equilibrium, balance, descend, counterflow, essential, reference, composition, repetition, successive, drawback, substance, cylindrical, pack, parked column, drip, downward, thorough, condensate, efficiency.

19.2 Answer the following questions 1. What is distillation?

2. What is the purpose of distillation?

2. What is the main difference between the simple and fractional distillation systems?

3. What is the purpose of a fractionating column for separate distillation?

4. What does a bubble plate column consist of?

5. What are the disadvantages of a bubble plate column?

19.3 Translate into English 1. Thiết bị chưng cất đơn giản bao gồm 1 bình cất, nhiệt kế, bộ ngưng tụ và bình hứng.

2. Chưng cất phân đoạn dùng để tách một hỗn hợp gồm các cấu tử có nhiệt độ sôi khác nhau.

3. Bộ phận quan trọng trong hệ chưng cất phân đoạn là cột chưng cất.

4. Nguyên tắc của chưng cất phân đoạn là sự phân tách các chất dựa trên sự khác nhau về nhiệt độ sôi.

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19.4 Describe a simple distillation process using the figure below.

Figure 7. Simple distillation process

19.5 Describe a fractional distillation process using the figure below.

Figure 8. Fractional distillation process 75

19.6 Translate the following sentences into Vietnamese, paying attention to the words in bold type 1. A great number of experiment concerning the nature and extent of filler- rubber adhesion have been conducted.

2. The thermoplastic industry was first concerned with rigid polymers, which displaced traditional ones 3. Artificial ageing tests concerned are an extremely important part of rubber testing.

4. The development of that part of the rubber industry concerned with the fabrication of rubber articles has been primarily concerned with two processes.

19.7 Translate the following sentences into Vietnamese, paying attention to the words in bold type 1. Though thermoplastic elastomers have some rubbery characters, they do not compare with conventional vulcanizates as regards rapid retraction with low set from high elongation, resilience, or as regards versatility and aesthetic appeal in many applications.

2. Petroleum and its distillates cannot be regarded as a source of raw elemental sulfur.

3. The problems regarding the use of pigments in latex are similar to those in other types of coatings and finishes.

4. Gerlach developed an interesting table with regard to the boiling points of glycerol solutions.

19.8 Write a short summary of the text

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UNIT 20 VACUUM DISTILLATION

Since the boiling temperature of a liquid is decreased by diminishing the pressure on its surface, you can distill at a lower temperature by using an apparatus that is connected to a vacuum pump that maintains a lower inside pressure. This procedure is useful for purifying liquids (or low-melting solids) that decompose at elevated temperatures. For example, glycerol boils with some decomposition at 290°C under 760 mmHg pressure, but it may be distilled without decomposition under 12-mm pressure, where its boiling point is 180°C. A possible disadvantage of fractional distillation under reduced pressure is the reduction in separation effìciency of most fractionating columns.

In planning a vacuum distillation, three aspects must be considered: the pressure needed to achieve the desired boiling point, the type of vacuum pump needed to lower the pressure to the required level, and finally, the associated glassware, pressure measuring devices, and heat sources.

Effect of pressure on boiling temperature Estimation of boilling point. One useful relationship between pressure and boiling point is given in equation (1), where P is the pressure over the liquid and T is the boiling point at this pressure. In this equation, both boiling temperatures are expressed in degrees Kelvin (K = °C + 273). Equation (1) is fairly precise for most organic liquids, but is in error for substances possessing unusually large attractions between molecules (water, alcohols, acids).

More precise relationships have been developed, but the extra work required to use them is not justified for preparative organic chemistry. 𝒍𝒐𝒈𝟏𝟎

𝟕𝟔𝟎 𝑷

= 𝟓. 𝟒𝟔

𝒏𝒐𝒓𝒎𝒂𝒍 𝒃𝒐𝒊𝒍𝒊𝒏𝒈 𝒑𝒐𝒊𝒏𝒕 𝑻

-1

(1)

The use of equation (2) is outlined here for nitrobenzene.

- Normal boiling point of nitrobenzene = 211°C = 484°K - If the desired boiling point is 100°C = 373°K, the equation becomes 𝒍𝒐𝒈𝟏𝟎

𝟕𝟔𝟎 𝑷

𝟒𝟖𝟒

= 𝟓. 𝟒𝟔 𝟑𝟕𝟑 − 𝟏 = 𝟏. 𝟔𝟐

(1)

- The expression is solved for P. Ppredicted = 18.0 mm Hg - At a pressure of 18.0 mm Hg, it is observed that nitrobenzene boils at 98°C instead of the desired 100°C. That is about as good agreement as you could hope for.

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Another approach to estimating the boiling points at reduced pressure is to use a nomograph, such as the one shown in Figure 9. To estimate the boiling point at some reduced pressure of a hydrocarbon for which boiling point at 760 mm is known, place a straightedge (preferably transparent) on the nomograph connecting the known boiling point on scale B and the reduced pressure on line C for hydrocarbons. The boiling point of the compound at the reduced pressure is read from the intersection of the straightedge and the left-hand A scale. If the compound contains a carboxylic acid functional group, line C for carboxylic acids is used instead. The boiling points of polar molecules and less strongly hydrogen bonded molecules can be estimated as the average of the boiling points obtained by using both the hydrocarbons and carboxylic acid lines. Note that for compounds boiling near 100°C both lines give about the same result; it is only for high boiling liquids that different predicted boiling points are obtained.

Figure 9. Nomograph for boiling points at reduced pressure

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Exercises 20.1 Read and translate into Vietnamese Diminishing, vacuum, pump, maintain, decompose, decomposition, efficiency, estimation, alcohol, acid, precise, justify, estimate, approach, straightedge, transparent, intersection, carboxylic acid, predict.

20.2 Answer the following questions 1. What is the principle of vacuum distillation?

2. When do we use vacuum distillation?

3. What is the advantage of vacuum distillation?

4. What is the disadvantage of vacuum distillation?

5. How can we estimate the boiling point of a given compound at a certain reduced pressure?

20.3 Translate the following sentences paying attention to the Passive Voice 1. The employment of latex is being aimed at reinforcing furs, particularly rabbit skins, which are very soft and weak.

2. When a solid is attacked by a liquid reagent the product might be either soluble or insoluble in the liquid.

3. Polyvinyl chloride was not thought of as a competitor of rubber until the war.

4. Branching may be referred to as changing mainly the shape of the molecule.

5. It was assumed that the rate of reaction at high conversion would be governed by the diffusion rate of the monomer.

6. Fundamental investigations concerning chemical catalysis were aimed at a quantitative expression of activity.

7. Polyethylene is not affected by aggressive mediums such as acids, alkalis and salt solutions.

8. Rubber is known to be unaffected by many neutral salts, organic acids, etc.

9. Soft vulcanized rubber in the presence of antioxidants was acted upon by the oxygen of the air.

10. If the substance being ground is a reactive one, the possibility of chemical alteration of the surface by chemisorption of oxygen or water vapour from the air must be reckoned with.

11. Since adhesion is greatly influenced by adsorption of gases and vapours, one would expect the bulk density to depend on the humidity of the air.

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20.4 Translate into Vietnamese paying attention to the Gerund 1. Reheating rubber is always attention by increasing its volume.

2. Merret identified the component responsible for producing the sol with the graft copolymer.

3. Many surface coatings shrink slowly on having been aged.

4. Natural rubber vulcanized with zinc oxide in the absence of free sulfur is known for being resistant to ageing.

5. The highly coiled rubber chains permit their being extended up to seven times their original length.

20.5 Translate into English 1. Nhiệt độ sôi của một chất giảm nếu giảm áp suất tác dụng lên bề mặt chất lỏng đó.

2. Chưng cất chân không dùng để tinh chế các chất có nhiệt độ sôi cao hoặc bị phân huỷ ở nhiệt độ sôi.

3. Chưng cất chân không cần thiết bị phức tạp.

4. Có thể ước tính được áp suất cần thiết để chưng cất một chất cho trước ở một nhiệt độ mong muốn và ngược lại.

20.6 Write a short summary of the text

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UNIT 21 STEAM DISTILLATION

Steam distillation consists of distilling a mixture of water and an insoluble or partly soluble substance. The practical advantage of steam distillation is that the mixture usually distills at a temperature below the boiling point of the lower boiling component.

Consequently, it is possible to steam distill a high boiling organic compound at a temperature much below its boiling point (in fact, below 100°) without resorting to vacuum distillation.

Steam distillation is useful also in separating mixtures when one component has an appreciable vapor pressure (at least 5 mm) in the vicinity of 100° and the other has a negligible vapor pressure. The process of steam distillation is widely employed in the laboratory and in industry; e.g., for the isolation of α-pinene, aniline, nitrobenzene, and many natural essences and flavoring oils.

Principles of Steam Distillation Mixtures of two insoluble substances behave quite differently from homogeneous solutions, and the description of their behavior requires a different physical law. The basis of this law can be grasped, by considering the consequence of increasingly positive deviations from Raoult’s law. One symptom of small positive deviations is a skewed boiling point composition diagram, as is found with methanol-water solutions. Greater positive deviations, as occur in ethanol-water solutions, lead to maxima in the total vapor pressure curve and to low-boiling azeotropes. With still greater positive deviations, the two components can separate into two immisible layers. In the limit of very large positive deviations from Raoult’s law, the two components are essentially insoluble and each component vaporizes independently of the other to give a total vapor pressure that is the sum of the individual vapor pressures. The physical basis for this independent behavior of the two components is depicted in Figure 10. In this diagram component B is represented as two globules suspended in component A; an incipient bubble in contact with both components is shown in the center of the diagram. The vapor pressure of component A inside the bubble is PA° (the vapor pressure of pure A) just as it would be if no B were present. In the same fashion the vapor pressure of B inside the bubble is PB°. Most water insoluble organic compounds approximate this extreme behavior so that steam distillation calculations are normal based on the simple law: The total vapor pressure equals the sum of the pressures of the two components.

Distillation Temperature and Composition of Distillate As with ordinary distillations, the boiling point is the temperature at which the total vapor pressure equals the atmospheric pressure. If the vapor pressure of the two components are known at several temperatures, the distillation temperature is found readily by plotting the vapor pressure curves of the individual components and making a third curve showing the sum of the vapor pressure at the various temperatures. The steam distillation temperssures will be the point where the sum equals the atmospheric pressure.

Knowing the distillation temperature of the mixture and the vapor pressure of the pure components at that temperature, one can calculate the composition of the distillate by means of Dalton’s law of partial pressures.

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Figure 10. Vapor Pressure inside Bubble During Steam Distillation

According to Dalton’s law, the total pressure (P) in any mixture of gases is equal to the sum of the partial pressures of the individual gaseous components (PA, PB, etc). The proportion by volume of the two components in the distilling vapor will consequently be equal to the ratio of the partial pressures at that temperature; the molar proportion of the two components (nA and nB) in steam distillation will be given by the relationship nA/nB = pA/pB, where pA + pB equals the atmospheric pressure. The weight proportion of the components is obtained by introducing the molecular weights (MA and MB). 𝒎𝑨 𝑷𝑨 𝒙 𝑴𝑨 = 𝒎𝑩 𝑷𝑩 𝒙 𝑴𝑩 Where mA, mB are mass of A and B Example. Consider a specific case, such as the steam distillation of bromobenzene and water. Since the sum of the individual vapor pressures attains 760 mm Hg at 95.2°C, the mixture will distill at this temperature. At 95.2°C the vapor pressures are bromobenzene, 120 mm Hg and water, 640 mm Hg. According to Dalton’s law, the vapor at 95.2°C will be composed of molecules of bromobenzene and of water in the proportion of 120: 640. The proportion by weight of the components can be obtained by introducing their molecular weights. 𝒎𝒃𝒓𝒐𝒎𝒐𝒃𝒆𝒏𝒛𝒆𝒏𝒆 𝟏𝟐𝟎 𝒙 𝟏𝟓𝟕 𝟏. 𝟔𝟑 = = 𝒎𝒘𝒂𝒕𝒆𝒓 𝟔𝟒𝟎 𝒙 𝟏𝟖 𝟏 The weight composition of the distillate will therefore be 62% bromobenzene and 38% water.

This calculation gives the minimum amount of water in the distillate. In the practice, an excess of water or steam is used in the distilling flash to sweep out the vapor mixture and to compensate for imperfect mixing.

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Calculations of the type illustrated with bromobenzene indicate that there are several requirements for the practical use of steam distillation in the laboratory: the substance to be steam distilled must be insoluble or only sparingly soluble, in water; it must not be decomposed by prolonged contact with boiling water or steam; and it must have an appreciable vapor pressure (preferably, at least 5 mm Hg) in the neighborhood of 100°C. That water has a very low molecular weight (18) compared with those of typical organic compounds is a favorable circumstance for steam distillation because this permits a substance to be steam distilled at a practical rate eventhough its vapor pressure is relatively small near 100°C. Exercises 21.1 Read and translate into Vietnamese Steam, steam distillation, insoluble, soluble, consequently, resort, vicinity, negligible, α-pinene, aniline, nitrobenzene, grasp, deviation, skew, diagram, independent, depict, globule, suspend, incipient, extreme, sum, plot, curve, partial, proportion, compose.

21.2 Answer the following questions 1. What is the principle of steam distillation?

2. When do we use steam distillation?

3. What is the advantage of steam distillation?

4. What are the requirements for the practical use of steam distillation in the laboratory?

5. How can we calculate the weight composition of distillate in steam distillation?

21.3 Translate into Vietnamese paying attention to the function of the infinitive 1. The mixture to be separated is introduced at the beginning of the column.

2. The electrons have come to be known as valence electrons, because the valence of any given element depends on the number of these electrons.

3. Valence is the tendency of the atoms of any given element to donate or accept a strictly definite number of electrons.

4. Chlorine requires only one electron to form the stable electron layer of the following inert gas.

5. Hydrogen is a combustible gas, burning in air or oxygen to form water.

6. The organic compounds to be discussed are of great importance in the study of plastics.

7. Carbon has a tendency to combine with oxygen from the air to form gaseous carbon dioxide.

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8. There is no problem to be associated with exuding, leaching or deterioration with polyethylene plastic.

9. The stability of polyethylene plastic in storage is to be associated with the lack of chemical active functional groups in the molecular structure.

10. To regard the polyethylene as a substitute for stainless steel is not a proper design procedure.

21.4 Translate the following sentences into Vietnamese, paying attention to the words in bold type 1. Vulcanization is a vitally important part of all rubber processing.

2. To impart the materials hardness, softness and other desirable properties, the materials can be modified.

3. Rigid polymers displaced traditional materials partly because of the economic advantages.

4. A number of scientists took part in the research of new elastic materials to be applied in surgery.

5. The alkyl of R group parts company from the carbonyl carbon exists for a time as a free radical.

21.5 Translate the following sentences into Vietnamese paying attention to the words in bold type 1. Thermoplastic elastomers are available in nib form, and since they need no vulcanization, the mastication and mixing steps required with conventional rubbers are avoided.

2. There are still some plastics, more or less rubbery, available in emulsion or dispersion form.

3. Vinyl chloride and vinyl copolymer latices are available both untreated and preplasticized.

4. There are now available several modified Buna n latices having rather distinctive properties.

5. Butadiene, which can be made from readily available acetylene, is one of the raw materials of synthetic rubber.

21.6 Translate into English 1. Chưng cất với hơi nước dùng để tinh chế các chất không tan hoặc ít tan trong nước.

Phương pháp này thường được dùng để phân lập các hợp chất thiên nhiên.

2. Áp suất hơi của hỗn hợp hai chất không tan vào nhau bằng tổng áp suất hơi tinh khiết của mỗi chất.

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3. Khi chưng cất với hơi nước hỗn hợp được cất ra ở nhiệt độ thấp hơn nhiệt độ sôi của chất sôi thấp.

4. Chất chưng cất với hơi nước phải không hoặc ít tan trong nước, không phân huỷ trong nước sôi hoặc hơi nước và phải có áp suất hơi ít nhất 5 mm Hg ở gần 100°C. 21.7 Write a short summary of the text

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UNIT 22 CRYSTALLIZATION Crystallization is used to purify chemicals by dissolving both impurities and a compound in an appropriate solvent, either the desired compound or impurities can be removed from the solution, leaving the other behind. In a typical synthesis process, a crystalline solid product separating from the reaction mixture is contaminated with impurities.

Purification is accomplished by crystallization from an appropriate solvent. In outline, the procedure consists of the following steps.

1. Dissolving the substance in as small amount of solvent as possible at an elevated temperature 2. Filtering the hot solution to remove insoluble impurities (optional step) 3. Allowing the hot solution to cool and deposit crystals of the substance 4. Filtering the cold solution to separate the crystals from the supernatant solution (quaintly still known as the mother liquor) 5. Washing the crystals to remove adhering mother liquor 6. Drying the crystals to remove the last traces of solvent.

There are several factors to consider in selecting a suitable solvent for crystallization.

A good solvent for crystallization is one that will dissolve a moderate quantity of the substance at an elevated temperature (about 10-20 mL/g of compound) but only a small quantity at low temperatures. The solvent should dissolve the impurities readily (except for mechanical impurities) even at low temperatures and should be easy to remove from the crystals of the purified substance. It is essential that the solvent not react in any way with the substance to be purified. Other factors such as flammability and cost should also be taken into consideration. In selecting a solvent for the purification of a given substance, one should consider its effectiveness for removal of the particular impurities that are likely to be present.

The following general categories of impurities may be encountered.

Mechanical impurities (dust, grit, particles of paper, etc.) are readily removed by filtering the hot solution, since they are insoluble in all of the common solvents. Inorganic salts may often be separated in this way by using an organic solvent in which they are insoluble; an alternative method is to wash the crystals before recrystallization with a solvent such as water, in which the inorganic salts are soluble and the organic compound is insoluble.

Traces of coloring matter and resinous impurities may often be removed by warming the solution with a small amount of decolorizing carbon (about 0.2 g/ 100 mL of solution) or other adsorbent (Norit, Darco, Nuchar, etc.) before filtering the hot solution. The action of decolorizing agents varies widely, and effectiveness in removing a particular impurity may differ markedly from one solvent to another. An excessive amount of decolorizing agent should be avoided because it will also adsorb the compound that is being purified, thereby reducing the amount of pure compound isolated. This is particularly true for large molecules, which tend to be held quite strongly on charcoal.

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Impurities more soluble in the solvent are readily removed by crystallization, since they will be retained in the mother liquor. Likewise, impurities having about the same solubility as the substance being purified, when present in moderately small amounts, are readily eliminated in the mother liquor.

Impurities less soluble in the solvent are very difficult to remove if they are present in considerable amount because the hot solvent will dissolve an appreciable amount of the impurity and, on cooling, the impurity will crystallize out and contaminate the product. It is for this reason that one tries to select a solvent that will readily dissolve the impurities, even at room temperature.

Exercises 22.1 Read and translate into Vietnamese Crystallization, recrystallization, crystalline crystallize, technique, impurity, purify, purification, appropriate, appreciate, precipitate, co-precipitate, contaminate, contamination, elevated, soluble, insoluble, filter, filtrate, filtration, deposit, supernatant, procedure, quaintly, adhering, flammability, effectiveness, categories, encounter, mechanical impurity, grit, trace, resinous, absorbent, decolorize, markedly, excessive, adsorb, reduce, saturate, saturated, drop, retain, moderately.

22.2 Answer the following questions 1. What is the purpose of recrystallization technique?

2. What is the principle of recrystallization technique?

3. What is the saturated solution?

4. Why do we need to prepare the saturated solution?

5. What is a good solvent?

22.3 Describe the recrystallization of benzoic acid using water as solvent Complete the sentences: In this experiment benzoic acid is… by…

The apparatus consists of…

Below is the procedure: First, the apparatus is set up as shown.

Then, the water is …. dropwise, Meanwhile the mixture is stirred so that the amount of water is minimum.

Next, the saturated solution…

After that, the solution is… and the crystal …

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Then, the solution is … again Finally, the pure….

Figure11. Recrystalization of benzoic acid

22.4 Translate the following sentences paying attention to the Absolute Participle Construction 1. The drops of rubber are suspended in water, when first obtained from the plant, the system resembling an emulsion.

2. Emulsion may “ cream “, i. e., separate into layers of aqueous phase with a concentrated layer of oil droplets floating on the top, the rate depending primarily on the viscosity of the aqueous phase, the size of the droplets, etc.

3. The emulsifier being a solubilizing agent for the monomer, the rate of polymerization varies with the emulsifier content.

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4. Most of the accelerators used today are derivatives of carbon disulfide, the commonest one being mercaptobenzothiazole.

5. The rate of polymerization varies with the emulsifier content, the emulsifier being a solubilizing agent for the monomer.

22.5. Translate into English 1. Kết tinh lại là phương pháp tinh chế các hợp chất dựa vào sự khác nhau về độ tan của các chất trong các dung môi khác nhau.

2. Để thu được tinh thể tinh khiết cần lặp lại quá trình kết tinh lại vài lần.

3. Các tạp chất cơ học thường không tan trong các dung môi thông thường nên chúng được loại ra bằng cách lọc nóng.

22.6 Write a short summary of the text

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UNIT 23 ADSORPTION Adsorption is a separation process in which certain components of a fluid phase are transferred to the surface of a solid adsorbent. Usually the small particles of adsorbent are held in a fixed bed, and fluid is passed continuously through the bed until the solid is nearly saturated and the desired separation can no longer be achieved. The flow is then switched to a second bed until the saturated adsorbent can be replaced or regenerated. Ion exhange is another process that is usually carried out in this semibatch fashion in a fixed bed. Water that is to be softened or deionized is passed over beads of ion-exchange resin in a column until the resin becomes nearly saturated. The removal of trace impurities by reaction with solids can also be carried out in fixed beds, and the removal of H2S from synthesis gas with ZnO pellets is a well-known example. For all these processes, the performance depends on solid-fluid equilibria and on mass-transfer rates. In this chapter the emphasis is on adsorption, but the general methods of analysis and design are applicable to other fixed-bed processes.

ADSORBENTS AND ADSORPTION PROCESSES. Most adsorbents are highly porous materials, and adsorption takes place primarily on the walls of the pores or at specific sites inside the particle. Because the pores are generally very small, the internal surface area is orders of magnitude greater than the external area and may be as large as 2000 m 2/gSeparation occurs because differences in molecular weight, shape, or polarity cause some molecules to be held more strongly on the surface than others or because the pores are too small to admit the larger molecules. In many cases, the adsorbing components (or adsorbate) is held strongly enough to permit complete removal of that component from the fluid with very little adsorption of other components. Regeneration of the adsorbent can then be carried out to obtain the adsorbate in concentrated or nearly pure form.

Applications of vapor-phase adsorption include the recovery of organic solvents used in paints, printing inks, and solutions for film casting or fabric coating. The solvent-laden air may first be sent to a water-cooled or refrigerated condenser to collect some of the solvent, but it is generally impractical to cool the gas far below ambient temperature in an attempt to eliminate solvent losses. The air with a small amount of solvent is passed through a bed of carbon adsorbent particles, which can reduce the solvent concentration to less than 1 ppm.

The concentration may be set by government emission standards rather than by the economics of solvent recovery. Adsorption on carbon is also used to remove pollutants such as H2S, CS2 and other odorous compounds from air circulating in ventilation systems, and canisters of carbon are placed in most new automobiles to prevent gasoline vapors from being vented to the air.

Drying of gases is often carried out by adsorbing the water on silica gel, alumina, or other inorganic porous solids. The zeolites, or molecular sieves, which are natural or synthetic aluminosilicates with a very regular, fine pore structure, are especially effective in preparing gases with low dew points ( — 75°C). Adsorption on molecular sieves can also be used to separate oxygen and nitrogen, to prepare pure hydrogen for synthesis gas, and to separate normal paraffins from branched paraffins and aromatics.

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Adsorption from the liquid phase is used to remove organic components from aqueous wastes, colored impurities from sugar solutions and vegetable oils, and water from organic liquids. Adsorption can also be used to recover reaction products that are not easily separated by distillation or crystallization. Some of the same types of solids are used for both vaporphase and liquid-phase adsorption, though often adsorbents with larger pores are preferred for use with liquids.

Exercises 23.1 Translate into Vietnamese Adsorption, adsorbent, switched, regenerate, regeneration, achieve, exchange, soften, deionize, bead, column, trace, emphasis, applicable, fixed bed, ink, printing ink, paint, casting, fabric, laden, refrigerate, impractical, attempt, concentration, emission, circulating, ventilation, canister, vent, porous, zeolite, sieve, aluminosilicate, regular, pore, effective, dew point, crystallization.

23.2 Translate the following sentences paying attention to the words in bold type 1. Unvulcanized rubber is both plastic and elastic.

2. Rubber either in the form of latex or solid sheet, when stored for considerable periods develops increased hardness.

3. The generation of oxygenated groups in secondary reactions is consistent with our present knowledge of polyisoprene biosynthesis.

4. It has been suggested that the carbonyl groups (in storage hardening) are incorporated at intervals along the “hydrocarbon chain”.

5. As a result of Goodyear’s work, along with improvements by Hancock, rubber goods of wide utility and durability could be made.

6. Modern industry could no longer function properly without reinforced rubber.

7. Polystyrene has been used commercially long before the high styrene resins.

23.3 Find (in the list given below) synonyms to the following words. Translate these words in to Vietnamese to be able to

can

behaviour

certain

compressed

complete

definite

contracted

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enough

to detect

to find out

different

form

evident

full

lightly

get

motion

matter

obtain

movement

property

obvious

shape

slightly

substance

strong

sufficient

various

total

whole

violent

23.4 What do you know about a branched chain

a molecular chain

a coiled chain

an oriented chain

a crumpled chain

a side chain

a flexible chain

a straight chain

a main chain 23.5 Translate the following sentences paying attention to the words in bold type 1. When parts of the long molecules of the natural rubber arrange themselves in an ordered state crystallizing they are assumed to exhibit a first - order transition.

2. There is a rubber like state, which many substances made from long molecules may assume under suitable conditions.

3. Mendeleyev’s theoretically assumed value of 240 for the atomic weight of uranium was confirmed by the scientists.

4. Synthetic rubber produced from isoprene was presumed to a long chain structure built up from isoprene units by 1-2, 1-4 linkages 23.5 Give a summary of the text 92

UNIT 24 EVAPORATION The objective of evaporation is to concentrate a solution consisting of a nonvolatile solute and a volatile solvent. In the overwhelming majority of evaporations the solvent is water. Evaporation is conducted by vaporizing a portion of the solvent to produce a concentrated solution of thick liquor. Evaporation differs from drying in that the residue is a liquid—sometimes a highly viscous one—rather than a solid; it differs from distillation in that the vapor usually is a single component, and even when the vapor is a mixture, no attempt is made in the evaporation step to separate the vapor into fractions; it differs from crystallization in that emphasis is placed on concentrating a solution rather than forming and building crystals. In certain situations, e.g., in the evaporation of brine to produce common salt, the line between evaporation and crystallization is far from sharp. Evaporation sometimes produces a slurry of crystals in a saturated mother liquor.

Normally, in evaporation the thick liquor is the valuable product and the vapor is condensed and discarded. In one specific situation, however, the reverse is true. Mineralbearing water often is evaporated to give a solid-free product for boiler feed, for special process requirements, or for human consumption. This technique is often called water distillation, but technically it is evaporation. Large-scale evaporation processes have been developed and used for recovering potable water from seawater. Here the condensed water is the desired product. Only a fraction of the total water in the feed is recovered, and the remainder is returned to the sea.

LIQUID CHARACTERISTICS. The practical solution of an evaporation problem is profoundly affected by the character of the liquor to be concentrated. It is the wide variation in liquor characteristics (which demands judgment and experience in designing and operating evaporators) that broadens this operation from simple heat transfer to a separate art. Some of the most important properties of evaporating liquids are as follows.

Concentration. Although the thin liquor fed to an evaporator may be sufficiently dilute to have many of the physical properties of water, as the concentration increases, the solution becomes more and more individualistic. The density and viscosity increase with solid content until either the solution becomes saturated or the liquor becomes too viscous for adequate heat transfer. Continued boiling of a saturated solution causes crystals to form; these must be removed or the tubes clog. The boiling point of the solution may also rise considerably as the solid content increases, so that the boiling temperature of a concentrated solution may be much higher than that of water at the same pressure.

Foaming. Some materials, especially organic substances, foam during vaporization. A stable foam accompanies the vapor out of the evaporator, causing heavy entrainment. In extreme cases the entire mass of liquid may boil over into the vapor outlet and be lost.

Temperature sensitivity. Many fine chemicals, pharmaceutical products, and foods are damanged when heated to moderate temperatures for relatively short times. In concentrating such materials special techniques are needed to reduce both the temperature of the liquid and the time of heating.

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Scale. Some solutions deposit scale on the heating surface. The overall coefficient then steadily diminishes, until the evaporator must be shut down and the tubes cleaned. When the scale is hard and insoluble, the cleaning is difficult and expensive.

Materials of construction. Whenever possible, evaporators are made of some kind of steel. Many solutions, however, attack ferrous metals or are contaminated by them. Special materials such as copper, nickel, stainless steel, aluminum, impervious graphite, and lead are then used. Since these materials are expensive, high heat-transfer rates become especially desirable to minimize the first cost of the equipment.

Many other liquid characteristics must be considered by the designer of an evaporator.

Some of these are specific heat, heat of concentration, freezing point, gas liberation on boiling, toxicity, explosion hazards, radioactivity, and necessity for sterile operation. Because of the variation in liquor properties, many different evaporator designs have been developed.

The choice for any specific problem depends primarily on the characteristics of the liquid.

SINGLE- AND MULTIPLE-EFFECT OPERATION. Most evaporators are heated by steam condensing on metal tubes. Nearly always the material to be evaporated flows inside the tubes. Usually the steam is at a low pressure, below 3 atm abs; often the boiling liquid is under moderate vacuum, at pressures down to about 0.05 atm abs. Reducing the boiling temperature of the liquid increases the temperature difference between the steam and the boiling liquid and thus increases the heat-transfer rate in the evaporator.

When a single evaporator is used, the vapor from the boiling liquid is condensed and discarded. This method is called single-effect evaporation, and although it is simple, it utilizes steam ineffectively. To evaporate 1 kg of water from a solution calls for from 1 to 1.3 kg of steam. If the vapor from one evaporator is fed into the steam chest of a second evaporator and the vapor from the second is then sent to a condenser, the operation becomes double-effect.

The heat in the original steam is reused in the second effect, and the evaporation achieved by a unit mass of steam fed to the first effect is approximately doubled. Additional effects can be added in the same manner. The general method of increasing the evaporation per kilogram of steam by using a series of evaporators between the steam supply and the condenser is called multiple-effect evaporation.

Exercise 24.1 Translate into Vietnamese Objective, evaporation, nonvolatile, overwhelming, vaporize, evaporate, evaporator, crystal, brine, slurry, liquor, recover, portable, profoundly, judgment, boaden, dilute, sufficient, individualistic, tube, clog, foam, entrainment, outlet, inlet, sensitive, pharmaceutical, moderate, coefficient, steady, diminish, ferrous steel, impervious, graphite, liberate, radioactivity, sterile, discard, single-effect operation, multi-effect operation, ineffectively, approximately.

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24.2 Translate the following sentences paying attention to the function of the verb to do 1. Monosaccharides do not hydrolyze to simpler substances.

2. An organic chemist has much to do with different reactions.

3. It is known that most fibers when suspended in an alkaline aqueous medium have a negative charge as do the particles in alkaline latex.

4. Upon what structural arrangement does the colour of an organic compound depend?

5. Some grades of synthetic material have lower cis- content than do natural rubber.

6. The results of the experiment show that adhesion does increase for a time after curing, at least when measured at room temperature.

7. On the basis of oxidizability, the zinc salt had the effect, as did mercaptobenzimidazole itself.

24.3 Translate the following sentences paying attention to the “Complex Object” 1. We consider the natural rubber to be isomerized.

2. Investigators find the infra-red spectrum to be closely similar to that of natural rubber.

3. One might expect the increase in hardness to be a result of intra- particle crosslinking.

4. Researchers dealing with latex know biologically induced oxidation to proceed in the vicinity of the tapping cut.

24.4 Form nouns from the following adjectives capable

mobile

flexible

versatile

labile 24.5 Translate into Vietnamese, paying attention to the Prefixed covalent

premastication

degradation

recycle

displace

unaffected

interchain

undesirable

intermolecular

unduly

immobile

unusable 95

24.6 Translate into Vietnamese paying attention to the prefix reheat - reheat

melt - remelt

soften - resoften

construct - reconstruct

form - reform 24.7 Translate the following derivative into Vietnamese develop, development

tough, toughness

compose, composition

introduce, introduction

monomer, monomeric

rigid, rigidity

adopt, adoptation

resist, resistant, resistance

polymer, copolymer, polymerization, polymerize

apply, application

nature, natural

viscous, viscosity

improve, improvement

use, useful, useless process, processing

24.8 Translate into Vietnamese paying attention to the words in bold type 1. The name ABS, based on the first letters of each of the monomeric components has been adopted for this family.

2. By introducing acrylonitrile monomer into a similar system, a significant improvement in all these properties is obtained, as well as outstanding toughness and resistance.

3. Various combinations of properties are possible, thus making these polymers most attractive for a larger number of current and newly developed applications.

4. ABS plastics are extremely useful and versatile, since ease of processing and forming allows them to be used for a great number of applications.

5. The strength of a fabricated item produced from ABS plastic is dependent on a number of variables.

24.9 Give a summary of the text

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UNIT 25 CHROMATOGRAPHY

Chromatography is a versatile separation technique in chemistry and chemical engineering. In any chromatographic separation there are two phases (solid, liquid, or gas); these move relative to each other while maintaining intimate contact. There are several forms of chromatography such as gas chromatography, gas-liquid chromatography, liquid-solid chromatography, high performance liquid chromatography, e.g.

Gas chromatography Gas chromatography is a method for separating components of mixtures of volatile compounds. In most applications, the separations are made to identify and determine the quantity of each component of a sample of the mixture, and analytical gas chromatographic apparatus includes additional devices for this purpose. In some applications, separations are made for preparative purposes, but the scale is not generally greater than that required for quantities of the order of 100g.

The central item in the apparatus for gas chromatography is the chromatographic column, a long tube packed permeably with some adsorbent. In the commonest technique of gas chromatography, the elution technique, a stream of inert gas, the carrier gas, passes continuously through the column, and the mixture to be separated is introduced at the beginning of the column as a sample either of a gas or a volatile liquid. Let us suppose that the sample consists of one pure component. After introduction, it is swept by the carrier gas on to the column, first evaporating to form a vapor if it is introduced as a liquid. When it reaches the column, it is largely adsorbed, but the equilibrium is set up between the column and the gas in the interstices of the column so that a proportion of the sample always remains in the gas phase. This portion moves a little further along the column in the carrier gas stream, where it again equilibrates with the column. At the same time, material already adsorbed in the column re - enters the gas phase so as to restore equilibrium with the clean carrier gas which follows up the zone of vapor.

The speed at which the zone moves depends on two factors, the rate of flow of the carrier gas and the extent to which the vapor is adsorbed. The faster the flow of carrier gas, the faster the zone moves; and the more strongly the vapor is adsorbed on the column, the more slowly the zone moves. When two or more components are present in the sample, each usually behaves, independently of the others so that for a given carrier gas flow rate, the speed of the zone of each component will depend on the extent to which it is adsorbed. Since different substances differ in their adsorption, they may therefore be separated by making use of their different speeds of progress through the column. If they are eluted to the far end of the column, they will appear one after the other in the gas stream, the fastest first and the lowest last.

Adsorbents such as carbon, alumina, or silica gel are used as the packing material for columns, but in more than 90% of applications, the column material is the liquid held in place on the column by being adsorbed on an inert solid support. Gas chromatography with this kind of column is called Gas Liquid Chromatography (GLC). This method is used for separating solutes from mixed solutions.

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Exercises 25.1 Read and translate into Vietnamese Chromatography, chromatographic, exceptional, exceptionally, versatile, intimate, stationary, mobile, analogy, conveyor, belt, lag, introduce, detect, device, apparatus, column, elute, inert, carrier, sweep, interstice, equilibrate, restore, differ, pack, packing material.

25.2 Answer the following questions 1. What does gas chromatography mean?

2. What is the central item in the apparatus for gas chromatography?

3. What gas passes through the column?

4. How does the process of chromatography pass?

5. What are adsorbents such as carbon, alumina, or silica gel used for?

6. What method is used for separating solutes from mixed solutions?

25.3 Read and translate the following derivative 1. analytical, analysis, analyze; 2. scheme, schematic, schematically; 3. compress, compression; 4. identify, identification; 5. include, inclusion, inclusive; 6. prepare, preparation, preparative; 7. adsorb, adsorbent, adsorption; 8. technique, technical, technician; 9. evaporation, vapor; 10. equilibrium, equilibrate, equilibration; 11. behavior, behave; 12. solute, solution, solvent, soluble, dissolve; 25.4 Translate into Vietnamese paying attention to the words in bold type 1. The mixture is introduced as a sample either of a gas or a volatile liquid.

2. The material already adsorbed in the column re-enters the gas phase so as to restore equilibrium with the clean carrier gas.

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3. The speed at which the zone moves depends on the rate of flow of the carrier gas and the extent to which the vapor is adsorbed.

4. The faster the flow of the carrier gas, the faster the zone moves.

5. The more strongly the vapor is adsorbed on the column, the more slowly the zone moves.

6. The speed of the zone of each component will depend on the extent to which it is adsorbed.

25.5 Translate into English 1. Sắc kí khí là phương pháp tách các cấu tử của hỗn hợp các chất dễ bay hơi.

2. Việc tách được tiến hành để định lượng mỗi cấu tử trong hỗn hợp.

3. Bộ phận chính của thiết bị sắc kí khí là cột sắc kí (là một ống dài được nhồi một chất có khả năng hấp phụ).

4. Khí mang liên tục đi qua cột sắc kí. Hỗn hợp cần tách được cho vào cột hoặc ở dạng khí hoặc ở dạng lỏng dễ bay hơi.

25.6 Write a short summary of the text

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UNIT 26 LIQUIS-SOLID CHROMATOGHRAPHY

The next chromatographic technique to be considered is liquid-solid chromatography.

The stationary phase is made up of very small particles of solid packed in a column (hence, the common name column chromatography), and the mobile phase is a liquid that percolates through the column and past the surfaces of the solid particles.

Solid surfaces adsorb thin layers of foreign molecules as a result of electrostatic and van der Waals forces. Since adsorption strengths differ with the character of the solid surface, a properly chosen solid may adsorb selectively one component of a mixture. An important example of selective adsorption employed in the previous chapter is the use of charcoal in crystallization to remove large, polar (usually colored) impurities. The ideal limiting law governing adsorption from a dilute solution is

amount of solute A adsorbed per unit surface area = KA concentration of solute A in solution The structural features that determine the extent of adsorption of a molecule on a solid surface are pretty much the same as those considered when solubility was discussed. A complication in thinking about adsorption is that the solvent and the solute are competing for the same active sites on the surface. For molecules with polar functional groups, the value of KA (the adsorption coefficient) is determined principally by the relative polarities of the group and the solvent. If the solvent is more polar than the solute, the solute will have a low KA (i.e., be poorly adsorbed) and move along rapidly with the mobile phase. For molecules containing hydroxyl groups, their relative abilities to form hydrogen bonds to the solid or the solvent are also significant.

Two solutes with different adsorption coefficients for a certain solid can, at least in principle, be separated by liquid-solid chromatography. The traditional method is to prepare a cylindrical column of the solid (with a height about 5 to 10 times the diameter) and place a concentrated solution of the sample at the top of the column. As the solution penetrates the column, the solutes are adsorbed. As soon as the solution has completely penetrated the column, fresh solvent is added at the top. The solvent flows down the column under the force of gravity and capillary attraction, and redissolves the solutes in amounts determined by the adsorption law and carries them to lower clean sections of the column, where they are readsorbed (always in amounts governed by the adsorption law). As more solvent percolates through the column, the cycle of adsorption-solution continues, and the solutes gradually move down the column in concentrated bands (development). With solutes having different adsorption coefficients, the least tightly adsorbed material moves faster. If the adsorption coefficients are sufficiently different or the column is sufficiently long, the faster-moving component will form a separate band below the slower- moving one. At the bottom of the column the solutes are forced off (elution) and can be collected separately in successive fractions.

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For satisfactory separation by liquid-solid column chromatography, it is essential to choose an appropriate combination of solid adsorbent and eluent that is compatible with the compounds to be separated. Compounds that are adsorbed very tightly require an excessive volume of solvent (eluent) for development. Compound adsorbed weakly may move too rapidly to give separation before being eluted. Table 2 gives some generalizations that are useful as a guide in selecting appropriate solid-solvent combinations.

A common variation of liquid-solid chromatography is the use of a thin film of solid (mixed with a binder such as plaster of pans) on a sheet of glass or plastic. The solution is added as a spot at the bottom of the plate and the plate is dipped vertically into a shallow layer of solvent, which ascends (against gravity) by capillary action and moves the solutes with it. The particular advantage of this technique is that the solutes are exposed and can be isolated readily or treated on the plate at any moment. The method is widely used for qualitative identification of mixture components because it is fast and has exceptionally good resolution. For a fixed combination of solid, binder, and solvent, each substance will travel along the thin-layer plate a characteristic fraction of the distance traveled by the solvent. It is customary to report thin-layer chromatography data as RF values (retardation or retention factor), defined as the distance of the spot from the starting point divided by the distance of the solvent front from the starting point.

Thin-layer chromatography is restricted to very small samples. Larger samples can be separated by using thick layers of plaster of paris, but there is a practical upper limit of a few tenths of a gram. A method known as “flash” When all components of a mixture are held tightly, as happens frequently, it is necessary to percolate dilute acid through the column to move the components (displacement development).

Table 1 Adsorbents and Solvents for Liquid - Solid Chromatography

Chromatographic solids in order of decreasing adsorption strength far polar molecules

Solvents in order of increasing eluting ability

Activated alumina

Saturated hydrocarbons

Activated magnesium sulfate

Aromatic hydrocarbons

Activated silicic acid

Partially hydrogenated hydrocarbons

Inorganic carbonates

Ethers

Starch, cellulose

Ketones Alcohols

Basic columns also are available (such as Dowex 3, a resin of polystyrene beads containing free amino groups); these accept protons and can be used to separate mixtures of organic acids of different acid strengths. Special column materials that form ionic complexes with various inorganic cations or anions are useful, as are columns containing ions that form complexes with certain organic molecules.

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Exercise 26.1 Read and translate into Vietnamese Stationary phase, mobile phase, percolate, adsorb, electrostatic, selectivity, employ, dilute, govern, active, site, polar, functional, coefficient, traditional, cylindrical, penetrate, solute, gravity, capillary, redissolve, readsorb, compatible, generalization, shallow, capillary, exceptional, resolution, thin-layer plate, customary, charcoal, resin, polystyrene.

26.2 Answer the following questions 1. What are the two phases of gas-liquid chromatography?

2. What are the essential properties of two solutes those can be separated by solid liquid chromatography?

3. What is an eluent?

4. What is thin layer chromatography used for?

26.3 Read and translate the following derivative 1. chromatography, chromatographic; 2. separate, separation, separator; 3. volatile, volatility, volatilization, volatilize; 4. detector, detect, detection; 5. concentrate, concentration; 6. solid, solidity, solidify; 7. quality, qualitative, qualitatively; 8. quantity, quantitative, quantitatively; 9. particular, particularly; 26.4 Read and translate the following sentences paying attention to the functions of the Infinitive 1. Carrier gas from the tank of compressed gas first passes to a controller, the usual purpose of which is to maintain a constant flow of gas.

2. In the inlet to the column there is a simple injector through which the sample to be analyzed can be introduced.

3. The purpose of the detector is to detect the separate components of the mixture as they emerge one by one.

4. A further piece of apparatus not always incorporated is a flow meter to measure the rate of the flow of gas.

5. Almost any high boiling liquid may be used.

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6. Sample injectors aim to inject a temperature control of the column.

7. In the years to come many new synthetic products will appear.

8. It has taken centuries of scientific research and invention to develop the civilization of the modern age.

9. The chemical industry of the Soviet Union began to develop in the prewar five-year periods.

10. Chemical processing method made it possible rationally to utilize industrial wastes to speed up technological processes and to ensure automation.

11. The second use of the chromatogram is to enable one to identify the individual components of a mixture qualitatively.

12. For the preparation of an aerosol, the substance to be dispersed is first evaporated, and the vapor is then quickly cooled.

26.5 Translate into Vietnamese paying attention to the words in bold type 1. Not a single property, but rather the combination of the properties has made this substance outstanding.

2. In integrating detectors the deflection is proportional to the total quantity rather than to the concentration.

3. The supernatant fraction appeared to degrade lysolecithin rather than to utilize it for lecithin production.

4. When no vapor is passing through, the recorder gives a straight line.

5. No traces of water have been obtained during the test.

6. A quantitative analysis of the mixture is provided by the detector rather than the column.

7. Gas chromatography is mainly used for quantitative analysis, for the method is suitable for the routine analysis of industrial samples, the interpretation of the data is simple, and the apparatus does not require skilled personnel.

26.6 Translate into English 1. Thiết bị được sử dụng trong sắc kí khí rất đơn giản.

2. Nhiệm vụ của detector là để phát hiện các cấu tử riêng rẽ của hỗn hợp khi chúng lần lượt đi ra khỏi cột.

3. Detector sử dụng một số tính chất hóa học và vật lý của các hợp chất, mà nhờ chúng các cấu tử được phát hiện và nếu cần thì được xác định.

4. Sắc ký lớp mỏng thường được dùng để phân tích lượng chất rất nhỏ.

26.7 Make up an outline of the text and retell the text 103

REFERENCES 1. Bùi Thị Lệ Thủy, Giáo trình Anh văn chuyên ngành (dùng cho sinh viên ngành Lọc Hóa Dầu), Hà nội, Trường đại học Mỏ- Địa chất, 2003.

2. Nguyễn Thị Hiền, Nguyễn Trọng Đàn và Lê Thị Lan Chi, The laguage of chemistry, food and biology technology in English, Đại học Bách khoa Hà Nội, 2009.

3. Mgr. Božena Velebná. English for Chemists. Univerzita Pavla Jozefa Šafárika v Košiciach, Szech Republic.

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PART 3 THE PETROCHEMICAL INDUSTRY AND REFINERY UNITS

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III.1 TYPICAL UNITS UNIT 27 ON OIL AND GAS INDUSTRY Petroleum is the name mineral oil. Oil comes from under the ground. Crude oil comes from the well or bore-holes. Boreholes are often very deep. The steel framework over the well is the derrick. From the derrick the machinery drills holes through rock, earth or sand. Oil usually flows freely but man control its natural flow. The natural flow of oil is the result of the pressure of the natural gas in oil or the result of the pressure between the petroleum and the roof of the rock above it.

Crude oil contains various materials, liquids. By the process of refining we obtain petrol, paraffin, and other products from crude oil. We obtain various fuels from it too. Fuel drive ships, planes, buses, and so on. Diesel engines burn oil fuel. Many tractors burn diesel oil. Jet engines burn kerosene (paraffin oil).

The growth of the manufacture of engines and machines and of the petrochemical industry increase rapidly. Today, the oil industry is an advanced, highly mechanized and reliable sector of the economy. It has highly productive rigs that can drill down to oil and gas deposits lying at depth of more than six kilometers. Today, more than 2,000 products are made from oil: fuel for aircraft and for internal combustion engines, fuel for boilers and furnaces, lubricants, bitumen for the manufacture of asphalt, lacquers, solvents, and so on. Oil by-products are used in making plastics and synthetic substances.

Exercises 27.1 Read and translate into Vietnamese Petroleum, crude oil, mineral oil, bore-holes, framework, derrick, drill, roof, petrol, engine, fuel, diesel oil, kerosene, mechanize, rig, internal combustion engine, boiler, furnace, lubricant, bitumen, asphalt, lacquer, plastic.

27.2 Answer the following questions 1. What is the result of the pressure of the natural gas in oil?

2. Where does the oil come from?

3. From where does the machinery drill hole?

4. What does fuel drive?

5. What does the crude oil contain?

6. By what process do we obtain petrol, paraffin and other products from crude oil?

7. How many product we make from oil today?

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27.3 Fill in the blanks with the proper words from those given below 1. …knows that crude oil contains various materials.

2. …saw your friend in the laboratory some minutes ago.

3. Was there … in the boot of your car?

4. He told me … new about oil extraction?

5. Does … control the natural flow of oil?

6. It is possible to find these tubes Somebody, something, anybody, everybody, everyone, anything, everywhere 27.4 Rewrite the following sentences according to the model Model: I don’t know anything about this liquid.

I know nothing about this liquid.

1. We did not meet anybody in the laboratory yesterday.

2. My fried did not go anywhere last year.

3. He did not see any tube on the desk.

4. We did not see anybody in the shop.

5. We did not find anything in our compartment.

27.5 Translate into English 1. Rất nhiều sản phẩm được tạo ra từ quá trình chế biến dầu mỏ.

2. Quá trình chưng cất dầu mỏ được phát minh từ năm 1913 do nhà bác học Burton để tinh chế dầu mỏ.

3. Giàn khoan là khung bằng thép mà từ đó máy khoan các lỗ khoan qua lớp đất đá hoặc cát.

4. Ngành công nghiệp dầu mỏ là một trong những bộ phận quan trọng của nền kinh tế.

27.6 Write a short summary of the text

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UNIT 28 COMPOSITION OF PETROLEUM

Petroleum is a natural mixture of various hydrocarbons and their derivatives containing sulfur, nitrogen, oxygen, metals, etc. a. Hydrocarbons The main constituents of petroleum - hydrocarbons - may differ in the number of carbon and hydrogen atoms in the molecule and in the molecular structure. Petroleum hydrocarbons may relate to the following groups or series: paraffins (saturated or stable hydrocarbons, alkanes), naphthenes (cycloalkanes), and benzene hydrocarbons (arenes). In most grades of petroleum, paraffins and naphthenes prevail. During processing of petroleum, unsaturated hydrocarbons (olefins and diolefins) may also form. The specific properties of petroleum products are decided by the predominance of some or other group of hydrocarbons in crude petroleum and by the presence of compounds containing sullur, nitrogen or oxygen. b. Oxygen- containing compounds These include naphthenic acids, phenols and tar- asphaltene compounds.

Naphthenic acids are compounds containing a carboxyl group-COOH. Their density is from 0.96 to 1.05 g/cm3 and the general formula, CnH2n-zO2. Naphthenic acids strongly smell oily liquids. They may be present in kerosene, diesel- fuel and light oil distillates of petroleum and are corrosion- aggressive; they are removed from petroleum fractions by leaching. Naphthenic acids and their salts are widely used in industry as components of greases, for impregnation of fabrics and footwear, etc.

Phenols are contained only in some grades of petroleum and are liberated together with naphthenic acids during leaching of distillates.

Tar- asphaltene compounds may be present in petroleum in considerable quantities (from traces to 25% and even more). They are complex high-molecular compounds containing carbon (82-87.4%), hydrogen (10.3-12.5%), oxygen (up to 2.5%), sulfur (0.8-7%), and nitrogen (up to 1%). Low molecular tar compounds can partially be distilled off together with petroleum distillates, while high molecular ones remain in fuel-oil fractions and especially in oil residue (goudron). The presence of tar in these products makes them dark and promotes carbonization in cylinders of internal combustion engines. Tar- asphaltene products are harmful is white petroleum products and oils, but are desirable constituents in such products as bitumen, coke, insulating and impregnating materials.

All tar-asphaltene products are usually classed into neutral resins soluble in light gasoline; asphaltenes (the products of polymerization of neutral resins and oxyacids) which are insoluble in light gasoline, but soluble in benzene, chloroform and carbon bisulfide; asphaltogenous acids and their anhydrides of acid nature which are insoluble in light gasoline, but soluble in alcohol.

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All the three types of tar-asphaltene compounds are high-molecular compounds of unsaturated nature containing oxygen and sulfur. At normal temperature they are very thick and viscous liquids or are solid and have a density above 1.0 g/cm3. The content of tarasphaltene compounds is greater in petroleum grades of higher density and in those high in sulfur. c. Sulfur compounds Sulfur is present in petroleum and petroleum products mostly in combined state, i.e. in the form of organic sulfur compounds. Sulfur compounds of the following types may be found in petroleum products: mercaptans RSH (where R is a hydrocarbon radical); sulfides RS, disulfides RS-SR, thiophene C4H4S and its derivatives, and sometimes hydrogen sulfide and elemental sulfur. Hydrogen sulfide and mercaptans which have acid properties, and elemental sulfur form a group of active sulfur compounds which can cause strong corrosion of equipment and pipelines.

Another group includes sulfides and disulfides which are neutral at low temperatures, but are thermally unstable; at 130-160oC they decompose (with breaking of C-S bonds) and form hydrocarbons, mercaptans and hydrogen sulfide. A third group includes thiophane and thiophene and their derivatives, such as benzothiophene.

Like benzene hydrocarbons, they have low reactivity and are relatively stable at elevated temperatures.

High- molecular sulfur compounds are unstable and can be oxidized under relatively soft conditions; the products of oxidation increase the content of tar in petroleum products. In the atmosphere of hydrogen, they are reduced to corresponding hydrocarbons and hydrogen sulfide; this is the basis of the processes of hydrogen refining (hydrofining) of petroleum and petroleum products.

In straight distillation of petroleum (without destruction) the content of sulfur increases from lighter fraction to heavier ones, with the residue having the highest concentration of sulfur. When higher temperatures and pressures are applied, however, organic sulfur compounds are destroyed together with high - molecular hydrocarbons to form hydrogen sulfide and mercaptans which are corrosive and toxic. Corrosion is enhanced in the presence of water vapors and hydrochloric acid which forms by decomposition of calcium and magnesium chlorides contained in undesalted petroleum.

In order to diminish corrosion and improve labor conditions, petroleum before distillation might be desalted and dehydrated. The content of sulfurous compounds in petroleum products can be lowered by various methods of refining, mainly by hydrogen refining. d. Nitrogen Compounds The content of nitrogen compounds is usually greater in heavier grades of petroleum.

Nitrogen compounds are divided into basic, which contain nuclei of pyridine and quinoline, and neutral, which contain pyrrole and indole homologues.

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In petroleum processing, nitrogen compounds are distributed between fractions much like sulfur compounds, i.e., their concentration increases from lighter fractions to heavier ones, and the largest amount (65-75%) is concentrated in the residue.

Among nitrogen compounds, porphyrins occupy a special place. They may be present in petroleum either in free state (four pyrrol rings) or as complexes containing organic nitrogen compounds and organic derivatives of vanadium and nickel. Notwithstanding the high thermal stability of nitrous compounds in the technological processes, they decompose partially, which is detected by the formation of ammonia. Certain refining processes (for instance, hydrogen refining) can remove an appreciable portion of sulfurous compounds (as hydrogen sulfide) and a part of nitrogen compounds (as ammonia) and oxygen compounds (as water vapors). e. Mineral Substances Mineral substances are found in petroleum only in very small concentrations (provided that crude petroleum has been refined properly from mechanical impurities at the oil well). As has been established by combustion of many samples of petroleum, the elements found in the ash form (in the decreasing order) the following row: S-O-N-V-P-K-Ni-I-Si-CaFe-Mg-Na-Al-Mn-Pb-As-Cu-Ti-V-Sn-As. The total amount of ash in various grades of petroleum may vary from a few thousandths of a percent to 0.8 percent.

Exercises 28.1 Read and translate into Vietnamese Sulfur, metal, constituent, predominance, extreme, satisfy, isomer, isomeric, possess, deposit, antiknock, butylene, amylene, propylene, butylene, constitute, appreciable, polypropylene, propylene, oxide, butadiene, isoprene, tar, asphaltene, naphtenic acid, oily, considerable, partial, partially, promote, carbonization, cylinder, internal combustion, bitumen, insulating, impregnate, resin, polymerization, oxyacid, asphaltogeneuous acid, anhydride, mercaptane, sulfide, disulfide, thiophene, corrosion, pipeline, thiophene, benzothiophene, soft conditions, refining, hydrofining, straight distillation, enhance, desalt, diminish, dehydrate, pyridine, quinoline, pyrrol, indol homologue, distribute, porphyrin, vanadium, notwithstanding, decompose, detect, provided that, ash, properly.

28.2 Answer the following questions 1. What is the elemental composition of petroleum?

2. What are the main constituents of petroleum?

3. Which series of hydrocarbon are present in petroleum?

4. Which series of hydrocarbon are formed during processing of petroleum?

5. What can you say about the chemical properties of paraffin hydrocarbons?

6. What are the physical properties of paraffin hydrocarbons?

7. Which compounds are called isomers?

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8. What can you say about the chemical and physical properties of isomers?

9. What are the difference and the similarity in structure and properties between paraffinic and naphthenic hydrocarbons?

10. What are the difference and the similarity in structure and properties between naphthenic and benzene hydrocarbons?

11. What are the applications of benzene hydrocarbons?

12. What can you say about the properties of olefins and diolefins?

13. What are the applications of olefins and diolefins?

14. What are the applications of naphthenic acids?

15. What is the elemental composition of tar-asphaltene compounds?

16. How can you classify tar-asphaltene products?

17. Which types of sulfurous compounds are present in petroleum products?

18. How can the content of sulfurous compounds in petroleum products be lowered?

19. How are the nitrogen compounds distributed in petroleum products?

28.3 Translate into English 1. Thành phần chính của dầu mỏ là các hydrocacbon và phi hydrocacbon từ C5 đến C60.

2. Các hydrocacbon trong dầu mỏ gồm có paraffin, naphthen và aromatic. Các hydrocacbon không no không tồn tại trong dầu mỏ.

3. Ngoài hydrocacbon, trong dầu mỏ còn có các hợp chất chứa oxi, nito, lưu huỳnh, kim loại…

4. Trong các hợp chất chứa dị tố (O, N, S) thì các hợp chất chứa S là ít mong muốn nhất vì chúng gây ô nhiễm môi trường và ảnh hưởng xấu tới hệ sinh thái.

28.4 Write a short summary of the text

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UNIT 29 BASIC PHYSICO-CHEMICAL PROPERTIES OF PETROLEUM AND PETROLEUM PRODUCTS

a. Density The density of petroleum and petroleum products can be expressed in either absolute or relative values. The relative density is the ratio of the density of a petroleum product at temperature t2 to the density of distilled water at temperature t1. The density of petroleum products is normally measured at 20oC and that of water, at 4oC. Since the latter is taken as unity, the numerical values of the relative and absolute density coincide.

To find the absolute density  (kg/m3 or g/cm3) the mass of a product is divided by its volume, i. e.,  = m/V. The density of petroleum and petroleum products depends on the content and composition of light low-boiling (which have a low density) and heavy high-boiling constituents (fractions). Indeed, among the components having roughly the same boiling point, paraffin hydrocarbons have the lowest density, and benzene hydrocarbons have the highest value, with that of naphthalenes being in the middle. This is why density is one of the principal characteristics of petroleum and petroleum products.

The density of petroleum and petroleum products decreases with the increasing temperature, and their volume respectively increases. The temperature relationship for density can be expressed by Mendeleev's formula: dt4

= d204 -

a(t-20)

where dt4 is the relative density of a product at temperature t; d204 is the relative density of a product at 20oC; a is a temperature correction factor. b. Molecular Mass This is one of the basic physico-chemical characteristics of petroleum and petroleum products. The molecular mass of paraffin hydrocarbons can be found approximately by using the formula: M = 60 + 0.3t + 0.001t2 where t is the average temperature of boiling of a petroleum fraction, oC; it is calculated as the arithmetic mean of the temperatures at which equal volumes of the liquid, say, 10% fraction, is distilled off.

The relationship between the molecular mass and relative density of petroleum fractions is determined by the following empirical formula: 112

M = 44.29d1515/1.03- d1515 Using this formula, it is also possible to find (with a certain approximation) the molecular mass of all classes of hydrocarbons. c. Boiling Point. Fractional Composition The boiling point of a liquid is the temperature at which the pressure of vapors is equal to the external pressure; on reaching this point, vaporization, which up to that moment occurred from the surface only, begins in bulk of the liquid (at the bottom and walls of the vessel being heated), where vapor bubbles are formed; this is what is called the boiling proper. If vapors are not removed off the liquid surface during heating, equilibrium is established between the liquid and vapor phase. Vapors in equilibrium with the liquid are called saturated. At a higher temperature of heating of a liquid, vaporization occurs more intensively, more vapors are formed above the liquid, and the pressure of saturated vapors is higher.

The boiling point of a liquid depends on the external pressure. For instance, water at a pressure of 0.1 MPa boils at 100oC. At a higher pressure, say 0.4 MPa, boiling begins only at 144oC. Thus, the boiling point is higher at a higher external pressure and at a lower external pressure or in vacuum, water boils at a lower temperature. The same effect of pressure is found in other liquids. This phenomenon is utilized in vacuum distillation of fuel oil.

Petroleum and petroleum products can be separated into individual hydrocarbons only with certain difficulties. Usually, separation is carried out by distillation which gives simpler mixtures of hydrocarbons than the original mixture. These mixtures are called fractions. They boil not at a constant temperature, but in a temperature range between the point of the beginning of boiling and that of its end. Depending on the boiling points and contents of various hydrocarbons, a product may have different boiling ranges; i. e., may have a different fractional composition.

All petroleum products obtained from crude petroleum by distillation are essentially fractions that can boil off within particular temperature ranges. For instance, gasoline fractions boil off within 35-205oC, kerosene fraction within 150-315oC, diesel-fuel fractions within 180-350oC, light oil distillates within 350-420oC, heavy oil distillates within 420490oC, and oil residues at temperatures above 490oC. d. Thermal Properties of Petroleum and Petroleum products These properties are of high practical importance for calculating the heat balance of all processes associated with heating or cooling.

Specific heat is the quantity of heat needed to heat up 1 kg of a substance by 1oC. The approximate values of specific heat, kJ/kg K, are as follows: petroleum 2.1, petroleum vapors 2.1, water 4.19.

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With the specific heat of a petroleum product being known, it is possible to calculate the quantity of heat for heating. For this, the specific heat is multiplied by the mass of the product (kg) and by the difference between the final and initial temperature (oC). The specific heat of petroleum products increases with increasing temperature and is higher for products of lower density.

Specific latent heat of evaporation is the quantity of heat spent to vaporize 1 kg of a liquid at its boiling point (this characteristic is called latent, since the heat is spent for evaporation and the temperature of the product remains constant during heating). Thus, the latent heat of evaporation decreases with increasing density and molecular mass of petroleum products, and also with increasing temperature and pressure.

The heat of condensation is the quantity of heat liberated by vapors during their condensation and is numerically equal to the latent heat of evaporation.

The latent heat of fusion is the quantity of heat absorbed during fusion of 1 kg of a solid at the melting point.

The heat of combustion (calorific value) of fuel is the quantity of heat liberated by the fuel on full combustion. A distinction is made between the high and low heat of combustion: the former (Qh) takes into account the heat of condensation of the water present in the fuel and formed during combustion (it is taken conditionally that the combustion products contain liquid water rather than water vapors). The low heat of combustion, Ql, implies that the water of the fuel and the water formed by combustion is removed as vapors with combustion gases (i.e. it is lower than the high heat of combustion by the quantity of heat spent for evaporation of the moisture of the fuel and of the water formed through combustion of hydrogen in the fuel). e. Distillation curves Fractional distillation is a process that separates a mixture of liquids based on their volatility, or tendency, to vaporize. In a mixture of two liquids, the temperature will remain constant as one distills and shoots up abruptly to a different temperature where the other liquid will distill. A distillation curve plots temperature versus the amount of distillate collected. A distillation curve will clearly show the boiling point of each liquid in the mixture and their respective volumes. There are several types of Distillation Curve: True Boiling point (TBP) Distillation, ASTM Distillation, Semi-fractionating Distillation, and Equilibrium Flash Vaporization (EFV).

- TBP: This type of distillation is commonly used due to the accuracy of the results obtained by this method which is very close to that obtained via real distillation or industrial distillation. In this distillation, there is a fractionation column located between the condenser and the flask. In general, this type of distillation is carried out by two steps: firstly, under atmospheric pressure until 300°C (1% distilled very 2 min), secondly under vacuum pressure (to prevent cracking process and to reduce the boiling point) at 40mmHg (1% distilled every 3-5 min).

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- ASTM: In this type of distillation there is on fractionation column located between the condenser and the flask. On the other hand, the raised vapor will not be fractionated in this process. This distillation is used with fractions having a short range of the boiling point.

- Semi-fractionating distillation: In this type of distillation, there will be some fractionating process on the raised vapor via package located between the condenser and the flask.

- Equilibrium Flash Vaporization (EFV): Is a single stage separation technique. A liquid mixture feed is pumped through a heater to raise the temperature and enthalpy of the mixture. It then flows through a valve and the pressure is reduced, causing the liquid to partially vaporize. Because the vapor and liquid are in such close contact up until the "flash" occurs, the product liquid and vapor phases approach equilibrium.

Exercises 29.1 Read and translate into Vietnamese Physico-chemical, express, absolute, relative value, relative density, measure, coincide, roughly, fraction, external, essential, gasoline, kerosene, multiply, specific latent heat of evaporation, liberate, numerically equal, latent heat of fusion, distinction, tendency, shoot, abruptly, versus, accuracy, flash, equilibrium.

29.2 Answer the following questions 1. How can they express the density of petroleum and petroleum products?

2. What is the relative density of a petroleum product?

3. How can you calculate the absolute density?

4. Is there any relationship between the density of petroleum products and their boiling points? What is it?

5. What are the relationship between the density of petroleum products and their temperature and volume?

6. What is the boiling point of a liquid?

7. What is the relationship between the boiling point and the external pressure?

8. What are fractions of petroleum?

9. What is specific heat?

10. How can you calculate the quantity of heat for heating?

11. What is the specific latent heat of evaporation?

12. How can you understand the term "latent"?

13. How can you distinguish the high and low heat of combustion?

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29.3 Translate into English 1. Khối lượng riêng là một thông số quan trọng để đánh giá dầu mỏ.

2. Nhiệt độ sôi của một phân đoạn dầu mỏ phụ thuộc vào thành phần định tính và định lượng của nó.

3. An toàn cháy nổ của một phân đoạn dầu mỏ phụ thuộc vào nhiệt độ chớp cháy và nhiệt độ tự bắt cháy của nó.

4. Cần phải chú ý tới giới hạn cháy nổ của một phân đoạn dầu mỏ khi chế biến nó.

29.4 Write a short summary of the text

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UNIT 30 BASIC PHYSICO-CHEMICAL PROPERTIES OF PETROLEUM AND PETROLEUM PRODUCTS (CONTINUED)

f. Viscosity (internal friction) Viscosity is the ability of a liquid (or gas) to resist the motion of a layer relative to other layers. As regards petroleum products, a distinction is made between dynamic, kinematic and relative viscosity.

Dynamic viscosity  is measured in pascal-second (Pa s). An inverse value of dynamic viscosity is called fluidity.

In process calculations and for testing the quality of many petroleum products, use is made of kinematic viscosity, which is the ratio of the dynamic viscosity  to the relative density of a liquid, d, at the same temperature, i.e.  = /d Kinematic viscosity  is measured in square meter (square millimeter) per second (m /s, mm2/s).

2

In practical calculations, especially for quality control of petroleum products, use is often made of relative viscosity which is the time of efflux of 200 ml of a petroleum product at the testing temperature related to the time of efflux of the same volume of distilled water at 20oC (the time of efflux of 200 ml of water at 20 oC is what is called the water number of a viscometer).

Viscosity-temperature relationships. Viscosity becomes lower with increasing temperature and vice versa. The pattern of variation of viscosity with temperature is an important characteristic of petroleum products, especially of lubricating oils. These variations can be determined by various methods, for instance, by the ratio of the viscosity at 50 oC to that at 100oC, which is now specified for many lubricating oils, or by the viscosity index; the latter is found from monograms for the known values of viscosity at 50oC and 100oC. With a higher ratio of viscosities, the temperature curve of viscosity is steeper and on the contrary with a lower ratio, the curve is less steep and the quality of the oil is better. g. The Setting and Fusion points When being cooled, petroleum and petroleum products gradually loss mobility and can set (solidify) notwithstanding the fact that they contain some substances that might be liquid at the temperature considered.

The setting (solidification) point of a petroleum product is the temperature at which the product loses mobility under strictly specified testing conditions. The loss of mobility and freezing of petroleum and petroleum products depend mainly on the content of hydrocarbons which are solid (at the normal temperature). The higher the content of such hydrocarbons (in 117

dissolved or crystalline state), the more quickly the product loses its mobility during cooling, i.e., the products have a relatively high setting point. Tarry products and asphaltenes can retard somewhat the crystallization of solid hydrocarbons that is why the setting point of detarred products is always higher than that of the distillates from which they have been obtained.

During cooling to their setting point, white petroleum products pass through a number of intermediate stages- the stage of turbidity (blushing) and that of the beginning of crystallization. The highest temperature at which crystals (say, of benzene, etc.) can be detected in the cooled fuel by naked eye is called the temperature of the beginning of crystallization, or the chilling temperature (point). The temperature at which crystals of hydrocarbons (mainly of paraffins) start to precipitate and make the product turbid is called the blushing temperature (point). Along with the temperature of chilling of liquid petroleum products, the temperature of fusion of some products which are solid at normal temperature (paraffin and ceresin) is also practical importance.

The fusion point is the temperature at which a solid product becomes liquid under strictly specified testing conditions.

With these constants being known it is possible to select properly the method of petroleum processing and take the required measures to ensure pipeline transportation, especially in winter time, and also to choose the methods of storage and transportation of solid products having a high chilling point. h. Flash and Ignition Points. Self- ignition temperature. Explosibility The fire hazard of petroleum products is judged by their flash, ignition and selfignition temperatures (point). At lower values of these characteristics, a product is more firehazardous.

The flash point is the temperature, at which a mixture of air and vapors of a product being heated under standard conditions ignites on contact with an ignition source, but the product proper is not ignited and the flame is damped. For light petroleum products (with the flash point not above 50oC) the flash point is measured in a closed apparatus and that of heavier products (with the flash point above 70oC) can be determined in an open vessel. The product to be tested is poured into the apparatus and a thermometer is put inside. With light products, the apparatus is covered by a lid with a window which can be closed by a gate.

During the test, the window is opened periodically and a burner is brought close to it. In an open apparatus, the burner is moved close to the liquid surface. Tests in an open apparatus give a higher value of a flash point, since the vapor formed are partially dissipated to the surroundings.

In further heating, a petroleum product can ignite at a certain temperature. This temperature is called the ignition point.

There is a certain relationship between the fractional composition of a product and its flash and ignition points: lighter hydrocarbons in its composition lower these points. For instance, gasoline has the flash point below – 50oC, whereas the flash point of fuel oil is above 110oC. 118

According to international recommendations, easily igniting liquids include those flash point is below 61oC (in a closed vessel) or 66oC (in an open vessel). These liquids can be ignited by a short action or even a small ignition source (say, a spark) and without preliminary heating.

The temperature of self- ignition of a petroleum product is lower at a higher content of heavy hydrocarbons. This is the temperature at which a product ignites spontaneously on contact with the air, i.e., in the absence of flame or spark. Some products, such as fuel oils, goudron, soot and coke, self- ignite quite easily at a temperature slightly above 300 0C. Selfignition usually occurs in untight pipelines and apparatus in which petroleum products are at a temperature above their ignition point. It is therefore essential to check the equipment for tightness to prevent self- ignition and fires.

Explosibility. In petroleum processing plants, mixtures of vapors of some products with air may be explosive. Such mixtures may form in open air, in closed premises, and inside processing equipment. A mixture of vapors of a product with air becomes explosive when the concentration of the vapors in mixture exceeds a definite limit. At lower concentrations, the mixture is not explosion hazardous, since the greatest portion of the heat evolved in the ignition zone is spent to heat up the air. A mixture cannot explode, too, if it contains little air and therefore there is not enough oxygen to sustain combustion.

The lowest concentration of vapors of a petroleum product (or other substance) in the air at which explosion is probable is called the lower explosive limit, and the highest concentration of vapors at which explosion is still possible is respectively the upper explosive limit. The concentration range between the two limits in which an explosion can take place on contact with open fire (or spark) is called the explosibility range.

The upper and lower explosive limits and the explosibility are different for various vapors and gases. The highest permissible concentration of vapors of a product in working premises depends on the composition of that product.

Exercises 30.1 Read and translate into Vietnamese Viscosity, friction, resist, dynamic, kinematic, inverse, fluidity, efflux, viscometer, variation, lubricate, monogram, steeper, setting point, fusion point, mobility, solidify, retard, detar, turbidity, blushing, naked eye, chilling point, precipitate, ceresin, transportation, flash point, ignition point, self-ignition point, explosibility, judg, damp, ignite, lid, periodical, dissipate, preliminary, spontaneous, spark, goudron, soot, coke, tightness, explosive, explode, premise, sustain, lower explosive limit, upper explosive limit, explosibility range.

30.2 Answer the following questions 1. What is the viscosity of a liquid?

2. How many types of viscosity of liquid do you know?

3. What is the relationship between the viscosity index and the quality of oil?

4. What is the setting point of a petroleum product?

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5. Why do the setting points of distillates decrease after detaring?

6. What is fusion point?

7. What is flash point?

8. How can you measure the flash point?

9. What is ignition point?

10. What is temperature of self-ignition?

11. When does the explosibility happen?

30.3 Translate into English 1. Độ nhớt phụ thuộc vào thành phần định tính và định lượng của phân đoạn và nhiệt độ của môi trường.

2. Các thông số nhiệt độ chớp cháy, nhiệt độ tự bắt cháy và giới hạn cháy nổ đặc trưng cho mức độ an toàn cháy nổ của sản phẩm.

3. Giới hạn nổ dưới là nồng độ thấp nhất của hơi của một sản phẩm dầu mỏ trong không khí mà sự nổ có thể xảy ra.

30.4 Write a short summary of the text

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UNIT 31 DISTILLATION OF PETROLEUM The property that differentiates most petroleum products from each other is "volatility", or tendency to vaporize. More volatile products are called "lighter", less volatile products, "heavier". The volatility of a product is determined, of course, by the boiling points of its components. Inasmuch as distillation separates liquid by boiling points, distillation is the principal separation process.

Basic components of distillation There are varieties of configuration for distillation columns, each designed to perform specific types of separations. A simplified way of classifying distillation column is to look at how they are operated. In this manner, the two major types are batch and continuous columns.

In the batch operation, the feed to the column is introduced bath-wise. That is, the column is charged with a ‘batch’ and then the distillation process is conducted. When the designed separation is achieved, a next batch of feed is introduced. In contrast, continuous column posses a continuous feed stream. No interruptions occur unless there is a problem or upsets with the column or surrounding process units. They are capable of handling high throughputs and are the more common of the two types.

Continuous column can be further classified according to: (1) the nature of the feed that they are processing (binary column feed contains only two components, and multicomponent column – feed contains more than two components; (2) the number of product streams they have (multiproduct column – column has more than two product streams); (3) where the extra feed exists when it is used to help with the separation (extractive distillation- where the extra feed appears in the bottom product stream, and azeotropic distillation- where the extra feed appears at the top product stream); (4) the type of column internals (tray column – where trays of various designs are used to hold up the liquid to provide better contact between vapor and liquid, and hence achieve better separation, and the packed column- where instead of trays, packings are employed to effect contact between vapor and liquid).

There are several important components in a distillation column, each of which is used either to transfer heat energy or enhance mass transfer. The major components in typical distillation are: - A vertical shell where the separation of liquid components is carried out, - Column internals such as trays/plates and/or packings, which are used to enhance component separation, - A reboiler to provide the necessary vaporization for the distillation process, - A condenser to cool and condense the vapor leaving the top of the column 121

- A reflux drum to hold the condensed vapor from the top of the column. The liquid (reflux) is recycled back to the column.

The column internals are housed within a vertical shell, and together with the condenser and reboiler, constitute a distillation column. A schematic of typical distillation unit with a single feed and two product streams is shown in figure 12.

The liquid mixture that is to be processed is called the feed. The feed is introduced usually somewhere near the middle of the column to the tray known as the feed tray. The feed tray divides the column into a top (enriching or rectification) section and a bottom (stripping) section. The feed flows down the column where it is collected at the bottom in the reboiler.

Heat is supplied to the reboiler to generate vapor. The source of heat input can be any suitable fluid, although in most chemical plants this is normally steam. In refineries, the heat source may be the output streams of other columns. The vapor raised in the reboiler is re-introduced into the unit at the bottom of the column. The liquid removed from the reboiler is known as the bottom product or simply, the bottoms. The vapor travels up the column, and as it exits the top of the unit, it is cooled by the condenser. The condensed liquid is stored in a holding vessel known as the reflux drum. Some of this liquid is recycled back to the top of the column and this is called the reflux. The condensed liquid that is removed from the system is known as the distillate or top product.

Extractive and Azeotropic Distillation Because distillation separates by virtue of differences in volatility, distillation cannot normally be used to separate close- boiling materials. However, when the materials to be separated are chemically dissimilar, modified distillation procedures can be used. Examples are the separation of butenes from butanes and of toluene from isooctane. In such cases; an extraneous liquid can be added which has an affinity for one of the components in the charge; as a result, the relative volatilities of the original components change, and separation becomes possible. If the added material is less volatile than the original components, it is added at the top of the column and withdrawn from the bottom, and the operation is called extractive distillation. If the added material is more volatile than the original components, it is added at the top of the column or with the feed and is withdrawn in the overhead product; the operation is then called azeotropic distillation.

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Figure 12. Basic component of distillation Solvents and Entrainers. In extractive distillation, the extraneous liquid is called a solvent; in azeotropic distillation, it is called entrainer. In either case, its effectiveness is determined by its concentration in the liquid phase. Consequently, the boiling point of an entrainer is limited; it must be about as volatile as the lighter feed components so that it will pass overhead, but it must not be so volatile that it will disappear from the downflowing liquid stream much above the bottom of the tower. An entrainer must be separable, of course, from the overhead product- by distillation or by some other technique. Similarly, a solvent in extractive distillation must be separable from the bottoms product. How the entrainer or the solvent is separated from the overhead or bottoms product is an important consideration, because large volumes must be used. To be effective in changing the relative volatilities of the original components, an entrainer or a solvent must constitute at least 40% of the liquid phase (60), and its concentration is usually much higher.

Effects of Reflux. In extractive distillation, reflux has two opposing effects. By increasing the counterflow of liquid and vapor, increasing the reflux promotes the separation.

However, increasing the reflux lowers the concentration of the solvent in the liquid streams; this lessens its effect in spreading the volatilities of the original feed components and thus retards their separation. Because of these conflicting effects, there is apt to be sharp optimum in the reflux rate for an extractive distillation operation.

Feed Preparation. Only narrow-boiling materials are charged to extractive or azeotropic distillation. The reason may be seen most readily from an example. Consider extractive distillation for the separation of toluene from a mixture with isooctane, which 123

normally boils very closely to toluene. Lower- boiling materials (like hexane and benzene) and higher - boiling materials (like isononanes) are first separated by ordinary distillation.

The sharpness of removing the light ends affects only the amount of material charged to extractive distillation. On the other hand, the purity of the toluene product will depend upon the sharpness of prefractionating the heavy ends out of the feed.

How poor removal of heavy ends affects product purity may be seen by considering the normal volatilities of the feed components and how they are affected by the presence of a solvent. Toluene and isooctane boil together, and isononanes are about half as volatile. In the concentration usually employed, a solvent approximately doubles the volatilities of the paraffins relative to toluene. In the presence of the solvent, then, the isononanes have about the same volatility as toluene, and their separation is very difficult, and sometimes impossible.

Even when heavy materials can be taken overhead in extractive distillation, they may be very undesirable in the feed. When phenol is used as the solvent, for example, volatility relationships are such that heavy paraffins in the overhead tend to carry some phenol with them. Phenol is expensive, and only small losses can be tolerated.

Exercises 31.1 Read and translate into Vietnamese Differentiate, volatility, tendency, inasmuch, simplify, batchwise, conduct, interruption, throughput, binary, tray, tray column, enhance, vertical, horizontal, plate, packing, reboiler, reflux, recycle, schematic, feed tray, enriching, rectification, stripping, generate, refinery, bottom product, bottoms, distillate, extraneous liquid, affinity, charge, extractive distillation, azeotropic, entrainer, extraneous, consequently, overhead, disappear, downflowing, oppose, opposing, counterflow, lessen, spread, conflict, apt, narrow-boiling materials, sharpness, fractionate, prefractionate, overhead, tolerate.

31.2 Answer the following questions 1. What are the major components in a typical distillationn unit?

2. What are the distilling towers?

3. Where can they withdraw product of distillation?

4. What is reflux?

5. What are the rectifying section and stripping section?

6. What are the purposes of the rectifying section and stripping section?

7. When must they add the extraneous liquid in distillation?

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8. What is the extractive distillation?

9. What is the azeotropic distillation?

10. What is a solvent or an entrainer?

11. What can you say about the boiling point of entrainer?

12. What are the important characteristics of solvent or a entrainer?

13. Which materials are used in extractive or azeotropic distillation?

31.3 Translate into English 1. Chưng cất là quá trình tách một hỗn hợp của hai hay nhiều chất thành các phân đoạn chứa các cấu tử của nó 2. Bộ phận chính của một hệ chưng cất là tháp chưng cất. Nó bao gồm bình chưng, bộ phận ngưng tụ và thiết bị bay hơi.

3. Nếu hỗn hợp cần tách là các chất có nhiệt độ sôi gần nhau thì phương pháp chưng cất đẳng phí hoặc chưng cất chiết được sử dụng.

4. Phần cột phía trên đĩa nạp liệu gọi là phần chưng và phần nằm dưới đĩa nạp liệu gọi là phần cất.

31.4 Write a short summary of the text

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UNIT 32 THERMAL PROCESSES IN REFINERY THERMAL CRACKING

Thermal processes At high temperatures, the bonds between atoms in molecules of hydrocarbons are weakened and can break to form new compounds. In any homologous series, lighter (lowboiling) hydrocarbons split less easily than high-boiling ones. Along with splitting into lighter hydrocarbons, other transformations can take place, in particular, packing of molecules in which larger molecules are formed. The processes in which heavier fractions from preliminary petroleum processing are decomposed at elevated temperatures are called thermal processes. In petroleum processing industry, the most common processes of this type are thermal cracking, coking, and pyrolysis.

Thermal cracking, usually carried out at pressures up to 5 MPa and temperatures of 420-550oC, is a process in which the starting material is changed qualitatively with the formation of new compounds having different physicochemical properties. Depending on the composition of the starting material and the process conditions, the yield of gasoline cracking is 7-30 % of the mass of the starting material; the process also gives some other products: gaseous, liquid and solid (coke).

Coking of residue is done at temperatures of 445-560oC (still coking) or 485-540oC. Depending on the quality of the starting material and the type and conditions of the process, it may yield 15-18 % of commercial coke, 49-77.5 % of liquid products (including 7-17 % of gasoline fractions) and 5-12 % of gases (up to C4).

Pyrolysis of distillates and light hydrocarbons (from ethane to butane) is usually affected at 650-850oC. The main object of pyrolysis is to produce ethylene and propylene; earlier, it was aimed at producing aromatic (benzene) hydrocarbons.

In 1930-1950's, pyrolysis played an important part as a method for increasing the manufacture of gasoline for carburetor engines. At a later time, the quality of gasoline produced in thermal cracking plants could no more satisfy the rising requirements of consumers. Upon development of catalytic processes, thermal cracking still retains its role mainly for the manufacture of low-viscous fuel oils from residue products of preliminary petroleum processing, and also of gas oils intermediate products for making carbon black.

The processes of coking are being developed further, mainly to satisfy the demands for coke, especially electrode coke. Liquid products of coking are utilized for increasing production of white petroleum products. Pyrolysis is being developed rapidly in association with increasing demands for olefin materials for the chemical and petrochemical industries.

Thermal Cracking In 1890, V.G. Shukhov, a famous Russian scientist, designed the first cracking plant for producing light petroleum products from fuel oil. Later, as the need for automobile gasoline increased, a system with reaction chambers was developed, in which the starting material, preheated to the reaction temperature in the furnace coil, was retained and subjected 126

to cracking up to the formation of coke. The time of filling of the reactor with coke determined the length of the whole working cycle of the plant. At a later time, the reaction chamber was replaced by the reaction volume formed in radiant pipes of a furnace. To prevent the clogging of the apparatus with coke, the reaction products were chilled at the exit from the furnace by the cold starting material (quench) which stopped the cracking process (in particular, Winker-Koch plants operated by this principle). In later years, further improvements have been made in thermal cracking in other countries and in the USSA where the process was implemented in 1927-28.

As has been given earlier, the principal reaction of thermal cracking is the decomposition (or cracking) reaction. Among various hydrocarbons, paraffins can be cracked most easily. Then follow naphthenic hydrocarbons. Benzene hydrocarbons are most stable against cracking. In any homologous series, hydrocarbons of a higher molecular mass are cracked more readily. Thus heavier fraction of petroleum products are less stable and can be cracked more easily than lighter ones. Brief data on the chemistry and mechanisms of cracking of the principal classes of hydrocarbons will be given below.

Paraffinic hydrocarbons. Cracking of commercial paraffins which consist mainly of C24H50, C25H52 and C26H54 hydrocarbons forms paraffin hydrocarbons and olefins composed of 12, 13, or 14 carbon atoms, i.e. roughly one-half of the carbon atoms in the original paraffin. This is an indication of that the breakdown of C-C bonds in cracking of paraffins of high molecular mass occurs in the middle of a molecule. The new paraffin hydrocarbons formed by cracking can in turn break down into simpler molecules say a molecule of a paraffin hydrocarbon and that of an olefin, for instance: C12H26 dodecane (paraffinic)

 C6H14 hexane

+

C6H12 hexene

(paraffinic) (olefinic)

At higher temperatures of cracking of paraffinic hydrocarbons, reactions in which the breakdown of molecules occurs at the end portion of the chain begin to prevail over those in which molecules break in the middle. The larger fragment of a broken molecule is an olefin, and the smaller one is the paraffinic hydrocarbon (gaseous) or hydrogen. Isoparaffinic hydrocarbons are thermally less stable than those of the normal structure. The rate of the reaction at a given temperature increases almost linearly with the molecular mass. This is true of all groups of hydrocarbons.

Olefinic Hydrocarbons. These are the principal ones among all unsaturated hydrocarbons produced by cracking. They prevail as gaseous compounds (from ethylene C2H4 to butylene C4H8) and liquid ones (from amylenes C5H10 to pentadecenes C15H30). Cyclic olefins and diolefins form in relatively small quantities. In contrast to paraffinic hydrocarbons, olefins undergo appreciably more diverse primary reactions during cracking, the most important among them being polymerization reactions (i.e. combination of a few molecules into a single molecule) and depolymerization reactions, especially at an early stage of the process. Polymerization is the main reaction at moderately high and high pressures; it can occur not only between like molecules, but also between unlike molecules of olefins, for instance: 127

C2H4

+

C3H6



C5H10

At later stages of the process, olefins are dehydrogenated partially and form diolefins, which typically have two double bonds, and hydrogen or split into diolefins and paraffinic hydrocarbons: CH3- CH2- CH= CH2  CH2= CH- CH= CH2 + H2 butylene

divinyl

(olefin)

(diolefin)

Secondary reactions between olefins and diolefins may give cycloolefins which are present in cracking products in very small quantities. Olefins can transform into cyclic hydrocarbons (naphthenes): n-hexene -1

 cyclohexane

Naphthenic hydrocarbons. The main reactions in cracking of these hydrocarbons are dealkylation (splitting of paraffinic side chains) and dehydrogenation of hexacyclic naphthenic hydrocarbons into benzene hydrocarbons; the two reactions can occur simultaneously.

Dehydrogenation of hexacyclic naphthenes in thermal cracking with the formation of benzene hydrocarbons is of minor importance. Owing to the dealkylation reaction taking place in thermal cracking, naphthenic and benzene hydrocarbons loss most of their long side chains. Paraffinic side chains in turn break to form gaseous and low-boiling paraffinic hydrocarbons and olefins. In high-temperature processes, naphthenic rings can break; the result is that hydrocarbons lose their cyclic structure and that polycyclic structures are partially decycled (if they had several rings). In that case, paraffinic, olefinic and naphthenic hydrocarbons form.

Benzene Hydrocarbons. These are obtained by dehydrogenation of the cycloolefins or naphthenes which were formed at earlier stages of the process. Benzene hydrocarbons are quite stable at high temperatures, especially benzene, toluene and xylenes. The main reaction in cracking of benzene hydrocarbons with alkyl chains are dealkylation and condensation.

Condensation may occur between the molecules of benzene hydrocarbons (or some other unsaturated hydrocarbons). This gives polycyclic benzene hydrocarbons which can condense further to asphaltenes and coke.

Sulfur compounds. They are decomposed in cracking and form hydrogen sulfide.

Cyclic sulfur-organic compounds, such as thiophene and thiophane, have the greatest stability against decomposition. Hydrogen sulfide and elemental sulfur (as the product of oxidation of hydrogen sulfide) which form in cracking of sulfurous petroleum grades can cause strong corrosion of process equipment.

Inert tars and asphaltenes. These may contain various heterocyclic compounds (usually including oxygen, sulfur, nitrogen, and some metals). In cracking they form gases, liquid products and a large amount of coke. The yield of coke in cracking of asphaltenes may reach 60% and that in cracking of tars 7-20% (depending on the molecular mass of tars).

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Since the starting materials for industrial thermal cracking are usually mixtures of many hydrocarbons of complicated structure, many reactions can occur simultaneously and the mechanism of thermal cracking cannot be explained in detail. It is assumed however, that most reaction of thermal cracking can be described by the theory of formation of free radicals.

Exercises 32.1 Read and translate into Vietnamese Thermal process, thermal cracking, weaken, break, homologous, split, preliminary, decompose, qualitatively, consumer, association, chamber, radiant, pipe, furnace, clogging, chill, quench, prevail, linearly, diverse, dehydrogenation, hexacyclic, dealkylation, condensation, polycyclic, heterocyclic, assume.

32.2 Answer the following questions 1. What are thermal processes?

2. What are the products of thermal cracking?

3. What are the products of coking?

4. What are the products of pyrolysis?

5. Who designed the first cracking plant?

6. Which types of hydrocarbons can be cracked most easily?h 7. Which C-C bonds are broken down in cracking of high paraffins at lower temperature?

8. Which C-C bonds are broken down in cracking of high paraffins at higher temperature?

9. What are the products of cracking of high molecular weight paraffins at higher temperature?

10. What is the relationship between the rate of a reaction and its temperature?

11. What are the primary reactions of olefins during thermal cracking condition?

12. What are the secondary reactions of olefins during thermal cracking condition?

13. Which reactions happen with naphthenic hydrocarbons during thermal cracking condition?

14. Why are gaseous, low-boiling parafinic hydrocarbons and olefins formed during thermal cracking of naphthenic hydrocarbons?

15. What are the main reactions of benzene hydrocarbons during thermal cracking?

16. Which compounds can be obtained during cracking of benzene hydrocarbons?

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17. Which sulfurous compounds are formed during cracking?

18. What is the main product during cracking of tars and asphalthenes?

19. What is the main mechanism of thermal cracking?

32.3 Translate into English 1. Trong các quá trình nhiệt, các phân đoạn nặng của dầu mỏ bị phân hủy ở nhiệt độ cao thành các phân tử nhẹ hơn.

2. Phân tử paraffin bị bẻ gẫy ở giữa tạo ra một phân tử olefin và một phân tử paraffin 3. Ở áp suất cao phản ứng polyme hóa xảy ra mạnh giữa các olefin cùng loại hoặc khác loại.

4. Các xicloparaffin bị đề alkyl hóa và đề hydro hóa tạo thành benzen và dẫn xuất.

5. Hydrocacbon thơm tương đối bền ở nhiệt độ cao. Phản ứng chính của chúng là đề alkyl hóa và ngưng tụ.

32.4 Write a short summary of the text

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UNIT 33 CATALYTIC PROCESSES IN REFINERY

A typical feature of catalytic processes is the use of catalysts, i.e., substances which can accelerate (or decelerate) the reactions and cause the formation of new hydrocarbons and other substances not present in the starting material. Catalytic processes occur under softer conditions (at lower temperatures and pressures) than thermal ones, but may involve the reactions which are impossible in purely thermal processes.

A catalyst usually consists of an active substance (which determines the course of desirable reactions) applied onto a carrier substance (mostly alumina) having a largely extended surface. In some cases, some other substances (promoters) are added to improve characteristics of catalytic process. The particles (granules) of catalytic posses an enormous porosity and, therefore, have a very large internal surface area. The activity of a catalyst is due mainly to the surface of pores rather than to their external surface. The name of a catalyst depends on the process where it is to be used, for instance, reforming catalysts, cracking catalysts, etc.

The technico-economical characteristics of a catalytic process are determined by the quality of the starting material and the process conditions, as well as by the properties of the catalyst used. The capability of a catalyst to accelerate the rate of desirable reactions and retain the rate of unwanted ones at a constant low level is called selectivity. Activity is another important characteristic of catalysts; it is estimated in terms of the yield of the end product relative to the use of the starting material. In particular, the catalyst activity in catalytic cracking is determined as the yield of gasoline (end product).

Catalysts can participate in process reactions in a stationary (fixed-bed) or moving (circulating) state. In both cases, they gradually lose their activity and selectivity owing to aging. This may be called normal aging; it is unavoidable and can only be accelerated under more rigid process conditions. Along with normal aging, quick aging of a catalyst may also take place. This occurs often when the process is run under abnormal conditions, say, at an excessively high temperature. Many catalysts can be affected by certain substances containing sulfur, nitrogen and heavy metals (V, Ni, and other) and by water in the starting material.

Catalysts can be regenerated to restore their activity and partially, the selectivity, which is usually done by removal (burning-off) of the coke deposits settled on catalyst particles during operation. By another method, the properties of catalysts (especially of fixedbed type) are restored by gradually raising the temperature in the reactor. With circulating catalysts, a fresh catalyst is added in portions to compensate for the loss of the catalyst in the system.

Catalytic processes make it possible to remove unwanted impurities, for instance, sulfurous compounds, and to convert certain hydrocarbons into the products which cannot be obtained by preliminary distillation of petroleum or in thermal processes.

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Brief Description of Catalyst processes Catalytic cracking is the process of conversion of high-boiling petroleum fractions into high-octane base components of aviation and automobile gasoline and middle distillates.

Industrial processes of catalytic cracking are based on contacting the starting material with an active catalyst under appropriate conditions to convert a considerable portion of the material into gasoline and other light products. In cracking reactions, carbon deposits form on the particles of the catalyst and thus reduce sharply the activity, in particular, the cracking ability. The activity of the catalyst is restored by burning off the carbon precipitates (usually called coke) in air.

There exist many types and systems of catalytic cracking plants, those with circulating flow of the catalyst, especially in a fluidized bed, being most popular.

Catalytic reforming is employed widely to obtain high-octane gasoline from lowoctane gasoline fractions. Reforming of gasoline or gasoline fractions in combination with various methods of separation of benzene hydrocarbons, for instance, with solvent extraction, make it possible to produce benzene hydrocarbons (benzene, toluene, xylenes and higher aromatics) for the petrochemical and chemical industries.

Catalytic reforming processes are based on contacting the starting material with an active catalyst usually containing platinum. The yield of reformate may vary within 63 to 85 % of the mass of the starting material. The catalyst is regenerated periodically to restore its activity. A feature of importance is that the catalytic reforming occurs in a medium of hydrogen-containing gas at high temperatures and pressures. The hydrogen formed in various reactions of reforming is removed from the system as an excess of hydrogen-containing gas.

The high content of hydrogen in the gas mixture (up to 80% by volume) makes it possible to utilize it in hydrogenation processes, in particular, for hydrofining of diesel fuels.

Hydrogenation processes occur in the medium of hydrogen at elevated temperatures and pressures. They can be used for preparing high-quality products from sulfurous and highsulfurous petroleum grades, the yields and quality of these products being varied depending on the degree of destruction and the prevailing reactions. Among the processes of this kind, hydrofining of various fractions and products is most important.

Hydrofining of petroleum distillates and products is one of the most popular catalytic processes, especially for treating sulfurous and high-sulfurous petroleum grades. The process is carried out in a hydrogen medium at a pressure of 3-5 MPa. The main object of hydrofining of petroleum distillates and products is to reduce the content of sulfur and other harmful compounds in them. These substances are destructed in the process, and the destruction products (hydrogen sulfide and ammonia) are removed from the system with gases.

Hydrofining processes are based on contacting petroleum distillates and products with a fixed-bed or circulating catalyst, usually alumina-cobalt-molybdena or alumina-nikelmolybdena. The process takes place in the medium of hydrogen at elevated temperatures and pressures so as to convert 95-99% of the starting material into the refined product or distillate (hydrogenate). Minor quantities of gasoline, hydrogen sulfide and ammonia also form in the process.

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Alkylation is a process by which isoparaffinic hydrocarbons are combined with olefins to form higher-boiling isoparaffinic hydrocarbons which can be used as high-octane components in aviation and automobile gasoline. Other kinds of alkylation are also in use, in particular, alkylation of benzene hydrocarbons by olefins (for instance, alkylation of benzene by ethylene to make ethylbenzene or alkylation of benzene by propylene to make isopropylbenzene).

Up to quite recently, catalytic alkylation of isobutane was carried out by butylenes in the presence of sulfuric or hydrofluoric acid as a catalyst. In modern plants, alkylation of isobutane is done by using the materials containing ethylene, propylene and even amylenes, as well as butylenes.

Alkylation processes may differ in the starting material, catalysts, productivity, and especially in the design of catalytic plants. With the use of sulfuric acid as a catalyst, the alkylation process is characterized by a low temperature of the reaction and the necessity to maintain a high concentration of isobutane and olefins in the reaction zone. The total yield of alkylate from olefinic starting materials is 1.5-1.8 units per unit volume of the starting material, depending on the quality of the material and the process conditions. The significance and scope of alkylation increase with the rising production of high- octane automobile gasoline having a low content of TEL. Isomerisation is the process of conversion of relatively low-octane paraffinic hydrocarbons (mostly C5-C6 and their mixtures) into corresponding isoparaffinic hydrocarbons having a high octane number. In industrial isomerisation plants using various catalysts, including alumo-platinum ones, the yield of isomerisates attains 97%. The process of isomerisation takes place in a hydrogen atmosphere. As in other processes, the catalyst is regenerated periodically.

Isomerisates are used together with alkylates for preparation of high-quality gasolines, by compounding them with high-aromatic gasolines of catalytic cracking and reforming.

Disproportionation is based on converting two molecules of a hydrocarbon into two unlike molecules, one having by one carbon atom more and the other, by one atom less than the original molecules, for instance: 2C3H6  C2H4 + C4H8 The process is carried out at 66-260oC and a pressure of 1.4-4.1 MPa, with the starting material being supplied at a high rate (10 to 100 h -1). Disproportionation takes place with a high selectivity: the total yield of ethylene and butylenes attains 97% of the propylene converted and the degree of conversion of the latter, up to 45%. Disproportionation can be employed for making benzene from toluene (2C7H8  C6H6 + C8H10) to replace the less efficient process of toluene alkylation.

In industrial practice, a number of processes are often combined in a single plant (for instance, hydrogen cracking and catalytic reforming). This makes it possible to process lowoctane starting materials into high- octane gasoline with a high concentration of benzene hydrocarbons (obtained by reforming) and isoparaffinic ones (obtained by hydrogen cracking). In this combined technique, the process of hydrogen cracking occurs without hydrogen supply from the outside.

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Exercises 33.1 Read and translate into Vietnamese Feature, accelerate, decelerate, alumina, promoter, granule, enormous, porosity, surface area, pore, technico-economical, capability, unwanted, selectivity, participate, circulating, ageing, unavoidable, abnormal, excessive, regenerate, fixed-bed reactor, restore, portion, compensate, fluidized bed, reform, periodical, destruction, destruct, harmful, maintain, isomerisation, atmosphere, attain, disproportionation.

33.2 Answer the following questions 1. What is the typical feature of catalytic processes?

2. What can you say about the conditions of catalytic processes?

3. What are the general compositions of a catalyst?

4. What is the main characteristic of a catalyst?

5. What is the selectivity of a catalyst?

6. How can catalysts participate in process reactions?

7. When does the quick aging happen?

8. What can affect on the activity and selectivity of catalysts?

9. How can you regenerate spent catalysts?

10. Do you know what are the main catalytic processes 11. Can you show the basis of catalytic cracking?

12. What is the purpose of catalytic reforming?

13. In which condition does catalytic reforming happen?

14. What is the purpose of hydrogenation processes?

15. Which process is the most important in hydrogenation processes?

16. What is the basis of hydrofining process?

17. Can you define the alkylation reaction?

18. Which alkylation processes are used in petroleum processing?

19. How can they carry out the catalytic alkylation of isobutene?

20. What do the alkylation processes depend on?

21. What is the characteristic of alkylation processes catalyzed by sulfuric acid as a catalyst?

22. What is the purpose of isomerization?

23. What is disproportionation?

24. How can you say about the characteristic of gasoline obtained by catalytic processes?

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33.3 Translate into English 1. Quá trình cracking xúc tác chuyển hóa các phân đoạn có nhiệt độ sôi cao thành các phân đoạn xăng có giá trị cao hơn 2. Quá trình reforming xúc tác chuyển hóa các phân đoạn xăng có chỉ số octan thấp thành các phân đoạn có chỉ số octan cao.

3. Quá trình xử lý với hydro dùng để xử lý các phân đoạn chứa nhiều dị tố như lưu huỳnh và nitơ.

4. Sự kết hợp các olefin nhẹ và iso-butan thành các hydrocacbon thuộc phân đoạn xăng được gọi là quá trình ankyl hóa.

5. Quá trình isome hóa chuyển hóa các phân tử n-paraffin thành các isoparaffin tương ứng có chỉ số octan cao hơn.

33.4 Write a short summary of the text

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III.2 ADDITIONAL UNITS UNIT 34 CATALYTIC CRACKING OF PETROLEUM There are two main types of catalytic cracking: one is carried out in the presence of a catalyst -porous solid particles of a definite composition and structure; the other is also carried out with a catalyst, but in a hydrogen atmosphere at a high pressure (up to 30 MPa) and a slightly reduced temperature (hydrocracking).

As compared to thermal cracking, catalytic cracking gives lower yields of methane, ethane and olefins, but higher yields of C3 and C4 hydrocarbons and of gasolines high in benzene and isoparaffinic hydrocarbons. This is the principal advantage of catalytic cracking over thermal cracking. Aluminosilicates are used most often as cracking catalysts now. In recent time, zeolite-containing (crystalline aluminosilicate) catalysts with rare-earth additives have come into wide use.

The main object of catalytic cracking is to produce high-octane components for automobile or, less frequently, for aviation gasolines. The process gives the highest yield of white products with any kind of petroleum. The by-products obtained in catalytic cracking plants include gases, catalytic gas oils (light grades boiling off up to 350oC and heavier ones, which begin to boil above 350oC) and coke which precipitates on the catalyst and is burned off in regeneration.

The operation of catalytic cracking plants can be characterized by what is called cracking ratio, i.e., the relative quantity of the starting material converted into gasoline, gas and coke. Thus, the depth of conversion is 100 minus the yield of gas oil (in percent). In single cracking, the cracking ratio does not exceed 55%, whereas in deeper kinds of cracking (recycle cracking) it may reach 80% by mass. In some cases use is made of the cracking efficiency, which is the ratio of the total yield of debutanized gasoline and C 4 fraction to the cracking ratio. The cracking efficiency is usually 0.75 to 0.80.

Principal reactions of catalytic cracking In the cracking process, the contact of crude petroleum with a catalyst results in the formation of gas, gasoline, coke and some liquid products with the boiling temperature above the boiling -off temperature of gasoline. These products come from the following principal reactions.

Cracking of hydrocarbons with the formation of lighter molecules: for instance, nbutyl radical splits from a molecule of n-butylbenzene to form benzene and butylene. The molecules of cetane C16H34 give on splitting C8H18, C8H16 and some other hydrocarbons. The rate of hydrocarbon splitting increases substantially with increasing temperature, which makes it possible to control the process, i.e., to increase or diminish the yields of certain products by changing the temperature.

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Dehydrogenation. In this reaction, only hydrogen molecules split from hydrocarbon molecules. A typical example is the catalytic reaction of dehydrocyclization of methylcyclohexane C7H14 (naphthenic hydrocarbon), which gives up three hydrogen molecules and converts into toluene. Part of the hydrogen liberated in dehydrogenation is attached in catalytic cracking to olefinic hydrocarbons, thus reducing the content of unsaturated hydrocarbons in catalytic cracking gasolines.

Isomerisation is characterized by that the atoms in a molecule change their positions, but their number remains the same. Isomerisation of normal paraffinic hydrocarbons gives hydrocarbons of a branched structure, for instance, isopentane forms from n-pentane.

Hydrogenation. In this reaction, the molecules of the starting material attach hydrogen and thus form new compounds more saturated in hydrogen. For instance, octylene (an olefinic hydrocarbon) is converted into octane by the reaction: C8H16

+ H2

 C8H18

The hydrogenation reaction is quite common and can take place not only with olefins, but with other classes of hydrocarbons as well. For instance, cyclohexane can be obtained by hydrogenation of benzene.

Polymerisation. In this reaction, two or more molecules combine into a single large molecule. For example, two molecules of ethylene are polymerized into a higher boiling hydrocarbon, butylene. Using polymerization, gaseous olefinic hydrocarbons (ethylene, propylene, butylenes) can be converted into liquid or even solid hydrocarbons of a higher molecular mass.

In catalytic cracking, the rate of breakdown of paraffinic hydrocarbons is higher at a higher molecular mass. At the ordinary temperatures of catalytic cracking, i.e., 450-520oC, catalysts have almost no effect on light paraffinic hydrocarbons: propane and butane, white high-boiling paraffins undergo deep changes. For instance, the cracking rate of cetane, whose boiling temperature is 287oC is roughly 13 times that heptane which boils at 98oC. The olefins formed on breakdown of normal paraffinic hydrocarbons are isomerised, partially saturated by hydrogen and convert into paraffinic hydrocarbons of a branched structure and a lower molecular mass. Olefins can be subjected to catalytic cracking much more easily than paraffinic hydrocarbons. The reactions of splitting, isomerisation, polymerization and hydrogen attachment are very typical of them. Some other reactions are also possible, by which olefins are converted into benzene hydrocarbons and high boiling compounds.

Catalytic cracking of naphthenic hydrocarbons occurs at higher rates than that of paraffinic ones and gives more light liquid products and fewer gases. Besides, naphthenic hydrocarbons give many benzene hydrocarbons on the splitting of hydrogen atoms. Distillates high in naphthenic hydrocarbons are a valuable starting material for catalytic cracking. They give more gasoline and of higher quality than do distillates of a similar fractional composition obtained from paraffinic grades of petroleum.

The nuclei of benzene hydrocarbons are thermally stable and split insignificantly even at 450-500oC. On the contrary, the molecules of benzene hydrocarbons with side paraffinic chains are cracked easily: their bonds break mainly in sites of attachment of a side chain to 137

the benzene nucleus. Benzene hydrocarbons with no side chains in the molecule and paraffinic hydrocarbons of normal structure turn to be most stable against catalytic cracking.

Hydrocarbons of other homologous series (with the same number of carbon atoms in the molecule), such as olefinic, naphthenic, aromatic with long side chains, are less stable and can be cracked more easily.

Starting materials and products of the process Starting materials. The starting materials for catalytic cracking are various distillate fractions obtained by atmospheric or vacuum distillation of crude petroleum. In catalytic cracking plants for obtaining the components of base aviation gasoline, lighter types of the starting material are used; in particular, distillates with the boiling-off range of 220-360oC and relative density of 0.83-0.87. The plants for making the components of automobile gasoline use heavier distillates with the boiling-off range of 300-550oC and relative density of 0.870.93. In some cases, starting materials of an intermediate composition can be used, such as mixtures of various distillates obtained in preliminary processing of petroleum (atmospheric or vacuum distillation) and in secondary processes of preparation of fuels and oils; these mixtures can be used only for making automobile gasolines. In recent time, attempts have been made to process low-ash fuel oils and deasphatizates by catalytic cracking.

The starting material must contain no fractions boiling below 190oC, since they remain practically unchanged upon catalytic cracking and lower the octane number of the final gasoline.

The processing of starting materials containing harmful impurities involves certain difficulties, in particular, stronger corrosion of equipment and heavier coking of the catalyst, which may result in a lower yield of gasoline and lower productivity of the plant. Metal compounds can be present in vacuum distillates owing to carry-over of goudron droplets into the top portion of the column. Some compounds are volatile at high temperatures. For that reason, the operation of a vacuum column should be carefully checked and sometimes it is advisable to lower the boiling-off temperature of a vacuum distillate to be used for catalytic cracking.

The coking ability of the starting material should usually be not less than 0.25%. The materials with the coking ability of up to 0.7% can be processed by the regenerator having extra capacity for coke burn-off. Moist material should not be used for processing, since moisture can disturb the process conditions, in particular, raise the pressure in the reactor, disturb the normal circulation of the catalyst, increase the flow rate of vapors in the rectification column, and impair the quality of the end products. In some cases, this may form emergency situations. The composition of the starting material can also influence the yield and quality of the products of catalytic cracking.

Products of catalytic cracking. Catalytic cracking plants produce up to 20% (by mass) of gases (containing hydrogen and light hydrocarbons up to C 4), up to 60% of highoctane components of automobile gasolines, and up to 2.5-8% of coke, the balance (except for losses) being light and heavy gas oils. Some plants make unstable gasolines which are further delivered to gas separation. Besides, catalytic cracking for production of the base aviation 138

component may give ligroin and polymers as by-products, and also motor gasoline- an intermediate product which is subjected to catalytic refining at the second stage.

Wet gas. Its composition is characterized by a high concentration of isomeric hydrocarbons, in particular of isobutane, which increases the value of the gas as of an intermediate product for further processing.

These data disregard steam, hydrogen sulfide and inert gases which may be present in various minor amounts in gases of catalytic cracking.

Wet gas and unstable gasoline from catalytic cracking plants are fed into an absorption- gas fractionation plant for separation of light gases. Apart from stable gasoline, the products obtained in such a plant include propane-propylene, butane-butylene and pentane-amilene fractions. Propane-propylene and butane-butylene fractions are further polymerized and alkylated to prepare gasoline components or are used in petrochemical processes (propane and butane can also be used as domestic fuel).

Unstable gasoline. It is stabilized to obtain a stable component for preparing highoctane automobile and aviation gasolines.

Light catalytic gasoil. As compared to the products of similar fractional composition obtained by preliminary distillation of petroleum, light catalytic gas oil (a distillate with the beginning of boiling at 175-2000C and the end of boiling at 320-3500C) has a lower cetane number (up to 25), higher contents of sulfur (roughly the same as in crude petroleum) and benzene hydrocarbons (up to 55 %), and a certain concentration of unsaturated hydrocarbons.

The setting temperature of these gas oils is however substantially lower than that of the starting material for catalytic cracking. Under more rigid conditions of the process, and without an increase in recirculation light gas oil is produced in smaller amounts and with a lower cetane number, but with a higher concentration of benzene hydrocarbons.

Light catalytic gas oil is utilized as the starting material the manufacture of commercial carbon (carbon black), as a component in commercial grades of fuel oil, and for some other purposes. In rare cases, it can be used as a component of diesel fuel, provided that other components of the fuel produced by preliminary distillation have a higher cetane number and a reduced content of sulfur (compared to the standard value). In some cases, light catalytic gas oil is extracted; the refined layer with a reduced content of benzene hydrocarbons and a higher cetane number is used as a component of diesel fuels and the extracted layer, which is high in benzene hydrocarbons, is a valuable by-product for preparing carbon black.

Heavy catalytic gasoil is the liquid residue of catalytic cracking. Its quality depends mainly on the process conditions and the boiling -off temperature of the light gas oil produced. Heavy gas oil often contains many mechanical impurities (rests of the catalyst). Its sulfur content is usually higher than that of the starting material used for cracking. Heavy catalytic gas oil is used for making fuel oils and carbon black.

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Exercises 34.1 Read and translate into Vietnamese Crackate, porous, reduced pressure, hydrogen atmosphere, principle, aluminosilicate, zeolite, rare-earth, automobile, burn off, minus, recycle cracking, cetane, substantially, dehydrogenation, branched structure, high-boiling paraffin, subjected, polymerization, insignificant, aviation, deasphatise, attempt, productivity, droplet, volatile, advisable, regenerator, capacity, disturb, circulation, impair, deliver, disregard, inert gas, fractionation, alkylate, recirculation, refine.

34.2 Answer the following questions 1.

How many main kinds of catalytic cracking are there? What are they?

2.

Is there any difference between the products of thermal cracking and catalytic cracking?

3. What is the principal advantage of catalytic cracking over thermal cracking?

4. Which compounds are used as cracking catalysts?

5. What is the main object of catalytic cracking?

6. What are the by-products of catalytic cracking?

7. What is the operation characteristics of catalytic cracking plants?

8. What is cracking efficiency?

9. How many principal reactions happen during atalytic cracking?

10. Which molecules are formed during cracking of hydrocarbons?

11. How does the rate of hydrocarbon splitting depend on temperature?

12. Which compounds are formed in the dehydrocyclisation of methylcyclohexane C7H14?

13. Why is the content of unsaturated hydrocarbons reduced during catalytic cracking of gasolines?

14. What is the isomerisation characterized by?

15. What is polymerization?

16. What is the rate of breakdown of paraffins depended on?

17. How can the molecular weight of hydrocarbons affect on the rate of cracking?

18. Olefins can be subjected to catalytic cracking more easily than paraffinic hydrocarbons, can't they?

19. Which reaction happens with olefin in catalytic cracking?

20. What can you say about the content of naphthenic hydrocarbons in starting material for catalytic cracking?

21. What can you say about the reaction ability of benzene hydrocarbons?

22. Which hydrocarbons are more stable in catalytic cracking?

23. Which materials are used as starting materials for catalytic cracking?

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24. Which starting materials are used in catalytic cracking units for obtaining the components of base aviation gasoline?

25. Why aren't fractions boiling below 1900C used in catalytic cracking?

26. Why is it advisable to lower the boiling -off temperature of a distillate to be used for catalytic cracking?

27. Why shouldn't moist materials be used for catalytic cracking?

28. What are the products of catalytic cracking?

29. What are the by-products of catalytic cracking?

30. What is the composition of wet gas?

31. How can they separate the light gasses from wet gas?

32. What can you say about the composition of light gas oil?

33. What is the light catalytic gas oil used for?

34. What does the quality of heavy catalytic gas oil depend on?

35. What can you say about the composition of heavy gas oil?

36. What can heavy catalytic gas oil be used for?

34.3 Translate into English 1. Các phản ứng trong quá trình cracking xúc tác xảy ra ở điều kiện nhiệt độ thấp hơn và chọn lọc hơn so với quá trình nhiệt.

2. Ưu điểm của quá trình cracking xúc tác so với cracking nhiệt là tạo ra nhiều hydrocacbon phân đoạn xăng và ít khí hơn.

3. Các phản ứng xảy ra trong quá trình cracking xúc tác là: cracking các hydrocacbon nặng, hydro hóa, đề hydro hóa và polyme hóa.

4. Các sản phẩm của quá trình cracking là: xăng, gasoil nhẹ và gasoil nặng.

5. Nguyên liệu của cracking xúc tác là các phân đoạn khác nhau thu được từ chưng cất khí quyển và chưng cất chân không dầu thô.

34.4 Write a short summary of the text

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UNIT 35 CATALYTIC REFORMING OF PETROLEUM

Because higher-octane gasoline permit the building of engines that extract more power from gasoline, there has been a constant push toward higher octanes since differences is octane quality were first recognized. A major factor in this development has been the large scale use of catalytic reforming to raise octane ratings of gasoline stocks. The first commercial unit, hydroformer, went on stream just before World War II, and the process proved to be a major source of aromatics and aviation gasoline for military uses. However, catalytic reforming did not "catch on" until about 1950, when Haensel and others at the Universal Oil Products Co. demonstrated that platinum catalysts could be used commercially despite their high cost. By 1955, catalytic reforming processes had almost completely supplanted thermal reforming. Catalytic processes not only give higher quality products, they give higher yields as well.

Reactions In catalytic reforming, the principal object is to convert other hydrocarbon to aromatics. The reason may be seen by comparing the octane numbers of some corresponding hydrocarbons. Thus, high conversions to aromatics result in high octane products. There is a loss in volume, because aromatics are denser than other hydrocarbons; however, the loss is small in comparison with the loss (to gas and tar) suffered in thermal reforming. Other reactions of some importance in catalytic reforming are cracking and isomerisation.

Production of Aromatics. Because aromatics contain less hydrogen than do other hydrocarbons, dehydrogenation is the primary reaction. Of the nonaromatics, cyclohexane derivatives are dehydrogenated most readily: 

C6H11CH3

Methylcyclohexane

C6H5CH3

+

3H2

Toluene

Cyclopentane derivatives react similarly, but they require a preliminary isomerisation to cyclohexan derivatives: C5H9CH2CH3



Ethylcyclopentane

C6H11CH3  Methylcyclohexane

C6H5CH3

+

3H2

Toluene

Conversion of paraffins to aromatics involves a cyclization step. For normal heptane, the reactions may be written: n-C7H16 C6H11CH3

 

C6H11CH3 C6H5CH3

+

H2

+

3H2

To undergo these reactions, paraffin must have at least six carbon atoms in a chain or be isomerisable to such a compound.

Aliphatic olefins can also be converted to aromatics directly, but this fact is of little practical significance because such olefins are readily hydrogenated to paraffins under the 142

conditions used in catalytic reforming. Thus, aliphatic olefins behave as paraffins, with the exception that they deactivate the catalyst more rapidly. Similarly, cyclic olefins behave as naphthenes.

Hydrocracking. Under the conditions employed in catalytic reforming, cracking completes with dehydrogenation reactions. Because high hydrogen pressure is used, any olefins that form are saturated immediately, and the reaction usually called "hydrocracking".

Whether hydrocracking occurs in one step or two is of little consequence. In either case, a typical over-all reaction is: n-C8H18

+



H2

C3H8

n-Octane

+

Propane

n-C5H12 Pentane

Because lower-boiling paraffins have higher octane numbers, hydrocracking improves octane ratings; however, the improvement is less than if the paraffins were converted to aromatics. Also, there is considerable loss of gasoline to butanes and lighter materials, and the vapor pressure of the debutanised product is raised. Increasing the vapor pressure reduces the amount of butane that can be blended into the product to make a finished gasoline; thus, the effective yield of gasoline is reduced still further.

Hydrocracking of naphthenes also occurs to some extent. Cyclopentane derivatives are more susceptible than cyclohexane derivatives, especially over catalysts with little isomerisation activity. The first step in the hydrocracking of naphthenes is probably scission of the ring: C5H9CH2CH3

+

H2



n-C7H16

The paraffins are formed may react further to produce aromatics, or it may be hydrocracked.

Isomerisation. With some catalysts, paraffins are isomerised under reforming conditions. Usually, isomerisation of paraffins does not have a large effect on octane quality because the production of highly branched paraffins is small. If the paraffins in a given charge were chiefly normal, their isomerisation would have a large effect on octane. In most instances, however, paraffin’s in the charge are mixtures of isomers; therefore the isomerising activity of a catalyst is important chiefly for the isomerisation of cyclopentane derivatives.

Catalysts Although aromatics can be produced from hydrocarbons without catalysts, but severe conditions are required, and yields are low. To obtain acceptable yields, dehydrogenation catalysts must be employed. Those of commercial interest include platinum on alumina, platinum on sillica-alumina, chromia on alumina, molybdena on alumina, and cobalt molybdate on alumina. The ideal catalyst would convert all other hydrocarbons selectively to aromatics rapidly, with only a small catalyst inventory. Such a catalyst would not promote hydrocracking, and it would have to operate under conditions thermodynamically favorable to production of aromatics. To the extent that a catalyst deviates from these conditions it is a poorer catalyst. Derivations may be either in the selectivity of the catalyst toward the 143

production of aromatics or in the activity of the catalyst for the several reactions that actually occur. Selectivity is determined by the relative rates of the competing reactionsdehydrogenation to aromatics and hydrocracking, and isomerisation in so far as it affects the other two. Activity is determined by the magnitude of the rate constants. Platinum catalysts appear to be the most selective and the most active, as well as the most expensive.

Dehydrogenation of Naphthenes. Selectivities of catalysts depend to some extent on the make-up of the feed stock. Alkylcyclohexanes are readily converted to aromatics by all dehydrogenation catalysts, provided that the reaction conditions are favorable thermodynamically. For the conversion of alkylcyclopentanes, on the other hand, there are large differences. Because alkylcyclopentanes require an isomerisation step, their conversion to aromatics depends upon the isomerisation activity of the catalyst. Published data on platinum, molybdena, and chromia catalysts show that platinum has the highest isomerisation activity, chromia the lowest. Even with platinum catalysts, the isomerisation reaction is the rate-controlling step. Thus the conversion of alkylcyclopentanes to aromatics is lower than the conversion of alkylcyclopentanes to aromatics is lower than the conversion of cyclohexane derivatives; consequently there is more opportunity for hydrocracking, and yields of aromatics are poorer.

Dehydrocyclization of Paraffins. Data on platinum, molibdena, and chromia catalysts have also been published for the conversion of paraffins to aromatics. When operating in the pressure range normally use in catalytic reforming, platinum is the most effective catalyst, chromia the least. The poor results obtained with chromia catalyst are surprising, inasmuch as high conversions of n-heptane to toluene are obtained at low pressures. Apparently, the chromia catalyst has the unusual property of adsorbing hydrogen so strongly at higher pressure that paraffins cannot readily reach its surface.

Reaction Mechanism Extensive studies have been made to elucidate the mechanism of reforming over platinum catalysts. Such catalysts are duel-functional; they contain platinum as a dehydrogenating agent and an acidic material, such as chlorine, fluorine, or alumina-promoted silica, as an isomerisation agent. In commercial catalysts, enough platinum is used to ensure that the dehydrogenation activity is large in comparison with the isomeriszation activity.

Although only traces of olefins can exist under reforming conditions, they apparently are intermediates in the reactions. Both naphthenes and paraffins are dehydrogenated to olefins (in trace amounts) on dehydrogenation sites in the catalyst. Cyclohexenes continue to dehydrogenate rapidly to aromatics. Alkylcyclopentenes transfer to acid sites, where they are isomerised to cyclohexenes; the cyclohexenes then pass back to dehydrogenation sites, where they are converted to aromatics. Alkyl olefins also transfer to acid sites where they may either isomerise to other alkyl structures or cyclise to naphthenes. The isomerised olefins pass back to dehydrogenation sites, where alkyl olefins are hydrogenated to paraffins and cyclohexenes are dehydrogenated to aromatics.

In view of the low isomerisation activity of chromia catalysts, the excellent results obtained with them at low pressure suggest that n-heptane is easier to aromatize than are its isomers. This idea is also suggested by data on the conversion of n-heptane over a platinum 144

catalyst; the ratio of aromatics production to hydrocracking was higher at low conversions (where n-heptane predominates in the reactants) than at higher conversion (where isoheptanes predominate). It has also been shown that paraffins with more than seven carbon atoms are converted more readily to aromatics than are heptanes. All these observations fit the hypothesis that naphthene intermediates are not formed from paraffins over platinum catalysts by linking of two end (primary) carbon atoms. It has been suggested that platinum catalysts form derivatives of cyclopentane by the linkage of second and sixth carbon atoms; the alkylcyclopentanes so formed isomerise to alkylcyclohexanes, which are dehydrogenated to aromatics. This mechanism could not apply for chromia catalysts, which have little isomerisation activity. When n-heptane is processed over a chromia catalyst, the second and seventh carbon atoms appear to link up to form methylcyclohexane directly.

Exercises 35.1 Read and translate into Vietnamese Reforming, reformate, octane rating, hydroformer, military, supplant, suffer, denser, dehydrogenation, dehydrogenate, nonaromatic, cyclize, cyclization, isomerizable, aliphatic, debutanize, naphthene, susceptible, reforming, chief, thermodynamic, molybdena, molybdate, inventory, deviate, magnitude, alkylcyclohexane, chromia, aromise.

35.2 Answer the following questions 1. What is the purpose of catalytic reforming?

2. Why had catalytic reforming supplanted thermal reforming?

3. Do you know why conversion other hydrocarbons to aromatics is principle of catalytic reforming?

4. What are the main reactions in catalytic reforming?

5. Would isomerisation have a large effect on octane number?

6. What is the activity of catalysts determined by?

7. What is the characteristic of platinum catalysts?

8. Why is the conversion of alkylcyclopentanes to aromatics lower than that of cyclohexane derivatives?

9. What does the selectivity of catalysts depend on?

10. Which catalyst has the highest isomerization activity?

11. Why is the rate of the dehydrocyclization of paraffins low at pressure range normally used in catalytic reforming?

12. What are dual-functional catalysts?

13. Which reactions are performed in dehydrogenation sites?

14. Which reactions are performed in acid sites?

15. Why are the paraffins with more than seven carbon atoms converted to aromatics easier than heptanes?

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16. Can you show the mechanism of the conversion of paraffins to aromatics?

35.3 Translate into English 1. Các phản ứng chính xảy ra trong quá trình reforming xúc tác là đề hydro hóa các naphten, hydrocracking, isome hóa và đề hydro hóa đóng vòng các paraffin.

2. Sản phẩm của quá trình reforming xúc tác là các hydrocacbon có chỉ số octan cao hơn như isoparafin, hydrocacbon thơm…

3. Chất xúc tác dùng cho quá trình reforming xúc tác là loại lưỡng chức: chức hydro-đề hydro hóa (chức kim loại) và chức axit.

4. Các hydrocacbon mạch nhánh và hydroacbon thơm có chỉ số octan cao hơn các hydrocacbon mạch thẳng và không thơm.

35.4 Write a short summary of the text

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REFERENCES Bùi Thị Lệ Thủy, Giáo trình Anh văn chuyên ngành (dùng cho sinh viên ngành Lọc Hóa Dầu), Hà nội, Trường đại học Mỏ- Địa chất, 2003.

1.

Mgr. Božena Velebná. English for Chemists. Univerzita Pavla Jozefa Šafárika v Košiciach, Szech Republic.

2.

Thái Doãn Hòa, Tạ Thị Phương Hòa, Nguyễn Vân Anh, Trần Vân Anh và Mai Thanh Tùng, Giáo trình dành cho sinh viên ngành Công nghệ hóa học, Nhà xuất bản Khoa học và Kỹ Thuật Hà Nội, 2004.

3.

Nguyễn Thị Hiền, Nguyễn Trọng Đàn và Lê Thị Lan Chi, The laguage of chemistry, food and biology technology in English, Đại học Bách khoa Hà Nội, 2009.

4.

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PART 4 ACADEMIC WRITING

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UNIT 36 INTRODUCTION TO ACADEMIC WRITING

What is academic writing? Academic writing is generally formal, objective (impersonal) and technical. The casual or conversational language, such as contractions or informal vocabulary is avoided. The direct reference to people or feelings, and instead emphasising objects, facts and ideas also are avoided If you want to be a good academic writer, you need to know the specific styles and structures for your discipline, as well as for each individual writing task. You should ask your supervisor, learn the writing style of the academic articles in the most prestigious journals in your discipline, and look at the successful writing by others in your field.

Formal language To make your writing more formal through you need to carefully choose the vocabulary that you use. For instance, you should choose the formal instead of informal vocabulary (‘somewhat’ and ‘insufficient’ are more formal than ‘a bit’ and ‘not enough’), avoid contractions (‘cannot’ is better than ‘cann’t’), avoid emotional language (more moderate words such as ‘helpful’ or ‘problematic’ are better than strong words such as ‘wonderful’ or ‘terrible’), and use more cautious evaluations such as ‘strong evidence’ or ‘less convincing’ instead of using absolute positives and negatives such as ‘proof’ or ‘wrong’.

Objective language To express your point of view, such as interpret findings, evaluate a theory, develop an argument, and critique the work of others and still write in an objective style, you can use the following methods.    

Emphasize things and ideas, instead of people and feelings. For instance, write ‘The results indicate that the temperature is an important factor’ instead of writing ‘I believe the temperature is an important factor, based on the results’.

Avoid evaluative words that are non-technical. For example, instead of ‘amazing’ or ‘disappointment’, write ‘valid’ or ‘did not demonstrate’.

Show caution about your views, or to allow others to disagree. For example, instead of writing ‘I think drink alcohol causes digestion diseases’, write ‘There is evidence to support the possibility that drink alcohol increases the risk of digestion diseases’.

Find authoritative sources, which support your point of view, and refer to them in your writing.

Technical language To write technically you need to develop a large vocabulary for the concepts specific to the discipline or specialisation you’re writing for. Please take note of terminology used by your lecturer, as well as in your readings.

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Exercises 36.1 Read and translate into Vietnamese Academic, formal, informal, objective, impersonal, casual, contraction, reference, emphasis, discipline, humanity, style, prestigious, emotional, convince, strategy, intense, emotion, emotional, abuse, digestion, disease, modality, specialization, terminology, discourse, multiple, statute.

36.2 Answer the following questions 1. What is the difference between academic writing and conversational language?

2. What should you do if you want to be a good writer?

3. What is formal language?

4. What is objective language?

5. What is the technical language?

36.3 State the function of the words after and before and translate the sentences 1. The polyamine is added after the dispersion.

2. After dispersion is complete, the polyamine is added.

3. Before the discovery of vulcanization, the great drawbacks of rubber were its thermoplastic nature and its sensibility to oxidation.

4. Neoprene was used for balloons, before natural rubber was available.

5. Polymerization starts at room temperature and is complete after a few hours.

6. After substantial proportions of stabilizing soaps are avoided, polymerization takes place.

36.4. State the functions of the words in bold type 1. Some scientists observed that aerated latex could initiate polymerization.

2. A plasticizer is a material that increases the plasticity of a mass.

3. Sekhar considers that reactive sites are formed on the rubber during aeration, these probably being hydroperoxidic.

4. The vulcanization of plastic chloroprene polymer differs from that of all other rubbers in requiring the addition of no vulcanizing ingredient.

5. The methods of producing modified latices depend on those of initiation.

6. In the case of methyl methacrylate it is found that the pattern of combination in the same as that found when polymerization takes place in solution.

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36.5 Translate the following sentences into Vietnamese paying attention to the words in bold type 1. The colloidal behavior of latex rubber is largely the result of the protective layer of protein with which the particles are surrounded.

2. It is necessary, for certain purposes, to make use of the latex itself as a raw material.

3. Proteins, fats, soaps, and other substances are present in the milky fluid, which is called “latex”.

4. We shall not consider synthetic plastic materials, partly because of their similarity.

5. The utility of rubber is ultimately related to the ease, with which it sustains very large distortions, returning to its original shape when released.

6. Concentration may be effected by using a centrifuge, in a manner similar to the centrifuging of milk to give cream.

7. Numerous ingredients other than sulfur are normally included in the rubber mixing, the proportions depending on the grade of rubber required.

8. The rubber molecule may have a molecular weight as high as 250.000.

9. The sulfur, zinc oxide and accelerators are referred to collectively as the vulcanizing system.

10. Apart from its use in such specialized products as adhesive, the full potentialities of rubber latex are only realized on vulcanization.

36.6 Give Vietnamese equivalents to break down

to run off

to build from

to split up

to centrifuge off

to squeeze out

to correspond to

to pass through

to rise through 36.7 Translate into English 1. Trong văn viết cần phải tránh sử dụng ngôn ngữ thông tục và văn nói.

2. Để viết tốt bạn nên học những kiểu mẫu và cấu trúc đặc biệt cho chuyên ngành của bạn cũng như nhiệm vụ của mỗi phần bài viết riêng biệt.

151

3. Ngôn ngữ trang trọng có thể được tạo ra nhờ cách dùng từ vựng của người viết và tránh viết tắt, dùng ngôn ngữ biểu cảm hay quá tiêu cực hoặc tích cực.

4. Để viết tốt bạn cần hỏi thông tin người hướng dẫn, thầy cô giáo, tham khảo các bài viết thành công trong lĩnh vực của bạn 36.8 Write a short summary of the text

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UNIT 37 TYPES AND STRUCTURE OF ACADEMIC WRITING

1. Types of academic writing There are four main types of academic writing. They are descriptive, analytical, persuasive, and critical.

Descriptive The descriptive is the simplest type of academic writing. It provides facts or information. A summary of an article or a report of the results of an experiment would be an example.

Analytical Analytical writing includes descriptive writing and re-organisation the facts and information you describe into categories, groups, parts, types or relationships.

Persuasive Persuasive writing is a one step further than analytical writing. In addition to all the features of analytical writing, you need to add of your own point of view. Points of view in academic writing can include an argument, a recommendation, and interpretation of results or evaluation of the work of others. Each claim you make needs to be supported by some evidence, for example a reference to research findings or published sources.

Critical For research, postgraduate and advanced undergraduate writing you usually use critical writing. In addition to all the features of persuasive writing, you need to add least one other point of view. Critical writing requires you to consider at least two points of view, including your own on an issue or topic while persuasive writing requires you to have your own point of view.

2. Structuring written work Essay and report are two types of writing in university. All assay and report has the same basic three-part structure: introduction, main body and conclusion. However, the main body can be structured in many different ways.

Introductions The purpose an introduction is to clearly tell the reader the topic, purpose and structure of the paper. An introduction might be between 10 and 20 percent of the length of the whole paper. It begins with the most general information, such as background and/or definitions, then shows the overall topic, purpose, your point of view, hypotheses and/or

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research questions, and ends with the most specific information, describing the scope and structure of your paper.

Paragraphs Most academic writing has some paragraphs and each paragraph may have a three-part structure. Firstly the topic sentence introduces a general overview of the topic and the purpose of the paragraph. Next, definitions, classifications, explanations, contrasts, examples and evidence are given in the body of the paragraph. Lastly, the final sentence not only presents new information, but often either summarises or comments on the paragraph content.

Conclusions The conclusion is closely related to the introduction and is often described in an opposite order. It usually begins by briefly summarising the main scope or structure of the paper, then confirms the topic that was given in the introduction, and ends with a more general statement about how this topic relates to its context.

Exercises 37.1 Read and translate into Vietnamese Descriptive, analytical, persuasive, critical, empirical, interpretation, assignment, category, context, argument, argue, recommendation, effectiveness, sustainable, sustainability, coherent, scope, assumption, postgraduate, evaluate, merit, alternation, alternative, critique, debate, disagree, accurately, appropriate, authoritative, thorough, instructions, lab report, contrast, chronology, counter, sub-topic, sequence, highlight, pile, diagram, discard, heading, sub-heading, hypotheses, predictable, template, summarize, mention, outcome, implication, elaborate, themes.

37.2 Answer the following questions 1. Which type of academic writing do you need to use in an empirical thesis? What are they?

2. What is the purpose of descriptive writing?

3. What is analytical writing?

4. How do you make your writing more analytical?

5. What are the kinds of instructions for a persuasive assignment?

6. How can you develop your argument?

7. What is the difference between persuasive and critical writing?

8. What do you need to write critical writing?

9. What are the parts of an essay?

10. What should you do to writing a good essay?

11. What is the difference between the main body structure of an essay and a report?

12. What is the purpose of introduction of a text?

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13. When should you write your introduction of the text?

14. What is the body of the paragraph about?

37.3 Rewrite the sentences in a more academic style using verbs from the list below.

Note that you may need to change the verb tense Investigate, assist, raise, discover, establish increase, eliminate 1. Systems analysts can help out managers in many different ways.

2. This program was set up to improve access to medical care.

3. Medical research expenditure has gone up to nearly $350 million.

4. Researchers have found out that this drug has serious side effects.

5. Exercise alone will not get rid of medical problems related to blood pressure.

6. Researchers have been looking into this problem for 15 years now.

7. This issue was brought up during the coroner's inquest.

37.4 Translate into Vietnamese paying attention to the word with: 1. to coat positively charge electrodes with the particles; 2. to combine with rubber molecules; 3. to extract with acetone; 4. to mix with sulfur; 38 to smoke with fume; 39 to stabilize with ammonia; 40 when tested with iodine; 41 some substances remain with impurities; 42 with avoidance of agitation; 37.5 Translate the following sentences into Vietnamese and state the function of will and would a) 1. When stretched rubber flows, it will not return to its original shape.

2. If heating is carried on long enough in the presence of curatives, the latex will not form a continuous film on drying but will crack into a multitude of small pieces.

3. Styrene will polymerize to produce polymers other than rubber- like bodies.

4. Ethylene chloride will react with sodium polysulfide to form high molecular weight rubberlike substances.

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b) 1. Coagulation would prevent the use of latex for special methods of manufacture.

2. To suppress bacterial action, which would eventually lead to coagulation, a preservative must be added to latex.

3. Were unstretched rubber cooled, a slow crystallization would take place, giving a harder and less extensible material.

4. The atoms of the molecule share in the general thermal motion at any temperature, so that a free molecule would be continually coiling, twisting and, changing its shape.

5. Density considerations make it impossible to accept a theory, which would require substances to polymerize with the decrease in density as, would be the case if the polymers spin.

37.6 Translate into English 1. Có 4 cách viết văn phạm khoa học, đó là: mô tả, phân tích, thuyết phục và phê bình.

2. Văn mô tả là loại đơn giản nhất, ví dụ như một tóm tắt bài báo hay một báo cáo kết quả thực nghiệm 3. Văn phạm khoa học thường gồm văn phân tích.

4. Trong văn phạm thuyết phục, mỗi nhận xét bạn đưa ra cần được thuyết phục bởi một số bằng chứng, ví dụ như từ tài liệu đã công bố.

5. Cấu trúc của tất cả các bài luận gồm 3 phần: giới thiệu, thân bài và kết luận.

6. Cũng giống như bài luận, cấu trúc của bài báo cáo cũng gồm 3 phần: giới thiệu, thân bài và kết luận.

7. Trước khi viết bạn cần phải có một kế hoạch chi tiết.

8. Chiều dài của phần giới thiệu khoảng 10-20 phần trăm chiều dài của cả bài báo.

9. Phần giới thiệu cần được xem lại khi phần thân bài kết thúc.Microsoft Office 37.7 Write a short summary of the text

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UNIT 38 HOW TO WRITE A SUCCESSFUL SCIENTIFIC MANUSCRIPT A manuscript allows the researchers to share their original ideas and new discoveries with the scientific community as well as to the general population. Researchers spend a significant amount of time and effort during the investigative stages conducting the required research before it is released into the public domain. Specific language and format of scientific manuscripts must be adhered to communicate the results to the scientific community.

Organization Researchers need to organize the scientific manuscripts in a logical format, which fits specific criteria as determined by the scientific community. Writing methodology has been standardized in journals. The common components of a well-written manuscript are: a title, abstract, introductory paragraph, methods and materials section, and discussion of results, conclusion, and a list of references. The structure of each component of a journal article should follow a logical sequence, which is accustomed to members of the science community.

Structural Contents Title or Heading Titles are important because audience first notices it when encountering your manuscript. It introduces your reader to the subject matter you intend to discuss in the next thousands words. A well-formatted title could encourage readers delving into your manuscript further.

Abstract Abstract is a brief summary of the methods taken to achieve your goals along with a short version of the results. Some readers only read this part of the paper, therefore, it should be considered as an abbreviated version of your complete manuscript.

Introduction The introduction supplies background material indicating why the research performed is important along with the direction the research took. It includes a brief discussion the technical aspects of the experimental approach utilized to reach the article’s stated conclusions. A well-written introduction will encourage readers to delve further into the body of the paper.

Methodology and Materials 157

This part of the manuscript is mandatory. Fellow researchers will glean from this section the methods and materials you utilized either to validate your work, reproduce it, and/or develop the concepts further. You should present the statistical analysis and tests here.

Discussion of Results This is the core part of the manuscript. All the results are presented here using tables and graphs, communicating the essence of the research and the outcomes they generate. Then results should be interpretated, the implications of these findings, and potential future research to follow should be discussed.

Conclusions This is the endpoint in the manuscript. You should write the conclusions in a concise manner utilizing words not numbers. Only the information taken from the performed research is conveyed in this section. References are not placed here. It is imperative to interpret full and complete of your findings in this part. Comparisons to similar work in your field may be discussed here.

References The preparation of reference section should follow the guidelines of each journal.

There exist several formats for reference creation. Familiarize yourself with them. The sequence of references listed should be in the order in which they appear in the research paper.

Production of a scientific manuscript is a necessity to introduce your research to a wide audience. The complexity of the research and the results generated must be written in a manner that is clear and concise, follows the current journal formats, and is verifiable. The guidelines embedded in this paper will help the researcher introduce your research to a wide audience. Never write anything that cannot be justified by the performed research. Your scientific manuscript will be a success with these simple rules in mind.

Exercises 38.1 Read and translate into Vietnamese Manuscript, endeavor, challenges, rewarding, fruition, community, conduct, domain, thorough, adhere, ethical, colleague, debate, reflect, embed, criteria, transmit, upfront, energize, accustom, crisp, encounter, everstate, dissuade, delve, glean, index, algorithms, amphasise, abbreviate, premise, amplify, aspect, rationale, reveal, clarity, mandatory, glean, validade, validity, protocol, suspicion, cast, detect, core, elaboration, ulitise, implication, ambiguous, controversy, convey, imperative, essential, misinterpretation, submission, authentication, familiarize, verifiable.

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38.2 Answer the following questions 1. What is the purpose of writing a scientific manuscript?

2. What are the characteristics of a scientific manuscript?

3. What are the components of a well-written manuscript?

4. How important is the title of a scientific manuscript?

5. What does include in the abstract of a scientific manuscript?

6. What should be presented in the methodology and material section of a scientific manuscript?

38.3 Translate the following sentences paying attention to the -ing forms 1. On reheating, “melting” occurs and rubber increases in volume.

2. Reinforcing agents harden the rubber and make it more wear resistant.

3. Katz showed that ordinary, unstretched rubber has a disordered structure, resembling that of a liquid.

4. In an ideal rubber-like substance no energy is used in separating chains and in increasing their separation during stretching.

5. The highly coiled and folded condition of the rubber chains permits their being extended up to seven times their original length.

38.4 Translate the following sentences into Vietnamese paying attention to the - ing forms 1. Latex may be used for impregnating paper, leather, or cloth, the rubberized product being water proof.

2. The initial effect of the creaming agent is to cause a clustering of the rubber particles.

3. Clustering is influenced by the action of the creaming agent on this surface layer.

4. Soon after the addition of the creaming agent to the tank, a very deep cream layer is formed, which is built of clusters linked together, with water filling the space.

5. Articles are formed by dipping shapes in the latex, drying and vulcanizing in hot air.

6. The “drops” of rubber are suspended in water, when first obtained from the plant, the system resembling an emulsion.

38.5 Translate into English 1. Các nhà khoa học viết bản thảo khoa học để chia sẻ các ý tưởng và phát minh của mình.

2. Để viết được bản thảo hay cần đầu tư thời gian và cố gắng nhiều.

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3. Một bản thảo khoa học bao gồm: tên, tóm tắt, giới thiệu, thực nghiệm và nguyên liệu, kết quả và thảo luận và kết luận.

4. Phần giới thiệu viết hay sẽ khuyến khích độc giả tìm hiểu thêm về nội dung bản thảo.

5. Mục kết quả và thảo luận là các mục chích của bản thảo. Nó đưa ra các kết quả thực nghiệm, giải thích và thảo luận các kết quả đó.10/2/2016 12:48 38.6. Write a short summary of the text

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REFERENCES 1.

Bùi Thị Lệ Thủy, Giáo trình Anh văn chuyên ngành (dùng cho sinh viên ngành Lọc Hóa Dầu), Hà nội, Trường đại học Mỏ- Địa chất, 2003.

2.

Nguyễn Thị Hiền, Nguyễn Trọng Đàn và Lê Thị Lan Chi, The laguage of chemistry, food and biology technology in English, Đại học Bách khoa Hà Nội, 2009 3. https://library.leeds.ac.uk/info/14011/writing/106/academic_writing 4. http://libguides.usc.edu/writingguide/academicwriting

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