THE ESSENTIAL CHEMICAL INDUSTRY
About the CIEC
T
he Department of Chemistry at the University of York is one of the top five research departments in the UK and a leader in the development of innovative chemistry teaching resources. Growing from its strong relationships with industry, the Department founded the Chemical Industry Education Centre (CIEC) in 1988 in collaboration with the Chemical Industries Association. The Essential Chemical Industry has become one of CIEC’s leading publications, being used extensively in education and by the industry itself as an essential reference tool. In total CIEC has developed over 100 printed and electronic resources for teachers and students at all levels of education. By using the chemical industry as their context, they all aim to enthuse and inform students about science and how it impacts on ordinary day to day life. Further details can be found at www.ciec.org.uk
The Essential Chemical Industry
Allan Clements Mike Dunn Valmai Firth Lizzie Hubbard John Lazonby David Waddington
Published by Chemical Industry Education Centre University of York York YO10 5DD UK First edition
1985
Second edition
1989
Third edition
1995
Fourth edition
1999
Fifth edition
2010
All the contents of this book have limited copyright clearance. They may be photocopied or duplicated for use in connection with work within the establishment for which they were purchased. They may not be duplicated for lending, hire or sale. Š Chemical Industry Education Centre at The University of York ISBN: 978 1 85342 595 0
Foreword
B
eing fortunate enough to have been a teenager in the 1960s, I had plenty of opportunities for distractions from my schoolwork in those near-revolutionary days, and as a result I managed to fail two ‘O-levels’ (the forerunner of today’s GCSEs, of course), Ancient Greek and Chemistry (and to this day I believe I made a better job of the Ancient Greek than I did the Chemistry). But for those of us who were not especially turned on by Chemistry, the text books, I seem to recall, were rather dull affairs and sadly were not able to inspire a spark of excitement in this particular young man. The Essential Chemical Industry and books like it on the other hand have, I believe, long rectified this particular difficulty. The Essential Chemical Industry (referred to somewhat affectionately as “ECI”) is aimed at both GCSE and A-level students and therefore rather ahead of the level I managed, but even I believe it is written in a style that is attractive and pleasing. It brings a reality to Chemistry in its connection with the Industry here in the UK, an Industry which has done so much to make our lives so immeasurably more convenient and pleasurable - even compared to those infamous 60s. The book was first published some 25 years ago, with various updates over the years, and this latest edition owes everything to those who have worked so hard on it. Those of us who have managed to enjoy a good lifelong career in the Chemicals and Plastics Industry here in the UK should be grateful to those academics who most painstakingly assemble books such as these and to those teachers who spread to others the knowledge contained therein. I wish I had been more inspired by Chemistry in those wonderful teenage years, and I can only hope that ECI will bring a real inspiration to today’s students. I am delighted and proud that Arkema, a Chemicals and Plastics Group which together with its antecedents has kept me gainfully employed for some 33 years, is associated with this excellent and far-reaching publication. Long may it continue. Paul F Jukes Arkema President of the British Plastics Federation
Contents Introduction
1 The chemical industry
Processes
2 Catalysis in industry
11
3 Chemical reactors
20
4 Cracking, isomerisation and reforming
26
5 Distillation
30
6 Green chemistry
34
7 Recycling in the chemical industry
41
8 Biofuels
44
Materials and Applications
Chemicals
1
9 Biorefineries
50
10 Biotechnology in the chemical industry
52
11 Colorants
56
12 Composites
65
13 Crop protection chemicals
69
14 Edible fats and oils
79
15 Fertilizers
81
16 Nanomaterials
83
17 Paints
89
18 Soaps
94
19 Surfactants
95
20 Ammonia
102
21 Benzene
106
22 Bromine
108
23 Buta-1,3-diene
109
24 Calcium carbonate
110
25 Chlorine
114
26 Epoxyethane
118
27 Ethane-1,2-diol
120
28 Ethanoic acid
121
29 Ethanol
122
30 Ethene
124
31 Fluorine
125
32 Hydrogen
126
33 Hydrogen chloride
128
34 Hydrogen fluoride
129
35 Hydrogen peroxide
131
36 Iodine
133
37 Methanal
135
38 Methanol
136
39 Methyl tertiary-butyl ether
138
Contents Chemicals continued...
Polymers
Metals
Index
40 Nitric acid
140
41 Oxygen, nitrogen and the rare gases
142
42 Phenol
147
43 Phosphoric acid
149
44 Phosphorus
151
45 Propanone
154
46 Propene
155
47 Sodium carbonate
156
48 Sodium hydroxide
158
49 Sulfur
160
50 Sulfuric acid
161
51 Titanium dioxide
163
52 Urea
165
53 Polymers: an overview
166
54 Degradable plastics
172
55 Methanal plastics
175
56 Polyamides
177
57 Polycarbonates
180
58 Poly(chloroethene)
182
59 Polyesters
184
60 Poly(ethene)
187
61 Poly(methyl 2-methylpropenoate)
191
62 Poly(phenylethene)
193
63 Poly(propene)
195
64 Poly(propenoic acid)
198
65 Poly(propenonitrile)
200
66 Poly(tetrafluoroethene)
202
67 Polyurethanes
204
68 Silicones
209
69 Aluminium
213
70 Copper
216
71 Iron
221
72 Lead
224
73 Magnesium
227
74 Steel
229
75 Titanium
234
76 Zinc
237
Index
241
Using this book
T
he first unit provides a contemporary overview of the chemical industry worldwide, describing the development and operation of industrial processes – the what, why, where and how of the conversion of raw materials into useful chemicals and products. This is followed by 75 concise illustrated units. Illustrated units These are presented in five thematic groups: 1. Industrial processes - with topics such as distillation, catalysis and the range of chemical reactors available. 2. Materials and applications - including colorants, crop protection chemicals, fertilizers, paints,surfactants and nanomaterials. 3. Chemicals - with units on all the major organic and inorganic building blocks such as ethene, propene, butadiene and benzene and chlorine, sodium hydroxide, sulfuric acid and titanium dioxide. Units explore the sources, manufacture and applications for each chemical. 4. Polymers - including the techniques employed in the design of materials with the necessary properties for specific uses. All the major polymer groups are included such as the polyalkenes, polyurethanes, acrylics, polycarbonates and silicones. 5. Metals - including aluminium, copper, iron and steel, lead, titanium, zinc and their important alloys. Units in sections 3-5 have the same consistent headings: • Uses • Annual production quantities • Manufacture These guide you quickly to the specific information that you want. Researching a topic Individual units are written so that you can ‘dip in’ to them to retrieve the information you need. Although self-contained, they have cross-references to other units throughout the book. This helps you to research a topic more widely.
Catalysis in industry
C
atalysts are substances that speed up reactions by providing an alternative pathway for the breaking and making of bonds. Key to this alternative pathway is a lower activation energy than that required for the uncatalysed reaction. Catalysts are often specific for one particular reaction and this is particularly so for enzymes which catalyse biological reactions, for example in the fermentation of carbohydrates (Unit 8). Much fundamental and applied research is done by
The gas molecules interact with atoms or ions on the
industrial companies and university research laboratories
surface of the solid. The first process usually involves
to find out how catalysts work and to improve their
the formation of very weak intermolecular bonds, a
effectiveness. If catalytic activity can be improved, it may
process known as physisorption, followed by chemical
be possible to lower the temperature and/or the pressure
bonds being formed, a process known as chemisorption.
at which the process operates and thus save fuel which is
Physisorption can be likened to a physical process such
one of the major costs in a large-scale chemical process. Further, it may be possible to reduce the amount of reactants that are wasted forming unwanted by-products.
as liquefaction. Indeed the enthalpy changes that occur in physisorption are ca –20 to –50 kJ mol-1, similar to those of enthalpy changes when a gas condenses to
If the catalyst is in the same phase as the reactants,
form a liquid. The enthalpies of chemisorption are similar
it is referred to as a homogeneous catalyst. A
to the values found for enthalpies of reaction. They have
heterogeneous catalyst on the other hand is in a
a very wide range, just like the range for non-catalytic
different phase to the reactants and products, and is
chemical reactions.
often favoured in industry, being easily separated from
An example of the stepwise processes that occur in
the products, although it is often less specific and allows side reactions to occur.
2
heterogeneous catalysis is the oxidation of carbon monoxide to carbon dioxide over palladium. This is a very important process in everyday life. Motor vehicles
Heterogeneous catalysis The most common examples of heterogeneous catalysis in industry involve the reactions of gases being passed over the surface of a solid, often a metal, a metal oxide or a zeolite (Table 1).
are fitted with catalytic converters. These consist of a metal casing in which there are two metals, palladium and rhodium, dispersed very finely on the surface of a ceramic support that resembles a honeycomb of holes. The converter is placed between the engine and the outlet of the exhaust pipe.
Process
Catalyst
Equation
Unit
Making ammonia
Iron
20
Making synthesis gas (carbon monoxide and hydrogen)
Nickel
20
Catalytic cracking of gas oil
Zeolite
Produces:
a gas (e.g. ethene, propene)
4
a liquid (e.g. petrol) a residue (e.g. fuel oil) Reforming of naphtha
Platinum and rhenium on alumina
Making epoxyethane
Silver on alumina
26
Making sulfuric acid
Vanadium(V) oxide on silica
50
Making nitric acid
Platinum and rhodium
40
4
Table 1 Examples of industrial processes using heterogeneous catalysis.
11
Catalysis in industry The exhaust gases contain carbon monoxide and unburned hydrocarbons that react with the excess oxygen to form carbon dioxide and water vapour, the reaction being catalysed principally by the palladium:
It is not simply the ability of the heterogeneous catalyst’s surface to interact with the reactant molecules, chemisorption, that makes it a good catalyst. If the adsorption is too exothermic, i.e. the enthalpy of chemisorption is too high, further reaction is likely to be too endothermic to proceed. The enthalpy of
2
chemisorption has to be sufficiently exothermic for The exhaust gases also contain nitrogen(II) oxide (nitric oxide, NO), and this is removed by reactions catalysed principally by the rhodium:
chemisorption to take place, but not so high that it does not allow further reaction to proceed. For example, in the oxidation of carbon monoxide, molybdenum might at first sight be favoured as a choice, as oxygen is readily chemisorbed by the metal. However, the resulting oxygen atoms do not react further as they are
The accepted mechanism for the oxidation of carbon monoxide to carbon dioxide involves the chemisorption of both carbon monoxide molecules and oxygen molecules on the surface of the metals. The adsorbed oxygen molecules dissociate into separate atoms of oxygen. Each of these oxygen atoms can combine with a chemisorbed carbon monoxide molecule to form a carbon dioxide molecule. The carbon dioxide molecules are then desorbed from the surface of the catalyst. A representation of these steps is shown in Figure 1. oxygen atoms
carbon atoms
palladium catalyst surface
too strongly adsorbed on the surface. Platinum and palladium, on the other hand, have lower enthalpies of chemisorption with oxygen, and the oxygen atoms can then react further with adsorbed carbon monoxide. Another point to consider in choosing a catalyst is that the product must not be able to adsorb too strongly to its surface. Carbon dioxide does not adsorb strongly on platinum and palladium and so it is rapidly desorbed into the gas phase. A testimony to the importance of catalysis today is the award of the Nobel Prize in Chemistry in 2007 to Gerhard Ertl for his work in elucidating, amongst other processes,
O2(g)
2O(ads)
CO(g)
CO(ads)
O(ads) + CO(ads) CO2(ads)
the mechanism for the synthesis of ammonia (the Haber Process): CO2(ads)
CO2(g)
Figure 1 A mechanism for the oxidation of carbon monoxide.
Ertl obtained crucial evidence on how iron catalyses the dissociation of the nitrogen molecules and hydrogen molecules leading to the formation of ammonia (Figure 2):
Each of these steps has a much lower activation energy than the homogeneous reaction between the carbon monoxide and oxygen. The removal of carbon monoxide, unburned hydrocarbons and nitrogen(II) oxide from car and lorry exhausts is very important for this mixture leads to photochemical smogs which aggravate respiratory diseases such as asthma. Platinum, palladium and rhodium are all used but are very expensive metals and indeed each is more expensive than gold. Recently, much work has been devoted to making catalysts with very tiny particles of the metals, an example of the advances being made by nanotechnology (Unit 16).
12
Figure 2 A mechanism for the catalytic synthesis of ammonia.
Figure 3 shows how the activation energy barriers are much lower than the estimated activation energy barrier (which would be at least 200 kJ mol-1) for the uncatalysed synthesis of ammonia.
Catalysis in industry
activation energy without catalyst
1
2N2(g)
activation energy with catalyst
+ 11 2 H2(g)
H 1
2N2(ads)
= – 46 kJ mol-1
2
NH3(g)
+ 11 2 H2(g)
NH3(ads)
Energy NH2(ads) + H(ads)
This potential energy diagram illustrates the synthesis of ammonia using a catalyst. Each step is shown as a simple energy diagram, with its own activations energy and enthalpy change of reaction. The estimated activation energy for the reaction without a catalyst is very high.
NH(ads) + 2H(ads)
When a catalyst is used, the activation energy barriers for individual steps are much lower, as shown in this diagram.
Overall equation: 1 2 N2(g)
+ 112 H2(g)
NH3(g)
N(ads) + 3H(ads) Progress of reaction
Figure 3 The activation energy barriers for the reactions occurring during the catalytic synthesis of ammonia.
General requirements for a heterogeneous catalyst To be successful the catalyst must allow the reaction
palladium. Thus all traces of sulfur compounds must be removed from the petrol used in cars fitted with catalytic converters.
to proceed at a suitable rate under conditions that are
Further, solid catalysts are much more effective if they
economically desirable, at as low a temperature and
are finely divided as this increases the surface area.
pressure as possible. It must also be long lasting. Some reactions lead to undesirable side products. For example in the cracking of gas oil (Unit 4), carbon is formed which is deposited on the surface of the catalyst, a zeolite, and leads to a rapid deterioration of its effectiveness. Many catalysts are prone to poisoning which occurs when an impurity attaches itself to the surface of the catalyst and prevents adsorption of the reactants. Minute traces of such a substance can ruin the process, One example is sulfur dioxide, which poisons the surface of platinum and
Figures 4 and 5 Two ways by which the surface area of a catalyst can be increased. In Figure 4, vandium(V) oxide (used in the manufacture of sulfuric acid (Unit 50)) has been produced in a ‘daisy’ shape. In Figure 5, above, the platinumrhodium alloy (used in the manufacture of nitric acid (Unit 40)) is in the form of very fine wire that has been woven to construct a gauze.
13
Catalysis in industry At high temperatures, the particles of a finely divided
Aluminosilicates are also used as catalysts when an acid
catalyst tend to fuse together and the powder may
site is required. These are made from silicon dioxide
‘cake’, a process known as sintering. This reduces the
(silica) and aluminium oxide. They contain silicate
activity of the catalyst and steps must be taken to avoid
ions, SiO4 that have a tetrahedral structure which can
this. One way is to add another substance, known as a
2
4-
be linked together in several ways. When some of the
promoter. When iron is used as the catalyst in the Haber
Si atoms are replaced with Al atoms, the result is an
Process, aluminium oxide is added and acts as a barrier
aluminosilicate. Hydrogen ions are again associated with
to the fusion of the metal particles. A second promoter
the aluminium atoms:
is added, potassium oxide, that appears to cause the nitrogen atoms to be chemisorbed more readily, thus accelerating the slowest step in the reaction scheme.
Aluminium oxide, aluminosilicates and zeolites Aluminium oxide, Al2O3, (often referred to as alumina) is frequently used as a catalyst when an acid is required. There are hydroxyl groups on the surface of alumina which are, in effect, sites which are negatively charged to which a hydrogen ion is attached that can act as an acid catalyst.
A particular class of aluminosilicates that has excited huge interest in recent years is the zeolites. There are many different zeolites because of the different ways in which the atoms can be arranged. Their structure of silicate and aluminate ions can have large vacant spaces in three dimensional structures that give room for cations such as sodium and calcium and molecules
Alumina becomes particularly active if it has been
such as water. The spaces are interconnected and form
washed with an acid, for example hydrochloric acid,
long channels and pores which are of different sizes in
or coated with an acid (such as phosphoric acid),
different zeolites.
thereby increasing the number of active acidic sites. For example, ethanol is manufactured by the hydration of ethene using alumina, coated with phosphoric acid (Unit 29):
The mechanism involves the formation of a carbocation (Figure 6):
The zeolite acts as a molecular sieve. Only straight-chain molecules can pass through the holes in the zeolite structure.
Figure 7 The structure of a zeolite (example figure).
A zeolite which is commonly used in many catalytic reactions is ZSM-5 which is prepared from sodium aluminate (a solution of aluminium oxide in aqueous sodium hydroxide) and a colloidal solution of silica, Figure 6 A mechanism for the hydration of ethene to ethanol.
14
sodium hydroxide, sulfuric acid and tetrapropylammonium bromide.
Catalysis in industry It is, for example, a very effective catalyst for the conversion of methylbenzene to the three dimethylbenzenes. Alas, the mixture produced only contains about 25% 1,4-dimethylbenzene, the isomer needed for the manufacture of the polyesters (Unit 59), and the rest, 1,2- and 1,3-dimethylbenzenes, is not wanted in such large quantities.
2
CH3 2
mixture of dimethylbenzenes
benzene
methylbenzene
CH3 CH3 1,2-dimethylbenzene
CH3 1
CH3
2
1,3-dimethylbenzene 3 4
CH3 CH3
The three dimethylbenzene isomers are named to show the positions of the two methyl groups.
1,4-dimethylbenzene
CH3
Figure 8 A zeolite acting an a molecular sieve and a catalyst during the formation of 1,4-dimethylbenzene from methylbenzene.
However, if the zeolite is washed with phosphoric acid
The ability of the zeolite to adsorb some molecules and
and heated strongly, minute particles of phosphorus(V)
to reject others gives it the ability to act as a molecular
oxide are deposited on the surface making the pores
sieve. For example, in the manufacture of ethanol from
slightly smaller. This restricts the diffusion of the 1,2- and
ethene or from biomass, an aqueous solution of ethanol
1,3-isomers and they are held in the pores until they are
is produced, in which there is 4% water still present even
converted into the 1,4-isomer and can escape (Figure 8).
after repeated distillations. Further purification requires
This remarkable selectivity enables the yield of the 1,4-
the use of a zeolite which absorbs the water preferentially
isomer to be increased from 25% to 97%.
(Unit 29). Table 2 gives examples of industrial processes involving zeolites.
Process
Catalyst
Catalytic cracking of gas oil
Zeolite
Reforming of naphtha
Platinum and rhenium on zeolite
Disproportionation of methylbenzene
Zeolite
Dealkylation of methylbenzene
Zeolite
Equation Produces:
Unit
a gas (e.g. ethene, propene)
4
a liquid (e.g. petrol) a residue (e.g. fuel oil) For example:
21
Zeolite (ZSM-5)
21
CH3 (g)
Making cumene (1methylethyl)benzene
4
H2 (g)
(g)
CH4(g)
42
Table 2 Examples of industrial processes using zeolites.
15
Catalysis in industry Bifunctional catalysts
Branched alkanes have a much higher octane rating than
Bifunctional catalysts are able, as the name implies, to catalyse the conversion of one compound to another, using two substances on the surface. For example, in reforming naphtha (a mixture of straight
2
chain alkanes, with 6-10 carbon atoms (Unit 4)) a bifunctional catalyst is used. The most well known one is platinum impregnated on the surface of alumina and both the metal and the oxide play their parts in the process. As can be seen (Figure 9), the first step is the dehydrogenation of the alkanes to alkenes, catalysed by the metal, followed eventually by adsorption of the alkene
straight chain ones (Unit 4). Not only are the alkanes now branched, but cycloalkanes are also formed and, from them, aromatic hydrocarbons. All three classes of hydrocarbon have a higher octane rating than naphtha.
Other metal oxides Besides aluminium oxide and silicon dioxide, other oxides are important catalysts. For example, in the Contact Process used to manufacture sulfuric acid, the catalyst for the oxidation of sulfur dioxide to sulfur trioxide is vanadium(V) oxide on the surface of silica:
molecules on alumina. In this example butane is dehydrogenated to butene. CH3CH2CH2CH3(g)
CH2 CHCH2CH3(g) + H2(g)
allows it to spread out as a very thin layer over the entire CH2 CHCH2CH3(ads) + H+ (ads)
Here they react with a hydrogen ion to form carbocations. Rearrangement of the secondary carbocation through a series of alkyl group and hydrogen atom migrations leads to an equilibrium in which the relatively stable tertiary carbocation predominates.
action is not absolutely clear but it appears to be because its presence lowers the melting point of the catalyst, and
butane The butenes are released into the gas phase until they are adsorbed on to an aluminium oxide site on the surface of the catalyst.
Potassium sulfate is added as a promoter. Its mode of
+
CH3 C
CH2 CH3(ads)
+
mixed metal oxides. The surfaces contain two or more are particularly useful in the oxidation of hydrocarbons,
CH3(ads)
CH3 The tertiary carbocation loses a hydrogen ion to form a branched alkene.
- H+ (ads)
CH3 C
Several important industrial processes are catalysed by different metal atoms, O2- ions and –OH groups. They
H CH3 C
surface.
CH2(ads)
CH3
2-methylpropene
Figure 9 A mechanism for the reforming of butane to 2methylpropene.
The branched alkene molecule is desorbed into the gas phase until it is readsorbed on to a metal site where it is hydrogenated to form a branched alkane,
where selective oxidation is required. For example, propene can be oxidised to propenal (Unit 64) using a mixture of bismuth(III) and molybdenum(VI) oxides. Without the catalyst, propene is oxidised to a large number of organic compounds, including methanal and ethanal, and eventually forming carbon dioxide. The oxygen atoms on the surface of molydenum(VI) oxide are not very reactive, reacting selectively with propene and breaking the weakest bond in the alkene to form an allyl radical:
2-methylpropane, which is then desorbed into the gas phase.
O H C without catalyst
The rhenium is thought to play an interesting role. If a sulfur compound is allowed to pass over the surface of the catalyst, it is preferentially adsorbed by the rhenium. If sulfur compounds are not removed, reactions occur leading eventually to the formation of carbon which causes the activity of the catalyst to be markedly reduced.
16
H
H3C C H
ethanal
H C H
H2O
O
O2
platinum and rhenium (ca 0.3% each) which are finely dispersed over aluminium oxide.
methanal
CO2
In the industrial process, naphtha vapour is passed over
CH3 C H
H
propene
O2
H C
with catalyst
H
CH2
H
H
H
C
allyl radical
Figure 10 The oxidation of propene.
C
C O C H
propenal
H2O
Catalysis in industry The allyl radical is then oxidised on the surface to yield
However, there are several important industrial processes
propenal. It is postulated that the allyl radical is oxidised
that are catalysed homogeneously, often using an acid or
by an oxygen atom that is adsorbed at a molybdenum
base (Table 3).
site. Another oxygen atom, adsorbed on a bismuth site,
One example is in the manufacture of ethane-1,2-diol
is then transported to the reduced molybdenum site to replace that oxygen. There is a compensating transport of electrons to complete the cycle.
from epoxyethane where the catalyst is a trace of acid (Unit 27):
The same catalyst is also used to manufacture propenonitrile (Unit 65):
2
O H
C
C
H
H
H epoxyethane
+ H+
H +
H2O
O+ H
Homogeneous catalysis
C
C
H
H
H
H2 O
H
OH
C
C
H
H
HO H
- H+
H
OH
C
C
H
H
H
ethane-1,2-diol
Homogeneous catalysts are less frequently used in industry than heterogeneous catalysts as, on completion
Figure 11 A mechanism for the formation of ethane-1,2-diol from epoxyethane.
of the reaction, they have to be separated from the
In the mechanism for this reaction a hydrogen ion is
products, a process that can be very expensive.
added at the start, and lost at the end. The hydrogen ion functions as a catalyst.
Manufacture
Catalyst
Equation
Unit
Ethane-1,2-diol
Sulfuric acid
27
2,2,4-Trimethylpentane
Hydrogen fluoride
34
Phenol and propanone
Sulfuric acid
42, 45
Bisphenol A
Sulfuric acid
45
Table 3 Examples of industrial processes using homogeneous catalysis.
17
Catalysis in industry
2
Two other examples are concerned with the production
The alkene monomer attaches itself to an empty
of 2,2,4-trimethylpentane from 2-methylpropene, again
coordination site on the titanium atom and this alkene
using an acid as the catalyst. One uses 2-methylpropane
molecule then inserts itself into the carbon-titanium bond
(Table 3) which yields the alkane directly. The other uses
to extend the alkyl chain. This process then continues,
only 2-methylpropene.
thereby forming a linear polymer, poly(ethene).
The mechanism of the reaction also involves the addition
The polymer is precipitated when the catalyst is
of a hydrogen ion to a reactant (Figure 12).
destroyed on addition of water. Because it is linear, the
CH3 H3C C
+ HX
CH2
H3C C
CH3
+
2-methylpropene
CH3
CH3
CH2 +
+
C
CH3
H3C C
CH3 +
CH3
CH2 C
CH3
CH3
CH2 C
+
CH3
H3C C
giving the polymer a higher melting point and density
+X
than poly(ethene) produced by radical initiation. The
CH3 H3C C
polymer molecules are able to pack together closely,
CH3
manufacture of poly(ethene) is described in Unit 60.
CH3
CH3
+X
CH3 H3C C
CH3
CH
CH3 C
CH3 + HX
CH3 2,4,4-trimethyl-2-pentene
Figure 12 Part of a mechanism for the formation of 2,4,4-trimethyl-2-pentene from 2-methylpropene.
The alkene is then hydrogenated, using nickel as the catalyst, to 2,2,4-trimethylpentane (isooctane):
2,2,4-trimethylpentane is often added to petrol to enhance its anti-knock properties, now that methyl t-butyl ether (MTBE) is being phased out (Unit 39).
Catalysts for polymerization reactions Ziegler-Natta catalysts Ziegler-Natta catalysts are organometallic compounds, prepared from titanium compounds with an aluminium trialkyl which acts as a promoter:
Figure 13 Illustrating the role of a Ziegler-Natta catalyst.
Not only do Ziegler-Natta catalysts allow for linear polymers to be produced but they can also give stereochemical control. Propene, for example could polymerize, even if linear, in three ways, to produce either atactic, isotactic or syndiotactic poly(propene) (Unit 63). However, this catalyst only allows the propene to be inserted in one way and isotactic polypropene is produced. Even greater control of the polymerization is obtained using a new class of catalysts, the metallocenes, which are discussed in Unit 63.
The alkyl groups used include ethyl, hexyl and octyl. The role of the titanium catalyst can be represented as shown in Figure 13.
18
Recycling in the chemical industry
R
ecycling of materials has become common practice over the last ten years or so, with households in many countries encouraged to save used cans, glass, plastics, paper and garden rubbish for special collection. These are then recycled for two main reasons. One is local, to save land which would otherwise be used as dumps for the waste. In the European Union alone, 1.3 billion tonnes of waste - some 40 million tonnes of it hazardous - are thrown away annually. This amounts to about 3.5 tonnes of solid waste for every man, woman and child. On top of this there is also a further 700 million tonnes of agricultural waste to dispose of. The other main reason for recycling has global significance – to help conserve valuable resources, such as metals, wood and energy.
7
This unit is devoted to the recycling of metals, some basic chemicals and polymers, all within the context of the chemical industry.
Recycling of basic chemicals
HCl from both streams is absorbed in water to make
Sulfuric acid
collect all the HCl gas, and emissions to air are a problem
Some sulfuric acid is produced from ‘spent’ (used) acid and related compounds such as ammonium sulfate
18% hydrochloric acid for reuse. It is difficult however to with this process.
which is a by-product in the manufacture of methyl 2-
Recycling within processes
methylpropenoate (Unit 61).
Many processes recycle reactants and products in
The acid and compounds are usually in dilute solution which is evaporated under vacuum to produce concentrated solutions. These are fed into a furnace with oxygen at about 1200 K to produce sulfur dioxide:
order to conserve materials and make the processes as efficient as possible. An example is in the manufacture of chloroethene, the monomer for the manufacture of PVC (Unit 58). Cholorethene is made from ethene via 1,2-dichloroethane, which is then cracked: CH2 CH2(g) + Cl2(g)
ClCH2 CH2Cl (g)
ethene
1,2-dichloroethane cracked
The sulfur dioxide is dried by passage through
CH2 CHCl(g) + HCl(g)
concentrated sulfuric acid. It is then oxidised to sulfur
chloroethene (required monomer)
trioxide and hence sulfuric acid using the Contact Process (Unit 50).
Hydrochloric acid The steel industry is a major user of hydrochloric acid for the pickling process to remove impurities (Unit 33). The industry uses a process known as pyrohydrolysis to recover the spent acid, which now contains a mixture of iron chlorides. The spent liquor is first concentrated in an evaporator, with dissolved HCl being given off and collected. The concentrated liquor is then fed into a roaster at ca 800-1000 K which converts the iron chlorides into HCl and iron(III) oxide, the HCl again being collected. For example:
The hydrogen chloride is recycled and reacted with oxygen and more ethene. The overall reaction can be represented by: CH2 CH2(g) + 2HCl(g) + ½O2(g)
ClCH2 CH2Cl(g) + H2O(g)
recycled hydrogen chloride
Recycling of polymers The most written about aspect of polymers is not their enormous usefulness but the problems that they bring as waste. This is not surprising, as the world’s annual production of plastics is about 100 million tonnes and at present less than 10% of this is being recycled. To put these numbers in perspective, 20 000 large bottles can be made from just one tonne of plastic. Further, the plastics industry uses nearly 5% of the world’s oil supply.
41
Recycling in the chemical industry Reusing plastics Reusing plastics would be ideal, and already happens for example, with bottle crates and increasingly with
7
Recycling of polyesters, for example PET (in bottles), is now widely used. The recovered bottles are washed, ground into flakes, melted and extruded as fibres. The
shopping bags. At first sight, collecting plastics which
fibres are then used to make products such as carpets.
can be remoulded, for example the thermoplastics, such
High density poly(ethene), HDPE, used for juice and milk
as poly(ethene) and poly(propene), would appear to be
bottles, is also ground into flakes, melted and pressed
an attractive solution. However, collecting and sorting
into sheets to be made, for example, into bin-liners or
plastic articles into specific polymers is an expensive
moulded into containers.
and difficult process. It is often done manually by trained
Recycling of plastic bags saves about two thirds of the
staff who sort the plastics into polymer type and/or colour. Technology is being introduced to sort plastics automatically, using various spectroscopic techniques. First, infrared spectrometry is used to distinguish
energy used to produce a new bag. PVC is similarly recycled and extruded for pipes or used for window frames.
between clear and translucent plastic. Next a vision
Converting polymers into monomers
colour sensor, programmed to ignore labels, identifies
Some polymers can be depolymerized to reform
various coloured plastics (Figure 1). X-ray spectrometry
monomers, which can then be purified by distillation and
is then used to detect the Cl atom in poly(chloroethene)
polymerized again to produce the polymer. This still has
(PVC). Finally a near infrared spectrometer is used to
the drawback that the polymer waste has to be sorted
detect resin type, most importantly for the separation of
prior to being heated.
high density poly(ethene) (HDPE) and a polyester such
PET waste is dissolved in the dimethyl ester of benzene-
as PET. Typical sorting rates are of the order of 3 items per second.
1,4-dicarboxylic acid and then heated with methanol under pressure at 600 K. This produces the two monomers of PET, ethane-1,2-diol and the dimethyl ester which are subsequently purified by distillation.
Polyamide 6 (nylon 6), used in carpets, is converted back to its monomer, caprolactam. The backing is removed from the carpet and the carpet is then shredded and pulverised. On heating, polyamide 6 depolymerizes:
O
H N
Figure 1 This machine, which has a colour sensor, is one of a series used to sort automatically different polymers prior to recycling.
C
n
H N
O n polyamide 6
caprolactam
After purification, by distillation, the monomer is
Plastic can also be separated on the basis of density
polymerized again to yield polyamide 6. In another
by flotation. One recently developed method involves
process, it is not necessary to remove the backing
spreading the plastic and passing it through a series of
(which is an added expense). Instead, the polyamide 6
pipes in suspension in water. The flow rate of the plastic
fibres are heated in a stream of superheated steam and
depends on the density, enabling streams to be taken off
depolymerized.
at different points along the pipe.
42
(CH2)5
C
Recycling in the chemical industry It is less easy to reuse polyamide 6,6 which is made from
Mixtures of polymers can be converted into useful
two monomers. Nevertheless, DuPont has a process
compounds either by pyrolysis or by oxidation. This
where carpets, with the backing removed, made from
has the advantage that the plastics do not have to be
both polyamide 6 and polyamide 6,6 are shredded and
rigorously sorted before being treated. The mixture of
pulverised before being heated strongly in an atmosphere
polymers is heated in a stream of hydrogen at about
of ammonia gas. Among the products are caprolactam
500 K. If the polymers contain chlorine (for example,
(from polyamide 6) and 1,6-diaminohexane (from
PVC), hydrogen chloride is formed and is washed out.
polyamide 6,6). These are purified by distillation and
The remaining gases are then heated at about 700 K
reused to make the polyamides.
and cracked to form the usual mixture of hydrocarbons
Polyamides from recycled carpet are being used to make
(alkanes, alkenes, aromatics) which can be fed into the
new carpets and to make cushions and resilient flooring.
stream of hydrocarbons formed from the cracking of oil
Although many recycling programmes are restricted to
fractions (Unit 4).
collecting carpets used commercially (for example in
Alternatively, the gases formed from heating the mixture
large hotels and offices), this too is about to change and
of polymers and following removal of the hydrogen
domestic carpets will be used more extensively.
chloride, are mixed with air and passed through a furnace
Cracking the polymer
at ca 1500 K to form a mixture of carbon monoxide and hydrogen, synthesis gas. This is then fed into the
Polymers, like other high molecular mass organic
synthesis gas produced by the usual methods (Unit 20).
compounds such as the alkanes in oil, can be cracked
This latter process, at present, appears to be the more
at high temperatures to form smaller molecules. For
favoured.
example, if they are steam cracked, polymers such
7
as poly(ethene) and poly(propene) yield alkenes and
Polymers as fuels
alkanes of small molecular mass which can be used in
Polymers can be burnt to produce energy. The problems
the same way as those formed in the cracking of naphtha
are that the incineration can produce noxious fumes
(Unit 4). Small cracking plants are being built for this
which must be trapped and the carbon is not recycled
purpose.
even if the energy can be used.
Recycling of metals The recycling of metals (often referred to as secondary production) is becoming increasingly important with more aluminium and lead being produced from recycled sources than from their ores, and vast quantities of steel and copper also being produced via recycling. The processes are described in the units devoted to the individual metals, aluminium (Unit 69), copper (Unit 70), steel (Unit 74), lead (Unit 72) and zinc (Unit 76). In all cases the properties of the metals following recycling are completely unimpaired. Their quality is just the same as for metal produced from the ore. The materials for recycling come from three sources. One is the waste material generated by the initial manufacture and processing of the metal. Another is waste material from the fabrication of the metals into products. Both of these sources are referred to as new scrap. The third, most commonly regarded by the public as recycling, is the discarded metal-based product itself (old scrap). Thus in manufacturing a car, each of the three sources of recyclable metal becomes available from Figure 2 This yacht is using sails made from recycled poly(ethene).
the steel mill itself, from the factory making the cars and lastly when the car itself is eventually recycled.
43
Biotechnology in the chemical industry
B
iotechnology is defined as the application of the life sciences to chemical synthesis. This unit discusses its increasingly important role in the direct production of speciality chemicals via fermentation, such as citric acid, lactic acid, propane-1,3-diol and some amino acids.
10
Other uses of biotechnology are discussed elsewhere, for example the production of biofuels (bioethanol and biodiesel) in Unit 8, the production of basic feedstocks from biomass such as synthesis gas (carbon monoxide and hydrogen) in Unit 9, and the production of biodegradable polymers such as the poly(hydroxyalkanoates) in Unit 54. The biotechnology industry has a long history in the
amount of research is being done by chemists,
UK. As long ago as 1916, in the First World War, the
biotechnologists and engineers to make these reactions
bacterium Clostridium acetobutylicum was fed with
more efficient and cost-effective.
mashed potato and corn (both containing starch) to produce a mixture of propanone (acetone), butanol and ethanol (known as the ABE process (Unit 8)). The propanone was required to produce cordite for munitions. At one time ABE was second only to the production of ethanol as the largest industrial fermentation process.
The most important chemicals produced directly by fermentation include 2-hydroxypropane-1,2,3-tricarboxylic acid (citric acid), 2-hydroxypropanoic acid (lactic acid), propane-1,3-diol and amino acids, and each of these is discussed in this unit.
However, the rise of the petrochemical industry in the 1950s provided much cheaper feedstocks for making chemicals, sending the ABE industry into decline around the world. Petrochemicals are a finite resource which will become more expensive as oil becomes scarce, and their use is associated with the release of greenhouse gases that lead to global warming. Producing more chemicals using biotechnology could reduce our dependence on natural gas and oil and reduce the environmental impact of the chemical industry. Some chemicals, such as 2-hydroxypropane-1,2,3-tricarboxylic acid (citric acid), have for many years been routinely produced on the million-tonne scale using biotechnology, as the chemical synthetic routes are complex and expensive. Other notable examples are described in this unit but there are many other processes still in the developmental stage, with chemicals being produced in small reactors on the scale of a few tonnes. A huge
Figure 1 The progress of 3 fermentation in a 500 dm fermenter in the biotechnology pilot plant is being monitored. The pilot plant is equpped with a large number of pilotscale batch reactors (Unit 3) used in the development of new large-scale fermentation processes.
52
Figure 2 The compounds (other than ethanol) produced by fermentation reactions in the chemical industry.
Biotechnology in the chemical industry 3-Carboxy-3-hydroxypentanoic acid (citric acid)
2-Hydroxypropanoic acid (lactic acid)
OH
Annually, about 275 000 tonnes of lactic acid are
HO2C CH2 C CH2 CO2H
produced globally.
CO2H 3-carboxy-3-hydroxypentanoic acid (citric acid)
10
The annual global production of citric acid is about 1.4 million tonnes.
Uses
Figure 3 The uses of citric acid.
Citric acid’s major use is in the food industry as an acidulant in soft drinks, as a flavouring and as a preservative. It is often listed as the E number E330.
Uses
Figure 4 The uses of lactic acid.
An important use is in the manufacture of the biodegradable polymer, poly(lactic acid), PLA (Unit 54). CH3 O
It is used with sodium hydrogencarbonate in effervescent
O C
products, both for ingestion (aspirin or antacids) and for
H
personal care (bath salts). It is also used in detergents
C n
poly(2-hydroxypropanoic acid) poly(lactic acid), PLA
and soaps to control pH and to chelate metal ions in hard water, which allows detergents to produce more foam (Unit 19).
Manufacture The main production route uses of the fungus Aspergillus niger, which is grown in solutions of sucrose or glucose. The citric acid produced is precipitated with calcium hydroxide solution to form calcium citrate. This salt is filtered off and the acid regenerated with sulfuric acid.
Another major use of lactic acid is in food and drinks, as a preservative (it is an anti-oxidant) and to adjust the pH. Lactic acid can be esterified with ethanol to form ethyl 2-hydroxypropanoate (ethyl lactate) which is a non-toxic and biodegradable solvent. Lactate ester solvents are replacing more toxic substances such as halogenoalkanes as solvents in inks, paints, cleaners and degreasers.
53
Biotechnology in the chemical industry
10
Although lactic acid can be directly polymerized in a
stretch-recovery properties to PET and it is also easy to
condensation reaction, the reaction is reversible and the
dye (Unit 11). It is being increasingly used in fibre form
water that is produced tends to hydrolyse the polymer
in textiles, clothes and carpets, but it can also be used
chain. Instead, lactic acid is first dimerized to make a
as a thermoplastic in car parts, electrical and electronics
cyclic lactide. This produces water which is removed.
systems.
The lactide is then polymerized into PLA by a ring-
Propane-1,3-diol is also used in the preparation of
opening polymerization reaction, using tin(II) octanoate
cosmetics, laminates, adhesives, paints and inks. It is
as catalyst:
also being used as a replacement for ethane-1,2-diol as O
O H3C
H3C
C OH
CH HO
+
H
OH
HO C
C
O
O
C
H
C
dimer
CH
an engine coolant and as a solvent (Unit 27).
C
CH3
O
CH3
tin octanoate catalyst
O 2-hydroxypropanoic acid (lactic acid)
CH3 O O C
C
H
n
poly(2-hydroxypropanoic acid) poly(lactic acid), PLA
Manufacture Lactic acid (2-hydroxypropanoic acid) is produced by fermentation of sugars from maize (corn syrup) and cane sugar (molasses) using a lactobacillus bacterium.
Propane-1,3-diol CH2 CH2
HO
CH2 OH
propane-1,3-diol (PDO)
A particularly important use of propane-1,3-diol (PDO) is in the manufacture of the polyester, polytrimethylene terephthalate (PTT). PTT is formed by the condensation reaction between PDO and benzene-1,4-dicarboxylic acid (often called terephthalic acid). The most commonly used catalysts for the reaction are titanium alkoxylates such as tetrabutyl titinate(IV).
maize is cooked, and then ground to release the starch.
known polyester polyethylene terephthalate
The starch is hydrolysed to produce glucose. This is fed
(PET), which is produced from ethane-1,2-diol
to a genetically modified Escherichia coli, which ferments
and benzene-1,4-dicarboxylic acid (Unit 59). O
C
C
O
CH2
CH2
the glucose into PDO.
Amino acids
O
Amino acids contain both amino and carboxyl functional
n polyethylene terephthalate (PET)
O
O
C
C
groups. Linear chains of amino acids are the building blocks of proteins. Industrially, amino acids are used in
O
CH2
CH2
CH2
food additives, animal feeds and pharmaceuticals.
O n
polytrimethylene terephthalate (PTT)
However, the extra methylene groups in PTT gives the polymer pronounced kinks in the chain and hence different properties to PET. PTT is felt to have superior
54
Manufacture Propane-1,3-diol is manufactured from maize (corn). The
PTT is very similar in structure to the well-
O
Figure 4 The carpet contains 37% of polytrimethylene terephthalate derived from maize via propane-1,3-diol.
With the exception of aminoethanoic acid (glycine), the industrially produced amino acids are chiral and the two isomers (D and L) have different properties in biologically induced reactions. However, chemical synthesis produces equimolar quantities of D- and L- forms and
Biotechnology in the chemical industry additional expensive steps are required to produce a pure
Most is used in the form of the salt, monosodium
stereoisomer. However, biotechnological routes have the
glutamate (MSG) which is commonly used as a flavour
great advantage of producing pure optically active amino
enhancer, particularly in processed food. The sodium
acids.
salt is used rather than the acid as it is the glutamate
Amino acids are produced from the fermentation of
ion that produces flavour and the salt is more soluble in
sugar to which small quantities of nitrogen-containing
water than the parent acid.
compounds (for example, ammonia or urea) have been
L-Lysine
added. Mutants of Corynebacterium glutamicum or
10 NH2
genetically modified E. coli are used. The two acids produced on the largest scale are L-glutamic acid and L-lysine.
(CH2)4 H2N
C CO2H H
L-Glutamic acid
(L-lysine)
2,6-diaminohexanoic acid
NH2 HO2C CH2 CH2 C CO2H H (L-glutamic acid)
2-aminopentanedioic acid
About 1.7 million tonnes of L-glutamic acid are produced
The annual production of L-lysine is about 1 million tonnes, with China producing 35%. It is an essential amino acid, meaning that most vertebrates cannot synthesise it. It is often deficient in livestock diets so the major use of L-lysine is in animal feed.
by fermentation per year, the majority being produced in Asia, with one company in China producing 33% of the world’s output.
55
Chlorine
C 25
hlorine, along with its important by-product, sodium hydroxide, is produced from the readily available starting material, rock salt (sodium chloride). It is well known for its use in sterilizing drinking water and in particular swimming pool water. However, most chlorine is used in the chemical industry in the manufacture of other products. Sometimes chlorine is in the product molecule but on other occasions it is used to produce intermediates in the manufacture of products that do not contain chlorine and the element is recycled.
Uses The largest use is in the manufacture of poly(chloroethene), PVC (Unit 58). Other major polymers produced using chlorine include the polyurethanes (Unit 67). Although chlorine does not appear in the polyurethane molecule, chlorine is used to make the intermediates, the isocyanates. The oxygenates (Figure 1) are principally epoxypropane and propane1,3-diol, which are used to make polyols. These, like the isocyanates, are used in turn to make polyurethanes. 1-Chloro-2,3-epoxypropane has many industrial uses, the most important being in the manufacture of the epoxy resins (Unit 17). Among the uses of the chloromethanes are the manufacture of silicones (Unit 68) and poly(tetrafluoroethene), PTFE, (Unit 66).
Figure 1 The uses of chlorine.
However, some chlorine needs to be transported for example, when it is to be used to purify water. For this,
The solvents (including trichloroethene) are used in dry
the chlorine is dried by passing it through concentrated
cleaning.
sulfuric acid and then compressed and liquefied into
Chlorine is also used in the manufacture of many
cylinders, ready for transportation.
inorganic compounds, notably titanium dioxide (Unit 51)
Annual production
and hydrogen chloride (Unit 33). Most chlorine is produced on the site on which it is going to be used, for example, to make hydrochloric acid (Unit 33) and the other compounds described above.
UK
590 000 tonnes
Europe
16.4 million tonnes
World
69.1 million tonnes
Figure 2 Although much rock salt is pumped to the surface as brine, some is mined, as is being done in this large underground deposit in Cheshire.
114
Chlorine Manufacture
(a) Cation exchange membrane cell
Most chlorine is manufactured by the electrolysis of
The anodes are made of titanium coated with ruthenium
sodium chloride solutions. The other main commercial
dioxide. The cathodes are nickel, often with a coating
product is sodium hydroxide (Unit 48). The primary raw
to reduce energy consumption. The anode and cathode
material for this process is rock salt (sodium chloride),
compartments are completely separated by an ion-
available worldwide usually in the form of underground
permeable membrane (Figure 3). The membrane
deposits of high purity (Unit 48). It is pumped to the
is permeable to cations, but not anions; it allows the
surface with high pressure water as a concentrated
passage of sodium ions but not chloride or hydroxide
solution. This solution is often called brine.
ions. Sodium ions pass through in hydrated form (Na. +
+
A solution of sodium chloride contains Na (aq) and -
Cl (aq) ions and, from the dissociation of water, very low +
-
xH2O) so some water is transferred, but the membrane is impermeable to free water molecules.
concentrations of H (aq) and OH (aq) ions. During the
The sodium hydroxide solution leaving the cell is at
electrolysis of the solution, chlorine and hydrogen gases
ca 30% (w/w) concentration. It is concentrated by
are produced:
evaporation using steam, under pressure, until the
Anode:
2Cl-(aq)
Cathode: H2O(l)
Cl2(g) + 2eH+(aq) + OH-(aq)
2H+(aq) + 2e-
25
H2(g)
As the hydrogen ions are discharged, more water
solution is ca 50% (w/w), the usual concentration needed for ease of transportation and storage.
fresh salt
chlorine gas coated Cl2 titanium anode
hydrogen gas nickel cathode
H2
dissociates forming more hydrogen and hydroxide ions. This results in a gradual build up of the concentrations
H2
solution of sodium hydroxide. The essential requirement Cl-
separating the anode and cathode reactions so that the sodium hypochlorite. This separation has been achieved
Na+
brine concentrator
NaOH 33%
OH
Na+
historically by the mercury amalgam and diaphragm processes. However, these are being phased out and
OH-
Cl-
is to maintain an effective and economic means of products, chlorine and caustic soda, will not react to form
H2
Cl2
Cl2
of hydroxide ions around the cathode, thus producing a
HNa+
ion exchange membrane
NaOH 33%
pure water
Figure 3 The membrane cell.
most new plants use ion exchange membranes, which are the most environmentally and economically sound
The membrane (0.15-0.3 mm thick) is a co-polymer of
means of chlorine production.
tetrafluoroethene ((Unit 66) and a similar fluorinated
(a) Cation exchange membrane cell The cation exchange membrane does not allow any gas + or negative ions to flow through it but it allows Na ions to move between the brine and caustic compartments.
(b) Mercury amalgam cell In the flowing mercury cathode process sodium ions are discharged in the form of a mercury sodium amalgam and chloride ions are converted to chlorine. The amalgam flows to a totally separate compartment, the decomposer (denuder) in which it reacts with water to yield sodium hydroxide solution and hydrogen gas.
(c) Percolating diaphragm cell A percolating diaphragm, usually of asbestos, allows a through flow of brine from anode to cathode. It separates the chlorine and hydrogen gas spaces. The – migration of OH ions from the cathode to the anode is prevented by the velocity of liquid flow against them. Table 1 The key features of the three electrolytic processes.
monomer with anionic (carboxylate and sulfonate) groups.
(b) The mercury cell Typical modern gas-tight, rubber-lined or PVC-lined steel cells (Figure 4) are used, which measure about 2 m x 15 m. They have a slightly sloping base over which flows a thin layer of mercury, acting as a cathode. The anodes are a series of titanium plates coated with a precious metal oxide layer, and positioned about 2 mm from the cathode. The cells typically operate in series of approximately 100. Purified, saturated brine (25% (w/w) sodium chloride solution) at typically 333 K flows through the cell in the same direction as the mercury. This high salt concentration and the anode coating ensures the oxidation of chloride ions rather than that of water which would yield oxygen at the titanium anodes.
115
Chlorine sodium. It moves on to a decomposer cell situated
coated titanium anodes
chlorine
alongside the mercury cell. The exit brine, containing typically 15-20% (w/w) sodium
saturated brine in
spent brine out 2Cl-(aq)
25
2Na+(aq) + 2e-
chloride, is freed of chlorine by blowing air through it, or subjecting the solution to a vacuum. The solution is resaturated with sodium chloride and returned to the cell.
Cl2(g) + 2e-
2Na(l)
Hg(l)
The decomposer cell (Figure 4) is made of steel and contains graphite blocks fixed in the flow of amalgam.
2Na/Hg(l)
mercury in
sodium-mercury amalgam Na/Hg to decomposer
flowing mercury cathode
Alternatively, the decomposer is a tower packed with graphite spheres. The decomposer acts as a short circuited cell. At the anode sites, sodium is oxidized and the ions pass into solution. At the cathode sites, hydrogen is discharged.
hydrogen
The mercury is returned to the electrolysis cell and the hydrogen passes out of the decomposer. A 50%
decomposer water in H2O(l) 2H+(aq) + 2e-
2Na/Hg(l) mercury returned to electrolysis cell
H+(aq) + OH-(aq)
sodium hydroxide solution
decomposer and most of it is sold in this form. Some is concentrated by evaporation to 75% (w/w) and then
H2(g)
heated to 750-850 K to obtain solid sodium hydroxide.
2Na+(aq) + 2e- + Hg(l) graphite blocks
(w/w) solution of sodium hydroxide is produced in the
sodium-mercury amalgam Na/Hg from cell
Figure 4 The mercury cell and decomposer.
The chlorine is led off as shown in Figure 4. At the mercury cathode, sodium ions are discharged in preference to hydrogen ions due to the high overvoltage of hydrogen. The sodium forms an amalgam with the mercury. The amalgam contains approximately 0.3% (w/w)
(c) The percolating diaphragm cell In the diaphragm cell (Figure 5), the anodes are titanium coated with a precious metal oxide and the cathodes are steel. There is a porous asbestos diaphragm to separate chlorine and hydrogen that are liberated during electrolysis. The hydroxide ions formed in the cathode compartment, together with the sodium ions, produce a solution of sodium hydroxide. The electrolyte level is maintained higher in the anode
Figure 5 Chlorine being manufactured using mercury cells. Usually, about 100 cells operate in series. Great care is taken to prevent loss of mercury.
116
Chlorine compartment so that the brine percolates through the diaphragm into the cathode section from where it flows out of the cell with the sodium hydroxide solution.
25
Figure 6 The diaphragm cell.
The chlorine formed on the anodes rises and is led away. The cathode solution contains about 10-12% (w/w) sodium hydroxide and 15% (w/w) sodium chloride. This is evaporated to one-fifth of its original volume when the much less soluble sodium chloride crystallizes to leave a solution containing 50% (w/w) sodium hydroxide and less than 1% (w/w) sodium chloride.
Figure 7 Chlorine is stored under pressure as a liquid. This photograph was taken in southern France.
The chlorine-alkali balance For every tonne of chlorine, 2.25 tonnes of 50% sodium 3
hydroxide and 340 m of hydrogen (under normal
Comparison of mercury, diaphragm and membrane cells Factors such as capital and energy costs and environmental concerns all favour the membrane process (Table 2) but its development was not possible until work by Du Pont in the US in the early 1960s, and more recently in Japan, resulted in the production of the membrane material discussed above.
conditions) are also produced. It is necessary, therefore, to ensure that all these products can be sold.
The future A large research programme in Germany, led by Bayer, is looking at ways of reducing the amount of electrical power used which, at present, contributes half the cost of chlorine production and also produces large amounts of carbon dioxide from the power stations. When
Diaphragm
Membrane
hydrogen ions migrate to the cathode, hydrogen is
construction costs
expensive
relatively cheap
cheaper than mercury cell
liberated. However, if oxygen is pumped into this part
operation
toxic mercury must be removed from effluent
frequent asbestos diaphragm replacement
low maintenance costs
voltage needed for the electrolysis process is reduced by
NaOH product concentration
high purity 50% - as required
less pure 12% - needs concentration
high purity 30% - needs concentration
typical cell energy consumption (kW hours per tonne of chlorine)
3 360
2 720
2 500
steam consumption for caustic evaporation
nil
purity of brine
important
Mercury
of the cell, the hydrogen reacts to form water and the a third. This, in turn, reduces the power costs and thus the amount of carbon dioxide formed in the power station by a third. A disadvantage is that the hydrogen is no longer available as an important and valuable by-product (Unit 32), together with oxygen being consumed as an additional raw material. There are technical difficulties in applying this process (known as an oxygen-depolarised cathode, ODC) to
high
medium
the electrolysis of brine. However it is easier to apply to the electrolysis of aqueous hydrochloric acid in order to generate chlorine. A large commercial plant has been
important
very important
constructed in China, using ODC technology.
Table 2 Comparison of the three cells.
117
Polyesters
P
olyesters are polymers formed from a dicarboxylic acid and a diol. They have many uses, depending on how they have been produced and the resulting orientation of the polymer chains.
59
O C R n O
Uses
As fibres
Polyesters are extremely important polymers. Their most
The polyester is produced as small granules. These are
familiar applications are in clothing, food packaging and
melted and squeezed through fine holes and the resulting
plastic water and carbonated soft drinks bottles.
filaments spun to form a fibre. This fibre, commonly
The most used of the polyesters has the formula:
known as Terylene or Dacron, is widely used in clothing (for example, in suits, shirts and skirts) either alone or in blends with other manufactured or natural fibres, principally cotton.
Being an ester, it is made from an acid, benzene-1,4dicarboxylic acid, and an alcohol, ethane-1,2-diol (Unit 27).
It is also used for filling anoraks and bedding duvets to give good heat insulation. Other uses include car tyre cords, conveyor belts and hoses, where its strength and resistance to wear are paramount.
It is often known by its trivial name, polyethylene terephthalate (PET). The annual world wide production of PET is approximately 40 million tonnes and is growing at ca 7% per year. Of this, about 65% is used to make fibres, 5% for film and 30% for packaging. Another useful polyester is produced from benzene1,4-dicarboxylic acid and propane-1,3-diol (which replaces ethane-1,2-diol). It is known by its trivial name, polytrimethylene terephthalate, PTT (Unit 10). The different uses of polyesters depend on their structure. The benzene rings in the molecular chain give them a rigid structure, leading to high melting points (over 500 K) and great strength. They do not discolour in light. In PET fibres, the molecules are mainly arranged in one direction, in film, they are in two directions and for
Figure 2 Polyesters are often used to make the suits and parachutes for sky divers.
packaging, they are in three directions (Figure 1).
Figure 1 Diagram to show the arrangement of PET molecules in PET fibres, films and packaging.
184
Polyesters As films The polyester can also be made into thin films which can be used in food packaging, audio and video tapes,
Using the acid provides a direct esterification reaction, while the dimethyl ester reaction involves ester interchange. The dimethyl ester route requires the use
electrical insulation, and X-ray films.
of an acid catalyst whereas direct esterification is self-
As packaging
The dimethyl ester route was originally preferred because
A relatively newer use is for packaging, for example for bottles (see Figure 3). The small granules of the polyester are heated to about 500 K and further polymerization takes place. This heating is sometimes called solid-state polymerizing. The polymer is melted,
catalysed by the carboxylic acid groups. the ester could be purified more readily than the acid. Very pure acid is now available in large commercial quantities; the modern processes therefore start from the acid.
orientated in three directions giving the plastic great
(i) Starting from the acid: Direct Esterification Reaction
strength.
The acid reacts directly with ethane-1,2-diol:
moulded and then stretched. The molecules are now
59
O
O C
C
HO CH2 CH2 OH + HO ethane-1,2-diol
OH + HO CH2 CH2 OH
benzene-1,4-dicarboxylic acid (terephthalic acid)
O
O C
C
HO CH2 CH2 O
O CH2 CH2 OH + 2H2O ‘PET’ monomer
(ii) Starting from the dimethyl ester: Ester Interchange Reaction The acid reacts with methanol to form the dimethyl ester, with manganese(II) ethanoate being commonly used as the catalyst. The dimethyl ester is then reacted with ethane-1,2-diol, by a process known as transesterification, in which one alcohol (ethane-1,2-diol) exchanges for another (methanol): Figure 3 For beverage packaging the barrier properties of the PET to certain gases, the excellent mass to strength ratio and the recyclability of the final product are very important features influencing the choice of PET over other plastics or more traditional packaging materials.
O CH3 OH + HO
O C
C
OH + HO CH3
methanol catalyst
Manufacture of PET (a) The production of the monomer Ethane-1,2-diol is reacted with benzene-1,4-dicarboxylic acid (sometimes known as terephthalic acid), or its dimethyl ester, in the presence of a catalyst, to produce initially the monomer and low molecular mass oligomers (containing up to about 5 monomer units).
O
O C
C
CH3 O
O CH3
+
+ HO CH2 CH2 OH
HO CH2 CH2 OH ethane-1,2-diol
catalyst
O
O C
C
HO CH2 CH2 O
O CH2 CH2 OH ‘PET’ monomer
+ 2CH3OH
185
Polyesters Figure 4 Granules of PET from both batch and continuous processes are used as feedstocks for extrusion and moulding machines for the production of film and some moulded articles.
59
(b) Polymerization of the monomer The monomer then undergoes polycondensation with the elimination of ethane-1,2-diol: O
para-xylene).
O CH2 CH2 OH
One method is to pass air into the liquid hydrocarbon
C
n HO CH2 CH2 O
dissolved in ethanoic acid under pressure, in the
‘PET’ monomer
C O
presence of cobalt(ll) and manganese(ll) salts as
O
O
Benzene-1,4-dicarboxylic acid is manufactured by oxidation of 1,4-dimethylbenzene (commonly known as
O C
Benzene-1,4-dicarboxylic acid
C O CH2 CH2
+ n HO CH2 CH2 OH
catalysts, at about 500 K:
n
‘PET’ polymer
The polycondensation stage requires a catalyst, antimony(lll) oxide, and is carried out at high temperatures (535-575 K) when the monomer and polymer are molten. Low pressures are used to favour product formation. Ethane-1,2-diol is recycled. Polyester production can be carried out using both batch and continuous processes (Unit 3). In the production of polyester fibre, the products of a continuous process can be fed directly into melt-spinning heads. This removes the casting, chipping, blending and drying stages that are necessary with batch processing.
186
The pure acid used in PET production is obtained from the crude product by further processing to remove colour-forming impurities, and then by crystallization, washing and drying stages.
Poly(ethene)
O
ver 60 million tonnes of poly(ethene), often known as polyethylene and polythene, is manufactured each year making it the world’s most important plastic. Its uses include film, packaging and containers, from bottles to buckets.
Uses
All forms can be used for injection-moulded products
Poly(ethene) is produced in three main forms: low density (LDPE) (< 0.930 g cm-3) and linear low density ( LLDPE)
such as buckets, food boxes and washing-up bowls (Table 1).
(ca 0.915-0.940 g cm-3) and high density (HDPE) (ca
Process
0.940-0.965 g cm ).
(Unit 53)
-3
The LDPE or LLDPE form is preferred for film packaging and for electrical insulation. HDPE is blow-moulded
Making film
to make containers for household chemicals such as washing-up liquids and drums for industrial packaging. It is also extruded as piping.
60
Injection moulding Blow moulding
Extrusion
HDPE Food packaging Shopping bags
LDPE
Cling film Milk carton lining
Dustbins
Buckets
Crates
Bowls
Detergent bottles Drums
Water pipes
LLDPE
Stretch film
Food boxes
Squeezable bottles Flexible water pipes Cable jacketing
Cable coating
Table 1 Examples of uses of poly(ethene).
HDPE
Figure 2 Poly(ethene) is used to make large water pipes -
LDPE/LLDPE Figure 1 Uses of poly(ethene).
Figure 3 - and far smaller pipes.
187
Poly(ethene) Annual production/tonnes UK
60
density of the material. LDPE is generally amorphous
Europe
World
LDPE
170 000
4.5 million
18.3 million
HDPE
145 000
5.4 million
26.3 million
LLDPE
Zero
3.1 million
16.5 million
Another form, discussed below, mLLDPE, is, at present, produced in much smaller quantities.
Manufacture The production of ethene, from which poly(ethene), is made is outlined in Unit 30. A new plant is being constructed in Brazil for the production of poly(ethene), from ethene, that is made from sugar cane via ethanol (Units 8 and 9).
and transparent with about 50% crystallinity. The branches prevent the molecules fitting closely together and so it has low density.
High density poly(ethene) (HDPE) Two types of catalyst are used principally in the manufacture of HDPE: â&#x20AC;˘ a Ziegler-Natta organometallic catalyst (titanium compounds with an aluminium alkyl) (Unit 2). â&#x20AC;˘ an inorganic compound, known as a Phillips-type catalyst. A well-known example is chromium(VI) oxide on silica, which is prepared by roasting a chromium(III) compound at ca 1000 K in oxygen and then storing prior to use, under nitrogen.
Low density poly(ethene) (LDPE)
HDPE is produced by three types of process. All
The process is operated under very high pressure (1000-
operate at relatively low pressures (10-80 atm) in the
3000 atm) at moderate temperatures (420-570 K) as may
presence of a Ziegler-Natta or inorganic catalyst. Typical
be predicted from the reaction equation:
temperatures range between 350-420 K. In all three processes hydrogen is mixed with the ethene to control the chain length of the polymer.
An initiator, such as a small amount of oxygen, and/or an organic peroxide is used.
(i) Slurry process (either CSTR (continuous stirred tank reactor) or a loop (Unit 3)
Ethene (purity in excess of 99.9%) is compressed and passed into a reactor together with the initiator. The molten poly(ethene) is removed, extruded and cut into granules. Unreacted ethene is recycled. The average polymer molecule contains 4000-40 000 carbon atoms, with many short branches. For example,
It can be represented by:
There are about 20 branches per 1000 carbon atoms. The relative molecular mass, and the branching, influence the physical properties of LDPE. The branching affects the degree of crystallinity which in turn affects the
188
Figure 4 The slurry process.
Poly(ethene) The Ziegler-Natta catalyst (Unit 2), as granules, is mixed
A mixture of ethene and hydrogen is passed over a
with a liquid hydrocarbon (for example, 2-methylpropane
Phillips catalyst in a fixed bed reactor (Unit 3) (Figure 6).
or hexane), which simply acts as a diluent. A mixture of
Ethene polymerizes to form grains of HDPE, suspended
hydrogen and ethene is passed under pressure into the slurry and ethene is polymerized to HDPE. The reaction takes place in a large reactor with the mixture constantly stirred (Figure 5). On opening a valve, the product is released and the solvent is evaporated to leave the polymer, still containing the catalyst. Water vapour, on flowing with nitrogen through the polymer, reacts with the catalytic sites, destroying their activity. The residue of the catalyst, titanium(IV) and aluminium oxides, remains mixed, in minute amounts, in the polymer.
in the flowing gas, which pass out of the reactor when the valve is released. Modern plants sometimes use two or more of the individual reactors in series (for example two or more slurry reactors or two gas phase reactors) each of
60
which are under slightly different conditions, so that the properties of different products from the reactors are present in the resulting polymer mixture, leading to a broad or bimodal molecular mass distribution. This provides improved mechanical properties such as stiffness and toughness.
Figure 5 The manufacture of poly(ethene) using the slurry process.
(ii) Solution process The second method involves passing ethene and hydrogen under pressure into a solution of the ZieglerNatta catalyst in a hydrocarbon (a C10 or C12 alkane). The polymer is obtained in a similar way to the slurry method.
Figure 7 Granules of poly(ethene) which are then used to make film, extruded into pipes or moulded.
The HDPE powder coming out of any of the reactors discussed above is separated from the diluent or solvent (if used) and is extruded and cut up into granules. This method gives linear polymer chains with few branches. The poly(ethene) molecules can fit closer together. The polymer chains can be represented thus:
(iii) Gas phase process
This leads to strong intermolecular bonds, making the material stronger, denser and more rigid than LDPE. The polymer is not transparent.
Linear low density poly(ethene) (LLDPE) Low density poly(ethene) has many uses but the high pressure method of manufacture by which it is produced has high capital costs. However, an elegant Figure 6 Low pressure gas-phase process.
189
Poly(ethene) technique has been developed, based on both Ziegler-
a sandwich. There is a transition metal (often zirconium
Natta and inorganic catalysts to produce linear low
or titanium) â&#x20AC;&#x2DC;fillingâ&#x20AC;&#x2122; a hole between layers of organic
density poly(ethene) LLDPE, which has even improved
compounds.
properties over LDPE. Any of the three processes, slurry,
The catalysts are even more specific than the original
solution and gas phase, can be used when a ZieglerNatta catalyst is chosen. The gas phase process is used
60
when the inorganic catalyst is employed.
Ziegler-Natta catalysts and it is possible to control the polymerâ&#x20AC;&#x2122;s molecular mass as well as its configuration. Either the slurry or solution processes are usually used.
Small amounts of a co-monomer such as but-1-ene or
Metallocenes are discussed in more detail in Unit 63.
hex-1-ene are added to the feedstock. The monomers
Poly(ethene) produced using a metallocene can be
are randomly polymerized and there are small branches made up of a few carbon atoms along the linear chains. For example, with but-1-ene, CH3CH2CH=CH2, the structure of the polymer is:
CH2
CH3
CH3
CH2
CH2
CH
CH2
CH2
CH2
CH2
CH2
CH
used as very thin film which has excellent optical properties and sealing performance, thus making them very effective for wrapping foods. The real plus for the metallocene catalysts are the enhanced mechanical properties of the films made out of mLLDPE.
CH2
The side chains are known as pendant groups, or short chain branching. The molecule can be represented as:
Co-polymers The manufacture of co-polymers of ethene are described in Unit 63.
The structure is essentially linear but because of the short chain branching it has a low density. The structure gives the material much better resilience, tear strength and flexibility without the use of plasticisers (Unit 53). This makes linear low density poly(ethene) an ideal material for the manufacture of film products, such as those used in wrappings. The properties of the polymer, and hence its uses, can be varied by varying the proportion of ethene and co-monomer and by using different co-monomers. All this can be done without shutting down the plant, an enormous advantage.
Metallocene linear low density poly(ethene) (mLLDPE) This poly(ethene), known as mLLDPE, is produced by a new family of catalysts, the metallocenes. Another name for this family is single site catalyst. The benefit is that the mLLDPE is much more homogenous in terms of molecular structure than classical LLDPE produced by Ziegler-Natta catalysts. Each catalyst is a single site catalyst which produces the same PE chain. Chemists have compared the structure of metallocenes to that of
190
Figure 8 Poly(ethene) film is used extensively for wrapping foods.
Poly(methyl 2-methylpropenoate)
P
oly(methyl 2-methylpropenoate), often known as polymethyl methacrylate or PMMA, is one of the best known polymers, used widely under trade names such as Lucite, Perspex and Altuglas.
61 Uses Poly(methyl 2-methylpropenoate) is better known as
The monomer is used in adhesives, surface coatings and in paints (Unit 17).
Lucite, Perspex and Altuglas (when in sheet form) and as Diakon (when in powder form). The cast sheet is used in baths and other sanitary ware, which along with illuminated signs, is the largest use of the polymer. High molecular mass cast sheet (Perspex) is also used as a lightweight replacement for glass. Lower molecular mass products, made by suspension or solution polymerization (Diakon), are used in car lights and domestic lighting.
Figure 2 Uses of poly(methyl-2-methylpropenoate).
Annual production Polymer UK
Europe World
Monomer
50 000 tonnes 490 000 tonnes 1.9 million tonnes
UK
220 000 tonnes
Europe
890 000 tonnes
World
3.3 million tonnes
Manufacture (a) The monomer The monomer is the methyl ester of 2-methylpropenoic acid, methyl 2-methylpropenoate (methyl methacrylate):
Figure 1 The elevator cage installed in La Grande Arche in Paris is made of sheets of poly(methyl 2methylpropenoate).
Special grades are used in diverse applications such as
Worldwide, over 80% of the monomer is made from
false teeth and eyes and as a major component of bone
propanone (Unit 45) by a sequence of steps which begins
cements.
by reacting propanone with hydrogen cyanide.
191
Poly(methyl 2-methylpropenoate) The resulting ester, methyl propionate, is reacted with methanal (Unit 37) to form methyl 2-methylpropenoate. A fixed bed reactor is used (Unit 3) and the reactor and catalyst (for example, caesium hydroxide on silica) are The product, on reaction with concentrated sulfuric acid
61
heated to 600 K:
at about 430 K, is dehydrated and the nitrile goup (CN) hydrolysed to the amide. This is a step-wise process involving both dehydration and hydrolysis. The reactions can be summarised as:
(b) The polymer Polymerization of methyl 2-methylpropenoate is achieved The temperature is decreased to 370 K and methanol is added. The amide group is hydrolysed and esterified. The reactions can be summarised as:
using free radical initiators, such as an azo compound or a peroxide: CH3 n H2C C
CH3 H2C
CO2CH3
C
n CO2CH3
The amount of initiator employed affects both polymerization rate and resulting molecular mass of The product is continuously removed by steam distillation. A drawback to the process is the co-production of ammonium sulfate. It is converted back to sulfuric acid for reuse (Unit 7). Together with ‘spent’ acid from the reactions above, it is heated strongly in oxygen in a furnace. The products formed are nitrogen, carbon dioxide and sulfur dioxide. The latter is then converted to sulfuric acid using the Contact Process (Unit 50). The use of pure oxygen reduces the size of the furnace which saves on both energy and equipment costs. Much work has been done to find alternative sources of the monomer and a promising route, which is now in use, uses a mixture of ethene, carbon monoxide and methanol
the polymer. Polymerization is carried out commercially in several ways, i.e. in bulk, solution, suspension and emulsion.
(c) Co-polymers Co-monomers are often used together with the methyl 2-methylpropenoate. For example, most commercial grades of poly(methyl 2-methylpropenoate) used in injection moulding or extrusion applications contain a small amount (ca. 4%) of co-monomer, such as methyl propenoate (methyl acrylate) (when casting sheets of the polymer) and ethyl propenoate (when extruding sheets of the polymer). In these co-polymers, the groups are randomly arranged (Unit 53). The resulting polymers have increased thermal
in the liquid phase under pressure of about 10 atm at
stability compared to the homopolymer.
350 K:
With butyl propenoate, a co-polymer is produced which is used as a base for emulsion paints (Unit 17). It is also co-polymerized with ABS (Unit 62) to produce a very tough polymer which is both rigid and has excellent clarity. It is used, for example, in medical applications and in cosmetic packaging.
192
Poly(phenylethene)
P
oly(phenylethene), commonly known as polystyrene, is the third most important polymer, in terms of amount made from ethene. Its physical properties can be adjusted to suit a range of everyday uses. Techniques have been developed which increase its mechanical strength, its ability to absorb shock and its thermal insulating properties.
Uses The largest use for poly(phenylethene) is for packaging,
(a) The manufacture of ethylbenzene from benzene
particularly for foods such as poultry and eggs, for cold
Benzene vapour and ethene are mixed and passed over
drinks and take-away meals.
an acid catalyst, at 650 K and 20 atm pressure:
62
This is an example of a Friedel-Crafts reaction. The acid catalyst now used is a zeolite, ZSM-5, an aluminosilicate (Unit 2).
(b) The manufacture of phenylethene Ethylbenzene vapour is mixed with excess steam and passed over heated iron(lll) oxide. It is dehydrogenated:
Figure 1 Uses of poly(phenylethene).
It is also used in making appliances, including refrigerators, microwaves and blenders. It is the leading
A small amount of potassium oxide is mixed with the iron(lll) oxide (which keeps the catalyst in the iron(lll)
choice for jewel boxes (cases for CDs and DVDs) and is
state).
also widely used for its insulating properties.
The steam reduces ‘coking’ (the formation of soot on the
Annual production UK
Europe World
70 000 tonnes
3.4 million tonnes 14.6 million tonnes
Manufacture Poly(phenylethene) is manufactured from its monomer, phenylethene. Phenylethene, in turn, is produced from benzene and ethene via ethylbenzene. There are thus three stages: a) the manufacture of ethylbenzene from benzene b) the manufacture of phenylethene c) the polymerization of phenylethene
catalyst from the decomposition of ethylbenzene at the high temperatures used).
(c) The polymerization of phenylethene Radical polymerization is used to produce the polymer (Unit 53). The predominant polymerization technique is continual thermal mass polymerization which is initiated by heat alone. Suspension polymerization is also used. This technique requires the use of an initiator such as dibenzoyl peroxide. Poly(phenylethene) is a clear thermoplastic, with good moisture resistance, but is rather brittle. A tougher product is also manufactured by polymerizing phenylethene containing 5–10% dissolved poly(buta-1,3diene) rubber. This tougher product – generally known
193
Poly(phenylethene)
62
as High Impact Polystyrene (HIPS) – is made exclusively
ABS is tougher, scratch proof and more chemically
by continuous thermal mass polymerization, in which
resistant than rubber-modified poly(phenylethene) and
heat is required to initiate the polymerization reaction.
is used, for example, in casings for computers, cycle
This toughened polymer is translucent.
helmets, calculators, telephones, vacuum cleaners and
The structure of poly(phenylethene) made by these
toys. Often ABS is blended with SAN to make it even
technologies is atactic. By modification of the
more rigid.
polymerization technique – principally by the use of
Another variation is the co-polymer formed between
metallocene catalysts – stereoregular (syndiotactic)
ABS and methyl 2-methylpropenoate, which has a high
structures can be obtained (Unit 53). This syndiotactic
resistance to chemical attack, high transparency and is
polymer (sPS) has improved properties – particularly
very tough (Unit 61).
thermal and mechanical. Another co-polymer is formed on polymerizing a mixture of phenylethene (styrene) and propenonitrile (acrylonitrile). It is known as SAN (styrene-
Expanded poly(phenylethene) Expanded poly(phenylethene) is manufactured as beads containing pentane (a liquid at room temperature).
acrylonitrile). It is less flexible, more transparent
When they are heated in steam, the hydrocarbon
and has more resistance to heat and chemicals than
volatilises and the beads expand (Figure 3). These
poly(phenylethene). It is used in car headlamps, cassette
are subsequently blown into moulds and fused by
covers, syringes and high quality kitchen appliances.
further steaming and then cooling. The expanded
A further modification involves the co-polymerization (Unit 53) of phenylethene (styrene) with propenonitrile
poly(phenylethene) has good thermal insulation and shock absorbing properties.
(acrylonitrile) in the presence of poly(buta-1,3-diene) to make ABS plastics. A, B, S represent acrylonitrile, butadiene and styrene, which give strength (A), flexibility (B), and hardness (S). Typically this plastic has a composition: 60% (w/w) phenylethene (styrene), 25% propenonitrile (acrylonitrile), 15% buta-1,3-diene. The initiator used is often potassium peroxydisulfate, K2S2O8.
Figure 2 This Triumph motorcycle has a fairing (the structure around the bike that reduces drag by streamlining) made of a blend of ABS and a polyamide (Unit 56). It is light, very strong and has a high chemical and heat resistance, which means the fairing can be installed near the engine and the exhaust pipe.
194
Figure 3 These poly(phenylethene) beads are shown prior to and after expansion. They were impregnated during manufacture with very fine particles of graphite to improve further their ability to absorb heat.
Poly(propene)
P
ropene undergoes addition polymerization to produce poly(propene), often known as polypropylene, which is one of the most versatile thermoplastic polymers available commercially. Mixtures of propene and other monomers form a wide range of important co-polymers.
Uses
• easy to weld (design)
Poly(propene) is processed into film, for packaging and
• recyclabililty
into fibres for carpets and clothing. It is also used for injection moulded articles ranging from car bumpers to washing up bowls, and can be extruded into pipe (Figure 1).
63
The majority (ca 60% of the total produced) of poly(propene) is produced as a homopolymer. Co-polymers are discussed below. Poly(propene) is one of the lightest thermoplastics -3
(density 0.905 g cm ). It has a melting point of 440 K
films (food packaging)
and a crystallinity of ca 50-60%. The polymer, unlike
16% rigid packaging textiles (carpets, carpet backing)
(crates, pails, CD and DVD boxes, corrugated boards)
28%
21%
poly(ethene), is transparent.
Structure of the polymer The propene molecule is asymmetrical,
technical parts (car bumpers, dashboards, consumer products sewage pipes, drain pipes, (furniture, electric cables) housewares, 20% toys)
15%
Figure 1 Uses of poly(propene).
and, when polymerized, can form three basic chain structures dependent on the position of the methyl groups: isotactic, syndiotactic and atactic (Unit 53) as shown diagrammatically below:
Materials suitable for a much wider range of applications can be made by compounding poly(propene) with, for example, fillers and pigments (Unit 53), and elastomers. Poly(propene) has remarkable properties, making it suitable to replace glass, metals, cartons and other polymers. These properties include: • low density (weight saving) • high stiffness • heat resistance • chemical inertness • steam barrier properties (food protection) • good transparency • good impact/rigidity balance • stretchability (film and fibre applications) • good hinge property (for example where a lid and box are made together, for DVD boxes) • high gloss (appearance)
Figure 2 Molecular structures of poly(propene).
195
Poly(propene) The ‘one handed’ structure of isotactic poly(propene)
(ii) The gas phase process
causes the molecules to form helices. This regular form
A mixture of propene and hydrogen is passed over a bed
permits the molecules to crystallize to a hard, relatively rigid material, which, in its pure form, melts at 440 K. The syndiotactic polymer, because of its regular
63
structure, is also crystalline. Atactic chains are completely random in structure and consequently they do not crystallize. High molecular mass atactic poly(propene) is a rubber-like material. Commercial poly(propene) is a predominantly isotactic polymer containing 1-5% by mass of atactic material.
Annual production UK
containing the Ziegler-Natta catalyst at temperatures of 320-360 K and a pressure of 8-35 atm. The polymer is separated from the gaseous propene and hydrogen using cyclones and the unreacted gas is recycled. A diagram, Figure 6 in Unit 60, illustrates this process. Both processes can be operated continuously and use ‘stereospecific’ Ziegler-Natta catalysts to effect the polymerization. The catalyst remains in the product and needs to be destroyed using water or alcohols, before the polymer is converted into pellets. Both bulk and gas phase processes have virtually
490 000 tonnes
eliminated gaseous and aqueous effluents by the use of
Europe
13.1 million tonnes
high activity catalysts, resulting in low residues in the final
World
52.2 million tonnes
polymer.
Manufacture
(b) Using a metallocene as catalyst
Poly(propene) is produced from propene. Propene is
Metallocenes are being increasingly used as catalysts
produced in large quantities from gas oil, naphtha, ethane
for the production of poly(ethene) (Unit 60) and
and propane (Unit 4).
poly(propene).
(a) Using a Ziegler-Natta catalyst
Metallocenes are strictly defined as molecules which
Ziegler-Natta catalysts are used in the polymerization process (Unit 2). These are produced by interaction of titanium(IV) chloride and an aluminium alkyl, such as
have a transition metal atom bonded between two cyclopentadienyl ligands which are in parallel planes. Ferrocene is a particularly well known example:
triethyl aluminium. Two main processes are used for making the polymer with these catalysts, although the slurry method (Unit 60) is used as well.
(i) The bulk process Polymerization takes place in liquid propene, in the absence of a solvent at a temperature of 340-360 K and pressures of 30-40 atm (to keep the propene as a liquid). After polymerization, solid polymer particles are separated from liquid propene, which is then recycled. The use of liquid propene as a solvent for the polymer as it is formed means that there is no need to use hydrocarbons such as the C4-C8
alkanes which are used in the parallel manufacture of poly(ethene).
Figure 3 A loop reactor (Unit 3) is used in the manufacture of poly(propene). The reactor is further illustrated in Figure 5, Unit 60.
196
Poly(propene) However, the term is now used more widely to include
The crystallinity and melting point are reduced and the
other ligands related to cyclopentadienyl. One such
products are more flexible and are optically much clearer.
metallocene is based on zirconium:
Major uses for these random co-polymers are for medical products (pouches, vials and other containers) and packaging (for example, bottles, CD and video boxes). Many other co-polymers of ethene and propene, with higher alkenes such as hexene, are being developed which will produce polymers similar to LLDPE (Unit 60)
63
but which have better mechanical and optical properties. Zirconium has an oxidation state of 4 and is bonded to
The second type of co-polymers is the so-called â&#x20AC;&#x2DC;blockâ&#x20AC;&#x2122;
two indenyl ligands (a cyclopentadienyl ligand fused to
co-polymers (Unit 53). These are made by following
a benzene ring). They are joined by two CH2 groups.
the poly(propene) homopolymerization with a further,
In conjunction with an organoaluminium compound, it
separate stage, in which ethene and propene are co-
acts as a catalyst for the polymerization of alkenes such
polymerized in the gas phase. Thus these two processes
as ethene and propene. The specific orientation of the
are in series (Figure 5).
zirconium compound means that each propene molecule, for example, as it adds on to the growing polymer chain is in the same orientation and an isotactic polymer is produced. When a different zirconium compound is used, Figure 5 lllustrating the homopolymer and the block copolymer formed from propene and ethene.
The products of these two processes form a composite (Unit 12) in which nodules of the block co-polymer are distributed with the homopolymer (Figure 6). the syndiotactic form of poly(propene) is produced. This is the only way of making syndiotactic poly(propene) commercially. As with the Ziegler-Natta catalysts, either the bulk or gas phase or slurry process (Unit 60) is used. Metallocenes also catalyse the production of co-polymers of propene and ethene. Poly(propenes) made in this way, mPP, are used in particular to make non-woven fibres and heat-seal films.
Co-polymers There are two main types of co-polymer (Unit 53). The simplest are the random co-polymers, produced by polymerizing together ethene and propene. Ethene units, usually up to 6% by mass, are incorporated randomly in the poly(propene) chains (Figure 4).
Figure 6 The propene-ethene block co-polymer nodules dissipate impact energy and prevent cracking.
The ethene content of the block co-polymer is larger (between 5 and 15%) than used in randomly alternating co-polymers. It has rubber-like properties and is tougher and less brittle than the random co-polymer. Consequently, the composite is particularly useful
Figure 4 llustrating an alternating co-polymer formed from propene and a small amount of ethene.
in making crates, pipes, furniture and toys, where toughness is required.
197
Poly(propenoic acid)
T
here is a group of polymers, the acrylics, which can be regarded as based on acrylic acid, more formally named propenoic acid. It also includes compounds derived from the acid, which include the methyl, ethyl and butyl esters and propenonitrile (acrylonitrile), all of which form widely used polymers.
64 This unit is concerned with propenoic acid, its esters and the polymers produced from them.
Uses of poly(propenoic acid) Poly(propenoic acid) is used in detergents to remove calcium and magnesium ions from the water, thus softening it. This has meant that phosphates need not be used for this purpose thus producing a much more environmentally friendly detergent.
A second use is the production of the so-called superabsorbents. These are polymers of mainly propenoic acid and sodium propenoate. Polymerization is initiated with, for example, potassium (or ammonium) peoxodisulfate, K2S2O8, which decomposes to form
radicals. Another compound is added at the same time to cross-link the chains via the carboxyl groups. One of these compounds is N,Nי-methylenebis(2-propenamide). A gel is formed which absorbs water more than 1000fold its mass (Figure 1), and is used as the basis of disposable nappies.
Uses of polypropenoates The polymers derived from the esters of propenoic acid are used as a base in many paints and varnishes (Unit 17). The polymers of ethyl and butyl propenoates are used in water-based emulsion paints, as is the co-polymer of butyl propenoate and methyl (2methylpropenoate). Methyl propenoate is used to produce a co-polymer with propenonitrile (Unit 65) which is one of the most widely used ‘acrylic’ fibres. Methyl and ethyl propenoates are co-polymerized with methyl 2-methylpropenoate to assist in the fabrication of poly(methyl 2-methylpropenoate), the range of polymers such as Perspex (Unit 61).
Uses of propenoic acid (acrylic acid) About 50% is used to make esters, mainly methyl, ethyl Figure 1 The child’s shoes are made of a fabric with pores which allow air to circulate around the feet. They are lined with a fleece made of poly(propenoic acid). In the wet, the polymer soaks up the water and expands, sealing the shoe, making it watertight. When dry, the water evaporates and the polymer contracts allowing the fleece to become porous to air.
and butyl propenoates. These are, in turn, polymerized (see below). About 30% is used to make poly(propenoic acid) and thus superabsorbents.
Annual production of propenoic acid Europe World
198
380 000 tonnes
1.8 million tonnes
Poly(propenoic acid) Manufacture of propenoic acid
Manufacture of the polypropenoates
Propenoic acid (acrylic acid) is manufactured from
Propenoic acid is reacted with an alcohol (for example,
propene in two steps.
methanol, ethanol, butan-1-ol) in the liquid phase with a
The first stage is the oxidation of propene to propenal.
trace of sulfuric acid as a catalyst to produce the esters. For example:
The alkene and air are mixed and passed over a heated catalyst, often a mixture of bismuth(III) and
64
molybdenum(VI) oxides on silica, at ca 650 K (Unit 2): Subsequently the esters are polymerized, using an organic peroxide as an initiator. The pure monomer may be used (known as bulk polymerization), but again
The second stage occurs when propenal and air are
more frequently the reaction is carried out in an aqueous
passed over another catalyst, a mixture of vanadium(V)
solution or in an emulsion in water. For example:
and molybdenum(VI) oxides on silica at ca 550 K:
Manufacture of poly(propenoic acid) The polymerization of propenoic acid, using an organic peroxide as an initiator, can be carried out with the pure
If co-polymers of the esters are required, the two
monomer (known as bulk polymerization), but more
monomers are mixed prior to the polymerization reaction
often it is polymerized in an aqueous solution or as an
under similar conditions.
emulsion, also in water:
A postscript on propene All the propenoate (acrylic) polymers are derived from propene as the summary shows: H2C CH CH3 propene NH3/O2
O2 benzene cumene process
H2C CH
CHO O2
H2C CH
CO2H
CH2 C H
OH
CO2H
N
n
poly(propenonitrile)
CO2R
n poly(propenoic acid)
This unit
C
CN
CN H3C C CH3
ROH
H2C CH
H2C CH
HCN
propenoic acid
CH2 C H
H3C CO CH3
Unit 65 CN H2C C CH3
CO2R CH2 C H
CO2H n
H2C C CH3
polypropenoates
This unit
CO2CH3 H2C C CH3 CO2CH3 CH2 C CH3
n
poly(methyl 2-methylpropenoate)
Unit 61
199
Poly(propenonitrile)
P
oly(propenonitrile), usually known as polyacrylonitrile, is manufactured from propene via propenonitrile. It is very widely used in co-polymers, particularly in fabrics and when materials need to be made hard and shock proof.
N C CH2 C H
n
65 Uses Poly(propenonitrile) itself is a very harsh fibre, rather like horse hair. An almost pure homopolymer is used when a very tough fabric is needed, for example for awnings,
The co-polymers with phenylethene (styrene) known as SAN and with butadiene and phenylethene, known as ABS, are plastics which are very strong and able to withstand shocks (Unit 62).
a soft top of a car or in brake linings. It is even used to reinforce concrete and in road construction. However, the vast majority of the polymer is co-polymerized. Although these co-polymers often contain more than 85% of propenonitrile units, they are much softer. The fibres formed from them are known as ‘acrylic’ fibres. Two of the most used acrylic fibres are formed from the co-polymerization of propenonitrile with ethenyl ethanoate (vinyl acetate) and propenonitrile with methyl propenoate. The former is often mixed with cotton fibres to produce a light fabric, used in women’s clothes. The latter is often used with wool (Figure 1).
Figure 2 The high heels are made from a blend of ABS and a polyamide (Unit 56) which is very strong.
Other co-polymers of propenonitrile include those when the co-monomer is methyl 2-methylpropenoate (Unit 61) and with 1,1-dichloroethene. With 1,1-dichloroethene as the co-monomer, a block copolymer (Unit 53) is formed which is fire-resistant and is often used in children’s clothing. An increasing use of poly(propenonitrile) co-polymers is in producing carbon fibres. If fibres of the polymer are heated under strictly controlled conditions the resulting fibres have remarkable strength (Unit 12). Figure 1 The co-polymer of propenonitrile and methyl propenoate is a wool substitute and is often mixed with wool itself for heavier fabrics, used in pullovers and jumpers and in suits.
200
Annual production of propenonitrile UK
280 000 tonnes
Europe
1.8 million tonnes
World
5.9 million tonnes
Poly(propenonitrile) Manufacture
initiator. When, ethenyl ethanoate is used as the co-
(a) The monomer
potassium hydrogensulfite and potassium peroxodisulfate
polymer, polymerization is initiated with small amounts of
Propenonitrile, the monomer, is manufactured from
which get incorporated into the co-polymer, giving it sites
propene. The alkene is mixed with ammonia and oxygen
which can bind to colorants and make them fast (Unit 11).
(from air) (1:1:2 volume ratio) and passed over a mixture
Alternatively, a small amount of a third monomer
of bismuth(III) and molybdenum(VI) oxides (Unit 2):
containing, for example a sulfonic acid group, serves the same purpose.
65
The co-polymer contains a more or less regular As it is a very exothermic reaction, and the temperature must be controlled at ca 600 K, a fluidized bed reactor
alternation of the individual monomers, an example of an alternating co-polymer (Unit 53).
(Unit 3) is used. A small amount of hydrogen cyanide (3-6%) is also formed, which can be used in the manufacture of methyl 2-methylpropenoate (Unit 61). The process has been modified, in Japan, to use propane
Similar procedures are used when other co-monomers
as the feedstock. It will become particularly important
are used.
if propane becomes much cheaper than propene. The
With methyl propenoate and methyl 2-methylpropenoate,
catalyst used is based on vanadium(V) and antimony(III)
block co-polymers are produced:
oxides.
(b) The polymer The polymer is manufactured by radical polymerization initiated by either a peroxide or by a mixture of potassium peroxydisulfate, K2S2O8 and a reducing agent such as potassium hydrogensulfite, KHSO3.
About equal amounts of the stereoregular polymer, isotactic and syndiotactic, are produced. The polymerization is either in solution or as a slurry.
(c) Co-polymers Polymerization takes place as for the homopolymer, the
An alternating polymer is produced with 1,1-
two monomers being mixed prior to addition of the
dichloroethene as the co-monomer.
Figure 3 The soft tops for high quality cars are produced from almost pure homopolymer.
201
Poly(tetrafluoroethene)
T
he uses of poly(tetrafluoroethene) (PTFE) are a function of its resistance to chemical attack, unreactivity (even above 500 K), low friction, non-stick properties and high electrical resistance.
CF2 CF2
n
66 Uses In many applications, tetrafluoroethene (TFE) is co-
• solid lubricants
polymerised with other fluorinated monomers, such as
• combinations with magnesium and aluminium as an
hexafluoropropene and perfluoropropyl vinyl ether, and also with ethene. Poly(tetrafluoroethene) (PTFE) and its co-polymers are used in: • cable insulation • reactor and plant equipment linings, when reactants
igniter for explosives
Annual production UK
Europe World
4000 tonnes
15 000 tonnes 200 000 tonnes
or products are highly corrosive to ordinary materials
Manufacture
such as steel
PTFE is made from methane in a series of reactions:
• semi-permeable membranes in chlor-alkali cells (Unit 25) and fuel cells • bearings and components in mechanical devices such as small electrical motors and pumps • permeable membrane (e.g. Gore-TexTM), for clothing
a) production of trichloromethane b) production of chlorodifluoromethane c) production of tetrafluoroethene (TFE) d) polymerization of tetrafluoroethene
(a) Production of trichloromethane
and shoes, which allows water vapour to diffuse away
Trichloromethane is one of the products formed by
from the skin but prevents liquid water (rain) from
the reaction of methane and a mixture of chlorine and
soaking in
hydrogen chloride. This can be performed in the liquid
• non-stick domestic utensils, e.g. frying pans • medical - catheter tubing • hose and tubing
phase at 370-420 K using a zinc chloride catalyst. Alternatively, the reaction is carried out in the vapour phase, using alumina gel or zinc oxide on silica as a catalyst at 620-720 K.
(b) Production of chlorodifluoromethane Trichloromethane is reacted with anhydrous hydrogen fluoride in the presence of antimony(III) and antimony(V) chlorofluoride to give chlorodifluoromethane: CHCl3(g) + 2HF(g)
CHClF2(g) + 2HCl(g) chlorodifluoromethane
(c) Production of tetrafluoroethene (TFE) Since TFE is an explosive gas (bp 197 K), it is usually made when and where required for polymerization so that Figure 1 The retractable roof installed over the Centre Court at Wimbledon in 2009 is made of poly(tetrafluoroethene).
202
there is minimum storage time of the monomer between its production and its polymerization.
Poly(tetrafluoroethene) Chlorodifluoromethane is heated in the absence of air, a process known as pyrolysis:
Co-polymers There is a group of co-polymers (Unit 53) which are formed by the co-polymerization of tetrafluoroethene and other unsaturated organic compounds such as ethene, hexafluoropropene and perfluoropropylvinyl ether. As
Low pressures (atmospheric) and high temperatures (940-1070 K) favour the reaction. Steam, preheated to 1220 K, and chlorodifluoromethane, at 670 K, are fed into a reactor. Steam is used to dilute
described above, these co-polymers are used in many of the examples given for PTFE. F3C CF
CF2
F3C CF2 CF2
hexafluoropropene
O CF
CF2
66
perfluoropropylvinyl ether
the reaction mixture and hence reduce the reactant
The co-polymer produced from ethene and
partial pressure, and thus the formation of carbon and
tetrafluroethene is an alternating co-polymer (Unit
toxic by-products. The steam also supplies all the
53) usually known by its trivial name, ethylene
heat required by this endothermic reaction. Very little
tetrafluoroethylene (ETFE):
hydrolysis of reactant and product occurs. Once formed, the product must be rapidly cooled to 770 K to prevent the reverse reaction occurring and the explosive decomposition of TFE:
It is used, in particular as a lining for containers as it is stable to attack by concentrated solutions of acids and alkalis, and because of its good electrical properties of insulation and its strength, it is used as a coating
The cooling is done by passing the vapour through a water-cooled heat exchanger, made of graphite to resist chemical attack and thermal shock. Reactor residence
for wires and cables. Its most spectacular use is as a roofing material in buildings such as the O2 Arena in
London, the Eden Project in Cornwall and the Birds Nest
time is 1 second.
Olympic Stadium in Beijing. The roofs are made up of
(d) Polymerization of tetrafluoroethene
also used as an outer skin of large buildings (Figure 2).
2 – 5 layers of large cushions of ETFE (Unit 12). It is
Polymerization is carried out by passing TFE into water containing a radical initiator, e.g. ammonium persulfate, (NH4)2S2O8, at 310-350 K and a pressure of 10-20 atm. Two different procedures are used: • granular polymerization gives a suspension of string-like PTFE particles up to 1 cm long in water. These are milled to produce fine powders (30 μm) used for moulding. The fine powders are also agglomerated to larger particles (500 μm) to give better flow. Unlike other thermoplastics, such as PVC, PTFE cannot be processed by melt extrusion. The powder is therefore moulded into rods for extrusion and heating at temperatures above 530 K to force the particles to stick together. • dispersion polymerization can be used to obtain a colloidal dispersion of PTFE particles (0.25 μm) in water. The dispersion can be concentrated and used for dip coating or spraying articles. The dispersion can also be coagulated and dried to give a powder, which, in turn, is made into a paste and extruded on to wire.
Figure 2 The outer skin of the Allianz Arena in Munich is made of cushions of ETFE. There are lights inside the cushions which are changed depending on which team is playing: white when the German national team is playing, red for FC Bayern Munich and blue for TSV 1860 Munich.
203
Polyurethanes
T 67
he polymeric materials known as polyurethanes form a family of polymers which are essentially different from most other plastics in that there is no urethane monomer and the polymer is almost invariably created during the manufacture of a particular object.
H N C O n O
R
Polyurethanes are made by the exothermic reactions between alcohols with two or more reactive hydroxyl (-OH) groups per molecule (diols, triols, polyols) and isocyanates that have more than one reactive isocyanate group (-NCO) per molecule (diisocyanates, polyisocyanates). For example a diisocyanate reacts with a diol: nO C N R1 N C O
+
nHO
R2 OH
N
R1 N
C
O H
H
O
C
O R2 O n
The group formed by the reaction between the two molecules is known as the ‘urethane linkage’. It is the essential part of the polyurethane molecule.
Uses
Polyurethanes, on the other hand are usually made
The physical properties, as well as the chemical structure, of a polyurethane depend on the structure 1
of the original reactants, in particular the R and the 2
R groups. The characteristics of the polyols - relative molecular mass, the number of reactive functional groups per molecule, and the molecular structure - influence the properties of the final polymer, and hence how it is used.
Figure 1 Uses of polyurethanes.
There is a fundamental difference between the manufacture of most polyurethanes and the manufacture
directly into the final product. Much of the polyurethanes produced are in the form of large blocks of foam, which are cut up for use in cushions, or for thermal insulation. The chemical reaction can also take place in moulds, leading to, for example, a car bumper, a computer casing or a building panel. It may occur as the liquid reactants are sprayed onto a building surface or coated on a fabric.
Figure 2 No other plastic allows itself to be made to measure in the same way as a polyurethane. Foams can be flexible or rigid, resistant to cold or particularly kind to skin. It all comes down to the way in which the polyurethane ‘building blocks’ are blended.
of many other plastics. Polymers such as poly(ethene) and poly(propene) are produced in chemical plants and sold as granules, powders or films. Products are subsequently made from them by heating the polymer, shaping it under pressure and cooling it. The properties of such end-products are almost completely dependent on those of the original polymer.
204
The combined effects of controlling the polymer properties and the density lead to the existence of a very wide range of different materials so that polyurethanes are used in very many applications (Table 1).
Polyurethanes The mixture of diisocyanates known as TDI consists of Some examples of the main reasons for choosing
two isomers:
polyurethanes as shown in Table 1. Uses
Reasons
cushioning
low density, flexibility, resistance to fatigue
shoe soles
flexibility, resistance to abrasion, strength, durability
building panels
thermal insulation, strength, long life
artificial heart valves
flexibility and biostability
electrical equipment
electrical insulation, toughness, resistance to oils
The starting material is methylbenzene (toluene). When
67
it reacts with mixed acid (nitric and sulfuric), two isomers of nitromethylbenzene (NMB) are the main products.
Table 1 Properties and uses of polyurethanes.
Polyurethanes can be rigid or rubbery at any density -3
-3
between, say 10 kg m and 100 kg m . The overall range of properties available to the designer and the manufacturer is clearly very wide and this is reflected in the many, very different, uses to which polyurethanes are put.
If this mixture is nitrated further, a mixture of dinitromethylbenzenes is produced. In industry they are known by their trivial names, 2,4-dinitrotoluene and 2,6-dinitrotoluene (DNT). 80% is 2,4-DNT and 20% is 2,6-DNT:
Annual production UK
11 000 tonnes
Europe World
4.4 million tonnes 11.7 million tonnes
Manufacture As polyurethanes are made from the reaction between an
The mixture of dinitrobenzenes is then reduced to the corresponding amines:
isocyanate and a polyol, the section is divided into three parts: a) production of isocyanates b) production of polyols c) production of polyurethanes
(a) Production of isocyanates
In turn, the amines, known commercially as Toluene Diamines or TDA, are heated with carbonyl chloride
Although many aromatic and aliphatic polyisocyanates
(phosgene) to produce the diisocyanates and this
exist, two are of particular industrial importance. Each
process can be carried out in the liquid phase with
of them has variants and together they form the basis of
chlorobenzene as a solvent at about 350 K:
about 95% of all the polyurethanes. They are: â&#x20AC;˘ TDI (toluene diisocyanate or methylbenzene diisocyanate) â&#x20AC;˘ MDI (methylene diphenyl diisocyanate or diphenylmethane diisocyanate). TDI was developed first but is now used mainly in the production of low density flexible foams for cushions.
205
Polyurethanes
67
Alternatively, these reactions are carried out in the gas
The choice of polyol, especially the number of reactive
phase by vaporizing the diamines at ca 600 K and mixing
hydroxyl groups per polyol molecule and the size and
them with carbonyl chloride. This is an environmental
flexibility of its molecular structure, ultimately control the
and economic improvement over the liquid phase
degree of cross-linking between molecules. This has
process as no solvent is needed.
an important effect on the mechanical properties of the
In either process, the reagent is the isomeric mixture of
polymer.
the dinitrocompounds, 80% 2,4- and 20% 2,6-, so the
An example of a polyol with two hydroxyl groups (ie
product is a mixture of the diisocyanates in the same
a long chain diol) is one made from epoxypropane
proportions.
(Unit 46), by interaction with propane-1,2-diol, (which
It is expensive to produce this mixture in different
itself is formed from epoxypropane, by hydrolysis):
proportions. It means purifying the mixture of the nitromethylbenzenes, NMB, by very careful distillation. It is more fruitful to produce different properties in the polyurethanes by using different polyols which react with the 80:20 mixture of TDI to produce the polymers. MDI is more complex and permits the polyurethane manufacturer more process and product versatility. The mixture of diisocyanates is generally used to make rigid foams.
An example of a polyol which contains three hydroxyl
The starting materials are phenylamine (aniline)
groups is produced from propane-1,2,3-triol (glycerol)
and methanal (formaldehyde) (Unit 37) which react
and epoxypropane:
together to form a mixture of amines, known as MDA (methylenedianiline). This mixture reacts with carbonyl chloride (phosgene) to produce MDI in a similar way to the manufacture of TDI. MDI contains the following diisocyanates:
Figure 2 Isomers of MDI.
The term MDI refers to the mixture of the three isomers in Figure 2. They can be separated by distillation.
(b) Production of polyols The polyols used are either hydroxyl-terminated polyethers (in about 90% of total polyurethane manufacture) or hydroxyl-terminated polyesters. They have been developed to have the necessary reactivity with the isocyanate that will be used and to produce polyurethanes with specific properties.
206
Soya bean oil contains triglycerides of long chain saturated and unsaturated carboxylic acids, which, after hydrogenation, can, on reaction with epoxypropane, form a mixture of polyols suitable for the manufacture of a wide range of polyurethanes. The use of these biopols means that at least part of the polymer is derived from renewable sources.
Polyurethanes (c) Production of polyurethanes If the polyol has two hydroxyl groups and is mixed with either TDI or MDI, a linear polymer is produced (Unit 53). For example, a linear polyurethane is produced by reaction with a diisocyanate and the simplest diol, ethane-1,2-diol: nO C N
67
N C O + n HO CH2 CH2 OH
CH2
ethane-1,2-diol
4,4â&#x20AC;&#x2122;- MDI
O
O
C N
CH2
H
N C O CH2 CH2 O H
a polyurethane
n the urethane linkage
A much used polyurethane is made from TDI and a polyol
Figure 3 Broken limbs can now be encased in a polyester bandage, impregnated with a linear polyurethane. After the bandage has been wound around the limb, it is soaked in water, which produces cross-links between the polyurethane molecules, producing a strong but light cast.
derived from epoxypropane: Additives
If the polyol has more than two reactive hydroxyl groups, adjacent long-chain molecules become linked at intermediate points. These crosslinks create a stiffer polymer structure with improved mechanical characteristics which is exploited in the development of â&#x20AC;&#x2DC;rigidâ&#x20AC;&#x2122; polyurethanes. Thus a diisocyanate, such as MDI
Reasons for use
catalysts
to speed up the reaction between polyol and polyisocyanate
cross-linking and chain-extending agents
to modify the structure of the polyurethane molecules and to provide mechanical reinforcement to improve physical properties (for example, adding a polyisocyanate or polyol with more functional groups)
blowing agents
to create polyurethane as a foam
surfactants
to control the bubble formation during the reaction and, hence, the cell structure of the foam
pigments
to create coloured polyurethanes for identification and aesthetic reasons
fillers
to improve properties such as stiffness and to reduce overall costs
flame retardants
to reduce flammability of the end product
smoke suppressants
to reduce the rate at which smoke is generated if the polyurethane is burnt
plasticisers
to reduce the hardness of the product
Table 2 Additives used in the manufacture of polyurethanes.
or TDI which reacts with a polyol with three hydroxyl groups, such as one derived from propane-1,2,3-triol and epoxyethane, undergoes crosslinking and forms a rigid thermosetting polymer (Unit 53).
Manufacturing process As an example, consider the manufacture of a moulded item that might otherwise be made from a
As well as polyisocyanates and polyols, the manufacture
thermoplastic polymer by injection moulding. To make it
of polyurethanes needs a variety of other chemicals to
of polyurethane, it is necessary to mix exactly the right
control the polyurethane-forming reactions and to create
masses of the two major components (polyisocyanate
exactly the right properties in the end-product.
and polyol), which must be liquids. The reaction starts
All practical polyurethane systems include some, but not necessarily all, of those described in Table 2.
immediately and gives the solid polymer. Depending on the formulation, the catalysts used and the application,
207
Polyurethanes the reaction is typically completed in between a few
polymer, and the available gas pressure cannot create
seconds and some minutes. In this time, therefore, it
any further expansion.
is essential to dispense the reacting liquid mixture into
A shoe sole, for example, may be ‘blown’ to double the
the mould and also to clean the combined ‘mixing and dispensing’ equipment ready for the next operation. The exothermic chemical reaction is completed within the
67
mould and the manufactured article can be taken from the mould immediately.
Foamed polyurethanes When the two liquids react, a solid polymer is formed.
volume of solid polymer. This process is so versatile that the expansion can be taken much further. In low-density foams for upholstery or thermal insulation less than 3% of the total volume is polyurethane. The gas has expanded the original volume occupied by the liquid by 30 to 40 times. In the case of cushions, only just enough solid polymer is needed to ensure that we can sit comfortably.
The polymer may be elastic or rigid. However, it may
In thermal insulation, it is the gas trapped in the cells
also contain bubbles of gas so that it is cellular - a foam.
which insulates. The polymer that encloses the cells
When producing a foamed polyurethane, there are two possible ways to generate a gas inside the reacting liquid mixture. The so called chemical blowing uses water that may have been added to the polyol which reacts with some of the polyisocyanate to create carbon dioxide:
reduces the insulation efficiency, so it makes sense to have as little of it as possible.
Adhesion In the final stages of the polyurethane-forming reaction, the mixture becomes a gel with very effective surface adhesion. Hence polyurethanes can be
Alternatively (physical blowing), a liquid with a low boiling point, for example pentane, is mixed into the polyol. The reaction is exothermic and so, as it proceeds, the mixture warms up and the pentane vaporizes. A tiny amount of air is dispersed through the mixture of polyisocyanate and polyol. This provides nucleation seeds for the multitude of gas bubbles that are produced throughout the polymer. Heat makes the bubbles expand until the chemical reaction changes the liquid to solid
used as adhesives. Equally important is the fact that polyurethanes, which are being created as, for example, cushioning or insulation materials, can be bonded to surface materials without the introduction of separate adhesives. Flexible foam and fabric can create a composite cushion or rigid foam and sheet building materials (e.g. plasterboard, steel sheet, plywood) can provide composite building insulation panels.
Figure 4 During manufacture, the chair’s textile cover is filled with a mixture of reactants which produce the polyurethane foam. The chair is given its individual shape by filling out the seat surface with the foam as a life-size doll sits in the chair.
208
Silicones
S
ilicones have unique properties amongst polymers because of the simultaneous presence of organic groups attached to a chain of inorganic atoms. They are used in many industries including those devoted to electronics, paints, construction and food.
68
Structures and properties of silicones Silicones are synthetic polymers with a silicon-oxygen
The most widely used silicones are those which have
backbone similar to that in silicon dioxide (silica), but
methyl groups along the backbone. Properties such
with organic groups attached to the silicon atoms by C-Si
as solubility in organic solvents, water-repellence and
bonds. The silicone chain exposes organic groups to the
flexibility can be altered by substituting other organic
outside.
groups for the methyls. For example, silicones with R
phenyl groups are more flexible polymers than those with
R O
methyl groups. They are also better lubricants and are
O
Si
Si
R
R
superior solvents for organic compounds. The structure of the repeating units of silicones can be represented as:
Thus, despite having a very polar chain, the physical
R
properties of silicones are similar to those of an alkane.
Si
However, the -Si-O-framework of the silicone gives the
R
R O
Si
O
R
polymers thermal stability, as in silica, and so they can be used where comparable organic materials would melt
Where R represents organic groups attached to the
or decompose.
silicone backbone, for example:
To distinguish between different silicones, systematic names are used, based on the monomer. The simplest CH3
silicon compound is silane, SiH4 which belongs to the homologous series of silanes. Silanes correspond to the alkanes whose simplest member is methane, CH4. H Si
H
H H
H silane
H
C
methyl
HC phenyl
CH2 CH2CH2CF3
ethenyl
trifuoropropyl
Uses Silicones can be sub-divided into four classes:
H
a) Silicone fluids
H methane
b) Silicone gels c) Silicone elastomers (rubbers)
The presence of the oxygen atoms in the silicone chain
d) Silicone resins
is indicated by using the systematic name, siloxane, so
Their physical form and uses depend on the structure of
termed as it contains a silicon atom, an oxygen atom
the polymer.
and it is saturated as in an alkane.
(a) Silicone fluids are typically straight chains of
Thus if the groups attached
poly(dimethylsiloxane), with the repeating structure:
to the siloxane chain are phenyl groups, the resulting silicone is called poly(diphenylsiloxane) and has repeating units along the
CH3 O
Si
O
Si CH3
chain.
209
Silicones They usually have trimethylsilyl groups, Si(CH3)3, at each end of the chain: CH3 H3C
Si
CH3 O
CH3
68
CH3
Si CH3
O n
Si
CH3
CH3
poly(dimethyl)siloxane
The silicones with short chains are fluids which, compared to hydrocarbons, have a more or less constant viscosity over a wide temperature range (200 to 450 K). They also have very low vapour pressures. The low surface tension of silicone fluids gives them unique surface properties. They are, for example, used as lubricants in polishes (a mixture of wax and a silicone fluid dissolved in an organic solvent), in paints (Unit 17) and for water-proofing fabrics, paper and leather. They also have anti-foaming properties and have been used, for example, to suppress the foaming of detergents in sewage disposal plants. They have a low enthalpy of vaporization and a smooth, silky feel and thus are attractive as a basis for personal care products such as perspirants and skin care lotions. A range of fluids is made by mixing polysiloxanes of low molecular masses with others with higher molecular masses. Some use the cyclic silicones which are formed during the preparation of the linear polysiloxanes. (b) Silicone gels are based on the poly(dimethylsiloxane) chains but with a few crosslinks between the chains, giving it a very open threedimensional network. Often the cross-linking is done after a silicone fluid, together with a reactive group, is poured into a mould and then warmed or catalysed so that there is interaction to form cross-linking between the polymer chains. This is a very effective technique for protecting sensitive electronic equipment from damage from vibration and the polymer also acts as an electrical insulator. Pads containing a silicone gel are also used as shock absorbers in shoes, particularly in highperformance trainers and running shoes. (c) Silicone elastomers (rubbers) are made by introducing even more cross-linking into the linear chain polymers. The structure is somewhat similar to natural rubber and they behave as elastomers (Unit 53). Their structure is determined by the amount of cross linking and the length of the chains.
210
Figure 1 These silicone elastomer particles are used in skin creams. Their small and perfectly spherical shape combined with a rubbery texture improves the feel of the cream as it is applied to the skin.
Although their strength at normal temperatures is inferior to that of natural rubber, silicone rubbers are more stable at both low temperatures (200 K) and high temperatures (450-600 K) and are generally more resistant to chemical attack. Silica is added as a filler (Unit 53) to make the elastomer stronger. (d) Silicone resins have a three-dimensional structure with the atoms arranged tetrahedrally about the silicon atoms. The resins are usually applied as a solution in an organic solvent, and are used as an electrical insulating varnish or for paints where water repellence is desired, for example, to protect masonry. They are also used to give an ‘anti-stick’ surface to materials coming into contact with ‘sticky’ materials such as dough and other foodstuffs. Hydroxyl groups on the resin react with hydroxyl groups that are on the surfaces of various inorganic surfaces such as silica and glass, thus making the surface waterrepellent. A large range of silanes, known as coupling agents, has been developed to enable chemists to bond an inorganic substrate (such as glass, minerals and metals) to organic materials (for example, organic polymers such as the acrylics, polyamides, urethanes and polyalkenes). The resulting coatings confer the surface properties of a silicone to a very wide range of materials. Similar mechanisms enable some resins to be used as adhesives.
Silicones Manufacture
The product is a disilanol. The suffix -ol in a silanol is to
Silicones are manufactured from pure silicon which has been obtained by the reduction of silicon dioxide (silica) in the form of sand with carbon at high temperatures: SiO2(s) + 2C(s)
show that the molecule contains at least one hydroxyl group attached to a silicon atom and the simplest example is dimethyldisilanol: CH3
Si(s) + 2CO(g) HO
The production of silicones from silicon takes place in
Si
68
OH
CH3
three stages:
dimethyldisilanol
a) synthesis of chlorosilanes b) hydrolysis of chlorosilanes
This nomenclature is similar to that of the alcohols,
c) condensation polymerization (Unit 53)
the simplest alcohol with two hydroxyl groups being ethane-1,2-diol:
(a) Synthesis of chlorosilanes Silicon is first converted into chlorosilanes, e.g. RSiCl3,
HO CH2 CH2
R2SiCl2 and R3SiCl, where R is an organic group. When chloromethane is passed through heated silicon at about 550 K under slight pressure and in the presence of a copper catalyst (often copper itself but other coppercontaining materials can be used, for example, brass or
OH
ethane-1,2-diol
The hydroxyl groups of silanols react spontaneously to form a siloxane:
copper(II) chloride), a volatile mixture of chlorosilanes distils over. For example:
R n HO
Si(s) + 2CH3Cl(g)
(CH3)2SiCl2(g)
The mixture of liquids contains these three compounds: CH3 Cl
Si
CH3 Cl
Cl
Si
Cl
Si
OH
HO
R
Si
O
R
H
+ (n-1)H2O
n
If R is a methyl group, the polymer is a poly(dimethylsiloxane).
CH3 Cl
Si
R
CH3
Cl
CH3
CH3
CH3SiCl3
(CH3)2SiCl2
(CH3)3SiCl
Poly(dimethylsiloxanes) are produced with n = 20-50, which is not long enough to produce useful silicones. These relatively short polymers are known as oligomers (Unit 53). Cyclic polymers, for example ((CH3)2SiO)4, are also produced and then separated out.
Careful distillation of the liquid mixture of chlorosilanes
H3C
produces pure fractions of each chlorosilane.
H3C Si
Dimethyldichlorosilane is the main product (ca 70-90%,
H3C Si
(b) Hydrolysis of chlorosilanes hydroxyl groups:
Si R
R Cl + 2H2O
O
O
Si CH3 CH3
The oligomers are washed and dried. The hydrochloric acid is recycled and reacts with methanol to regenerate
R Cl
H3C
CH3 Si CH3
O
the amount depending on the conditions used).
A dichlorosilane is hydrolysed to a molecule with two
O
HO
Si
chloromethane: OH + 2HCl
CH3OH + HCl
CH3Cl + H2O
R
211
Silicones (c) Condensation polymerization
(ii) Cross-linking can also be achieved by using
The oligomers condense rapidly in the presence of an acid catalyst to form long chain polymers: CH3 HO
68
Si CH3
H
+
HO
Si
O
H
CH3
m
CH3 Si
n
Si
CH
CH2 + H
Si
CH3
CH3 HO
containing Si-H groups, with a platinum compound as catalyst:
CH3 O
siloxanes with ethenyl (vinyl) groups and other siloxanes
O
CH3
H
+ H2O
m+n
CH3
and so on...
Si
These materials are silicone fluids.
CH2
CH2
Si
CH3
The value of (m+n) is usually between 2000 and 4000. The production of longer chains is favoured if the water is removed, for example by working under vacuum. To form silicone gels, elastomers and resins, the long siloxane chains are induced to cross-link. There are four main ways of doing this:
(iii) A further way of producing cross-linking is to have an ethanoyl group in the silane. When these silicones are exposed to the air, the moisture reacts with the functional group, yielding a cross-linked silicone. An organometallic tin compound catalyses the reaction. These systems are often used as sealants and can be used in the home.
(i) Cross-linking is often effected by first synthesizing silanes
The other product formed is ethanoic acid which can be
with a functional group, in place of a methyl group, that will
recognized by its vinegary smell.
react further. For example, a silane containing an ethenyl (vinyl) group such as ethenylmethyldichlorosilane, can be added to, for example, dimethyldichlorosilane. However with ethenyl groups in the chain, the chains are also able to undergo free radical addition reactions, in a similar way
(iv) If some methyltrichlorosilane is added to the reactant, say dimethyldichlorosilane, the three chlorine atoms are hydrolysed, thus producing a three dimensional network.
to the free radical polymerization of chloroethene (Units 53 and 58). This leads to cross-linking between the polymer chains. As with this polymerization, the addition reactions are initiated by radicals supplied on decomposition of an organic peroxide (for example, dicumyl peroxide): R
O
O
2 RO .
R CH3
where R =
C CH3
Figure 2 Silicones played an important part in the construction of the London Eye, the largest observation wheel in the world. For example, the windows of the capsules are made of reinforced glass (using poly vinyl butyral, PVB (Unit 54) as the laminate) which is anchored to the metal frame with a silicone resin. This resin is prepared in situ from two components one of which is a silicone with alkoxy groups which provide the cross-linking needed to form the resin. The result is that the capsule can withstand winds of 280 -1 km h . These systems are also being used in buildings which are considered to be vulnerable to terrorist attacks, the glass, resistant to bomb blasts and bullets, will keep in place because of the very strong bonding to the metal frames.
212
In all four methods, the physical properties of the silicone can be modified by varying the proportions of the reactants, which controls the extent of cross-linking and hence how rubbery is the product.
Steel
S
teel is one of the most widely used materials, particularly in construction and engineering and in the manufacture of cars. It is estimated that there are over 20 billion tonnes of steel in use, equivalent to well over 2 tonnes for every person on Earth. Steels are alloys of iron, carbon and other metals and non-metals. The composition of the steel is adjusted so that it has the precise properties needed.
74
The term alloy steel is confined to steels containing some combination of one or more of the following elements: nickel, chromium, tungsten, molybdenum, vanadium, manganese, cobalt, copper, niobium, zirconium, selenium and lead. Steels can be repeatedly recycled without any loss of performance.
Uses The construction industry is a main user of steel, from small buildings to huge bridges, and uses it in multiple ways, even within a single construction. A bridge, for example, might use steel in the huge suspension ropes, the steel plate flooring for the road, the beams for the columns, and for the safety barriers and lighting columns. Much steel is also used to reinforce concrete (Unit 12).
Figure 3 Uses of steel in the UK.
Chromium increases the corrosion resistance of steel, and a minimum of 12% chromium is necessary to produce a stainless steel. The best known of the stainless steels contains about 74% iron, 18% chromium and 8% nickel (known as 18-8 stainless). Stainless steel is perhaps most familiar as kitchenware (sinks, kettles and cutlery).
Figures 1 and 2 Both these structures used about 45 000 tonnes of steel in their construction. Figure 1 is the barrier across the River Thames, to protect London from flooding. It is a system of stainless steel plated hollow flood gates. Figure 2 is the interwoven structure of the Olympic Stadium in Beijing made of steel plate. Unwrapped, the strands of the â&#x20AC;&#x2DC;Birdâ&#x20AC;&#x2122;s Nestâ&#x20AC;&#x2122; would stretch for 36 km.
229
Steel Steels containing molybdenum, vanadium, chromium and tungsten in various combinations produce very hard, if brittle, steels. These are used, for example, in drill bits which need to retain a cutting edge. Steels are used widely in the manufacture of electrical motors, power
74
generators (nuclear, conventional fuels and wind), gears and engines, which have to be very tough and withstand high temperatures.
Figure 5 The container ship and the containers are both constructed from steel plate.
Manufacture There are two main processes used to make steel. The Basic Oxygen Steelmaking Process, which is used for the majority of steel production, uses iron freshly produced from the blast furnace (Unit 71) together with some scrap steel. The Electric Arc Furnace Process uses scrap steel only.
The Basic Oxygen Steelmaking Process Figure 4 A wind turbine constructed from steel.
Steels with cobalt are used as magnets and those with nickel are used in the construction of nuclear reactors. There is a group of steels known as Advanced High Strength Steels, AHSS, which are specially treated steels that can be rolled very thin without losing the element of strength needed for the specific purpose. They are particularly useful in the manufacture of cars, helping to reduce the overall mass and thus decrease fuel consumption. Steels with a thin coating of tin are used to make cans for beverages and food. Steels coated in various ways with zinc are used in roofing, for example, and in cars as the zinc gives protection against rusting (Unit 76).
Annual production UK
Europe World
14 million tonnes
227 million tonnes 1360 million tonnes
Steel production in Asia has expanded rapidly, with China now accounting for nearly 40% of world production.
230
Figure 6 IIllustrating the Basic Oxygen Steelmaking (BOS) Process. The process uses modern furnaces lined with special bricks containing 90% magnesium oxide and 10% carbon. These can take up to 350 tonnes of reactants and convert them to steel in less than 40 minutes.
The furnace (also known as a converter or vessel) is charged with steel scrap (up to about 30%) and molten
Steel iron from a ladle. An oxygen lance, cooled by circulating
furnace. An arc is struck by passing an electric current
water, is lowered into the furnace and high purity oxygen
through the metal. The heat generated melts the scrap
is injected into the vessel at twice the speed of sound
metal. Lime (as calcium oxide or calcium carbonate),
which ensures that all the impurities are converted into
fluorspar (which helps to keep the hot slag as a fluid) and
their oxides. The main chemical reactions are:
iron ore are added and these combine with impurities to form a slag. When the steel has reached the correct composition the slag is poured off and the steel tapped from the furnace.
74
With the exception of the carbon monoxide, the products react with lime, added during the oxygen blow, to form a slag. The above reactions are all exothermic and controlled quantities of scrap are added as a coolant to maintain the desired temperature. The steel at this stage contains ca 0.04% carbon.
The Electric Arc Furnace Process Steel scrap is first tipped from an overhead crane into a furnace. The scrap comes from three sources: • Home scrap: excess material from steel works and foundries. • Industrial scrap: from processes using steel (such as excess steel from making a car). • Obsolete scrap: discarded used products (for example, used cans).
Figure 8 The liquid steel is tapped (poured) into a ladle and the slag is tapped into a separate ‘slag pot’. This photo shows a later stage when the molten slag is poured from the slag pot. The slag is treated so that any iron left is recovered and the residue is then used as an aggregate.
The furnace is a circular bath with a movable roof through
Secondary steelmaking The term secondary production is often used when referring to recycling (Unit 74). However, in steelmaking the term secondary steelmaking refers to the production of steels which are needed for specific purposes and which require the addition of very carefully controlled quantities of other elements. Molten steel from either process is transferred to a ladle where the alloying elements are added. Figure 7 Illustrating the Electric Arc Process which uses scrap steel to produce pure steel very efficiently.
The process provides precise control of harmful impurities (particularly sulfur, phosphorus and, in some cases, trace metals and hydrogen) by adding materials
which three graphite electrodes are raised or lowered.
via ladle injection. For example, aluminium and silicon
These electrodes are massive, often 6 m high and 4 m
are added to reduce any oxidised material.
wide, and the furnace can hold over 100 tonnes of liquid
Other techniques used to help to improve the quality
steel.
of the steel include stirring (ladle stirring) and applying
After the steel scrap is placed in the furnace, the roof
a vacuum to the steel to remove gases (vacuum
is put into position and the electrodes lowered into the
degassing).
231
Steel Casting Steel is produced in three forms, the form chosen being
sheet, used for example in the manufacture of cars.
dependent on its ultimate use:
Blooms and billets are used to roll long bars of steel for
• as a slab, a long thick piece of metal with a rectangular cross-section
74
of ships. The sheet is rolled further to produce thinner
• as a bloom, a long piece of metal with a square crosssection • as a billet, similar to a bloom but with a smaller crosssection. Most steel is continuously cast to the desired shape, but a small quantity (ca 10-20%) is first cast into ingots which are cooled and then worked on to produce the shape
construction and for drawing into wires. Often there are three stages to this part of the process, hot rolling, cold rolling and drawing. Hot rolling occurs when the slabs, blooms and billets are heated in a furnace until they are red hot (ca 1400 K) and then rolled until they have acquired the desired shape. The speed at which the hot steel is subsequently cooled is a crucial factor, affecting the strength and other properties of the steel. Cooling is done by spraying water
required.
as the steel passes through the rollers.
The casting is a very precise set of processes. The
During this rolling, oxygen in the air has reacted with
following descriptions are an outline.
the hot iron to form a very thin layer of iron(III) oxide
Continuous casting
thicker does it appear red). This must be stripped from
on the surface. It is blue/grey in colour (only when it is
In continuous casting, the steel, still molten from the
the surface prior to the next stage, otherwise the final
furnace, is poured into a water-cooled mould (teeming)
product will be susceptible to rusting and unsuitable
from which it emerges as a strand which is solidifying
for galvanizing with zinc (Unit 76) and other surface
at the surface. The strand passes through a series of
treatments.
rollers which are water sprayed to produce a solid (a
The stripping process is known as pickling. The steel
slab, bloom or billet) which is then sent to be hot rolled.
is passed through several baths of hydrochloric acid (sometimes sulfuric acid) which dissolves the oxide without attacking the metal (Unit 33). The spent acid is recycled (Unit 7). The ‘pickled’ steel is then subjected to cold rolling. As the name implies, the steel, following hot rolling, is rolled cold and gradually compressed to the required thickness. This improves the quality of the surface and also hardens the steel. On annealing (heating the strip very carefully), it can be pressed into shapes without cracking. Such sheet is used, for example, to press out car bodies. Steel
Figure 9 Steel tube is being produced in a continuous casting process.
Ingot casting
entity, needing only the top to be fitted after filling. Very strong wires are produced by cold drawing.
Molten steel is poured into a cast iron mould to solidify as
Recycling
an ingot. This generally weighs less than 20 tonnes but
The recovery of scrap steel probably constitutes the
rotor forgings can weigh up to 500 tonnes.
world’s largest scale recycling process. The scrap is
When the ingot has solidified, the mould is removed.
either part of the charge for the Basic Oxygen Process
Each ingot is of carefully pre-arranged dimensions and
or is the complete charge for the Electric Arc Furnace
mass from which articles of the required size can be
Process.
rolled.
About 40% of the iron-containing materials used in
Rolling Steel products are classified into flat products and long products. Slabs of steel are rolled to produce flat products, for example steel sheet for the construction
232
cans are pressed out with sides and bottoms as a single
steel production are now from recycled sources. It is estimated that recycling one tonne of steel saves 1.1 tonnes of iron ore, 0.6 tonnes of coal and 0.5 tonnes of limestone, with an overall energy saving of 60-75%.
Index
A
2-Aminoethanoic acid 2-Aminoethanol
ABE process ABS
Aminopyralid
48, 52
Ammonium carbamate
Acephate 73 Acetamiprid
Ammonium chloride
75
Acetyl-CoA-carboxylase, inhibitors of
72
59-60 90-91, 200-201
Acrylics - see polypropenoates, poly(methyl propenoate) and poly(propenonitrile) Acrylonitrile - see propenonitrile Adipic acid - see hexanedioic acid Advanced High Strength Steel
230
Agrochemicals – see crop protection chemicals Alcohols, long chain Aldicarb
Alkylaluminium
96-97
99, 101 97, 101
97
Alkyl sulfates
145, 213, 237, 240
Alloys, aluminium
213, 220, 238, 239, 240
Alloys, copper Alloys, iron
152, 220, 229-232, 234
Alloys, lead
229, 238
Alloys, magnesium
213, 227, 240
Alloys, manganese
213, 220
Alloys, nickel
220
Alloys, phosphorus Alloys, platinum Alloys, silicon Alloys, steel Alloys, tin
220
13, 67
Alloys, rhodium
13, 67
229 220
Alloys, zinc
233-236, 237
213, 220, 237, 238, 240
Altuglas - see poly(methyl 2-methylpropenoate) Alumina - see aluminium oxide Aluminium
213-215, 227, 233
Aluminiumalkyl - see alkylaluminum Aluminium bronze
220
Aluminium chloride
96
Aluminium fluoride
213, 214
Aluminium hydroxide Aluminium oxide
Amyloses
173
Anastase
163
Aniline
213-214
14, 213-214
98, 101
45, 173 45
147
131 58-59
Anthraquinone dyes Antifreeze
134
96-98
Anionic surfactants
120
Apatite - see phosphate rock Aramid reinforced polymer composites – see composites, aramid reinforced polymer 67
Aramids Argon
143, 146, 235
Asahi process
178
Atactic poly(propene) Auxins
195-196
36-37
Atom economy 70
57
Auxochromes
74
Avermectins Azeotrope
45-46, 122-123, 141
Azobenzene
58
58
Azo dyes
Azoxystrobin
B
213
Alloys, titanium
Amylases
Anthraquinone
Alkylbenzene sulfonates Alkyl ether sulfates
41, 81, 161, 192
Amphoteric surfactants
96, 97
18, 96, 97, 196
Alkyl betaines
Ammonium sulfate
Anion exchange resin
91-92, 94
Alkyd resins
150 157
81, 82
97, 98
73
Alkenes, long chain
Ammonium nitrate
Amyloglucoside
167
Addition polymers
Ammonium hydrogencarbonate
Ammonium phosphates - see also ammonium dihydrogenphosphate and diammonium hydrogenphosphate
Acrylic acid - see propenoic acid Acrylic resins
165
238
Ammonium dihydrogenphosphate
Acetic acid - see ethanoic acid Acid dyes
70
11, 12, 13, 40, 102-105, 141, 157, 165, 201
Ammonia
168, 169, 180, 192, 200
152
119, 146, 160
Bagasse
78
50 60-61
Basic dyes
Basic Oxygen Steelmaking Process
234-235
Batch reactors – see reactors, batch Battery, dry cell Bauxite
238
213
Beckmann rearrangement Bendiocarb Bensultap Benzene
179
73 75 15, 26, 28, 29, 96, 106-107, 147,178
Benzenediazonium chloride
58
Benzene-1,2-dicarboxylic acid
91
Aluminiumtriethyl - see triethylaluminium
Benzene-1,4-dicarboxylic acid
184, 185, 186
Aluminosilicates - see zeolites
Benzophenylureas
Aluminium phosphide
Amino acids
32-33
153
Betaines
76
99, 101
241
index
Binders
90-92
Biobrom
108
Calcium iodate
16-17
Bifunctional catalysts
Calcium phosphide Calcium sulfate
48
Biobutanol
46-47
Biodiesel
44-46, 47
Bioethanol
44-49
Biofuels
Bioleaching, copper Bioleaching, zinc
218
Biopol
Bisphenol A Bixafen
Carbon fibres
11, 36, 92, 154, 181
78
219
Bordeaux mixture
78
Cartap Cast iron
78
220, 238
Bronze BTX
108 220
Buta-1,3-diene
84
26, 29, 109, 175, 200
172
Butyl propenoate
139
12-13, 104
Catalysis, manufacture of benzene
107
Catalysis, manufacture of buta-1,3-diene Catalysis, manufacture of butanal
90, 192, 198
109
155
Caesium sulphate
147
Catalysis, manufacture of cyclohexane
178
Catalysis, manufacture of cyclohexanol
178 178, 179
Catalysis, manufacture of 1,2-dichloroethane
183
Catalysis, manufacture of dimethylbenzene-1,4-dioate Catalysis, manufacture of dimethyl ether Catalysis, manufacture of epoxyethane
162
Catalysis, manufacture of ethanoic acid
236
Calcium ammonium nitrate Calcium bromide
110-113, 156, 218, 222, 223, 231 157
Calcium dihydrogenphosphate Calcium fluoride Calcium hydroxide
118, 139 120 120
14, 122
Catalysis, manufacture of ethanol from synthesis gas
108
Calcium carbonate Calcium chloride
Catalysis, manufacture of ethanol
81
81, 149, 150
130 78, 110, 113, 157, 231
Catalysis, manufacture of ethenyl ethanoate Catalysis, manufacture of ethylbenzene
48
90
193
Catalysis, manufacture of ethyl t-butyl ether
139
Catalysis, manufacture of hexanedioic acid
179
Catalysis, manufacture of hydrogen
185
181
137
Catalysis, manufacture of ethane-1,2-diol
227
202
211
Catalysis, manufacture of dimethyl carbonate 238, 239, 240
186
46, 47-48
Catalysis, manufacture of cyclohexanone
Butyl rubber - see poly(2-methylpropene)
242
96
Catalysis, manufacture of ammonia
Catalysis, manufacture of cumene
48, 155
t-Butyl hydroperoxide
Calcium
48, 80
28-29
Catalysis, manufacture of chlorosilanes
Butyl acrylate - see butyl propenoate
Calcining
Catalysis, isomerisation
Catalysis, manufacture of chlorodifluoromethane
155
Butane-1,4-diol
Cadmium
Catalysis, hydrogenation of oils
Catalysis, manufacture of biodiesel
Butadiene - see buta-1,3-diene
C
11-19
Catalysis, manufacture of benzene-1,4-dicarboxylic acid
Buckmasterfullerene
Butanol
221
Catalysis, manufacture of alkylbenzenes
106
Butanal
74
Catalysis, cracking- see cracking, catalytic
104
Brine - see sodium chloride Bromine
53
79-80
Catalysis, bifunctional - see bifunctional catalysts
BOS Process â&#x20AC;&#x201C; see Basic Oxygen Steelmaking Process Brass
36, 181, 205, 206
78
Catalysis - see also zeolites
217
Bosch, Carl
Carbonyl chloride
47
66, 84, 87, 88, 135
Carboxylic acids, long chain
168
Boscalid
145
3-Carboxy-3-hydroxypentanoic acid
82
Block co-polymer Bornite
Carbon nanotubes Carboxamides
225-226
Blister copper
66
Carbon monoxide - see also synthesis gas
199
Blended fertilizer
157
Carbon molecular sieve
70
Blast Furnace
68
Carbon fibre reinforced polymer composites â&#x20AC;&#x201C; see composites, carbon fibre reinforced polymer
52-55
Bismuth(III) oxide
175-176
68
Carbon dioxide
50-51
Bipyridyliums
174
Carbon black
206
Biotechnology
42, 179
Caprolactone
Carbides
48, 51
Biorefineries
171
Caprolactam
Carbamide - methanal plastics
172
Biopols
Calendering
Carbamide - see urea
239
48, 51
Biophotolysis
153
111, 130, 149
Carbamates - see methyl carbamates
Biomass - see biofuels Bio-oil
177 110-113, 157, 223, 227, 231
Calcium oxide
103, 126
Catalysis, manufacture of hydrogen peroxide
131-132
index Catalysis, manufacture of long chain alkenes Catalysis, manufacture of methanal
135
Catalysis, manufacture of methanol
137
96, 97
Catalysis, manufacture of methyl 2-methylpropenoate Catalysis, manufacture of 2-methylpropene
Citric acid - see 3-carboxy-3-hydroxypentanoic acid 192
139
Catalysis, manufacture of methyl propenoate Catalysis, manufacture of PET
199
Clothianidin
140-141
Coal gas Cobalt
190
Catalysis, manufacture of polycarbonates Catalysis, manufacture of poly(ethene) Catalysis, manufacture of propan-2-ol
Coke
Catalysis, manufacture of silicones
56-64
Composites
199 196-197, 201
212
Catalysis, manufacture of sulfuric acid
174
151, 221, 222
Complex fertilizer
199
Catalysis, manufacture of propenonitrile
221
Colour Index International
139
Catalysis, manufacture of propenoic acid
75
68, 229, 230, 239
Colorants
196-197
48
48
Cobalt octadecanoate
181
188-190
Catalysis, manufacture of poly(propene) Catalysis, manufacture of propenal
Clostridium acetobutylicum Clostridium ljungdahii
185
Catalysis, manufacture of phenylethene
57
Chromophores 138
188
57
Chromogens
Catalysis, manufacture of methyl t-butyl ether
Catalysis, manufacture of nitric acid
Chromium(VI) oxide
57
82
65-68, 135
65-66
Catalysis, manufacture of sulfur trioxide
162, 196-197
Composites, glass fibre reinforced polymer
Catalysis, manufacture of synthesis gas
103
Composites, nanomaterials
Catalysis, manufacture of trichloromethane
202
Catalysis, manufacture of 2,2,4-trimethylpentane 129-130 Catalysis, manufacture of waxes Catalysis, metallocenes
190
Catalysis, nanoparticles
86
17-18, 29,
51
Catalysis, reforming - see reforming, catalytic Catalysis, Ziegler-Natta catalysts - see Ziegler-Natta catalysts 11-12, 86
Cathode, oxygen depleting Cation exchange resin
Cellulose enzymes
121 86
85
11-12 75
Chlorine 108, 109, 114-117, 128, 152, 158-9, 181, 182, 183, 202, 228, 235 2-Chlorobuta-1,3-diene
109
Chlorodifluoromethane
129, 202-203 92, 114
Chloroethane
183
Chloroethene
19, 41, 182-183
Chlorofluorocarbons
129, 202
Chloroform - see trichloromethane Chloroprene - see 2-chlorobuta-1,3-diene 92
Chlorosilanes
211
Chlorothalonil
78
229, 230, 233
197
181, 218
218 88
Copper(I) sulfide
218
Copper(II) sulfate
78, 219
11, 15, 26-29, 106
Cracking, steam
11, 15, 28 26- 28, 106
Crop protection chemicals Cryolite
1-Chloro-2,3-epoxypropane
197
216-220, 239
Cracking, catalytic
Chlorantaniliprole
120
168, 197
Copper(I) oxide
217
Chemical vapour deposition
Chromium
Coolant for engines
Cracking
3-Chloropropene
65
Continuous reactors - see reactors, continuous
Copper matte
217
Chemisorption
Continuous phase
Copper(II) chloride
68
Chalcopyrite
167
16, 162
Contact process
Copper
68, 111, 223
Chalcocite
68, 111, 229
Condensation polymers
Co-polymers, of propene
Cerium(IV) oxide, nanoparticles Cermet
68
82
Co-polymers, of ethene
47
Cellulose ethanoate Cement
117
154
120
Cativa process
Concrete
Co-polymers
98, 101
Cationic surfactants
86-87
Composites, particle reinforced Compound fertilizer
67
Constant boiling mixture - see azeotrope
Catalysis, Phillips catalysts - see Phillips-type catalysts
Catalytic converters
66-67
Composites, carbon fibre reinforced polymer Composites, fibre reinforced polymer
162
67-68
Composites, aramid reinforced polymer
69-78
213, 214
CSTR - see reactors, continuous stirred tank Cumene
15, 147-148, 154
Cumene hydroperoxide Cupronickel Curing
D
148
220
179
Dacron - see polyesters Dealkylation
15, 107
Decabromodiphenyl ethane Decabromodiphenyl ether Degradable plastics Deltamethrin
108 108
172-174
76
243
index Depreciation
7-8
Epoxypropane
99-101
Detergents
Diakon - see poly(methyl 2-methylpropenoate) Diamides
75-76 43, 109
Diaphragm cells
150
115-117
12, 104
73 79
Ester interchange - see transesterification 98
Esterquats
213
ETFE - see ethylene tetrafluoroethylene
1,2-Dichloroethane
41, 182, 183
Ethanal
172, 173
1,1-Dichloroethene
200, 201
Ethane
27, 28, 29, 31, 183
Dichlorophenols
147
Dichroism
70
64
17, 38, 121
Ethanoic acid
Ethanoic anhydride Ethanol
Diethylene glycol
Ethanolamines
118-119
Diethylene glycol monoether Diflubenzuron
119
1,1-Difluoroethene
1,6-Diisocyanotohexane
Ethenylmethyldichlorosilane Ethenyl sulfones
81
Ethyl acrylate - see ethyl propenoate
15, 107
1,3-Dimethylbenzene
15, 107
1,4-Dimethylbenzene
15, 107, 186
2-Ethylanthraquinol
36-37, 181
211
Dimethyl terephthalate - see polyesters 2,4-Dinitrobenzene
205
2,6-Dinitrobenzene
205
Diphenyl carbonate
36-37, 181
Diphenylmethane diisocyanate - see MDI 60
Disodium pyrophosphate
150
Dispersed phase
30-33, 122
Distillation, of air
144, 145, 146
Distillation, of oil
30-33
Disulfoton
Duralumin Dyes
E
78
Extrusion
171
F
82
46 48, 51
94 79-80
Fatty acid methyl ester process Ferrophosphorus Ferrosilicon
46
44-46, 50-51, 52-55, 172
Fermentation
152
227 234
81-82, 102, 140, 149, 150, 165
Fibreglass
213
236
67
Fibre reinforced polymer composites - see composites, fibre reinforced polymer 169-170
Fibres
65, 111, 171
Filler
169
Electric arc furnace Emamectin benzoate
Fipronil
231, 240
Electric Arc Furnace Process Epoxyconazole
90, 192, 198
FFC Cambridge process
56-63, 64
Epoxyethane
171
Fertilizers
227
Elastomers
Extender
Ferrotitanium
73
Dithiocarbamates Dolomite
107, 125
203 31
Ethylene - see ethene
Fats, edible
Disproportionation, methylbenzene Distillation
Ethyl propenoate
Fats
107
Disproportionation
Ethyl 2-hydroxypropanoate
Fast pyrolysis
65
119
118-119
Ethylene tetrafluoroethylene
FAME process
150
61
Disperse dyes
Ethylene glycol - see ethane-1,2-diol
Eutrophication
Disodium hydrogenphosphate
139
Ethyl t-butyl ether
Ethylene glycols
1,1-Dimethylethyl hydroperoxide - see t-butyl hydroperoxide Dimethylsilanol
131
Ethylene glycol monoether
211
137
Dimethyl ether
132
2-Ethylanthraquinone
Dimethyl benzene-1,4-dimethylcarboxylate â&#x20AC;&#x201C; see polyesters Dimethyldichlorosilane
212
61-62
2-Ethoxy-2-methylpropane - see ethyl t-butyl ether
91
1,2-Dimethylbenzene
Dimethyl carbonate
90, 120, 200, 201
Ethenyl ethanoate
129
129
Dihydrogenphosphate ion
119
14, 19, 41, 90, 118, 122, 123, 124, 182, 183, 188, 192,
Ethene 203
76
2,4-Difluoroaminobenzene
121
14, 44-46, 122-123
Diethanolamine - see 2,2´-iminodiethanol
Direct dyes
17, 42, 118, 120, 184, 185, 186, 207
Ethane-1,2-diol
2,4-Dichlorophenoxyethanoic acid
244
Ertl, Gerhard
Essential fatty acids
Diammonium hydrogenphosphate Diaspore
92
Eserin
1,6-Diaminohexane
139, 155, 173, 206
Epoxy resins
231
74
77 17, 40, 97, 98, 118-119, 120
74
Fischer-Tropsch process Fixed costs Fluorine
47-48, 51
7
125, 129
2-Fluoroaminobenzene
129
index Fluoroanhydrite
130
Hexanedioic acid
172, 179
Fluoroapatite - see phosphate rock
High density poly(ethene) - see poly(ethene)
Fluorocarbons
High impact polystyrene
168, 194
Homogeneous catalysis
17-18
125, 129, 202-203
Fluorosilicic acid Fluorspar
149
130
168, 195
Homopolymers
Formaldehyde - see methanal
Hydrated lime - see calcium hydroxide
Formalin
Hydrazine
135
Fractional distillation - see distillation 217, 238
Froth flotation
G
Gasification
47, 51
Hydroformylation
Hydrogenation, of oils
156 67
Glass fibre reinforced polymer composites - see composites, glass fibre reinforced polymer Glass transition temperature Glucoamylases
166
45
Glycerides – see triglycerides Glycerol - see propane-1,2,3-triol Glycine - see 2-aminoethanoic acid 70
Glycines
71
Glyphosate
40, 70-71, 153
219
Gold, nanoparticles Graphene
2, 6, 7
Group 1 dyes
59-61
Group 2 dyes
61-62
149
Haematite
75
2,2'-Iminodiethanoic acid 2,2'-Iminodiethanol 62 70
Initiator, manufacture of poly(ethene)
Initiator, manufacture of poly(phenylethene) Initiator, manufacture of poly(propenonitrile)
80
69, 72-77
133-134
Iprovalicarb
24-25, 103, 141, 144, 162
120
13-17
Heteropolymers - see co-polymers 202, 203
Hexamethylene diisocyanate - see 1,6-Diisocyanotohexane Hexamethylenediamine – see 1,6-Diaminohexane 1,6-Hexanediamine
179
134, 154 121
218, 221-223, 234, 238
Iron(III) chloride
69, 70-72
Heterogeneous catalysis
115, 117
78
Iridium(IV) chloride Iron
203
65
Ion-exchange resin
142, 143, 146
199 201
64
Ion exchange membrane cell
Hexafluoropropene
193
Initiator, manufacture of poly(tetrafluoroethene)
Iodomethane
221
Heat exchangers
183
188
Initiator, manufacture of poly(methyl 2-methylpropenoate) 192
Iodine
104
HDPE - see poly(ethene)
Herbicides
40
40,119
62
Ink jet printing
104
Hardening, oils
7
163, 164, 234
Interface
Haber process
Helium
IBIT – (Income Before Interest and Tax)
Insecticides
Haber, Fritz
31, 53-54, 172-173
Initiator, manufacture of poly(propenoic acid)
GVA - see Gross Value Added
H
154
Initiator, manufacture of poly(chloroethene)
Gross margin - see Gross Value Added
Gypsum
I
Indole-3-ethanoic acid
34-40
Gross Value Added
99, 131-132 102, 146, 160
2-Hydroxypropanoic acid
Indigoid dyes
66
Green chemistry
11, 17, 129-130
Hydrogen peroxide
Indigo
87
168
Graft co-polymer
Hydrogen fluoride
Imidacloprid
Glyfosinate Gold
172, 201
Ilmenite
119
Glycol ethers
128, 183, 202
Hydrogen cyanide
4-Hydroxy-4-methylpentane-2-one
33
47, 48, 102-104, 126-127
80
Hydrogen chloride
Hydrogen sulfide
45, 173
L-Glutamic acid
126
97, 155
Hydrogen - see also synthesis gas
213
Glucose
129
Hydroforming - see also reforming, catalytic
237
Glass fibre
28, 48, 51
96, 129-130, 214
Hydrofluorocarbons
Galvanizing
Glass
129
Hydrocracking - see also cracking, catalytic Hydrofluoric acid
Gibbsite
41
Hydrochlorofluorocarbons
69, 77-78
Fungicides
128, 232
Hydrochloric acid
Hydrochloric acid, recycling
127
Fuel cell
132
218
Iron(III) oxide, nanoparticles Iron(III) sulfate Iron sulfide
238
Isasmelt process Isomerisation
87
239 218, 219, 226
28-29
Iso-octane - see 2,2,4-trimethylpentane
245
index Isoprene - see 2-methylbuta-1,3-diene
Melamine
Isopyrazam
Melamine-methanal plastics
78
Isotactic poly(propene)
195-197
Melt transition temperature
ITP Armstrong process
232
Membrane cell
J
239
Jatropha
46
KA
Mesotrione
176 166
115, 117
Mercury amalgam cell Mesosulfuron
Jarosite
K
115-117
71 72
Metalaxyl
78 60
Metal-complex dyes
Metallocene linear low density poly(ethene) Methamidophos
76-79
Kevlar
67-68
Knock
138 235
143, 146
Krypton
L
175-176
Methane
26, 28, 29, 31, 102-103, 126, 202
Methanol
36, 46, 121, 127, 135, 136-137, 138, 192
2-Methoxy-2-methylpropane - see methyl t-butyl ether Methyl acrylate - see methyl propenoate
Lactic acid - see 2-hydroxypropanoic acid Laser dyes Lasers
64
224-226, 229, 238, 240
Lime - see calcium hydroxide and calcium oxide Limestone - see calcium carbonate Linear low density poly(ethene) - see poly(ethene) Linoleic acid
79
Linolenic acid
79
Liquid crystals
64
138-139
Methyl carbamates
73
Methylene diphenyl diisocyanatee - see MDI (1-Methylethyl)benzene - see cumene Methyl isobutyl ketone - see 4-methylpentane-2-one Methyl methacrylate - see methyl 2-methylpropenoate
Low density poly(ethene) - see poly(ethene) LPG - see liquid petroleum gas
139
2-Methylpropene
18, 138-139
Methyl propenoate Methyl propionate Milbemectin
55
Mixed oil 74
178-179 137
Molecular sieve - see also zeolites
227- 228, 235, 237
Magnesium
47
Mobil MTG Process
227
211, 212
74
Miscanthus
Magnesite
192, 198, 199, 201 192
74
Milbemycins
Macrocyclic lactones
154
2-Methylpropane
Methyltrichlorosilane
191
90, 154, 191-192, 198, 201
154
4-Methylpent-3-en-2-one
31, 137
Loop reactors - see reactors, loop
M
68
Methyl t-butyl ether
4-Methylpentane-2-one
LLDPE - see poly(ethene)
L-Lysine
Methylbenzene diisocyanate - see TDI
Methyl 2-methylpropenoate
Liquid petroleum gas
Lucite
15, 29, 107, 205
Methylbenzene
2-Methyl-buta-1,3-diene
64, 142, 143
LDPE - see poly(ethene) Lead
73
135, 175, 176, 192
Methanal
Methanal plastics
Kroll process
Molybdenum
15, 29, 46, 123, 145
229, 230, 233
Magnesium bromide
108
Molybdenum(VI) oxide
Magnesium chloride
227, 228
Mono alkyl quaternary systems, surfactants
Magnesium hydroxide Magnesium oxide Magnetite Maltose
228
227
Monosodium dihydrogenphosphate Moulding
45
Manganese(IV) oxide Margarine
79-80
Marmatite
238
Meal
65 56
205, 206 45
150
171
238
Myristic acid
174
Manganese(II) oxide, nanoparticles
MDI
53
MTBE - see methyl t-butyl ether 223, 227, 229, 233
Manganese octadecanoate
Mauveine
199
166
Monomers
221
Manganese
Matrix
190
190, 196-197
Metallocenes
178, 179
Ketoenols
246
176
88
N
Nahcolite
79
156, 157 83-88
Nanomaterials Nanoparticles
48, 85, 87-88, 177
Nanotechnology - see nanomaterials and nanoparticles Naphtha Neon
11, 15, 26-28, 33, 103
143, 146
Neonicotinoids
74-75
index 74
Neoprene - see poly(2-chlorobuta-1,3-diene)
Phenylpyrazoles
Nereistoxin
Phillips-type catalysts
75 74-75
Nereistoxin analogues Nickel
48, 68, 219, 220, 229, 230, 239
Nickel silver
Phosphate rock Phosphides
Nicosulfuron
71
81, 149, 151
153
Phosphine
153
Nicotine
75
Phosphor bronze
Niobium
229
Phosphoric acid
11, 140-141
Nitric acid
220 149-150
Phosphoric acid, thermal
Nitric oxide - see nitrogen(II) oxide
Phosphorous acid
Nitrobenzene
Phosphorus
106
142-146
Nitrogen
188, 190
Phosgene - see carbonyl chloride
149-150, 151
152
149, 150, 151-153, 221
Phosphorus(V) oxide - see phosphorus pentoxide
Nitrogen monoxide - see nitrogen(I) oxide
Phosphorus oxychloride
Nitrogen(I) oxide
142-146
Phosphorus pentachloride
Nitrogen(II) oxide
12, 140-141
Phosphorus pentoxide
Nitroglycerine
94
152 152
15, 150
151, 152
Phosphorus, red
2-Nitromethylbenzene
205
Phosphorus sulfides
4-Nitromethylbenzene
205
Phosphorus trichloride
153 152
151-152
Nitrous oxide - see nitrogen(I) oxide
Phosphorus, white
Nobel Prize
Phosphorus, yellow - see phosphorus and phosphorus, white
12, 66, 104
Nonionic surfactants Novalac resin
98-99, 101
Phthalic acid - see benzene-1,2-dicarboxylic acid
175
Physical vapour deposition
Nylon - see polyamide
O
Octa-9,12-dienoic acid Octa-9-enoic acid Octane rating Oils
79
79
29, 138
94
Oligomers
79
Omega-6 acids
79
P
Paints
73
41, 128, 161, 232
Picloram
70
Pigments
56, 62-63, 92
Pinoxaden
72
Plasticiser
171
183
13, 126
Polyacrylic acid - see poly(propenoic acid) 177, 178-179
Polyamide 6
Polyamide 6,10
42-43
177 177, 178, 179
Polyamide 6,6 Polyamide 11
89-93, 198
42-43
Particle reinforced composites â&#x20AC;&#x201C; see composites, particle reinforced 127
Peracetic acid - see peroxyethanoic acid Percolating diaphragm cell Perfluoropropylvinyl ether Permethrin
115, 117-118 202, 203
76
Peroxyethanoic acid 69
PET, recycling - see polyesters, recycling 17, 147-148, 154, 175, 178
Phenylamine Phenylethene
147 193, 200
177 42-43, 86, 177-179
Poly(butadiene)
68, 109, 166
Poly(caprolactone) Polycarbonates
172, 174
36-37, 180-181
Poly(2-chlorobuta-1,3-diene) Poly(chloroethene)
86, 109
19, 42, 43, 182-183
Polychloroprene - see poly(2-chlorobuta-1,3-diene) 128
Poly(dimethylsiloxane)
209-212
Poly(diphenylsiloxane)
209
Poly(epoxyethane) - see polyethylene glycol
PET - see polyesters
Phenol-methanal plastics
Polyamides
Poly(1,1-difluoroethene)
100
Perspex - see poly(methyl 2-methylpropenoate) Pesticides
177
Polyamide 12
70
PEM cell
29
6, 11, 15, 28, 29, 48, 140
Polyamide 6,6, recycling
Paraquat
Phenol
Pickling, steel
Polyamide 6, recycling
142-146
Oxygen
73
Polyacetal resins - see polymethylene resins
155
Oxychlorination
11
Physostigmin
Poisoning
Organophosphorus compounds OXO process
Physisorption
Platinum
211
Omega-3 acids
85
Platforming - see also reforming, catalytic
79-80
Oils, edible
59
Phthalocyanines
81-82
Nutrients
175
Poly Electrolyte Membrane - see PEM cell Polyesters
54, 66, 180, 184-185
Polyesters, recycling Poly(ethene)
42
18, 129, 173, 187-190
Poly(ethene), recycling
42, 43
247
index Poly(ethenyl alcohol)
174
Poly(ethenyl ethanoate) Polyether alcohol
Propane-1,2,3-triol
174
Propan-2-ol
206
17, 48, 148, 154
Propanone
Polyethylene - see poly(ethene)
Propenal
16, 155, 199
Polyethylene glycol
Propene
16, 17, 19, 147, 155, 196, 199, 201
118-119 32
Polyethylene terephthalate
Propenonitrile
Polyglycolic acid - see poly(hydroxyethanoic acid)
Propineb
Poly(hydroxyalkanoates)
Prothioconazole
172 172, 174
Poly(hydroxyethanoic acid) Poly(hydroxypentanoate)
172, 173
Polyisocyanates – see also MDI and TDI
204-208
PVC - see poly(chloroethene) Pyrethins Pyrites
Polylactic acid - see poly(2-hydroxypropanoic acid)
Pyrolysis
68
135 184
Polymethyl methacrylate - see poly(methyl 2-methylpropenoate) Poly(methyl 2-methylpropenoate) Poly(methylpentene)
19, 166, 191-192, 198
146
Poly(methylpropenaote) Poly(2-methylpropene)
Poly(phenylpropene) Polyphenylsulfone Poly(propene)
19, 173, 195-197 42, 43
198-199 19, 66, 200-201
Poly(propenonitrile)
Polypropylene – see poly(propene) Poly(tetrafluoroethene)
19, 202-203
Polytrimethylene terephthalate Polyurethanes
61 - 62
20-25
Reactors
20
Reactors, batch
20-24, 188-189
Reactors, continuous stirred tank
54
21-22, 29, 103, 104, 122, 137, 140, 147,
Reactors, fluid bed
22-23, 28, 201
24, 189, 196 21, 27, 103
Reactors, tubular
Recycling - see also secondary production Red List
11, 15, 16, 29, 106-107, 126
Reforming, catalytic
11, 27-28, 102-103, 126-127
Polyvinyl acetate - see poly(ethenyl ethanoate)
Refractory carbides
Polyvinyl alcohol -see poly(ethenyl alcohol)
Responsible Care
Polyvinyl butyral
174
Rhenium
11, 15, 16, 29
Polyvinyl chloride - see poly(chloroethene)
Rhodium
6, 11, 48, 140
Polyvinylidenefluoride - see poly(1,1-difluoroethene)
Rock phosphate - see phosphate rock
Portland cement
Rotary furnace
68
Potassium chloride Potassium iodate
133
Potassium iodide
133
Potassium sulfate
16
Rutile
S
66
Prepeg
123, 144, 145-146
Pressure swing adsorption Prilling
81-82, 134, 165
Primicarb Promoter Propane
6
14, 16, 120 27, 28, 29, 31, 201
Propane-1,2-diol
206
Propane-1,3-diol
32, 184
8-9
226
163, 164, 234
Sacrificial metal SAN SBS
237
194, 200
Saponification
73
Profit and Loss Accounts
68
RPG - see raw pyrolysis gas
81, 82
41-43, 232
9
Reforming, steam
66, 204-208
23-24, 188-189
Reactors, fixed bed 162, 189 Reactors, loop
198-199
Poly(propenoic acid)
28
9
Reactors, continuous
37
Polypropenoates
Quicklime - see calcium oxide
Reactive dyes
173
Poly(propene), recycling
Q R
REACH
19, 68, 167, 168, 169, 193-194
Poly(phenylethene)
48, 51, 66
Raw pyrolysis gas
88
135
Polyoxymethylene
76
161
Rare gases - see argon, helium, krypton, neon, xenon
199
119, 139, 206, 207
Polyols
76
Pyrethoids
Polyisoprene - see poly(2-methylbuta-1.3-diene)
Polymethylene terephthalate
77
PTT - see polymethylene terephthalate
Polyhydroxyvalerate – see poly(hydroxypentanoate)
Polymethylene resins
78
PTFE - see poly(tetrafluoroethene)
53-54, 172-173
Poly(2-methylbuta-1,3-diene)
19, 198, 200-201
Proton Exchange Membrane - see PEM Cell
172
Poly(2-hydroxypropanoic acid)
198-199
Propenoic acid
Polyfluorocarbons - see poly(tetrafluoroethene)
Poly(hydroxybutanoate)
248
46, 80, 91, 94, 95
139, 154
94, 95
168
Scrap, aluminium
215
Scrap, recycling of metals
43
Secondary production, aluminium Secondary production, copper Secondary production, lead
215
219
226
index Secondary production, magnesium 240
Secondary production, zinc Selenium
228
231
Secondary production, steel 229
Strobilurin A
77 77-78
Strobilurins Sucrose
45 81, 160, 161, 223
Sulfur
Shell Higher Olefines Process
97
Sulfur concrete
Shell Middle Distillate Process
47, 51
Sulfur dioxide 225, 238
237
Sheradizing
SHOP - see Shell Higher Olefines Process Silane
209
Silanes
Sunfuel
210, 212
Silicone elastomers
Superphosphate
211, 212
Silicone rubbers - see silicone elastomers 209-212
Silicones
Silicon hydride
85
Siloxanes Silver Sinter
209-212
Synthetic anhydrite
87, 88
SMDS â&#x20AC;&#x201C; see Shell Middle Distillate Process SNG â&#x20AC;&#x201C; see synthetic natural gas 94, 96, 98 97
101, 156-157 133, 180
Sodium hydrogencarbonate Sodium hydroxide
157
94, 95, 97, 115-117, 158-159, 213, 214
Sodium hypophosphite
153
Sodium 2,2'-iminodiethanoate Sodium iodate
134
Sodium nitrate
134
Sodium perborate
40
TAED - see tetraacetyl ethylene diamine Tantalum
236
205-206
Tembotrione
72
Terephthalic acid - see benzene-1,4-dicarboxylic acid Terylene - see polyesters Tetraacetyl ethylene diamine Tetrabromobisphenol A
1,1,1,2-Tetrachloroethane Tetradecanoic acid
99, 131
Sodium phosphate - see monosodium dihydrogenphosphate, disodiumhydrogenphosphate, disodium pyrophosphate and trisodium phosphate
167, 202-203
Tetrafluoroethene
Tetramethylbisphenol A Thermoforming
171
Thermoplastics
169
Thermosets
Thiamethoxam
156-157
Thiobadilus ferrooxidans 75 74, 75
76-77
Thiocyclam
Spiromesifen
76-77
Thiosultap
171
Tin
74-75 227, 233-236
Titanium
Starch
Titanium carbide
68
Steam cracking - see cracking, steam
Titanium(IV) chloride
Steam reforming - see reforming, steam
Titanium dioxide
Steel
229-232
Steel scrap
164, 196, 235
163-164
Titanium dioxide, nanoparticles
230-232
Steel, stainless
218
219, 230, 233
Stainless steel - see steel, stainless 173
75
Thiocloprid
Spirodiclofen
123
169
101
238
181
Thermal swing regeneration
Solvay Process
Stabiliser
183
79
Sodium silicate Sphalerite
100
108, 154, 181
Tetrafluoroethylene - see tetrafluoroethene
99, 131
Sodium percarbonate
T TDI
Sodium aluminium fluoride - see cryolite Sodium chloride
49
TDA - see toluene diamines
213-214
Sodium carbonate
130
Synthetic Natural Gas
14, 240
Sodium alkyl ether sulfates
195-196, 197
11, 43, 47, 48, 51, 102-104, 136, 137
Synthesis gas
11, 219, 240
Sodium aluminate
47
Syngas - see synthesis gas
Slaked lime - see calcium hydroxide
Soaps
35
Sustainability
Syndiotactic poly(propene)
125, 130
Silver nanoparticles
38
150
95-101
Surfactants Syndiesel
Silicon tetrafluoride
198
Supercritical liquids
210, 212
Silicone resins
47
Superabsorbents
209-210, 212
Silicone gels
71
Sulphonylureas
211
Silicone fluids
41
16, 97, 162
Sulfur trioxide
211
Silicon
Sulfuric acid 11, 16, 17, 97, 160, 161-162, 179, 192, 218, 219, 225, 232, 238, 239, 240 Sulfuric acid, recycling
209-212
Silanols
62
Sulfur dyes
103, 126-127
Shift reaction
160 16, 41, 111, 133, 134, 160, 161-162, 192, 218,
229
Toluene diamines
87-88, 177
205
Toluene diisocyanate - see TDI
249
index Toluene - see methylbenzene Totally Degradable Plastic Additives 46, 80, 185
Transesterification Translocation
Variable costs 174
70
Trialkyl phosphites 61
Triazoles
77
153
Tricalcium phosphate
81
112
Vinyl sulfones
61-62
W
Working capital
6, 7
Wrought iron
221
Triethylaluminium
18, 96, 97, 196
X
Triethylene glycol
118-119
o-Xylene - see 1,2-dimethylbenzene
202
Trichloromethane Triethanolamine
Trifloxystrobin Triflumuron
119
78
Triglycerides Triketones
129
79, 80, 95, 206 71-72
Trimethylchlorosilane Trimethyl phosphate
111, 17-18, 29, 129-130
153
Triple superphosphate Trisodium phosphate
81, 82, 150 150
U
Zeolites 179
Zinc
68
11, 14-15, 28, 39, 40, 97, 126, 137, 144, 145, 147,
125, 129
Uranium(VI) fluoride
125
Urea-methanal plastics - see carbamide-methanal plastics
V
204, 207
Vacuum swing adsorption Vanadium
144, 146
229, 230, 233
Vanadium(V) oxide
Zinc ferrite
11, 13, 162, 199
238 238, 239
Zinc, nanoparticles Zinc oxide
81, 82, 165, 176
18, 188, 189, 190, 196
238
Zinc chloride
Urethane linkage
96
227, 230, 237-240
Zinc blende
Uranium(IV) fluoride Urea
Z
35-36
Ziegler-Natta catalysts
229, 230
Tungsten carbide
Y
Ziegler catalyst
156, 157
Tungsten
Xylenes - see 1,2-, 1,3-, 1,4-dimethylbenzene
Yield
211
2,2,4-Trimethylpentane
Trona
143, 146
Xenon
m-Xylene - see 1,3-dimethylbenzene p-Xylene - see 1,4-dimethylbenzene
76
Trifluoromethylbenzene
250
Vertical Shaft Kiln
Vinyl chloride - see chloroethene
Trialkylaluminium - see Ziegler-Natta catalysts Triazines
6, 7
62
Vat dyes
88
238, 239
Zinc oxide, nanoparticles Zinc phosphide Zinc sulfate
238, 239
Zinc sulfide
238
Zirconium
88
153
227, 229, 233
Zirconium metallocene
197