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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


http://www.ciec.org.uk/eci/ECI_Extract