the essential chemical industry

THEESSENTIALCHEMICALINDUSTRY

About the CIEC

The 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 essenTialChemiCal 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.

© Chemical Industry Education Centre at The University of York

ISBN: 978 1 85342 595 0

Foreword

Being 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

2 Catalysis in industry 113 Chemical reactors 204 Cracking, isomerisation and reforming 265 Distillation 306 Green chemistry 347 Recycling in the chemical industry 41

8 Biofuels 449 Biorefineries 5010 Biotechnology in the chemical industry 5211 Colorants 5612 Composites 6513 Crop protection chemicals 6914 Edible fats and oils 7915 Fertilizers 8116 Nanomaterials 8317 Paints 8918 Soaps 9419 Surfactants 95

Materials and Applications

Processes

Introduction 1 The chemical industry 1

Chemicals 20 Ammonia 10221 Benzene 10622 Bromine 10823 Buta-1,3-diene 10924 Calcium carbonate 11025 Chlorine 11426 Epoxyethane 11827 Ethane-1,2-diol 12028 Ethanoic acid 12129 Ethanol 12230 Ethene 12431 Fluorine 12532 Hydrogen 12633 Hydrogen chloride 12834 Hydrogen fluoride 12935 Hydrogen peroxide 13136 Iodine 13337 Methanal 13538 Methanol 13639 Methyl tertiary-butyl ether 138

ConTenTs

Chemicals continued... 40 Nitric acid 14041 Oxygen, nitrogen and the rare gases 14242 Phenol 14743 Phosphoric acid 14944 Phosphorus 15145 Propanone 15446 Propene 15547 Sodium carbonate 15648 Sodium hydroxide 15849 Sulfur 16050 Sulfuric acid 16151 Titanium dioxide 16352 Urea 165

Polymers 53 Polymers: an overview 16654 Degradable plastics 17255 Methanal plastics 17556 Polyamides 17757 Polycarbonates 18058 Poly(chloroethene) 18259 Polyesters 18460 Poly(ethene) 18761 Poly(methyl 2-methylpropenoate) 19162 Poly(phenylethene) 19363 Poly(propene) 19564 Poly(propenoic acid) 19865 Poly(propenonitrile) 20066 Poly(tetrafluoroethene) 20267 Polyurethanes 20468 Silicones 209

Metals 69 Aluminium 21370 Copper 21671 Iron 22172 Lead 22473 Magnesium 22774 Steel 22975 Titanium 23476 Zinc 237

Index Index 241

ConTenTs

The 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.

Using this book

11

2

CaTalysis in indusTry

Catalysts 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 industrial companies and university research laboratories to find out how catalysts work and to improve their effectiveness. If catalytic activity can be improved, it may be possible to lower the temperature and/or the pressure at which the process operates and thus save fuel which is 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.

If the catalyst is in the same phase as the reactants, it is referred to as a homogeneous catalyst. A heterogeneous catalyst on the other hand is in a different phase to the reactants and products, and is often favoured in industry, being easily separated from the products, although it is often less specific and allows side reactions to occur.

Heterogeneous catalysisThe 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).

The gas molecules interact with atoms or ions on the surface of the solid. The first process usually involves the formation of very weak intermolecular bonds, a process known as physisorption, followed by chemical bonds being formed, a process known as chemisorption.

Physisorption can be likened to a physical process such 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 form a liquid. The enthalpies of chemisorption are similar to the values found for enthalpies of reaction. They have a very wide range, just like the range for non-catalytic chemical reactions.

An example of the stepwise processes that occur in heterogeneous catalysis is the oxidation of carbon monoxide to carbon dioxide over palladium. This is a very important process in everyday life. Motor vehicles 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 UnitMaking 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)

a liquid (e.g. petrol)

a residue (e.g. fuel oil)

4

Reforming of naphtha Platinum and rhenium on alumina

4

Making epoxyethane Silver on alumina 26

Making sulfuric acid Vanadium(V) oxide on silica

50

Making nitric acid Platinum and rhodium 40

Table 1 Examples of industrial processes using heterogeneous catalysis.

12

2


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 chemisorption has to be sufficiently exothermic for 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 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, the mechanism for the synthesis of ammonia (the Haber Process):

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):

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.

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:

The exhaust gases also contain nitrogen(II) oxide (nitric oxide, NO), and this is removed by reactions catalysed principally by the rhodium:

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.

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).

Figure 1 A mechanism for the oxidation of carbon monoxide.

Figure 2 A mechanism for the catalytic synthesis of ammonia.

palladiumcatalystsurface

carbon atomsoxygen atoms

O (g)2 2O(ads)

CO(g) CO(ads)

O(ads) + CO(ads) CO (ads)2

CO (ads)2 CO (g)2

13

2


General requirements for a heterogeneous catalystTo be successful the catalyst must allow the reaction to proceed at a suitable rate under conditions that are economically desirable, at as low a temperature and 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

palladium. Thus all traces of sulfur compounds must be removed from the petrol used in cars fitted with catalytic converters.

Further, solid catalysts are much more effective if they are finely divided as this increases the surface area.

Figure 3 The activation energy barriers for the reactions occurring during the catalytic synthesis of ammonia.

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 platinum-rhodium 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.

N(ads) + 3H(ads)

Overall equation:

NH(ads) + 2H(ads)

NH (ads) + H(ads)2

NH (ads)3

NH (g)3

= – 46 kJ mol-1

Energy

Progress of reaction

This potential energy diagramillustrates the synthesis ofammonia using a catalyst.

Each step is shown as a simpleenergy diagram, with its ownactivations energy and enthalpychange of reaction.

The estimated activation energy forthe reaction without a catalyst isvery high.

When a catalyst is used, theactivation energy barriers forindividual steps are much lower, asshown in this diagram.

H

H (g)21

21N (ads) +21

2

H (g)21

21N (g) +21

2

H (g)2 NH (g)3N (g) +21211

2

activation energywithout catalyst

activation energywith catalyst

14

2


At high temperatures, the particles of a finely divided catalyst tend to fuse together and the powder may ‘cake’, a process known as sintering. This reduces the activity of the catalyst and steps must be taken to avoid this. One way is to add another substance, known as a promoter. When iron is used as the catalyst in the Haber Process, aluminium oxide is added and acts as a barrier to the fusion of the metal particles. A second promoter 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 zeolitesAluminium 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.

Alumina becomes particularly active if it has been washed with an acid, for example hydrochloric acid, or coated with an acid (such as phosphoric acid), 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):

Aluminosilicates are also used as catalysts when an acid site is required. These are made from silicon dioxide (silica) and aluminium oxide. They contain silicate ions, SiO4

4- that have a tetrahedral structure which can be linked together in several ways. When some of the Si atoms are replaced with Al atoms, the result is an aluminosilicate. Hydrogen ions are again associated with the aluminium atoms:

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 such as water. The spaces are interconnected and form long channels and pores which are of different sizes in different zeolites.

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, sodium hydroxide, sulfuric acid and tetrapropylammonium bromide.

Figure 6 A mechanism for the hydration of ethene to ethanol.

Figure 7 The structure of a zeolite (example figure).

The zeolite acts as amolecular sieve.Only straight-chain moleculescan pass through the holes inthe zeolite structure.

15

2


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.

However, if the zeolite is washed with phosphoric acid and heated strongly, minute particles of phosphorus(V) oxide are deposited on the surface making the pores slightly smaller. This restricts the diffusion of the 1,2- and 1,3-isomers and they are held in the pores until they are converted into the 1,4-isomer and can escape (Figure 8).

This remarkable selectivity enables the yield of the 1,4-isomer to be increased from 25% to 97%.

The ability of the zeolite to adsorb some molecules and to reject others gives it the ability to act as a molecular sieve. For example, in the manufacture of ethanol from ethene or from biomass, an aqueous solution of ethanol is produced, in which there is 4% water still present even after repeated distillations. Further purification requires the use of a zeolite which absorbs the water preferentially (Unit 29). Table 2 gives examples of industrial processes involving zeolites.

Figure 8 A zeolite acting an a molecular sieve and a catalyst during the formation of 1,4-dimethylbenzene from methylbenzene.

Table 2 Examples of industrial processes using zeolites.

CH3

CH3

CH3

CH3

CH3

CH3

CH3

benzene

1,2-dimethylbenzene

1,3-dimethylbenzene

1,4-dimethylbenzene

methylbenzene

mixture of dimethylbenzenes

CH31

2

3

4

The three dimethylbenzeneisomers are named to showthe positions of the twomethyl groups.

2

Process Catalyst Equation UnitCatalytic cracking of gas oil

Zeolite Produces: a gas (e.g. ethene, propene)

a liquid (e.g. petrol)

a residue (e.g. fuel oil)

4

Reforming of naphtha Platinum and rhenium on zeolite

For example: 4

Disproportionation of methylbenzene

Zeolite 21

Dealkylation of methylbenzene

Zeolite

CH (g)4

CH3

(g) (g)H2(g)

21

Making cumene (1-methylethyl)benzene

Zeolite (ZSM-5)

42

16

2


Bifunctional catalystsBifunctional 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 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 molecules on alumina.

In this example butane is dehydrogenated to butene.

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, 2-methylpropane, which is then desorbed into the gas phase.

In the industrial process, naphtha vapour is passed over platinum and rhenium (ca 0.3% each) which are finely dispersed over aluminium oxide.

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.

Branched alkanes have a much higher octane rating than 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 oxidesBesides 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:

Potassium sulfate is added as a promoter. Its mode of action is not absolutely clear but it appears to be because its presence lowers the melting point of the catalyst, and allows it to spread out as a very thin layer over the entire surface.

Several important industrial processes are catalysed by mixed metal oxides. The surfaces contain two or more different metal atoms, O2- ions and –OH groups. They are particularly useful in the oxidation of hydrocarbons, 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:

Figure 10 The oxidation of propene.

Figure 9 A mechanism for the reforming of butane to 2-methylpropene.

CH CH CH CH (g)3 2 2 3 CHCH CH (g)2 3CH2 + H (g)2

CHCH CH (ads)2 3CH2

CH3 C CH2 CH (ads)3

H

+ H+ (ads)

CH3 C CH (ads)3

CH3

The butenes are released into thegas phase until they are adsorbedon to an aluminium oxide site onthe surface of the catalyst.

Rearrangement of the secondarycarbocation through a series ofalkyl group and hydrogen atommigrations leads to an equilibriumin which the relatively stabletertiary carbocationpredominates.

The tertiary carbocation loses ahydrogen ion to form a branchedalkene.

CH3 C CH (ads)2

CH3 2-methylpropene

+

+

- H+ (ads)

butane

Here they react with a hydrogenion to form carbocations.

CH3H

H

C

H

C

CH2H

H

C

H

C

CH

H

C

H

C

O

Hpropene

CO2 H O2

H O2

CO

H

H

methanal

CO

H

H C3

ethanal

allyl radical propenal

O2

without catalyst

with catalyst

O2

17

2


The allyl radical is then oxidised on the surface to yield propenal. It is postulated that the allyl radical is oxidised by an oxygen atom that is adsorbed at a molybdenum site. Another oxygen atom, adsorbed on a bismuth site, is then transported to the reduced molybdenum site to replace that oxygen. There is a compensating transport of electrons to complete the cycle.

The same catalyst is also used to manufacture propenonitrile (Unit 65):

Homogeneous catalysisHomogeneous catalysts are less frequently used in industry than heterogeneous catalysts as, on completion of the reaction, they have to be separated from the products, a process that can be very expensive.

Table 3 Examples of industrial processes using homogeneous catalysis.

However, there are several important industrial processes that are catalysed homogeneously, often using an acid or base (Table 3).

One example is in the manufacture of ethane-1,2-diol from epoxyethane where the catalyst is a trace of acid (Unit 27):

In the mechanism for this reaction a hydrogen ion is added at the start, and lost at the end. The hydrogen ion functions as a catalyst.

Figure 11 A mechanism for the formation of ethane-1,2-diol from epoxyethane.

Manufacture Catalyst Equation UnitEthane-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

+ H+

C CH

H

H

H

H O2 OH

C C

O

H

H

H

H

H

C C

O

H

H

H

H

H O2C CH

H

H

H

HO OH- H

+

epoxyethane

ethane-1,2-diol

++

18

2


The alkene monomer attaches itself to an empty coordination site on the titanium atom and this alkene molecule then inserts itself into the carbon-titanium bond to extend the alkyl chain. This process then continues, thereby forming a linear polymer, poly(ethene).

The polymer is precipitated when the catalyst is destroyed on addition of water. Because it is linear, the polymer molecules are able to pack together closely, giving the polymer a higher melting point and density than poly(ethene) produced by radical initiation. The manufacture of poly(ethene) is described in Unit 60.

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.

Two other examples are concerned with the production of 2,2,4-trimethylpentane from 2-methylpropene, again using an acid as the catalyst. One uses 2-methylpropane (Table 3) which yields the alkane directly. The other uses only 2-methylpropene.

The mechanism of the reaction also involves the addition of a hydrogen ion to a reactant (Figure 12).

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 reactionsZiegler-Natta catalystsZiegler-Natta catalysts are organometallic compounds, prepared from titanium compounds with an aluminium trialkyl which acts as a promoter:

The alkyl groups used include ethyl, hexyl and octyl.

The role of the titanium catalyst can be represented as shown in Figure 13.

Figure 13 Illustrating the role of a Ziegler-Natta catalyst.

Figure 12 Part of a mechanism for the formation of 2,4,4-trimethyl-2-pentene from 2-methylpropene.

H C3 C

CH3

CH2

H C3 C

CH3

CH2

H C3 C

CH3

CH3

+ HX

C

CH3

CH3

CH3

+ C

CH3

CH3

CH3

H C3 C

CH3

CH2

C

CH3

CH3

CH3

H C3 C

CH3

CH2 + HXC

CH3

CH3

CH3

H C3 C

CH3

CH

2,4,4-trimethyl-2-pentene

2-methylpropene+

+ X

+

+

+

+ X

41

7

reCyCling in The ChemiCal indusTry

Recycling 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.

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 chemicalsSulfuric acidSome sulfuric acid is produced from ‘spent’ (used) acid and related compounds such as ammonium sulfate which is a by-product in the manufacture of methyl 2-methylpropenoate (Unit 61).

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:

The sulfur dioxide is dried by passage through concentrated sulfuric acid. It is then oxidised to sulfur trioxide and hence sulfuric acid using the Contact Process (Unit 50).

Hydrochloric acidThe 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:

HCl from both streams is absorbed in water to make 18% hydrochloric acid for reuse. It is difficult however to collect all the HCl gas, and emissions to air are a problem with this process.

Recycling within processesMany processes recycle reactants and products in 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:

The hydrogen chloride is recycled and reacted with oxygen and more ethene. The overall reaction can be represented by:

Recycling of polymersThe 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.

CH2 CH (g)2 + 2HCl(g) + ½O (g)2 ClCH2 CH Cl(g)2 + H O(g)2recycled

hydrogen chloride

CH2 CH (g)2ethene

+ Cl (g)2 ClCH2 CH Cl2

1,2-dichloroethane

CH2 CHCl(g) + HCl(g)chloroethene

( monomer)required

cracked

(g)

42

7


Reusing plasticsReusing plastics would be ideal, and already happens for example, with bottle crates and increasingly with shopping bags. At first sight, collecting plastics which can be remoulded, for example the thermoplastics, such as poly(ethene) and poly(propene), would appear to be an attractive solution. However, collecting and sorting plastic articles into specific polymers is an expensive and difficult process. It is often done manually by trained 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 between clear and translucent plastic. Next a vision colour sensor, programmed to ignore labels, identifies various coloured plastics (Figure 1). X-ray spectrometry is then used to detect the Cl atom in poly(chloroethene) (PVC). Finally a near infrared spectrometer is used to detect resin type, most importantly for the separation of high density poly(ethene) (HDPE) and a polyester such as PET. Typical sorting rates are of the order of 3 items per second.

Plastic can also be separated on the basis of density by flotation. One recently developed method involves spreading the plastic and passing it through a series of pipes in suspension in water. The flow rate of the plastic depends on the density, enabling streams to be taken off at different points along the pipe.

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 fibres are then used to make products such as carpets.

High density poly(ethene), HDPE, used for juice and milk bottles, is also ground into flakes, melted and pressed into sheets to be made, for example, into bin-liners or moulded into containers.

Recycling of plastic bags saves about two thirds of the energy used to produce a new bag. PVC is similarly recycled and extruded for pipes or used for window frames.

Converting polymers into monomersSome polymers can be depolymerized to reform monomers, which can then be purified by distillation and polymerized again to produce the polymer. This still has the drawback that the polymer waste has to be sorted prior to being heated.

PET waste is dissolved in the dimethyl ester of benzene-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:

After purification, by distillation, the monomer is polymerized again to yield polyamide 6. In another process, it is not necessary to remove the backing (which is an added expense). Instead, the polyamide 6 fibres are heated in a stream of superheated steam and depolymerized.

C N

O H

N

H

C

O

(CH )2 5

n

n

polyamide 6 caprolactamFigure 1 This machine, which has a colour sensor, is one of a series used to sort automatically different polymers prior to recycling.

43

7


It is less easy to reuse polyamide 6,6 which is made from two monomers. Nevertheless, DuPont has a process where carpets, with the backing removed, made from both polyamide 6 and polyamide 6,6 are shredded and pulverised before being heated strongly in an atmosphere of ammonia gas. Among the products are caprolactam (from polyamide 6) and 1,6-diaminohexane (from polyamide 6,6). These are purified by distillation and reused to make the polyamides.

Polyamides from recycled carpet are being used to make new carpets and to make cushions and resilient flooring. Although many recycling programmes are restricted to collecting carpets used commercially (for example in large hotels and offices), this too is about to change and domestic carpets will be used more extensively.

Cracking the polymerPolymers, like other high molecular mass organic compounds such as the alkanes in oil, can be cracked at high temperatures to form smaller molecules. For example, if they are steam cracked, polymers such as poly(ethene) and poly(propene) yield alkenes and alkanes of small molecular mass which can be used in the same way as those formed in the cracking of naphtha (Unit 4). Small cracking plants are being built for this purpose.

Mixtures of polymers can be converted into useful compounds either by pyrolysis or by oxidation. This has the advantage that the plastics do not have to be rigorously sorted before being treated. The mixture of polymers is heated in a stream of hydrogen at about 500 K. If the polymers contain chlorine (for example, PVC), hydrogen chloride is formed and is washed out. The remaining gases are then heated at about 700 K and cracked to form the usual mixture of hydrocarbons (alkanes, alkenes, aromatics) which can be fed into the stream of hydrocarbons formed from the cracking of oil fractions (Unit 4).

Alternatively, the gases formed from heating the mixture of polymers and following removal of the hydrogen chloride, are mixed with air and passed through a furnace at ca 1500 K to form a mixture of carbon monoxide and hydrogen, synthesis gas. This is then fed into the synthesis gas produced by the usual methods (Unit 20). This latter process, at present, appears to be the more favoured.

Polymers as fuelsPolymers can be burnt to produce energy. The problems are that the incineration can produce noxious fumes which must be trapped and the carbon is not recycled even if the energy can be used.

Recycling of metalsThe 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 the steel mill itself, from the factory making the cars and lastly when the car itself is eventually recycled.

Figure 2 This yacht is using sails made from recycled poly(ethene).

52

10

BioTeChnology in The ChemiCal indusTry

Biotechnology 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.

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 UK. As long ago as 1916, in the First World War, the bacterium Clostridium acetobutylicum was fed with 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. 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

amount of research is being done by chemists, biotechnologists and engineers to make these reactions more efficient and cost-effective.

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.

Figure 1 The progress of fermentation in a 500 dm3 fermenter in the biotechnology pilot plant is being monitored. The pilot plant is equpped with a large number of pilot-scale batch reactors (Unit 3) used in the development of new large-scale fermentation processes.

Figure 2 The compounds (other than ethanol) produced by fermentation reactions in the chemical industry.

53

10


3-Carboxy-3-hydroxypentanoic acid (citric acid)

The annual global production of citric acid is about 1.4 million tonnes.

Uses

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.

It is used with sodium hydrogencarbonate in effervescent products, both for ingestion (aspirin or antacids) and for personal care (bath salts). It is also used in detergents and soaps to control pH and to chelate metal ions in hard water, which allows detergents to produce more foam (Unit 19).

ManufactureThe 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.

2-Hydroxypropanoic acid (lactic acid)Annually, about 275 000 tonnes of lactic acid are produced globally.

Uses

An important use is in the manufacture of the biodegradable polymer, poly(lactic acid), PLA (Unit 54).

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.

HO C2 CH2 CH2 CO H2

CO H2

C

OH

3-carboxy-3-hydroxypentanoic acid (citric acid)

Figure 3 The uses of citric acid.

C

H

O C

O

n

CH3

poly(2-hydroxypropanoic acid)poly(lactic acid), PLA

Figure 4 The uses of lactic acid.

54

10


Although lactic acid can be directly polymerized in a condensation reaction, the reaction is reversible and the water that is produced tends to hydrolyse the polymer chain. Instead, lactic acid is first dimerized to make a cyclic lactide. This produces water which is removed.

The lactide is then polymerized into PLA by a ring-opening polymerization reaction, using tin(II) octanoate as catalyst:

ManufactureLactic 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

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).

PTT is very similar in structure to the well-known polyester polyethylene terephthalate (PET), which is produced from ethane-1,2-diol and benzene-1,4-dicarboxylic acid (Unit 59).

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

HO CH2 CH2 OHC

propane-1,3-diol (PDO)

H2

C

O

C

O

O CH2 CH2 O

n

polyethylene terephthalate (PET)

C

O

C

O

O CH2 CH2 O

n

CH2

polytrimethylene terephthalate (PTT)

stretch-recovery properties to PET and it is also easy to dye (Unit 11). It is being increasingly used in fibre form in textiles, clothes and carpets, but it can also be used as a thermoplastic in car parts, electrical and electronics systems.

Propane-1,3-diol is also used in the preparation of cosmetics, laminates, adhesives, paints and inks. It is also being used as a replacement for ethane-1,2-diol as an engine coolant and as a solvent (Unit 27).

ManufacturePropane-1,3-diol is manufactured from maize (corn). The maize is cooked, and then ground to release the starch. The starch is hydrolysed to produce glucose. This is fed to a genetically modified Escherichia coli, which ferments the glucose into PDO.

Amino acidsAmino acids contain both amino and carboxyl functional groups. Linear chains of amino acids are the building blocks of proteins. Industrially, amino acids are used in food additives, animal feeds and pharmaceuticals.

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

Figure 4 The carpet contains 37% of polytrimethylene terephthalate derived from maize via propane-1,3-diol.

C

CHH C3

CHHO

O

COH

CH3

O

HO OHC

O

C

CH3

C

C

OH C3

O

O+

2-hydroxypropanoic acid(lactic acid)

C

H

O C

O

n

CH3

poly(2-hydroxypropanoic acid)poly(lactic acid), PLA

tin octanoatecatalyst

dimer

H H

55

10


additional expensive steps are required to produce a pure stereoisomer. However, biotechnological routes have the great advantage of producing pure optically active amino acids.

Amino acids are produced from the fermentation of sugar to which small quantities of nitrogen-containing compounds (for example, ammonia or urea) have been added. Mutants of Corynebacterium glutamicum or genetically modified E. coli are used. The two acids produced on the largest scale are L-glutamic acid and L-lysine.

L-Glutamic acid

About 1.7 million tonnes of L-glutamic acid are produced by fermentation per year, the majority being produced in Asia, with one company in China producing 33% of the world’s output.

Most is used in the form of the salt, monosodium glutamate (MSG) which is commonly used as a flavour enhancer, particularly in processed food. The sodium salt is used rather than the acid as it is the glutamate ion that produces flavour and the salt is more soluble in water than the parent acid.

L-Lysine

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.

CO H2

H

C

NH2

(CH )2 4

H N2

(L-lysine)

2,6-diaminohexanoic acid

HO C2 CH2 CO H2

H

C

NH2

CH2

(L-glutamic acid)

2-aminopentanedioic acid

114

25

Chlorine

Chlorine, 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.

UsesThe 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 propane-1,3-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).

The solvents (including trichloroethene) are used in dry cleaning.

Chlorine is also used in the manufacture of many inorganic compounds, notably titanium dioxide (Unit 51) 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.

However, some chlorine needs to be transported for example, when it is to be used to purify water. For this, the chlorine is dried by passing it through concentrated sulfuric acid and then compressed and liquefied into cylinders, ready for transportation.

Annual productionUK 590 000 tonnesEurope 16.4 million tonnesWorld 69.1 million tonnes

Figure 1 The uses of chlorine.

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.

115

25

Chlorine

ManufactureMost chlorine is manufactured by the electrolysis of sodium chloride solutions. The other main commercial product is sodium hydroxide (Unit 48). The primary raw material for this process is rock salt (sodium chloride), available worldwide usually in the form of underground deposits of high purity (Unit 48). It is pumped to the surface with high pressure water as a concentrated solution. This solution is often called brine.

A solution of sodium chloride contains Na+(aq) and Cl-(aq) ions and, from the dissociation of water, very low concentrations of H+(aq) and OH-(aq) ions. During the electrolysis of the solution, chlorine and hydrogen gases are produced:

As the hydrogen ions are discharged, more water dissociates forming more hydrogen and hydroxide ions. This results in a gradual build up of the concentrations of hydroxide ions around the cathode, thus producing a solution of sodium hydroxide. The essential requirement is to maintain an effective and economic means of separating the anode and cathode reactions so that the products, chlorine and caustic soda, will not react to form sodium hypochlorite. This separation has been achieved historically by the mercury amalgam and diaphragm processes. However, these are being phased out and most new plants use ion exchange membranes, which are the most environmentally and economically sound means of chlorine production.

(a) Cation exchange membrane cellThe 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 cellIn 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 cellA 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.

Anode: Cl (g) + 2e2-

H (g)2

2Cl (aq)-

Cathode: H O(l)2 H (aq) + OH (aq)+ -

2H (aq) + 2e+ -

(a) Cation exchange membrane cellThe anodes are made of titanium coated with ruthenium dioxide. The cathodes are nickel, often with a coating to reduce energy consumption. The anode and cathode compartments are completely separated by an ion-permeable membrane (Figure 3). The membrane is permeable to cations, but not anions; it allows the passage of sodium ions but not chloride or hydroxide ions. Sodium ions pass through in hydrated form (Na.xH2O)+ so some water is transferred, but the membrane is impermeable to free water molecules.

The sodium hydroxide solution leaving the cell is at ca 30% (w/w) concentration. It is concentrated by evaporation using steam, under pressure, until the solution is ca 50% (w/w), the usual concentration needed for ease of transportation and storage.

The membrane (0.15-0.3 mm thick) is a co-polymer of tetrafluoroethene ((Unit 66) and a similar fluorinated monomer with anionic (carboxylate and sulfonate) groups.

(b) The mercury cellTypical 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.

Table 1 The key features of the three electrolytic processes.

Cl2

Cl-

Cl-

Cl2

Na+ Na+

Na+ OH

OH-

H2

H2

H2Cl2

chlorinegas

hydrogengas

H-

coatedtitaniumanode

nickelcathode

brineconcentrator

purewater

freshsalt

NaOH33%

ion exchangemembrane

NaOH33%

Figure 3 The membrane cell.

116

25

Chlorine

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)

sodium. It moves on to a decomposer cell situated alongside the mercury cell.

The exit brine, containing typically 15-20% (w/w) sodium 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.

The decomposer cell (Figure 4) is made of steel and contains graphite blocks fixed in the flow of amalgam. 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.

The mercury is returned to the electrolysis cell and the hydrogen passes out of the decomposer. A 50% (w/w) solution of sodium hydroxide is produced in the decomposer and most of it is sold in this form. Some is concentrated by evaporation to 75% (w/w) and then heated to 750-850 K to obtain solid sodium hydroxide.

(c) The percolating diaphragm cellIn 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 4 The mercury cell and decomposer.

Figure 5 Chlorine being manufactured using mercury cells. Usually, about 100 cells operate in series. Great care is taken to prevent loss of mercury.

coatedtitaniumanodes

flowing mercury cathode

mercury in sodium-mercuryamalgam Na/Hgto decomposer

chlorine

saturatedbrinein

spentbrine

out

hydrogen

waterin

sodium

hydroxide

solution

sodium-mercuryamalgam Na/Hg

from cell

mercury returnedto electrolysis cell

decomposer

graphiteblocks

H2(g)

H2O(l) H+

(aq) + OH (aq)-

2H+

(aq) + 2e-

Cl (g) + 2e2-

2Cl (aq)-

2Na+(aq) + 2e- 2Na(l)

2Na+(aq) + 2e-2Na/Hg(l) + Hg(l)

Hg(l)2Na/Hg(l)

117

25

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.

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.

Comparison of mercury, diaphragm and membrane cellsFactors 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.

Mercury Diaphragm Membraneconstruction costs expensive relatively

cheapcheaper than mercury cell

operation toxic mercury must be removed from effluent

frequent asbestos diaphragm replacement

low maintenance costs

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 high medium

purity of brine important important very important

Figure 6 The diaphragm cell.

The chlorine-alkali balanceFor every tonne of chlorine, 2.25 tonnes of 50% sodium hydroxide and 340 m3 of hydrogen (under normal conditions) are also produced. It is necessary, therefore, to ensure that all these products can be sold.

The futureA 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 hydrogen ions migrate to the cathode, hydrogen is liberated. However, if oxygen is pumped into this part of the cell, the hydrogen reacts to form water and the voltage needed for the electrolysis process is reduced by 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 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 constructed in China, using ODC technology.

Table 2 Comparison of the three cells.

Figure 7 Chlorine is stored under pressure as a liquid. This photograph was taken in southern France.

184

59

polyesTers

Polyesters 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.

UsesPolyesters are extremely important polymers. Their most familiar applications are in clothing, food packaging and plastic water and carbonated soft drinks bottles.

The most used of the polyesters has the formula:

Being an ester, it is made from an acid, benzene-1,4-dicarboxylic acid, and an alcohol, ethane-1,2-diol (Unit 27).

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 benzene-1,4-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 packaging, they are in three directions (Figure 1).

As fibresThe polyester is produced as small granules. These are melted and squeezed through fine holes and the resulting filaments spun to form a fibre. This fibre, commonly 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.

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.

O RC

On

Figure 1 Diagram to show the arrangement of PET molecules in PET fibres, films and packaging.

Figure 2 Polyesters are often used to make the suits and parachutes for sky divers.

185

59

polyesTers

As filmsThe polyester can also be made into thin films which can be used in food packaging, audio and video tapes, electrical insulation, and X-ray films.

As packagingA 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, moulded and then stretched. The molecules are now orientated in three directions giving the plastic great strength.

Manufacture of PET(a) The production of the monomerEthane-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).

Using the acid provides a direct esterification reaction, while the dimethyl ester reaction involves ester interchange. The dimethyl ester route requires the use of an acid catalyst whereas direct esterification is self-catalysed by the carboxylic acid groups.

The dimethyl ester route was originally preferred because 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.

(i) Starting from the acid: Direct Esterification ReactionThe acid reacts directly with ethane-1,2-diol:

(ii) Starting from the dimethyl ester: Ester Interchange ReactionThe 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.

CH2 CH2HO OHC

OH

OC

HO

O

CH2 CH2HO OH

CH2 CH2 OHC

O

OC

O

O

CH2 CH2HO

‘PET’ monomer

+ 2H O2

benzene-1,4-dicarboxylic acid(terephthalic acid)

ethane-1,2-diol

+ +

COH

OC

HO

O

CH3 OH CH3HO

CH3

CO

OC

O

O

CH3

CH2 CH2HO OHCH2 CH2HO OH

CO

OC

O

O

CH2 CH2HO CH2 CH2 OH

+ 2CH OH3‘PET’ monomer

catalyst

methanol

catalyst

ethane-1,2-diol

++

++

186

59

polyesTers

(b) Polymerization of the monomerThe monomer then undergoes polycondensation with the elimination of ethane-1,2-diol:

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.

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.

Benzene-1,4-dicarboxylic acidBenzene-1,4-dicarboxylic acid is manufactured by oxidation of 1,4-dimethylbenzene (commonly known as para-xylene).

One method is to pass air into the liquid hydrocarbon dissolved in ethanoic acid under pressure, in the presence of cobalt(ll) and manganese(ll) salts as catalysts, at about 500 K:

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.

CH2 CH2 OHC

O

OC

O

O

CH2 CH2HOn

‘PET’ monomer

CH2 CH2

CO

OC

O

O

n‘PET’ polymer

OHCH2 CH2HO+ n

187

60

poly(eThene)

Over 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.

UsesPoly(ethene) is produced in three main forms: low density (LDPE) (< 0.930 g cm-3) and linear low density ( LLDPE) (ca 0.915-0.940 g cm-3) and high density (HDPE) (ca 0.940-0.965 g cm-3).

The LDPE or LLDPE form is preferred for film packaging and for electrical insulation. HDPE is blow-moulded to make containers for household chemicals such as washing-up liquids and drums for industrial packaging. It is also extruded as piping.

All forms can be used for injection-moulded products such as buckets, food boxes and washing-up bowls (Table 1).

Process

(Unit 53)

HDPE LDPE LLDPE

Making film

Food packaging

Shopping bags

Cling film

Milk carton lining

Stretch film

Injection moulding

Dustbins

Crates

Buckets

BowlsFood boxes

Blow moulding

Detergent bottles

Drums

Squeezable bottles

Extrusion Water pipes

Flexible water pipes

Cable jacketing

Cable coating

HDPE

LDPE/LLDPEFigure 1 Uses of poly(ethene).

Table 1 Examples of uses of poly(ethene).

Figure 2 Poly(ethene) is used to make large water pipes -

Figure 3 - and far smaller pipes.

188

60

poly(eThene)

Annual production/tonnesUK 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.

ManufactureThe 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).

Low density poly(ethene) (LDPE)The process is operated under very high pressure (1000-3000 atm) at moderate temperatures (420-570 K) as may be predicted from the reaction equation:

An initiator, such as a small amount of oxygen, and/or an organic peroxide is used.

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

density of the material. LDPE is generally amorphous 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:

• a Ziegler-Natta organometallic catalyst (titanium compounds with an aluminium alkyl) (Unit 2).

• 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.

HDPE is produced by three types of process. All operate at relatively low pressures (10-80 atm) in the presence of a Ziegler-Natta or inorganic catalyst. Typical temperatures range between 350-420 K. In all three processes hydrogen is mixed with the ethene to control the chain length of the polymer.

(i) Slurry process (either CSTR (continuous stirred tank reactor) or a loop (Unit 3)

Figure 4 The slurry process.

189

60

poly(eThene)

The Ziegler-Natta catalyst (Unit 2), as granules, is mixed with a liquid hydrocarbon (for example, 2-methylpropane or hexane), which simply acts as a diluent. A mixture of 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.

(ii) Solution processThe second method involves passing ethene and hydrogen under pressure into a solution of the Ziegler-Natta catalyst in a hydrocarbon (a C10 or C12 alkane). The polymer is obtained in a similar way to the slurry method.

(iii) Gas phase process

A mixture of ethene and hydrogen is passed over a Phillips catalyst in a fixed bed reactor (Unit 3) (Figure 6).

Ethene polymerizes to form grains of HDPE, suspended 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 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.

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:

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 5 The manufacture of poly(ethene) using the slurry process.

Figure 6 Low pressure gas-phase process.

Figure 7 Granules of poly(ethene) which are then used to make film, extruded into pipes or moulded.

190

60

poly(eThene)

technique has been developed, based on both Ziegler-Natta and inorganic catalysts to produce linear low density poly(ethene) LLDPE, which has even improved properties over LDPE. Any of the three processes, slurry, solution and gas phase, can be used when a Ziegler-Natta catalyst is chosen. The gas phase process is used when the inorganic catalyst is employed.

Small amounts of a co-monomer such as but-1-ene or hex-1-ene are added to the feedstock. The monomers 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:

The side chains are known as pendant groups, or short chain branching. The molecule can be represented as:

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

a sandwich. There is a transition metal (often zirconium or titanium) ‘filling’ a hole between layers of organic compounds.

The catalysts are even more specific than the original Ziegler-Natta catalysts and it is possible to control the polymer’s molecular mass as well as its configuration. Either the slurry or solution processes are usually used. Metallocenes are discussed in more detail in Unit 63.

Poly(ethene) produced using a metallocene can be 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.

Co-polymersThe manufacture of co-polymers of ethene are described in Unit 63.

Figure 8 Poly(ethene) film is used extensively for wrapping foods.

CH2 CH CH2 CH2 CHCH2 CH2

CH2

CH3

CH2CH2

CH2

CH3

191

61

poly(meThyl 2-meThylpropenoaTe)

Poly(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.

UsesPoly(methyl 2-methylpropenoate) is better known as 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.

Special grades are used in diverse applications such as false teeth and eyes and as a major component of bone cements.

The monomer is used in adhesives, surface coatings and in paints (Unit 17).

Annual productionPolymer

UK 50 000 tonnesEurope 490 000 tonnesWorld 1.9 million tonnes

MonomerUK 220 000 tonnesEurope 890 000 tonnesWorld 3.3 million tonnes

Manufacture(a) The monomerThe monomer is the methyl ester of 2-methylpropenoic acid, methyl 2-methylpropenoate (methyl methacrylate):

Worldwide, over 80% of the monomer is made from propanone (Unit 45) by a sequence of steps which begins by reacting propanone with hydrogen cyanide.

Figure 2 Uses of poly(methyl-2-methylpropenoate).

Figure 1 The elevator cage installed in La Grande Arche in Paris is made of sheets of poly(methyl 2-methylpropenoate).

192

61

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 heated to 600K:

(b) The polymerPolymerization of methyl 2-methylpropenoate is achieved using free radical initiators, such as an azo compound or a peroxide:

The amount of initiator employed affects both polymerization rate and resulting molecular mass of the polymer.

Polymerization is carried out commercially in several ways, i.e. in bulk, solution, suspension and emulsion.

(c) Co-polymersCo-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 stability compared to the homopolymer.

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.

The product, on reaction with concentrated sulfuric acid 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:

The temperature is decreased to 370 K and methanol is added. The amide group is hydrolysed and esterified. The reactions can be summarised as:

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 in the liquid phase under pressure of about 10 atm at 350 K:

CH3

CO CH2 3

CH C2n

CH3

CO CH2 3

CH C2 n

193

62

poly(phenyleThene)

Poly(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.

UsesThe largest use for poly(phenylethene) is for packaging, particularly for foods such as poultry and eggs, for cold drinks and take-away meals.

It is also used in making appliances, including refrigerators, microwaves and blenders. It is the leading choice for jewel boxes (cases for CDs and DVDs) and is also widely used for its insulating properties.


ManufacturePoly(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 benzeneb) the manufacture of phenylethenec) the polymerization of phenylethene

(a) The manufacture of ethylbenzene from benzeneBenzene vapour and ethene are mixed and passed over an acid catalyst, at 650 K and 20 atm pressure:

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 phenyletheneEthylbenzene vapour is mixed with excess steam and passed over heated iron(lll) oxide. It is dehydrogenated:

A small amount of potassium oxide is mixed with the iron(lll) oxide (which keeps the catalyst in the iron(lll) state).

The steam reduces ‘coking’ (the formation of soot on the catalyst from the decomposition of ethylbenzene at the high temperatures used).

(c) The polymerization of phenyletheneRadical 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-1,3-diene) rubber. This tougher product – generally known

Figure 1 Uses of poly(phenylethene).

194

62

poly(phenyleThene)as High Impact Polystyrene (HIPS) – is made exclusively by continuous thermal mass polymerization, in which heat is required to initiate the polymerization reaction. This toughened polymer is translucent.

The structure of poly(phenylethene) made by these technologies is atactic. By modification of the polymerization technique – principally by the use of metallocene catalysts – stereoregular (syndiotactic) structures can be obtained (Unit 53). This syndiotactic polymer (sPS) has improved properties – particularly thermal and mechanical.

Another co-polymer is formed on polymerizing a mixture of phenylethene (styrene) and propenonitrile (acrylonitrile). It is known as SAN (styrene-acrylonitrile). It is less flexible, more transparent and has more resistance to heat and chemicals than poly(phenylethene). It is used in car headlamps, cassette covers, syringes and high quality kitchen appliances.

A further modification involves the co-polymerization (Unit 53) of phenylethene (styrene) with propenonitrile (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.

ABS is tougher, scratch proof and more chemically resistant than rubber-modified poly(phenylethene) and is used, for example, in casings for computers, cycle helmets, calculators, telephones, vacuum cleaners and toys. Often ABS is blended with SAN to make it even more rigid.

Another variation is the co-polymer formed between ABS and methyl 2-methylpropenoate, which has a high resistance to chemical attack, high transparency and is very tough (Unit 61).

Expanded poly(phenylethene)Expanded poly(phenylethene) is manufactured as beads containing pentane (a liquid at room temperature).

When they are heated in steam, the hydrocarbon volatilises and the beads expand (Figure 3). These are subsequently blown into moulds and fused by further steaming and then cooling. The expanded poly(phenylethene) has good thermal insulation and shock absorbing properties.

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.

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.

195

63

poly(propene)

Propene 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.

UsesPoly(propene) is processed into film, for packaging and 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).

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)

rigid packaging

(crates,

orrugated boards)

pails,CD and DVD boxes,c

28%

consumer products

(furniture,housewares,

toys)

15%

technical parts

(car bumpers, dashboards,sewage pipes, drain pipes,

electric cables)

20%

textiles

(carpets,carpet backing)

21%

films

16%(food packaging)

• easy to weld (design)

• recyclabililty

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 (density 0.905 g cm-3). It has a melting point of 440 K and a crystallinity of ca 50-60%. The polymer, unlike poly(ethene), is transparent.

Structure of the polymerThe propene molecule is asymmetrical,

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:

Figure 1 Uses of poly(propene).

Figure 2 Molecular structures of poly(propene).

196

63

poly(propene)

The ‘one handed’ structure of isotactic poly(propene) causes the molecules to form helices. This regular form 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 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.


ManufacturePoly(propene) is produced from propene. Propene is produced in large quantities from gas oil, naphtha, ethane and propane (Unit 4).

(a) Using a Ziegler-Natta catalyst 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 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 processPolymerization 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).

(ii) The gas phase processA mixture of propene and hydrogen is passed over a bed 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 eliminated gaseous and aqueous effluents by the use of high activity catalysts, resulting in low residues in the final polymer.

(b) Using a metallocene as catalystMetallocenes are being increasingly used as catalysts for the production of poly(ethene) (Unit 60) and poly(propene).

Metallocenes are strictly defined as molecules which have a transition metal atom bonded between two cyclopentadienyl ligands which are in parallel planes. Ferrocene is a particularly well known example:

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.

197

63

poly(propene)

However, the term is now used more widely to include other ligands related to cyclopentadienyl. One such metallocene is based on zirconium:

Zirconium has an oxidation state of 4 and is bonded to two indenyl ligands (a cyclopentadienyl ligand fused to a benzene ring). They are joined by two CH2 groups. In conjunction with an organoaluminium compound, it acts as a catalyst for the polymerization of alkenes such as ethene and propene. The specific orientation of the 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,

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-polymersThere 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).

The crystallinity and melting point are reduced and the products are more flexible and are optically much clearer. 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) but which have better mechanical and optical properties.

The second type of co-polymers is the so-called ‘block’ co-polymers (Unit 53). These are made by following the poly(propene) homopolymerization with a further, separate stage, in which ethene and propene are co- polymerized in the gas phase. Thus these two processes are in series (Figure 5).

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 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 in making crates, pipes, furniture and toys, where toughness is required.

Figure 5 lllustrating the homopolymer and the block co-polymer formed from propene and ethene.

Figure 6 The propene-ethene block co-polymer nodules dissipate impact energy and prevent cracking.

Figure 4 llustrating an alternating co-polymer formed from propene and a small amount of ethene.

198

64

poly(propenoiC aCid)

There 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.

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 1000-fold its mass (Figure 1), and is used as the basis of disposable nappies.

Uses of polypropenoatesThe 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 (2-methylpropenoate).

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 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 acidEurope 380 000 tonnes

World 1.8 million tonnes

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.

199

64

poly(propenoiC aCid)

Manufacture of propenoic acidPropenoic acid (acrylic acid) is manufactured from propene in two steps.

The first stage is the oxidation of propene to propenal. The alkene and air are mixed and passed over a heated catalyst, often a mixture of bismuth(III) and molybdenum(VI) oxides on silica, at ca 650 K (Unit 2):

The second stage occurs when propenal and air are passed over another catalyst, a mixture of vanadium(V) 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 monomer (known as bulk polymerization), but more often it is polymerized in an aqueous solution or as an emulsion, also in water:

Manufacture of the polypropenoatesPropenoic acid is reacted with an alcohol (for example, methanol, ethanol, butan-1-ol) in the liquid phase with a trace of sulfuric acid as a catalyst to produce the esters. For example:

Subsequently the esters are polymerized, using an organic peroxide as an initiator. The pure monomer may be used (known as bulk polymerization), but again more frequently the reaction is carried out in an aqueous solution or in an emulsion in water. For example:

If co-polymers of the esters are required, the two monomers are mixed prior to the polymerization reaction under similar conditions.

A postscript on propeneAll the propenoate (acrylic) polymers are derived from propene as the summary shows:

propene

H C2 CH CHO

H C2 CH CO H2

H C2 CH CO R2

CH2

CO R2

C

H n

H C2 CH C N

CH2

CN

C

H n

CH2

CO CH2 3

C

n

HCN

H C3 CO CH3

H C3 CH3

CN

OH

C

NH /O3 2

CH2

CO H2

C

H n

O2

cumeneprocess

benzene

O2

ROH

H C2 CCN

CH3

polypropenoates

poly(methyl 2-methylpropenoate)

poly(propenonitrile)

poly(propenoic acid)

propenoic acid

Unit 61

Unit 65

H C2 CH CH3

H C2 CCH3

CO H2

H C2 CCH3

CO CH2 3

CH3

This unit

This unit

200

65

poly(propenoniTrile)

Poly(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.

UsesPoly(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, 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).

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).

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 co-polymer (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).

Annual production of propenonitrileUK 280 000 tonnesEurope 1.8 million tonnesWorld 5.9 million tonnes

Figure 2 The high heels are made from a blend of ABS and a polyamide (Unit 56) which is very strong.

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.

CH2

C

C

H n

N

201

65

poly(propenoniTrile)Manufacture(a) The monomerPropenonitrile, the monomer, is manufactured from propene. The alkene is mixed with ammonia and oxygen (from air) (1:1:2 volume ratio) and passed over a mixture of bismuth(III) and molybdenum(VI) oxides (Unit 2):

As it is a very exothermic reaction, and the temperature must be controlled at ca 600 K, a fluidized bed reactor (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 as the feedstock. It will become particularly important if propane becomes much cheaper than propene. The catalyst used is based on vanadium(V) and antimony(III) oxides.

(b) The polymerThe 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-polymersPolymerization takes place as for the homopolymer, the two monomers being mixed prior to addition of the

initiator. When, ethenyl ethanoate is used as the co-polymer, polymerization is initiated with small amounts of potassium hydrogensulfite and potassium peroxodisulfate which get incorporated into the co-polymer, giving it sites which can bind to colorants and make them fast (Unit 11). Alternatively, a small amount of a third monomer containing, for example a sulfonic acid group, serves the same purpose.

The co-polymer contains a more or less regular alternation of the individual monomers, an example of an alternating co-polymer (Unit 53).

Similar procedures are used when other co-monomers are used.

With methyl propenoate and methyl 2-methylpropenoate, block co-polymers are produced:

An alternating polymer is produced with 1,1-dichloroethene as the co-monomer.

Figure 3 The soft tops for high quality cars are produced from almost pure homopolymer.

202

66

poly(TeTrafluoroeThene)

The 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.

UsesIn many applications, tetrafluoroethene (TFE) is co-polymerised with other fluorinated monomers, such as 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 or products are highly corrosive to ordinary materials such as steel

• 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 and shoes, which allows water vapour to diffuse away from the skin but prevents liquid water (rain) from soaking in

• non-stick domestic utensils, e.g. frying pans

• medical - catheter tubing

• hose and tubing

• solid lubricants

• combinations with magnesium and aluminium as an igniter for explosives

Annual productionUK 4000 tonnesEurope 15 000 tonnesWorld 200 000 tonnes

ManufacturePTFE is made from methane in a series of reactions:

a) production of trichloromethaneb) production of chlorodifluoromethanec) production of tetrafluoroethene (TFE)d) polymerization of tetrafluoroethene

(a) Production of trichloromethaneTrichloromethane is one of the products formed by the reaction of methane and a mixture of chlorine and hydrogen chloride. This can be performed in the liquid 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 chlorodifluoromethaneTrichloromethane is reacted with anhydrous hydrogen fluoride in the presence of antimony(III) and antimony(V) chlorofluoride to give 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 there is minimum storage time of the monomer between its production and its polymerization.

CHCl (g) + 2HF(g)3 CHClF (g) + 2HCl(g)2

chlorodifluoromethane

CF2n

CF2

Figure 1 The retractable roof installed over the Centre Court at Wimbledon in 2009 is made of poly(tetrafluoroethene).

203

66

poly(TeTrafluoroeThene)Chlorodifluoromethane is heated in the absence of air, a process known as pyrolysis:

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 the reaction mixture and hence reduce the reactant partial pressure, and thus the formation of carbon and toxic by-products. The steam also supplies all the heat required by this endothermic reaction. Very little 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:

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 time is 1 second.

(d) Polymerization of tetrafluoroethenePolymerization 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.

Co-polymersThere 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 described above, these co-polymers are used in many of the examples given for PTFE.

The co-polymer produced from ethene and tetrafluroethene is an alternating co-polymer (Unit 53) usually known by its trivial name, ethylene tetrafluoroethylene (ETFE):

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 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 Olympic Stadium in Beijing. The roofs are made up of 2 – 5 layers of large cushions of ETFE (Unit 12). It is also used as an outer skin of large buildings (Figure 2).

CF2F C3 CF

hexafluoropropene

CF2F C3 CFCF2 CF2 O

perfluoropropylvinyl ether

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.

204

67

polyureThanes

The 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.

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:

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.

O C N R1 OCN nHO R2 OHO

C N R1 OCN

HO H

R2 O

n+n

UsesThe physical properties, as well as the chemical structure, of a polyurethane depend on the structure of the original reactants, in particular the R1 and the R2 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.

There is a fundamental difference between the manufacture of most polyurethanes and the manufacture 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.

Polyurethanes, on the other hand are usually made 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.

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).

N

H

C

O

Rn

O

Figure 1 Uses of polyurethanes. 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.

205

67

polyureThanes

Some examples of the main reasons for choosing polyurethanes as shown in Table 1.

Uses Reasonscushioning 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

Polyurethanes can be rigid or rubbery at any density between, say 10 kg m-3 and 100 kg m-3. 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.


ManufactureAs polyurethanes are made from the reaction between an isocyanate and a polyol, the section is divided into three parts:

a) production of isocyanatesb) production of polyolsc) production of polyurethanes

(a) Production of isocyanatesAlthough many aromatic and aliphatic polyisocyanates exist, two are of particular industrial importance. Each of them has variants and together they form the basis of about 95% of all the polyurethanes. They are:

• TDI (toluene diisocyanate or methylbenzene diisocyanate)

• 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.

The mixture of diisocyanates known as TDI consists of two isomers:

The starting material is methylbenzene (toluene). When it reacts with mixed acid (nitric and sulfuric), two isomers of nitromethylbenzene (NMB) are the main products.

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:

The mixture of dinitrobenzenes is then reduced to the corresponding amines:

In turn, the amines, known commercially as Toluene Diamines or TDA, are heated with carbonyl chloride (phosgene) to produce the diisocyanates and this process can be carried out in the liquid phase with chlorobenzene as a solvent at about 350 K:

Table 1 Properties and uses of polyurethanes.

206

67

polyureThanes

The choice of polyol, especially the number of reactive hydroxyl groups per polyol molecule and the size and flexibility of its molecular structure, ultimately control the degree of cross-linking between molecules. This has an important effect on the mechanical properties of the polymer.

An example of a polyol with two hydroxyl groups (ie a long chain diol) is one made from epoxypropane (Unit 46), by interaction with propane-1,2-diol, (which itself is formed from epoxypropane, by hydrolysis):

An example of a polyol which contains three hydroxyl groups is produced from propane-1,2,3-triol (glycerol) and epoxypropane:

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.

Alternatively, these reactions are carried out in the gas phase by vaporizing the diamines at ca 600 K and mixing them with carbonyl chloride. This is an environmental and economic improvement over the liquid phase process as no solvent is needed.

In either process, the reagent is the isomeric mixture of the dinitrocompounds, 80% 2,4- and 20% 2,6-, so the product is a mixture of the diisocyanates in the same proportions.

It is expensive to produce this mixture in different 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.

The starting materials are phenylamine (aniline) and methanal (formaldehyde) (Unit 37) which react 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:

The term MDI refers to the mixture of the three isomers in Figure 2. They can be separated by distillation.

(b) Production of polyolsThe 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.

Figure 2 Isomers of MDI.

207

67

polyureThanes

(c) Production of polyurethanesIf 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:

A much used polyurethane is made from TDI and a polyol derived from epoxypropane:

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 ‘rigid’ polyurethanes. Thus a diisocyanate, such as MDI 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).

As well as polyisocyanates and polyols, the manufacture of polyurethanes needs a variety of other chemicals to control the polyurethane-forming reactions and to create exactly the right properties in the end-product.

All practical polyurethane systems include some, but not necessarily all, of those described in Table 2.

CH2N N

4,4’- MDI

CO OC HO CH2 CH2 OH

ethane-1,2-diol

+

CH2N NC OC

O

H

O

H

CH2 CH2 O

n

a polyurethane

n n

the urethane linkage

Additives Reasons for usecatalysts 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

surfactants

to create polyurethane as a foam

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

Manufacturing processAs an example, consider the manufacture of a moulded item that might otherwise be made from a thermoplastic polymer by injection moulding. To make it of polyurethane, it is necessary to mix exactly the right masses of the two major components (polyisocyanate and polyol), which must be liquids. The reaction starts immediately and gives the solid polymer. Depending on the formulation, the catalysts used and the application,

Table 2 Additives used in the manufacture of polyurethanes.

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.

208

67

polyureThanes

the reaction is typically completed in between a few seconds and some minutes. In this time, therefore, it is essential to dispense the reacting liquid mixture into 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 mould and the manufactured article can be taken from the mould immediately.

Foamed polyurethanesWhen the two liquids react, a solid polymer is formed. The polymer may be elastic or rigid. However, it may also contain bubbles of gas so that it is cellular - a foam.

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:

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

polymer, and the available gas pressure cannot create any further expansion.

A shoe sole, for example, may be ‘blown’ to double the 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.

In thermal insulation, it is the gas trapped in the cells which insulates. The polymer that encloses the cells reduces the insulation efficiency, so it makes sense to have as little of it as possible.

AdhesionIn the final stages of the polyurethane-forming reaction, the mixture becomes a gel with very effective surface adhesion. Hence polyurethanes can be 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.

209

68

siliCones

Silicones 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.

Structures and properties of siliconesSilicones are synthetic polymers with a silicon-oxygen backbone similar to that in silicon dioxide (silica), but with organic groups attached to the silicon atoms by C-Si bonds. The silicone chain exposes organic groups to the outside.

Thus, despite having a very polar chain, the physical properties of silicones are similar to those of an alkane. However, the -Si-O-framework of the silicone gives the polymers thermal stability, as in silica, and so they can be used where comparable organic materials would melt or decompose.

To distinguish between different silicones, systematic names are used, based on the monomer. The simplest silicon compound is silane, SiH4 which belongs to the homologous series of silanes. Silanes correspond to the alkanes whose simplest member is methane, CH4.

The presence of the oxygen atoms in the silicone chain is indicated by using the systematic name, siloxane, so termed as it contains a silicon atom, an oxygen atom and it is saturated as in an alkane.

Thus if the groups attached to the siloxane chain are phenyl groups, the resulting silicone is called poly(diphenylsiloxane) and has repeating units along the chain.

O

SiSi

O

R

R

R

R

H Si

H

H

H

H

H

H

H

C

silane methane

The most widely used silicones are those which have methyl groups along the backbone. Properties such as solubility in organic solvents, water-repellence and flexibility can be altered by substituting other organic groups for the methyls. For example, silicones with phenyl groups are more flexible polymers than those with methyl groups. They are also better lubricants and are superior solvents for organic compounds.

The structure of the repeating units of silicones can be represented as:

Where R represents organic groups attached to the silicone backbone, for example:

UsesSilicones can be sub-divided into four classes:

a) Silicone fluidsb) Silicone gelsc) Silicone elastomers (rubbers)d) Silicone resins

Their physical form and uses depend on the structure of the polymer.

(a) Silicone fluids are typically straight chains of poly(dimethylsiloxane), with the repeating structure:

O SiO Si

CH3

CH3

Si O Si O

R

R

R

R

HC CH2 CH2CH2CF3

phenyl ethenyl trifuoropropyl

CH3

methyl

210

68

siliCones

They usually have trimethylsilyl groups, Si(CH3)3, at each end of the chain:

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 cross-links between the chains, giving it a very open three-dimensional 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 high-performance 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.

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 water-repellent.

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.

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.

Si O Si O

CH3 CH3

CH3 CH3

H C3 Si

CH3

CH3n

CH3

poly(dimethyl)siloxane

211

68

siliCones

ManufactureSilicones 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:

The production of silicones from silicon takes place in three stages:

a) synthesis of chlorosilanesb) hydrolysis of chlorosilanesc) condensation polymerization (Unit 53)

(a) Synthesis of chlorosilanesSilicon is first converted into chlorosilanes, e.g. RSiCl3, 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 copper-containing materials can be used, for example, brass or copper(II) chloride), a volatile mixture of chlorosilanes distils over. For example:

The mixture of liquids contains these three compounds:

Careful distillation of the liquid mixture of chlorosilanes produces pure fractions of each chlorosilane. Dimethyldichlorosilane is the main product (ca 70-90%, the amount depending on the conditions used).

(b) Hydrolysis of chlorosilanesA dichlorosilane is hydrolysed to a molecule with two hydroxyl groups:

The product is a disilanol. The suffix -ol in a silanol is to show that the molecule contains at least one hydroxyl group attached to a silicon atom and the simplest example is dimethyldisilanol:

This nomenclature is similar to that of the alcohols, the simplest alcohol with two hydroxyl groups being ethane-1,2-diol:

The hydroxyl groups of silanols react spontaneously to form a siloxane:

If R is a methyl group, the polymer is a poly(dimethylsiloxane).

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.

Si

O

Si

SiSi

O

O O

CH3

CH3

CH3

CH3

H C3

H C3

H C3

H C3

The oligomers are washed and dried. The hydrochloric acid is recycled and reacts with methanol to regenerate chloromethane:

Si

R

HO OH

R

Si

R

HO O

R

H

n

n + ( )H On-1 2

Si

CH3

Cl Cl

CH3

Si

CH3

Cl

CH3

CH3

CH SiCl3 3 (CH ) SiCl3 2 2 (CH ) SiCl3 3

Si

CH3

Cl Cl

Cl

HO CH2CH2 OH

ethane-1,2-diol

CH OH3 + HCl CH Cl3 + H O2

Si(s) + 2CH Cl(g)3 (CH ) SiCl (g)3 2 2

SiO (s) + 2C(s)2 Si(s) + 2CO(g)

Si

R

Cl Cl

R

+ 2H O2 Si

R

HO OH

R

+ 2HCl

Si

CH3

CH3

HO OH

dimethyldisilanol

212

68

siliCones

(c) Condensation polymerizationThe oligomers condense rapidly in the presence of an acid catalyst to form long chain polymers:

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:

(i) Cross-linking is often effected by first synthesizing silanes with a functional group, in place of a methyl group, that will 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 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):

(ii) Cross-linking can also be achieved by using siloxanes with ethenyl (vinyl) groups and other siloxanes containing Si-H groups, with a platinum compound as catalyst:

(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. The other product formed is ethanoic acid which can be recognized by its vinegary smell.

(iv) If some methyltrichlorosilane is added to the reactant, say dimethyldichlorosilane, the three chlorine atoms are hydrolysed, thus producing a three dimensional network.

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.

R OO R OR2 .

C

CH3

CH3

where R =

H SiSi

CH3

CH3

CH CH2 +

Si

CH3

CH3

CH2 CH2 Si

Si O H

CH3

CH3

HO

m

Si O H

CH3

CH3

HO

n

Si O H

CH3

CH3

HO

m+n

+

+ H O2

These materials are silicone fluids.

and so on...

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 km h

-1. 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.

229

74

sTeel

Steel 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.

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.

UsesThe 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).

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).

Figure 3 Uses of steel in the UK.

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 ‘Bird’s Nest’ would stretch for 36 km.

230

74

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 generators (nuclear, conventional fuels and wind), gears and engines, which have to be very tough and withstand high temperatures.

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 productionUK 14 million tonnesEurope 227 million tonnesWorld 1360 million tonnes

Steel production in Asia has expanded rapidly, with China now accounting for nearly 40% of world production.

ManufactureThere 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

The furnace (also known as a converter or vessel) is charged with steel scrap (up to about 30%) and molten

Figure 4 A wind turbine constructed from steel.

Figure 5 The container ship and the containers are both constructed from steel plate.

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.

231

74

sTeel

iron from a ladle. An oxygen lance, cooled by circulating water, is lowered into the furnace and high purity oxygen is injected into the vessel at twice the speed of sound which ensures that all the impurities are converted into their oxides. The main chemical reactions are:

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 ProcessSteel 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).

The furnace is a circular bath with a movable roof through

which three graphite electrodes are raised or lowered. These electrodes are massive, often 6 m high and 4 m wide, and the furnace can hold over 100 tonnes of liquid steel.

After the steel scrap is placed in the furnace, the roof is put into position and the electrodes lowered into the

furnace. An arc is struck by passing an electric current through the metal. The heat generated melts the scrap metal. Lime (as calcium oxide or calcium carbonate), fluorspar (which helps to keep the hot slag as a fluid) and 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.

Secondary steelmakingThe 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.

The process provides precise control of harmful impurities (particularly sulfur, phosphorus and, in some cases, trace metals and hydrogen) by adding materials via ladle injection. For example, aluminium and silicon are added to reduce any oxidised material.

Other techniques used to help to improve the quality of the steel include stirring (ladle stirring) and applying a vacuum to the steel to remove gases (vacuum degassing).

Figure 7 Illustrating the Electric Arc Process which uses scrap steel to produce pure steel very efficiently.

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.

232

74

sTeel

CastingSteel is produced in three forms, the form chosen being dependent on its ultimate use:

• as a slab, a long thick piece of metal with a rectangular cross-section

• as a bloom, a long piece of metal with a square cross-section

• as a billet, similar to a bloom but with a smaller cross-section.

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 required.

The casting is a very precise set of processes. The following descriptions are an outline.

Continuous castingIn continuous casting, the steel, still molten from the furnace, is poured into a water-cooled mould (teeming) from which it emerges as a strand which is solidifying at the surface. The strand passes through a series of rollers which are water sprayed to produce a solid (a slab, bloom or billet) which is then sent to be hot rolled.

Ingot castingMolten steel is poured into a cast iron mould to solidify as an ingot. This generally weighs less than 20 tonnes but rotor forgings can weigh up to 500 tonnes.

When the ingot has solidified, the mould is removed. Each ingot is of carefully pre-arranged dimensions and mass from which articles of the required size can be rolled.

RollingSteel 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

of ships. The sheet is rolled further to produce thinner sheet, used for example in the manufacture of cars.

Blooms and billets are used to roll long bars of steel for 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 as the steel passes through the rollers.

During this rolling, oxygen in the air has reacted with the hot iron to form a very thin layer of iron(III) oxide on the surface. It is blue/grey in colour (only when it is thicker does it appear red). This must be stripped from the surface prior to the next stage, otherwise the final product will be susceptible to rusting and unsuitable for galvanizing with zinc (Unit 76) and other surface treatments.

The stripping process is known as pickling. The steel 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 cans are pressed out with sides and bottoms as a single entity, needing only the top to be fitted after filling.

Very strong wires are produced by cold drawing.

RecyclingThe recovery of scrap steel probably constitutes the world’s largest scale recycling process. The scrap is either part of the charge for the Basic Oxygen Process or is the complete charge for the Electric Arc Furnace Process.

About 40% of the iron-containing materials used in 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%.

Figure 9 Steel tube is being produced in a continuous casting process.

241

index

AABE process 48, 52ABS 168, 169, 180, 192, 200Acephate 73Acetamiprid 75Acetic acid - see ethanoic acidAcetyl-CoA-carboxylase, inhibitors of 72Acid dyes 59-60Acrylic acid - see propenoic acidAcrylic resins 90-91, 200-201Acrylics - see polypropenoates, poly(methyl propenoate) and poly(propenonitrile)Acrylonitrile - see propenonitrileAddition polymers 167Adipic acid - see hexanedioic acidAdvanced High Strength Steel 230Agrochemicals – see crop protection chemicalsAlcohols, long chain 97, 98Aldicarb 73Alkenes, long chain 96, 97Alkyd resins 91-92, 94Alkylaluminium 18, 96, 97, 196Alkylbenzene sulfonates 96-97Alkyl betaines 99, 101Alkyl ether sulfates 97, 101Alkyl sulfates 97Alloys, aluminium 145, 213, 237, 240Alloys, copper 213, 220, 238, 239, 240Alloys, iron 152, 220, 229-232, 234Alloys, lead 229, 238Alloys, magnesium 213, 227, 240Alloys, manganese 213, 220Alloys, nickel 220Alloys, phosphorus 220Alloys, platinum 13, 67Alloys, rhodium 13, 67Alloys, silicon 213Alloys, steel 229Alloys, tin 220Alloys, titanium 233-236, 237Alloys, zinc 213, 220, 237, 238, 240Altuglas - see poly(methyl 2-methylpropenoate)Alumina - see aluminium oxideAluminium 213-215, 227, 233Aluminiumalkyl - see alkylaluminumAluminium bronze 220Aluminium chloride 96Aluminium fluoride 213, 214Aluminium hydroxide 213-214Aluminium oxide 14, 213-214Aluminium phosphide 153Aluminiumtriethyl - see triethylaluminiumAluminosilicates - see zeolitesAmino acids 32-33

2-Aminoethanoic acid 1522-Aminoethanol 119, 146, 160Aminopyralid 70Ammonia 11, 12, 13, 40, 102-105, 141, 157, 165, 201Ammonium carbamate 165Ammonium chloride 238Ammonium dihydrogenphosphate 150Ammonium hydrogencarbonate 157Ammonium nitrate 81, 82Ammonium phosphates - see also ammonium dihydrogenphosphate and diammonium hydrogenphosphateAmmonium sulfate 41, 81, 161, 192Amphoteric surfactants 98, 101Amylases 45, 173Amyloglucoside 45Amyloses 173Anastase 163Aniline 147Anion exchange resin 134Anionic surfactants 96-98Anthraquinone 131Anthraquinone dyes 58-59Antifreeze 120Apatite - see phosphate rockAramid reinforced polymer composites – see composites, aramid reinforced polymerAramids 67Argon 143, 146, 235Asahi process 178Atactic poly(propene) 195-196Atom economy 36-37Auxins 70Auxochromes 57Avermectins 74Azeotrope 45-46, 122-123, 141Azobenzene 58Azo dyes 58Azoxystrobin 78

BBagasse 50Basic dyes 60-61Basic Oxygen Steelmaking Process 234-235Batch reactors – see reactors, batchBattery, dry cell 238Bauxite 213Beckmann rearrangement 179Bendiocarb 73Bensultap 75Benzene 15, 26, 28, 29, 96, 106-107, 147,178Benzenediazonium chloride 58Benzene-1,2-dicarboxylic acid 91

Benzene-1,4-dicarboxylic acid 184, 185, 186

Benzophenylureas 76Betaines 99, 101

242

index

Bifunctional catalysts 16-17Binders 90-92Biobrom 108Biobutanol 48Biodiesel 46-47Bioethanol 44-46, 47Biofuels 44-49Bioleaching, copper 218Bioleaching, zinc 239Biomass - see biofuelsBio-oil 48, 51Biophotolysis 48, 51Biopol 172Biopols 206Biorefineries 50-51Biotechnology 52-55Bipyridyliums 70Bismuth(III) oxide 199Bisphenol A 11, 36, 92, 154, 181Bixafen 78Blast Furnace 225-226Blended fertilizer 82Blister copper 219Block co-polymer 168Bordeaux mixture 78Bornite 217Boscalid 78Bosch, Carl 104BOS Process – see Basic Oxygen Steelmaking ProcessBrass 220, 238Brine - see sodium chlorideBromine 108Bronze 220BTX 106Buckmasterfullerene 84Buta-1,3-diene 26, 29, 109, 175, 200Butadiene - see buta-1,3-dieneButanal 155Butane-1,4-diol 172Butanol 48, 155Butyl acrylate - see butyl propenoatet-Butyl hydroperoxide 139Butyl propenoate 90, 192, 198Butyl rubber - see poly(2-methylpropene)

CCadmium 238, 239, 240Caesium sulphate 162Calcining 227Calcium 236Calcium ammonium nitrate 81Calcium bromide 108Calcium carbonate 110-113, 156, 218, 222, 223, 231Calcium chloride 157Calcium dihydrogenphosphate 81, 149, 150Calcium fluoride 130Calcium hydroxide 78, 110, 113, 157, 231

Calcium iodate 177Calcium oxide 110-113, 157, 223, 227, 231Calcium phosphide 153Calcium sulfate 111, 130, 149Calendering 171Caprolactam 42, 179Caprolactone 174Carbamates - see methyl carbamatesCarbamide - see ureaCarbamide - methanal plastics 175-176Carbides 68Carbon black 68Carbon dioxide 157Carbon fibre reinforced polymer composites – see composites, carbon fibre reinforced polymerCarbon fibres 66Carbon molecular sieve 145Carbon monoxide - see also synthesis gas 47Carbon nanotubes 66, 84, 87, 88, 135Carbonyl chloride 36, 181, 205, 206Carboxamides 783-Carboxy-3-hydroxypentanoic acid 53Carboxylic acids, long chain 79-80Cartap 74Cast iron 221Catalysis - see also zeolites 11-19Catalysis, bifunctional - see bifunctional catalystsCatalysis, cracking- see cracking, catalyticCatalysis, hydrogenation of oils 48, 80Catalysis, isomerisation 28-29Catalysis, manufacture of alkylbenzenes 96Catalysis, manufacture of ammonia 12-13, 104Catalysis, manufacture of benzene 107Catalysis, manufacture of benzene-1,4-dicarboxylic acid 186Catalysis, manufacture of biodiesel 46, 47-48Catalysis, manufacture of buta-1,3-diene 109Catalysis, manufacture of butanal 155Catalysis, manufacture of chlorodifluoromethane 202Catalysis, manufacture of chlorosilanes 211Catalysis, manufacture of cumene 147Catalysis, manufacture of cyclohexane 178Catalysis, manufacture of cyclohexanol 178Catalysis, manufacture of cyclohexanone 178, 179Catalysis, manufacture of 1,2-dichloroethane 183Catalysis, manufacture of dimethylbenzene-1,4-dioate 185Catalysis, manufacture of dimethyl carbonate 181Catalysis, manufacture of dimethyl ether 137Catalysis, manufacture of epoxyethane 118, 139Catalysis, manufacture of ethane-1,2-diol 120Catalysis, manufacture of ethanoic acid 120Catalysis, manufacture of ethanol 14, 122Catalysis, manufacture of ethanol from synthesis gas 48Catalysis, manufacture of ethenyl ethanoate 90Catalysis, manufacture of ethylbenzene 193Catalysis, manufacture of ethyl t-butyl ether 139Catalysis, manufacture of hexanedioic acid 179Catalysis, manufacture of hydrogen 103, 126Catalysis, manufacture of hydrogen peroxide 131-132

243

index

Catalysis, manufacture of long chain alkenes 96, 97Catalysis, manufacture of methanal 135Catalysis, manufacture of methanol 137Catalysis, manufacture of methyl t-butyl ether 138Catalysis, manufacture of methyl 2-methylpropenoate 192Catalysis, manufacture of 2-methylpropene 139Catalysis, manufacture of methyl propenoate 199Catalysis, manufacture of nitric acid 140-141Catalysis, manufacture of PET 185Catalysis, manufacture of phenylethene 190Catalysis, manufacture of polycarbonates 181Catalysis, manufacture of poly(ethene) 188-190Catalysis, manufacture of poly(propene) 196-197Catalysis, manufacture of propan-2-ol 139Catalysis, manufacture of propenal 199Catalysis, manufacture of propenoic acid 199Catalysis, manufacture of propenonitrile 196-197, 201Catalysis, manufacture of silicones 212Catalysis, manufacture of sulfuric acid 162Catalysis, manufacture of sulfur trioxide 162, 196-197Catalysis, manufacture of synthesis gas 103Catalysis, manufacture of trichloromethane 202Catalysis, manufacture of 2,2,4-trimethylpentane 17-18, 29, 129-130Catalysis, manufacture of waxes 51Catalysis, metallocenes 190Catalysis, nanoparticles 86Catalysis, Phillips catalysts - see Phillips-type catalystsCatalysis, reforming - see reforming, catalyticCatalysis, Ziegler-Natta catalysts - see Ziegler-Natta catalystsCatalytic converters 11-12, 86Cathode, oxygen depleting 117Cation exchange resin 154Cationic surfactants 98, 101Cativa process 120Cellulose enzymes 47Cellulose ethanoate 121Cement 68, 111, 223Cerium(IV) oxide, nanoparticles 86Cermet 68Chalcocite 217Chalcopyrite 217Chemical vapour deposition 85Chemisorption 11-12Chlorantaniliprole 75Chlorine 108, 109, 114-117, 128, 152, 158-9, 181, 182, 183, 202, 228, 2352-Chlorobuta-1,3-diene 109Chlorodifluoromethane 129, 202-2031-Chloro-2,3-epoxypropane 92, 114Chloroethane 183Chloroethene 19, 41, 182-183Chlorofluorocarbons 129, 202Chloroform - see trichloromethaneChloroprene - see 2-chlorobuta-1,3-diene3-Chloropropene 92Chlorosilanes 211Chlorothalonil 78Chromium 229, 230, 233

Chromium(VI) oxide 188Chromogens 57Chromophores 57Citric acid - see 3-carboxy-3-hydroxypentanoic acidClostridium acetobutylicum 48Clostridium ljungdahii 48Clothianidin 75Coal gas 221Cobalt 68, 229, 230, 239Cobalt octadecanoate 174Coke 151, 221, 222Colorants 56-64Colour Index International 57

Complex fertilizer 82

Composites 65-68, 135

Composites, aramid reinforced polymer 67-68

Composites, carbon fibre reinforced polymer 66-67

Composites, fibre reinforced polymer 65-66

Composites, glass fibre reinforced polymer 67

Composites, nanomaterials 86-87Composites, particle reinforced 68Compound fertilizer 82Concrete 68, 111, 229Condensation polymers 167Constant boiling mixture - see azeotropeContact process 16, 162Continuous phase 65Continuous reactors - see reactors, continuousCoolant for engines 120Co-polymers 168, 197Co-polymers, of ethene 197Co-polymers, of propene 197Copper 216-220, 239Copper(II) chloride 181, 218Copper matte 218Copper(I) oxide 88Copper(I) sulfide 218Copper(II) sulfate 78, 219Cracking 11, 15, 26-29, 106Cracking, catalytic 11, 15, 28Cracking, steam 26- 28, 106Crop protection chemicals 69-78Cryolite 213, 214CSTR - see reactors, continuous stirred tankCumene 15, 147-148, 154Cumene hydroperoxide 148Cupronickel 220Curing 179

DDacron - see polyesters

Dealkylation 15, 107

Decabromodiphenyl ethane 108Decabromodiphenyl ether 108Degradable plastics 172-174Deltamethrin 76

244

index

Depreciation 7-8Detergents 99-101Diakon - see poly(methyl 2-methylpropenoate)Diamides 75-761,6-Diaminohexane 43, 109Diammonium hydrogenphosphate 150Diaphragm cells 115-117Diaspore 2131,2-Dichloroethane 41, 182, 1831,1-Dichloroethene 200, 201Dichlorophenols 1472,4-Dichlorophenoxyethanoic acid 70Dichroism 64Diethanolamine - see 2,2´-iminodiethanolDiethylene glycol 118-119Diethylene glycol monoether 119Diflubenzuron 762,4-Difluoroaminobenzene 1291,1-Difluoroethene 129Dihydrogenphosphate ion 811,6-Diisocyanotohexane 911,2-Dimethylbenzene 15, 1071,3-Dimethylbenzene 15, 1071,4-Dimethylbenzene 15, 107, 186Dimethyl benzene-1,4-dimethylcarboxylate – see polyestersDimethyl carbonate 36-37, 181Dimethyldichlorosilane 211Dimethyl ether 1371,1-Dimethylethyl hydroperoxide - see t-butyl hydroperoxideDimethylsilanol 211Dimethyl terephthalate - see polyesters2,4-Dinitrobenzene 2052,6-Dinitrobenzene 205Diphenyl carbonate 36-37, 181Diphenylmethane diisocyanate - see MDIDirect dyes 60Disodium hydrogenphosphate 150Disodium pyrophosphate 150Disperse dyes 61Dispersed phase 65Disproportionation 107Disproportionation, methylbenzene 107, 125Distillation 30-33, 122Distillation, of air 144, 145, 146Distillation, of oil 30-33Disulfoton 73Dithiocarbamates 78Dolomite 227Duralumin 213Dyes 56-63, 64

EElastomers 169Electric arc furnace 231, 240Electric Arc Furnace Process 231Emamectin benzoate 74Epoxyconazole 77Epoxyethane 17, 40, 97, 98, 118-119, 120

Epoxypropane 139, 155, 173, 206Epoxy resins 92Ertl, Gerhard 12, 104Eserin 73Essential fatty acids 79Ester interchange - see transesterification Esterquats 98ETFE - see ethylene tetrafluoroethyleneEthanal 172, 173Ethane 27, 28, 29, 31, 183Ethane-1,2-diol 17, 42, 118, 120, 184, 185, 186, 207Ethanoic acid 17, 38, 121 Ethanoic anhydride 121Ethanol 14, 44-46, 122-123Ethanolamines 119Ethene 14, 19, 41, 90, 118, 122, 123, 124, 182, 183, 188, 192, 203 Ethenyl ethanoate 90, 120, 200, 201Ethenylmethyldichlorosilane 212Ethenyl sulfones 61-622-Ethoxy-2-methylpropane - see ethyl t-butyl etherEthyl acrylate - see ethyl propenoate2-Ethylanthraquinol 1322-Ethylanthraquinone 131Ethyl t-butyl ether 139Ethylene glycol - see ethane-1,2-diolEthylene glycol monoether 119Ethylene glycols 118-119Ethylene tetrafluoroethylene 203Ethyl 2-hydroxypropanoate 31Ethyl propenoate 90, 192, 198Ethylene - see etheneEutrophication 82Extender 171Extrusion 171

FFAME process 46Fast pyrolysis 48, 51Fats 94Fats, edible 79-80Fatty acid methyl ester process 46Fermentation 44-46, 50-51, 52-55, 172 Ferrophosphorus 152Ferrosilicon 227Ferrotitanium 234Fertilizers 81-82, 102, 140, 149, 150, 165FFC Cambridge process 236Fibreglass 67Fibre reinforced polymer composites - see composites, fibre reinforced polymerFibres 169-170Filler 65, 111, 171Fipronil 74Fischer-Tropsch process 47-48, 51Fixed costs 7Fluorine 125, 1292-Fluoroaminobenzene 129

245

index

Fluoroanhydrite 130Fluoroapatite - see phosphate rockFluorocarbons 125, 129, 202-203Fluorosilicic acid 149Fluorspar 130Formaldehyde - see methanalFormalin 135Fractional distillation - see distillationFroth flotation 217, 238 Fuel cell 127Fungicides 69, 77-78

GGalvanizing 237Gasification 47, 51Gibbsite 213Glass 156Glass fibre 67Glass fibre reinforced polymer composites - see composites, glass fibre reinforced polymerGlass transition temperature 166Glucoamylases 45Glucose 45, 173L-Glutamic acid 33Glycerides – see triglyceridesGlycerol - see propane-1,2,3-triolGlycine - see 2-aminoethanoic acid Glycines 70Glycol ethers 119Glyfosinate 71Glyphosate 40, 70-71, 153Gold 219Gold, nanoparticles 87Graft co-polymer 168Graphene 66Green chemistry 34-40Gross margin - see Gross Value AddedGross Value Added 2, 6, 7Group 1 dyes 59-61Group 2 dyes 61-62GVA - see Gross Value Added

Gypsum 149

HHaber, Fritz 104Haber process 104Haematite 221Hardening, oils 80HDPE - see poly(ethene)

Heat exchangers 24-25, 103, 141, 144, 162Helium 142, 143, 146Herbicides 69, 70-72Heterogeneous catalysis 13-17Heteropolymers - see co-polymersHexafluoropropene 202, 203Hexamethylene diisocyanate - see 1,6-DiisocyanotohexaneHexamethylenediamine – see 1,6-Diaminohexane1,6-Hexanediamine 179

Hexanedioic acid 172, 179High density poly(ethene) - see poly(ethene)High impact polystyrene 168, 194Homogeneous catalysis 17-18Homopolymers 168, 195Hydrated lime - see calcium hydroxideHydrazine 132Hydrochloric acid 128, 232Hydrochloric acid, recycling 41Hydrochlorofluorocarbons 129Hydrocracking - see also cracking, catalytic 28, 48, 51Hydrofluoric acid 96, 129-130, 214Hydrofluorocarbons 129Hydroforming - see also reforming, catalytic 126Hydroformylation 97, 155Hydrogen - see also synthesis gas 47, 48, 102-104, 126-127Hydrogenation, of oils 80Hydrogen chloride 128, 183, 202Hydrogen cyanide 172, 201Hydrogen fluoride 11, 17, 129-130Hydrogen peroxide 99, 131-132Hydrogen sulfide 102, 146, 1604-Hydroxy-4-methylpentane-2-one 1542-Hydroxypropanoic acid 31, 53-54, 172-173

IIBIT – (Income Before Interest and Tax) 7Ilmenite 163, 164, 234Imidacloprid 752,2'-Iminodiethanoic acid 402,2'-Iminodiethanol 40,119Indigo 62Indigoid dyes 62Indole-3-ethanoic acid 70Initiator, manufacture of poly(chloroethene) 183Initiator, manufacture of poly(ethene) 188Initiator, manufacture of poly(methyl 2-methylpropenoate) 192Initiator, manufacture of poly(phenylethene) 193Initiator, manufacture of poly(propenoic acid) 199Initiator, manufacture of poly(propenonitrile) 201Initiator, manufacture of poly(tetrafluoroethene) 203Ink jet printing 64Insecticides 69, 72-77Interface 65Iodine 133-134Iodomethane 120Ion exchange membrane cell 115, 117Ion-exchange resin 134, 154Iprovalicarb 78Iridium(IV) chloride 121Iron 218, 221-223, 234, 238Iron(III) chloride 218Iron(III) oxide, nanoparticles 87Iron(III) sulfate 239Iron sulfide 238Isasmelt process 218, 219, 226Isomerisation 28-29Iso-octane - see 2,2,4-trimethylpentane

246

index

Isoprene - see 2-methylbuta-1,3-dieneIsopyrazam 78Isotactic poly(propene) 195-197

ITP Armstrong process 232

JJarosite 239Jatropha 46

KKA 178, 179Ketoenols 76-79Kevlar 67-68Knock 138Kroll process 235

Krypton 143, 146

LLactic acid - see 2-hydroxypropanoic acidLaser dyes 64Lasers 64, 142, 143LDPE - see poly(ethene)Lead 224-226, 229, 238, 240Lime - see calcium hydroxide and calcium oxideLimestone - see calcium carbonateLinear low density poly(ethene) - see poly(ethene)Linoleic acid 79Linolenic acid 79Liquid crystals 64Liquid petroleum gas 31, 137LLDPE - see poly(ethene)Loop reactors - see reactors, loopLow density poly(ethene) - see poly(ethene)LPG - see liquid petroleum gasLucite 191L-Lysine 55

MMacrocyclic lactones 74Magnesite 227Magnesium 227- 228, 235, 237Magnesium bromide 108Magnesium chloride 227, 228Magnesium hydroxide 228Magnesium oxide 227Magnetite 221Maltose 45Manganese 223, 227, 229, 233Manganese octadecanoate 174Manganese(II) oxide, nanoparticles 88Manganese(IV) oxide 238Margarine 79-80Marmatite 238Matrix 65Mauveine 56MDI 205, 206Meal 45

Melamine 176Melamine-methanal plastics 176Melt transition temperature 166Membrane cell 115, 117Mercury amalgam cell 115-117Mesosulfuron 71Mesotrione 72Metalaxyl 78Metal-complex dyes 60Metallocene linear low density poly(ethene) 190Metallocenes 190, 196-197Methamidophos 73Methanal 135, 175, 176, 192Methanal plastics 175-176Methane 26, 28, 29, 31, 102-103, 126, 202Methanol 36, 46, 121, 127, 135, 136-137, 138, 1922-Methoxy-2-methylpropane - see methyl t-butyl etherMethyl acrylate - see methyl propenoateMethylbenzene 15, 29, 107, 205Methylbenzene diisocyanate - see TDI2-Methyl-buta-1,3-diene 68Methyl t-butyl ether 138-139Methyl carbamates 73Methylene diphenyl diisocyanatee - see MDI(1-Methylethyl)benzene - see cumeneMethyl isobutyl ketone - see 4-methylpentane-2-oneMethyl methacrylate - see methyl 2-methylpropenoateMethyl 2-methylpropenoate 90, 154, 191-192, 198, 2014-Methylpentane-2-one 1544-Methylpent-3-en-2-one 1542-Methylpropane 1392-Methylpropene 18, 138-139Methyl propenoate 192, 198, 199, 201Methyl propionate 192Methyltrichlorosilane 211, 212Milbemectin 74Milbemycins 74Miscanthus 47Mixed oil 178-179Mobil MTG Process 137Molecular sieve - see also zeolites 15, 29, 46, 123, 145Molybdenum 229, 230, 233Molybdenum(VI) oxide 199Mono alkyl quaternary systems, surfactants 53Monomers 166Monosodium dihydrogenphosphate 150Moulding 171MTBE - see methyl t-butyl etherMyristic acid 79

NNahcolite 156, 157Nanomaterials 83-88Nanoparticles 48, 85, 87-88, 177Nanotechnology - see nanomaterials and nanoparticlesNaphtha 11, 15, 26-28, 33, 103Neon 143, 146Neonicotinoids 74-75

247

index

Neoprene - see poly(2-chlorobuta-1,3-diene)Nereistoxin 75Nereistoxin analogues 74-75Nickel 48, 68, 219, 220, 229, 230, 239Nickel silverNicosulfuron 71Nicotine 75Niobium 229Nitric acid 11, 140-141Nitric oxide - see nitrogen(II) oxideNitrobenzene 106Nitrogen 142-146Nitrogen monoxide - see nitrogen(I) oxideNitrogen(I) oxide 142-146Nitrogen(II) oxide 12, 140-141Nitroglycerine 942-Nitromethylbenzene 2054-Nitromethylbenzene 205Nitrous oxide - see nitrogen(I) oxideNobel Prize 12, 66, 104Nonionic surfactants 98-99, 101Novalac resin 175Nutrients 81-82Nylon - see polyamide

OOcta-9,12-dienoic acid 79Octa-9-enoic acid 79Octane rating 29, 138Oils 94Oils, edible 79-80Oligomers 211Omega-3 acids 79Omega-6 acids 79Organophosphorus compounds 73OXO process 155Oxychlorination 183Oxygen 142-146

PPaints 89-93, 198Paraquat 70Particle reinforced composites – see composites, particle reinforced PEM cell 127Peracetic acid - see peroxyethanoic acidPercolating diaphragm cell 115, 117-118Perfluoropropylvinyl ether 202, 203Permethrin 76Peroxyethanoic acid 100Perspex - see poly(methyl 2-methylpropenoate)Pesticides 69PET - see polyestersPET, recycling - see polyesters, recyclingPhenol 17, 147-148, 154, 175, 178Phenol-methanal plastics 175Phenylamine 147Phenylethene 193, 200

Phenylpyrazoles 74Phillips-type catalysts 188, 190Phosgene - see carbonyl chloridePhosphate rock 81, 149, 151Phosphides 153Phosphine 153Phosphor bronze 220Phosphoric acid 149-150Phosphoric acid, thermal 149-150, 151Phosphorous acid 152Phosphorus 149, 150, 151-153, 221Phosphorus(V) oxide - see phosphorus pentoxidePhosphorus oxychloride 152Phosphorus pentachloride 152Phosphorus pentoxide 15, 150Phosphorus, red 151, 152Phosphorus sulfides 153Phosphorus trichloride 152Phosphorus, white 151-152Phosphorus, yellow - see phosphorus and phosphorus, whitePhthalic acid - see benzene-1,2-dicarboxylic acidPhthalocyanines 59Physical vapour deposition 85Physisorption 11Physostigmin 73Pickling, steel 41, 128, 161, 232Picloram 70Pigments 56, 62-63, 92Pinoxaden 72Plasticiser 171Platforming - see also reforming, catalytic 29Platinum 6, 11, 15, 28, 29, 48, 140Poisoning 13, 126Polyacetal resins - see polymethylene resinsPolyacrylic acid - see poly(propenoic acid)Polyamide 6 177, 178-179Polyamide 6, recycling 42-43Polyamide 6,10 177Polyamide 6,6 177, 178, 179Polyamide 6,6, recycling 42-43Polyamide 11 177Polyamide 12 177Polyamides 42-43, 86, 177-179Poly(butadiene) 68, 109, 166Poly(caprolactone) 172, 174Polycarbonates 36-37, 180-181Poly(2-chlorobuta-1,3-diene) 86, 109Poly(chloroethene) 19, 42, 43, 182-183Polychloroprene - see poly(2-chlorobuta-1,3-diene)Poly(1,1-difluoroethene) 128Poly(dimethylsiloxane) 209-212Poly(diphenylsiloxane) 209Poly(epoxyethane) - see polyethylene glycolPoly Electrolyte Membrane - see PEM cellPolyesters 54, 66, 180, 184-185Polyesters, recycling 42Poly(ethene) 18, 129, 173, 187-190Poly(ethene), recycling 42, 43

248

index

Poly(ethenyl alcohol) 174Poly(ethenyl ethanoate) 174 Polyether alcohol 206Polyethylene - see poly(ethene)Polyethylene glycol 118-119Polyethylene terephthalate 32Polyfluorocarbons - see poly(tetrafluoroethene)Polyglycolic acid - see poly(hydroxyethanoic acid)Poly(hydroxyalkanoates) 172Poly(hydroxybutanoate) 172, 174Poly(hydroxyethanoic acid) 172, 173 Poly(hydroxypentanoate) 172Poly(2-hydroxypropanoic acid) 53-54, 172-173Polyhydroxyvalerate – see poly(hydroxypentanoate)Polyisocyanates – see also MDI and TDI 204-208 Polyisoprene - see poly(2-methylbuta-1.3-diene)Polylactic acid - see poly(2-hydroxypropanoic acid)Poly(2-methylbuta-1,3-diene) 68Polymethylene resins 135Polymethylene terephthalate 184Polymethyl methacrylate - see poly(methyl 2-methylpropenoate)Poly(methyl 2-methylpropenoate) 19, 166, 191-192, 198 Poly(methylpentene) 146Poly(methylpropenaote) 199Poly(2-methylpropene) 88Polyols 119, 139, 206, 207Polyoxymethylene 135Poly(phenylethene) 19, 68, 167, 168, 169, 193-194Poly(phenylpropene) 173Polyphenylsulfone 37Poly(propene) 19, 173, 195-197Poly(propene), recycling 42, 43Polypropenoates 198-199Poly(propenoic acid) 198-199Poly(propenonitrile) 19, 66, 200-201Polypropylene – see poly(propene)Poly(tetrafluoroethene) 19, 202-203Polytrimethylene terephthalate 54Polyurethanes 66, 204-208Polyvinyl acetate - see poly(ethenyl ethanoate)Polyvinyl alcohol -see poly(ethenyl alcohol)Polyvinyl butyral 174Polyvinyl chloride - see poly(chloroethene)Polyvinylidenefluoride - see poly(1,1-difluoroethene)Portland cement 68Potassium chloride 81, 82Potassium iodate 133Potassium iodide 133Potassium sulfate 16Prepeg 66Pressure swing adsorption 123, 144, 145-146Prilling 81-82, 134, 165Primicarb 73Profit and Loss Accounts 6Promoter 14, 16, 120Propane 27, 28, 29, 31, 201Propane-1,2-diol 206Propane-1,3-diol 32, 184

Propane-1,2,3-triol 46, 80, 91, 94, 95Propan-2-ol 139, 154Propanone 17, 48, 148, 154Propenal 16, 155, 199Propene 16, 17, 19, 147, 155, 196, 199, 201Propenoic acid 198-199Propenonitrile 19, 198, 200-201Propineb 78Prothioconazole 77Proton Exchange Membrane - see PEM CellPTFE - see poly(tetrafluoroethene)PTT - see polymethylene terephthalatePVC - see poly(chloroethene)Pyrethins 76Pyrethoids 76Pyrites 161Pyrolysis 48, 51, 66

QQuicklime - see calcium oxide

RRare gases - see argon, helium, krypton, neon, xenonRaw pyrolysis gas 28REACH 9Reactive dyes 61 - 62Reactors 20-25Reactors, batch 20Reactors, continuous 20-24, 188-189Reactors, continuous stirred tank 23-24, 188-189Reactors, fixed bed 21-22, 29, 103, 104, 122, 137, 140, 147, 162, 189Reactors, fluid bed 22-23, 28, 201Reactors, loop 24, 189, 196 Reactors, tubular 21, 27, 103Recycling - see also secondary production 41-43, 232Red List 9Reforming, catalytic 11, 15, 16, 29, 106-107, 126Reforming, steam 11, 27-28, 102-103, 126-127Refractory carbides 68Responsible Care 8-9Rhenium 11, 15, 16, 29Rhodium 6, 11, 48, 140Rock phosphate - see phosphate rockRotary furnace 226RPG - see raw pyrolysis gasRutile 163, 164, 234

SSacrificial metal 237SAN 194, 200Saponification 94, 95SBS 168Scrap, aluminium 215Scrap, recycling of metals 43Secondary production, aluminium 215Secondary production, copper 219Secondary production, lead 226

249

index

Secondary production, magnesium 228Secondary production, steel 231Secondary production, zinc 240Selenium 229Shell Higher Olefines Process 97 Shell Middle Distillate Process 47, 51Sheradizing 237Shift reaction 103, 126-127SHOP - see Shell Higher Olefines Process Silane 209Silanes 209-212Silanols 211Silicon 211Silicone elastomers 210, 212Silicone fluids 209-210, 212Silicone gels 210, 212Silicone resins 211, 212Silicone rubbers - see silicone elastomersSilicones 209-212Silicon hydride 85Silicon tetrafluoride 125, 130Siloxanes 209-212Silver 11, 219, 240Silver nanoparticles 87, 88Sinter 14, 240 Slaked lime - see calcium hydroxideSMDS – see Shell Middle Distillate Process SNG – see synthetic natural gasSoaps 94, 96, 98Sodium alkyl ether sulfates 97Sodium aluminate 213-214Sodium aluminium fluoride - see cryoliteSodium carbonate 101, 156-157Sodium chloride 133, 180

Sodium hydrogencarbonate 157Sodium hydroxide 94, 95, 97, 115-117, 158-159, 213, 214Sodium hypophosphite 153Sodium 2,2'-iminodiethanoate 40Sodium iodate 134Sodium nitrate 134Sodium perborate 99, 131Sodium percarbonate 99, 131Sodium phosphate - see monosodium dihydrogenphosphate, disodiumhydrogenphosphate, disodium pyrophosphate and trisodium phosphateSodium silicate 101Solvay Process 156-157Sphalerite 238Spirodiclofen 76-77Spiromesifen 76-77Stabiliser 171Stainless steel - see steel, stainlessStarch 173Steam cracking - see cracking, steamSteam reforming - see reforming, steamSteel 229-232Steel scrap 230-232Steel, stainless 229

Strobilurin A 77Strobilurins 77-78Sucrose 45Sulfur 81, 160, 161, 223Sulfur concrete 160Sulfur dioxide 16, 41, 111, 133, 134, 160, 161-162, 192, 218, 225, 238Sulfur dyes 62Sulfuric acid 11, 16, 17, 97, 160, 161-162, 179, 192, 218, 219, 225, 232, 238, 239, 240Sulfuric acid, recycling 41Sulfur trioxide 16, 97, 162Sulphonylureas 71Sunfuel 47Superabsorbents 198Supercritical liquids 38Superphosphate 150Surfactants 95-101Sustainability 35Syndiesel 47Syndiotactic poly(propene) 195-196, 197Syngas - see synthesis gasSynthesis gas 11, 43, 47, 48, 51, 102-104, 136, 137 Synthetic anhydrite 130Synthetic Natural Gas 49

TTAED - see tetraacetyl ethylene diamineTantalum 236TDA - see toluene diaminesTDI 205-206Tembotrione 72Terephthalic acid - see benzene-1,4-dicarboxylic acidTerylene - see polyestersTetraacetyl ethylene diamine 100Tetrabromobisphenol A 108, 154, 1811,1,1,2-Tetrachloroethane 183Tetradecanoic acid 79Tetrafluoroethene 167, 202-203Tetrafluoroethylene - see tetrafluoroetheneTetramethylbisphenol A 181Thermal swing regeneration 123 Thermoforming 171Thermoplastics 169Thermosets 169Thiamethoxam 75Thiobadilus ferrooxidans 218Thiocloprid 75Thiocyclam 74, 75Thiosultap 74-75Tin 219, 230, 233Titanium 227, 233-236Titanium carbide 68Titanium(IV) chloride 164, 196, 235Titanium dioxide 163-164Titanium dioxide, nanoparticles 87-88, 177Toluene diamines 205Toluene diisocyanate - see TDI

250

index

Toluene - see methylbenzeneTotally Degradable Plastic Additives 174Transesterification 46, 80, 185Translocation 70Trialkylaluminium - see Ziegler-Natta catalystsTrialkyl phosphites 153Triazines 61Triazoles 77Tricalcium phosphate 81Trichloromethane 202Triethanolamine 119Triethylaluminium 18, 96, 97, 196Triethylene glycol 118-119Trifloxystrobin 78Triflumuron 76Trifluoromethylbenzene 129Triglycerides 79, 80, 95, 206Triketones 71-72Trimethylchlorosilane 2112,2,4-Trimethylpentane 111, 17-18, 29, 129-130Trimethyl phosphate 153Triple superphosphate 81, 82, 150Trisodium phosphate 150Trona 156, 157Tungsten 229, 230Tungsten carbide 68

UUranium(IV) fluoride 125, 129Uranium(VI) fluoride 125Urea 81, 82, 165, 176Urea-methanal plastics - see carbamide-methanal plasticsUrethane linkage 204, 207

VVacuum swing adsorption 144, 146Vanadium 229, 230, 233Vanadium(V) oxide 11, 13, 162, 199

Variable costs 6, 7Vat dyes 62Vertical Shaft Kiln 112Vinyl chloride - see chloroetheneVinyl sulfones 61-62

WWorking capital 6, 7Wrought iron 221

XXenon 143, 146m-Xylene - see 1,3-dimethylbenzeneo-Xylene - see 1,2-dimethylbenzenep-Xylene - see 1,4-dimethylbenzeneXylenes - see 1,2-, 1,3-, 1,4-dimethylbenzene

YYield 35-36

ZZeolites 11, 14-15, 28, 39, 40, 97, 126, 137, 144, 145, 147, 179Ziegler catalyst 96Ziegler-Natta catalysts 18, 188, 189, 190, 196Zinc 227, 230, 237-240Zinc blende 238Zinc chloride 238Zinc ferrite 238, 239Zinc, nanoparticles 88Zinc oxide 238, 239Zinc oxide, nanoparticles 88Zinc phosphide 153Zinc sulfate 238, 239Zinc sulfide 238Zirconium 227, 229, 233Zirconium metallocene 197

the essential chemical industry

Documents

essential chemical industry

plastics industry

levels of education

ddukfirst edition

latest edition

level students

ancient greek

essential reference