The Chemical Industry Introduction The chemical industry is one of the UK’s largest manufacturing industries. The average growth rate of the chemical industry between 1995 and 2000 was nearly 5 times that of all manufacturing industries. New products Before a new product can be manufactured testing involving several stages needs to be done to find best conditions for full-scale production: 1. Research & Development 2. Laboratory Process 3. Pilot Plant 4. Production 5. Review

Finding out about the material and how it can be made Investigate possible processes and routes for synthesis of the product in the laboratory Medium-sized investigation of to assess product quality, hazards and costs Full-scale factory production of the product Evaluation of operational procedures with a view to improving efficiency, profit or safety.

The manufacturing process Most manufacturing processes also involve a sequence of steps. Eg. Production of sulphuric acid by the Contact Process: 1. Sulphur burning

S(s) + O2(g)  SO2(g)

2. Sulphur dioxide conversion 450oC SO2(g) + ½O2(g) SO3(g) V2O5 catalyst 3. Sulphur trioxide absorption

ΔH = -297 kJ mol-1

ΔH = -94 kJ mol-1

SO3(g) + H2O(l)  H2SO4(l)

Raw materials and feedstocks Feedstock

A reactant from which other chemicals can be extracted or synthesised to manufacture a required product

Raw material

The original source of the feedstock

The major raw materials used in the chemical industry are: Crude oil, Metallic ores and minerals, Air and Water

Crude oil The naphtha fraction of crude oil is important as a feedstock for the chemical processes of:  

Steam cracking to produce ethene and propene for plastics manufacture Reforming to produce aromatic hydrocarbons for the manufacture of dyes, drugs, etc.

Metallic ores and minerals 

Bauxite produces alumina, Al2O, to manufacture aluminium Bauxite  Alumina  Aluminium



Rock salt produces NaOH, Cl2 and HCl on electrolysis of its aqueous solution

 

Provides nitrogen in ammonia production Provides oxygen for oxidation of: - Sulphur to sulphur oxides in sulphuric acid manufacture - Ammonia to nitrogen oxides in nitric acid manufacture

Air

Water Water is a raw material in the steam cracking of naphtha and ethane in the hydration of ethene to produce ethanol Water is a widely used solvent while both air and water can be used as coolants. Choosing a manufacturing route When choosing a manufacturing route several factors need to be taken into account:       

Cost, availability and suitability of feedstocks Yield of product Recyclability of unreacted materials Marketability of by-products Difficulty and cost of waste disposal Energy consumption Atmospheric emissions

Batch or continuous process Batch process In a batch process the reactants are added to the reactor and the reaction is started. The progress is carefully monitored and the reactor is emptied at the end of the reaction. The product mixture then continues on to the separation and purification stages. A batch reactor is usually a large cylindrical tank. Examples of Batch Processes  Making margarine 

Colourants



Production of aspirin(salicyclic acid)

Continuous process In a continuous process reactants flow into the reactor at one end and products flow out of the other end. Reactor design varies from one process to another. Examples of Continuous Processes  Steam cracking 

Contact Process- manufacture of sulphuric acid



Production of Nitric Acid – Ostwald Process

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Production of ammonia- Haber Process

Advantages and Disadvantages of Batch/Continuous processes

Advantages

Disadvantages

Batch process Better suited to small quantities Plant cheaper to build Plant more versatile Good for multi-step reactions Reactants in any physical state Filling and emptying plant increases production time Can be hard to control if reaction is exothermic

Continuous process Ideal for large quantities of product Product is cheaper if operated at capacity Smaller workforce Good for fast, single-step reactions Difficult to use solid reactants unless ‘fluidised’ Can be difficult to control when starting up, but easier to control when in operation

Economic aspects The chemical industry is capital intensive rather than labour intensive ie. it only employs about 1.5% of the British workforce. Capital intensive industry

Large amounts of money needed to set up the process.

Labour intensive industry

Large work-force needed to produce a relatively small volume of product.

The conditions under which an industrial chemical process operates are based on research and are chosen to maximise economic efficiency. Manufacturing costs can be divided into three categories: Capital costs

The large amounts of money needed to set up a process. Eg. Buying property, constructing the plant, infrastructures and research and development

Variable costs

Costs variable in relation to chemical process involved. These costs are not incurred if production stops. Eg. Raw materials, energy, distribution of product, overheads and effluent treatment/disposal.

Fixed costs

The cost in relation to volume of production. These costs are still incurred whether production is low or high, but the effect on the selling price of the product lessens as scale of production increases. Eg. Labour costs, depreciation of plant, plant maintenance, land rental and sales expenses.

The use of energy Wasted energy causes pollution and contributes to global warming. Energy is a major variable cost in the chemical industry due to the rapid price increases that can occur with oil, therefore manufacturing plants tend to:    

Switch to processes requiring less energy Utilise the heat energy from exothermic reactions elsewhere Use ‘waste’ heat to generate energy Sell excess energy to supply heating for local housing

Location of chemical industry Major chemical manufacturing sites are positioned as a result of historical and practical considerations. Example Grangemouth chemical works This plant began in 1919 as a dyeworks then expanded to produce pharmaceuticals, pigments and speciality chemicals. The Grangemouth site was chosen for several practical reasons:     

Large flat area of land available Good supply of water Good transport links by rail and sea for import of raw materials and export of products Good supply of skilled labour due to presence of other chemical industry in the area Sea was accessible for effluent disposal

There was also a shortage of dyes in Britain after the start of World War I as most used to be imported from Germany.

Safety As with all industries the chemical industry must operate without causing accidental injury or health risk to employees or the public. However, some major incidents have occurred. Eg.  

1974, Flixborough, Lincolnshire – cyclohexane plant had an explosion and fire killing 28 and injuring 104 1984, Bhopal, India – toxic gas leak killing several thousand

In the 1980’s health, safety and the environmental impact of industry became a major priority for governing bodies. The chemical industry is now regulated to ensure that strict rules are enforced regarding any chemical exposure.