The UK chemical industry is a major contributor to both the quality of our life and our national economy. It makes a positive contribution to the UK's balance of trade with the rest of the world.
It earns its money by carrying out chemical conversions and selling products either for further modification or for formulation into final products. The equipment needed to carry out chemical conversions is called the chemical plant. Important issues to address when deciding which product to make include:
Most chemical processes involve a sequence of events as shown below:
This sequence may be organised in one of two ways: batch or continuous. In a batch process, the raw materials are put into a vessel and allowed to react together. When the reaction is complete the product is separated from the reaction mixture. The process is repeated in an identical manner. In a continuous process, the raw materials are fed in at one end of the plant in a continuous flow.
The raw materials for a chemical process are naturally occurring minerals, gases etc. Before they can be processed in a chemical plant, they have to be converted into the feedstock. The feedstock then forms the reactants which go into the chemical process.
If more than one possible raw material is available, a choice is made on cost and suitability. Preparation of pure feedstock may be the most expensive part of the process.
The efficiency of a process may depend on conditions such as temperature, pressure. It is normal to find the conditions which give the most economical conversion. The choice of conditions can have a significant impact on yield. In ammonia production, too high a temperature reduces the yield. Too low a temperature reduces the rate of reaction. A compromise has to be made to allow a reasonable yield in a reasonable time.
In many industrial processes a catalyst is used to speed up the process. Many catalysts are precious metals; because they are not used up the cost is not prohibitive. The performance of the catalyst is judged on:
A catalyst can be poisoned by impurities over a period of time and may have to be replaced. In many processes the recycling of unreacted materials is an important aspect for both economy and environmental reasons. In ammonia production, unreacted nitrogen and hydrogen are recycled.
Many processes involve the use of energy. Many chemical reactions involve the release of energy. By using heat exchangers the energy released in exothermic reactions can be used to raise the temperature of the reactants in an endothermic reaction.
Products formed in a reaction surplus to the required product which have no use are called by-products. A supplementary product produced in a reaction which is useful is called a co-product.
Chemical engineers calculate two values for a reaction step. The conversion shows the proportion of the feedstock that reacts:
The selectivity shows the proportion that gets turned into the products wanted:
These can be combined into the yield:
The higher the selectivity of a particular reaction step the better.
Safety is a major consideration in all operations in the chemical industry. It is affected by national and European Community legislation. Safety considerations play a crucial part in the design stage with particular note taken of plant layout. Usually people are employed on site with a responsibility for safety throughout the plant.
It is not acceptable to allow harmful substances to escape into the environment. There is an increasing quantity of regulation which regulates this. Chemical processes will always produce some waste.
Waste must be treated and can only be disposed of when in a state which is not harmful to the environment. Liquid waste has to meet legal requirements on such things as pH and metal ion content before it can be released into natural waters or sewage systems. Gases which contain contaminants are purified by passing then through neutralising solutions to remove soluble contaminants; particles of dust can be removed by filtration.
The profit generated is the difference between selling price and costs of production. Production costs are made up of:
Capital costs, on the other hand, relate to establishing chemical plant, buildings around which manufacture is based. These are usually 'written off' over ten years.
Well, you've got to the end, but are you the wiser for it? Are you going to be a glutt for punishment and study Chemistry or something similar at University? Whether you are or not, best of luck with your exams, and I hope you found this resource useful.
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