Design of industrial scale chemical reactions
Reversible reactions in industry
The yieldThe mass of product made in a chemical reaction. The percentage yield is a measure of the yield obtained compared to the maximum possible yield. and rate of a chemical reaction depend on conditions such as temperature and pressure.
In industry, chemical engineers design processes that maximise the yield and the rate at which the productA substance formed in a chemical reaction. is produced. They also aim to reduce waste and energy costs at all stages of the process.
Data on yields and rate of reaction help to select reaction conditions that make the process as safe and as efficient as possible.
Reversible reactions in closed systemIn chemistry, a system in which no substances can enter or leave during a reaction. do not reach 100% yield. This is a problem in an industrial process which requires a high percentage yieldA measure of the percentage conversion of a chemical reaction..
The percentage yield is decreased if the reactants do not completely form the products. To make a given mass of product, a process with a low percentage yield requires more of the reactants than a process with high percentage yield. In addition, the desired products must be separated out from a mixture that also contains some of the original reactants. Extra stages in a process cost money.
Selecting reaction conditions - Higher
The reaction conditions used are chosen to get an acceptable yield of product in an acceptable time.
For example, there would be little profitThe difference between revenue and costs. A key aim for all businesses. in getting a very high yield if it took several weeks or months to achieve.
High temperature and pressure produce the highest rate of reaction. However, this must be balanced with the high cost of the energy needed to maintain these conditions.
catalystA substance that changes the rate of a chemical reaction without being changed by the reaction itself. increase the rate of reaction without affecting the yield. This can help create processes which work well even at lower temperatures.
Equilibrium position - Higher
The equilibrium positionA measure of the relative concentrations of substances in an equilibrium, showing if there are more reactants or products at equilibrium. is related to the ratio of the concentration of the products to the concentration of reactantA substance that reacts together with another substance to form products during a chemical reaction.:
- if the position of equilibrium lies to the right, the concentration of the products is greater than the concentration of the reactants
- if the position of equilibrium lies to the left, the concentration of the reactants is greater than the concentration of the products
In general, the aim is for the equilibrium position of an industrial process to lie to the right. This maximises the yield of products.