What methods are used to manufacture alkenes?

Alkenes are primarily manufactured through the processes of cracking, dehydration of alcohols, and dehydrohalogenation of alkyl halides.

Cracking is a common method used to manufacture alkenes. This process involves breaking down larger hydrocarbon molecules into smaller ones, often with the application of heat. There are two types of cracking: thermal and catalytic. Thermal cracking uses high temperatures (up to 900°C) and pressures to break the carbon-carbon bonds in the hydrocarbon molecules. Catalytic cracking, on the other hand, uses a catalyst to lower the temperature and pressure needed for the reaction. The products of cracking include alkenes, alkanes, and hydrogen.

Another method of manufacturing alkenes is through the dehydration of alcohols. This process involves the removal of a water molecule from an alcohol molecule, resulting in the formation of an alkene. The reaction is typically catalysed by an acid, such as concentrated sulphuric acid or phosphoric acid. The alcohol is heated with the acid, and the water molecule is eliminated, leaving behind an alkene.

Dehydrohalogenation of alkyl halides is also a method used to produce alkenes. In this process, a hydrogen atom and a halogen atom are removed from an alkyl halide molecule, resulting in the formation of an alkene. This reaction is typically carried out in the presence of a strong base, such as sodium hydroxide or potassium hydroxide. The base abstracts a proton from the alkyl halide, leading to the formation of a double bond and the release of a halide ion.

These methods are widely used in the industrial production of alkenes due to their efficiency and the high yield of alkenes they produce. However, they also require careful control of reaction conditions to ensure safety and to optimise the yield of the desired alkene product.