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Science

Alkenes

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Fractions that are produced by the distillation of crude oil can go through a process called cracking, a chemical reaction which produces smaller hydrocarbons, including alkanes and alkenes. Ethene and other alkenes are unsaturated hydrocarbons and can be used to make polymers.

Cracking

Fuels made from oil mixtures containing large hydrocarbonhydrocarbons: Hydrocarbons are a group of compounds which contain the elements hydrogen and carbon. molecules are not efficient: they do not flow easily and are difficult to ignite. Crude oil often contains too many large hydrocarbon molecules and not enough small hydrocarbon molecules to meet demand. This is where cracking comes in.

Cracking allows large hydrocarbon molecules to be broken down into smaller, more useful hydrocarbon molecules. Fractions containing large hydrocarbon molecules are heated to vaporise them. They are then either:

  • passed over a hot catalyst, or
  • mixed with steam and heated to a very high temperature.

These processes break chemical bonds in the molecules, causing thermal decomposition reactions. Cracking produces smaller alkanes and alkenes (another type of hydrocarbon).

Some of the smaller hydrocarbons formed by cracking are used as fuels, and the alkenes are used to make polymerspolymers: Polymers are large molecules formed from many identical smaller molecules (monomers). in plastics manufacture.

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