Crude Oil - Substances from Crude Oil

Crude oil is an important source of the chemicals that are needed to manufacture plastics. It was formed by the anaerobic decay of dead marine plants and animals as the mud on the bottom of the sea gradually turned into rock over a time period of millions of years. Oil is a liquid and can therefore flow through pores and cracks in rock. It is less dense than the surrounding rock and it is under pressure because of the weight of the rocks above so it will rise upwards. If it reaches an impermeable rock layer, it becomes trapped - otherwise it just seeps out at the surface of the Earth. Drilling a hole through the impermeable rock allows us to release the oil trapped underground.

The chemicals used to make plastics and fuels don't come directly from crude oil - they need to be manufactured. One starting point is the process of thermal catalytic cracking of the larger molecules like those found in the bitumen fraction. Cracking produces a mixture of shorter chain alkanes and alkenes. The alkenes have a double bond and this makes them more reactive than alkanes. They can therefore either be used directly to make plastics or converted into chemicals that can then be used to make plastics.

Plastics are long chain chemicals called polymers. Their chains can be made from the same chemical e.g. ethene is used to make poly(ethene), better known as polythene, or from different chemicals e.g. nylon. Changing the conditions of polymerisation very slightly can greatly alter the nature of the polymer produced e.g the different types of poly(ethene).

Have a go at this quiz and see what you have learned about the fuels, plastics and other substances we get from crude oil.