Crude oil is a thick, black liquid found deep under the Earth’s surface. It was formed millions of years ago from the bodies of tiny animals and plants which lived in the sea. Crude oil is a mixture of many very useful chemicals.
Crude oil is pumped up to the Earth’s surface and is piped to a refinery. Here the different liquids are separated from each other. Some of the liquids, such as petrol and paraffin, can be used as fuels. Others are changed chemically to produce compounds, such as plastics and waxes. Chemicals that come from oil are contained in many of the things we use every day, such as plastic bags and bottles, drain pipes, and some window frames and carpets.
Each liquid chemical boils at a different temperature. The temperature at which it boils is called its ‘boiling point’. When crude oil is heated at the refinery, its temperature slowly rises. The liquid with the lowest boiling point is the first one to boil and form a gas.
This rises upwards, then cools back to a liquid and is collected. As the heating continues, the liquids are separated and collected one by one. The last liquid to be collected is the one with the highest boiling point. This process of separation is called ‘distillation’.