When crude oil reaches the refinery it is a thick black, smelly liquid. In this form, it is not much use to anyone. Crude oil contains mixture of hydrocarbons. At the refinery these areseparated into fractions which are more useful. This is done by a process called fractional distillation. This process separates compounds by using the difference in boiling points. See diagram below.
Crude oil enters the fractionating column as gas. The column is quite hot at the bottom and cooler at the top. This difference in the temperature up and down the column sorts the different fractions from each other.
The larger hydrocarbons, with the high boiling points, turn back into liquids at the base of the column and the smaller hydrocarbons stay as gases. They rise up the column and condenseat different levels, as shown in the above diagram. At the top of the column there are a number of hydrocarbons with low boiling points - between 20ºC and 70ºC. These remain as gases.
The discovery of the the crude oil has played a very big part in the development of modern life. It provides the fuel for most of today's transport as well as the raw material for making various chemical like PLASTICS.
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