About Oil Refining

Crude oil is a complex mixture of hydrocarbons with minor proportions of other chemicals such as compounds of sulphur, nitrogen and oxygen. To use the different parts of the mixture they must be separated from each other. This separation is called refining.

Crude oil from different parts of the world, or even from different depths in the same oilfield, contains different mixtures of hydrocarbons and other compounds. This is why they vary from light coloured volatile liquids to thick, dark oils - so viscous that they are difficult to pump from the ground.

Refining involves a series of processes to separate and sometimes alter the hydrocarbons in crude oil. It relies on a basic difference between chemicals - in this case their boiling points.

When crude oil is distilled, many fractions (or parts) of the oil and gas have to be separated. This is called fractional distillation. Small molecules of hydrocarbons have low boiling points, while larger molecules have higher boiling points.

There are many other processes involved in refining. One of these is Cracking, which is the process for breaking down larger molecules into smaller ones. This is an important process because it is a way of matching supply for particular hydrocarbons with demand.

In the UK there are oil refineries at 12 sites, most of which process oil from the North Sea, as well as crude oil imported from other parts of the world.

Oil refineries are enormous complexes with hundreds of employees working around the clock. Safety is an important issue for the people who work in a refinery and the community living nearby, so regular training is taken very seriously. Monitoring the environment in and around an oil refinery is a continuous process, needed to discover the impact of this particular industry.