crude oil distillation

Higher and foundation tiers

Fractional distillation of crude oil

Beaker containing a sample of crude oil sitting on the bench in a chemistry lab.

Crude oil despite being one of the world's most valuable natural resources is a useless, smelly and thick black "liquid" when it comes out of the ground. The main reason for this is that it is a mixture of thousands of different hydrocarbon molecules; now recall that hydrocarbons are compounds containing only the elements hydrogen and carbon.

There are thousands of valuable hydrocarbons all mixed together in crude oil and it is the job of an oil refinery to separate out all these valuable hydrocarbons from the crude oil. Some of the hydrocarbon molecules are small, some are medium sized and some are large. At an oil refinery this mixture of hydrocarbons present in the crude oil is separated into different fractions of hydrocarbons which contain similar sized molecules; this is easily done since similar sized molecules have similar boiling points.

The fractionating column

The image below shows some of the valuable hydrocarbon fractions that are obtained from crude oil and the uses these hydrocarbon molecules are put to.

Fractionating column at an oil refinery showing all the different fractions obtained-illustrated image.  Fractional distillation of crude oil

Fractional distillation- how it works

The mixture of hydrocarbons present in the crude oil are separated out into various fractions at the oil refinery, now these fractions are themselves mixtures of many thousands of similar sized hydrocarbon molecules and since these molecules are similar in size they will have boiling points which are relative close to each other. The crude oil is separated in a fractionating column at the oil refinery. To separate the crude oil into its various fractions the crude oil is:


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Crude oil and its fractions

Image of an oil refinery The larger the hydrocarbon molecule the higher will be its boiling point. The fractionating column will basically separate out hydrocarbon molecules according to their boiling points into separate parts or fractions. Each fraction will contain many different hydrocarbon molecules each with similar boiling points; these fractions will also contain hydrocarbon molecules of a similar size.

As you can see from the image above lots of very valuable substance such as:

Are all separated out from the crude oil. Each fraction collected will contain a mixture of many different hydrocarbon molecules. These molecules will be of a similar size with similar boiling points.


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