Fractional Distillation

This lesson covers the process of fractional distillation as required by the AQA GCSE Chemistry specification (5.8.1). Fractional distillation is the key industrial process used to separate crude oil into useful fractions. Understanding how and why this process works is essential for your exam.

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Why Separate Crude Oil?

Crude oil in its raw form is not very useful. It is a mixture of hundreds of different hydrocarbons with different chain lengths and properties. To make use of crude oil, it must be separated into groups of hydrocarbons with similar numbers of carbon atoms. Each group is called a fraction.

Each fraction has different uses depending on its properties. The separation is possible because the different hydrocarbons have different boiling points.

Exam Tip: Never say crude oil is "split" by fractional distillation — it is separated. Splitting suggests a chemical change, but fractional distillation is a physical process.

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The Process of Fractional Distillation

Fractional distillation takes place in a fractionating column at an oil refinery. The process works as follows:

Step-by-Step Process