Distillation is a technique for separating liquids from one another, using the differences in boiling point between the individual components. Liquids are vaporised through heating either at atmospheric pressure or at reduced pressure (under vacuum) and the vapours are condensed and collected. Components are separated on the basis of boiling point. The wider the separation in boiling point, the easier the distillation is to achieve. Distillations may be used to separate and isolate a number of compounds (which is very common on an industrial scale, for example the fractional distillation of crude oil), or to purify a single compound from impurities present.

For all distillations, the following properties are generally required:

• The liquids are relatively volatile, either at atmospheric pressure or under reduced pressure.

• The liquids are thermally stable and do not readily decompose when heated

Distillations are categorised in various ways although all methods share the same principles.

• Simple distillation – used to distill one major component, separating it from any impurities. Often used to purify starting materials or products.

• Fractional distillation –used to separate a number of components from one another. Results in the collection of many fractions.

• Steam distillation – used to separate insoluble organics from water.