Fractional Distillation

Fractional distillation is a process that separates the hydrocarbons present in petroleum according to their boiling points. It is the basis for a massive industry that involves billions of dollars.

The process is based on the fact that different components (or fractions) of petroleum have different boiling points. Crude oil is heated until it vaporises and is passed up a fractionating tower which is very hot at the bottom and becomes cooler towards the top. The fraction containing the smallest molecules has the lowest boiling point range, so this boils off first and rises to the top of the tower. The fractions with the highest boiling points condense first and are piped off when they settle on cooling trays at the appropriate level.