Fractional Distillation

Fractional distillation

Fractional distillation is the separation process in which the volatile components (having different boiling points) of a mixture (such as crude oil) are split from one another by heating the mixture in a column and collecting and condensing the vapors drawn from different levels of the column.
Description of process
Process used to split complex mixtures (such as petroleum) into their components, usually by repeated heating, boiling, and condensation; see distillation. In the laboratory it is carried out using a fractionating column. The process depends on the components of the mixture having different boiling points. The liquid is heated so that it turns into a gas. The vapors pass up a fractionating column where they are gradually cooled. As each of the components of the mixture cools to its boiling point, it turns back into a liquid. The different components of the mixture condense at different levels in the fractionating column and thus may be separated.

In industry, fractional distillation is used to separate the compounds in crude oil (unrefined petroleum) into useful fractions, each fraction containing compounds with similar boiling points. Air is also separated by fractional distillation. This is done by cooling air until it condenses and then allowing the temperature of the liquid air to rise. Each gas will distill off at its own boiling point.


Theoretical principal
The principal that allows distillations to succeed is the fact that the composition of vapor over a liquid composed of two or more materials will be higher in the material with the lower boiling point. The relative partial pressure of the lower boiling point material will be greater.
Every one of the vaporization and condensation cycles is a theoretical plate. The more theoretical plates in a distillation set up the better the separation. In
practice, simple distillation is carried out without any column packing, while
fractional distillation...