Fractional distillation is a process by which a chemical compound is separated into components by crystallization on the basis of their different solubilities, by means of evaporating the solution.
In this process the compound is mixed with a solvent, heated, and then gradually cooled so that, as each of its constituent components crystallizes and it can be removed in its pure form from the solution.
For example, fractional distillation is used in oil refineries to separate crude oil into useful substances having different hydrocarbons of different boiling points.