Distillation is a process of separation of two miscible liquids having different boiling points. In this process,  a volatile liquid is first vaporised at its boiling point and its vapours are condensed to get back the liquid in pure form.

If the difference in boiling points of the two miscible liquids in the mixture is less than 250C, the method of fractional distillation is used to separate them.

The fractional distillation method is the same as simple distillation except that in the apparatus a fractionating column is fitted in between the distillation flask and the condenser.

It makes the apparatus more efficient. A fractionating column is a wide tube packed with glass beads, which provides a larger surface area for cooling. Vapours of liquid having a higher boiling point are condensed on the surface of the beads present in the lower part of the fractionating column, while the vapours of lower boiling point liquid move towards the top of the fractionating column. The length of the column also increases the efficiency of the process.

Example: In an oil refinery, the different petroleum products are separated by fractional distillation of crude petroleum.