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Fractional Distillation

Fractional distillation means that a type of distillation that involves the separation of miscible liquids. The fractional distillation process involves repeated condensation and distillation. Usually, the separation of a mixture into component parts takes place in fractional distillation. The separation takes place when the mixture is in exposure to heat at a particular temperature where fractions of mixture start to vaporise. Fractional distillation’s basic process or principle is that different liquids evaporate and boil at various different temperatures. Therefore in fractional distillation during the heating of the mixture, the substance which has a lower boiling point, will start to boil first and hence convert into vapours.

Fractional Distillation 

The Procedure of Fractional Distillation

  • Some of the fractional distillation apparatuses in use for the process are distilling flask, receiver, thermometer, heat source, condenser and fractionating column.
  • After we set up the apparatus the mixture of liquids A and B, which are miscible are taken, where A has greater volatility than B substance.
  • The solution is put into the distilling flask, and the tip of the flask is in connection with the fractionating column.
  • The heat increases the temperature slowly. The vapours start to rise in the flask as soon as the mixture starts to boil. The vapours come out from the volatile component A.
  • Also, the vapours move towards the condenser through the fractionating column, where it cools down to form a liquid which is then collected in the receiver.
  • Until there is complete separation of the two mixtures vaporisation and condensation take place repeatedly throughout the process.

Fractional Distillation of Crude Oil

The separation of various components of crude oil is one of the very common examples of fractional distillation in the industry. Paraffin wax, diesel, lubricating oil, gasoline, kerosene and naphtha are the substances that crude oil contains.  The separation of these components takes place productively with the help of the distillation process.  Crude oil is put in the chamber and is given heat along with high-pressure steam. As a result, the mixture starts to boil and thus the formation of vapour takes place. At this particular point, various substances start entering the vapour phase. The vapour then rises up the fractional distillation column consisting of several plates.

The plates consist of holes that allow the vapour to pass through. At the top of the fractionating column, the temperature is low. We find that components that have the highest boiling point condense in the lower part of the column, on the other hand, the substance with a low boiling point condenses at the top. From the sides of the column, the vapours or liquid fractions are removed. Later, the liquid fractions are further in process in the condensers to cool them even more.

Applications of Fractional Distillation

  1. Fractional distillation is useful for the production of high-purity silicon from chlorosilanes. Silicon is very much in use in semiconductors.
  2. It is in use for the separation of liquefied air. We obtain components like liquid nitrogen, concentrate argon and oxygen.
  3. Fractional distillation has also its use in various industries like oil refineries and even in chemical plants mainly for the separation and purification of several organic compounds.
  4. It is useful in the process of purification of water.
  5. Fractional isolation is in use for the separation of acetone and water.

FAQs on Fractional Distillation 

Q1. What do you understand by Industrial distillation?

Answer. As we know that fractional distillation is one of the popular separation techniques in industries, hear the principle For the process remains the same, but only the distillation takes place on a larger scale. Huge vertical cylindrical columns,“ distillation or fractionation Towers“ or “ distillation columns“ are in use. The complete separation of the mixtures is taken care of by these industrial towers which use reflux.

Q2. The fractional distillation method is in use for which type of liquids?

Answer. Those liquids, which possess nearly the same boiling points, which means their boiling point is not very high. Such liquids are in use in this method.

Q3. List the various methods which consist in the purification process.

Answer. The methods are

  1. Sublimation
  2. Crystallisation
  3. Distillation
  4. Differential extraction
  5. Chromatography

Q4. Name the two important conditions for fractional distillation.


  1. The liquids should be miscible With one another.
  2. The difference in boiling point between the two liquids must be less than 25-degree Celsius.
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