Have you ever wondered how different parts of crude oil or mixtures like alcohol and water are separated? That’s where fractional distillation comes in. It’s a method used to separate mixtures of liquids based on their boiling points. This process is widely used in industries and labs to get pure substances from mixture. In this article, we’ll learn what fractional distillation is, how it works, and where it’s used in real life.

What is Fractional Distillation?

Fractional distillation is the process of separating the various components of a mixture by heating. If the boiling points of the two liquids are very close to one another, the separation cannot be achieved by a simple distillation method. It is because, with the boiling point of the more volatile liquid of the mixture, there will also be sufficient vapours of the less volatile liquid. As a result, both the liquids will distill together, and the separation will not be completed.

The separation of such liquid mixture into individual components can be achieved by a process called fractional distillation, which involves repeated distillations and condensations. It is used in processes like oil refining, perfume manufacturing and separation of crude oil in the industry. The below diagram explains this process:

Consider a mixture of two liquids, X and Y. X is more volatile than Y in this mixture. Because of the sluggish rise in temperature, such a liquid mixture begins to boil when heated. The vapours generated are mostly made up of the more volatile liquid X and a somewhat less volatile liquid Y. The vapours of the less volatile liquid Y condense more quickly than those of more volatile liquid X as they go up the fractionating column. As a result, the ascending vapours get richer in X, while the liquid going down becomes richer in Y. This distillation and condensation process is repeated at each position in the fractionating column.

As a result of successive distillations, by the time the vapours reach the top of the column and escape into the condenser, they consist mainly of the more volatile component A. Similarly, after a series of successive distillations, the remaining liquid in the distillation flask gets enriched in the higher boiling component. Each successive condensation and vapourization is called a theoretical plate.

Procedure of Fractional Distillation

Apparatus used for fractional distillation includes a round-bottomed flask, burner, condenser, adapter, receiver and fractionating column. We also need a mixture of liquids with different boiling points. The fractionating column consists of a long glass tube with a wide bore either packed with glass beads, small stones, porcelain rings or coke or blown into several spherical or pear-shaped bulbs. The actual purpose of the fractionating column is to increase the cooling surface area and to provide hurdles or obstructions to the ascending vapours and descending liquid. There are various types of fractionating columns used in the laboratories. Given below is the stepwise procedure of the fractional distillation:

• Step 1:- The mixture of liquids is heated in a round-bottomed flask, and the vapours rise and enter the fractionating column.
• Step 2:- The vapours then move to the condenser where the temperature is low.
• Step 3:- The vapours cool down and get converted into liquid form.
• Step 4:- The receiver collects the distilled liquid.

Simple Distillation Vs Fractinal Distillation

Applications of Fractional Distillation

Some main applications of fractional distillation are as follows.

• One of the technological applications of this process is to separate crude oil in the petroleum industry into various useful fractions such as gasoline, kerosene oil, diesel oil, lubricating oil etc.
• It is also known to separate acetone and methyl alcohol from pyroligneous acid obtained by destructive distillation of wood.
• It separates ethanol from fermented liquor and nitrogen and oxygen from liquid air.
• It is also used in the purification of water.
• It has a role in the preparation of alcohol.

Advantages and Limitations of Fractional Distillation

Let’s look at some advantages and disadvantages of fractional distillation.

Advantages 

• It is a very easy process and purifies the components of a mixture very well.
• The liquids having very little difference in boiling points can be separated by this process.
• The fractionating column makes the separation of components easy.

Limitations

• It consumes more energy, and the setup is complicated and costly.
• It cannot separate miscible liquids as they take longer to get separated.

Summary Key takeaways for Fractional Distillation

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