Fractional distillation is a method of separating two or more miscible liquids from a mixture. This method is widely used in industries to separate liquids with close boiling points. For example, separating different fractions from crude oil.
Fractional distillation works because the different liquids in the mixture have different boiling points.
To carry out fractional distillation with two liquids:
1. Heat the mixture to the temperature of the substance with the lowest boiling point (B.P).
2. As you heat the mixture, the substance with the lowest B.P will evaporate more easily.
3. So, the mixture of the two different vapours rises into the fractionating column
4. The substance with the lower B.P will remain as a vapour, even at cooler temperatures. It will rise through the column, then cool and condense in the condenser, turning into a liquid.
5. Collect the liquid in the receiving flask.
Below, is the apparatus for fractional distillation in a lab.
This procedure and apparatus are suitable for carrying out fractional distillation in the lab. However, they are not as effective for larger volumes of liquid.
If liquids in the mixture have similar boiling points, then it will be much more difficult to separate them. In this case, we may need to carry out multiple rounds of fractional distillation.