Question

The distillation techniques most suited for separating glycerol from spent-Lye in the soap industry?
(A) Fractional distillation
(B) Steam distillation
(C) Distillation under reduced pressure
(D) Simple distillation

Answer 1

Hint To figure out the answer to this question we should know that in the distillation process we usually increase the temperature of the solution to the boiling point of components present in it. Glycerol would decompose before its boiling point. Now, you have to consider the most suitable answer which satisfies these conditions.

Complete step by step answer:
We will try to understand the different types of distillation methods mentioned in the options and then try to identify the type of distillation suitable for separating the mixture given in the question.
Fractional distillation is the type of separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature such that more than one fraction of the mixture will vaporize.
Steam distillation is considered as a separation process which purifies temperature-sensitive materials mainly such as aromatic compounds. Dry steam is passed through the material mixture.
Simple distillation on the other hand is considered as a method of separation by which two liquids with different boiling points are separated.
Distillation under reduced pressure - In this method, the liquid is made to boil at a lower temperature than its normal temperature by lowering the pressure on its surface. So, if the external pressure is reduced, then the boiling point of the liquid is lowered.
We should know that at atmospheric pressure, the boiling point of glycerol is 290${}^0$C. Glycerol decomposes before it reaches this temperature, or we can say it decomposes before it distils. Hence, we need to decrease its boiling point, that we can do by reducing pressure. Therefore, the distillation is carried out under reduced pressure by applying a vacuum which decreases the boiling temperature of glycerol and prevents its decomposition. Now, we can say that the distillation technique most suited for separating glycerol from spent-lye in the soap industry is distillation under reduced pressure.

Therefore, we can conclude that the correct answer to this question is option C.

Note: We should also know that spent lye is the alkaline glycerol-containing liquor that results in saponification of fat with boiling lye solution in soapmaking and that is drawn off after cooling from the floating curd.