Mass Transfer

Q1: Steam distillation is not recommended to be used, if the

A azeotropic mixture is to be separated and the final product is miscible with water.

B liquids decompose, if distilled directly at atmospheric pressure.

C material can not be distilled by indirect heating even under low pressure, because of the high boiling temperature.

D material to be distilled is thermally unstable or has the tendency to react with other components associated with it, at the boiling temperature.

ANS:A - azeotropic mixture is to be separated and the final product is miscible with water.

An azeotropic mixture is a liquid mixture of two or more substances that boils at a constant temperature and composition, meaning that the vapor phase has the same composition as the liquid phase. This makes separating the components of an azeotropic mixture challenging through conventional distillation methods because the vapor and liquid phases remain in equilibrium throughout the distillation process. In cases where an azeotropic mixture needs to be separated, and the final product is miscible with water, steam distillation is not recommended. Here's why:

  1. Steam Distillation: Steam distillation is a technique used to separate volatile compounds, particularly those that are heat-sensitive or decompose at high temperatures. It involves passing steam through the mixture to be distilled, vaporizing the volatile components, and then condensing the mixture to obtain the desired product. However, if the final product is miscible with water, steam distillation may not effectively separate the components of an azeotropic mixture.
  2. Miscibility with Water: If the final product is miscible with water, it implies that the components of the azeotropic mixture are also likely soluble in water. In steam distillation, the volatile components are carried over with the steam and condensed, resulting in a mixture of the desired product and water. However, if the components form an azeotropic mixture with water, they will remain in equilibrium and will not separate as desired.
To effectively separate an azeotropic mixture with a final product that is miscible with water, alternative separation techniques may be required. These techniques could include solvent extraction, membrane separation, or molecular distillation, depending on the specific properties of the components involved and the desired purity of the final product.



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