Distillation is the process of separating components from their liquid mixtures with the use of thermal energy as the separating medium. It takes advantage of the fact that at equilibrium, the concentration of the more volatile components in the vapor phase is greater than that in the liquid phase. The basic data required in solving distillation problems are the equilibrium composition relationships between the liquid and vapor phases of the system undergoing distillation. In this review, emphasis is placed on the binary(two component) systems.

Ideal Systems and Raoult's Law:

Ideal liquid mixtures obey Raoult's law which relates the partial pressure of a component in the vapor phase to the liquid phase composition by the expression

p _i = x _iP _i

Combining Dalton's law referred to in chapter 2 earlier with Raoult's law, the following expression can be obtained to describe mixtures of ideal vapors and liquids in equilibrium

For a single component, y _iP _t = x _iP _i

where

p i	=	partial pressure of component i in the vapor phase
x i	=	mol fraction of component i in liquid phase
P i	=	vapor pressure of pure component i at the system temperature
y i	=	mol fraction of component i in vapor phase
P t	=	total pressure of the system

Relative Volatility:

The relative volatility a _ij of a component i with respect to component j in a mixture is defined by the relation

For an ideal mixture,...