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Distillation Column
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Here you will learn some basic terminologies used in distillation columns

Distillation Principle

Separation of components from a liquid mixture via distillation depends on the differences in boiling points of the individual components and also on the vapor pressure characteristics of liquid mixtures

Vapor-Liquid Equilibria

We will consider a binary mixture of A-B, where A is more volatile,ie. vapor pressure of pure A at any temperature is higher than the vapor pressure of pure B.

Here is a diagram for Constant-pressure vapor-liquid equilibria

Consider First Diagram. Upper curve is called Dew point curve. Lower curve is called Bubble point curve. Consider a solution at G. The solution is entirely liquid. If it is heated first bubbles appears at H and has a composition of J, richer in more volatile substance. On further heating we reach point P where both vapor and liquid phases coexist with liquid concentraion of L and vapor concentration of K. Last drop of liquid vaporises at M. After M we have only vapor present.

Note : For distillation we are mainly interested in region between Boiling point curve and Dew point curve

Now consider the second figure. The greater the distance between the equilibrium curve and diagonal of the figure, the greater the difference in liquid and vapor compositions and easier the separation by distillation.

Relative Volatility

Relative volatility is the ratio of concentration ratio of A and B in one phase to that in the other.
Thus if relative volatility is close to 1, then it implies that it is very difficult to separate two components