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Equilibrium diagram (X-Y) diagram is simple diagram than boiling point diagram in which plot of temperature is eliminated. The boiling point diagram represents dynamic equilibrium of mole fraction of vapor and liquid phase at certain temperature at constant pressure. Boiling point diagram at constant pressure for binary mixture having component A and B is as below.
The equilibrium between the liquid and vapor phases of the system to be subjected to distillation is represented by vapor liquid equilibrium (VLE) diagram. Distillation columns are designed based on boiling point properties in the mixture being separated. Thus, the size particularly height of distillation column are determined by VLE data for the mixture.
Miscible liquid mixtures are of three types which can be revealed by plotting the vapor pressure against mole fraction of component.
1. First type of mixture:
The Vapor pressure curve exhibit minimum area. If we take mixture which has excess of ‘x’ (more volatile compound), we are somewhere at ‘C’ on the curve. On distillation, vapor will contain excess of ‘x’ and thus the remaining mixture will get richer in ‘y’. Finally we reach the point ‘D’ where vapor pressure is minimum and thus the boiling point is maximum. Here the mixture will distill unchanged in composition. Read more
Henry’s Law states that partial pressure on component on a solution is directly proportional to mole fraction in liquid.
