General correlations of vapor‐liquid equilibria

Abstract

The vapor-liquid equilibria ratio K i = y i / x i for the components of coexisting equilibrium vapor and liquid mixtures is a complex function of the conditions and compositions of the coexisting phases. Many investigators have attempted to develop a generalized method for predicting vapor-liquid equilibrium. However, most of these methods in their present form include some parameter (or parameters) which depends on the mixtures. In other words, most of these methods do not satisfy the need for generality. Chao and Seader (1961) developed a general correlation of vapor-liquid equilibria in hydrocarbon mixtures. Their method is quite popularly used by industry today. Lee and Edmister (1971) developed a new generalized method for predicting vapor-liquid equilibrium to compare with Chao-Seader's correlation.When a reader applies Lee-Edmister's correlation to evaluate vapor-liquid equilibrium, he may find that the calculated result does not give a good comparison with the experimental result. This is because of an error in their correlation of activity coefficient in liquid solution yi. Lee and Edmister derived the activity coefficient y i from an expression of the excess Gibbs free energy of a mixture, which was proposed by them. A reader may not be able to follow their derivation to obtain the present form n n