REPRESENTATION OF VAPOR-LIQUID-EQUILIBRIA USING SELECTED EQUATIONS OFSTATE

Four equations of state, two cubic and two perturbed hard-sphere equat ions, are examined with regard to their prediction of vapor-liquid equ ilibria. The computed predictions are compared with experimental data. Results of the comparison are reported for mixtures of polar, non-pol ar, and highly associated compounds. The experimental data base of the comparison includes fifteen binary systems covering a wide range of p ressure, temperature, and molecular variety. The same computational te chnique was used throughout this study. The results indicate that both cubic equations give better predictions of the vapor-liquid equilibri a for non-polar and symmetric mixtures, while both perturbed hard-sphe re equations give significantly better predictions for the highly asym metric and associated systems of CO2-fatty acid methyl esters. All equ ations failed to predict the vapor-liquid, equilibria for, some mixtur es, especially the highly associated systems. However, the phase equil ibrium behavior of these systems is greatly improved using mixing rule s other than the simple quadratic mixing rule. Generally, no single eq uation of state currently exists that is equally suitable-for the pred iction of vapor-liquid equilibria of all classes of binary systems.