Prediction of Vapor-Liquid Equilibria Using CEOS /GE Models

The present study investigates the use of different GE mixing rules in cubic equations of state for prediction of phase behavior of multicomponent hydrocarbon systems. To predict VLE data in multicomponent symmetric and asymmetric mixtures such as systems that contain light gases (nitrogen, carbon dioxide, etc.) and heavy hydrocarbons, the SRK equation of state has been combined with excess Gibbs energy models. In this study, the PSRK method, developed by Holderbuom and Gmehling for VLE data prediction, is re-examined. To visualize the effect of different mixing rules in predicting VLE data, Wong and Sandler mixing rule was applied. New group and molecular interaction parameters in UNIFAC and W-S models were introduced. These parameters were obtained by regressing the available VLE data. The results of comparisons between applied models and experimental data are presented. These indicate that although all suggested models could provide reasonably good VLE information for the systems containing components of similar size in a wide range of temperatures and pressures, but only PSRK method shows minimum absolute and relative errors for both vapor and liquid compositions in asymmetric systems.