Estimation of Liquid−Liquid−Vapor Equilibria in Binary Mixtures of n-Alkanes

Abstract

This study tests the ability of the best presently available semipredictive models, namely, predictive Soave−Redlich−Kwong (PSRK), linear combination of Vidal mixing rules (LCVM), and the novel global phase diagram approach (GPDA), to estimate the three-phase liquid−liquid−vapor equilibrium (LLVE) in the homologous series methane−n-alkanes, ethane−n-alkanes, propane−n-alkanes, and n-butane−n-alkanes. It is demonstrated that at high pressures GE mixing rules predict the wrong shape of the liquid−liquid critical curves, which involves fictitious closed loops of liquid−liquid equilibrium. Such a behavior is responsible for predicting nonrealistic three-phase LLVE behavior along the homologous series under consideration. In addition, both PSRK and LCVM fail in estimating the lower critical end-point curve. The results presented here for the GE-based models under consideration are probably characteristic for them. In contrast, GPDA is consistent in the entire thermodynamic phase space and does not predict nonp...