Prediction of vapor–liquid equilibria for supercritical alcohol + fatty acid ester systems by SRK equation of state with Wong–Sandler mixing rule based on COSMO theory

Abstract

Vapor–liquid equilibria for supercritical alcohol + fatty acid ester systems were predicted by Soave–Redlich–Kwong (SRK) equation of state with the Wong–Sandler (WS) mixing rules based on an activity coefficient model by Conductor-like Screening Model (COSMO) theory. The predicted systems were methanol + methyl laurate, methanol + methyl myristate, ethanol + ethyl laurate, and ethanol + ethyl myristate systems from 493 to 543 K, near the critical temperatures of methanol ( T c = 512.6 K) and ethanol ( T c = 513.9 K). The excess Gibbs free energies for the mixing rule were determined from the COSMO-Segment Activity Coefficient (COSMO-SAC) model. The universal parameters in COSMO-SAC model were determined by fitting vapor–liquid equilibrium data for alcohol + alkyl acetate systems at low pressures. Predictions for the liquid phase by SRK/WS/COSMO-SAC reproduced the experimental data more accurately than calculations made with SRK/WS/UNIFAC.