Predicting the phase equilibria of esters/alcohols mixtures and biodiesel density from its fatty acid composition using the modified group-contribution PC-SAFT

Abstract

An empirical approach proposed recently (Fluid Phase Equilibria, 434 (2017) 176–192) to distinguish different isomer molecules is extended in this paper aiming to apply for alkyl-esters. The vapor pressure, saturated liquid density of heavy unsaturated and branched alkyl-ester are predicted using the transferred parameters of groups from n-alkanes, branched alkane, cis-alkenes and alkyl-ester. For pressures up to 2100 bar, density data for esters, ranging from C8:0 to C18:0, with up to two unsaturated bonds, are predicted with deviations inferior to 3%.Different binary ester + ester systems were investigated. Furthermore, the VLE of methanol/ethanol + ester mixtures are predicted using a transferable cross-association parameters approach. The general agreement between mg-SAFT and experimental data is very good (within 2–3% deviation on pressure).Finally, in order to validate the predictive ability of the model to be applied in the biodiesel groundwork, the mg-SAFT was then applied to predict the liquid density of 74 biodiesel mixtures based on its fatty acid ester composition. Overall average prediction errors at atmospheric pressure data were 0.71% for 64 multi-component mixtures, and that of 1.36% compared to experimental data for 10 biodiesel systems at high pressure up to 1300 bar.