Including dispersive interactions in the F–SAC model

Abstract

The recently introduced F–SAC (Functional–Segment Activity Coefficient) model combines the group contribution idea with a COSMO-RS surface contacting theory. This model has a reduced dependency on binary interaction parameters when compared to classical UNIFAC type models and improved accuracy when compared with COSMO based models. In the present work a modified F–SAC formulation is proposed for including dispersive interactions. For testing the modification, experimental data of alkanes, cycloalkanes, alkenes and perfluorocarbons were considered. The proposed model was able to correlate pure compound enthalpies of vaporization, not considered in previous versions of the model. Regarding mixture infinite dilution activity coefficient and vapor–liquid equilibrium data, the modified model maintained the good performance of the original model, also similar to other competing models such as UNIFAC variants. Additionally, the modified model now can compute consistent values for the excess enthalpy and entropy for systems where the interactions are mainly dispersive. For these systems, most activity coefficient models predict zero excess enthalpies, counterbalancing that with distorted excess entropies.