A modified free-volume-based model for predicting vapor–liquid and solid–liquid equilibria for size asymmetric systems

The main purpose of this work is to present a free-volume combinatorial term in predicting vapor–liquid equilibrium (VLE) and solid–liquid equilibrium (SLE) of polymer/solvent and light and heavy hydrocarbon/hydrocarbon mixtures. The proposed term is based on a modification of the original Freed Flory–Huggins model, replacing the molar volume with a free-volume (FV) term. Using an extensive database for athermal polymer solutions at finite dilution, the single parameter of the model has been well adjusted. The results obtained from the model proposed in this work were favorably compared with those obtained from the well-established entropic-FV based models, i.e., the original entropic-FV (EFV) and the modified entropic-FV (MEFV) models. The results were also compared with those of the original UNIFAC-FV model as well as a modified UNIFAC-FV model, Kannan-FV, recently proposed model by Kannan et al. The results obtained from the proposed model showed that better improvement can be attained for the polymer systems with energetic interactions as well as for VLE and SLE study of heavy alkane solutes in light alkane solvents. This observation can be further verified by comparison of the results obtained from the proposed model with those of the molecular simulation data.