EQUATIONS ON STATE AND ACTIVITY-COEFFICIENT MODELS FOR VAPOR-LIQUID-EQUILIBRIA OF POLYMER-SOLUTIONS

Four noncubic equations of state (EOS) and five activity coefficient models are applied to binary polymer and solvent solutions. Solvent activities at intermediate concentrations and equilibrium pressures are predicted with the perturbed-soft-chain theory (PSCT), group-perturbed-soft-chain theory, (GPSCT), group-contribution-lattice fluid (GCLF) EOS, GC-Flory EOS, UNIFA C-FV, entropic-FV and GK-FV models, ''new'' UNIFA C, and modified Flory-Huggins model. Free-volume activity coefficient models (UNIFAC-FV, entropic-FV) are simpler and, when applied to polymer solutions, more accurate than the EOS. Activity coefficient models are restricted to low-pressure calculations and require accurate values of pure-component volumes. Mixture parameters for activity coefficient models and GC-Flory EOS have been previously evaluated from experimental vapor-liquid equilibrium data for mixtures with only low-molecular-weight compounds. The GC-Flory EOS, though more complicated than activity coefficient models, provides equally good or in some cases better predictions. The application of GC-Flory EOS developed as an activity coefficient model is restricted to low-pressure calculations. On the other hand, PSCT and GCLF developed as ''true'' EOS provide reliable equilibrium predictions using mixture parameters evaluated solely from pure-component properties together with standard mixing and combining rules. PSCT EOS performs generally better than GCLF EOS for polymer solutions considered in this study.