EQUATIONS ON STATE AND ACTIVITY-COEFFICIENT MODELS FOR VAPOR-LIQUID-EQUILIBRIA OF POLYMER-SOLUTIONS
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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 perturbedsoftchain theory (PSCT), groupperturbedsoftchain theory, (GPSCT), groupcontributionlattice fluid (GCLF) EOS, GCFlory EOS, UNIFACFV, entropicFV and GKFV models, new UNIFAC, and modified FloryHuggins model. Freevolume activity coefficient models (UNIFACFV, entropicFV) are simpler and, when applied to polymer solutions, more accurate than the EOS. Activity coefficient models are restricted to lowpressure calculations and require accurate values of purecomponent volumes. Mixture parameters for activity coefficient models and GCFlory EOS have been previously evaluated from experimental vaporliquid equilibrium data for mixtures with only lowmolecularweight compounds. The GCFlory EOS, though more complicated than activity coefficient models, provides equally good or in some cases better predictions. The application of GCFlory EOS developed as an activity coefficient model is restricted to lowpressure calculations. On the other hand, PSCT and GCLF developed as true EOS provide reliable equilibrium predictions using mixture parameters evaluated solely from purecomponent properties together with standard mixing and combining rules. PSCT EOS performs generally better than GCLF EOS for polymer solutions considered in this study. Copyright 1994 American Institute of Chemical Engineers
