REVISION OF THE GROUP-CONTRIBUTION FLORY EQUATION OF STATE FOR PHASE-EQUILIBRIA CALCULATIONS IN MIXTURES WITH POLYMERS .1. PREDICTION OF VAPOR-LIQUID-EQUILIBRIA FOR POLYMER-SOLUTIONS

A revised group-contribution Flory equation of state (GC-Flory EOS) for predicting activity coefficients of polymer solutions is presented in this work. Three modifications are introduced: (a) the extra binary entropic interaction parameter, DELTAS(ij)hb, which was used in the original model for corrections due to hydrogen bonding of the OH and H2O groups is found not be needed in the present version; (b) the values attributed to the segmental volume parameters R(OH) and R(H2O) and the surface area parameters Q(OH) and Q(H2O) are those derived by Bondi; (c) new EOS parameters have been determined for 15 main groups and 32 subgroups from pure component and binary mixtures properties of low molar mass compounds only. Extensive comparison of the accuracy of the predictions of activity coefficients using the revised GC-Flory EOS with two other predictive models, UNIFAC-FV (Oishi and Prausnitz, 1978) and Entropic-FV (Elbro et al., 1990, Kontogeorgis et al., 1993) is carried out. It is shown that the revised GC-Flory EOS gives much better predictions of vapor-liquid equilibria than does the original model, and it performs now as well as the Entropic-FV model. It gives, in general, predictions of vapor-liquid equilibria (VLE) of the same quality as the Entropic-FV model for finite concentrations as well as for the dilute regions. Until now, the GC-Flory model is the only model tested which can reasonably predict VLE behavior for solutions with poly(vinyl chloride) and hydrocarbons.