PREDICTION OF VAPOR-LIQUID-EQUILIBRIA FOR MIXTURES WITH COPOLYMERS

Three group-contribution models for predicting the activity coefficients of solvents in copolymer solutions are considered. These models include the UNIFAC-free-volume model, the entropic- free-volume model, and the group-contribution-Flory equation of state. An extensive evaluation of these models and a comparison of the accuracy of the prediction of the activity coefficients of many of solvents in 10 different copolymers with various molar masses and various chemical compositions are carried out. The activity coefficients are calculated using the pseudocomponent approach. It is investigated how the prediction of solvent activity coefficients is influenced by the number of discrete pseudocomponents, and whether the polydispersity of copolymers with respect to molar mass and chemical composition is important for vapor-liquid equilibrium (VLE) calculations. It was found that the effect of the number of pseudocomponents on VLE prediction is not significant, and that VLE calculations can be carried out without incorporation of the polydispersity of copolymers into the thermodynamic models. From the obtained results it can be seen that all three models perform similarly and are capable of predicting activity coefficients of solvents in copolymer solutions rather accurately, and that over the whole spectrum of the investigated copolymer/solvent systems there is not one model that is superior.