Modeling phase equilibria in polymer-solvent systems for process design

An excess Gibbs energy model is presented for calculating phase equilibria in multicomponent systems containing polymers and solvents. The model represents a combination of a physical contribution obtained from a lattice model and a chemical contribution that accounts for association and solvation effects. The lattice model is based on a revised version of Freed's latticc-field theory developed by Hu, Prausnitz, and co-workers. The model accurately represents solvent activities and liquid-liquid equilibria in binary and ternary polymer solutions over wide ranges of temperature and polymer molecular weight. It is capable of reproducing liquid-liquid equilibria with upper and lower critical solution temperatures as well as closed-loop and hourglass-shaped phase diagrams. Because of its numerical simplicity, a reasonably small number of binary parameters, and its applicability to multicomponent systems, the model cm be useful for modeling industrial processes involving polymers.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.