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 lattice-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 can be useful for modeling industrial processes involving polymers.