Polymer−Solvent Vapor−Liquid Equilibrium: Equations of State versus Activity Coefficient Models

Abstract

A Soave−Redlich−Kwong (SRK) cubic equation of state (EOS) combined with the Flory−Huggins activity coefficient (Gex) model in a Huron−Vidal type (EOS + Gex) mixing rule was used to correlate binary vapor−liquid equilibrium (VLE) of polymer−solvent mixtures. To extend the SRK EOS to pure polymers, suitable critical constants were selected based on available information for long-chain hydrocarbons. In mixture applications, the only binary interaction parameter, χ of the Flory−Huggins model, was obtained from the infinite-dilution activity coefficient data of solvent in polymer, without using any experimental VLE information. The results show that this EOS + Gex approach can represent polymer−solvent VLE accurately. It was also observed that χ is much less temperature- and composition-dependent when the Flory−Huggins model is coupled with the SRK EOS than it is when used directly as an activity coefficient model.