POLYMER-SOLVENT VAPOR-LIQUID-EQUILIBRIUM - EQUATIONS OF STATE VERSUS ACTIVITY-COEFFICIENT MODELS

A Soave-Redlich-Kwong (SRK) cubic equation of state (EOS) combined wit h the Flory-Huggins activity coefficient (G(ex)) model in a Huron-Vida l type (EOS + G(ex)) mixing rule was used to correlate binary vapor-li quid 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 appli cations, the only binary interaction parameter, chi of the Flory-Huggi ns model, was obtained from the infinite-dilution activity coefficient data of solvent in polymer, without using any experimental VLE inform ation. The results show that this EOS + G(ex) approach can represent p olymer-solvent VLE accurately. It was also observed that chi is much l ess temperature-and composition-dependent when the Flory-Huggins model is coupled with the SRK EOS than it is when used directly as an activ ity coefficient model.