Prediction of ternary liquid-liquid equilibria in polymer-solvent-solvent systems

The performance of the entropic free-volume (FV) activity coefficient model and the Holten-Andersen et al. equation of state (EOS:) in predicting the liquid-liquid equilibrium (LLE) for solutions involving one polymer and two solvents is examined. Both models are purely predictive since only the structures of the compounds involved and, in the case of the entropic FV model, the molar volumes are required, The necessary interaction parameters for both models are obtained from vapor-liquid equilibrium (VLE) data for mixtures of low molecular weight compounds. The entropic FV model qualitatively predicts the ternary LLE phase envelope for all the systems studied, while for some of them the predictions can be considered quantitative as well. The Holten-Andersen et al. EOS provides quite satisfactory results for some of the systems, while it fails for others. In addition, due to the UNIFAC parameter table employed, the entropic FV model is of wider applicability compared to the Holten-Andersen et al. EOS.