Phase equilibria of binary and ternary polymer solutions using modified UNIQUAC-based local composition model

In the present research, a modification on UNIQUAC activity coefficient model was done based on the local composition concept. The model was applied for binary and ternary systems containing different polymers and protic solvents. The newly modified model was compared with several local composition models such as Wilson, NRTL, UNIQUAC, polymer-NRTL, UNIQUAC-LBY and UNIQUAC-DMD in vapor–liquid. Also, comparison of the model with NRTL, UNIQUAC and UNIQUAC-LBY was done for liquid–liquid equilibrium data. In the presented model, a Freed-FV term was added to activity coefficient expression to consider the free volume effects in the mixture. Also, new surface and volumetric structural parameters were applied for studied alcoholic and aqueous solutions. AARD % of the new model (known as M-UNIQUAC-LBY model) was 1.98% for 28 vapor–liquid equilibrium data set (314 data points) of binary polymer–solvent systems. Moreover, RMSD % of 14 studied liquid–liquid systems in equilibria (155 tie-lines) was equal to 10.6431. The results of presented model were superior to previously presented ones in both VLE and LLE. Therefore, it can be successfully utilized to predict phase equilibria in mixtures, which contain pertinent components for industrial applications.