Modeling of liquid-liquid phase equilibria in aqueous solutions of poly(ethylene glycol) with a UNIFAC-based model

\An activity coefficient model, which is a combination of the entropic-free volume combinatorial term and a UNIFAC residual term, referred to as EFV/UNIFAC, is applied to the correlation and prediction of the molecular weight effect on liquid-liquid equilibria (LLE) of aqueous poly(ethylene glycol) (PEG) solutions. Interaction parameters between the end group of PEG and its repeating unit, as well as between the end group and the water molecule, are estimated by fitting activity coefficient experimental data of mixtures containing low molecular weight compounds. Interaction parameters between the water molecule and the repeating unit of PEG are determined from experimental LLE data for a single PEG molecular weight with water. These interaction parameters are used to predict the effect of the polymer molecular weight on miscibility. The proposed model provides a good compromise between accuracy and simplicity.