On extension of UNIQUAC-NRF model to study the phase behavior of aqueous two phase polymer–salt systems

The UNIQUAC-NRF model for aqueous two-phase polymer–polymer systems is extended to correlate liquid–liquid equilibria of aqueous polymer–salt two-phase systems. The systems investigated are polyethylene glycol+ammonium sulfate+water and polyethylene glycol+potassium monohydrogen phosphate (K2HPO4)+water for five molecular weights of PEG. In this model, the nonrandom state is selected as a reference state. The model has six binary adjustable parameters that were determined by an optimization program. The Debye–Huckel equation based on Fowller–Guggenheim equation is used to calculate the long-range electrostatic interaction of the ions. The results obtained by this model are in good agreement with experimental data.