Thermodynamics of magnesium sulfate–polypropylene glycol aqueous two-phase system. Experiment and correlation

Liquid–liquid equilibrium data were obtained for magnesium sulfate–polypropylene glycol (PPG) 425 aqueous two-phase system at 25°C. The improved regular solution theory was used to correlate the equilibrium data. In this theory the Fowler–Guggenheim equation was used to calculate the long-range electrostatic interactions of the ions. The volume and interaction energy parameters of polymer in this model were obtained by using isopiestic data. The applicability of the model was further tested for some other aqueous two-phase systems. These systems are PPG425+NaCl+H2O, ethanol+Na2SO4+H2O, 1-propanol+MgSO4+H2O, 2-propanol+MgSO4+H2O and t-butanol+MgSO4+H2O.