Phase diagrams of aqueous two-phase systems formed by polyethylene glycol + ammonium sulfate + water: equilibrium data and thermodynamic modeling

Abstract Phase diagrams of aqueous two-phase systems (ATPS) composed of polyethylene glycol (PEG) of different molar mass (400 or 10,000 or 35,000) g mol −1  + ammonium sulfate + water were investigated at (10.0, 25.0, and 40.0) °C. For all ATPS, the temperature had no a remarkable effect on the phase equilibrium compositions of the ATPS. The increase in the equilibrium temperature promoted a slight increase in the biphasic region, indicating the endothermic character of the phase separation process. Additionally, the slopes of the tie-lines tended to increase with increasing temperature. The increase in the polymer molar mass provides ATPS with larger biphasic region. The tie-line compositions were estimated and correlated using the Othmer–Tobias and Bancroft equations, and the parameters are reported. The liquid–liquid equilibrium (LLE) experimental data obtained was well correlated to the activity coefficients of the Non Random Two-Liquid (NRTL) model, and the experimental data were recovered with average error between 0.94% and 10.16% for tie line lengths and less than 9.31% for slope of the tie line.