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

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.