LAUSR

Abstract Experimental liquid–liquid equilibrium data for aqueous two-phase systems (ATPSs) formed by polyethylene glycol (4000 or 6000 g mol−1)/potassium phosphate and alcohol (1-propanol or 2-propanol)/potassium phosphate + water were determined at 298.15 K and pH 7.0. Four binodal curves and five tie-lines for each curve were obtained. The effective excluded volume (EEV) and salting-out effect parameters were determined. The diagrams formed by PEG 6000/salt and 1-propanol/salt showed a higher biphasic region as well as higher values of EEV and salting-out coefficient when compared to those of ATPSs formed by PEG 4000/salt or 2-propanol/salt, respectively. The interaction parameters were obtained using the UNIversal Functional Activity Coefficient (UNIFAC) model. From the interaction energy values calculated using the new binary interaction parameters estimated in the thermodynamic modeling it was possible to gain a better understanding of the phase-forming process. The UNIFAC model showed satisfactory agreement between the experimental data and the correlated values, indicating that its use is reliable to obtain equilibrium data for systems that contain the same contribution groups.