Liquid–liquid equilibrium of aqueous two-phase systems containing poly(propylene glycol) and salt ((NH4)2SO4, MgSO4, KCl, and KAc): experiment and correlation

Binodal data of poly(propylene glycol) PPG400 + salt ((NH4)2SO4, MgSO4, and KCl) + H2O systems were determined at T = 298.15 K, and binodal data of PPG400 + KAc + H2O system was determined at T = (298.15, 308.15, and 318.15) K. Moreover, the binodal curves were fitted to Merchuk equation, and the tie-lines were fitted to both the Othmer–Tobias and Bancroft equations. The effects of temperature and salts on the binodals and tie-lines of the investigated ATPSs were also studied. Finally, the salting-out ability of salts on the polymer was obtained by fitting the Setschenow-type equation to the tie-line data to derive a salting-out coefficient (kS) for each salt. For potassium salts, the relative effectiveness of the anions in inducing the phase segregation in ATPSs follows the Hofmeister series. The relative salting-out effectiveness of the sulfate salts is influenced by complexation of the cations by PPG.

Research highlights
► We determine the binodal/liquid–liquid equilibrium data of PPG400-salt ATPSs.
► We correlate the binodal curves and the tie-lines using some appropriate equations.
► The salting-out ability follows the order: K3PO4 > K2HPO4 > K2CO3 > KAc > KCl.
► The two-phase area increases with increasing temperature. The absolute values of slopes of the tie-lines are similar.