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) PPG 400   +   salt ((NH 4 ) 2 SO 4 , MgSO 4 , and KCl)   +   H 2 O systems were determined at T   =   298.15   K, and binodal data of PPG 400   +   KAc   +   H 2 O 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 ( k S ) 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.