The salting-out effect and phase separation in aqueous solutions of sodium phosphate salts and poly(propylene glycol)

Phase diagrams and liquid-liquid equilibrium (LLE) data of the aqueous poly(propylene glycol) (PPG) + di-sodium hydrogen phosphate and PPG + tri-sodium phosphate two-phase systems have been determined experimentally at 298.15, 303.15, 308.15, 313.15 and 318.15 K. The effects of temperature and charge on the anion of electrolyte on the binodal curves and tie-lines have been studied and it was found that an increasing in temperature and charge on the anion caused the expansion of two-phase region. The results show that the effect of charge on the anion of electrolyte on the binodal curves becomes smaller by increasing temperatures. It was also found that the concentration of salt, which is in equilibrium with a certain concentration of PPG, decreases by increasing temperature. Based on cloud point values, the energetics of the clouding process has been estimated and it was found that entropy increase is the driving force for biphasic formation. (C) 2009 Elsevier B.V. All rights reserved.