LIQUID-LIQUID AND VAPOR-LIQUID-EQUILIBRIA IN WATER PLUS POLY(ETHYLENEGLYCOL) PLUS SODIUM-SULFATE

In this work we have measured liquid-liquid equilibria (LLE) and vapor -liquid equilibria (VLE) in aqueous solutions of poly(ethylene glycol) (PEG) and sodium sulfate. The liquid-liquid equilibria have been dete rmined over a range of polymer molar masses (1550-6000 g/mol), pH valu es (5.2-8.1), and temperatures (293.15-313.15 K) using a density-sound analyzer. The VLE in the system water + PEG 3000 + sodium sulfate hav e been measured over the entire homogeneous mixing range at 293.15 and 313.15 K by vapor-pressure osmometry. To demonstrate that the experim ental data do not contain any obvious thermodynamic inconsistency, we described VLE and LLE simultaneously using the osmotic virial equation (McMillan, W. G., Jr.; Mayer, J. E. J. Chem. Phys. 1945,13,276) exten ded with a Debye-Huckel term (Debye, P.; Huckel, E. Z. Phys. 1923, 24, 195, 305. Pitzer, K. S. J. Phys. Chem. 1973, 77, 268).