Modeling of liquid-liquid equilibrium of polyethylene glycol salt aqueous two-phase systems - the effect of partial dissociation of the salt

The modified NRTL model proposed in the previous paper [Y.-T., Wu, D.-Q, Li n, Z.-Q. Zhu, L.-H. Mel, Fluid Phase Equilibria 124 (1996) 67-79.] is furth er extended to include the effect of partial dissociation of salts in polye thylene glycol (PEG)-salt aqueous two-phase systems (ATPS), and is used to calculate the Liquid-liquid equilibrium phase diagrams such as PEG-(NH4)(2) SO4 and PEG-MgSO4 ATPS. The phase diagrams of PEG-uni-bivalent salt ATPS ca n be correctly represented in the cases of both complete dissociation and p artial dissociation of the salt, while those of PEG-MgSO4 ATPS can only be described in the case of partial dissociation of the salt, The analysis sho ws that the salts may have different existing states in the ATPS. The effec t of partial dissociation of the salts on the phase diagrams should be cons idered, especially for systems such as PEG-MgSO4 ATPS. (C) 1999 Elsevier Sc ience B.V. All rights reserved.