Somayeh Kazemi - Department of Chemical and Petroleum Engineering, Sharif University of Technology, zadi Ave., Tehran, Iran.
Mohammed Taghi Zafarani-Moattarb - Physical Chemistry Department, University of Tabriz, Tabriz, Iran.
Cyrus Ghotbi - Department of Chemical and Petroleum Engineering, Sharif University of Technology,Azadi Ave., Tehran, Iran.
Vahid Taghikhani - Department of Chemical and Petroleum Engineering, Sharif University of Technology,Azadi Ave., ehran, Iran.

In this study, water activities for the ternary systems of PEG6000 + sodium citrate (Na3Cit) + H2O and PEG6000 + potassium citrate (K3Cit) + H2O have been measured using an improved isopiestic method over the entire homogeneous mixing range at 298.15 K. From these measurements, values of the vapor pressure of solutions were also determined. The experimental data for the activity of water, collected in this work, were accurately correlated with local composition b ased models of the NRTL, modified NRTL, Wilson and modified Wilson for Aqueous Two Phase Systems (ATPS) studied. The results showed that these models can accurately correlate the water activity data generated in this work.

Aqueous two phase system; vapor-liquid equilibrium; Poly(ethylene glycol); Citrate salts; modeling