Measurement of water activities and prediction of liquid-liquid equilibriafor water plus ethylene oxide-propylene oxide random copolymer plus ammonium sulfate systems

The water activities in aqueous mixtures containing ethylene oxide-propylen e oxide random copolymer (EOPO) with different molecular weights, both bina ry and ternary systems, were measured using the improved isopiestic method. The modified NRTL model was extended to predict the phase behavior in poly mer + salt aqueous two-phase systems at 298.15 K. The model parameters were evaluated directly from the experimental water activities. The phase diagr ams of LLE of EOPO + (NH4)(2)SO4 aqueous two-phase systems with different m olecular weights were successfully predicted using only one group of model parameters. Good agreement with experimental data is obtained, with most of average absolute deviations being less than 2.2 w/w %. (C) 2000 Elsevier S cience B.V, All rights reserved.