Experimental Evaluation and Thermodynamic Modeling of Aqueous Two-Phase Systems Based on Poly(ethylene oxide-ran-propylene oxide (50:50)) as an Environmentally Friendly Thermosensitive Copolymer and Phosphate Salts

Abstract

This study focuses on the equilibrium behaviors of a novel aqueous two-phase system (ATPS) based on phosphate salts and poly(EO₅₀-ran-PO₅₀) at various pH (6, 7, and 8) and temperatures (25, 35, and 40 °C). The main distinction of this system is the application of a thermosensitive copolymer with a mild critical solution temperature (48 °C), which allows easy recovery of polymers from temperature-sensitive materials for purification purposes. The phase diagrams for the ATPS indicated that the increase in pH and temperature resulted in expansion of the biphasic region. The Merchuk equation was applied for description of the experimental data, and the length and slope of the tie lines in different conditions were calculated. The experimental tie-line compositions were correlated to the Othmer–Tobias and Bancroft equations, and the relevant parameters of the models were determined. The experimental data of this system were best described by the activity coefficients of the nonrandom two liquid (NRTL) model. Also, a simplified model of the NRTL equation based on the use of mass fraction has been proposed in the present study, in which the mean deviation of 1.40% between experimental and calculated mass fractions revealed its prediction power from the equilibrium compositions of the system.