Measurement and Correlation of Phase Equilibria in Aqueous Two-Phase Systems Containing Polyoxyethylene Cetyl Ether and Three Organic Salts at Different Temperatures.

The polymer polyoxyethylene(20) cetyl ether (C56H114O21, POELE20) and three salts (K2C2O4, K2C4H4O6, and K3C6H5O7) were the phase-forming materials to build the aqueous two-phase system (ATPS) at the temperatures 288.15, 298.15, and 308.15 K. The data of the phase diagram including binodal curve data and tie-line data were determined and fitted by classical equations, and they obtained the satisfactory correlation effect. The phase-forming ability of salt composed of the same cation was investigated by three factors, namely, the valence of the anion, the Gibbs free energy of the anion, and the value of effective excluded volume (EEV). It was found that the phase-forming ability of salt strengthened when the values of said three factors went up. The results of the analysis on the data from the present work and that in our previous paper showed that the order of the phase-forming ability of salts was KOH > K2C2O4 > K2C4H4O6 > K2CO3 > K3C6H5O7 > K3PO4. The effect of temperature on phase-forming of the studied ATPSs was discussed through the phase diagram and EEV value, and it was showed that the increase in temperature is beneficial to separating two phases for ATPSs. For the investigated systems, the effect of temperature on the liquid-liquid equilibrium of ATPSs was studied by the phase diagram and the slope of the tie-line (STL), and it was found that the absolute value of the STL increased with rising temperature. [ABSTRACT FROM AUTHOR]