Liquid–Liquid Equilibrium of Various Aqueous Two-Phase Systems: Experiment and Correlation

Abstract

Liquid–liquid equilibrium (LLE) data for aqueous two-phase systems (ATPS) were discussed through experiment and correlation at 25 °C, in polymer–organic salt ATPS, alcohol–salt ATPS, and polymer–surfactant ATPS, respectively. Various binodal curves empirical equations combined with simple experiments were applied to determine the LLE data with as wide composition concentrations as possible. The tie-line length (TLL) ranges of the investigated ATPS were also determined experimentally. Both the two-phase regions and the TLL ranges of polymer–organic salt ATPS or alcohol–salt ATPS were generally wider than polymer–surfactant ATPS, which would be caused by the solubility of two compositions in different ATPS. The parameters of tie-line equations including Othmer–Tobias and Bancroft equations were further obtained by LLE data, which can be used to predict the unknown tie-line data. The experimental volume ratios of various tie-lines in ATPS showed good agreement with the predicted data based on the small standard deviation (SD < 0.05). Compared to the complicated experimental method for the determination of ATPS LLE data, the binodal curves and tie-line empirical equations combined with simple experiments can provide the LLE data for various ATPS.