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

Liquid-liquid equilibrium (LLE) data for aqueous two-phase systems (ATPS) were discussed through experiment and correlation at 25 degrees 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.