| Aqueous two phase system (ATPS) consists of hydrophilic organic solvent (HOS) and salt, which is formed when salt exceeds a specific threshold value. It is generally believed that the formation of HOS-salt ATPSs results from competition between hydration of the HOS and the salt. As a new low-cost two-phase system, the HOS-salt extraction system has outstanding advantages such as rapid phase separation and mass transfer, low toxicity, low viscosity, easy removal of the extraction reagent, easy operation, while the system is unlikely to cause a mild environment damage and destruction of biological substances. This system has been used for purification and analysis, and achieved the desired results, which also gained increasing attention.Up to now, reports on HOS-salt ATPS mainly focuses on the determination of binodal curve and liquid-liquid equilibrium (LLE) data, while research for liquid/liquid/solid boundary is relatively few. Based on prediction of phase rule, we determined the liquid/liquid/solid boundaries of some HOS-salts-water systems. A phase ratio database of ethanol/(NH4)2SO4/water system was constructed for compensation for the low foreseeability of ATPS. The main contents are as follows:(1) Theoretical derivation and properties of liquid/liquid/solid boundary. Based on Gibbs’ phase rule and lever rule, we deduced that there is a linear relationship existing on the liquid/liquid/solid boundary. The liquid/liquid/solid triple-phase data of some ATPSs containing hydrophilic organic solvents and simple salts were explored. The systems studied comprise aqueous solutions containing ethanol,1-propanol,2-propanol or acetone with (NH4)2SO4, and solutions containing1-propanol with (NH4)2SO4, NaCl or KCl at different temperature. The linear liquid/liquid/solid boundaries were investigated, and the effects of temperature, solvent, and salt on the boundary were explored.(2) LLE data in the complete two-phase region. Phase diagram for ethanol/(NH4)2SO4/water system were determined, including binodal curve data and liquid/liquid/solid data. The complete two-phase region in the phase diagram of the ethanol/(NH4)2SO4/water system was exhibited in rectangular coordinate and triangular coordinate. A full factorial experimental design was applied to determine the LLE data of the systems distributed uniformly in the complete two-phase region. At the same time, ATPSs distributed on the liquid/liquid/solid triple-phase boundary were investigated.(3) Phase ratio database construction. A continuous procedure was developed to iterate over the complete two-phase region for determination of the phase ratio of ethanol-(NH4)2SO4-water system. In order to increase the accuracy of the data, two analogous procedures were repeated. Based on the raw data, two-dimensional interpolation was adopted to construct a phase ratio by Matlab’s Gridata function, which is an ideal and mature modeling and analysis system. We also plotted contours of phase ratio to study the distribution characteristics, and verified accuracy of database.(4) Application of liquid/liquid/liquid boundary and phase ratio database. A new method was developed to determine the contents of organic solvent or salt in an unknown sample. For example, the liquid/liquid/solid triple-phase boundary of ethanol-(NH4)2SO4-water system was used as a calibration curve to determine the concentration of (NH4)2SO4and ethanol in sample. The results show that this method was simple, fast, and has high accuracy and reliability. The phase ratio database was used to facilitate separation process design. The distribution behavior of papain in ethanol-(NH4)2SO4-water system was investigated considering the phase ratio between0.9and1.1. |
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