Novel Aqueous Two-Phase System Consisting of 1,4-Bis(2-hydroxypropyl)-piperazine, Na2SO4, and H2O: Temperature-Dependent Equilibrium Data and Physical Properties

In this work, we have developed a novel aqueous two-phase system (ATPS) composed of 1,4-bis(2-hydroxypropyl)-piperazine (HPP), Na2SO4, and H2O, which can determine the liquid–liquid equilibrium and phase diagrams at the temperatures of 303.15–323.15 K. Simultaneously, the physical properties such as density, viscosity, refractive index, and surface tension have been determined for the top phases and bottom ones of the ATPS. The results indicate that temperature has no significant effect upon the biphasic region, implying a small enthalpy contribution during phase separation. However, the changes in temperature result in a decrease of tie line slope, because H2O molecules are transferred from the bottom phase to the top phase. In determining the physical properties of the system, viscosity and refraction index increase with the system components increasing, during the phase of both HPP and Na2SO4, while density and surface tension fall with the increase of system components in the top phase and decrease in...