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

Abstract

In this work, we have developed a novel aqueous twophase system (ATPS) composed of 1,4-bis(2-hydroxypropyl)piperazine (HPP), Na 2 SO 4 , and H 2 O, 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 H 2 O 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 Na 2 SO 4 , while density and surface tension fall with the increase of system components in the top phase and decrease in the bottom one. ATPS would be a new method for removing the heat-stable salts (HSS) containing sulfuric acid root of absorbent for flue gas desulfurization, which is as HPP.

Equilibrium Data and Correlation with Redefined NRTL Equation of Aqueous Two-phase Systems Based on 1,4-Bis-(2-hydroxyethyl)-piperazine and Na₂SO₄

“…The sulfate concentration of the top phase was determined through the volumetric method, and that in the bottom phase was determined using the weight method [1]. The content of BHEP was determined by potentiometric titration [22].…”

“…It is feasible to separate heat stable salt (HSS) from diamine flue gas desulfurizer [1] and flue gas decarburizer [2] by aqueous two-phase systems (ATPS). Compared with electrodialysis [3], reverse osmosis [4], and ion exchange adsorption [5] currently used in industry, the process significantly reduces the production of liquid waste, requires less equipment and instruments, and has a better effect on the treatment for high concentration of HSS in absorbents.…”