Phase Behavior in Aqueous Two-Phase Systems Based-Ionic Liquid Composed of 1-Butyl-3-methylimidazolium Tetrafluoroborate and Copper Sulfate in Different Temperatures

Abstract

Phase behavior of new aqueous two-phase systems (ATPSs) composed by 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]­BF4) + copper sulfate (CuSO4) + water systems were determined experimentally at T = (283.15, 298.15, and 313.15) K. The phase diagrams obtained at the different study temperatures describe the liquid–liquid equilibrium (LLE) and, in some cases, the liquid–liquid–solid equilibrium for different mixture compositions. The effects of the temperature, composition, and ion exchange in the formation of this ATPS were available. The temperature had a remarkable effect on the position of phase diagrams. The decrease in temperature promoted phase separation indicating the exothermic character of formation of these ATPSs, and further, at temperatures of 283.15 and 298.15 K it was observed that there was phase inversion for some mixture compositions that occurred. The extent of the ionic exchange of the original ionic pairs between the phases in equilibrium was evaluated considering the electroneutrality of the phases. It was observed experimentally that, in the LLE condition established, there was no significant exchange of the ionic pairs. The ability of different cations, from different sulfate salts, to induce the formation of ATPSs in mixtures involving [Bmim]­BF4 was evaluated. For this, thermodynamic data of hydration of different cations reported in the literature were used together with experimental data of saturation solubility to establish a scale. Thermodynamic parameters of transfer of components (cations, anions, and water) between the phases were also calculated from the experimental data and indicated that the material transfer of the bottom phase to the top is not spontaneous and tends to be less spontaneous as the length of the tie line value increases. Additionally, the equilibrium data and binodal curves were fitted to an empirical nonlinear expression (Merchuk equation), and the salting out effect was explored using the type-Setschenow equation.

Phase Behavior of Ionic Liquid-Based Aqueous Two-Phase Systems

“…As shown in Figure 2 C, the decrease in the temperature slightly caused the expansion of the two-phase area. Although the above phenomenon is different from the traditional polymer + salt system [ 74 , 75 , 76 , 77 ], it can be found in most ILs + salt ATPSs. However, there are a few ATPSs composed of IL and inorganic salt, which undergo the expansion of immiscibility regime with the increase in temperature [ 45 , 78 ].…”