Liquid–Liquid Equilibrium of Thermo-Sensitive Magnetic Ionic Liquid Aqueous Biphasic Systems with pH-Sensitive Copolymers at Different Temperatures

Thermosensitive magnetic ionic liquid was applied to fabricate an aqueous biphasic system with pH-sensitive copolymers. These novel systems are responsive to an external magnetic field, enabling accelerated phase separation with the simple application of a magnet. The phase-forming reagents, comprising thermosensitive magnetic ionic liquid and pH-sensitive copolymers, can be effortlessly recovered through heating and pH adjustment, without the need for any use of organic solvents. In this study, liquid–liquid equilibrium data of the developed triple-responsive aqueous biphasic systems ([BMIMPPG400BMIM][Tempo-OSO3]2 + different PADB + H2O) at three different temperatures were determined under 0.1 MPa. The Merchuk equation was utilized to model the experimental binodal data, with all systems demonstrating satisfactory correlation performance. Higher temperatures were found to be beneficial for the formation of the aqueous biphasic system, and the phase-forming abilities of pH-sensitive copolymers are ranked in this order: PADB4.06 > PADB4.7 > PADB6.0. The tie-line data for different PADB at 298.15 K were ascertained and correlated by two empirical equations, both exhibiting good correlation performance. All of these measured liquid–liquid equilibrium data and the theoretical correlations of these green triple-responsive aqueous biphasic systems provide us a valuable reference for future endeavors in the field of extraction and purification.