Liquid-liquid equilibrium of aqueous two-phase systems formed by non-ionic surfactant (Triton X-165 or Triton X-305) and ionic liquid based on the choline cation (choline bitartrate or choline dihydrogen citrate)

Abstract

Liquid-liquid equilibrium data for aqueous two-phase systems (ATPSs) formed by Triton X-165 or Triton X-305 + ionic liquid based on the choline cation (choline bitartrate or choline dihydrogen citrate) + water were obtained at different temperatures (298.2, 313.2, and 328.2 K). The effects of temperature, electrolyte anion, and surfactant on the equilibrium data were evaluated. For all the ATPSs investigated, the upper phase was found to be surfactant-rich and the lower phase was electrolyte-rich. An increase of the biphasic region was observed with increasing temperature, showing that the phase separation process was endothermic and entropically driven. The potential of phase segregation between the different anions studied was in the order bitartrate > dihydrogen citrate, which was attributed to the different capacities of the anions to form hydration complexes and induce a surfactant salting-out effect. The TX-305 surfactant was more efficient in inducing phase segregation, compared to the TX-165 surfactant, indicating that the molar mass/hydrophobicity balance of the surfactant determined the immiscibility region of the ATPS.