Equilibrium phase behavior of ternary systems formed by polyethylene glycol + choline salts + water

The economic and environmental potentialities of the application of choline salts in aqueous two-phase systems (ATPS), as well as the incipiency of works of these ionic liquids (ILs) combined with polyethylene glycol (PEG), are the reasons for the characterization of new “green” ATPS formed by PEG (400 and 1500 g.mol−1) combined with choline-based ILs (choline chloride, choline bitartrate, and choline dihydrogen citrate). Choline chloride was preferentially concentrated in the top phase, while the lower phase was rich in PEG. The opposite behavior was observed for bitartrate and dihydrogen citrate. ATPS formed by PEG1500 exhibits a significant increase in the biphasic area as the temperature increases; while for systems formed by PEG400, this same trend is slight, demonstrating that phase segregation has an endothermic character. The salting-out effect and the hydrophobicity of the polymer explain the increase of the biphasic area with increasing the charge density of the anion and increasing polymer molar mass, respectively. The data were fitted with good correlation using the Merchuk equation for the binodal curves and Guan equation for the tie-lines.