Salting-Out Effect of Ionic Liquids on Poly(propylene glycol) (PPG): Formation of PPG plus Ionic Liquid Aqueous Two-Phase Systems

In the present work, aqueous poly(propylene glycol) (PPG) solution was separated into aqueous two-phase systems (ATPSs) in the presence of ionic liquid 1-allyl-3-methylimidazolium chloride ([Amim]Cl), 1-butyl-3-methylimidazolium acetate ([C(4)mim]Ac), or 1-butyl-3-methylimidazolium chloride ([C(4)mim]Cl). The top phase was PPG-rich, whereas the bottom phase was ionic liquid (IL)-rich. Liquid-liquid equilibrium data for the ATPSs and the salting-out coefficients of the ILs have been determined at 298.15 K and atmospheric pressure. It was shown that the binodal curves and the tie-lines could be described by a three-parameter equation and the Othmer-Tobias and Bancroft equations, respectively. The salting-out ability of the ILs on PPG was found to follow the order: [Amim]Cl > [C(4)mim]Ac > [C(4)mim]Cl > [C(4)mim][BF4]. Since PPG is a thermo-sensitive polymer and can be recovered simply by heating, these novel ATPSs are expected to have applications in the recycling and/or enrichment of hydrophilic ILs from aqueous solutions.