Influence of Aprotic Solvents on the Phase Behavior of Ionic Liquid Based Aqueous Biphasic Systems

Although aprotic solvents (ASs) have been largely explored as cosolvents of ionic liquids (ILs) for biomass resources pretreatment, the separation and recovery of ILs along with ASs were seldom investigated. To evaluate the influence of ASs on the phase behavior of IL-based aqueous biphasic systems (ABSs) formed with 1-N-butyl-3-methylimidazolium chloride ([Bmim]Cl) and salts (K3PO4 and K2HPO4), different ASs including dimethyl sulfoxide (DMSO), N,N-dimethyl formamide (DMF), and N,N-dimethyl acetamide (DMAC), and different concentrations of these ASs were investigated. It is shown that biphasic area increased when the concentrations of aprotic solvents increase, and the ability of the ASs to induce ABSs follows the trend: DMAC > DMF > DMSO. The phase diagram data suggest that the higher concentration, molar volume, and intrinsic hydrophobicity of aprotic solvents resulting in greater biphasic area in IL-based ABS's. Furthermore, the quaternary ABSs have a prominent advantage that the IL could be recovered along with aprotic solvents. The recovery yield of [Bmim]Cl and DMAC could reach 96.14 % and 67.16 %, respectively.