Phase equilibrium for polymer/ionic liquid aqueous two-phase systems

Abstract

In this work, the use of ionic liquids as phase-forming components of Aqueous Two-Phase Systems (ATPS) has been evaluated. All ionic liquids used are based on the imidazolium cation, with different alkyl side chains and anions (chloride, bromide, acetate or dicyanamide). As counterpart on the ATPS, a random co-polymer of ethylene oxide and propylene oxide monomers (named EOPO or UCON) was used. Phase diagrams (tie-lines and binodal curves) for a set of UCON/ionic liquid ATPS were measured experimentally at T = (288.15, 298.15 and 308.15 K), using the density and refractive index of the mixtures to obtain the composition of equilibrium phases. The extension of the heterogeneous region increases but the slope of the tie-lines did not change significantly with temperature. Anions had a dramatic effect on the ATPS immiscibility, where acetate produced the largest heterogeneous region and thiocyanate the smallest, following the series OAc− > Cl− > Br− > SCN−. The Chen-NRTL and modified Wilson models were used to correlate the liquid–liquid equilibrium data, but better results were obtained with the Chen-NRTL model.