Recovery of the ionic liquids [C2mim][OAc] or [C2mim][SCN] by distillation from their binary mixtures with methanol or ethanol

Abstract

The ionic liquids 1-ethyl-3-methyl-imidazolium acetate ([C2mim][OAc]) and 1-ethyl-3-methylimidazolium thiocyanate ([C2mim][SCN]) have been proposed to improve many processes from the point of view of efficiency and/or sustainability. In a number of those proposals, mixtures of these ionic liquids with alcohols are generated. On the assumption of easy separation of the volatile alcohol and the totally non-volatile ionic liquid by distillation, little attention has been paid to the recovery of the ionic liquid to date. However, this is a critical step to transform a process tested at laboratory level into an industrial reality. To analyse the viability of using distillation to recover the above mentioned ionic liquids from their mixtures with methanol or ethanol, in this work the isobaric vapour-liquid equilibria of the corresponding binary systems at pressures of 101.32, 50, and 25 kPa were determined. Several physical and derived properties were also determined for the studied systems at 298.15 K and atmospheric pressure. The simulation of a flash unit, using the correlation of the experimental data with the NRTL model, was carried out with Aspen Plus at different temperatures and pressures. High ionic liquid purities were obtained in the case of the systems comprising [C2mim][SCN], which could be satisfactorily recovered at moderate vacuum. However, in the case of systems involving [C2mim][OAc], the recovery was limited by the relatively low degradation temperature of this ionic liquid.