Separation of methyl acetate plus methanol azeotropic mixture using ionic liquid entrainers

Two ionic liquids (ILs), namely 1-butyl-1-methylpyrrolidinium dicyanamide [BMPYR][DCA] and 1-ethyl-3-methylimidazolium thiocyanate [EMIM][SCN], were studied as agents for the separation of the methyl acetate + methanol azeotropic mixture by extractive distillation. Isothermal vapor-liquid equilibria of the ternary systems with the ILs and all the constituting binary subsystems were measured by headspace gas chromatography (HSGC) to examine the effect of the IL additives on the separation factor. Two HSGC methods were combined to this end: one employing a commercial headspace autosampler and the other employing our own setup with external equilibrium cell and forced circulation of the vapor phase through the GC sampling loop. The HSGC methodology developed herein presents distinct advantages compared to conventional dynamic measurements using recirculation stills. The measurements were conducted at 327.31 K, a temperature close to the normal boiling point of the methyl acetate + methanol azeotropic mixture, and at various compositions covering well the composition ranges of involved binaries and ternaries, particularly at compositions keeping constant IL contents. The ample experimental data allowed us to test the performance of several activity coefficient models and data treatment strategies. Using binary information only and the NRTL model gave fairly accurate predictions of the effect of ILs on separation factors. We found that both [BMPYR][DCA] and [EMIM][SCN] increase considerably the methyl acetate/methanol separation factor, breaking the azeotropic behavior at rather low levels of IL mole fractions (>0.043 and 0.087, respectively). As potential entrainers to separate methyl acetate from methanol by extractive distillation, [BMPYR][DCA] and [EMIM][SCN] outperform other ILs previously tested for this purpose in the literature. (C) 2013 Elsevier B.V. All rights reserved.