Ionic liquid 1-ethyl-3-methylimidazolium tetracyanoborate: An efficient entrainer to separate methanol + dimethyl carbonate azeotropic mixture

Abstract

The ionic liquid (IL) 1-ethyl-3-methylimidazolium tetracyanoborate [EMIM][TCB] was studied as an agent for the separation of the methanol + dimethyl carbonate (DMC) azeotropic mixture by extractive distillation. Isothermal vapor-liquid equilibria of the methanol + DMC binary system and the ternary system with the IL were measured by headspace gas chromatography (HSGC) to examine the effect of the IL additive on the separation factor. The measurements were conducted at 336.2 K, a temperature close to the normal boiling point of the methanol + DMC azeotropic mixture, and at various compositions keeping constant IL mole fractions x3=(0.05, 0.10, 0.50). The new binary and ternary VLE data together with previously measured infinite dilution activity coefficients of methanol and DMC in [EMIM][TCB] were correlated well by the NRTL excess Gibbs energy model yielding their description at the level of experimental uncertainty. We found that [EMIM][TCB] increases the methanol/DMC separation factor considerably, thus eliminating the isovolatility behavior at quite low IL contents (x3 > 0.080 at 101.325 kPa). Compared to other IL and non-IL entrainers studied for the purpose in the literature, [EMIM][TCB] ranks among the best performing ones, though its prohibitively high price would certainly hinder the process application at present.