Separation of acetonitrile and methanol azeotropic mixture using imidazolium-based ionic liquids as entrainers

In this work, three imidazolium-based ionic liquids (ILs) with different anions, namely 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), 1-butyl-3-methylimidazolium bromide ([BMIM][Br]) and 1-butyl-3-methylimidazolium acetate ([BMIM][OAc]), were tested as entrainers to separate acetonitrile and methanol mixtures. Isobaric vapor-liquid equilibrium (VLE) data of the acetonitrile (1) + methanol (2) + IL ternary systems were measured at 101.3 kPa. Addition of ILs produced a salting-out effect on acetonitrile, thus leading to the increase of the relative volatility of acetonitrile to methanol. As IL content increased to a certain value, the azeotropic point of acetonitrile and methanol could be totally eliminated. In addition, the separation performance of ILs was closely related to anion structure, with [BMIM][OAc] producing the most significant salting-out effect orderly followed by [BMIM][Cl] and [BMIM][ Br]. Finally, the measured ternary VLE data were correlated with the nonrandom two-liquid (NRTL) model, and σ-Profiles were used to explain the separation performance differences of the three ILs.