Two imidazolium-based ionic liquids: 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) and 1-octyl-3-methylimidazolium tetrafluoroborate ([OMIM][BF4]) were studied as entrainer candidates for the separation of methanol + acetonitrile system. Isobaric vapor-liquid equilibrium (VLE) for the binary methanol + acetonitrile and the ternary mixtures containing imidazolium-based ionic liquids were determined at atmospheric pressure (101.3 kPa). The experimental VLE results indicated ionic liquids (ILs) studied both showed a crossover salting effect for methanol. More importantly, when the amount of IL added increases, the azeotropic point of methanol + acetonitrile will disappear at one specific content. Meanwhile, the separation capacity of imidazolium-based ionic liquids follows the order: [OMIM][BF4] > [EMIM][BF4]. Finally, two different excess Gibbs free energy models were used to correlate the VLE data: the non-random two-liquid (NRTL), and the universal quasi-chemical (UNIQUAC). (C) 2016 Elsevier Ltd.