We investigated the isobaric vapor-liquid equilibria (VLE) of the binary system methanol + tetrahydrofuran (THF), the ternary system methanol + THF + 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf2]), as well as methanol + THF + 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([HMIM][NTf2]) in a modified Othmer still. The results indicated that the ionic liquids ([BMIM][NTf2] and [HMIM][NTf2]) produced a consistent salting -in effect of THF, resulting in the incremental relative volatility of methanol to THF. The experimental data were correlated using the e-NRTL model, and the parameters were obtained with a good consistency. The ionic liquids even eliminated the azeotropic phenomenon when the mole ratio of [BMIM][NTf2] was up to 0.173 and [HMIM[NTf2] up to 0.128 as calculated by the e-NRTL model. [HMIM][NTf2] had a stronger effect on the separation of azeotropic mixtures than [HMIM][NTf2] did. (C) 2016 Elsevier B.V. All rights reserved.