Two sulfate-based anion ionic liquids: 1-ethyl-3-methylimidazolium hydrogen sulfate [EMIM](+)[HSO4](-) and 1-ethyl-3-methylimidazolium methyl sulfate [EMIM]+[MeSO4](-) were investigated as entrainer candidates for the separation of the binary azeotropic system acetone + methanol. Vapor-liquid equilibria (VLE) for the binary system acetone + methanol and the ternary mixtures with these sulfate-based anion ionic liquids were measured by headspace gas chromatography. From the experimental VLE data, the influence of the ionic liquid on the separation factors was investigated. The experimental results for the ternary systems show that the two ionic liquids investigated enhance the separation factor of the binary system acetone + methanol. The calculated separation factors of the two ionic liquids for the binary system acetone + methanol were compared with those of the ionic liquid hexylpyridinium bis(trifluoromethylsulfonyl)imide [HPY](+)[BTI](-), and the conventional organic entrainers: ethylene glycol and water. (C) 2012 Elsevier B.V. All rights reserved.