In recent years,Ionic liquids (ILs) as a new kind of solvent have many unique attributes,e.g.negligible vapor pressure,good thermal stability and environment-friendly,which make them attractive and potential being used as a suitable solvent in special distillation processes[1].To select a suitable IL entrainer for extractive distillation,the infinite dilution activity coefficients of acetonitrile and water in hundreds of ILs were calculated using the COAMO-RS model[2,3].Then selectivity and solubility were calculated according the infinite dilution activity coefficients.Acetonitrile + water system is a completely miscible binary azeotropic system (azeotropic composition is 85% acetonitrile and 15% water,azeotropic point is 76 °C).Extractive distillation and salt distillation were widely used in the separation of acetonitrile + water mixtures.However,the organic solvent in extractive distillation demanded high energy and the salt distillation required high quality of equipment[4].So ILs were chosen as a suitable solvent in extractive distillation.Calculated results showed that ionic liquid 1-ethyl-3-metnylimidazolium acetate([EMIM]OAc) has high selectivity and good solubility.In this work,isobaric vapor–liquid equilibrium (VLE) data for the acetonitrile + water system containing IL 1-ethyl-3-metnylimidazolium acetate at atmospheric pressure (101.3kPa) were measured.The results showed that [EMIM]OAc could increase the relative volatility of acetonitrile in the whole concentration range,and eliminate the azeotropic point.VLE data for acetonitrile + water + [EMIM]OAc system were correlated by NRTL model.And the NRTL model was applicable to the correlation of ILs containing systems with the average deviation being 7.65%.