Measurement, correlation, and prediction of vapor pressure for binary and ternary systems containing an alkylsulfate-based ionic liquid

• Alkylsulfate-based ionic liquids were studied as entrainer to separate azeotropic mixtures by extractive distillation.
• Vapor pressure data for six binary systems and four ternary systems were measured.
• NRTL model can correlate binary vapor pressure and predict ternary vapor pressure.
• The separation ability of different ionic liquids was compared by the method of isobaric VLE prediction and quantum chemical calculation.

Vapor pressure data for water, 1-propanol, 2-propanol, as well as the mixtures of {water + 1-propanol} and {water + 2-propanol}, were measured by a quasi-static ebulliometric method, in the presence of an alkylsulfate-based IL, namely, 1-ethyl-3-methylimidazolium methylsulfate ([EMIM][MS]) or 1-ethyl-3-methylimidazolium ethylsulfate ([EMIM][ES]). The experimental vapor pressure data for binary systems containing IL were correlated by NRTL model with an overall relative root mean square deviation (rRMSD) of 0.0053, and the obtained binary NRTL parameters were employed to predict the vapor pressure for two ternary systems with an overall rRMSD of 0.0196. In addition, isobaric vapor–liquid equilibria were predicted for the ternary systems containing [EMIM][MS], [EMIM][ES], 1,3-dimethylimidazolium methylsulfate ([MMIM][MS]), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [EMIM][OTf], respectively, with IL mole fraction of 0.05, 0.15, and 0.25 at 101.325 kPa. It was found that the addition of IL can enhance the relative volatility of propanol to water, and the separation ability follows the order of [MMIM][MS] > [EMIM][MS] > [EMIM][ES] > [EMIM][BF4] > [EMIM][OTf], which was further explained at electronic level with quantum chemical calculation. Therefore, the azeotropic mixtures of {water + 1-propanol}, and {water + 2-propanol} might be separated effectively by the addition of the alkylsulfate-based ILs in extractive distillation.

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