物理化学学报 >> 2018, Vol. 34 >> Issue (2): 194-200.doi: 10.3866/PKU.WHXB201707262

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用恒温热重法测定1-己基-3-甲基咪唑苏氨酸离子液体[C6mim][Thr]蒸汽压和蒸发焓

佟静*(),屈晔,井立强,刘璐,刘春辉   

  • 收稿日期:2017-06-16 发布日期:2017-11-13
  • 通讯作者: 佟静 E-mail:tongjinglnu@sina.com
  • 基金资助:
    国家自然科学基金(21273003)

Measurement of Vapor Pressure and Vaporization Enthalpy for Ionic Liquids 1-Hexyl-3-methylimidazolium Threonine Salt[C6mim][Thr]by Isothermogravimetric Analysis

Jing TONG*(),Ye QU,Liqiang JING,Lu LIU,Chunhui LIU   

  • Received:2017-06-16 Published:2017-11-13
  • Contact: Jing TONG E-mail:tongjinglnu@sina.com
  • Supported by:
    the National Natural Science Foundation of China(21273003)

摘要:

用中和法合成了氨基酸离子液体(AAIL)1-己基-3-甲基苏氨酸盐[C6mim][Thr],并用核磁共振氢谱(1H NMR)和核磁共振碳谱(13C NMR)进行了表征。以苯甲酸为参考物质,用恒温热重法确定了AAIL[C6mim][Thr]的蒸汽压和在平均温度下(Tav= 438.15 K)的蒸发焓(ΔglHm? (Tav) =128.5 ± 6.0 kJ·mol-1)。利用Verevkin等人提出的方法计算得到AAIL[C6mim][Thr]气态和液态的恒压热容差(ΔglCpm? = -70.8 J·K-1·mol-1),进而计算了不同温度的蒸发焓,其中参考温度(298.15 K)下的蒸发焓ΔglHm? (298.15 K) = 138.4 kJ·mol-1,只比应用我们提出的蒸发焓理论模型估算值大1.6 kJ·mol-1,小于恒温热重法的实验误差3.0 kJ·mol-1,说明这个蒸发焓的理论模型有一定的合理性。借助Clausius-Clapeyron方程估算了AAIL[C6mim][Thr]的假想的正常沸点Tb= 522.07 K,以及沸点的蒸发熵ΔglSm? (Tb) = 228.5 J·K-1·mol-1,进一步得到了不同温度的蒸发熵和蒸发自由能ΔglGm? (T),其结果表明蒸发自由能随着温度的上升而减小,达到沸点温度Tb时变为零,而蒸发熵则随着温度上升而增大,是AAIL[C6mim][Thr]蒸发过程的驱动力。

关键词: 离子液体, 恒温热重分析法, 蒸发焓, 蒸汽压, 苏氨酸

Abstract:

The amino acid ionic liquid (AAIL) 1-hexyl-3-methylimidazolium threonine salt, [C6mim][Thr], was prepared by the neutralization method and its structure was confirmed by 1H and 13C NMR spectroscopy. Using benzoic acid as the reference material, the vapor pressure and evaporation enthalpy ΔglHm? (Tav) of [C6mim][Thr] were determined by isothermogravimetric analysis at the average temperature (Tav = 438.15 K) and DglHm? (Tav)was found to be (128.5 ± 6.0) kJ·mol-1. Using Verevkin's method, the difference between the heat capacities of the vapor and liquid phases, ΔglCpm?, was calculated to be -70.8 J·K-1·mol-1. Subsequently, the enthalpy of vaporization for AAIL [C6mim][Thr] at different temperatures was determined based on the reference enthalpy of vaporization at 298.15 K, ΔglHm? (298.15 K) = 138.4 kJ·mol-1. This value is 1.6 kJ·mol-1 higher than that predicted by our theoretical model and less than the experimental error (±3.0 kJ·mol-1) of the isothermogravimetric method. These results show that our theoretical model for determining the evaporation enthalpy of ILs is reasonable. In terms of the Clausius-Clapeyron equation, the hypothetical normal boiling point, Tb, was estimated to be 522.07 K. Thus, the evaporation entropy, ΔglSm? (T), and the evaporation Gibbs free energy, ΔglGm? (T), of [C6mim][Thr] could be determined for different temperatures. These results showed that DglGm? (T) decreases as the temperature increases, the evaporation entropy increases with increaseing temperature. Furthermore, the latter is the driving force in the evaporation process of the AAIL [C6mim][Thr].

Key words: Ionic liquid, Isothermogravimetrical analysis, Enthalpy of vaporization, Vapor pressure, Threonine

MSC2000: 

  • O642