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

作者：Tong Jing^*; Qu Ye; Jing Liqiang; Liu Lu; Liu Chunhui

来源：Acta Physico - Chimica Sinica, 2018, 34(2): 194-200.

DOI：10.3866/PKU.WHXB201707262

• Ionic liquid
• Isothermogravimetrical analysis
• Enthalpy of vaporization
• Vapor pressure
• Threonine

The amino acid ionic liquid (AAIL) 1-hexyl-3-methylimidazolium threonine salt, [C(6)mim][Thr], was prepared by the neutralization method and its structure was confirmed by H-1 and C-13 NMR spectroscopy. Using benzoic acid as the reference material, the vapor pressure and evaporation enthalpy. Delta H-g(l)m(partial derivative) (T-av) of [C(6)mim][Thr] were determined by isothermogravimetric analysis at the average temperature (T-av = 438.15 K) and Delta H-g(l)m(partial derivative) (T-av) 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,. glC. pm, 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, Delta H-g(l)m(partial derivative) (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, Delta H-g(l)m(partial derivative)(T), and the evaporation Gibbs free energy, Delta H-g(l)m partial derivative(T), of [C(6)mim][Thr] could be determined for different temperatures. These results showed that Delta H-g(l)m(partial derivative)(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 [C(6)mim][Thr].

• 出版日期2018
• 单位辽宁大学