Brunetti Bruno, Ciccioli Andrea, Gigli Guido, Lapi Andrea, Misceo Nicolaemanuele, Tanzi Luana, Vecchio Ciprioti Stefano
Istituto per lo Studio dei Materiali Nanostrutturati, CNR, c/o Dipartimento di Chimica, Sapienza Università di Roma, P.le A. Moro 5, I-00185, Rome, Italy.
Phys Chem Chem Phys. 2014 Aug 7;16(29):15653-61. doi: 10.1039/c4cp01673d. Epub 2014 Jun 24.
The vaporization behaviour and thermodynamics of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethyl)sulfonylimide (BMImNTf2) were studied by combining the Knudsen Effusion Mass Loss (KEML) and Knudsen Effusion Mass Spectrometry (KEMS) techniques. KEML studies were carried out in a large temperature range (398-567) K by using effusion orifices with 0.3, 1, and 3 mm diameters. The vapor pressures so measured revealed no kinetically hindered vaporization effects and provided second-law vaporization enthalpies at the mean experimental temperatures in close agreement with literature. By exploiting the large temperature range covered, the heat capacity change associated with vaporization was estimated, resulting in a value of -66.8 J K(-1) mol(-1), much lower than that predicted from calorimetric measurements on the liquid phase and theoretical calculations on the gas phase. The conversion of the high temperature vaporization enthalpy to 298 K was discussed and the value Δ(l)(g)H(m)(298 K) = (128.6 ± 1.3) kJ mol(-1) assessed on the basis of data from literature and present work. Vapor pressure data were also processed by the third-law procedure using different estimations for the auxiliary thermal functions, and a Δ(l)(g)H(m)(298 K) consistent with the assessed value was obtained, although the overall agreement is sensitive to the accuracy of heat capacity data. KEMS measurements were carried out in the lower temperature range (393-467) K and showed that the largely prevailing ion species is BMIm(+), supporting the common view of BMImNTf2 vaporizing as individual, neutral ion pairs also under equilibrium conditions. By monitoring the mass spectrometric signal of this ion as a function of temperature, a second-law Δ(l)(g)H(m)(298 K) of 129.4 ± 7.3 kJ mol(-1) was obtained, well consistent with KEML and literature results. Finally, by combining KEML and KEMS measurements, the electron impact ionization cross section of BMIm(+) was estimated.
通过结合克努森泻流质量损失（KEML）和克努森泻流质谱（KEMS）技术，研究了离子液体1-丁基-3-甲基咪唑双（三氟甲基）磺酰亚胺（BMImNTf2）的汽化行为和热力学。KEML研究在较大温度范围（398 - 567）K内进行，使用直径为0.3、1和3毫米的泻流孔。如此测得的蒸气压未显示出动力学阻碍的汽化效应，并在平均实验温度下提供了与文献密切一致的第二定律汽化焓。通过利用所覆盖的较大温度范围，估计了与汽化相关的热容变化，得到的值为 - 66.8 J K⁻¹ mol⁻¹，远低于根据液相量热测量和气相理论计算预测的值。讨论了高温汽化焓到298 K的转换，并根据文献数据和当前工作评估了值Δ(l)(g)H(m)(298 K) = (128.6 ± 1.3) kJ mol⁻¹。蒸气压数据也通过第三定律程序使用对辅助热函数的不同估计进行处理，并且获得了与评估值一致的Δ(l)(g)H(m)(298 K)，尽管总体一致性对热容数据的准确性敏感。KEMS测量在较低温度范围（393 - 467）K内进行，结果表明主要存在的离子物种是BMIm⁺，支持了BMImNTf2在平衡条件下也以单个中性离子对形式汽化的普遍观点。通过监测该离子的质谱信号随温度的变化，获得了第二定律Δ(l)(g)H(m)(298 K)为129.4 ± 7.3 kJ mol⁻¹，与KEML和文献结果非常一致。最后，通过结合KEML和KEMS测量，估计了BMIm⁺的电子碰撞电离截面。
