Jorabchi Majid Namayandeh, Ludwig Ralf, Paschek Dietmar
Institut für Chemie, Physikalische und Theoretische Chemie, Universität Rostock, Albert-Einstein-Str. 21, D-18059 Rostock, Germany.
Institut für Chemie, Physikalische und Theoretische Chemie, Universität Rostock, Dr.-Lorenz-Weg 2, D-18059 Rostock, Germany.
J Phys Chem B. 2021 Feb 18;125(6):1647-1659. doi: 10.1021/acs.jpcb.0c10721. Epub 2021 Feb 3.
In this work, the temperature-dependent solvation behavior of a number of important light gases, such as carbon dioxide, xenon, krypton, argon, oxygen, methane, nitrogen, neon, and hydrogen, in two important imidazolium-based ionic liquids (ILs) of the type 1--alkyl-3-methylimidazolium hexafluorophosphate ([Cmim][PF]) and 1--alkyl-3-methylimidazolium tetrafluoroborate ([CmimBF]) with varying chain lengths ( = 2, 4, 6, and 8) are investigated using molecular dynamics simulations for a temperature range between 300 and 500 K at a pressure of 1 bar. The aim of this work is first to propose a reliable estimate for the temperature-dependent solubility behavior of (very) light gases, e.g., hydrogen and nitrogen, where reported experimental data are inconsistent. Moreover, we would like to rationalize the common features of the temperature-dependent solvation of light gases for various imidazolium-based ionic liquids. For the selected solute gases in our simulated imidazolium-based ILs, we applied the potential distribution theorem using both Bennet's overlapping distribution method (ODM) and Widom's particle insertion technique to determine the temperature-dependent solvation free energies with good statistical accuracy. We observed from the simulations that the quantity of the solvation free energy of a gas molecule and its temperature derivatives are connected in regard to each other at a chosen reference temperature. This trend was observed for all the studied light gases. Moreover, the computed solvation enthalpies of all gases obey an enthalpy-entropy compensation behavior, which is almost identical for all the studied ILs. Based on this observation, we report a correlation between the temperature-dependent solubility behavior of light gases in various ILs at their reference state so that we are now able to semiquantitively predict the temperature-dependent solubility behavior of a certain gas in various imidazolium-based ionic liquids based on a single solubility value of that gas in one of the ILs at a certain temperature.
在本研究中，使用分子动力学模拟，在1巴压力下，对温度范围为300至500K的多种重要轻气体（如二氧化碳、氙、氪、氩、氧、甲烷、氮、氖和氢）在两种重要的基于咪唑鎓的离子液体（ILs）——1-烷基-3-甲基咪唑鎓六氟磷酸盐（[Cmim][PF]）和1-烷基-3-甲基咪唑鎓四氟硼酸盐（[CmimBF]），且链长不同（m = 2、4、6和8）中的温度依赖性溶剂化行为进行了研究。本研究的目的首先是针对（非常）轻气体（如氢和氮）的温度依赖性溶解度行为提出可靠的估计，因为已报道的实验数据不一致。此外，我们希望阐明各种基于咪唑鎓的离子液体中轻气体温度依赖性溶剂化的共同特征。对于我们模拟的基于咪唑鎓的离子液体中的选定溶质气体，我们使用贝内特重叠分布方法（ODM）和维登粒子插入技术应用势能分布定理，以具有良好统计精度地确定温度依赖性溶剂化自由能。我们从模拟中观察到，在选定的参考温度下，气体分子的溶剂化自由能及其温度导数在相互关系上是相关的。所有研究的轻气体都观察到了这种趋势。此外，所有气体的计算溶剂化焓都遵循焓 - 熵补偿行为，这在所有研究的离子液体中几乎相同。基于这一观察结果，我们报告了各种离子液体中轻气体在其参考状态下的温度依赖性溶解度行为之间的相关性，这样我们现在能够基于某一气体在某一温度下在一种离子液体中的单一溶解度值，半定量地预测该气体在各种基于咪唑鎓的离子液体中的温度依赖性溶解度行为。
