分子模拟研究气体在室温离子液体中的溶解度

在作者先前建立的分子力场基础上, 采用Widom粒子插入法预测了CO₂、N₂、O₂、Ar及CH₄等5种气体在多种咪唑类离子液体中的溶解度, 包括2种侧链长度的阳离子和3种阴离子. 首先考察了256个离子对组成的体系中溶质分子插入次数对计算结果的影响, 在此基础上计算了不同温度下气体在1-丁基-3-甲基咪唑的四氟化硼盐(bmim]BF₄])和六氟化磷盐(bmim]PF₆])中的溶解度. 计算结果正确反映了CO₂气体溶解度的变化趋势, 在bmim]BF₄]中溶解度的模拟结果与实验值符合很好, 且明显优于Pádua等的模拟结果；在bmim]PF₆]中的溶解度较实验值偏高, 精度与文献模拟结果相当；并预测了较高温度下CO₂气体在bmim]BF₄]和bmim]PF₆]中的溶解度. 计算结果也正确地反映了5种气体在bmim]PF₆]中溶解度实验值的相对大小. 另外考察了常温下几种气体在不同室温离子液体中的溶解度, 模拟结果表明气体在含有较长碳链和双-三氟甲基磺酰胺阴离子(Tf₂N^－)的离子液体中溶解度较大.

Molecular Dynamics Simulation of Gas Solubility in Room Temperature Ionic Liquids

The solubilities of five gases, CO₂, N₂, O₂, Ar and CH₄, in room temperature ionic liquids were studied by Widom test-particle insertion method. A number of 200000 insertions of the solute was decided. The solubility of CO₂ in 1-butyl-3-methylimidazolium tetrafluoroborate (bmim]BF₄]) obtained in this work is superior to that of Pádua et al. As for CO₂ in 1-butyl-3-methylimidazolium hexafluorophosphate (bmim]PF₆]), the result in this work is similar to previous studies. Furthermore, the solubilities of CO₂ in bmim]BF₄] and bmim]PF₆] at high temperatures were predicted. The experimental relative solubility order for the 5 gases in bmim]PF₆] is reproduced by simulation. In addition, the solubility of 5 gases in different ionic liquids shows that it is bigger in ionic liquids with long alkyl chain or with bis((trifluoromethyl)sulfonyl) amide anion than in bmim]BF₄].