Cadena Cesar, Anthony Jennifer L, Shah Jindal K, Morrow Timothy I, Brennecke Joan F, Maginn Edward J
Department of Chemical and Biomolecular Engineering, University of Notre Dame, Indiana 46556 USA.
J Am Chem Soc. 2004 Apr 28;126(16):5300-8. doi: 10.1021/ja039615x.
Experimental and molecular modeling studies are conducted to investigate the underlying mechanisms for the high solubility of CO2 in imidazolium-based ionic liquids. CO2 absorption isotherms at 10, 25, and 50 degrees C are reported for six different ionic liquids formed by pairing three different anions with two cations that differ only in the nature of the "acidic" site at the 2-position on the imidazolium ring. Molecular dynamics simulations of these two cations paired with hexafluorophosphate in the pure state and mixed with CO2 are also described. Both the experimental and the simulation results indicate that the anion has the greatest impact on the solubility of CO2. Experimentally, it is found that the bis(trifluoromethylsulfonyl)imide anion has the greatest affinity for CO2, while there is little difference in CO2 solubility between ionic liquids having the tetrafluoroborate or hexafluorophosphate anion. The simulations show strong organization of CO2 about hexafluorophosphate anions, but only small differences in CO2 structure about the different cations. This is consistent with the experimental finding that, for a given anion, there are only small differences in CO2 solubility for the two cations. Computed and measured densities, partial molar volumes, and thermal expansion coefficients are also reported.
开展了实验和分子模拟研究，以探究二氧化碳在咪唑基离子液体中高溶解度的潜在机制。报告了六种不同离子液体在10℃、25℃和50℃下的二氧化碳吸收等温线，这些离子液体由三种不同的阴离子与两种阳离子配对形成，这两种阳离子仅在咪唑环2位上“酸性”位点的性质上有所不同。还描述了这两种阳离子与六氟磷酸根在纯态以及与二氧化碳混合时的分子动力学模拟。实验和模拟结果均表明，阴离子对二氧化碳的溶解度影响最大。实验发现，双（三氟甲基磺酰）亚胺阴离子对二氧化碳的亲和力最大，而具有四氟硼酸根或六氟磷酸根阴离子的离子液体之间二氧化碳溶解度差异不大。模拟显示二氧化碳围绕六氟磷酸根阴离子有强烈的聚集，但围绕不同阳离子的二氧化碳结构差异较小。这与实验结果一致，即对于给定的阴离子，两种阳离子的二氧化碳溶解度差异较小。还报告了计算和测量的密度、偏摩尔体积和热膨胀系数。
