Li Song, Zhao Wei, Feng Guang, Cummings Peter T
State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology , Wuhan 430074, China.
Langmuir. 2015 Mar 3;31(8):2447-54. doi: 10.1021/la5048563. Epub 2015 Feb 19.
Recent studies on CO2 capture using dicationic ionic liquids (DILs) demonstrated that DILs are promising absorbents for CO2 uptake especially compared with monocationic ionic liquids (MILs) analogues, in which each cation carries single positive charge in contrast to two unit charges of a dication. However, DILs/CO2 interfacial properties at the molecular level are still unknown. This work investigated the CO2 absorption properties of representative DILs, 1-alkyl-3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, Cn(mim)22 (n = 3, 6, 12), using molecular dynamics (MD) simulations. The higher interfacial CO2 density at DIL than that at MIL interfaces suggests the increased CO2 interaction sites in DILs. The interfacial CO2 density also exhibits an alkyl chain length dependence which decreases with the elongation of alkyl chain and proportionally correlates with the content of fluorine atoms at interfaces. Different alkyl chain orientations in DILs were illustrated in contrast to those of MILs; both DILs and CO2 inside DILs exhibit lower diffusivity than MILs, in agreement with the stronger cation-anion binding energy of DILs. Moreover, DILs show a lower H2O and N2 uptake from flue gas compared with MILs, implicating the higher CO2/H2O and CO2/N2 selectivity.
最近关于使用双阳离子离子液体（DILs）捕获二氧化碳的研究表明，DILs是很有前景的二氧化碳吸收剂，特别是与单阳离子离子液体（MILs）类似物相比，在MILs中每个阳离子带有单个正电荷，而双阳离子带有两个单位电荷。然而，DILs/二氧化碳在分子水平上的界面性质仍然未知。这项工作使用分子动力学（MD）模拟研究了代表性DILs，即1-烷基-3-二甲基咪唑鎓双（三氟甲基磺酰）亚胺，Cn(mim)22（n = 3、6、12）的二氧化碳吸收特性。DILs界面处较高的二氧化碳密度表明DILs中二氧化碳相互作用位点增加。界面二氧化碳密度还表现出烷基链长度依赖性，随着烷基链的延长而降低，并与界面处氟原子的含量成比例相关。与MILs相比，说明了DILs中不同的烷基链取向；DILs内部的DILs和二氧化碳的扩散率均低于MILs，这与DILs更强的阳离子-阴离子结合能一致。此外，与MILs相比，DILs从烟道气中吸收的水和氮气较少，这意味着更高的二氧化碳/水和二氧化碳/氮气选择性。
