Shen Yan, Abedin Rubaiyet, Hung Francisco R
Department of Chemical Engineering , Northeastern University , Boston , Massachusetts 02115 , United States.
Langmuir. 2019 Mar 12;35(10):3658-3671. doi: 10.1021/acs.langmuir.8b03990. Epub 2019 Mar 1.
Classical molecular dynamics simulations were used to investigate the performance of slit graphite and titania (rutile) pores of 5.2 nm in width, partially and completely filled with deep eutectic solvents (DESs) or ionic liquids (ILs), for gas separations of a carbon dioxide-methane mixture of 5:95 molar ratio and temperatures and pressures on the order of 318 K and 100 bar, respectively. The DESs studied were ethaline and levuline (1:2 molar mixtures of choline chloride with ethylene glycol or levulinic acid), and the IL considered was 1- n-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [bmim][NTf]. The performance of these systems in terms of solubility selectivity, diffusion selectivity, and permselectivity was compared against the performance of the bulk solvents (which could also be viewed as a model system for the micrometer-sized pores of a supported IL or DES membrane) and against carbon and rutile pores without preadsorbed solvent. The best performance in terms of permselectivity is obtained for bulk levuline and by rutile pores fully filled by ethaline, followed by graphite pores filled by ethaline and the IL. Empty rutile pores have the largest value of solubility selectivity, followed by bulk ethaline and rutile pores completely filled by the IL. The largest values of diffusivity selectivity were observed for bulk levuline, followed by ethaline completely filling a rutile nanopore and a graphite nanopore completely filled with the IL. These observations are rationalized by examining local density profiles and interaction energies among the different entities in our systems. In general, systems of nanopores fully filled by solvents, as well as the bulk solvents, have larger permselectivities than pores partially filled by the IL or the DESs. Drops of 2-3 orders of magnitude are observed in the gas diffusivity in pores filled with solvents with respect to systems of empty pores, which may be problematic if gas permeation is mainly controlled by diffusion. However, if adsorption dominates the gas permeation within the membrane, our results suggest that systems of levuline in the micrometer-sized pores of a supported DES membrane or ethaline confined in the rutile nanopores of a supported DES phase material might represent promising systems for gas separation.
采用经典分子动力学模拟方法，研究了宽度为5.2 nm的狭缝石墨孔和二氧化钛（金红石）孔在部分和完全填充有低共熔溶剂（DESs）或离子液体（ILs）时，对摩尔比为5:95的二氧化碳 - 甲烷混合气体的分离性能，温度和压力分别约为318 K和100 bar。所研究的DESs为乙酰胺和乙酰丙酸（氯化胆碱与乙二醇或乙酰丙酸的1:2摩尔混合物），所考虑的IL为1 - 正丁基 - 3 - 甲基咪唑双（三氟甲基磺酰）亚胺，[bmim][NTf₂]。将这些体系在溶解选择性、扩散选择性和渗透选择性方面表现与本体溶剂（也可视为负载型IL或DES膜微米级孔的模型体系）以及未预吸附溶剂的碳孔和金红石孔的性能进行了比较。在渗透选择性方面，乙酰丙酸本体以及完全填充乙酰胺的金红石孔表现最佳，其次是填充乙酰胺和IL的石墨孔。空的金红石孔具有最大的溶解选择性值，其次是乙酰胺本体和完全填充IL的金红石孔。在乙酰丙酸本体中观察到最大扩散选择性值，其次是完全填充金红石纳米孔的乙酰胺和完全填充IL的石墨纳米孔。通过研究体系中不同实体之间的局部密度分布和相互作用能，对这些观察结果进行了合理的解释。一般来说，完全由溶剂填充的纳米孔体系以及本体溶剂，比部分填充IL或DESs的孔具有更大的渗透选择性。与空孔体系相比，在填充溶剂的孔中气体扩散率下降2 - 3个数量级，如果气体渗透主要由扩散控制，这可能会带来问题。然而，如果吸附在膜内气体渗透中起主导作用，我们的结果表明，负载型DES膜微米级孔中的乙酰丙酸体系或负载型DES相材料金红石纳米孔中受限的乙酰胺体系可能是有前景的气体分离体系。
