Enhanced Gas Absorption in the Ionic Liquid 1- n -Hexyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)amide ([hmim][Tf 2 N]) Confined in Silica Slit Pores: A Molecular Simulation Study
Two-dimensional NP{sub xy}T and isostress-osmotic (N{sub 2}P{sub xy}Tf{sub 1}) Monte Carlo simulations were used to compute the density and gas absorption properties of the ionic liquid (IL) 1-n-hexyl-3- methylimidazolium bis(Trifluoromethylsulfonyl)amide ([hmim][Tf{sub 2}N]) confined in silica slit pores (25-45 Å). Self-diffusivity values for both gas and IL were calculated from NVE molecular dynamics simulations using both smooth and atomistic potential models for the silica. Simulations show that the molar volume for [hmim][Tf{sub 2}N] confined in 25-45 Å silica slit pores are 12-31% larger than for the bulk IL at 313-573 K and 1 bar. The amounts of CO{sub 2}, H{sub 2}, and N{sub 2} absorbed in the confined IL are typically 1.1-3 times larger than in the bulk IL due to larger molar volumes for the confined IL compared to the bulk IL. The CO{sub 2}, N{sub 2}, and H{sub 2} molecules are generally absorbed close to the silica wall where the IL density is very low. This arrangement causes the self-diffusivities for these gases in the confined IL to be 2 to 8 times larger than in the bulk IL at 298-573 K. The solubility for water in the confined and bulk ILs are similar, which is likely due to strong water interactions with [hmim][Tf{sub 2}N] through hydrogen-bonding resulting in the confined IL molar volume playing a less important role in determining H{sub 2}O solubility. Water molecules were largely absorbed in the IL-rich region rather than close to the silica wall. The self-diffusivities for water correlate with the confined IL. The confined IL exhibits self-diffusivities larger than the bulk IL at lower temperatures, but smaller than the bulk IL at higher temperatures. The findings from simulations are consistent with available experimental data for similar confined IL systems.
- Research Organization:
- National Energy Technology Lab. (NETL), Pittsburgh, PA, and Morgantown, WV (United States). In-house Research; National Energy Technology Laboratory (NETL), Pittsburgh, PA, Morgantown, WV (United States)
- Sponsoring Organization:
- USDOE Office of Fossil Energy (FE)
- DOE Contract Number:
- DE-FE0004000
- OSTI ID:
- 1127152
- Report Number(s):
- CONTR-PUB-045
- Journal Information:
- Langmuir, Vol. 29, Issue 18; ISSN 0743-7463
- Publisher:
- American Chemical Society
- Country of Publication:
- United States
- Language:
- English
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