Molecular dynamics and Gibbs ensemble Monte Carlo simulations were used to compute the self-diffusion coefficients and solubilities of CO 2 , CH 4 , and H 2 in model membranes consisting of slit pores with diameters of 2 and 5 nm. Solubility selectivities, diffusion selectivities, and permselectivities of CO 2 for binary gas mixtures of CO 2 / CH 4 and CO 2 /H 2 were also computed. The calculations were repeated for the same pores filled with the ionic liquid (IL) 1-n-butyl-3m e t h y l i m i d a z o l i u m b i s ( t r i fl u o r o m e t h y l s u l f o n y l ) i m i d e ([C 4 mim] + [Tf 2 N] − ) and for bulk IL. The bulk IL system was used as a model for a supported ionic liquid membrane separator having large pores, while the confined IL systems were used to assess whether extreme nanoconfinement of ILs has an effect on permselectivity. Permselectivities were about a factor of 10 higher in all the IL systems compared to the empty nanopores. Nanoconfinement tends to increase the solubility and decrease the diffusivity of all gases relative to the bulk IL. The bulk IL has significantly higher solubility selectivity for CO 2 over CH 4 and H 2 relative to the empty pores, and nanoconfinement of the IL further increases solubility selectivity a modest amount. Diffusion selectivites in the nanoconfined IL for CO 2 over CH 4 are slightly enhanced relative to bulk IL but are slightly smaller for CO 2 over H 2 . The net result is that nanoconfinement of the IL is predicted to slightly increase permselectivity for CO 2 over CH 4 but has little effect on the permselectivity of CO 2 over H 2 when compared to bulk IL. Although the IL leads to significantly enhanced permselectivities of CO 2 compared to the empty nanopores, gas diffusivities are more than 2 orders of magnitude smaller in the IL when compared to the empty nanopores. This suggests that while the use of this IL in a supported ionic liquid membrane separator will lead to enhanced selectivities, the overall permeation rate may be reduced relative to a conventional membrane if diffusion in the pores is rate limiting.

Self-diffusion and related short-time dynamic and structural properties were investigated for mixtures of carbon dioxide and the ionic liquid 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [bmim](+)[Tf2N](-) for a broad range of carbon dioxide molar fractions and at different temperatures. The studies were performed by a novel multinuclear pulsed field gradient (PFG) NMR technique, which combines the advantages of a high magnetic field (17.6 T) and a high magnetic field gradient (up to 30 T/m), in combination with molecular dynamics simulations. In general, a satisfactory agreement was observed between the experimental and simulation diffusion data. Under all conditions examined, the self-diffusion coefficients of carbon dioxide were found to be approximately an order of magnitude larger than the corresponding self-diffusion coefficients of the ions. It was observed that an increase in temperature and in the amount of carbon dioxide in the ionic liquid led to an increase in the ion self-diffusivities without changing the relationship between the self-diffusion coefficients of the cations and anions. An observation of a slightly higher diffusivity of the cations in comparison to that of the anions is attributed to the preferential mobility of the cations in the direction of the ring plane. The diffusion activation energies of the ions were found to decrease gradually with an increase of the carbon dioxide content in the ionic liquid. The activation energy of the carbon dioxide diffusion in all cases was found to be smaller than those of the ions.

Mixed matrix membranes are being studied for their potential use in post-combustion carbon capture on the premise that they could dramatically lower costs relative to mature technologies available today.

The knowledge of the mixture solubility and diffusivity of gases in ILs is critical for the design of supported ionic liquid membranes (SILMs). Since mixed gas solubilities and diffusivities in ILs are much more difficult to measure than pure gas properties, pure gas solubility and diffusivity data are typically used along with an ideal solubility/diffusivity assumption to estimate permselectivities. It is not clear, however, if the ideal solubility and diffusivity assumptions are valid. In this work molecular dynamics (MD) and Gibbs ensemble Monte Carlo (GEMC) simulations were used to compute the diffusion selectivity and solubility selectivity of CO 2 and CH 4 in the ionic liquid (IL) 1-n-butyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide ([C 4 mim] + [Tf 2 N] − ), along with the pure gas solubilities and diffusivities, in order to test the ideal permselectivity assumption. Pure gas solubilities of CO 2 and CH 4 in [C 4 mim] + [Tf 2 N] − at 333 K and pressures ranging from 1-100 bar were found to be in excellent agreement with literature values. Simulated CO 2 :CH 4 solubility selectivities in [C 4 mim] + [Tf 2 N] − at CO 2 :CH 4 gas phase mole ratios of 4:96, 8:92 and 16:84 were found tobe less than the ideal solubility selectivities computed from pure gas solubilities. Self-diffusion coefficients of pure CO 2 and CH 4 dissolved in the IL were independent of the concentration of the dissolved gases, within the studied pressure range. In CO 2 /CH 4 -[C 4 mim] + [Tf 2 N] − mixtures, self-diffusion coefficients of CO 2 and CH 4 were similar for all CO 2 :CH 4 mole ratios.Computed permselectivites were only slightly smaller than the ideal permselectivites computed from pure gas properties. Since the self-diffusion coefficients for CO 2 and CH 4 are similar, only solubility selectivity was found to influence the overall permselectivity of CO 2 over CH 4 in the IL.2

Recent developments in CO2 capture using porous organic polymers (POPs) have received an accressant attention due to their sorbent properties such as high CO2 uptake capacity and selectivity, tunable chemical...

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NMR exchange spectroscopy (EXSY) and NMR diffusion spectroscopy (PFG NMR) were applied in combination with kinetic Monte Carlo (MC) simulations to investigate self-diffusion in a mixture of carbon dioxide and an amine-functionalized ionic liquid under conditions of an exchange of carbon dioxide molecules between the reacted and unreacted states in the mixture. EXSY studies enabled residence times of carbon dioxide molecules to be obtained in the two states, whereas PFG NMR revealed time-dependent effective diffusivities for diffusion times comparable with and larger than the residence times. Analytical treatment of the PFG NMR attenuation curves as well as fitting of the PFG NMR effective diffusivities by KMC simulations enabled determination of diffusivities of carbon dioxide in the reacted and unreacted states. In contrast to carbon dioxide, the ion diffusivities were found to be diffusion time independent.

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