Molecular Simulation Study of the Solubility, Diffusivity and Permselectivity of Pure and Binary Mixtures of CO₂ and CH₄ in the Ionic Liquid 1-n-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Abstract

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

Elucidation on the Effect of Operating Temperature to the Transport Properties of Polymeric Membrane Using Molecular Simulation Tool

“…In current work, the diffusivity of gas penetrants has been determined adopting the means of molecular positioning theory, or more commonly known as the Einstein relationship [18][19][20][21][22][23][24]. In Einstein correlation, he related the self-diffusion coefficient of gas particles i, D i to the mean square displacement (MSD) as a function of observation time, such as that presented in (1), through the assumption of particle random walk [25].…”

A DFT study on lignin dissolution in imidazolium-based ionic liquids

“…It is worth mentioning that some gases, such as CO 2 , SO 2 and CH 4 , show great solubility in functional ILs. [22][23][24][25][26][27] Their use may be extended to lignocellulose composites. 28,29 These experiments proved that RTILs have effectively promoted the dissolution and catalytic conversion of biomass materials.…”

Understanding CO2 capture kinetics and energetics by ionic liquids with molecular dynamics simulation

“…7 Numerous research groups have systematically studied the capturing capacity of various ILs for various gases, including CO 2 , CH 4 , H 2 and so on, by both experimental and theoretical approaches. 1,2,[8][9][10][11][12][13][14][15] Ramdin et al experimentally studied the CO 2 solubility and diffusivity in numbers of ILs and proposed that ILs have great solubility capacity to CO 2 . 1 Anthony et al reported that 1-n-butyl-3-methlimidazolium hexauorophosphates have strong dissolving ability for CO 2 .…”