Permeation behavior of CO₂, H₂S, and CH₄ in imidazolium-based ionic liquids: A molecular dynamics study

This work investigates the absorption and transport behavior of CO₂, H₂S, and CH₄ in the ionic liquids [BMIM][SCN] and [BMIM][DCA] using molecular dynamics simulations with umbrella sampling at 298 K and 373 K. Analysis of free energy profiles and density distributions shows that CO₂ and H₂S preferentially accumulate at the IL-vacuum interface, with [BMIM][DCA] exhibiting stronger surface interactions and higher barriers for permeation into the bulk. Radial distribution function analysis reveals that CO₂ forms the most pronounced local associations with IL anions, while CH₄ displays weak, non-specific interactions in both ILs. Diffusion coefficient calculations demonstrate that gas mobility increases with temperature and is consistently higher in [BMIM][SCN] at lower temperature, but rises more sharply in [BMIM][DCA] at 373 K. These results provide comprehensive molecular-level insights into the factors governing gas selectivity and transport in cyanide-functionalized ionic liquids, informing the rational design of IL-based gas separation processes.