The Absorption Mechanisms of CO2, H2S and CH4 Molecules in [EMIM][SCN] and [EMIM][DCA] Ionic Liquids: A Computational Insight

This study investigates the absorption mechanisms of carbon dioxide (CO2), hydrogen sulfide (H2S), and methane (CH4) molecules in two imidazolium-based ionic liquids, namely 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) and 1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA]). We employed molecular dynamics (MD) simulations applying umbrella sampling technique to calculate free energy profiles (FEPs) for gas molecules in the ILs. The results reveal CO2's pronounced affinity for the interface over the bulk in both ionic liquids (IL), whereas H2S exhibits facile penetration into both regions. CH4 shows limited penetration into the IL bulk, remaining predominantly near the interface. We further explore the influence of ILs' anionic structures on gas accumulation sites by performing normal MD simulations. For instance, density profiles also confirm CO2's higher density in [EMIM][DCA] compared to [EMIM][SCN], reflecting the influence of anionic composition on CO2 solubility. These insights offer valuable knowledge for designing efficient ILs for gas capture and separation applications.