A Quantum Chemistry Study for Ionic Liquids Applied to Gas Capture and Separation

In recent years, the global climate change is in evidence and it is almost a consensus that it is caused by the greenhouse gases emissions. An alternative to reduce these emissions is carbon capture and storage (CCS), which employs solvents based on amine compounds. In this scene, ionic liquids (IL) have been investigated to a greater extent for this application. In this work, we make an evaluation of interactions between gases (CO2, SO2, and H2S) and anion/cation from IL, as well as cation–anion interactions. For this, quantum calculations under vacuum were performed at the B3LYP/6-311+G** level of theory and using the M06-2X functional, where dispersion effects are considered. Among the well-studied systems based on imidazolium cations and fluorinated anions, we also studied the tetraalkylammonium, tetraalkylphosphonium, ether-functionalized imidazolium based systems, and tetrahexylammonium bis­(trifluoromethanesulfonyl)­imide, [THA]­[Tf2N], as a potential prototype. The ion pairs evaluated include [Tf2N]−-based IL, with alkyl chain varying from [C1mim]+ to [C8mim]+ and [C1mim]+-based IL. We found that the anion becomes more available to interact with gas with the weakening of the cation–anion interaction. [THA]­[Tf2N] has a binding energy of −274.89 kJ/mol at the B3LYP/6-311+G** level of theory, which is considered energetically interesting to gas capture applications.