Understanding CO ₂ Capture at the Molecular Level in Imidazolium‐Based Ionic Liquids

Abstract Molecular dynamics (MD) simulations are performed to investigate CO 2 absorption in eight different ionic liquids (ILs). Imidazolium‐based cations with varied alkyl chain lengths are paired with anions of various sizes and hydrophobicity. The simulated solubility follows the pattern [OMIM][BF 4 ] > [HMIM][BF 4 ] > [BMIM][BF 4 ] > [EMIM][BF 4 ] > [OMIM][SCN] > [HMIM][SCN] > [BMIM][SCN] > [EMIM][SCN], which is in good agreement with the experiment. The higher solubility of CO 2 in [OMIM][BF 4 ] (0.0183, 0.0165, and 0.0144) at different temperatures (298, 313, and 322 K) appears to be due to a higher fraction of larger cavities and more favorable interaction with CO 2 . CO 2 molecules strongly interact with [BF 4 ] − anion as compared to [SCN] − anion. We find that the solvation structure of anions and cations surrounding the CO 2 molecule differs; anions are significantly more confined close to the carbon atom of CO 2 , whereas cations prefer to stay on both sides of the oxygen atoms of CO 2 . The total interaction energy between CO 2 and [OMIM][BF 4 ] was found to be higher than that of other ILs. The diffusivity of CO 2 decreases with increasing molar volume of ILs. The computational analysis provides quantitative microscopic insight into the role of anion and cation of IL in CO 2 absorption.