Luke WYLIE1, Gabriel PERLI2, Jocasta AVILA3, Sebastien LIVI2, Jannick DUCHET-RUMEAU2, Margarida COSTA-GOMES3, Agilio PADUA3
1University of Bonn, Bonn, Germany
2Université de Lyon, Lyon, France
3ENS de Lyon, Lyon, France
The ability to capture carbon dioxide has been of significant interest, with ionic liquids in particular showing the ability to physically absorb CO2. In this study we theoretically examined the ability to couple this physical absorption ability of ILs to the chemical absorption of CO2 possible with epoxy functional groups. The chemical absorption was analyzed by taking the novel tri- and tetra-epoxidized imidazolium and using static quantum chemical calculations to determine the thermodynamic efficiency of adding CO2 to epoxy groups. The physical absorption was calculated using large-scale polarizable molecular dynamics to determine the interaction strength and probability for CO2 with the ionic liquid backbone, in particular the imidazolium ring.
Analysis of the chemical absorption through addition of CO2 to the epoxy functional group proved to be exergonic overall with the addition having an overall ΔrG° of −52.5 kJ mol−1 for the tetraepoxidized imidazolium CO2 addition. The rate limiting step proved to be the ring opening reaction, wherein only the single epoxy side of the epoxidized imidazolium was shown to be able to form a more stable intermediate at this point than any other step, with an overall ΔrG° in this step of 71.8 kJ mol−1 compared to 102.6 kJ mol−1 for the ring opening of the tetraepoxidized imidazolium. This is due to the typically unstable negative oxygen being sterically favored to interact with the imidazolium positive charge. This interaction is not possible in the bulkier tetraepoxidized imidazolium due to the steric hindrance present. The epoxy groups were also shown to not significantly prevent physical absorption of the CO2 to the imidazolium ring, as it was shown that the CO2 to interact strongly with the positively charge group, even showing the strongest stoichiometrically adjusted interaction of any group examined.