(58a) A Quantum Chemical Study on the CO2-Amine Reaction Pathway

To achieve the targets set in the Paris Agreement, global CO₂ emissions must be reduced by 7.6% annually over the next decade. This requires an effective use of carbon capture and storage (CCS) technologies. However, one of the barriers to the use of such systems is their absorption phase. Carbon capture costs are primarily influenced by the energy required for solvent regeneration, directly related to CO₂–solvent interactions and the separation efficiency from other gases. Improving the efficiency lowers the carbon capture cost, facilitating the use of CCS technologies.

With this background, developing efficient and sustainable CO₂-absorbing liquids has received immense attention in chemical engineering and related fields. While there are several types of CO₂ absorbers, in our previous works, we have intensively studied physisorbents, that is, ionic liquids (ILs; room-temperature molten salts [1]) and deep eutectic solvents (DESs; hydrogen-bonded mixtures in a broad sense [2]). Assisted by statistical thermodynamic calculations and machine learning results, a new phosphonium-based ionic liquid was experimentally proven to have higher CO₂ solubility than the previous best. However, the high viscosity of ILs prevented their practical application.

This study discusses the solvation effect (dielectric constant of the solvent) on the amine-CO₂ chemical reaction from a quantum chemical viewpoint to develop new amines that chemisorb CO₂ with low energy cost.

[1] N. Kuroki, Y. Suzuki, D. Kodama, F. A. Chowdhury, H. Yamada, H. Mori, Machine Learning-Boosted Design of Ionic Liquids for CO₂ Absorption and Experimental Verification, J. Phys. Chem. B 127, 9, 2022–2027 (2023).

[2] S. Watabe, N. Kuroki, H. Mori, COSMO-RS Exploration of Highly CO₂-Selective Hydrogen-Bonded Binary Liquid Absorbents under Humid Conditions: Role of Trace Ionic Species, ACS Omega 8, 16, 14478–14483 (2023).