Comparison of Solvation Effects on CO₂ Capture with Aqueous Amine Solutions and Amine-Functionalized Ionic Liquids

Amines are the most widely utilized chemicals for postcombustion CO₂ capture, because the reversible reactions between amines and CO₂ through their moderate interaction allow effective "catch and release". Usually, CO₂ is dissolved in the form of an anion such as carbamate or bicarbonate. Therefore, the reaction energy diagram is potentially governed to a large extent by the polarity of the surrounding solvent. Herein, we compared aqueous amine solutions and amine-functionalized ionic liquids by investigating their dielectric constants and performing an intrinsic reaction coordinate analysis of the CO₂ absorption process. Quantum mechanical calculations at the CCSD(T)/6-311++G(d,p)//B3LYP/6-311++G(d,p) level within the continuum solvation model (SMD/IEF-PCM) revealed contrasting dependencies of C-N bond formation on the dielectric constant in those solutions. Amines react with CO₂ on an energy surface that is significantly affected by the dielectric constant in conventional aqueous amine solutions, whereas amine-functionalized anions and CO₂ form stable C-N bonds with a comparatively lower activation energy regardless of the dielectric constant.