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

Amines are the most widely utilized chemicals for postcombustion CO capture, because the reversible reactions between amines and CO through their moderate interaction allow effective "catch and release". Usually, CO 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 CO 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 CO on an energy surface that is significantly affected by the dielectric constant in conventional aqueous amine solutions, whereas amine-functionalized anions and CO form stable C-N bonds with a comparatively lower activation energy regardless of the dielectric constant.