Comparison of Solvation Effects on CO<sub>2</sub> Capture with Aqueous Amine Solutions and Amine-Functionalized Ionic Liquids

2016-09-22T00:00:00Z (GMT) by Hidetaka Yamada
Amines are the most widely utilized chemicals for postcombustion CO<sub>2</sub> capture, because the reversible reactions between amines and CO<sub>2</sub> through their moderate interaction allow effective “catch and release”. Usually, CO<sub>2</sub> 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<sub>2</sub> 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<sub>2</sub> on an energy surface that is significantly affected by the dielectric constant in conventional aqueous amine solutions, whereas amine-functionalized anions and CO<sub>2</sub> form stable C–N bonds with a comparatively lower activation energy regardless of the dielectric constant.