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Comparison of Solvation Effects on CO2 Capture with Aqueous Amine Solutions and Amine-Functionalized Ionic Liquids
journal contribution
posted on 2016-09-22, 00:00 authored by Hidetaka YamadaAmines
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.