Tuning CO2 Capture at the Gas/Amine Solution Interface by Changing the Solvent Polarity.

Abstract

Carbon dioxide scrubbing by aqueous amine solution is considered as a promising technology for post-combustion CO2 capture, while mitigating climate change. The lack of physicochemical details for this process, especially at the interface between the gas and the condensed phase, limits our capability in designing novel and more cost-effective scrubbing systems. Here, we present classical and first-principles molecular dynamics results on CO2 capture at the gas/amine solution interfaces using solvents of different polarities. Even if it is apolar, carbon dioxide is absorbed at the gas/monoethanolamine (MEA) aqueous solution interface, forming stable and interfacial [CO2·MEA] complexes, which are the first reaction intermediate toward the chemical conversion of CO2 to carbamate ions. We report that the stability of the interfacial [CO2·MEA] precomplex depends on the nature and polarity of the solution, as well as on the conformer population of MEA. By changing the polarity of the solvent, using chloroform, we observed a shift in the interfacial MEA population toward conformers that form more stable [CO2·MEA] complexes and, at the same time, a further stabilization of the complex induced by the solvent environment. Thus, while lowering the polarity of the solvent could decrease the solubility of MEA, at the same time, it favors conformers that are more prone to CO2 capture and mineralization. The results presented here offer a theoretical framework that helps in designing novel and more cost-effective solvents for CO2 scrubbing systems, while shedding further light on the intrinsic reaction mechanisms of interfacial environments in general.