CO capture using mixed amines: experimental DFT investigation with focus on improvements in cyclic efficiency and NO interference.

Post-combustion CO capture offers a promising solution for reducing carbon from power plants and marine emissions. By capturing CO from exhaust gases, it helps lessen the environmental impact. This paper evaluates the comparative performance of a hybrid blend of such absorbents as N-methyldiethanolamine (MDEA), ethanolamine (MEA), tetraethylenepentamine (TEPA), aminomethylpropanol (AMP), and piperazine (PZ) for CO capture, with emphasis on imitations of the flue gases for a marine engine. MDEA was taken as a base amine, while the percentages of MEA, TEPA, AMP, and PZ were taken in variable proportions to optimize absorption, desorption, and cyclic CO capacity. The absorbents were tested under simulated marine engine flue gas conditions with exposure to NO to test their performance and robustness in real-world CO capture scenarios. The highest initial CO absorption capacity was recorded for the TEPA + MDEA mixture; however, the presence of NO causes a serious decrease in this absorption. Under identical conditions, an opposite effect-that is, the increase of its CO absorption-was found in the AMP + MDEA mixture, pointing out how complex interactions between blend composition and gas contaminants are. Density functional theory (DFT) calculations were obtained with frontier molecular orbital (FMO) analysis, natural bond orbital (NBO) analysis, electron density difference (EDD) mappings, and non-covalent interaction (NCI) analysis. FMO analysis of the adsorption of CO showed a decrease in highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps, potentially signifying higher reactivity. Relevant charge transfer from CO to the blends was evidenced by NBO analysis, which is consistent with the outcomes of EDD and NCI analyses that indicated non-bonding van der Waals interactions between CO and absorbent components. The study throws new light on mixed absorbents for post-combustion CO capture and emphasizes the role of computational techniques in understanding molecular interactions, energy dynamics, and bonding mechanisms, thus assisting the design of advanced absorbents for sustainable CO capture technologies.