A study on the multiscale mass transfer and desorption mechanisms of CO₂ capture using composite amine solutions under low-concentration flue gas conditions

This study evaluates the CO₂ capture performance and multiscale mechanisms of three tertiary amine–promoter blends: DEEA + PZ, DMEA + PZ, and DEEA + AMP. Spectroscopic characterization at 12 vol% CO₂ identified dominant reaction pathways, while cyclic performance was evaluated under simulated gas-fired power plant flue gas conditions (4 vol% CO₂, 95 °C regeneration). DMEA + PZ achieves a cyclic working capacity of 8.49 g CO₂/kg solvent—1.92 times that of the 30 wt% MEA benchmark—with a 48% reduction in relative regeneration energy consumption. In situ Raman and quantitative ¹H qNMR analyses show that all three systems operate predominantly via the bicarbonate pathway, with the PZ-carbamate decomposition rate considerably higher for DMEA + PZ (∼22%) than for DEEA + PZ (∼17%). AMP forms no detectable carbamate, relying exclusively on the bicarbonate pathway and exhibiting a discernible solvent volatilization trend. DFT calculations reveal that the stronger basicity of DEEA, arising from the inductive effect of its ethyl groups, yields higher absorption capacity but greater regeneration energy, whereas the narrower HOMO–LUMO gap of PZ enables rapid nucleophilic kinetics and the steric shielding of AMP precludes stable carbamate formation. Classical MD simulations show that compact PZ diffuses considerably faster than the sterically encumbered tertiary amines, while AMP-containing systems exhibit restricted diffusion; RDF analyses indicate steric shielding between the N centers of the main amine and promoter, with –OH-mediated hydrogen-bonding networks providing potential proton relay pathways. These insights offer a theoretical foundation for designing blended amine solvents for low-partial-pressure, waste-heat-driven CCUS applications.