CO2 Capture Kinetics and Sorbent Efficiency under Fluctuating Engine Load Conditions using Amine–Amino Acid Hybrid Formulations

Mitigating CO2 emissions from mobile combustion sources has been recognized as a pressing need, as heavy-duty engines continue to serve remote and mission-critical applications. Capture systems for such sources faced rapidly fluctuating exhaust compositions, temperatures, and flows, under which solvent performance had been poorly characterized. The research gap concerned the limited availability of transient metrics and comparative evidence for hybrid amine–amino acid sorbents under realistic load changes. The objective was to determine how formulation influenced instantaneous capture efficiency, response time, and regeneration energy during stepwise engine operation. A bench-scale packed column was coupled to a diesel generator subjected to programmed load steps; six solvents—30% MEA, 8% PZ, an MEA+PZ blend, and lysine, arginine, and alanine salts—were evaluated. Efficiency and response time were determined from 1 Hz inlet–outlet CO2 measurements using a 90% approach-to-steady criterion; regeneration energy was calculated from batch desorption duties normalized per mole of CO2 released. The MEA+PZ blend achieved sub-minute response times across all steps and the highest cumulative uptake, while maintaining high capture as the Load increased. Lag times were reduced by 55–67% relative to MEA and by approximately 25% relative to PZ. Amino-acid solutions exhibited longer lags and lower uptake consistent with higher viscosity and reduced free-amine availability. Energy analysis indicated that a disproportionate regeneration penalty did not offset the blend’s kinetic advantage. These findings suggest that hybrid amine systems offer robust operation under dynamic exhaust conditions, potentially enabling smaller columns or reduced circulation rates. Future work should examine long-duration cycling, promoter optimization, and integration with real-world duty cycles and control strategies.