CO2 capture performance and mechanism of blended amine solvents regulated by N-methylcyclohexyamine

Highlights: • The biphasic DMCA-MCA absorbent became homogenous at a CO₂ loading above 0.41 mol/L. • MCA-carbamate converted to bicarbonate and ensured a CO₂ capacity near 1 mol/mol. • MCA accelerated the CO₂ absorption, leading to a faster mass transfer than MEA. • The total regeneration energy was 2.20 GJ/t CO₂, 45% lower than 5 M MEA. Blended amine solvents are considered potential alternatives to monoethanolamine for CO₂ capture, for the fast absorption kinetics of primary/secondary amine and low regeneration penalty of tertiary amine. In this research, blended amine solvents comprising N,N-dimethylcyclohexylamine (DMCA) and N-methylcyclohexyamine (MCA) were proposed. CO₂ absorption increased the polarity of the products and ensured the absorbent remained homogenous throughout the absorption/desorption cycles. Through quantum chemical calculation, the low stability of MCA-carbamate was confirmed by a ΔΔG₃ value of −6.41 kcal/mol, and a possible reaction route from carbamate to bicarbonate was revealed. Thus, the CO₂ capacity of DMCA-MCA reached 0.875–0.985 mol CO₂/mol amine. Moreover, MCA exhibited considerably low forward energy barrier for zwitterion formation (2.7 kcal/mol), and the CO₂ absorption of DMCA could be accelerated through the proton transfer reaction with the MCA-zwitterion. Accordingly, the total mass transfer coefficient of CO₂ in DMCA-MCA approached 2.02 × 10⁻¹⁰ mol/cm² s Pa, which was 1.2-fold higher than that of 5 M MEA. The total regeneration energy of DMCA-MCA blend was estimated at 2.20 GJ/t CO₂, which was 44.9% lower than 5 M MEA. This study developed a novel DMCA-MCA blended solvent with rapid absorption rate, huge CO₂ capacity and efficient regeneration for CO₂ capture.