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

Blended amine solvents are considered potential alternatives to monoethanolamine for CO 2 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. CO 2 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 ΔΔG 3 value of −6.41 kcal/mol, and a possible reaction route from carbamate to bicarbonate was revealed. Thus, the CO 2 capacity of DMCA-MCA reached 0.875–0.985 mol CO 2 /mol amine. Moreover, MCA exhibited considerably low forward energy barrier for zwitterion formation (2.7 kcal/mol), and the CO 2 absorption of DMCA could be accelerated through the proton transfer reaction with the MCA-zwitterion. Accordingly, the total mass transfer coefficient of CO 2 in DMCA-MCA approached 2.02 × 10 −10  mol/cm 2  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 CO 2 , which was 44.9% lower than 5 M MEA. This study developed a novel DMCA-MCA blended solvent with rapid absorption rate, huge CO 2 capacity and efficient regeneration for CO 2 capture.