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

• Published in: Energy (Oxford) 2021-01, Vol.215, p.119209, Article 119209
• Main Authors: Wang, Rujie, Liu, Shanshan, Li, Qiangwei, Zhang, Shihan, Wang, Lidong, An, Shanlong
• Format: Article
• Language: English
• Subjects: Absorption; Absorption rate; Bicarbonates; Blended amines; Carbon dioxide; Carbon sequestration; CO2 capture; Hybrid amines; Mass transfer; Monoethanolamine (MEA); Polarity; Quantum chemistry; Regeneration; Regeneration heat; Solvents; Zwitterions
• ISSN: 0360-5442; 1873-6785
• DOI: 10.1016/j.energy.2020.119209

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. [Display omitted] •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.