An experimental/computational study of steric hindrance effects on <scp>CO<sub>2</sub></scp> absorption in (non)aqueous amine solutions
Qinlan Luo, Rui Dong, Bohak Yoon, Hongxia Gao, Mengjie Chen, Gyeong S. Hwang, Zhiwu Liang
Abstract
Abstract The reaction kinetics and molecular mechanisms of CO 2 absorption using nonaqueous and aqueous monoethanolamine (MEA)/methyldiethanolamine (MDEA)/2‐amino‐2‐methy‐1‐propanol (AMP) solutions were analyzed by the stopped‐flow technique and ab initio molecular dynamics (AIMD) simulations. Pseudo first‐order rate constants ( k 0 ) of reactions between CO 2 and amines were measured. A kinetic model was proposed to correlate the k 0 to the amine concentration, and was proved to perform well for predicting the relationship between k 0 and the amine concentration. The experimental results showed that AMP/MDEA only took part in the deprotonation of MEA‐zwitterion in nonaqueous MEA + AMP/MEA + MDEA solutions. In aqueous solutions, AMP can also react with CO 2 through base‐catalyzed hydration mechanism beside the zwitterion mechanism. Molecular mechanisms of CO 2 absorption were also explored by AIMD simulations coupled with metadynamics sampling. The predicted free‐energy barriers of key elementary reactions verified the kinetic model and demonstrated the different molecular mechanisms for the reaction between CO 2 and AMP.