The reaction kinetics and molecular mechanisms of CO2 absorption using
nonaqueous and aqueous amine solutions were analyzed by the stopped-flow
technique and ab initio molecular dynamics (AIMD) simulations. Pseudo
first-order rate constants (k0) of reactions between CO2 and amines were
measured. A kinetic model was proposed to correlate the k0 to the amine
concentration, and was proved to perform well for predicting the
relationship between k0 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. In aqueous solutions, AMP
can also react with CO2 through base-catalyzed hydration mechanism
beside the zwitterion mechanism. The molecular mechanisms of CO2
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 CO2 and AMP in
nonaqueous and aqueous systems.
Computational Study of CO2 Absorption in Aqueous and Non-aqueous Solutions Using MEA
