Study on the mechanism and kinetics of amine with steric hindrance absorbing CO2 in non-aqueous/aqueous solution

• The kinetics of the six sterically hindered amines for CO 2 absorption was explore. • The k 0 can be well fitted by the kinetic models based on the zwitterion mechanism. • The reaction rate is simultaneously controlled by steric hindrance and pKa of amines. • The carbamate with larger steric hindrance is prone to be hydrolyzed to bicarbonate. Several alkanolamines (1A2P, 2A1P, AMP, MAE, EAE, and IPAE) were selected to study the steric hindrance effect on reaction kinetics between amine and CO 2 in ethanol and aqueous solutions. Pseudo first-order reaction rate constant k 0 was measured by the stopped-flow apparatus. Zwitterion mechanism was applied to describe the reaction and the k 0 was well fitted by the corresponding kinetic model with average absolute relative deviation (AARD) in a range of 1.08%-3.44%. Apparent second-order reaction rate constant K A revealed that the reaction rate is simultaneously controlled by steric hindrance and pKa of amines. Additional alkyl groups increase the steric hindrance of amines and accelerate the decomposition of zwitterions. As a result, the reaction rate decreases with stronger steric hindrance effect. The larger pKa is conducive to a better proton receiving of amine. This leads to an acceleration of the deprotonation reaction of zwitterion intermediate. In addition, the relative influence of steric hindrance and pKa on the reaction kinetics is also related to the solvent environment.