Reaction kinetics of the absorption of carbon dioxide (CO2) in aqueous solutions of sterically hindered secondary alkanolamines using the stopped-flow technique

- The kinetics of CO2 reaction with MAE, EAE, IPAE and TBAE were investigated.
- The termolecular mechanism and base-catalyzed hydration mechanism were studied.
- The CO2 capacity in aqueous solutions was following the order: MAE < EAE < IPAE < TBAE.

In this work, pseudo first-order reaction rate constants (k0) for the reaction of CO2 with sterically hindered secondary amines at temperatures of 293-313 K and various amine concentrations were studied using the rapid-mixing stopped-flow technique. It was found that the values of k0 increased as the concentration of amine in aqueous solution increased and as solution temperatures were increased. The second order rate constant (k2) at 293-313 K was also determined based on the proposed reaction mechanisms. The termolecular mechanism was able to fit the experimental data with predicted CO2 absorption rates of MAE and EAE with an absolute average deviation (AAD) of 2.81% and 14.96%, respectively. However, the base-catalyzed hydration mechanism is more precise in terms of the hindered amines (IPAE and TBAE) in predicting the CO2 absorption rates with AAD of 7.97% and 5.15%. The combined data for the CO2 loading showed that all four amines have good properties for the post-combustion CO2 capture process in comparison with MEA. In comparison with the amine reference MEA (CO2 loading = 0.58 mol CO2/mole of amine), the CO2 loading of the four amines is between 0.66 and 0.93 mol of CO2/mole amine. These results show that IPAE and TBAE are good candidates for CO2 capture as alternatives to MEA because of their good CO2 absorption and high reaction rate with CO2.