Catalyst-aided CO2 Capture and Utilization in Cement-based Industry

By: Emma Kwarteng Brakwah

As we look at minimizing the cost of CO2 capture process by removing the desorption unit and its ancillary equipment, there is also a need to pay attention to the size of the absorption column as it equally translates into cost. Smaller absorption columns result in minimal cost compared to bigger absorption columns. This is where the application of catalysts come into play in CO2 capture. Since the introduction of catalysts to CO2 absorption by our research group, the focus of CO2 capture has geared towards developing the best catalyst that possess good characteristics and gives the best performance as well. In looking out for catalysts with best characteristics and performance, it is expedient that we understand how the catalyst works in order to achieve the best performance.

As proposed by Caplow in 1967, carbamate formation is the rate determining step of the reaction mechanism of CO2 absorption. In the rate limiting step of the non-catalyzed process, a molecule of the amine in the solution has to donate an electron pair to the zwitterion to form a stable carbamate and a protonated amine. The reaction is represented as:

RN+H2COO + RNH2  <->  RNHCOO + RH3+

However, in the catalyzed process, the catalyst being used for the absorption process, which is principally a Lewis base (electron pair donor) comes in to replace the amine which donates the electron pair to the zwitterion. The catalyst then quickly donates an electron pair to the zwitterion instead of waiting for the amine to do so. This helps to speed up the carbamate formation process, providing an alternate route with lower activation energy. At the end of the process, the catalyst helps to boost the CO2 loading causing the rich loading of the catalyzed process to be higher than the non-catalyzed process as well as the initial absorption rate.

At the end of this work, CO2 emissions from large point sources would be reduced by capturing it using an ionic solvent at a faster rate with the help of the catalyst. The rich ionic solvent (ionic solvent + CO2) would then be utilized in the cement industry to replace the water content in mortar, concrete and grout.