Amine and Catalyst Stability Studies in the Catalyst-Aided CO2 Capture Process

Abstract

The application of sol id base and sol id acid catalysts to improve CO2 capture has been one of the most notable technological advancements in amine-based post -combust ion capture. Despite the inherent benefits of the catalysts, the amine solvent is st i l l prone to degradation, which is a major operational problem associated with the capture process. The nature of solvent degradation in catalyst -aided CO2 capture has not been reported before, and thus, the effect of catalyst on solvent or vice versa is unknown. This work evaluates the effect of catalyst on solvent degradation and vice versa using BEA-AMP bi -blend solvent and recent absorber and desorber catalysts , which have produced remarkable CO2 capture performance. The absorber and desorber catalysts are CNTs/K-MgO and Ce(SO4 )2 /ZrO2 , respectively. A preliminary stability study was conducted under typical absorption conditions in a semi -batch mode. The results revealed that CNTs/K-MgO increases solvent degradation. Degradation was direct ly proportional to temperature in the region of 313-333K. It was also found that the catalyst reduces the activat ion energy of degradation by 11%. In addition, NH3 emissions from the degradation cell s increased wi th temperature . However, emissions were lower with the addition of catalyst due to the presence of colloidal silica used in binding the catalyst . The absorber catalyst was further investigated using normal conditions of the absorber during capture . The results showed 41 and 30% increments in degradation rates of BEA and AMP, respectively, with the catalyst . The effect of Ce(SO4 )2 /ZrO2 on the solvent was investigated in a bench-scale CO2 capture plant . The catalyst increased degradation by 23% for BEA and 20% for AMP. The effect of catalytic degradation on performance was evaluated by comparing the CO2 cyclic capacities of the catalytic and non-catalytic runs on the f irst and last days of the experiment . The results showed that the cyclic capacity of the catalytic run was 25% higher than the non-catalytic run on the last day, which is 18% lower than that obtained on the first day. Again, the decline in cyclic capacity of the catalytic system was faster by 10% due to the additional effect of catalyst on speeding amine degradation. The Ce(SO4 )2 /ZrO2 -aided degraded solvent was further tested with CNTs/K-MgO in the semi -batch mode. Further degradation was observed, showing that the combined ef fect of both catalysts would be higher in a typical capture plant . The fresh and spent catalysts from the test runs were characterized and compared to assess the stability of the catalysts. From the results, there were changes to the physical and chemical properties of the catalysts, which are known to be essential for CO2 capture. Increased degradation translates to a higher solvent replacement cost . Therefore, the findings of this work would represent the first step in developing better catalysts that would have a significantly reduced effect on the stability of the solvent to lower the cost of capture.