Solid Waste of Fly Ash Toward Energy-Efficient CO2 Capture

Fly ash, a solid waste, could serve asa good hybrid catalystcandidate for CO2 absorption and desorption. Catalytic CO2 absorption-desorptionhas attractedbroad interest due to its potential for improving CO2 absorptionefficiency and reducing energy consumption in CO2 separation.However, most utilized catalysts are synthetic and pure, with thedevelopment of a natural and hybrid catalyst with acid-basebifunctional catalytic characteristics remaining a significant challenge.In this work, three fly ashes (1-FA, 2-FA, and 3-FA) with differentcompositions were used as catalysts, and the provided synergisticbenefits in the overall MEA-CO2 absorption-desorptionprocesses were evaluated. The results showed that Bronsted acidsites, Lewis acid sites, and Lewis base sites were available on thefly ash surface, which provided proton and electron donation capability.1-FA exhibited the best catalytic performance by enhancing the CO2 cyclic absorption capacity by 6.7-26.1%, improvingthe CO2 desorption rate with the highest value of 96.0%,and decreasing the sensible heat by 24-28% compared to MEAas a blank run. Furthermore, 1-FA exhibited comparable catalytic performanceto typical HZSM-5. The results of this study demonstrated that flyash with zero cost and high availability could serve as a good hybridcatalyst candidate for CO2 absorption and desorption.