Catalytic activity of facilely synthesized mesoporous HZSM-5 catalysts for optimizing the CO2 desorption rate from CO2-rich amine solutions

Abstract

Post-combustion CO2 capture using aqueous alkanolamine solutions has a great potential to reduce anthropogenic CO2 emissions but the large-scale deployment of this technique is hindered due to a highly energy-intensive solvent regeneration mainly because of poor CO2 desorption kinetics. To overcome this limitation, we synthesized a series of mesoporous HZSM-5 catalysts through facile alkaline desilication and surfactant-induced re-assembly of dissolved species originating from the parent HZSM-5 crystals, and evaluated their performance to optimize the CO2 desorption rate from benchmark 30 wt% monoethanolamine (MEA) solution under mild temperature condition (40–82 °C). X-ray diffraction (XRD) patterns showed that the synthesized catalysts retained their crystallinity. Desilication by treatment in the alkaline medium led to a remarkable development of mesoporosity, with an increase in the Brunauer–Emmett–Teller (BET) surface area as well. The experimental results suggested that the synthesized catalysts significantly enhanced the CO2 desorption rate at low temperatures (up to 350–580% at ≤82 °C), improved the total amount of desorbed CO2 up to 60%, and minimized the heat duty by 24–37%. Detailed characterization revealed that the synergistic effect of higher mesoporosity and increased number of Lewis acid sites (LAS) and Brønsted acid sites (BAS) was crucial to improve the CO2 desorption rate. Based on the characterization and experimental results, a plausible reaction mechanism for catalyst aided CO2 desorption was also presented. This investigation highlights the role of catalysts in optimizing the CO2 capture process and presents new understanding for the design of high-performance catalysts for this purpose.