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 oC). 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 oC), 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 highperformance catalysts for this purpose.

Unraveling the Role of Metal Oxide Catalysts in the CO2 Desorption Process from Nonaqueous Sorbents: An Experimental Study Carried out with 13C NMR

“…The pyridine molecules can interact with the uncoordinated metal atoms to show peaks at around 1440 and 1590 cm –1 , indicating the presence of Lewis acid sites . The pyridine molecules can also interact with the surface hydroxyl groups and generate a peak at around 1540 cm –1 corresponding to the Brønsted acid sites . The peak appearing at 1490 cm –1 is attributed to the combination of Lewis acid sites and Brønsted acid sites.…”

“…45 The pyridine molecules can also interact with the surface hydroxyl groups and generate a peak at around 1540 cm −1 corresponding to the Brønsted acid sites. 29 The peak appearing at 1490 cm −1 is attributed to the combination of Lewis acid sites and Brønsted acid sites. From the recorded spectra, all four tested metal oxides contained the Lewis acid sites on them, while the Brønsted acid sites were recorded for the V 2 O 5 only.…”

“…Various solid metal oxides have been shown to optimize the CO 2 desorption rate, reducing the energy requirement of an aqueous alkanolamine solutions − (see Table S1 for comparison of metal oxide-aided regeneration of aqueous absorbents). Modified montmorillonite clay, zeolites, and metal-supported silicas − have also been demonstrated to successfully decompose the carbamate and improve the CO 2 desorption by up to 1000%, significantly increase the CO 2 desorption rate at low temperatures (<90 °C) and reduce the energy penalty by up to 44%. Though several catalysts have been reported to improve the sorbent regeneration, so far, the catalyst-aided desorption technique has remained limited to conventional aqueous solutions (30 wt % MEA in most cases), and less attention has been paid to understanding the catalytic activity during the regeneration process. − Now, as new classes of absorbents are rapidly gaining interest, it is crucial to investigate whether solid acid catalysts can assist the regeneration of nonaqueous solutions in the same way they assist the regeneration of aqueous solutions.…”

Water-Dispersible Nanocatalysts with Engineered Structures: The New Generation of Nanomaterials for Energy-Efficient CO2 Capture

“…Among different CO 2 capture techniques, like absorption, , adsorption, , cryogenic distillation, , and membrane separation, , chemical absorption using aqueous amine solutions, particularly monoethanolamine (MEA), has attracted great attention as a mature technology for large-scale operations . Nevertheless, the energy-intensive nature of CO 2 absorption–desorption processes markedly impacts the costs of operation, creating a solid barrier to its widespread deployment in different industries. , This drawback is mainly due to the slow kinetics of CO 2 desorption reactions in the solvent regeneration process. A high operating temperature of 120–140 °C is usually applied to compensate for the slow rate of CO 2 desorption, which remarkably increases the cost of operation .…”

“…16 Nevertheless, the energy-intensive nature of CO 2 absorption−desorption processes markedly impacts the costs of operation, creating a solid barrier to its widespread deployment in different industries. 17,18 This drawback is mainly due to the slow kinetics of CO 2 desorption reactions in the solvent regeneration process. A high operating temperature of 120−140 °C is usually applied to compensate for the slow rate of CO 2 desorption, which remarkably increases the cost of operation.…”