Reducing energy consumption of CO₂ desorption in CO₂-loaded aqueous amine solution using Al₂O₃/HZSM-5 bifunctional catalysts

The aim of this work is to find a potential way for great decrease in CO₂ capture energy requirement. Here, for the first time, a series of bifunctional Al₂O₃/HZSM-5 catalysts (Al-ZSM) were prepared by the combined precipitation ultrasound method and used for the CO₂ desorption process. All the investigated catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), N₂ adsorption–desorption, ammonia and CO₂ temperature programmed desorption (NH₃/CO₂-TPD) and pyridine-adsorption infrared spectroscopy (Py-IR). The regeneration behaviors of a 5 M monoethanolamine (MEA) solvent with four Al-ZSM catalysts were studied at an initial CO₂ loading of 0.5 mol CO₂/mol amine and the temperature of 96 °C. The results reveal that all the catalysts improve the CO₂ desorption performance, the Al-ZSM catalysts show higher catalytic performance than the single catalysts Al₂O₃ and HZSM-5, and the Al-ZSM can reduce the heat duty by 23.3–34.2% as compared with the catalyst-free test. The use of Al-ZSM in the MEA regeneration process improves the desorption performance by 2–3 times in comparison with the blank run. A possible dual sites mechanism of CO₂ desorption with Al-ZSM is suggested. The excellent performance of Al-ZSM can be attributed to their enhanced Brϕnsted acid sites (BAS), mesopore surface area (MSA) and basic sites, which resulted from the good synergistic reaction between the Al₂O₃ and HZSM-5, and the base treatment for HZSM-5. Besides, the stability test of the Al-ZSM was conducted. Based on the results, the Al-ZSM demonstrate a superior catalytic performance for the rich amine regeneration process, and present an excellent cyclic stability, explicitly have the potential to be a promising industrial catalyst for CO₂ capture. Furthermore, the dual sites catalytic CO₂ desorption over bifunctional catalysts will open a new path to design better catalysts for the rich amine solution regeneration process to increase the desorption performance, reduce the regeneration energy consumption, and thus further decreasing the operation costs of CO₂ capture.