Effect of crystallization time and template addition method in the synthesis of SAPO-۳۴ on its efficiency in methanol converting to light olefins

The methanol-to-olefin (MTO) process is a crucial catalytic reaction that produces light olefins—such as ethylene and propylene. The most effective catalysts for the MTO reaction are zeolite-based solid acids, particularly SAPO-۳۴ with a chabazite (CHA) topology. To optimize the catalyst performance, various parameters can be investigated, including crystallization time and temperature, the template addition method, and the Si/Al ratio in the initial synthesis gel. Also, to conserve energy and reduce production costs, it is important to keep the crystallization temperature low in the process of synthesis, especially on an industrial scale. Therefore, the crystallization temperature in this work is ۱۶۵ °C. In this study, SAPO-۳۴ molecular sieves were synthesized by hydrothermal crystallization, using tetraethyl ammonium hydroxide (TEAOH) and morpholine as the template. This work investigated the influence of crystallization time (۲۴ and ۲۷ hours) and template addition methodology on the hydrothermal synthesis of SAPO-۳۴ catalysts at ۱۶۵ °C. Two distinct approaches were employed for introducing the template: (۱) mixing the template separately with both silica and aluminum sources before final combination, and (۲) incorporating the template solely with the silica source before its addition to the aluminum source. The effects of these synthesis parameters on the selectivity and yield of light olefins and alkanes in the methanol-to-olefins (MTO) reaction were systematically evaluated. These samples were characterized by Fourier transform-infrared (FTIR), N₂ adsorption–desorption, Ammonia Temperature Programed Desorption (NH₃-TPD), and catalytic performance was investigated. Compared to other samples, the catalyst synthesized by the second procedure and crystallization time of ۲۴ hours showed higher selectivity toward light olefins and longer lifetime of ۸۸% and ۱۶۳ minutes, respectively, due to its suitable surface area of ۴۴۸ m²/g and milder acidity. In addition, this catalyst produced the highest amount of light olefins and the lowest amount of undesirable alkanes.

کلیدواژه ها:

MTO ، SAPO-۳۴ ، Yield of light olefins