Modification of H-[B]-ZSM-5 zeolite for methanol to propylene (MTP) conversion: Investigation of extrusion and steaming treatments on physicochemical characteristics and catalytic performance

摘要

High-silica H-[B]-ZSM-5 zeolite was synthesized by a hydrothermal method and was then extruded by a conventional process. The influence of mesoporosity formation and acidity modification was investigated using extrusion and combined extrusion-steam treatment over the synthesized zeolite. The catalysts were characterized by BET, FE-SEM, TGA, PXRD and NH3-TPD techniques. The catalytic performance of the powder H-[B]-ZSM-5 (BZP), extruded (BZE) and steam-treated extruded (BZEH) samples was evaluated in the methanol to propylene (MTP) conversion reaction. The reactions were performed in a fixed-bed reactor at 480 degrees C using a feed containing a mixture of 50 wt% methanol in water with a methanol weight hourly space velocity (WHSV) of 0.9 h(-1). The results showed that extrusion of H-[B]-ZSM-5 with alumina sol as a binder followed by steam-treatment led to the formation of narrow and uniform mesoporosity without severely destructing the crystal structure. The life time of the BZEH catalyst (750 h) was higher than that of BZE (520 h) and BZP (580 h) samples. This considerable enhancement of the lifetime could be attributed to the synergetic effect of extruding and steaming of H-[B]-ZSM-5 zeolite, leading to weakening of the acid sites strength and reduction of strong/weak acid sites ratio as well as formation of mesoporous structure, which are helpful for attenuating coke deposition in the micropore channels even at a high coking level. Besides, BZEH exhibited higher selectivity to propylene, butylenes and total light olefins, while its selectivity to C-1-C-4 alkanes and ethylene was relatively lower. The insights attained in this work would help to design a promising catalyst for methanol to propylene process.