The Conversion Of Methanol To Gasoline (MTG) Over Modified ZSM-5 And ZSM-11 Zeolites

Methanol-to-gasoline process has gained much more attention of researchers for its simple operation technology and qualified gasoline it produces. The design of surperior catalysts plays a vital role in MTG technology. ZSM-5 with great hydrothermal stability and shape selectivity serves as the catalyst of MTG reaction. In this paper, we investigated the effects of crystalline size and framework aluminum distribution for MTG in a fixed-bed reactor. At the same time, two catalysts modified by TPAOH and NaOH were also evaluated in MTG reaction. Considering that ZSM-11 has similar pore structure and pore size with ZSM-5, ZSM-11 with different temperature hydrothermal treatment were studied and an optimal hydrothermal treatment temperature was obtained.The influence of crystalline size for MTG reaction was investigated based on ZSM-5 catalyst. It was found that smaller crystals had higher reactivity and stronger anti-carbon deposition ability, which showed better catalytic stability and longer lifetime in MTG reaction.The impact of framework aluminum distribution over ZSM-5 catalyst for MTG reaction was studied. ZSM-5 with heterogeneous aluminum distribution showed higher initial methanol conversion, but much more external acid sites led to faster deactivation. While ZSM-5 with homogeneous aluminum distribution showed stronger stability. Its lifetime was 224 h, which was 3.8 times than the former.ZSM-5 synthesized using TPAOH as the template had a silicon-rich interior, while both high and low temperature desilication led to hollow structure. The Al content enhanced a lot after selective desilication by NaOH treatment especially for outer Al content which was prone to faster deactivation. The desilication-recrystallization by TPAOH treatment caused a silicon-rich external surface, while the bulk Si/Al kept nearly unchanged with the migration of a part of extra-framework Al into framework Al. It showed superior catalytic performance in MTG reaction. Furthermore, the alkila treatment resulted in more pore volume, which was in favour of producing gasoline components and the gasoline yield was increased by 2%.The effect of hydrothermal treatment over ZSM-11 on the catalytic performance in MTG reaction was researched. The results indicated that coupling of hydrothermal treatment and acid washing removed a part of framework aluminum, thus leading to less acid amount and acid strength. Higher hydrothermal treatment temperature resulted in less framework aluminum. The catalysts after hydrothermal treatment were evaluated in MTG reaction. We found that the aromatics decreased and the olefins increased in liquid products. At the same time, the alkanes reduced and the olefins increased in gasous products. The stability of the catalysts improved significantly and the lifetime extended clearly at the proper hydrothermal treatment temperature. However, when the hydrothermal treatment temperature was too high, the catalyst acid sites almost disappeared, leading to reduced reactivity and lowered stability. Experiments showed that 500℃ was the optimal hydrothermal treatment temperature and its lifetime was 324 h.