Synthesis Hierarchical ZSM-5 Zeolite And Membrane Reactor In Methane Dehydroaromatization

Methane Dehydroaromatization(MDA) is an important way for methane to directly catalytic transformation and open a new approach for the comprehensive utilization of natural gas. Regarding this reaction, many progress have been made in terms of the reaction pathways, catalyst development. Mo/HZSM-5 catalyst is regarded as one of the best catalysts for MDA. However, the traditional ZSM-5 zeolite which has the microporous structure limits the diffusion of reaction product of benzene molecules. Hierarchical zeolite has very good shape selectivity and mass transport ability. If hierarchical zeolite applies in MDA, it will make a significant impact.In this thesis, hierarchical ZSM-5 zeolites were synthesized by adding secondary template. Hierarchical pore structure ZSM-5 zeolite catalysts were obtained by one step hydrothermal synthesis through carefully manipulating the synthesis condition using cationic surfactants; Hierarchical ZSM-5 nanospheres were synthesized by rotating hydrothermal crystallization with hard template; Furthermore, we synthesis hierarchical ZSM-5 microspheres by two step of changing temperature with mixed templates. The hierarchical ZSM-5 zeolites were applied in MDA and showed an exceptional catalytic performance. Meanwhile, membrane reactors were introduced in MDA reaction. The methane conversion and benzene yield were increased by continuous removal of co-produced hydrogen, which prompting the reaction to the formation of aromatics. The main results and conclusion obtained in this thesis were as follows:(1) In the process of synthesis zeolite adding cationic surfactant as secondary template, Mesoporous ZSM-5 zeolites were obtained, which were assembled by many stick-nanocrystals. The particle size is 300-400 nm, and mesoporous mainly came from intercrystalline pore. When used in MDA, the hierarchical Mo/HZSM-5 catalyst showed good performance. The CH4 conversion was higher than conventional catalyst.(2) When used carbon nanotubes and M700 carbon black microsphere as secondary template, hierarchical ZSM-5 nanospheres can also be synthesized by rotating hydrothermal crystallization. MDA test showed that hierarchical Mo/HZSM-5 catalyst get good catalytic performance. The initial methane conversion was 18%, which is higher than conversional catalyst (12%). It improved 6 percent. The initial benzene yield was 7%. when the reaction came to 10 h, the benzene yield was 5%. (3) When used carbon nanotubes and PDDA mixture as secondary template, hierarchical ZSM-5 microsphere was synthesized by two step varying crystallization temperature method. The particle size was 10μm. When MDA reaction temperature was 750℃, the initial methane conversion was 23%, which is higher than conversional catalyst (16%). The initial benzene yield was 10.5%. when the reaction came to 10 h, the benzene yield was 5%, which closed to balance conversion.(4) Carbon molecular sieve membrane and Pd membrane reactor were adopted to MDA membrane reaction. The methane conversion and benzene yield were improved effectively by 100%, compared to the fixed bed. For the first time, we introduced two step membrane reactor for MDA. The initial methane conversion and benzene yield were 30% and 13%. For the reaction time to 24 h, the methane conversion and benzene yield were 13% and 6% respectively.