Effect of hierarchical ZSM-5 zeolites on product distribution of low rank coal fast pyrolysis in a fluidized bed

A series of hierarchical ZSM-5 zeolites was prepared by seed induction method and alkali-treated method, and their crystal structural, textural and acidic properties were characterized by XRD, TEM, NH₃-TPD, and N₂-sorption. The effect of hierarchical ZSM-5 zeolites on product distribution of low rank coal fast pyrolysis in fluidized bed was investigated. The results showed that the specific surface area, mesoporous pore volume and average pore size of the zeolites were increased to different degree after alkali treatment. Hierarchical ZSM-5 zeolites promoted the cyclization of aliphatics and the dissociation of phenol pool of volatile from coal pyrolysis, and increased the content of light aromatics. The yield of light aromatics reached the maximum at 0.3 mol NaOH. The content of mono-aromatics and naphthalene/methylnaphthalene increased by 2.7 times and 0.9 times respectively compared with microporous zeolites. The catalysts performance decreased at 0.4 mol NaOH due to excessive desilication.