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 were prepared by seed induction method and alkali-treated method. The crystal structural, textural and acidic properties were characterized by XRD, TEM, NH3-TPD, and N2-sorption. The effect of hierarchical ZSM-5 zeolites on the product distribution of low rank coal fast pyrolysis in a fluidized bed was investigated. The results showed that the specific surface area, mesoporous pore volume and average pore size of the zeolites increase to different degrees after alkali treatment. Hierarchical ZSM-5 zeolites could promote the cyclization of aliphatics and the dissociation of phenol pool of volatile from coal pyrolysis, increasing the content of light aromatics. The yield of light aromatics reaches the maximumwhen the zeolites used are treated with 0.3 mol NaOH, in which the content of mono-aromatics and naphthalene/methylnaphthalene increases by 2.7 times and 0.9 times, respectively, compared with microporous zeolites. The performance of catalysts decreases when treated with 0.4 mol NaOH due to the excessive desilication.