Promoted production of hydrocarbons in the catalytic pyrolysis of rape straw over composite HZSM-5@MCM-41 catalysts

Abstract In order to promote the production of hydrocarbons in the catalytic pyrolysis of rape straw, a core-shell catalyst fabricated by external recrystallization method was employed. The composite catalyst HZSM-5@MCM-41 was prepared by varying the mass ratio of template and HZSM-5 (THR), and the effect of zeolite acidity and mesoporosity on the production of hydrocarbons was analyzed. A final pyrolysis temperature of 450 °C was suitable to obtain high yield of hydrocarbons over composite catalysts. Compared with ZSM-5 with a favorable pyrolysis temperature of 550 °C, a lower pyrolysis temperature meant a more efficient process, which may be related closely to the good diffusion of large-sized pyrolysis vapors over HZSM-5@MCM-41 catalysts. In addition, the highest yield of monocyclic aromatic hydrocarbons obtained over HZSM-5@MCM-41 with THR of 1 was 11.43 wt.%, which was boosted by 2.5 times compared with HZSM-5. A proper THR was suitable to fabricate a core-shell catalyst with excellent crystallinity, acidity and mesoporosity, and resulting in a high yield of hydrocarbons. Furthermore, the core-shell catalyst presents less formation of graphite-like coke, which indicated the easier removal of coke. Therefore, the composite HZSM-5@MCM-41 catalysts were more appropriate for upgrading of pyrolysis vapors for hydrocarbons.