Co-pyrolysis of neem sawdust and high-density polyethylene towards aromatic-rich bio-oil: Significance of zeolite mesopores

Co-pyrolysis of biomass and plastic was conducive to aromatics-rich bio-oil production, though the significance of zeolite mesopores in co-pyrolysis was still lacking and required further investigation. Herein, a conventional ZSM-5 and its two mesoporous deviants (hollow HS-ZSM-5 and core–shell hierarchical ZSM-5@SBA-15) were synthesized and utilized as catalysts in the co-pyrolysis of neem sawdust (NS) and high-density polyethylene (HDPE). Results showed that compared to ZSM-5, both the mesoporous zeolites enhanced aromatics production. And HS-ZSM-5 with an interior mesoporous cavity performed better in improving the monocyclic aromatic hydrocarbons (MAHs) fraction. An optimization of co-pyrolysis conditions (e.g., HDPE percentage, catalyst loading, co-pyrolysis temperature) further improved the MAHs selectivity to 33.8 area%. The synergy between NS and HDPE over mesoporous zeolites was also compared. While the aromatization between short-chain olefins was dominant in aromatics production over ZSM-5@SBA-15, the Diels–Alder reaction between NS-derived furans and HDPE-derived olefins contributed more in that over HS-ZSM-5.