Recycling rice husk and low-density polyethylene via co-pyrolysis: Semi-continuous system development and catalytic performance evaluation

Co-pyrolysis of rice husk biomass (RH) and hydrogen-rich low-density polyethylene (LDPE) is a key strategy for valorizing waste materials into valuable resources. However, these two raw materials decompose at different temperature stages during heating, resulting in a mismatch in the pyrolysis process, and potentially limiting the effective interaction between their main volatiles. To address the key challenge of the large difference in pyrolysis temperature ranges between RH and LDPE during co-pyrolysis, an optimized system combining semi-continuous feeding and a downdraft reactor was established in a microwave-assisted pyrolysis system with an ex-situ HZSM-5/SiC foam ceramic catalyst, and the evolution of catalyst activity and stability was studied. Under the system, the semi-continuous feeding strategy establishes a relatively stable temperature environment, and the design of a downdraft reactor further extends the mass transfer path and the residence time of volatile substances. The results showed that under the optimal conditions (pyrolysis temperature: 550 ℃, catalytic temperature: 500 ℃), the relative content of monocyclic aromatic hydrocarbons (MAHs) in the pyrolysis oil reached 83.00%, an increase of 18.64% compared with the traditional intermittent upward co-pyrolysis system. Even after five consecutive uses, the catalyst still maintained high aromatization activity. The relative content of MAHs (60.26%) was still significantly higher than that obtained in non-catalytic reactions (21.45%). Finally, a relatively balanced optimal result between coke removal and the maintenance of catalyst structural stability was obtained. This study provides an effective strategy to enhance the synergistic effect of co-pyrolysis of biomass and plastics, and to produce MAHs with high selectivity.