Comparative study on microwave-assisted co-pyrolysis of tissue paper and polyethylene: Effects of zeolite, metal oxide, and carbon-based additives on syngas production

Microwave-assisted pyrolysis for syngas production represents a promising technology for the resource utilization of solid waste. Due to the selective heating nature of microwaves, the introduction of microwave absorbers or catalysts is a prevalent strategy to enhance the process. This study investigated the effects of 3 representative categories of microwave absorbers/catalysts—zeolites (HZSM-5), metal oxides (CaO), and carbon-based materials (biochar)—on gas evolution and product characteristics during the co-pyrolysis of tissue paper and polyethylene (PE). The results indicated that HZSM-5 exhibited the most pronounced catalytic performance, notably intensifying the synergistic interaction between the feedstocks. CaO functioned effectively as both a CO₂ sorbent and a microwave absorber, while biochar significantly improved the heating rate and temperature throughout the reaction stage. The optimal loading for all 3 additives was determined to be 20 wt.%. The effect of the additives in promoting gas production followed the order: HZSM-5 > CaO > biochar. Specifically, with the addition of 20% HZSM-5, the gas yield and volume increased from 26.1% and 247 mL/g to 48.5% and 465 mL/g, respectively.