Synergistic effects of biomass-plastic co-pyrolysis: Enhanced performance with microwave assistance and biomass type variability

The significant environmental challenges and human health threats posed by waste plastics and biomass are driving the development of innovative management methods. Co-pyrolysis emerges as a potentially solution for the waste reduction and energy recovery. Despite extensive research on co-pyrolysis processes in recent years, the role of microwaves in enhancing synergistic effects and the influence of biomass heterogeneity on these synergies have not been investigated. This study compared microwave and conventional pyrolysis to elucidate their distinct synergistic effects, systematically revealing the unique advantages of microwave heating in co-pyrolysis. Additionally, the influence of biomass component heterogeneity on co-pyrolysis processes was conducted. The results show that the rapid heating of microwave pyrolysis can minimize the differences in decomposition time scales caused by structural variations between plastics and biomass, thereby enhancing the synergistic effect. Compared to conventional catalytic co-pyrolysis, the peak area percentage of monocyclic aromatic hydrocarbons (MAHs) increased by 16.1 % under microwave catalytic co-pyrolysis. Furthermore, the coke yield of the catalyst was effectively reduced. For different biomass types, as the lignin content in the biomass feedstock decreased, the synergistic effect in inhibiting catalyst coking became weaker. Due to the differences in pyrolysis characteristics between biomass and plastics, the Diels-Alder reaction might not play a dominant role in the blended co-pyrolysis process. Instead, the enhancement of the hydrogen transfer reaction from lignin derivatives may be the primary internal cause of the synergistic effect. This study provides valuable insights into biomass-plastics interaction and provides an idea for sustainable and high-efficiency utilization of solid waste.