In-situ sulfur fixation mechanism during microwave fluidized-bed co-pyrolysis of waste tires and biomass

The disposal of waste tires (WT) presents significant environmental challenges, and microwave fluidized-bed pyrolysis offers a sustainable solution, though research remains limited. A major issue in WT pyrolysis is sulfur emission, which can be mitigated through co-pyrolysis with biomass. Co-pyrolysis between WT and two types of biomass (peanut shell (PS), Ascophyllum (AS)) was investigated, using a microwave fluidized-bed reactor, focusing on the in-situ sulfur fixation mechanism. The results show that co-pyrolysis led to higher char yield and lower gas yield than expected, with less sulfur released into the pyrolysis oil and more sulfur retained in the char. The interaction between the products of WT and biomass promoted the formation of macromolecular organic compounds, leading to an increase in aromatic hydrocarbons in the pyrolysis oil and inhibiting the release of sulfur-containing organic compounds. Sulfur in WT was oxidized by -OH radicals from biomass, forming solid oxygenated organic sulfur and reducing the catalytic decomposition of sulfur. Additionally, the retention of alkaline metals in biomass ash enhanced sulfur fixation. These findings suggest that microwave fluidized-bed copyrolysis of WT and biomass is effective in capturing sulfur and generating valuable hydrocarbons, providing a promising solution for managing urban and agricultural solid wastes sustainably.