Co-pyrolysis of pine sawdust and polyolefin with solid heat carrier: Synergistic deoxygenation and high-yield hydrocarbon production in rotary kiln

The global depletion of fossil fuels necessitates the efficient valorization of biomass and plastic wastes. This study investigates the co-pyrolysis of pine sawdust (PS) with polyolefins (polyethylene, PE; polypropylene, PP) using a solid heat carrier in a rotary kiln to intensify bio-oil production. Thermal degradation behaviours and kinetic analyses revealed significant synergistic interactions: molten polyolefins permeated the biomass matrix, facilitating hydrogen radical transfer that suppressed oxygenated compounds (e.g., phenolics, furans) and enhanced hydrocarbon formation. Optimized pyrolysis with solid heat carrier parameters (570 °C, 8 % filling ratio, 0.45 mm particle size) maximized bio-oil yield (43.1 wt%) from PS. Co-pyrolysis with PE or PP at a 1:2 ratio further increased the bio-oil yield to 53.3 wt%, while reducing oxygenated compounds by over 70 % and significantly enriching aliphatic hydrocarbons (81.2 % with PE; 78.4 % with PP). The effective hydrogen-to-carbon ratio governed hydrocarbon selectivity, yielding 30.7-32.4% (C₈–C₂₃) alkanes suitable for jet/diesel fuels. The gas calorific value surged to 31.6 MJ/m³ due to the synergistic generation of C₂–C₄ hydrocarbons (45.2 vol%). The process intensification, primarily driven by enhanced heat transfer and hydrogen-donor plasticity of polyolefins, establishes a foundational platform for subsequent studies on in-situ catalytic co-pyrolysis using functionalized solid heat carriers. This work validates co-pyrolysis with a solid heat carrier as a technically viable route for producing high-value bio-oil from biomass and plastic wastes.