Catalytic and Non-Catalytic Pyrolysis of Pine Wood Residues: A Temperature-Based Study

Abstract

Non-catalytic and magnetite-catalyzed pyrolysis of pine wood residues was systematically investigated in a fixed-bed reactor over the temperature range of 400–800 °C to elucidate the effects of temperature and magnetite catalysis on product distribution, composition, and energy quality. Calcined natural magnetite was employed as a low-cost catalyst to enhance cracking and reforming reactions during pyrolysis. Increasing temperature shifted product yields from liquids and char toward permanent gases in both systems; however, magnetite catalysis significantly intensified vapor-phase cracking and reforming reactions. Gas yields increased from 39.2–69.1 wt.% under catalytic conditions, compared to 18.2–54.8 wt.% for non-catalytic pyrolysis. Magnetite markedly reduced CO₂ formation and promoted syngas enrichment, with H₂, CO, and CH₄ contents reaching 19.1, 39.5, and 27.5 vol.% at 800 °C, respectively. As a result, the higher heating value of the gas increased from 16.4–28.9 MJ Nm⁻³, exceeding that of the non-catalytic system (11.2–24.5 MJ Nm⁻³). Compositional analysis showed that magnetite catalysis suppressed oxygenated compounds in the liquid phase via enhanced decarboxylation and decarbonylation, while promoting aromatization and polycyclic aromatic hydrocarbon formation; naphthalenes increased to 42.6 wt.% at 800 °C under catalytic conditions. Biochar produced in the presence of magnetite exhibited higher fixed carbon content, lower O/C and H/C ratios, and improved energy density, with a maximum higher heating value of 40.6 MJ kg⁻¹ at 800 °C. These results demonstrate that calcined natural magnetite effectively tailors the biomass pyrolysis toward high-quality syngas, aromatics-rich liquids, and energy-dense biochar, supporting its application in integrated bioenergy systems.