Dry torrefaction of biomass waste into high-energy biochar and selective formation of levoglucosenone and 1,4:3,6-dianhydro-α-D-glucopyranose

For the first time, the non-catalytic formation of value-added liquid products, such as levoglucosenone (LGO) and 1,4:3,6-dianhydro-α-D-glucopyranose (DGP) from wood cellulose pulp residue (WCPR) has been achieved using dry torrefaction (DT) under solvent-free conditions and in a nitrogen atmosphere. This study systematically examined the influence of reaction conditions on the DT process, evaluating their effects on the surface morphology and elemental composition of the resulting biochar. This process encompassed a temperature range of 210 to 300 °C and reaction durations spanning from 15 to 60 min. Optimal conditions for liquid product selectivity were identified, achieving 67.7% selectivity for LGO at 270 °C after 15 min and 32.6% selectivity for DGP at 240 °C after 30 min. The highest yields were obtained at 300 °C after 60 min, reaching 10.5% for LGO and 8.5% for DGP. Various properties of the obtained biochar were thoroughly assessed, including the higher heating value (HHV), decarbonization, dehydrogenation, deoxygenation, enhancement factor, surface area, pore diameter, as well as solid, carbon, hydrogen, and energy yields. The highest carbon content, reaching 65.3%, was achieved at 300 °C after 60 min of treatment, resulting in an HHV of 25.6 MJ/kg and an enhancement factor of 1.33. Finally, a comprehensive reaction pathway for the conversion of cellulose into LGO and DGP was proposed to elucidate the DT mechanism of WCPR. The results suggest that the autocatalytic nature of WCPR facilitates the selective formation of LGO and DGP through thermally induced dehydration and molecular rearrangement reactions, thereby enhancing the overall efficiency of biomass valorization.