Valorization of Bay Tree Pruning by Autohydrolysis: Chemical Characterization and Energy Potential

Bay laurel (Laurus nobilis L.) leaves and branches represent promising lignocellulosic residues for biorefinery and bioenergy applications. This study evaluated the effect of autohydrolysis at different temperatures and residence times on the chemical composition, structural properties, and higher heating value (HHV) of both biomass fractions. The initial characterization revealed that leaves were richer in extractives and lignin, whereas branches contained higher amounts of α-cellulose and hemicelluloses. Autohydrolysis promoted the selective solubilization of biomass components, reaching maximum values of approximately 38% for leaves and 32% for branches. Increasing treatment severity enhanced hemicellulose removal and resulted in a relative enrichment of lignin and cellulose in the solid residues, while FTIR analysis showed that the main lignocellulosic structure was largely preserved. Temperature had a stronger influence than residence time, particularly for leaf deconstruction. Liquefaction produced more pronounced chemical transformations and significantly improved the fuel properties of the resulting solids, achieving maximum HHVs of 30.08 MJ kg⁻¹ for leaves and 29.46 MJ kg⁻¹ for branches at 180 °C for 30 min. Overall, the results indicate that autohydrolysis is a suitable strategy for the selective extraction of hemicellulose-rich fractions and the production of lignin-enriched solid residues. This process contributes to the sustainable valorization of bay laurel biomass within an integrated biorefinery framework.