Production of Alkyl Levulinates by the Alcoholysis of Furfuryl Alcohol over Biomass-Derived Sulfonated Hydrothermal Carbons

High Resolution Image Download MS PowerPoint Slide Biomass has attracted increasing attention as a renewable alternative to fossil fuels and as a versatile carbon source for the development of heterogeneous solid catalysts. Among the different types of biomass, agro-industrial residues stand out as particularly attractive precursors due to their abundance, low cost, and contribution to waste valorization within a circular economy framework. In this study, Salix babylonica leaves and the solid residue obtained after essential oil extraction, an underutilized agro-industrial byproduct, were employed as precursors for the synthesis of sulfonated carbon-based acid catalysts via hydrothermal treatment with concentrated sulfuric acid. Comprehensive characterization confirmed the formation of functionalized sulfonated carbon structures. The catalytic performance of the materials was evaluated in the alcoholysis of furfuryl alcohol (FA) to produce ethyl levulinate (EL), a high-value compound widely recognized as a promising biofuel additive. Among the catalysts, the material derived from the postextraction residue─Residue-(HCl)–SO 3 H– exhibited the highest activity, affording a 99% EL yield under optimized conditions (190 °C, 180 min, 15 wt %, 0.5 mmol FA, 5 mL ethanol). The methodology was further extended to the synthesis of other alkyl levulinates from different alcohols, achieving yields above 70%. Product quantification was performed by 1 H NMR using 1,3,5-trimethoxybenzene (TMB) as an internal standard, and reaction intermediates were identified by gas chromatography mass spectrometry (GC–MS). Reusability tests demonstrated that the catalyst could be recycled for up to four cycles, although a gradual decrease in activity was observed, attributed to partial leaching of sulfonic groups. Overall, this study presents an efficient and sustainable strategy for the valorization of residues from essential oil extraction, highlighting their potential as low-cost and underexplored raw materials for the development of heterogeneous catalysts and the sustainable production of biofuels and other value-added chemicals.