Integrated Valorization of Waste Biomass via Low-Temperature Pyrolysis and Biochar Application as Heterogeneous Catalyst for SAF Production

Common waste biomasses such as fruit and vegetable peels and spent coffee grounds are valorized via low-temperature pyrolysis (400◦C) to produce valuable biochar and bio-oil for diverse downstream applications. Detailed and comprehensive characterization of the resulting biochar, including carbonization degree, morphology, surface acidity/basicity, and energy content, enables the assessment of their suitability for technological and environmental uses, based on the specific properties developed during thermal conversion. The bio-oils exhibit feedstock-dependent chemical profiles enriched in platform chemicals (e.g., HMF, furfural, cyclic ketones), lipid-derived compounds, and aromatics, supporting their targeted utilization in energy, materials, and chemical synthesis. Upon sulfonation, selected biochars display promising properties as acidic heterogeneous catalysts (1.65–1.75 mmol H+ g−1), showing high activity in industrially relevant reactions such as esterification and condensation. Their application in the cross-aldol condensation between bio-based cyclopentanone and cyclohexanone, targeting sustainable aviation fuel (SAF) precursors (C10-C18 cyclic compounds), is explored in detail. Among all samples, sulfonated biochar derived from coffee grounds and orange peel achieves superior catalytic performance, matching or surpassing commercial Amberlyst-15 under mild conditions (120◦C, 4 h, atmospheric pressure). Catalyst stability and recyclability tests confirm performance retention after regeneration, with surface deactivation by heavy compounds deposition being fully reversible.