Application of hydrochar co-product in levulinic acid production from sugarcane leaf as efficient catalyst supporting material for isosorbide production

Comprehensive utilization of lignocellulosic residues is critical for the development of sustainable and economically viable biorefineries. In this study, the hydrochar generated as a co-product during levulinic acid (LA) production from sugarcane leaf (SCL) was converted into a renewable dehydration catalyst for isosorbide (ISS) synthesis via sorbitol dehydration. SCL was converted to LA through a catalytic hydrothermal process (C-HTP) of SCL, and the hydrochar co-product was sulfonated at temperatures between 140 and 200 °C. The resulting catalysts were thoroughly characterized by elemental analysis, acid–base titration, nitrogen physisorption, TPD, TGA, XPS, FTIR, XRD, Raman spectroscopy, SEM, and TEM. Their catalytic performance in sorbitol dehydration to ISS was evaluated at different reaction temperatures (160–240 °C), times (15–27 h), catalyst amounts (0.05–0.45 g), sorbitol masses (0.5–2.5 g), and solvent volumes (15–35 mL). The catalyst sulfonated at 200 °C (200-SH) showed the highest activity, affording an ISS yield of 58.36%, ISS selectivity of 59.04%, and sorbitol conversion of 98.85% at 220 °C for 21 h using 0.25 g of catalyst, 1.0 g of sorbitol, and 20 mL of solvent. This outstanding performance is attributed to its large surface area and high density of acid sites. In addition, 200-SH exhibited excellent thermal and structural stability, retaining its activity over five consecutive cycles. When benchmarked against the commercial Amberlyst-15 catalyst, 200-SH delivered comparable performance, underscoring its promise as a competitive, sustainable catalyst for scalable ISS production.