Circular valorization of Argemone ochroleuca seed meal: biomass fractionation, bioethanol production, and hydrothermal carbonization

Valorization of waste from the agro-industry is important for the advancement of the circular bioeconomy framework and the establishment of integrated, sustainable biorefineries. This study demonstrates the valorization of Argemone ochroleuca seed meal, a hexane-defatted lignocellulosic biomass, for the simultaneous production of bioethanol, hydrochar, and biopolymer precursor. Compositional analysis shows that 30.2% cellulose, 19.7% hemicellulose, and 22.1% lignin, showing the potential conversion to biofuels and carbonaceous products. Structural characterization confirmed the presence of reactive functional groups, appropriate porosity, moderate crystallinity, and good thermal stability, ideal for hydrothermal process for biomaterial synthesis. Organosolv pre-treatment using acidified ethanol-water mixture enabled effective fractionation with 89.4% cellulose recovery and solubilization of over 86% hemicellulose and lignin. Recovered cellulose was hydrolysed and fermented with Saccharomyces cerevisiae to yield 2.17 g ethanol per 10 g biomass (67.2% theoretical yield). Parallel to this, hydrothermal carbonization of A. ochroleuca seed meal at 180-230 °C for 2-4 h yielded hydrochar with fixed carbon as high as 41.2% and a higher heating value of 27.5 MJ/kg. From the recovered hemicellulose fraction 0.887 g of pentose sugars per gram of hemicellulose obtained. On polymeric content adjustment, pentosan content was 0.781 g g^-1 or 78.1% of isolated hemicellulose. Coupling organosolv and hydrothermal valorization processes makes A. ochroleuca seed meal as a suitable feedstock for zero-waste biorefineries to co-produce bioethanol, hydrochar, and biopolymers precursors in a systemic manner. Pilot-scale validation, life-cycle analysis, and techno-economic viability should be targeted in subsequent studies.