Hemicellulose Integration Enhances Lignin Valorization to Sustainable High-Performance Potassium Fulvic-like Fertilizer

Abstract

Global agricultural sustainability faces dual threats from inorganic fertilizer overuse and soil organic matter degradation. To address this, we developed a catalytic-hydrothermal humification process that transforms lignin into high-performance potassium fulvic-like (KFA) fertilizers. Using organosolv pulping, we elucidated the structure-function relationship between lignin and derived KFA fertilizers. Optimized organosolv processing (160°C, 4 h) yielded divergent lignins: acid-catalyzed ethanosolv (AEL-7/3, 96.16% yield) and base-catalyzed ethanosolv (NEL-3/7, 93.01% yield). Spectral and compositional analysis revealed exclusive hemicellulose incorporation in NEL-3/7. Subsequent catalytic-hydrothermal humification (140°C, 2h) demonstrated that potassium fulvic-like substances from hemicellulose-containing lignin (NEL-3/7) met all parameters (fulvic acid (FA), K₂O, moisture, insolubles, pH) of bio-based potassium fulvate standards and even surpassed fossil-based equivalents. Crucially, hemicellulose integration enhanced conversion to small-molecular acids bound to lignin, boosting FA content to 54.93%-confirming its superior functionality in FA formation. This strategy establishes a sustainable pathway for structure-guided lignin valorization into fertilizers, reducing agriculture’s reliance on non-renewable resources while enabling green plant growth.