Kinetics and mechanism of green conversion of hemicellulose to functional monosaccharides catalyzed by levulinic acid

Directed hydrolysis of hemicellulose to produce high-purity derivative sugars offers a green and value-added utilization pathway. This study investigates the catalytic hydrolysis kinetics of hemicellulose using levulinic acid (Lev), focusing on the effects of temperature, reaction time, and acid concentration on the distribution of target products (xylose, arabinose) and inhibitory by-products (furfural, acetic acid). Under optimized conditions, xylose and arabinose concentrations reached 8.02 and 0.86 g/L. A two-phase kinetic model reveals that reaction temperature optimization enhances monosaccharides selectivity and limits by-product accumulation. Incorporating the pKa of Lev into the kinetic rate constant improves model accuracy across varying acid concentrations. In the Lev system, the activation energy for xylose degradation (87.06 kJ·mol −1 ) exceeds that of the hydrolysis (51.28 kJ·mol −1 in the fast stage and 78.31 kJ·mol −1 in the slow stage), a trend opposite to that observed with inorganic acids, indicating enhanced selectivity for monosaccharide production. Density functional theory analysis reveals that the carboxyl group in Lev facilitates glycosidic bond cleavage through hydrogen bonding at the molecular level. Thermodynamic analysis shows that hemicellulose hydrolysis is an endothermic, non-spontaneous process driven by temperature, with a more favorable energy profile for xylose formation than degradation, which helps to achieve the effective accumulation of monosaccharides. These findings reveal the catalytic role of Lev in hemicellulose hydrolysis and support its application in the efficient and sustainable production of value-added sugars.