Multidimensional synergistic model for sustainable and directed conversion of hemicellulose to xylose via mandelic acid pretreatment

While current research largely emphasizes high-value utilization through hemicellulose separation, the potential of its sugar components remains underexplored. This study systematically investigates the structural evolution and kinetic behavior of sugar products during mandelic acid (MA) pretreatment. At low MA concentrations (2 %), the process primarily induces mild hydrolysis of the hemicellulose main chain, yielding high-value xylooligosaccharides (31.45 g/kg). As MA concentration increases, xylooligosaccharides are further hydrolyzed into xylose, alongside the formation of degradation products such as furfural. Post-pretreatment, the main structure of residual hemicellulose is β-D-xylose. Notably, key side-chain groups, including 4-O-methyl-α-D-glucuronic acid and O-acetyl groups, are preserved under mild acidic conditions but progressively cleaved with increasing pretreatment severity. This structural evolution lays the foundations for targeted depolymerization into xylose. Kinetic analysis reveals a biphasic hydrolysis pattern: a fast phase (k_f = 6.09 ×10⁵ min⁻¹, E_a = 62.39 kJ/mol) associated with the amorphous region, and a slower phase (k_s = 1.10 ×10¹³ min⁻¹, E_a = 123.54 kJ/mol) corresponding to crystalline resistance. The overall hydrolysis rate of hemicellulose exceeds the degradation rate of xylose (k₂ = 7.06 ×10⁶ min⁻¹, E_a = 76.66 kJ/mol), enabling selective xylose production. Optimal conditions, 150 °C and 5 % MA, maximize xylose yield while minimizing degradation. The activation energy landscape positions xylose degradation between the fast and slow hydrolysis phases of hemicellulose. Based on these findings, a multi-parameter synergistic model integrating temperature, acidity, and time was developed to guide the efficient and selective conversion of hemicellulose to xylose. This approach enhances the valorization of hemicellulose and supports ecological sustainability and the advancement of a green sugar-based bioeconomy.