Mechanocatalytic depolymerization of hemicellulose to xylooligosaccharides: New insights into the influence of impregnation solvent

Mechanocatalytic depolymerization of lignocellulose constitutes a new frontier in biorefinery. In this study, a weak alkali-oxidation pretreatment with sodium percarbonate was employed to isolate hemicellulose from corncob, which was comprehensively characterized by FTIR, ¹H, ¹³C, and 2D HSQC NMR. The influences of impregnation solvent, the type and dosage of acid catalyst, and ball-milling time on the mechanocatalytic depolymerization of hemicellulose have been systematically investigated. A mathematical model based on Kamlet-Taft parameters was first proposed to reveal the relationship between the reaction conversion and the solvent properties, and the results suggested a solvent possessing a high polarity/polarizability and Lewis basicity is favorable for the reaction. Under the optimal conditions, 97.1% conversion of hemicellulose with 93.1% selectivity of xylooligosaccharides based on xylans could be achieved within 2 h. Qualitative high-resolution ESI-MS and quantitative HPAEC analysis demonstrated the good solubility of the obtained xylooligosaccharides was ascribed to the depolymerization of hemicellulose rather than the formation of sulfonated oligosaccharides.