Hydrothermal degradation of hemicelluloses from triploid poplar in hot compressed water at 180-340 °C

Hemicelluloses isolated from triploid poplar were subjected to hydrothermal degradation at 180-340 °C. The detailed physicochemical characteristics of hydrothermal degradation products including monosaccharide and XOS, molecular weight, inhibitory and organic compounds were detected by HPAEC, GPC, HPLC, and GC-MS, respectively. An increase in temperature led to a significant decrease in molecular weight and an increase in C2-C5 organic alcohols and acids. More importantly, besides two well-known routes that hemicelluloses are hydrolyzed to monosaccharide, followed by further degraded to furfural, a series of reaction routes was proposed to clarify and explain the mechanisms of the hydrothermal degradation of hemicelluloses from triploid poplar, which involved: (i) a predominant route of fragmentation; (ii) side reactions such as oxidation, dehydration, isomerization/rearrangement, and self-lactonization; (iii) larger molecular fragments from sugars by deoxydation or/and oxidation, followed by self-lactonization; and (iv) very few extensive re-polymerization including esterification and condensation among hemicelluloses and lignin fragments.