Study on the hydrothermal gradient extraction of hemicellulose by a flow-through reactor

The hydrothermal gradient extraction process based on the hemicellulose constituent units is important for obtaining high quality hemicellulose products. The hydrothermal extraction of sawdust hemicellulose was performed under both non-isothermal and isothermal operations using a flow-through reactor for investigating the extraction patterns. The results show that there were significant differences in the major forms of hemicellulose units at different extraction stages. For glucose, xylose, and galactose units, the selectivity of oligomeric form decreased gradually with increasing temperature, whereas it decreased and then increased under thermostatic operation. The selectivity of the mannose oligomeric form decreased and then increased in both operation modes, reaching a trough at 170 °C (96.81 %) and 60 min (55.21 %), respectively. The molecular weight of extracted hemicelluloses were mainly distributed below 70,000 Da, and gradually decreased with temperature, but increased with time. The results contribute to the quantitative and qualitative understanding of the hemicellulose gradient extraction process.