Investigation of the degradation process of biomass during oxidative alkaline treatment by a flow-through reactor

The oxidative alkaline treatment of sawdust was performed under both non-isothermal and isothermal operations using a flow-through reactor for investigating the degradation process. The contributions of alkaline hydrolysis and oxidative degradation vary significantly across the three stages of sawdust degradation. The early stage (rate of similar to 1.20 %/min) was dominated by alkaline hydrolysis (contribution over 80 %) of the loose fraction (similar to 30 %), while the middle and late stages (rate of 0.20-0.60 %/min) were dominated by oxidative degradation (contribution over 90 %) of the firm fraction (similar to 50 %). Approximately 70 %-C of the sawdust was converted into CO2, lignin fragments, carbohydrates, and organic acids (formic, acetic, lactic, glycolic, and oxalic acid), among other things. Under non-isothermal operation, degradation products decreased and then increased sharply as temperature increased, whereas during isothermal operation, they decreased sharply, stabilized, and then decreased slowly over time. The loose part degradation in the early stages was more likely to produce organic acids than the firm part, while the firm part degradation in the middle and late stages produced primarily lignin and carbohydrate fragments. Lignin was gradually degraded into acid-insoluble (Mw=2000-5000 Da) and acid- soluble fragments (Mw=250-1000 Da), with carbonyl groups increasing and oxygen-containing linkages decreasing significantly. Overall, this study revealed the sawdust stepwise degradation process and the generation of degradation products, and also provided a superior method for investigating biomass degradation mechanisms in other liquid-solid treatment technologies.