8-43: Mass balance closure of xylose oligomers during total xylose content analysis

Xylose oligomers, which are chains of xylose molecules linked with β-1,4-bonds with the degree of polymerization greater than 2, are the intermediate products of xylan depolymerization into xylose monomer. The study of depolymerization kinetics of xylose oligomers is critical in describing hemicellulose depolymerization because the results will help determine the depolymerization processing conditions such that the formation of undesired by-products are minimized and the desired xylose monomers are maximized. The quantification of xylose oligomers is thus important to allow for the accurate tracking of the oligomer concentration during various stages of xylose oligomers depolymerization. The objectives of this research were to perform mass balance closure of xylose during the total sugar hydrolysis and to determine the rate of reaction of xylose degradation. Results indicated that xylose degradation is 1^st order kinetics, with the average rate constant of 0.0019 /min. The values reported in the work are 2 to 10 times lower than previously reported; the lower rate in this work could be attributed to the lower pretreatment temperature of 121°C, while previously reported values were determined at 160°C. Interestingly, furfural does not account completely for all the degraded xylose for extended hydrolysis time, such as 120 min, as some solid precipitation was observed. For the NREL recommended procedure of 60 min of xylose hydrolysis, 90% of xylose remained after hydrolysis.