A theoretical study on the mechanism of xylobiose during pyrolysis process

In order to better understand the pyrolysis behavior of hemicellulose and unveil pyrolytic products distribution at molecular level, xylobiose was selected as a model compound of hemicellulose and relevant degradation processes were theoretically investigated by employing density functional theory (DFT) method. Several important reaction routes including directly bond breaking, Retro-Aldol reaction and Retro-Diels-Alder mechanism were analyzed, and the influence from adjacent xylose on the pyrolytic mechanism of xylobiose was interpreted systematically. The results indicate that the ring -opening of xylose unit dominates in the initial stage, followed by the cleavage of beta-1,4 -glycosides bond. Retro-Aldol reaction is kinetically favored and therefore leads to the formation of glycolaldehyde. Furfural, on the other hand, is generated via the cleavage of C1-O bond and subsequent ring forming between C2 and C5, which has a lower reaction energy barrier than that of 1-hydroxy-2-propanone. Aldehyde prefers to generate via Retro-Aldol reaction and decarbonylation. Although dehydration reaction is hard to occur in the initial pyrolysis process, it is still the major reaction channel to obtain formaldehyde and 1-hydroxy-2-propanone. (C) 2017 Elsevier B.V. All rights reserved.