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Comprehensive insights into xylan structure evolution via multi-perspective analysis during slow pyrolysis process

Liang, Jiajin, Chen, Jiao, Wu, Shubin, Liu, Chao, Lei, Ming
Fuel processing technology 2019 v.186 pp. 1-7
Fourier transform infrared spectroscopy, acids, carbon, carbonation, chemical structure, cleavage (chemistry), decarboxylation, free radicals, ketones, nuclear magnetic resonance spectroscopy, pyrolysis, renewable energy sources, stable isotopes, xylan
Comprehension in hemicellulose pyrolysis is critical to generate renewable fuel and valuable chemical. Herein, a self-designed tubular reactor was applied to observe the appearance alteration and chemical structure evolution during the whole xylan pyrolysis process. Before 200 °C, it was free moisture removal stage without significant chemical structure alteration. Xylan began to depolymerize at 200 °C corresponding with the appearance change from its original state to dark brown, cleavage of branched-chain and primary product acids & ketones generation. The main chain of xylan was completely broken at 250–350 °C via β‑1,4‑glycosidic bond cleavage, dehydration, decarboxylation, and decarbonylation reaction. Acids were mainly originated from hemicellulose pyrolysis. The typical signals from FTIR, 13C CP/MAS NMR were disappeared at 350 °C. In the carbonation stage, the C/H and C/O ratio reached 2.01 and 4.54, leading to the aromaticity enhancement of char and formation of carbon-centered radicals.