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

Abstract

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.