On the mechanism of xylan pyrolysis by combined experimental and computational approaches

Pyrolysis is the initial stage of biomass combustion, whereas, the pyrolysis mechanism of biomass, espe-cially the hemicellulose component, is still not well elucidated. Herein, a common hemicellulose polysaccharide, xylan, was investigated to reveal the evolution of volatiles and solid residue through combined thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) and in-situ diffuse reflectance in-frared Fourier transform spectroscopy (in-situ DRIFT) techniques. Quantum chemistry calculation was also conducted to analyze the primary xylan pyrolysis mechanism by using a long-chain xylan model which was built based on the structural characterization of xylan. The experimental results indicated that the functional groups in solid-phase evolved intensively during the main weight loss zone (200-350 degrees C), leading to the vio-lent release of volatiles. The decomposition of branches, especially the arabinose unit, was prior to that of the backbone, with relatively low energy barriers and high rate constants. The initial enhancement of C=O vibration in solid-phase above 200 degrees C derived from the formation of the furanose unit. Both dehydration and breakage of glycosidic bonds were responsible for the formation of C=C bond in solid-phase from 300 degrees C. The cracking of the 4-O-Me group resulted in the release of aldehydes to gas-phase in the main weight loss zone (200-350 degrees C). The scission of the whole 4-O-MeGlc unit and/or the rupture of the uronic acid group led to the gas-phase C=O bond formation. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

The study investigated the pyrolysis mechanism of a common hemicellulose polysaccharide, xylan, using TG-FTIR and in-situ DRIFT techniques, revealing intense evolution of functional groups in the solid phase during the main weight loss zone (200-350 degrees C) leading to the violent release of volatiles.