Hemicellulose pyrolysis mechanism based on functional group evolutions by two-dimensional perturbation correlation infrared spectroscopy

To gain an improved understanding of the hemicellulose pyrolysis mechanism, two-dimensional correlation infrared spectroscopy (2D-PCIS) was employed to analyze the functional group evolution in xylan chars between 200 and 600 degrees C, and through combination with the obtained volatiles releasing properties. Simultaneously, the pathway of xylan decomposition was deduced to illustrate the pyrolysis mechanism. The depolymerization and ring-opening reactions of xylan started at 200 degrees C. After that, it was mainly xylan matrix degradation reaction to form char structure which mainly consisted of phenyl rings and oxygen-containing cyclic compounds with aliphatic chains. With temperature increasing (300-450 degrees C), the decarbonylation reaction, removal of C=C and fatty chains reactions were intensified and the molecular structures of xylan char reconstructed to form fusedring compounds on the order of 1 x 2 and 2 x 2 through condensation. Dehydrogenation and polycondensation reaction of xylan increased at higher temperature (450-600 degrees C). The char structure was composed of high-order fused-ring compounds, and the production of H-2 and CH4 increased greatly.