Experimental and computational study on hemicellulose main chain monosaccharides: The pyrolysis mechanism of glucose, mannose and xylose

This study selected typical main chain monosaccharides of hemicellulose (D-glucose, D-mannose, and D-xylose) as research objects. By combining thermogravimetry-Fourier infrared spectroscopy-gas chromatography-mass spectrometry (TG-FTIR-GC-MS) pyrolysis experiments and density functional theory (DFT) calculations, their pyrolysis behaviors and reaction mechanisms were deeply studied. Firstly, the experimental results show that the three monosaccharides all have two main weight loss peaks. H2O and CO2 are their main gaseous products. Other same products include furfural, furan, 2(5 H)-furanone, 5-methyl-2-Furancarboxaldehyde, etc. In addition, each of the three forms unique products such as furans, phenols, ketones, acids, and some other heterocyclic compounds. Next, the DFT results of the three monosaccharides show that the ring-opening reaction among the initial reactions is the most advantageous. Among the three monosaccharides, the overall energy barrier for the generation of 2(5 H)-furanone from β-D-xylose is the lowest (62.1 kcal/mol), attributed to the absence of C5-linked hydroxymethyl (C5-CH2OH) group. The overall energy barrier for furfural generation from β-D-mannose is 51.3 kcal/mol, which is the lowest among the three monosaccharides. β-D-glucose shows the highest tendency for furan formation, its overall energy barrier is 57.4 kcal/mol. And this is in line with the experimental results. In conclusion, this research aids in deepening the comprehension of the pyrolysis mechanism underlying hemicellulose.