Pyrolysis mechanism of β-d-glucopyranose as a model compound of cellulose: A joint experimental and theoretical investigation

This study aims to reveal the pyrolysis reaction mechanism and product formation pathway of cellulose by combining experimental and theoretical calculation results. First, pyrolysis experiments of glucose, cellobiose, and cellulose were conducted by combined thermogravimetry-Fourier infrared spectroscopy-gas chromatography-mass spectrometry (TG-FTIR-GC-MS). The results show that glucose and cellobiose have two obvious mass loss peaks in their pyrolysis processes and cellulose has only a distinct mass loss peak. In the severe weight loss stage, cellulose forms more H2O, CO2, alkanes, and carbonyl compounds than glucose and cellobiose. Then, β-d-glucopyranose was selected as a model compound of cellulose to carry out density functional theory (DFT) calculations. The formation mechanism of furan derivatives and carbohydrate derivatives was systematically studied. And their competitive relationship was revealed. A reaction network from β-d-glucopyranose to main products was constructed. Based on the concerted reaction mechanism, β-d-glucopyranose is easier to generate furfural, followed by furan, 1,4:3,6-dianhydro-α-d-glucopyranose, and levoglucosenone, and finally 2(5H)-furanone. Based on the H radical attack mechanism, β-d-glucopyranose is easier to form 1-(2-furanyl)-ethanone, followed by 5-methyl-2-furancarboxaldehyde, and finally 2-methyl-furan. Finally, the relationship between the functional groups and the pyrolysis behavior of β-d-glucopyranose was clarified by combining the product distribution detected in experiments and DFT calculations.