Theoretical studies on pyrolysis mechanism of xylopyranose

In order to understand the mechanism of thermal decomposition of hemicellulose and to identify the chemical pathways for the formation of key products during pyrolysis, the pyrolysis processes of xylopyranose (a recyclable monomer of xylan) are investigated by using density functional theory (DFT) methods at B3LYP/6-31++G(d,p) level. Five possible pyrolytic pathways were proposed and the standard kinetic parameters in each reaction pathway were calculated. In the pyrolysis, xylopyranose is firstly converted to acyclic carbonyl isomer IM1 via transition state TS1 with a low energy barrier of 170.4 kJ/mol, and then IM1 decomposes to form all sorts of small molecules through five possible pyrolytic reaction pathways. Based on kinetic and thermodynamics analysis results, we can infer that reaction pathways (2) and (5) are the major reaction channels in pyrolysis of xylopyranose and the major products of xylopyranose pyrolysis are low molecular products such as glycolaldehyde, acetaldehyde, furfural, acetone and CO. The above analysis results are in accordance with the related experimental results.