Investigation into the pyrolysis mechanism of α-D-galactose to furfural and furan

Abstract

In this study, the density functional theory calculations were utilized to reveal the formation mechanisms and pathways of the significant products from α-D-galactose (the model compound of hemicellulose) pyrolysis. For the two main pyrolysis products, furan and furfural, 21 possible detailed reaction pathways were discussed for each product based on the concerted reaction mechanism. The results indicated that the energy barrier for the ring-opening reaction was the lowest at 190.07 kJ/mol in the initial reaction steps of α-D-galactose. The dominant pathway for the formation of furfural from α-D-galactose involves sequential ring-opening, isomerization, hemiacetal formation, two-step dehydration, and combined de-aldehyde and dehydration reactions, with an energy barrier of 291.53 kJ/mol. For furan, two highly competitive dominant pathways were identified, with energy barriers of 287.21 and 288.51 kJ/mol, respectively. In the former pathway, the small molecule volatiles formed are glycolic acid and water. While in the latter pathway, they are formic acid, formaldehyde, and water. In summary, this study could provide an in-depth understanding of the formation mechanisms of furan and furfural during the pyrolysis of α-D-galactose, which is helpful for better design, optimization, and control of biomass conversion.