Kinetics and molecular mechanisms for the gas-phase degradation of levoglucosan as a cellulose gasification intermediate

- Kinetics of the gas-phase degradation suggest radical chain mechanisms.
- Restraint in the bicyclic ring affect the cyclic Grob and pinacol reactions.
- Radical chain pathways from the C- and O-centered radicals are postulated.
- Double bond formation causes fragmentation rather than furans formation.
- Dehydration via the C-centered radicals lead to the hydrocarbon gas formation.

Molecular mechanisms for the gas-phase degradation of levoglucosan, the major intermediate in cellulose gasification, were studied by kinetic analysis at 550-700 °C (residence time: 0.11-0.45 s), and a mixed mechanism including heterolysis and radical chain reactions is suggested. Density functional theory calculations indicated that one of the cyclic Grob reactions can proceed (Ea 57.4 kcal mol−1), which is supported by the selective formation of acrolein and glyoxal at 500 °C. Nevertheless, contributions of these heterolytic reactions were suggested to be smaller than radical chain reactions, which would proceed via the C- and O-centered radicals. Influences of the bicyclic ring and the hydrocarbon/oxygenated gas selectivity are also discussed. These results provide insights into the upgrading of the gasification processes of cellulosic biomass.