Insight into the mechanism of secondary reactions in cellulose pyrolysis: interactions between levoglucosan and acetic acid

Biomass pyrolysis process involves complex primary and secondary decomposition reactions which together determine the final pyrolytic product distribution. Carboxylic acids produced by primary pyrolysis have significant influences on the secondary reactions, whereas the specific manifestation of these influences has not been determined. In this work, acetic acid (AA) and levoglucosan (LG) are selected as the research objects to explore the influence of carboxylic acids on secondary pyrolysis process, considering AA is usually the most abundant carboxylic acid product, while LG is the major depolymerization product of cellulose as well as the representative of polyhydroxy compounds. The interaction mechanisms between them are investigated by density functional theory calculation. The results indicate that there are four types of important interactions between AA and LG, namely esterification reactions, organic redox reactions, AA-catalyzed LG dehydration reactions, LG-catalyzed AA decomposition reactions. These interaction reactions are more competitive than the unimolecular decomposition reactions of AA and LG. Moreover, AA-catalyzed dehydration reactions dominate interaction reactions.