Kinetics study on thermal dissociation of levoglucosan during cellulose pyrolysis

The mechanisms and kinetics studies of the levoglucosan (LG) primary decomposition during cellulose pyrolysis have been carried out theoretically in this paper. Three decomposition mechanisms (C–O bond scission, C–C bond scission, and LG dehydration) including nine pathways and 16 elementary reactions were studied at the B3LYP/6-31 + G(D,P) level based on quantum mechanics. The variational transition-state rate constants for every elementary reaction and every pathway were calculated within 298–1550 K. The first-order Arrhenius expressions for these 16 elementary reactions and nine pathways were suggested. It was concluded that computational method using transition state theory (TST) without tunneling correction gives good description for LG decomposition by comparing with the experimental result. With the temperature range of 667–1327 K, one dehydration pathway, with one water molecule composed of a hydrogen atom from C3 and a hydroxyl group from C2, is a preferred LG decomposition pathway by fitting well with the experimental results. The calculated Arrhenius plot of C–O bond scission mechanism is better agreed with the experimental Arrhenius plot than that of C–C bond scission. This C–O bond scission mechanism starts with breaking of C1–O5 and C6–O1 bonds with formation of CO molecule (C1–O1) simultaneously. C–C bond scission mechanism is the highest energetic barrier pathway for LG decomposition.