Processes forming Gas, Tar, and Coke in Cellulose Gasification from Gas-Phase Reactions of Levoglucosan as Intermediate

The gas-phase pyrolysis of levoglucosan (LG), the major intermediate species during cellulose gasification, was studied experimentally over the temperature range of 400-900 degrees C. Gaseous LG did not produce any dehydration products, which include coke, furans, and aromatic substances, although these are characteristic products of the pyrolysis of molten LG. Alternatively, at >500 degrees C, gaseous LG produced only fragmentation products, such as noncondensable gases and condensable C-1-C-3 fragments, as intermediates during noncondensable gas formation. Therefore, it was determined that secondary reactions of gaseous LG can result in the clean (tar- and coke-free) gasification of cellulose. Cooling of the remaining LG in the gas phase caused coke formation by the transition of the LG to the molten state. The molecular mechanisms that govern the gas- and molten-phase reactions of LG are discussed in terms of the acid catalyst effect of intermolecular hydrogen bonding to promote the molten-phase dehydration reactions.