The primary products of cellulose pyrolysis in the absence of extraparticle reactions

Abstract

Cellulose pyrolysis leads to formation of char, gases and condensable species, with levoglucosan being one of the main components among the latter. However, the literature is not conclusive regarding which of these pyrolysis products are primary as opposed to form through reactions of volatiles in the pyrolyser once they have been released from the cellulose particle. To understand these cellulose pyrolysis pathways, cellulose, levoglucosan and cellulose/levoglucosan mixtures were pyrolyzed in a wire mesh reactor, which suppresses interactions between volatiles released from one particle and other particles. The product distribution and levoglucosan yield were compared at different temperatures in slow and fast heating rate. Above 60% levoglucosan was obtained at low temperature and in slow pyrolysis. Fast pyrolysis produced a large amount of small particles/aerosols in liquid phase. Gas was mainly formed in the initial stage of pyrolysis possibly due to the amorphous cellulose decomposition. The levoglucosan did not undergo secondary reactions. For cellulose/levoglucosan mixture, the vaporization of levoglucosan was not affected by cellulose pyrolysis. These results showed that levoglucosan and low molecular weight species are both formed directly from cellulose in reactions taking place in parallel. The alternative sequential pathway where levoglucosan is produced initially and then reacts to form low molecular weight species was not observed in these conditions.