Role of levoglucosan physiochemistry in cellulose pyrolysis

The fate of levoglucosan after it forms during cellulose pyrolysis was investigated experimentally using time-resolved thermogravimetric analysis/differential scanning calorimetric combined with mass spectrometry measurements followed by high performance liquid chromatography and gel filtration chromatography of the pyrolysis residue. This study indicates that levoglucosan formed during cellulose pyrolysis is initially a liquid that undergoes two simultaneous, competing processes of evaporation and polymerization. Levoglucosan that evaporates escapes the high temperature pyrolysis zone while levoglucosan that polymerizes is trapped in the pyrolysis zone and dehydrates to low molecular weight volatile products and char. The oligosaccharides that form during polymerization are subject to two simultaneous reaction pathways: direct decomposition to low molecular weight products such as water, carbon dioxide, 5-hydroxymethylfurfural, furfural, furan and acetic acid, and formation of polysaccharides that eventually dehydrate to char and low molecular weight volatiles. Based on the experimental observations and quantitative measurements, a modified cellulose pyrolysis pathway involving levoglucosan as the major intermediate is proposed.