(620c) Mechanistic Insights into the Pyrolysis of Crystalline and Amorphous Celluloses

Over the years, researchers have been able to elucidate some of the key reactions governing biomass pyrolysis through model compounds such as cellulose. A range of cellulose samples with different particle sizes and model compounds such as cellobiose and glucose have been used to comprehend the influence of temperature, pressure, and sample amounts on product distribution. When subjected to pyrolysis, cellulose yielded about 60-70 wt.% of levoglucosan (LVG) at 400–500 ̊C. However, the experimental studies which were used to validate suffer from issues such as water quantification and mass balance closures. Further, studies on thin-film cellulose pyrolysis suggest a drastic decrease in the production of LVG, with a reduction in film thickness at 400–500 ̊C. A detailed study on cellulose pyrolysis with different particle sizes and a comprehensive analysis of its products using advanced analytics is needed to address these anomalies.

The current work investigates the effects of particle size and crystallinity on cellulose pyrolysis at 400–600 ̊C. The experiments were performed using a Py-GC×GC-FID/TOF-MS and a customized GC for the simultaneous detection of low molecular weight products (LMWPs), permanent gases, and water. Crystalline cellulose with an average particle size of 50µm yielded about 50-60 wt.% LVG. On the other hand, amorphous samples with an average particle size of 15µm produced only 10-15 wt.% LVG upon pyrolysis, along with increased water and glycolaldehyde yields. A detailed kinetic model was employed to elucidate plausible mechanistic pathways responsible for such differences in product evolution. Increased mid-chain dehydration and fragmentation reactions led to smaller chains with LVG-ends that may further react to form LMWPs. Mid-chain dehydration reactions are alternative pathways to LVG formation via chain-end reactions, indicating that chain arrangement may influence the dominant pathways of cellulose pyrolysis.