(82f) Hydroxyl Group Stabilization for Increased Yields of Low Molecular Weight Products in the Co-Pyrolysis of Cellulose and Thermoplastics
Plant-derived biomass as a renewable resource for value added chemical production has the potential to meet the needs of reducing the usage of fossil fuels even with growing global population. Fast pyrolysis is one of the most simple and robust thermochemical methods for biomass conversion, but producing value added chemicals via fast pyrolysis is still challenging due to diverse production distributions, potentially incurring significant cost due to subsequent upgrading and separation operations. For inexpensive and sustainable chemical production processes, it is crucial to understand reaction mechanism of the pyrolysis of cellulose - the largest fraction of biomass. Cellulose pyrolysis typically produces anhydrosugars, including levoglucosan (LG) and its oligomers, and low molecular weight products (LMWPs), which can be potentially upgraded into biofuels or value-added chemicals. In this work, we present a strategy to promote the yields of LMWPs from cellulose pyrolysis via hydroxyl group stabilization using molten polymers. Three types of thermoplastics, high-density polyethylene (HDPE), polyethylene glycol (PEG), and polystyrene (PS), representing different functional groups (e.g., aromatics, ethers, etc.), are individually co-pyrolyzed with cellulose to investigate the roles of these moieties in cellulose pyrolysis. The experimental results show that the yields of LMWPs can be significantly increased in the presence of PS, suggesting that the aromatic groups in PS stabilize the cellulosic hydroxyl groups during glycosidic bond cleavage, inhibiting the reactions leading to anhydrosugar molecules. Our experiments also suggest that both ether and aromatic groups stabilize the hydroxyl groups in glycosyl rings during dehydration, leading to increased yields of products from retro Diels-Alder fragmentation and decreased yields of dehydration products. Our work demonstrates that by manipulating the compositions of the molten polymers in cellulose/molten polymer co-pyrolysis, product distributions can be manipulated and yields of desired products can be enhanced.