Enhanced Levoglucosan Yields from the Copyrolysis of Cellulose and High-Density Polyethylene

Abstract

The wide availability of biomass resources could present a sustainable and alternative feedstock to fossil fuels for the production of energy sources and platform chemicals. Fast pyrolysis is one of the simplest methods for biomass conversion, but producing value-added chemicals via fast pyrolysis is still challenging due to diverse product distributions and low product selectivity. Thermoplastics that melt at high temperatures are potential candidates to trap escaping products from biomass pyrolysis, promoting secondary cellulose pyrolysis reactions for increased product selectivity. In this work, a strategy to promote the yields of levoglucosan (LG), a potential high-value chemical from cellulose pyrolysis, is presented using molten high-density polyethylene (HDPE) for the inhibition of product escape. Cellulose and HDPE mixtures were pyrolyzed with controlled mixing patterns in a custom-made laboratory reactor to investigate the interplay between chemical kinetics and mass transfer. Our experimental results showed that the yields of LG and low-molecular-weight products (LMWPs) both increased due to the presence of HDPE. This is likely resulted from the inhibition of evaporation of anhydrosugar oligomers in cellulose pyrolysis, leading to increased secondary pyrolysis reactions in the molten HDPE phase. The morphology of the HDPE layers on top of cellulose is the determining factor affecting the interplay between chemical kinetics and mass transfer in cellulose/HDPE copyrolysis, thus altering product distributions. The highest LG yield observed in this work reached 74.2% at 400 °C when significant amount of HDPE was coated on top of cellulose, an increase of approximately 30%. The HDPE pyrolysis was also accelerated by the presence of cellulose, likely due to the catalytic effect caused by LG.