Co-pyrolysis of corn stalk and polyethylene at a gas phase contacting mode and aromatization mechanism study

The co-pyrolysis of “hydrogen-deficient” biomass and plastics is an efficient method to produce aromatic-rich bio-oils. However, the distinct pyrolysis characteristics and complex interactions between biomass and plastics in conventional reactors limited aromatics production and synergy study. A modified Y-shaped tube reactor was therefore established, in which corn straw and high-density polyethylene (HDPE) were placed in two branches respectively, with a co-pyrolysis ZSM-5 catalyst at the junction for co-pyrolysis. Firstly, optimal pyrolysis conditions (temperature, catalyst-to-feedstock ratio) were studied for each feedstock to boost furans/light olefins production. As a result, the Diels-Alder reaction raised the aromatics to 21.7 area% in non-catalytic trial. The addition of co-pyrolysis ZSM-5(60) further strengthened this reaction and doubled aromatics to 44.8 area%. It is noteworthy that even with the same catalyst (ZSM-5(60)), the gas-phase contact mode outperformed the conventional co-pyrolysis mode (39.4 area%) in aromatic generation. Subsequently, the synergy between HDPE and cellulose/hemicellulose/lignin was respectively investigated. Results showed that the Diels-Alder reaction between furans and light olefins contributed most to aromatics production, followed by the aromatization of HDPE-derived light olefins.