Pyrolysis of lignocellulosic biomass with high-density polyethylene to produce chemicals and bio-oil with high liquid yields

Abstract The pyrolysis of waste plastic and lignocellulosic material feedstocks increases the hydrogen/carbon ratio of the plastic-biomass mixture and may be advantageous for refining the properties of pyrolysis oil, which can be directly used as a fuel without any need for upgrading by catalytic hydrodeoxygenation. In this paper, high-density polyethylene (HDPE) and brown salwood were tested in a custom-built laboratory-scale fixed-bed reactor to investigate the co-pyrolysis reaction at temperatures ranging from 500 to 650 °C, nitrogen flow rates ranging from 40 to 160 mL min−1, and HDPE-to-biomass ratios ranging from 0.1 to 0.9. The results revealed that the temperature mostly influenced the pyrolysis products, whereas increasing the temperature to 600 °C promoted pyrolysis oil production, reaching a yield of 35.10 ± 1.20 wt%. Further increasing the reaction temperature to 650 °C decreased the yield to 34.57 ± 0.49 wt% because secondary cracking reactions produce a noncondensable gas rich in hydrocarbons. Physicochemical analysis of the pyrolyzed organic phase revealed a gross calorific heating value of up to approximately 38.19 MJ kg−1. Additionally, co-pyrolysis of HDPE improved the production of furans, and acid derivatives were obtained in the aqueous fraction via the thermal conversion of hemicellulose and lignin; conversely, the obtained char exhibited a notably low surface area and few superficial micropores and was used to further develop activated carbon for use as a catalyst in the catalytic pyrolysis of waste materials.