Effect of torrefaction on the co-pyrolysis of pinewood with PET and HDPE: Impacts on products distribution

This study investigated the co-pyrolysis behavior and product distribution of torrefied pinewood mixed with polyethylene terephthalate (PET) and high-density polyethylene (HDPE) at a 1:1 mass ratio. Pinewood was pretreated through torrefaction at various temperatures (240, 260, and 280 °C) and durations (20, 40, and 60 min). A comprehensive analysis was performed using proximate analysis, elemental analysis, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) to assess the impact of torrefaction on pyrolysis behavior and products yield. These results indicated that torrefaction significantly enhance the fixed carbon content and energy density of pinewood, while reducing its volatile matter content and hydrophilicity. During co-pyrolysis with HDPE, the high hydrogen content of HDPE facilitates hydrocarbon formation, and torrefied pinewood further improves the product distribution. In contrast, during co-pyrolysis with PET, the cleavage of PET ester bonds leads to a significant increase in acid products. However, torrefaction at 280 °C for 20 min effectively suppresses the formation of acid compounds. The integration of torrefaction pretreatment and co-pyrolysis technology provides an effective strategy for the high-value utilization of biomass and waste plastics. Co-pyrolysis with HDPE is more favorable for producing hydrocarbon-based chemical feedstocks, whereas co-pyrolysis with PET can benefit from high-temperature, short-duration torrefaction to effectively suppress acid formation.