Catalytic Pyrolysis Oil from Landfilled Plastics through Ni/HZSM-5 and Co/HZSM-5 Catalysts

Plastic waste poses a significant environmental challenge. To address this issue, the pyrolysis process offers a promising solution to convert plastic waste into valuable products. This study investigated the pyrolysis of plastic waste sourced from a Hat Yai municipal landfill, aiming to optimize process conditions and characterize the resulting products. The plastic waste was classified into three primary types: polyethylene terephthalate (PET) (7 wt %), polypropylene (PP) (23 wt %), and polyethylene (PE) (70 wt %). Thermogravimetric analysis (TGA) revealed that the waste decomposed completely within the temperature range of 520-600 °C. To optimize pyrolysis conditions, experiments were conducted on both unwashed and water-washed plastic waste, varying particle size, catalyst type, and loading. Nickel- and cobalt-based zeolite catalysts (Ni/HZSM-5 and Co/HZSM-5) were employed to enhance the pyrolysis process. The results indicated that medium-sized, water-washed plastic waste, pyrolyzed at 560 °C with 5 wt % of 5 wt % Co/HZSM-5 catalyst, yielded the highest pyrolysis oil (47.42 ± 1.00 wt %) and a high heating value (HHV) of 38.06 ± 0.67 MJ/kg. To further optimize the process, central composite design (CCD) and response surface methodology (RSM) were utilized to investigate the effects of the temperature and catalyst loading on the pyrolysis oil yield and HHV. Optimal conditions were determined for both unwashed and washed plastic waste. Gas chromatography-mass spectrometry (GC-MS) analysis of the pyrolysis oil from both optimum conditions revealed a high proportion of hydrocarbon compounds similar to fossil fuels, including gasoline, jet fuel, and diesel. This study successfully optimized the catalytic pyrolysis of plastic waste, resulting in significant improvement in oil yield and product quality. The use of water-washed plastic waste and 5% Co/HZSM-5 catalyst proved to be effective in enhancing the pyrolysis process. These findings provide valuable insights into the sustainable management of plastic waste and the production of valuable resources.