Pyrolysis-Catalysis of Plastic Wastes for Production of Liquid Fuels and Chemicals

The use of pyrolysis as a waste disposal method for waste plastics has been well established. However, the market value of the recycled plastic products and separate upgrading of the pyrolysis product liquid are some of the challenges facing the process. Therefore, the use of pyrolysis-catalysis of waste plastic in a two-stage pyrolysis-catalysis reactor system could bring a balance between sustainability and market value of the products generated. Hence, this work investigated the influence of different types of zeolite catalysts on the pyrolysis-catalytic upgrading of waste plastics for quality liquid fuels and valuable chemical production. Initially, two zeolite Y and ZSM-5 catalysts, in the form of pellets, were used for pyrolysis-catalysis of WEEE. Zeolite catalyst with a lower Si-Al ratio (Y zeolite) produced a higher conversion of the styrene to other aromatic products, particularly benzene and toluene. Thereafter, the influence of six zeolite catalysts with different surface areas and Si: Al ratios was investigated on the catalytic pyrolysis of waste high-density polyethylene (HDPE). Overall, the results suggest that the catalyst properties influenced the conversion of HDPE to more valuable products such as fuel-range hydrocarbons and chemicals. Similarly, pyrolysis of real-world mixed plastics, simulated mixed plastic (SMP), and virgin plastics were investigated in the presence of HZSM-5 catalyst. In addition, a sample of spent FCC catalyst was also tested for the pyrolysis of the plastic samples. Finally, the influence of spent FCC, fresh zeolite Y and ZSM-5 catalysts was investigated under different bed temperatures from 400 – 600 °C. This final work confirmed that the choice of a bed tempetrure of 500 °C, for most of this research was appropriately justified. Overall, the product oils gave fuel properties similar to gasoline, the aromatic content of the oil make them suitable as chemical feedstocks, the gas products with very high-calorific values can be used as fuel gas.