Impact of CO2 on the pyrolysis of mixed polymer wastes into combustible fuel: A case study for footwear waste

Plastic waste is a promising resource for producing liquid fuels that can be integrated into existing hydrocarbon infrastructures. However, the heterogeneous nature of plastic-derived liquid fuels limits direct application in internal combustion engines, necessitating their refinement into a usable form. To address these issues, this study explored the enhancement of combustible gaseous fuels derived from plastic waste, footwear waste, as a viable alternative. This approach involves the introduction of carbon dioxide as a reactive feedstock during the pyrolysis process. Analytical techniques were employed to precisely determine the types and compositions of four polymers present in footwear waste. The compositional matrices of the primary pyrogenic products were also identified. However, incorporating carbon dioxide into pyrolysis leads to its interaction with volatile compounds, converting them into lighter gaseous products, particularly carbon monoxide. The homogeneous reactivity of carbon dioxide was further enhanced by the application of heat and a nickel-based catalyst. The gaseous product yield from catalytic pyrolysis in the presence of carbon dioxide increased proportionally with the test temperature. Specifically, the use of carbon dioxide led to a 1.92-fold increase in gaseous product yield at 700 ˚C, in reference to the results from nitrogen. This study demonstrates a technical advancement in pyrolytic valorisation of footwear waste by incorporating carbon dioxide and provides a detailed investigation into its mechanical role in maximising the production of combustible gaseous fuels.