Insight into co-pyrolysis of waste polypropylene and engine oil for liquid hydrocarbons and interaction mechanism by kinetic analysis and DFT simulation

Plastic pyrolysis is an efficient and cost-effective way of processing plastic waste, producing oil, gas, and coke. Oil production from waste plastics is a promising technology, and co-pyrolysis of multicomponent materials can help to promote reactions and optimize the products. Therefore, this study examines the co-pyrolysis reaction of another hazardous waste, engine oil, with waste plastics. The co-pyrolysis performance of plastic is first evaluated and the TG-DTG curve is dynamically analyzed. Then the synergistic behavior of polypropylene and engine oil co-pyrolysis is revealed through a combination of experiments, kinetic analysis, and DFT calculations. For physical interactions, waste engine oil can improve heat and mass transfer performance during pyrolysis, significantly increase the heating rate of the reactants. Furthermore, the yield of liquid-phase products is increased. For chemical interactions, the optimal pyrolysis path was studied according to activation energies and the interaction mechanism was elucidated. Moreover, the optimal pyrolysis paths of the engine oil and PP were identical, with the resulting pyrolysis products having minimal difference in carbon chains. However, the detailed reaction paths need to be further explored owing to the complexity of the process. And the detailed composition of the pyrolysis products requires further comprehensive analysis.