Enhancing Chemical Recycling of Polyethylene: A Free Radical-Based Kinetic Model for Precise Prediction of Pyrolysis Products

Pyrolysis kinetic models are essential for predicting product distribution, optimizing reactor design, and adjusting process parameters, and they play a key role in the chemical recycling of waste polyethylene into liquid fuels. Existing kinetic models for plastic pyrolysis focus on specific radicals and lack insights into the molecular structures of polyethylene pyrolysis products. Using the Structure-Oriented Lumping (SOL) method and genetic algorithms, a molecular-level kinetic model is developed to simulate the formation of alkanes, mono-olefins, and diolefins. The model accurately predicts product yields with errors under 3% and is validated under various experimental conditions, including fixed-bed and fluidized-bed reactors. Predictions for temperatures ranging from 500 to 650 °C and the vapor residence times of 10–60 s provide insights into the formation of different carbon-numbered products. By incorporating free radical mechanisms, the model significantly enhances the accuracy of polyethylene pyrolysis predictions, offering strong theoretical support for optimizing pyrolysis processes and improving industrial application efficiency.