Kinetic modeling of polyethylene pyrolysis under microwave irradiation toward predictive product distribution

Microwave-assisted pyrolysis offers an approach for the chemical recycling of polymeric waste, contributing to sustainable energy solutions and environmental mitigation. The efficient tracking of pyrolytic gas for further upgrading necessitates a comprehensive understanding of the dominant reaction mechanisms and identifying optimal operating conditions. This study investigates the thermal pyrolysis of low-density polyethylene (LDPE) under microwave irradiation, focusing on the effects of temperature on product distribution while developing a non-isothermal kinetic model for hydrocarbon cracking. The potential decomposition mechanism was explored through ab initio molecular dynamics (AIMD) simulations, conducted over a 4–6 ps time frame at each temperature in the range of 800–4500 K. These simulations revealed fundamental product formation trends as a function of temperature, which were further validated against experimentally obtained primary gas evolution profiles. Pyrolysis experiments were conducted at microwave power levels ranging from 400 to 800 W, categorizing the resulting products into hydrogen and hydrocarbons of varying molecular weights. Model validation against experimental data confirmed a dominant second-order reaction mechanism driven by rapid microwave heating, with Sestak-Berggren Pearson's linear correlation and associated parameter values of n at 1.7 and m at 0.02. Kinetic analysis through the iso-conversional Friedman method revealed an activation energy range of 101 ± 4 kJ·mol −1 , exhibiting slight variation with conversion. A simplified reaction network was developed to predict product evolution, incorporating sinusoidal temperature fluctuations induced by microwave irradiation. The proposed kinetic model advances the design of microwave-assisted pyrolysis processes, offering potential for integration with catalytic stages and further upgrading to enhance process efficiency and product selectivity. • Non-isothermal kinetic model for LDPE microwave pyrolysis validated experimentally • AIMD simulations revealed temperature-dependent decomposition and product pathways. • Dominant second-order mechanism identified with reaction parameters n = 1.7, m = 0.02 • Activation energy of 101 ± 4 kJ·mol −1 determined by iso-conversional Friedman method • The simplified reaction network predicts product evolution under microwave fluctuations.