(508f) Theoretical Assessment of PET Pyrolysis Via Reactive Molecular Dynamic Simulation and Kinetic Modeling

The rapid growth of demand for PET plastic products has resulted in a critical need to develop effective processes to reduce PET pollution by establishing a circular economy. Pyrolysis, a promising technology to produce lighter and recyclable components from wasted plastic products, has received considerable attention as a means of chemical recycling. While significant progress has been made in the experimental studying of the decomposition of PET, molecular-level observations of PET pyrolysis and its detailed reaction model remain largely missing. In this work, the pyrolysis process of PET was studied using reactive molecular dynamics (MD) simulations to elucidate its mechanism and develop kinetic models capable of describing the process. The ester oxygen-alkyl carbon bond dissociation was observed in the simulations, producing ethylene and TPA radicals. These radicals can be further transformed into long-chain components such as char, and CO₂ was released as a product. MD simulations revealed a chain reaction pattern for yielding gas species, which includes the generation of TPA radicals from long-chain breaking and condensation reactions to form a long chain with phenyl benzoate structure to consume TPA radicals. This mechanism explained the correlation between CO₂ release and long-chain formation.

Moreover, since atomistic simulations are generally conducted at the time scale of a few nanoseconds, a high temperature (i.e., > 1000 K) is typically adopted for accelerated reaction. To address the issue of the limitation of time and temperature scale, we developed a set of ordinary differential equations-based kinetic models that could describe the key products of PET pyrolysis under practical temperature scales and analyze the optimal reaction conditions. Overall, this study conducted a detailed mechanism study on PET pyrolysis and established a kinetic model with effective assessment. The workflow presented herein is capable of extracting key information from atomistic MD simulations for establishing kinetic models, which can be used in related areas for performing pre-experimental screening and mechanism prediction in order to further assist in the development of effective pyrolysis solutions. This study highlights the importance of theoretical research on pyrolysis and its potential for innovative solutions to address the growing issue of plastic pollution by developing a circular economy.