Pyrolysis-driven chemical recycling: Tailoring kinetics to polymer waste complexity

Precise kinetic models are required for the chemical recycling of polymer waste by pyrolysis to predict conversion and reaction rates, which are fundamental for developing a reactor model. This study evaluates the pyrolysis kinetics of three polymer wastes of different complexity: end-of-life tires, polyethylene terephthalate, and polystyrene. For this purpose, thermogravimetric data obtained at three different heating rates were analyzed using two complementary approaches: 1) a single-step method combining isoconversional and master plot techniques, and 2) a multi-step distributed activation energy model. This work is crucial because it provides the first systematic comparison of fitted conversion and reaction rate curves against experimental data, filling a gap in the existing literature. The results show that the complexity of the feedstock influences the accuracy of the model: The distributed activation energy model outperforms single-step methods for end-of-life tires and correctly captures their multi-component degradation (complex matrix containing natural and synthetic rubber). On the other hand, Friedman/master plots work better for simpler polymers such as polyethylene terephthalate and polystyrene, which contain ethylene glycol and terephtalic acid, and styrene, respectively. The derived kinetic parameters enable precise description of temperature-dependent reaction progress, and are the first step in reactor design. This work establishes a waste-specific framework for selecting kinetic models, thereby advancing scalable pyrolysis processes.