Pyrolysis kinetic modelling of abundant plastic waste (PET) and in-situ emission monitoring

Background
Recycling the ever-increasing plastic waste has become an urgent global concern. One of the most convenient methods for plastic recycling is pyrolysis, owing to its environmentally friendly nature and its intrinsic properties. Understanding the pyrolysis process and the degradation mechanism is crucial for scale-up and reactor design. Therefore, we studied kinetic modelling of the pyrolysis process for one of the most common plastics, polyethylene terephthalate (PET). The focus was to better understand and predict PET pyrolysis when transitioning to a low carbon economy and adhering to environmental and governmental legislation. This work aims at presenting for the first time, the kinetic triplet (activation energy, pre-exponential constant, and reaction rate) for PET pyrolysis using the differential iso-conversional method. This is coupled with the in-situ online tracking of the gaseous emissions using mass spectrometry.

Results
The differential iso-conversional method showed activation energy (Ea) values of 165–195 kJ mol−1, R2 = 0.99659. While the ASTM-E698 method showed 165.6 kJ mol−1 and integral methods such as Flynn-–Wall and Ozawa (FWO) (166–180 kJ mol−1). The in-situ Mass Spectrometry results showed the gaseous pyrolysis emissions, which are C1 hydrocarbons and H–O-C=O along with C2 hydrocarbons, C5–C6 hydrocarbons, acetaldehyde, the fragment of O–CH=CH2, hydrogen, and water.

Conclusions
From the obtained results herein, thermal predictions (isothermal, non-isothermal and step-based heating) were determined based on the kinetic parameters. They can be used at numerous scale with a high level of accuracy compared with the literature.