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

Abstract

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 the 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 (E a ) values of 165-195 kJ.mol -1 , R 2 = 0.99659. While the ASTM-E698 showed 165.6 kJ.mol -1 and integral methods such as Flynn-Wall and Ozawa (FWO) (166-180 kJ.mol -1 ). The in-situ MS results showed the pyrolysis gaseous emissions which are C 1 -hydrocarbon and H-O-C=O along with C 2 hydrocarbons, C 5 - C 6 hydrocarbons, acetaldehyde, the fragment of O-CH=CH 2 , hydrogen and water. Conclusions: The kinetic triplet along with the in-situ monitoring of the gaseous emissions of PET pyrolysis can benefit in the process modelling of this system to help better understand the process at scale. This ultimately aids in reactor optimization and design at scale, as it gives a better insight into the reaction mechanism. This can be used by plastic recyclers worldwide and the predictions made in this study can be used to determine how the rate of reaction changes based on temperature and heating rate beyond experimental results both isothermally, non-isothermally and in stepwise heating regimes.