(293c) Pathway to a Plastic Circular Economy: Intrinsic Kinetics of Polyethylene Pyrolysis Via Pulse-Heated Analysis of Solid Reactions (PHASR)

Over the past several decades, the use of plastics has grown exponentially with no signs of slowing down, yet the current plastic linear economy model is insufficient for meeting demand and effectively remediating waste. Development of advanced recycling techniques is thus required to address these needs and enable a plastic circular economy, whereby all used plastics are recycled through a closed-loop process to regenerate monomers and, in turn, produce new plastics. To this end, pyrolysis, or thermal degradation under an inert atmosphere, has shown significant promise in recent years. However, fully understanding the kinetics and mechanisms underlying plastic pyrolysis has proven challenging, with various systematic limitations only allowing measurement of apparent kinetics. This complicates lab-scale analyses and hinders development of scalable systems, since large-scale reactor and catalyst design is much more efficient with intrinsic reaction kinetics.

We have applied the Pulse-Heated Analysis of Solid Reactions (PHASR) system to polyethylene pyrolysis in order to measure intrinsic reaction kinetics for the first time. First, extensive work was done to redesign the PHASR system for use with plastics, since polyolefin pyrolysis requires much harsher conditions than that of cellulose, the reactant for which PHASR was originally developed. [1] In this work, we have fully established that PHASR is capable of operating without heat and mass transport limitations, kinetic measurement limitations, or secondary reactions, and it can therefore operate in the isothermal, reaction-controlled regime required for elucidating intrinsic reaction kinetics. [2] These intrinsic lumped kinetics are described for polyethylene, as well as initial analyses of post-pyrolysis residues. [2] Finally, comparisons are made between the intrinsic kinetics reported here and the apparent kinetics reported in the literature, and a roadmap is presented for applying PHASR data to industrial catalysis and reactor design. [2]

References:

[1] ChemSusChem, 2021, 14 (19), 4214-4227.

[2] In preparation, 2022.