Over the past several decades, there has been a rapid and continual growth in global polymer production due to the increasing demand for plastics in modern life. This growth in plastic production has resulted in billions of tons of plastic waste, the majority of which has been discarded in landfills or the environment. Accounting for almost 20% of global plastic production, polypropylene is a material of primary importance. To achieve a circular plastic economy, wherein end-of-life plastics are recycled in a closed loop recreating the original polymers with complete fidelity, a new approach to plastic waste management is needed. Pyrolysis has high potential as a technology to promote a circular plastic economy, by which polymers are thermally cracked to their constituent monomers. The mechanisms of polymer pyrolysis are highly complex and the quantification of the kinetics of pyrolysis remains a challenge. In this work, the ‘pulse-heated analysis of solid reactions’ (PHASR) method has been applied to polypropylene pyrolysis. The PHASR reactor is uniquely capable of measuring the intrinsic kinetics of polypropylene pyrolysis with millisecond scale resolution at temperatures up to 700 °C. Polypropylene pyrolysis was also studied using a Visual PHASR experimental system, which allows for direct observation of pyrolysis reactions via high speed photography. This work validates the ability of the PHASR reactor to pyrolyze polypropylene under isothermal, kinetically limited conditions, presenting yield vs. reaction time data and intrinsic lumped kinetics. In addition, visual analysis of polypropylene pyrolysis, with highlighted reaction phenomena, is shown with comparison to experimental results. These insights into polypropylene pyrolysis will help to enable the development of more efficient industrial pyrolysis reactors and ultimately a circular plastic economy.

Application of pulse-heated analysis of solid reactions (PHASR) to promote a circular plastic economy: Intrinsic kinetics of polypropylene pyrolysis

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ACS Fall 2022

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