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A lumped kinetic model and experimental investigation of poly(ethylene terephthalate) condensed-phase pyrolysis
Summary
Researchers developed the first quantitative kinetic model for the condensed-phase pyrolysis of PET plastic, combining molecular and radical reaction pathways across 85 species and 700 reactions to simulate thermochemical recycling. The model was validated against new experimental data from TGA and GCxGC-MS analyses, providing a publicly available framework to improve chemical recycling of mixed plastic waste.
• Unsorted PET in waste thermochemical recycling forms char and alters product yields. • First quantitative kinetic model for PET condensed-phase thermal degradation. • Critical evaluation of molecular and radical pathways by gas-phase analogies. • Experimental investigation by GCxGC-MS/FID, RGA, TGA, and elemental analyses. • Model validation on mass-loss profiles, gas and tar distribution, char composition. In a circular economy perspective, plastic waste (PW) is a valuable source of chemicals and energy vectors. Understanding the effect of poly(ethylene terephthalate) (PET) in thermochemical valorisation of complex and contaminated PW mixtures requires definition of suitable kinetic models. This work proposes a condensed-phase semi-detailed kinetic model for PET pyrolysis based on a consolidated functional group approach already validated for other polymers. The reaction network is built considering studies on thermal degradation of PET, model compounds, and small gas-phase esters. Reaction pathways proposed in the scientific literature are critically assessed through analogy with high accuracy gas-phase calculation and are complemented by new proposed pathways. The resulting model couples molecular and radical mechanism and consists of 85 gas and liquid species with 700 liquid-phase reactions, being suitable for CFD simulations of PW pyrolysis upon further reduction. This work also presents new experimental data including TG analysis coupled with GC × GC speciation measurements and elemental characterization of the solid residue. The model is validated by comparison with the new experimental data and a comprehensive set of literature data in terms of characteristic degradation times and detailed product yields. The present work expands the relevant data available for chemistry models development and extends the CRECK kinetic framework for thermochemical recycling of PW mixtures. The proposed kinetic model is attached as Supplementary material and freely available as an open GitHub repository.