Kinetic model for the pyrolysis and combustion of poly-(ethylene terephthalate) (PET)

The kinetics of the global primary thermal decomposition of poly-(ethylene terephthalate) (PET) waste was studied in strict pyrolysis conditions and with different proportions of oxygen by TGA, between temperatures of 25 and 800°C. Prior to the decomposition, the polymer first melts at around 250°C. The pyrolysis of PET, which starts at 400°C, is modeled assuming that it is formed by two different parts which decompose by two independent reactions. The introduction of oxygen produces the appearance of a new process, which does not start until the pyrolysis finishes. This fact is interpreted as the combustion reaction of the char formed in the pyrolysis, and was modeled kinetically with a common combustion reaction to the solid char residues obtained from each initial fraction. One pyrolysis run and one combustion run at 850°C, at fuel-rich conditions were carried out to analyze the different gas compositions evolved, where an appreciable amount of poly aromatic hydrocarbons (PAH) was detected.