Waste tires pyrolysis kinetics and reaction mechanisms explained by TGA and Py-GC/MS under kinetically-controlled regime.

The fast pyrolysis of waste tires (WTs) is studied by quasi-isothermal thermogravimetric (TGA) analysis, kinetic modelling and an analytical pyrolyzer coupled with gas chromatography/mass spectrometry (Py-GC/MS). The TGA demonstrated that the WTs pyrolysis is ruled by devolatilization/condensation and depropagation reactions, up to 482 °C. At higher temperatures, the cyclization and aromatization of primary products take place to form mostly monoaromatics. Py-GC/MS experiments were performed under kinetic regime according to the thermal map established by the ratio between Biot́s (31.25) and Py-numbers (7.7⋅10). Limonene (51%) and isoprene (20.5%) were the major compounds detected at temperatures below 435 °C, while above 600 °C limonene was converted to mono-aromatics (S = 28.7%). The approach to equilibrium of Diels-Alder reaction demonstrated that there is an equilibrium-ruled behavior between isoprene and limonene, particularly at T > 600 °C. The E values calculated by the Starinḱs model ranged from 101.5 to 176.7 kJ/mol, while for model-based kinetics it was 152.7 kJ/kmol. The integration of TGA, kinetic modelling and Py-GC/MS provided insights into pyrolysis reaction mechanism.