Thermal decomposition characteristics of the tire pyrolysis oil derived from a twin-auger reactor: Study of kinetics and evolved gases

This study presents the characterization of the thermal decomposition (oxidation and pyrolysis) behavior of the oil (TPO) derived from the pyrolysis of End-of-Life Tires (ELT) in a twin-auger pyrolyzer, by means of thermogravimetric and calorimetric analyses, coupled with Fourier transform infrared spectroscopy (TG–FTIR). TPO oxidation and pyrolysis were conducted using air and N₂, respectively, at three different heating rates (5, 10, and 20 °C/min) in a temperature range between 30 and 700 °C. Along the temperature program, the evolved gases were directed to the FTIR cell, where the functional groups within species present were measured. A global kinetic analysis was performed for the TPO oxidation, using four isoconversional methods, as well as the distributed activation energy model (DAEM) developed by Miura and Maki. The results obtained suggest that the oxidation process of TPO can be divided into three different reaction stages, namely: low-temperature oxidation (LTO) (<400 °C), fuel decomposition (400–500 °C), and high-temperature oxidation (HTO) (500–700 °C). Within the LTO stage, oxygen addition reaction to produce hydroperoxides were considered dominant in the initial stages, while the decomposition of the formed hydroperoxides was more significant at the later stage. Due to the characteristics of TPO, e.g., the presence of highly volatile compounds, the evaporation of hydrocarbons played an important role within the LTO stage. In the fuel decomposition stage, the formation of coke by the oxidative cracking of LTO residue and oxygen addition were believed to be the main reactions leading to gaseous products such as CO, CO₂, H₂O. Finally, in the HTO stage, the oxidation of coke was considered as the main reaction, exhibiting an evident exothermic activity. The activation energy distribution shows a similar pattern among the isoconversional methods and DAEM, with fluctuations between 40 and 200 kJ/mol. The analysis presented in this work sheds new light on the thermal decomposition of oil derived from the pyrolysis of ELT, which is relevant for its use in combustion systems.