Mechanistic Understanding of Polycyclic Aromatic Hydrocarbons (PAHs) from the Thermal Degradation of Tires under Various Oxygen Concentration Atmospheres

Abstract

The thermal degradation of tires under various oxygen concentrations (7-30%/Bal. N-2) was investigated thermo-gravimetrically at 10 degrees C min(-1) heating rate over a temperature range from ambient to 1000 degrees C. Significant mass loss (similar to 55%) was observed at the temperature of 300-500 degrees C, where the thermal degradation rate was almost identical and independent of oxygen concentrations due to simultaneous volatilization and oxidation. A series of gas chromatography/mass spectroscopy (GC/MS) measurements taken from the effluent of a thermo-gravimetric analysis (TGA) unit at temperature of 300-5000 degrees C leads to the overall thermal degradation mechanisms of waste tires and some insights for understanding evolution steps of air pollutants including volatile organic carbons (VOCs) and polycyclic aromatic hydrocarbons (PAHs). In order to describe the fundamental mechanistic behavior on tire combustion, the main constituents of tires, styrene butadiene rubber (SBR) and polyisoprene (IR), has been investigated in the same experimental conditions. The thermal degradation of SBR and IR suggests the reaction mechanisms including bond scissions followed by hydrogenation, gas phase addition reaction, and/or partial oxidation.