Physicochemical properties and reaction characteristics of pyrolysis chars produced from various spent tires components and temperatures: A case study

Waste tires are one of the most abundant waste streams. Recycling processes that adapt to the complexity of waste tires, such as pyrolysis, need to be improved. In this study, the tread (TT) and sidewall (SW) of the tires were pyrolyzed separately and the resulting chars were systematically investigated for their physicochemical and combustion properties. The results showed that the fixed carbon content of the SW was higher than that of the TT, and that there was an enrichment of harmful elements (Zn) during the pyrolysis process. The main tem-perature range for pyrolysis was 350-500 degrees C. Only natural rubber was present in TT, while synthetic rubber was also present in SW. The char produced by TT consisted of a large amount of amorphous carbon with a higher specific surface area and more developed pores. A large number of Si-O bonds were present on the surface of TT, while more Zn-S bonds were present in SW. The char produced by TT was less graphitized and the spacing between the aromatic lamellae was greater. The functional groups of TT and SW pyrolysis char are relatively single, mainly C-H/C-O. The volatile content of SW pyrolysis carbon is only 3.72%, and the ignition temperature and activation energy are lower than those of TT pyrolysis carbon, which can reduce the consumption of fossil fuels as a higher quality fuel. The ash of TT and SW pyrolysis chars can be used as Si and Zn raw materials respectively, thus realizing a deeper resource utilization.