Effects of molten salt thermal treatment on the properties improvement of waste tire pyrolytic char

Pyrolysis is a technical means for waste tires recycling, which can promote the enrichment of carbon black and facilitate the subsequent recovery. However, carbon black particles aggregated and the inorganic impurities tended to be enriched in pyrolytic char during the waste tire pyrolysis process, which is not conducive to the substitution of commercial carbon black by pyrolytic char. In the present study, a novel method using molten salts thermal treatment was proposed for the impurities removal from pyrolytic chars with different characteristics. In addition, the proper thermal treatment conditions were further estimated to obtain better performance for the physical-chemical properties improvement of pyrolytic char. Six kinds of char samples were chosen to conduct molten salts thermal treatment (MSTT) experiments at 350, 400, and 450 °C. The experimental results show that MSTT can effectively remove the impurities of different pyrolytic chars, and the most optimum reaction conditions are at 400 °C, 2 h of reaction time, and molten salt/char ratio of 10:1. In addition, after MSTT, the pyrolytic char was depolymerized, and the average particle size reduced from 36.63 μm to 19.08 μm, the specific surface area increased from 49 m2/g to 73 m2/g. At the same time, the graphite carbon content of the pyrolytic char increased from 24.41% to 70.90%, and the hydroxyl content on the pyrolytic char surface increased significantly. In summary, the physical-chemical properties of waste tire pyrolytic char were improved by MSTT, which is close to the carbon black N550 level.