Untreated and HNO3-treated pyrolysis char as catalysts for pyrolysis of waste tire: In-depth analysis of tire-derived products and char characterization

The pyrolysis char produced in the pyrolysis of scrap tire rubber has few market outlets, reducing the economic viability. Thus, the char properties was firstly studied in this work, and then untreated and 5M HNO3-treated chars were investigated for their potentials as the catalysts for pyrolysis of waste tire. The product distribution and the quality of tire pyrolysis oil were examined. The gas products were analyzed by using GC/FID whereas the oil products were analyzed by using SIMDIST-GC and GC×GC/TOF-MS. Sulfur and nitrogen contents were determined by using CHNS-analyzer. The catalysts were also characterized by using BET, XRD, XRF, FTIR, FE-SEM, and TG/DTA. The results indicated that the surface area and pore size of treated char were enhanced by the acid treatment. Furthermore, it can be noted that the increase in the total acidity of treated char was caused by the enhancement of carboxyl (-COOH) group on the surface. Additionally, the treatment using 5M HNO3 can demineralize and significantly reduce sulfur content in the char. When employed as a catalyst, the HNO3-treated char increased the gas production due to its enhanced acidity, surface area and pore size, consequently promoting the greater cracking activity. However, both untreated and treated chars dramatically decreased gas oil, light vacuum gas oil, and heavy vacuum gas oil, leading to the drastic enhancement of gasoline and kerosene. Moreover, even though the char catalysts cannot reduce nitrogen content in oil, they can greatly remove sulfur in oil (approximately 26.6–27.3%). Nevertheless, the untreated char that contained a larger content of elements or minerals than the treated one gave significantly higher petrochemical production, which indicates that deminerization by the acid treatment may not always be needed for better activity, especially for petrochemical production.