Simulating vulcanization process during tire production to explore sulfur migration during pyrolysis

Abstract

This paper systematically investigated sulfur transformation during pyrolysis of waste tires by simulating vulcanization process. Three formulas with rubbers, carbon black, ZnO, and typical vulcanization accelerators were prepared by vulcanization and compounded process as simulated tires. Stepwise temperature programmed pyrolysis was conducted in thermogravimetric analyzer and fixed bed reactor. Vulcanization promoted the weight loss rate for thermal degradation of vulcanized rubbers at 300–400 °C, but weakened it at 400–500 °C. The addition of vulcanization accelerators made these effects even more pronounced. Accordingly, more pyrolytic oil was obtained at 300–400 °C for vulcanized rubbers which should contribute to the partial destruction of polymer chains by vulcanization. Besides, vulcanized rubbers attained higher proportion of aromatics but less cyclenes than compounded rubbers. Vulcanized rubbers with ethyl ziram accelerator inhibited H2S release, while vulcanized rubbers with N-tert-Butyl-2-benzothiazolesulfenamide inhibited the formation of CH3SH. The detailed sulfur compounds in gas, oil, and solid char were analyzed. Vulcanization seemed to exhibit positive effect on sulfur transformation in pyrolytic products, i.e., higher retention rate in pyrolytic char but lower proportion ratio in gas. Sulfurization promoted the conversion of thiophene sulfur to inorganic sulfur and sulfides found in pyrolytic char was only ZnS.