Optimization of iodine number of carbon black obtained from waste tire pyrolysis plant via response surface methodology

Recovered carbon black (RCB) obtained from a tire pyrolysis plant was subjected to chemical and thermal treatments for application as a filler in rubber compounds. Carbon black was chemically treated with nitric acid by varying the temperature, time, and chemical-to-carbon black ratio. The iodine number was optimized using response surface methodology (RSM) and the Design Expert software. To increase the iodine number, the Box–Behnken design was utilized to optimize three parameters: temperature (30–50 °C), time (6–24 h), and ratio of carbon black to chemical (0.25–1.0 g/mL). Under optimal conditions, the surface area increased, and RCB was upgraded to commercial carbon black N330. RSM analysis indicted that the iodine number was maximized (117.34 mg/g) after treatment at 46.74 °C for 23.24 h using a carbon black/chemical ratio of 0.76 g/mL. The simulated data were experimentally validated by analyzing RCB_ EQ, which yielded an iodine number of 119.12 mg/g. The content of most heavy metals in RCB decreased by more than 90%, whereas the sulfur and chlorine content decreased by 43.27% and 53.96%, respectively. Based on thermogravimetric analysis, the RCB_13 carbon black additive was eliminated at temperatures of 620–800 °C.