Thermogravimetric kinetic analysis and demineralization of chars from pyrolysis of scrap tire pretreated by waste coal tar

With the remarkable increase in the number of vehicles worldwide, the disposal of scrap tire is a pressing issue. Pyrolysis is one treatment option to recover resources from the scrap tire, by which pyrolytic char with a high ash and sulfur content is generated, restricting its utilization value. The focus of this study was to improve the quality of the solid product obtained from scrap tire pyrolysis. In this paper, a feasible and effective approach is presented to remove ash from the char using a bench-scale unit. Unlike direct co-pyrolysis of the mixture of scrap tire and other materials, in the study, prior to pyrolysis, the scrap tire was soaked in waste coal tar for a few hours, and then, char was obtained from pyrolysis of the as-prepared scrap tire. According to the comparative analysis of thermogravimetric kinetics of the scrap tire and the as-prepared scrap tire, it revealed that the as-prepared scrap tire was more easily pyrolyzed under relatively low temperature with activation energy of 45.65 kJ/mol and at higher temperature with activation energy of 142.12 kJ/mol. With three kinds of acid (HCl, HNO3, and H2SO4) as the demineralization agent, comparative experiments on the removal of ash from the chars arising from pyrolysis of the as-prepared scrap tire (Char1) and the scrap tire (Char2) were carried out. The results showed that there were the highest efficiencies of ash removal from chars soaked in HCl solution, at 84.9% for Char1 and 59.6% for Char2. With HCl as the demineralization agent, a series of experiments on the removal of ash from Char1 and Char2 was conducted in which the effects of parameters, such as the mass ratio of the acid to the char (L/S), acid concentration, heating temperature, reaction time, stirring rate, particle size of the char, and the number of filtrate cycles, were systematically performed. Under the optimum conditions, the ash removal efficiencies for Char1 and Char2 reached 87.5% and 77.2%, respectively. The kinetics of the char demineralization process was also performed, conforming to a quasi-first-order rate equation. The results obtained indicated that the process of soaking scrap tire in waste coal tar is very useful for removing ash from the char.