Pyrolytic transformation behavior of hydrocarbons and heteroatom compounds of scrap tire volatiles

Pyrolysis has been a major method to dispose the problem of scrap tires and it is gaining enormous attention all over the world. But less is known about its comprehensive transformation behavior of pyrolysis products. Experiments on pyrolysis of scrap tires were carried out using Py-GC/MS to investigate the distribution of volatile products at five typical temperatures of 200, 300, 400, 500, and 800 °C. Products generated at each temperature stage were categorized according to their functional group for exploring the possible chemical formation pathways. It was found that pyrolysis products were distributed at all temperature stages and predominantly produced at 300–400 °C. Hydrocarbon volatiles were mainly composed of alkenes, especially sesquiterpenes, D-limonene and isoprene. Heteroatom volatile products were all generated below 500 °C. Fatty acids, alkenyl alcohols, sulfides, diphenylamine, nitriles, and benzothiazole were predominant heteroatom products identified in this study. Based on Py-GC/MS results, pyrolytic transformation behavior of hydrocarbons and heteroatom compounds was proposed. In addition, a deeper investigation into the evolution of sulfur was conducted since it was the leading contaminant during the overall pyrolysis process. Results showed that about 60.98 wt% of total sulfur was distributed in the solid residues and was mostly in the form of sulfides and thiophenes. Sulfur content in liquid and gas products was 29.52 wt%, and 7.64 wt%, respectively. Overall, the results of this research presented an in-depth pyrolysis regularity of scrap tire volatiles and provided theoretical guidance for directional valorization of pyrolytic oil.