The fate of sulfur during rapid pyrolysis of scrap tires

• Sulfur species in pyrolysis char, tar and gases from scrap tires were investigated.
• Sulfur was mostly in the form of thermally unstable thiophenic in scrap tires.
• Besides H2S, CH3SH, COS and SO2 were formed during rapid pyrolysis of scrap tires.
• Interactions between volatiles and char promoted thiophenic and sulfones formation.

The fate of sulfur during rapid pyrolysis of scrap tires at temperatures from 673 to 1073 K was investigated. Sulfur was predominant in the forms of thiophenic and inorganic sulfides in raw scrap tires. In the pyrolysis process, sulfur in organic forms was unstable and decomposed, leading to the sulfur release into tar and gases. At 673 and 773 K, a considerable amount of sulfur was distributed in tar. Temperature increasing from 773 to 973 K promoted tar decomposition and facilitated sulfur release into gases. At 1073 K, the interactions between volatiles and char stimulated the formation of high-molecular-weight sulfur-containing compounds. After pyrolysis, almost half of the total content of sulfur in raw scrap tires still remained in the char and was mostly in the form of sulfides. Moreover, at temperatures higher than 873 K, part of sulfur in the char was immobilized in the sulfates. In the pyrolysis gases, H2S was the main sulfur-containing gas. Increasing temperature stimulated the decomposition of organic polymers in scrap tires and more H2S was formed. Besides H2S, other sulfur-containing gases such as CH3SH, COS and SO2 were produced during the rapid pyrolysis of scrap tires.