Behavior of sulfur during pyrolysis of waste tires: A critical review

Waste tires (WT) are known as "black pollution", and their quantity is growing year by year. The rational disposal of WT has become an urgent problem. Pyrolysis is an economical method to treat WT, and the pyrolysis products can be further utilized. A large number of studies have reported on the effects of various parameters of pyrolysis on the yield and quality of pyrolysis products, as well as the further utilization of pyrolysis products. It is worth noting that WT contain a certain amount of sulfur. The sulfur will be released during the treatment process and may further cause secondary pollution. This paper approaches multidisciplinary aspects for the evaluation of sulfur in the process, such as the sulfur content in WT and pyrolysis products, the type of sulfur-containing compounds, transformation mechanism of sulfur, relevant influencing factors and sulfur-containing pollutants control methods. Moreover, the behavior of sulfur during co-pyrolysis is also reviewed. The challenges of the pyrolysis process were suggested. Finally, helpful suggestions and feasible research directions are presented in this paper. This paper can provide a theoretical reference for the enhancement of the pyrolysis process. • More than half of the sulfur remains in the pyrolysis char. • Possible transformation mechanism of sulfur during waste tire pyrolysis was suggested. • The desulfurization effect of some catalysts in the pyrolysis process of waste tires was summarized. • Desulfurization methods of pyrolysis oil were analyzed and compared. • Challenges and future research directions were pointed out.