Theoretical study on the mechanism of sulfur migration to gas in the pyrolysis of benzothiophene

Abstract

The release and control of sulfur species in the pyrolysis of fossil fuels and solid wastes have attracted attention worldwide. Particularly, thiophene derivatives are important intermediates for the sulfur gas release from organic sulfur, but the underlying migration mechanisms remain unclear. Herein, the mechanism of sulfur migration during the release of sulfur-containing radicals in benzothiophene pyrolysis was explored through quantum chemistry modeling. The C₁-to-C₂ H-transfer has the lowest energy barrier of 269.9 kJ·mol^–1 and the highest rate constant at low temperatures, while the elevated temperature is beneficial for C−S bond homolysis. 2-Ethynylbenzenethiol is the key intermediate for the formation of S and SH radicals with the overall energy barriers of 408.0 and 498.7 kJ·mol^–1 in favorable pathways. The generation of CS radicals is relatively difficult because of the high energy barrier (551.8 kJ·mol^–1). However, it can be significantly promoted by high temperatures, where the rate constant exceeds that for S radical generation above 930 °C. Consequently, the strong competitiveness of S and SH radicals results in abundant H₂S during benzothiophene pyrolysis, and the high temperature is more beneficial for CS₂ generation from CS radicals. This study lays a foundation for elucidating sulfur migration mechanisms and furthering the development of pyrolysis techniques.

Graphical abstract

Keywords

benzothiophene / sulfur migration / pyrolysis / density functional theory

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Acknowledgments

The authors thank the National Natural Science Foundation of China (Grant Nos. 52006069, 51922040, 51821004), Fundamental Research Funds for the Central Universities (Grant No. 2020MS020), and Hunan Science and Technology Planning Project (Grant No. 2020RC5008) for financial support.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://dx.doi.org/10.1007/s11705-022-2209-4 and is accessible for authorized users.

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