Theoretical Study on the Unimolecular Pyrolysis of Thiophene and Modeling

Tianshuang Li; Hongliang Zhang; Yun Li; Jie Li; Jingkun Wang; Jin Xiao

doi:10.1021/acsomega.1c02155

Theoretical Study on the Unimolecular Pyrolysis of Thiophene and Modeling

ACS Omega. 2021 Jul 28;6(31):20471-20482. doi: 10.1021/acsomega.1c02155. eCollection 2021 Aug 10.

Authors

Tianshuang Li^{1

2}, Hongliang Zhang^{1

2}, Yun Li¹, Jie Li^{1

2}, Jingkun Wang³, Jin Xiao^{1

2}

Affiliations

¹ School of Metallurgy and Environment, Central South University, Hunan Province, Changsha 410083, China.
² National Engineering Laboratory of High Efficient Recovery of Refractory Nonferrous Metals, Central South University, Hunan Province, Changsha 410083, China.
³ China Hongqiao Group Limited, Zouping 256200, China.

Abstract

Thiophenic sulfur is the most stable and abundant organic sulfur species in petroleum. Removal of thiophenes has profound significance in environmental protection. In this work, we investigate the unimolecular pyrolysis of thiophene from a kinetic perspective. High-level ab initio methods have been employed to deduce the potential energy surface. Rate coefficients of the elementary reactions are computed using variational transition-state theory at the CCSD(T)/CBS level to develop a kinetic model. By comparison with preceding experimental results, the kinetic model shows good performance in calculating the thiophene pyrolysis rate. The Arrhenius expression for thiophene unimolecular pyrolysis has been redetermined as k = 1.21 × 10¹³ × exp[(78.96 kcal/mol)/(RT)]. The unimolecular pyrolysis of thiophene is mainly initiated by the ring-H migrations, whereas the C-S bond rupture has limited contribution to the overall pyrolysis rate. Thioketene (SC₂H₂) and ethyne (C₂H₂) are the major pyrolysis products at all temperatures. Significant amounts of the thioformyl (HCS) radical and CS could also be yielded. By contrast, atomic sulfur and H₂S are difficult to be directly produced. Possible secondary reactions in the products have also been discussed.