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

Formation of Sulfur Species from Thiophene Decomposition and the Impact of Alkali Metal Ions: A Density Functional Theory Study

“…58,59 In addition, COS and CS 2 mainly form at high temperatures, attributed to the high energy barrier for CS radical formation and the drastic rate constant increase of its generation with temperature rising (Table 1 and Figures 9 and 13). 14,30,55 In addition, the byproduct (propadiene, c3-3m) formed in path C3 was also detected in thiophene pyrolysis, 36 which also confirms the correctness of the DFT calculations.…”

“… − , H 2 S generally accounts for more than 90% in S-containing gases . In addition, the multiple paths for the thiol function group-involved intermediate (a3-3m) verify the significance of the thiol group and SH radical for the abundant formation of H 2 S. ,, COS and CS 2 are formed by the interaction of the CS radical and other O-/S-containing radicals, and the high formation energy barrier of the CS radical limits the yield of COS and CS 2 . − ,,, Specifically, the yield of COS and CS 2 usually accounts for 5 to 15% of the yield of H 2 S during pyrolysis. , In addition, COS and CS 2 mainly form at high temperatures, attributed to the high energy barrier for CS radical formation and the drastic rate constant increase of its generation with temperature rising (Table and Figures and ). ,, In addition, the byproduct (propadiene, c3-3m) formed in path C3 was also detected in thiophene pyrolysis, which also confirms the correctness of the DFT calculations.…”

“…[24][25][26]36 H 2 S generally accounts for more than 90% in S-containing gases. 57 In addition, the multiple paths for the thiol function group-involved intermediate (a3-3m) verify the significance of the thiol group and SH radical for the abundant formation of H 2 S. 14,55,56 COS and CS 2 are formed by the interaction of the CS radical and other O-/S-containing radicals, and the high formation energy barrier of the CS radical limits the yield of COS and CS 2 . 21 −23,26,30,55 Specifically, the yield of COS and CS 2 usually accounts for 5 to 15% of the yield of H 2 S during pyrolysis.…”

“…Alkali metal ions raise the formation competitiveness of H 2 S and reduce that of other S-containing gases. They promote the H 2 S and S radical formation thermodynamically (Table 1) by accelerating the hydrogen transfer reaction (Figures 5 and 12), and the inferior path B1 for SH radical formation is enhanced ( Figures 7,8,and 14). As for the formation of CS radicals, it is hampered by alkali metal ions both in thermodynamics and kinetics.…”

“…The sustainable and efficient treatment of organic solid wastes has raised worldwide concern in recent decades. , Pyrolysis is a clean and low-carbon technical route for the utilization of organic solid wastes, producing value-added products (char, oil, and gas) to be further used as chemicals, fuels, or materials. − As for the S-containing solid wastes, e.g., wasted tire, the sulfur concentration can be up to 1.5 to 2 wt %, , and the presence of sulfur significantly degrades the quality of the pyrolysis products. Enrichment of H 2 S in the pyrolysis gas is a good choice to control the migration of sulfur so as to improve the quality of the liquid and solid products as well as the further utilization of sulfur. − Hydrogen sulfide methane (CH 4 ) reformation (HSMR) (2H 2 S + CH 4 ↔ 4H 2 + CS 2 ) can achieve the valorization of H 2 S to produce H 2 without direct CO 2 emission. − However, the existence of COS and CS 2 in the pyrolysis gas is disadvantageous to HSMR and may lead to amplification of carbon deposition. ,− Consequently, clarifying the formation mechanism of S-containing gases and the enrichment method of H 2 S is essential for the control of sulfur in the pyrolysis process and the efficient utilization of S-containing organic solid wastes.…”