Structural evolution characteristics of sulfur in coal during gold-tube thermal simulation

Abstract

This study used a gold tube thermal simulation experiment to investigate the release of gases, the formation of free sulfur-containing compounds, and the evolution of coal macromolecules and organic sulfur structures. Results indicate that at Easy%R_o = 0.71, the drying coefficient (C₁/ΣC_1–5) of high-organic‑sulfur coal is significantly higher than that of low-organic‑sulfur coal. When Easy%R_o ≥ 3.64, the organic sulfur content in coal significantly promotes methane generation. At Easy%R_o = 1.75, small molecules of free organic sulfur are most abundant in coal. At Easy%R_o ≥ 3.64, low and high-organic‑sulfur coals produce elemental sulfur S₈ and ester sulfate compounds. FTIR analysis reveals that high-organic‑sulfur coal contains more aliphatic hydrocarbon structures, resulting in lower aromaticity parameter I than low-organic‑sulfur coal at the same coalification level. In contrast, the hydrocarbon generation potential factor “A” is higher, indicating that organic sulfur inhibits coal aromatization, and high-organic‑sulfur coal has a higher hydrocarbon generation potential. XPS analysis shows that thiophene and sulfoxide are relatively more abundant in high-organic‑sulfur coal, with the highest reaching 91.24 % in SHOS coal. The aromaticity of organic sulfur rapidly increases when Easy%R_o < 1.75, followed by possible inhibition of thiophenic sulfur production by sulfones and sulfoxides in coal, resulting in decreased aromaticity.