矿床地球化学国家重点实验室知识库

Elemental sulfur, as a transient intermediate compound, by-product, or catalyst, plays significant roles in thermochemical sulfate reduction (TSR) reactions. However, the mechanisms of the reactions in S–H₂O–hydrocarbons systems are not clear. To improve our understanding of reaction mechanisms, we conducted a series of experiments between 200 and 340 °C for S–H₂O–CH₄, S–D₂O–CH₄, and S–CH₄–1m ZnBr₂ systems in fused silica capillary capsules (FSCCs). After a heating period ranging from 24 to 2160 h (hrs), the quenched samples were analyzed by Raman spectroscopy. Combined with the in situ Raman spectra collected at high temperatures and pressures in the S–H₂O and S–H₂O–CH₄ systems, our results showed that (1) the disproportionation of sulfur in the S–H₂O–CH₄ system occurred at temperatures above 200 °C and produced H₂S, SO₄²⁻, and possibly trace amount of HSO₄⁻; (2) sulfate (and bisulfate), in the presence of sulfur, can be reduced by methane between 250 and 340 °C to produce CO₂ and H₂S, and these TSR temperatures are much closer to those of the natural system (<200 °C) than those of any previous experiments; (3) the disproportionation and TSR reactions in the S–H₂O–CH₄ system may take place simultaneously, with TSR being favored at higher temperatures; and (4) in the system S–D₂O–CH₄, both TSR and the competitive disproportionation reactions occurred simultaneously at temperatures above 300 °C, but these reactions were very slow at lower temperatures. Our observation of methane reaction at 250 °C in a laboratory time scale suggests that, in a geologic time scale, methane may be destroyed by TSR reactions at temperatures >200 °C that can be reached by deep drilling for hydrocarbon resources.