Experimental investigation on thermochemical sulfate reduction by H2S initiation
- 作者：Tongwei Zhang ; Alon Amrani ; Geoffrey S. Ellis ; Qisheng Ma ; Yongchun Tang
- 关键词：Scanning electron microscopy ; Etching ; Liquid phase epitaxy ; Selective epitaxy ; Semiconducting allium arsenide
- 刊名：Geochimica et Cosmochimica Acta
- 出版年：2008
- 期刊代码：27_00167037
- 类别：ear
- 出版时间：15 July 2008
- 卷：72
- 期：14
- 页码：3518-3530
- 文件大小：553 K
摘要
Hydrogen sulfide (H2S) is known to catalyze thermochemical sulfate reduction (TSR) by hydrocarbons (HC), but the reaction mechanism remains unclear. To understand the mechanism of this catalytic reaction, a series of isothermal gold-tube hydrous pyrolysis experiments were conducted at 330 °C for 24 h under a constant confining pressure of 24.1 MPa. The reactants used were saturated HC (sulfur-free) and CaSO4 in the presence of variable H2S partial pressures at three different pH conditions. The experimental results showed that the in-situ pH of the aqueous solution (herein, in-situ pH refers to the calculated pH of aqueous solution under the experimental conditions) can significantly affect the rate of the TSR reaction. A substantial increase in the TSR reaction rate was recorded with a decrease in the in-situ pH value of the aqueous solution involved. A positive correlation between the rate of TSR and the initial partial pressure of H2S occurred under acidic conditions (at pH 
3–3.5). However, sulfate reduction at pH 5.0 was undetectable even at high initial H2S concentrations. To investigate whether the reaction of H2S(aq) and 
occurs at pH 3, an additional series of isothermal hydrous pyrolysis experiments was conducted with CaSO4 and variable H2S partial pressures in the absence of HC at the same experimental temperature and pressure conditions. CaSO4 reduction was not measurable in the absence of paraffin even with high H2S pressure and acidic conditions. These experimental observations indicate that the formation of organosulfur intermediates from H2S reacting with hydrocarbons may play a significant role in sulfate reduction under our experimental conditions rather than the formation of elemental sulfur from H2S reacting with sulfate as has been suggested previously (Toland W. G. (1960) Oxidation of organic compounds with aqueous sulphate. J. Am. Chem. Soc. 82, 1911–1916).
3–3.5). However, sulfate reduction at pH 5.0 was undetectable even at high initial H2S concentrations. To investigate whether the reaction of H2S(aq) and 3, an additional series of isothermal hydrous pyrolysis experiments was conducted with CaSO4 and variable H2S partial pressures in the absence of HC at the same experimental temperature and pressure conditions. CaSO4 reduction was not measurable in the absence of paraffin even with high H2S pressure and acidic conditions. These experimental observations indicate that the formation of organosulfur intermediates from H2S reacting with hydrocarbons may play a significant role in sulfate reduction under our experimental conditions rather than the formation of elemental sulfur from H2S reacting with sulfate as has been suggested previously (Toland W. G. (1960) Oxidation of organic compounds with aqueous sulphate. J. Am. Chem. Soc. 82, 1911–1916).