Kinetics of uncatalyzed thermochemical sulfate reduction by sulfur-free paraffin
Kinetics of uncatalyzed thermochemical sulfate reduction by sulfur-free paraffin
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DOI：
10.1016/j.gca.2012.08.010
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发表时间：
2012-11
影响因子：
5
通讯作者：
Tongwei Zhang;Geoffrey S. Ellis;Qisheng Ma;A. Amrani;Yongchun Tang
中科院分区：
文献类型：
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作者：
Tongwei Zhang;Geoffrey S. Ellis;Qisheng Ma;A. Amrani;Yongchun Tang
为了确定在初始不存在低价硫的情况下碳氢化合物（HC）还原硫酸盐的动力学参数，我们在24.1MPa的恒定约束压力下在320、340和360℃下进行了一系列等温金管水热解实验。所用反应物由饱和 HC（无硫）和 CaSO4 水溶液组成，缓冲至三种不同的 pH 条件，不添加元素硫 (S8) 或 H2S 作为引发剂。反应过程中产生的H2S与最初唯一的含硫反应物CaSO4的还原程度成正比。我们的结果表明，水溶液的原位pH（这里，原位pH是指在一定实验条件下计算出的水溶液的pH值）可以显着影响热化学硫酸盐还原（TSR）反应的速率。随着原位 pH 值的降低，TSR 反应速率显着增加。我们的实验结果表明，非催化 TSR 是一级反应。实验测量的硫酸盐还原产生的 H2S 产率的温度依赖性符合阿伦尼乌斯方程。在我们的实验中，在 pH 值范围为 3.0 至 3.5 时，确定 HC（无硫）与 HSO4 反应的活化能为 246.6kJ/mol，略高于使用从头计算类似反应的量子化学计算得到的理论值 227.0kJ/mol。尽管活性硫酸盐的可用性显着影响反应速率，但通过考虑 HSO4−离子浓度来确定一致的速率常数。通过重新评估几个已发表的实验 TSR 数据集（最初不存在天然硫或 H2S），进一步验证了我们确定 TSR 动力学的实验和理论方法。当适当考虑活性硫酸盐浓度的影响时，已发表的实验 TSR 数据产生与我们的值一致的动力学参数。假设 MgSO4 接触离子对 ([MgSO4]CIP) 是石油储层地层水中硫酸盐的反应形式，我们通过实验得出的 HSO4−还原动力学作为 [MgSO4]CIP 的代理，进行简单外推到地质上合理的条件，预测起始温度 (130–140°C) 与在自然界中观察到的温度相当。
To determine kinetic parameters of sulfate reduction by hydrocarbons (HC) without the initial presence of low valence sulfur, we carried out a series of isothermal gold-tube hydrous-pyrolysis experiments at 320, 340, and 360°C under a constant confined pressure of 24.1MPa. The reactants used consisted of saturated HC (sulfur-free) and CaSO4in an aqueous solution buffered to three different pH conditions without the addition of elemental sulfur (S8) or H2S as initiators. H2S produced in the course of reaction was proportional to the extent of the reduction of CaSO4that was initially the only sulfur-containing reactant. Our results show that the in situ pH of the aqueous solution (herein, in situ pH refers to the calculated pH value of the aqueous solution at certain experimental conditions) can significantly affect the rate of the thermochemical sulfate reduction (TSR) reaction. A substantial increase in the TSR reaction rate was observed with a decrease in the in situ pH. Our experimental results show that uncatalyzed TSR is a first-order reaction. The temperature dependence of experimentally measured H2S yields from sulfate reduction was fit with the Arrhenius equation. The determined activation energy for HC (sulfur-free) reacting with HSO4-in our experiments is 246.6kJ/mol at pH values ranging from 3.0 to 3.5, which is slightly higher than the theoretical value of 227.0kJ/mol using ab initio quantum chemical calculations on a similar reaction. Although the availability of reactive sulfate significantly affects the rate of reaction, a consistent rate constant was determined by accounting for the HSO4−ion concentration. Our experimental and theoretical approach to the determination of the kinetics of TSR is further validated by a reevaluation of several published experimental TSR datasets without the initial presence of native sulfur or H2S. When the effect of reactive sulfate concentration is appropriately accounted for, the published experimental TSR data yield kinetic parameters that are consistent with our values. Assuming MgSO4contact-ion-pair ([MgSO4]CIP) as the reactive form of sulfate in petroleum reservoir formation waters, a simple extrapolation of our experimentally derived HSO4−reduction kinetics as a proxy for [MgSO4]CIPto geologically reasonable conditions predicts onset temperatures (130–140°C) that are comparable to those observed in nature.