Electrochemical remediation of sulfide in sour brine

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The extraction of natural gas is always accompanied by production of pressurized water, which is contaminated by salts, principally sodium chloride (brine). Frequently, such brines are also contaminated with sulfide; in that case they are known as "sour brines" because of their odour of hydrogen sulfide. Besides being odorous, sour brines are both corrosive and highly toxic, especially when the pressure is released, liberating hydrogen sulfide to the atmosphere (similar to releasing carbon dioxide when a can of pop is opened). One method of disposing of sour brines is reinjection to the ground at a suitable site, but this is expensive because of the need to transport the sour brine from the producer well to the reinjection well without releasing the pressure. The proposed research is based on the electrochemical oxidation of sulfide ion to elemental sulfur, which is environmentally benign. Previous work in our laboratory using synthetic solutions of sodium sulfide and sodium chloride in water has demonstrated that oxidation occurs with excellent chemical efficiency and excellent current efficiency (meaning that the electrical energy is used productively, rather than wasted in parastic reactions such as the electrolysis of water). However, sour brines produced in the field are more complex, principally due to having high concentrations of naphthenic acids, which are ydrocarbon-based carboxylic acids. Our intention is to exploit the surfactant properties of naphthenic acids to enhance electrochemical oxidation by avoiding fouling of the electrode by the elemental sulfur, which is a solid at ambient temperatures.