Electrochemical removal of sulfide ions was achieved in salt water using graphite anodes in an autoclave under high temperatures and pressures, simulating geothermal fluids. The reaction products were characterized using microscopy and X-ray photoelectron spectroscopy (XPS). At low temperatures the reaction rate is quite small. It decreases rapidly with time down to a negligibly small value, which increases only slightly with temperature. The reaction produces elemental sulfur, which was seen under the microscope and identified using XPS. It passivates the electrode and hence diminishes its activity. Above about 115°C, much higher removal rates can be sustained for much longer times, while the increase of temperature has a much stronger effect on the reaction rate. Under this condition, elemental sulfur was no longer detected among the reaction products, while the electrode retained its activity for continuous operation. The XPS spectra at high temperatures reveal the presence of oxygen bearing sulfur species, such as sulfates. The melting of sulfur (at 115°C) has a much stronger effect on the efficiency of the process than the transition of orthorhombic to monoclinic sulfur (at 95°C). A Clausius-Clapeyron's analysis reveals that the melting point of sulfur inside the autoclave is nearly equal to its normal melting point.
A new method was proposed for the application of azole corrosion inhibitors on the surface of copper. This method depends on the vacuum pyrolysis of the inhibitor in the presence of copper specimens. Three azole inhibitors namely; benzotriazole (Azole (1) (2)) and N-[Benzotriazol-1-yl-(4-methoxy-phenyl)-methylene]-N-phenyl-hydrazine (Azole (3)) were tested. After pyrolysis copper samples were electrochemically tested in sulfide polluted salt water and compared to the behavior of copper tested in the sulfide polluted salt water containing dissolved benzotriazole. Results showed that copper specimens treated in the presence of Azoles (2) and (3) exhibit excellent corrosion resistance. Those samples could resist the poisoning effect of sulfide ions. Azole (1) shows good resistance at low sulfide concentration and failed at the high concentration. Surface investigation support the results of electrochemical tests.
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