Study On Direct Electrolysis Of H₂S-loaded Sodium Hydroxide Solution

As a noxious industrial gas, hydrogen sulfide widely exists in the fields of petroleum,chemical industry, metallurgical manufacture and natural gas treating, etc. In the industry, theefficiency of removing hydrogen sulfide by sodium hydroxide solution is high, but theregeneration of sodium sulfide is difficult. Aiming at this problem, a new process nameddirect electrolysis is suggested. In this work, the alkaline solution absorbed with hydrogensulfide was used to prepare sulfur and hydrogen, which would have realistic and significantvalue for environment protection and rational utilization of resource and energy.The electrochemical measure method was employed to investigate the mechanisms ofanode reaction and passivation. Results indicate that the oxidation process of alkaline sulfidemainly includes two stages. At the first stage, hydrogen sulfide ion is oxidized to polysulfide.At the second stage, the oxidation of polysulfide is dominated with the product of sulfur. Thecharacterization of recovered sulfur with XRD and SEM methods showed that the producedsulfur was heavily crystallized and appeared with orthorhombic crystal with bigger particlediameter, which was favorable to solid-liquid separation.Direct electrolysis method was used to recycle sulfur and hydrogen by a self-made plateand frame electrolyzer. Graphite was used as anode and H2S-loaded sodium hydroxidesolution as anolytes; Titanium mesh was used as cathode and sodium hydroxide solution ascatholytes. In order to restrain the anode passivation, reduce the adverse event and increasethe current efficiency, the effects of some parameters on anodic reactions were investigated,such as temperature, pH, initial concentration and current density. Moreover, the appropriateelectrolytic conditions were: temperature of75°C, initial sodium sulfide concentration above 0.5mol/L, current density of10-20mA/cm2. Anode passivation emerges and is graduallyaccelerated when S2is transformed above85%. Therefore, the appropriate electrolysisdegree was obtained with the condition of S2conversion85%.Experiment studies on hydrogen sulfide decompose to sulfur were performed. Theeffects of temperature, gas flow rate and hydrogen sulfide concentration on the reactions ofprecipitated sulfur were investigated. And the solution that precipitated sulfur was circularlyelectrolyzed. Results obtained that, electrolysis show that the change trend of current densityand pH with time are consistent during cyclic electrolysis with three times and the curvesoverlap well, which indicates that the cyclic electrolytic process is feasible.In this study, direct electrolysis method was used to recycle sulfur and hydrogen could besignality and promising.