Treatment Of The PSA Desorbed H₂S With Absorption And Electrolysis In The Solution Of Sodium Sulfide

This article aimed at treating of the PSA desorbed H₂S with absorption and electrolysis in the solution of sodium sulfide. we are trying to explore a new process for removing H₂S from natural gas, with the objective of miniature and cleanliness.In view of such goal and the reusage of H₂S, appropriate conditions of direct electrolysis of H₂S in alkaline solution was first studied. The anodic oxidation of sodium sulfide formed polysulfide ions, whereas the cathodic product was hydrogen, with the electrolyte in the cathode chamber being NaOH. In a double-compartment cell of H type employing ion-exchange membrane as separator, such effects as anolyte concentration, temperature, current density, and pH are discussed. Also the absorption of minor H₂S with sodium sulfide under the optimal conditions for electrolysis was conducted.Electrolytic experiment showed the optimal conditions are as follows: Na₂S concentration of more than 0.50 mol·L^-1, temperature of 55 oC～70oC, current density of 10 mA/cm²ï½ž20 mA/cm² and pH of 13.2 or so. In the original stage, sulfur produced took the form of polysulfides for solving in the anolyte. Only minimal, if any passivation of anode by sulfur product was observed under these conditions. But when the conversion rate of reactant S^2- is above 70%, sulfur would begin to be attached on the anode with the continual electrolysis, accompanied by decreasing of sulfides and the conglomeration of the amount of sulfur in the solution. Then voltage rose, current declined and passivation of the anode became serious. Polysulfide is unstable, so sulfur would separate out in such conditions as being saturated and acidity increase.This made direct electrolysis of H2S become possible.Thus in order to achieve the goal of sucession and steady-going in the electrolysis, it is necessary to discharge the sulfur produced and maintain the high level of S^2- concentration.Absorption results indicated Na₂S solution can fully absorb H2S in natural gas. Based on dual-membrane theory, the control step during absorption and pH limits were given. In order to attain good results, pH value of absorping solution should be more than 8.57.