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In a cyclic hydrogen sulfide oxidation-catalyst regeneration process using an aqueous chelated polyvalent metal catalyst solution, excessive degradation of the aminopolycarboxylic acid chelating agent is prevented by incorporating in the solution an effective amount of a stabilizing agent capable of

In a cyclic hydrogen sulfide oxidation-catalyst regeneration process using an aqueous chelated polyvalent metal catalyst solution, excessive degradation of the aminopolycarboxylic acid chelating agent is prevented by incorporating in the solution an effective amount of a stabilizing agent capable of retarding or preventing rupture of nitrogen-carbon bonds in the chelating agent during oxidative regeneration of the catalyst solution. Alkaline thiosulfates are the preferred stabilizing agents. Particularly good results are obtained using an alkaline thiosulfate stabilizer in a catalyst solution comprising the dimer form of the NTA-iron complex.

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A method of preventing excessive degradation of chelating agent during prolonged continuous operation of a hydrogen sulfide removal process using a chelated polyvalent metal catalyst solution wherein an aqueous solution of a polyvlent metal chelated with at least one chelating agent comprising an am

A method of preventing excessive degradation of chelating agent during prolonged continuous operation of a hydrogen sulfide removal process using a chelated polyvalent metal catalyst solution wherein an aqueous solution of a polyvlent metal chelated with at least one chelating agent comprising an aminopolycarboxylic acid is contacted with a hydrogen sulfide-containing fluid stream to effect oxidation of the hydrogen sulfide to elemental sulfur and concomitant reduction of said polyvalent metal from its higher valence state to its lower valence state, and wherein the catalyst solution is regenerated by contacting said solution with an oxygen-containing gas to oxidize said polyvalent metal from its lower valence state to its higher valence state, and wherein said chelating agent is susceptible to rapid progressive degradation by rupture of nitrogen-carbon bonds during the process, thereby necessitating addition of replacement chelating agent, said method comprising the steps of: incorporating in said catalyst solution an effective concentration of a stabilizing agent sufficient to retard the rate of degradation or to prevent degradation of said aminopolycarboxylic acid chelating agent during operation of the process, said stabilizing agent being selected from the group consisting of alkaline thiosulfates and dihydroxy alcohols having 2 to 3 carbon atoms; and maintaining said effective concentration of said stabilizing agent in said catalyst solution substantially throughout the operation of the process for at least about 170 hours by incorporating additional amounts of stabilizing agent in said solution or withdrawing used solution if and when required.