Removal of hydrogen sulfide from sour water

A continuous process for treating sour water with an aqueous catalyst solution of chelated iron to effect catalytic liquid phase oxidation of dissolved hydrogen sulfide to sulfur by means of dissolved oxygen, wherein said iron is reduced from its ferric state to its ferrous state during said oxidation of hydrogen sulfide, said process comprising:

• providing a recirculating system having a reaction zone for said oxidation of hydrogen sulfide and an interconnected oxygenation zone for introducing oxygen into said catalyst solution, each of said zones having an inlet and an outlet;
• continuously recirculating between said reaction zone and said oxygenation zone a liquid mixture comprising a dilute aqueous catalyst solution containing a catalytic amount of chelated iron such that the liquid mixture has a predetermined iron content selected from the range of from about 0.5 ppm by weight to about 5 ppm by weight;
• introducing sour water feed containing dissolved hydrogen sulfide adjacent said inlet of said reaction zone, and immediately mixing and diluting said sour water feed with a massive excess of oxygenated liquid mixture recirculated from said outlet of said oxygenation zone to said inlet of said reaction zone so as to maintain the molar ratio of dissolved oxygen plus one-half the ferric ion to sulfide ion in said liquid mixture in said reaction zone greater than about 1:1, said mixing and diluting being effected substantially entirely in liquid phase in said reaction zone so that said sour water feed is not contacted with air or gaseous oxygen or a stripping gas capable of stripping dissolved hydrogen sulfide from the liquid mixture until after the sour water has been diluted and has passed through said reaction zone;
• introducing air or other oxygen-containing gas adjacent said inlet of said oxygenation zone, and contacting the air or other oxygen-containing gas with said liquid mixture recirculated from said outlet of said reaction zone under conditions effective to increase the dissolved oxygen content of said liquid mixture and also to oxidize the ferrous iron to its ferric state;
• said zones being separate but contiguous and being in open fluid communication in a common vessel containing said liquid mixture, and said liquid mixture being recirculated between said zones by reason of the density difference between the higher density gas-free liquid mixture in said reaction zone and the lower density gas-containing liquid mixture in said oxygenation zone;
• withdrawing through an overflow extending adjacent said outlet of said oxygenation zone a minor portion of the resultant oxygenated liquid mixture as the sweet water product of the process, substantially the balance of the oxygenated liquid mixture being recirculated from said oxygenation zone to said reaction zone;
• introducing replacement chelated iron into the system adjacent said outlet from said oxygenation zone whereby said replacement chelated iron is rapidly mixed with said liquid mixture being recirculated from said oxygenation zone, the rate of introduction of said replacement chelated iron being sufficient to replace that removed in said sweet water product and to maintain said predetermined iron content in said liquid mixture;
• regulating the sour water feed rate and the sweet water product withdrawal rate to provide a predetermined residence time of the sour water in the system selected from the range of from about 5 to about 120 minutes;
• and
• correlating said predetermined residence time and said predetermined iron content so as to obtain a hydrogen sulfide removal efficiency of at least about 90%.