Patent ID: 7655211

Claim:
A process for producing ammonium thiosulfate comprising: (a) contacting, in a first contact zone, a first gaseous feed stream comprising ammonia and hydrogen sulfide with a first liquid stream comprising ammonium thiosulfate and ammonium sulfite, wherein a portion of the ammonium sulfite is converted to ammonium thiosulfate upon contact with the first gaseous feed stream, the first contact zone producing a first contact zone effluent liquid stream comprising ammonium thiosulfate and a first contact zone overhead gas stream comprising hydrogen sulfide and ammonia; (b) contacting, in a second contact zone, a second gaseous feed stream comprising ammonia and hydrogen sulfide with a second liquid stream comprising ammonium thiosulfate and ammonium sulfite, wherein a portion of the ammonium sulfite is converted to ammonium thiosulfate upon contact with the second gaseous feed stream, the second contact zone producing a second contact zone effluent liquid stream comprising ammonium thiosulfate and ammonium sulfite with a sufficient concentration of sulfite to act as a buffer to keep the pH low enough to dissolve essentially all of the ammonia from the second gaseous feed stream and a second contact zone overhead gas stream comprising hydrogen sulfide and essentially free of ammonia, (c) removing a first portion of the first contact zone effluent liquid stream to form a product liquid stream; (d) combining the second contact zone effluent liquid stream with a second portion of the first contact zone effluent liquid stream to produce a third liquid stream; (e) contacting the third liquid stream with a third gaseous feed stream comprising sulfur dioxide in a third contact zone, wherein a portion of the sulfur dioxide is converted to ammonium sulfite upon contact with the third liquid stream, the third contact zone producing a third contact zone effluent liquid stream comprising ammonium thiosulfate and ammonium sulfite and a third contact zone overhead gas stream comprising ammonia and sulfur dioxide; (f) feeding a first portion of the third contact zone effluent liquid stream to the first contact zone as the first liquid stream; and (g) feeding a second portion of the third contact zone effluent liquid stream to the second contact zone as the second liquid stream.