Process for producing hydrogen and sulfur from hydrogen sulfide

Claim 1

A process for producing hydrogen and sulfur from hydrogen sulfide, which comprises: (a) contacting hydrogen sulfide and iodine in a molar excess of said hydrogen sulfide with respect to said iodine, in an aqueous solution of hydriodic acid containing from 50 to about 20% by weight of hydrogen iodide, at a temperature of from 10° to 80° C and at a pressure equal to or higher than atmospheric, thereby to convert said iodine into hydrogen iodide and form sulphur by reaction between said iodine and hydrogen sulfide, the amount of iodine being such as to obtain an aqueous suspension of sulphur, containing in dissolved form unreacted hydrogen sulfide, having a content of hydrogen iodide not exceeding 50% by weight; (b) recovering said sulphur from said suspension; (c) desorbing hydrogen sulfide from the resulting solution and recycling said desorbed hydrogen sulfide to stage (a); (d) rectifying in a distillation column the residual solution obtained in (c), at superatmospheric pressure, thereby to recover hydrogen iodide at the top and an aqueous solution of hydriodic acid at the bottom, said aqueous solution having a content of hydrogen iodide equal to or higher than that of the water-hydrogen iodide azeotrope at the operating pressure, and recycling said aqueous solution of (d) to stage (a); (e) forming hydrogen and iodine by thermal dissociation of the hydrogen iodide recovered in (d), at a temperature of at least 400° C and a pressure of at least 10 atmospheres, while removing hydrogen from the resulting mixture by diffusion through one or more membranes of palladium alloy and recovering said hydrogen having diffused, recovering iodine from the resulting residual mixture and recycling said recovered iodine to stage (a).