Catalytic desulfurization process of an acid gas containing H.sub.2 S

The process of catalytic desulfurization of an acid gas comprising H.sub.2, and optionally a total amount of at most 3% by volume of CS.sub.2 and/or COS, so that the total content, called potential content of H.sub.2 S, of free H.sub.2 S and of H.sub.2 S theoretically available from any CS.sub.2 and COS that may be present in the acid gas in above about 5% by volume, with the recovery of sulfur, wherein said acid gas is treated by the steps of:

• passing said acid gas through a plurality of catalytic zones in series comprising a first catalytic zone and a last catalytic zone, optionally separated by one or more intermediate catalytic zones, each of said first and intermediate zones containing said catalyst which is calcined, whereas at least the final 1/8 of the catalyst used in the last catalytic zone consists of a catalyst comprising a support containing a major weight proportion of alumina, said support having a specific surface between 30 and 300 m.sup.2 /g and containing a quantity of a metal compound corresponding to a total quantity of metal ranging from 0.5 to 10% by weight of the calcined catalyst, the optional supplemental portion of the catalyst in the last catalytic zone being constituted of the catalyst based on oxide of titanium and sulfate of alkaline earth metal,
• injecting into each said catalytic zone, a quantity of gas containing free oxygen such that the proportion of oxygen entering each of the first and intermediate catalytic zones represents 0.7 to 1.2 times that which is theoretically necessary to convert into sulfur a quantity of potential H.sub.2 S representing from 3 to 5% by volume of the acid gas,
• adjusting the temperatures of the gases entering each of the catalytic zones to values ranging from 180.degree. C. to 350.degree. C.,
• maintaining in each zone a contact time between reaction gases and catalyst between 1 and 6 seconds,
• treating the gaseous effluent from each first and intermediate catalytic zone to separate the sulfur which it contains by condensation and directing said effluent freed of sulfur toward the inlet of the next catalytic zone,
• adjusting the molar ratio of O.sub.2 to potential H.sub.2 S at the inlet of the last catalytic zone to obtain an effluent containing H.sub.2 S and SO.sub.2 in a molar ratio of H.sub.2 S to SO.sub.2 equal to about two to one, then
• subjecting the gaseous effluent from the last catalytic zone, after separation of the sulfur which it contains, to a regenerative purification process utilizing the sulfur forming reaction of H.sub.2 S and SO.sub.2 in contact with a conventional CLAUS catalyst based on alumina, at temperatures between 80.degree. C. and 160.degree. C., said catalyst, when it is saturated with sulfur, being regenerated by sweeping it with a gas free of free oxygen at a temperature between 200.degree. and 400.degree. C.