Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Carbon dioxide or hydrogen sulfide component
Patent
1983-08-16
1985-10-01
Thomas, Earl C.
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Carbon dioxide or hydrogen sulfide component
423244, 423573R, B01D 5336, C01B 1704
Patent
active
045445346
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process of catalytic desulfurization of an acid gas containing H.sub.2 S, and optionally also a total amount of at most 3% by volume of CS.sub.2 and/or COS, with recovery of these sulfur compounds in the form of sulfur or optionally SO.sub.2.
Various industrial operations give rise to acid gases which contain H.sub.2 S in concentration of at most 15% by volume. The content of H.sub.2 S in such gases is too small to be able to treat them in conventional sulfur plants which comprise as a first stage combustion of the acid gas in a burner. Indeed this combustion is technically feasible only with acid gases whose H.sub.2 S content exceeds 15% by volume. To recover as sulfur the H.sub.2 S contained in acid gases which contain less than 15% of H.sub.2 S by volume, it has been proposed to subject them to a catalytic oxidation in the presence of oxygen or air, using various catalysts.
Thus, in United Kingdom Pat. No. 622,324, there is described a process in which the H.sub.2 S contained in low concentration in an acid gas is oxidized into sulfur by passage of a mixture of the acid gas with a suitable quantity of oxygen or air in contact with a catalyst consisting of an oxide of titanium and particularly orthotitanic acid activated by heating, the contact being effectuated at temperatures between 100.degree. C. and 400.degree. C.
Although of interest, such a process has certain shortcomings. The process particularly calls for the use of an orthotitanic acid which is free of any soluble salt as the catalyst. To obtain such a pure product, several successive operations of neutralization and of washing are necessary which leads to an expensive catalyst. Moreover, the catalyst being constituted exclusively of orthotitanic acid, this results in a selectivity for sulfur which is insufficient for industrial exploitation, and it is necessary to carry out a pre-sulfurization of the catalyst to improve this selectivity, which constitutes an additional step raising the cost of the process.
It has now been discovered that the efficiency of the above-described process can be improved by using a particular catalyst comprising an oxide of titanium associated with an alkaline earth metal sulfate. Such a catalyst provides reliability and increased activity, which permits the oxidation of H.sub.2 S with increased conversion yield and an excellent selectivity for sulfur which has long-term persistence.
The process of the invention for the catalytic desulfurization of an acid gas containing H.sub.2 S and optionally also a total amount of at most 3% by volume of CS.sub.2 and/or COS, with recovery of these sulfur compounds as sulfur and optionally as SO.sub.2, is of the type in which said acid gas is contacted with a controlled quantity of a gas containing free oxygen, preferably as a mixture, with a catalyst based upon titanium oxide, at temperatures between 100.degree. C. and 600.degree. C., and is characterized in that the catalyst, in addition to the titanium oxide, comprises also an alkaline earth metal sulfate, selected from the group consisting of calcium, strontium, barium, and magnesium.
Among the catalysts comprising titanium oxide and an alkaline earth metal sulfate as stated above for use in the inventive process, a preferred catalyst comprises an oxide of titanium and calcium sulfate. Such a catalyst is mechanically exceptionally resistant.
The catalysts comprising titanium oxide and an alkaline earth metal sulfate defined above may contain also up to 30% by weight of a constituent selected from silica, alumina, clays, silicates, titanium sulfate and ceramic fibers.
Among the catalysts used in accordance with the invention, whether they be essentially constituted by titanium oxide and an alkaline earth metal sulfate, or whether they also contain an additional constituent as described above, the weight ratio of titanium oxide, relative to the total weight of the calcined catalyst and expressed as TiO.sub.2, is preferably between about 60% and about 99%, and more preferably between 80%, and
REFERENCES:
patent: 4310497 (1982-01-01), Deschamps et al.
patent: 4399112 (1983-08-01), Voirin
patent: 4422958 (1983-12-01), Dupin
patent: 4427576 (1984-01-01), Dupin
Dupin Thierry
Voirin Robert
Societe Nationale Elf Aquitaine
Thomas Earl C.
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