Catalyst for the oxidation of sulfur compounds

Abstract

In a broad form the present invention relates to a method for oxidation of a species comprising sulfur in an oxidation state below +4, such as H.sub.2S, CS.sub.2, COS and S.sub.8 vapor, to SO.sub.2 said method comprising the step of contacting the gas and an oxidant with a catalytically active material consisting of one or more elements taken from the group consisting of V, W, Ce, Mo, Fe, Ca, Mg, Si, Ti and Al in elemental, oxide, carbide or sulfide form, optionally with the presence of other elements in a concentration below 1 wt %, at a temperature between 180° C. and 290° C., 330° C., 360° C. or 450° C., with the associated benefit of such a temperature being highly energy effective, and the benefit of said elements having a low tendency to form sulfates under the conditions, with the related benefit of an increased stability of the catalytically active material. The other elements present may be catalytically active noble metals or impurities in the listed materials.

Claims

1. A method for the oxidation of a gas comprising one or more sulfur species having an oxidation state below +4, and selected from H.sub.2S, CS.sub.2, COS and S.sub.8 vapor to SO.sub.2, said method comprising contacting the gas and an oxidant with a catalytically active material consisting of one or more metal oxides in which the metal is taken from the group consisting of V, W, Ce, Mo, Fe, Ca, and Mg, and one or more supports taken from the group consisting of Al.sub.2O.sub.3 , SiO.sub.2, SiC and TiO.sub.2, and a stabilizing constituent comprising WO.sub.3, optionally in the presence of other elements in a concentration below 1 wt %, at a temperature between 180° C. and 450° C.

2. A method according to claim 1 in which said catalytically active material comprises from 1 wt % to 50 wt % V.sub.2O.sub.5.

3. A method according to claim 2 comprising above 2 wt % to 50 wt % V.sub.2O.sub.5.

4. A method according to claim 1, in which the porous support comprises TiO.sub.2.

5. A method according to claim 1, in which the support comprises SiO.sub.2 as a diatomaceous earth or a highly porous artificial silica.

6. A method according to claim 1, in which said stabilizing constituent comprises from 2 wt % to 50 wt %.

7. A method according to claim 1, in which said catalytically active material comprises a monolithic catalyst substrate comprising one of metal, high silicon glass fibres, glass paper, cordierite and silicon carbide, and a catalyst layer.

8. A method according to claim 7, wherein the monolithic catalyst has a void volume of from 65 vol to % 80 vol %.

9. A method according to claim 7, wherein the catalyst layer has a thickness of 10-150 μm.

10. A method to claim 1, in which said catalytically active material further comprises from 0.01 wt % to 1 wt % of a noble metal.

11. A method to claim 10, in which said noble metal comprises from 0.05 wt % to 1 wt % of one of Pd and Pt.

12. A method according to claim 1 in which the oxidant is O.sub.2 and is present in at least a stoichiometric amount for oxidation of said sulfur containing compounds to SO.sub.2.

13. A method for oxidation of a gas comprising one or more sulfur species selected from H.sub.2S, CS.sub.2, COS and/or S.sub.8 vapor, comprising contacting the gas, an oxidant with a supported catalytically active material at a temperature from 180° C. to 450° C., said catalytically active material consisting of one or more oxides of a metal selected from the group consisting of V, W, Ce, Mo, Fe, Ca, and Mg, and one or more supports taken from the group consisting of Al.sub.2O.sub.3, SiO.sub.2, SiC and TiO.sub.2, said supported catalytically active material further including from 3 wt. % to 50 wt. % of a stabilizing constituent and, optionally less than 1 wt. % of other elements, to convert said sulfur species to SO.sub.2.

Description

EXAMPLE 1

(1) 900 g anatase TiO.sub.2 powder was suspended in 1100 g of a solution of tetra-isopropyl-titanate in butanol containing 4% by weight of Ti and 4% by weight of water. This slurry was mixed thoroughly in a laboratory dissolver in order to secure intimate mixture of the constituents and to break down any agglomerate to be smaller than 400 mesh. An Erichsen Grindometer was used to control this. Glass fibre mats having a thickness of approximately 1 mm were cut to dimensions of approximately 18 by 5 cm. These mats were dipped into the above mentioned slurry to obtain a fully wetted fibre mat. After drying, the material was calcined at 600° C. for 2 hours.

(2) After calcination, the catalyst support material was impregnated with solutions made from NH.sub.4VO.sub.3 and (NH.sub.4).sub.6H.sub.2W.sub.12O.sub.40 and treated at 400° C. in air to give a final catalyst containing 3 wt % V.sub.2O.sub.5 and 3 wt % WO.sub.3, having a void of approximately 75%.

EXAMPLE 2

(3) The catalyst produced according to Example 1 was further impregnated with palladium by suspension in a solution of palladium tetra-ammine bicarbonate in nitric acid. The resulting Pd concentration was approximately 0.35 wt %.

EXAMPLE 3

(4) The unpromoted catalyst prepared according to Example 1 was tested for the oxidation of hydrogen sulfide, H.sub.2S.

(5) A stream of 380 ppm H.sub.2S, and 2.9% O.sub.2 was directed to contact the unpromoted catalyst at temperatures from 172° C. to 212° C. in an oven, with a NHSV of 8600 Nm3/h/m.sup.3. To simplify the evaluation, the relative amount of H.sub.2S found as SO.sub.2 in the product gas is tabulated.

(6) Table 1 shows the results of these examples, according to which the ignition temperature for oxidation of H.sub.2S to SO.sub.2 was found to be around 180° C.

(7) TABLE-US-00001 TABLE 1 Temperature [° C.] S oxidation to SO.sub.2 172 55% 177 82% 182 97% 192 100% 212 100%

EXAMPLE 3

(8) The Pd promoted catalyst produced according to Example 2, was tested for the oxidation of carbon disulfide, CS.sub.2, which produces CO as an intermediate product.

(9) A stream of 904 ppm CS.sub.2, 1769 ppm SO.sub.2, 2.3% H.sub.2O and 17% O.sub.2 was directed to contact the Pd-promoted catalyst at temperatures from 260° C. to 320° C. in an oven with a NHSV of 8800 Nm3/h/m.sup.3.

(10) Under similar conditions the unpromoted catalyst according to Experiment 1 showed a good sulfur oxidation activity, but insufficient carbon monoxide and carbonyl oxidation activity below 400° C.

(11) In Table 2 the experimental results are shown. At 315° C. full oxidation of CS.sub.2 to CO.sub.2 and SO.sub.2 occurs. At lower temperatures some indication of deactivation with respect to CO oxidation was observed but this deactivation was reversible.

(12) TABLE-US-00002 TABLE 2 Promoted catalyst Temperature [° C.] S oxidation to SO.sub.2 C oxidation to CO.sub.2 262 <70% <65% 291 <80% <90% 315 100% 100%