Chemistry of inorganic compounds – Sulfur or compound thereof – Elemental sulfur
Reexamination Certificate
1999-03-26
2001-06-26
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Sulfur or compound thereof
Elemental sulfur
C423S576800, C502S517000
Reexamination Certificate
active
06251359
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to a method for oxidizing hydrogen sulfide to elemental sulfur, and more particularly to a method for recovering elemental sulfur from a gas mixture containing hydrogen sulfide.
BACKGROUND OF THE INVENTION
In the petroleum refinery process for producing various fuel oil such as gasoline, diesel, kerosene, etc., the sulfur in the crude oil is removed as hydrogen sulfide gas by hydrodesulfurization process. The highly toxic hydrogen sulfide gas is then converted to elemental sulfur in sulfur-recovery plants or so-called Claus plants. During the last two decades, a great number of Claus tail-gas treating (TGT) processes have been developed to increase the total sulfur-recovery efficiency. Conventional Claus TGT processes involve a hydrogen sulfide absorption step, in which a tail gas containing unreacted hydrogen sulfide is introduced into an alkaline bath. Removing the last percentages of sulfur by means of these conventional Claus TGT processes is relatively expensive, both in terms of capital investment cost and energy consumption.
Recently, in order to avoid the shortcomings of these solution-absorption type Claus TGT processes, two dry types of TGT processes have been developed, that is, Mobil-direct-oxidation process developed by Mobil AG Company in Germany (Oil and Gas Journal, 86, p.63, 1988) and Super-Claus Process developed by Comprimo Company in Netherlands (Catalysis Today, 16, p263-271, 1993), both of which comprise a step of recovering elemental sulfur from Claus tail gas by selective oxidation of hydrogen sulfide in the presence of a catalyst. The catalyst used in Mobil-direct-oxidation process contains titanium dioxide (TiO
2
). The catalyst used in Super-Claus Process is an active mixture of iron and chromium oxides deposited on an alpha-alumina support. These dry type Claus TGT processes are simple and economical; however, the chromium atom contained in the catalyst is a toxic substance.
In our experimental studies, it was found that vanadium and magnesium mixed catalyst can effectively oxidize hydrogen sulfide to elemental sulfur (U.S. Pat. No. 5,653,953 and Taiwan Patent Published No. 92615) However, as the content of magnesium in the mixed catalyst is increased, the yield of sulfur will be significantly reduced.
Therefore, a major object of the present application is to improve the defects encountered with the prior arts.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for oxidizing hydrogen sulfide to elemental sulfur.
Another object of the present invention is to provide a method for recovering elemental sulfur from a gas mixture containing hydrogen sulfide.
Another further object of the present invention is to provide a catalyst adapted to be used to oxidize hydrogen sulfide to elemental sulfur.
According to the present invention, the method includes a step of oxidizing hydrogen sulfide to elemental sulfur in the presence of a catalyst including an antimony-containing substance and a vanadium-and-magnesium-containing material.
In accordance with one aspect of the present invention, the antimony-containing substance is one selected from a group consisting of metallic antimony, antimonic oxide, antimonic sulfide, antimonic halogenide, antimonic carbide, antimonic hydroxide, antimonic hydride, antimonous oxychloride, antimonous sulfate, and antimonate. Preferably, the antimony-containing substance is antimonous oxide (Sb
2
O
3
) or antimony tetroxide (&agr;-Sb
2
O
4
).
The vanadium-and-magnesium-containing material is one selected from a group consisting of metallic vanadium and magnesium, vanadium and magnesium oxides, vanadium and magnesium sulfides, vanadium and magnesium halogenides, and a mixture thereof. Preferably, the vanadium-and-magnesium-containing material is magnesium pyrovanadate (Mg
3
V
2
O
8
) or Mg
2
V
2
O
7
.
The vanadium-and-magnesium-containing substance is deposited on a carrier in a form selected from a group consisting of monolith, particle, pellet, and porous carrier. The porous carrier is one selected from a group consisting of alumina, silica, aluminum-and-silicon-containing compound, zeolite, titanium oxide, and zirconium oxide.
Preferably, the molar ratio of antimony of the antimony-containing substance to vanadium and magnesium of the vanadium-and-magnesium-containing material is ranged from 0.01:1 to 100:1, preferably from 0.1:1 to 10:1.
The oxidizing reaction is performed at a temperature ranged between 50° C. and 400° C., preferable 100-350° C.
The oxidizing reaction is performed at a pressure ranged from 0.1 to 50 atm, preferably 1-10 atm.
The present invention will be further illustrated by the following examples.
REFERENCES:
patent: 4444908 (1984-04-01), Hass et al.
patent: 5597546 (1997-01-01), Li et al.
patent: 5653953 (1997-08-01), Li et al.
patent: 5700440 (1997-12-01), Li et al.
patent: 5948382 (1999-09-01), Li et al.
P.F.M.T. van Nisselrooy, et al., “Superclaus Reduces SO2Emission by the Use of a new Selective Oxidation Catalyst,”Catalysis Today,No., 16, Elsevier Science Publishers B.V., 1993, pp. 263-271.
R. Kettner, et al., “New Claus Tail-gas Process Proved in German Operation,”Technology,Oil and & Journal, Jan. 11, 1988, pp. 63-66.
Chi Ren-Hai
Li Kuo-Tseng
Fay Sharpe Fagan Minnich & McKee LLP
Griffin Steven P.
National Science Council
Vanoy Timothy C.
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