Chemistry of inorganic compounds – Sulfur or compound thereof – Elemental sulfur
Reexamination Certificate
1999-06-17
2001-10-09
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Sulfur or compound thereof
Elemental sulfur
C423S576800, C502S517000
Reexamination Certificate
active
06299851
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.63-67, 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 Taiwanese 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 a rare-earth-containing substance and a vanadium-containing material.
Preferably, the rare-earth containing substance is one selected from a group consisting of scandium (Sc), yttrium (Y), lanthanoid, actinoid, and a compound thereof.
Certainly, lanthanoid includes lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).
Certainly, actinoid includes actinium (Ac), thorium (Th), protactinium (Pa), uranium (U), neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), fermium (Fm), mendelevium (Md), nobelium (No), and lawrencium (Lr).
Preferably, the vanadium-containing material is one selected from a group consisting of metallic vanadium, vanadium oxide, vanadium sulfide, vanadium halogenide, vanadium nitride, vanadium phosphide, vanadium carbide, vanadium carbonyl, vanadium hydride, vanadium hydroxide, vanadium sulfate, vanadium nitrate, vanadium carbonate, vanadium acetate, vanadium oxalate, vanadium formate, vanadium phosphate, vanadium citrate, vanadium oleate, ammonium vanadium oxalate, ammonium vanadium citrate, vanadium hypohalogenate, vanadyl carbonate, vanadyl salicylate, vanadium chromate, ammonium vanadate, and vanadate.
The catalyst can be deposited on a carrier selected from a group consisting of monolith, particle, pellet, and porous carrier, wherein the porous carrier is one selected from a group consisting of alumina, silica, aluminum-and-silicon-containing compound, zeolite, titanium oxide, and zirconium oxide.
The molar ratio of rare-earth element of the rare-earth-containing substance to vanadium atom of the vanadium-containing material is ranged from 0.01:1 to 100:1, preferably from 0.1:1 to 10:1.
In another preferred embodiment of the present invention, the catalyst further includes a promoter for increasing the yield of the elemental sulfur. The molar ratio of the promoter to vanadium and rare earth element of the catalyst is ranged from 0.01:1 to 100:1, preferably from 0.1:1 to 10:1.
The promoter can be metallic antimony, antimony oxide, antimony sulfide, antimony halogenide, antimony carbide, antimony hydroxide, antimony hydride, antimony oxychloride, antimony sulfate, or antimonate.
The oxidizing reaction is performed at a temperature ranged between 50° C. and 400° C., preferably between 100° C. and 350° C.
In addition, the oxidizing reaction is performed at a pressure ranged from 0.1 to 50 atm, preferably 1 to 10 atm.
The present invention will be further illustrated by the following examples.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will now be described more detailedly with reference to the following embodiments. It is to be noted that the following descriptions of the preferred embodiments of this invention are presented herein for the purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.
The present invention provides a method for oxidizing hydrogen sulfide to elemental sulfur, especially for recovering elemental sulfur from a gas mixture containing hydrogen sulfide. This oxidation is performed in the presence of a catalyst including a rare-earth-containing substance and a vanadium-containing material. The oxidation is performed at a temperature ranged from 50° C. to 400 ° C., preferably between 100° C. and 350° C., and under a pressure ranged from 0.1 to 50 atm, preferably 1 to 10 atm.
In our previous studies, we surprisedly found that the yield of sulfur can be greatly increased when a rare-earth containing substance is added to the vanadium-containing catalyst. More specially, the yield of sulfur can be further increased after adding an antimony-containing compound to the above-described mixed catalyst.
REFERENCES:
patent: 4314983 (1982-02-01), Hass et al.
patent: 5653953 (1997-08-01), Li et al.
patent: 5693588 (1997-12-01), Poston
patent: 5700440 (1997-12-01), Li et al.
patent: 5891415 (1999-04-01), Alkhazov et al.
P.F.M.T. van Nisselrooy and J.A. Lagas, “Catalysis Today”, 16, p 263-271, 1993. “Superclaus reduces SO2emission by the use of a new selective oxidation catalyst”.
R. Kettner and N. Liermann,Oil and Gas Journal,86, p. 63-65, Jan. 11, 1988 “New Claus tail-gas process proved in German operation”.
Chi Ren-Hai
Li Kuo-Tseng
Fay, Sharpe, Fagan, Fagan, Minnich & McKee, LLP
Griffin Steven P.
National Science Council
Vanoy Timothy C
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