Chemistry of inorganic compounds – Sulfur or compound thereof – Elemental sulfur
Patent
1995-05-09
1997-10-28
Straub, Gary P.
Chemistry of inorganic compounds
Sulfur or compound thereof
Elemental sulfur
423224, C01D 1702, C01D 1716
Patent
active
056815409
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the recovery of sulfur from a hydrogen sulfide bearing feedstock. The dissociation of hydrogen sulfide into its constituents of hydrogen and sulfur is an important industrial procedure.
BACKGROUND OF THE INVENTION
Sulfur is an important industrial commodity and one important source of sulfur is "sour gas" which is natural gas containing hydrogen sulfide. It is well known to treat hydrogen sulfide removed from "sour gas" in the natural gas fields of North America. Most of the processes to date produce sulfur and water.
Two prior systems are respectively concerned with thermal or electrochemical dissociation. The thermal dissociation process entails raising the temperature to about 1500.degree. C. and looks very clean until recombination is considered. Electrochemical dissociation with the oxidation of sulfide ion at one electrode and hydrogen reduction at the other electrode looks ideal until the coating of the anode with sulfur causes deactivation.
So far as the electrochemical process is concerned there are a number of interesting publications:
U.S. Pat. No. 3,249,522 (Bolmer-1966) discloses a process for electrolyzing liquid hydrogen sulfide to obtain hydrogen at the cathode and sulfur at the anode. It appears that the efficiency drops precipitously as the sulfur coats the anode.
U.S. Pat. No. 3,409,520 (Bolmer-1968) discloses the use of benzene to dissolve any sulfur which is formed, the benzene being recycled. As is known, benzene residuals in sulfur are unacceptable to users of sulfur. Bolmer also suggested using ammonium hydroxide in place of sodium hydroxide to induce ionization of the hydrogen sulfide, but highly corrosive ammonium polysulfides in water result. Industry has determined that such a process is uneconomic at the moment.
Other patents concerned with electrochemical processes are U.S. Pat. No. 3,150,998 (Reitemeir 1964), U.S. Pat. No. 3,266,941 (Johnson-1966) and U.S. Pat. No. No. 4,544,461 (Venkatesoii-1985). However, it is not known how far the practical use of those inventions has proceeded.
One of the first patents in the electrochemical field is believed to have been U.S. Pat. No. 1,891,974 (Fisher-1932) and this disclosed a combination of chemical and electrochemical processes where, by using potassium ferricyanide, the sulfide was oxidized to sulfur and the solution was then electrolyzed to produce hydrogen.
Iron redox chemistry and indirect electrochemical methods are disclosed in U.S Pat. Nos. 4,443,423, 4,443,424, 4,431,714 and 4,540,561 (Olson, 1984 and 1985). Methods using halogens (chlorine, iodine and bromine molecules or ions) as additives in electrochemical processes are in the public domain by way of technical literature as are high temperature electrochemical methods using molten carbonates as electrolyte. A fuel cell that uses hydrogen sulfide as a fuel and produces power plus some unburned hydrogen has been reported.
Turning now to the thermal dissociation of hydrogen sulfide, it will be appreciated that the method is not thermodynamically favorable until temperatures of 1500.degree. C. are reached and exceeded. Some dissociation does occur at lower temperatures but the rates are low and the recombination rates are rapid even in the presence of catalysts for dissociation of hydrogen sulfide. U.S. Pat. No. 3,962,409 (Kotera et al-1976) teaches that a hot stream of hydrogen sulfide (720.degree.-1070.degree. K) passed over molybdenum sulfide, tungsten sulfide or ruthenium sulfide when the product is cooled in a room temperature trap and recirculated so that multiple cycles will reach a maximum conversion of 80%.
Methods of separation of the dissociated hydrogen by pressure swing adsorption, adsorption, effusion and thermal diffusion are to some extent effective. Patents which have issued on these separation methods are as follows:
Japanese Patent No. 7,899,078 (Kameyama et al 1979) discloses that hydrogen-hydrogen sulfide separation using Vycor, silicon trioxide plus silicon nitride membranes is possible. A syst
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N.G. Vilesov et al., "Recovery of sulfur from waste gases containing sulfur dioxide and hydrogen sulfide," p. 141, (see abstract & SU,A,1 111 985 Vilesov).
R. and O. Ore Processing Ltd.
Straub Gary P.
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