Chemistry of inorganic compounds – Sulfur or compound thereof – Elemental sulfur
Reexamination Certificate
2001-10-09
2003-12-02
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Sulfur or compound thereof
Elemental sulfur
Reexamination Certificate
active
06656445
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to chemical methods for scavenging hydrogen sulfide (H
2
S) from molten sulfur, and more particularly relates, in one embodiment, to methods of inhibiting the evolution of H
2
S from molten sulfur.
BACKGROUND OF THE INVENTION
The removal of H
2
S from various streams is a problem that has challenged many workers in many industries. One such industry concerns streams and quantities of molten sulfur. When sulfur is produced in a refinery it is in a molten or liquid form that is typically stored in pits in the ground or possibly in insulated storage tanks. The reaction of the sulfur with hydrocarbon impurities present in the material and the decomposition of sulfhydryl compounds—typically with the general formula H—S—(S)
x
—S—H— which are also present in the sulfur form hydrogen sulfide. The hydrogen sulfide in turn is a safety and odor problem. The problem may occur at the refinery in their storage pits/tanks or in vessels such as rail cars and tank trucks, which transport the sulfur from the refinery. It is desirable to prevent the evolution of hydrogen sulfide from molten sulfur during storage and/or distribution.
The presence of H
2
S presents many environmental and safety hazards. Hydrogen sulfide is highly flammable, toxic when inhaled, and strongly irritates the eyes and other mucous membranes. Flaring of gas that contains H
2
S does not solve the problem for gas streams because, unless the H
2
S is removed prior to flaring, the combustion products will contain unacceptable amounts of pollutants, such as sulfur dioxide (SO
2
)— a component of “acid rain.”
Hydrogen sulfide has an offensive odor, and natural gas containing H
2
S often is called “sour” gas. Treatments to reduce or remove H
2
S from substrates often are called “sweetening” treatments. The agent that is used to remove or reduce H
2
S levels sometimes is called a “scavenging” agent. The prevention of H
2
S evolution from molten sulfur is only one example of where H
2
S level inhibition, reduction or removal must be performed.
The problem of removing or reducing H
2
S from molten sulfur has been solved in many different ways in the past. Oxidizers such as sodium or calcium hypochlorite or hypobromite have been used as scavengers in liquid sulfur. Air has also been used as an oxidizer to convert H
2
S to elemental sulfur.
Other approaches involve intentionally promoting the evolution or degassing of H
2
S from the molten sulfur. That is, various additives are used to intentionally cause sulfhydryl species such as H—S—(S)
x
—S—H to decompose. The H
2
S formed is then swept away to a vapor recovery system. Once these materials are decomposed, the sulfur is left with reduced potential to form more H
2
S and may be relatively safer to transport. Typical compounds used in such methods contain nitrogen.
U.S. Pat. No. 5,552,060 describes a method for scavenging H
2
S from aqueous and hydrocarbon substrates using an epoxide. Preferred epoxides are styrene oxide, 1,3-butadiene diepoxide, and cyclohexene oxide.
A continuing need exists for alternative processes and compositions to inhibit H
2
S evolving from molten sulfur. It would be desirable if compositions and methods could be devised to aid and improve the ability accomplish this task and do not any disadvantageous impact on the end uses of the sulfur.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method for inhibiting the evolution of H
2
S from the molten sulfur.
It is another object of the present invention to inhibit the evolution of H
2
S from the molten sulfur by adding a readily available scavenging agent to the molten sulfur.
Another object of the present invention is to inhibit the evolution of H
2
S from the molten sulfur without adversely affecting the quality of the sulfur.
In carrying out these and other objects of the invention, there is provided, in one form, a method for inhibiting the evolution of hydrogen sulfide (H
2
S) from molten sulfur involving contacting the molten sulfur contaminated with at least one sulfhydryl compound with an effective amount of a scavenging agent which include anhydrides, conjugated ketones, carbonates, epoxides, monoesters and diesters of unsaturated dicarboxylic acids and/or polymers of these esters, where the scavenging agent is a liquid at ambient temperature.
DETAILED DESCRIPTION OF THE INVENTION
It has been discovered that the scavenging agents of the present invention may be used to treat molten sulfur that contain “sulfhydryl compounds,” such as hydrogen sulfide (H
2
S), organosulfur compounds having at least one sulfhydryl (—SH) group, known as mercaptans, also known as thiols (R—SH, where R is a hydrocarbon group), thiol carboxylic acids (RCO—SH), dithio acids (RCS—SH), and related compounds. Sulfhydryl compounds may also be represented by the very general formula H—S—(S)
x
—S—H.
It will be appreciated that by the term H
2
S evolution inhibition is meant any prevention, suppression, hindrance, impeding, controlling, lowering, diminishing, retarding, abatement, decreasing or other reduction in the amount of H
2
S evolved as compared with the case where a scavenging agent of this invention is not employed. Further, it should be understood that the inventive method is a success as long as H
2
S evolution is reduced or inhibited at least somewhat from the levels that would occur in the absence of the scavenging agent. It is not necessary that H
2
S evolution completely cease for the method of the invention to be considered successful.
The scavenging agents of the present invention may be monoesters and diesters of, anhydrides, conjugated ketones, carbonates, epoxides, and/or unsaturated dicarboxylic acids.
In the case of the epoxides, and without wanting to limit the invention to any particular theory, the epoxide portion of the molecule is believed to react with the sulfhydryl compounds according to the following equation:
Any epoxide should function in the present invention as long as the remainder of the compound does not interfere with this reaction.
Epoxides suitable for use in the present invention generally have the formula:
where R
1
, R
2
, R
3
, and R
4
independently are selected from the group consisting of hydrogen and hydrocarbon groups having between about 1-20 carbon atoms, selected from the group consisting of straight, branched, and cyclic alkyl groups, aryl, alkaryl, and aralkyl groups, and straight, branched, and cyclic alkyl groups substituted with oxygen, heterocyclic alkyls containing oxygen as a ring constituent, wherein R
2
and R
3
may be joined to form a cycloalkyl or a heterocyclic alkyl having oxygen as a ring constituent.
Preferred scavenging agents are those that are liquid at ambient temperature. Thus, in the case of epoxides, ethylene oxide, which is a gas at ambient temperature, would be excluded in this embodiment. Particularly preferred epoxide scavenging agents include, but are not necessarily limited to, styrene oxide, ethylhexyl glycidyl ether, butyl glycidyl ether, butylene oxide, 1-decene oxide, phenyl glycidyl ether, epoxidized fatty acids and esters, and mixtures thereof.
As noted, the epoxide portion of the molecule is believed to be the functional group that actually reacts with the sulfur moiety; therefore, molecules in which the epoxide group is more “accessible” to the sulfur should be more efficient scavengers.
Epoxides suitable for use in the present invention are commercially available from a number of sources. Epoxides also may be readily prepared using well established procedures, such as those described in Morrison and Boyd,
Organic Chemistry
(5th Ed. 1987) pp. 713-715, incorporated herein by reference.
Monoesters and diesters of unsaturated dicarboxylic acids having the formula
have also been found to be useful in inhibiting H
2
S evolution, where R
5
are independently selected from the group consisting of hydrogen, C
1
to C
12
alkyl, alkenyl, aryl and polyhydric alcohol moieties having 1 to 60 carbon atoms, preferably 1-30 carbon atoms. In one non-limiting
Cappel Weldon J.
Roof Glenn L.
Schield John A.
Weers Jerry J.
Baker Hughes Incorporated
Madan Mossman & Sriram P.C.
Silverman Stanley S.
Vanoy Timothy C.
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