Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Carbon dioxide or hydrogen sulfide component
Reexamination Certificate
2000-09-15
2002-11-26
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Carbon dioxide or hydrogen sulfide component
C423S224000, C423S232000, C423S233000, C423S576400, C423S576500
Reexamination Certificate
active
06485697
ABSTRACT:
BACKGROUND OF THE INVENTION
With an increasing concern over the pollution in the atmosphere, there is a great burden placed on industry to produce environmentally safe products and to do so in an environmentally safe manner. An area that has been of particular concern is the release of sulfur and sulfur compounds into the atmosphere during the refining of petroleum, the sweetening of natural gas, the processing of ore, the destructive distillation of coal, and other processes which produce sulfur containing gases.
The presence of significant quantities of hydrogen sulfide (H
2
S) and carbon dioxide (CO
2
) in various “sour” industrial gaseous streams poses a persistent problem. Although there are various procedures that have been developed to remove and recover these contaminants, these procedures are deficient in some way or another. For example, one process that has been developed utilizes aqueous alkaline solutions to absorb H
2
S from a gas stream and to convert the absorbed H
2
S to elementary. sulfur. Generally, this type of a process utilizes an aqueous alkaline solution containing vanadium ions and anthraquinone disulfonate, i.e., acid (ADA). This particular type of process, however, only works with dilute aqueous solutions and low H
2
S loading. A dilute aqueous solution is required because when higher concentrations are used, sufficient levels of vanadium that oxidize the sulfur compounds can not be maintained in solution. Low concentrations, however, result in high circulation rates, large capital investments, and higher production costs. In addition, a dilute aqueous alkaline solution is not capable of CO
2
removal.
Another problem associated with these processes is the breakdown and disposal of the ADA, an additive used in this type of process. The breakdown and disposal of this compound and compounds similar to it is difficult and expensive. Thus, adding ADA and/or ADA-like compounds actually increase the cost associated with this type of process.
Accordingly, there is a need for an improved process to control the removal of H
2
S and C0
2
from various “sour” gases in an economical and environmentally safe way. The improved process should be capable of removing H
2
S and CO
2
with solutions having adequate H
2
S loads without using harmful additives like ADA or ADA-like compounds. The present invention is directed to such an improved process.
SUMMARY OF THE INVENTION
The present invention relates to a process for the removal of minor sulfur compounds—mainly H
2
S and CO
2
from a gaseous mixture that contains the same. Examples of a gaseous mixture include natural gas, iron ore reduction gas, etc. The process contacts a sour gas mixture with an aqueous alkaline solution comprising an oxidizing agent in a 10 to 1 molar ratio of an oxidizing agent to H
2
S gas. The oxidizing agent is contacted with the gaseous mixture at a temperature of about 150 degrees F. to about 300 degrees F. so that the gaseous mixture is absorbed into the aqueous alkaline solution.
Once absorbed, H
2
S is oxidized by vanadium ions present in the aqueous alkaline solution into elementary sulfur. The elementary sulfur is removed from the aqueous mixture to produce an aqueous alkaline solution having less sulfur than the initial gaseous mixture absorbed into the aqueous alkaline solution. After H
2
S is removed from the aqueous alkaline solution as elementary sulfur, CO
2
is stripped from the aqueous alkaline solution to produce an aqueous alkaline solution containing less H
2
S and less CO
2
than the initial gaseous mixture absorbed into the aqueous alkaline solution.
The aqueous alkaline solution used in the process described above comprises about 15% to about 40% by weight of K
2
CO
3
, up to about 10% by weight of V
2
O
5
, and up to about 10% by weight of equivalent H
3
BO
3
The pH of the aqueous alkaline solution is buffered at a pH below 10 and the pressure is maintained above atmospheric pressure. The pressure and temperature ranges maintained keep a more concentrated alkaline solution and, therefore, help to maintain the tetravalent vanadium ions from V
2
O
5
, above 65% of the total vanadium ions in the aqueous solution. This high percentage of tetravalent vanadium ions facilitates regeneration of spent V
+5
and, thus complete oxidization of the sulfur compounds in the aqueous gaseous mixture without the use of additives like ADA and/or ADA-like compounds.
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patent: 4430312 (1984-02-01), Eickmeyer
patent: 4434143 (1984-02-01), Weber
patent: 4434145 (1984-02-01), Weber
patent: 4460554 (1984-07-01), Shafer
patent: 4537752 (1985-08-01), Weber
patent: 4871468 (1989-10-01), Jeffrey
patent: 4921682 (1990-05-01), De Haan et al.
patent: 0 066 306 (1982-12-01), None
Kohl et al. “Gas Purification” (4th ed.) Gulf Publishing Co. Houston TX USA, ISBN 0-87201-314-6, pp. 190-195 (1985).
Bryan Cave LLP
Eickmeyer & Associates
Silverman Stanley S.
Vanoy Timothy C.
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