Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
2000-07-20
2001-08-14
Tran, Hien (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S247000, C208S20800M, C208S248000, C208S244000, C208S299000, C208S243000
Reexamination Certificate
active
06274031
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an improved process for removing hydrogen sulfide from fluid streams. In another aspect, this invention relates to a composition suitable for use in such process. A further aspect of this invention relates to an improved method for the manufacture of a sulfur sorbent suitable for use in the removal of hydrogen sulfide from fluid streams.
The removal of sulfur from fluid streams can be desirable or necessary for a variety of reasons. If the fluid stream is to be released as a waste stream, removal of sulfur from the fluid stream can be necessary to meet the sulfur emission requirements set by various air pollution control authorities. Such requirements are generally in the range of about 10 ppm to 500 ppm of sulfur in the fluid stream. If the fluid stream is to be burned as a fuel, removal of sulfur from the fluid stream can be necessary to prevent environmental pollution. If the fluid stream is to be processed, removal of the sulfur is often necessary to prevent the poisoning of sulfur sensitive catalysts or to satisfy other process requirements.
Traditionally, sulfur sorbents used in processes for the removal of sulfur from fluid streams have been agglomerates utilized in fixed bed applications. Because of the various process advantages from the use of fluidized beds, it can be desirable to utilize a fluidized bed of zinc oxide based sorbent in the removal of sulfur components from fluid streams. There are, however, a number of problems associated with the development of the use of fluidized beds in sulfur sorption that, prior to the discovery of the invention described herein, have not been resolved. Particularly, conventional methods for the production of fluidizable materials have necessarily required spray drying techniques in order to obtain particle sizes in the fluidizable range and to obtain the sufficiently spherically shaped particles thought to be necessary for fluidization. Spray drying techniques, however, have drawbacks due to their relatively high cost and comparatively low production capacity. It would be desirable to have a method for economically producing a fluidizable sorbent material without resort to costly spray drying techniques and to utilize the advantages of a fluidized bed in the removal of sulfur compounds from sulfur-containing fluid streams.
Another concern associated with the use of fluidizable materials is the attrition losses resulting from the fluidized particles colliding with each other and with the equipment walls which define a fluidization zone that contains the fluidized bed. It is desirable to keep attrition losses of the sorbent as low as is possible in order to minimize replenishment of the material and disposal requirements. The attrition resistance of a fluidizable material provides a measure of the weight loss of the fluidizable material when it is used under the harsh operating conditions of a fluidized bed.
While fluidized bed reactors can provide benefits over other types of reactors, such as fixed bed and moving bed reactors, they still present certain disadvantages. Among them are the capital costs associated with the special equipment required for operating fluidized bed reactors. Another disadvantage of the use of fluidized bed systems in sulfur sorption is the need to use diluted air for regeneration of a used sulfur sorbent.
A transport reactor system can be a desirable system for use in the removal of hydrogen sulfide due to the lower capital costs associated with such system. However, the effectiveness of a transport reactor system is substantially dependent upon the sorbent used in the system. The sorbent must have the physical properties that make it circulatable while still having properties suitable for use as a sulfur sorbent. To be circulatable, the sorbent must be able to be fluidized within a fluidization zone by a fluid stream and to be conveyed within such fluidization zone against the force of gravity at high linear velocities, and it must also be circulatable within a transfer zone in the direction of gravity but at linear circulating velocities significantly lower than those within the fluidization zone. Only sorbent particles with certain specific properties are circulatable within a transport reactor system.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide a novel method for economically producing a fluidizable sulfur sorbent material without resort to the use of a spray drying technique.
Another object of this invention is to provide a process for removing hydrogen sulfide from a fluid stream utilizing a fluidized bed of sorbent material.
A further object of this invention is to provide a fluidizable material having an enhanced attrition resistance when utilized in a fluidized bed.
A still further object of this invention is to provide a fluidized bed for recovering sulfur from a fluid stream utilizing a fluidizable material having an enhanced attrition resistance for reducing the loss of fluidizable material due to attrition.
Yet another object of the present invention is to provide a sulfur sorbent that is circulatable within a transport desulfurization process system.
Yet another object of this invention is to provide a transport desulfurization process for removing hydrogen sulfide from a fluid stream by use of a circulatable sorbent material.
Yet still a further object of this invention is to provide a method for making a zinc oxide based sorbent that is circulatable within a transport desulfurization process system.
In accordance with one aspect of the present invention, there is provided a particulate fluidizable sorbent having a mean particle size in the range of from about 20 micrometers to about 500 micrometers and comprising alumina, silica and zinc oxide. The particulate fluidizable sorbent can further have an enhanced attrition resistance by the incorporation of an effective concentration of metal oxide for providing the enhanced attrition resistance.
In accordance with another aspect of the invention, there is provided a method of making a fluidizable, zinc oxide based sorbent material having a mean particle size in the range of from about 20 micrometers to about 500 micrometers and containing alumina, silica and zinc oxide. One embodiment of this method includes the enhancement of the attrition resistance of the fluidizable sorbent material by providing an effective concentration of metal oxide in the fluidizable sorbent for providing an enhanced attrition resistance. This method, among others, can include mixing appropriate proportions of alumina, silica and zinc oxide to form a mixture with the mixture being impregnated with an aqueous solution of a metal containing compound to form an impregnated mixture. The impregnated mixture is agglomerated followed by granulation to provide a granulated material suitable for use as a fluidizable material.
Another aspect of the invention is a process for removing hydrogen sulfide from a fluid stream containing hydrogen sulfide by contacting the fluid stream with a fluidizable, zinc oxide based sorbent material, and recovering a stream having a concentration of hydrogen sulfide lower than that of the hydrogen sulfide containing fluid stream. The fluidizable, zinc oxide based sorbent material can be a fluidizable sorbent comprising particulates having a mean particle size in the range of from about 20 micrometers to about 500 micrometers and comprising alumina, silica and zinc oxide. The fluidizable sorbent can further contain an effective concentration of metal oxide for providing an enhanced attrition resistance of the particulates.
The fluidizable, zinc oxide based sorbent material used in the hydrogen sulfide sorption process include those produced by the novel method for making such sorbent material which includes the provision of an effective concentration of metal oxide in the fluidizable sorbent for providing an enhanced attrition resistance.
One approach to making the fluidizable sorbent having the enhanced attrition resistance includes the step of mixing
Cass Bryan W.
Engelbert Donald R.
Khare Gyanesh P.
Dang Thuan D.
Phillips Petroleum Company
Richmond, Hitchcock, Fish & Dollar
Tran Hien
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