Mineral oils: processes and products – Refining – Sweetening
Reexamination Certificate
2000-10-05
2003-03-11
Yildirim, Bekir L. (Department: 1764)
Mineral oils: processes and products
Refining
Sweetening
C208S20800M, C208S246000, C208S250000, C502S414000
Reexamination Certificate
active
06531052
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to adsorbents and processes for removing sulfur species from hydrocarbon fluids. More specifically, the invention relates to a regenerable adsorbent comprising alumina and silver oxide for adsorbing sulfur species from refined fuels.
BACKGROUND OF THE INVENTION
Naturally occurring petroleum generally contains varying amounts of sulfur compounds, including mercaptans and thiophenes. Transport of petroleum through a pipeline can also introduce elemental sulfur as an impurity. To avoid corrosion problems associated with elemental sulfur contamination, petroleum refining processes often are designed to convert the elemental sulfur impurities to separable organic disulfides and polysulfides. Sulfur species in liquid fuels have a corrosive effect on brass parts of valves, gauges, and fuel pumps. Also, sulfur species in refined fuels such as gasoline, kerosene, diesel fuel, and jet fuel are objectionable because combustion of the fuel converts sulfur species to sulfur oxides that are released to the atmosphere. Most refining processes change only the form of the sulfur, so that the products may still be objectionable because of their high sulfur content.
As used herein, the term “sulfur species” refers to all forms of sulfur compounds and elemental sulfur appearing in liquid fuels. The sulfur compounds in refined gasoline may include organic disulfides and polysulfides. Varying concentrations of aliphatic thiols, aromatic thiols, thiophenes and benzothiophenes are also present.
Adsorption processes for removing sulfur species from liquid hydrocarbons are known in the prior art. Some patents describing adsorption processes include Jacobson U.S. Pat. No. 4,163,708; Felsky U.S. Pat. No. 4,430,205; Poirier U.S. Pat. No. 5,951,851; and Poirier U.S. Pat. No. 6,027,636. One disadvantage of the known prior art adsorption processes is that their adsorbents are difficult to regenerate in an environmentally acceptable and economical way. Accordingly, there still remains a need for an efficient and economical process for removing sulfur species from hydrocarbon fluids. The need for such process is particularly timely because the U.S. Environmental Protection Agency has proposed new industry standards limiting sulfur content in gasoline, to be implemented in 2004.
A principal objective of the present invention is to provide a process for removing sulfur species from a hydrocarbon fluid, by contacting the fluid with an alumina-containing adsorbent impregnated with silver oxide.
A related objective of the invention is to provide a process for regenerating the alumina and silver oxide adsorbent of our invention.
Additional objectives and advantages of the present invention will become apparent to persons skilled in the art from the following detailed description of a particularly preferred embodiment.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a process for removing at least one sulfur species from a hydrocarbon fluid. The fluid is contacted with a solid adsorbent impregnated with silver oxide.
The hydrocarbon fluid preferably comprises a refined fuel. Examples of such fuels include gasoline, diesel fuel, kerosene, and jet fuel. The refined fuel is generally treated to convert some sulfur species to disulfides and polysulfides. The fuel may contain various amounts of other sulfur species, including elemental sulfur, mercaptans, thiophenes, and benzothiophenes.
The solid adsorbent substrate preferably comprises alumina or alumina combined with at least one other adsorbent selected from zeolite, clay, silica, hydrotalcite, and brucite. Most preferably, the substrate is comprised only of activated alumina. A solid adsorbent substrate comprising about 50-95 wt. % alumina and about 5-50 wt. % zeolite is also suitable. Another suitable solid adsorbent substrate is made with about 25 wt. % sodium Y-zeolite and about 75 wt. % alumina. The substrate preferably has more than about 200 m
2
/g surface area. Additional details of this solid adsorbent substrate are disclosed in Fleming et al. U.S. Pat. No. 4,762,537, the disclosure of which is incorporated herein by reference.
Various shapes of adsorbent substrates are suitable for use in the present invention, including balls, pellets, and irregularly shaped powders. Balls having an average diameter of about 0.2-5 mm are particularly preferred.
The solid adsorbent is prepared for adsorption of sulfur species by impregnating the substrate with an aqueous solution of a water-soluble silver compound, drying the adsorbent, and then oxidizing the silver compound to silver oxide. The water-soluble silver compound may be any water soluble silver salt, such as silver nitrate, silver fluoride, or silver acetate. Silver concentration in the aqueous solution should be about 0.1-2N. A 1N silver nitrate solution is utilized in a particularly preferred embodiment. Silver oxide contents in the solid adsorbent are obtained from elemental analysis using Proton Induced X-ray Emission (PIXE). Silver oxide content in the solid absorbent is about 1-20 wt. %. A particularly preferred solid adsorbent contains between 5 and 10 wt. % silver oxide.
One important advantage of the solid adsorbent described herein is that it can be regenerated easily, with the regenerated adsorbent retaining most of its activity. The used adsorbent is heated to an elevated temperature in an inert atmosphere, for example, an atmosphere containing nitrogen and less than about 1 vol. % oxygen, thereby stripping the sulfur species from the adsorbent without oxidizing them. After the adsorbent is heated in nitrogen it is again heated in an atmosphere containing oxygen, for example in air, thereby oxidizing the silver and removing any remaining sulfur species from the adsorbent. Heating in an oven for about 2 hours at about 500° C. is suitable, both for the step of heating in nitrogen and for the step of heating in air. The regenerated adsorbent retains at least about 70% of the original capacity to remove sulfur, and this regeneration is repeatable. Experimental tests have verified successful regeneration up to at least five cycles.
REFERENCES:
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patent: 4163708 (1979-08-01), Jacobson et al.
patent: 4430205 (1984-02-01), Felsky
patent: 4474896 (1984-10-01), Chao
patent: 4762537 (1988-08-01), Fleming et al.
patent: 5053209 (1991-10-01), Yan
patent: 5454933 (1995-10-01), Savage et al.
patent: 5458861 (1995-10-01), Buchanan et al.
patent: 5951851 (1999-09-01), Poirier et al.
patent: 6027636 (2000-02-01), Poirier
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patent: 6271173 (2001-08-01), Khare
Frye Robert A.
Mophett Elise M.
Rehms Dana L.
Alcoa Inc.
Klepac Glenn E.
Yildirim Bekir L.
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