Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
1999-01-29
2001-05-15
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S219000, C208S238000, C208S226000
Reexamination Certificate
active
06231755
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the reduction in the organic sulfur content of petroleum products.
BACKGROUND OF THE INVENTION
Sulfur-containing compounds are present to a greater or lesser extent in petroleum and in the refined products from petroleum. Organic sulfur compounds are undesirable in petroleum products for several reasons. They can poison catalysts used in petroleum refining. In addition, the greater the amount of organic sulfur compounds in hydrocarbon fuels, such as gasoline and heating oil that are products of refining, the greater the potential for pollution when these fuels are burned. Such pollution can be reduced by treating the emissions, but treatment increases costs, and organic sulfur compounds in automotive exhaust are known poisons for automotive catalytic converters, reducing both their efficiencies and their lifetimes. Though organic sulfur compounds have always been present in petroleum and its products, the problems posed by organic sulfur compounds to refiners and consumers have increased with time. First, the demand for petroleum products is leading to the exploitation of sources of petroleum that had been previously passed over as undesirable because of high organic sulfur content. Second, more stringent environmental regulations are reducing permissible levels of sulfur in emissions and in fuels.
Methods have been developed over the years to deal with the problems posed by organic sulfur compounds in petroleum. These range from simple treatments aimed at rendering less offensive the malodorous sulfur compounds, to more complex processes to reduce or remove the sulfur compounds. The latter include absorption, extraction, oxidation, and hydrodesulfurization. A description of these processes in detail can be found in U.S. Pat. No. 4,383,916. Hydrodesulfurization is the most widely used of these processes and is growing in importance as the demand for fuels with low sulfur content increases. However, hydrodesulfurization is energy intensive, consumes expensive hydrogen gas, and requires high pressure vessels and piping. Furthermore, non-sulfur compounds in the hydrocarbon stream can be changed by hydrogenation or hydrogenolysis, and this is not always desirable. For example, under certain conditions aromatic and olefinic compounds may be hydrogenated.
In an attempt to reduce the organic sulfur concentration in hydrocarbon streams without the undesirable costs and side effects of hydrodesulfurization, acid catalysts have been employed. Acids can react with organic sulfur compounds to convert the sulfur to forms, such as hydrogen sulfide, which can be cheaply and easily removed from petroleum streams. A number of patents have disclosed acidic zeolites as catalysts for desulfurization without the accompanying use of hydrogen gas, for example, U.S. Pat. Nos. 4,383,916, 5,401,391, and 5,482,617. Zeolites are limited, however, because their acid strength is not sufficiently high for effective desulfurization. Furthermore, it can be difficult to remove fouling from the zeolites and their sensitivity to alkali limits the range of cleaning agents that may be used for this purpose.
SUMMARY OF THE INVENTION
The invention describes a process for reducing the organic sulfur content of a hydrocarbon stream by contacting it with an acidic organic polymer. Unlike hydrodesulfurization processes, a hydrogen atmosphere is not necessary to achieve effective desulfurization using the process in accordance with the invention. Preferable polymers for use in accordance with the invention are highly fluorinated, and most preferably are perfluorinated. Organic acidic polymers having sulfonic acid groups are a preferred polymer for use in accordance with the invention.
The preferred processes in accordance with the invention have been found to be especially effective in reducing the amount of intractable organic sulfur compounds in hydrocarbon streams, i.e., organic sulfur compounds not removable by alkaline extraction
In a process in accordance with the invention, the preferred catalysts have long lives, are resistant to fouling because of the low surface energy and chemical inertness characteristic of fluoropolymers, and are easily regenerated because of their resistance to oxidizing agents and to strongly acidic or alkaline conditions.
DETAILED DESCRIPTION
It has been discovered that acidic organic polymers can be contacted with a hydrocarbon stream derived from petroleum at various stages in the process of refining to effectively reduce its organic sulfur content. Even brief exposure at mild temperatures to the preferred acidic organic polymers effects a significant reduction in organic sulfur content of the treated hydrocarbon stream. Such treatment is effective for reducing or eliminating offensive odors and also reducing the organic sulfur components that, though not malodorous, contribute to catalyst poisoning, and to pollution when the hydrocarbon is burned.
Though hydrogen gas may be used in a process in accordance with the invention in combination with the acidic organic polymers, hydrogen gas is not needed for effective desulfurization. Accordingly, it is preferred for the contacting of the hydrocarbon stream with the acidic organic polymer to be performed without supplying hydrogen gas to the hydrocarbon stream. Without the need for hydrogen gas, desulfurization can be achieved economically at lower pressures, and in simpler process equipment than is typically used in hydrodesulfurization processes.
Acidic organic polymers useful for the present invention include polymers with acidic functional groups including sulfonic, carboxylic, phosphonic, imide, sulfonimide and sulfonamide groups. Preferably, polymers containing sulfonic acid groups are used because of their strongly acidic character and ready commercial availability. Various known acidic organic polymers, provided that they are not soluble in the hydrocarbon stream being treated, can be used including polymers and copolymers of trifluoroethylene, tetrafluoroethylene, styrene/divinyl benzene, &agr;,&bgr;,&bgr;-trifluorostyrene, etc., in which acidic functional groups have been introduced. Sulfonated &agr;,&bgr;,&bgr;-trifluorostyrene copolymer is described in U.S. Pat. No. 5,773,480.
Preferred acidic organic polymers are highly fluorinated polymers. “Highly fluorinated” means that at least 90% of the total number of univalent atoms in the polymer are fluorine atoms. Most preferably, perfluorinated acidic organic polymers are used.
In preferred polymers for use in accordance with the invention, the polymers comprise a polymer backbone with recurring side chains attached to the backbone with the side chains carrying the cation exchange groups. In use the polymers should be principally in the acid form, that is, the proton or hydrogen ion form, though some cation exchange groups may be in the salt form, that is, associated with cations other than the proton or hydrogen ion. Especially preferred are polymers in which the side chains are fluorinated as this enhances the acidity of the ion exchange group. Highly fluorinated and perfluorinated acidic polymers for use in accordance with the invention can be homopolymers or copolymers of two or more monomers. Copolymers are typically formed from one monomer that is a nonfunctional monomer and which provides carbon atoms for the polymer backbone. A second monomer provides both carbon atoms for the polymer backbone and also contributes the side chain carrying the cation exchange group or its precursor, e.g., a sulfonyl halide group such as sulfonyl fluoride (—SO
2
F), which can be subsequently hydrolyzed and acid exchanged to a sulfonic acid group. For example, copolymers of a first fluorinated vinyl monomer together with a second fluorinated vinyl monomer having a sulfonyl fluoride group (—SO
2
F) can be used. By fluorinated vinyl monomer is meant a molecule with a carbon-carbon double bond in which there is at least one fluorine atom attached to a carbon atom which is doubly bonded to another carbon atom. Possible first monomers include tetrafluo
Howard Edward G.
Lloyd Ralph Birchard
Mesher Shaun Terrance Einar
E. I. Du Pont de Nemours and Company
Griffin Walter D.
Nguyen Tam M.
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