Patent Application
20130206646
The present invention relates to methods of removing heteroaromatic sulfides from hydrocarbons (e.g. petroleum products such as gasoline and fuel oils), using polyoxometalate catalysts such as H5PV2Mo10O40, or solvates thereof.
The removal of sulfur containing compounds from petroleum products such as gasoline, diesel oil and jet fuel is an important part of the petroleum refining industry. Most sulfur containing compounds are removed by dehydrosulfurization (HDS) where H2 gas is used to form hydrocarbons and H2S.1 Some sulfur containing compounds, in particular heteroaromatic sulfur derivatives such as dibenzothiophene and its alkylated derivatives are refractory towards HDS and require high reaction temperatures and pressures to be effective. Since environmental considerations and requirements mandate the removal of sulfur from fuels, so-called “deep” FIDS of refractory sulfur compounds is both difficult and expensive.
Thus, alternative “deep” desulfurization without H2, or high pressure or temperature is desirable and in recent years, other techniques have been suggested to remove sulfur-containing compounds from commercial fuels. Such alternative techniques include (1) the relatively facile catalytic oxidation of sulfides by hydrogen peroxide or organic hydroperoxides such as tert-butylhydroperoxide to yield sulfones.2,3 Numerous homogeneous and heterogeneous catalysts have been described in the literature for this reaction. The sulfones formed then need be removed from the fuel product by extraction, distillation, decomposition or adsorption. This approach is problematic since organic hydroperoxides are expensive and the use of hydrogen peroxide implies working with water that then requires careful drying of the fuel. Other approaches are (2) selective adsorption of refractory sulfides over solids such as Cu(I)—Y Zeolite,4 or S Zorb SRT5; (3) selective extraction for example, using ionic liquids;6 (4) biodesulfurization; and (5) photooxidation.7
There remains an unmet need for efficient methods for removing sulfide products from hydrocarbons, especially from petroleum products such as gasoline, fuel oils and the like.
The present invention relates to methods for removing heteroaromatic sulfides from hydrocarbon mixtures containing these sulfides (e.g., petroleum products such as crude oil, gasoline, fuel and the like). The methods involve contacting the hydrocarbons with a polyoxometalate catalyst such as H5PV2Mo10O40 or solvates thereof.
The inventors of the present invention have previously reported that polyoxometalate catalysts such as H5PV2Mo10O40 catalyze the electron transfer-oxygen transfer oxidation of sulfides, RSR′ (R, R′=e.g., aryl, alkyl) to yield sulfoxides, RS(O)R′. 8,9 It was contemplated that the reactions take place by initial formation of a cation radical, RSR′+., and a reduced polyoxometalate, H5PVVVIVMo10O40; RSR′+. is then oxygenated by oxygen transfer from the polyoxometalate. It has now been surprisingly found that heteroaromatic sulfides, e.g., thiophene derivatives such as benzothiophene (BT), dibenzothiophene (DBT), 4-methyldibenzothiophene (MDBT) and 4,6-dimethyldibenzothiophene (DMDBT) are not oxygenated to the corresponding sulfoxides, but rather can be oxidatively polymerized by polyoxymetalates such as H5PV2Mo10O40 and its solvates. In some preferred embodiments, the polyoxometalates are supported on an inert solid matrix such as silica or alumina. In other embodiments, the polymer formed is adsorbed or deposited onto the solid support and in this way these heterogeneous catalysts can be used to remove refractory heteroaromatic sulfides from hydrocarbons such as oil, gasoline or fuel products. Conveniently, the catalyst can be regenerated, e.g., by pyrolysis at high temperatures, e.g., 300-350° C. Using such methods, heteroaromatic sulfide derivatives can be aerobically and oxidatively polymerized over polyoxometalate catalysts so as to remove them from hydrocarbons down to non-detectable levels as analyzed by, e.g., gas chromatography with a flame photometric detector (GC-FPD).
Thus, in one embodiment, the present invention provides method for removing heteroaromatic sulfides from a hydrocarbon mixture comprising such sulfides, the method comprising the steps of (a) contacting the hydrocarbon mixture with a polyoxometalate catalyst or a solvate thereof so as polymerize the sulfides; and (b) separating the polymerized sulfides from the hydrocarbon mixture. In another embodiment, the present invention provides a method for polymerizing a heteroaromatic sulfide comprising the step of contacting the sulfide with a polyoxometalate catalyst or a solvate thereof.
In some embodiments, the polyoxometalate catalyst is supported by a solid support that can be, e.g., silica (such as SiO2) or alumina (such as Al2O3). The polymerized sulfides are adsorbed or deposited onto the solid support and in such manner separated from the hydrocarbon mixture.
Polyoxometalate catalysts suitable for use in the present invention are typically polyoxoanion salt represented by the general formula [XxMmOy]q− or a solvate thereof, wherein X is a metal or non-metal heteroatom, or a proton; M are addenda atoms selected from the group consisting of tungsten (W), molybdenum (Mo), niobium (Nb), vanadium (V), tantalum (Ta), bismuth (Bi), antimony (Sb), tin (Sn) and any combination thereof; O is oxygen; x is an integer between 0 and 6; m is an integer between 4 and 200; y is an integer between 5 and 1000; and q is an integer between 0 and 30. Non-limiting examples of such catalysts are provided hereinbelow. In a currently preferred embodiment, the polyoxometalate catalyst is H5PV2Mo10O40 In some embodiments, the polyoxometalate catalyst is not H3PMo12O40. In other embodiments, the polyoxometalate catalyst is not H3PW12O40.
Also, polyoxometalate catalysts are often in solvated forms, for example hydrates. Thus, the present invention encompasses the use of polyoxometalate solvates, such as but not limited to polyoxometalate hydrates. Each possibility represents a separate embodiment of the present invention.
Without wishing to be bound by any particular mechanism or theory, it is contemplated that the polymerization reaction is an electron transfer initiated oxidative polymerization of the heteroaromatic sulfide by the polyoxometalate. Thus, in one embodiment, the polyoxometalate catalyst is an oxidizing catalyst, i.e., it is able to transfer electrons from the heteroaromatic sulfides to the catalyst. An oxidizing catalyst preferably has a minimum oxidation potential, which can vary from catalyst to catalyst. An example of such an oxidizing catalyst is H5PV2Mo10O40 In some preferred embodiments, M is molybdenum (Mo) in a high valence state (i.e., +4, +5 or +6). In other preferred embodiments, M is tungsten (W) in a high valence state (i.e., +4, +5 or +6). In other embodiments, the catalyst may be reoxidized with molecular oxygen. Each possibility represents a separate embodiment of the present invention.
The applicants have found that, in general, molybdates (M=Mo) are more oxidizing than tungstates (M=W), but catalysts comprising both metals can be used in the context of the present invention. Furthermore, insertion of a transition metal such as cobalt can have a positive effect on the activity of the catalyst. For example, Co(III)W12O40 has been found to be active whereas PW12O40 (i.e., H3PW12O40) is not.
In some embodiments, the hydrocarbon mixture is a petroleum product selected from the group consisting of crude petroleum oil, gasoline, diesel oil, fuel oil, jet fuel, kerosene, liquefied petroleum gas (LPG), lubricating oil, paraffin wax, petrochemicals, liquefied coal, gasified coal, liquefied oil shale, gasified oil shale derived from crude oil, coal, natural gas, oil shale, oil sands and tars, as well as mixtures and combinations thereof Each possibility represents a separate embodiment of the present invention. The nature of the heteroaromatic sulfide can vary. In some embodiments, the heteroaromatic sulfide is a thiophene derivative, a thiazole derivative or an isothiazole derivative. Examples of thiophene derivatives include, but are not limited to benzothiophene (BT), dibenzothiophene (DBT), 4-methyldibenzothiophene (MDBT) and 4,6-dimethyldibenzothiophene (DMDBT).
The ratio of catalyst relative to sulfide is preferably between about 1 equivalent of polyoxometalate catalyst to about 3-10 equivalents of sulfide. In one embodiment, the ratio of polyoxometalate to sulfide is about 1 equivalent of polyoxometalate to about 4-5 equivalents of sulfide.
The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the appended figures:
The present invention relates to compositions and methods for removing heteroaromatic sulfides from hydrocarbon mixtures containing these sulfides (e.g., petroleum products such as crude oil, gasoline, fuel and the like). The methods involve contacting the hydrocarbons with a polyoxometalate catalyst such as H5PV2Mo10O40 or solvates thereof. The catalyst may be supported on a solid support (e.g., silica or alumina). The sulfides are oxidatively polymerized and the so formed polymer is deposited or adsorbed onto the solid support, thereby separating the sulfides from the hydrocarbon mixture. The polymer-containing polyoxometalate-solid support matrix can then be separated from the hydrocarbon and the catalyst can conveniently be recycled for additional cycles of reaction.
A variety of polyoxometalate catalysts can be used in the methods of the present invention. In some embodiments, the catalysts are soluble polyoxoanion salts represented by the general formula [XxMmOy]q− or a solvate thereof, wherein X is a metal or non-metal heteroatom, or a proton; M are addenda atoms selected from the group consisting of tungsten (W), molybdenum (Mo), niobium (Nb), vanadium (V), tantalum (Ta), bismuth (Bi), antimony (Sb), tin (Sn) and any combination thereof; O is oxygen; x is an integer between 0 and 6; m is an integer between 4 and 200; y is an integer between 5 and 1000; and q is an integer between 0 and 30. The catalyst is not
One non-limiting class of polyoxometalate catalysts are Keggin compounds represented by the general formula Qq[XM12O40], or a solvate thereof, wherein X is selected from the group consisting of (i) B, Al, Ga, In, Si, Ge, Sn, P, As, Sb, S, Se, Te; (ii) a proton; and (iii) a transition metal selected from Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn; M comprises tungsten (W), molybdenum (Mo) or combinations thereof (but can further comprise additional addenda atoms as defined above), wherein the tungsten and/or molybdenum are in a high valence state such as +4, +5 or +6; Q is a counter cation selected from a proton, an alkali metal, an alkaline earth metal, a transition metal including lanthanides or actinides, a main group metal, and an organic cation such as a quaternary ammonium or phosphonium cation; and q is an integer between 0 and 30. In some preferred embodiments, Q is a proton. In other preferred embodiments, X is phosphorous (P). In other preferred embodiments, X is Cobalt (Co). Each possibility represents a separate embodiment of the present invention. In one embodiment, the polyoxometalate catalyst is not H3PMo12O40. In another embodiment, the polyoxometalate catalyst is not H3PW12O40.
The Keggin structure has an approximate tetrahedral symmetry based on a central XO4 tetrahedron surrounded by twelve MO6 octahedra arranged in four groups of three edge shared octahedra, M3O13. Without wishing to be bound by any particular mechanism or theory, one may distinguish between four kinds of oxygen atoms: 4 internal oxygens connecting the heteroatom to the addenda, 12 edge sharing oxygens, 12 corner sharing oxygens connecting M3O13 units, and 12 terminal oxygens.
In some embodiments, the polyoxometalate catalyst is represented by the general formula Qq[XM12-nM′nO40], or a solvate thereof, wherein X is selected from the group consisting of (i) B, Al, Ga, In, Si, Ge, Sn, P, As, Sb, S, Se, Te; (ii) a proton; and (iii) a transition metal selected from Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn; M is selected from the group consisting of tungsten (W), molybdenum (Mo) and combinations thereof, wherein the tungsten and/or molybdenum are in a high valence state such as +4, +5 or +6; Q is a counter cation selected from a proton, an alkali metal, an alkaline earth metal, a transition metal including lanthanides or actinides, a main group metal, and an organic cation such as a quaternary ammonium or phosphonium cation; q is an integer between 0 and 30, M′ selected from the group consisting of niobium (Nb), tantalum (Ta), antimony (Sb), bismuth (Bi), tin (Sn) and vanadium (V); and n is 0, 1, 2, 3, 4, 5 or 6. In other embodiments, the polyoxometalates are vanadium substituted molybdates represented by the formula Qq[XMo12-nVnO40]. Each possibility represents a separate embodiment of the present invention. In one currently preferred embodiment, the polyoxometalate catalyst is H5PV2Mo10O40 or a solvate thereof. In other embodiments, the polyoxometalate catalyst is not H3PMo12O40In other embodiments, the polyoxometalate catalyst is not H3PW12O40.
Polyoxometalate catalysts are often found in solvated forms, for example hydrates. Thus, the present invention encompasses the use of polyoxometalate solvates, such as but not limited to polyoxometalate hydrates. Other solvate molecules of polyoxometalate catalysts include, but are not limited to diethylether, acetonitrile, dimethylsulfoxide and tetrahydrofuran, solvates, as well as alcoholates (e.g., methanolates and ethanolates) and so forth. The amount of solvate molecules can vary from one to a few hundred. Each possibility represents a separate embodiment of the present invention.
A currently preferred solvated form is a hydrate. Thus, the polyoxometalate catalysts of the present invention may be in the form of a hemihydrate, hydrate, sesquihydrate, dihydrate, trihydrate, or multi-hydrate wherein the number of water molecules can be up to a few hundred. In some embodiments, the polyoxometalate catalyst is a hydrated form of H5PV2Mo10O40, such as H5PV2Mo10O40x35H2O. Generally, the number of water molecules can range from about ½ to about 500 molecules of water. Each possibility represents a separate embodiment of the present invention. In one particular embodiment, the polyoxometalate is H5PV2Mo10O40x35H2O. In another embodiment, the polyoxometalate catalyst is an oxidizing catalyst, i.e., it is able to transfer electrons from the heteroaromatic sulfides to the catalyst.
The polyoxometalate catalysts used in the methods of the present invention can exist in many isomeric forms, non-limiting examples of which are presented in
In some embodiments, the catalyst is linked to a solid support so as to facilitate removal of the polymerized heteroaromatic catalyst by taking advantage of a heterogeneous catalyst system. The nature of the solid support is not particularly limiting. Some examples of solid support include, but are not limited to, silica (e.g., SiO2), alumina (e.g., Al2O3), magnesia, titania, zirconia, montmorillonite, phyllosilicate, zeolites, talc, clays, layered double hydroxides, apatites, and the like. Each possibility represents a separate embodiment of the present invention. Also, combinations of these support materials may be used, for example, silica-chromium, silica-alumina, silica-titania and the like. In one particular embodiment, the solid support is silica (SiO2). In another particular embodiment, the solid support is alumina (Al2O3).
The ratio of catalyst relative to sulfide is preferably between 1 equivalent of polyoxometalate catalyst to about 3-10 equivalents of sulfide. In one embodiment, the ratio of polyoxometalate to sulfide is about 1 equivalent of polyoxometalate to about 4-5 equivalents of sulfide. In another embodiment, the ratio of polyoxometalate to sulfide is about 1 equivalent of polyoxometalate to about 10 equivalents of sulfide. In another embodiment, the ratio of polyoxometalate to sulfide is about 1 equivalent of polyoxometalate to about 6 equivalents of sulfide. In another embodiment, the ratio of polyoxometalate to sulfide is about 1 equivalent of polyoxometalate to about 2 equivalents of sulfide. However, it should be apparent to a person of skill in the art that any ratio of catalyst to sulfide that appears appropriate to a person of skill in the art can be used in the context of the present invention.
A variety of hydrocarbons and hydrocarbon mixtures can be used in the context of the present invention. Basically any hydrocarbon which contains any amount of heteroaromatic sulfides can be used as a substrate for the methods of the present invention.
In some embodiments, the hydrocarbon mixture is a petroleum product. Non-limiting examples of petroleum products are crude petroleum oil, gasoline, diesel oil, fuel oil, jet fuel, kerosene, liquefied petroleum gas (LPG), lubricating oil, paraffin wax, petrochemicals, liquefied coal, gasified coal, liquefied oil shale, gasified oil, shale derived from crude oil, coal, natural gas, oil shale, oil sands and tars, and any combinations thereof. Each possibility represents a separate embodiment of the present invention.
The term “heteroaromatic sulfide”, as used herein, refers to a heteroaromatic system containing one or more sulfur atoms. The heteroaromatic system generally contains 5 or more ring atoms. The heteroaromatic system can be monocyclic, bicyclic, tricyclic and the like. Also included in this expression are the benzoheteroaromatic sulfide and dibenzoheteroaromatic sulfide derivatives. The nature of the heteroaromatic sulfide can vary. The heteroaromatic sulfide may contain, in addition to the sulfur, one or more additional heteroatoms such as O, N etc. In some embodiments, the heteroaromatic sulfide is a thiophene derivative, including benzothiophene and dibenzothiophene derivatives. In other embodiments, the heteroaromatic sulfide is a thiazole derivative, including benzothiazole derivatives. In other embodiments, the heteroaromatic sulfide is an isothiazole derivative, including benzoisothiazole derivatives. In other embodiments, the heteroaromatic sulfide is a thiadiazole derivative, including benzothiadiazole derivatives. In other embodiments, the heteroaromatic sulfide is a thiatriazole derivative, including benzothiatriazole derivatives.
The heteroaromatic sulfide may be unsubstituted or may be substituted by groups such as, but not limited to alkyl, aryl, alkylaryl, cycloalkyl, aryl, heterocyclyl, heteroaryl, halogen, hydroxy, alkoxy, aryloxy, alkylaryloxy, heteroaryloxy, oxo, phenyl, naphthyl, amino, alkylamino, arylamino, heteroarylamino, dialkylamino, diarylamino, alkylarylamino, alkylheteroarylamino, arylheteroarylamino, acyl, acyloxy, nitro, carboxy, carbamoyl, carboxamide, cyano, sulfonyl, sulfonylamino, sulfinyl, sulfinylamino, thiol, alkylthio, arylthio, or alkylsulfonyl groups.
Examples of thiophene derivatives include, but are not limited to thiophene, benzothiophene (BT), dibenzothiophene (DBT), 4-methyldibenzothiophene (MDBT) and 4,6-dimethyldibenzothiophene (DMDBT). Examples of thiazole derivatives include, but are not limited to thiazole, benzothiazole, and dibenzothiazole. Examples of thiadiazole derivatives include 1,2,3 thiadiazoles, 1,2,4 thiadiazoles, 1,2,5 thiadiazoles, 1,3,4 thiadiazolesand benzo-derivatives thereof. Examples of thiatriazole derivatives include 1,2,3,4 thiatriazole, 1,2,3,5 thiatriazole, and their benzo-derivatives thereof. Examples of isothiazole derivatives include, but are not limited to isothiazole, benzoisothiazole, dibenzoisothiazole and the like. Each possibility represents a separate embodiment of the present invention.
The process of the present invention can be used to remove small or large amounts of heteroaromatic sulfides from hydrocarbons. Thus, as little as 1 ppm or as much as 5,000 ppm or even more of heteroaromatic sulfide in a hydrocarbon mixture can be removed by the process of the present invention.
Benzothiophene (84 mM) was reacted with H5PV2Mo10O40 (30 mM) dissolved in acetic acid (1 mL) at 70° C. for 1 h. In contrast to a reaction using thioanisole as substrate,9 no sulfoxide was formed but benzothiophene was almost completely consumed and a brown-black insoluble material was formed. Similarly mixing benzothiophene with H5PV2Mo10O40 at 22° C. yielded a green solution whose UV-vis spectrum indicated the formation of a reduced polyoxometalate, H5PVVVIVMo10O40. Without wishing to be bound by any particular mechanism or theory, it is contemplated that the polymerization reaction is an electron transfer initiated oxidative polymerization of the heteroaromatic sulfide by the polyoxometalate.
A heterogeneous catalyst, 10 wt % H5PV2Mo10O40/SiO2 was prepared by wet impregnation. Thus, H5PV2Mo10O40 (1 gm) prepared according to the literature,' I was dissolved in water (50 mL) and added to silica gel 60, (10 g, Merck, 0.040-0.063 mm, surface area 480-540 m2/g) suspended in water (50 mL). The resulting mixture was stirred at RT for 2 h and the water was then evaporated under vacuum. H5PV2Mo10O40/SiO2 was dried under reduced pressure for 2 h.
In order to test the effectiveness of H5PV2Mo10O40 for removal of refractory heteroaromatic sulfides from hydrocarbons, benzothiophene, dibenzothiophene or 4,6-dimethyldibenzothiophene dissolved in decane were used as model reaction mixtures. A typical reaction procedure for oxidative desulfurization was as follows: 100 mg 10% H5PV2Mo10O40/SiO2, a known amount of sulfide, and 1 mL of decane were placed into 4 mL vial and stirred under air at the appropriate temperature. Analysis of the sulfides was carried out by gas chromatography with a flame photometric detector (GC-FPD) that has high sensitivity for sulfides using a 30 m, 0.32 mm i.d. 5% phenyl methylsilicone column with a 0.25 μm coating using He as eluent.
The results obtained using relatively concentrated solutions (1400 ppm) are presented in Table 1.
a10 mg catalyst.
The results show that using the preferred polyoxometalate, H5PV2Mo10O40, both on silica and alumina supports, sulfides can be polymerized effectively leaving behind sub-ppm amounts of the sulfides. The polymer formed has a brown-black color and covers the catalyst. In a preferred but non-limiting embodiment, the catalyst loading is relatively high relative to sulfide, for example about 4 to 5 equivalents of sulfide per polyoxometalate.
Advantageously, the H5PV2Mo10O40/SiO2 catalyst can be recycled by pyrolysis of the solid under wet oxygen at 300-350° C. for 12 h. The activity of the catalyst is retained over the five cycles tested and the catalyst appeared to be stable, judging from IR spectroscopy.
The catalytic activity of H5PV2Mo10O40/SiO2 for removal of relatively small amounts of heteroaromatic sulfides under mild conditions, e.g., 70° C., was tested on a mixture of 10 ppm each of benzothiophene, dibenzothiophene and 4,6-dimethyldibenzothiophene in decane. The kinetic profile of the disappearance of the sulfides from solution is presented in
As demonstrated, the methods of the present invention are also applicable to the removal of low concentrations of heteroaromatic sulfides from solution even under very mild conditions.
The ability of H5PV2Mo10O40/SiO2 to remove heteroatomic sulfides from actual gasoline was also tested. Thus, 95 octane gasoline containing approximately 15 ppm sulfides was treated with catalyst as noted in the footnote of Table 1. All the sulfides were removed from the gasoline.
Thus, H5PV2Mo10O40/SiO2 is a recyclable catalyst for the removal of heteroaromatic sulfides that are normally refractory to HDS, from hydrocarbons. It is contemplated that the reactions proceed by oxidative polymerization.
While certain embodiments of the invention have been illustrated and described, it will be clear that the invention is not limited to the embodiments described herein. Numerous modifications, changes, variations, substitutions and equivalents will be apparent to those skilled in the art without departing from the spirit and scope of the present invention as described by the claims, which follow.
| Number | Date | Country | Kind |
|---|---|---|---|
| 61408678 | Nov 2010 | US | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IL11/00840 | 10/31/2011 | WO | 00 | 4/23/2013 |
