WO2013052102A1 - Oxidation catalysts derived from heteropoly acids and quaternized nitrogen compounds, methods for synthesis and activation thereof, and methods for use thereof - Google Patents

Abstract

Oxidation catalysts can be prepared from heteropoly acids and quaternized nitrogen compounds. The oxidation catalysts can be used in oxidation processes such as oxidative desulfurization, for example. Such oxidative desulfurization processes can comprise: providing an oxidation catalyst comprising a solid reaction product obtained from a reaction between a quaternized nitrogen compound and a heteropoly acid that has been at least partially neutralized with a base, the solid reaction product having a molar ratio of an alkali metal to phosphorus of less than about 1; combining the oxidation catalyst with an oxidizing agent and a petroleum source comprising an oxidizable sulfur compound; reacting at least a portion of the oxidizable sulfur compound to form an oxidized sulfur compound; and removing the oxidized sulfur compound from the petroleum source to form a reduced sulfur content petroleum product.

Description

OXIDATION CATALYSTS DERIVED FROM HETEROPOLY ACIDS AND QUATERNIZED NITROGEN COMPOUNDS, METHODS FOR SYNTHESIS AND

ACTIVATION THEREOF, AND METHODS FOR USE THEREOF

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priority of United States Provisional

Patent Application 61/542,496, filed on October 3, 2011, which is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR

DEVELOPMENT

[0002] Not applicable.

BACKGROUND

[0003] The present disclosure generally relates to oxidation catalysts derived from heteropoly acids and quaternized nitrogen compounds, and, more specifically, to desulfurization methods using the oxidation catalysts and desulfurized products made therefrom.

[0004] Many forms of sulfur are commonly present in crude oil. Sulfur can be present in the form of hydrogen sulfide, in which case the crude oil is commonly referred to as sour gas. In other instances, sulfur-containing organic compounds such as mercaptans and thiophenes can be present. If not removed during the refining process, residual sulfur-containing compounds can present significant health and environmental issues when the refined product is combusted.

[0005] Hydrorefining processes can be used in some instances to transform certain sulfur-containing organic compounds to hydrogen sulfide in order to affect their removal. This process can be highly energy intensive and costly. Furthermore, the environmental and health impacts of the produced hydrogen sulfide cannot be ignored. In addition, thiophenes, particularly benzothiophene and dibenzothiophene, are generally not efficiently removed through hydrorefining processes.

[0006] Oxidative desulfurization processes can be used as an alternative to or in combination with hydrorefining processes in order to better reduce organic sulfur levels during refining. Oxidative desulfurization processes involve converting sulfur-containing organic compounds to a higher oxidation state, such as a sulfoxide or a sulfone. The higher oxidation state sulfur- containing organic compounds are generally more polar than are the parent sulfur-containing organic compounds, which can make them more easily removable from a petroleum source than are the parent sulfur-containing organic compounds. In the case of thiophenes, the higher sulfur oxidation state is generally a thiophene sulfone, which can oftentimes be separated from residual hydrocarbons by a combination of precipitation, adsorption, and/or extraction.

[0007] Oxidative desulfurization can be conducted in a biphasic or emulsion-type reaction mixture using a phase transfer catalyst. In particular, phase transfer catalysts formed as a reaction product of quaternary ammonium salts and heteropoly acids such as, for example, phosphomolybdic acid, phosphotungstic acid, silomolybdic acid and silotungstic acid can be used to promote the oxidation of thiophene compounds. Many times, catalysts of the form Q₃PW12O₄0 (Q = a cation containing a quaternized nitrogen atom) have been prepared in situ as a direct reaction product of a heteropoly acid and a quaternary ammonium salt, although there are limited instances detailing the preparation of such catalysts in solid form. Catalysts containing a PWn0₃9^7" anion have also been prepared from sodium tungstate/sodium dihydrogen phosphate or ammonium metatungstate/sodium phosphate under various pH conditions.

SUMMARY

[0008] The present disclosure generally relates to oxidation catalysts derived from heteropoly acids and quaternized nitrogen compounds, and, more specifically, to desulfurization methods using the oxidation catalysts and desulfurized products made therefrom.

[0009] In some embodiments, the present invention provides methods comprising : providing an oxidation catalyst comprising a solid reaction product obtained from a reaction between a quaternized nitrogen compound and a heteropoly acid that has been at least partially neutralized with a base, the solid reaction product having a molar ratio of an alkali metal to phosphorus of less than about 1; combining the oxidation catalyst with an oxidizing agent and a petroleum source comprising an oxidizable sulfur compound; reacting at least a portion of the oxidizable sulfur compound to form an oxidized sulfur compound; and removing the oxidized sulfur compound from the petroleum source to form a reduced sulfur content petroleum product. [0010] In some embodiments, the present invention provides methods comprising : forming a partially neutralized heteropoly acid at a pH ranging between about 2 and about 7; combining the partially neutralized heteropoly acid with a quaternized nitrogen compound in an aqueous reaction medium; reacting the partially neutralized heteropoly acid and the quaternized nitrogen compound in the aqueous reaction medium to form a solid reaction product that precipitates from the aqueous reaction medium; and isolating the solid reaction product.

[0011] In some embodiments, the present invention provides oxidation catalysts comprising : a solid reaction product obtained from a reaction between a quaternized nitrogen compound and a heteropoly acid that has been at least partially neutralized with a base, the solid reaction product having a molar ratio of an alkali metal to phosphorus of less than about 1.

[0012] In some embodiments, the present invention provides methods comprising : providing an oxidation catalyst comprising a solid reaction product obtained from a reaction between a quaternized nitrogen compound and a heteropoly acid that has been at least partially neutralized with a base; combining the oxidation catalyst with an oxidizing agent in the absence of an oxidizable compound; after combining the oxidation catalyst and the oxidizing agent, combining a petroleum source comprising an oxidizable sulfur compound with the oxidation catalyst and the oxidizing agent; reacting at least a portion of the oxidizable sulfur compound to form an oxidized sulfur compound; and removing the oxidized sulfur compound from the petroleum source to form a reduced content sulfur petroleum product.

[0013] In some embodiments, the present invention provides methods comprising : providing an oxidation catalyst comprising a solid reaction product obtained from a reaction between a quaternized nitrogen compound and a heteropoly acid; combining the oxidation catalyst with an oxidizing agent in the absence of an oxidizable compound; after combining the oxidation catalyst and the oxidizing agent, combining a petroleum source comprising an oxidizable sulfur compound with the oxidation catalyst and the oxidizing agent; reacting at least a portion of the oxidizable sulfur compound to form an oxidized sulfur compound; and removing the oxidized sulfur compound from the petroleum source to form a reduced sulfur content petroleum product. [0014] The features and advantages of the present invention will be readily apparent to one having ordinary skill in the art upon a reading of the description of the preferred embodiments that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The following figures are included to illustrate certain aspects of the present invention, and should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to one having ordinary skill in the art and having the benefit of this disclosure.

[0016] FIGURE 1 shows an illustrative titration curve of phosphotungstic acid with a standardized sodium hydroxide solution.

[0017] FIGURE 2 shows a generalized apparatus for making a catalyst from a quaternized nitrogen compound and a partially neutralized heteropoly acid.

[0018] FIGURE 3 shows a chart summarizing the catalytic activity of the oxidation catalyst obtained following partial neutralization of phosphotungstic acid with 3, 4.5, 6 and 7.8 equivalents of NaOH over 8 catalyst recycling operations.

[0019] FIGURES 4A - 4E show illustrative FTIR spectra of phosphotungstic acid, Comparative Samples 1A and IB, and catalysts from Table 11.

[0020] FIGURE 5 shows stacked illustrative ³¹P MAS NMR spectra of phosphotungstic acid, Comparative Samples 1A and IB, and the catalysts from Table 11.

DETAILED DESCRIPTION

[0021] The present disclosure generally relates to oxidation catalysts derived from heteropoly acids and quaternized nitrogen compounds, and, more specifically, to desulfurization methods using the oxidation catalysts and desulfurized products made therefrom.

[0022] Of the heteropoly acids, phosphotungstic acid (H₃PWi₂0₄o) is the strongest acid and is fully deprotonated at a pH of less than about 2. The structure of phosphotungstic acid, as well as that of other heteropoly acids, is commonly known as the lacunary Keggin structure. The Keggin structure of phosphotungstic acid contains a cluster of tungsten atoms octahedrally coordinated to oxygen atoms with both terminal and bridging oxygen atoms present about the central phosphorus atom. Above a pH of about 2, phosphotungstic acid begins to revert to various other species, and at a pH of about 8.3, hydrogen phosphate ions and tungstate ions are formed. At a pH between about 2 and about 7, phosphotungstic acid loses one tungsten atom and one oxygen atom to form PW₁1O3₉ ^7" (commonly referred to as the monovalent lacunary Keggin structure), which subsequently decomposes to PW9O3₄ ^9" (commonly referred to as the trivalent lacunary Keggin structure) at even higher pH values. Tungstate ions are formed during decomposition. The overall base-promoted decomposition of phosphotungstic acid to tungstate is described by Formula (1), where 23 equivalents of hydroxide ions are needed to affect full decomposition.

PW₁₂0₄o^3" + 230H-→ 12W0₄ ^2" + HPO4^2" +11H₂0 (Formula 1) At a pH between about 2 and about 7, the PW11O₃9^7" species predominates, and at a pH between about 7 and about 8, the PW₉0₃₄ ^9" species predominates.

[0023] A number of oxidation catalysts derived from heteropoly acids have been previously described in the art, particularly for use in desulfurization reactions. Such catalysts have sometimes been prepared in situ from a quaternary ammonium salt, such as a quaternary ammonium halide. For such in situ-formed catalysts, residual halide ions from the quaternary ammonium salt remain in the oxidation reaction mixture. We have discovered that residual halide ions associated with such in situ-formed oxidation catalysts, particularly chloride, bromide and iodide ions, react readily to decompose hydrogen peroxide under oxidative reaction conditions to result in inefficient use of the oxidizing agent. In order to achieve high yields of oxidized products in such cases, significant excesses of oxidizing agent are often used. On an industrial scale, the use of excessive oxidizing agent quantities represents a significant added expense, which ultimately translates into increased costs for a desulfurized product stream.

[0024] In cases where oxidation catalysts derived from heteropoly acids have actually been isolated from a reaction mixture, relatively complex syntheses have oftentimes been employed. For example, organic solvents have either been used as a reaction medium or washing solvent during catalyst preparation, or complicated procedures can be involved to isolate and purify the catalyst. In either case, such processes are generally considered less desirable for commercial scale production. [0025] In the embodiments herein, synthetic routes for oxidation catalysts derived from heteropoly acids are presented that are entirely different than those previously described in the art. A particularly advantageous feature of these syntheses is that they can be conducted in an aqueous reaction medium to produce a solid reaction product, most often in absence of organic solvents. In this sense, the catalyst preparations described herein can be considered to be "green" synthetic routes. In addition, the catalyst preparations described herein involve the combination of fewer reaction components with less required pH control than in conventionally practiced oxidation catalyst syntheses. In many cases, the present synthetic methods advantageously result in only small losses of heteropoly acid in the mother liquor of the reactions, which further attests to the their synthetic efficiency. Moreover, the isolation and purification techniques for the synthetic methods described herein generally involve only simple filtration and washing techniques that are also highly compatible with commercial scale processes.

[0026] In addition to the foregoing advantages, since the oxidation catalysts described herein are easily isolated as solid reaction products, residual halide ion levels can generally be kept low, in contrast to many other catalyst syntheses, particularly those of in s i -formed catalysts. Since the oxidation catalysts described herein can have low residual halide levels, they may be much less likely to promote oxidizing agent decomposition, thereby allowing more efficient oxidizing agent usage and lower cost oxidation processes to be realized.

[0027] In some embodiments, the oxidation catalysts described herein can be prepared from a heteropoly acid that has been partially neutralized with a base, specifically at pH ranging between about 2 and about 7. Depending upon the amount of base used to partially neutralize the heteropoly acid and the corresponding pH reached, the recyclability of the catalyst can surprisingly be impacted to a significant degree. As described in more detail below, oxidation catalysts prepared within the high end of this pH range may display better recyclability characteristics than do catalysts prepared when fewer equivalents of base are used to partially neutralize the heteropoly acid. Moreover, the foregoing synthetic methods that improve catalyst recyclability may also provide the oxidation catalysts in a condition such that their protic salt forms predominate, in contrast to other synthetic processes. [0028] In addition to the foregoing advantages, we have also surprisingly discovered that, in some embodiments, the order in which the oxidizing agent and the catalyst are combined with an oxidizable sulfur compound in a desulfurization reaction can significantly impact the extent of oxidation obtained. Specifically, we have discovered that contacting the oxidation catalyst with an oxidizing agent before its exposure to an oxidizable compound can improve the amount of oxidized product formed. Without being bound by theory or mechanism, it is believed that prior contact of the oxidation catalyst with the oxidizing agent can modify the surface of the oxidation catalyst such that it is more active for promoting oxidation.

[0029] As used herein, the term "reaction product" refers to a compound or mixture of compounds obtained from a chemical reaction of one or more substances.

[0030] As used herein, the term "quaternized nitrogen compound" refers to any compound having a nitrogen atom bearing a positive charge, where the positive charge does not result from protonation of the nitrogen atom. Illustrative compounds having a nitrogen atom bearing a positive charge can include quaternary ammonium salts and nitrogen-containing heteroaromatic compounds in which a nitrogen atom within the heteroaromatic ring has become functionalized.

[0031] As used herein, the term "oxidizable compound" refers to a compound that contains a functional group that is operable to undergo oxidation in the presence of an oxidation catalyst. As used herein, the term "oxidizable sulfur compound" refers to a sulfur-containing compound in which a sulfur atom therein is operable to undergo oxidation to a higher oxidation state.

[0032] As used herein, the term "alkali metal" refers to a metal or metal ion from Group I of the periodic table of the elements. Particularly, alkali metals may include, for example, sodium, potassium, rubidium, cesium, or any combination thereof.

[0033] According to some embodiments, oxidation catalysts described herein can be prepared by reacting a quaternized nitrogen compound with a heteropoly acid to form a solid reaction product. According to some further embodiments, such solid reaction products can be further contacted with an oxidizing agent in the absence of an oxidizable compound. In some embodiments, the oxidizing agent can comprise a hydrogen peroxide solution having a concentration ranging between about 30% and about 35% by weight, and in some embodiments, the solid reaction product and the hydrogen peroxide solution can be heated while contacting each other.

[0034] In some embodiments, methods for making oxidation catalysts from a quaternized nitrogen compound and a heteropoly acid can comprise combining a quaternized nitrogen compound and a heteropoly acid in an aqueous reaction medium, forming a solid reaction product that precipitates from the aqueous reaction medium, and isolating the solid reaction product.

[0035] According to some embodiments, oxidation catalysts described herein can be prepared by reacting a quaternized nitrogen compound and a heteropoly acid that has been at least partially neutralized with a base to form a solid reaction product. According to some further embodiments, such solid reaction products can be further contacted with an oxidizing agent in the absence of an oxidizable compound. In some embodiments, the oxidizing agent can comprise a hydrogen peroxide solution having a concentration ranging between about 30% and about 35% by weight, and in some embodiments, the solid reaction product and the hydrogen peroxide solution can be heated while contacting each other.

[0036] In some embodiments, methods for making oxidation catalysts from a quaternized nitrogen compound and a heteropoly acid that has been partially neutralized with a base can comprise combining a partially neutralized heteropoly acid with a quaternized nitrogen compound in an aqueous reaction medium, reacting the partially neutralized heteropoly acid and the quaternized nitrogen compound in the aqueous reaction medium to form a solid reaction product that precipitates from the aqueous reaction medium, and isolating the solid reaction product. In some embodiments, the methods can further comprise forming the partially neutralized heteropoly acid by adjusting a solution of heteropoly acid to a pH ranging between about 2 and about 7-

[0037] Illustrative heteropoly acids that can be used in the present embodiments can include, for example, phosphotungstic acid (H3PW₁2O₄0), phosphomolybdic acid (Η₃ΡΜθι₂0₄ο), silotungstic acid (H₃SiWi₂0₄o), and silomolybdic acid (H3S1M0₁2O₄0). Various combinations and hydrates of these heteropoly acids can also be used as well.

[0038] Various quaternized nitrogen compounds can be used for reaction with the heteropoly acid or partially neutralized heteropoly acid according to the present embodiments. In some embodiments, the quaternized nitrogen compound can comprise a pyridinium salt (e.g. , a pyridinium halide), wherein the pyridine nitrogen atom can be functionalized with an alkyl, alkenyl, alkynyl, aryl, aralkyl, alkylaryl or cycloalkyl group. In some embodiments, the quaternized nitrogen compound can comprise a quinolinium salt (e.g., a quinolinium halide), wherein the quinoline nitrogen atom can be functionalized with an alkyl, alkenyl, alkynyl, aryl, aralkyl, alkylaryl or cycloalkyl group. In some embodiments, the quaternized nitrogen compound can comprise a compound having a formula of R₄N⁺X^" (e.g., a quaternary ammonium salt), wherein X is a halide or halide equivalent and each R group can independently be an alkyl, alkenyl, alkynyl, aryl, aralkyl, alkylaryl or cycloalkyl group. In some embodiments, each R group can comprise 1 to about 50 carbon atoms. In other embodiments, at least one R group can comprise 3 to about 30 carbon atoms. In still other embodiments, at least one R group can comprise 6 to about 30 carbon atoms. Illustrative quaternized nitrogen compounds that can be suitable for practicing the embodiments described herein include, for example, a tetramethylammonium halide, a tetraethylammonium halide, a tetrabutylammonium halide, an octadecyltrimethylammonium halide, a dimethyldioctadecylammonium halide, a benzyldimethyloctadecylammonium halide, a hexadecylpyridinium halide, a benzalkonium halide (e.g., alkylbenzyldimethylammonium halide with alkyl = 60% Ci₂H₂5 and 40% C₁₄H29), and any combination thereof.

[0039] In general, the quaternized nitrogen compound and the heteropoly acid or partially neutralized heteropoly acid can be combined in any stoichiometric or non-stoichiometric ratio. In some embodiments, between about 1 equivalent and about 3 equivalents of the quaternized nitrogen compound can be combined with a heteropoly acid. In some embodiments, between about 1 equivalent and about 7 equivalents of the quaternized nitrogen compound can be combined with a partially neutralized heteropoly acid. In some embodiments, between about 3 equivalents and about 7 equivalents of the quaternized nitrogen compound can be combined with a partially neutralized heteropoly acid. In still other embodiments, between about 4 equivalents and about 6 equivalents of the quaternized nitrogen compound can be combined with a partially neutralized heteropoly acid. [0040] FIGURE 1 shows an illustrative titration curve of phosphotungstic acid with a standardized sodium hydroxide solution . Similar titration curves are observed for other heteropoly acids. As illustrated in FIGURE 1, when between about 3 equivalents and about 8 equivalents of sodium hydroxide have been added to the phosphotungstic acid, the pH ranges between about 2 and about 7. The large amount of sodium hydroxide needed to affect partial neutralization to within this pH range can be explained by the reaction stoichiometry for the degradation of phosphotungstic acid to tungstate ions (see Formula 1). At a pH ranging between about 2 and about 7, the predominate equilibrium species is believed to be PW11O39^7". As discussed further below, depending upon the amount of added base, oxidation catalysts can sometimes more readily promote oxidation and/or display better recyclability in subsequent runs of an oxidation reaction.

[0041] In some embodiments, between about 3 equivalents and about 8 equivalents of an alkali metal base can be used to partially neutralize a heteropoly acid prior to combining with a quatemized nitrogen compound. In some embodiments, about 3 equivalents of an alkali metal base can be used to partially neutralize a heteropoly acid. In some embodiments, about 4 equivalents of an alkali metal base can be used to partially neutralize a heteropoly acid. In some embodiments, about 4.5 equivalents of an alkali metal base can be used to partially neutralize a heteropoly acid. In some embodiments, about 5 equivalents of an alkali metal base can be used to partially neutralize a heteropoly acid. In some embodiments, about 5.5 equivalents of an alkali metal base can be used to partially neutralize a heteropoly acid. In some embodiments, about 6 equivalents of an alkali metal base can be used to partially neutralize a heteropoly acid. In some embodiments, about 6.5 equivalents of an alkali metal base can be used to partially neutralize a heteropoly acid. In some embodiments, about 7 equivalents of an alkali metal base can be used to partially neutralize a heteropoly acid. In some embodiments, about 7.5 equivalents of an alkali metal base can be used to partially neutralize a heteropoly acid. In some embodiments, about 7.8 equivalents of an alkali metal base can be used to partially neutralize a heteropoly acid. In some embodiments, about 8 equivalents of an alkali metal base can be used to partially neutralize a heteropoly acid. In some embodiments, between about 3 and about 4 equivalents of alkali metal base, or between about 4 and about 4.5 equivalents of alkali metal base, or between about 4.5 and about 5 equivalents of alkali metal base, or between about 5 and about 5.5 equivalents of alkali metal base, or between about 5.5 and about 6 equivalents of alkali metal base, or between about 6 and about 6.5 equivalents of alkali metal base, or between about 6.5 and about 7 equivalents of alkali metal base, or between about 7 and about 7.5 equivalents of alkali metal base can be used to partially neutralize a heteropoly acid in practicing the methods described herein.

[0042] When preparing oxidation catalysts from a heteropoly acid that has been at least partially neutralized with an alkali metal base, the oxidation catalysts may contain a low content of the alkali metal. More specifically, oxidation catalysts may be prepared from partially neutralized heteropoly acids such that the oxidation catalysts contain less than a stoichiometric amount of alkali metal relative to other elements in the oxidation catalyst. For example, in the case of oxidation catalysts prepared from partially neutralized phosphotungstic acid, the oxidation catalysts may have a molar ratio of alkali metal {e.g. sodium) to phosphorus of less than about 1. In some or other embodiments, the oxidation catalysts may have a molar ratio of alkali metal to phosphorus of less than about 0.9, or less than about 0.8, or less than about 0.7, or less than about 0.6, or less than about 0.5, or less than about 0.4, or less than about 0.3, or less than about 0.2, or less than about 0.1.

[0043] When preparing oxidation catalysts from a partially neutralized heteropoly acid, a protic salt form of the oxidation catalysts may predominate over alkali metal salt forms. In some embodiments, the oxidation catalysts may have a composition in which the chemical formula Q7_-xH_xYZii0₃9 predominates, wherein Y is Si or P, Z is W or Mo, and x is a real number ranging between 0 and about 3. More particularly, in some embodiments, the oxidation catalysts may be prepared via partial neutralization of phosphotungstic acid and have a composition in which the chemical formula Q7-_xH_xPWii0₃9 is a predominant species, where Q is a quaternary ammonium ion and x is a real number ranging between 0 and about 3. Although the oxidation catalysts may be obtained in forms such that they contain a low content of alkali metal, as described above, they are not necessarily free of alkali metals, even when protic salt forms predominate. For example, the oxidation catalysts may comprise a minor component of a mixed protic/alkali metal salt, and/or the oxidation catalysts may contain alkali metals taken up from their surrounding environment. Thus, even though the foregoing chemical formulas do not contain an alkali metal, it is to be recognized that a sub-stoichiometric amount of alkali metal may be present in the oxidation catalysts, in some embodiments.

[0044] Illustrative oxidizing agents suitable for practicing the present embodiments can include, for example, hydrogen peroxide, organic peroxides (e.g. , t-butyl peroxide, benzoyl peroxide, or the like), nitrogen oxides, oxygen, ozone, superoxides, OXONE (potassium peroxymonosulfate available from DuPont) and the like. In some embodiments, the oxidizing agent can comprise a hydrogen peroxide solution. In some embodiments, the hydrogen peroxide solution can have a hydrogen peroxide concentration ranging between about 30% and about 35% by weight. In some embodiments, the hydrogen peroxide solution can have a hydrogen peroxide concentration of up to about 50% by weight.

[0045] In some embodiments, solid reaction products of a quaternized nitrogen compound and either a heteropoly acid or a partially neutralized heteropoly acid can be contacted with an oxidizing agent, particularly a hydrogen peroxide solution, in the absence of an oxidizable compound. In some embodiments, contact of the solid reaction product and the oxidizing agent in the absence of an oxidizable compound can make the solid reaction product more active as an oxidation catalyst, particularly for the oxidation of oxidizable sulfur compounds.

[0046] In some embodiments, the oxidizing agent, particularly a hydrogen peroxide solution, can be heated while contacting the solid reaction product in the absence of an oxidizable compound. In some embodiments, heating can take place at a temperature ranging between about 30°C and about 100°C. In other embodiments, heating can take place at a temperature ranging between about 30°C and about 50°C. In still other embodiments, heating can take place at a temperature ranging between about 30°C and about 40°C. In alternative embodiments, the solid reaction product and the oxidizing agent can be contacted at room temperature.

[0047] The length of time over which the solid reaction product and the oxidizing agent are contacted in the absence of an oxidizable compound can likewise vary over a considerable range. In some embodiments, the solid reaction product and the oxidizing agent can be contacted for between about 10 seconds and about 1 hour. In some embodiments, the solid reaction product and the oxidizing agent can be contacted for between about 1 minute and about 1 hour. In still other embodiments, the solid reaction product and the oxidizing agent can be contacted for between about 5 minutes and about 30 minutes. In still other embodiments, the solid reaction product and the oxidizing agent can be contacted for between about 10 minutes and about 30 minutes.

[0048] In some embodiments, methods for making an oxidation catalyst from a quaternized nitrogen compound and a partially neutralized heteropoly acid can comprise: forming a partially neutralized heteropoly acid at a pH ranging between about 2 and about 7; combining the partially neutralized heteropoly acid with a quaternized nitrogen compound in an aqueous reaction medium; reacting the partially neutralized heteropoly acid and the quaternized nitrogen compound in the aqueous reaction medium to form a solid reaction product that precipitates from the aqueous reaction medium; and isolating the solid reaction product. In some embodiments, between about 3 equivalents and about 8 equivalents of an alkali metal base can be used to partially neutralize the heteropoly acid. In some embodiments, between about 4 equivalents and about 7 equivalents of the quaternized nitrogen compound can be reacted with the partially neutralized heteropoly acid. In some embodiments, between about 4 equivalents and about 6 equivalents of the quaternized nitrogen compound can be reacted with the partially neutralized heteropoly acid.

[0049] As noted previously, the present methods for forming a reaction product from a quaternary ammonium salt and a partially neutralized heteropoly acid can be particularly advantageous due to the inexpensive and environmentally friendly solvents that can be used. In some embodiments, the aqueous reaction medium can lack any organic solvents. However, in other embodiments, the aqueous reaction medium can optionally comprise a water- miscible organic solvent. In some embodiments, the aqueous reaction medium can be water.

[0050] In the present methods for making an oxidation catalyst, the quaternized nitrogen compound and the partially neutralized heteropoly acid can generally be combined in any order. In some embodiments, the partially neutralized heteropoly acid can be added to the quaternized nitrogen compound. In other embodiments, the quaternized nitrogen compound can be added to the partially neutralized heteropoly acid. [0051] FIGURE 2 shows a generalized apparatus for making a catalyst from a quaternized nitrogen compound and a partially neutralized heteropoly acid. A general description of the method of making the catalysts now follows with reference to the apparatus of FIGURE 2. It is to be understood the various details such as, for example, motors, pumps, conveyors, agitators, separators, dryers, packing, instrumentation, process control and the like have not been included in the drawing of the apparatus, since such features are within the understanding of one having ordinary skill in the art.

[0052] Referring to apparatus 30 in FIGURE 2, water or a like aqueous reaction medium can be added to reaction vessels 12 and 13 via conduit 1. A heteropoly acid can be added to reaction vessel 13 by conduit 2 from storage vessel 9. Thereafter, an alkali metal base can be added to reaction vessel 13 via conduit 19 from tank 20, thereby forming a partially neutralized heteropoly acid. A quaternized nitrogen compound can be added to reaction vessel 12 via conduit 3 from storage vessel 10. Thereafter, the partially neutralized heteropoly acid in reaction vessel 13 can then be added to reaction vessel 12 via conduit 4. The solid reaction product that forms in reaction vessel 12 can then be transferred to washing and separation station 14 via conduit 5. Thereafter, the solid reaction product can then be transferred to drying system 15 via conduit 6, followed subsequently to packing system 16 via conduit 7. The discharge washes of washing and separation station 14 can be sent via conduit 17 to waste or transported via conduit 18 to reaction vessel 12.

[0053] In the present methods for making a catalyst, the quaternized nitrogen compound and the partially neutralized heteropoly acid can be reacted over a wide range of reaction times. In some embodiments, the quaternized nitrogen compound and the partially neutralized heteropoly acid can be reacted for between about 1 second and about 60 minutes. In other embodiments, the quaternized nitrogen compound and the partially neutralized heteropoly acid can be reacted for between about 1 minute and about 30 minutes. In still other embodiments, the quaternized nitrogen compound and the partially neutralized heteropoly acid can be reacted for between about 1 minute and about 10 minutes or between about 1 minute and about 5 minutes.

[0054] In the present methods for making a catalyst, the quaternized nitrogen compound and the partially neutralized heteropoly acid can be reacted over a wide range of temperatures. In some embodiments, the quaternized nitrogen compound and the partially neutralized heteropoly acid can be reacted at about room temperature. In some embodiments, the aqueous reaction medium can be heated while reacting occurs. In some embodiments, the quatemized nitrogen compound and the partially neutralized heteropoly acid can be reacted at a temperature ranging between about 30°C and about 100°C. In other embodiments, the quatemized nitrogen compound and the partially neutralized heteropoly acid can be reacted at a temperature ranging between about 30°C and about 50°C. In still other embodiments, the quatemized nitrogen compound and the partially neutralized heteropoly acid can be reacted at a temperature ranging between about 40°C and about 50°C or between about 45°C and about 50°C.

[0055] In various embodiments, the oxidation catalysts described herein can be used to promote the oxidation of sulfur-containing organic compounds. In more specific embodiments, the oxidation catalysts described herein can be used to promote the oxidative desulfurization of a petroleum source containing at least one sulfur-containing organic compound. In still more specific embodiments, the oxidation catalysts described herein can be used to promote the oxidative desulfurization of a petroleum source containing dibenzothiophene.

[0056] In some embodiments, the oxidation catalyst and the oxidizing agent can be contacted with one another in the absence of an oxidizable compound prior to being combined with a petroleum source comprising an oxidizable sulfur compound. As described above, contacting of the oxidation catalyst and the oxidizing agent can take place over a range of times and temperatures. In other embodiments, the oxidation catalyst and oxidation agent can remain separate before being combined with the petroleum source.

[0057] In some embodiments, oxidative desulfurization methods described herein can comprise providing an oxidation catalyst comprising a solid reaction product obtained from a reaction between a quatemized nitrogen compound and heteropoly acid; combining the oxidation catalyst with an oxidizing agent in the absence of an oxidizable compound; after combining the oxidation catalyst and the oxidizing agent, combining a petroleum source comprising an oxidizable sulfur compound with the oxidation catalyst and the oxidizing agent; reacting at least a portion of the oxidizable sulfur compound to form an oxidized sulfur compound; and removing the oxidized sulfur compound from the petroleum source to form a reduced sulfur content petroleum product. In some embodiments, the methods can further comprise heating the oxidation catalyst and the oxidizing agent while they are combined with one another before the petroleum source is combined.

[0058] In some embodiments, oxidative desulfurization methods described herein can comprise providing an oxidation catalyst comprising a solid reaction product obtained from a reaction between a quaternized nitrogen compound and heteropoly acid that has been at least partially neutralized with a base; combining the oxidation catalyst with an oxidizing agent in the absence of an oxidizable compound; after combining the oxidation catalyst and the oxidizing agent, combining a petroleum source comprising an oxidizable sulfur compound with the oxidation catalyst and the oxidizing agent; reacting at least a portion of the oxidizable sulfur compound to form an oxidized sulfur compound; and removing the oxidized sulfur compound from the petroleum source to form a reduced sulfur content petroleum product. In some embodiments, the methods can further comprise heating the oxidation catalyst and the oxidizing agent while they are combined with one another.

[0059] In some embodiments, oxidative desulfurization methods described herein can comprise providing an oxidation catalyst comprising a solid reaction product obtained from a reaction between a quaternized nitrogen compound and heteropoly acid that has been at least partially neutralized with a base; combining the oxidation catalyst with an oxidizing agent and a petroleum source comprising an oxidizable sulfur compound; reacting at least a portion of the oxidizable sulfur compound to form an oxidized sulfur compound; and removing the oxidized sulfur compound from the petroleum source to form a reduced sulfur content petroleum product. In various embodiments, the solid reaction product may have a molar ratio of an alkali metal to phosphorus of less than about 1.

[0060] In various embodiments, removing the oxidized sulfur compound from the petroleum source can take place using any technique familiar to one having ordinary skill in the art. In various embodiments, removal of the oxidized sulfur compound can take place using a single technique or combination of techniques such as, for example, adsorption, precipitation, filtration, centrifugation, solvent extraction, and the like. [0061] In various embodiments, the oxidizing agent for the oxidative desulfurization methods described herein can comprise at least one of a hydrogen peroxide solution or an organic peroxide. In some embodiments, the oxidizing agent can comprise a hydrogen peroxide solution having a concentration ranging between about 30% and about 35% by weight. In some embodiments, an amount of hydrogen peroxide solution can be used such that there are between about 2 equivalents and about 50 equivalents of hydrogen peroxide relative to the oxidizable sulfur compound in the petroleum source. In other embodiments, an amount of hydrogen peroxide solution can be used such that there are between about 3 equivalents and about 10 equivalents of hydrogen peroxide relative to the oxidizable sulfur compound in the petroleum source. Hydrogen peroxide quantities within the foregoing ranges can be used when the oxidation catalyst is contacted with the oxidizing agent in the absence of an oxidizable compound.

[0062] Generally, only relatively low quantities of oxidation catalysts derived from heteropoly acids are needed to affect high levels of desulfurization when practicing the present methods. In various embodiments, an amount of the oxidation catalyst used in the present desulfurization reactions can be about 0.05 equivalents or less relative to the oxidizable sulfur compound. In some embodiments, an amount of the oxidation catalyst can be about 0.02 equivalents or less relative to the oxidizable sulfur compound. In still other embodiments, an amount of the oxidation catalyst can be about 0.01 equivalents or less relative to the oxidizable sulfur compound.

[0063] In some embodiments, an amount of the oxidation catalyst and an amount of the hydrogen peroxide solution can be varied such that a satisfactory emulsion is obtained. In some embodiments a molar ratio of hydrogen peroxide to the oxidation catalyst can range between about 200 and about 600. In other embodiments, a molar ratio of hydrogen peroxide to the oxidation catalyst can range between about 300 and about 450. In still other embodiments, a molar ratio of hydrogen peroxide to the oxidation catalyst can range between about 300 and about 400.

[0064] Illustrative petroleum sources that can be desulfurized according to the present methods include, for example, crude oil, gasoline, diesel and the like. In some embodiments, the resulting reduced sulfur content petroleum product can have a sulfur content that is about 90% or less than that of the petroleum source. In other embodiments, the reduced sulfur content petroleum product can have a sulfur content that is about 95% or less than that of the petroleum source. In still other embodiments, the reduced sulfur content petroleum product can have a sulfur content that is about 97% or less than that of the petroleum source. In some embodiments, the reduced sulfur content petroleum product can have a sulfur content of about 50 ppm or less. In other embodiments, the reduced sulfur content petroleum product can have a sulfur content content of about 25 ppm or less. In still other embodiments, the reduced sulfur content petroleum product can have a sulfur content of about 15 ppm or less. It is to be recognized that a desired sulfur content for the reduced sulfur content petroleum product will be dependent upon the intended end use thereof, and the desired sulfur content may be further dictated by local environmental regulations. It is also to be recognized that the present methods can be repeated or modified as necessary to achieve a desired sulfur content.

[0065] The present desulfurization methods can be carried out over a wide temperature range. In various embodiments, the present methods can be conducted over a temperature ranging between about 25°C and about 100°C. In other various embodiments, the present methods can be conducted over a temperature ranging between about 100°C and about 150°C. In some embodiments, the present methods can be conducted over a temperature ranging between about 50°C and about 60°C. In some embodiments, the present methods can be conducted over a temperature ranging between about 60°C and about 70°C. In some embodiments, the present methods can be conducted over a temperature ranging between about 70°C and about 80°C. In some embodiments, the present methods can be conducted over a temperature ranging between about 80°C and about 90°C. In some embodiments, the present methods can be conducted over a temperature ranging between about 90°C and about 100°C.

[0066] In some embodiments, the oxidizable sulfur compound present in the petroleum source can comprise a thiophene. In more particular embodiments, the oxidizable sulfur compound can comprise benzothiophene, dibenzothiophene, an alkyl-substituted benzothiophene, an alkyl-substituted dibenzothiophene, and/or other high molecular weight thiophene compounds. Although the present desulfurization embodiments have been particularly described with regard to these compounds, it is to be recognized that the present methods are not limited thereto, and generally any oxidizable sulfur compound can be oxidized according to the present methods. Furthermore, although the catalysts described herein have been primarily described with reference to their ability to oxidize oxidizable sulfur compounds, particularly thiophenes and more particularly dibenzothiophene, it is also to be recognized that the catalysts may be used in other types of oxidation processes. Such processes may include, without limitation, epoxidation of alkenes, alcohol oxidation and aldehyde oxidation. Extension of the oxidation catalysts to these other types of compounds will be within the capabilities of one having ordinary skill in the art.

[0067] Generally, the oxidation catalyst and the petroleum source containing an oxidizable sulfur compound can be reacted using equipment and techniques familiar to one having ordinary skill in the art. In various embodiments, the petroleum source, the catalyst and the oxidizing agent can be combined in a reactor. In some embodiments, the combination can take place under batch conditions with mechanical mixing. In other embodiments, the combination can take place under flow conditions.

[0068] In some embodiments, the present methods can further comprise separating the oxidation catalyst from the reduced sulfur content petroleum product. In some embodiments, the present methods can further comprise recycling the separated oxidation catalyst in another oxidation process. In some embodiments, the subsequent oxidation process can be another desulfurization reaction. In other embodiments, the subsequent oxidation reaction can be another type of oxidation including, for example, an alkene epoxidation, alcohol oxidation or aldehyde oxidation. Separation of the catalyst upon completion of the desulfurization reaction can be carried out through any technique known to one having ordinary skill in the art. Illustrative but non- limiting separation techniques can include, for example, precipitation, filtration, centrifugation, solvent addition, decantab^'on, and the like. In some embodiments, the catalyst can be separated before the oxidized sulfur compound is removed. In other embodiments, the catalyst can be separated after the oxidized sulfur compound is removed.

[0069] Although any of the oxidation catalysts described herein can be recycled in a subsequent oxidation process, we have surprisingly discovered that oxidation catalysts prepared from a partially neutralized heteropoly acid have varying degrees of recyclability depending upon the number of equivalents of base used to affect partial neutralization. In many cases, oxidation catalysts prepared from a partially neutralized heteropoly acid can maintain good catalytic activity over at least 4 catalyst process runs, and sometimes up to 9 or more catalyst process runs. Furthermore, we have observed that catalysts prepared using higher quantities of base to partially neutralize the heteropoly acid to within a pH range of about 2 to about 7 can display greater recyclability than when the heteropoly acid is neutralized to a pH value in the lower end of this range. Still further, it has been observed in many cases that oxidation catalysts prepared from a partially neutralized heteropoly acid may maintain higher catalytic activity over a greater number of catalyst process runs than do comparable oxidation catalysts prepared without partial neutralization of the heteropoly acid.

[0070] To facilitate a better understanding of the present invention, the following examples of preferred embodiments are given. In no way should the following examples be read to limit, or to define, the scope of the invention.

EXAMPLES

[0071] Example 1: Synthesis of Oxidation Catalysts via Direct Reaction of a Quaternized Nitrogen Compound and a Heteropoly Acid. Method 1: 1 mmol of a quaternized nitrogen compound and 1/3 mmol of phosphotungstic acid were added to 40 mL of heptane. The resulting suspension was vigorously stirred, and 7 mL of H₂0 was added all at once. Stirring was continued for 2 hours at 30°C, during which time the volume of solids increased and the heptane layer became cloudy. Thereafter, stirring was discontinued, and the reaction mixture was placed in a cold water bath. The clear heptane layer was then decanted and the solid was triturated with 20 mL of 1 : 1 methanol/ethanol. The solid was collected by vacuum filtration and washed with chilled 1 : 1 methanol/ethanol. The solid was then air-dried, followed by drying with gentle heat to achieve a constant weight. When the quaternized nitrogen compound was hexadecylpyridinium chloride, a gel formed when 1 : 1 methanol/ethanol was added. In this case, the gel became a powder upon evaporation. When the quaternized nitrogen compound was dimethyldioctadecylammonium chloride, an emulsion was obtained following the reaction. In this case, the reaction mixture was gravity filtered, and the solid reaction product was obtained by triturating with 1 : 1 methanol/ethanol. Method 1A: 2 mmol of quatemized nitrogen compound was added to 30 mL of heptane and stirred vigorously, and 7 mL of water containing 2/3 mmol phosphotungstic acid was added all at once. The reaction mixture was stirred for 4 hours at 30 - 35°C. Thereafter, the reaction mixture was allowed to settle until the heptane layer cleared. The heptane layer was decanted, and the solid was triturated with 10 mL of 1 : 1 methanol/ethanol. The solid then cooled in an ice bath and triturated again with 5 mL of 1 : 1 methanol/ethanol. Thereafter, the solid was collected by vacuum filtration and washed with 1 : 1 methanol/ethanol. Finally, the solid was air dried, followed by drying with gentle heat to achieve a constant weight. Method 2: 1 mmol of a quatemized nitrogen compound was dissolved in 10 - 15 mL of 1 : 1 methanol/ethanol. This solution was then added in small portions to an aqueous solution of 1/3 mmol phosphotungstic acid in 10 mL H₂0. A precipitate formed immediately in most cases. The reaction mixture was thereafter stirred for 2 hours at 30°C. The precipitate was then collected by vacuum filtration and washed with chilled 1 : 1 methanol/ethanol. The solid was then air-dried, followed by drying with gentle heat to achieve a constant weight. When the quatemized nitrogen compound was tetramethylammonium fluoride or tetraethylammonium fluoride, partial neutralization of the reaction mixture was conducted in order to induce precipitation. Thereafter, the solid product was isolated as described above. Method 2A: 2 mmol of a quatemized nitrogen compound was added to 20 mL of deionized water and broken up into a suspension of fine particles. The suspension was warmed and stirred until the quatemized nitrogen compound dissolved. A solution of 2/3 mmol phosphotungstic acid in 10 mL H₂0 was added dropwise with stirring to the quatemized nitrogen compound solution. A precipitate generally formed immediately. The reaction mixture was stirred for an additional 75 minutes at a temperature between 35°C and 37°C. The precipitate was then collected by gravity filtration and washed 3 times with 10 mL of chilled deionized water. The precipitate was then air dried, followed by drying with gentle heat to achieve a constant weight.

[0072] Example 2: Synthesis Oxidation Catalysts via Reaction of a Quatemized Nitrogen Compound and a Partially Neutralized Heteropoly Acid. Method 3A: 1000 mg of phosphotungstic acid was dissolved in 3 mL distilled H₂0. Thereafter, the phosphotungstic acid was partially neutralized by adding between 3 to 7.8 equivalents of 1 M NaOH solution (1, 1.5, 2 or 2.6 mL NaOH— 3, 4.5, 6 and 7.8 equivalents, respectively). After adding the NaOH solution, the pH was allowed to stabilize. 4 to 7 equivalents of a quaternized nitrogen compound were dissolved in 15 - 20 mL deionized water at 45°C, and the partially neutralized phosphotungstic acid solution was then added dropwise to the quaternized nitrogen compound solution at 45°C. An immediate precipitate formed upon combining the two solutions. Stirring was continued for 1 hour at 45 - 50°C, and the reaction mixture was then chilled in a cold water bath for 30 minutes thereafter. The precipitate was then collected by vacuum filtration, washed 3 times with 10 mL of chilled water, and air dried to constant weight. Method 3B: The synthesis was repeated as in Method 3A, except the reaction time was shortened from 1 hour to 5 minutes. Similar results and catalytic activity (see below) were obtained.

[0073] Example 3: Characterization of Catalysts Prepared via

Reaction of a Quaternized Nitrogen Compound and a Partially Neutralized Heteropoly Acid. The catalysts of Example 2 (Method 3A) were qualitatively and quantitatively analyzed to determine their composition. For the data indicated below in Tables 1 and 2, the catalysts were prepared using 6 equivalents of NaOH for partial neutralization of the phosphotungstic acid, which was then reacted with either 4 or 6 equivalents of quaternized nitrogen compound. The quaternized nitrogen compound was octadecyltrimethylammonium bromide. Table 1: Unsealed Semi-Quantitative and Quantitative Analyses of Catalysts Prepared via Reaction of 4 and 6 Equivalents of a Quaternized Nitrogen Compound and a Heteropoly Acid Neutralized with 6

Equivalents of Sodium Hydroxide

4 Equiv. 6 Equiv.

(C₁₈H37)N ⁺ (CH3)3 (C₁₈H₃7)N⁺(CH₃)3

(Composition Wt. % ) (Composition Wt. %)

Na₂0 by x-ray analysis 0.64 0.74

P₂0₅ by x-ray analysis 2.80 2.43

Br by x-ray analysis 0.23 1.33

W0₃ by x-ray analysis 96.32 95.49 C (combustion) 29.86 31.47

H (combustion) 5.57 5.82

N (combustion) 1.64 1.81

S (combustion) <0.1 <0.1

[0074] Regarding the data in Table 1, it should be noted that the Na₂0, P₂0₅, Br and W0₃ semi-quantitative x-ray analyses are scaled to 100% without consideration for the C, H, N and S amounts. Upon obtaining the C, H, N and S analyses, the semi-quantitative x-ray analyses were then scaled on a molar basis to obtain the total composition scaled to 100%. Table 2 summarizes the scaled elemental composition values and the theoretical composition for varying amounts of the quaternized nitrogen compound, assuming a theoretical molecular formula of

(Q = octadecyltrimethylammonium, x = 1 - 3).

Table 2: Scaled Semi-Quantitative and Quantitative Analyses of Catalysts Prepared via Reaction of 4 and 6 Equivalents of a Quaternized Nitrogen Compound and a Heteropoly Acid Neutralized with 6 Equivalents of Sodium Hydroxide and Theoretical Values for Q₇.

xHxPWuCVjg (Q = octadecyltrimethylammonium, x = 1 - 3)

4 Equiv. 6 Equiv. 4 Equiv. 5 Equiv. 6 Equiv.

(Wt. %, (Wt. %, (Wt. %, (Wt. %, (Wt. °/o,

Measured ) Measured) Theoretical) Theoretical) Theoretical) c 29.86 31.47 25.66 29.73 33.23

H 5.57 5.82 4.80 5.52 6.14

N 1.64 1.81 1.43 1.65 1.85

P 0.77 0.65 0.79 0.73 0.68

W 48.07 46.11 51.40 47.67 40.37

O 13.66 13.00 15.87 14.71 13.70

S <0.1 <0.1 0 0 0

[0075] The elemental composition for each catalyst was fairly low in sodium, which is more consistent with the general formula

(Q = octadecyltrimethylammonium). In each case, sodium content corresponded to less than a stoichiometric equivalent of sodium relative to tungsten, thereby leading to the conclusion that the acid form of the catalyst, rather than the sodium salt form is the predominant species. Possible sources of the residual sodium may include environmental sodium contamination and/or residual sodium bromide resulting from partial neutralization of the phosphotungstic acid. The presence of bromide in the elemental analyses suggests that the sodium arises, at least in part, from the latter. Mixtures of the acid form of the catalyst with small amounts of a partial sodium salt form may also be present.

[0076] Semi-quantitative analyses of the aqueous mother liquors from each reaction mixture indicated considerably less tungsten was lost when 6 equivalents of the quaternized nitrogen compound were used to form the catalyst as compared to that lost when 4 equivalents were used. That is, when greater quantities of the quaternized nitrogen compound were used to form the catalyst, fewer of the tungsten atoms remained solubilized and unreacted, and more efficient catalyst formation was observed. Specifically, semi-quantitative x-ray analyses demonstrated that when 4 equivalents of quaternized nitrogen compound was used, 34.42 wt. % W0₃ was found in the reaction mother liquor. In contrast, when 6 equivalents of the quaternized nitrogen compound was used, only 0.69 wt. % W0₃ was found in the mother liquor.

[0077] Example 4: Desulfurization Reactions in Model Diesel Fuel Using a Reaction Product of a Quaternized Nitrogen Compound and a Heteropoly Acid— General Conditions. Model desulfurization reactions were conducted in a hydrocarbon solvent (8: 1 heptane/toluene, pure heptane or pure toluene) containing a dibenzothiophene (DBT) and using hydrogen peroxide (35% solution) as the oxidizing agent. The catalyst, the hydrocarbon solvent, the DBT and the hydrogen peroxide solution were combined in a reactor. Quantities of the catalyst and hydrogen peroxide are set forth in Table 3 below. In some cases, the catalyst and the hydrogen peroxide were heated together for a period of time prior to being combined with the DBT. The reactor was then heated to a set temperature, and this temperature was maintained for 10 minutes to 3 hours, as set forth in Table 3. After the period of heating was completed, the reaction was quenched by adding a small amount of water. The oxidized DBT (dibenzothiophene sulfone) was removed from the hydrocarbon solvent as a precipitate, and the percentage sulfur removal was determined by reversed phase HPLC of the organic phase as measured using the DBT peak at an absorption wavelength of 225 nm. Reaction progress was monitored by removing 1 mL aliquots of the reaction mixture at various time points during the course of the reaction and monitoring the DBT absorbance for concentration determination. Determination of the DBT concentration was conducted using standard calibration curve techniques. Table 3: Model Desulfurization Reactions Using the Reaction Product of a Quaternized Nitrogen Compound and a Heteropoly Acid as a Catalyst

[0078] As shown in Table 3, the rate of oxidation was generally greater in 8: 1 heptane/toluene than in pure toluene. In pure heptane, the oxidation rate was generally comparable to that of the mixed solvent. Depending on the catalyst used, contacting the catalyst with the hydrogen peroxide prior to oxidation was sometimes beneficial. Generally, a H₂0₂ to catalyst ratio of about 350 - 400 produced the best oxidation results. Without being bound by theory or mechanism, it is believed that in this range, there are sufficient quantities of surfactant molecules to adequately emulsify the H₂0₂ oxidant. Accordingly, if the H₂0₂ to catalyst ratio was kept in this range while increasing the amount of catalyst or oxidant, the rate of oxidation generally increased. In some cases, working outside this range produced a lower oxidation rate even when higher quantities of catalyst were present (compare entries 18 and 19).

[0079] A control experiment (entry 40) conducted without a catalyst showed very little conversion of DBT into DBT sulfone. The control experiment demonstrates the criticality of the catalyst in the oxidation reaction.

[0080] Example 5: Desulfurization Reactions in Diesel (NIST SRM 8771) Containing Added DBT Using a Reaction Product of a Quaternized Nitrogen Compound and a Heteropoly Acid. Desulfurization reactions were conducted in a "true" diesel using NIST SRM 8771, which is a low sulfur commercial diesel standard reference material containing 0.071 + 0.014 ppm sulfur. Prior to conducting the desulfurization reaction, the sulfur content of NIST SRM 8771 was raised to approximately 500 ppm by adding an appropriate amount of DBT. Actual amounts are presented in Table 4 below. Desulfurization reactions were conducted using the general conditions described in Example 4 above and set forth specifically in Table 4 below.

30

4 Table 4: Desulfurization of NIST SRM 8771 Containing Added DBT Using a Reaction Product of a Quaternized Nitrogen Compound and a

Heteropoly Acid

¹ 25 min. mixture of catalyst and H₂0₂ with periodic heating to

[0081] In contrast to the desulfurization reactions presented in Example 4, contacting the catalyst and the oxidizing agent prior to oxidation was less effective in this example. Without being bound by theory or mechanism, it is believed that in the ASTM SRM 8771 material the catalyst and hydrogen peroxide do not form an emulsion as readily as in heptane/toluene, thereby leading to poorer oxidation kinetics. [0082] Example 6: Desulfurization Reactions in Diesel (NIST SRM 2770) Containing Added DBT Using a Reaction Product of a Quaternized Nitrogen Compound and a Heteropoly Acid. Desulfurization reactions were conducted in "true" diesel using NIST SRM 2770, which is a low 5 sulfur commercial diesel standard reference material containing 41.57 + 0.39 ppm sulfur. Prior to conducting the desulfurization reaction, the total sulfur content of NIST SRM 2770 was raised to approximately 500 ppm by adding an appropriate amount of DBT. A portion of DBT-spiked NIST SRM 2770 was reacted for 30 minutes at 80°C with 0.01 equivalents of the catalyst derived

10 from Q = [(Ci₈H37)N⁺(CH₃)3] and phosphotungstic acid (Example 1, Method 1) and 3.5 equivalents of hydrogen peroxide. No catalyst contact with the oxidant was performed prior to oxidation. DBT sulfone precipitated from the NIST SRM 2770 during the reaction. Thereafter, the reaction mixture was quenched with 0.5 volumes of H₂0, which was then decanted . Subsequently, the reaction 5 mixture was extracted with 1 volume of methanol. Sulfur concentrations presented in the table were determined by a combination of HPLC and chemical analysis of total sulfur (ASTM D4294), since there was an interfering material in NIST SRM 2770 having a like retention time to that of DBT. Analytical results are presented in Table 5 below.

0

Table 5: Desulfurization of NIST SRM 8771 Containing Added DBT Using

a Reaction Product of a Quaternized Nitrogen Compound and a

Heteropoly Acid

[S]

Catalyst H₂0₂/ Total as

Q Pre- Equiv. Equiv. Catalyst Temp. Time [S]¹, DBT²,

Entry (Method) treat? Catalyst H₂0₂ Ratio (°C) (min) PPm ppm

1 [(C₁₈H₃₇)N⁺(CH₃)3]3 N 0.01 3.5 350 80 0 506 456

(Method 1)

30³ 112 60

30⁴ <15 05 ¹ chemical analysis (ASTM D4294)

² by HPLC

³ after H₂0 quench

⁴ after methanol extraction [0083] Example 7: Extractive Removal of DBT Sulfone from Desulfurization Reactions. Desulfurization reactions were conducted as described above (see Examples 4 and 5). Upon completion of the desulfurization reaction, the reaction medium (i.e. , toluene, 8: 1 heptane/toluene or NIST SRM 8771) was extracted with various solvents to attempt removal of DBT sulfone. Extraction was generally conducted by vigorously shaking 1 mL of the reaction mixture with 1 mL of the indicated extraction solvent. Following extraction and separation of the extraction solvent, the concentrations of DBT and DBT sulfone remaining in the reaction mixture were determined by HPLC. Analytical data is summarized in Table 6.

Table 6: Analytical Data for Extractive Removal of DBT Sulfone from

Desulfurization Reactions

[DBT], [DBT Sulfone],

Reaction Medium Extraction Solvent ppm ppm

Toluene no extraction 193 938

1 x 10% acetic acid 185 899

2 x 10% acetic acid 179 845

1 x 25% acetic acid 182 889

2 x 25% acetic acid 184 831

1 x 0.1% tannic acid 184 921

2 x 0.1% tannic acid 180 858

Toluene, ½ toluene no extraction 112 518

dilution

1 x 10% acetic acid 108 511

2 x 10% acetic acid 113 512

1 x 25% acetic acid 109 502

2 x 25% acetic acid 114 508

1 x 0.1% tannic acid 110 505

2 x 0.1% tannic acid 113 524

1 x 1 : 1 111 483 methanol/water

2 x 1 : 1 109 468 methanol/water

NIST SRM 8771 no extraction 98 11

1 x 10% acetic acid 87 6 [DBT], [DBT Suifone],

Reaction Medium Extraction Solvent ppm ppm

1 x 25% acetic acid 93 3

1 x 0.1% tannic acid 94 8

1 x methanol 51 3

1 x acetonitrile 61 1

NIST SRM 8771 no extraction 64 10

1 x 10% acetic acid 64 7

2 x 10% acetic acid 58 5

1 x 25% acetic acid 63 3

2 x 25% acetic acid 62 1

1 x 0.1% tannic acid 66 8

2 x 0.1% ta nnic acid 62 7

1 x methanol 32 < 1

2 x methanol 26 < 1

1 x acetonitrile 27 < 1

NIST SRM 8771 no extraction 13 9

1 x 10% acetic acid 13 6

1 x 25% acetic acid 13 3

1 x 0.1% ta nnic acid 13 8

1 x methanol 9 <1

1 x acetonitrile 8 < 1

8 : 1 heptane/toluene no extraction 69 26

1 x methanol 57 2

8: 1 heptane/toluene no extraction 25 24

1 x methanol 16 2

[0084] As shown in Table 6, both methanol and acetonitrile were effective solvents for removing DBT sulfone from either NIST SRM 8771 or 8: 1 heptane/toluene. None of the solvents tested were effective at removing DBT sulfone from toluene due to the high solubility of DBT sulfone in this solvent.

[0085] Example 8: Desulfurization Reactions in Model Diesel

Fuel Using a Reaction Product of a Quaternized Nitrogen Compound and a Partially Neutralized Heteropoly Acid— General Conditions. Catalysts prepared using pre-neutralized phosphotungstic acid (3, 4.5, 6 and 7.8 equivalents NaOH— Example 2) and 4 equivalents of quaternized nitrogen compound were used for desulfurization reactions. Generally, between 9.0 and 9.5 mg of the catalyst were combined with 25 mL of a 8: 1 heptane/toluene solution that had a DBT concentration of approximately 500 ppm. Unless otherwise indicated, catalyst pre-treatment with hydrogen peroxide was not used in these examples. After combining the catalyst with the DBT solution, the reaction mixture was heated to 75°C with stirring. Thereafter, 3.5 equivalents of 35% H₂0₂ was added, and the reaction progress was monitored after 15 and 25 minutes of reaction. After 25 minutes, the reactions were quenched by cooling in chilled water for 25 minutes. Upon cooling, the reaction mixtures de- emulsified quickly in the absence of stirring, and the catalyst and DBT sulfone precipitated. After standing overnight, most of the clear organic layer was decanted, and about the last 1 mL of organic layer and aqueous layer was evaporated in an oven at 100°C. Table 7 summarizes the catalytic activity of the first catalyst batch run after 15 and 25 minutes of reaction. The Q for table 7 was [(C₁₈H₃7)N⁺(CH₃)3]4 Table 7: Model Desulfurization Reactions Using the Reaction Product of a Quaternized Nitrogen Compound and a Partially Neutralized

o/o %

Catalyst H₂0₂/ Conv. Conv. Pre- Equiv. Equiv. Catalyst Temp. Equiv. (15 (25

Entry treat? Catalyst H₂0₂ Ratio (°C) NaOH min.) min.)

1 N 0.01 3.5 350 75 3 60.6 92.4

4.5 91.0 99.1

6 97.5 99.8

7.8 98.8 99.8

[0086] For catalyst recycling, the recovered catalyst, plus precipitated DBT sulfone which was not removed following evaporation, was treated with fresh DBT solution, and after dispersing the catalyst, fresh H₂0₂ solution was added. For the second catalyst run and subsequent catalyst recycling runs, a single aliquot was withdrawn after 30 minutes of reaction, and layer separation was conducted as described above. FIGURE 3 shows a chart summarizing the catalytic activity of the catalyst obtained from partial neutralization of phosphotungstic acid with 3, 4.5, 6 and 7.8 equivalents of NaOH over 8 catalyst recycling operations. As shown in FIGURE 3, good catalytic activity was maintained over the first four catalytic cycles for all catalysts. Between the fourth and fifth catalyst recycles, the catalytic activity of the catalyst prepared from 4.5 equivalents of NaOH dropped considerably in activity, and between the sixth and seventh cycles, the catalytic activity of the catalyst prepared from 3 equivalents of NaOH dropped considerably in activity. The catalysts prepared from 6 and 7.8 equivalents of NaOH, in contrast, maintained good catalytic activity over all cycles tested.

[0087] Table 8 illustrates the effect of contacting the catalyst with hydrogen peroxide prior to oxidation. In this case, the above catalyst prepared from phosphotungstic acid pre-neutralized with 6 equivalents of sodium hydroxide was used. The catalyst and the hydrogen peroxide were stirred together for about 15 minutes, during which time the catalyst partially dissolved to form a slurry. Thereafter, a 9: 1 heptane/toluene solution containing 500 ppm DBT was added to the catalyst slurry, and the reaction mixture was heated to 65°C. Comparative data (entry 2) was obtained without prior treatment of the catalyst, which demonstrated that measurably faster oxidation was obtained with catalyst pre-treatment (entry 1). The Q for table 8 was

Table 8: Effects of Contacting Catalysts Comprising a Reaction Product of a Quaternized Nitrogen Compound and a Partially Neutralized

Heteropoly Acid with Hydrogen Peroxide Prior to Oxidation

Catalyst H₂0₂/

Pre- Equiv. Equiv. Catalyst Temp. °/o Conv. % Conv.

Entry treat? Catalyst H₂0₂ Ratio (°C) (15 min.) (25 min.)

1 Y 0.01 2.8 280 65 95.1 98.9

2 N 0.01 2.8 280 65 87.1 97.3

[0088] Table 9 illustrates the temperature-dependent kinetic data for the catalysts prepared using 4 equivalents of quaternized nitrogen compound and 6 or 7.8 equivalents of sodium hydroxide to partially neutralize the phosphotungstic acid. The desulfurization reactions were carried out and analyzed as described immediately above. Table 9: Kinetic Data for Catalysts Prepared Using 6 Equivalents and 7.8 Equivalents of Sodium Hydroxide to Partially Neutralize Phosphotungstic Acid and Reacted with 4 Equivalents of Quaternized Nitrogen Compound

1 [(C₁₈H37) ⁺(CH₃)3]4 N 0.01 3.5 350 45 0 0 461

(6 equiv. NaOH)

10 43.8 259

15 60.1 184

20 74.2 119

25 89.8 47

30 93.9 28

2 [(C₁₈H37)N⁺(CH₃)3], N 0.01 3.5 350 55 0 0 443

(6 equiv. NaOH)

10 60.7 174

15 77.6 99

20 88.7 50

25 96.2 17

3 [(C₁₈H37)N⁺(CH₃)3]4 N 0.01 3.5 350 65 0 0 483

(6 equiv. NaOH)

10 79.9 97

15 92.5 36

20 96.5 17

25 98.8 6

4 [(C₁₈H37) ⁺(CH₃)3]4 N 0.01 3.5 350 75 0 0 467

(6 equiv. NaOH)

10 85.9 66

15 96.8 15

20 99.1 4

25 99.6 2

5 [(Ci₈H₃7)N⁺(CH₃)₃]4 N 0.01 3.5 350 45 0 0 461

(7.8 equiv. NaOH)

10 35.8 292

15 64.4 164

20 76.8 107

25 83.9 74

30 91.3 40

6 [(C₁₈H₃₇)N⁺(CH₃)₃]₄ N 0.01 3.5 350 55 0 0 443

(7.8 equiv. NaOH)

10 64.1 159 ^Etnry

15 84.4 69

20 93.9 27

25 96.8 14

7 t(Ci₈H37)N⁺(CH₃)3]4 N 0.01 3.5 350 65 0 0 465 (7.8 equiv. NaOH)

5 53.5 216

10 84.1 74 15 94.6 25 220 98.8 6

8 [(C₁₈H37)N⁺(CH₃)3]4 N 0.01 3.5 350 75 0 0 465 (7.8 equiv. NaOH)

5 69.5 142

10 94.8 24 15 98.7 6 20 99.4 3

[0089] The derived first-order rate constants for the catalysts prepared from 6 and 7.8 equivalents of sodium hydroxide are summarized in Table 10. The derived data for the catalyst prepared using only 3 equivalents of NaOH to partially neutralize the phosphotungstic acid is also presented for comparison (kinetic data not shown). Each of these catalysts produced superior reaction rates to catalysts prepared as in Example 1. As determined from the Arrhenius activation plots, the activation energy of the reaction was 27.0 kJ/mol with an A factor of 42 s ¹ when 6 equivalents NaOH was used to form the catalyst, and DBT, the activation energy of the reaction when the catalyst was 36.4 kJ/mol with an A factor of 1400 s^"1 when 7.8 equivalents NaOH was used to form the catalyst. By contrast, the reaction had an activation energy of 122 kJ/mol with an A factor of 2.9 x 10¹⁵ s^"1 when the catalyst was prepared without partially neutralizing the phosphotungstic acid beforehand.

Table 10: Derived First Order Rate Constants for Catalysts Prepared from 4 Equivalents of Quaternized Nitrogen Compound and Partially Neutralized Heteropoly Acid Using 3, 6 and 7.8 Equivalents of NaOH k (s ¹)

Temperature (°C) 3 equiv. NaOH 6 equiv. NaOH 7.8 equiv. NaOH

45 — 1.59 x 10^"3 1.37 x 10^"3

55 9.93 x 1(T⁴ 2.10 x 10^"3 2.37 x 10 ³

65 2.18 x 10^'3 2.91 x 10^-3 3.62 x 10 ³

75 2.78 x 10 ³ 3.79 x 10^"3 4.42 x 10 ³ The derived first order rate constants for comparable catalysts prepared as the reaction product of a quaternized nitrogen compound and a heteropoly acid without partial neutralization indicated slower reaction kinetics. Specifically, the rate constants were 2.15 x 10^"4, 8.55 x 10^~4 and 2.61 x 10^~3 at 60°C, 70°C and 80°C, respectively for the catalysts prepared without partial neutralization of the heteropoly acid.

[0090] Comparative data was also obtained using the catalyst prepared by combining 6 equivalents of quaternized nitrogen compound with phosphotungstic acid that had been partially neutralized with 6 equivalents of sodium hydroxide. Table 11 compares the observed percent conversion at various time points during catalyst recycle runs of the catalyst prepared from either 4 or 6 equivalents of octadecyltrimethylammonium bromide and phosphotungstic acid that was partially neutralized with 6 equivalents of sodium hydroxide. For the data presented in Table 11, desulfurization reactions were conducted at 75°C using the general conditions set forth immediately hereinabove. As shown in Table 11, both catalysts maintained good recyclability over several catalyst recycling runs.

Table 11: Comparison of Catalysts Prepared Using Either 4 or 6 Equivalents of Quaternized Nitrogen Compound and Heteropoly Acid

Partially Neutralized with 6 Equivalents of NaOH

Run # (Reaction 4 Equivalents Quaternized 6 Equivalents Quaternized

Nitrogen Compound, Nitrogen Compound, Time) % Conversion % Conversion

1 (15 min.) 96.8 95.3

1 (25 min.) 99.6 99.4

2 (30 min.) 98.7 99.0

3 (30 min.) 98.3 99.4 4 (30 min.) 94.8 99.4

5 (30 min.) 99.6 98.2

6 (30 min.) 96.7 96.0

[0091] In terms of conversion efficiency in more limited amounts of hydrogen peroxide, the catalyst prepared using 4 equivalents of quaternized nitrogen compound was slightly more efficient than was the catalyst prepared using 6 equivalents of quaternized nitrogen compound. For determining peroxide conversion efficiency, a sample of DBT in 8: 1 heptane/toluene was treated with 2.4 equivalents of hydrogen peroxide at 65°C or 75°C, and the percent conversion was determined after 30 minutes of reaction. The catalyst prepared using 4 equivalents of quaternized nitrogen compound produced a percent conversion of 88.0%, whereas the catalyst prepared using 6 equivalents of quaternized nitrogen compound produced a percent conversion of only 76.2%. Although the origin of this effect is not completely understood, one possible explanation is that the 6 equivalent sample contained residual halide (bromide), which resulted in decomposition of some of the hydrogen peroxide (see Example 3).

[0092] Additional data on catalyst recyclability was obtained for catalysts prepared using partially neutralized phosphotungstic acid (6 equivalents NaOH) that was reacted with varying quantities of quaternized nitrogen compounds. Desulfurization in each case was conducted at 75°C using the general reaction conditions set forth above (0.01 equivalents catalyst and 3.5 equivalents H₂0₂). Table 12 presents data showing the catalytic efficiency of catalysts prepared from varying amounts of quaternized nitrogen compound (4 - 7 equivalents) and the recyclability of each catalyst. For each catalyst presented in Table 12, the indicated number of catalyst runs was the number of consecutive catalyst runs conducted with catalyst recycling in which greater than 97% conversion of DBT was observed.

Table 12: Catalyst Recyclability for Catalysts Prepared Using Varying

Amounts of Quaternized Nitrogen Compound

Consecutive

°/o Conversion,

Q Catalytic Runs

Entry Run 1

(# of equivalents) with >97% DBT

(25 min, 75°C)

Conversion

1 [(C₁₈H₃₇)N⁺(CH3)3] 99.8 6

(4 equivalents)

2 t(C_l8H37)N⁺(CH₃)3] 99.4 3 Consecutive

% Conversion,

Catalytic Runs

Entry Q Run 1

(# of equivalents) with >97% DBT

(25 min, 75°C)

Conversion

(5 equivalents)

3 [(Ci8H₃7) ⁺(CH₃)3] 99.4 9

(6 equivalents)

4 [(C₁₈H₃7)N⁺(CH₃)3] 99.2 9

(7 equivalents)

As shown in Table 12, better catalyst recyclability was apparently observed when higher quantities of quaternized nitrogen compound were used to form the catalyst.

[0093] Table 13 presents catalyst recyclability data for catalysts prepared using additional quaternized nitrogen compounds. In each case, the catalyst was prepared using phosphotungstic acid that had been pre-neutralized with 6 equivalents of NaOH and then reacted with 4 equivalents of the indicated quaternized nitrogen compound.

Table 13: Catalyst Recyclability for Catalysts Prepared Using Other

Quaternized Nitrogen Compounds

H₂0₂/

Q Equiv. Equiv. Catalyst Temp. Time °/o

Run

Entry (# of equivalents) Catalyst H₂0₂ Ratio (°C) (min) Conv.

#

1 [(Ci₈H₃₇)₂N⁺(CH₃)₂] 0.01 3.5 350 75 1 25 87.3

(4 equiv.)

2 30 91.1

3 30 97.4

4 30 85.2

2 Benzalkonium¹ 0.012 3.5 292 75 1 25 68.1

(4 equiv.)

2 30 91.2 3 30 97.6 4 30 93.1 benzalkonium = benzyl(CH₃)₂R (R = 60% C₁₂H₂₅, 40% C₁₄H₂₉)

As shown in Table 13, the indicated quaternized nitrogen compounds produced somewhat poorer DBT conversion levels and catalyst recyclability than did the catalyst using octadecyltrimethylammonium bromide as the quaternized nitrogen compound.

[0094] Comparative Example 1: Synthesis of Related Heteropoly Acid Desulfurization Catalysts. Samples of comparative desulfurization catalysts were prepared as described in Zhang, et al., "The oxidation of benzothiophene using the Keggin-type lacunary polytungstophosphate as catalysts in emulsion" J. Mol. Catal. A, 332: 2010, pp. 59-64 (Comparative Sample 1A), and Example 24 of U.S. Patent Application Publication 2011/0015060 (Comparative Sample IB). Specifically, the comparative samples were synthesized using the procedures described in the following paragraphs.

[0095] Comparative Sample 1A: The catalyst of this example was prepared at 0.375-fold the scale described in Zhang, et al. 1.24 g of sodium tungstate dihydrate (3.75 mmol) and 0.12 g of disodium hydrogen phosphate (0.87 mmol) were dissolved in 30 mL deionized water. The pH was then adjusted to 4.8 using 1 M HN0₃ solution. The reaction mixture was then warmed to 80°C, and a solution of 0.6 g octadecyltrimethylammonium bromide (1.73 mmol) in 7.5 mL ethanol was added dropwise. A white precipitate formed immediately. After continuously stirring for 5 minutes at 80°C, the resulting mixture was filtered and dried at 60°C in vacuum for 12 hours to obtain the catalyst. The yield was 1.291 g (88%). Zhang et al. describes the reaction product as having the formula

.

[0096] Comparative Sample IB: The catalyst of this example was prepared at 0.25-fold - the scale described in Example 24 of the patent publication. 2.5 grams of ammonium metatungstate (0.85 mmol) and 0.25 g sodium phosphate (1.53 mmol) were dissolved in 20 mL of deionized water. After vigorously stirring in a water bath at 25°C for 30 minutes, 10 mL of 1 : 2 HCI was added, and a mixed solution was obtained after stirring for 30 minutes. The pH after HCI addition was 1.4. Thereafter, a solution of 0.65 g octadecyltrimethylammonium chloride (1.49 mmol) in 2.5 mL of deionized water was added dropwise to the above solution at 80°C for 1 hour while stirring vigorously. A white precipitate formed immediatel ._Stirring was continued for 3 hours. The white precipitate was isolated via filtration, washed with water, and dried in a vacuum. The yield was 1.74 g (94%). The patent publication describes the reaction product as having the formula [Ci8H37N(CH₃)3]4HNa₂[PW₁₁039] . It should be noted that the yield noted in the patent publication corresponds to a yield of 141%.

[0097] Comparative Example 2: Comparison of Catalytic Activity of Related Heteropoly Acid Desulfurization Catalysts to Catalysts Prepared as Described Herein. Comparative Samples 1A and IB were analyzed for catalytic activity side-by-side with the catalyst set forth in Table 11 above that was prepared using 4 equivalents of the quaternary ammonium salt. Specifically, the catalyst in Table 11 was prepared by partially neutralizing phosphotungstic acid with 6 equivalents of NaOH and combining the partially neutralized phosphotungstic acid with 4 equivalents of octadecyltrimethylammonium bromide (see Example 2). Freshly prepared samples of the catalysts were used for comparison of the catalytic activity as well as subsequent analytic measurements (see Comparative Example 3). Catalytic activity was measured using 500 ppm DBT in 9 : 1 heptane/toluene and 3.5 equivalents of 35 wt. % H₂0₂ at 75°C as generally described above. Results are summarized in Table 14 below.

Table 14: Comparison of Catalytic Activity at 75°C of Comparative

Time %

Entry Catalyst (min) Conv.

1 Comparative Sample 1A 15 97.9

25 99.3

2 Comparative Sample IB 15 8.1

25 23.0

3 Catalyst of Table 11 15 97.3

(4 equivalents of

[(C₁₈H37)N⁺(CH₃)3])

25 99.3

[0098] As demonstrated in Table 14, the catalyst prepared as described in Zhang, et al. (Comparative Sample 1A) had a similar catalytic activity to that of a corresponding catalyst prepared by the methods described herein. In contrast, the catalyst prepared as described in the patent publication (Comparative Sample IB) displayed a much lower catalytic activity.

[0099] Comparative Example 3: Analytical Characterization of Related Heteropoly Acid Desulfurization Catalysts in Comparison to Catalysts Prepared as Described Herein. Comparative Samples 1A and IB were analyzed by elemental analyses (semi-quantitative X-ray fluorescence and combustion analyses), thermogravimetric analysis/differential scanning calorimetry, infrared spectroscopy, and ³¹P magic angle spinning nuclear magnetic resonance (NMR) spectroscopy. Analogous measurements were made on samples of the catalysts of Table 11 that were prepared using either 4 or 6 equivalents of octadecyltrimethylammonium bromide. Again, it is to be emphasized that the analyses presented in this Comparative Example were obtained in side-by-side measurements using freshly prepared samples. Some of the analytical measurements of the catalysts of Table 11 replicate those presented previously. For those cases where replicate measurements were performed, there was good agreement between the data obtained from the freshly prepared sample and that of the historical data. Phosphotungstic acid was run as a standard in the analytical characterization methods, as appropriate.

[OOIOO] Elemental Analyses: Table 15 summarizes the X-ray fluorescence and combustion analyses of the comparative catalyst samples and the catalysts of Table 11.

Table 15: Unsealed Semi-Quantitative and Quantitative Analyses of

As in

iquantitative x-ray analyses in Table 15 are scaled to 100% without consideration for the C, H, and N amounts. Upon obtaining the C, H, and N analyses, the semi-quantitative x-ray analyses were then scaled on a molar basis to obtain the total composition scaled to 100% (wt. % unaccounted for by C, H and N). Table 16 summarizes the scaled elemental composition values taking into account the combustion analyses. The combustion analyses of Comparative Sample 1A are comparable to those reported in Zhang, et al. (C: 30.94%, H : 5.95%, N : 1.52%). Table 17 summarizes the experimentally determined mole ratios of several of the elements in the samples.

Table 16: Scaled Semi-Quantitative and Quantitative Analyses of Comparative Catalyst Samples and the Catalysts of Table 11

Catalyst of Table 11 Catalyst of Table 11

Comparative Comparative (4 equivalents of (6 equivalents of Sample 1A Sample IB [(C_l8H37)N⁺(CH₃)3]) [(C.₈H37)N⁺(CH₃)3])

(Wt. % of Composition)

c 30.55 24.18 26.98 30.27

H 5.68 4.39 4.83 5.47

N 1.69 1.27 1.44 1.62

Na 0.69 0.22 0.22

P 0.72 0.11 0.44 0.65

W 47.1 55.4 51.2 47.35

0 13.5 14.6 14.0 13.2

Table 17: Summary of Elemental Ratios in Comparative Catalyst

Samples and the Catalysts of Table 11

Mole Ratio Mole Ratio Mole Ratio Mole Ratio

Na/P Na/Br W/P O/W

Comparative Sample 1A 1.28 11.0 3.29

Comparative Sample IB 84.5 3.02

Catalyst of Table 11 0.68 0.91 19.5 3.14

(4 equivalents of

Catalyst of Table 11 0.45 0.63 12.3 3.21

(6 equivalents of

[(C₁₈H37)N⁺(CH₃)3])

[00101] As shown in Tables 15 - 17, the catalyst of Zhang, et al. displayed a considerably higher sodium level and higher sodium: phosphorus ratio than did the catalysts of Table 11. The analyses of these tables is consistent with the catalyst composition proposed by Zhang, et al. (i.e. , [Ci₈H37 (CH₃)3]5Na2[PW₁₁0₃₉]). In contrast, the analytical results of the catalysts from Table 11 are consistent with their composition being predominated by the protic salt form (i.e. , [Ci8H37N(CH3)3]4H₃[PWii039] or [C₁₈H37N(CH₃)3]6H[PW₁₁039]). It should be noted that both the 4-equivalent catalyst from Table 11 and phosphotungstic acid were disposed in a binder when conducting the X-ray fluorescence measurements, and both displayed lower than expected phosphorus analyses. The elemental analyses for Comparative Sample IB, except for a much lower than anticipated phosphorus analysis, were somewhat consistent with the proposed formulation from the patent publication. However, more detailed analyses presented herein below indicated that a completely different compound was formed when preparing Comparative Sample IB.

[OIOO] Thermogravimetric Analyses/Differential Scanning Calorimetry: Thermal breakdown of the catalyst samples into W0₃ was monitored by thermogravimetric analysis and differential scanning calorimetry. A temperature range of 25°C to 800°C was scanned at a ramp rate of 10°C/min for these measurements. Samples were heated in air during the analyses and purged for 10 minutes prior to the commencement of heating. The thermogravimetric analysis and differential scanning calorimetry results are summarized in Table 18.

Table 18: Thermogravimetric Analyses and Differential Scanning Calorimetry-Thermogravimetric Analyses of Comparative Catalyst

Total Total Weight Predicted

Weight Loss Loss by Weight

by TGA (%) DSC-TGA (o/o) Loss (%)

Comparative Sample 1A 41.02 40.5 40.5

Comparative Sample IB 32.97 31.15 35.4

35.56 34.80 35.1

40.13 39.92 39.9

[0101] Again, the weight loss data for Comparative Sample 1A was consistent with the composition proposed by Zhang, et al., and that of the catalysts of Table 11 was consistent with a predominant protic salt form. There was a considerable discrepancy between the observed weight loss of Comparative Sample IB and the proposed composition from the patent publication.

[0102] Fourier Transform Infrared (FTIR) Spectroscopy: FTIR spectra of each sample were next collected. Table 19 summarizes the FTIR results along with the proposed band assignment. FIGURES 4A - 4E show illustrative FTIR spectra of phosphotungstic acid, Comparative Samples 1A and IB, and catalysts from Table 11. Table 19: FTIR Analyses of Phosphotungstic Acid, Comparative Catalyst Samples and the Catalysts of Table 11

Wavenumbers (cm^'1)

(P-O) (W=0) (W-0-W)_comer (W-O-W)edge

Phosphotungstic Acid 1090 990 890 810

(FIGURE 4A)

Comparative Sample 1A 1075, 1050, 930 890, 850 820 (broad), (FIGURE 4B) 1040 760 and 730

(narrow)

Gomparative Sample IB 1080 (weak) 980 900 810

(FIGURE 4C)

Catalyst of Table 11 1080, 1040 930, 980 890 820 (broad,

(4 equivalents of 760 and 730 [(C₁₈H37)N⁺(CH₃)3]) (narrow) (FIGURE 4D)

Catalyst of Table 11 1080, 1040 930 890, 830 800 (broad),

(6 equivalents of 700 (narrow) [(C₁₈H37)N⁺(CH₃)3])

(FIGURE 4E)

As shown in Table 19 and FIGURES 4B, 4D, and 4E, the FTIR spectra of

Comparative Sample 1A and the catalysts of Table 11 were very similar to one another. In contrast, the FTIR spectrum of Comparative Sample IB differed markedly from those of the other samples. Taken together with this sample's very low phosphorus analysis, a different composition than that proposed by the patent publication is likely for this compound. Without being bound by any theory or mechanism, it is believed that Comparative Sample 2, synthesized according to Example 24 of the patent publication, corresponded to a quaternary ammonium salt of a metatungstate ion.

[0103] ³¹P Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy f³¹P MAS NMR): Solid state ³¹P MAS NMR spectra of each sample were next collected. Table 20 summarizes the ³¹P MAS NMR results relative to a phosphoric acid standard. FIGURE 5 shows stacked illustrative ³¹P MAS NMR spectra of phosphotungstic acid, Comparative Samples 1A and IB, and the catalysts from Table 11.

Table 20: ³¹P MAS NMR Analyses of Phosphotungstic Acid, Comparative

Catalyst Samples and the Catalysts of Table 11

ppm ppm ppm ppm (mole °/o) (mole %) (mole %) (mole %)

Phosphotungstic Acid -15.8 (100)

Comparative Sample -10.6 (80.4) -11.2 (19.6)

1A Comparative Sample -14.6 (15.6) IB -15.5 (84.4)

-11.3 (63.2) -13.0 (8.8) -15.5 (28.1)

-11.3 (18.8) -13.0 (40.7) -15.5 (10.3)

As with the FTIR spectra, the ³¹P MAS NMR spectra again demonstrated that Comparative Sample IB differed considerably from all of the other samples. The ³¹P MAS NM R data for Comparative Sample IB was more consistent with a PW₁2O4₀ structure. Furthermore, the weak ³¹P NMR signal for this sample suggests that it was a minor component of the sample, which is also consistent with this sample's low phosphorus content.

[0104] Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present invention. The invention illustratively disclosed herein suitably may be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein. While compositions and methods are described in terms of "comprising," "containing," or "including" various components or steps, the compositions and methods can also "consist essentially of" or "consist of" the various components and steps. All numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, "from about a to about b," or, equivalently, "from approximately a to b," or, equivalently, "from approximately a-b") disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles "a" or "an," as used in the claims, are defined herein to mean one or more than one of the element that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent or other documents that may be incorporated herein by reference, the definitions that are consistent with this specification should be adopted.

Claims

CLAIMS What is claimed is the following :

1. A method comprising :

providing an oxidation catalyst comprising a solid reaction product obtained from a reaction between a quaternized nitrogen compound and a heteropoly acid that has been at least partially neutralized with a base, the solid reaction product having a molar ratio of an alkali metal to phosphorus of less than about 1;

combining the oxidation catalyst with an oxidizing agent and a petroleum source comprising an oxidizable sulfur compound;

reacting at least a portion of the oxidizable sulfur compound to form an oxidized sulfur compound; and

removing the oxidized sulfur compound from the petroleum source to form a reduced sulfur content petroleum product.

2. The method of claim 1, wherein the oxidizing agent comprises at least one of a hydrogen peroxide solution or an organic peroxide.

3. The method of claim 1, wherein the oxidizing agent comprises a hydrogen peroxide solution having a hydrogen peroxide concentration ranging between about 30% and about 35% by weight.

4. The method of claim 1, wherein the oxidizing agent comprises a hydrogen peroxide solution and an amount of hydrogen peroxide combined with the oxidation catalyst ranges between about 2 equivalents and about 50 equivalents relative to the oxidizable sulfur compound.

5. The method of claim 1, wherein the oxidizing agent comprises a hydrogen peroxide solution and an amount of hydrogen peroxide combined with the oxidation catalyst ranges between about 3 equivalents and about 10 equivalents relative to the oxidizable sulfur compound.

6. The method of claim 1, wherein an amount of the oxidation catalyst combined with the oxidizing agent and the petroleum source is about 0.01 equivalents or less relative to the oxidizable sulfur compound.

7. The method of claim 1, wherein the oxidizable sulfur compound comprises dibenzothiophene.

8. The method of claim 1, wherein reacting takes place at a temperature ranging between about 25°C and about 100°C.

9. The method of claim 1, further comprising :

separating the oxidation catalyst from the reduced sulfur content petroleum product; and

recycling the oxidation catalyst in another oxidation process.

10. The method of claim 1, wherein combining the oxidation catalyst with the oxidizing agent and the petroleum source takes place using mechanical mixing or under flow conditions.

11. The method of claim 1, wherein the heteropoly acid comprises at least one heteropoly acid selected from the group consisting of H₃PWi₂0 o, H3PMO12O40, H₃SiW₁₂04o, and H3S1M012O40.

12. The method of claim 1, wherein the heteropoly acid has been partially neutralized to a pH ranging between about 2 and about 7.

13. The method of claim 1, wherein between about 3 equivalents and about 8 equivalents of an alkali metal base are used to partially neutralize the heteropoly acid.

14. The method of claim 1, wherein between about 4 equivalents and about 7 equivalents of the quaternized nitrogen compound are reacted with the partially neutralized heteropoly acid.

15. The method of claim 1, wherein the solid reaction product comprises a compound having a chemical formula of Q7-_xH_xPWii0₃9 ;

wherein Q is a quaternary ammonium ion and x is a real number ranging between 0 and about 3.

16. A method comprising :

forming a partially neutralized heteropoly acid at a pH ranging between about 2 and about 7;

combining the partially neutralized heteropoly acid with a quatemized nitrogen compound in an aqueous reaction medium;

reacting the partially neutralized heteropoly acid and the quatemized nitrogen compound in the aqueous reaction medium to form a solid reaction product that precipitates from the aqueous reaction medium; and

isolating the solid reaction product.

17. The method of claim 16, wherein between about 3 equivalents and about 8 equivalents of an alkali metal base are used to partially neutralize the heteropoly acid .

18. The method of claim 16, wherein between about 4 equivalents and about 7 equivalents of the quaternized nitrogen compound are reacted with the partially neutralized heteropoly acid.

19. The method of claim 16, further comprising :

heating the aqueous reaction medium while reacting occurs.

20. The method of claim 16, wherein the partially neutralized heteropoly acid is added to the quaternized nitrogen compound.

21 . The method of claim 16, wherein the aqueous reaction medium lacks any organic solvents.

22. The method of claim 16, wherein the aqueous reaction medium is water.

23. The method of claim 16, wherein the heteropoly acid comprises at least one heteropoly acid selected from the group consisting of H₃PWi₂0₄o, H3PMO12O40, H₃SiW₁₂0₄o, and H₃SiMoi₂O₄₀.

24. The method of claim 16, wherein the quaternized nitrogen compound comprises a pyridinium halide, a quinolinium halide or a compound having a formula of Ρ ⁺Χ^", wherein X is a halide and each R comprises 1 to about 50 carbon atoms, each R being selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an aralkyi group, an alkylaryl group and a cycloalkyl group.

25. The method of claim 16, wherein the solid reaction product comprises a compound having a chemical formula of

wherein Q is a cation comprising a quaternized nitrogen atom, Y is Si or P, Z is W or Mo, and x is a real number ranging between 0 and about 3.

26. The method of claim 16, wherein the solid reaction product comprises a compound having a chemical formula of Q7-xH_xPWii0₃₉;

wherein Q is a quaternary ammonium ion and x is a real number ranging between 0 and about 3.

27. The method of claim 16, wherein the solid reaction product has a molar ratio of an alkali metal to phosphorus of less than about 1 .

28. An oxidation catalyst comprising:

a solid reaction product obtained from a reaction between a quatemized nitrogen compound and a heteropoly acid that has been at least partially neutralized with a base, the solid reaction product having a molar ratio of an alkali metal to phosphorus of less than about 1.

29. The oxidation catalyst of claim 28, wherein the heteropoly acid has been partially neutralized to a pH ranging between about 2 and about 7.

30. The oxidation catalyst of claim 28, wherein between about 3 equivalents and about 8 equivalents of an alkali metal base are used to partially neutralize the heteropoly acid.

31. The oxidation catalyst of claim 28, wherein the heteropoly acid comprises at least one heteropoly acid selected from the group consisting of H₃PW₁₂0₄o, H3PM012O40, H₃SiW₁₂0₄o, and H₃SiM O12O40.

32. The oxidation catalyst of claim 28, wherein the quatemized nitrogen compound comprises a pyridinium halide, a quinolinium halide or a compound having a formula of P N⁺X^", wherein X is a halide and each R comprises 1 to about 50 carbon atoms, each R being selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an aralkyi group, an alkylaryl group and a cycloalkyl group.

33. The oxidation catalyst of claim 28, wherein the quatemized nitrogen compound is selected from the group consisting of a tetramethylammonium halide, a tetraethylammonium halide, a tetrabutylammonium halide, an octadecyltrimethylammonium halide, a dimethyldioctadecylammonium halide, a benzyldimethyloctadecylammonium halide, a hexadecylpyridinium halide, a benzalkonium halide, and any combination thereof.

34. The oxidation catalyst of claim 28, wherein between about 4 equivalents and about 7 equivalents of the quatemized nitrogen compound are reacted with the partially neutralized heteropoly acid.

35. The oxidation catalyst of claim 28, wherein the solid reaction product comprises a compound having a chemical formula of (^ xHxPWuOsg;

wherein Q is a quaternary ammonium ion and x is a real number ranging between 0 and about 3.

36. A method comprising :

providing an oxidation catalyst comprising a solid reaction product obtained from a reaction between a quaternized nitrogen compound and a heteropoly acid that has been at least partially neutralized with a base;

combining the oxidation catalyst with an oxidizing agent in the absence of an oxidizable compound;

after combining the oxidation catalyst and the oxidizing agent, combining a petroleum source comprising an oxidizable sulfur compound with the oxidation catalyst and the oxidizing agent;

reacting at least a portion of the oxidizable sulfur compound to form an oxidized sulfur compound; and

removing the oxidized sulfur compound from the petroleum source to form a reduced content sulfur petroleum product.

37. The method of claim 36, wherein the solid reaction product has a molar ratio of an alkali metal to phosphorus of less than about 1.

38. The method of claim 36, wherein the oxidizing agent comprises at least one of a hydrogen peroxide solution or an organic peroxide.

39. The method of claim 36, wherein the oxidizing agent comprises a hydrogen peroxide solution having a hydrogen peroxide concentration ranging between about 30% and about 35% by weight.

40. The method of claim 36, further comprising :

heating the oxidation catalyst and the oxidizing agent before combining the petroleum source.

41. The method of claim 36, wherein the oxidizing agent comprises a hydrogen peroxide solution and an amount of hydrogen peroxide combined with the oxidation catalyst ranges between about 2 equivalents and about 50 equivalents relative to the oxidizable sulfur compound.

42. The method of claim 36, wherein the oxidizing agent comprises a hydrogen peroxide solution and an amount of hydrogen peroxide combined with the oxidation catalyst ranges between about 3 equivalents and about 10 equivalents relative to the oxidizable sulfur compound.

43. The method of claim 36, wherein an amount of the oxidation catalyst combined with the oxidizing agent and the petroleum source is about 0.01 equivalents or less relative to the oxidizable sulfur compound.

44. The method of claim 36, wherein the oxidizable sulfur compound comprises dibenzothiophene.

45. The method of claim 36, wherein reacting takes place at a temperature ranging between about 25°C and about 100°C.

46. The method of claim 36, further comprising :

separating the oxidation catalyst from the reduced sulfur content petroleum product; and

recycling the oxidation catalyst in another oxidation process.

47. The method of claim 36, wherein combining the oxidation catalyst with the oxidizing agent and the petroleum source takes place using mechanical mixing or under flow conditions.

48. The method of claim 36, wherein the heteropoly acid comprises at least one heteropoly acid selected from the group consisting of H₃PWi₂0₄o, H₃PMo₁₂O₄₀, H₃SiW₁₂0₄o, and H₃SiMOi₂O₄₀.

49. The method of claim 36, wherein the heteropoly acid has been partially neutralized to a pH ranging between about 2 and about 7.

50. The method of claim 36, wherein between about 3 equivalents and about 8 equivalents of an alkali metal base are used to partially neutralize the heteropoly acid.

51. The method of claim 36, wherein between about 4 equivalents and about 7 equivalents of the quaternized nitrogen compound are reacted with the partially neutralized heteropoly acid.

52. The method of claim 36, wherein the solid reaction product comprises a compound having a chemical formula of

wherein Q is a quaternary ammonium ion and x is a real number ranging between 0 and about 3.

53. A method comprising :

providing an oxidation catalyst comprising a solid reaction product obtained from a reaction between a quaternized nitrogen compound and a heteropoly acid;

combining the oxidation catalyst with an oxidizing agent in the absence of an oxidizable compound;

after combining the oxidation catalyst and the oxidizing agent, combining a petroleum source comprising an oxidizable sulfur compound with the oxidation catalyst and the oxidizing agent; reacting at least a portion of the oxidizable sulfur compound to form an oxidized sulfur compound; and

removing the oxidized sulfur compound from the petroleum source to form a reduced sulfur content petroleum product.

54. The method of claim 53, wherein the oxidizing agent comprises at least one of a hydrogen peroxide solution or an organic peroxide.

55. The method of claim 53, wherein the oxidizing agent comprises a hydrogen peroxide solution having a hydrogen peroxide concentration ranging between about 30% and about 35% by weight.

56. The method of claim 53, further comprising :

heating the oxidation catalyst and the oxidizing agent before combining the petroleum source.

57. The method of claim 53, wherein the oxidizing agent comprises a hydrogen peroxide solution and an amount of hydrogen peroxide combined with the oxidation catalyst ranges between about 2 equivalents and about 50 equivalents relative to the oxidizable sulfur compound.

58. The method of claim 53, wherein the oxidizing agent comprises a hydrogen peroxide solution and an amount of hydrogen peroxide combined with the oxidation catalyst ranges between about 3 equivalents and about 10 equivalents relative to the oxidizable sulfur compound.

59. The method of claim 53, wherein an amount of the oxidation catalyst combined with the oxidizing agent and the petroleum source is about 0.01 equivalents or less relative to the oxidizable sulfur compound.

60. The method of claim 53, wherein the oxidizable sulfur compound comprises dibenzothiophene.

61. The method of claim 53, wherein reacting takes place at a temperature ranging between about 25°C and about 100°C.

62. The method of claim 53, further comprising :

separating the oxidation catalyst from the reduced sulfur content petroleum product; and

recycling the oxidation catalyst in another oxidation process.

63. The method of claim 53, wherein combining the oxidation catalyst with the oxidizing agent and the petroleum source takes place using mechanical mixing or under flow conditions.

64. The method of claim 53, wherein the heteropoly acid comprises at least one heteropoly acid selected from the group consisting of H₃PWi₂0₄o, H₃PMo₁₂O₄₀ H₃SiW₁₂O₄₀, and H₃SiMo₁₂O₄₀.