Patent Publication Number: US-2009217570-A1

Title: Method of Controlling By-Products or Pollutants from Fuel Combustion

Description:
FIELD OF INVENTION 
     The present invention relates to a method comprising supplying to the fuel a dispersion, the dispersion comprises: (a) a mixture of at least two metal bases, wherein each metal of the metal bases has an average oxidation state of (+2) or higher. The method is capable of controlling by-products or pollutants from fuel combustion. 
     BACKGROUND OF THE INVENTION 
     In recent years attempts have been made to reduce the amount of pollutants/emissions released from combustion of fuels. Examples of pollutants include sulphur oxides (e.g. sulphur trioxide), nitrogen oxides, carbon monoxide, carbon dioxide and particulate matter. These pollutants are known to adversely affect levels of green-house gases or contribute to other problems, such as, smog. In the case of particulate matter, studies have also indicated adverse effects on human, animal and plant well being. Other by-products of fuel combustion include vanadate deposits. Vanadate deposits are believed to form corrosive low-melting slag that forms deposits. It would be desirable to combust fuels whilst keeping pollutants to a minimum. 
     International Publication WO 2005/097952 discloses providing a fuel composition containing a metal base with a solids content of greater than about 35 wt % of the dispersion. The composition disclosed employs one metal base per dispersion. 
     International Publication WO 04/026996 discloses a fuel additive composition capable of reducing vanadate deposits. The composition contains a metal inorganic oxygen containing compound, a liquid soluble in oil and a dispersant including fatty acid or ester derivatives thereof. 
     However, none of the dispersions provide an improved method of reducing numerous pollutants emitted during fuel combustion. Therefore it would be advantageous to provide a method of controlling pollutants from fuel combustion. The present invention provides such a method, by providing a dispersion which synergistically reduces numerous pollutants emitted during fuel combustion. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method of controlling by-products or pollutants from fuel combustion, comprising combusting a fuel containing a dispersion, the dispersion comprises: (a) a mixture of at least two metal bases, wherein each metal of the metal bases has an average oxidation state of about (+2) or higher, (b) at least one surfactant; and (c) at least one organic medium, wherein the metal bases are uniformly dispersed in the organic medium. 
     In one embodiment the invention provides a method of controlling by-products or pollutants from fuel combustion, comprising combusting a fuel containing a dispersion, the dispersion comprises: (a) a mixture of at least three metal bases, wherein each metal of the metal bases has an average oxidation state of about (+2) or higher, (b) at least one surfactant; and (c) at least one organic medium, wherein the metal bases are uniformly dispersed in the organic medium. 
     In one embodiment the invention provides a dispersion comprising: (a) a mixture of at least three metal bases, wherein each metal of the metal bases has an average oxidation state of about (+2) or higher, (b) at least one surfactant; and (c) at least one organic medium, wherein the metal bases are uniformly dispersed in the organic medium. 
     In one embodiment the invention provides a composition comprising: (i) a fuel; and (ii) a dispersion, wherein the dispersion comprises: (a) a mixture of at least two metal bases, wherein each metal of the metal bases has an average oxidation state of about (+2) or higher, (b) at least one surfactant; and (c) at least one organic medium, wherein the metal bases are uniformly dispersed in the organic medium. 
     In one embodiment the invention provides a composition comprising: (i) a fuel; and (ii) a dispersion, the dispersion comprises: (a) a mixture of at least three metal bases, wherein each metal of the metal bases has an average oxidation state of about (+2) or higher, (b) at least one surfactant; and (c) at least one organic medium, wherein the metal bases are uniformly dispersed in the organic medium. 
     In one embodiment the invention provides for the use of a dispersion, (the dispersion comprises: (a) a mixture of at least three metal bases, wherein each metal of the metal bases has an average oxidation state of about (+2) or higher, (b) at least one surfactant; and (c) at least one organic medium, wherein the metal bases are uniformly dispersed in the organic medium) in a fuel for the reduction of by-products or pollutants formed from fuel combustion. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a method of controlling by-products or pollutants from fuel combustion as disclosed above. The invention further provides a composition as disclosed above. 
     In one embodiment the invention is other than a water-containing emulsion. 
     As used herein the term “free of” for all chemistry disclosed herein except for the metal base, as used in the specification and claims, defines the absence of a material except for the amount which is present as impurities, e.g., a trace amount or a non-effective amount. Typically in this embodiment, the amount present will be less than about 0.05% or less than about 0.005 wt % by weight of the dispersion. 
     As a person skilled in the art will appreciate, impurities in the metal base are typically about 1 wt % to about 3 wt % of the metal base. The reason for the impurities being typically about 1 wt % to about 3 wt % of the metal base is believed to be due to mining processes. Typically the major impurities in the metal base include calcium carbonates, silica or silicates. 
     In different embodiments the dispersion may be opaque or semi-translucent or translucent or transparent, or any gradation between such descriptions. 
     Fuel 
     The fuel comprises a liquid fuel, biofuel, a solid fuel, or mixtures thereof. In one embodiment the fuel is a solid fuel. In another embodiment the fuel is a liquid fuel. Examples of a suitable solid fuel include coal. 
     When the fuel comprises a liquid fuel, the liquid fuel may also be utilized as a suitable organic medium for preparing the dispersion. Therefore to avoid duplication of description a more detailed description of the liquid fuel is disclosed below in the organic medium section. 
     Metal Base 
     The dispersion of the metal base comprises di-, tri-, tetra-valent metal or a mixture thereof. 
     In embodiment the metal base may further comprise a monovalent metal base. In one embodiment the metal base is derived from a monovalent metal including lithium, potassium, sodium, copper, or mixtures thereof. In one embodiment the metal oxidation state of the metal base is other than (+1). 
     In another embodiment the average oxidation state of the metal base ranges from about (+2) to about (+4), or from about (+2) to about (+3). Typically the metal of the metal base is a divalent or trivalent metal. In one embodiment the metal base is derived from a divalent metal including magnesium, calcium, barium or mixtures thereof. The metal may also have multiple valences, e.g., mono- or di- or tri-valent with cerium, copper or iron as examples. In one embodiment the metal base is derived from a tetravalent metal including cerium. 
     In different embodiments the base of the metal base comprises oxides, carbonates, bicarbonates, hydroxides, sulphonates, carboxylates (e.g. C 1-30  or C 8-24  linear or branched alkyl carboxylates), nitrates, phosphates, sulphates, sulphites, nitrites, phosphonates, or mixtures thereof. 
     In different embodiments the base of the metal base comprises oxides, carbonates, bicarbonates, hydroxides, sulphonates, carboxylates, or mixtures thereof. Optionally the metal base further comprises water of crystallization or adsorped (or absorbed) water. In one embodiment the metal base is crystalline. 
     In different embodiments a first metal base comprises iron oxide (Fe 2 O 3 , FeO or Fe 3 O 4 ), iron carboxylates (e.g. an octadecanoic acid salt with iron), magnesium hydroxide, calcium hydroxide, calcium carbonate, magnesium carbonate, calcium oxide, magnesium oxide or mixtures thereof. 
     In different embodiments a second metal base comprises cerium oxide (CeO or CeO 2 ), cerium sulphonate, iron oxide (Fe 2 O 3 , FeO or Fe 3 O 4 ), iron carboxylates (e.g. an octadecanoic acid salt with iron), copper oxide (CuO) or chromium oxides. 
     In one embodiment the metal base is substantially free of metal bases other than two or three bases selected from the group consisting of magnesium hydroxide, calcium hydroxide, calcium carbonate, magnesium carbonate, calcium oxide, magnesium oxide, cerium oxide (CeO or CeO 2 ), iron oxide (Fe 2 O 3 , FeO or Fe 3 O 4 ), copper oxide (CuO) or chromium oxides, and mixtures thereof. 
     In one embodiment a first metal base contains a metal selected from the group consisting of iron, magnesium, calcium and mixtures thereof; and a second metal base contains a metal selected from the group consisting of magnesium, calcium, cerium, iron, copper, chromium, and mixtures thereof, with the proviso that the first metal base is different from the second metal base. 
     In one embodiment when there are at least two metal bases in the mixture, each metal of the metal bases has an oxidation state of about (+2) or higher are employed, and the metals may be chosen from: 
     (i) a first metal base contains a metal selected from the group consisting of iron, magnesium, calcium and mixtures thereof; 
     (ii) a second metal base contains a metal selected from the group consisting of magnesium, calcium, cerium, iron, copper, chromium, and mixtures thereof, with the proviso that the first metal base is different from the second metal base; and 
     (iii) optionally another metal base other than the metal base of (i) or (ii). 
     In one embodiment the first metal base is present in a weight greater than the second metal base. The weight of the first metal base present may be greater than about 50 wt %, or greater than about 75 wt %, or greater than about 95 wt % of the total amount of metal base present. The weight of the second metal base present may be less than about 50 wt %, or less than about 25 wt %, or less than about 5 wt % of the total amount of metal base present. 
     In one embodiment when there are at least three metal bases in the mixture, each metal of the metal bases has an oxidation state of about (+2) or higher are employed, and the metals may be chosen from:
         (i) a first metal base contains a metal selected from the group consisting of iron, magnesium, calcium and mixtures thereof;   (ii) a second metal base contains a metal selected from the group consisting of magnesium, calcium, cerium, iron, copper, chromium, and mixtures thereof, with the proviso that the first metal base is different from the second metal base; and   (iii) at least one other metal base, wherein the metal of the metal base is selected from the group consisting of calcium, magnesium, cerium, iron, copper, chromium, barium, platinum, lead, manganese, strontium, and mixtures thereof, with the proviso that the third metal base is a different from the metal base already employed in (i) and (ii).       

     In one embodiment the metal of the metal base of (iii) is selected from the group consisting of calcium, magnesium, cerium, iron, copper, chromium, and mixtures thereof; with the proviso that the third metal base is different from a metal base already employed in (i) and (ii). 
     When at least three metal bases are employed in one embodiment two of the metal bases are derived from a calcium and magnesium base. The third (or higher i.e. fourth or fifth) metal base may be derived from a metal selected from the group consisting of cerium, iron, copper, chromium, and mixtures thereof. 
     The amount of metal base present in the dispersion, that is, the solids content, is greater than about 15 wt % and may range from about 17 wt % to about 90 wt %, or from about 25 wt % to about 80 wt %, or from about 35 wt % to about 70 wt %, or from about 40 wt % to about 65 wt % of the dispersion. This amount is determined on the basis of the original dispersion and does not include any additional diluent into which the dispersion may be subsequently admixed to form, for instance, a fully formulated lubricating composition, nor does it include solids or non-volatile components from other sources. 
     The metal base is typically in the form of a solid and is not appreciably soluble in the organic medium. In different embodiments the metal base has a mean particle size in the dispersion ranging from about 20 nanometres to less than about 1 μm, or about 30 nanometres to about 0.7 μm, or about 50 nanometres to about 0.4 μm, or about 80 nanometres to about 0.3 μm. 
     The metal base generally comprises at least one of oxides, hydroxides or carbonates. Examples of a suitable metal base include magnesium hydroxide, calcium hydroxide, calcium carbonate, magnesium carbonate, calcium oxide, magnesium oxide, cerium oxide, iron oxide or mixtures thereof. In one embodiment of the invention the metal base is present in a mixture, for instance, dolmitic lime, which is commercially available. 
     If the invention further comprises a metal base with an oxidation state of (+1), examples of a suitable metal base include sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, potassium hydroxide, sodium hydroxide, anhydrous lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium oxide or mixtures thereof. 
     In one embodiment the dispersion further comprises a co-ordination compound, such as, ferrocene (cyclopentadienyl based), carboxylates or sulphonates. 
     Surfactant 
     The surfactant includes an ionic (cationic or anionic) or non-ionic compound. Generally, the surfactant stabilises the dispersion of the metal base in the organic medium. 
     Suitable surfactant compounds include those with a hydrophilic lipophilic balance (HLB) ranging from about 1 to about 40, or about 1 to about 20, or about 1 to about 18, or about 2 to about 16, or about 2.5 to about 15. In different embodiments the HLB may be about 11 to about 14, or less than about 10 such as about 1 to about 8, or about 2.5 to about 6. Combinations of surfactants may be used with individual HLB values outside of these ranges, provided that the composition of a final surfactant blend is within these ranges. When the surfactant has an available acidic group, the surfactant may become the metal salt of the acidic group and where the metal is derived from the metal base. 
     Examples of surfactants suitable for the invention are disclosed in  McCutcheon&#39;s Emulsifiers and Detergents,  1993, North American &amp; International Edition. Generic examples include alkanolamides, alkylarylsulphonates, amine oxides, poly(oxyalkylene) compounds, including block copolymers comprising alkylene oxide repeat units (e.g., Pluronic™), carboxylated alcohol ethoxylates, ethoxylated alcohols, ethoxylated alkyl phenols, ethoxylated amines and amides, ethoxylated fatty acids, ethoxylated fatty esters and oils, fatty esters, glycerol esters, glycol esters, imidazoline derivatives, phenates, lecithin and derivatives, lignin and derivatives, monoglycerides and derivatives, olefin sulphonates, phosphate esters and derivatives, propoxylated and ethoxylated fatty acids or alcohols or alkyl phenols, sorbitan derivatives, sucrose esters and derivatives, sulphates or alcohols or ethoxylated alcohols or fatty esters, polyisobutylene succinicimide and derivatives. 
     In one embodiment the surfactant comprises polyesters as defined in column 2, line 44 to column 3, line 39 of U.S. Pat. No. 3,778,287. Examples of suitable polyester surfactants are prepared in U.S. Pat. No. 3,778,287 as disclosed in Polyester Examples A to F (including salts thereof). 
     In one embodiment the surfactant is a hydrocarbyl substituted aryl sulphonic acid (or sulphonate) of an alkali metal, alkaline earth metal or mixtures thereof. The aryl group of the aryl sulphonic acid may be phenyl or naphthyl. In one embodiment the hydrocarbyl substituted aryl sulphonic acid comprises alkyl substituted benzene sulphonic acid. 
     The hydrocarbyl (especially an alkyl) group typically contains about 8 to about 30, or about 10 to about 26, or about 10 to about 15 carbon atoms. In one embodiment the surfactant is a mixture of C 10  to C 15  alkylbenzene sulphonic acids. Examples of sulphonates include dodecyl and tridecyl benzene sulfonates or condensed naphthalenes or petroleum sulfonates, as well as sulphosuccinates and derivatives. 
     In one embodiment the surfactant is in the form of a neutral or overbased surfactant, typically salted with an alkali or alkaline earth metal. The alkali metal includes lithium, potassium or sodium; and the alkaline earth metal includes calcium or magnesium. In one embodiment the alkali metal is sodium. In one embodiment the alkaline earth metal is calcium. 
     In one embodiment the surfactant is a derivative of a polyolefin. Typical examples of a polyolefin include polyisobutene; polypropylene; polyethylene; a copolymer derived from isobutene and butadiene; a copolymer derived from isobutene and isoprene; or mixtures thereof. 
     Typically the derivative of a polyolefin comprises a polyolefin-substituted acylating agent optionally further reacted to form an ester and/or aminoester. The acylating agent may be prepared from carboxylic reactants (which when reacted with a polyolefin give the desired acylating agent, i.e. substrate for the surfactant). The carboxylic reactants include functional groups, such as a carboxylic acid or anhydride thereof. Examples of carboxylic reactants include an alpha, beta-unsaturated mono- or polycarboxylic acid, anhydride ester or derivative thereof. Examples of carboxylic reactants thus include (meth) acrylic acid, methyl(meth)acrylate, maleic acid or anhydride, fumaric acid, itaconic acid or anhydride, or mixtures thereof, each of which may typically be in the form of the saturated materials (e.g. succinic anhydride) after reaction with the polyolefin. 
     In one embodiment the polyolefin is a derivative of polyisobutene with a number average molecular weight of at least 250, 300, 500, 600, 700, or 800, to 5000 or more, often up to 3000, 2500, 1600, 1300, or 1200. Typically, less than about 5% by weight of the polyisobutylene used to make the derivative molecules have  Mn  less than about 250, more often the polyisobutylene used to make the derivative has  Mn  of at least about 800. The polyisobutylene used to make the derivative preferably contains at least about 30% terminal vinylidene groups, more often at least about 60% or at least about 75% or about 85% terminal vinylidene groups. The polyisobutylene used to make the derivative may have a polydispersity,  Mw /  Mn , greater than about 5, more often from about 6 to about 20. 
     In various embodiments, the polyisobutene is substituted with succinic anhydride, the polyisobutene substituent having a number average molecular weight ranging from about 1,500 to about 3,000, or about 1,800 to about 2,300, or about 700 to 1 about 700, or about 800 to about 1000. The ratio of succinic groups per equivalent weight of the polyisobutene typically ranges from about 1.3 to about 2.5, or about 1.7 to about 2.1, or about 1.0 to about 1.3, or about 1.0 to about 1.2. 
     In one embodiment the surfactant is polyisobutenyl-dihydro-2,5-furandione ester with pentaerythritol or mixtures thereof. In one embodiment the surfactant is a polyisobutylene succinic anhydride derivative such as a polyisobutylene succinimide or derivatives thereof. In one embodiment the surfactant is substantially free to free of a basic nitrogen. 
     Other typical derivatives of polyisobutylene succinic anhydrides include hydrolysed succinic anhydrides, esters or diacids. Polyisobutylene succan derivatives are preferred to make the metal base dispersions. A large group of polyisobutylene succinic anhydride derivatives are taught in U.S. Pat. No. 4,708,753, and U.S. Pat. No. 4,234,435. 
     In another embodiment the surfactant comprises a salixarene (or salixarate if in the form of a metal salt). The salixarene is defined as an organic substrate of a salixarate. The salixarene may be represented by a substantially linear compound comprising at least one unit of the formulae (I) or (II): 
     
       
         
         
             
             
         
       
     
     each end of the compound having a terminal group of formulae (III) or (IV): 
     
       
         
         
             
             
         
       
     
     such groups being linked by divalent bridging groups, which may be the same or different for each linkage; wherein f is about 1, 2 or 3, in one embodiment about 1 or 2; R 2  is hydroxyl or a hydrocarbyl group and j is about 0, 1, or 2; R 3  is hydrogen or a hydrocarbyl group; R 4  is a hydrocarbyl group or a substituted hydrocarbyl group; g is about 1, 2 or 3, provided at least one R 4  group contains 8 or more carbon atoms; and wherein the compound on average contains at least one of unit (I) or (III) and at least one of unit (II) or (IV) and the ratio of the total number of units (I) and (III) to the total number of units of (II) and (IV) in the composition is about 0.1:1 to about 2:1. 
     The U group in formulae (I) and (III) may be an —OH or an —NH 2  or —NHR 1  or —N(R X ) 2  group located in one or more positions ortho, meta, or para to the —COOR 3  group. R 1  is a hydrocarbyl group containing 1 to 5 carbon atoms. When the U group comprises a —OH group, formulae (I) and (III) are derived from 2-hydroxybenzoic acid (often called salicylic acid), 3-hydroxybenzoic acid, 4-hydroxybenzoic acid or mixtures thereof. When U is a —NH 2  group, formulae (I) and (III) are derived from 2-aminobenzoic acid (often called anthranilic acid), 3-aminobenzoic acid, 4-aminobenzoic acid or mixtures thereof. 
     The divalent bridging group, which may be the same or different in each occurrence, includes an alkylene or methylene bridge such as —CH 2 — or —CH(R)— and an ether bridge such as —CH 2 OCH 2 — or —CH(R)OCH(R)— where R is an alkyl group having 1 to 5 carbon atoms and where the methylene and ether bridges are derived from formaldehyde or an aldehyde having 2 to 6 carbon atoms. 
     Often the terminal group of formulae (III) or (IV) further contains 1 or 2 hydroxymethyl groups ortho to a hydroxy group. In one embodiment of the invention hydroxymethyl groups are present. In one embodiment of the invention hydroxymethyl groups are not present. A more detailed description of salixarene and salixarate chemistry is disclosed in EP 1 419 226 B1, including methods of preparation as defined in Examples 1 to 23 (page 11, line 42 to page 13, line 47). 
     In one embodiment the surfactant is substantially free of, to free of, a fatty acid or derivatives thereof, such as esters. In one embodiment the surfactant is other than a fatty acid or derivatives thereof. 
     In one embodiment the surfactant comprises at least of hydrocarbyl substituted aryl sulphonic acids, derivatives of polyolefins, polyesters or salixarenes (or salixarates). 
     In different embodiments the surfactant is substantially free of, to free of, phospholipids, (such as lecithin) and/or amino acids (such as sarcosines). 
     In one embodiment the surfactant has a molecular weight of less than 1000, in another embodiment less than about 950, for example, about 250, about 300, about 500, about 600, about 700, or about 800. The amount of surfactant and metal base in the dispersion may vary as is shown in Table 1, the balance being the organic medium and optionally water. 
     In one embodiment the amount of the organic medium present in the dispersion varies from about 25 wt % to about 55 wt %. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Embodiments (wt % of dispersion) 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Additive 
                 1 
                 2 
                 3 
                 4 
               
               
                   
                   
               
               
                   
                 Metal Base 
                   17-90 
                 25-80 
                 35-70 
                 40-65 
               
               
                   
                 Surfactant 
                 0.01-30 
                  1-30 
                  2-30 
                  5-25 
               
               
                   
                   
               
            
           
         
       
     
     Organic Medium 
     The organic medium may comprise an oil of lubricating viscosity, a liquid fuel, a hydrocarbon solvent or mixtures thereof. Typically the organic solvent comprises an oil of lubricating viscosity or a liquid fuel. 
     Optionally the organic medium contains water, typically up to about 1 wt %, or about 2 wt % or about 3 wt % of the dispersion. In different embodiments the organic medium is substantially free of, to free of, water. 
     Oils of Lubricating Viscosity 
     In one embodiment the organic medium comprises an oil of lubricating viscosity. Such oils include natural and synthetic oils, oil derived from hydrocracking, hydrogenation, and hydrofinishing, unrefined, refined and re-refined oils and mixtures thereof. 
     Unrefined oils are those obtained directly from a natural or synthetic source generally without (or with little) further purification treatment. 
     Refined oils are similar to the unrefined oils except they have been further treated in one or more purification steps to improve one or more properties. Purification techniques are known in the art and include solvent extraction, secondary distillation, acid or base extraction, filtration, percolation and the like. 
     Re-refined oils are also known as reclaimed or reprocessed oils, and are obtained by processes similar to those used to obtain refined oils and often are additionally processed by techniques directed to removal of spent additives and oil breakdown products. 
     Natural oils useful in making the inventive lubricants include animal oils, vegetable oils (e.g., castor oil, lard oil), mineral lubricating oils such as liquid petroleum oils and solvent-treated or acid-treated mineral lubricating oils of the paraffinic, naphthenic or mixed paraffinic-naphthenic types and oils derived from coal or shale or mixtures thereof. 
     Synthetic lubricating oils are useful and include hydrocarbon oils, such as, polymeric tetrahydrofurans, polymerised and interpolymerised olefins (e.g., polybutylenes, polypropylenes, propyleneisobutylene copolymers); poly(1-hexenes), poly(1-octenes), poly(1-decenes), and mixtures thereof; alkyl-benzenes (e.g. dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes, di-(2-ethylhexyl)-benzenes); polyphenyls (e.g., biphenyls, terphenyls, alkylated polyphenyls); alkylated diphenyl ethers and alkylated diphenyl sulphides and the derivatives, analogs and homologs thereof or mixtures thereof. 
     Other synthetic lubricating oils include. Synthetic oils may be produced by Fischer-Tropsch reactions and typically may be hydroisomerised Fischer-Tropsch hydrocarbons or waxes. 
     Oils of lubricating viscosity may also be defined as specified in the American Petroleum Institute (API) Base Oil Interchangeability Guidelines. The five base oil groups are as follows: Group I (sulphur content&gt;0.03 wt %, and/or &lt;90 wt % saturates, viscosity index 80-120); Group II (sulphur content≦0.03 wt %, and ≧90 wt % saturates, viscosity index 80-120); Group III (sulphur content≦0.03 wt %, and ≧90 wt % saturates, viscosity index≧120); Group IV (all polyalphaolefins (PAOs)); and Group V (all others not included in Groups I, II, III, or IV). The oil of lubricating viscosity comprises an API Group I, Group II, Group III, Group IV, Group V oil and mixtures thereof. Often the oil of lubricating viscosity is an API Group I, Group II, Group III, Group IV oil and mixtures thereof. Alternatively the oil of lubricating viscosity is often an API Group I, Group II, Group III oil or mixtures thereof. 
     Liquid Fuel 
     The liquid fuel is normally a liquid at ambient conditions. The liquid fuel includes a hydrocarbon fuel, a biofuel (such as, bio-diesel), a nonhydrocarbon fuel, or a mixture thereof. The hydrocarbon fuel may be a petroleum distillate such as a gasoline as defined by ASTM (American Society for Testing and Materials) specification D4814 or a diesel fuel as defined by ASTM specification D975. In an embodiment the liquid fuel is a gasoline, and in another embodiment the liquid fuel is a leaded gasoline, or a nonleaded gasoline. In another embodiment the liquid fuel is a diesel fuel. The hydrocarbon fuel includes a hydrocarbon prepared by a gas to liquid process for example hydrocarbons prepared by a process such as the Fischer-Tropsch process. The nonhydrocarbon fuel includes an oxygen containing composition (often referred to as an oxygenate), an alcohol, an ether, a ketone, an ester of a carboxylic acid, a nitroalkane, or a mixture thereof. The nonhydrocarbon fuel includes methanol, ethanol, methyl t-butyl ether, methyl ethyl ketone, transesterified oils and/or fats from plants and animals such as rapeseed methyl ester and soybean methyl ester, and nitromethane. Mixtures of hydrocarbon and nonhydrocarbon fuels include gasoline and methanol and/or ethanol, diesel fuel and ethanol, and diesel fuel and a transesterified plant oil such as rapeseed methyl ester. In one embodiment the liquid fuel is a nonhydrocarbon fuel or a mixture thereof. 
     The dispersion may be used as a sole additive for a fuel composition. In one embodiment the dispersion is used as one additive in combination with other performance additives to provide a fuel composition. In one embodiment the invention provides a fuel composition comprising (i) a dispersion comprising: (a) a metal base; (b) a surfactant; and (c) an organic medium in which the metal base is dispersed; (ii) an oil of lubricating viscosity; and (iii) other performance additives. 
     The fuel composition may thus comprise an oil of lubricating viscosity as defined above, in addition to the amount which may be present as the organic medium of the dispersion. 
     Other Performance Additives 
     The fuel composition optionally comprises other performance additives. The other performance additives comprise at least one of metal deactivators, detergents, dispersants, friction modifiers, corrosion inhibitors, antioxidants, foam inhibitors, demulsifiers, pour point depressants, seal swelling agents, biocides, anti-foulants, flow improvers (include polymethacrylates, maleic anhydride-styrene interpolymers, polyalphaolefins, and ethylene vinyl acetates), cold flow improvers, or mixtures thereof. Typically, fully-formulated fuel will contain one or more of these performance additives. 
     Performance additives such as antiwear agents are typically included in a fuel in 2-stroke marine diesel cylinder lubricant. 
     Demulsifiers 
     Demulsifiers are known. In one embodiment the dispersion further comprises demulsifiers, or mixtures thereof. Examples of demulsifiers include trialkyl phosphates, polyethylene glycols, polyethylene oxides, polypropylene oxides and (ethylene oxide-propylene oxide) polymers, alkoxylated alkyl phenol resins or mixtures thereof. 
     Dispersants 
     Dispersants are often known as ashless-type dispersants because, prior to mixing in a lubricating oil composition, they do not contain ash-forming metals and they do not normally contribute any ash forming metals when added to a lubricant. Dispersants also include polymeric dispersants. Ashless type dispersants are characterised by a polar group attached to a relatively high molecular weight hydrocarbon chain. Typical ashless dispersants include N-substituted long chain alkenyl succinimides. Examples of N-substituted long chain alkenyl succinimides include polyisobutylene succinimide with number average molecular weight of the polyisobutylene substituent in the range 350 to 5000, or 500 to 3000. Succinimide dispersants and their preparation are disclosed, for instance in U.S. Pat. No. 4,234,435. Succinimide dispersants are typically the imide formed from a polyamine, typically a poly(ethyleneamine). 
     In one embodiment the invention further comprises at least one dispersant derived from polyisobutylene succinimide with number average molecular weight in the range 350 to 5000, or 500 to 3000. The polyisobutylene succinimide may be used alone or in combination with other dispersants. 
     In one embodiment the invention further comprises at least one dispersant derived from polyisobutylene, an amine and zinc oxide to form a polyisobutylene succinimide complex with zinc. The polyisobutylene succinimide complex with zinc may be used alone or in combination. 
     Another class of ashless dispersant is Mannich bases. Mannich dispersants are the reaction products of alkyl phenols with aldehydes (especially formaldehyde) and amines (especially polyalkylene polyamines). The alkyl group typically contains at least 30 carbon atoms. 
     In one embodiment the dispersant includes a polyisobutylene-amine as described in U.S. Pat. Nos. 5,567,845 and 5,496,383; and commercially available from BASF. 
     The dispersants may also be post-treated by conventional methods by a reaction with any of a variety of agents. Among these are boron sources such as boric acid or borates, urea, thiourea, dimercaptothiadiazoles, carbon disulphide, aldehydes, ketones, carboxylic acids, hydrocarbon-substituted succinic anhydrides, maleic anhydride, nitriles, epoxides, and phosphorus compounds. 
     Detergents 
     The fuel composition optionally further comprises neutral or overbased detergents. Suitable detergent substrates include sulphonates, salixarates, salicylates, carboxylates, phosphorus acid salts, mono- and/or di-thiophosphoric acid salts, phenates including alkyl phenates and sulphur coupled alkyl phenates, or saligenins. 
     In different embodiments, the fuel composition further comprises at least one of sulphonates and phenates. When present, the detergents are typically overbased. The ratio of TBN delivered by the dispersion to that delivered by the detergent may range from 1:99 to 99:1, or 15:85 to 85:15. 
     Antioxidant 
     Antioxidant compounds are known and include an amine antioxidant (such as an alkylated diphenylamine), a hindered phenol, a molybdenum dithiocarbamate, and mixtures thereof. Antioxidant compounds may be used alone or in combination. 
     The hindered phenol antioxidant often contains a secondary butyl and/or a tertiary butyl group as a sterically hindering group. The phenol group is often further substituted with a hydrocarbyl group and/or a bridging group linking to a second aromatic group. Examples of suitable hindered phenol antioxidants include 2,6-di-tert-butylphenol, 4-methyl-2,6-di-tert-butylphenol, 4-ethyl-2,6-di-tert-butylphenol, 4-propyl-2,6-di-tert-butylphenol or 4-butyl-2,6-di-tert-butylphenol 2,6-di-tert-butylphenol. In one embodiment the hindered phenol antioxidant is an ester and may include, e.g., Irganox™ L-135 from Ciba. A more detailed description of suitable ester-containing hindered phenol antioxidant chemistry is found in U.S. Pat. No. 6,559,105. 
     Suitable examples of molybdenum dithiocarbamates which may be used as an antioxidant include commercial materials sold under the trade names such as Vanlube 822™ and Molyvan™ A from R. T. Vanderbilt Co., Ltd., and Adeka Sakura-Lube™ S-100, S-165 and S-600 from Asahi Denka Kogyo K. K and mixtures thereof. 
     Antiwear Agent 
     The fuel composition optionally further comprises at least one antiwear agent. Examples of suitable antiwear agents include a sulphurised olefin, sulphur-containing ashless anti-wear additives, metal dihydrocarbyldithiophosphates (such as zinc dialkyldithiophosphates), thiocarbamate-containing compounds, such as thiocarbamate esters, thiocarbamate amides, thiocarbamic ethers, alkylene-coupled thiocarbamates, and bis(S-alkyldithiocarbamyl) disulphides. 
     The dithiocarbamate-containing compounds may be prepared by reacting a dithiocarbamic acid or salt with an unsaturated compound. The dithiocarbamate containing compounds may also be prepared by simultaneously reacting an amine, carbon disulphide and an unsaturated compound. Generally, the reaction occurs at a temperature from 25° C. to 125° C. U.S. Pat. Nos. 4,758,362 and 4,997,969 describe dithiocarbamate compounds and methods of making them. 
     Examples of suitable olefins that may be sulphurised to form an the sulphurised olefin include propylene, butylene, isobutylene, pentene, hexane, heptene, octane, nonene, decene, undecene, dodecene, undecyl, tridecene, tetradecene, pentadecene, hexadecene, heptadecene, octadecene, octadecenene, nonodecene, eicosene or mixtures thereof. In one embodiment, hexadecene, heptadecene, octadecene, octadecenene, nonodecene, eicosene or mixtures thereof and their dimers, trimers and tetramers are especially useful olefins. Alternatively, the olefin may be a Diels-Alder adduct of a diene such as 1,3-butadiene and an unsaturated ester such as butyl(meth)acrylate. 
     Another class of sulphurised olefin includes fatty acids and their esters. The fatty acids are often obtained from vegetable oil or animal oil and typically contain 4 to 22 carbon atoms. Examples of suitable fatty acids and their esters include triglycerides, oleic acid, linoleic acid, palmitoleic acid or mixtures thereof. Often, the fatty acids are obtained from lard oil, tall oil, peanut oil, soybean oil, cottonseed oil, sunflower seed oil or mixtures thereof. In one embodiment fatty acids and/or ester are mixed with olefins. 
     In an alternative embodiment, the ashless antiwear agent may be a monoester of a polyol and an aliphatic carboxylic acid, often an acid containing 12 to 24 carbon atoms. Often the monoester of a polyol and an aliphatic carboxylic acid is in the form of a mixture with a sunflower oil or the like, which may be present in the friction modifier mixture from 5 to 95, in different embodiments from 10 to 90, or 20 to 85, or 20 to 80 weight percent of said mixture. The aliphatic carboxylic acids (especially a monocarboxylic acid) which form the esters are those acids typically containing 12 to 24 or 14 to 20 carbon atoms. Examples of carboxylic acids include dodecanoic acid, stearic acid, lauric acid, behenic acid, and oleic acid. 
     Polyols include diols, triols, and alcohols with higher numbers of alcoholic OH groups. Polyhydric alcohols include ethylene glycols, including di-, tri- and tetraethylene glycols; propylene glycols, including di-, tri- and tetrapropylene glycols; glycerol; butane diol; hexane diol; sorbitol; arabitol; mannitol; sucrose; fructose; glucose; cyclohexane diol; erythritol; and pentaerythritols, including di- and tripentaerythritol. Often the polyol is diethylene glycol, triethylene glycol, glycerol, sorbitol, pentaerythritol or dipentaerythritol. 
     The commercially available monoester known as “glycerol monooleate” is believed to include 60±5 percent by weight of the chemical species glycerol monooleate, along with 35±5 percent glycerol dioleate, and less than 5 percent trioleate and oleic acid. 
     Other performance additives such as corrosion inhibitors including octylamine octanoate, condensation products of dodecenyl succinic acid or anhydride and a fatty acid such as oleic acid with a polyamine; metal deactivators including derivatives of benzotriazoles, 1,2,4-triazoles, benzimidazoles, 2-alkyldithiobenzimidazoles or 2-alkyldithiobenzothiazoles; foam inhibitors including copolymers of ethyl acrylate and 2-ethylhexylacrylate and optionally vinyl acetate; pour point depressants including esters of maleic anhydride-styrene, polymethacrylates, polyacrylates or polyacrylamides; and friction modifiers including fatty acid derivatives such as amines, esters, epoxides, fatty imidazolines, condensation products of carboxylic acids and polyalkylene-polyamines and amine salts of alkylphosphoric acids may also be used in the lubricant composition. 
     Process for Dispersion Preparation 
     The dispersion may be prepared by physical processes, that is, by any one or more of various physical processes, i.e., physical processing steps. Examples of physical process include agitating, milling, grinding, crushing or mixtures thereof. Typically the process grinds the metal base to a mean average particle size of at least 10 nanometres to less than 1 μm. Milling processes include using a rotor stator mixer, a vertical bead mill, a horizontal bead mill, basket milling, ball mill, pearl milling or mixtures thereof. In one embodiment, the physical processes for preparing the dispersion comprise using a vertical or horizontal bead mill. 
     In one embodiment the invention further provides a process for preparing a dispersion comprising the steps of: 
     (1) mixing (a) at least two metal bases, wherein each metal of the metal bases has an average oxidation state of about (+2) or higher; (b) a surfactant and (c) a organic medium, to form a slurry; 
     (2) grinding the slurry of step (1) to form a dispersion. 
     In another embodiment the dispersion may be prepared by forming a single metal dispersion as taught in WO 2005/097952, with the additional step of combining multiple single metal base dispersions (by mixing them together) to form a dispersion comprising at least two metal bases, wherein each metal of the metal bases has an average oxidation state of about (+2) or higher; (b) a surfactant and (c) a organic medium. When a dispersion is prepared by combining multiple single metal base dispersions, it is common for all single metal base dispersions to comprise the same or compatible surfactant compounds and organic media. If the surfactants and organic media are not compatible, unstable dispersions may be formed. 
     In different embodiments the milling process may be carried out in a vertical or horizontal bead mill. Either bead mill processes cause the reduction of particle size of the metal base by high energy collisions of the metal base with at least one bead; and/or other metal base agglomerates, aggregates, solid particles; or mixtures thereof. The beads typically have a mean particle size and mass greater than the desired mean particle size of the metal base. In some instances the beads are a mixture of different mean particle size. The beads used in the grinding may be of materials known to those skilled in the art, such as metal ceramic, glass, stone, or composite materials. 
     The mill typically contains beads present at least about 40 vol %, or at least about 60 vol % of the mill. A range include for example about 60 vol % to about 95 vol %. A more detailed description of making the dispersion is disclosed in U.S. patent application Ser. No. 05/010631. 
     INDUSTRIAL APPLICATION 
     The method of controlling by-products or pollutants from fuel combustion dispersion is useful for numerous open or closed flame combustion systems. Suitable combustion systems include power stations, internal combustion engines, industrial and marine compression engines and turbines (commonly combusting a distillate, residual or heavy fuel oils). 
     In different embodiments a suitable dispersion is added to the fuel in ranges from about 1 ppm to about 10,000 ppm, or from about 20 ppm to about 7500 ppm, or from about 100 ppm to about 5000 ppm, or from about 200 ppm to about 3000 ppm, or from about 500 ppm to about 2000 ppm. 
     In one embodiment, the invention provides a method of controlling by-products or pollutants from fuel combustion, comprising supplying thereto a fuel comprising the dispersion as described herein. The use of the dispersion in a fuel may impart a means of controlling by-products or pollutants from fuel combustion. Typically, the by-products or pollutants from fuel combustion comprise two or more properties from modified sulphur oxide emissions, modified nitrogen oxide emissions, modified particulate matter production, modified vanadate production or mixtures thereof. In one embodiment the fuel dispersion comprises a calcium base and the base is capable of modifying sulphur oxide emissions, and particulate matter production. In one embodiment the fuel dispersion comprises a magnesium base and the base is capable of modifying vanadate production, sulphur oxide emissions, and particulate matter production. 
     The following examples provide an illustration of the invention. These examples are non exhaustive and are not intended to limit the scope of the invention. 
     EXAMPLES 
     Preparative Examples of Dispersions 
     A series of dispersions (Preparative Examples 1 to 3) containing a metal base, an organic medium and a surfactant were prepared from a slurry weighing about 15 kg are prepared using a lab scale Dyno-Mill ECM Multi-Lab horizontal bead mill commercially available from W.A.B. A.G., Basel, using 0.3 mm Ø zirconia/yttria beads and a residence time of about 10 minutes at a tip speed of about 8 ms-1. Where appropriate, the mean particle size of the dispersion particles is determined after cooling by Coulter® LS230 Particle Size Analyser. The dispersions prepared are pourable. 
     Preparative Example 1 
     Magnesium Oxide Dispersion 
     A dispersion is prepared by milling about 50 wt % Magnesium oxide, Magchem 40 ex Martin Marietta, in the presence of about 40 wt % 100 N base oil and about 10 wt % of an alkyl benzene sulphonic acid surfactant. 
     Preparative Example 2 
     Iron Oxide Dispersion 
     A dispersion is prepared by milling about 70 wt % of iron oxide (Fe2O3) commercially available from Bayer as Bayferrox®160, about 18 wt % of 100 N base oil and about 12 wt % of an alkyl benzene sulphonic acid surfactant. 
     Preparative Example 3 
     Cerium Oxide Dispersion 
     A dispersion is prepared by milling about 50 wt % of cerium oxide (CeO), about 40 wt % of 100 N base oil and about 10 wt % of a surfactant (polyolefin amino ester esterified with 2-(dimethylamino)ethanol). 
     Example 1 
     Three Metal Dispersion 
     A three metal dispersion is prepared by mixing the product of Preparative Example 1 with a commercially available cerium sulphonate powder and a octdecanoic acid salt of iron. The final product has a metal weight ratio of magnesium:cerium:iron of about 150:10:5. The product forms a stable dispersion that shows no significant stratification after 12 weeks. 
     Example 2 
     Three Metal Dispersion 
     A three metal dispersion is prepared by blending portions of the products formed in Preparative Examples 1 to 3. The final product has a metal weight ratio of magnesium:cerium:iron of about 150:10:5. The product forms a stable dispersion that shows no significant stratification after 12 weeks The dispersion has greater than about 85% of dispersion particles have a particle size of less than about 0.46 microns. 
     Example 3 
     Three Metal Dispersion 
     A three metal dispersion is prepared by blending in a powder form magnesium oxide, calcium hydroxide and iron oxide (Fe2O 3 ). The resultant three metal powder is then added to about 10 wt % of a succinimide surfactant, and about 39.6 wt % of SN 100 base oil and about 0.4 wt % of a demulsifier. The final dispersion contains 37.5 wt % magnesium oxide, about 10.5 wt % calcium hydroxide and about 2 wt % iron oxide. The resultant dispersion is pourable and with a mean particle size of about 0.14 to about 0.2 microns. 
     Fuel Compositions 1-3 
     Examples 1 to 3 are treated into a liquid fuel at about 1000 ppm respectively. The resultant fuel is combusted and the use of the dispersion provides reduces by-products or pollutants from fuel combustion. 
     Fuel Compositions 4-6 
     Examples 4 to 6 are treated into a liquid fuel at about 1300 ppm respectively. The resultant fuel is combusted and the use of the dispersion provides reduces by-products or pollutants from fuel combustion. 
     Fuel Compositions 7-9 
     Examples 7 to 9 are treated into a liquid fuel at about 1500 ppm respectively. The resultant fuel is combusted and the use of the dispersion provides reduces by-products or pollutants from fuel combustion. 
     Fuel Compositions 10-12 
     Examples 10 to 12 are treated into a liquid fuel at about 700 ppm respectively. The resultant fuel is combusted and the use of the dispersion provides reduces by-products or pollutants from fuel combustion. 
     Fuel Compositions 13-15 
     Examples 13 to 15 are treated into a liquid fuel at about 1750 ppm respectively. The resultant fuel is combusted and the use of the dispersion provides reduces by-products or pollutants from fuel combustion. 
     While the invention has been explained in relation to its preferred embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.