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  Diesel fuel additive compositions for improvement of particulate trapsRelated Patent Categories: Fuel And Related Compositions, Liquid Fuels (excluding Fuels That Are Exclusively Mixtures Of Liquid Hydrocarbons), Aluminum Or Heavy Metal, Other Than Lead, ContainingThe Patent Description & Claims data below is from USPTO Patent Application 20060230672. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This invention relates to novel fuel additive compositions. More particularly, this invention relates to a metal salt-ashless detergent additive combination which has been found highly effective in improving the quality of emissions from the combustion of diesel fuels. These additives are especially effective in improving the performance of particulate traps which are used in the exhaust systems of diesel engines, amongst other uses. [0002] Diesel engines equipped with particulate traps, mounted in the exhaust stream, to "trap" or collect particulates in the exhaust to prevent their emission to the atmosphere are expected to be in greater use in the next few years. [0003] Diesel engines running without particulate traps emit unburned hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NO.sub.x), and particulates, all of which are subject to current or proposed regulation. The problems of controlling these pollutants are compounded because there is a trade-off between particulates and nitrogen oxides: when the combustion conditions are modified to favor low nitrogen oxides emissions, particulates are increased. Particulate traps are employed to reduce the severity of the particulate emissions. [0004] It now appears that a combination of techniques, including diesel traps and systems that use nitrogen oxides, will be required to meet realistic clean air goals. This manner of reducing particulates will be necessary because the techniques available for NO.sub.x reduction, such as timing changes and exhaust gas recirculation, require a trade-off with particulates. The achievement of lower emissions of NO.sub.x, unburned hydrocarbons, and carbon monoxide, while controlling particulates over reasonable periods of time, continues to present a technical challenge. [0005] Diesel particulates, their effect and control, are at the center of much concern and controversy. Their chemistry and environmental impact present complex issues. Generally, the diesel particulate matter is principally solid particles of carbon and metal compounds with adsorbed hydrocarbons, sulfates and aqueous species. Among the adsorbed species are aldehydes and polycyclic aromatic hydrocarbons. Some of these organics have been reported to be potential carcinogens or mutagens. Unburned hydrocarbons are related to the characteristic diesel odor and include aldehydes such as formaldehyde and acrolein. The need to control nano-particles is likely to lead to mandates requiring traps. [0006] Unfortunately, increasing the recovery of particulates simply by modifying trap design or size would increase the rate of back pressure buildup within the trap, which causes increased fuel consumption and poor driveability. Moreover, control of the various pollutants seems to be interrelated, with reduction of one sometimes increasing levels of another. By modifying combustion to achieve more complete oxidation, decreases can be achieved for pollutants resulting from incomplete combustion, but NO.sub.x is typically increased under these conditions. [0007] It is clear that diesel traps (either catalyzed or uncatalyzed) will be required in order to control particulates, especially where efforts are made to control NO.sub.x. [0008] The use of diesel traps and the need to improve them has resulted in a great deal of research and a great number of patents and technical publications. The traps are typically constructed of metal or ceramic and are capable of collecting the particulates from the exhaust and withstanding the heat produced by oxidation of carbonaceous deposits which must be burned off at regular intervals. [0009] This burning off, or regeneration, could occur by itself if the operating temperature of the trap were sufficiently high. However, in the typical situation, the exhaust temperature is not constantly high enough, and secondary measures such as electrically heating to raise the trap temperature or using a catalyst on the washcoat to reduce the combustion temperature of particulates, have not been fully successful. [0010] The use of organometallic salts and complexes to improve the operation of diesel engine particulate traps is disclosed, for example, in U.S. Pat. No. 5,344,467 issued Sep. 6, 1994, which teaches the use of a combination of an organometallic complex and an antioxidant. The organometallic complex is soluble or dispersible in the diesel fuel and is derived from an organic compound containing at least two functional groups attached to a hydrocarbon linkage. [0011] WO99/36488 published Jul. 22, 1999 discloses fuel additive compositions which contain at least one iron-containing fuel-soluble or fuel-dispersible species in synergistic combination with at least one alkaline earth group metal-containing fuel-soluble or fuel-dispersible species. This combination of metallic additives is said to improve the operation of the diesel particulate filter traps. [0012] Also pertinent to the subject matter of this invention is U.S. Pat. No. 4,946,609 issued Aug. 7, 1990, which teaches the use of iron compounds such as ferrocene, ferrocene derivatives and iron salts of organic acids as additives for lubricating oils used for diesel engines. It is taught that the presence of the iron compounds in the lubricating oil facilitates the regeneration of the diesel particle filters. [0013] WO94/11467 published May 26, 1994 teaches a method to improve the operation of diesel traps through the use of a fuel additive comprising fuel-soluble compositions of a platinum group metal in effective amounts to lower the emissions of unburned hydrocarbons and carbon monoxide from the trap. The platinum group metals comprise platinum, palladium, rhodium or iridium. [0014] The present invention is based upon the discovery that the novel additive combination of oil soluble metal salt additives and nitrogen containing ashless detergents is a stable additive system and is cooperatively effective in fuel in improving the operation of diesel engine particulate traps. [0015] In accordance with the present invention there have been discovered additive compositions for diesel fuel oils for use in diesel engines equipped with particulate traps which comprise the combination of a metal oil soluble or dispersible salt additive and a nitrogen containing oil soluble ashless detergent additive present in the diesel fuel in such amounts so as to provide in the fuel 1-25 ppm (by weight) of the metal and 10-500 ppm of the dispersant additive. Preferably, there is employed a metal salt additive so as to provide about 2-10 ppm of metal in the fuel, such as about 5-10 ppm metal, and 10-250 ppm of the ashless detergent additive such as about 10-25, 10-50, 50-200 ppm or 10-200 ppm of the ashless detergent (active ingredient basis). [0016] Stable solutions or dispersions of the additive compositions of this invention in a suitable solvent comprise a further embodiment of this invention. Such additive concentrates will contain 20 to 80% of active material, which is the combination of the metal salt and ashless detergent. The active materials are present in the solvent in such amounts so as to provide in the fuel 1 to 25 ppm of metal and 10 to 500 ppm of ashless detergent. Such solutions or dispersions remain stable over a broad temperature range, especially solutions or dispersions containing iron or calcium. [0017] The solvent used to prepare the stable additive solutions or dispersions may generally be characterized as a normally liquid petroleum or synthetic hydrocarbon or oxygenated hydrocarbon or alcohol solvents, such as hexanol, 2-ethylkexanol or isodecyl alcohol solvent. Typical examples include kerosene, hydrotreated kerosene, isoparaffinic and paraffinic solvents and naphthenic aliphatic hydrocarbon solvents, aromatic solvents, dimers and higher oligomers or propylene, butene and similar olefins and mixtures thereof. Commercial products such as "Solvesso", "Varsol", "Norpar" and "Isopar" are suitable. Such solvents may also contain functional groups other than carbon and hydrogen provided such groups do not adversely affect the performance of the additive composition. Preferred are isoparaffinic and paraffinic hydrocarbon solvents. Preferably, the solvent has a flash point greater than 20.degree. C., more preferably greater than 40.degree. C., most preferably greater than 55.degree. C. [0018] A wide variety of metals are suitable for forming the metal salt useful as additives in the present invention. The metal may be an alkali metal, preferably Na, an alkaline earth metal, such as Ca, Mg or Sr, a Group IVB metal, especially Ti or Zr, a Group VIII metal, such as Mn, a Group VIIB metal, particularly Fe, a Group IB metal, especially Cu, a Group IIB metal, such as Zn or any of the rare earth (lanthanide series of metals) metals having atomic numbers 57-71, especially cerium, or mixtures of any of the foregoing metals. The most preferred metal is iron. [0019] It has been found that the combined additive system greatly improves the operation of diesel exhaust particulate traps by lowering the ignition temperature of the particulates which build up in the trap, and this improvement is observed by noting the reduction in back pressure buildup when fuels containing the metal salt dispersant combination are used in the diesel engine. The improvements observed in accordance with the present invention are particularly surprising since it has been found that diesel fuels containing only the dispersant and not the metal salt will not improve the operation of the particulate traps and will in fact cause a greater back pressure buildup then what is observed with the same fuel containing no additive. Similarly, diesel fuels containing only the metal salt additive and not the ashless detergent do not provide as great an improvement in the performance of the diesel particulate traps. [0020] In one embodiment of the invention the additive combination is admixed with the diesel fuel by direct addition, or as part of a concentrate with other additives, and the diesel fuel is used to operate a diesel engine equipped with an exhaust system particulate trap. The diesel fuel containing the additive is contained in a fuel tank, transmitted to the diesel engine where it is burned, and the additive reduces the ignition temperature of exhaust particles collected in the exhaust system particulate trap. In another embodiment, the foregoing operational procedure is used except that the additive combination is maintained on board the apparatus being powered by the diesel engine (e.g., automobile, bus, truck, etc.) in a separate fuel additive dispenser apart from the diesel fuel. The additive is combined or blended with the diesel fuel during re-filling of the diesel fuel tank. Typically, the additive is dispensed in the form of a solution in a hydrocarbon solvent. In this latter embodiment, the additive is maintained in the fuel additive dispenser and can form a part of a fuel additive concentrate of the concentrate being combined with the diesel. Other techniques comprise adding the additive combination into the intake or exhaust manifold or adding the additive to the fuel at fuel depots prior to filling the tank of the diesel powered vehicle. Also, the metal salt may be added to a fuel which already has the ashless detergent present. However, the fuels compositions embodiments of the present invention do not extend to fuels compositions containing a metal salt where the metal salt is a mixture composed of one or more cerium fatty acid carboxylates, such as cerium octadecanoate or other cerium C8-C22 fatty acid carboxylates, and 50% or more cerium oxide, unless such mixture has been added to the fuel as part of an additive combination with ashless detergent. [0021] A category of metal salt additives useful in this invention are those which comprise a polar head with long hydrophobic tail, with the polar head comprising a metal salt of an acid organic compound. The salts may contain a substantially stoichiometric amount of the metal in which they are usually described as normal or neutral salts, and would typically have a total base number (TBN), as may be measured by ASTM D-2896 of from 0 to 80. It is possible to include large amounts of a metal base by reacting an excess of a metal compound such as an oxide or hydroxide with an acid gas such as carbon dioxide. The resulting overbased salt comprises neutralized salt as the outer layer of a metal base (e.g., carbonate) micelle. Such overbased salts may have a TBN of 150 or greater, and typically from 250 to 600, such as in the range of from 350 to 450 TBN. Overbasing for all metals useful in this invention may be from the use of metal oxide. [0022] The salt may be neutral in that it contains a stoichiometric ratio of metal cations to carboxylate anions. It may also be acidic or overbased. Acidic salts contain an excess of carboxylic acid/carboxylate over that which would be considered stoichiometric and overbased salts contains an excess of metal species over the stoichiometric ratio. This excess metal may exist in one or a combination of forms including oxide, hydroxides or mixed oxidic salts. Lattice-like polynuclear-metal complexes may also be present. [0023] For overbased salts, the excess metal may be introduced, either intentionally or unintentionally, during the main reaction process or alternatively may be introduced subsequent to this via post treatment. The elemental metal, oxides and hydroxides are common feedstocks for the overbasing process. [0024] Metal salts that may be used include oil soluble or dispersible neutral and overbased sulfonates, phenates, sulfurized phenates, thiophosphonates, salicylates, and naphthenates and other oil-soluble carboxylates of a metal, particularly iron, cerium and the alkali or alkaline earth metals, e.g., sodium, potassium, lithium, calcium, and magnesium. The most commonly used metals are iron, cerium, calcium and magnesium, and mixtures of calcium and/or magnesium with sodium. Particularly convenient metal salts are neutral and overbased calcium sulfonates having TBN of from 20 to 600 TBN, and neutral and overbased calcium phenates and sulfurized phenates having TBN of from 50 to 600 as well as iron neodecanoates and naphthenates. Sulfonates, salicylates and naphthenates are preferred. The metal salts may also be acidic, i.e., it may contain up to 20% of unreacted free acid such as 1-20% by weight free acid. Continue reading... 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