EP1951847A2

EP1951847A2 - Biodiesel fuel compositions having increased oxidative stability

Info

Publication number: EP1951847A2
Application number: EP06839891A
Authority: EP
Inventors: Ibrahim Abou-Nemeh
Original assignee: Novus International Inc
Current assignee: Novus International Inc
Priority date: 2005-11-23
Filing date: 2006-11-15
Publication date: 2008-08-06
Also published as: WO2007062304A2; WO2007062304A3; BRPI0618942A2; US20070113467A1; CA2629613A1

Abstract

The present invention relates to biodiesel fuel compositions that have improved oxidation stability. More specifically, the biodiesel fuel compositions include at least one antioxidant that increases the oxidative stability of the fuel. The biodiesel fuel compositions may also include an antioxidant mixture, or an antioxidant mixture in combination with a polar and/or nonpolar solvent, that increases the oxidative stability of the fuel.

Description

BIODIESEL FUEL COMPOSITIONS HAVING INCREASED OXIDATIVE STABILITY

FIELD OF THE INVENTION

[0001] The present invention relates to biodiesel fuel compositions that have improved oxidation stability. More specifically, the biodiesel fuel compositions include at least one antioxidant that increases the oxidative stability of the fuel.

BACKGROUND OF THE INVENTION

[0002] The use and production of biodiesel as an alternative to vehicle fuel, heating fuel, and engine fuel has increased in recent years due to concerns with limited resources of petroleum based fuels. Biodiesel is typically produced from the transesterification of, for example, vegetable oils, animal fats, and used cooking oils.

[0003] Biodiesel, as it has a higher content of unsaturated fatty acid esters, easily oxidizes in the presence of oxygen, UV light, heat, trace metals, such as iron and copper, among others. The products formed from this oxidation give rise to sediment and gum formation within the fuel and lead to corrosion and plugging in injection pumps and/or fuel lines in engines, heaters, and/or machines which utilize biodiesel as a fuel source.

[0004] As such, there is a need for a biodiesel fuel composition having improved oxidation stability that reduces or eliminates sedimentation and gum formation within the fuel and as such reduces or eliminates corrosion and plugging in injection pumps and/or fuel lines in engines.

SUMMARY OF THE INVENTION

[0005] One aspect of the present invention provides a fuel composition comprising a biodiesel from a source other than rapeseed oil, frying oil, sunflower oil, and beef tallow and at least one antioxidant. The antioxidant is selected from the group consisting of 3,4,5-trihydroxybenzoic acid n-propyl ester, 1 ,2,3- trihydroxybenzene, butylated hydroxyanisole, 2,6-Di-tert-Butyl-1-Hydroxy-4- Methylbenzene, alpha-tocopherol acetate, alpha-tocopherol, gamma-tocopherol, delta-tocopherol, dilauryl thiodipropinate, isopropyl 2-hydroxy-4-methylthio butanoate, propyl gallate, dodecyl gallate, gallic acid, octyl gallate, ascorbyl palmitatθ, lecithin, stearyl citrate, palmityl citrate, chlorophyl, pyrogallol, alpha naphthol, ascorbic acid, natural tocopherol, citric acid, sage extract, rosemary, eugenol, and 6-ethoxy-1 ,2-dihydro~2,2,4-trimethylquinoline.

[0006] Another aspect of the invention provides a fuel composition comprising a biodiesel and an antioxidant mixture. The mixture comprises at least two antioxidants selected from the group consisting of 2-tert-butylhydroquinone, 3,4,5-trihydroxybenzoic acid n-propyl ester, 1 ,2,3-trihydroxybenzene, butylated hydroxyanisole, 2,6-Di-tert-Butyl-1 -Hydroxy-4-Methylbenzene, alpha-tocopherol acetate, alpha-tocopherol, gamma-tocopherol, delta-tocopherol, dilauryl thiodipropinate, isopropyl 2-hydroxy-4-methylthio butanoate, propyl gallate, dodecyl gallate, gallic acid, octyl gallate, ascorbyl palmitate, lecithin, stearyl citrate, palmityl citrate, chlorophyl, pyrogallol, alpha naphthol, ascorbic acid, natural tocopherol, citric acid, sage extract, rosemary, eugenol, and 6-ethoxy-1 ,2-dihydro-2,2,4- trimethylquinoline.

[0007] Yet another aspect of the invention provides a fuel composition comprising a first antioxidant having the Formula (I),

wherein:

R¹, R², R³ and R⁴ are independently selected from the group consisting of hydrogen and an alkyl group having from 1 to about 6 carbons; and

R⁵ is an alkoxy group having from 1 to about 12 carbons a second antioxidant not having the Formula (I), a polar solvent, and a nonpolar solvent, wherein the two solvents form a homogenous liquid.

[0008] A further aspect of the invention provides a method of increasing the oxidative stability of a fuel composition comprising contacting a biodiesel and an antioxidant mixture comprising at least two antioxidants. The two antioxidants are selected from the group consisting of 2-tert-butylhydroquinone, 3,4,5- trihydroxybenzoic acid n-propyl ester, 1 ,2,3-trihydroxybenzene, butylated hydroxyanisole, 2,6-Di-tert-Butyl-1 -Hydroxy-4-Methylbenzene, alpha-tocopherol acetate, alpha-tocopherol, gamma-tocopherol, delta-tocopherol, dilauryl thiodipropinate, isopropyl 2-hydroxy-4-methylthio butanoate, propyl gallate, dodecyl gallate, gallic acid, octyl gallate, ascorbyl palmitate, lecithin, stearyl citrate, palmityl citrate, chlorophyl, pyrogallol, alpha naphthol, ascorbic acid, natural tocopherol, citric acid, sage extract, rosemary, eugenol, and 6-ethoxy-1 ,2-dihydro-2,2,4- trimethylquinoline.

[0009] Other aspects and features of the invention will be in part apparent and in part pointed out hereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Advantageously, the present invention provides biodiesel fuel compositions that have improved oxidation stability. The fuel compositions of the invention comprise a biodiesel and at least one antioxidant that increases the oxidative stability of the fuel. The fuel compositions of the present invention, as such, not only have improved oxidative stability, but also have longer induction times, lower amounts of insolubles, and lower peroxide values.

/. Biodiesel

[001 1 ] The fuel composition of the invention includes a biodiesel. Generally speaking, a biodiesel suitable for use in the invention is typically an ester, such as a mono-alkyl ester, of long chain fatty acids derived from a lipid source. The lipid source may be naturally occurring, such as a lipid derived from a plant or animal, or it may be synthetically produced. In one embodiment, the biodiesel may be produced from vegetable oil, spent cooking oil, or animal fat. In one embodiment, the biodiesel is produced from a vegetable oil. In another embodiment, the biodiesel is produced from a vegetable oil selected from the group consisting of soybean oil, corn oil, rapeseed oil, coconut oil, peanut oil, palm oil, cottonseed oil, sunflower oil, mustard seed oil, camelina oil, jojoba oil, safflower oil, and hemp oil. Other vegetable oils may also be used without departing from the scope of the invention. In an exemplary embodiment, the biodiesel is produced from soybean oil. In another exemplary embodiment, the biodiesel is produced from rapeseed oil. In another embodiment, the biodiesel is produced from plant oil, such as jatropha oil and algae oil. In a further embodiment, the biodiesel is produced from spent cooking oil, such as used frying oil. In yet another embodiment, the biodiesel is produced from animal fat selected from the group consisting of tallow, poultry fat, and lard. In still another embodiment, the biodiesel may be produced from a yellow grease. In yet another embodiment, the biodiesel may be produced from a fish oil, such as menhaden oil, anchovy oil, and mackerel oil, among others. In a further embodiment, the biodiesel may be produced from marine oil, such as whale oil or shark oil. As will be appreciated by the skilled artisan, the biodiesel may also be produced from a combination of lipids derived from different sources. For example, the biodiesel may be produced from soybean oil and animal fat.

[0012] A variety of methods generally known in the art may be used to make the biodiesel of the present invention from any lipid sources known in the art or identified herein. In general, biodiesel is produced through the transesterifcation of vegetable oils, spent cooking oils, or animal fats. Such methods typically include base catalyzed transesterification of the oil or fat with an alcohol, and direct acid catalyzed esterification of the oil or fat with methanol, conversion of the oil or fat to fatty acids, and then to alkyl esters with an acid catalyst. In a base catalyzed transesterification process, an oil or fat is reacted with an alcohol, such as methanol or ethanol, in the presence of a catalyst, such as sodium hydroxide or potassium hydroxide, to produce glycerine and methyl or ethyl esters. The glycerin is then separated from the biodiesel. Once the separation of glycerin and biodiesel is complete, the alcohol is removed by distillation. The glycerin is generally neutralized with an acid and sent to storage as crude glycerin. Once separated from the glycerin, the biodiesel is generally purified by washing it gently with warm water (the methyl ester wash) to remove residual catalysts or soaps, dried and sent to storage.

[0013] The present invention also contemplates blends of biodiesels and petroleum based diesel fuels. It will be appreciated by the skilled artisan that the amount of biodiesel and petroleum diesel present in the fuel composition of the present invention can and will vary depending upon the fuel's intended use. For example, the fuel composition may comprise from about 10% to about 40% by weight biodiesel and from about 60% to about 90% by weight petroleum based diesel. In another embodiment, the fuel composition may comprise from about 20% to about 30% by weight biodiesel and from about 70% to about 80% by weight petroleum based diesel. In yet another embodiment, the fuel composition comprises about 20% by weight biodiesel and about 80% by weight petroleum based diesel, which is known as B20.

//. Antioxidants

[0014] The fuel composition of the invention also includes one or more antioxidants. Generally speaking, antioxidants suitable for use in the present invention inhibit the oxidation process and thus, enhance the fuel composition's oxidative stability and reduce insolubles formation. In particular, applicants have found that by contacting at least one antioxidant with a biodiesel to form a biodiesel fuel composition, the fuel has increased oxidative stability. In addition, to increasing the oxidative stability of the fuel, the antioxidant will further decrease the NO_x, carbon monoxide and other fuel emissions. Those skilled in the art will appreciate that different antioxidants may be used depending on the type of biodiesel to be stabilized.

a. Individual Antioxidants

[0015] In one embodiment, the antioxidant may be selected from the group comprised of butylated hydroxyanisole (BHA); butylated hydroxytoluene; gallates such as octyl gallate, dodecyl gallate, and 3,4,5-trihydroxybenzoic acid n-propyl ester (propyl gallate); 1 ,2,3-trihydroxybenzene (pyrogallol); gallic acid; fatty acid esters including, but not limited to, methyl esters such as methyl linoleate, methyl oleate, methyl stearate, and other esters such as ascorbic palmitate; disulfiram; tocopherols, such as gamma-tocopherol, delta-tocopherol alpha-tocopherol acetate, and alpha- tocopherol marketed under the name COPHEROL 1300® by the company Henkel, and tocopherol derivatives and precursors, such as Coviox T-50 by the company Cognis; deodorized extract of rosemary; propionate esters and thiopropionate esters such as isopropyl 2-hydroxy-4-methylthio butanoate, lauryl thiodipropionate, or dilauryl thiodipropionate; beta-lactoglobulin; ascorbic acid; amino acids such as phenylalanine, cysteine, tryptophan, methionine, glutamic acid, glutamine, arginine, leucine, tyrosine, lysine, serine, histidine, threonine, asparagine, glycine, aspartic acid, isoleucine, valine, and alanine; 2,2,6,6-tetramethylpiperidinooxy, also referred to as tanan; 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, also referred to as tanol; dimethyl-p-phenylaminophenoxysilane; di-p-anisylazoxides; p- hydroxydiphenylamine, and carbonates, phthalates, and adipates thereof; and diludin, a 1 ,4-dihydropyridine derivative.

[0016] In another embodiment, the antioxidant may be selected from the group comprising oil-soluble antioxidants, including, but not limited to ascorbyl palmitate, butylated hydroxytoluene, lecithin, alpha-tocopherol, phenyl-alpha- naphthylamine, hydroquinone, nordihydroguaiaretic acid, and rosemary extract.

[0017] In a further embodiment, the antioxidant may be a synthetic or natural antioxidants selected from the group comprising of Vitamin C and derivatives (ascorbic acid); Vitamin E and derivatives (tocopherols, tocotrienols, acetate); sage extract; eugenol; rosemary; flavonoids and derivatives (including catechins); phenolic acids and derivatives; 2-tert-butylhydroquinone (TBHQ); mixtures of TBHQ, glyceryl oleate, propylene glycol, vegetable oil, and citric acid such as TENOX 20® and TENOX 21® by the company Eastman Chemical Company; imidazolidinyl urea, quaternary ammoniums, diazolidinyl urea; erythorbic acid; sodium erythorbate, lactic acid, calcium ascorbate, sodium ascorbate, potassium ascorbate, ascorbyl stearate, erythorbin acid; sodium erythorbin; butylhydroxinon; sodium or potassium or calcium or magnesium lactate; citric acid; sodium, monosodium, disodium or trisodium citrates; potassium, monopotassium or tripotassium citrate; stearyl citrate; palmityl citrate; tartaric acid; sodium, monosodium or disodium tartrates; potassium, monopotassium tartrate or dipotassium tartrate; sodium potassium tartrate; phosphoric acid; sodium, monosodium, disodium or trisodium phosphates; potassium, monopotassium, dipotassium and tripotassium phosphates; stannous chloride; chlorophyl; lecithin; nordihydroguaiaretic acid (NDGA); alcoholic esters of the gallates; ascorbyl stearate; 2-tertiarybutyl-4-hydroxyanisole; 3-tertiarybutyl-4- hydroxyanisole; 1 -cysteine hydrochloride; gum guaiacum; lecithin citrate; monoglyceride citrate; monoisopropyl citrate; Ethylenediaminetetraacetic acid; 2,6- di-tert-butyl-4-hydroxymethylphenol; 2-6-di-tert-butyl-4-methylphenol (BHT) and t- tert-butyl-4-methylphenol (t-BHT); polyphosphates; trihydroxy butyrophenone; anoxomer; and combinations thereof such as RENDOX® by the company Kemin Industries which contains a mixture of propylene glycol, mono- and diglycerides, butylated hydroxyanisole and citric acid. Other synthetic antioxidants include the antioxidants marketed under the names BIOCAPS GP, BIOCAPS A-70, BIOCAPS TL, BIOCAPS ER, BIOCAPS PA, AP, CONTROX VP, COPHEROL 1300, DADEX, VANLUBE 848, IONOL and BAYNOX.

[0018] In yet another embodiment, the antioxidant may be a water soluble antioxidants selected from the group comprising of ascorbic acid, sodium metabisulfite, sodium bisulfite, sodium thiosulfite, sodium formaldehyde sulfoxylate, isoascorbic acid, thioglyerol, thiosorbitol, thiourea, thioglycolic acid, cysteine hydrochloride, 1 ,4-diazobicyclo-(2,2,2)-octane, malic acid, fumaric acid, and licopene.

[0019] In an exemplary embodiment, the antioxidant may be a substituted 1 ,2-dihydroquinoline compounds. Substituted 1 ,2-dihydroquinoline compounds suitable for use in the invention generally correspond to formula (I):

(I) wherein:

R¹, R², R³ and R⁴ are independently selected from the group consisting of hydrogen and an alkyl group having from 1 to about 6 carbons;

R⁵ is an alkoxy group having from 1 to about 12 carbons. [0020] In another embodiment, the substituted 1 ,2-dihydroquinoline will have formula (I) wherein:

R¹, R², R³ and R⁴ are independently selected from the group consisting of hydrogen and an alkyl group having from 1 to about 4 carbons; and R⁵ is an alkoxy group having from 1 to about 4 carbons. [0021] In one preferred embodiment, the substituted 1 ,2-dihydroquinoline will be 6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline having the formula:

6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline, commonly known as ethoxyquin, is sold under the trademark SANTOQU IN^® or AG RADO^®. The present invention also encompasses salts of ethoxyquin and other compounds having formula (I). Ethoxyquin and other compounds having formula (I) may be purchased commercially from Novus International, Inc. or made in accordance with methods generally known in the art, for example, as detailed in U.S. Patent No. 4,772,710, which is hereby incorporated by reference in its entirety.

Jb. Antioxidant Formulations

[0022] In one embodiment, the antioxidant of the present invention is an antioxidant mixture comprising at least two antioxidants as described in Part ll(a). In another embodiment, the antioxidant mixture comprises a first antioxidant of substituted 1 ,2-dihydroquinoline compound of Formula (I) and a second antioxidant that does not have the Formula (I). The second antioxidant may be any of the antioxidants described in Part ll(a) above other than the antioxidant of Formula (I). In other embodiments, the antioxidant mixture may include at least three different antioxidants. In additional embodiments, the combination may include four or more antioxidants. Non-limiting examples of suitable antioxidant mixtures are set-forth in Table A. A preferred composition comprises 6-ethoxy-1 ,2-dihydro-2,2,4- trimethylquinoline (ethoxyquin) and 2-tert-butylhydroquinone. Other preferred compositions comprise 6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline, as well as one or more of the following: 2-tert-butylhydroquinone, 3,4,5-trihydroxybenzoic acid n- propyl ester, 1 ,2,3-trihydroxybenzene, butylated hydroxyanisole, 2,6-Di-tert-Butyl-1 - Hydroxy-4-Methylbenzene, alpha-tocopherol acetate, alpha-tocopherol, gamma- tocopherol, delta-tocopherol, dilauryl thiodipropinate, isopropyl 2-hydroxy-4- methylthio butanoate, propyl gallate, dodecyl gallate, gallic acid, octyl gallate, ascorbyl palmitate, lecithin, stearyl citrate, palmityl citrate, chlorophyl, pyrogallol, alpha naphthol, ascorbic acid, natural tocopherol, citric acid, sage extract, rosemary, and eugenol.

Table A. Formulations of the antioxidant mixtures.

[0023] Other suitable combinations of antioxidants are detailed in the examples.

c. Solvents

[0024] The antioxidant composition may further comprise a polar solvent. Generally speaking, the polar solvent solubilizes the water-soluble antioxidants. Suitable examples of polar solvents include, but are not limited to, glycerol, isopropyl alcohol, ethyl alcohol, propylene glycol, erythritol, xylitol, sorbitol, maltitol, mannitol, water, polyol, or combinations thereof. In one embodiment, the polar solvent is glycerol. In another embodiment, the polar solvent is propylene glycol. The concentration of the polar solvent will vary depending upon the combination of antioxidants in the composition. In general, the percent by volume of the polar solvent may range from about 5% to about 50%. The percent by volume of glycerol may be about 5%, 10%, 15%, 20%, or 25%. The percent by volume of propylene glycol may be about 5%, 10%, 15%, 20%, or 25%.

[0025] The antioxidant composition may further comprise a nonpolar solvent. In general, the nonpolar solvent solubilizes the lipid-soluble antioxidants, and helps make the antioxidant composition miscible in an oil or fat sample. In one preferred embodiment, the nonpolar solvent is a biodiesel as described in Part I above. Suitable examples of other nonpolar solvents include, but are not limited to, vegetable oils, monoglycerides, diglycerides, triglycerides, and combinations thereof. The vegetable oil may be corn oil, soybean oil, canola oil, cottonseed oil, palm oil, peanut oil, safflower oil, and sunflower oil. The monoglycerides and diglycerides may be isolated and distilled from vegetable oils, or the monoglycerides and diglycerides may be synthesized chemically via an esterification reaction. In one embodiment, the nonpolar solvent may be corn oil. In another embodiment, the nonpolar solvent may comprise corn oil and monoglycerides. The concentration of the nonpolar solvent will vary depending upon the combination of antioxidants in the composition. In general, the percent by volume of the nonpolar solvent may range from about 5% to about 50%. The percent by volume of monoglycerides may be 10%, 15%, 20%, or 25%. The percent by volume of corn oil may be 5%, 10%, 15%, 20%, or 25%. In one embodiment, percent by volume of corn oil may be 15-25%. In another embodiment, the percent by volume of monoglycerides may be 15-20% and the percent by volume of corn oil may be about 5-10%.

JW. Fuel Compositions

[0026] The fuel compositions comprise biodiesel, one or more antioxidants and optionally, a polar solvent, a nonpolar solvent, and/or a petroleum based diesel. In one embodiment, the fuel composition of the invention comprises a biodiesel and at least one antioxidant that increases the oxidative stability of the fuel composition. In this embodiment, the biodiesel may be any of the biodiesels described in Part I in combination with any of the antioxidants described in Part II. In an alternative embodiment, the fuel composition comprises any of the biodiesel as described in Part I of the specification other than those produced from undistilled or distilled rapeseed oil, frying oil, sunflower oil, and beef tallow and at least one antioxidant as described in Part Il of the specification above. Examples of exemplary fuel compositions are presented in Table B below. Alternatively, each fuel composition detailed in Table B may also include 6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline.

[0027] In one preferred embodiment, the fuel composition comprises a biodiesel produced from soybean oil and 6-ethoxy-1 ,2-dihydro-2,2,4- trimethylquinoline. In another preferred embodiment, the fuel composition comprises a biodiesel produced from soybean oil and 2-tert-butylhydroquinone. In yet another embodiment, the fuel composition comprises a biodiesel produced from yellow grease (80% vegetable oil and 20% inedible tallow) and 6-ethoxy-1 ,2-dihydro-2,2,4- trimethylquinoline. In a further embodiment, the fuel composition comprises a biodiesel produced from fish oil and 6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline. Those skilled in the art will appreciate that the concentration of antioxidants added to the biodiesel will vary depending on the source of biodiesel. In one embodiment, the fuel composition comprises a biodiesel produced from soybean oil and from about 20 ppm to about 2000 ppm of 6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline. In another embodiment, the fuel composition comprises a biodiesel produced from soybean oil and from about 50 ppm to about 500 ppm of 6-ethoxy-1 ,2-dihydro-2,2,4- trimethylquinoline.

[0028] The present invention is also directed to a fuel composition comprising a biodiesel and an antioxidant mixture comprising at least two antioxidants and optionally, a polar solvent, a nonpolar solvent, and/or a petroleum based diesel. In one embodiment, the fuel composition comprises any of the biodiesels as described in Part I and an antioxidant mixture comprising at least two antioxidant as described in Part Il of the specification above. In another embodiment, the fuel composition comprises a first antioxidant having Formula (I), a second antioxidant not having Formula (I), a polar solvent, and a nonpolar solvent, as described in Part Il of the specification above, wherein the two solvents form a homogeneous liquid. Preferably, the nonpolar solvent is a biodiesel as described in Part I of the specification above. Of course those skilled in the art will appreciate that the antioxidant mixtures will vary considerably depending on the type of biodiesel to be stabilized. Exemplary fuel compositions are presented in Table C below.

[0029] In a preferred embodiment, the fuel composition comprises a biodiesel produced from soybean oil and an antioxidant mixture comprising 2-tert- butylhydroquinone (TBHQ), 6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline (EQ), and vegetable oil. In another embodiment, the fuel composition comprises a biodiesel produced from soybean oil and an antioxidant mixture comprising Butylated Hydroxyanisole (BHA), 2,6-Di-tert-Butyl-1 -Hydroxy-4-Methylbenzene (BHT), and vegetable oil. Such an antioxidant mixture is sold under the trademark PETGUARD^® and PETGUARD 4^® (PG4) and may be purchased commercially from Novus International, Inc. In yet another embodiment, the fuel composition comprises a biodiesel produced from soybean oil and an antioxidant mixture comprising 2-tert- butylhydroquinone (TBHQ), citric acid, and vegetable oil. Such an antioxidant mixture is sold under the trademark FEEDGUARD^® and may be purchased commercially from Novus International, Inc.

[0030] In yet another embodiment, the fuel composition comprises a biodiesel produced from soybean oil and an antioxidant mixture comprising 2-tert- butylhydroquinone and 6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline and corn oil. Such an antioxidant mixture is sold under the trademark SANTOQUIN Q^® and may be purchased commercially from Novus International, Inc. In a further embodiment, the fuel composition comprises a biodiesel produced from soybean oil and an antioxidant mixture comprising 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline, 2-tert- butylhydroquinone, 1 ,2-Propanediol, citric acid, and corn oil. Such an antioxidant mixture is sold under the trademark AGRADO R^® and may be purchased commercially from Novus International, Inc. In yet another embodiment, the fuel composition comprises a biodiesel produced from soybean oil and an antioxidant mixture comprising butylated hydroxyanisole, 2,6-Di-tert-Butyl-1-Hydroxy-4- Methylbenzene, 6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline, 2-tert- butylhydroquinone.

[0031] In one embodiment, the fuel composition comprises a biodiesel produced from yellow grease and an antioxidant mixture comprising 6-ethoxy-1 ,2- dihydro-2,2,4-trimethylquinoline, 2-tert-butylhydroquinone, 1 ,2-Propanediol, citric acid, and corn oil. In one embodiment, the fuel composition comprises a biodiesel produced from fish oil and an antioxidant mixture comprising 6-ethoxy-1 ,2-dihydro- 2,2,4-trimethylquinoline, 2-tert-butylhydroquinone, 1,2-Propanediol, citric acid, and corn oil.

[0032] In one embodiment, the fuel composition comprises a first antioxidant having Formula (I), preferably 6-ethoxy-1 ,2-dihydro-2,2,4- trimethylquinoline, a second antioxidant not having Formula (I), a polar solvent, and a nonpolar solvent, preferably a biodiesel produced from soybean oil. In another embodiment, the fuel composition comprises a biodiesel produced from soybean oil, a first antioxidant, preferably 6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline, a second antioxidant, preferably a mixture of propyl gallate, dilauryl thiodipropionate, ascorbyl palmitate, and butylated hydroxyanisole, and a polar solvent, preferably propylene glycol. In yet another embodiment, the fuel composition comprises a biodiesel produced from soybean oil, a first antioxidant, preferably 6-ethoxy-1 ,2-dihydro-2,2,4- trimethylquinoline, a second antioxidant, preferably a mixture of dodecyl gallate, alpha naphthol, natural tocopherol, and ascorbyl palmitate, and a polar solvent, preferably propylene glycol. In a further embodiment, the fuel composition comprises a biodiesel produced from soybean oil, a first antioxidant, preferably 6- ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline, a second antioxidant, preferably a mixture of 2-6-di-tert-butyl-4-methylphenol, pyrogallol, 2-tert-butylhydroquinone, and stearyl citrate, and a second nonpolar solvent, preferably corn oil. In another embodiment, the fuel composition comprises a biodiesel produced from soybean oil, a first antioxidant, preferably 6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline, a second antioxidant, preferably a mixture of natural mixed tocopherols, ascorbyl palmitate, propyl gallate, 2-tert-butylhydroquinone, and lecithin, and a second nonpolar solvent, preferably corn oil. In yet another embodiment, the fuel composition comprises a biodiesel produced from soybean oil, a first antioxidant, preferably 6-ethoxy-1 ,2- dihydro-2,2,4-trimethylquinoline, a second antioxidant, preferably a mixture of citric acid, 2-tert-butylhydroquinone, and 1 ,2-Propanediol, and a second nonpolar solvent, preferably corn oil.

[0033] Those skilled in the art will appreciate that the concentration of antioxidants added to the biodiesel will vary depending on the source of biodiesel. In one embodiment, the fuel composition comprises a biodiesel produced from soybean oil and an antioxidant mixture comprising from about 20 ppm to about 500 ppm of 6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline, from about 20 ppm to about 500 ppm of a mixture of Butylated Hydroxyanisole and 2,6-Di-tert-Butyl-1-Hydroxy-4- Methylbenzene, and from about 10 to about 60 ppm of 2-tert-butylhydroquinone. In another embodiment, the fuel composition comprises a biodiesel produced from soybean oil and an antioxidant mixture comprising about 400 ppm of 6-ethoxy-1 ,2- dihydro-2,2,4-trimethylquinoline, about 40 ppm of a mixture of Butylated Hydroxyanisole and 2,6-Di-tert-Butyl-1-Hydroxy-4-Methylbenzene, and about 50 ppm of 2-tert-butylhydroquinone. In yet another embodiment, the fuel composition comprises a biodiesel produced from soybean oil and an antioxidant mixture comprising about 40 ppm of 6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline, about 40 ppm of a mixture of Butylated Hydroxyanisole and 2,6-Di-tert-Butyl-1-Hydroxy-4- Methylbenzene, and about 50 ppm of 2-tert-butylhydroquinone.

[0034] In addition, the concentration of antioxidants will also vary in accordance with the oxidative stability desired for the fuel. There are various methods generally known in the art to measure the oxidative stability of a fuel, including the Rancimat Method, the Oxidative Stability Index (OSI) Method, Active Oxygen Method (AOM), the Standard Test Method for Oxidation Stability of Distillate Fuel oil (ASTM D-2274), both of which are detailed in the examples. These methods may be utilized by a skilled artisan to formulate blends of antioxidants having a suitable concentration of each ingredient in order for the antioxidant blend to impart the desired oxidative stability for the fuel of the invention. For example, all oils and fats have a resistance to oxidation, which depends on the degree of saturation, natural or added antioxidants, prooxidants or prior abuse. Oxidation is slow until this resistance is overcome, at which point oxidation accelerates and becomes very rapid. The length of time before this rapid acceleration of oxidation is the measure of the resistance to oxidation and is commonly referred to as the induction period. The OSI Method measures this induction period. Another method used in the art to measure induction period is the Rancimat Method. The fuel compositions of the present invention, as shown in Example 2, typically have an induction time greater than 6 hours.

[0035] The AOM Method measures the time (in hours) required for a sample of fat or oil to attain a predetermined value under the specific conditions of the test. The length of this period of time is assumed to be an index of resistance to rancidity. The fuel compositions of the present invention, as shown in Example 1 , generally have a peroxide value of from about 4 meq/kg fat to about 400 meq/kg fat after 20 hours under the AOM Method.

[0036] The ASTM Method (D-2274) measures the insolubles of fuels under specified oxidizing conditions at 95°C. In particular, the method calculates the total insoluble mass (mg/100 ml_) as the sum of the filterable insolubles and the adherent insolubles. The calculations are further described in the examples. In one example, a fuel composition comprising a biodiesel produced from yellow grease and 6- ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline has a total insoluble mass of 0.9 mg/mL, as shown in Example 3.

[0037] In one embodiment, a fuel composition of the invention comprises a biodiesel and a petroleum based diesel wherein the fuel composition has improved oxidative stability. In another embodiment, the fuel composition comprises any of the composition of Table A and a petroleum based diesel fuel wherein the fuel composition has improved oxidative stability. In yet another embodiment, the fuel composition comprises any of the compositions of Table C and a petroleum based diesel fuel. [0038] In one embodiment, the method of increasing the oxidative stability of a fuel composition comprises contacting a biodiesel with an antioxidant mixture that increases the oxidative stability of the fuel.

[0039] It is generally known that the addition of biodiesel to diesel fuel increases nitrogen oxide (NO_x) emissions. Wyatt, et al. Fuel Properties and Nitrogen Oxide Emission Levels of Biodiesel Produced from Animal Fats, Journal of the American Oil Chemists' Society, Vol. 82, No. 8, pg 585-591 (2005). The addition of antioxidants to the biodiesel fuel of the invention or a fuel comprising a biodiesel and petroleum based diesel of the invention, however, has lowered the NO_x emissions of the fuels as compared to a B20 fuel without the addition of at least one antioxidant or to a petroleum based diesel fuel. In one embodiment, a fuel composition of the invention comprises a biodiesel source other than rapeseed oil, frying oil, sunflower oil, and beef tallow and at least one antioxidant selected from the group consisting of 1 ,2,3-trihydroxybenzene, alpha-tocopherol acetate, gamma-tocopherol, delta- tocopherol, dilauryl thiodipropinate, isopropyl 2-hydroxy-4~methylthio butanoate, dodecyl gallate, gallic acid, octyl gallate, lecithin, stearyl citrate, palmityl citrate, chlorophyl, and 6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline wherein the fuel composition has a lower NO_x emission than a B20 fuel without the addition of at least one antioxidant. In another embodiment, a fuel composition of the invention comprises a biodiesel source other than rapeseed oil, frying oil, sunflower oil, and beef tallow and at least one antioxidant selected from the group consisting of 1 ,2,3- trihydroxybenzene, alpha-tocopherol acetate, gamma-tocopherol, delta-tocopherol, dilauryl thiodipropinate, isopropyl 2-hydroxy-4-methylthio butanoate, dodecyl gallate, gallic acid, octyl gallate, lecithin, stearyl citrate, palmityl citrate, chlorophyl, and 6- ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline wherein the fuel composition has a lower NO_x emission than a petroleum based diesel fuel.

[0040] In one embodiment, a fuel composition of the invention comprises any of the compositions of Table 2 and a petroleum based diesel wherein the fuel composition has a lower NO_x emission than a B20 fuel without the addition of at least one antioxidant. In another embodiment, the fuel composition comprises any of the compositions of Table 2 and a petroleum based diesel wherein the fuel composition has a lower NO_x emission than a petroleum based diesel fuel. In a further embodiment, the fuel composition has a reduction of NO_x emissions of at least about 1 % as compared to B20 fuel without the addition of at least one antioxidant. In yet another embodiment, the fuel composition has a reduction of NO_x emissions of at least about 2%, 4%, 6%, 8%, 10% as compared to B20 fuel without the addition of at least one antioxidant.

[0041] In one embodiment, the method of reducing the NO_x emissions of a fuel composition comprises contacting a biodiesel with an antioxidant mixture that decreases the NO_x emissions of the fuel.

[0042] Those skilled in the art will appreciate that the properties of the biodiesel fuel compositions of the invention will also vary considerably depending the combination of fuel and antioxidant used. The physical and chemical properties that are generally measured for a biodiesel composition include kinematic viscosity at 40°C, acid value, density, cold filter plugging point, and sulphated ash. The ASTM Standard for the kinematic viscosity of a 100% biodiesel composition at 40°C (D- 445) is between 1.9 and 6.0 mm²/sec. The biodiesel fuel compositions of the invention have a kinematic viscosity at 40°C of less than about 5.0 mm²/sec, less than about 4.5 mm²/sec, and less than about 4.0 mm²/sec. The ASTM Standard for the acid value of a 100% biodiesel composition (D-664) is 0.8 mg KOH/g. The biodiesel fuel compositions of the invention have an acid value of less than about 0.75 mg KOH/g, less than about 0.6 mg KOH/g, less than about 0.5 mg KOH/g, less than about 0.45 mg KOH/g, less than about 0.3 mg KOH/g, less than about 0.2 mg KOH/g, less than about 0.1 mg KOH/g. The biodiesel fuel compositions of the invention have a density at 20°C of less than 0.884 g/cm³, less than about 0.88 g/cm³, less than about 0.87 g/cm³, less than about 0.865 g/cm³. The biodiesel compositions of the invention have a cold filter plugging point (CFPP) of at least -1 ⁰C, at least -2 °C, at least -5 ⁰C, at least -10 °C. The ASTM standard for the maximum percent by mass of sulphated ash of a 100% biodiesel composition (D- 874) is 0.002 % by mass. The biodiesel compositions of the invention have a sulphated ash percent by mass of less than about 0.002% by mass, less than about 0.001 % by mass.

IV. Additional Agents

[0043] The biodiesel fuel compositions of the invention may contain additional agents that enhance one or more characteristics of the fuel. Those skilled in the art will appreciate that the selection of the particular agent will vary considerably depending on the type of fuel used. In particular, these additives may be particularly beneficial when the fuel composition comprises a biodiesel and a petroleum based diesel. Suitable additives, for example, may include, but are not limited to, cetane improvers and/or ignition accelerator agent, corrosion inhibitors and/or metal deactivators, cold flow improvers, and the like, as described below.

[0044] Preferred organic nitrates are substituted or unsubstituted alkyl or cycloalkyl nitrates having up to about 10 carbon atoms, preferably from 2 to 10 carbon atoms. The alkyl group may be either linear or branched. Specific examples of nitrate compounds suitable for use in preferred embodiments include, but are not limited to the following: methyl nitrate, ethyl nitrate, n-propyl nitrate, isopropyl nitrate, allyl nitrate, n-butyl nitrate, isobutyl nitrate, sec-butyl nitrate, tert-butyl nitrate, n-amyl nitrate, isoamyl nitrate, 2-amyl nitrate, 3-amyl nitrate, tert-amyl nitrate, n-hexyl nitrate, 2-ethylhexyl nitrate, n-heptyl nitrate, sec-heptyl nitrate, n-octyl nitrate, sec- octyl nitrate, n-nonyl nitrate, n-decyl nitrate, n-dodecyl nitrate, cyclopentylnitrate, cyclobexylnitrate, methylcyclohexyl nitrate, isopropylcyclohexyl nitrate, and the esters of alkoxy substituted aliphatic alcohols, such as l-methoxypropyl-2-nitrate, 1- ethoxpropyl-2 nitrate, 1-isopropoxy-butyl nitrate, 1-ethoxylbutyl nitrate and the like. Preferred alkyl nitrates are ethyl nitrate, propyl nitrate, amyl nitrates, and hexyl nitrates. Other preferred alkyl nitrates are mixtures of primary amyl nitrates or primary hexyl nitrates. By primary is meant that the nitrate functional group is attached to a carbon atom that is attached to two hydrogen atoms. Examples of primary hexyl nitrates include n-hexyl nitrate, 2-ethylhexyl nitrate, 4-methyl-n-pentyl nitrate, and the like. Preparation of the nitrate esters may be accomplished by any of the commonly used methods: such as, for example, esterification of the appropriate alcohol, or reaction of a suitable alkyl halide with silver nitrate. Another additive suitable for use in improving cetane and/or reducing particulate emissions is di-t- butyl peroxide.

[0045] Conventional ignition accelerators may also be used, such as hydrogen peroxide, benzoyl peroxide, di-tert-butyl peroxide, and the like. Moreover, certain inorganic and organic chlorides and bromides, such as, for example, aluminum chloride, ethyl chloride or bromide may find use in the preferred embodiments as primers when used in combination with the other ignition accelerators.

[0046] The low temperature operability of diesel fuel is commonly characterized by the cloud point, and the cold filter plugging point (CFPP) or the low temperature filterability test (LTFT). Thermal Stabilizers may also be added to the biodiesel composition. In one embodiment, the composition may also contain jojoba oil as an additional component. It is a liquid that has antioxidant characteristics and is capable of withstanding very high temperatures without losing its antioxidant abilities. Jojoba oil is a liquid wax ester mixture extracted from ground or crushed seeds from shrubs native to Arizona, California and northern Mexico. The source of jojoba oil is the Simmondsia chinensis shrub, commonly called the jojoba plant. It is a woody evergreen shrub with thick, leathery, bluish-green leaves and dark brown, nutlike fruit. Jojoba oil may be extracted from the fruit by conventional pressing or solvent extraction methods. The oil is clear and golden in color. Jojoba oil is composed almost completely of wax esters of monounsaturated, straight-chain acids and alcohols with high molecular weights (C16-C26). Jojoba oil is typically defined as a liquid wax ester with the generic formula RCOOR", wherein RCOOH represents oleic acid (C18), eicosanoic acid (C20) and/or erucic acid (C22), and wherein -ROH represents eicosenyl alcohol (C20), docosenyl alcohol (C22) and/or tetrasenyl alcohol (C24) moieties. Pure esters or mixed esters having the formula RCOOR", wherein R is a C20-C22 alk(en)yl group and wherein R" is a C20-C22 alk(en)yl group, may be suitable substitutes, in part or in whole, for jojoba oil. Acids and alcohols including monounsaturated straight-chain alkenyl groups are most preferred.

[0047] Other oils that are known for their thermal stability include peanut oil, cottonseed oil, rape seed (canola) oil, macadamia oil, avocado oil, palm oil, palm kernel oil, castor oil, all other vegetable and nut oils, all animal oils including mammal oils (e.g., whale oils) and fish oils, and combinations thereof. In one embodiment, the oil may be alkoxylated, for example, methoxylated or ethoxylated. Alkoxylation is preferably conducted on medium chain oils, such as castor oil, macadamia nut oil, cottonseed oil, and the like. Alkoxylation may offer benefits in that it may permit coupling of oil/water mixtures in a fuel, resulting in a potential reduction in nitrogen oxides and/or particulate matter emissions upon combustion of the fuel. [0048] Other suitable thermal stabilizers known in the art include liquid mixtures of alkyl phenols, including 2-tert-butylphenol, 2,6-di-tert-butylphenol, 2-tert- butyl-4-n-butylphenol, 2,4,6-tri-tert-butylphenol, and 2,6-di-tert-butyl-4-n-butylphenol which are suited for use as stabilizers for middle distillate fuels (U.S. Pat. No. 5,076,814 and U.S. Pat. No. 5,024,775 to Hanlon, et al.). Other commercially available hindered phenolic antioxidants that also exhibit a thermal stability effect include 2,6-di-t~butyl-4-methylphenol; 2,6-di-t-butylphenol; 2,2'-methylene-bis(6-t- butyl-4-methylphenol); n-octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate; 1 ,1 ,3-tris(3-t-butyl-6-methyl-4hydroxyphenyl) butane; pentaerythrityl tetrakis[3-(3,5- di-t-butyl-4-hydroxyphenyl) propionate]; di-n-octadecyl(3,5-di-t-butyl-4- hydroxybenzyl)phosphonate; 2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl) mesitylene; and tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate (U.S. Pat. Nos. 4,007,157, U.S. Pat. No. 3,920,661 ). Other suitable thermal stabilizers include: pentaerythritol co- esters derived from pentaerythritol, (3-alkyl-4-hydroxyphenyl)-alkanoic acids and alkylthioalkanoic acids or lower alkyl esters of such acids which are useful as stabilizers of organic material normally susceptible to oxidative and/or thermal deterioration. (U.S. Pat. No. 4,806,675 and U.S. Pat. No. 4,734,519 to Dunski, et al.); hindered phenyl phosphites (U.S. Pat. No. 4,207,229 to Spivack); hydrocarbyl thioalkylene phosphites (U.S. Pat. No. 3,524,909); hydroxybenzyl thioalkylene phosphites (U.S. Pat. No. 3,655,833); and the like.

[0049] Certain compounds suitable for use are capable of performing as both antioxidants and as thermal stabilizers. Therefore, in certain embodiments it may be preferred to prepare formulations containing as additional components a hydrophobic plant oil extract in combination with a single compound that provides both a thermal stability and antioxidant effect, rather than two different compounds, one providing thermal stability and the other antioxidant activity. Examples of compounds known in the art as providing some degree of both oxidation resistance and thermal stability include diphenylamines, dinaphthylamines, and phenylnaphthylamines, either substituted or unsubstituted, e.g., N₁N'- diphenylphenylenediamine, p-octyldiphenylamine, p,p-dioctyldiphenylamine, N- phenyl-1 -naphthylamine, N-phenyl-2-naphthylamine, N-(p-dodecyl)phenyl-2- naphthylamine, di-1 -naphthylamine, and di-2naphthylamine; phenothazines such as N-alkylphenothiazines; imino(bisbenzyl); and hindered phenols such as 6-(t- butyl)phenol, 2,6-di-(t-butyl)phenol, 4-methyl-2,6-di-(t-butyl) phenol, 4,4- methylenebis(-2,6-di-(t-butyl)phenol), and the like.

[0050] Certain lubricating fluid base stocks are known in the art to exhibit high thermal stability and as such, may be beneficial in certain embodiments of the invention. Such base stocks may be capable of imparting thermal stability to the formulations of preferred embodiments, and as such may be substituted, in part or in whole, for jojoba oil. Suitable base stocks include polyalphaolefins, dibasic acid esters, polyol esters, alkylated aromatics, polyalkylene glycols, and phosphate esters.

[0051] A variety of polyalphaolefins may be utilized in the fuel composition of the invention. Polyalphaolefins are hydrocarbon polymers that contain no sulfur, phosphorus, or metals. Polyalphaolefins have good thermal stability, but are typically used in conjunction with a suitable antioxidant. Dibasic acid esters also exhibit good thermal stability, but are usually also used in combination with additives for resistance to hydrolysis and oxidation.

[0052] Several polyol esters may be used in the fuel composition of the invention. Polyol esters include molecules containing two or more alcohol moieties, such as trimethylolpropane, neopentylglycol, and pentaerythritol esters. Synthetic polyol esters are the reaction product of a fatty acid derived from either animal or plant sources and a synthetic polyol. Polyol esters have excellent thermal stability and may resist hydrolysis and oxidation better than other base stocks. Naturally occurring triglycerides or vegetable oils are in the same chemical family as polyol esters. However, polyol esters tend to be more resistant to oxidation than such oils. The oxidation instabilities normally associated with vegetable oils are generally due to a high content of linoleic and linolenic fatty acids. Moreover, the degree of unsaturation (or double bonds) in the fatty acids in vegetable oils correlates with sensitivity to oxidation, with a greater number of double bonds resulting in a material more sensitive to and prone to rapid oxidation.

[0053] Several trimethylolpropane esters are suitable for use in the fuel compositions of the invention. Trimethylolpropane esters may include mono, di, and tri esters. Neopentyl glycol esters may include mono and di esters. Pentaerythritol esters include mono, di, tri, and tetra esters. Dipentaerythritol esters may include up to six ester moieties. Preferred esters are typically of those of long chain monobasic fatty acids. Esters of C20 or higher acids are preferred, e.g., gondoic acid, eicosadienoic acid, eicosatrienoic acid, eicosatetraenoic acid, eicosapentanoic acid, arachidic acid, arachidonic acid, behenic acid, erucic acid, docosapentanoic acid, docosahexanoic acid, or ligniceric acid. However in certain embodiments, esters of C18 or lower acids may be preferred, e.g., butyric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristoleic acid, myristic acid, pentadecanoic acid, palmitic acid, palmitoleic acid, hexadecadienoic acid, hexadecatienoic acid, hexadecatetraenoic acid, margaric acid, margroleic acid, stearic acid, linoleic acid, octadecatetraenoic acid, vaccenic acid, or linolenic acid. In certain embodiments, it may be preferred to esterify the pentaerythritol with a mixture of different acids.

[0054] In certain embodiments, an alkylated aromatic may be utilized in the fuel compositions of the invention. Alkylated aromatics are formed by the reaction of olefins or alkyl halides with aromatic compounds, such as benzene. Thermal stability is similar to that of polyalphaolefins, and additives are typically used to provide oxidative stability. Polyalkylene glycols are polymers of alkylene oxides exhibiting good thermal stability, but are typically used in combination with additives to provide oxidation resistance. Phosphate esters are synthesized from phosphorus oxychloride and alcohols or phenols and also exhibit good thermal stability.

[0055] In certain embodiments, it may be preferred to prepare formulations containing jojoba oil in combination with other vegetable oils. For example, it has been reported that crude meadowfoam oil resists oxidative destruction nearly 18 times longer than the most common vegetable oil, namely, soybean oil. Meadowfoam oil may be added in small amounts to other oils, such as triolein oil, jojoba oil, and castor oil, to improve their oxidative stability. Crude meadowfoam oil stability could not be attributed to common antioxidants. One possible explanation for the oxidative stability of meadowfoam oil may be its unusual fatty acid composition. The main fatty acid from meadowfoam oil is 5-eicosenoic acid, which was found to be nearly 5 times more stable to oxidation than the most common fatty acid, oleic acid, and 16 times more stable than other monounsaturated fatty acids. See "Oxidative Stability Index of Vegetable Oils in Binary Mixtures with Meadowfoam Oil," Terry, et al., United States Department of Agriculture, Agricultural Research Service, 1997. [0056] Any of a number of different types of suitable detergent additives can be included in diesel fuel compositions of various embodiments. These detergents include succinimide detergent/dispersants, long-chain aliphatic polyamines, and long-chain Mannich bases. Use of fuel-soluble long chain aliphatic polyamines as induction cleanliness additives in distillate fuels is described, for example, in U.S. Pat. No. 3,438,757. Use of fuel-soluble Mannich base additives formed from a long chain alkyl phenol, formaldehyde (or a formaldehyde precursor thereof), and a polyamine to control induction system deposit formation in internal combustion engines is described, for example, in U.S. Pat. No. 4,231 ,759. The detergent additives, for example, are effective in reducing carburetor deposits and fuel injector deposits.

[0057] The diesel fuel compositions of various embodiments advantageously may contain one or more antiwear agents. Preferred antiwear agents include long chain primary amines incorporating an alkyl or alkenyl radical having 8 to 50 carbon atoms. The amine to be employed may be a single amine or may consist of mixtures of such amines. Examples of long chain primary amines which can be used in the preferred embodiments are 2-ethylhexyl amine, n-octyl amine, n-decyl amine, dodecyl amine, oleyl amine, linolylamine, stearyl amine, eicosyl amine, triacontyl amine, pentacontyl amine and the like. A particularly effective amine is oleyl amine obtainable from Akzo Nobel Surface Chemistry LLC of Chicago, III. under the name ARMEEN^® O or ARMEEN^® OD. Other suitable amines which are generally mixtures of aliphatic amines include ARMEEN® T and ARMEEN^® TD, the distilled form of ARMEEN^® T which contains a mixture of 0-2% of tetradecyl amine, 24% to 30% of hexadecyl amine, 25% to 28% of octadecyl amine and 45% to 46% of octadecenyl amine. ARMEEN^® T and ARMEEN^® TD are derived from tallow fatty acids. Lauryl amine is also suitable, as is ARMEEN^® 12D obtainable from the supplier indicated above. This product is about 0-2% of decylamine, 90% to 95% dodecylamine, 0-3% of tetradecylamine and 0-1 % of octadecenylamine. Amines of the types indicated to be useful are well known in the art and may be prepared from fatty acids by converting the acid or mixture of acids to its ammonium soap, converting the soap to the corresponding amide by means of heat, further converting the amide to the corresponding nitrile and hydrogenating the nitrile to produce the amine. In addition to the various amines described, the mixture of amines derived from soya fatty acids also falls within the class of amines above described and is suitable for use according to this invention. It is noted that all of the amines described above as being useful are straight chain, aliphatic primary amines. Those amines having 16 to 18 carbon atoms per molecule and being saturated or unsaturated are particularly preferred. Other preferred antiwear agents include dimerized unsaturated fatty acids, preferably dimers of a comparatively long chain fatty acid, for example one containing from 8 to 30 carbon atoms, and may be pure, or substantially pure, dimers. Alternatively, and preferably, the material sold commercially and known as "dimer acid" may be used. This latter material is prepared by dimerizing unsaturated fatty acid and consists of a mixture of monomer, dimer and trimer of the acid. A particularly preferred dimer acid is the dimer of linoleic acid.

[0058] The fuel composition may include a variety of demulsifiers. Demulsifiers are molecules that aid the separation of oil from water usually at very low concentrations. They prevent formation of a water and oil mixture. A wide variety of demulsifiers are available for use in the fuel formulations of various embodiments, including, for example, organic sulfonates, polyoxyalkylene glycols, oxyalkylated phenolic resins, and like materials. Particularly preferred are mixtures of alkylaryl sulfonates, polyoxyalkylene glycols and oxyalkylated alkylphenolic resins, such as are available commercially from Baker Petrolite Corporation of Sugar Land, Tex. as TOLAD®. Other known demulsifiers can also be used.

[0059] A variety of corrosion inhibitors are available for use in the fuel formulations of various embodiments. Use can be made of dimer and trimer acids, such as are produced from tall oil fatty acids, oleic acid, linoleic acid, or the like. Products of this type are currently available from various commercial sources, such as, for example, the dimer and trimer acids sold under the EMPOL® by Cognis Corporation of Cincinnati, Ohio. Other useful types of corrosion inhibitors are the alkenyl succinic acid and alkenyl succinic anhydride corrosion inhibitors such as, for example, tetrapropenylsuccinic acid, tetrapropenylsuccinic anhydride, tetradecenylsuccinic acid, tetradecenylsuccinic anhydride, hexadecenylsuccinic acid, hexadecenylsuccinic anhydride, and the like. Also useful are the half esters of alkenyl succinic acids having 8 to 24 carbon atoms in the alkenyl group with alcohols such as the polyglycols. [0060] If desired, the fuel compositions may contain a conventional type of metal deactivator of the type having the ability to form complexes with heavy metals such as copper and the like. Typically, the metal deactivators used are gasoline soluble N,N'-disalicylidene-1 ,2-alkanediamines or N,N'-disalicylidene-1 ,2- cycloalkanediamines, or combinations thereof. Examples include N.N'-disalicylidene- 1 ,2-ethanediamine, N,N'-disalicylidene-1 ,2-propanediamine, N,N'-disalicylidene-1 ,2- cyclo-hex- anediamine, and N,N"-disalicylidene-N'-methyl-dipropylene-triamine.

[0061] The various additives that can be included in the diesel compositions of this invention are used in conventional amounts. The amounts used in any particular case are sufficient to provide the desired functional property to the diesel composition, and such amounts are well known to those skilled in the art.

DEFINITIONS

[0062] To facilitate understanding of the invention, a number of terms and abbreviations as used herein are defined below:

[0063] The term "AGRADO®" refers to a form of ethoxyquin.

[0064] The term "AGRADO R®" refers to a form of ethoxyquin and TBHQ.

[0065] The term "Acid Number" refers to the milligrams of KOH required in tests to neutralize all the acidic constituents present in a 1 gram sample of fuel product. This property is often used to indicate the extent of contamination or oxidation of fuels.

[0066] The term "AOM" stands for the Active Oxygen Method. The method measures the time (in hours) required for a sample of fat or oil to attain a predetermined value under the specific conditions of the test.

[0067] The term "B20" refers to a fuel composition having about 20% by weight biodiesel and about 80% by weight petroleum based diesel.

[0068] The term "Cloud Point" refers to the temperature at which small solid crystals are first visually observed as the fuel is cooled. This is the most conservative measurement of cold flow properties.

[0069] The term "Cold Filter Plugging Point (CFPP) (or LTFT)" refers to the temperature at which a fuel will cause a fuel filter to plug due to fuel components, which have begun to crystallize or gel. [0070] The term "FEEDGUARD 20^®" refers to an antioxidant mixture of TBHQ, citric acid, and vegetable oil.

[0071] The term "Induction time" stands one the measure of the resistance to oxidation.

[0072] The term "Kinematic viscosity at 40°C" refers to the measure of a fuel's resistance to flow under gravity at a specific temperature, in this case 4O⁰C.

[0073] The term "Oxidative Stability" refers to the ability to slow down the oxidation of a fuel.

[0074] The term "OSI" stands for the Oil Stability Index. The method measures the induction time of a fuel.

[0075] The term "PETGUARD^®" refers to an antioxidant mixture of BHA, BHT, and vegetable oil.

[0076] The term "PETGUARD 4^®" refers to an antioxidant mixture of BHA, BHT, and vegetable oil.

[0077] The term "PV" stands for peroxide value.

[0078] The term "PPM" stands for parts per million.

[0079] The term "SANTOQUIN®" refers to a form of ethoxyquin.

[0080] The term "SANTOQUIN Q®" refers to a form of ethoxyquin and TBHQ.

[0081] The term "TENOX 21®" refers to an antioxidant mixture of TBHQ, glyceryl oleate, propylene glycol, vegetable oil, and citric acid.

[0082] The term "yellow grease" as used herein refers to waste grease from restaurants and low-grade fats from rendering plants; yellow grease is a mixture of vegetable oils and animal fats.

EXAMPLES

[0083] The following examples illustrate various embodiments of the invention.

Example 1 : Effectiveness of Various Antioxidants to Stabilize Biodiesel

[0084] The stability of biodiesel alone or in the presence of various antioxidants was tested using two methods approved by the American Oil Chemists Society, i.e., the Active Oxygen Method (AOM) (AOCS Official Method Cd 12-57) and the Oxidation Stability Index (OSI) method (AOCS Official Method Cd 12b-92) which is equivalent to the Rancimat method. The biodiesel comprised soybean oil, yellow grease, or menhaden oil. Unless completely liquefied, each sample was melted at a temperature not more than 10 ⁰C above its melting point. The antioxidants included SANTOQUIN®, SANTOQUIN Q®, AGRADO®, AGRADO R®, PETGUARD™ and PETGUARD 4™. The levels of the antioxidants tested are presented in Table 1. All of the conditions were tested in duplicate.

[0085] AOM measures the levels of peroxides, or oxidation products, in a lipid sample after exposure to air and heat. For this, 20 ml of sample (± antioxidant) was added to the reaction tubes. The aeration tubing assembly was inserted into the reaction tube and adjusted such that the end of the air delivery tubing was 5 cm below the surface of the sample. The tube and the sample were placed in a container of vigorously boiling water for 5 min. The tube was then removed from the water, wiped dry, and transferred immediately to the constant temperature heater maintained at 97.8 ± 0.2 ⁰C. The aeration tubing was connected to the capillary on the manifold, and air was bubbled into the sample to accelerate oxidation. After 20 hr, the sample was analyzed for peroxide content. The lower the peroxide or AOM value (expressed in meq/kg of lipid) the more stable the lipid sample. For animal- derived lipids, an AOM value of 20 meq/kg or greater indicates rancidity.

[0086] During the OSI method, a stream of air is passed through a lipid sample and the effluent air from the lipid sample is bubbled through a test vessel containing deionized water, whose conductivity is continuously monitored. As the oil oxidizes, volatile organic acids are generated and become trapped in the water, thereby increasing its conductivity. To perform OSI, conductivity tubes were filled with 50 ml of deionized water and probes were attached. The conductivity of the water in the tubes was verified to be constant with a reading of 25 μS/cm or less. Twenty ml of (liquefied) sample (± antioxidant) was placed directly into the bottom of the reaction tube. Assays performed with biodiesel soybean oil or yellow grease were conducted at 110 ⁰C, and assays performed with fish (menhanden) oil were performed at 80 ⁰C. The tubing from the air manifold was connected to the conductivity measurement tube, and the aeration tubing was adjusted so that it was within 5 mm of the bottom of both the reaction and the conductivity tubes. The airflow was adjusted to 2.5 ± 0.2 ml/sec. A computer was used to monitor the conductivity of each probe in the instrument and a plot of water conductivity vs. time obtained from the reader was generated. The OSI value is defined as the induction period in hours and mathematically represents the inflection point (second derivative) of the plot that reflects the maximum change in the oxidation rate. The higher the OSI value, the more stable the oil. The EU standard for stabilization is a value of 6 (hr) or greater.

[0087] The AOM and OSI values for the different antioxidants are presented in Table 1. These tests revealed that SANTOQUIN® Q, AGRADO R®, and TBHQ were effective at reducing the oxidation of soybean oil, and that AGRADO R® was effective at reducing the oxidation of yellow grease or menhanden oil.

Table 1. Effectiveness of Various Antioxidants to Stabilize Biodiesel

Example 2: Effectiveness of Antioxidant Mixtures to Stabilize Soybean Biodiesel

[0088] The ability of various antioxidants or combinations of antioxidants to stabilize biodiesel comprising soybean oil were compared using the AOM and OSI methods, essentially as described in Example 1. The antioxidants included ethoxyquin (EQ), FeedGuard 20 (FG20), PETGUARD 4™ (PG4), TBHQ, and BHT. Each of the antioxidants or antioxidant combination was used at a concentration of 500 ppm. Table 2 presents the various conditions, as well as the AOM and OSI values. TBHQ was the best antioxidant in preventing the oxidation of soybean oil, as assayed by both methods.

Table 2. Antioxidant Effectiveness to Prevent Oxidation

Example 3: Ability of Antioxidant Mixtures to Stabilize Soybean Biodiesel

[0089] The effectiveness of various formulations of ethoxyquin (EQ), PETGUARD 4™ (PG4), and TBHQ to stabilize a biodiesel comprised of soybean oil were compared using the AOM and OSI methods, as detailed in Example 1. Table 3 presents the concentration of each component of the formulations, and the AOM and OSI values. This experiment revealed that any formulation comprising TBHQ at 50 ppm had excellent antioxidant activity.

Table 3. Effectiveness of Antioxidant Formulations

Example 4: Effectiveness of Antioxidant Blends (#1) to Stabilize Biodiesel

[0090] Additional combinations of antioxidants were compared for their effectiveness to inhibit oxidation of a biodiesei comprising soybean oil. The stability of the biodiesel alone or in the presence of an antioxidant formulation was tested using the AOM and OSI methods, as detailed in Example 1. The antioxidants (AOX) tested were ethoxyquin (EQ), BHT, pyrogallol (PY), TBHQ, and stearyl citrate (SC). The nonpolar solvent was corn oil (CO). The level of each antioxidant in the formulations is presented in Table 4. The application rate of each formulation was 2000 ppm. Table 4 also presents the AOM and OSI values. It was found that formulations comprising 500 ppm of ethoxyquin (25%) and 200 ppm of pyrogallol (10%) were particularly effective in stabilizing the biodiesel (shaded in Table 4).

Example 5: Effectiveness of Antioxidant Blends (#2) to Stabilize Biodiesel

[0091] Additional combinations of antioxidants were compared for their effectiveness to inhibit soybean oil biodiesel oxidation. The stability of the biodiesel alone or in the presence of an antioxidant formulation was tested using the AOM and OSI methods, as detailed in Example 1. The antioxidants tested were propyl gallate (PG), ethoxyquin (EQ), dilauryl thiodipropionate (DD), ascorbyl palmitate (AP), and BHA. The polar solvent was propylene glycol (PGL). The level of each antioxidant in the formulations is presented in Table 5. The application rate of each formulation was 2000 ppm. As shown in Table 5, formulations comprising 300 ppm of propyl gallate (15%) and 500 ppm of ethoxyquin (25%) were effective in preventing biodiesel oxidation.

Example 6: Effectiveness of Antioxidant Blends (#3) to Stabilize Biodiesel

[0092] Additional combinations of antioxidants were compared for their effectiveness to inhibit soybean oil biodiesel oxidation. The stability of the biodiesel alone or in the presence of an antioxidant formulation was tested using the AOM and OSI methods, as detailed in Example 1. The antioxidants tested were dodecyl gallate (DG), ethoxyquin (EQ), alpha naphthol (AN), natural tocopherols (NT), and ascorbic acid (AA). The polar solvent was propylene glycol (PGL). The level of each antioxidant in the formulations is presented in Table 5. The application rate of each formulation was 2000 ppm. As shown in Table 6, formulations comprising 300 ppm of dodecyl gallate (15%) and 500 ppm of ethoxyquin (25%) prevented biodiesel oxidation.

Example 7: Effectiveness of Various Antioxidant Blends Applied at Different Rates to Stabilize Biodiesel

[0093] The effectiveness of different concentrations of various antioxidant blends to prevent biodiesel oxidation was compared using the AOM and OSI methods, as described in Example 1. The antioxidants tested were ethoxyquin (EQ), natural mixed natural tocopherols (NMT), ascorbyl palmitate (AP)j propyl gallate (PG), TBHQ, and lecithin (LE). The nonpolar solvent was corn oil. The level of each antioxidant in the formulations is presented in Table 7. Each formulation was applied at either 200 ppm or 500 ppm. As shown in Table 7, the formulation comprising EQ, NMT, AP, PG, and TBHQ at 500 ppm was most effective at stabilizing biodiesel.

Table 7. Effectiveness of Different A lication Rates of Various Antioxidant Blends

Example 8: Effectiveness of Antioxidant Blends to Reduce lnsolubles in Biodiesel

[0094] The standard test method for oxidation stability of distillate fuel oil

(ASTM D2274; accelerated method) was also used to rate the effectiveness of the different antioxidant blends. This method measures the filterable insolubles, the adherent insolubles, and the total insolubles after an accelerated oxidative process. For this method, 400 ml of fuel was filtered through a cellulose ester surfactant-free membrane filter having a nominal pore size of 0.8 μm. A clean oxygen delivery tube was placed in each clean oxidation test cell, and 350 ml of the filtered fuel was added to the test cell. The test cell was placed in a 95°C heating bath, and oxygen was bubbled through the test sample at a rate of 3 l/h for 16 hr. The test sample was allowed to cool to room temperature for no longer than four hours. The sample was then filtered through two filters simultaneously (Whatman GF/F filters). After all the fuel was pulled through the filters, three washes of 50 ml of isooctane were used to rinse the oxidation cell and the oxygen delivery tube. All rinses were passed through the filter assembly. Additionally, the rim of the filter media and the adjacent parts of the filter assembly were washed with another 50 ml of isooctane. The filtrate was discarded. The two filters were dried at 80 ⁰C for 30 min, and then cooled for 30 min. Both filters were weighed. The upper filter is considered the sample filter, while the lower filter is considered the blank filter. The filterable insolubles mass {A) in milligrams per 100 ml was calculated. The mass of the blank (bottom) filter W₁ was subtracted from the weight of the sample (top) filter W₂ and divided by 3.5 to reduce the result to a 100 ml basis (A = (W₂-Wi)/3.5).

[0095] After the oxidation cell and oxygen delivery tube were rinsed (above), the adherent insolubles from the surfaces of those pieces were dissolved using three 75 ml rinses of trisolvent (equal parts of toluene, acetone, and methanol). If needed, a fourth 75 ml rinse of trisolvent was used. The trisolvent rinses were collected in pre-tared beakers, and evaporated. Two sets of weights were recorded - the tare weight and the after evaporation weight for the sample beaker, and then a tare and after evaporation weight for a blank beaker that contained only an equivalent volume of trisolvent. The adherent insolubles mass (B) in milligrams per 100 ml was also calculated. The tare mass of the blank (W₃) and sample (W₄) beakers were subtracted from the final mass (after evaporation) of the blank (MZ₅) and sample (We) beakers. The difference between the blank and the sample was then calculated, and divided by 3.5 to reduce the result to a 100 ml basis (B = ((W₆ - WA) - (Ws- W₃))β.b). The total insolubles mass (C) in milligrams per 100 ml was calculated as the sum of the filterable insolubles (A) and the adherent insolubles (B), such that C = A + B.

[0096] A fuel composition comprising a biodiesel produced from yellow grease was analyzed in the absence or presence of 2000 ppm SANTOQUIN® using the above method. It was found that the total insoluble mass decreased from 5.5 mg/100 Ml to 0.9 mg/10 Ml in the presence of the antioxidant.

[0097] Antioxidant blends were tested and the filterable insolubles, adherent insolubles, and total insolubles were determined. The following antioxidant blends were tested: 1-6, 1-8, 1-14, and 1-16 from Example 4 (see Table 4); 2-4 and 2-12 from Example 5 (see Table 5); and 3-12 from Example 6 (see Table 6). Each blend was tested at 500 ppm, 1000 ppm, and 2000 ppm. Controls included biodiesel, and biodiesel containing 1000 ppm of TBHQ or 1000 ppm of TENOX-21 (TNX21 ). The results are presented in Table 8. All of the antioxidant blends, with the exception of the lowest concentration of blend 3-12, reduced the amount of insolubles in the biodiesel.

Table 8. Reduction of Insolubles by Antioxidant Blends

Filterable Insolubles (mg/1 OQmI)

Control TBHQ TNX21 1-6 1-8 I 1-14 I 1-16 I 2-4 2-12 3-12

Claims

CLAIMSWhat is Claimed is:

1. A fuel composition, the composition comprising: a. a biodiesel from a source other than rapeseed oil, frying oil, sunflower oil, and beef tallow; and b. at least one antioxidant selected from the group consisting of 3,4,5- trihydroxybenzoic acid n-propyl ester, 1 ,2,3-trihydroxybenzene, butylated hydroxyanisole, 2,6-Di-tert-Butyl-1-Hydroxy-4- Methylbenzene, alpha-tocopherol acetate, alpha-tocopherol, gamma- tocopherol, delta-tocopherol, dilauryl thiodipropinate, isopropyl 2- hydroxy-4-methylthio butanoate, propyl gallate, dodecyl gallate, gallic acid, octyl gallate, ascorbyl palmitate, lecithin, stearyl citrate, palmityl citrate, chlorophyl, pyrogallol, alpha naphthol, ascorbic acid, natural tocopherol, citric acid, sage extract, rosemary, eugenol, natural antioxidant, and 6-ethoxy-1 ,2-dihydro~2,2,4-trimethylquinoline.

2. The fuel composition of claim 1 , wherein the biodiesel is produced from soybean oil, the antioxidant is 6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline, and the fuel contains from about 50 ppm to about 500 ppm 6-ethoxy-1 ,2- dihydro-2,2,4-trimethylquinoline.

3. The fuel composition of claim 1 , further comprising an additive selected from the group comprising of cetane improvers, ignition accelerators, metal deactivators, corrosion inhibitors, thermal stabilizers, detergents, antiwear agents, and demulsifiers.

4. A fuel composition, the composition comprising: a. a biodiesel; and b. an antioxidant mixture, the mixture comprising at least two antioxidant selected from the group consisting of 2-tert-butylhydroquinone, 3,4,5- trihydroxybenzoic acid n-propyl ester, 1 ,2,3-trihydroxybenzene, butylated hydroxyanisole, 2,6~Di-tert-ButyI-1-Hydroxy-4- Methylbenzene, alpha-tocopherol acetate, alpha-tocopherol, gamma- tocopherol, delta-tocopherol, dilauryl thiodipropinate, isopropyl 2- hydroxy-4-methylthio butanoate, propyl gallate, dodecyl gallate, gallic acid, octyl gallate, ascorbyl palmitate, lecithin, stearyl citrate, palmityl citrate, chlorophyl, pyrogallol, alpha naphthol, ascorbic acid, natural tocopherol, citric acid, sage extract, rosemary, eugenol, natural antioxidant, and 6~ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline.

5. The fuel composition of claim 4, wherein the biodiesel is produced from a source selected from the group consisting of soybean oil, yellow grease, corn oil, rapeseed oil, coconut oil, peanut oil, palm oil, fish oil, marine oil, cottonseed oil, mustard seed oil, camelina oil, jojoba oil, hemp oil, tallow, poultry fat, lard, safflower oil, jatropha oil, algae oil, and sunflower oil.

6. The fuel composition of claim 4, wherein the biodiesel is produced from rapeseed oil.

7. The fuel composition of claim 4, wherein the biodiesel is produced from algae oil.

8. The fuel composition of claim 4, wherein the biodiesel is produced from soybean oil.

9. The fuel composition of claim 8, wherein the antioxidant mixture comprises 6- ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline and 2-tert-butylhydroquinone.

10. The fuel composition of claim 8, wherein the antioxidant mixture comprises butylated hydroxyanisole, 2,6-Di-tert-Butyl-1-Hydroxy-4-Methylbenzene, 6- ethoxy-6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline, 2-tert- butylhydroquinone.

11. The fuel composition of claim 10, wherein the antioxidant mixture comprises from about 20 ppm to about 500 ppm of a mixture of Butylated Hydroxyanisole and 2,6-Di-tert-Butyl-1-Hydroxy-4-Methylbenzene, from about 20 ppm to about 500 ppm of 6-ethoxy-1 ,2-dihydro-2,2,4-trimethylquinoline, and from about 10 to about 60 ppm of 2-tert-butylhydroquinone.

12. The fuel composition of claim 8, further comprising a nonpolar solvent.

13. The fuel composition of claim 12, wherein the antioxidant mixture comprises butylated hydroxyanisole, and 2,6-Di-tert-Butyl-1-Hydroxy-4-Methylbenzene and the nonpolar solvent is a vegetable oil.

14. The fuel composition of claim 4, further comprising a polar solvent.

15. The fuel composition of claim 4, the composition further comprising a petroleum based diesel fuel.

16. The fuel composition of claim 15, the composition comprising from about 20% to about 30% by weight of the fuel composition of claim 4 and from about 70% to about 80% by weight petroleum based diesel fuel.

17. The fuel composition of claim 4, further comprising an additive selected from the group comprising of cetane improvers, ignition accelerators, metal deactivators, corrosion inhibitors, thermal stabilizers, detergents, antiwear agents, and demulsifiers.

18. A fuel composition, the composition comprising: a. a biodiesel; b. a first antioxidant having Formula (I);

wherein:

R¹, R², R³ and R⁴ are independently selected from the group consisting of hydrogen and an alkyl group having from 1 to about 6 carbons; and R⁵ is an alkoxy group having from 1 to about 12 carbons; c. a second antioxidant not having Formula (I); d. a polar solvent; and, e. a nonpolar solvent, wherein the two solvents form a homogeneous liquid.

19. The fuel composition of claim 18, wherein the second antioxidant is selected from the group consisting of 2-tert-butylhydroquinone, 3,4,5-trihydroxybenzoic acid n-propyl ester, 1 ,2,3-trihydroxybenzene, butylated hydroxyanisole, 2,6- Di-tert-Butyl-1-Hydroxy-4-Methylbenzene, alpha-tocopherol acetate, alpha- tocopherol, gamma-tocopherol, delta-tocopherol, dilauryl thiodipropinate, isopropyl 2-hydroxy-4-methylthio butanoate, propyl gallate, dodecyl gallate, gallic acid, octyl gallate, ascorbyl palmitate, lecithin, stearyl citrate, palmityl citrate, chlorophyl, pyrogallol, alpha naphthol, ascorbic acid, natural tocopherol, citric acid, sage extract, rosemary, eugenol, natural antioxidant, and combinations thereof.

20. The fuel composition of claim 18, wherein the polar solvent is selected from the group consisting of glycerol, propylene glycol, propylene glycol, polyol, a sugar alcohol, and combinations thereof.

21. The fuel composition of claim 18, wherein the nonpolar solvent is selected from the group consisting of vegetable oil, monoglycerides, diglycerides, triglycerides, and combinations thereof.

22. The fuel composition of claim 18, wherein the biodiesel is produced from a source selected from the group consisting of soybean oil, yellow grease, corn oil, rapeseed oil, coconut oil, peanut oil, palm oil, fish oil, marine oil, cottonseed oil, mustard seed oil, camelina oil, jojoba oil, hemp oil, tallow, poultry fat, lard, safflower oil, jatropha oil, algae oil, and sunflower oil.

23. The fuel composition of claim 18, wherein the biodiesel is produced from rapeseed oil.

24. The fuel composition of claim 18, wherein the biodiesel is produced from algae oil.

25. The fuel composition of claim 18, wherein the biodiesel is produced from soybean oil.

26. The fuel composition of claim 25, wherein the first antioxidant is 6-ethoxy-1 ,2- dihydro-2,2,4-trimethylquinoline, the second antioxidant is a natural antioxidant.

27. The fuel composition of claim 25, wherein the first antioxidant is 6-ethoxy-1 ,2- dihydro-2,2,4-trimethylquinoline, the second antioxidant is a mixture of propyl gallate, dilauryl thiodipropionate, ascorbyl palmitate, and butylated hydroxyanisole, and the polar solvent is propylene glycol.

28. The fuel composition of claim 25, wherein the first antioxidant is 6-ethoxy-1 ,2- dihydro-2,2,4-trimethylquinoline, the second antioxidant is a mixture of dodecyl gallate, alpha naphthol, natural tocopherol, and ascorbyl palmitate, and the polar solvent is propylene glycol.

29. The fuel composition of claim 25, wherein the first antioxidant is 6-ethoxy-1 ,2- dihydro-2,2,4-trimethylquinoline, the second antioxidant is a mixture of 2-6-di- tert-butyl-4-methylphenol, pyrogallol, 2-tert-butylhydroquinone, and stearyl citrate, and the nonpolar solvent is corn oil.

30. The fuel composition of claim 25, wherein the first antioxidant is 6-ethoxy-1 ,2- dihydro-2,2,4-trimethylquinoline, the second antioxidant is a mixture of natural mixed tocopherols, ascorbyl palmitate, propyl gallate, 2-tert- butylhydroquinone, and lecithin, and the nonpolar solvent is corn oil.

31. The fuel composition of claim 25, wherein the first antioxidant is 6-ethoxy-1 ,2- dihydro-2,2,4-trimethylquinoline, the second antioxidant is citric acid, and the nonpolar solvent is corn oil.

32. The fuel composition of claim 31 , wherein the second antioxidant further comprises 2-tert-butylhydroquinone and 1 ,2-Propanediol.

33. The fuel composition of claim 25, wherein the first antioxidant is 6-ethoxy-1 ,2- dihydro-2,2,4-trimethylquinoline, the second antioxidant is 2-tert- butylhydroquinone, and the second nonpolar solvent is com oil.

34. The fuel composition of claim 18, further comprising an additive selected from the group comprising of cetane improvers, ignition accelerators, metal deactivators, corrosion inhibitors, thermal stabilizers, detergents, antiwear agents, and demulsifiers.

35. A method of increasing the oxidative stability of a fuel composition, the method comprising contacting a biodiesel with an antioxidant mixture comprising at least two antioxidants selected from the group consisting of 2- tert-butylhydroquinone, 3,4,5-trihydroxybenzoic acid n-propyl ester, 1 ,2,3- trihydroxybenzene, butylated hydroxyanisole, 2,6-Di-tert-Butyl~1-Hydroxy-4- Methylbenzene, alpha-tocopherol acetate, alpha-tocopherol, gamma- tocopherol, delta-tocopherol, dilauryl thiodipropinate, isopropyl 2-hydroxy-4- methylthio butanoate, propyl gallate, dodecyl gallate, gallic acid, octyl gallate, ascorbyl palmitate, lecithin, stearyl citrate, palmityl citrate, chlorophyl, pyrogallol, alpha naphthol, ascorbic acid, natural tocopherol, citric acid, sage extract, rosemary, eugenol, natural antioxidant, and 6-ethoxy-1 ,2-dihydro- 2,2,4-trimethylquinoline.

36. The method of claim 35, wherein the biodiesel is produced from a source selected from the group consisting of soybean oil, yellow grease, corn oil, rapeseed oil, coconut oil, peanut oil, palm oil, fish oil, marine oil, cottonseed oil, mustard seed oil, camelina oil, jojoba oil, hemp oil, tallow, poultry fat, lard, safflower oil, jatropha oil, algae oil, and sunflower oil.

37. The method of claim 35, wherein the biodiesel is produced from rapeseed oil.

38. The method of claim 35, wherein the biodiesel is produced from algae oil.

39. The method of claim 35, wherein the biodiesel is produced from soybean oil.

40. The method of claim 39, further comprising a polar solvent.

41. The method of claim 40, wherein the antioxidant mixture comprises 6-ethoxy- 1,2-dihydro-2,2,4-trimethylquinoline, propyl gallate, dilauryl thiodipropionate, ascorbyl palmitate, and butylated hydroxyanisole, and the polar solvent is propylene glycol.

42. The method of claim 40, wherein the antioxidant mixture comprises 6-ethoxy- 1 ,2-dihydro-2,2,4-trimethylquinoline, dodecyl gallate, alpha naphthol, natural tocopherol, and ascorbyl palmitate, and the polar solvent is propylene glycol.

43. The method of claim 39, further comprising a nonpolar solvent.

44. The method of claim 43, wherein the antioxidant mixture comprises 6-ethoxy- 1 ,2-dihydro-2,2,4-trimethylquinoline, 2-6-di-tert-butyl-4-methylphenol, pyrogallol, 2-tert-butylhydroquinone, and stearyl citrate, and the nonpolar solvent is corn oil.

45. The method of claim 43, wherein the antioxidant mixture comprises 6-ethoxy- 1 ,2-dihydro-2,2,4-trimethylquinoline, natural mixed tocopherols, ascorbyl palmitate, propyl gallate, 2-tert-butylhydroquinone, and lecithin, and the nonpolar solvent is corn oil.

46. The method of claim 43, wherein the antioxidant mixture comprises 6-ethoxy- 1,2~dihydro-2,2,4-trimethylquinoline and citric acid, and the nonpolar solvent is corn oil.

47. The method of claim 46, wherein the antioxidant mixture further comprises 2- tert-butylhydroquinone and 1 ,2-Propanediol.

48. The method of claim 43, wherein the antioxidant mixture comprises 6-ethoxy- 1 ,2-dihydro-2,2,4-trimethylquinoline, 2-tert-butylhydroquinone, and the nonpolar solvent is corn oil.

49. The method of claim 35, further comprising contacting an additive with the biodiesel and the antioxidant mixture.

50. The method of claim 49, wherein the additive is selected from the group comprising of cetane improvers, ignition accelerators, metal deactivators, corrosion inhibitors, thermal stabilizers, detergents, antiwear agents, and demulsifiers.

51. The method of claim 35, wherein the antioxidant mixture comprises 6-ethoxy- 1 ,2-dihydro-2,2,4-trimethylquinoline and a second antioxidant and the fuel composition has less than 2.8 mg/100 ml of filterable insolubles.

52. The method of claim 35, wherein the antioxidant mixture comprises 6-ethoxy- 1 ,2-dihydro-2,2,4-trimethylquinoline and a second antioxidant and the fuel composition has less than 4.3 mg/100 ml of adherent insolubles.

53. The method of claim 35, wherein the antioxidant mixture comprises 6-ethoxy- 1 ,2-dihydro-2,2,4-trimethylquinoline and a second antioxidant and the fuel composition has less than 6.8 mg/100 ml of total insolubles.

54. The method of claim 35, wherein the fuel has a kinematic viscosity at 40⁰C of from about 4.00 mm²/sec to about 5.0 mm²/sec.

55. The method of claim 35, wherein the fuel has an acid value of from about 0.1 mg KOH/g to about 0.75 mg KOH/g.

56. The method of claim 35, wherein the fuel has a density at 2O⁰C of from about 0.865 g/cm³to about 0.884 g/cm³.

57. The method of claim 35, wherein the fuel has a cold filter plugging point (CFPP) of from about -1⁰C to about -1O⁰C.

58. The method of claim 35, wherein the fuel has a sulphated ash percent by mass of from about 0.001 % by mass to about 0.002% by mass.