EP2087074A1

EP2087074A1 - Stabilised biodiesel fuel compositions

Info

Publication number: EP2087074A1
Application number: EP07847200A
Authority: EP
Inventors: Natalie R. Li; Eugene Scanlon Iv; Patrice Cusatis
Original assignee: Ciba Holding AG
Current assignee: BASF Schweiz AG
Priority date: 2006-11-27
Filing date: 2007-11-19
Publication date: 2009-08-12
Also published as: WO2008065015A1; US20080127550A1; BRPI0719687A2; KR20090089851A; MX2009005565A; NZ576674A; TW200846458A; CN101541928A; JP2010511067A; CA2670065A1

Abstract

The invention relates to stabilized biodiesel fuel compositions, which compositions comprise a biodiesel fuel and a combination of i) one or more compounds selected from the group consisting of the sterically hindered phenolic antioxidants and ii) one or more compounds selected from the group consisting of the triazole metal deactivators.

Description

Stabilised biodiesel fuel compositions

The invention is aimed at biodiesel fuel (or bio-fuel) compositions, stabilized against the deleterious effects of heat, light, oxygen and metals by an effective amount of a combination of one or more compounds selected from the group consisting of the sterically hindered phe- nolic antioxidants and one or more compounds selected from the group consisting of the tria- zole metal deactivators.

Biodiesel fuel is of increasing importance as a renewable fuel source. It may, for example, be employed as a fuel itself, or may be used in combination with diesel fuel.

WO 2004055141 teaches the stabilization of fats, oils and food. The stabilizers are selected from the group consisting of the 3-arylbenzofuranones, long chain N,N-dialkylhydroxyl- amines, substituted hydroxylamines, nitrones and amine oxides.

EP-A-1 486 555, EP-A-1 484 387 and EP-A-1 484 388 disclose a low corrosive fuel composition for use in a blue flame burner or an optimized yellow flame burner of a boiler.

U.S. Pat. Spec. No. 4,701,273 discloses lubricants and discloses combinations of a benzotri- azole metal deactivator and phenolic antioxidants.

U.S. Pat. Spec. No. 6,410,490 teaches a composition comprising a hydrotreated oil or a hy- drowaxed oil and a combination of a triazole metal deactivator, a phenolic antioxidant, an aromatic amine antioxidant, an alkylphenoxy alkanoic acid and an N-acyl sarcosine derivative. U.S. Pat. Publication No. 2006/0218855 discloses a method of increasing the oxidation stability of biodiesel.

The invention relates to improved biodiesel fuel compositions stabilized against the deleterious effects of heat, light, oxygen and metals, which compositions comprise

A biodiesel fuel; and An effective stabilizing amount of a combination of i) At least one compound selected from the group consisting of the sterically hindered phenolic antioxidants and ii) At least one compound selected from the group consisting of the triazole metal deactivators. Also disclosed is a process for the stabilization of a biodiesel fuel against the deleterious effects of heat, light, oxygen and metals, which process comprises incorporating into a biodiesel fuel

An effective stabilizing amount of a combination of i) At least one compound selected from the group consisting of the sterically hindered phenolic antioxidants and ii) At least one compound selected from the group consisting of the triazole metal deactivators.

Biodiesel fuels are a renewable resource and are of increasing importance. Biodiesel fuels comprise lower alkyl fatty acid esters, prepared, for example, by transesteri- fying triglycerides with lower alcohols, e.g. methanol or ethanol. A typical biodiesel fuel is the fatty acid methyl ester of rapeseed oil or of soy oil. Sources for biodiesel fuel include vegetable and animal sources. Recycled cooking oil may be a source of biodiesel fuel.

Biodiesel fuel and its preparation is taught, for example, in U.S. Pat. Spec. Nos. 5,578,090, 5,713,965, 5,891,203, 6,015,440, 6, 174,501 and 6,398, 707.

Biodiesel fuel of the invention, for example, comprises lower esters of a mixture of saturated and unsaturated straight chain fatty acids of from 12 to 22 carbon atoms, derived from vegetable or oleaginous seeds. The term "lower alkyl ester" means CrC₅ esters, in particular methyl and ethyl esters. The mixture of methyl esters of the saturated, monounsaturated and polyunsaturated C₁6-C₂₂ fatty acids is known as "biodiesel" or "rapeseed methyl ester".

Biodiesel fuel according to the invention essentially consists of up to 100 wt.-% lower alkyl fatty acid ester, or is a combination of a lower alkyl fatty acid ester with regular diesel fuel. The biodiesel fuel contains, for example, from about 2 to about 98 wt.-% fatty acid ester and from about 98 to about 2 wt.-% regular diesel fuel. For example, the biodiesel fuel contains from about 10 to about 90 wt.-% fatty acid ester and from about 90 to about 10 wt.-% diesel fuel. For instance, the biodiesel fuel contains from about 25 to about 75 wt.-% fatty acid ester and from about 75 to about 25 wt.-% diesel fuel.

Representative examples of hindered phenolic antioxidants are:

1. Alkylated monophenols, for example 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-methyl- phenol, 2-tert-butyl-4,6-dimethylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,6-di-tert-butyl-

4-n-butylphenol, 2,6-di-tert-butyl-4-isobutylphenol, 2,6-dicyclopentyl-4-methylphenol, 2- (α-methylcyclohexyl)-4,6-dimethylphenol, 2,6-dioctadecyl-4-methylphenol, 2,4,6- tricyclohexylphenol, 2,6-di-tert-butyl-4-methoxymethylphenol, nonylphenols which are linear or branched in the side chains, for example, 2,6-di-nonyl-4-methylphenol, 2,4- dimethyl-6-(1 -methylundec-1 -yl)phenol, 2,4-dimethyl-6-(1 -methylheptadec-1 -yl)phenol, 2,4-dimethyl-6-(1-methyltridec-1-yl)phenol and mixtures thereof.

2. Alkylthiomethylphenols, for example 2,4-dioctylthiomethyl-6-tert-butylphenol, 2,4-dioc- tylthiomethyl-6-methylphenol, 2,4-dioctylthiomethyl-6-ethylphenol, 2,6-di-dodecyl- thiomethyl-4-nonylphenol.

3. Hydroquinones and alkylated hydroquinones, for example 2,6-di-tert-butyl-4-methoxy- phenol, 2,5-di-tert-butylhydroquinone, 2,5-di-tert-amylhydroquinone, 2,6-diphenyl-4- octadecyloxyphenol, 2,6-di-tert-butylhydroquinone, 2,5-di-tert-butyl-4-hydroxyanisole, 3,5-di-tert-butyl-4-hydroxyanisole, 3,5-di-tert-butyl-4-hydroxyphenyl stearate, bis-(3,5- di-tert-butyl-4-hydroxyphenyl) adipate.

4. Tocopherols, for example α-, β-, γ- and δ-tocopherol and mixtures thereof (Vitamin E).

5. Hydroxylated thiodiphenyl ethers, for example 2,2'-thiobis(6-tert-butyl-4-methylphenol), 2,2'-thiobis(4-octylphenol), 4,4'-thiobis(6-tert-butyl-3-methylphenol), 4,4'-thiobis(6-tert- butyl-2-methylphenol), 4,4'-thiobis-(3,6-di-sec-amylphenol), 4,4'-bis(2,6-dimethyl-4-hy- droxyphenyl)disulfide.

6. Alkylidenebisphenols, for example 2,2'-methylenebis(6-tert-butyl-4-methylphenol), 2,2'- methylenebis(6-tert-butyl-4-ethylphenol), 2,2'-methylenebis[4-methyl-6-(α-methylcyclo- hexyl)phenol], 2,2'-methylenebis(4-methyl-6-cyclohexylphenol), 2,2'-methylenebis(6- nonyl-4-methylphenol), 2,2'-methylenebis(4,6-di-tert-butylphenol), 2,2'-ethylidenebis-

(4,6-di-tert-butylphenol), 2,2'-ethylidenebis(6-tert-butyl-4-isobutylphenol), 2,2'-methyle- nebis[6-(α-methylbenzyl)-4-nonylphenol], 2,2'-methylenebis[6-(α,α-dimethylbenzyl)-4- nonylphenol], 4,4'-methylenebis(2,6-di-tert-butylphenol), 4,4'-methylenebis(6-tert-butyl- 2-methylphenol), 1 ,1-bis(5-tert-butyl-4-hydroxy-2-methylphenyl)butane, 2,6-bis(3-tert- butyl-5-methyl-2-hydroxybenzyl)-4-methylphenol, 1 ,1 ,3-tris(5-tert-butyl-4-hydroxy-2- methylphenyl)butane, 1 ,1-bis(5-tert-butyl-4-hydroxy-2-methyl-phenyl)-3-n-dodecylmer- captobutane, ethylene glycol bis[3,3-bis(3-tert-butyl-4-hydroxyphenyl)butyrate], bis(3- tert-butyl-4-hydroxy-5-methyl-phenyl)dicyclopentadiene, bis[2-(3'tert-butyl-2-hydroxy-5- methylbenzyl)-6-tert-butyl-4-methylphenyl]terephthalate, 1 ,1-bis-(3,5-dimethyl-2-hy- droxyphenyl)butane, 2,2-bis-(3,5-di-tert-butyl-4-hydroxyphenyl)propane, 2,2-bis-(5-tert- butyl-4-hydroxy2-methylphenyl)-4-n-dodecylmercaptobutane, 1 ,1 ,5,5-tetra-(5-tert-butyl- 4-hydroxy-2-methylphenyl)pentane.

7. Benzyl compounds, for example 3,5,3',5'-tetra-tert-butyl-4,4'-dihydroxydibenzyl ether, octadecyl-4-hydroxy-3,5-dimethylbenzylmercaptoacetate, tridecyl-4-hydroxy-3,5-di-tert- - A-

butylbenzylmercaptoacetate, tris(3,5-di-tert-butyl-4-hydroxybenzyl)amine, 1 ,3,5-tri-(3,5- di-tert-butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene, di-(3,5-di-tert-butyl-4-hydroxy- benzyl) sulfide, S.S-di-tert-butyM-hydroxybenzyl-mercapto-acetic acid isooctyl ester, bis-(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)dithiol terephthalate, 1 ,3,5-tris-(3,5-di- tert-butyl-4-hydroxybenzyl) isocyanurate, 1 ,3,5-tris-(4-tert-butyl-3-hydroxy-2,6-di- methylbenzyl) isocyanurate, 3,5-di-tert-butyl-4-hydroxybenzyl-phosphoric acid diocta- decyl ester and 3,5-di-tert-butyl-4-hydroxybenzyl-phosphoric acid monoethyl ester, calcium-salt.

8. Hydroxybenzylated malonates, for example dioctadecyl-2,2-bis-(3,5-di-tert-butyl-2-hy- droxybenzyl)-malonate, di-octadecyl-2-(3-tert-butyl-4-hydroxy-5-methylbenzyl)-malo- nate, di-dodecylmercaptoethyl-2,2-bis-(3,5-di-tert-butyl-4-hydroxybenzyl)malonate, bis[4-(1 ,1 ,3,3-tetramethylbutyl)phenyl]-2,2-bis(3,5-di-tert-butyl-4-hydroxybenzyl)malo- nate.

9. Aromatic hydroxybenzyl compounds, for example 1 ,3,5-tris-(3,5-di-tert-butyl-4-hydroxy- benzyl)-2,4,6-trimethylbenzene, 1 ,4-bis(3,5-di-tert-butyl-4-hydroxybenzyl)-2,3,5,6-tetra- methylbenzene, 2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)phenol.

10. Triazine compounds, for example 2,4-bis(octylmercapto)-6-(3,5-di-tert-butyl-4-hydroxy- anilino)-1 ,3,5-triazine, 2-octylmercapto-4,6-bis(3,5-di-tert-butyl-4-hydroxyanilino)-1 ,3,5- triazine, 2-octylmercapto-4,6-bis(3,5-di-tert-butyl-4-hydroxyphenoxy)-1 ,3,5-triazine, 2,4,6-tris(3,5-di-tert-butyl-4-hydroxyphenoxy)-1 ,2,3-triazine, 1 ,3,5-tris-(3,5-di-tert-butyl-

4-hydroxybenzyl)isocyanurate, 1 ,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)iso- cyanurate, 2,4,6-tris(3,5-di-tert-butyl-4-hydroxyphenylethyl)-1 ,3,5-triazine, 1 ,3,5-tris(3,5- di-tert-butyl-4-hydroxyphenylpropionyl)-hexahydro-1 ,3,5-triazine, 1 ,3,5-tris(3,5-dicyclo- hexyl-4-hydroxybenzyl)isocyanurate. 1 1. Benzylphosphonates, for example dimethyl-2,5-di-tert-butyl-4-hydroxybenzylphospho- nate, diethyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate, dioctadecyl3,5-di-tert-butyl- 4-hydroxybenzylphosphonate, dioctadecyl-δ-tert-butyl^-hydroxy-S-methylbenzylphos- phonate, the calcium salt of the monoethyl ester of 3,5-di-tert-butyl-4-hydroxybenzyl- phosphonic acid. 12. Acylaminophenols, for example 4-hydroxy-lauric acid anilide, 4-hydroxy-stearic acid anilide, 2,4-bis-octylmercapto-6-(3,5-tert-butyl-4-hydroxyanilino)-s-triazine and octyl-N- (3,5-di-tert-butyl-4-hydroxyphenyl)-carbamate.

13. Esters of β-(3,5-di-tert-butyl-4-hvdroxyphenyl)propionic acid with mono- or polyhydric alcohols, e.g. with methanol, ethanol, n-octanol, i-octanol, octadecanol, 1 ,6-hexanediol, 1 ,9-nonanediol, ethylene glycol, 1 ,2-propanediol, neopentyl glycol, thiodiethylene glycol, diethylene glycol, triethylene glycol, pentaerythritol, tris(hydroxyethyl)isocyanurate, N,N'-bis(hydroxyethyl)oxamide, 3-thiaundecanol, 3-thiapentadecanol, trimethylhex- anediol, trimethylolpropane, 4-hydroxymethyl-1 -phospha^θj-trioxabicyclo- [2.2.2]octane.

14. Esters of β-(5-tert-butyl-4-hvdroxy-3-methylphenyl)propionic acid with mono- or polyhy- dric alcohols, e.g. with methanol, ethanol, n-octanol, i-octanol, octadecanol, 1 ,6-hex- anediol, 1 ,9-nonanediol, ethylene glycol, 1 ,2-propanediol, neopentyl glycol, thiodiethylene glycol, diethylene glycol, triethylene glycol, pentaerythritol, tris(hydroxyethyl) iso- cyanurate, N,N'-bis(hydroxyethyl)oxamide, 3-thiaundecanol, 3-thiapentadecanol, trimethylhexanediol, trimethylolpropane, 4-hydroxymethyl-1 -phospha-2,6,7-trioxabicy- clo[2.2.2]octane.

15. Esters of β-(3,5-dicvclohexyl-4-hvdroxyphenyl)propionic acid with mono- or polyhydric alcohols, e.g. with methanol, ethanol, octanol, octadecanol, 1 ,6-hexanediol, 1 ,9-non- anediol, ethylene glycol, 1 ,2-propanediol, neopentyl glycol, thiodiethylene glycol, diethylene glycol, triethylene glycol, pentaerythritol, tris(hydroxyethyl)isocyanurate, N, N'- bis(hydroxyethyl)oxamide, 3-thiaundecanol, 3-thiapentadecanol, trimethylhexanediol, trimethylolpropane, 4-hydroxymethyl-1-phospha-2,6,7-trioxabicyclo[2.2.2]octane.

16. Esters of 3,5-di-tert-butyl-4-hvdroxyphenyl acetic acid with mono- or polyhydric alco- hols, e.g. with methanol, ethanol, octanol, octadecanol, 1 ,6-hexanediol, 1 ,9-nonanediol, ethylene glycol, 1 ,2-propanediol, neopentyl glycol, thiodiethylene glycol, diethylene glycol, triethylene glycol, pentaerythritol, tris(hydroxyethyl)isocyanurate, N,N'-bis(hydroxy- ethyl)oxamide, 3-thiaundecanol, 3-thiapentadecanol, trimethylhexanediol, trimethylolpropane, 4-hydroxymethyl-1-phospha-2,6,7-trioxabicyclo[2.2.2]octane. 17. Amides of β-(3,5-di-tert-butyl-4-hvdroxyphenyl)propionic acid e.g. N,N'-bis(3,5-di-tert- butyl-4-hydroxyphenylpropionyl)hexamethylenediamide, N,N'-bis(3,5-di-tert-butyl-4-hy- droxyphenylpropionyl)trimethylenediamide, N,N'-bis(3,5-di-tert-butyl-4-hydroxyphenyl- propionyl)hydrazide, N,N'-bis[2-(3-[3,5-di-tert-butyl-4-hydroxyphenyl]propiony- loxy)ethyl]oxamide (Naugard^®XL-1 supplied by Uniroyal). For example, the sterically hindered phenolic compounds are selected from the group consisting of butylated phenol, butylated hydroxytoluene, butylated hydroxyanisole, tocopherol, benzylphosphonates, esters of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid with mono- or polyhydric alcohols, esters of β-(5-tert-butyl-4-hydroxy-3-methylphenyl)propionic acid with mono- or polyhydric alcohols, esters of β-(3,5-dicyclohexyl-4-hydroxyphenyl)propionic acid with mono- or polyhydric alcohols and esters of 3,5-di-tert-butyl-4-hydroxyphenyl acetic acid with mono- or polyhydric alcohols.

For instance, the sterically hindered phenolic antioxidants are selected from the group consisting of 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol (BHT), 2,2'-methylene bis- (4,6-di-tert-butylphenol), 1 ,6-hexamethylene-bis-(3,5-di-tert-butyl-4-hydroxyhydrocinnamate), ((3,5-bis(1 ,1-dimethylethyl)-4-hydroxphenyl)methylthio)acetic acid Ci₀-Ci₄isoalkyl esters, 3,5- di-tert-butyl-4-hydroxyhydrocinnamic acid Cβ-Cgalkyl esters, 3,5-di-tert-butyl-4-hydroxyhydro- cinnamic acid methyl ester, tetrakis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionyloxy- methyl)methane, thiodiethylene bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate), octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate and 2,5-di-tert-butylhydroquinone.

For example, the sterically hindered phenolic antioxidants are selected from the group consisting of 2,6-di-tert-butylphenol, 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid methyl ester and tetrakis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionyloxymethyl)methane.

Suitable triazole metal deactivators are of the 1 ,2,4-triazole class or the benzotriazole class. Metal deactivators of the 1 ,2,4-triazole class are disclosed, for example, in U.S. Pat. Spec. No. 4, 734,209.

Suitable 1 ,2,4-triazole metal deactivators are, for example, of the formula

wherein Ri and R₂ are the same or different and are hydrogen, CrC₂oalkyl, C₃-C₂oalkenyl, C₅-C₁₂Cy- cloalkyl, C₇-Ci₃aralkyl, Cβ-C-ioaryl or hydroxy or R₁ and R₂, together with the nitrogen atom to which they are each attached may form a 5-, 6- or 7-membered heterocylic ring, or R₁ and R₂ are a group of the partial formula

R₃XK-R₄-PU-R₄)-, wherein

X represents O, S or NR₃,

R₃ represents hydrogen or CrC₂₀alkyl,

R₄ represents CrC₁₂alkylene, n represents 0 or an integer from 1 to 6,

Or one of Ri and R₂ represents a group of the partial formula

or R₂ represents a group of formula (II) and Ri represents a group of the partial formula -[R₄]_n-N(R₅)-A-[N(R₅)₂ ]_m, wherein m represents 0 or 1 and, when m represents zero, A represents a group of formula (II) and, when m represents 1 , A represents alkylene or C₆-Ci₀ arylene and

R₅ represents a group of formula (II). R₄ represents, for example, a Ci-C₆alkylene group, for instance a C₂-C₃alkylene. n represents for instance 0, 1 , 2, 3, 4, 5 or 6. Specific compounds of formula (I) include:

1 -(or 4)-(Dimethylaminomethyl)triazole, 1 -(or 4)-(diethylaminomethyl)triazole, 1 -(or 4)-(di-iso- propylaminomethyl)triazole, 1 -(or 4)-(di-n-butylaminomethyl)triazole, 1 -(or 4)-(di-n-hexylami- nomethyl)triazole, 1-(or 4)-(di-isooctylaminomethyl)triazole, 1-(or 4)-(di-(2-ethylhexyl)ami- nomethyl)triazole,1-(or 4)-(di-n-octylaminomethyl)triazole, 1-(or 4)-(di-n-decylaminomethyl)- triazole, 1 -(or 4)-(di-n-dodecylaminomethyl)triazole, 1 -(or 4)-(di-n-octadecylaminomethyl)- triazole, 1 -(or 4)-(di-n-eicosylaminomethyl)triazole, 1 -(or 4)-[di-(prop-2'-enyl)aminomethyl]- triazole, 1 -(or 4)-[di-(but-2'-enyl)aminomethyl]triazole, 1 -(or 4)-[di-(eicos-2'-enyl)amino- methyl]triazole, 1-(or 4)-(di-cyclohexylaminomethyl)triazole, 1-(or 4)-(di-benzylaminomethyl)- triazole, 1-(or 4)-(di-phenylaminomethyl)triazole, 1-(or 4)-(4'-morpholinomethyl)triazole, 1-(or 4)-(1 '-pyrrolidinomethyl)triazole, 1 -(or 4)-(1 '-piperidinomethyl)triazole, 1 -(or 4)-(1 '-perhydoro- azepinomethyl)triazole, 1-(or 4)-(2',2"-dihydroxyethyl)aminomethyl]triazole, 1-(or 4)-(dibutoxy- propyl-aminomethyl)triazole, 1 -(or 4)-(dibutylthiopropyl-aminomethyl)triazole, 1 -(or 4)-(di- butylaminopropyl-aminomethyl)triazole, N,N-bis-(1- or 4-triazolylmethyl) laurylamine, N,N-bis- (1- or 4-triazolylmethyl) oleylamine, N,N-bis-(1- or 4-triazolylmethyl) ethanolamine and N, N, N', N'-tetra(1- or 4-triazolylmethyl) ethylene diamine.

A preferred compound of formula (I) is, for example, 1-(di-isooctylaminomethyl)triazole, that is 1-(di-isooctylaminomethyl)-1 ,2,4-triazole, or is 1-(di-(2-ethylhexyl)aminomethyl)-1 ,2,4-triazole. Suitable benzotriazole metal deactivators are, for example, those disclosed in U.S. Pat. Spec. Nos. 5,032,300 and 5, 171,463.

Suitable benzotriazole metal deactivators are, for example, of the formula

wherein

R₆ represents d-C^alkyl,

R₇ represents d-C^alkyl, d-C^alkyl interrupted by one or more O atoms or represents C₅- Ci₂cycloalkyl and

R₈ and R₉ represent hydrogen or methyl. Specific examples of compounds of formula (III) include:

1 -(2-Methoxyprop-2-yl)tolyltriazole, 1 -(1 -methoxyethyl)tolyltriazole, 1 -(1 -methoxpropyl)tolyltri- azole, 1 -(1 -isobutoxybutyl)tolyltriazole, 1 -(1 -tert-butoxybutyl)tolyltriazole, 1 -(1 -hexyloxybutyl)- tolyltriazole, 1 -(1 -octyloxybutyl)tolyltriazole, 1 -(1 -butoxy-2-methylpropyl)tolyltriazole, 1 -(1 -do- decyloxybutyl)tolyltriazole, 1 -(1 -isopropyloxyethyl)tolyltriazole, 1 -(1 -isopropyloxypropyl)tolyl- triazole, 1-(1-isopropyloxybutyl)tolyltriazole, 1-(1-cyclohexyloxypropyl)tolyltriazole, 1-(1-cyclo- hexyloxyheptyl)tolyltriazole, 1 -(1 -cyclohexyloxybutyl)tolyltriazole, 1 -[1 -(2-methoxyethoxy)- butyl]tolyltriazole and 1 -[1 -(2-ethoxyethoxy)butyl]tolyltriazole.

A preferred compound of formula (III) is, for example, 1-(2-methoxyprop-2-yl)tolyltriazole, 1- (1 -cyclohexyloxypropyl)tolyltriazole, 1 -(1 -cyclohexyloxyheptyl)tolyltriazole or 1 -(1 -cyclohexyl- oxybutyl)tolyltriazole.

(1-(2-methoxyprop-2-yl)tolyltriazole is represented by the formula

1-(1-cyclohexyloxyheptyl)tolyltriazole is represented by the formula

The benzotriazole metal deactivators may also be, for example, those disclosed in U.S. Pat. Spec. Nos. 5,580,482 and 6,410,490.

Suitable benzotriazole metal deactivators are, for example, of the formula

wherein Rio represents hydrogen or CrC₁₂alkyl, Rn and Ri₂ are the same or different and are hydrogen, CrC₂oalkyl, C₃-C₂oalkenyl, C₅-

Ci₂cycloalkyl, C₇-Ci₃aralkyl, C₆-Ci₀aryl or hydroxy or R₁₁ and R₁₂, together with the nitrogen atom to which they are each attached may form a 5-, 6- or 7-membered heterocylic ring, or R₁₁ and R₁₂ are a group of the partial formula

Ri₃X[(-Ri4-)O]_n(-R₁₄)- wherein

X represents O, S or NR₁₃,

R₁₃ represents hydrogen or CrC₂₀alkyl, Ri₄ represents d-C^alkylene, n represents 0 or an integer from 1 to 6, or one of Rn and Ri₂ represents a group of formula

or R₁₂ represents a group of formula (II) and Rn represents a group of the partial formula

-[R₁₄]_n-N(R₁₅)-A-[N(R₁₅)₂ ]_m wherein m represents 0 or 1 and, when m represents zero, A represents a group of formula (II) and, when m represents 1 , A represents alkylene or C₆-Ci₀arylene and Ri₅ represents a group of formula (II).

Representative benzotriazoles (IV) are, for example,

4-(or 5)-Methyl-1-(di(2-ethylhexyl)-aminomethyl)-benzotriazole, 4-(or 5)-methyl-1-(dimethyl- aminomethyl)-benzotriazole, 4-(or 5)-methyl-1-(diethylaminomethyl)-benzotriazole, 4-(or 5)- methyl-1 -(di-isopropylaminomethyl)-benzotriazole, 4-(or 5)-methyl-1 -(di-n-butylaminomethyl)- benzotriazole, 4-(or 5)-methyl-1 -(di-n-hexylaminomethyl)-benzotriazole, 4-(or 5)-methyl-1 -(di- isooctylaminomethyl)-benzotriazole,4-(or 5)-methyl-1-(di-n-octylaminomethyl)-benzotriazole, 4-(or 5)-methyl-1-(di-n-decylaminomethyl)-benzotriazole, 4-(or 5)-methyl-1-(di-n-dodecylami- nomethyl)-benzotriazole, 4-(or 5)-methyl-1-(di-n-octadecylaminomethyl)-benzotriazole, 4-(or 5)-methyl-1 -(di-n-eicosylaminomethyl)-benzotriazole, 4-(or 5)-methyl-1 -[di-(prop-2'-enyl)ami- nomethyl]-benzotriazole, 4-(or 5)-methyl-1-[di-(but-2'-enyl)aminomethyl]-benzotriazole, 4-(or 5)-methyl-1 -[di-(eicos-2'-enyl)aminomethyl]-benzotriazole, 4-(or 5)-methyl-1 -(di-cyclohexyl- aminomethyl)-benzotriazole, 4-(or 5)-methyl-1-(di-benzylaminomethyl)-benzotriazole, 4-(or 5)-methyl-1 -(di-phenylaminomethyl)-benzotriazole, 4-(or 5)-methyl-1 -(4'-morpholinomethyl)- benzotriazole, 4-(or 5)-methyl-1 -(1 '-pyrrolidinomethyl)-benzotriazole, 4-(or 5)-methyl-1 -(1 '- piperidinomethyl)-benzotriazole, 4-(or 5)-methyl-1 -(1 '-perhydoroazepinomethyl)-benzo- triazole, 4-(or 5)-methyl-1-(2',2"-dihydroxyethyl)aminomethyl]-benzotriazole, 4-(or 5)-methyl- 1 -(dibutoxypropyl-aminomethyl)-benzotriazole, 4-(or 5)-methyl-1 -(dibutylthiopropyl- aminomethyl)-benzotriazole and4-(or 5)-methyl-1 -(di-butylaminopropyl-aminomethyl)- benzotriazole. Preferred benzotriazoles of formula (IV) are, for example, 4-(or 5)-methyl-1-(di(2-ethylhexyl)- aminomethyl)-benzotriazole or 4-(or 5)-methyl-1-(di-isooctylaminomethyl)-benzotriazole. Alkyl is a branched or unbranched radical such as, for example, methyl, ethyl, propyl, isopro- pyl, n-butyl, sec-butyl, isobutyl, tert-butyl, 2-ethylbutyl, n-pentyl, isopentyl, 1-methylpentyl, 1 ,3-dimethylbutyl, n-hexyl, 1-methylhexyl, n-heptyl, isoheptyl, 1 ,1 ,3,3-tetramethylbutyl, 1- methylheptyl, 3-methylheptyl, n-octyl, 2-ethylhexyl, 1 ,1 ,3-trimethylhexyl, 1 ,1 ,3,3-tetramethyl- pentyl, nonyl, decyl, undecyl, 1-methylundecyl, dodecyl, 1 ,1 ,3,3,5,5-hexamethylhexyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, eicosyl or docosyl.

Alkenyl is a branched or unbranched radical such as, for example, propenyl, 2-butenyl, 3- butenyl, isobutenyl, n-2,4-pentadienyl, 3-methyl-2-butenyl, n-2-octenyl, n-2-dodecenyl, iso- dodecenyl, oleyl, n-2-octadecenyl or n-4-octadecenyl. Preference is given to alkenyl having 3 to 18, especially 3 to 12, for example, 3 to 6, in particular 3 to 4 carbon atoms.

Cycloalkyl is, for example, cyclopentyl, methylcyclopentyl, dimethylcyclopentyl, cyclohexyl, methylcyclohexyl, dimethylcyclohexyl, trimethylcyclohexyl, tert-butylcyclohexyl, cycloheptyl or cyclooctyl. Preference is given to cyclohexyl and tert-butylcyclohexyl.

Aralkyl is, for example, benzyl, α-methylbenzyl, α,α-dimethylbenzyl or 2-phenylethyl. Benzyl and α,α-dimethylbenzyl are preferred.

Aryl is, for example, phenyl or naphthyl, but also comprised are Ci-C₄alkyl substituted phenyl, d-C₄alkoxy substituted phenyl, hydroxy, halogen or nitro substituted phenyl. Examples for alkyl substituted phenyl are ethylbenzene, toluene, xylene and its isomers, mesity- lene or isopropylbenzene. Halogen substituted phenyl is, for example, dichlorobenzene or bromotoluene.

Alkylene is a branched or unbranched radical such as, for example, methylene, ethylene, propylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, octamethylene, decamethylene, dodecamethylene or octadecamethylene. Preference is given to Ci-C₈alkylene. Arylene is a divalent aryl, for instance phenylene or naphthalene.

Components i) and ii) each are employed at levels of about 5 ppm to about 5000 ppm, for example from about 50 ppm to about 5000 ppm, for example from about 100 to about 5000 ppm by weight, based on the weight of the biodiesel fuel. For example, each of the additives are present from about 150 to about 4000 ppm, from about 200 to about 3000 ppm, or from about 250 to about 2500 ppm by weight, based on the weight of the biodiesel fuel. The levels may be as high as about 1 %, about 2% or about 3% by weight, based on the weight of the biodiesel fuel. The stabilized biodiesel fuels exhibit increased storage stability vs. unstabilized samples. Degradation of biodiesel fuels under the conditions of heat, light, oxygen or metals is observed by the formation of carboxylic acids, peroxides, aldehydes and alcohols. Degradation under the conditions of metals means metal contamination. The stabilized biodiesel fuels may also contain known metal chelating compounds. The known metal chelating compounds include hydroxycarboxylic acid chelators such as citric acid, hydroxycarboxylic acid ester chelators such as triethyl citrate and monostearyl citrate, Schiff bases such as N,N-disalicylidene-1 ,2-propanediamine (DMD), aminoalcohols such as triethanolamine and N-hydroxyethylethylenediamine, polyamines such as ethylenediamine and diethylenetriamine and aminocarboxylic acid chelators such as ethylenediamine- tetraacetic acid (EDTA). Mixtures of these compounds may also be employed.

The stabilized biodiesel fuels may also contain one or more stabilizers selected from the group consisting of the 3-arylbenzofuranone stabilizers and the sterically hindered amine light stabilizers. A preferred embodiment relates to

Suitable 3-arylbenzofuranones antioxidants are, for example, those disclosed in U.S. patent Spec. Nos. 4,325,863;4,388,244;5, 175,312; 5,252,643; 5,216,052; 5,369, 159; 5,488, 117; 5,356,966; 5,367,008; 5,428, 162; 5,428, 177; and 5,516,920.

Particularly suitable benzofuranone type stabilizers include 3-[4-(2-acetoxyethoxy)phenyl]- 5,7-di-tert-butyl-benzofuran-2-one; 5,7-di-tert-butyl-3-[4-(2-stearoyloxyethoxy)phenyl]benzo- furan-2-one; 3,3'-bis[5,7-di-tert-butyl-3-(4-[2-hydroxyethoxy]phenyl)benzofuran-2-one]; 5,7-di- tert-butyl-3-(4-ethoxyphenyl)benzofuran-2-one; 3-(4-acetoxy-3,5-dimethylphenyl)-5,7-di-tert- butylbenzofuran-2-one; 3-(3,5-dimethyl-4-pivaloyloxy-phenyl)-5,7-di-tert-butyl-benzofuran-2- one; 5,7-di-tert-butyl-3-phenylbenzofuran-2-one; 5,7-di-tert-butyl-3-(3,4-dimethylphenyl)-ben- zofuran-2-one; or 5,7-di-tert-butyl-3-(2,3-dimethylphenyl)benzofuran-2-one.

So-called sterically hindered amines are disclosed, for example, in U.S. Pat. Spec. Nos. 5,004,770, 5,204,473, 5,096,950, 5,300,544, 5, 112,890, 5, 124,378, 5, 145,893, 5,216, 156, 5,844,026, 5,980, 783, 6,046,304, 6, 117,995, 6,271,377, 6,297,299, 6,392,041, 6,376,584 and 6,472,456, and U.S. Pat. App. Nos. 09/714, 717, and 10/485,377. Suitable so-called sterically hindered amines include for example:

1 ) 1 -Cyclohexyloxy^^θ.θ-tetramethyM-octadecylaminopiperidine,

2) bis(2,2,6,6-Tetramethylpiperidin-4-yl) sebacate,

3) bis(1-Acetoxy-2,2,6,6-tetramethylpiperidin-4-yl) sebacate, 4) bis(1 _!2_!2_!6,6-Pentamethyl-4-yl) sebacate,

5) bis(1 -Cyclohexyloxy^^θ.θ-tetramethylpiperidin^-yl) sebacate,

6) bis(1-Octyloxy-2,2,6,6-tetramethylpiperidin-4-yl) sebacate;

7) bis(1-Acyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate, 8) bis(1 ,2,2,6,6-Pentamethyl-4-piperidyl) n-butyl-3,5-di-tert-butyl-4-hydroxybenzylmalo- nate,

9) 2,4-bis[(1-Cyclohexyloxy-2,2,6,6-tetramethylpiperidin-4-yl)butylamino]-6-(2-hydroxy- ethylamino-s-triazine,

10) bis(1 -Cyclohexyloxy^^θ.θ-tetramethylpiperidin^-yl) adipate, 1 1 ) 2,4-bis[(1-Cyclohexyloxy-2,2,6,6-piperidin-4-yl)butylamino]-6-chloro-s-triazine,

12) 1 -(2-Hydroxy-2-methylpropoxy)-4-hydroxy-2,2,6,6-tetramethylpiperidine,

13) 1 -(2-Hydroxy-2-methylpropoxy)-4-oxo-2,2,6,6-tetramethylpiperidine,

14) 1 -(2-Hydroxy-2-methylpropoxy)-4-octadecanoyloxy-2,2,6,6-tetramethylpiperidine,

15) bis(1 -(2-Hydroxy-2-methylpropoxy)-2,2,6,6-tetramethylpiperidin-4-yl) sebacate, 16) bis(1-(2-Hydroxy-2-methylpropoxy)-2,2,6,6-tetramethylpiperidin-4-yl) adipate,

17) 2,4-bis{N-[1 -(2-Hydroxy-2-methylpropoxy)-2,2,6,6-tetramethylpiperidin-4-yl]-N-butyl- amino}-6-(2-hydroxyethylamino)-s-triazine,

18) 4-Benzoyl-2,2,6,6-tetramethylpiperidine,

19) Di-(1 ,2,2,6,6-pentamethylpiperidin-4-yl) p-methoxybenzylidenemalonate, 20) 4-Stearyloxy-2,2,6,6-tetramethylpiperidine,

21 ) bis(1-Octyloxy-2,2,6,6-tetramethylpiperidyl) succinate,

22) 1 ,2,2,6,6-Pentamethyl-4-aminopiperidine,

23) 2-Undecyl-7,7,9,9-tetramethyl-1-oxa-3,8-diaza-4-oxo-spiro[4,5]decane,

24) tris(2,2,6,6-Tetramethyl-4-piperidyl) nitrilotriacetate, 25) tris(2-Hydroxy-3-(amino-(2,2,6,6-tetramethylpiperidin-4-yl)propyl) nitrilotriacetate,

26) tetrakis(2,2,6,6-Tetramethyl-4-piperidyl)-1 ,2,3,4-butane-tetracarboxylate,

27) tetrakis(1 ,2,2,6,6-Pentamethyl-4-piperidyl)-1 ,2,3,4-butane-tetracarboxylate,

28) 1 ,1 '-(1 ,2-Ethanediyl)-bis(3,3,5,5-tetramethylpiperazinone), 29) 3-n-Octyl-7,7,9,9-tetramethyl-1 ,3,8-triazaspiro[4.5]decan-2,4-dione,

30) δ-Acetyl-S-dodecyl-yj^θ-tetramethyl-I Aδ-triazaspiroμ.δldecane^-dione,

31 ) 3-Dodecyl-1-(2,2,6,6-tetramethyl-4-piperidyl)pyrrolidin-2,5-dione,

32) 3-Dodecyl-1 -(1 ,2,2,6,6-pentamethyl-4-piperidyl)pyrrolidine-2,5-dione, 33) N,N'-bis-Formyl-N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)hexamethylenediamine,

34) The reaction product of 2,4-bis[(1-cyclohexyloxy-2,2,6,6-piperidin-4-yl)butylamino]-6- chloro-s-triazine with N,N'-bis(3-aminopropyl)ethylenediamine),

35) The condensate of 1-(2-hydroxyethyl)-2,2,6,6-tetramethyl-4-hydroxypiperidine and succinic acid, 36) Linear or cyclic condensates of N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)-hexamethyl- enediamine and 4-tert-octylamino-2,6-dichloro-1 ,3,5-triazine,

37) Linear or cyclic condensates of N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)-hexamethyl- enediamine and 4-cyclohexylamino-2,6-dichloro-1 ,3,5-triazine,

38) Linear or cyclic condensates of N,N'-bis-(2,2,6,6-tetramethyl-4-piperidyl)hexamethyl- enediamine and 4-morpholino-2,6-dichloro-1 ,3,5-triazine,

39) Linear or cyclic condensates of N,N'-bis-(1 ,2,2,6,6-pentamethyl-4-piperidyl)hexamethyl- enediamine and 4-morpholino-2,6-dichloro-1 ,3,5-triazine,

40) The condensate of 2-chloro-4,6-bis(4-n-butylamino-2,2,6,6-tetramethylpiperidyl)-1 ,3,5- triazine and 1 ,2-bis(3-aminopropylamino)ethane, 41 ) The condensate of 2-chloro-4,6-di-(4-n-butylamino-1 ,2,2,6, 6-pentamethylpiperidyl)- 1 ,3,5-triazine and 1 ,2-bis-(3-aminopropylamino)ethane,

42) The reaction product of /J^Θ-tetramethyl^-cycloundecyl-i-oxa-S.δ-diaza^-oxospiro [4,5]decane and epichlorohydrin,

43) Poly[methyl,(3-oxy-(2,2,6,6-tetramethylpiperidin-4-yl)propyl)] siloxane, CAS Reg. No.182635-99-0,

44) The reaction product of maleic acid anhydride-Ci₈-C₂₂-α-olefin-copolymer with 2,2,6,6- tetramethyl-4-aminopiperidine,

45) The oligomeric compound which is the condensation product of 4,4'-hexamethylene- bis(amino-2,2,6,6-tetramethylpiperidine) and 2,4-dichloro-6-[(2,2,6,6-tetramethyl- piperidin-4-yl)butylamino]-s-triazine end-capped with 2-chloro-4,6-bis(dibutylamino)-s- triazine, 46) The oligomeric compound which is the condensation product of 4,4'-hexamethylene- bis(amino-1 ,2,2,6,6-pentamethylpiperidine) and 2,4-dichloro-6-[(1 ,2,2,6,6-pentamethyl- piperidin-4-yl)butylamino]-s-triazine end-capped with 2-chloro-4,6-bis(dibutylamino)-s- triazine, 47) The oligomeric compound which is the condensation product of 4,4'-hexamethylene- bis(amino-1 -propoxy-2,2,6,6-tetramethylpiperidine) and 2,4-dichloro-6-[(1 -propoxy- 2,2,6,6-tetramethylpiperidin-4-yl)butylamino]-s-triazine end-capped with 2-chloro-4,6- bis(dibutylamino)-s-triazine,

48) The oligomeric compound which is the condensation product of 4,4'-hexamethylene- bis(amino-1-acyloxy-2,2,6,6-tetramethylpiperidine) and 2,4-dichloro-6-[(1-acyloxy-

2,2,6,6-tetramethylpiperidin-4-yl)butylamino]-s-triazine end-capped with 2-chloro-4,6- bis(dibutylamino)-s-triazine and

49) The product obtained by reacting a product, obtained by reacting 1 ,2-bis(3-aminopro- pylamino)ethane with cyanuric chloride, with (2,2,6,6-tetramethylpiperidin-4-yl)butyl- amine.

Also included are the sterically hindered N-H, N-methyl, N-methoxy, N-propoxy, N-octyloxy, N-cyclohexyloxy, N-acyloxy and N-(2-hydroxy-2-methylpropoxy) analogues of any of the above mentioned compounds. For example, replacing an N-H hindered amine with an N- methyl hindered amine would be employing the N-methyl analogue in place of the N-H. The benzofuranone and sterically hindered amine stabilizers are employed at the same concentration levels as components i) and ii).

The loss in stability of biodiesel may be observed by gum formation.

A particularly preferred embodiment of the invention relates to a composition, which comprises At least one sterically hindered phenolic antioxidant selected from the group consisting of 2,6-di-tert-butylphenol, 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid methyl ester and tetrakis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionyloxymethyl)methane;

At least one triazole metal deactivator selected from the group consisting of 1-(di-isooc- tylaminomethyl)-1 ,2,4-triazole, 1 -(di-(2-ethylhexyl)aminomethyl)1 ,2,4-triazole, 1 -(2-meth- oxyprop-2-yl)tolyltriazole, 1-(1-cyclohexyloxypropyl)tolyltriazole, 1-(1-cyclohexyloxyhep- tyl)tolyltriazole and 1-(1-cyclohexyloxybutyl)tolyltriazole.

The following Examples illustrate the invention. Unless otherwise indicated, parts and percentages are by weight. Examples

Material and Methods

Rancimat Tests

The Rancimat test, developed by the food industry, is employed to test the oxidative stability of soy biodiesel (methyl ester of soy fatty acid). A 3.0 g sample of soy biodiesel is held at 1 11.7⁰C and exposed to a bubbling stream of air (10 I per hour). The sample vessel is vented to a secondary container, where the off-gases are bubbled through 50 ml of distilled water. The test measures the volatile oxidation decomposition products such as peroxides, alcohols, aldehydes and carboxylic acids. The volatile decomposition products (chiefly formic acid) are swept through the sample vessel and vented into the secondary container where they are trapped by the distilled water. The conductivity of the water is constantly monitored as a function of time through use of an electrode. The inflection point (not a specific value) of the conductivity curve is the measured induction time. It should be pointed out that some samples will be highly conductive before the inflection point is achieved, while others will only be slightly conductive. An increase of the induction time indicates an increase in oxidative stability. Results are in the tables below. Levels of additive are in wt.-% based on the weight of the biodiesel.

The stabilizer combination of components i) and ii) provide for outstanding performance for the Rancimat test. A 6 hour induction time is necessary to meet the EN 14214 specification. Additive Components used in test series P: butylated hydroxytoluene (BHT) Q: 2,6-di-tert-butylphenol R: Vitamin E S: Mixture of 4-(and 5)-methyl-1-(di(2-ethylhexyl)-aminomethyl)-benzotriazole T: 41 wt.-% tetrakis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionyloxymethyl)methane, 29 wt.-% 2,6-di-tert-butylphenol, 30 wt.-% methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)- propionate

U: 1-(di-(2-ethylhexyl)aminomethyl)1 ,2,4-triazole Additive mixtures of the invention: A: 90% Additive T, 10% Additive S B: 90% Additive P, 10% Additive S C: 90% Additive Q, 10% Additive S D: 90% Additive R, 10% Additive S E: 89% Additive T, 1 1 % Additive S F: 89% Additive T, 1 1% Additive U G: 86% Additive T, 14% Additive S H: 86% Additive T, 14% Additive U Results Example 1

Table 1 Rancimat Induction Time

Example 2

The above test are repeated where the biodiesel is spiked with 5 ppm of copper. The first control formulation contains no copper.

Table 2

Rancimat Induction Time

Example 3

Soy biodiesel is stored outdoors from August 3, 2006 until October 13, 2006. The Rancimat induction times are monitored as a function of time (weeks) and additive level. The containers are closed and opened once per week for sampling. The following results are observed.

Table 3

Rancimat Induction Times

Example 4

The tests are repeated with other fatty acid methyl esters, rapeseed oil methyl ester, recycled cooking oil methyl ester and jatropha oil methyl ester. The following induction time results are found. Table 4

Rancimat Induction Times

Example 5

Further rancimat induction time tests in soy biodiesel are performed.

Table 5

Rancimat Induction Times

Example 6

The tests of Example 5 are repeated with soy biodiesel spiked with 0.25 ppm Fe naphthen- ate and with 0.01 ppm Cu naphthenate. Table 6

Rancimat Induction Times

Example 7

Tests are performed on a blend B20, 20% soy biodiesel and 80% petroleum diesel and on B20 spiked with 1 ppm Cu naphthenate.

Table 7

Rancimat Induction Times

Example 8

Tests are performed in soy bioediesel spiked with different levels of Cu acetate.

Table 8

Rancimat Induction Times [hours]

Example 9

Experiments are performed with soy biodiesel contaminated with mixed metals. The mixed metal spike is 0.00006 ppm Cu naphthenate and 0.0032 ppm Fe naphthenate.

Table 9

Rancimat Induction Times

Claims

Claims:

1. A biodiesel fuel composition stabilized against the deleterious effects of heat, light, oxygen and metals, which composition comprises

A biodiesel fuel and An effective stabilizing amount of a combination of i) At least one compound selected from the group consisting of the sterically hindered phenolic antioxidants and ii) At least one compound selected from the group consisting of the triazole metal deactivators. 2. A composition according to claim 1 comprising one or more sterically hindered phenolic antioxidants selected from the group consisting of 2,6-di-tert-butylphenol, 2,6-di-tert- butyl-4-methylphenol (BHT), 2,

2'-methylene bis-(4,6-di-tert-butylphenol), 1 ,6-hexame- thylene-bis-(3,5-di-tert-butyl-4-hydroxyhydrocinnamate), ((3,5-bis(1 ,1-dimethylethyl)-4- hydroxphenyl)methylthio)acetic acid Ci₀-Ci₄isoalkyl esters, 3,5-di-tert-butyl-4-hydroxy- hydrocinnamic acid C₆-C₉alkyl esters, 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid methyl ester, tetrakis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionyloxymethyl)me- thane, thiodiethylene bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate), octadecyl 3,5-di- tert-butyl-4-hydroxyhydrocinnamate and 2,5-di-tert-butylhydroquinone.

3. A composition according to claim 1 comprising one or more sterically hindered phenolic antioxidants selected from the group consisting of 2,6-di-tert-butylphenol, 3,5-di-tert- butyl-4-hydroxyhydrocinnamic acid methyl ester and tetrakis-(3-(3,5-di-tert-butyl-4-hy- droxyphenyl)-propionyloxymethyl)methane.

4. A composition according to claim 1 comprising one or more triazole metal deactivators selected from the group consisting of compounds of the formula

wherein

Ri and R₂ are the same or different and are hydrogen, CrC₂oalkyl, C₃-C₂oalkenyl, C₅-Ci₂cycloalkyl, C₇-Ci₃aralkyl, C₆-Ci₀aryl or hydroxy or R₁ and R₂, together with the nitrogen atom to which they are each attached may form a 5-, 6- or 7-membered het- erocylic ring, or R₁ and R₂ are a group of formula

R₃XK-R₄-PU-R₄)-, wherein

X represents O, S or NR₃,

R₃ represents hydrogen or CrC₂₀alkyl,

R₄ represents CrC₁₂alkylene, n represents 0 or an integer from 1 to 6, Or one of R₁ and R₂ represents a group of formula

or R₂ represents a group of formula (II) and R₁ represents a group of the partial formula

-[R₄]_n-N(R₅)-A-[N(R₅)₂ ]_m, wherein m represents 0 or 1 and, when m represents zero, A represents a group of formula (II) and, when m represents 1 , A represents alkylene or C₆-C₁₀ arylene and R₅ represents a group of formula (II).

5. A composition according to claim 4 comprising 1-(di-isooctylaminomethyl)-1 ,2,4-triazole or 1-(di-(2-ethylhexyl)aminomethyl)1 ,2,4-triazole.

6. A composition according to claim 1 comprising one or more triazole metal deactivators selected from the group consisting of compounds of the formula

wherein

R₆ represents d-C^alkyl,

R₇ represents d-C^alkyl, d-C^alkyl interrupted by one or more O atoms or represents C₅-Ci₂cycloalkyl and Rs and Rg are hydrogen or methyl.

7. A composition according to claim 6 comprising 1-(2-methoxyprop-2-yl)tolyltriazole, 1- (i-cyclohexyloxypropyl)tolyltriazole, 1-(1-cyclohexyloxyheptyl)tolyltriazole or 1-(1- cyclohexyloxybutyl)tolyltriazole.

8. A composition according to claim 1 comprising At least one sterically hindered phenolic antioxidant selected from the group consisting of 2,6-di-tert-butylphenol, 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid methyl ester and tetrakis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionyloxymethyl)methane and

At least one triazole metal deactivator selected from the group consisting of 1 -(di-iso- octylaminomethyl)-1 ,2,4-triazole, 1 -(di-(2-ethylhexyl)aminomethyl)1 ,2,4-triazole, 1 -(2- methoxyprop-2-yl)tolyltriazole, 1-(1-cyclohexyloxypropyl)tolyltriazole, 1-(1-cyclohexy- loxyheptyl)tolyltriazole and 1 -(1 -cyclohexyloxybutyl)tolyltriazole.

9. A composition according to claim 1 further comprising one or more stabilizers selected from the group consisting of the 3-arylbenzofuranone stabilizers and the sterically hindered amine light stabilizers.

10. A process for the stabilization of a biodiesel fuel against the deleterious effects of heat, light, oxygen and metals, which process comprises incorporating into a biodiesel fuel an effective stabilizing amount of a combination of i) At least one compound selected from the group consisting of the sterically hindered phenolic antioxidants and ii) At least one compound selected from the group consisting of the triazole metal deactivators.