FUEL OIL COMPOSITIONS AND ADDITIVES THEREFOR

The present invention relates to fuel additives. In particular the invention relates to additives for biofuels or fuels containing biofuels, especially biodiesel or fuels containing biodiesel; and biofuels suitable for use in fuel oil compositions, for example heating oil or heavy fuel oil.

The biofuel compositions of the present invention are suitable for use in diesel engines, for automotive or non- automotive use, or as fuel oils for example heating oils or heavy fuel oils. Often middle distillate fuel oils having the same composition can be used in diesel engines or as heating oils and thus the fuel compositions described herein as biofuel or biodiesel compositions may also be suitable for use as fuel oils, for example heating oils or heavy fuel oils.

Biodiesel is an alternative to mineral diesel fuel (or petrodiesel) and contains esters of, for example, vegetable oils, animal fats and used cooking fats. Biodiesel is obtained by transesterification of oils, for example rapeseed oil, soybean oil, safflower oil, palm oil, corn oil, peanut oil, cotton seed oil, tallow, coconut oil, physic nut oil (Jatropha) , sunflower seed oil, used cooking oils or any mixture thereof , with an alcohol, usually a monoalcohol, in the presence of a catalyst. For environmental reasons the importance of biodiesel as an alternative for diesel fuel increases each year. The present invention relates to fuels consisting essentially of biodiesel and also to blended fuel

compositions comprising, for example, mineral diesel fuel from crude oil and biodiesel.

The present invention also relates to fuel compositions comprising biodiesel and a fuel selected from heavy fuel oil, gasoline, aviation fuel, marine fuel, bunker fuel and heating oil; middle distillate oil and heavy fuel oil; and GTL (gas-to-liquid) , CTL (coal-to-liquid) , BTL (biomass- to-liquid) and OTL (oil sands-to-liquid) .

The chemistry of middle distillate fuel stability and instability is complex. Naphthenic acids, heterocyclic compounds containing sulphur and nitrogen and naphthenoaromatic compounds can be found in distillate fuel components. Degradation through condensation type reactions can be common. Middle distillate fuel may also contain olefinic species which may react with atmospheric oxygen to produce hydroperoxides. These can react further and take part in the condensation reactions to produce high molecular weight deposit forming compounds. Whilst antioxidant compounds, effective at preventing free radical oxidative degradation of fuel, such as the traditional hindered phenol and phenylenediamine antioxidants are well known, these additives are often insufficient to provide the desired stability performance of middle distillate fuel.

Middle distillate fuel stabilisers are often mixtures of various additives having different functions. These stabilisers may or may not contain an antioxidant and may often include a dispersant. The purpose of the dispersant is to prevent the formation of insoluble gums and sediments, to prevent their deposition on metal surfaces

and in some cases to solubilise or disperse any existing deposits .

The terms dispersant and detergent are sometimes used to refer to different characteristics or chemistries of an additive but throughout this specification the terms are used interchangeably.

The stability of diesel fuel is typically measured by looking at the gum forming tendency, the sediment forming tendency and the colour of a fuel. The addition of a dispersant reduces the gum and sediment forming tendency.

Typical additive packages for mineral diesel fuels are described in GB2156848.

There are a number of standard tests available for assessing the stability of diesel fuel, including the following ASTM methods.

In the method of ASTM D4625, four 100ml samples of filtered fuel are aged for 0, 4, 8, 12, 18 and 24 weeks at 43°C. After aging for a selected time, the sample is cooled to room temperature and then analysed for filterable and adherent insoluble materials.

In the method of ASTM D6488, two 50ml samples of filtered fuel are aged for 90 or 180 mins at 150 ⁰ C in open tubes with exposure to air. After aging and cooling the samples are filtered and an estimate of the sediment is made by measuring the reflectance of the filter pad.

In the method of ASTM D2274, a 350ml sample of filtered fuel is aged at 95°C for 16h while oxygen is bubbled

through the sample at a rate of 3L/h. After aging, the sample is cooled to room temperature and filtered to give filterable insolubles. Adherent insolubles are removed by rinsing the glassware with solvent, evaporating the solvent and weighing the residue. The sum of filterable and adherent insolubles is the total insolubles, expressed in mg/100ml .

In each of these three ASTM tests, the addition of a dispersant can have a positive effect due to its ability to prevent the formation of insoluble gums and sediments.

Oxidation stability can be measured by a number of different methods. For biofuels a frequently used method is the Rancimat test. The Rancimat test is an accelerated oxidation test in which a sample is heated with air bubbling through. Volatile breakdown products pass over into deionised water and the conductivity of the water is measured. The time taken for fuel to breakdown is measured by recording the time at which an increase in conductivity is observed. As the Rancimat measures conductivity of acids produced during decomposition typical dispersants would not be expected to produce a positive result in the Rancimat test.

In recent years, diesel fuels have been hydrotreated to remove sulphur compounds. This has led to a decrease in the lubricity of diesel fuels and thus lubricity additives are now added. It is also thought that the sulphur containing compounds and/or other materials removed by hydrotreatment may have antioxidant properties. Peroxide formation is sometimes observed in hydrotreated fuels. If necessary antioxidant compounds may be added. These

compounds are typically hindered phenol compounds or phenylenediamine compounds as are described in "Ondeo/Nalco Fuel Field Manual" by Kim B Peyton, McGraw- Hill Publishing Co., 2 Rev Ed (1 Dec 2001).

More recently for environmental reasons fuels comprising biodiesel have become increasingly used.

Biodiesel has a high content of unsaturated fatty acid esters which can be easily oxidized by atmospheric oxygen.

Products formed by oxidation can lead to corrosion and blockages in injection pumps and/or fuel lines. As a result, antioxidant compounds are added to biodiesel and fuels containing biodiesel. These compounds are typically phenylenediamines or especially hindered phenol compounds such as those described in US2006/0218855.

The addition of fuel additives increases the cost of a fuel and in a competitive marketplace it is desirable to minimise concentrations of additives, and to limit the number and type of additives which are added to a fuel.

It is an object of the present invention to provide additised fuel compositions comprising biodiesel which have improved properties.

According to a first aspect of the present invention there is provided the use of a nitrogen-containing dispersant as an antioxidant additive in a fuel composition comprising biofuel.

Preferably the biofuel is biodiesel.

The fuel composition may be based on heavy fuel oil, diesel, gasoline, aviation fuel, bio fuel, marine fuel, bunker fuel and heating oil; middle distillate oil and heavy fuel oil; and GTL (gas-to-liquid), CTL (coal-to- liquid) , BTL (biomass-to-liquid, OTL (oil sands-to-liquid) or any mixture thereof. Preferably it is a diesel fuel composition .

Any suitable nitrogen-containing ashless detergent or dispersant known in the art for use in lubricant or fuel oil may be used.

Preferably the dispersant is selected from:

(i) the product of a carboxylic acid-derived acylating agent and an amino compound, the acylating agent being linked to said amino compound through an imido, amido, amidine, or acyloxy ammonium linkage and the product containing a substituent of at least 8 aliphatic carbon atoms;

(ii) hydrocarbyl-substituted amines wherein the hydrocarbyl substituent is substantially aliphatic and contains at least 8 carbon atoms;

(iii) nitrogen-containing condensates of a phenol, aldehyde and primary or secondary amine;

(iv) esters of a substituted carboxylic acid;

(v) polymeric dispersants;

(vi) hydrocarbon-substituted phenolic dispersants; and

(vii) fuel-soluble alkoxylated derivatives of an alcohol, phenol or amine.

Preferably the dispersant is selected from (i) , (ii) , (iϋ) or a mixture thereof. Most preferably the dispersant is selected from (i) , (iii) or a mixture thereof .

(i) Product of a carboxylic acid-derived acylating agent and amine

A number of acylated, nitrogen-containing compounds having a hydrocarbyl substituent of a least 8 carbon atoms and made by reacting a carboxylic acid acylating agent with an amino compound are known to those skilled in the art. In such compositions the acylating agent is linked to the amino compound through an imido, amido, amidine or acyloxy ammonium linkage. The hydrocarbyl substituent of at least 8 carbon atoms may be in either the carboxylic acid acylating agent derived portion of the molecule or in the amino compound derived portion of the molecule, or both. Preferably, however, it is in the acylating agent portion. The acylating agent can vary from formic acid and its acylating derivatives to acylating agents having high molecular weight aliphatic substituents of up to 5,000, 10,000 or 20,000 carbon atoms. The amino compounds can vary from ammonia itself to amines having aliphatic substituents of up to about 30 carbon atoms.

A typical class of acylated amino compounds suitable for use in the present invention are those formed by the reaction of an acylating agent having a hydrocarbyl substituent of at least 8 carbon atoms and a compound

comprising at least one primary or secondary amine group.

The acylating agent may be a mono- or polycarboxylic acid

(or reactive equivalent thereof) for example a substituted succinic, phthalic or propionic acid and the amino compound may be a polyamine or a mixture of polyamines, for example a mixture of ethylene polyamines.

Alternatively the amine may be a hydroxyalkyl-substituted polyamine. The hydrocarbyl substituent in such acylating agents preferably comprises at least 10, more preferably at least 12, for example 30 or 50 carbon atoms. It may comprise up to about 200 carbon atoms. Preferably the hydrocarbyl substituent of the acylating agent has a number average molecular weight (Mn) of between 170 to 2800, for example from 250 to 1500, preferably from 500 to 1500 and more preferably 500 to 1100. An Mn of 700 to 1300 is especially preferred.

Illustrative of hydrocarbyl substituent based groups containing at least eight carbon atoms are n-octyl, n- decyl, n-dodecyl, tetrapropenyl, n-octadecyl, oleyl, chloroctadecyl, triicontanyl, etc. The hydrocarbyl based substituents may be made from homo- or interpolymers (e.g. copolymers, terpolymers) of mono- and di-olefins having 2 to 10 carbon atoms, for example ethylene, propylene, butane-1, isobutene, butadiene, isoprene, 1-hexene, 1- octene, etc. Preferably these olefins are 1-monoolefins . The hydrocarbyl substituent may also be derived from the halogenated (e.g. chlorinated or brominated) analogs of such homo- or interpolymers. Alternatively the substituent may be made from other sources, for example monomeric high molecular weight alkenes (e.g. 1-tetra- contene) and chlorinated analogs and hydrochlorinated analogs thereof, aliphatic petroleum fractions, for

example paraffin waxes and cracked and chlorinated analogs and hydrochlorinated analogs thereof, white oils, synthetic alkenes for example produced by the Ziegler- Natta process (e.g. poly (ethylene) greases) and other sources known to those skilled in the art. Any unsaturation in the substituent may if desired be reduced or eliminated by hydrogenation according to procedures known in the art.

The term "hydrocarbyl" as used herein denotes a group having a carbon atom directly attached to the remainder of the molecule and having a predominantly aliphatic hydrocarbon character. Suitable hydrocarbyl based groups may contain non-hydrocarbon moieties. For example they may contain up to one non-hydrocarbyl group for every ten carbon atoms provided this non-hydrocarbyl group does not significantly alter the predominantly hydrocarbon character of the group. Those skilled in the art will be aware of such groups, which include for example hydroxyl, halo (especially chloro and fluoro) , alkoxyl, alkyl mercapto, alkyl sulfoxy, etc. Preferred hydrocarbyl based substituents are purely aliphatic hydrocarbon in character and do not contain such groups .

The hydrocarbyl-based substituents are preferably predominantly saturated, that is, they contain no more than one carbon-to-carbon unsaturated bond for every ten carbon-to-carbon single bonds present. Most preferably they contain no more than one carbon-to-carbon non- aromatic unsaturated bond for every 50 carbon-to-carbon bonds present.

Preferred hydrocarbyl-based substituents are poly- (isobutene)s known in the art.

Particularly preferred hydrocarbyl-substituted succinic acid derivatives include polyisobutene succinic acid derivatives having a PIB molecular weight of from 500 to 1500, preferably from 500 to 1100 or 700 to 1300 and most preferably from 700 to 1100.

Amino compounds useful for reaction with these acylating agents include the following:

(1) polyalkylene polyamines of the general formula:

(R ³ ) ₂ N[U-N(R ³ )] _n R ³

wherein each R ³ is independently selected from a hydrogen atom, a hydrocarbyl group or a hydroxy-substituted hydrocarbyl group containing up to about 30 carbon atoms, with proviso that at least one R ³ is a hydrogen atom, n is a whole number from 1 to 10 and U is a Cl-18 alkylene group. Preferably each R ³ is independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, butyl and isomers thereof. Most preferably each R ³ is ethyl or hydrogen. U is preferably a Cl-4 alkylene group, most preferably ethylene.

(2) heterocyclic-substituted polyamines including hydroxyalkyl-substituted polyamines wherein the polyamines are as described above and the heterocyclic substituent is selected from nitrogen-containing aliphatic and aromatic heterocycles, for example piperazines, imidazolines, pyrimidines, morpholines, etc.

(3) aromatic polyamines of the general formula:

Ar(NR ³ ₂ ) _y

wherein Ar is an aromatic nucleus of 6 to 20 carbon atoms, each R ³ is as defined above and y is from 2 to 8.

Specific examples of polyalkylene polyamines (1) include ethylene diamine, tetra (ethylene) pentamine, tri-

(trimethylene) tetramine, pentaethylenehexamine, hexaethyleneheptamine, 1, 2-propylene diamine, and other commercially available materials which comprise complex mixtures of polyamines. For example, higher ethylene polyamines optionally containing all or some of the above in addition to higher boiling fractions containing 8 or more nitrogen atoms etc. Specific examples of hydroxyalkyl-substituted polyamines include N- (2- hydroxyethyl) ethylene diamine, N, N' -bis (2-hydroxyethyl) ethylene diamine, N- (3-hydroxybutyl) tetramethylene diamine, etc. Specific examples of the heterocyclic- substituted polyamines (2) are N-2-aminoethyl piperazine, N-2 and N-3 amino propyl morpholine, N-3 (dimethyl amino) propyl piperazine, 2-heptyl-3- (2-aminopropyl) imidazoline, 1,4-bis (2-aminoethyl) piperazine, 1- (2-hydroxy ethyl) piperazine, and 2-heptadecyl-l- (2-hydroxyethyl) - imidazoline, etc. Specific examples of the aromatic polyamines (3) are the various isomeric phenylene diamines, the various isomeric naphthalene diamines, etc.

Preferably the polyamine is selected from ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, dimethylaminopropylamine, aminoethylethanolamine, and mixtures thereof.

Many patents have described useful acylated nitrogen compounds including U.S. Pat. Nos. 3,172,892; 3,219,666; 3,272,746; 3,310,492; 3,341,542; 3,444,170; 3,455,831; 3,455,832; 3,576,743; 3,630,904; 3,632,511; 3,804,763, 4,234,435 and US6821307.

A typical acylated nitrogen-containing compound of this class is that made by reacting a poly (isobutene) - substituted succinic acid-derived acylating agent (e.g., anhydride, acid, ester, etc.) wherein the poly (isobutene) substituent has between about 12 to about 200 carbon atoms with a mixture of ethylene polyamines having 3 to about 9 amino nitrogen atoms per ethylene polyamine and about 1 to about 8 ethylene groups. These acylated nitrogen compounds are formed by the reaction of a molar ratio of acylating agent : amino compound of from 10:1 to 1:10, preferably from 5:1 to 1:5, more preferably from 2:1 to 1:2 and most preferably from 2:1 to 1:1. This type of acylated amino compound and the preparation thereof is well known to those skilled in the art and are described in the above- referenced US patents.

Another type of acylated nitrogen compound belonging to this class is that made by reacting the afore-described alkylene amines with the afore-described substituted succinic acids or anhydrides and aliphatic mono-carboxylic acids having from 2 to about 22 carbon atoms. In these types of acylated nitrogen compounds, the mole ratio of succinic acid to mono-carboxylic acid ranges from about 1:0.1 to about 1:1. Typical of the monocarboxlyic acid are formic acid, acetic acid, dodecanoic acid, butanoic acid, oleic acid, stearic acid, the commercial mixture of stearic acid isomers known as isostearic acid, tolyl acid,

etc. Such materials are more fully described in U.S. Pat. Nos. 3,216,936 and 3,250,715.

A further type of acylated nitrogen compound suitable for use in the present invention is the product of the reaction of a fatty monocarboxylic acid of about 12-30 carbon atoms and the afore-described alkylene amines, typically, ethylene, propylene or trimethylene polyamines containing 2 to 8 amino groups and mixtures thereof. The fatty mono-carboxylic acids are generally mixtures of straight and branched chain fatty carboxylic acids containing 12-30 carbon atoms. Fatty dicarboxylic acids could also be used. A widely used type of acylated nitrogen compound is made by reacting the afore-described alkylene polyamines with a mixture of fatty acids having from 5 to about 30 mole percent straight chain acid and about 70 to about 95 percent mole branched chain fatty acids. Among the commercially available mixtures are those known widely in the trade as isostearic acid. These mixtures are produced as a by-product from the dimerization of unsaturated fatty acids as described in U.S. Pat. Nos. 2,812,342 and 3,260,671.

The branched chain fatty acids can also include those in which the branch may not be alkyl in nature, for example phenyl and cyclohexyl stearic acid and the chloro-stearic acids. Branched chain fatty carboxylic acid/alkylene polyamine products have been described extensively in the art. See for example, U.S. Pat. Nos. 3,110,673; 3,251,853; 3,326,801; 3,337,459; 3,405,064; 3,429,674; 3,468,639; 3,857,791. These patents are referenced for their disclosure of fatty acid/polyamine condensates for their use in lubricating oil formulations.

(ii) Hydrocarbyl-Substituted Amines

Hydrocarbyl-substituted amines suitable for use in the fuel compositions of the present invention are well known to those skilled in the art and are described in a number of patents. Among these are U.S. Pat. Nos. 3,275,554;

3,438,757; 3,454,555; 3,565,804; 3,755,433 and 3,822,209.

These patents describe suitable hydrocarbyl amines for use in the present invention including their method of preparation.

(iii) Nitrogen-Containing Condensates of Phenols, Aldehydes, and Amino Compounds

Phenol/aldehyde/amine condensates useful as dispersants in the fuel compositions of the present invention include those generically referred to as Mannich condensates. Such compounds can be made by reacting simultaneously or sequentially at least one active hydrogen compound for example a hydrocarbon-substituted phenol (e.g., an alkyl phenol wherein the alkyl group has at least an average of about 8 to 200; preferably at least 12 up to about 200 carbon atoms) , having at least one hydrogen atom bonded to an aromatic carbon, with at least one aldehyde or aldehyde-producing material (typically formaldehyde or a precursor thereof) and at least one amino or polyamino compound having at least one NH group. The amino compounds include primary or secondary monoamines having hydrocarbon substituents of 1 to 30 carbon atoms or hydroxyl- substituted hydrocarbon substituents of 1 to about 30 carbon atoms. Another type of typical amino compound are the polyamines described above in relation to acylated nitrogen-containing compounds.

One class of preferred nitrogen containing dispersant for use in the present invention are those formed by a Mannich reaction between: (a) an aldehyde; (b) a polyamine; and

(c) an optionally substituted phenol.

Any aldehyde may be used as aldehyde component (a) but preferred are aliphatic aldehydes. Preferably the aldehyde has 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms. Most preferably the aldehyde is formaldehyde.

Polyamine component (b) may be selected from any compound including two or more amine groups. Preferably the polyamine is a polyalkylene polyamine. Suitable polyalkylene polyamines are as previously defined herein.

Preferably the polyamine has 1 to 15 nitrogen atoms, preferably 1 to 10 nitrogen atoms, more preferably 3 to 8 nitrogen atoms.

Preferably the polyamine is selected from ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, and heptaethyleneoctamine . Most preferably it is tetraethylenepentamine or ethylene diamine .

Commercially available sources of polyamines typically contain mixtures of isomers and/or oligomers, and products prepared from these commercially available mixtures fall within the scope of the present invention.

Optionally substituted phenol component (c) may be substituted with 0 to 4 groups on the aromatic ring (in addition to the phenol OH) . For example it may be a tri- or di- substituted phenol. Most preferably component (c) is a mono-substituted phenol. Substitution may be at the ortho, and/or meta, and/or para position (s).

Preferably the phenol component (c) carries one or more optionally substituted alkyl substituents . Preferably the component (c) is a monoalkyl phenol, especially a para- substituted monoalkyl phenol.

In some preferred embodiments component (c) comprises an alkyl substituted phenol in which the phenol carries one or more alkyl chains having a total of less than 28 carbon atoms, preferably less than 24 carbon atoms, preferably less than 20 carbon atoms, more preferably less than 18 carbon atoms, preferably less than 16 carbon atoms and most preferably less than 14 carbon atoms.

For example component (c) may have from 4 to 20 carbons atoms, preferably 6 to 18, more preferably 8 to 16, especially 10 to 14 carbon atoms. In some particularly preferred embodiments, component (c) is a phenol having a C12 alkyl substituent.

In other preferred embodiments component (c) is substituted with a larger alkyl chain, for example those having in excess of 20 carbon atoms. Particularly preferred compounds are those in which the phenol is substituted with a hydrocarbyl residue made from homo or interpolymers

(e.g. copolymers, terpolymers) of mono- and di-olefins having 2 to 10 carbon atoms, for example ethylene,

propylene, butane-1, isobutene, butadiene, isoprene, 1- hexene, 1-octene, etc. Preferably these olefins are 1- monoolefins . The hydrocarbyl substituent may also be derived from the halogenated (e.g. chlorinated or brominated) analogs of such homo- or interpolymers . Alternatively the substituent may be made from other sources which are well known to those skilled in the art.

Especially preferred are phenols substituted with a polyisobutene residue of molecular weight of between 250 and 5000, for example between 500 and 1500, preferably between 650 and 1200, most preferably between 700 and 1000.

Suitable dispersants include the reaction product obtained by reacting components (a) , (b) and (c) in a ratio of from 5:1:5 to 0.1:1:0.1, more preferably from 3:1:3 to 0.5:1:0.5.

Components (a) and (b) are preferably reacted in a ratio of from 4:1 to 1:1 (aldehyde :polyamine) , preferably from 2:1 to 1:1. Components (a) and (c) are preferably reacted in a ratio of from 4:1 to 1:1 (aldehyde :phenol) , more preferably from 2:1 to 1:1.

Especially preferred dispersants are those formed by reacting components (a), (b) and (c) in a ratio of 1:1:1 or 2:1:2. Mixtures of these compounds may also be used. Typically component (b) comprises a mixture of isomers and/or oligomers. Component (c) may also comprise a mixture of isomers and/or homologues.

The present invention covers the use of a nitrogen- containing dispersant as an antioxidant additive in any fuel containing biodiesel. This may be a fuel which consists essentially of biodiesel. Alternatively it may be a fuel which comprises mineral diesel fuel (extracted from crude oil) blended with an amount of biodiesel. For example the fuel composition of the present invention may contain up to 1 wt% of biodiesel, for example up to 2 wt%, up to 3 wt%, up to 4 wt%, up to 5 wt%, up to 10 wt%, up to 15 wt%, up to 20 wt%. The fuel composition may contain up to 25 wt%, up to 30 wt%, up to 40 wt%, up to 50 wt%, up to 60 wt%, up to 70 wt%, up to 75 wt%, up to 80 wt%, up to 85 wt%, up to 90 wt%, up to 95 wt%, or up to 99 wt% biodiesel .

In one preferred embodiment the fuel composition comprises from 1 to 30 wt% biodiesel.

A fuel which comprises 100% biodiesel is denoted as BlOO, a fuel which comprises 90% mineral diesel and 10% biodiesel is known as BlO; fuel comprising 50% mineral diesel and 50% biodiesel is know as B50; and so on.

In some embodiments fuel compositions of the present invention are prepared by adding the nitrogen-containing dispersant to pure BlOO biodiesel and then blending the mixture with mineral diesel in the appropriate ratio.

Suitably the nitrogen-containing dispersant additive is added to the fuel in an amount of at least 5 ppm, preferably at least 10 ppm, more preferably at least 15 ppm and most preferably at least 20 ppm. Suitably the nitrogen-containing dispersant / antioxidant additive is

added to the fuel composition in an amount of up to 20,000 ppm, preferably up to 10,000 ppm, more preferably up to 5,000 ppm, preferably up to 1,000 ppm and most preferably up to 500 ppm.

Preferably the nitrogen-containing dispersant is present in the fuel composition in an amount of from 10 ppm to 5000 ppm (by weight) of the amount of biodiesel present in the composition, preferably from 50 ppm to 3000 ppm, more preferably from 100 ppm to 2000 ppm and most preferably from 200 ppm to 1000 ppm.

The oxidation stability of a biofuel may be measured by the Rancimat method. The Rancimat test is an accelerated oxidation test carried out at elevated temperatures in which a fuel sample is exposed to air.

Figure 1 shows a schematic measuring arrangement used in a typical Rancimat test method. In the Rancimat method, a sample of biofuel 4 is held in a sealed reaction tube 1 at a constant temperature selected from a range of between 50 and 220 ⁰ C controlled by heating block 3 while a continuous flow of air is passed through the sample via inlet tube 2. Fatty acid methyl esters in the sample are oxidized to peroxides as primary oxidation products. After some time, the fatty acids completely decompose into secondary oxidation products. In addition to volatile organic compounds, these include low-molecular weight organic acids, mainly formic and acetic acids. An air flow transports them via outlet tube 5 to a measuring vessel 6 containing distilled water as an absorption solution 7. The conductivity of this water is recorded continuously using conductivity measuring cell 8. As soon as volatile

carboxylic acids are formed in the sample an increase in conductivity in the measuring vessel is observed. The time that elapses until the secondary oxidation products are detected is known as the induction time and the time taken until a predetermined increase in conductivity is observed is known as the stability time. These measures provide a good characteristic value for the oxidation stability.

In the European standard test method EN 14112 of the Rancimat test, the test sample is a fatty acid methyl ester, the test temperature is 110 ⁰ C and the measure of oxidation stability is the induction period.

In the European standard for Biodiesel quality EN 14214, the specified minimum induction period is 6 hours.

In tests carried out by the inventors of the present invention the stability time was measured. In this case the time taken to achieve an increase in conductivity of 200 μS/cm was recorded.

Preferably the use of a nitrogen-containing dispersant increases the oxidation stability as measured by the Rancimat test of a fuel composition containing biodiesel by at least 5%, preferably at least 10%, more preferably at least 15%.

Surprisingly it has been found that when a nitrogen- containing dispersant is used in conjunction with a known antioxidant additive in a fuel composition containing biodiesel, a large increase in the oxidation stability of the fuel is observed. It was found that the effect of the

two additives shows an unexpected improvement which may be synergistic. Oxidation stability of a fuel may, for example, be measured by the Rancimat test procedure.

According to a second aspect of the present invention, there is provided the use of a nitrogen-containing dispersant additive to improve the oxidation stability of a fuel composition containing biodiesel and an antioxidant additive .

Any known antioxidant additive may be used. Preferred antioxidants are phenolic antioxidants and phenylenediamine antioxidants. Also useful are naturally occurring antioxidants for example tocopherol (vitamin E and derivatives therefore); and nitroxide compounds, for example 2, 2, 6, 6-tetramethylpiperidine-l-oxyl (TEMPO), 4- hydroxy-TEMPO, 4-oxo-TEMPO etc.

By phenolic antioxidant additive we mean to include any compound which contains a phenol moiety i.e., a benzene ring which is substituted with a hydroxyl group. This may be a very simple compound, for example a benzene diol, alkyl substituted phenol or a benzene triol.

Alternatively the phenolic antioxidant may be part of a more complex molecule. It may include two phenol moieties, for example, see the compounds disclosed in US

2006/0219979.

Suitable phenolic antioxidant compounds for use in the present invention include those of formula II:

I I

wherein R ¹ is selected from an optionally substituted alkyl or alkenyl group, an aryl group, an ester, a carboxylic acid, an aldehyde, a ketone, an ether, an alcohol, an amine or an amide; R ² and R ³ are independently selected from hydrogen, an optionally substituted alkyl or alkenyl group, an aryl group, an ester group, a ketone, an aldehyde, a carboxylic acid, an ether, an alcohol, an amine or an amide; and n is an integer from 1 to 5.

Preferably R ¹ is an alkyl group, preferably having 1 to 9 carbon atoms, and may be straight chained or branched. Preferably R ¹ is selected from methyl, ethyl, isopropyl, and tertiarybutyl . R ¹ and R ² may together form a cyclic substituent, either alkyl or aryl. R ² and R ³ are preferably hydrogen or an alkyl group having 1 to 9 carbon atoms. Preferably R ² and R ³ are independently selected from hydrogen, methyl, ethyl, tertiarybutyl and isopropyl. Preferably n is 1, 2 or 3.

Preferred phenolic antioxidant compounds for use in the present invention are substituted benzene compounds having 1 or more hydroxy substituents . Examples include tertiarybutylhydroquinone (TBHQ or MTBHQ), 2,5-di- tertiarybutylhydroquinone (DTBHQ) , pyrogallol, pyrocatechol 2, 6-di- tert-butyl-4-methylphenol (BHT), propylgallate and tertiarybutylcatechol .

Preferred phenylenediamine antioxidants suitable for use in the present invention include those of formula III:

wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are independently selected from an optionally substituted alkyl or alkenyl group, an aryl group, an ester, a carboxylic acid, an aldehyde, a ketone, an ether, an alcohol, an amine or an amide. Preferably R ¹ is hydrogen. Preferably R ³ is hydrogen. Preferably R ² is an alkyl group, preferably having 1-10 carbon atoms. More Preferably R ² is an alkyl group having 1-5 carbon atoms. Preferably R ² is selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, secbutyl and tertiarybutyl . Most preferably R ² is isopropyl or secbutyl. Preferably R ⁴ is an alkyl group, preferably having 1-10 carbon atoms. More preferably R ⁴ is an alkyl group having 1-5 carbon atoms. R ⁴ is preferably selected from methyl, ethyl, propyl, isopropyl, secbutyl, butyl, tertiarybutyl and isobutyl. Most preferably R ⁴ is isopropyl or sec butyl.

R ⁵ , R ⁶ and R ⁷ are preferably selected from hydrogen or alkyl groups, more preferably from hydrogen and alkyl groups having 1-10 carbon atoms, more preferably from hydrogen and alkyl groups having 1-5 carbon atoms. Preferably R ⁵ , R ⁶ and R ⁷ are independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, butyl,

tertiarybutyl and isobutyl. Most preferably R ⁵ is hydrogen. Most preferably R ⁶ is hydrogen. Most preferably R ⁷ is hydrogen.

In a preferred embodiment however the antioxidant component of the present invention is a phenolic antioxidant compound especially a hindered phenolic antioxidant compound. By hindered phenolic antioxiodant, we refer to a phenol compound which is preferably ortho- substituted. It may also be para substituted.

In some embodiments in which the nitrogen containing dispersant is the reaction product of a carboxylic acid- derived acylating agent and an amino compound, the antioxidant additive does not comprise 2, 4-di-tert- butylhydroxytoluene or 2, 5-di-tert-butylhydroquinone .

Suitably the antioxidant additive is present in an amount of at least 1 ppm, more preferably at least 5 ppm, preferably at least 10 ppm, more preferably at least 15 ppm and most preferably at least 20 ppm (by weight) . The phenolic antioxidant may be present in the composition in an amount of up to 20,000 ppm, preferably up to 10,000 ppm, more preferably up to 5,000 ppm, preferably up to 1,000 ppm and most preferably up to 500 ppm.

Preferably the antioxidant additive is present in the fuel composition in an amount from 10 ppm to 5000 ppm (by weight) of the biodiesel present in the composition, preferably from 50 ppm to 1000 ppm, more preferably from 100 ppm to 500 ppm and most preferably from 150 ppm to 300 ppm.

Suitably the weight ratio of nitrogen-containing dispersant to phenolic antioxidant is from 20:1 to 1:20, suitably from 10:1 to 1:10, preferably from 5:1 to 1:5, more preferably from 3:1 to 1:3, for example from 2:1 to 1:2.

Preferably the use of a nitrogen-containing dispersant increases the oxidation stability as measured by the Rancimat test of a fuel composition containing biodiesel and an antioxidant additive by at least 5%, preferably at least 10%, more preferably at least 15%.

The present invention provides a fuel composition comprising biodiesel, optionally an antioxidant additive and an amount of a nitrogen-containing dispersant sufficient to improve the oxidation stability of the composition compared to a composition which does not contain said nitrogen-containing dispersant. Suitably the oxidation stability is improved by at least 10%, preferably by at least 20%, more preferably by at least 30%, most preferably by at least 40%.

The oxidation stability may suitably be measured by recording the stability time or the induction time as measured by a Rancimat test.

Preferred features of the composition are as defined above .

As well as improving the oxidation stability of a fuel containing biodiesel and optionally a phenolic antioxidant, the applicant has also found that nitrogen- containing dispersants alone show excellent antioxidant

properties at elevated temperatures, for example, at temperatures typically found in modern diesel engines.

Modern diesel engines include HSDI (High Speed Direct Injection) engines which provide improved performance and are more environmentally friendly.

The fuel in these engines can be re-circulated and thus may reach very high temperatures, for example temperatures of 150 ⁰ C or more.

Biodiesel fuels have poorer oxidation stability than mineral diesel and this effect is particularly apparent at higher temperatures.

According to a third aspect of the present invention there is provided the use of a nitrogen-containing dispersant to improve the oxidation stability of a fuel composition containing biodiesel at temperatures above 110 ⁰ C.

The nitrogen-containing dispersant and fuel are preferably as defined in relation to the first and/or second aspects, where appropriate.

Suitably the nitrogen-containing dispersant improves the oxidation stability of a fuel composition at temperatures of above 120 ⁰ C, preferably above 130 ⁰ C, more preferably above 140°C, for example, 150 ⁰ C.

Thus a nitrogen-containing dispersant may be used to improve the oxidation stability of a fuel composition containing biodiesel when used in an HSDI engine.

Because the nitrogen-containing dispersant has excellent antioxidant properties at high temperatures, it may not always be necessary to include a traditional antioxidant additive. Thus the present invention further provides a fuel composition containing biodiesel and a nitrogen- containing dispersant which is substantially free of traditional antioxidant additives.

By "substantially free of" it is meant that no antioxidants of the hindered phenolic or phenylenediamine type are added but trace amounts may be naturally present in the fuel. Such a fuel composition is highly advantageous as a single additive is used to provide dispersancy and oxidation stability, and is thus cost- effective.

The present invention may therefore provide a fuel composition containing biodiesel and from 1 to 10000 ppm, for example 1 to 1000 ppm, nitrogen-containing dispersant, the composition being substantially free of traditional antioxidant additives. By "traditional antioxidant additives" we mean to refer to hindered phenol antioxidant compounds and phenylenediamine antioxidants.

Alternatively the present invention may provide a fuel composition comprising a nitrogen containing dispersant and a traditional antioxidant wherein the treat rate of traditional antioxidant is less than would be needed to achieve an equivalent oxidation stability in a composition which did not contain the nitrogen containing dispersant. The present invention may thus provide a composition comprising biodiesel, from 1 to 10000 ppm, for example 1 to 1000 ppm, nitrogen-containing dispersant and less than

100 ppm traditional antioxidant, preferably less than 50 ppm, for example, less than 30 ppm, preferably less than 20 ppm, more preferably less than 10 ppm, most preferably less than 5 ppm, for example less than 1 ppm traditional antioxidant; by weight of biodiesel.

Suitably said composition contains at least 5 ppm, preferably at least 10 ppm, more preferably at least 15 ppm and most preferably at least 20 ppm nitrogen- containing dispersant by weight of biodiesel.

Suitably said composition contains up to 500 ppm, preferably up to 400 ppm, preferably up to 300 ppm of nitrogen-containing dispersant, by weight of biodiesel.

The oxidation stability at high temperatures may suitably be measured using a Rancimat test run at a temperature of 150 ⁰ C.

Suitably the present invention provides the use of a nitrogen-containing dispersant to increase the oxidation stability of a fuel composition containing biodiesel as measured by a Rancimat test at 150 ⁰ C by at least 5%, preferably at least 10%, more preferably at least 15% and most preferably by at least 20%. This improvement should be measured with reference to the unadditised fuel.

The present invention further provides the use of a composition as hereinbefore described as heating oil, or a heavy fuel oil.

Any feature of any aspect of the invention may be combined with any other aspect, as appropriate.

The invention will now be further described by way of the following non-limiting examples.

Example 1

A sample of biodiesel comprising rapeseed methylester base fuel sourced from Spain was subjected to a Rancimat test method. The sample was heated to 110 ⁰ C with air bubbling through. Volatile breakdown products pass over into deionised water and the conductivity is measured The time taken for the stability of the fuel to breakdown was measured by recording the stability time, the time taken to increase the conductivity by 200 μS/cm. Various additives were then added to the base biodiesel fuel and the Rancimat test repeated. The results are given in table 1.

TABLE 1

Additive A is a 60% active ingredient solution (in aromatic solvent) of a polyisobutenyl succinimide obtained from the condensation reaction of a polyisobutenyl succinic anhydride derived from polyisobutene of Mn

approximately 750 with a polyethylene polyamine mixture of average composition approximating to tetraethylene pentamine. Additive Al is a 60% active ingredient solution

(in aromatic solvent) of a polyisobutenyl succinimide obtained from the condensation reaction of a polyisobutenyl succinic anhydride derived from polyisobutene of Mn approximately 750 with a polyethylene polyamine mixture of average composition approximating to tetraethylene pentamine. The mole ratio of polyisobutenyl succinic anhydride : polyethylene polyamine was approximately 1:1.

BlOO refers to a fuel composition which consists of entirely of biodiesel base fuel.

Example 2

The Rancimat test of example 1 was then run on samples of biodiesel BlOO at 110 ⁰ C using on this occasion just a single additive, and additive combinations. Additive A is as defined in relation to Example 1. The results are shown in table 2.

TABLE 2

The above results clearly show that for each of the biodiesel fuels containing a phenolic antioxidant additive, a synergistic improvement in stability was found upon co-addition of the nitrogen-containing dispersant additive A.

Example 3

The tests of Example 1 were then repeated except that the Rancimat test was carried out at 150 ⁰ C, with all other

variables being constant. The results are shown in table 3.

TABLE 3

These results clearly show that at an increased temperature of 150 ⁰ C, a temperature commonly found in modern HSDI diesel engines, additive A, a nitrogen- containing dispersant, performs better than standard phenolic antioxidant additives.

Example 4

The Rancimat tests at 150 ⁰ C were then carried out on a sample BlO which contains 10% by weight base RME biodiesel from Spain, and 90% standard mineral diesel oil sourced from Haltermans and known as RF-O 6.

The results are shown in table 4. The specification of fuel RF-06 is shown in table 5.

TABLE 4

TABLE 5

A nitrogen-containing dispersant would typically be added to a BlO fuel (to achieve dispersancy/detergency) at a treat rate of about 100 ppm. The results shown in table 4 show that this alone will improve oxidation stability at 150 ⁰ C in an amount greater than the addition of a standard phenolic antioxidant additive.

Example 6

The Rancimat test of example 1 was then run on samples of biodiesel BlOO (RME biodiesel derived from canola, sourced from the USA) at 110 ⁰ C, including the nitrogen dispersant additives of the present invention listed in table 6.

TABLE 6

Additive Al is a 60% active ingredient solution (in aromatic solvent) of a polyisobutenyl succinimide obtained from the condensation reaction of a polyisobutenyl succinic anhydride derived from polyisobutene of Mn approximately 750 with a polyethylene polyamine mixture of average composition approximating to tetraethylene

pentamine. The mole ratio of polyisobutenyl succinic anhydride : polyethylene polyamine was 1:1.

Additive A2 is a 60% active ingredient solution (in aromatic solvent) of a polyisobutenyl succinimide obtained from the condensation reaction of a polyisobutenyl succinic anhydride derived from polyisobutene of Mn approximately 750 with a polyethylene polyamine mixture of average composition approximating to tetraethylene pentamine. The mole ratio of polyisobutenyl succinic anhydride : polyethylene polyamine was 4:1.

Additive Bl is a 60% active ingredient solution (in aromatic solvent) of a polyisobutenyl succinimide obtained from the condensation reaction of a polyisobutenyl succinic anhydride derived from polyisobutene of Mn approximately 750 with a polyethylene polyamine mixture of average composition approximating to hexaethylene heptamine. The mole ratio of polyisobutenyl succinic anhydride : polyethylene polyamine was 1:1.

Additive B2 is a 60% active ingredient solution (in aromatic solvent) of a polyisobutenyl succinimide obtained from the condensation reaction of a polyisobutenyl succinic anhydride derived from polyisobutene of Mn approximately 750 with a polyethylene polyamine mixture of average composition approximating to hexaethylene heptamine. The mole ratio of polyisobutenyl succinic anhydride : polyethylene polyamine was 1.4:1.

Additive B3 is a 60% active ingredient solution (in aromatic solvent) of a polyisobutenyl succinimide obtained from the condensation reaction of a polyisobutenyl

succinic anhydride derived from polyisobutene of Mn approximately 750 with a polyethylene polyamine mixture of average composition approximating to hexaethylene heptamine. The mole ratio of polyisobutenyl succinic anhydride : polyethylene polyamine was 2:1.

Additive B4 is a 60% active ingredient solution (in aromatic solvent) of a polyisobutenyl succinimide obtained from the condensation reaction of a polyisobutenyl succinic anhydride derived from polyisobutene of Mn approximately 750 with a polyethylene polyamine mixture of average composition approximating to hexaethylene heptamine. The mole ratio of polyisobutenyl succinic anhydride : polyethylene polyamine was 4:1.

Additive Cl is a 75 % active ingredient solution (in aromatic solvent) of a mannich reaction product prepared by mixing 4-dodecylphenol, paraformaldehyde, tetraethylenepentamine and toluene. The mixture was heated to 110 ⁰ C and refluxed for 6 hours. The solvent and water of reaction were then removed under vacuum. The molar ratio of aldehyde : polyamine : phenol was 2:1:2.

Additive C2 is a 83% active ingredient mannich reaction product prepared by reacting a polyisobutenyl substituted phenol in which the polyisobutene has a molecular weight of approximately 780, paraformaldehyde and tetraethylenepentamine in toluene. The mixture was heated to 110 ⁰ C and refluxed for 6 hours. The solvent and water of reaction were then removed under vacuum. The molar ratio of aldehyde : polyamine : phenol was 1:1:1.

Additive C3 is a 100 % active ingredient mannich reaction product prepared by reacting a polyisobutenyl substituted phenol in which the polyisobutene has a molecular weight of approximately 750, paraformaldehyde and tetraethylenepentamine in toluene. The mixture was heated to 110 ⁰ C and refluxed for 6 hours. The solvent and water of reaction were then removed under vacuum. The molar ratio of aldehyde : polyamine : phenol was 2:1:2.

Example 7

The Rancimat test of example 1 was then run on samples of biodiesel BlOO (RME biodiesel derived from canola, sourced from the USA) at 110 ⁰ C, including the nitrogen dispersant additives of the present invention in combination with phenolic antioxidants as detailed in table 7.

TABLE 7