NO329622B1 - Additive for a fuel oil composition and its use. - Google Patents

Abstract

Fuel oil compositions containing specific mixtures of esters of unsaturated monocarboxylic acids show improved lubricity properties.

Description

The present invention relates to additives for improving the lubricity of fuel oils such as diesel fuel oil. Diesel engine oil compositions including the additives exhibit improved lubricity and reduced engine wear. The invention further relates to the use of the additives.

Concern for the environment has resulted in measures to significantly reduce harmful components in emissions when fuel oils are burned, especially in engines such as diesel engines. Attempts are being made, for example, to minimize sulfur dioxide emissions. As a result of this, attempts are being made to minimize the sulfur content in fuel oils. For example, although typical diesel fuel oils have previously contained 1% by weight or more of sulfur (expressed as elemental sulfur), it is now considered desirable to reduce the level, preferably to 0.05% by weight and advantageously to less than 0.01% by weight -%, especially less than 0.001% by weight.

Further refining of fuel oils, which is necessary to achieve these low sulfur levels, often results in reductions in levels of polar components. In addition, refinery processes can reduce the level of polynuclear aromatic compounds present in such fuel oils.

Reduction of the level of one or more of the sulfur, polynuclear aromatic or polar components in diesel fuel oil can reduce the oil's ability to lubricate the engine's injection system, so that, for example, the fuel injection pump in engines fails relatively early in an engine's life. Failures can occur in fuel injection systems, such as high-pressure rotary distributors, direct-coupled pumps and injectors. The problem of poor lubricity in diesel fuel oils is likely to be exacerbated by future engine developments which aim at further emission reduction, and which will have more demanding requirements for lubricity than existing engines. For example, it is expected that the advent of high-pressure unit injectors will increase the demands on fuel oil lubricity.

Likewise, poor lubricity can lead to wear problems in other mechanical devices which depend on the natural lubricity of fuel oil for lubrication.

Lubricity additives for fuel oils have been described in the prior art. WO 94/17160 describes an additive comprising an ester of a carboxylic acid and an alcohol where the acid has 2-50 carbon atoms and the alcohol has one or more carbon atoms. Glycerol monooleate is specifically described as an example. Although general mixtures are relevant, no particular mixtures of esters are described.

US-A-3,273,981 describes a lubricity additive which is a mixture of A+B where A is a polybasic acid, or a polybasic acid ester prepared by reacting the acid with C1-C5 monohydric alcohols; while B is a partial ester of a polyhydric alcohol and a fatty acid, for example glyceryl monooleate, sorbitan monooleate or pentaerythritol monooleate. The mixture is used in jet engine fuels.

Under certain conditions, however, it has unexpectedly been found that such previously known esters promote the blocking of fuel filters, especially the fine-mesh filters that typically occur in fuel lubrication systems in diesel vehicles. This filter blockage problem can result in insufficient fuel flow and impaired engine operation, and is especially evident at low temperatures.

Furthermore, it has unexpectedly been found that fuels containing the preferred ester (additive D) described in WO 94/17160 show a loss of lubricity performance after a period of cold storage and filtration. The loss of performance can be evident even in the absence of serious filter blockage problems. This loss of performance in itself represents a significant problem, because under field conditions a stored fuel is typically exposed to temperature cycles and must still be able to provide effective lubrication to mechanical devices downstream of fuel line filters. In a diesel vehicle fuel system, for example, diesel fuel must first flow through a fine quality filter before reaching the fuel injection system, including the fuel pump. Reduced lubricity performance after this filtration point therefore exposes the injection system to increased wear.

There is therefore a need for improved lubricity additives which exhibit better filterability and which in fuel oils do not show loss of performance after filtration which follows periods of cold temperature storage.

Such problems have now surprisingly been solved by means of additives comprising special mixtures of certain esters.

GB-A-1,505,302 describes ester combinations including, for example, glycerol monoesters and glycerol diesters as diesel fuel additives, where it is stated that the combinations lead to advantages including less wear on the fuel injection equipment, piston rings and cylinder liners. However, GB-A-1,505,302 concerns overcoming the operational disadvantages of corrosion and wear of acidic combustion products, residues in the combustion chamber and in the exhaust system. The GB document states that these disadvantages are due to incomplete combustion under certain operating conditions. Typical diesel fuels available at the time of said GB document contained, for example, from 0.5 to 1% by weight of sulfur, as elemental sulfur, based on the weight of the fuel.

US-A-3,287,273 describes lubricity additives which are reaction products of a dicarboxylic acid and an oil-soluble glycol. The acid is typically predominantly a dimer of unsaturated fatty acids such as linoleic acid or oleic acid, although smaller amounts of the monomeric acid may also be present. Only alkanediols or oxalkanediols are specifically suggested as the glycol reactant.

According to a first aspect, therefore, the present invention provides an additive for a fuel oil composition comprising a major proportion of a middle distillate fuel oil having a sulfur content of 0.2% by weight or less, characterized in that the additive is lubricating and includes:

(a) an ester of an unsaturated monocarboxylic acid and a polyhydric alcohol, and

(b) an ester of a polyunsaturated monocarboxylic acid and a polyhydric alcohol having

at least three hydroxy groups,

wherein the esters (a) and (b) are different and both are partial esters, and the relative weight proportions of (a) and (b) are in the range of 1:10 to 2:1.

According to another aspect, the invention comprises the use of the additive defined in the first aspect to improve the lubricity of a middle distillate fuel oil.

According to a third aspect, the invention provides for the use of the additive for a fuel composition according to the first aspect in a combustion apparatus to reduce the degree of wear in said apparatus's fuel supply system.

The mixture of esters (a) and (b) may provide unexpectedly improved lubricity performance compared to the individual performance of component (a) or (b). Furthermore, the mixture of (a) and (b) shows improved filterability and maintains good lubricity performance after cold storage followed by filtration.

The invention will now be described in more detail.

The fuel oil composition (first aspect of the invention)

(i) The additive

The term "polyhydric alcohol" is used to describe a compound that has more than one hydroxy group. It is preferred that (a) is the ester of a polyhydric alcohol having at least 3 hydroxy groups.

Examples of polyhydric alcohols that have at least 3 hydroxy groups are those that have 3-10, preferably 3-6, more preferably 3-4 hydroxy groups, and have 2-90, preferably 2-30, more preferably 2-12 and most preferably 3- 4 carbon atoms in the molecule. Such alcohols may be aliphatic, saturated or unsaturated, and straight-chain or branched, or cyclic derivatives thereof. Saturated, aliphatic, straight chain alcohols are preferred.

Both (a) and (b) are advantageously esters of trihydric alcohols, especially glycerol or unmethylolpropane. Other suitable polyhydric alcohols include pentaerythritol, sorbitol, mannitol, inositol, glucose and fructose.

The unsaturated monocarboxylic acids from which the esters are derived may have an alkenyl, cycloalkenyl or aromatic hydrocarbyl group attached to the carboxylic acid group. The term "hydrocarbyl" means a group containing carbon and hydrogen which can be straight-chain or branched and which is attached to the carboxylic acid group with a carbon-carbon bond. The hydrocarbyl group can be interrupted by one or more heteroatoms such as O, S, N or P.

It is preferred that (a) and (b) are both esters of alkenyl monocarboxylic acids, where the alkenyl groups preferably have 10-36, for example 10-22, more preferably 18-22, especially 18-20 carbon atoms. The alkenyl group can be mono- or polyunsaturated. It is particularly preferred that (a) is an ester of a mono-unsaturated alkenyl carboxylic acid, and that (b) is an ester of a polyunsaturated alkenyl monocarboxylic acid. The polyunsaturated acid is preferably di- or tri-unsaturated. Such acids can be derived from natural materials, for example vegetable or animal extracts.

Particularly preferred monounsaturated acids are oleic acid and elaidic acid. Particularly preferred polyunsaturated acids are linoleic acid and linolenic acid.

It has been found that the mixtures where (a) is an ester of a monounsaturated acid and (b) is an ester of a polyunsaturated acid have particularly good lubricity performance and exhibit particularly good filterability and resistance to cold storage.

The esters are partial esters, i.e. some of the hydroxy groups in each polyhydric alcohol are restricted. Particularly good performance is achieved when (a) and (b) are both partial esters and especially when both are monoesters.

The esters can be prepared using methods that are well known in the art, for example by condensation reactions. The alcohols can, if desired, be reacted with acid derivatives such as anhydrides or acyl chlorides to facilitate the reaction and improve yields.

The esters (a) and (b) can be prepared separately and then mixed together, the mixing taking place either before addition to the fuel, or as a result of separate addition of (a) and (b) to the fuel at the same time or at different times. Alternatively, the ester mixture can be prepared directly from a mixture of suitable starting materials. It has been found that the latter products (ie the ester mixtures formed directly from the reaction of a mixture of starting materials) have particularly good filterability and show particularly good lubricity performance. In particular, commercially available mixtures of suitable acids can be reacted with a selected alcohol such as glycerol to form a mixed ester product according to the present invention. Particularly preferred commercial acid mixtures are those comprising oleic acid and linoleic acid. In such mixtures, a smaller proportion of other acids, or acid polymerization products, may be present, but this proportion should preferably not exceed 15%, more preferably not more than 10%, and most preferably not more than 5% by weight of the total acid mixture .

Likewise, mixtures of esters can be prepared by reacting a single acid with a mixture of alcohols.

A very preferred ester mixture is that which is obtained by reacting a mixture of oleic acid and linoleic acid with glycerol, where the mixture mainly comprises (a) glycerol monooleate and (b) glycerol monolinoleate, preferably in approximately equal amounts by weight. In addition to the esters (a) and (b), the lubricity additive may further comprise a smaller proportion of other esters formed, for example, during esterification of the previously described acid mixtures.

(ii) The fuel oil

The fuel oil can be a petroleum-based fuel oil, suitably a middle distillate fuel oil, i.e. a fuel oil obtained by raffinating crude oil as the fraction between the fraction of lighter kerosene and jet fuels and the fraction of heavy fuel oil. Such distillate fuel oils generally boil above 100°C. The fuel oil may comprise atmospheric distillate or vacuum distillate, or cracked gas oil or a mixture in any proportion of directly distilled and thermally and/or catalytically cracked distillates. The most common petroleum-based fuel oils are kerosene, jet engine fuels and preferably diesel fuel oils.

The sulfur content of the fuel oil is 0.2% by weight or less, preferably 0.05% by weight or less, more preferably 0.01% by weight or less, and most preferably 0.001% by weight or less based on the weight of the fuel oil. The technique describes methods for reducing the sulfur content in hydrocarbon middle distillate fuels, where such methods include coagulant extraction, sulfuric acid treatment and hydrodesulphurisation.

Preferred fuel oils have a cetane number of at least 40, preferably above 45 and more preferably above 50. The fuel oil can have such cetane numbers before the addition of any cetane number improver or the cetane number of the fuel can be raised by adding a cetane number improver.

More preferably, the cetane number of the fuel is at least 52.

(iii) Processing amounts

The concentration of the additive in the fuel oil can for example be in the range 10-5000 ppm of additive (active ingredient) calculated on weight per weight part of fuel oil, for example 20-5000 ppm such as 50-2000 ppm (active ingredient) calculated on weight per weight part of fuel oil , preferably 75-300 ppm, more preferably 100-200 ppm.

The relative proportions of (a) and (b) calculated by weight in the fuel oil are in the range from 1:10 to 2:1. The 1:1 ratio is most preferred.

The use of the additive (second aspect of the invention)

The preferred additives for the second aspect of the invention are those described above in connection with the first aspect.

The use of the additive for the fuel composition (third aspect of the invention)

When the fuel oil is diesel fuel, the additive for the fuel oil composition according to the first aspect of the invention has application in diesel (compression ignition) engines as a fuel, which in addition to providing good combustion properties, reduces the degree of wear in the fuel supply system, and especially in the fuel injection pump. Use of the fuel thus extends the working life of the equipment and reduces the need to replace expensive mechanical parts.

The additive for the fuel oil composition according to the first aspect of the invention likewise finds use in other fuel oil systems where the mechanical devices in the fuel supply system depend on the fuel oil for lubrication, and are consequently exposed to wear.

Concentrates

Concentrates comprising the additive in admixture with a carrier liquid (eg, as a solution or a dispersion) are suitable as a means of incorporating the additive into bulk fuel oil, and this incorporation can be accomplished by methods known in the art. The concentrates can also contain other additives as required and preferably contain 3-75% by weight, more preferably 3-60% by weight, most preferably 10-50% by weight of the additives preferably in solution in oil. Examples of carrier liquid are organic solvents including hydrocarbon solvents, for example petroleum fractions such as naphtha, kerosene, diesel and heating oil; aromatic hydrocarbons such as aromatic fractions, e.g. those sold under the "SOLVESSO" trademark; paraffinic hydrocarbons such as hexane and pentane and isoparaffins; and oxygenated solvents such as alcohols. The carrier liquid must of course be selected taking into account its compatibility with the additive and with the fuel. The concentrates are added to the bulk fuel oil in quantities sufficient to supply the additive treatment quantity as discussed above.

The additives according to the invention can be incorporated into bulk fuel oil by other methods such as those known in the art. If co-additives are necessary, they can be incorporated into the bulk fuel oil at the same time as the additives according to the invention or at another time.

Co-additives

The fuel composition according to the first aspect of the invention can further comprise other known lubricity-enhancing agents as co-additives, for example mono- or polycarboxylic acids, such as dicarboxylic acids. These acids are preferably mixtures of polymerized unsaturated fatty acids, comprising mainly dimer and sometimes trimer acid, with smaller proportions of monomer and/or higher polymers. Typical examples are the fatty acids of oleic acid, linoleic acid or mixtures thereof. Esters of these acids with monohydric or dihydric alcohols can also be used in combination with the mixture of esters (a) and (b) to obtain further improved additives.

Likewise, lubricating co-additives of the ethoxylated amine type can be used.

The fuel oil in the first aspect of the invention can also advantageously comprise one or more fuel oil cold flow improvers, as co-additives such as one or more of:

(i) ethylenically unsaturated ester copolymers,

(ii) hydrocarbon polymers;

(iii) sulfur carboxy bond,

(iv) polar compounds,

(v) hydrocarbylated aromatics,

(vi) linear connections, and

(vii) comb polymers,

as defined below.

(i) Copolymer of ethylene and unsaturated ester

Ethylene copolymer flow improvers, e.g. ethylene unsaturated ester copolymer flow improvers, have a polymethylene main chain divided into segments of hydrocarbyl side chains interrupted by one or more oxygen atoms and/or carbonyl groups.

The copolymer may more particularly comprise an ethylene copolymer which, in addition to units derived from ethylene, has units of the formula

-CR<5>R<6->CHR<7->

where R<6> represents hydrogen or a methyl group; R<5> represents a -OOCR<8> or -COOR<8> group where R<8> represents hydrogen or a C1-C9, preferably C1-C6, more preferably C1-C3, straight chain or branched alkyl group; and R<7> represents hydrogen or a -COOR<8> or -OOCR<8> group.

These may comprise a copolymer of ethylene with an ethylenically unsaturated ester, or derivatives thereof. An example is a copolymer of ethylene with an ester of an unsaturated carboxylic acid such as ethylene acrylates (e.g. ethylene-2-ethylhexyl acrylate), but the ester is preferably one of an unsaturated alcohol with a saturated carboxylic acid as described in GB- A-1,263,152. An ethylene-vinyl ester copolymer is advantageous; an ethylene-vinyl acetate, ethylene-vinyl propionate, ethylene-vinyl hexanoate, ethylene-2-ethylhexanoate or ethylene-vinyl octanoate copolymer is preferred. The copolymers preferably contain from 1 to 25 such as less than 25, e.g. 1-20, mol-% of the vinyl ester, more preferably 3-15 mol-% vinyl ester. They may also be in the form of mixtures of two copolymers such as those described in US-A-3,961,916 and EP-A-113,581. The number average molecular weight, measured by vapor phase osmometry, for the copolymer is preferably 1000-10,000, more preferably 1000-5000. The copolymers may, if desired, be derived from further comonomers, they may for example be terpolymers or tetrapolymers or higher polymers, for example where the further comonomer is isobutylene or diisobutylene or another ester which gives rise to different units of the above formula and where the above mole % amounts of ester refer to total ester.

The copolymers can also include small proportions of chain transfer agents and/or molecular weight modifiers (e.g. acetaldehyde or propionaldehyde) which can be used in the polymerization process for producing the copolymer.

The copolymers can be prepared by direct polymerization of comonomers. Such copolymers can also be produced by cross-esterification, or by hydrolysis and re-esterification, of a copolymer of ethylene and unsaturated ester to obtain another copolymer of ethylene and unsaturated ester. For example, ethylene-vinyl hexanoate and ethylene-vinyl octanoate copolymers can be prepared in this way, for example from an ethylene-vinyl acetate copolymer.

The copolymers can for example have 15 or fewer, preferably 10 or fewer, more preferably 6 or fewer, most preferably 2-5, methyl terminating side branches per 100 methylene groups, measured by nuclear magnetic resonance, other than methyl groups on a comonomer residue and other than terminal methyl groups.

The copolymers can also have a polydispersity in the range 1-6, preferably 2-4, where polydispersity is the ratio of weight-average molecular weight to number-average molecular weight, both measured by gel permeation chromatography using polystyrene standards.

(ii) Hydrocarbon polymers

Linear hydrocarbon polymers

These have one or more polymethylene main chains, optionally divided into segments of short-chain hydrocarbyl groups, i.e. of 5 carbon atoms or less.

Examples are those represented by the following general formula

where

T represents H or R<1>;

U represents H, T or substituted or unsubstituted aryl; and R<1> represents a hydrocarbyl group of up to 5 carbon atoms,

and v and w represent molar ratios, where v is in the range 1.0-0.0, w is in the range 0.0-1.0. R<1> is preferably a straight-chain or branched alkyl group.

The polymers can be produced directly from ethylenically cross-linked monomers or indirectly by hydrogenation of the polymer produced from monomers such as isoprene and butadiene.

Preferred hydrocarbon polymers are copolymers of ethylene and at least one α-olefin. Examples of such olefins are propylene, 1-butene, isobutene and 2,4,4-trimethylpent-2-ene. The copolymer may also comprise small amounts, for example up to 10% by weight, of other copolymerizable monomers, for example olefins other than α-olefins, and non-conjugated dienes. The preferred copolymer is an ethylene-propylene copolymer. Advantageously, two or more different ethylene-α-oleifn copolymers of this type are included.

The number average molecular weight of the ethylene-α-oleifn copolymer is less than 150,000, as measured by gel permeation chromatography (GPC) relative to polystyrene standards. For some applications it is advantageously at least 60,000 and preferably at least 80,000. Functionally, no upper limit occurs, but mixing difficulties result from increased viscosity at molecular weights above approx. 150,000, and preferred molecular weight ranges are from 60,000 and 80,000 to 120,000. For other applications it is below 30,000, preferably below 15,000 such as below 10,000 or below 6,000.

The copolymer advantageously has a molar ethylene content between 50 and 85 percent. More preferably, the ethylene content is within the range from 55 to 80%, and preferably it is in the range 55-75%; more preferably 60-70%, and most preferably 65-70%.

Examples of ethylene-α-olefin copolymers are ethylene-propylene copolymers with a molar ethylene content of 60-75% and a number average molecular weight in the range 60,000-120,000, particularly preferred copolymers are ethylene-propylene copolymers with an ethylene content in the range 62- 71% and a molecular weight in the range 80,000-100,000.

The copolymers can be prepared by any of the methods known in the art, for example using a Ziegler type catalyst. Advantageously, the polymers are substantially amorphous, because highly crystalline polymers are relatively insoluble in fuel oil at low temperatures.

(iii) Sulfur carboxyl compounds

Examples are those described in EP-A-0,261,957 which describes the use of compounds of the general formula

where -Y-R<2> is S03("<X+>)NR<3>3<R2>, -S03(-)C+)HNR32R2, -SO^^NRV,

-S03("))(<+>)H3NR<2>} -S02NR<3>R<2> or -SO3R<2>; and -X-R<1> is -Y-R<2> or -CONR<3>R \ -C02(")C+)NR33R1, -C02( X+)HNR32R1J -R<4->COORi, -NR<3>COR\ - R* OR\ -R^COR1, -R<4>^<1> , -N(COR<3>)R<1> or ^'NR^R1; -ZH is S03<H> or -C02(); R<1> and R<2> are alkyl, alkoxyalkyl or polyalkoxyalkyl containing at least 10 carbon atoms in the main chain; R<3> is hydrocarbyl and each R<3> can be the same or different and R<4> is absent or is C1-C<:alkvlenoei

the carbon-carbon (C-C) bond is either a) ethylenically unsaturated when A and B may be alkyl, alkenyl or substituted hydrocarbyl groups or b) part of a cyclic structure which may be aromatic, polynuclear-aromatic or cyclo-aliphatic, and it is preferred that X-R<1> and Y-R<2> between them contain at least three alkyl, alkoxyalkyl or polyalkyloxyalkyl groups.

Multi-component additive systems can be used and the conditions for additives to be used will depend on the fuel to be treated.

(iv) Polar compounds

Such compounds comprise an oil-soluble polar nitrogen compound bearing one or more, preferably two or more, hydrocarbyl-substituted amino or imino substituents, the hydrocarbyl group(s) being monovalent and containing 8-40 carbon atoms, which substituent or one or more of which substituents may be in form of a cation derived therefrom. The oil-soluble polar nitrogen compound is either ionic or non-ionic and can act as a wax crystal growth modifier in fuels. The hydrocarbyl group is preferably linear or somewhat linear, i.e. it can have one hydrocarbyl branch of short length (1-4 carbon atoms). When the substituent is amino, it may have more than one of the aforementioned hydrocarbyl groups, these may be the same or different.

The term "hydrocarbyl" refers to a group having a carbon atom directly attached to the rest of the molecule and having a hydrocarbon or predominantly hydrocarbon character. Examples include hydrocarbon groups, including aliphatic (eg, alkyl or alkenyl), alicyclic (eg, cycloalkyl or cycloalkenyl), aromatic, and alicyclic-substituted aromatic, and aromatic-substituted aliphatic and alicyclic groups. Aliphatic groups are advantageously saturated. These groups may contain non-hydrocarbon substituents provided their presence does not alter the essential hydrocarbon character of the group. Examples include keto, halogen, hydroxy, nitro, cyano, alkoxy, and acyl. If the hydrocarbyl group is substituted, then a single (mono) substituent is preferred.

Examples of substituted hydrocarbyl groups include 2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl, 2-ketopropyl, ethoxyethyl and propoxypropyl. The groups may also or alternatively contain atoms other than carbon in a chain or ring which otherwise consists of carbon atoms. Suitable heteroatoms include, for example, nitrogen, sulfur and, preferably, oxygen.

More particularly, the amino or imino substituent or each of these is attached to a moiety via an intermediate linking group such as -CO-, -CO 2 <H>, -SO 3 H or hydrocarbylene. When the binding group is anionic, then the substituent is part of a cationic group, as in an amine salt group.

When the polar nitrogen compound carries more than one amino or imino substituent, the bonding groups for each substituent may be the same or different.

Suitable amino substituents are long-chain C12-C40, preferably Q2-C24, alkyl primary,

-secondary, -tertiary or -quaternary amino substituents.

The amino substituent is preferably a dialkylamino substituent, which, as indicated above, may be in the form of an amine salt thereof; tertiary and quaternary amines can only form amine salts. Said alkyl groups may be the same or different.

Examples of amino substituents include dodecylamino, tetradecylamino, coconut amino and hydrogenated tallow amino. Examples of secondary amino substituents include dioctadecylamino and methylbehenylamino. Mixtures of amino substituents may be present such as those derived from naturally occurring amines. A preferred amino substituent is the secondary hydrogenated tallow amino substituent, whose alkyl groups are derived from hydrogenated tallow fat and typically consist of approx. 4% C14, 31% Ci6 and 59% Ci8 n-alkyl groups, calculated by weight.

Suitable imino substituents are long-chain C12-C40, preferably C12-C24, alkyl substituents.

Said group part can be monomeric (cyclic or non-cyclic) or polymer. When it is non-cyclic, it can be obtained from a cyclic precursor such as an anhydride or a spirobislactone.

The cyclic ring system may include homocyclic, heterocyclic, or condensed polycyclic elements, or a system in which two or more such cyclic elements are joined to each other and in which the cyclic elements may be the same or different. When there are two or more such cyclic elements, the substituents may be on the same or different elements, preferably on the same element. The cyclic element or each such element is preferably aromatic, more preferably a benzene ring. Most preferably, the cyclic system is a single benzene ring when it is preferred that the substituents are in the ortho or meta positions, which benzene ring may optionally be further substituted.

The ring atoms of the cyclic element or elements are preferably carbon atoms, but may for example include one or more N, S or O ring atoms, in which case or cases the compound is a heterocyclic compound.

Examples of such polycyclic elements include

(a) condensed benzene structures such as naphthalene, anthracene, phenanthrene and pyrene; (b) fused ring structures in which none or all of the rings are benzene such as azulene, indene, hydroindene, fluorene and diphenylene oxides; (c) rings joined "end-to-end" such as diphenyl; (d) heterocyclic compounds such as quinoline, indole, 2,3-diliydroindole, benzofuran, coumarin, isocoumarin, benzothiophene, carbazole and thio&phenylamine; (e) non-aromatic or partially saturated ring systems such as decalin (i.e.

decahydronaphthalene), α-pinene, cardine and bornylene; and

(f) three-dimensional structures such as norbornene, bicycloheptane (ie norbornane),

bicyclooctane and bicyclooctene.

Examples of polar nitrogen compounds are described below:

(I) an amine salt and/or amide of a mono- or polycarboxylic acid, e.g. with 1-4 carboxylic acid groups. It can be prepared, for example, by reacting at least one molar proportion of a hydrocarbyl-substituted amine with a molar proportion of the acid or its anhydride.

When an amide is formed, the bonding group is -CO-, and when an amine salt is formed, the bonding group is -CO2f).

The group part can be cyclic or non-cyclic. Examples of cyclic moieties are those where the acid is cyclohexan-1,2-dicarboxylic acid; cyclohexane-1,2-dicarboxylic acid; cyclopentane-1,2-dicarboxylic acid; and naphthalenedicarboxylic acid. Such acids generally have 5-13 carbon atoms in the cyclic part. Preferred such cyclic acids are benzenedicarboxylic acids such as phthalic acid, isophthalic acid and terephthalic acid, and benzenetetracarboxylic acids such as pyromelletic acid, phthalic acid being particularly preferred. US-A-4,211,534 and EP-A-272,889 describe polar nitrogen compounds containing such moieties. Examples of non-cyclic moieties are those where the acid is a long-chain alkyl- or alkylene-substituted dicarboxylic acid such as a succinic acid, as described in US-A-4,147,520, for example.

Other examples of non-cyclic moieties are those where the acid is a nitrogenous acid such as ethylenediaminetetraacetic acid.

Further examples are the moieties obtained when a dialkylspirobislactone is reacted with an amine.

(H) EP-A-0,261,957 describes polar nitrogen compounds according to the description of the general formula

where -Y-R<2> is S03(<-x+>>NR3R<2>, -S03("<X+>)HNR<3>2R<2>,

-SO3(-X+)H2NR3R2,

-SO3<c-x+>)H3NR<2>, -SO2NR3R<2> or -SOaR<2>; and -X-R<1> is -Y-R<2> or

-CONR<3>R',

-COj^^aR1, -C02()(<+>>HNR<3>2R<1>, -R<4->COORi, -NR3COR\

-R4OR', -R^COR<1>, -R^R<1>, -N^OR^R<1> or Z^^NR^R<1>; -Z( <>> is S03(<_>) or-C02<0>;

R<1> and R<2> are alkyl, alkoxyalkyl or polyoxyalkyl containing at least 10 carbon atoms in the main chain;

R<3> is hydrocarbyl and each R<3> may be the same or different and R<4> is absent or is C1-C5 alkylene and i the carbon-carbon (C-C) bond is either a) ethylenically unsaturated when A and B can be alkyl, alkenyl or substituted hydrocarbyl groups or b) part of a cyclic structure which can be aromatic, polynuclear aromatic or cycloaliphatic, and it is preferred that X-R<1> and Y-R<2> between them contain at least three alkyl-, alkoxyalkyl - or polyalkyloxyalkyl groups.

Multi-component additive systems can be used and the conditions for additives to be used will depend on the fuel to be treated.

(IH) EP-A-0,316,108 discloses an amine or diamine salt of (a) a sulfuric acid, b) an ester or diester of a sulfuric acid, c) an amide or a diamide of a sulfuric acid, or d) an ester amide of a sulfuric acid.

(IV) A chemical compound comprising or including a cyclic ring system, where the compound carries at least two substituents of the general formula (I) indicated below on the ring system

where A is an aliphatic hydrocarbyl group which is optionally interrupted by one or more heteroatoms and which is straight-chain or branched, and R<1> and R<2> are the same or different and each is independently a hydrocarbyl group containing 9-40 carbon atoms optionally interrupted by one or more heteroatoms, the substituents being the same or different and the compound possibly being in the form of a salt thereof.

A preferably has 1-20 carbon atoms and is preferably a methylene or polymethylene group.

Each hydrocarbyl group constituting R<1> and R<2> according to the invention (formula 1) can be, for example, an alkyl or alkylene group or a mono- or polyalkyloxyalkyl group. Each hydrocarbyl group is preferably a straight chain alkyl group. The number of carbon atoms in each hydrocarbyl group is preferably 16-40, more preferably 16-24.

It is also preferred that the cyclic system is substituted with only two substituents of the general formula (I) and that A is a methylene group.

Examples of salts of the chemical compounds are the acetate and the hydrochloride.

The compounds can conveniently be prepared by reduction of the corresponding amide which has been prepared by reacting a secondary amine with the appropriate acid chloride. (V) A condensate of long-chain primary or secondary amine with a carboxylic acid-containing polymer.

Specific examples include polymers such as those described in GB-A-2,121,807, FR-A-2,S92,387 and DE-A-3,941,561; and also esters of telemeric acid and alkanolamines as described in US-A-4,639,256; and the reaction product of an amine containing a branched carboxylic acid ester, an epoxide and a monocarboxylic acid ester as described in US-A-4,631,071.

EP-0,283,292 describes amide-containing polymers and EP-0,343,981 describes amine salt-containing polymers.

It should be pointed out that the polar nitrogen compounds may contain other functionality such as ester functionality.

(v) Hydrocarbonated aromatics

These materials are condensates comprising aromatic and hydrocarbon moieties. The aromatic part is suitably an aromatic hydrocarbon which may be unsubstituted or substituted with, for example, non-hydrocarbon substituents.

Such an aromatic hydrocarbon preferably contains a maximum of these substituent groups and/or three fused rings, and is preferably naphthalene. The hydrocarbyl part is a hydrogen- and carbon-containing part connected to the rest of the molecule by a carbon atom. It may be saturated or unsaturated, and straight-chain or branched, and may contain one or more heteroatoms provided they do not significantly affect the hydrocarbyl nature of the moiety. The hydrocarbyl part is preferably an alkyl part, suitably with more than 8 carbon atoms.

(vi) Linear connections

Such compounds include a compound in which at least one substantially linear alkyl group of 10-30 carbon atoms is connected via an optional linking group which may be branched to a non-polymeric residue, such as an organic residue, to provide at least one linear chain of atoms which includes the carbon atoms in said alkyl groups and one or more non-terminal oxygen, sulfur and/or nitrogen atoms. The binding group can be polymer.

By "essentially linear" is meant that the alkyl group is preferably straight-chain, but that straight-chain alkyl groups with a small degree of branching, such as in the form of a single methyl group branching, can be used.

The compound preferably has at least two of said alkyl groups when the linear chain can include the carbon atoms in more than one of said alkyl groups. When the compound has at least three of said alkyl groups, there may be more than one of such linear chains, which chains may overlap. The linear chain or chains may provide part of the linking group between any two such alkyl groups in the compound.

The oxygen atom or atoms, if present, are preferably located directly between the carbon atoms in the chain and can, for example, be in the binding group, if one is present, in the form of a mono- or polyoxyalkylene group, where said oxyalkylene group preferably has 2 -4 carbon atoms, examples being oxyethylene and oxypropylene.

As indicated, the chain or chains include carbon, oxygen, sulfur and/or nitrogen atoms.

The compound can be an ester when the alkyl groups are connected to the rest of the compound as -O-CO n alkyl-, or -CO-0 n alkyl groups, the alkyl groups in the former being derived from an acid and the rest of the compound being derived from a polyhydric alcohol and where in the latter the alkyl groups are derived from an alcohol and the rest of the compound is derived from a polycarboxylic acid. The compound can also be an ether where the alkyl groups are connected to the rest of the compound as -O-n-alkyl groups. The compound can be both an ester and an ether or it can contain different ester groups.

Examples include polyoxyalkylene esters, ethers, esters/ethers and mixtures thereof,

especially those containing at least one, preferably at least two, C10-C30 linear alkyl groups and a polyoxyalkylene glycol group of molecular weight up to 5000, preferably 200-5000, the alkylene group in said polyoxyalkylene glycol containing from 1 to 4 carbon atoms, as described in EP-A-61 895 and in US patent 4,491,455.

The preferred esters, ethers or ester/ethers that can be used can include compounds in which one or more groups (such as 2,3 or 4 groups) of formula -OR<25> are bound to a residue E, where E can for example represent A (alkylene)q, where A represents C or N or is absent, q represents an integer from 1 to 4, and the alkylene group has from 1 to 4 carbon atoms, A (alkylene)q being, for example, N(CH2CH2)3; C(CH 2 ) 4 ; or (CH 2 ) 2 ; and R<25> can independently be

(a) n-alkyl-

(b) n-alkyl-CO-

(c) n-alkyl-OCO-(CH2)n-

(d) n-alkyl-OCO-(CH2)nCO-

where n is, for example, 1-34, where the alkyl group is linear and contains 10-30 carbon atoms. They can for example be represented by the formula R23OBOR24, with R23 and R<24> each defined as for R<25> above, and B represents the polyalkylene segment in the glycol where the alkylene group has 1-4 carbon atoms, for example a polyoxymethylene, polyoxyethylene or polyolcs<y>trimethylene moiety which is substantially linear; some degree of branching with lower alkyl side chains (such as in polyoxypropylene glycol) can be tolerated, but it is preferred that the glycol is substantially linear.

Suitable glycols are generally substantially linear polyethylene glycols (PEG) and polypropylene glycols (PPG) which have a molecular weight from approx. 100 to 5000, preferably from approx. 200 to 2000. Esters are preferred and fatty acids containing 10-30 carbon atoms are useful for reaction with the glycols to form the ester additives, it being preferred to use C1-C4 fatty acid, especially behenic acid. The esters can also be produced by esterification of polyethoxylated fatty acids or polyethoxylated alcohols.

Polyoxyalkylene diesters, -dieters, -ether/esters and mixtures thereof are suitable as additives, diesters being preferred when the petroleum-based component is a narrow boiling range distillate, when smaller amounts of monoethers and monoesters (which are often formed in the manufacturing process) may also be present . It is important for active performance that a greater amount of the dialkyl compound is present. Particularly preferred are stearic acid or behenic acid diesters of polyethylene glycol, polypropylene glycol or polyethylene/polypropylene glycol mixtures.

Examples of other compounds in this general category are those described in JP Patent Publications 2-51477 and 3-34790, and EP-A-117,108 and EP-A-326,356, and cyclic esterified ethoxylates as described in EP-A- 356,256.

(vii) Combat pollens

Comb polymers are discussed in "Comb-Like Polymers. Structure and Properties", N. A. Platé and V. P. Shibaev, J. Poly. Pollock. Macromolecular Revs., 8, pp. 117 to 253 (1974).

In general, comb polymers consist of molecules in which long-chain branches such as hydrocarbyl branches, optionally interrupted by one or more oxygen atoms and/or carbonyl groups, which have 6-30, such as 10-30, carbon atoms, are pendant from a main polymer chain, said branches being attached directly or indirectly to the main chain. Examples of indirect bonding include bonding via intercalated atoms or groups, which bonding may include covalent and/or electrovalent bonding such as in a salt. Comb polymers are generally distinguished by having a minimum molar proportion of units containing such long-chain branches.

Advantageously, the comb polymer is a homopolymer having, or a copolymer in which at least 25 and preferably at least 40, more preferably at least 50, molar percent of its units have, side chains containing at least 6 such as at least 8, and preferably at least 10 atoms, selected for example from carbon , nitrogen and oxygen, in a linear chain or a chain containing a small amount of branching such as a single methyl branch.

As examples of preferred comb polymers, those containing units of the general formula can be mentioned

where

D represents R<11>, COOR<11>, OCOR<1>1, R12COORu or OR11;

■in *y

E represents H, D or R;

G represents H or D;

J represents H, R 1 * 5 , R 10 COOR 11 , or a substituted or unsubstituted aryl or heterocyclic group;

K represents H, COOR<12>, OCOR12, OR<12> or COOH;

L represents H, R<12>, COOR<12>, OCOR<12> or substituted or unsubstituted aryl;

R<11> represents a hydrocarbyl group of 10 or more carbon atoms, and

R<12> represents a hydrocarbyl group which is divalent in the 12COORu group and is otherwise monovalent,

and m and n represent mole ratios where their sum is 1 and m has a finite magnitude and is up to and including 1 and n is from 0 to less than 1, preferably m being in the range of 1.0 to 0.4, n being in the range from 0 to 0.6. R<11> advantageously represents a hydrocarbyl group with from 10 to 30 carbon atoms, preferably 10-24, more preferably 10-18. R<11> is preferably a linear or slightly branched alkyl group and R<12> advantageously represents a hydrocarbyl group with 1-30 carbon atoms when it is monovalent, preferably with 6 or more, more preferably 10 or more, preferably up to 24, more preferably up to 18 carbon atoms. When R<12> is monovalent, it is preferably a linear or slightly branched alkyl group. When R<12> is divalent, it is preferably a methylene or ethylene group. By "weakly branched" is meant that it has a single methyl branch.

The comb polymer can contain units derived from other monomers if this is desirable or necessary, examples being CO, vinyl acetate and ethylene. The invention comprises two or more different comb polymers.

The comb polymers can, for example, be copolymers of maleic anhydride or fumaric acid and another ethylenically unsaturated monomer, e.g. an α-olefin or an unsaturated ester, for example vinyl acetate as described in EP-A-214,786. It is preferred, but not essential, that equimolar amounts of the comonomers are used, although molar proportions in the range from 2 to 1 and 1 to 2 are suitable. Examples of olefins that can be copolymerized with, for example, maleic anhydride include 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and styrene. Other examples of comb polymers include methacrylates and acrylates.

The copolymer may be esterified by any suitable technique, and although it is preferred, it is not essential that the maleic anhydride or fumaric acid be at least 50% esterified. Examples of alcohols that may be used include n-decan-l-ol, n-dodecan-l-ol, n-tetradecan-l-ol, n-hexadecan-l-ol and n-octadecan-l-ol. The alcohols may also include up to one methyl branch per chain, for example 1-methylpentadecan-1-ol, 2-methyltridecan-1-ol as described in EP-A-213,879. The alcohol can be a mixture of normal alcohols and alcohols with a single methyl branch. It is preferred to use pure alcohols instead of alcohol mixtures such as may be commercially available; if mixtures are used, the number of carbon atoms in the alkyl group is taken to be the average number of carbon atoms in the alkyl groups in the alcohol mixture; if alcohols containing a branch at the 1- or 2-positions are used, the number of carbon atoms in the alkyl group is taken to be the number in the straight-chain main chain segment in the alcohol's alkyl group.

The comb polymers may in particular be fumarate or itaconate polymers and copolymers such as, for example, those described in EP patent applications 153,176, 153,177, 156,577 and 225,688, and WO 91/16407.

Particularly preferred fumarate comb polymers are copolymers of alkyl fumarates and

vinyl acetate, in which the alkyl groups have 12-20 carbon atoms, more particularly polymers in which the alkyl groups have 14 carbon atoms or in which the alkyl groups are a mixture of C14/C16 alkyl groups, prepared for example by solution copolymerization of an equimolar mixture of fumaric acid and vinyl acetate and reaction of the resulting copolymer with the alcohol or mixture of alcohols, which are preferably straight chain alcohols. When the mixture is used, it is advantageously a 1:1, calculated by weight, mixture of normal C14 and Ci6 alcohols. Furthermore, mixtures of the Cn ester with the mixed CWCie ester can be used with advantage. In such mixtures, the ratio of C14 to C14/C16 is advantageously in the range from 1:1 to 4:1, preferably from 2:1 to 7:2, and most preferably approx. 3:1, calculated by weight. The particularly preferred fumarate comb polymers can, for example, have a number average molecular weight in the range 1000-100,000, preferably 1000-50,000, measured by vapor phase osmometry (VPO).

Other suitable comb polymers are the polymers and copolymers of α-olefins and esterified copolymers of styrene and maleic anhydride, and esterified copolymers of styrene and fumaric acid as described in EP-A-282,342; mixtures of two or more comb polymers can be used in the present invention and, as indicated above, such use can be advantageous.

Other examples of comb polymers are hydrocarbon polymers such as copolymers of ethylene and at least one α-olefin, preferably the α-olefin having at most 20 carbon atoms, examples being n-octene-1, iso-octene-1, n-decene-1 and -dodecene-1, n-tetradecene-1 and n-hexadecene-1 (for example as described in WO9319106).

The number average molecular weight measured by gel permeation chromatography against polystyrene standards of such a copolymer is for example preferably up to 30,000 or up to 40,000. The hydrocarbon copolymers can be prepared by methods known in the art, for example using a Ziegler-type catalyst. Such hydrocarbon polymers can, for example, have an isotacticity of 75% or higher.

As described above, cold flow improving co-additives can provide synergistic improvements to lubricity performance in combination with the mixture of esters (a) and (b).

Additional co-additives that may be used are those known in the art, for example, detergents, antioxidants, corrosion inhibitors, haze removers, demulsifiers, metal deactivators, antifoams, combustion improvers such as cetane improvers, co-solvents, gasket compatibilizers, reodorants and metal-based additives. such as metallic combustion enhancers.

Determination of the beneficial effects of the invention's various aspects

It is believed that the mixture of esters (a) and (b) is capable of forming at least partial layers of a lubricating composition on certain metal surfaces. This means that the layer that is formed is not necessarily complete on the contact surface. The formation of such layers and the degree of their coverage of the contact surface can be demonstrated, for example, by

measurement of electrical contact resistance or electrical capacitance.

A test that can be used to demonstrate one or more of a reduction in wear, a reduction in friction, or an increase in electrical contact resistance according to the present invention is the high frequency reciprocating rig test (or "HFRR"), described in Standard Test Methods CEC PF 06-T -94 or ISO/TC22/SC7/WG6/N188.

The degree to which an additive composition causes blockage of fuel oil leaching filters can be measured using a known filterability test. For example, a method for measuring the filterability of fuel oil compositions is described in the Institute of Petroleum's Standard designated "IP 387/190" and under the title "Determination of filter blocking tendency of gas oils and distillate diesel fuels". In summary, a sample of the fuel oil composition to be tested is passed at a constant discharge rate through a glass fiber filter medium; the pressure drop across the filter is monitored, and the volume of fuel oil passing the filter medium within a prescribed pressure drop is measured. The filter blocking tendency of a fuel composition can be described as the pressure drop across the filter medium required for 300 ml of fuel to pass at a rate of 20 ml/min. Reference is made to the above-mentioned Standard for further information. When determining the additive composition according to the present invention, this method was adapted by performing the measurements at different temperatures lower than those specified in the said Standard, in order to simulate cold storage conditions that occur in the relevant area.

The invention is further illustrated with reference to the following examples.

Example 1

The following materials and procedures were used.

Fuel oil

A "Class I" diesel fuel oil with the following properties:

Additives

Additives A, B, C and D were added to the diesel fuel oil in the quantities indicated in Table 1, and the filterability of each of the fuel compositions was determined according to the IP 387/90 test at the temperatures shown in Table 1.1 each case was tested - the refrigerant composition, after thorough mixing, cooled to the required temperature in a refrigeration unit and stored at temperatures for the specified period of time before being subjected to the filtration test. Additive A was prepared by esterifying a commercial mixture of oleic and linoleic acids with glycerol, to form a mixed ester product with the following predominant constituents (a) glycerol monooleate and (b) glycerol monolinoleate, in approximately equal amounts by weight, with smaller amounts of glycerol di- and - trioleate and -linoleate also present. In addition, the acid mixture contained a smaller proportion of other acids, whose esters were not thought to represent more than approx. 6% by weight of the mixed ester product

Additive B was prepared by esterification of oleic acid with glycerol, to form a product in which the predominant component was glycerol monooleate (additive D in WO 94/17160).

Additive C was prepared by esterification of linoleic acid with glycerol, to form a product in which the predominant component was glycerohnonoUnolate.

Additive D was a 1:1 molar mixture of additive B and additive C.

In Table 1, the test results show the pressure drop across the filter at the end of each test, where a higher pressure drop indicates a greater degree of partial filter blockage. When the pressure drop was greater than 103.4 kPa during the 15 minute test, the test time at which this pressure was reached was recorded (103.4 kPa, corresponds to strong filter blockage and is considered for these purposes as a failed test).

It appears from the results in Table 1 that sample 2 (fuel composition according to the invention) showed surprisingly improved filterability compared to sample 3 (comparative fuel composition containing additive D in WO 94/17160), both at 0°C and -10°C. Furthermore, although both samples exceeded 103.4 kPa in the test after 1 week at -10°C, sample 2 was a better performer (exceeding this pressure drop just before the end of the 15 minute test as opposed to sample 3 which exceeded this pressure drop almost immediately).

Furthermore, the results at -5°C indicate that samples 2 and 5 (fuel compositions according to the invention) showed greatly improved filterability compared to samples 3 and 4 (combination samples), these two comparison examples both failing the test. Sample 2 containing additive A (produced by esterification of a mixture of starting acids) also surprisingly showed improved performance compared to sample 5 containing additive D (produced by mixing the component esters).

Example 2

A small aliquot of each of the samples in Example 1 stored at -5°C for 2 weeks was removed immediately prior to the filtration step as described in Example 1, and HFRR performance at 60°C for each aliquot measured as an indication of "pre-filtration <l>, lubricity performance. The HFRR performance at 60°C for each corresponding sample filtrate prepared in Example 1 was also measured as an indication of "post-filtration" lubricity performance. The results are summarized in Table 2 below.

The results in Table 2 indicate that samples 3 and 4 (comparatives) show significantly worse lubricity performance after filtration (ie, a larger wear mark), in contrast to samples 2 and 5 (fuel compositions according to the invention) which maintained their lubricity performance.

The untreated fuel (sample 1) showed no change, confirming that the differences in the results for other samples are due to the additives present in the compositions.

The differences in wear mark diameter after filtration indicate a significant technical improvement and illustrate the improved lubricity properties provided by blends of esters (a) and (b) over comparative additives.

Claims (11)

1. Additive for a fuel oil composition comprising a major portion of a middle distillate fuel oil having a sulfur content of 0.2% by weight or less, characterized in that the additive is lubricating and includes: (a) an ester of a mono-unsaturated monocarboxylic acid and a polyhydric alcohol , and (b) an ester of a polyunsaturated monocarboxylic acid and a polyhydric alcohol having at least three hydroxy groups, wherein the esters (a) and (b) are different and both are partial esters, and the relative weight proportions of (a) and (b) are in the range from 1:10 to 2:1. 2. Additive according to claim 1, characterized in that the fuel oil has a sulfur content of 0.1% by weight or less. 3. Additive according to claim 1 or 2, characterized in that the fuel oil is a diesel fuel. 4. Additive according to any one of the preceding claims, characterized in that the (a)er is an ester of a polyhydric alcohol having at least three hydroxy groups. 5. Additive according to any one of the preceding claims, characterized in that (a) and (b) are esters of alkenyl monocarboxylic acids. 6. Additive according to claim 5, characterized in that both acids have alkenyl groups with 10 to 36 carbon atoms. 7. Additive according to any one of claims 4 to 6, characterized in that (a) and (b) are both esters of trihydric alcohols, especially glycerol. 8. Additive according to claim 7, characterized in that (a) and (b) are both monoesters. 9. Additive according to claim 8, characterized in that (a) is a monoester of oleic acid and glycerol, and (b) is a monoester of linoleic acid and glycerol. 10. Use of an additive according to any one of the preceding claims to improve the lubricity of middle distillate fuel oil. 11. Use of an additive according to any one of claims 1 to 9, in a combustion device to reduce the degree of wear in said device's fuel delivery system.