KR19990028955A - Additives and Fuel Oil Compositions - Google Patents

Abstract

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

Description

Additives and Fuel Oil Compositions

The growing interest in the environment has tended to significantly reduce the emission of toxic components during fuel oil combustion, especially in engines such as diesel engines. For example, attempts have been made to minimize sulfur dioxide emissions. As a result, attempts have been made to minimize the sulfur content of fuel oils. For example, typical diesel fuel oils contained at least 1% by weight sulfur (based on elemental sulfur), but at present the sulfur level is preferably 0.05% by weight, advantageously less than 0.01% by weight, in particular less than 0.001% by weight. It is considered desirable to reduce.

Further refinement of the fuel oil to achieve this low sulfur level often reduces the level of polar components. In addition, the level of multinuclear aromatic compounds present in such fuel oils may be reduced by the purification process.

Reducing one or more of the sulfur, polynuclear aromatic, or polar components of diesel fuel oil reduces the ability of the fuel oil to lubricate the injection system of the engine, such that, for example, the engine's fuel injection pump may fail earlier than the engine's life. Fuel injection systems such as high pressure rotary distributors, in-line pumps and injectors can fail. The poor lubricity problem of diesel fuel oil is a further problem in the development of future engines that require better lubricity than current engines to further reduce the emission of toxic components. For example, the emergence of high pressure unit injectors is believed to increase the demand for lubricity of fuel oil.

Similarly, poor lubrication can lead to wear problems in other mechanical devices that rely on fuel oil inherent lubrication.

Lubricating additives for fuel oils are described in the art. WO 94/17160 describes additives comprising esters of carboxylic acids having 2 to 50 carbon atoms and alcohols having at least one carbon atom. Glycerol monooleate is specifically exemplified. Although general mixtures have been considered, no specific ester mixtures have been presented.

US-A-3,273,981 is A + B (A is a polyacid, or a polyacid ester obtained by reacting a polyacid with a C ₁ -C ₅ monohydric alcohol; B is a partial ester of polyhydric alcohol and fatty acid, for example Lubricating additives which are a mixture of glyceryl monooleate, sorbitan monooleate or pentaerythritol monooleate) are disclosed. This mixture has use as a jet fuel.

In some situations, however, it has been unexpectedly found that this prior art ester facilitates the blockage of fuel filters, particularly the micro-mesh filters typically present in diesel vehicle fuel lines. This filter-blocking problem results in insufficient fuel flow and poor engine operation, which is particularly pronounced at low temperatures.

Moreover, it has been unexpectedly found that fuels containing the preferred esters (additive D) described in WO 94/17160 lose their lubricity after cold storage and filtration. The loss of lubricity can be evident even in the absence of serious filter clogging problems. The loss of lubrication itself presents a significant problem, since in practice the stored fuel oil typically applies to temperature cycles and must be able to give effective lubrication to the machinery behind the process of the fuel line filter. In diesel vehicle fuel systems, for example, diesel fuel must first flow through the fine-grade filter before reaching the fuel injection system including the injection pump. The reduced lubricity after filtration increases the wearability of the injection system.

There is therefore a need for improved lubricity additives that exhibit better filterability but do not lose performance after filtration following subsequent cold storage periods in fuel oil.

This problem has recently been solved by additives comprising certain mixtures of certain esters.

GB-A-1,505,302 discloses ester mixtures comprising, for example, glycerol monoesters and glycerol diesters as diesel fuel additives, which mixtures reduce the abrasion of fuel-injection devices, piston rings and cylinder liners. It is described as having the advantage. However, GB-A-1,505,302 relates to solving the operational disadvantages of corrosion and wear by acidic combustion products which are residues in combustion chambers and exhaust systems. The document states that the disadvantage is due to incomplete combustion under certain operating conditions. Typical diesel fuels available at the time of this writing contain, for example, from 0.5 to 1% by weight of elemental sulfur, based on the weight of the fuel.

US-A-3,287,273 describes lubricating additives which are the reaction products of dicarboxylic acids and oil-insoluble glycols. Acids are typically predominantly dimers of unsaturated fatty acids such as linoleic acid or oleic acid, although small amounts of monomeric acid may be present. In particular only alkane diols or oxa-alkane diols are shown as glycol reactants.

Summary of the Invention

Thus, as a first aspect the present invention relates to (a) esters of unsaturated monocarboxylic acids and polyhydric alcohols, and (b) esters of polyhydric alcohols having unsaturated monocarboxylic acids and three or more hydroxy groups (esters (a) and esters (b) are different). Fuel oil composition comprising a small amount of lubricant additive, and a large amount of middle distillate fuel oil having a sulfur content of 0.2% by weight or less.

In a second aspect, the present invention provides the use of an additive as defined in the first aspect for improving the lubricity of an intermediate distillate fuel oil.

In a third aspect, the present invention provides the use of the fuel composition of the first aspect for reducing the wear rate in the fuel supply system of the combustion device.

In another aspect, the invention provides a small amount of a lubricity additive comprising a blend of two different esters, each made from an unsaturated monocarboxylic acid and a polyhydric alcohol, and a polyhydric alcohol having an unsaturated monocarboxylic acid and three or more hydroxy groups, and 0.2 weight To reduce the wear rate of the fuel supply system of the combustion device, comprising adding fuel having intermediate distillate fuel oil containing up to% sulfur to the device in an amount effective to reduce the wear rate of the fuel supply system of the combustion device. Provide a method.

Mixtures of esters (a) and (b) can provide unexpectedly improved lubricity compared to the individual performance of components (a) and (b). Moreover, the mixture of (a) and (b) shows improved filterability and maintains good lubricity even after filtration following cold storage.

The invention will now be described in more detail.

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

Fuel Oil Compositions (First Aspect of the Invention)

(i) additives

The term "polyhydric alcohol" is used to describe compounds having two or more hydroxy groups. (a) is preferably an ester of a polyhydric alcohol having three or more hydroxy groups.

Examples of polyhydric alcohols having three or more hydroxy groups include 3 to 10, preferably 3 to 6, more preferably 3 or 4 hydroxy groups and 2 to 90, preferably 2 to 30, in the molecule. Dogs, more preferably 2 to 12, most preferably 3 or 4 carbon atoms. Such alcohols may be aliphatic, saturated or unsaturated, straight or branched chain, or cyclic derivatives thereof. Saturated aliphatic straight alcohols are preferred.

Advantageously, both (a) and (b) are esters of trihydric alcohols, in particular esters of glycerol or trimethylol propane. Other suitable polyhydric alcohols include pentaerythritol, sorbitol, mannitol, inositol, glucose and fructose.

The unsaturated monocarboxylic acids used to prepare the esters may have alkenyl, cyclo alkenyl or aromatic hydrocarbyl groups bonded to carboxylic acid groups. The term "hydrocarbyl" refers to a group containing carbon and hydrogen, which may be straight and branched and bonded to a carboxylic acid group by a carbon-carbon bond. Hydrocarbyl groups may be blocked by one or more heteroatoms such as O, S, N or P.

Both (a) and (b) preferably have alkenyl groups having 10 to 36, such as 10 to 22, more preferably 18 to 22, in particular 18 to 20 carbon atoms. Preference is given to esters of kenyl monocarboxylic acids. Alkenyl groups can be mono-unsaturated or polyunsaturated. It is particularly preferred that (a) is an ester of monounsaturated alkenyl monocarboxylic acid and (b) is an ester of polyunsaturated alkenyl monocarboxylic acid. The polyunsaturated acid is preferably a di- or tri-unsaturated acid. Such acids may be derived from natural substances, for example vegetable or animal extracts.

Particularly preferred mono-unsaturated acids are oleic acid and elaidic acid. Particularly preferred polyunsaturated acids are linoleic acid and linolenic acid.

Mixtures in which (a) is an ester of monounsaturated acid and (b) is an ester of polyunsaturated acid have particularly good lubricity and show particularly good filterability and resistance to cold storage.

The ester may be a partial or complete ester, that is, some or all of the hydroxy groups of each polyhydric alcohol may be esterified. It is preferred that at least one of (a) or (b) is a partial ester, in particular a monoester. Particularly good performance is that (a) and (b) are both partial esters and especially both monoesters.

Esters can be prepared by methods well known in the art, for example by condensation reactions. In some cases, the alcohol may be reacted with an acid derivative such as anhydride or acid chloride to facilitate the reaction and increase the yield.

The esters (a) and (b) can be prepared separately and then mixed together, either before addition to the fuel, or by mixing (a) and (b) separately to the fuel at the same or different times. can do. Alternatively, the ester mixture can be prepared directly from a mixture of suitable starting materials. The latter product (ie ester mixture formed directly from the reaction of a mixture of starting materials) has been found to have particularly good filterability and especially good lubricity. In particular, commercially available mixtures of suitable acids can be reacted with selected alcohols such as glycerol to produce the mixed esters according to the invention. Particularly preferred commercial acid mixtures are those comprising oleic acid and linoleic acid. In such mixtures, small amounts of other acids, or acid polymerization products may be present, but the proportion is preferably 15% by weight, more preferably 10% by weight or less, and most preferably 5% by weight or less of the total acid mixture. Should not exceed

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

Very preferred ester mixtures are obtained by reacting a mixture of oleic acid and linoleic acid with glycerol, which preferably comprises approximately equal parts by weight of (a) glycerol monooleate and (b) glycerol monolinoleate.

In addition to esters (a) and (b), the lubricity additives further comprise small amounts of other esters, for example, prepared during the esterification of the acid mixtures described above.

(ii) fuel oil

The fuel oil may be a petroleum fuel oil, suitably a middle distillate fuel oil, ie a fuel oil obtained by refining crude oil as a fraction between the lighter kerosene and jet fuel fractions and the heavy fuel oil fraction. Such distillate fuel oils generally boil above about 100 ° C. The fuel oil may comprise an air or vacuum distillate, or a blend of any proportion of fractionated diesel or direct current distillates with thermally and / or catalytically fractionated distillates. The most common petroleum fuel oils are kerosene and jet fuels, 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, most preferably 0.001% by weight or less, based on the weight of the fuel oil. The prior art describes methods for reducing the sulfur content of hydrocarbon middle distillate fuels, such as methods involving solvent extraction, sulfuric acid treatment and hydrodesulphurisation.

Preferred fuel oils have a cetane number of at least 40, preferably at least 45 and more preferably at least 50. The fuel oil may have such cetane number prior to the addition of any cetane improver or the cetane number of the fuel may be increased by adding the cetane improver.

More preferably, the cetane number of fuel oil is 52 or more.

(iii) throughput

The concentration of the additive in the fuel oil (based on the active ingredient) is for example 10 to 5,000 ppm by weight, for example 50 to 2000 ppm, preferably 75 to 300 ppm, more preferably 100 to 200, per weight of the fuel oil. Weight ppm.

The relative weight ratio of (a) and (b) in the fuel oil is 1:10 to 10: 1, preferably 1: 4 to 4: 1, more preferably 1: 2 to 2: 1. The ratio of 1: 1 is the most preferable.

Use of Additives (Second Aspects of the Invention) and Methods (Fourth Aspects of the Invention)

Preferred additives for the second and fourth aspects of the invention are those described in connection with the first aspect.

The fuel oils of the second and fourth aspects of the invention are preferably those described in connection with the first aspect.

Use of Fuel Compositions (Third Aspect of the Invention)

When the fuel oil is a diesel fuel, the fuel oil composition of the first aspect of the present invention is intended for use as a fuel in diesel (compression-ignition) engines in addition to providing excellent combustibility, as well as reducing wear in fuel supply systems, in particular fuel injection pumps. Have The use of such fuels therefore extends the operating life of the device and reduces the need to replace expensive mechanical parts.

Similarly, the fuel oil composition of the first aspect of the present invention can be applied to other fuel oil systems that are prone to wear because the mechanical device in the fuel supply system depends on the fuel oil for lubrication.

concentrate

Concentrates comprising additives as a mixture with a carrier liquid (eg a solution or dispersion) are useful as a means for introducing the additives into the fuel oil stock solution, which can be carried out by methods known in the art. The concentrate may optionally contain other additives, preferably from 3 to 75% by weight, more preferably from 3 to 60% by weight and most preferably from 10 to 50% by weight as a solution in oil. It contains. Examples of carrier solutions include hydrocarbon solvents such as organic solvents including petroleum fractions such as naphtha, kerosene, diesel and heater oils; Aromatic fractions such as aromatic hydrocarbons such as those sold under the trade name "SOLVESSO"; Paraffinic hydrocarbons such as hexane, pentane and isoparaffins; And oxygenated solvents such as alcohols. Of course, the carrier liquid should be chosen with miscibility in mind with the additive and the fuel. A sufficient amount of concentrate is added to the fuel oil stock to provide the throughput of the additives described above.

The additive of the present invention may be added to the fuel oil stock solution by a method such as known in the art. If co-additives are required, they may be added at the same time or at different times with the additives of the invention.

Supplementary Additives

The fuel composition of the first aspect of the invention may further comprise other known lubricant-enhancing compounds, for example mono- or polycarboxylic acids such as dicarboxylic acids, as co-additives. These acids are preferably mixtures of polymerized unsaturated fatty acids comprising mainly dimers and some trimer acids with small amounts of monomers and / or higher polymers. Typical examples are dimer acids of oleic acid, linoleic acid or mixtures thereof. Esters of these acids with mono or dihydric alcohols are also used in combination with mixtures of esters (a) and (b) to provide even more improved additives.

Similarly, ethoxylated-amine type lubricity co-additives can be used.

The fuel oil of the first aspect of the invention also advantageously comprises (i) an ethylene-unsaturated ester copolymer; (ii) hydrocarbon polymers; (iii) sulfur carboxy compounds; (iv) polar compounds; (v) hydrocarbylated aromatics; (vi) linear compounds; And (vii) one or more fuel oil cold flow improvers, such as comb polymers, as co-additives.

(i) ethylene-unsaturated ester copolymers

Ethylene copolymer flow improvers, such as ethylenically unsaturated ester copolymer flow improvers, have a polymethylene backbone that is segmented by hydrocarbyl side chains blocked by one or more oxygen atoms and / or carbonyl groups.

More particularly, the copolymer is a unit of formula -CR ⁵ R ⁶ -CHR ⁷ -in addition to units derived from ethylene, wherein R ⁶ is hydrogen or methyl group; R ⁵ is -OOCR or -COOR ⁸ group, R ⁸ is hydrogen or C ₁ -C ₉ , preferably C ₁ -C ₆ , more preferably C ₁ -C ₃ straight or branched alkyl group; R ⁷ is hydrogen or —COOR ⁸ or —OOCR ⁸ group Ethylene copolymers).

These may include copolymers of ethylene and ethylenically unsaturated esters or derivatives thereof. Esters of unsaturated carboxylic acids such as, for example, ethylene-acrylate (for example ethylene-2-ethylhexyl acrylate) with copolymers of ethylene, but the esters are preferably saturated as described in GB-A-1,263,152 Esters of carboxylic acids and unsaturated alcohols. Ethylene-vinyl ester copolymers are advantageous, with ethylene-vinyl acetate, ethylene vinyl propionate, ethylene-vinyl hexanoate, ethylene 2-ethylhexanoate or ethylene-vinyl octanoate copolymers being preferred. Preferably, the copolymer contains 1 to 25 mol%, such as 1 to 20 mol%, more preferably 3 to 15 mol%, of vinyl esters, such as less than 25 mol%. They may also be in the form of a mixture of two copolymers such as those described in US-A-3,961,916 and EP-A-113,581. Preferably, the number average molecular weight of the copolymer measured by vapor phase osmotic pressure measurement is 1,000 to 10,000, more preferably 1,000 to 5,000. If desired, the copolymer may be derived from additional comonomers, which may be terpolymers or quaternary polymers or higher polymers (for example, these may be further comonomers isobutylene or diisobutylene or another Esters to produce different units of the above formula and the mole% of the aforementioned esters relates to the total esters).

The copolymer may also include small amounts of chain transfer agents and / or molecular weight modifiers (eg acetaldehyde or propionaldehyde) that can be used in the polymerization process to prepare the copolymer.

Copolymers can be prepared by direct polymerization of comonomers. Such copolymers can be prepared by transesterification or hydrolysis and reesterification of the ethylenically unsaturated ester polymers to produce different ethylenically unsaturated ester copolymers. For example, ethylene vinyl hexanoate and ethylene vinyl octanoate copolymers can be prepared in this way, for example from ethylene vinyl acetate copolymers.

The copolymer may have, for example, 15 or less, preferably 10 or less, more preferably 10 or less methyl-terminated side branched chains, excluding methyl groups and terminating methyl groups on the comonomer esters, as determined by nuclear magnetic resonance methods. Preferably 6 or less, most preferably 2 to 5.

The copolymer has a polydispersity index of 1 to 6, preferably 2 to 4, which is the ratio of weight average molecular weight to number average molecular weight as measured by gel permeation chromatography using polystyrene standards.

(ii) hydrocarbon polymer

Linear hydrocarbon polymer

They optionally have one or more polymethylene backbones segmented by short-chain hydrocarbyl groups, ie hydrocarbyl groups having up to 5 carbon atoms.

For example, it is represented by the following chemical formula.

Wherein T is H or R ¹ , U is H, T or substituted or unsubstituted aryl, R ¹ is a hydrocarbyl group having up to 5 carbon atoms, v and w are molar ratios, v is 1.0 to 0.0 and w is 0.0 to 1.0. Preferably R ¹ is a straight or branched chain alkyl group.

Such polymers may be prepared directly from ethylenically unsaturated monomers or by hydrogenating polymers made from monomers such as isoprene and butadiene.

Preferred hydrocarbon polymers are copolymers of ethylene and one or more α-olefins. 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 such as olefins other than α-olefins and non-conjugated dienes. Preferred copolymers are ethylene-propylene copolymers. Two or more different ethylene-α-olefin copolymers of this type are also within the scope of the present invention.

The number average molecular weight of the ethylene-α-olefin copolymers relative to polystyrene standards as measured by gel permeation chromatography (GPC) is less than 150,000. In some applications, at least 60,000 is advantageous and is preferably at least 80,000. Although there is no upper limit in terms of function, the molecular weight is preferably in the range of 60,000 and 80,000 to 120,000 because the mixing becomes difficult due to the increase in viscosity when the molecular weight is about 150,000. In other applications the molecular weight is 30,000, preferably less than 15,000, for example less than 10,000 or 6,000.

Advantageously, the copolymer has an ethylene content of 50 to 85 mole percent. More advantageously, the ethylene content is 55 to 80%, preferably 55 to 75%, more preferably 60 to 70% and most preferably 65 to 70%.

Examples of ethylene-α-olefin copolymers are ethylene-propylene copolymers having an ethylene content of 60 to 75 mol% and a number average molecular weight of 60,000 to 120,000, particularly preferred copolymers having a ethylene content of 62 to 71 mol% and a molecular weight of Ethylene-propylene copolymers of 80,000 to 100,000.

The copolymer can be prepared by any method known in the art, for example using a Ziegler type catalyst. Advantageously, the polymer is substantially amorphous because the highly crystalline polymer is relatively insoluble in fuel oil at low temperatures.

(iii) sulfur carboxy compounds

For example, those described in EP-A-0,261,957 describing the use of compounds of the formula:

Wherein -YR ² is -SO ₃ ^{(-) (+)} NR ³ ₃ R ² , -SO ₃ ^{(-) (+)} HNR ³ ₂ R ² , -SO ₃ ^{(-) (+)} H ₂ NR ³ R ² , —SO ₃ ^{(−) (+)} H ₃ NR ² , —SO ₂ NR ³ R ² or —SO ₃ R ² ; -XR ¹ is -YR ² or -CONR ³ R ¹ , -CO ₂ ^{(-) (+)} NR ³ ₃ R ¹ , -CO ₂ ^{(-) (+)} HNR ³ ₂ R ¹ , -R ⁴ -COOR ₁ , -NR ³ COR ¹ , -R ⁴ OR ¹ , -R ⁴ OCOR ¹ , -R ⁴ , R ¹ , -N (COR ³ ) R ¹ or Z ^{(−) (+)} NR ³ ₃ R ¹ ; -Z ^(-) is SO ₃ ^(-) or -CO ₂ ^(-) .

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 may be the same or different and R ⁴ is absent or C ₁ -C ₅ alkylene, In which the carbon-carbon bond (CC) may be part of a cyclic structure which is (a) ethylenically unsaturated when A and B are alkyl, alkenyl or substituted hydrocarbyl groups, or (b) aromatic, polynuclear aromatic or cycloaliphatic, XR ¹ and YR ² contain at least three alkyl, alkoxyalkyl or polyalkoxyalkyl groups between them.

Multicomponent additive systems may be used and the ratio of additives to be used will depend on the fuel to be treated.

(iv) polar compounds

Such compounds may be amino or imino substituents substituted with one or more, preferably two or more hydrocarbyl group (s) (monovalent and containing from 8 to 40 carbon atoms) (one or more of these substituents are optionally in the form of the cation from which they are derived). Oil-soluble polar nitrogen compounds). Oil soluble polar nitrogen compounds are ionic or nonionic and can act as wax crystal growth modifiers in fuels. Preferably, the hydrocarbyl group is linear or slightly linear, ie may have one short chain (1 to 4 carbon atoms) hydrocarbyl branch. If the substituent is amino, it may carry one or more hydrocarbyl groups, which may be the same or different.

The term "hydrocarbyl" is a group having carbon atoms bonded directly to the rest of the molecule and having hydrocarbons or of predominantly hydrocarbon character. For example aliphatic (eg alkyl or alkenyl), cycloaliphatic (eg cycloalkyl or cycloalkenyl), aromatic and cycloaliphatic-substituted aromatics, and aromatic-substituted aliphatic and cycloaliphatic groups Hydrocarbon group. Aliphatic groups are advantageously saturated. These groups may contain non-hydrocarbon substituents, provided that the non-hydrocarbon substituents do not alter the major hydrocarbon properties of the group. Examples include keto, halo, hydroxy, nitro, cyano, alkoxy and acyl. If the hydrocarbyl group is substituted, a mono (mono) substituent is preferred.

Examples of substituted hydrocarbyl groups include 2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl, 2-ketopropyl, ethoxyethyl and propoxypropyl. Groups also contain atoms other than carbon in the chain or ring consisting of or alternatively carbon. Suitable here include, for example, nitrogen, sulfur and preferably oxygen.

More particularly amino or imino substituents or each of them are attached to the moiety via an intermediate linking group such as -CO-, -CO ₂ ^(-) , -SO ₃ ^(-) or hydrocarbylene. When the linking group is anionic, the substituent is part of the cationic group, as in the amine salt group.

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

Suitable amino substituents are long chain C ₁₂ -C ₄₀ , preferably C ₁₂ -C ₂₄ alkyl primary, secondary, tertiary or quaternary amino substituents.

Preferably the amino substituents are dialkylamino substituents, which may be in the form of amine salts as described above, and the tertiary and quaternary amines may only form amine salts. The alkyl groups can be the same or different.

Examples of amino substituents include dodecylamino, tetradecylamino, cocoamino and hydrogenated tallow amino. Examples of secondary amino substituents include dioctadecylamino and methylbehenylamino. Mixtures of amino substituents may be provided as derived from natural amines. Preferred amino substituents are secondary hydrogenated tallows wherein the alkyl group is derived from hydrogenated tallow fat and typically consists of about 4 wt% C ₁₄ , 31 wt% C ₁₆ and 59 wt% C ₁₈ n-alkyl groups Amino substituents.

Suitable imino substituents are long chain C ₁₂ -C ₄₀ , preferably C ₁₂ -C ₂₄ alkyl substituents.

The moiety is monomeric (cyclic or non-cyclic) or polymeric. If acyclic, it can be obtained from cyclic precursors such as anhydride or spirobilaclactone.

The cyclic ring system may comprise a homocyclic, heterocyclic or fused polycyclic structure, and may include a system in which two or more cyclic structures are bonded to each other and the cyclic structures may be the same or different. If there are two or more cyclic structures, the substituents may be the same or different structures, preferably the same structure. Preferably the cyclic structure or each of them is aromatic, more preferably a benzene ring. Most preferably, the cyclic ring system is a single benzene ring which may optionally be further substituted when it is desired that the substituent is in the ortho or meta position.

The ring atoms in the cyclic structure (s) are preferably carbon atoms but may include, for example, one or more ring N, S or O atoms, in which case the compound is a heterocycle compound.

Examples of such polycycle structures include (a) condensed benzene structures such as naphthalene, anthracene, phenanthrene and pyrene; (b) condensed ring structures in which all or part of the ring is not benzene, such as azulene, indene, hydroindene, fluorene and diphenylene oxide; (c) a ring bonded to the "end" such as diphenyl; (d) heterocycle compounds such as quinoline, indole, 2,3-dihydroindole, benzofuran, coumarin, isocoumarin, benzothiophene, carbazole and thiodiphenylamine; (e) non-aromatic or partially saturated ring systems such as decalin (ie decahydronaphthalene), α-pinene, cardinene and bonylene; (f) three-dimensional structures such as norbornene, bicycloheptane (ie norbornane), bicyclooctane and bicyclooctene.

Examples of polar nitrogen compounds are described below:

(I) for example amine salts and / or amides of mono- or poly-carboxylic acids having 1 to 4 carboxylic acid groups. For example, it may be prepared by reacting at least one molar proportion of hydrocarbyl substituted amine with one mole part of an acid or anhydride thereof.

When the amide is formed, the linking group is -CO- and when the amine salt is formed, the linking group is -CO ₂ ^(-) .

The residue can be cyclic or acyclic. Examples of cyclic moieties are those wherein the acid is cyclohexane 1,2-dicarboxylic acid, cyclohexane 1,2-dicarboxylic acid, cyclopentane 1,2-dicarboxylic acid and naphthalene dicarboxylic acid. Generally, such acids have 5 to 13 carbon atoms in the cyclic moiety. Preferred cyclic acids are benzene dicarboxylic acids such as phthalic acid, isophthalic acid and terephthalic acid and benzene tetracarboxylic acids such as pyromellitic acid, with phthalic acid being particularly preferred. US-A-4,211,534 and EP-A-272,889 describe polar nitrogen compounds containing such moieties.

Examples of acyclic residues are those in which the acid is a long chain alkyl or alkylene substituted dicarboxylic acid such as succinic acid, as described in US-A-4,147,520.

Another example of an acyclic residue is that the acid is a nitrogen-containing acid such as ethylene diamine tetraacetic acid.

Further examples are residues obtained by the reaction of dialkyl spirobilactone with amines.

(II) EP-A-0,261,957 describes polar nitrogen compounds according to the formula:

Wherein -YR ² is -SO ₃ ^{(-) (+)} NR ₃ R ² , -SO ₃ ^{(-) (+)} HNR ³ ₂ R ² , -SO ₃ ^{(-) (+)} H ₂ NR ³ R ² , —SO ₃ ^{(−) (+)} H ₃ NR ² , —SO ₂ NR ³ R ² or —SO ₃ R ² ; -XR ¹ is -YR ² or -CONR ³ R ¹ , -CO ₂ ^{(-) (+)} NR ³ ₃ R ¹ , -CO ₂ ^{(-) (+)} HNR ³ ₂ R ¹ , -R ⁴ -COOR ₁ , -NR ³ COR ¹ , -R ⁴ OR ¹ , -R ⁴ OCOR ¹ , -R ⁴ , R ¹ , -N (COR ³ ) R ¹ or Z ^{(−) (+)} NR ³ ₃ R ¹ ; -Z ^(-) is SO ₃ ^(-) or -CO ₂ ^(-) .

R ¹ and R ² are alkyl, alkoxyalkyl or polyalkoxyalkyl having 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 C ₁ -C ₅ alkylene, In which the carbon-carbon bond (CC) may be part of a cyclic structure which is (a) ethylenically unsaturated when A and B are alkyl, alkenyl or substituted hydrocarbyl groups, or (b) aromatic, polynuclear aromatic or cycloaliphatic, XR ¹ and YR ² preferably contain at least three alkyl, alkoxyalkyl or polyalkoxyalkyl groups between them.

Multicomponent additive systems may be used and the ratio of additives to be used will depend on the fuel to be treated.

(III) EP-A-0,316,108 includes (a) sulfosuccinic acid, (b) esters or diesters of sulfosuccinic acid, (c) amides or diamides of sulfosuccinic acid or (d) amines or diamines of ester-amides of sulfosuccinic acid. Describe the salt.

(IV) A compound comprising a cyclic ring system, carrying two or more substituents of formula I on a ring system:

-A-NR ¹ R ²

Wherein A is a straight or branched aliphatic hydrocarbyl group, optionally interrupted by one or more heteroatoms, R ¹ and R ² are the same or different and each independently 9 to 9, optionally interrupted by one or more heteroatoms Hydrocarbyl containing 40 carbon atoms, wherein the substituents are the same or different and the compound is optionally in its salt form.

Preferably, A has 1 to 20 carbon atoms and is preferably a methylene or polymethylene group.

In the present invention, each hydrocarbyl group constituting R ¹ and R ² is, for example, an alkyl or alkylene group or a mono- or polyalkoxyalkyl group. Preferably each hydrocarbyl group is a straight chain alkyl group. The number of carbon atoms in each hydrocarbyl group is preferably 16 to 40, more preferably 16 to 24.

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

Examples of salts of compounds are acetate and hydrochloride.

Compounds may be conveniently prepared by reducing the corresponding amides prepared by reacting the secondary amine with a suitable acid chloride.

(V) a condensate prepared by condensing a 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-2,592,387 and DE-A-3,941,561; And esters of telemeric acid and alkanolamines as described in US-A-4,639,256; And reaction products of amines, epoxides and mono-carboxylic acid polyesters containing branched carboxylic acid esters such as those described in US-A-4,631,071.

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

It should be appreciated that the polar nitrogen compound may contain other functionalities such as ester functionality.

(v) hydrocarbylated aromatics

These materials are condensates comprising aromatic and hydrocarbyl moieties. Aromatic moieties are conveniently aromatic hydrocarbons which are unsubstituted or substituted, for example with non-hydrocarbon substituents.

Such aromatic hydrocarbons preferably contain the largest substituted group and / or three condensed rings and are preferably naphthalene. Hydrocarbyl moieties are hydrogen and carbon containing moieties linked to the rest of the molecule by carbon atoms. It may be saturated or unsaturated, straight or branched, and may contain one or more heteroatoms, provided they do not significantly affect the hydrocarbyl properties of the hydrocarbyl moiety. Preferably the hydrocarbyl moiety is an alkyl moiety, conveniently an alkyl moiety having more than eight carbon atoms.

(vi) linear compounds

Such compounds have one or more substantially linear alkyl groups having from 10 to 30 carbon atoms linked through any linking group branched to a non-polymeric moiety, such as an organic moiety, such that Compounds that provide one or more linear chains comprising non-terminal oxygen, sulfur and / or nitrogen atoms. The linking group may be polymeric.

"Substantially linear" means that an alkyl group is preferably straight chain, but straight chain alkyl groups having a low level of branching, such as in the form of a single methyl group branch, can be used.

Preferably, the compound has two or more of said alkyl groups when the linear chain may comprise one or more carbon atoms of said alkyl group. If the compound has three or more such alkyl groups, there may be more than one such linear chain and these chains may overlap. The linear chain (s) may provide part of the linking group between any two such alkyl groups in the compound.

The oxygen atom (s), if present, can preferably be inserted directly between the carbon atoms in the chain and, for example, provided to the linking group in the form of a mono- or poly-oxyalkylene group, if present. And the oxyalkylene group preferably has 2 to 4 carbon atoms and is for example oxyethylene and oxypropylene.

The chain (s) have carbon, oxygen, sulfur and / or nitrogen atoms.

The compound may be an ester where the alkyl group is linked to the remainder of the compound, such as —O—CO n alkyl or —CO—O n alkyl group, and when the alkyl group is —O—CO n alkyl the alkyl group is derived from an acid and the compound The remainder of is derived from polyhydric alcohols, where the alkyl group is derived from an alcohol and the remainder of the compound is derived from polycarboxylic acids when the alkyl group is -CO-O n alkyl. In addition, the compound may be an ether wherein an alkyl group is linked as the —O—n-alkyl group to the rest of the compound. Both compounds may be esters and ethers and may contain different ester groups.

Examples include polyoxyalkylene esters, ethers, esters / ethers and mixtures thereof, especially those containing at least one, preferably at least two C ₁₀ -C ₃₀ linear alkyl groups and the alkylene groups having EP- Having a polyoxyalkylene glycol group having a molecular weight of 5,000, preferably 200 to 5,000, containing 1 to 4 carbon atoms as described in A-61 895 and US Pat. No. 4,491,455.

Preferred esters, ethers or esters / ethers which can be used are represented by the formula: OR ²⁵ (R ²⁵ is independently (a) n-alkyl- (b) n-alkyl-CO- (c) n-alkyl-OCO- (CH ₂ ) _n- (d) n-alkyl-OCO- (CH ₂ ) _n CO-, where n is for example 1 to 34, the alkyl group is linear and has 10 to 30 carbon atoms) A group (eg 2, 3 or 4 groups) is residue E (residue E is for example A (alkylene) _q , A is C or N or absent, q is an integer from 1 to 4, The alkylene group has 1 to 4 carbon atoms and A (alkylene) _q is for example bonded to N (CH ₂ CH ₂ ) ₃ ; C (CH ₂ ) ₄ or (CH ₂ ) ₂ ) It includes. For example, they are represented by the formula R ²³ OBOR ²⁴ , wherein R ²³ and R ²⁴ are each as defined above in R ²⁵ , and B is a polyalkylene of glycol having an alkylene group having 1 to 4 carbon elements Segment, for example a substantially linear polyoxymethylene, polyoxyethylene or polyoxytrimethylene moiety, and branching to lower alkyl side chains (such as polyoxypropylene glycol) is acceptable to some extent but glycol is substantially It is preferred to be linear.

Suitable glycols are generally substantially linear polyethylene glycol (PEG) and polypropylene glycol (PPG) having a molecular weight of 100 to 5,000, preferably 200 to 2,000. Esters are preferred, and fatty acids containing from 10 to 30 carbon atoms are useful for reacting glycols to produce ester additives, and preference is given to using C ₁₈ -C ₂₄ fatty acids, in particular behenic acid. Esters can be prepared by esterifying polyethoxylated fatty acids or polyethoxylated alcohols.

Polyoxyalkylene diesters, diethers, ethers / esters and mixtures thereof are useful as additives, when the petroleum component is a narrow boiling distillate and when small amounts of monoethers and monoesters (often formed in the manufacturing process) are present Diester is preferable. This is particularly important for the active performance provided by large amounts of dialkyl compounds. Particular preference is given to stearic acid or behenic acid diesters of polyethylene glycol, polypropylene glycol or polyethylene / polypropylene glycol mixtures.

Examples of other compounds in the general category are those described in Japanese Patent Publication Nos. 2-51477 and 3-34790, EP-A-117,108 and EP-A-326,356 and those described in EP-A-356,256. As cyclic esterified ethoxylates.

(vii) comb polymer

Comb polymers are described in "Comb-Like Polymers. Structure and Properties", N. A. Plate and V. P. Shivaev, J. Poly. Macromolecular Revs., 8, p 117 to 253 (1974).

Generally, comb polymers are optionally blocked with one or more oxygen atoms and / or carbonyl groups and long chain branches, such as hydrocarbyl branches having 6 to 30, for example 10 to 30 carbon atoms, are suspended in the polymer backbone, This branching consists of molecules bound directly or indirectly to the backbone. Examples of indirect bonds include bonds through an inserted atom or group, which bonds are ionic bonds such as in covalent bonds and / or salts. In general, comb polymers are distinguished by having at least molar parts of the unit containing the long chain branch.

Advantageously the comb polymers contain at least 6, for example at least 8, preferably at least 10 atoms selected from carbon, nitrogen and oxygen in the linear chain or chains containing small amounts of branches such as a single methyl branch. It is a homopolymer or copolymer which has a unit which has a side chain in 25 mol% or more, Preferably it is 40 mol% or more, More preferably, it is 50 mol% or more.

Examples of preferred comb polymers may be mentioned containing units of the formula:

In the above formula,

D is R ¹¹ , COOR ¹¹ , OCOR ¹¹ , R ¹² COOR ¹¹ or OR ¹¹ ;

E is H, D or R ¹² ;

G is H or D;

J is H, R ¹² , R ¹² COOR ¹¹ or a substituted or unsubstituted aryl or heterocyclic group;

K is H, COOR ¹² , OCOR ¹² , OR ¹² or COOH;

L is H, R ¹² , COOR ¹² , OCOR ¹² or substituted or unsubstituted aryl;

R ¹¹ is a hydrocarbyl group having 10 or more carbon atoms;

R ¹² is a hydrocarbyl group which is divalent and otherwise monovalent within a ¹² COOR ¹¹ group;

m and n are molar ratios, the sum of them is 1, m is a limited value and 1 or less, n is 0 to 1, preferably m is 1.0 to 0.4, and n is 0 to 0.6.

R ¹¹ is advantageously a hydrocarbyl group having 10 to 30, preferably 10 to 24, more preferably 10 to 18 carbon atoms. Preferably, R ¹¹ is a linear or slightly branched alkyl group and R ¹² is monovalent, advantageously 1 to 30, preferably 6 or more, more preferably 10 or more, preferably 24 or less, More preferably a hydrocarbyl group having up to 18 carbon atoms. Preferably, R ¹² , when monovalent, is a linear or slightly branched alkyl group. When R ¹² is divalent, R ¹² is preferably methylene or ethylene group. "Slightly branched" means having a single methyl branch.

Comb polymers may contain units derived from other monomers, such as CO, vinyl acetate and ethylene, if desired or necessary. Two or more different comb polymers are within the scope of the present invention.

Comb polymers can be, for example, copolymers of maleic anhydride or fumaric acid and other ethylenically unsaturated monomers such as α-olefins or unsaturated esters such as vinyl acetate as described in EP-A-214,786. It is preferable to use the same amount of comonomer, but it is not necessary to do so, and it is also suitable to be used in molar parts of 2 to 1 and 1 to 2. Examples of olefins that can be copolymerized with maleic anhydride, for example, include 1-dekene, 1-dodekene, 1-tetradekene, 1-hexadekene, 1-octadekene and styrene. Still other examples of comb polymers include methacrylates and acrylates.

The copolymer may be esterified by any suitable method, and maleic anhydride or fumaric acid is preferably, but not necessarily, esterified at least 50%. Examples of alcohols that can be used include n-decane-1-ol, n-dodecane-1-ol, n-tedecane-1-ol, n-hexadecane-1-ol and n-octadecane-1-ol This may be included. The alcohol may also have up to one methyl branch per chain, for example 1-methylpentadecan-1-ol and 2-methyltridecan-1-ol as described in EP-A-213,879. The alcohol can be a mixture of normal and single methyl branched alcohol. Preference is given to using pure alcohols rather than alcohol mixtures such as those commercially available, in which case the number of carbon atoms in the alkyl groups is equal to the average number of carbon atoms in the alkyl groups in the alcohol mixture and branched in positions 1 or 2 When the containing alcohol is used, the number of carbon atoms in the alkyl group is equal to the number of carbon atoms in the linear backbone segment of the alkyl group of the alcohol.

Comb polymers are in particular fumarate or itaconate polymers and copolymers such as those described in, for example, European Patent Applications 153 176, 153 177, 156 577 and 225 688 and WO 91/16407. to be.

Particularly preferred fumarate comb polymers are copolymers of alkyl fumarate and vinyl acetate having alkyl groups of 12 to 20 carbon atoms, more particularly alkyl groups having 14 carbon atoms or alkyl groups having C ₁₄ / C ₁₆ Polymers which are mixtures of alkyl groups, for example polymers obtained by solution copolymerizing a mixture of the same amount of fumaric acid and vinyl acetate and reacting the resulting copolymer with an alcohol or a mixture of alcohols, preferably straight chain alcohols. If a mixture is used, the weight ratio of normal C ₁₄ and C ₁₆ alcohols is advantageously 1: 1. Furthermore mixtures of C ₁₄ esters and mixed C ₁₄ / C ₁₆ esters can be advantageously used. In this mixture, the weight ratio of C ₁₄ to C ₁₄ / C ₁₆ is advantageously from 1: 1 to 4: 1, preferably from 2: 1 to 7: 2 and most preferably about 3: 1. Particularly preferred fumarate comb polymers have a number average molecular weight of, for example, 1,000 to 100,000, preferably 1,000 to 50,000, as measured by vapor phase osmotic pressure measurement (VPO).

Other suitable comb polymers are polymers and copolymers of α-olefins, esterification copolymers of styrene and maleic anhydride, and esterification copolymers of styrene and fumaric acid as described in EP-A-282,342, as described above. Mixtures of two or more comb polymers can be used according to the invention and preference is given to using them.

Another example of a comb polymer is one or more α-olefins, preferably α-olefins having up to 20 carbon atoms, for example n-octene-1, isooctene-1, n-deken-1 and n- Hydrocarbon polymers, such as copolymers of dodeken-1, n-tetradeken-1 and n-hexadeken-1 (as described, for example, in WO 9319106) and ethylene.

Preferably, the number average molecular weight of the copolymer, as measured by gel permeation chromatography, is for example 30,000 or less to 40,000 or less relative to the polystyrene standard. Hydrocarbon copolymers can be prepared by methods known in the art, for example using Ziegler type catalysts. Such hydrocarbon polymers have, for example, at least 75% isotacticity.

Some of the cold flow improver co-additives described above can be synergistically enhanced when mixed with a mixture of esters (a) and (b).

Additional co-additives that can be used are well known in the art and include, for example, combustion improvers such as detergents, antioxidants, preservatives, dehazers, demulsifiers, metal deactivators, antifoams, cetane improvers, etc. , Metal-based additives such as cosolvents, package compatibiliser, reodorant and metal combustion improver.

Evaluation of the Benefits of Various Aspects of the Invention

It is contemplated that mixtures of esters (a) and (b) may at least partially form a layer of lubricating composition on a particular metal surface. This means that the formed layer need not be completed at the contact surface. The formation of such layers and the extent to which they cover the contact surface can be determined, for example, by measuring electrical contact resistance or electrical capacitance.

Tests that can be used to demonstrate one or more of reduced wear, reduced friction or increased electrical contact resistance according to the invention are described in the standard test methods CEC PF 06-T-94 or ISO / TC22 / SC7 / WG6 / N188. High Frequency Reciprocating Rig test (HFRR).

The degree to which the additive composition plugs the fuel oil line filter can be measured by known filterability tests. For example, the method of measuring the filterability of fuel oil compositions is labeled "IP 387/190" and is called "Determination of filter blocking tendency of gas oils and distillate diesel fuels". It is described in the title "Institute of Petroleum's Standard." In summary, the fuel oil composition sample to be tested is passed through the glass fiber filter media at a constant flow rate; The pressure drop through the filter is measured and the volume of fuel oil penetrating the filter medium within the defined pressure drop. For 300 ml of fuel penetrating at a rate of 20 ml / min, the filter plug tendency of the fuel composition can be recorded as the pressure drop through the filter medium. For further information please refer to the guidelines mentioned above. In evaluating the additive composition of the present invention, the method was modified by performing measurements at various temperatures lower than the temperatures specified in the guidelines in order to approximate the cold storage conditions that may occur in actual workplaces.

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

The following materials and methods were used.

Fuel oil

Diesel fuel oil of "Group I" has the following characteristics:

Sulfur: 4.5ppm wt / wt

Cetane number: 51.6

CFPP (automatic): -36 ° C

Distillation: 50% evaporation 237.1 ° C.

Final boiling point 294.1 ° C

Residues (% volume) 1.2

additive

Additives A, B, C and D were added to the diesel fuel oil in the amounts recorded in Table 1 and the filterability of each fuel composition was evaluated according to the IP 387/90 test at the temperatures shown in Table 1. In each case, after mixing, the sample fuel composition was cooled to the desired temperature in a refrigerating device and stored at that temperature for a defined period before filtration testing.

Sample additive Additive concentration (ppm active ingredient, wt / wt) Filterability test results 0 ℃ -10 ℃ -5 ℃ 1 day 1 week 1 month 1 day 1 week 1 month One none 0 9.653 kPa (1.4 psi) 13.79 kPa (2.0 psi) - 15.17 kPa (2.2 psi) 13.79 kPa (2.0 psi) 18.62 kPa (2.7 psi) 2 A 200 11.032 kPa (1.6 psi) 11.72 kPa (1.7 psi) 13.10 kPa (1.9 psi) 15.17 kPa (2.2 psi) 14 minutes 28 seconds 21.38 kPa (3.1 psi) 3 B 200 6.895 kPa (1.0 psi) 8.27 kPa (1.2 psi) 5 minutes 39 seconds 7 minutes 14 seconds 1 minute 2 seconds 12 minutes 2 seconds 4 C 200 - - - - - 6 minutes 20 seconds 5 D 200 - - - - - 96.54 kPa (14 psi) Footnote: "-" indicates no measurement

Commercially available mixtures of oleic acid and linoleic acid are esterified with glycerol to predominantly mix (a) glycerol monooleate and (b) glycerol monolinoleate together with a small amount of glycerol di- and trioleate and linoleate in approximately equal weight ratios. An ester product was produced to make additive A. It is also contemplated that the acid mixture contains small amounts of other acids, with the double ester not more than about 6% by weight of the mixed ester product.

Additive B was prepared by esterifying oleic acid with glycerol to produce a product comprising primarily glycerol monooleate (additive D of WO 94/17160).

Additive C was prepared by esterifying linoleic acid with glycerol to produce a product comprising primarily glycerol monolinoleate.

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

The test results in Table 1 show the pressure drop for the filter at the end of each test, with the higher the pressure drop the greater the partial filter blockage. If the pressure drop is greater than 103.4 kPa (15 psi) during the 15-minute test, the test reached that pressure (103.4 kPa, or 15 psi, corresponds to a severe filter occlusion and is considered "failed" for this purpose). The time was recorded.

From the results in Table 1, Sample 2 (fuel composition of the present invention) has very improved filterability in both 0 ° C and -10 ° C compared to Sample 3 (control fuel composition containing additive D in WO 94/17160). It can be seen that the. Moreover, both examples exceeded 103.4 kPa in the test after one week at -10 ° C, and Sample 2 performed better (Sample 3 almost immediately exceeded the pressure drop while Sample 2 had a 15 minute test). Just beyond the pressure drop).

Moreover, the test results at −5 ° C. show that Samples 2 and 5 (fuel compositions of the present invention) showed much improved filterability than Samples 2 and 4, two control examples that failed the test. Sample 2 containing additive A (prepared by esterifying a mixture of starting acids) also showed a surprisingly improved performance compared to sample 5 containing additive D (prepared by mixing with the ester component).

Example 2

Measure the HFRR performance of each droplet at 60 ° C. as a measure of “pre-filtration” lubricity by removing a small amount of each sample 1 sample droplet stored at −5 ° C. for two weeks immediately before the filtration step described in Example 1. It was. The HFRR performance at 60 ° C. of each corresponding sample filtrate produced in Example 1 was also measured as a measure of “post-filtration” lubricity. The results were compared to Table 2 below.

Sample additive Concentration of additive (ppm active ingredient, wt / wt) Wear mark before HFRR filtration (㎛) Wear marks after HFRR filtration (㎛) One none 0 623 610 2 A 200 309 330 3 B 200 249 396 4 C 200 343 411 5 D 200 292 274

The results in Table 2 show that samples 3 and 4 (control) had much worse lubricity after filtration, in contrast to samples 2 and 5 (fuel compositions of the present invention) that maintain lubricity (i.e. worn The marks are bigger).

Since the untreated fuel (sample 1) showed no change, it can be clearly seen that the difference in results seen in the other samples is due to the additives present in these compositions.

The difference in the diameter of the worn marks after filtration shows that the mixture of esters (a) and (b) has been significantly improved technically with improved lubricity compared to the control additive.

Claims (12)

(a) esters of unsaturated monocarboxylic acids and polyhydric alcohols; And (b) esters of polyhydric alcohols having unsaturated monocarboxylic acids and three or more hydroxy groups (esters (a) and esters (b) are different), with minor amounts of lubricant additives and intermediates with a sulfur content of 0.2% by weight or less. A fuel oil composition comprising a large amount of distillate fuel oil. The method of claim 1, The fuel oil has a sulfur content of 0.01% by weight or less. The method according to claim 1 or 2, The fuel oil is a diesel fuel. The method according to any one of claims 1 to 3, (a) is an ester of a polyhydric alcohol having three or more hydroxy groups. The method according to any one of claims 1 to 4, A composition wherein (a) and (b) are esters of alkenyl monocarboxylic acids. The method of claim 5, wherein (a) is an ester of monounsaturated alkenyl monocarboxylic acid and (b) is an ester of polyunsaturated alkenyl monocarboxylic acid. The method of claim 6, Wherein both acids have alkenyl groups having from 10 to 36 carbon atoms. The method according to any one of claims 4 to 7, A composition wherein (a) and (b) are both esters of trihydric alcohols, in particular glycerol. The method of claim 8, A composition wherein (a) and (b) are both mono-esters. The method of claim 9, (a) is a mono-ester of oleic acid and glycerol, and (b) is a mono-ester of linoleic acid and glycerol. Use of an additive as defined in any of claims 1 to 10 for increasing the lubricity of middle distillate fuel oils. Use of a fuel oil composition as defined in any one of claims 1 to 10 for reducing the wear rate of the fuel supply system of the combustion device.