Composition and methods and uses relating thereto

Abstract

A diesel fuel composition comprising a paraffinic fuel and an ester lubricity additive; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.5

Description

[0001] Composition and Methods and Uses relating thereto

[0002] The present invention relates to fuel compositions and to methods and uses relating thereto. In particular the invention relates to fuel compositions comprising paraffinic fuel such as renewable diesel and lubricity additives and especially to combatting undesired effects after storing such compositions, especially at low temperatures.

[0003] Due to environmental considerations significant efforts have been made in developing alternative hydrocarbon fuels to fossil fuels to power internal combustion engines. The present invention relates in particular to alternatives to mineral diesel fuel.

[0004] One alternative fuel suitable for use in diesel engines is renewable diesel.

[0005] Renewable diesel fuels are obtained by the hydrotreatment of triglyceride oils, for example vegetable oils. These materials consist primarily of saturated hydrocarbons and do not contain significant levels of aromatic or polar species. Consequently such fuels (commonly referred to as hydrotreated vegetable oils or HVO) have very low natural lubricity.

[0006] Other fuels comprising high level paraffinic species also have poor lubricity. Such fuels include, for example, synthetic fuels made by Fischer-Tropsch synthesis, also known as gas-to-liquid fuels.

[0007] It is common practice to add lubricity improvers to fuels to protect engine parts which come into contact with the fuel from wear. This is particularly important in the case of renewable diesel fuels and other highly paraffinic fuels because of their low natural lubricity.

[0008] Renewable diesel contains mainly saturated, straight chain or branched, aliphatic hydrocarbons. Biodiesel consists primarily of mono alkyl esters. Mineral diesel often contains aromatic and sulfated species as well as aliphatic hydrocarbons. Because these fuels comprise different chemical components, their properties differ as they cool as different waxes and precipitates form.

[0009] The present inventors have identified recognised a particular problem that can occur with the performance of lubricity additives when highly paraffinic fuels, for example fuels comprising renewable diesel are stored, especially at low temperatures.

[0010] A variety of additives are commonly added to fuels to enhance performance and additised fuels are tested to ensure that particular specifications are met. After dosing of the additives fuels may be stored for a period of time, either before or after distribution. In some countries the fuel may be stored at low temperatures. It is essential therefore that fuel properties are maintained during storage.

[0011] Unfortunately it has been found that for some highly paraffinic fuels such as renewable diesel a period of cold storage may lead to uneven distribution of lubricity additives throughout the fuel. It is believed that the additive may not remain well dispersed throughout the fuel and may gradually settle towards the bottom of a storage tank. This means that fuel taken from an upper region of a storage tank may exhibit poorer lubricity performance than fuel taken from a lower region of a storage tank.

[0012] The industry standard test method for evaluating lubricity improving additives measures the wear between two metals components in a high frequency reciprocating rig (HFRR). Measurements of lubricity taken using this test may vary significantly throughout a fuel comprising renewable diesel following a period of cold storage, despite the presence of known lubricity additives such as those comprising glycerol monooleate.

[0013] This is a significant problem since the use of a fuel drawn from a region of a storage tank which is depleted of lubricity additive could cause engine failure.

[0014] Poor distribution of lubricity additive following storage, especially at low temperatures, has been found to be a problem in particular in paraffinic fuels comprising a high proportion of branched alkanes and / or in fuels having a low cloud point.

[0015] The present inventors have surprisingly found that the use of particular ester compounds as lubricity additives can provide fuel compositions comprising paraffinic fuels such as renewable diesel which maintain lubricity performance throughout the composition even after long periods of storage, including at low temperatures.

[0016] According to a first aspect of the present invention there is provided a diesel fuel composition comprising a paraffinic fuel and an ester lubricity additive; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.

[0017] According to a second aspect of the present invention there is provided a method of improving the lubricity of a diesel fuel composition comprising a paraffinic fuel, the method comprising dosing into the fuel composition an ester lubricity additive which is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound. According to a third aspect of the present invention there is provided a storage tank comprising a diesel fuel composition where the diesel fuel composition comprises a paraffinic fuel and an ester lubricity additive; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.

[0018] According to a fourth aspect of the present invention there is provided the use of an ester lubricity additive which is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound to improve the lubricity of a diesel fuel composition comprising a paraffinic fuel.

[0019] Preferred features of the first, second, third and fourth aspect of the invention will now be described. Unless otherwise stated any feature described in relation to one aspect of the invention may also apply to any other aspect.

[0020] The present invention relates to the use in diesel fuel compositions comprising a paraffinic fuel and an ester lubricity additive.

[0021] The ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.

[0022] By hydrocarbyl substituted succinic acid compound we mean to include hydrocarbyl substituted succinic acids in which both acid groups are present as the free acid; hydrocarbyl substituted succinic anhydrides; and monoesters of hydrocarbyl substituted succinic acids, i.e. compounds in which one of the acid groups of the succinic acid moiety has been esterified and the other acid group is present as the free acid. In the case of monoesters it is the free acid group which functions as the acylating agent.

[0023] In preferred embodiments the hydrocarbyl substituted succinic acid compound is a hydrocarbyl substituted succinic acid or a hydrocarbyl substituted succinic anhydride.

[0024] Hydrocarbyl substituted succinic acid compounds are typically prepared by the reaction of an alkene with maleic anhydride.

[0025] The product may be optionally hydrolysed to form the diacid which may be reacted with an alcohol to form an ester or the anhydride can be directly reacted with an alcohol.

[0026] In some embodiments the alkene may suitably have from 2 to 50 carbon atoms, preferably from 4 to 40, for example from 6 to 36 carbon atoms. In some embodiments the alkene may be a polyolefin, for example a polyisobutene. In some embodiments the alkene may be an a-olefin. The term a-olefin is used to refer to an alkene compound having a terminal double bond. Such compounds are also commonly described as terminal alkenes.

[0027] In some preferred embodiments the alkene is an internal olefin. The term internal olefin is used to refer to any alkene compound in which the alkene group is not terminal.

[0028] In one embodiment an internal olefin may be a p-olefin.

[0029] Internal olefins may be prepared by isomerisation of an a-olefin.

[0030] In some embodiments hydrocarbyl substituent of the hydrocarbyl substituted succinic acid compound has from 4 to 40 carbon atoms, suitably from 6 to 36 carbon atoms, preferably from 10 to 32 carbon atoms, for example from 12 to 30 carbon atoms, preferably from 12 to 24 carbon atoms, for example from 12 to 20 carbon atoms. In some embodiments the hydrocarbyl substituent may have from 14 to 18 carbon atoms.

[0031] In some embodiments the hydrocarbyl substituted succinic acid compound has a substituent derived from an a-olefin having 6 to 36 carbon atoms; preferably from 10 to 30 carbon atoms, suitably from 12 to 24 carbon atoms, for example from 14 to 18 carbon atoms.

[0032] In some embodiments the hydrocarbyl substituted succinic acid compound has a substituent derived from an internal olefin having 6 to 36 carbon atoms preferably from 10 to 32 carbon atoms, suitably from 12 to 24 carbon atoms, for example 14 to 18 carbon atoms.

[0033] In some embodiments the hydrocarbyl substituted succinic acid compound has a polyisobutenyl substituent having a number average molecular weight of from 80 to 5000, preferably from 100 to 1000, more preferably from 200 to 600.

[0034] Preferred polyisobutenyl substituted compounds include those having a polyisobutenyl substituent with a number average molecular weight of about 260 or about 550. A polyisobutenyl substituent number average molecular weight of about 260 is especially preferred.

[0035] To form the ester lubricity additives used in the present invention, the hydrocarbyl substituted succinic acid compound is reacted with a polyhydric alcohol. In embodiments in which the hydrocarbyl substituted succinic acid compound comprises a hydrocarbyl substituted succinic acid or anhydride, one or both of the carboxylic acid groups may react with the alcohol to form an ester.

[0036] Thus the ester lubricity additive may comprise a monoester of a succinic acid or a diester of succinic acid.

[0037] The ester lubricity additive comprises the reaction product of a hydrocarbyl substituted succinic acid compound and a polyhydric alcohol.

[0038] The term polyhydric alcohol is used to refer to any compound including two or more OH functional groups.

[0039] In the ester lubricity additive compounds one or more than one of the hydroxy groups of the polyhydric alcohol may be esterified.

[0040] Preferred polyhydric alcohols suitable for use herein are compounds having from 2 to 10 hydroxy groups, preferably from 2 to 6 hydroxy groups, more preferably 2 or 3 hydroxy groups.

[0041] When preparing the ester lubricity additives of the present invention, since the polyhydric alcohol has multiple functional groups, and the hydrocarbyl substituted succinic acid compound may have multiple functional groups, a mixture of products may be obtained.

[0042] In some embodiments the hydrocarbyl substituted succinic acid compound and the polyhydric alcohol are reacted in a molar ratio of from 5:1 to 1 :30, suitably from 2:1 to 1 :20, preferably from 1 :1 to 1 :10, based on the ratio of COOH groups (or reactive equivalent thereof) in the acylating compound to OH groups present in the alcohol compound.

[0043] In preferred embodiments an excess of alcohol groups are present relative to carboxylic acid groups or reactive equivalents thereof in the reaction used to prepare the ester lubricity additive.

[0044] For the avoidance of doubt an anhydride functional group is a reactive equivalent of two COOH groups.

[0045] In some embodiments in which the hydrocarbyl substituted succinic acid compound may be initially reacted with a first alcohol and then subsequently further reacted with a second different alcohol. In such embodiments the reaction product may comprise a diester compound including two different ester functional groups. In embodiments in which the first alcohol is a monohydric alcohol and the second alcohol is a polyhydric alcohol the acylating agent is a monoester of a hydrocarbyl substituted succinic acid.

[0046] For the avoidance of doubt the ester lubricity additives may comprise a mixture of compounds.

[0047] For the avoidance of doubt mixtures of ester lubricity additive compounds that may be present include mixtures formed by reacting a mixture of different polyhydric alcohols with a hydrocarbyl substituted succinic acid compound and / or mixtures formed by reacting a polyhydric alcohol with a mixture of hydrocarbyl substituted succinic acid compounds and / or compounds formed by reacting a mixture of polyhydric alcohols with a mixture of hydrocarbyl substituted succinic acid compounds. Already formed ester compounds may also be combined to form mixtures.

[0048] The use of mixtures may arise due to the availability of starting materials or a particular mixture may be deliberately selected.

[0049] In this specification any reference to “an additive” or “the additive” of the invention includes embodiments in which a single additive compound is present and embodiments in which two or more additive compounds are present. In embodiments in which two or more compounds are present the mixtures may be present due to a mixture of starting materials being used to prepare the additive compounds (e.g. a mixture of polyhydric alcohols and / or a mixture of hydrocarbyl substituted succinic acid compounds). Alternatively and / or additionally two or more pre-formed ester compounds may be mixed into a fuel composition.

[0050] The ester lubricity additives used in the present invention are preferably the reaction product of a polyhydric alcohol and a succinic acid of formula (I) or a succinic anhydride of formula (II): wherein one of R1and R3is an alkyl or alkenyl group, and the other of R1and R3is hydrogen.

[0051] Preferably one of R1and R3is an alkenyl group, and the other of R1and R3is hydrogen. Preferably one of R1and R3is a C12 to C32 group, for example a C14 to C18 group, especially a C16 group.

[0052] R1or R3may comprise a mixture of chain lengths and there can be some branching such as methyl, ethyl and higher alkyl branching. R1and R3can be derived from polymerised olefins, for example polymerised ethylene, polymerised propylene, polymerised butylene or polymerised mixtures of such olefins.

[0053] In some embodiments one of R1and R3is derived from an internal olefin.

[0054] Internal olefins contain predominantly a non-terminal double bond, such as a p or higher olefin. Preferably such materials are substantially completely p or higher olefins, for example containing less than 10% by weight a olefin, more preferably less than 5% by weight or less than 2% by weight. Typical internal olefins include Neodene 151810 available from Shell.

[0055] Internal olefins are sometimes known as isomerised olefins and can be prepared from a-olefins by isomerisation.

[0056] In some embodiments the number average molecular weight of the alkenyl group R1or R3is preferably at least 168, most preferably at least 180. The number average molecular weight of the alkenyl group R1or R3is preferably up to 1200, more preferably up to 1120, most preferably up to 448.

[0057] In some embodiments one of R1and R3is a Ci to C150 alkenyl group, such as an olefin or polyolefin.

[0058] In some embodiments one of R1and R3is the residue of an a-olefin having 6 to 36 carbon atoms; preferably from 10 to 30 carbon atoms, suitably from 12 to 24 carbon atoms, for example from 12 to 18 carbon atoms or from 14 to 18 carbon atoms.

[0059] In some embodiments one of R1and R3is the residue of an internal olefin having 6 to 36 carbon atoms; preferably from 10 to 30 carbon atoms, suitably from 12 to 24 carbon atoms, for example from 12 to 18 carbon atoms or from 14 to 18 carbon atoms.

[0060] In some embodiments one of R1and R3is preferably a C16 to C80 group and more preferably a polyisobutene (PIB) group. The number average molecular weight of the PIB is preferably from 200 to 2000, more preferably 260 to 1000, for example about 260, 320, 350, 550, 750 or 1000. Conventional PIBs and so-called "high-reactivity" PIBs (for example as described in EP565285) are suitable. High reactivity in this context is defined as a PIB wherein at least 50%, preferably 70% or more, of the terminal olefinic double bonds are of the vinylidene type, for example the GLISSOPAL compounds available from BASF.

[0061] The ester lubricity additives used in the present invention are prepared by the reaction of a hydrocarbyl substituted succinic acid compound and a polyhydric alcohol.

[0062] In some preferred embodiments the polyhydric alcohol is a compound of formula H-(OR2)n- OH, wherein R2is an optionally substituted alkylene group and n is at least 1 .

[0063] Preferably n is from 1 to 10, more preferably from 1 to 4. Most preferably n is 1 or 2.

[0064] R2is an optionally substituted alkylene group.

[0065] In some embodiments the alcohol of formula H-(OR2)n-OH has more than 2 hydroxy groups and the group R2is a hydroxy substituted alkylene group. Such a group may have 1 , 2 or more than 2 hydroxy groups.

[0066] In some embodiments the alcohol of formula H-(OR2)n-OH may be a sugar derived unit in which R2includes one or more hydroxy residues.

[0067] R2may be substituted to form a cyclic alkylene unit. One or more heteroatoms may be present in the cyclic alkylene unit. For example the unit may contain an ether linkage.

[0068] In some embodiments R2may be one or more saccharide units or may be substituted with one or more saccharide units.

[0069] In some embodiments H-(OR2)n-OH may be selected from glycerol, pentaerythritol and trimethylolpropane.

[0070] In some embodiments H-(OR2)n-OH may be a sugar component for example, trehalose or sorbitol.

[0071] In some embodiments R2is an unsubstituted alkylene group.

[0072] Preferably R2is an optionally substituted alkylene group having 1 to 50 carbon atoms, preferably 1 to 40 carbon atoms, preferably 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, suitably 1 to 10 carbon atoms, for example 2 to 6 or 2 to 4 carbon atoms. Preferably R2is an unsubstituted alkylene group having 1 to 50 carbon atoms, preferably 1 to 20, more preferably 1 to 10, suitably 2 to 6, for example 2 to 4 carbon atoms. R2may be straight chained or branched.

[0073] Suitably R2may be an ethylene, propylene, butylene, pentylene, or hexylene group. When R2has more than 2 carbon atoms any isomer may be present. In some preferred embodiments R2is an ethylene or a propylene group, most preferably an ethylene group.

[0074] In some embodiments in which n is 1 , R2may be a group of formula (CH2)x wherein x is from 2 to 12, preferably from 2 to 6.

[0075] In some embodiments in which n is 1 , R2is a straight chain or branched alkylene group and the polyhydric alcohol is selected from ethylene glycol, propylene glycol, 1 ,3-propanediol, 1 ,2- butanediol, 1 ,3-butanediol, 1 ,4-butanediol, 1 ,6-hexanediol and neopentyl glycol.

[0076] In some preferred embodiments in which n is 1 , R2is a straight chain or branched alkylene group having 2 to 6, preferably 2 to 5 carbon atoms.

[0077] Suitable compounds of this type include ethylene glycol, propylene glycol, 1 ,3-propanediol, 1 ,2- butanediol, 1 ,3-butanediol, 1 ,4-butanediol and neopentyl glycol.

[0078] R2may comprise a mixture of isomers. For example when R2is propylene, the polyhydric alcohol may include moieties -CH2CH(CH3)- and -CH(CH3)CH2- in any order within the chain.

[0079] R2may comprise a mixture of different groups for example ethylene, propylene or butylene units.

[0080] R2may be an ethylene, propylene or butylene group. R2may be an n-propylene or n-butylene group or an isopropylene or isobutylene group. For example R2may be -CH2CH2-, - CH2CH(CH3)-, -CH2CH2CH2-, -CH2C(CH3)2, -CH2CH2CH2CH2-, -CH(CH3)CH(CH3)- or - CH2CH(CH2CH3)-.

[0081] Preferably R2is selected from is -CH2CH2-, -CH2CH2CH2-, -CH(CH3)CH2- or -CH2CH(OH)CH2.

[0082] In some embodiments the polyhydric alcohol is selected from ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerol and diglycerol. The reaction product of the polyhydric alcohol and the compound of formula (I) or formula (II) may comprise compounds of formula (III), (IV) or (V): wherein of R1and R3are as previously defined and R2is an optionally substituted alkylene moiety.

[0083] The reaction product may also comprise oligomers of formula (VI): wherein m is 0 or an integer from 1 to 20, in each succinic acid moiety one of R1and R3is an alkyl or alkenyl group, and the other of R1and R3is hydrogen; and R2is an optionally substituted alkylene moiety.

[0084] R2is an optionally substituted alkylene moiety and is suitably derived from a polyhydroxy alcohol of formula H-(OR2)n-OH as described above. Suitably n is 1 or 2. R2may include one of more hydroxy substituents.

[0085] In any individual succinic acid moiety, if R1is alkyl or alkenyl then R3is hydrogen and vice versa. However the pattern of substitution along the oligomer chain need not be identical. Preferably m is at least 1 , more preferably at least 2. Suitably n may be up to 11 , more preferably up to 10, more preferably up to 8, more preferably up to 6 and most preferably up to 5.

[0086] In some embodiments the ester lubricity additive may comprise the reaction product of a compound of formula (I) or (II) with a polyhydric alcohol and a monohydric alcohol. In such embodiments the reaction product may comprise compounds of formula (VII) or (VIII): wherein R4is the residue of the monohydric alcohol and R1, R2and R3are as previously defined.

[0087] In preferred embodiments the ester lubricity additives comprise the reaction product of a compound of formula (I) or (II) and a polyhydric alcohol and the reaction product comprises compounds of formula (III), (IV), (V) and / or (VI).

[0088] R2is an optionally substituted alkylene group, preferably derived from a polyhydric alcohol.

[0089] The polyhydric alcohol from which R2is derived may, for example, be selected from ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerol and diglycerol.

[0090] In preferred embodiments the polyhydric alcohol is a dihydroxy alcohol, preferably having primary hydroxyl groups, at the respective ends of the carbon backbone.

[0091] Suitably the polyhydric alcohol is selected from ethylene glycol, glycerol or diethylene glycol.

[0092] In particularly preferred embodiments the polyhydric alcohol is ethylene glycol.

[0093] In embodiments in which the succinic acid or anhydride thereof is also reacted with a monohydric alcohol R4OH, R4in formulae (VII) and (VIII) is the residue of the monohydric alcohol. R4may be an optionally substituted alkyl, alkenyl or aryl group. Preferably R4is an alkyl group, preferably an unsubstituted alkyl group.

[0094] R4is preferably a C1 to C6 alkyl group, preferably methyl, ethyl, propyl or isopropyl. An especially preferred monohydric alcohol is isopropanol.

[0095] The succinic acid / anhydride ester lubricity additives comprise compounds that are always at least semi-esterified. Mixtures of the fully and semi-esterified compounds in a variety of ratios are also within the invention. The degree of esterification may be determined according to the acid number, i.e. the amount of NaOH required to neutralise 1 g of the compound. The acid number is suitably less than 90 mg NaOH / g, preferably less than 50 mg NaOH / g, for example less than 20 mg NaOH / g, less than 10 mg NaOH / g or less than 5 mg NaOH / g.

[0096] Suitably in preparing the ester lubricity additives the compound of formula (I) or (II) and a polyhydric alcohol are reacted in a molar ratio of from 5:1 to 1 :30, suitably from 2:1 to 1 :20, preferably from 1 :1 to 1 :10, based on the ratio of COOH groups (or reactive equivalent thereof) in the compound of formula (I) or (II) to OH groups present in the polyhydric alcohol.

[0097] Further details of succinic acid derived ester lubricity additives suitable of use herein and methods of preparing the same are described in EP1910504, GB2381789 and EP902804.

[0098] In preferred embodiments the ester lubricity additive is selected from one or more of:

[0099] (i) the reaction product of a polyhydric alcohol and a compound of formula (I) or (II) in which one of R1and R3is derived from an internal olefin having 12 to 32 carbon atoms and the other one of R1and R3is hydrogen;

[0100] (ii) the reaction product of a compound of formula (I) or (II) in which one of R1and R3is a hydrocarbyl group having 10 to 32 carbon atoms, a polyhydric alcohol and a monohydric alcohol wherein the reaction product comprises compounds of formula (VII) and (VIII);

[0101] (iii) the reaction product of a polyhydric alcohol and a compound of formula (I) or (II) in which one of R1and R3is derived from an a-olefin having 10 to 30 carbon atoms and the other one of R1and R3is hydrogen; and

[0102] (iv) the reaction product of a polyhydric alcohol and a compound of formula (I) or (II) in which one of R1and R3is a polyisobutylene group and the other one of R1and R3is hydrogen. Preferably the ester lubricity additive comprises the reaction product of a polyhydric alcohol and a compound of formula (I) or (II) in which one of R1and R3is derived from an internal olefin having 12 to 32 carbon atoms and the other one of R1and R3is hydrogen.

[0103] Suitably the ester the lubricity additive comprises the reaction product of a polyhydric alcohol selected from ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerol and diglycerol and compound of formula (I) or (II) in which one of R1and R3is derived from an internal olefin having 12 to 24 carbon atoms and the other one of R1and R3is hydrogen.

[0104] Preferably the ester lubricity additive comprises the reaction product of a polyhydric alcohol selected from ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerol and diglycerol and compound of formula (I) or (II) in which one of R1and R3is derived from an internal olefin having 14 to 18 carbon atoms and the other one of R1and R3is hydrogen, wherein the compound of formula (I) or (II) and the polyhydric alcohol are reacted in a molar ratio of from 2:1 to 1 :20 based on the ratio of COOH groups (or reactive equivalent thereof) in the compound of formula (I) or (II) to OH groups present in the polyhydric alcohol.

[0105] More preferably the ester lubricity comprises the reaction product of a polyhydric alcohol selected from ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerol and diglycerol and compound of formula (I) or (II) in which one of R1and R3is derived from an internal olefin having 14 to 18 carbon atoms and the other one of R1and R3is hydrogen, wherein the compound of formula (I) or (II) and the polyhydric alcohol are reacted in a molar ratio of from 1 :1 to 1 :10 based on the ratio of COOH groups (or reactive equivalent thereof) in the compound of formula (I) or (II) to OH groups present in the polyhydric alcohol.

[0106] In the present invention the ester lubricity additive is incorporated into a diesel fuel composition comprising a paraffinic fuel.

[0107] In some embodiments the diesel fuel composition may be a blended fuel comprising a paraffinic fuel and a further fuel component, for example a mineral diesel or biodiesel component.

[0108] In some preferred embodiments the paraffinic fuel provides at least 90 vol%, preferably at least 99 vol% of all fuel present in the diesel fuel composition. Most preferably the paraffinic fuel provides 100 vol% of all fuel present in the diesel fuel composition.

[0109] By a paraffinic fuel we mean to refer to a fuel that is highly paraffinic in nature. Paraffinic fuels typically comprise predominantly paraffin compounds. By paraffin compounds we mean to refer to saturated hydrocarbon compounds, commonly known as alkanes. Preferably the paraffinic fuel comprises at least 70 wt% paraffin compounds, preferably at least 80 wt%, more preferably at least 95 wt%.

[0110] Preferably the paraffinic fuel comprises less than 5 wt% non-paraffinic compounds, preferably less than 3 wt%, more preferably less than 1 wt%, suitably less than 0.5 wt%, for example less than 0.1 wt% or less than 0.01 wt%

[0111] Preferably the paraffinic fuel comprises less than 10 wt% aromatic compounds, preferably less than 5 wt% more preferably less than 1 wt%, suitably less than 0.5 wt%.

[0112] Preferably the paraffinic fuel comprises less than 10000 ppm aromatic compounds, preferably less than 5000 ppm, suitably less than 2500 ppm.

[0113] In some embodiments the paraffinic fuel comprises less than 1000 ppm aromatic compounds, for example less than 500 ppm or less than 350 ppm.

[0114] In this specification, unless otherwise specified ppm refers to parts per million by weight.

[0115] Aromatic content may be measured by any suitable method. Such methods will be known to the person skilled in the art.

[0116] Preferably aromatic content is measured according to the standard method described in IP 391 .

[0117] Preferably the paraffinic fuel has a sulfur content of less than 100 ppm, preferably less than 50 ppm, more preferably less than 10 ppm, for example less than 5 ppm.

[0118] Preferably the paraffinic fuel comprises less than 5 wt% oxygenated compounds, preferably less than 3 wt%, more preferably less than 1 wt%, suitably less than 0.5 wt%, for example less than 0.1 wt% or less than 0.01 wt%.

[0119] By oxygenated compounds we mean to refer to compounds including an oxygen-containing functional group, for example esters, ethers and alcohols.

[0120] Preferably the paraffinic fuel comprises less than 5 wt% unsaturated compounds, preferably less than 3 wt%, more preferably less than 1 wt%, suitably less than 0.5 wt%, for example less than 0.1 wt% or less than 0.01 wt%. One class of suitable paraffinic fuels are synthetic fuels. These fuels include Fischer-Tropsch fuels such as those described as GTL (gas-to-liquid) fuels, CTL (coal-to-liquid) fuels and OTL (oil sands-to-liquid) fuels.

[0121] In a preferred embodiment the paraffinic fuel comprises hydrotreated triglyceride oil. This fuel is sometimes referred to as renewable diesel fuel.

[0122] In some embodiments the fuel composition may comprise neat renewable diesel.

[0123] A fuel which comprises 100% renewable diesel is denoted as R100, a fuel which comprises 90% mineral diesel and 10% renewable diesel (by volume) is known as R10; fuel comprising 50% mineral diesel and 50% renewable diesel (by volume) is known as R50; and so on.

[0124] In preferred embodiments renewable diesel provides at least 90 vol%, preferably at least 99 vol% of all fuel present in the diesel fuel composition. Most preferably renewable diesel provides 100 vol% of all fuel present in the diesel fuel composition.

[0125] Thus the first aspect of the present invention preferably provides a fuel composition comprising renewable diesel and an ester lubricity additive; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.

[0126] The second aspect of the present invention preferably provides a method of improving the lubricity of a renewable diesel fuel, the method comprising dosing into the renewable diesel fuel an ester lubricity additive which is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.

[0127] The third aspect of the present invention preferably provides a storage tank comprising a diesel fuel composition wherein the diesel fuel composition comprises renewable diesel and an ester lubricity additive; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.

[0128] The fourth aspect of the present invention preferably provides the use of an ester lubricity additive which is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound to improve the lubricity of renewable diesel fuel.

[0129] By hydrotreated triglyceride oil or renewable diesel we mean to refer to diesel fuel obtained by the hydrodeoxygenation of fats and oils. Such fuels are also often referred to as second generation biodiesel and are derived from renewable resources such as vegetable oils, fish oils and animal oils. These oils are processed, often in the refinery, using, for example, hydroprocessing. Hydroprocessing processes include the H-Bio process developed by Petrobras. Especially preferred hydrotreated triglyceride oils are hydrotreated vegetable oils or HVO fuel. HVO fuel is marketed by ConocoPhillips as Renewable Diesel and by Neste as NExBTL.

[0130] The paraffinic fuel used in the present invention may comprise fuel commonly known as third generation biodiesel. Third generation biodiesel utilises gasification and Fischer-Tropsch technology including those described as BTL (biomass-to-liquid) fuels. Third generation biodiesel does not differ widely from some second generation biodiesel or hydrotreated triglyceride oil fuels, but aims to exploit the whole plant (biomass) and thereby widens the feedstock base.

[0131] The paraffinic fuel is preferably produced from raw materials of biological origin. These may suitably be selected from vegetable oils, animal fats, fish oils and mixtures thereof. Examples include rapeseed oil, canola oil, tall oil, sunflower oil, soybean oil, hemp oil, olive oil, linseed oil, mustard oil, carinata oil, palm oil, palm kernel oil, peanut oil, castor oil, coconut oil, animal fats such as tallow or recycled food fats, raw materials resulting from genetic engineering, and biological raw materials produced from microorganisms such as algae and bacteria.

[0132] Preferably, the paraffinic fuel is provided by a process involving hydrodeoxygenation (HDO) and optionally isomerization steps. The hydrodeoxygenation (HDO) step results in the decomposition of the structures of the biological esters or of the triglyceride constituents, in the elimination of the oxygen-bearing, phosphorus-bearing and sulfur-bearing compounds and in the hydrogenation of olefinic bonds. The product resulting from the hydrodeoxygenation reaction may then be isomerized. A fractionation step may optionally follow the hydrodeoxygenation and isomerization steps.

[0133] Preferably the paraffinic fuel has a cetane number of between 50 and 90, preferably between 55 and 90, more preferably between 60 and 85. Cetane number is suitably measured by the standard test method set out in IP 498.

[0134] Preferably the paraffinic fuel has a cloud point of less than 25°C, more preferably less than 10°C. Suitably the paraffinic fuel has a cloud point of less than -5°C, for example less than - 10°C. Cloud point may suitably be measured using the standard test method described in IP 219.

[0135] The inventors have surprisingly found that the present invention is particularly effective in fuels having a cloud point of less than -15°C, for example less than -20°C or less than -25°C. Preferably the paraffinic fuel has a kinematic viscosity at 40°C of 1 to 20 mm2s-1, preferably from 2 to 15 mm2s'1, more preferably from 2 to 10 mm2s1, most preferably from 2 to 4.5 mm2s-1. Kinematic viscosity may be measured according to ASTM D445.

[0136] Preferably the paraffinic fuel has an initial boiling point (IBP) and a final boiling point (FBP) within the range 265 to 380°C, more preferably within the range 275 to 380°C and most preferably within the range 290 to 375°C.

[0137] Preferably the paraffinic fuel has a boiling range of less than 80°C, preferably less than 70°C, suitably less than 60°C, for example from 30 to 60°C. Boiling range is used to refer to the difference between the final boiling point and the initial boiling point.

[0138] The initial boiling point, final boiling point and boiling range can be determined according to the method set out in IP 123.

[0139] The paraffinic fuel used suitably consists essentially of paraffinic compounds. Preferably the fuel may comprise n-paraffins (or straight chain alkanes), isoparaffins (i-paraffins or branched alkanes) or mixtures thereof.

[0140] In some embodiments the paraffinic fuel may further comprise cycloalkanes (also known as naphthenes). Examples of paraffinic fuels comprising cycloalkanes are described, for example in W02021 / 250115.

[0141] In preferred embodiments the paraffinic fuel comprises predominately straight chain alkanes and branched alkanes.

[0142] Preferably the paraffinic fuel comprises less than 20 wt% cycloalkanes, preferably less than 10 wt%, suitably less than 5 wt%, preferably less than 1 wt%, for example less than 0.1 wt%.

[0143] For the avoidance of doubt by the term cycloalkane or naphthene is used to refer to any saturated hydrocarbon compound which includes a non-aromatic cyclic moiety.

[0144] The present invention is particularly effective in fuels having a high proportion of isomerised paraffins.

[0145] Preferably the weight of ratio n-paraffins to i-paraffins present in the paraffinic fuel is from 99:1 to 1 :99. Techniques for determining the ratio of n-paraffins to i-paraffins are known to the person skilled in the art and include gas chromatography. In preferred embodiments the weight of ratio n-paraffins to i-paraffins present in the paraffinic fuel is from 1 :99 to 20:80; for example from 5:95 to 15:85.

[0146] Ratios of n-paraffins and i-paraffins present in a fuel typically depend on the hydrotreatment method used to prepare the fuel, which may also include an isomerisation step.

[0147] The paraffinic fuel may comprise less than 20 wt%, preferably less than 18 wt%, more preferably less than 16 wt%, for example less than 12 wt% or less than 10 wt% of C14 to C18 n-alkanes.

[0148] The paraffinic fuel may comprise less than 8 wt%, preferably less than 6 wt%, of C14 to C16 n- alkanes.

[0149] The paraffinic fuel may comprise from 50 to 98 wt%, preferably from 60 to 95 wt%, more preferably from 70 to 90 wt%, of C14 to C18 i-alkanes.

[0150] The paraffinic fuel may comprise from 2 to 12 wt%, preferably 5 to 10 wt% of C6 to C24 n- alkanes (i.e. n-paraffin).

[0151] The paraffinic fuel may comprise from 2 to 12 wt%, preferably 5 to 10 wt% of C6 to C24 n- alkanes (i.e. n-paraffin) and 88 to 98 wt%, preferably 90 to 95 wt% of i-alkanes (i.e. i-paraffins).

[0152] Suitably the paraffinic fuel complies with the standard specification set out in EN15940.

[0153] In preferred embodiments the paraffinic fuel is a hydrotreated triglyceride oil, for example a hydrotreated vegetable oil.

[0154] Preferably the paraffinic fuel is a hydrotreated triglyceride oil having an aromatic content of less than 2500 ppm, preferably less than 500 ppm; and a sulfur content of less than 50 ppm.

[0155] Preferably the paraffinic fuel is a hydrotreated triglyceride oil fuel having a cetane number of between 50 and 90, preferably between 55 and 90 (according to IP 498); a cloud point of less than 10°C, preferably less than -5°C (according to IP 219); and a kinematic viscosity at 40°C of from 1 to 20 mm2s-1, preferably from 2 to 10 mm2s-1(according to ASTM 445).

[0156] Preferably the paraffinic fuel is a hydrotreated triglyceride oil having an initial boiling point and a final boiling point within the range 265 to 380°C, preferably 290 to 375°C and a boiling range of less than 80°C, preferably 30 to 60°C. The ester lubricity additive maybe dosed in the diesel fuel according to the present invention in an amount of at least 5 ppm.

[0157] Preferably the ester lubricity additive is included in the diesel fuel composition in an amount of at least 10 ppm, preferably at least 20 ppm, more preferably at least 30 ppm, for example at least 50ppm or at least 80 ppm.

[0158] The ester lubricity additive may be present in the diesel fuel composition in an amount of up to 5000 ppm, preferably 2000 ppm, suitably up to 1000 ppm, for example up to 500 ppm or up to 350 ppm.

[0159] Preferably the ester lubricity additive is dosed in the diesel fuel according to the present invention in an amount of from 50 to 500 ppm, preferably from 100 to 300 ppm, more preferably from 150 to 250 ppm.

[0160] For the avoidance of doubt, when mixtures of ester lubricity additives are present, the above amounts refer to the total amount of all ester lubricity additives present in the composition.

[0161] The above amounts refer to the amount of active ester lubricity additives present and do not include any diluent, carrier, by-product or residual starting material which may be present.

[0162] The ester lubricity additives of the invention have been found to provide a consistent improvement in the lubricity of the fuel which is maintained even after long periods of storage, including at low temperatures. Surprisingly this effect is achieved for fuels having a low cloud point and for those fuels comprising a high proportion of isomerised paraffins. The invention is particularly applicable to renewable diesel fuels.

[0163] In some embodiments the first aspect of the present invention provides a diesel fuel composition comprising a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C and an ester lubricity additive; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.

[0164] In some embodiments the second aspect of the present invention provides a method of improving the lubricity of a diesel fuel composition comprising a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C’; the method comprising dosing into the fuel composition an ester lubricity additive which is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound. In some embodiments the third aspect of the present invention provides a storage tank comprising a diesel fuel composition where the diesel fuel composition comprises a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C and an ester lubricity additive; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.

[0165] In some embodiments the fourth aspect of the present invention provides the use of an ester lubricity additive which is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound to improve the lubricity of a diesel fuel composition comprising a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C.

[0166] In some embodiments the first aspect of the present invention provides a diesel fuel composition comprising renewable diesel fuel and an ester lubricity additive; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound; and wherein the weight of ratio n-paraffins to i-paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85.

[0167] In some embodiments the second aspect of the present invention provides a method of improving the lubricity of a diesel fuel composition comprising renewable diesel fuel; the method comprising dosing into the fuel composition an ester lubricity additive which is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound; wherein the weight of ratio n-paraffins to i-paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85.

[0168] In some embodiments the third aspect of the present invention provides a storage tank comprising a diesel fuel composition where the diesel fuel composition comprises renewable diesel fuel and an ester lubricity additive; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound; and wherein the weight of ratio n-paraffins to i-paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85.

[0169] In some embodiments the fourth aspect of the present invention provides the use of an ester lubricity additive which is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound to improve the lubricity of a diesel fuel composition comprising renewable diesel fuel; wherein the weight of ratio n-paraffins to i-paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85. In some embodiments the first aspect of the present invention provides a diesel fuel composition comprising a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C and an ester lubricity additive; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound; and wherein the weight of ratio n-paraffins to i-paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85.

[0170] In some embodiments the second aspect of the present invention provides a method of improving the lubricity of a diesel fuel composition comprising a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C; the method comprising dosing into the fuel composition an ester lubricity additive which is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound; wherein the weight of ratio n- paraffins to i-paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85.

[0171] In some embodiments the third aspect of the present invention provides a storage tank comprising a diesel fuel composition where the diesel fuel composition comprises a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C and an ester lubricity additive; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound; and wherein the weight of ratio n-paraffins to i-paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85.

[0172] In some embodiments the fourth aspect of the present invention provides the use of an ester lubricity additive which is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound to improve the lubricity of a diesel fuel composition comprising a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C; wherein the weight of ratio n-paraffins to i-paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85.

[0173] In some embodiments the first aspect of the present invention provides a diesel fuel composition comprising a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C and an ester lubricity additive; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound; and wherein the weight of ratio n-paraffins to i-paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85; and wherein renewable diesel provides 100 vol% of all fuel present in the diesel fuel composition. In some embodiments the second aspect of the present invention provides a method of improving the lubricity of a diesel fuel composition comprising a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C; the method comprising dosing into the fuel composition an ester lubricity additive which is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound; wherein the weight of ratio n- paraffins to i-paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85; and wherein renewable diesel provides 100 vol% of all fuel present in the diesel fuel composition.

[0174] In some embodiments the third aspect of the present invention provides a storage tank comprising a diesel fuel composition where the diesel fuel composition comprises a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C and an ester lubricity additive; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound; wherein the weight of ratio n- paraffins to i-paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85; and wherein renewable diesel provides 100 vol% of all fuel present in the diesel fuel composition.

[0175] In some embodiments the fourth aspect of the present invention provides the use of an ester lubricity additive which is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound to improve the lubricity of a diesel fuel composition comprising a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C; wherein the weight of ratio n-paraffins to i-paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85; and wherein renewable diesel provides 100 vol% of all fuel present in the diesel fuel composition.

[0176] In some embodiments the first aspect of the present invention provides a diesel fuel composition comprising a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C and an ester lubricity additive; and wherein the weight of ratio n-paraffins to i-paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85; and wherein the ester lubricity additive is the reaction product of hydrocarbyl substituted succinic acid compound, a polyhydric alcohol and a monohydric alcohol and comprises compounds of formula (VII) or (VIII): wherein R4is the residue of the monohydric alcohol and R1, R2and R3are as previously defined.

[0177] In some embodiments the second aspect of the present invention provides a method of improving the lubricity of a diesel fuel composition comprising a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C; the method comprising dosing into the fuel composition an ester lubricity additive; wherein the weight of ratio n-paraffins to i- paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85; and wherein the ester lubricity additive is the reaction product of hydrocarbyl substituted succinic acid compound, a polyhydric alcohol and a monohydric alcohol and comprises compounds of formula (VII) or (VIII): wherein R4is the residue of the monohydric alcohol and R1, R2and R3are as previously defined.

[0178] In some embodiments the third aspect of the present invention provides a storage tank comprising a diesel fuel composition where the diesel fuel composition comprises a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C and an ester lubricity additive; wherein the weight of ratio n-paraffins to i-paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85 and wherein the ester lubricity additive is the reaction product of hydrocarbyl substituted succinic acid compound, a polyhydric alcohol and a monohydric alcohol and comprises compounds of formula (VII) or (VIII): wherein R4is the residue of the monohydric alcohol and R1, R2and R3are as previously defined.

[0179] In some embodiments the fourth aspect of the present invention provides the use of an ester lubricity additive to improve the lubricity of a diesel fuel composition comprising a renewable diesel fuel having a cloud point of less than -20°C, preferably less than -25°C; wherein the weight of ratio n-paraffins to i-paraffins present in the renewable diesel fuel is from 1 :99 to 20:80; preferably from 5:95 to 15:85; and wherein the ester lubricity additive is the reaction product of hydrocarbyl substituted succinic acid compound, a polyhydric alcohol and a monohydric alcohol and comprises compounds of formula (VII) or (VIII): wherein R4is the residue of the monohydric alcohol and R1, R2and R3are as previously defined.

[0180] The present inventors have observed that for some known ester lubricity additives reliable performance cannot be maintained in paraffinic fuels such as those comprising renewable diesel when these fuels are stored, especially if they are stored at low temperatures. However for fuels according to the invention a substantially even distribution of the lubricity additive can be maintained throughout the fuel composition, even on storage. This means that measurements of lubricity improving performance are consistent for fuel samples drawn from different portions of the fuel.

[0181] Thus in some preferred embodiments the first aspect of the present invention provides a diesel fuel composition comprising a paraffinic fuel and an ester lubricity additive which fuel composition has been stored at a temperature of below 10°C for at least 12 hours; wherein the concentration of the ester lubricity additive is substantially equal throughout the diesel fuel composition and wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.

[0182] In some embodiments the diesel fuel composition has been stored at a temperature of below 10°C for at least 18 hours, for example at least 24 hours, suitably at least 48 hours.

[0183] In some embodiments the diesel fuel composition of the composition has been stored at a temperature of below 5°C, for example below 0°C or below -5°C or even below -10°C, for at least 12 hours.

[0184] In some embodiments the diesel fuel composition of the composition has been stored at a temperature of below 5°C, for example below 0°C or below -5°C or even below -10°C, for at least 24 hours or at least 48 hours.

[0185] In some embodiments the diesel fuel composition of the composition has been stored at a temperature of below 0°C, for more than 5 days, preferably more than 10 days, for example more than 20 days.

[0186] The diesel fuel composition of the first aspect of the present invention which has been stored at a temperature of below 10°C for at least 12 hours has a concentration of ester lubricity additive which is substantially equal throughout the diesel fuel composition.

[0187] By substantially equal it is meant that the concentration of ester lubricity additive does not vary by more than 30% throughout the batch of fuel, i.e. it does not depend on from what portion of the fuel a sample is taken. Preferably the concentration of ester lubricity additive does not vary by more than 20% throughout the batch of fuel. Most preferably the concentration of ester lubricity additive varies by less than 10%, more preferably less than 5% throughout the diesel fuel composition. In some preferred embodiments of the second aspect of the present invention there is provided a method of providing a consistent improvement in lubricity performance of a diesel fuel composition comprising a paraffinic fuel following cold storage, the method comprising:

[0188] (a) dosing an ester lubricity additive into the fuel composition; and

[0189] (b) storing the fuel composition at a temperature of below 10°C for at least 12 hours; wherein after step (b) the concentration of the ester lubricity additive is substantially equal throughout the fuel composition; and wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.

[0190] In some embodiments step (b) may involve storing the diesel fuel composition at a temperature of below 10°C for at least 18 hours, for example at least 24 hours, suitably at least 48 hours.

[0191] In some embodiments step (b) may involve storing the diesel fuel composition at a temperature of below 5°C, for example below 0°C or below -5°C or even below -10°C, for at least 12 hours.

[0192] In some embodiments step (b) may involve storing the diesel fuel composition at a temperature of below 5°C, for example below 0°C or below -5°C or even below -10°C, for at least 24 hours or at least 48 hours.

[0193] In some embodiments step (b) may involve storing the diesel fuel composition at a temperature of below 0°C, for more than 5 days, preferably more than 10 days, for example more than 20 days.

[0194] After step (b) the concentration of the ester lubricity additive is substantially equal throughout the diesel fuel composition. Substantially equal concentration is as defined above.

[0195] The method of the second aspect provides a consistent improvement in lubricity performance of a diesel fuel. By a consistent improvement in lubricity performance it is meant that that the same or similar level of lubricity enhancement is achieved no matter from what part of the diesel fuel composition a sample is taken.

[0196] Lubricity is evaluated by measuring wear between two metals components in a high frequency reciprocating rig (HFRR). This is a standard test method that is known to the person skilled in the art and is described, for example, in ISO 12156-1 :2023.

[0197] In this test a wear scar is measured. Preferably the present invention provides a consistent improvement in lubricity such that the wear scar is substantially the same for any sample taken from the diesel fuel composition. By substantially the same it is meant that the wear scar does not vary by more than 100 microns no matter from what part of the diesel fuel composition a sample is taken. Preferably the wear scar does not vary by more than 80 microns. More preferably the wear scar does not vary by more than 60 microns.

[0198] Preferably the wear scar of the diesel fuel composition is substantially the same after step (a) and after step (b).

[0199] Thus in preferred embodiments the wear scar of a sample of the diesel fuel composition measured after step (a) is suitably within 100 microns, preferably within 80 microns or 60 microns of the wear scar of the of a sample of the diesel fuel composition measured after step (b).

[0200] In some preferred embodiments of the third aspect of the present invention there is provided a storage tank comprising a diesel fuel composition wherein the diesel fuel composition comprises a paraffinic fuel and an ester lubricity additive which have been held in the storage tank for at least 12 hours; wherein the lubricity of a sample of the fuel composition taken from an upper region of the storage tank is substantially the same as the lubricity of a sample of the fuel composition taken from a lower region of the storage tank; and wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.

[0201] Suitably the diesel fuel composition has been held in the storage tank at a temperature of below 10°C for at least 12 hours.

[0202] Suitably the diesel fuel composition has been held in the storage tank for at least 18 hours, for example at least 24 hours, suitably at least 48 hours.

[0203] In some embodiments the diesel fuel composition has been held in the storage tank at a temperature of below 10°C for at least 18 hours, for example at least 24 hours, suitably at least 48 hours.

[0204] In some embodiments the diesel fuel composition of the composition has been held in the storage tank at a temperature of below 5°C, for example below 0°C or below -5°C or even below -10°C, for at least 12 hours.

[0205] In some embodiments the diesel fuel composition of the composition has been held in the storage tank at a temperature of below 5°C, for example below 0°C or below -5°C or even below -10°C, for at least 24 hours or at least 48 hours. In some embodiments the diesel fuel composition of the composition has been held in the storage tank at a temperature of below 0°C, for more than 5 days, preferably more than 10 days, for example more than 20 days.

[0206] In preferred embodiments of the third aspect of the invention the lubricity of a sample of the fuel composition taken from an upper region of the storage tank is substantially the same as the lubricity of a sample of the fuel composition taken from a lower region of the storage tank.

[0207] Suitably the difference in the wear scar measured for a sample of the diesel fuel composition taken from an upper region of the storage tank and a sample of the diesel fuel composition taken from a lower region of the storage tank using the same HFRR test is less than 100 microns. Preferably the difference is less than 80 microns, more preferably less than 60 microns.

[0208] In some preferred embodiments of the fourth aspect of the present invention there is provided the use of an ester lubricity additive to provide a consistent improvement in the lubricity of a diesel fuel composition comprising a paraffinic fuel during cold storage; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.

[0209] Suitably cold storage involves storing the fuel at a temperature of below 10°C.

[0210] In some embodiments cold storage may involve storing the fuel at a temperature of below 5°C, suitably below 0°C, for example below -5°C or below -10°C.

[0211] In some embodiments cold storage may involve storing the fuel at a temperature of below 10°C for at least 12 hours.

[0212] In some embodiments cold storage may involve storing the fuel at a temperature of below 10°C for at least at least 18 hours, for example at least 24 hours, suitably at least 48 hours.

[0213] In some embodiments cold storage may involve storing the fuel at a temperature of below 5°C for at least 12 hours, for example at least 24 hours, suitably at least 48 hours.

[0214] In some embodiments cold storage may involve storing the fuel at a temperature of below 5°C, for example below 0°C or below -5°C or even below -10°C, for at least 12 hours. In some embodiments cold storage may involve storing the fuel at a temperature of below 5°C, for example below 0°C or below -5°C or even below -10°C, for at least 24 hours or at least 48 hours.

[0215] In some embodiments cold storage may involve storing the fuel at a temperature of below 0°C, for more than 5 days, preferably more than 10 days, for example more than 20 days.

[0216] In preferred embodiments the use of the fourth aspect provides a fuel which has a concentration of ester lubricity additive which is substantially equal throughout the diesel fuel composition.

[0217] Suitably the use of the fourth aspect provides a diesel fuel composition having a consistent lubricity such that the wear scar is substantially the same for any sample taken from the diesel fuel composition. As detailed above, by substantially the same it is meant that the wear scar does not vary by more than 100 microns, preferably by not more than 80 microns, suitably by not more than 60 microns.

[0218] The present invention relates to the provision of a diesel fuel composition having improved lubricity.

[0219] Preferably the diesel fuel composition provided by the present invention has a wear scar diameter as measured in the HFRR test of less than 420 pm, preferably less than 400 pm.

[0220] Preferably the diesel fuel composition provided by the present invention has a wear scar diameter as measured in the HFRR test of less than 420 pm, preferably less than 400 pm; provides a consistent lubricity such that the wear scar does not vary by more than 100 microns, preferably by not more than 80 microns, suitably by not more than 60 microns, no matter from what part of the diesel fuel composition a sample is taken; and maintains said consistent performance following cold storage, for example at a temperature of below 0°C for at least 48 hours.

[0221] Suitably the addition of the ester lubricity additive according to the invention reduces the wear scar of the diesel fuel composition by at least 50 pm, preferably at least 70 pm, for example at least 100 pm compared with the wear scar of the base fuel without the ester lubricity.

[0222] The invention will now be further decided by reference to the following non-limiting examples.

[0223] Example 1 Fuel compositions 1 to 4 were prepared by dosing additives A to D into a hydrotreated vegetable oil (HVO) fuel, as detailed in table 1 . The additives and fuel were both stored at -20°C before dosing.

[0224] Table 1

[0225] The HVO fuel complied with the specification set out in EN15940 (2023). The cloud point of the fuel was - 31.2°C (measured according to IP 219) and the pour point was below -36°C (measured according to IP 15).

[0226] Characterisation of the fuel by gas chromatography showed the composition to comprise 7.3 wt% linear alkanes and 92.7 wt% isomerised alkanes. A detailed analysis of the fuel is shown in table 2:

[0227] Table 2

[0228] Additive A comprises an ester reaction product of ethylene glycol and a succinic anhydride obtained by the reaction of maleic anhydride and a C15 to C internal olefin.

[0229] Additive B comprises an ester of glycerol and a distilled soy oil fatty acid.

[0230] Additive C comprises a glycerol ester of a mixture of C16 to C20 fatty acids comprising predominantly oleic and linoleic acid.

[0231] Additive D comprises an ester of tall oil fatty acid and glycerol.

[0232] Fuel composition 1 is of the invention; fuel compostions 2 to 4 are comparative.

[0233] Example 2

[0234] Fuel compositions 1 to 4 were stored at -20°C for 28 days. HFRR tests were carried out from samples from the upper and lower regions of the stored fuel compositions after 0, 1 , 7, and 14 days.

[0235] In each case 2 mL samples were taken from the centre of the top and the centre of the bottom of the fuel taking care not to disturb the bulk fuel.

[0236] The results are shown in table 3:

[0237] Table 3

[0238] Table 4 summarises the difference in the wear scar for the upper and lower portions of the fuel over time for each of the tested compositions: Table 4

[0239] Compositions 1 and 2 were stored for a further 14 days. At the end of this period (28 days) there was no difference in wear scar for the upper and lower portions of composition 1. For composition 2 the difference was 190 microns.

Claims

Claims1. A diesel fuel composition comprising a paraffinic fuel and an ester lubricity additive; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.

2. A method of improving the lubricity of a diesel fuel composition comprising a paraffinic fuel, the method comprising dosing into the fuel composition an ester lubricity additive which is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.

3. A storage tank comprising a diesel fuel composition where the diesel fuel composition comprises a paraffinic fuel and an ester lubricity additive; wherein the ester lubricity additive is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound.

4. The use of an ester lubricity additive which is the reaction product of a polyhydric alcohol and a hydrocarbyl substituted succinic acid compound to improve the lubricity of a diesel fuel composition comprising a paraffinic fuel.

5. A diesel fuel composition, method, storage tank or use according to any preceding claim wherein the hydrocarbyl substituted succinic acid compound has a substituent derived from an internal olefin having 6 to 36 carbon atoms, preferably from 14 to 18 carbon atoms.

6. A diesel fuel composition, method, storage tank or use according to any preceding claim wherein the polyhydric alcohol is selected from ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerol and diglycerol.

7. A diesel fuel composition, method, storage tank or use according to claim 7 wherein the polyhydric alcohol is ethylene glycol.

8. A diesel fuel composition, method, storage tank or use according to any preceding claim wherein renewable diesel provides at least 90 vol%, preferably at least 99 vol% of all fuel present in the diesel fuel composition.

9. A diesel fuel composition, method, storage tank or use according to any preceding claim wherein the weight of ratio n-paraffins to i-paraffins present in the paraffinic fuel is from 1 :99 to 20:80; for example from 5:95 to 15:85.

10. A diesel fuel composition, method, storage tank or use according to any preceding claim wherein the paraffinic fuel has a cloud point of less than -15°C, preferably less than -20°C.

11. A diesel fuel composition according to any of claims 1 or 5 to 10 which has been stored at a temperature of below 10°C for at least 12 hours; wherein the concentration of the ester lubricity additive is substantially equal throughout the diesel fuel composition.

12. A diesel fuel composition according to claim 11 which has been stored at a temperature of below 0°C for more than 5 days.

13. A method according to any of claims 2 or 5 to 10 which provides a consistent improvement in lubricity performance and involves the steps of:(a) dosing the ester lubricity additive into the fuel composition; and(b) storing the fuel composition at a temperature of below 10°C for at least 12 hours; wherein after step (b) the concentration of the ester lubricity additive is substantially equal throughout the fuel composition.

14. A method according to claim 13 wherein step (b) involves storing the diesel fuel composition at a temperature of below 0°C for more than 5 days.

15. A method according to claim 13 or claim 14 wherein the wear scar does not vary by more than 60 microns for any sample taken from the diesel fuel composition.

16. A method according to any of claims 13 to 15 wherein the wear scar of the diesel fuel composition is substantially the same after step (a) and after step (b).

17. A storage tank according to any of claims 3 or 5 to 10 wherein the diesel fuel composition has been held in the storage tank for at least 12 hours; and wherein the lubricity of a sample of the fuel composition taken from an upper region of the storage tank is substantially the same as the lubricity of a sample of the fuel composition taken from a lower region of the storage tank.

18. A storage tank according to claim 17 wherein the diesel fuel composition has been held in the storage tank at a temperature of below 0°C for at least 48 hours.

19. A storage tank according to claim 17 or claim 18 wherein the difference in the wear scar measured for a sample of the diesel fuel composition taken from an upper region of the storage tank and a sample of the diesel fuel composition taken from a lower region of the storage tank using the same HFRR test is less than 60 microns.

20. A use according to any of claims 3 or 5 to 10 to provide a consistent improvement in the lubricity of the diesel fuel composition during cold storage.21 . A use according to claim 20 wherein cold storage involves storing the fuel at a temperature of below 0°C for at least 48 hours.

22. A diesel fuel composition, method, storage tank or use according to any preceding claim wherein the diesel fuel composition comprising the paraffinic fuel and an ester lubricity additive has a wear scar diameter as measured in the HFRR test of less than 400 pm.

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