Methods and uses relating to reducing NOX emissions from a diesel engine by nitrogen containing detergents

Abstract

A method of reducing the emission of nitrogen oxide and / or nitrogen dioxide from a diesel engine combusting a diesel fuel composition, the method comprising dosing into the diesel fuel composition as an additive at least one nitrogen-containing detergent.

Description

[0001] METHODS AND USES RELATING TO REDUCING NOX EMISSIONS FROM A DIESEL ENGINE BY NITROGEN CONTAINING DETERGENTS

[0002] The present invention relates to diesel fuel compositions and to methods and uses relating thereto. In particular the invention relates to diesel fuel compositions having reduced emissions of nitrogen oxides.

[0003] The combustion of fossil fuels leads to the formation of nitrogen oxide species. The nitrogen oxides formed, commonly termed NOX, include nitric oxide (NO) and nitrogen dioxide (NO2).

[0004] NOXare known to cause significant health and environmental problems. For example exposure to NOXcan trigger respiratory difficulties, especially asthma.

[0005] Currently attempts to reduce NOXemissions are focused on treatment of exhaust gases after they have left the combustion chamber, by the inclusion of a selective catalytic reduction (SCR) unit. The SCR unit converts NOXand other harmful gases in the exhaust stream into less harmful substances. The SCR unit commonly involves the use of urea as a reductant in the presence of a catalyst. The selective catalytic reduction unit comprises a porous ceramic support and a catalyst, typically comprising a metal or a zeolite. This unit is part of the post combustion system of a diesel engine which typically includes a series of components through which exhaust gases must flow before exiting the vehicle.

[0006] The SCR unit requires regular maintenance and may need to be treated with an additive. Some vehicles include means for dosing a separate additive into the exhaust stream specifically directed at regeneration of the catalyst. This adds costs and complexity to the vehicle maintenance procedure.

[0007] It would therefore be desirable to provide fuel compositions which on combustion provide reduced NO and NOXemissions. The present inventors have surprisingly found the inclusion of certain additives in a diesel fuel can advantageously lead to a reduction in NO and NOXemissions.

[0008] According to a first aspect of the present invention there is provided a method of reducing the emission of nitrogen oxide and / or nitrogen dioxide from a diesel engine combusting a diesel fuel composition, the method comprising dosing into the diesel fuel composition as an additive at least one nitrogen-containing detergent.

[0009] According to a second aspect of the present invention there is provided the use of at least one nitrogen-containing detergent as an additive to reduce the emission of nitrogen oxide and / or nitrogen dioxide from a diesel engine combusting a diesel fuel composition. The present invention relates to the use of an additive to reduce the emission of nitrogen oxide and / or nitrogen dioxide on combustion of a diesel fuel composition.

[0010] The present invention involves the use of one or more nitrogen containing detergents as an additive. By this we mean that the invention may include the use of one nitrogen containing detergent as an additive or the use of multiple nitrogen containing detergents as multiple additives.

[0011] For the avoidance of doubt each additive used in the present invention may comprise a mixture of compounds and references to an additive or the additive include mixtures, unless otherwise stated. In particular mixtures of isomers and mixtures of homologues are within the scope of the invention. The skilled person will appreciate that commercial sources of some of the additive compounds described herein may comprise mixtures of isomers and / or mixtures of homologues.

[0012] The invention relates to the use of one or more nitrogen containing detergents. Any suitable nitrogen containing detergent may be used.

[0013] Preferably the one or more nitrogen containing detergents are selected from:

[0014] (a) a quaternary ammonium salt additive;

[0015] (b) the reaction product of a carboxylic acid-derived acylating agent and an amine;

[0016] (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol;

[0017] (d) the reaction product of a carboxylic acid-derived acylating agent and hydrazine;

[0018] (e) a salt formed by the reaction of a carboxylic acid with a C1 to C10 alkyl amine such as di-n-butylamine or tri-n-butylamine;

[0019] (f) the reaction product of a hydrocarbyl-substituted dicarboxylic acid or anhydride and an amine compound or salt which product comprises at least one amino triazole group; and

[0020] (g) a compound of formula (I):

[0021] A— L— R1

[0022] (I) wherein: A is a nitrogen-containing group;

[0023] L is either a bond or a linker group; and

[0024] R1is an optionally substituted hydrocarbyl group; and wherein the compound has a nitrogen content of at least 4% by mass.

[0025] The one or more nitrogen containing detergents are preferably selected from one or more of:

[0026] (a) quaternary ammonium salt additives;

[0027] (b) the reaction product of a carboxylic acid-derived acylating agent and an amine;

[0028] (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol; and

[0029] (g) a compound of formula (I):

[0030] A— L— R1

[0031] (I) wherein:

[0032] A is a nitrogen-containing group;

[0033] L is either a bond or a linker group; and

[0034] R1is an optionally substituted hydrocarbyl group; wherein the compound has a nitrogen content of at least 4% by mass.

[0035] In some embodiments the one or more nitrogen containing detergents may comprise (a) a quaternary ammonium salt additive.

[0036] The term “quaternary ammonium compounds” is used herein interchangeably with “quaternary ammonium salt additive” and “quaternary ammonium salt”.

[0037] Preferably the quaternary ammonium salt additive is the reaction product of a compound including a tertiary amine group and a quaternising agent.

[0038] Any suitable quaternising agent may be used. The quaternising agent may suitably be selected from esters and non-esters.

[0039] Suitable quaternising agents include esters of a carboxylic acid, dialkyl sulfates, benzyl halides, hydrocarbyl substituted carbonates, hydrocarbyl substituted epoxides optionally in combination with an acid, alkyl halides, alkyl sulfonates, sulfones, hydrocarbyl substituted phosphates, hydrocarbyl substituted borates, alkyl nitrites, alkyl nitrates, hydroxides, N-oxides, chloroacetic acid or salts thereof, or mixtures thereof.

[0040] In some preferred embodiments, quaternising agents used to form the quaternary ammonium salt additives of the present invention are esters.

[0041] Preferred ester quaternising agents are compounds of formula (II): in which R3is an optionally substituted alkyl, alkenyl, aryl or alkylaryl group and R2is a C1 to C22 alkyl, aryl or alkylaryl group. The compound of formula (II) is suitably an ester of a carboxylic acid capable of reacting with a tertiary amine to form a quaternary ammonium salt.

[0042] Suitable quaternising agents include esters of carboxylic acids having a pKa of 3.5 or less.

[0043] The compound of formula (II) is preferably an ester of a carboxylic acid selected from a substituted aromatic carboxylic acid, an a-hydroxycarboxylic acid and a polycarboxylic acid.

[0044] In some preferred embodiments the compound of formula (II) is an ester of a substituted aromatic carboxylic acid and thus R3is a substituted aryl group.

[0045] Preferably R3is a substituted aryl group having 6 to 10 carbon atoms, preferably a phenyl or naphthyl group, most preferably a phenyl group. R3is suitably substituted with one or more groups selected from carboalkoxy, nitro, cyano, hydroxy, SRXor NRxRy. Each of Rxand Rymay be hydrogen or optionally substituted alkyl, alkenyl, aryl or carboalkoxy groups. Preferably each of Rxand Ryis hydrogen or an optionally substituted C1 to C22 alkyl group, preferably hydrogen or a C1 to C16 alkyl group, preferably hydrogen or a C1 to C10 alkyl group, more preferably hydrogen or a C1 to C4 alkyl group. Preferably Rxis hydrogen and Ryis hydrogen or a C1 to C4 alkyl group. Most preferably Rxand Ryare both hydrogen. Preferably R3is an aryl group substituted with one or more groups selected from hydroxyl, carboalkoxy, nitro, cyano and NH2. R3may be a poly-substituted aryl group, for example trihydroxyphenyl. In some embodiments R3may be a hydrocarbyl substituted aryl group, for example an alkyl substituted aryl group. In some embodiments R3may be an aryl group substituted with a hydroxy group and a hydrocarbyl group, such as an alkyl group, for example as described in EP2631283. Preferably R3is a mono-substituted aryl group. Preferably R3is an ortho substituted aryl group. Suitably R3is substituted with a group selected from OH, NH2, NO2 or COOMe. Preferably R3is substituted with an OH or NH2 group. Suitably R3is a hydroxy substituted aryl group. Most preferably R3is a 2-hydroxyphenyl group.

[0046] Preferably R2is an alkyl, aralkyl or alkaryl group. R2may be a C1 to C16 alkyl group, preferably a C1 to C10 alkyl group, suitably a C1 to C8 alkyl group. R2may be C7 to C16 aralkyl or alkaryl group, preferably a C7 to C10 aralkyl or alkaryl group. R2may be methyl, ethyl, propyl, butyl, pentyl, benzyl or an isomer thereof. Preferably R2is benzyl or methyl. Most preferably R2is methyl.

[0047] Especially preferred compounds of formula (II) are lower alkyl esters of salicylic acid such as methyl salicylate, ethyl salicylate, n- and / -propyl salicylate, and butyl salicylate, preferably methyl salicylate.

[0048] In some embodiments the compound of formula (II) is an ester of an a-hydroxycarboxylic acid. In such embodiments the compound has the structure: wherein R4and R5are the same or different and each is selected from hydrogen, alkyl, alkenyl, aralkyl or aryl. Compounds of this type suitable for use herein are described in EP1254889.

[0049] Examples of compounds of formula (II) in which R3COO is the residue of an a-hydroxycarboxylic acid include methyl-, ethyl-, propyl-, butyl-, pentyl-, hexyl-, benzyl-, phenyl-, and allyl esters of 2- hydroxyisobutyric acid; methyl-, ethyl-, propyl-, butyl-, pentyl-, hexyl-, benzyl-, phenyl-, and allyl esters of 2-hydroxy-2-methylbutyric acid; methyl-, ethyl-, propyl-, butyl-, pentyl-, hexyl-, benzyl-, phenyl-, and allyl esters of 2-hydroxy-2-ethylbutyric acid; methyl-, ethyl-, propyl-, butyl-, pentyl-, hexyl-, benzyl-, phenyl-, and allyl esters of lactic acid; and methyl-, ethyl-, propyl-, butyl-, pentyl- , hexyl-, allyl-, benzyl-, and phenyl esters of glycolic acid. Of the above, a preferred compound is methyl 2-hydroxyisobutyrate.

[0050] In some embodiments the compound of formula (II) is an ester of a polycarboxylic acid. In this definition we mean to include dicarboxylic acids and carboxylic acids having more than 2 acidic moieties. In such embodiments R3COO is preferably present in the form of an ester, that is the one or more further acid groups present in the group R3are in esterified form. However embodiments in which not all acid groups are esterified are within the invention. Mixed esters of polycarboxylic acids may also be used. Preferred esters are C1 to C4 alkyl esters.

[0051] The ester quaternising agent may be selected from the diester of oxalic acid, the diester of phthalic acid, the diester of maleic acid, the diester of malonic acid or the diester of citric acid. One especially preferred compound of formula (II) is dimethyl oxalate.

[0052] In preferred embodiments the compound of formula (II) is an ester of a carboxylic acid having a pKa of less than 3.5. In such embodiments in which the compound includes more than one acid group, we mean to refer to the first dissociation constant.

[0053] The ester quaternising agent may be selected from an ester of a carboxylic acid selected from one or more of oxalic acid, phthalic acid, salicylic acid, maleic acid, malonic acid, citric acid, nitrobenzoic acid, aminobenzoic acid, 2,4,6-trihydroxybenzoic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, acetylene dicarboxylic acid, glutaconic acid, muconic acid, citraconic acid, mesaconic acid, itaconic acid, tartronic acid, mesoxalic acid, tartaric acid, oxaloacetic acid, dioxosuccinic acid, alpha-hydroxyglutaric acid, diphenic acid and 2,6-naphthalenedicarboxylic acid.

[0054] The ester quaternising agent may be selected from an ester of a carboxylic acid selected from one or more of oxalic acid, phthalic acid, salicylic acid, maleic acid, malonic acid, citric acid, nitrobenzoic acid, aminobenzoic acid and 2,4,6-trihydroxybenzoic acid.

[0055] Preferred ester quaternising agents include dimethyl oxalate, methyl 2-nitrobenzoate and methyl salicylate.

[0056] In some preferred embodiments, quaternising agents used to form the quaternary ammonium salt additives of the present invention are esters selected from dimethyl oxalate, methyl 2- nitrobenzoate and methyl salicylate, preferably dimethyl oxalate and methyl salicylate.

[0057] Suitable non-ester quaternising agents include dialkyl sulfates, benzyl halides, hydrocarbyl substituted carbonates, hydrocarbyl substituted epoxides optionally in combination with an acid, alkyl halides, alkyl sulfonates, sulfones, hydrocarbyl substituted phosphates, hydrocarbyl substituted borates, alkyl nitrites, alkyl nitrates, hydroxides, N-oxides, chloroacetic acid or salts thereof, or mixtures thereof.

[0058] Preferred non-ester quaternising agents include dialkyl sulfates, benzyl halides, hydrocarbyl substituted carbonates, hydrocarbyl substituted epoxides in combination with an acid, alkyl halides, alkyl sulfonates, sulfones, hydrocarbyl substituted phosphates, hydrocarbyl substituted borates, N-oxides, chloroacetic acid or salts thereof, or mixtures thereof.

[0059] In some embodiments the quaternary ammonium salt may be prepared from, for example, an alkyl or benzyl halide (especially a chloride) and then subjected to an ion exchange reaction to provide a different anion as part of the quaternary ammonium salt. Such a method may be suitable to prepare quaternary ammonium hydroxides, alkoxides, nitrites or nitrates.

[0060] Suitable alkyl halides for use herein include chlorides, bromides and iodides.

[0061] Suitable benzyl halides include chlorides, bromides and iodides. The phenyl group may be optionally substituted, for example with one or more alkyl or alkenyl groups, especially when the chlorides are used. A preferred compound is benzyl bromide.

[0062] Suitable dialkyl sulfates for use herein as quaternising agents include those including alkyl groups having 1 to 10, preferably 1 to 4 carbons atoms in the alkyl chain. A preferred compound is dimethyl sulfate.

[0063] Suitable hydrocarbyl substituted carbonates may include two hydrocarbyl groups, which may be the same or different. Each hydrocarbyl group may contain from 1 to 50 carbon atoms, preferably from 1 to 20 carbon atoms, more preferably from 1 to 10 carbon atoms, suitably from 1 to 5 carbon atoms. Preferably the or each hydrocarbyl group is an alkyl group. Preferred compounds of this type include diethyl carbonate and dimethyl carbonate.

[0064] Suitable hydrocarbyl substituted epoxides have the formula: wherein each of R6, R7, R8and R9is independently hydrogen or a hydrocarbyl group having 1 to 50 carbon atoms. Examples of suitable epoxides include ethylene oxide, propylene oxide, butylene oxide, styrene oxide and stilbene oxide. The hydrocarbyl epoxides are used as quaternising agents in combination with an acid.

[0065] In some embodiments the compound including a tertiary amine group also includes an acid functional group. In these embodiments if an epoxide is used as the quaternising agent, a separate acid does not need to be added. However in other embodiments an acid, for example acetic acid, may be used. Especially preferred epoxide quaternising agents are propylene oxide and styrene oxide, optionally in combination with an additional acid.

[0066] Suitable alkyl sulfonates include those having 1 to 20, preferably 1 to 10, more preferably 1 to 4 carbon atoms.

[0067] Suitable sulfones include propane sulfone and butane sulfone.

[0068] Suitable hydrocarbyl substituted phosphates include monoalkyl phosphates, dialkyl phosphates, trialkyl phosphates and O,O-dialkyl dithiophospates. Preferred alkyl groups have 1 to 12 carbon atoms.

[0069] Suitable hydrocarbyl substituted borate groups include alkyl borates having 1 to 12 carbon atoms.

[0070] Preferred alkyl nitrites and alkyl nitrates have 1 to 12 carbon atoms.

[0071] Preferably the non-ester quaternising agent is selected from dialkyl sulfates, benzyl halides, hydrocarbyl substituted carbonates, hydrocarbyl substituted epoxides optionally in combination with an additional acid, chloroacetic acid or a salt thereof, and mixtures thereof.

[0072] Especially preferred non-ester quaternising agents for use herein are hydrocarbyl substituted epoxides in combination with an acid. These may include embodiments in which a separate acid is provided or embodiments in which the acid is provided by the tertiary amine compound that is being quaternised. Preferably the acid is provided by the tertiary amine molecule that is being quaternised.

[0073] Preferred quaternising agents for use herein include dimethyl oxalate, methyl 2-nitrobenzoate, methyl salicylate, chloroacetic acid or a salt thereof, and styrene oxide or propylene oxide optionally in combination with an additional acid.

[0074] In some embodiments mixtures of two or more quaternising agents may be used.

[0075] To form the quaternary ammonium salt additive the quaternising agent is reacted with a compound including a tertiary amine group.

[0076] Any suitable compound including a tertiary amine group may be used.

[0077] The compound including at least one tertiary amine group may be selected from: (i) the reaction product of a hydrocarbyl-substituted acylating agent and a compound comprising at least one tertiary amine group and a primary amine, secondary amine or alcohol group;

[0078] (ii) a Mannich reaction product comprising a tertiary amine group;

[0079] (iii) a polyalkylene substituted amine having at least one tertiary amine group; and

[0080] (iv) simple alkylamines and alkanolamines.

[0081] For avoidance of doubt, the compound comprising at least one tertiary amine group and a primary amine, secondary amine or alcohol group is a compound that contains at least one tertiary amine group and additionally at least one group selected from a primary amine group, secondary amine group or alcohol group within its molecular structure.

[0082] Examples of quaternary ammonium salt and methods for preparing the same are described in the following patents: US2008 / 0307698, US2008 / 0052985, US2008 / 0113890 and US2013 / 031827.

[0083] The preparation of some suitable quaternary ammonium salt additives in which the compound including at least one tertiary amine group includes component (i) is described in W02006 / 135881 , US2020 / 0024536 and WO2011 / 095819.

[0084] Component (ii) is a Mannich reaction product having a tertiary amine. The preparation of quaternary ammonium salts in which the compound including at least one tertiary amine group includes component (ii) is described in US 2008 / 0052985.

[0085] The preparation of quaternary ammonium salt additives in which the compound including at least one tertiary amine group includes component (iii) is described for example in US2008 / 0113890.

[0086] The preparation of some suitable quaternary ammonium salt additives in which the compound including at least one tertiary amine group includes component (i) is described, for example in WO2016 / 016641.

[0087] Other suitable quaternary ammonium salts include quaternised terpolymers, for example as described in US201 1 / 0258917; quaternised copolymers, for example as described in US2011 / 0315107; and the acid-free quaternised nitrogen compounds disclosed in US2012 / 0010112. In some embodiments the present invention does not encompass acid-free quaternised nitrogen compounds. In preferred embodiments the quaternary ammonium salt additives of the invention include a separate anion and a separate cation.

[0088] Further suitable quaternary ammonium salt additives for use in the present invention include the quaternary ammonium salt additives described in the applicant’s applications WO2011 / 095819, WO2013 / 017889, WO2015 / 011506, WO2015 / 011507, WO2016 / 016641 and WO2017 / 017454.

[0089] In some embodiments wherein the compound including at least one tertiary amine group is (i) the reaction product of a hydrocarbyl-substituted acylating agent and a compound comprising at least one tertiary amine group and a primary amine, secondary amine or alcohol group, the hydrocarbyl-substituted acylating agent may be provided by a hydrocarbyl substituted succinic acid derived acylating agent.

[0090] In such embodiments, the quaternary ammonium salt additive (a) is the quaternised reaction product of a hydrocarbyl substituted succinic acid derived acylating agent and a compound able to react with said acylating agent and which includes a tertiary amine group.

[0091] For the avoidance of doubt reference to the quaternised reaction product is meant to refer to a reaction product which comprises the tertiary amine which has then been quaternised to form a quaternary ammonium group. The quaternary ammonium salt additive is formed by reacting a quaternising agent with the reaction product of a hydrocarbyl substituted succinic acid derived acylating agent and a compound able to react with said acylating agent and which includes a tertiary amine group.

[0092] As used herein, the term "hydrocarbyl substituent" or "hydrocarbyl group" is used in its ordinary sense, which is well-known to those skilled in the art. Specifically, it refers to a group having a carbon atom directly attached to the remainder of the molecule and having predominantly hydrocarbon character. Examples of hydrocarbyl groups include:

[0093] (i) hydrocarbon groups, that is, aliphatic (which may be saturated or unsaturated, linear or branched, e.g., alkyl or alkenyl), alicyclic (e.g., cycloalkyl, cycloalkenyl) substituents, and aromatic (including aliphatic- and alicyclic-substituted aromatic) substituents, as well as cyclic substituents wherein the ring is completed through another portion of the molecule (e.g., two substituents together form a ring);

[0094] (ii) substituted hydrocarbon groups, that is, substituents containing non-hydrocarbon groups which, in the context of this invention, do not alter the predominantly hydrocarbon nature of the substituent (e.g., halo (e.g. chloro, fluoro or bromo), hydroxy, alkoxy (e.g. Ci to C4 alkoxy), keto, acyl, cyano, mercapto, amino, amido, nitro, nitroso, sulfoxy, nitryl and carboxy);

[0095] (iii) hetero substituents, that is, substituents which, while having a predominantly hydrocarbon character, in the context of this invention, contain other than carbon in a ring or chain otherwise composed of carbon atoms. Heteroatoms include sulphur, oxygen, nitrogen, and encompass substituents as pyridyl, furyl, thienyl and imidazolyl. In general, no more than two, preferably no more than one, non-hydrocarbon substituent will be present for every ten carbon atoms in the hydrocarbyl group; typically, there will be no non-hydrocarbon substituents in the hydrocarbyl group.

[0096] Suitable hydrocarbyl substituted succinic acid derived acylating agents and means of preparing them are well known in the art. For example a common method of preparing a hydrocarbyl substituted succinic acylating agent is by the reaction of maleic anhydride with an olefin using a chlorination route or a thermal route (the so-called “ene” reaction).

[0097] Illustrative of hydrocarbyl substituent based groups include n-octyl, n-decyl, n-dodecyl, tetrapropenyl, n-octadecyl, oleyl, chloroctadecyl, triicontanyl, etc. The hydrocarbyl based substituents may be made from homo- or interpolymers (e.g. copolymers, terpolymers) of mono- and di-olefins having 2 to 10 carbon atoms, for example ethylene, propylene, butane-1 , isobutene, butadiene, isoprene, 1 -hexene, 1 -octene, etc. Preferably these olefins are 1- monoolefins. Alternatively the substituent may be made from other sources, for example monomeric high molecular weight alkenes (e.g. 1-tetra-contene), aliphatic petroleum fractions, for example paraffin waxes and cracked analogs thereof, white oils, synthetic alkenes for example produced by the Ziegler-Natta process (e.g. poly(ethylene) greases) and other sources known to those skilled in the art. Any unsaturation in the substituent may if desired be reduced or eliminated by hydrogenation according to procedures known in the art.

[0098] Preferably the hydrocarbyl substituents are predominantly saturated, that is, they contain no more than one carbon-to-carbon unsaturated bond for every ten carbon-to-carbon single bonds present. Most preferably they contain no more than one carbon-to-carbon non-aromatic unsaturated bond for every 50 carbon-to-carbon bonds present.

[0099] The hydrocarbyl substituent of the succinic acid derived acylating agent preferably comprises at least 10, more preferably at least 12, for example at least 30 or at least 40 carbon atoms. It may comprise up to about 200 carbon atoms. Preferably the hydrocarbyl substituent of the acylating agent has a number average molecular weight (Mn) of between 170 to 2800, for example from 250 to 1500, preferably from 500 to 1500 and more preferably 500 to 1100. An Mn of 700 to 1300 is especially preferred. The skilled person would be familiar with standard techniques to measure number average molecular weight, such as by vapor pressure osmometry, end-group titration, proton NMR, boiling point elevation, freezing depression (cryoscopy), and GPC (gel permeation chromatography).

[0100] The hydrocarbyl substituted succinic acid derived acylating agent may comprise a mixture of compounds. For example a mixture of compounds having different hydrocarbyl substituents may be used.

[0101] Preferred hydrocarbyl-based substituents are polyisobutenes. Such compounds are known to the person skilled in the art.

[0102] Preferred hydrocarbyl substituted succinic acid derived acylating agents are polyisobutenyl succinic anhydrides. These compounds are commonly referred to as “PIBSAs” and are known to the person skilled in the art.

[0103] Conventional polyisobutenes and so-called "highly-reactive" polyisobutenes are suitable for use in the invention. Highly reactive polyisobutenes in this context are defined as polyisobutenes wherein at least 50%, preferably 70% or more, of the terminal olefinic double bonds are of the vinylidene type as described in EP0565285. Particularly preferred polyisobutenes are those having more than 80 mol% and up to 100 mol% of terminal vinylidene groups such as those described in US7291758. Preferred polyisobutenes have preferred molecular weight (Mn) ranges as described above for hydrocarbyl substituents generally.

[0104] Other preferred hydrocarbyl groups include those having an internal olefin for example as described in the applicant’s published application W02007 / 015080.

[0105] An internal olefin as used herein means any olefin containing predominantly a non-alpha double bond, that is a beta or higher olefin. Preferably such materials are substantially completely beta or higher olefins, for example containing less than 10% by weight alpha olefin, more preferably less than 5% by weight or less than 2% by weight. Typical internal olefins include Neodene 1518IO available from Shell.

[0106] Internal olefins are sometimes known as isomerised olefins and can be prepared from alpha olefins by a process of isomerisation known in the art, or are available from other sources. The fact that they are also known as internal olefins reflects that they do not necessarily have to be prepared by isomerisation. Preferred hydrocarbyl substituted succinic acid derived acylating agents for use in preparing quaternary ammonium salt additives (a) for use in the present invention are polyisobutenyl substituted succinic anhydrides or PIBSAs. Especially preferred PIBSAs are those having a PIB molecular weight (Mn) of from 300 to 2800, preferably from 450 to 2300, more preferably from 500 to 1300.

[0107] The hydrocarbyl substituted succinic acid derived acylating agent is suitably prepared by reacting maleic anhydride with an alkene, for example a polyisobutene. The product obtained (such as a PIBSA) still includes a double bond. The maleic anhydride is present in the resultant molecule as a succinic acid moiety. This initial product is a monomaleated PIBSA.

[0108] The monomaleated PIBSA may have the structure (A) or (B):

[0109] (A) (B)

[0110] The double bond in the monomaleated product can react with a further molecule of maleic anhydride to form a bismaleated PIBSA having the structure (C) or (D):

[0111] Thus it is possible to provide a hydrocarbyl group which is substituted with more than one succinic acid moiety.

[0112] The skilled person will appreciate that the additives used in the invention typically comprise mixtures of compounds and will be prepared from a mixture of monomaleated and bismaleated PIBSAs. The PIBSAs may be defined in terms of their level of bismaleation. One way in which this may be determined is by calculating the average number of succinic acid moieties per molecule of acylating agent.

[0113] A monomaleated PIBSA has one succinic acid moiety per module.

[0114] A bismaleated PIBSA has two succinic acid moieties per molecule.

[0115] A mixture comprising monomaleated PIBSA and bismaleated PIBSA in a 1 :1 molar ratio would comprise an average of 1 .5 succinic acid moieties per molecule of PIBSA.

[0116] The average number of succinic acid moieties per molecule of acylating agent is sometimes referred to in the art as “P value”.

[0117] Suitably the quaternary ammonium salt additive is prepared from a hydrocarbyl substituted succinic acid derived acylating agent comprising on average from 1 to 2 succinic acid moieties per molecule.

[0118] In some preferred embodiments the present invention may involve the use of quaternary ammonium salts derived from hydrocarbyl substituted acylating agents which include an average of at least 1 .2 succinic acid moieties per molecule.

[0119] As the skilled person will appreciate, a single molecule cannot have 1 .2 succinic acid moieties. What is meant by at least 1 .2 succinic acid moieties is the mean number of succinic acid moieties per molecule of acylating agent as the sum of all the succinic acid moieties present in a sample divided by the total number of molecules of acylating agent having one or more succinic acid moieties present in the sample.

[0120] Preferably the hydrocarbyl substituted succinic acid derived acylating agent comprises on average at least 1 .21 succinic acid moieties per molecule, more preferably at least 1 .22 succinic acid moieties per molecule.

[0121] In some embodiments the hydrocarbyl substituted succinic acid derived acylating agent may comprise at least 1 .23 or at least 1 .24 succinic acid moieties per molecule.

[0122] In some embodiments the hydrocarbyl substituted succinic acid derived acylating agent may comprise at least 1 .25, at least 1 .26 or at least 1 .27 succinic acid moieties per molecule. In some embodiments the hydrocarbyl substituted succinic acid derived acylating agent may comprise at least 1 .28, at least 1 .29 or at least 1 .30 succinic acid moieties per molecule.

[0123] By succinic acid moiety we mean to include residues of succinic acid present in diacid or anhydride form.

[0124] In some embodiments in which the compound including at least one tertiary amine group is (i) the reaction product of a hydrocarbyl-substituted acylating agent and a compound comprising at least one tertiary amine group and a primary amine, secondary amine or alcohol group, the hydrocarbyl-substituted acylating agent may be provided by a fatty acid. Suitable fatty acids are compounds of formula RZCOOH in which Rzis an alkyl or alkenyl group having 6 to 36 carbon atoms, preferably 8 to 30 carbon atoms or 12 to 24 carbon atoms. One preferred fatty acid is oleic acid.

[0125] The hydrocarbyl substituted acylating agent is reacted with a compound able to react with said acylating agent and which includes a tertiary amine group. The tertiary amine group is quaternised to provide the quaternary ammonium salt additive.

[0126] Examples of suitable compounds able to react with the hydrocarbyl substituted acylating agent and which include a tertiary amine group can include but are not limited to: N,N- dimethylaminopropylamine, N,N-diethylaminopropylamine, N,N-dimethylaminoethylamine. The nitrogen or oxygen containing compounds capable of condensing with the acylating agent and further having a tertiary amino group can further include amino alkyl substituted heterocyclic compounds such as 1-(3-aminopropyl)imidazole and 4-(3-aminopropyl)morpholine, 1-(2- aminoethyl)piperidine, 3,3-diamino-N-methyldipropylamine, and 3'3-aminobis(N,N- dimethylpropylamine). Other types of nitrogen or oxygen containing compounds capable of condensing with the acylating agent and having a tertiary amino group include alkanolamines including but not limited to triethanolamine, trimethanolamine, N,N-dimethylaminopropanol, N,N- dimethylaminoethanol, N,N-diethylaminopropanol, N,N-diethylaminoethanol, N,N- diethylaminobutanol, N,N,N-tris(hydroxyethyl)amine, N,N,N-tris(hydroxymethyl)amine, N,N,N- tris(aminoethyl)amine, N,N-dibutylaminopropylamine and N,N,N'-trimethyl-N'-hydroxyethyl- bisaminoethylether; N,N-bis(3-dimethylaminopropyl)-N-isopropanolamine ; N-(3- dimethylaminopropyl)-N,N-diisopropanolamine; N'-(3-(dimethylamino)propyl)-N,N-dimethyl 1 ,3- propanediamine; 2-(2-dimethylaminoethoxy)ethanol, N,N,N'-trimethylaminoethylethanolamine and 3-(2-(dimethylamino)ethoxy) propylamine.

[0127] Preferably the compound able to react with the hydrocarbyl substituted acylating agent and which includes a tertiary amine group is an amine of formula (III) or (IV): wherein R10and R11are the same or different alkyl, alkenyl, aryl, alkaryl or aralkyl groups having from 1 to 22 carbon atoms; X is a bond or an optionally substituted alkylene group having from 1 to 20 carbon atoms; n is from 0 to 20; m is from 1 to 5; and R12is hydrogen or a Ci to C22 alkyl group.

[0128] When a compound of formula (III) is used, R12is preferably hydrogen or a Ci to C alkyl group, preferably a Ci to Cw alkyl group, more preferably a Ci to Ce alkyl group. When R12is alkyl it may be straight chained or branched. It may be substituted for example with a hydroxy or alkoxy substituent. Preferably R12is not a substituted alkyl group. More preferably R12is selected from hydrogen, methyl, ethyl, propyl, butyl and isomers thereof. Most preferably R12is hydrogen.

[0129] When a compound of formula (IV) is used, m is preferably 2 or 3, most preferably 2; n is preferably from 0 to 15, preferably 0 to 10, more preferably from 0 to 5. Most preferably n is 0 and the compound of formula (IV) is an alcohol.

[0130] Preferably the hydrocarbyl substituted acylating agent is reacted with a diamine compound of formula (III).

[0131] R10and R11are the same or different alkyl, alkenyl, aryl, alkaryl or aralkyl groups having from 1 to 22 carbon atoms. In some embodiments R10and R11may be joined together to form a ring structure, for example a piperidine, imidazole or morpholine moiety. Thus R10and R11may together form an aromatic and / or heterocyclic moiety. R10and R11may be branched alkyl or alkenyl groups. Each may be substituted, for example with a hydroxy or alkoxy substituent.

[0132] Preferably each of R10and R11is independently a Ci to Cw alkyl group, preferably a Ci to Cw alkyl group. R10and R11may independently be methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, or an isomer of any of these. Preferably R10and R11is each independently Ci to C4 alkyl. Preferably R10is methyl. Preferably R11is methyl.

[0133] X is a bond or an optionally substituted alkylene group having from 1 to 20 carbon atoms. In preferred embodiments when X is an alkylene group this group may be straight chained or branched. The alkylene group may include a cyclic structure therein. It may be optionally substituted, for example with a hydroxy or alkoxy substituent. In some embodiments X may include a heteroatom within the alkylene chain, for example X may include an ether functionality.

[0134] X is preferably an alkylene group having 1 to 16 carbon atoms, preferably 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms, for example 2 to 6 carbon atoms or 2 to 5 carbon atoms. In some preferred embodiments X is an unsubstituted alkylene group. Most preferably X is an ethylene, propylene or butylene group, especially a propylene group.

[0135] Examples of compounds of formula (III) suitable for use herein include 1-aminopiperidine, 1-(2- aminoethyl)piperidine, 1- (3-aminopropyl)-2-pipecoline, 1-methyl-(4-methylamino)piperidine, 4- (1 -py rro lid iny I) pi pe rid i n e , 1 -(2-aminoethyl)pyrrolidine, 2-(2-aminoethyl)-1 - methylpyrrolidine, N,N-diethylethylenediamine, N,N-dimethylethylenediamine, N,N-dibutylethylenediamine, N,N- diethyl-l,3-diaminopropane, N,N-dimethyl-1 ,3-diaminopropane, N,N,N'- trimethylethylenediamine, N,N-dimethyl-N'-ethylethylenediamine, N,N-diethyl-N'- methylethylenediamine, N,N,N'- triethylethylenediamine, 3-dimethylaminopropylamine, 3- diethylaminopropylamine, 3-dibutylaminopropylamine, N,N,N'-trimethyl- 1 ,3- propanediamine, N,N,2,2-tetramethyl-l,3-propanediamine, 2-amino-5-diethylaminopentane, N,N,N',N'- tetraethyldiethylenetriamine, 3,3'-diamino-N-methyldipropylamine, 3,3'-iminobis(N,N- dimethylpropylamine), 1-(3-aminopropyl)imidazole and 4-(3-aminopropyl)morpholine, 1-(2- aminoethyl)piperidine, 3,3-diamino-N-methyldipropylamine, 3,3-aminobis(N,N- dimethylpropylamine), 3-(2-(dimethylamino)ethoxy) propylamine, or combinations thereof.

[0136] In some preferred embodiments the compound of formula (III) is selected from N,N-dimethyl- 1 ,3-diaminopropane, N,N-diethyl-1 ,3- diaminopropane, N,N-dimethylethylenediamine, N,N- diethylethylenediamine, N,N-dibutylethylenediamine, 3-(2-(dimethylamino)ethoxy) propylamine, or combinations thereof.

[0137] Examples of compounds of formula (IV) suitable for use herein include alkanolamines including but not limited to triethanolamine, N,N-dimethylaminopropanol, N,N-diethylaminopropanol, N,N- diethylaminobutanol, triisopropanolamine, 1-[2-hydroxyethyl]piperidine, 2-[2- (dimethylamine)ethoxy]-ethanol, N-ethyldiethanolamine, N-methyldiethanolamine, N- butyldiethanolamine, N,N-diethylaminoethanol, N,N-dimethyl amino- ethanol, 2-dimethylamino- 2-methyl-1 -propanol, N,N,N'-trimethyl-N'-hydroxyethyl-bisaminoethylether; N,N-bis(3- dimethylaminopropyl)-N-isopropanolamine ; N-(3-dimethylaminopropyl)-N,N- diisopropanolamine; N'-(3-(dimethylamino)propyl)-N,N-dimethyl 1 ,3-propanediamine; 2-(2- dimethylaminoethoxy)ethanol, and N,N,N'-trimethylaminoethylethanolamine.

[0138] In some preferred embodiments the compound of formula (III) is selected from Triisopropanolamine, 1-[2-hydroxyethyl]piperidine, 2-[2-(dimethylamine)ethoxy]-ethanol, N- ethyldiethanolamine, N-methyldiethanolamine, N-butyldiethanolamine, N,N- diethylaminoethanol, N,N-dimethylaminoethanol, 2-dimethylamino-2-methyl-1 -propanol, or combinations thereof.

[0139] An especially preferred compound of formula (III) is N,N-dimethyl-1 ,3-diaminopropane (dimethylaminopropylamine) .

[0140] In some embodiments the quaternary ammonium salt additives are the quaternised reaction product of a fatty acid, for example of formula RCOOH in which R is an alkyl or alkenyl group having 12 to 24 carbon atoms, and a compound of formula (II), suitably wherein both R10and R11are Ci to C4 alkyl groups and X is alkylene group having from 2 to 5 carbon atoms.

[0141] In some preferred embodiments the quaternary ammonium salt additive is the quaternised reaction product of oleic acid and dimethylaminopropyl amine.

[0142] In such embodiments, suitable quaternising agents for reaction with the reaction product described above are dialkyl sulfates, benzyl halides, hydrocarbyl substituted carbonates, hydrocarbyl substituted epoxides in combination with an acid, alkyl halides, alkyl sulfonates, sulfones, hydrocarbyl substituted phosphates, hydrocarbyl substituted borates, N-oxides, chloroacetic acid or salts thereof, or mixtures thereof. Preferably the quaternising agent is chloroacetic acid or salts thereof, for example sodium chloroacetate.

[0143] In such embodiments, the quaternary ammonium salt additive may have the formula (V): wherein R14is alkyl or alkenyl of 7 to 22 carbon atoms; R15and R16are each independently alkyl, hydroxyalkyl or carboxyalkyl of 1 to 6 carbon atoms; m is 2 to 4; n is 0 or 1 ; X is alkylene of 1 to 6 carbon atoms optionally substituted with hydroxyl; and Y is -CO2 or -SOs.

[0144] Preferably the quaternary ammonium salt additive is an amido betaine having the formula:

[0145] O R15

[0146] R 1144-C1 1— NH(CH2)m— N ' +— CH2CO2“

[0147] R16wherein R14, R15and R16are as defined above and wherein m is 2 or 3. Preferably R14has from 16 to 22 carbon atoms. R14is preferably an alkenyl group having from 16 to 22 carbon atoms. For example R14may be a C17 alkenyl group derived from oleic acid. R15and R16are preferably methyl.

[0148] In one preferred embodiment, the quaternary ammonium salt additive is the quaternised reaction product of oleic acid and dimethylaminopropyl amine, wherein the reaction product has been quaternised with chloroacetic acid or a salt thereof.

[0149] When a compound of formula (III) is reacted with a succinic acid derived acylating agent the resulting product is a succinic ester. When a succinic acylating agent is reacted with a compound of formula (II) in which R12is hydrogen the resulting product may be a succinimide or a succinamide. When a succinic acylating agent is reacted with a compound of formula (III) in which R12is not hydrogen the resulting product is an amide.

[0150] In some embodiments wherein the succinic acylating agent is reacted with a compound comprising a primary amine moiety, for example a compound of formula (III) in which R12is hydrogen, the reaction may form an amide bond, an imide bond or a mixture thereof. Therefore the reaction product may be a succinimide or a succinamide, or a mixture thereof. Whether a succinimide or a succinamide is formed may depend on the reaction conditions used. The skilled person would be able to select appropriate reaction conditions for forming predominantly the succinimide form or predominantly the succinamide form of the reaction product. The succinamide suitably comprises a free carboxylic acid moiety and an amide bond formed between the succinic acylating agent and the amine compound.

[0151] In some preferred embodiments, reaction product of a hydrocarbyl substituted succinic acid derived acylating agent and a compound able to react with said acylating agent and which includes a tertiary amine group (i.e. component (i)) is a succinimide, preferably a polyisobutenyl succinimide (known as a “PIBSI”).

[0152] In some preferred embodiments, reaction product of a hydrocarbyl substituted succinic acid derived acylating agent and a compound able to react with said acylating agent and which includes a tertiary amine group (i.e. component (i)) is a succinamide, preferably a polyisobutenyl succinamide.

[0153] In some embodiment to form the quaternary ammonium salt additive a hydrocarbyl substituted acylating agent is reacted with a compound able to react with said acylating agent and which includes a tertiary amine group. This reaction product is then quaternised by reaction with a quaternising agent. The reaction product of the acylating agent and compound which includes a tertiary amine group is preferably reacted with at least one molar equivalent of quaternising agent per mole of tertiary amine group present in the reaction product.

[0154] In some embodiments the reaction product of the acylating agent and compound which includes a tertiary amine group may be reacted with more than one molar equivalent of quaternising agent per mole of tertiary amine group present in the reaction product, preferably at least 1.2 molar equivalents of quaternising agent per mole of tertiary amine group, more preferably at least 1.5 molar equivalents of quaternising agent, suitably at least 1 .7 molar equivalents of quaternising agent, for example at least 1 .9 molar equivalents of quaternising agent.

[0155] In some embodiments the reaction product of the acylating agent and compound which includes a tertiary amine group may be reacted with two or more molar equivalents of quaternising agent per mole of tertiary amine group present in the reaction product, preferably at least 2.1 molar equivalents of quaternising agent.

[0156] In some embodiments the reaction product of the acylating agent and compound which includes a tertiary amine group is reacted with more than 2.2 molar equivalents of quaternising agent per mole of tertiary amine group present in the reaction product, for example from 2.3 to 4 molar equivalents, from 2.3 to 3 molar equivalents, or from 2.3 to 2.7 or from 2.5 to 3 molar equivalents.

[0157] To form some preferred quaternary ammonium salt additives of the present invention the compound of formula (II) is reacted with a compound formed by the reaction of a hydrocarbyl substituted acylating agent and an amine of formula (III) or (IV).

[0158] The compounds of formula (III) or formula (IV) are as described above.

[0159] Preferably the amine of formula (III) or (IV) is reacted with a hydrocarbyl substituted succinic acid derived acylating agent such as a succinic acid or succinic anhydride.

[0160] Suitably approximately one equivalent of amine is added per succinic acid moiety present in the acylating agent. The ratio of amine used will thus typically depend on the average number of succinic acid moieties present in each molecule of the acylating agent.

[0161] Preferred quaternary ammonium salts for use herein may be formed by reacting methyl salicylate, dimethyl oxalate or propylene oxide optionally in combination with an acid with the reaction product of a polyisobutylene-substituted succinic anhydride having a PIB molecular weight (Mn) of 700 to 1300 and dimethylaminopropylamine. A mixture of two or more such quaternary ammonium salts may be used.

[0162] An especially preferred quaternary ammonium salt for use herein is formed by reacting methyl salicylate or dimethyl oxalate with the reaction product of a polyisobutylene-substituted succinic anhydride having a PIB molecular weight (Mn) of 700 to 1300 and dimethylaminopropylamine.

[0163] In one preferred embodiment the polyisobutylene-substituted succinic anhydride includes on average at least 1 .2 succinic acid moieties per molecule.

[0164] In some preferred embodiments, the quaternary ammonium salt additive (a) is formed by reacting a quaternising agent with the reaction product of a polyisobutylene-substituted succinic anhydride having a PIB molecular weight (Mn) of 700 to 1300 and dimethylaminopropylamine, wherein the reaction product of the polyisobutylene-substituted succinic anhydride and the dimethylaminopropylamine is predominantly in the succinimide form. Preferably the quaternising agent is an alkylene oxide (preferably propylene oxide), optionally in combination with an acid, chloroacetic acid or a salt thereof, methyl salicylate or dimethyl oxalate. In some preferred embodiments, the quaternising agent is methyl salicylate.

[0165] In some preferred embodiments, the quaternary ammonium salt additive (a) is formed by reacting a quaternising agent with the reaction product of a polyisobutylene-substituted succinic anhydride having a PIB molecular weight (Mn) of 700 to 1300 and dimethylaminopropylamine, wherein the reaction product of the polyisobutylene-substituted succinic anhydride and the dimethylaminopropylamine is predominantly in the succinamide form. Preferably the quaternising agent is an alkylene oxide (preferably propylene oxide), optionally in combination with an acid, chloroacetic acid or a salt thereof, methyl salicylate or dimethyl oxalate. In some preferred embodiments, the quaternising agent is propylene oxide.

[0166] In some embodiments, the quaternary ammonium salt additive (a) is the reaction product of a quaternising agent and a compound including a tertiary amine group which is selected from (iv) simple alkylamines and alkanolamines.

[0167] In such embodiments, the compound including a tertiary amine group (iv) is a tertiary amine of formula R13R14R15N, wherein each of R13, R14and R15is independently an optionally substituted alkyl, alkenyl, aryl, alkaryl or aralkyl group.

[0168] The tertiary amine of formula R13R14R15N may be a small compound of low complexity and low molecular weight. In some embodiments the tertiary amine may be a complex molecule and / or a molecule of high molecular weight which includes a tertiary amine group. The tertiary amine compounds of formula R13R14R15N preferably do not include any primary or secondary amine groups. In some embodiments they may be derived from compounds including these groups but preferably these have been subsequently reacted to form additional tertiary amine species. The tertiary amine compound of formula R13R14R15N may contain more than one tertiary amine group. However tertiary amine compounds including primary or secondary amine groups are within the scope of the invention provided these groups do not prevent quaternisation of the tertiary amine species.

[0169] In some embodiment of the compounds of formula R13R14R15N, each of R13, R14and R15is independently an optionally substituted alkyl, alkenyl, aryl, aralkyl or alkaryl group.

[0170] R13, R14and R15may be the same or different. In some preferred embodiments R13and R14are the same and R15is different.

[0171] Preferably each of R13and R15is independently an optionally substituted alkyl, alkenyl, aryl, aralkyl or alkaryl group having from 1 to 50 carbon atoms, preferably from 1 to 40 carbon atoms, more preferably from 1 to 30 carbon atoms.

[0172] Each of R13and R14may be optionally substituted with one or more groups selected from halo (especially chloro and fluoro), hydroxy, alkoxy, keto, acyl, cyano, mercapto, alkylmercapto, dialkylamino, nitro, nitroso, and sulphoxy. The alkyl groups of these substituents may be further substituted.

[0173] Preferably each of R13and R14is independently an optionally substituted alkyl or alkenyl group. Preferably each of R13and R14is independently an optionally substituted alkyl group. In some embodiments each of R13and R14is independently an optionally substituted alkyl or alkenyl group having from 1 to 50 carbon atoms, preferably from 1 to 40 carbon atoms, more preferably from 1 to 30 carbon atoms, suitably from 1 to 20 carbon atoms, preferably from 1 to 12 carbon atoms, more preferably from 1 to 10 carbon atoms, suitably from 1 to 8 carbon atoms, for example from 1 to 6 carbon atoms.

[0174] In some preferred embodiments R13is an optionally substituted alkyl or alkenyl group, preferably having from 1 to 10, preferably from 1 to 4 carbon atoms. Preferably R13is an alkyl group. It may be a substituted alkyl group, for example a hydroxy substituted alkyl group. Preferably R13is an unsubstituted alkyl group. The alkyl chain may be straight-chained or branched. Preferably R13is selected from methyl, ethyl, propyl and butyl, including isomers thereof. Most preferably R13is methyl. In some preferred embodiments R14is an optionally substituted alkyl or alkenyl group, preferably having from 1 to 10, preferably from 1 to 4 carbon atoms. Preferably R14is an alkyl group. It may be a substituted alkyl group, for example a hydroxy substituted alkyl group. Preferably R14is an unsubstituted alkyl group. The alkyl chain may be straight-chained or branched. Preferably R14is selected from methyl, ethyl, propyl and butyl, including isomers thereof. Most preferably R14is methyl.

[0175] In some embodiments R15is an optionally substituted alkyl or alkenyl group having from 1 to 50 carbon atoms, preferably from 1 to 40 carbon atoms, more preferably from 1 to 30 carbon atoms, suitably from 1 to 20 carbon atoms, preferably from 1 to 12 carbon atoms, more preferably from 1 to 10 carbon atoms, suitably from 1 to 8 carbon atoms, for example from 1 to 6 carbon atoms. Suitable substituents include halo (especially chloro and fluoro), hydroxy, alkoxy, keto, acyl, cyano, mercapto, alkylmercapto, amino, alkylamino, nitro, nitroso, sulphoxy, amido, alkyamido, imido and alkylimido. The alkyl groups of these substituents may be further substituted.

[0176] In some embodiments R15is an optionally substituted alkyl or alkenyl group, preferably having from 1 to 10, preferably from 1 to 4 carbon atoms. Suitably R15is an optionally substituted alkyl group. Preferably R15is a substituted alkyl group. Preferred substituents include alkoxy and hydroxyl groups.

[0177] In some preferred embodiments R15is a hydroxyl-substituted alkyl group. The alkyl chain may be straight-chained or branched. Most preferably R15is a hydroxyethyl group.

[0178] Suitable tertiary amine compounds of formula R13R14R15N include simple alkylamino and hydroxyalkylamino compounds; trialkylamino compounds having a high molecular weight substituent; Mannich reaction products including a tertiary amine and substituted acylated amines or alcohols including a tertiary amine.

[0179] Simple alkylamino and hydroxyalkyl amino compounds are preferably compounds of formula R13R14R15N, wherein each of R13, R14and R15is an alkyl group or a hydroxyalkyl group. Each of R13, R14and R15may be the same or different. In some embodiments each of R13, R14and R15is independently selected from an alkyl or hydroxyalkyl group having 1 to 10, preferably 1 to 6 carbon atoms, for example 1 to 4 carbon atoms. Each of R13, R14and R15may be independently selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl, hydroxypentyl and hydroxyhexyl. The amine of formula R13R14R15N may be a trialkylamine, a dialkylhydroxyalkylamine, a dihydroxyalkylalkylamine or a trihydroxyalkylamine. There are many different compounds of this type and these will be known to the person skilled in the art. In some embodiments one or two of the groups R13, R14and R15is a short chain alkyl group having 1 to 6, preferably 1 to 4 carbon atoms and the other one or two groups is a longer chain alkyl or group having 6 to 30, preferably 10 to 24 carbon atoms.

[0180] In some embodiments each of R13and R14is Ci to C4 alkyl, preferably methyl and R15is an alkyl or alkenyl group having 6 to 36, preferably 10 to 30, for example 12 to 24 carbon atoms.

[0181] Compounds of this type include, for example, dimethyloctadecylamine and hexadecyl dimethyl amine.

[0182] In order to provide the quaternary ammonium salt additive, the hexadecyl dimethyl amine may be quaternised by reaction with propylene oxide (for example 1 to 3 molar equivalent of propylene oxide) and polyisobutylene succinic acid (for example 1 molar equivalent of polyisobutylene succinic acid).

[0183] For example in some embodiments R13is Ci to C4 alkyl, preferably methyl and each R14and R15is an alkyl or alkenyl having 6 to 36, preferably 8 to 30, for example 10 to 24 carbon atoms.

[0184] Compounds of this type include, for example, hexadecyl dimethyl amine, N-methyl N-N- ditallowamine and dicocomethyl amine.

[0185] Especially preferred tertiary amine compounds of formula R13R14R15N include N,N-dimethyl ethanolamine, dimethyloctadecylamine and N-methyl N-N-ditallowamine, and mixtures thereof.

[0186] In some preferred embodiments, the quaternary ammonium salt additive (a) is the reaction product of a compound including a tertiary amine group and a quaternising agent, wherein the compound including a tertiary amine group is selected from one or more of:

[0187] (i-a) the reaction product of a fatty acid of formula RZCOOH in which Rzis an alkyl or alkenyl group having 12 to 24 carbon atoms, and a compound of formula (II), wherein both R10and R11are Ci to C4 alkyl groups and X is alkylene group having from 2 to 5 carbon atoms;

[0188] (i-b) the reaction product of a hydrocarbyl substituted succinic acid derived acylating agent and a compound of formula (II), wherein both R10and R11are Ci to C4 alkyl groups and X is alkylene group having from 2 to 5 carbon atoms; and

[0189] (iv-a) a tertiary amine of formula R13R14R15N, wherein each of R13, R14and R15is independently an alkyl group or a hydroxyalkyl group. The quaternising agent is preferably selected from alkylene oxide (preferably propylene oxide), optionally in combination with an acid, chloroacetic acid or a salt thereof, methyl salicylate or dimethyl oxalate.

[0190] In some preferred embodiments, the quaternary ammonium salt additive (a) is the reaction product of a compound including a tertiary amine group and a quaternising agent, wherein the compound including a tertiary amine group is selected from one or more of:

[0191] (i-a) the reaction product of a fatty acid of formula RZCOOH in which Rzis an alkyl or alkenyl group having 12 to 24 carbon atoms, and a compound selected from N,N-dimethyl-1 ,3- diaminopropane, N,N-diethyl-1 ,3- diaminopropane, N,N-dimethylethylenediamine, N,N- diethylethylenediamine, N,N-dibutylethylenediamine, 3-(2-(dimethylamino)ethoxy) propylamine, or combinations thereof;

[0192] (i-b) the reaction product of a hydrocarbyl substituted succinic acid derived acylating agent and a compound selected from N,N-dimethyl-1 ,3-diaminopropane, N , N-diethyl-1 ,3- diaminopropane, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dibutylethylenediamine, 3-(2- (dimethylamino)ethoxy) propylamine, or combinations thereof; and

[0193] (iv-a) a tertiary amine of formula R13R14R15N, wherein each of R13, R14and R15is independently an alkyl group or a hydroxyalkyl group.

[0194] In some preferred embodiments, the quaternary ammonium salt additive (a) is the reaction product of a compound including a tertiary amine group and a quaternising agent; wherein the quaternising agent is selected from alkylene oxide (preferably propylene oxide), optionally in combination with an acid, chloroacetic acid or a salt thereof, methyl salicylate or dimethyl oxalate; wherein the compound including a tertiary amine group is selected from one or more of:

[0195] (i-a) the reaction product of a fatty acid of formula RZCOOH in which Rzis an alkyl or alkenyl group having 12 to 24 carbon atoms, and a compound selected from N,N-dimethyl-1 ,3- diaminopropane, N, N-diethyl-1 ,3- diaminopropane, N,N-dimethylethylenediamine, N,N- diethylethylenediamine, N,N-dibutylethylenediamine, 3-(2-(dimethylamino)ethoxy) propylamine, or combinations thereof;

[0196] (i-b) the reaction product of a hydrocarbyl substituted succinic acid derived acylating agent and a compound selected from N,N-dimethyl-1 ,3-diaminopropane, N, N-diethyl-1 ,3- diaminopropane, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dibutylethylenediamine, 3-(2- (dimethylamino)ethoxy) propylamine, or combinations thereof; and

[0197] (iv-a) a tertiary amine of formula R13R14R15N, wherein each of R13, R14and R15is independently an alkyl group or a hydroxyalkyl group.

[0198] In some especially preferred embodiments, the quaternary ammonium salt additive (a) is the reaction product of a compound including a tertiary amine group and a quaternising agent; wherein the quaternising agent is selected from alkylene oxide (preferably propylene oxide), optionally in combination with an acid, chloroacetic acid or a salt thereof, methyl salicylate or dimethyl oxalate; wherein the compound including a tertiary amine group is selected from one or more of:

[0199] (i-a) the reaction product of a fatty acid of formula RZCOOH in which Rzis an alkyl or alkenyl group having 12 to 24 carbon atoms, and N,N-dimethyl-1 ,3-diaminopropane (DMAPA);

[0200] (i-b) the reaction product of a polyisobutylene-substituted succinic anhydride having a PIB molecular weight (Mn) of 700 to 1300 and N,N-dimethyl-1 ,3-diaminopropane; and

[0201] (iv-a) a tertiary amine of formula R13R14R15N, wherein each of R13and R14is Ci to C4 alkyl, preferably methyl, and R15is an alkyl or alkenyl group having 12 to 24 carbon atoms.

[0202] In some embodiments the present invention involves the use as an additive of (b) the reaction product of a carboxylic acid-derived acylating agent and an amine.

[0203] These compounds may also be referred to herein in general as acylated nitrogen-containing compounds.

[0204] Suitable acylated nitrogen-containing compounds may be made by reacting a carboxylic acid acylating agent with an amine and are known to those skilled in the art.

[0205] Preferred hydrocarbyl substituted acylating agents are polyisobutenyl succinic anhydrides. These compounds are commonly referred to as “PIBSAs” and are known to the person skilled in the art. Conventional polyisobutenes and so-called "highly-reactive" polyisobutenes are suitable for use in the invention. These are suitably as previously described herein in relation to the preparation of some preferred quaternary ammonium detergents.

[0206] Especially preferred PIBSAs are those having a PIB molecular weight (Mn) of from 300 to 2800, preferably from 450 to 2300, more preferably from 500 to 1300.

[0207] In preferred embodiments the reaction product of the carboxylic acid derived acylating agent and an amine includes at least one primary or secondary amine group.

[0208] A preferred acylated nitrogen-containing compound for use herein is prepared by reacting a poly(isobutene)-substituted succinic acid-derived acylating agent (e.g., anhydride, acid, ester, etc.) wherein the poly(isobutene) substituent has a number average molecular weight (Mn) of between 170 to 2800 with a mixture of ethylene polyamines having 2 to about 9 amino nitrogen atoms, preferably about 2 to about 8 nitrogen atoms, per ethylene polyamine and about 1 to about 8 ethylene groups. These acylated nitrogen compounds are suitably formed by the reaction of a molar ratio of acylating agent:amino compound of from 10:1 to 1 :10, preferably from 5:1 to 1 :5, more preferably from 2:1 to 1 :2 and most preferably from 2:1 to 1 :1 . In especially preferred embodiments, the acylated nitrogen compounds are formed by the reaction of acylating agent to amino compound in a molar ratio of from 1.8:1 to 1 :1 .2, preferably from 1.6:1 to 1 :1.2, more preferably from 1.4:1 to 1 :1.1 and most preferably from 1.2:1 to 1 :1. Acylated amino compounds of this type and their preparation are well known to those skilled in the art and are described in for example EP0565285 and US5925151 .

[0209] In some preferred embodiments the composition comprises a detergent of the type formed by the reaction of a polyisobutene-substituted succinic acid-derived acylating agent and a polyethylene polyamine. Suitable compounds are, for example, described in W02009 / 040583.

[0210] In a preferred embodiment the reaction product of a carboxylic acid-derived acylating agent and an amine (b) comprises the reaction product of a polyisobutene-substituted succinic acid or succinic anhydride and a polyethylene polyamine selected from ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethylene-heptamine and mixtures and isomers thereof; wherein polyisobutene substituent has a number average molecular weight of between 500 and 2000, preferably between 600 and 1200.

[0211] In some embodiments the present invention may involve the use of (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol. Preferably component (c) comprises the product of a Mannich reaction between:

[0212] (x) an aldehyde;

[0213] (y) an amine; and

[0214] (z) an optionally substituted phenol.

[0215] Preferably the aldehyde component used to prepare the Mannich additive is an aliphatic aldehyde. Preferably the aldehyde has 1 to 10 carbon atoms. Most preferably the aldehyde is formaldehyde.

[0216] Suitable amines for use in preparing the Mannich additive include monoamines and polyamines. One suitable monoamine is butylamine.

[0217] The amine used to prepare the Mannich additive is preferably a polyamine. This may be selected from any compound including two or more amine groups. Preferably the polyamine is a polyalkylene polyamine, preferably a polyethylene polyamine. The polyamine may, for example, be selected from ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, heptaethyleneoctamine, propane-1 ,2-diamine, 2(2-amino-ethylamino)ethanol, and N1,N1-bis (2- aminoethyl) ethylenediamine (N(CH2CH2NH2)3). Most preferably the polyamine comprises tetraethylenepentamine or especially ethylenediamine.

[0218] The optionally substituted phenol component used to prepare the Mannich additive may be substituted with 0 to 4 groups on the aromatic ring (in addition to the phenol OH). For example it may be a hydrocarbyl-substituted cresol. Most preferably the phenol component is a monosubstituted phenol. Preferably it is a hydrocarbyl substituted phenol. Preferred hydrocarbyl substituents are alkyl substituents having 4 to 28 carbon atoms, especially 10 to 14 carbon atoms. Other preferred hydrocarbyl substituents are polyalkenyl substituents. Such polyisobutenyl substituents having a number average molecular weight of from 400 to 2500, for example from 500 to 1500.

[0219] Preferred Mannich reaction products used in the present invention are typically formed by reacting components (x), (y) and (z) in a molar ratio of 1 .1 to 5 parts (x) to 1 part (y) to 1 .1 to 2 parts (z).

[0220] Suitable Mannich reaction products and methods of preparing such additives will be known to the person skilled in the art and include the compounds described, for example, in the applicant’s publications W02009040582 and WO2013017887. Preferred Mannich reaction product additives are the reaction product of formaldehyde, polyethylene polyamine; and a para-substituted monoalkyl phenol.

[0221] An especially preferred Mannich reaction product additive for use herein is the reaction product of dodecyl phenol, formaldehyde and ethylene diamine.

[0222] In some embodiments the additive used in the present invention comprises (g) a compound of formula (I):

[0223] A— L— R1

[0224] (I) wherein:

[0225] A is a nitrogen-containing group;

[0226] L is either a bond or a linker group;

[0227] R1is an optionally substituted hydrocarbyl group; and wherein the compound has a nitrogen content of at least 4% by mass.

[0228] Preferably R1is an optionally substituted alkyl, alkenyl or aminoalkyl group, preferably having a molecular weight (Mn) of up to 1000.

[0229] The compounds of formula (I) comprise at least 4% by mass of nitrogen atoms. By this we mean that the at least 4% of the molecular weight of the nitrogen-containing compounds is provided by nitrogen atoms, preferably by number average molecular weight. The amount by mass of nitrogen in such compounds can be calculated using standard methods or determined by elemental analysis. As the additive may comprise a mixture of compounds of formula (I), for example isomers, homologues and / or structurally similar compounds produced by the reactions used to form the nitrogen-containing compounds, the percent by mass of nitrogen referred to above is suitably an average value of such a mixture of nitrogen-containing compounds.

[0230] Preferably the compounds of formula (I) comprise at least 5% by mass of nitrogen atoms, preferably at least 7% or at least 10%.

[0231] Suitably the compounds of formula (I) comprise up to 50% by mass of nitrogen atoms or up to 40%. Suitably the nitrogen-containing compounds comprise up to 35% by mass of nitrogen atoms, suitably up to 30%.

[0232] Suitably the compounds of formula (I) comprise from 4 to 50% by mass of nitrogen atoms, suitably from 4 to 40%. In preferred embodiments, the compounds of formula (I) comprise from 4 to 35% by mass of nitrogen atoms, suitably from 5 to 30% or from 10 to 30%. The inventors have found that this relatively high proportion of nitrogen atoms present in the additives of formula (I) is very beneficial.

[0233] The compounds of formula (I) useful in the present invention preferably comprise no more than twelve N-H bonds. The N-H bonds may be referred to as “free” N-H bonds. Preferably the nitrogen-containing compounds contains fewer than five N-H bonds, fewer than four N-H bonds or fewer than three N-H bonds. Preferably the limits to the number of N-H bonds described above apply only to N-H bonds on amino groups in the compounds of formula (I). For example, N-H bonds of amide groups and / or N-H bonds of nitrogen atoms in aromatic heterocyclic rings are not included in the N-H bond limits described herein.

[0234] The inventors have found that this relatively low number of such free N-H bonds in the additive, which contains a relatively high proportion of nitrogen, may be useful to provide the beneficial effects described herein.

[0235] A suitable compound of formula (I) is the reaction product of p) a hydrocarbyl substituted reagent; and q) a nitrogen-containing reagent.

[0236] In some embodiments, the compound of formula (I) is the reaction product of: p) hydrocarbyl substituted carboxylic acid acylating agent; and q) a nitrogen-containing reagent; as further described below.

[0237] In some embodiments, the compound of formula (I) is the reaction product of: p) an amine or polyamine comprising a hydrocarbyl group; q) a nitrogen-containing reagent; and r) an aldehyde; as further described below.

[0238] The additive compounds of formula (I) may be a mixture of reaction products of p) a hydrocarbyl substituted reagent and q) a nitrogen-containing reagent. For example, the additive compounds of formula (I) may comprise a reaction product of: p) hydrocarbyl substituted carboxylic acid acylating agent; and q) a nitrogen-containing reagent; and a reaction product of: p) an amine or polyamine comprising a hydrocarbyl group; q) a nitrogen-containing reagent; and r) an aldehyde; as further described below.

[0239] When the compound of formula (I) is the reaction product of p) a hydrocarbyl substituted reagent and q) a nitrogen-containing reagent, the nitrogen-containing reagent q) suitably comprises a nitrogen-containing group A. The hydrocarbyl substituted reagent p) suitably comprises a hydrocarbyl group R1.

[0240] The A group suitably provides a significant amount of the required nitrogen content of the additive and the R1group may be a solubilising group which provides the additive with sufficient solubility in the diesel fuel for the additive to be effective in use. The A and R1groups are suitably selected to provide the required nitrogen content of at least 4% by mass in the compound of formula (I).

[0241] In some embodiments the nitrogen-containing reagent q) suitably comprises a nitrogencontaining heterocyclic group. The heterocyclic group suitably provides a significant amount of the required nitrogen content of the additive. In such embodiments, the A group of the nitrogencontaining reagent q) is a nitrogen-containing heterocyclic group.

[0242] The nitrogen-containing heterocyclic group may be any heterocyclic group, either aromatic or aliphatic, which contains at least one nitrogen atom. The nitrogen-containing heterocyclic group may contain other heteroatoms, for example at least one oxygen atom or at least one sulphur atom, preferably at least one oxygen atom. In some embodiments, the nitrogen-containing heterocyclic group contains no other heteroatoms other than nitrogen. The nitrogen-containing heterocyclic group of the A group may be selected from optionally substituted piperazine, pyridine, pyrazine, pyridazine, pyrimidine, triazine, quinoline, isoquinoline, quinazoline, a fivemembered heterocyclic ring such as pyrazole or imidazole or a benzo-fused five-membered heterocyclic ring such as benzimidazole, and derivatives thereof. The nitrogen-containing heterocyclic group is suitably selected to provide the required nitrogen content of at least 4% by mass, along with any other nitrogen atoms present in the R1group.

[0243] Preferably the A group is selected from an optionally substituted five-membered nitrogencontaining heterocyclic ring or a benzo-fused five-membered nitrogen-containing heterocyclic ring and derivatives thereof. Preferably the A group is an optionally substituted benzotriazole, an indazole, a triazole, a tetrazole, an imidazole, a benzimidazole or an imidazoline, or a derivative thereof. Suitably the A group is an optionally substituted benzotriazole, benzimidazole, an indazole, a triazole or a tetrazole.

[0244] In some embodiments, the A group is a non-cyclic nitrogen-containing group. In such embodiments the A group may be an amine or a polyamine. Suitable polyamines may have the formula: wherein n is from 1 to 10. The additive may be a mixture compounds of formula (I) having different n numbers in the “A” group. Therefore n is suitably an average value of the different n numbers present in the mixture. Therefore n may be a non-integer value, of from 1 to 10, i.e from 1 .0 to 10.0. Preferably n is from 1 to 6, from 1 to 4 or from 1 to 3.

[0245] Therefore the A group may be provided by ethylenediamine, diethylene triamine (DETA) or triethylene tetramine (TETA) or tetraethylene pentaamine (TEPA). Preferably the A group is provided by TETA or TEPA.

[0246] The R1group of the hydrocarbyl substituted reagent p) preferably has a molecular weight (Mn) of up to 1000, up to 600 or up to 400. The R1group preferably has a molecular weight of at least 50, at least 100 or at least 150. The R1group preferably has a molecular weight in the range of from 50 to 500, preferably from 100 to 400 or from 150 to 350.

[0247] In some embodiments, the R1group is a hydrocarbyl group.

[0248] The hydrocarbyl group preferably comprises at least 10 carbon atoms, more preferably at least 14 carbon atoms or at least 18 carbon atoms. Preferably the hydrocarbyl group comprises up to 30 carbon atoms, preferably up to 28 carbon atoms or up to 26 carbon atoms. The hydrocarbyl group may comprise from 10 to 30 carbon atoms, from 14 to 26 carbon atoms, from 18 to 26 carbon atoms or more preferably from 20 to 24 carbon atoms.

[0249] The hydrocarbyl substituent may be a mixture of hydrocarbyl groups having the above range of carbon atoms, on average. Therefore the molecular weight of the hydrocarbyl group is suitably defined as a number average molecular weight (Mn). The hydrocarbyl group preferably has an Mn of from 50 to 500, preferably from 100 to 400 or from 150 to 350.

[0250] The skilled person would be familiar with standard techniques to measure number average molecular weight, such as by vapor pressure osmometry, end-group titration, proton NMR, boiling point elevation, freezing depression (cryoscopy), and gel permeation chromatography (GPC).

[0251] The hydrocarbyl substituent may be an olefin having the number of carbons and / or Mn described above.

[0252] The hydrocarbyl based substituents may be made from homo- or interpolymers (e.g. copolymers, terpolymers) of mono- and di-olefins having 2 to 10 carbon atoms, for example ethylene, propylene, butane-1 , isobutene, butadiene, isoprene, 1-hexene, 1-octene, etc. Preferably these olefins are 1 -monoolefins. The hydrocarbyl substituent may also be derived from the halogenated (e.g. chlorinated or brominated) analogs of such homo- or interpolymers. Alternatively the substituent may be made from other sources, for example monomeric high molecular weight alkenes (e.g. 1-tetra-contene) and chlorinated analogs and hydrochlorinated analogs thereof, aliphatic petroleum fractions, for example paraffin waxes and cracked and chlorinated analogs and hydrochlorinated analogs thereof, white oils, synthetic alkenes for example produced by the Ziegler-Natta process (e.g. poly(ethylene) greases) and other sources known to those skilled in the art. Any unsaturation in the substituent may if desired be reduced or eliminated by hydrogenation according to procedures known in the art.

[0253] The hydrocarbyl substituent may be a polyisobutene, preferably having the number of carbons and / or the Mn described above. Conventional polyisobutenes and so-called "highly-reactive" polyisobutenes are suitable for use in the invention. Highly reactive polyisobutenes in this context are defined as polyisobutenes wherein at least 50%, preferably 70% or more, of the terminal olefinic double bonds are of the vinylidene type as described in EP0565285. Particularly preferred polyisobutenes are those having more than 80 mol% and up to 100% of terminal vinylidene groups such as those described in EP1344785.

[0254] Other preferred hydrocarbyl groups include those having an internal olefin for example as described in the applicant’s published application W02007 / 015080. An internal olefin as used herein means any olefin containing predominantly a non-alpha double bond, that is a beta or higher olefin. Preferably such materials are substantially completely beta or higher olefins, for example containing less than 10% by weight alpha olefin, more preferably less than 5% by weight or less than 2% by weight. Typical internal olefins include Neodene 1518 IO available from Shell.

[0255] Internal olefins are sometimes known as isomerised olefins and can be prepared from alpha olefins by a process of isomerisation known in the art, or are available from other sources. The fact that they are also known as internal olefins reflects that they do not necessarily have to be prepared by isomerisation.

[0256] The reaction of the hydrocarbyl substituted reagent p) and the nitrogen-containing reagent q) preferably forms a linking group L between the nitrogen-containing group A and the hydrocarbyl group R1. The L group may be a bond, an amine, an amide, a succinimide, a succinic acid or an amide of a succinic acid.

[0257] The compound which is the reaction product of p) a hydrocarbyl substituted reagent and q) a nitrogen-containing reagent, has the formula (I):

[0258] A— L— R1

[0259] (I) wherein:

[0260] A is a nitrogen-containing group;

[0261] L is either a bond or a linker group; and

[0262] R1is an optionally substituted hydrocarbyl group, preferably an optionally substituted alkyl, alkenyl or aminoalkyl group, preferably having a molecular weight (Mn) of up to 1000. The groups A, L and R1are as defined above.

[0263] In some embodiments, the nitrogen-containing compound is the reaction product of p) a hydrocarbyl substituted reagent and q) a nitrogen-containing reagent, wherein p) is a hydrocarbyl substituted carboxylic acid acylating agent.

[0264] In such embodiments, the compound of formula (I) is preferably a reaction product of: p) a hydrocarbyl substituted carboxylic acid acylating agent; and q) a nitrogen-containing reagent. In such embodiments, the linking group L between the hydrocarbyl group R1and the nitrogencontaining group A is provided by an amide of a succinic acid or succinic acid derivative, as further described below.

[0265] Suitably component p) comprises the group R1as defined above. Suitably the component p) comprises a hydrocarbyl group as defined above, preferably a polyisobutylene or an alkene group as defined above.

[0266] Component p) suitably has the formula (VI): wherein R1is an optionally substituted alkyl, alkenyl or aminoalkyl group having a molecular weight (Mn) of up to 1000.

[0267] R1is preferably a hydrocarbyl group as discussed above, preferably having from 18 to 26 carbon atoms and / or an Mn of from 100 to 400.

[0268] R1may be a polyisobutylene group or an internal olefin group having from 18 to 26 carbon atoms and / or an Mn of from 100 to 400.

[0269] In some embodiments, component p) is a polyisobutenyl succinic anhydride. These compounds are commonly referred to as “PIBSAs” and are known to the person skilled in the art. Suitably the polyisobutylene group of the PIBSA is as defined above.

[0270] The PIBSA may be prepared by reacting a suitable polyisobutene with maleic anhydride.

[0271] The preparation of polyisobutenyl substituted succinic anhydrides (PIBSA) is documented in the art. Suitable processes include thermally reacting polyisobutenes with maleic anhydride (see for example US-A-3,361 ,673 and US-A-3, 018,250), and reacting a halogenated, in particular a chlorinated, polyisobutene (PIB) with maleic anhydride (see for example US-A-3, 172,892). Alternatively, the polyisobutenyl succinic anhydride can be prepared by mixing the polyolefin with maleic anhydride and passing chlorine through the mixture (see for example GB-A- 949,981).

[0272] In some embodiments, component p) is PIB having an Mn from 250-270. In some embodiments, component p) is an alkenyl succinic anhydride. These compounds are commonly referred to as “ASAs” and are known to the person skilled in the art. Suitably the alkene group of the ASA is as defined above. Preferably the ASA is a C16 to C18 alkenyl succinic anhydride (ASA), for example Pentasize 68.

[0273] The reaction of component p) with component q) suitably forms an amide bond, an imide bond or a mixture thereof.

[0274] Component q) preferably contains a reactive amino group or a reactive nitrogen which is part of a nitrogen-containing heterocyclic compound.

[0275] In some embodiments, component q) comprises a nitrogen-containing heterocycle, preferably selected from an optionally substituted piperazine, pyridine, pyrazine, pyridazine, pyrimidine, triazine, quinoline, isoquinoline, quinazoline, 2-aminoimidazoline, 5-phenyl-2-aminoimidazoline, 5-methyl-2-aminoimidazole, 5-amino-indazole, 6-aminoindazole, 2-aminobenzimidazole, a fivemembered heterocyclic ring or a benzo-fused five-membered heterocyclic ring. Preferably component q) comprises a five-membered heterocyclic ring such as pyrazole or imidazole, a benzo-fused five membered heterocyclic ring such as benzimidazole, an amino substituted fivemembered heterocyclic ring or an amino substituted benzo-fused five membered heterocyclic ring. Preferably component q) comprises a benzotriazole, an indazole, a triazole or a tetrazole. Component q) may be selected from an optionally substituted benzotriazole, aminobenzotriazole, indazole, amino-indazole, triazole, amino-triazole, tetrazole or amino-tetrazole.

[0276] In some embodiments, component q) comprises an amine or polyamine compound. Suitably component q) is a polyamine. Suitably component q) has the formula: wherein n is from 1 to 10. The nitrogen-containing compound may be a mixture compounds having different n numbers in the “A” group. Therefore n is suitably an average value of the different n numbers present in the mixture. Therefore n may be a non-integer value, of from 1 to 10, i.e from 1 .0 to 10.0. Preferably n is from 1 to 6, from 1 to 4 or from 1 to 3.

[0277] Component q) may be selected from ethylenediamine, diethylene triamine (DETA), triethylene tetramine (TETA) and tetraethylene pentamine (TEPA). Component q) may be selected from ethylenediamine, diethylene triamine (DETA) and triethylene tetramine (TETA). Preferably, the nitrogen-containing compound is a reaction product of: p) a polyisobutenyl succinic anhydride or an alkenyl succinic anhydride; and q) a polyamine selected from ethylenediamine, diethylene triamine (DETA), triethylene tetramine (TETA) and tetraethylene pentamine (TEPA); or a nitrogen-containing heterocycle selected from an optionally substituted benzotriazole, amino-benzotriazole, indazole, amino-indazole, triazole, amino-triazole, tetrazole or amino-tetrazole.

[0278] In such embodiments, the nitrogen-containing compound formed by the reaction of p) and q) may have the structures described below, for example as the major component in a mixture of compounds produced by the reaction.

[0279] The L group of the nitrogen-containing compound of formula (I) may be provided by an amide of a succinic acid or succinic acid derivative. In such embodiments, the nitrogen-containing compound formed from the reaction of p) and q) may have the formula (VIA): wherein:

[0280] R1is an optionally substituted alkyl, alkenyl or aminoalkyl group having a molecular weight (Mn) of up to 1000;

[0281] A is the nitrogen-containing group; and

[0282] R17is OH, NH2, OR24, OM, NHR24or NR24R25, or is a bond to A, wherein M is a cation, preferably an alkali metal cation or an ammonium cation, and wherein R24and R25are independently selected from optionally substituted C1-6 alkyl or alkenyl groups. The R24and R25may independently comprise a quaternary ammonium group.

[0283] Therefore in some embodiments the nitrogen-containing compound used in the first and second aspects of the present invention is preferably of formula (VIA).

[0284] In some preferred embodiments, R17is OH and therefore the L group is an amide of succinic acid. The R1solubilising group may be bonded to either of the carbon atoms between the acid and amide groups. The nitrogen-containing compound may be a mixture of isomers which differ in the position of the R1group.

[0285] In such embodiments, R1is preferably a hydrocarbyl group as discussed above, preferably having from 18 to 26 carbon atoms and / or an Mn of from 100 to 400.

[0286] In such embodiments, R1may be a polyisobutylene group or an internal olefin group having from 18 to 26 carbon atoms and / or an Mn of from 100 to 400.

[0287] In some embodiments of the nitrogen-containing compounds of formula (VIA), the nitrogencontaining group A may be selected from optionally substituted piperazine, pyridine, pyrazine, pyridazine, pyrimidine, triazine, quinoline, isoquinoline, quinazoline, a five-membered heterocyclic ring such as pyrazole or imidazole or a benzo-fused five-membered heterocyclic ring such as benzimidazole, and derivatives thereof. Preferably the A group is selected from an optionally substituted five-membered heterocyclic ring or a benzo-fused five membered heterocyclic ring, or derivatives thereof. Preferably the A group is an optionally substituted benzotriazole, an indazole, a triazole or a tetrazole.

[0288] In such embodiments, the A group is suitably a tetrazole. Therefore the nitrogen-containing compound preferably may have the formula (VII): wherein R1and R17are as defined above.

[0289] In such embodiments, the compound of formula (VII) may also be present in an imide form having the formula (VIII): In such embodiments, the nitrogen-containing compound may have the formula (IX), which is an isomer of formula (VII): wherein R1and R17are as defined above.

[0290] In such embodiments the nitrogen-containing compound may be a mixture of compounds of formulas (VII), (VIII) and (IX).

[0291] In such embodiments, R17is preferably OH or OX* wherein X is a cation, for example a metal cation or an ammonium ion.

[0292] In such embodiments, R1is preferably a hydrocarbyl group having an Mn of from 100 to 500, preferably from 150 to 350 or from 200 to 300.

[0293] For example, R1may be a polyisobutylene or an alkene, having an Mn of from 100 to 500, preferably from 150 to 350 or from 200 to 300.

[0294] In some embodiments, R1is a polyisobutylene group and therefore the nitrogen-containing compound has the formula (X), (XI) or (XII), or a mixture thereof: wherein n is from 1 to 3. The nitrogen-containing compound may be a mixture compounds having different n numbers in the polyisobutylene group. Therefore n is suitably an average value of the different n numbers present in the mixture. Therefore n may be a non-integer value, of from 1 to 3, i.e. such that n is from 1 .0 to 3.0.

[0295] In some embodiments, R1is a C10-24 alkene group, preferably a C12-22 alkene group or a C16-18 alkene group. In such embodiments, the nitrogen-containing compound may have the formula (XIII), (XIV) or (XV), or a mixture thereof: wherein each R18is an alkyl group and are independently selected to provide the R1group having from 12 to 22 carbon atoms.

[0296] In some embodiments of the nitrogen-containing compounds of formula (VIA), the A group is a non-cyclic nitrogen-containing group as described above, for example an amine or a polyamine group. In such embodiments, the major component of the nitrogen-containing compound may be a cyclic imide wherein R17is a bond with the A group, suitably with an amine group of the A group. Therefore the nitrogen-containing compound may have the formula (XVI): wherein R1is as defined above. In such embodiments, the A group may be a polyethyleneimine. Therefore the nitrogencontaining compound may have the formula (XVII): wherein n is from 1 to 10. The nitrogen-containing compound may be a mixture compounds having different n numbers in the “A” group. Therefore n is suitably an average value of the different n numbers present in the mixture. Therefore n may be a non-integer value, of from 1 to 10, i.e from 1 .0 to 10.0. Preferably n is from 1 to 6, from 1 to 4 or from 1 to 3.

[0297] In such embodiments, the nitrogen-containing compound may comprise some of the ring- opened analogue having the formula (XVIII):

[0298] (XVIII) wherein R17is preferably OH or OX* wherein X is a cation, for example a metal cation or an ammonium ion.

[0299] In such embodiments of the compounds of formula (XVII) and / or (XVIII), R1is preferably a hydrocarbyl group having an Mn of from 100 to 500, preferably from 150 to 350 or from 200 to 300.

[0300] For example, R1may be a polyisobutylene or an alkene, having an Mn of from 100 to 500, preferably from 150 to 350 or from 200 to 300.

[0301] In some embodiments, R1is a polyisobutylene group and therefore the nitrogen-containing compound has the formula (XIX) and / or (XX):

[0302] (XIX) (XX) wherein n is from 1 to 10; and wherein m is from 1 to 3. Preferably n is from 1 to 4 or from 1 to 3. As noted above, n and m can be average values wherein a mixture of compounds comprising different n and m numbers are present. Therefore n and m may be non-integer values representing averages, i.e. n is from 1 .0 to 10.0; and wherein m is from 1 .0 to 3.0.

[0303] In some embodiments, R1is a C10-24 alkene group, preferably a C12-22 alkene group or a C16-18 alkene group. Therefore the nitrogen-containing compound has the formula (XXI) and / or formula (XXII) or a mixture thereof: wherein n is from 1 to 10 and may be a non-integer average value; and wherein each R18is an alkyl group and are independently selected to provide the R1group having from 12 to 22 carbon atoms. Preferably n is from 1 to 4 or from 1 to 3.

[0304] In some embodiments of the invention, the nitrogen-containing compound is the reaction product of p) a hydrocarbyl substituted reagent and q) a nitrogen-containing reagent, wherein p) is an amine or polyamine comprising the hydrocarbyl group. In such embodiments, the nitrogencontaining compound may be the product of a Mannich reaction involving an aldehyde. Therefore the nitrogen-containing compound may be a reaction product of: p) an amine or polyamine comprising a hydrocarbyl group; q) a nitrogen-containing reagent; and r) an aldehyde. In such embodiments, the linking group L between the hydrocarbyl group R1and the nitrogencontaining group A is provided by a bond, as further described below.

[0305] Suitably component p) comprises the group R1as defined above. Suitably the component p) is an alkylamine as defined above, preferably having the formula NHR19R20wherein R19and R20are each independently selected from H, optionally substituted C1-20 alkyl groups or optionally substituted C1-20 alkenyl groups. Therefore component p) is preferably dialkylamine. Preferably R19and R20are each independently selected from C1-20 alkyl groups, preferably C2- 20 alkyl groups. The alkyl groups may be branched, linear or cyclic alkyl groups. Preferably branched or linear alkyl groups. Preferably R19and R20are the same and are selected from C1- 20 alkyl groups, preferably C2-20 alkyl groups.

[0306] Component p) may be selected from diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, bis(2-ethylhexyl)amine or dicocoalkylamine.

[0307] Component q) is preferably a nitrogen-containing reagent comprising a nitrogen containing heterocycle. Preferably component q) is selected from an optionally substituted five-membered nitrogen-containing heterocyclic compound or a benzo-fused five-membered nitrogencontaining heterocyclic compound. Preferably component q) is selected from an optionally substituted triazole, tetrazole, indole, indazole or benzotriazole. Preferably component q) is selected from triazole, tetrazole, indole, indazole or benzotriazole, preferably triazole, tetrazole or benzotriazole.

[0308] Component r) is suitably an aliphatic aldehyde. Preferably the aldehyde has 1 to 10 carbon atoms. Most preferably the aldehyde is formaldehyde or a source of formaldehyde.

[0309] In preferred embodiments, the nitrogen-containing compound is the reaction product of: p) an alkylamine having the formula NHR19R20wherein R19and R20are each independently selected from H, optionally substituted C1-20 alkyl groups or optionally substituted C1-20 alkenyl groups; q) a nitrogen-containing reagent selected from an optionally substituted triazole, tetrazole, indole, indazole or benzotriazole, and. r) formaldehyde or a source of formaldehyde. In such embodiments, the nitrogen-containing compound formed by the reaction of p), q) and r) may have the structures described below, for example as the major component in a mixture of compounds produced by the reaction.

[0310] In some embodiments of the invention, the nitrogen-containing compound of formula (I), L may be a bond. In such embodiments, the nitrogen-containing compound may have the formula (XXIII):

[0311] (XXIII) wherein:

[0312] R1is an optionally substituted alkyl, alkenyl or aminoalkyl group having a molecular weight (Mn) of up to 1000;

[0313] W, X, Y and Z are each independently selected from CH, C, N, NH, S and SH, which are optionally substituted where appropriate; and wherein the compound optionally comprises a cycloalkyl or aryl ring linking Y and Z.

[0314] Therefore in some embodiments the nitrogen-containing compound used in the first and second aspects of the present invention are preferably of formula (XXIII).

[0315] The R1solubilising group may be bonded to any suitable atoms of the nitrogen-containing heterocyclic group. The nitrogen-containing compound may be a mixture of isomers which differ in the position of the R1group. Preferably the R1is bonded to a nitrogen of the nitrogencontaining heterocyclic group.

[0316] In such embodiments, R1is preferably an aminoalkyl group having a molecular weight (Mn) of up to 1000. The aminoalkyl group preferably has a molecular weight (Mn) of from 50 to 500, preferably from 50 to 350 or from 50 to 300.

[0317] R1may have the formula -CH2NR19R20wherein R19and R20are each independently selected from H, optionally substituted C1-20 alkyl groups or optionally substituted C1-20 alkenyl groups. Preferably R19and R20are each independently selected from C1-20 alkyl groups, preferably C2- 20 alkyl groups. The alkyl groups may be branched or linear alkyl groups. Preferably R19and R20are the same and are selected from C1-20 alkyl groups, preferably C2-20 alkyl groups. In some embodiments, R19and R20are each independently selected from C1-12 alkyl groups, preferably from C2-10 alkyl groups. In some embodiments of the nitrogen-containing compound of formula (XXIII), the heterocyclic group is an optionally substituted five-membered nitrogen-containing heterocycle. In such embodiments, W, X, Y and Z are each independently selected from CH, C, N and NH. In such embodiments, the heterocyclic group is preferably selected from an optionally substituted triazole or tetrazole. For example, the nitrogen-containing compound may have the formula (XXIV): wherein R19and R20are each independently selected from optionally substituted C1-20 alkyl groups, preferably optionally substituted C2-20 alkyl groups. In some embodiments, R19and R20are each independently selected from optionally substituted C1-12 alkyl groups, preferably from optionally substituted C2-10 alkyl groups.

[0318] The nitrogen-containing compound may have the formula (XXV) and / or (XXVI) or a mixture thereof:

[0319] (XXV) (XXVI) wherein R19and R20are each independently selected from C1-20 alkyl groups, preferably C2- 20 alkyl groups. The nitrogen-containing compound may be a mixture of such compounds. For example, the nitrogen-containing compound may be a mixture of compounds of formula (XXV) and (XXVI) in a ratio of from 1 :10 to 10:1 , suitably from 1 :5 to 5:1 ,

[0320] In some embodiments of the nitrogen-containing compound of formula (XXIII), the heterocyclic group is an optionally substituted benzo-fused five-membered nitrogen-containing heterocycle. In such embodiments, the nitrogen-containing compound has the formula (XXVII):

[0321] (XXVII) wherein: R1is an optionally substituted alkyl, alkenyl or aminoalkyl group having a molecular weight (Mn) of up to 1000;

[0322] W and X are each independently selected from C and N; and each R21is independently selected from H, C1-6 alkyl or C1-6 alkenyl.

[0323] Preferably each R21is H.

[0324] In such embodiments, R1is preferably an aminoalkyl group having a molecular weight (Mn) of up to 1000. The aminoalkyl group preferably has a molecular weight (Mn) of from 50 to 500, preferably from 50 to 350 or from 50 to 300.

[0325] As described above, R1preferably has the formula -CH2NR19R20wherein R19and R20are each independently selected from H, optionally substituted C1-20 alkyl groups or optionally substituted C1-20 alkenyl groups. Preferably R19and R20are each independently selected from C1-20 alkyl groups, preferably C2-20 alkyl groups. The alkyl groups may be branched, linear or cyclic alkyl groups. Preferably branched or linear alkyl groups. Preferably R19and R20are the same and are selected from C1-20 alkyl groups, preferably C2-20 alkyl groups.

[0326] Therefore the nitrogen-containing compound may have the formula (XXVIII):

[0327] (XXVIII) wherein:

[0328] W and X are each independently selected from C and N; each R21is independently selected from H, C1-6 alkyl or C1-6 alkenyl; and

[0329] R19and R20are each independently selected from C1-20 alkyl groups, preferably C2-20 alkyl groups.

[0330] In some embodiments, the nitrogen-containing heterocycle is an optionally substituted benzotriazole and the nitrogen compound has the formula (XXIX): wherein:

[0331] R1is an optionally substituted alkyl, alkenyl or aminoalkyl group having a molecular weight (Mn) of up to 1000; and each R21is independently selected from H, C1-6 alkyl or C1-6 alkenyl.

[0332] In a preferred embodiment, the compound of formula (I) has the formula (XXX): wherein: each R21is independently selected from H, C1-6 alkyl or C1-6 alkenyl; and

[0333] R19and R20are each independently selected from C1-20 alkyl groups, preferably C2-20 alkyl groups.

[0334] Suitable treat rates of the one or more nitrogen-containing detergents used in the present invention may depend on the type of fuel used and different levels of additive may be needed to achieve different levels of performance.

[0335] In preferred embodiments the one or more nitrogen containing detergents are selected from:

[0336] (a) a quaternary ammonium salt additive;

[0337] (b) the reaction product of a carboxylic acid-derived acylating agent and an amine;

[0338] (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol; and

[0339] (g) a compound of formula (I): A— L— R1

[0340] (I) wherein:

[0341] A is a nitrogen-containing group;

[0342] L is either a bond or a linker group;

[0343] R1is an optionally substituted hydrocarbyl group; wherein the compound has a nitrogen content of at least 4% by mass.

[0344] Preferably the diesel fuel composition used in the present invention comprises in total from 0.1 to 10000 ppm, preferably from 1 to 1000 ppm, preferably from 2 to 500 ppm, for example from 5 to 250 ppm of nitrogen containing detergents.

[0345] In some embodiments the diesel fuel composition comprises from 0.1 to 10000 ppm, preferably from 1 to 1000 ppm, preferably from 5 to 250 ppm, for example 5 to 100 ppm of (a) a quaternary ammonium salt additive.

[0346] In some embodiments the diesel fuel composition comprises from 0.1 to 10000 ppm, preferably from 1 to 1000 ppm, preferably from 5 to 500 ppm, for example 5 to 250 ppm of (b) the reaction product of a carboxylic acid-derived acylating agent and an amine.

[0347] In some embodiments the diesel fuel composition comprises from 0.1 to 10000 ppm, preferably from 1 to 1000 ppm, preferably from 5 to 500 ppm, for example 5 to 100 ppm of (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol.

[0348] In some embodiments the diesel fuel composition comprises from 0.1 to 10000 ppm, preferably from 1 to 1000 ppm, preferably from 5 to 500 ppm, for example 5 to 100 ppm of (g) a compound of formula (I):

[0349] A— L— R1

[0350] (I) wherein:

[0351] A is a nitrogen-containing group;

[0352] L is either a bond or a linker group;

[0353] R1is an optionally substituted hydrocarbyl group; and wherein the compound has a nitrogen content of at least 4% by mass.

[0354] Each of additives (a), (b), (c) and (g) may be provided as a mixture of compounds. The above amounts refer to the total of all such compounds present in the composition. For the avoidance of doubt the above amounts refer to the amount of active additive compound present in the composition and ignore any impurities, solvents or diluents which may be present.

[0355] Unless otherwise stated, in this specification ppm refers to parts per million by weight.

[0356] In some embodiments the diesel fuel composition comprises (a) a quaternary ammonium salt additive and (b) the reaction product of a carboxylic acid-derived acylating agent and an amine.

[0357] In some embodiments the diesel fuel composition comprises (a) a quaternary ammonium salt additive and (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol.

[0358] In some embodiments the diesel fuel composition comprises (b) the reaction product of a carboxylic acid-derived acylating agent and an amine and (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol.

[0359] In some embodiments the diesel fuel composition comprises (a) a quaternary ammonium salt additive, (b) the reaction product of a carboxylic acid-derived acylating agent and an amine and (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol.

[0360] In some embodiments the diesel fuel composition comprises (b) the reaction product of a carboxylic acid-derived acylating agent and an amine and (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol; wherein component (b) comprises the reaction product of a polyisobutene-substituted succinic acid or succinic anhydride and a polyethylene polyamine selected from ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine and mixtures and isomers thereof; wherein polyisobutene substituent has a number average molecular weight of between 500 and 2000, preferably between 600 and 1000; and component (c) comprises the reaction product of formaldehyde, a polyethylene polyamine and a para-substituted monoalkyl phenol, preferably dodecyl phenol.

[0361] In some embodiments the diesel fuel composition comprises (a) a quaternary ammonium salt additive and (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol, suitably wherein (a) and (c) are present in a weight ratio of from 1 :2 to 1 :4, preferably around 1 :3; wherein component (a) comprises a quaternary ammonium salt formed by reacting methyl salicylate, dimethyl oxalate or propylene oxide (optionally in combination with an acid) with the reaction product of a polyisobutylene-substituted succinic anhydride having a PIB molecular weight (Mn) of 700 to 1300 and dimethylaminopropylamine; and component (c) comprises the reaction product of formaldehyde, a polyethylene polyamine and a para-substituted monoalkyl phenol, preferably dodecyl phenol.

[0362] In some embodiments the diesel fuel composition comprises (a) a quaternary ammonium salt additive, (b) the reaction product of a carboxylic acid-derived acylating agent and an amine and (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol; wherein component (a) comprises a quaternary ammonium salt formed by reacting methyl salicylate, dimethyl oxalate or propylene oxide (optionally in combination with an acid) with the reaction product of a polyisobutylene-substituted succinic anhydride having a PIB molecular weight (Mn) of 700 to 1300 and dimethylaminopropylamine; component (b) comprises the reaction product of a polyisobutene-substituted succinic acid or succinic anhydride and a polyethylene polyamine selected from ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine and mixtures and isomers thereof; wherein polyisobutene substituent has a number average molecular weight of between 500 and 2000, preferably between 600 and 1000; and component (c) comprises the reaction product of formaldehyde, a polyethylene polyamine and a para-substituted monoalkyl phenol, preferably dodecyl phenol.

[0363] In the method of the first aspect and / or the use of the second aspect, the diesel fuel composition suitably comprises (a) a quaternary ammonium salt additive and (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol, suitably wherein (a) and (c) are present in a weight ratio of from 1 :2 to 1 :4, preferably around 1 :3; wherein component (a) comprises a quaternary ammonium salt formed by the reaction of a compound including a tertiary amine group and a quaternising agent; wherein the quaternising agent is selected from alkylene oxide (preferably propylene oxide), optionally in combination with an acid, chloroacetic acid or a salt thereof, methyl salicylate or dimethyl oxalate; wherein the compound including a tertiary amine group is selected from one or more of:

[0364] (i-a) the reaction product of a fatty acid of formula RZCOOH in which Rzis an alkyl or alkenyl group having 12 to 24 carbon atoms, and N,N-dimethyl-1 ,3-diaminopropane (DMAPA);

[0365] (i-b) the reaction product of a polyisobutylene-substituted succinic anhydride having a PIB molecular weight (Mn) of 700 to 1300 and N,N-dimethyl-1 ,3-diaminopropane; and (iv-a) a tertiary amine of formula R13R14R15N, wherein each of R13and R14is Ci to C4 alkyl, preferably methyl, and R15is an alkyl or alkenyl group having 12 to 24 carbon atoms; and component (c) comprises the reaction product of formaldehyde, a polyethylene polyamine and a para-substituted monoalkyl phenol, preferably dodecyl phenol.

[0366] In some embodiments the diesel fuel composition comprises (a) a quaternary ammonium salt additive, (b) the reaction product of a carboxylic acid-derived acylating agent and an amine and (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol; wherein component (a) comprises a quaternary ammonium salt formed by the reaction of a compound including a tertiary amine group and a quaternising agent; wherein the quaternising agent is selected from alkylene oxide (preferably propylene oxide), optionally in combination with an acid, chloroacetic acid or a salt thereof, methyl salicylate or dimethyl oxalate; wherein the compound including a tertiary amine group is selected from one or more of:

[0367] (i-a) the reaction product of a fatty acid of formula RZCOOH in which Rzis an alkyl or alkenyl group having 12 to 24 carbon atoms, and N,N-dimethyl-1 ,3-diaminopropane (DMAPA);

[0368] (i-b) the reaction product of a polyisobutylene-substituted succinic anhydride having a PIB molecular weight (Mn) of 700 to 1300 and N,N-dimethyl-1 ,3-diaminopropane; and

[0369] (iv-a) a tertiary amine of formula R13R14R15N, wherein each of R13and R14is Ci to C4 alkyl, preferably methyl, and R15is an alkyl or alkenyl group having 12 to 24 carbon atoms; component (b) comprises the reaction product of a polyisobutene-substituted succinic acid or succinic anhydride and a polyethylene polyamine selected from ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethylene-heptamine and mixtures and isomers thereof; wherein polyisobutene substituent has a number average molecular weight of between 500 and 2000, preferably between 600 and 1000; and component (c) comprises the reaction product of formaldehyde, a polyethylene polyamine and a para-substituted monoalkyl phenol, preferably dodecyl phenol.

[0370] In some embodiments the diesel fuel composition comprises (a) a quaternary ammonium salt additive and (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol, suitably wherein (a) and (c) are present in a weight ratio of from 1 :2 to 1 :4, preferably around 1 :3; wherein component (a) comprises a quaternary ammonium salt formed by the reaction of a compound including a tertiary amine group and a quaternising agent; wherein the quaternising agent is selected from alkylene oxide (preferably propylene oxide), optionally in combination with an acid, chloroacetic acid or a salt thereof, methyl salicylate or dimethyl oxalate; wherein the compound including a tertiary amine group is (i-a) the reaction product of a fatty acid of formula RZCOOH in which Rzis an alkyl or alkenyl group having 12 to 24 carbon atoms, and N,N-dimethyl-1 ,3-diaminopropane (DMAPA); and component (c) comprises the reaction product of formaldehyde, a polyethylene polyamine and a para-substituted monoalkyl phenol, preferably dodecyl phenol.

[0371] In some embodiments the diesel fuel composition comprises (a) a quaternary ammonium salt additive, (b) the reaction product of a carboxylic acid-derived acylating agent and an amine and (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol; wherein component (a) comprises a quaternary ammonium salt formed by the reaction of a compound including a tertiary amine group and a quaternising agent; wherein the quaternising agent is selected from alkylene oxide (preferably propylene oxide), optionally in combination with an acid, chloroacetic acid or a salt thereof, methyl salicylate or dimethyl oxalate; wherein the compound including a tertiary amine group is (i-a) the reaction product of a fatty acid of formula RZCOOH in which Rzis an alkyl or alkenyl group having 12 to 24 carbon atoms, and N,N-dimethyl-1 ,3-diaminopropane (DMAPA); component (b) comprises the reaction product of a polyisobutene-substituted succinic acid or succinic anhydride and a polyethylene polyamine selected from ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethylene-heptamine and mixtures and isomers thereof; wherein polyisobutene substituent has a number average molecular weight of between 500 and 2000, preferably between 600 and 1000; and component (c) comprises the reaction product of formaldehyde, a polyethylene polyamine and a para-substituted monoalkyl phenol, preferably dodecyl phenol. In some embodiments the diesel fuel composition comprises (a) a quaternary ammonium salt additive and (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol, suitably wherein (a) and (c) are present in a weight ratio of from 1 :2 to 1 :4, preferably around 1 :3; wherein component (a) comprises a quaternary ammonium salt formed by the reaction of a compound including a tertiary amine group and a quaternising agent; wherein the quaternising agent is selected from alkylene oxide (preferably propylene oxide), optionally in combination with an acid, chloroacetic acid or a salt thereof, methyl salicylate or dimethyl oxalate; wherein the compound including a tertiary amine group is (iv-a) a tertiary amine of formula R13R14R15N, wherein each of R13and R14is Ci to C4 alkyl, preferably methyl, and R15is an alkyl or alkenyl group having 12 to 24 carbon atoms; and component (c) comprises the reaction product of formaldehyde, a polyethylene polyamine and a para-substituted monoalkyl phenol, preferably dodecyl phenol.

[0372] In some embodiments the diesel fuel composition comprises (a) a quaternary ammonium salt additive, (b) the reaction product of a carboxylic acid-derived acylating agent and an amine and (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol; wherein component (a) comprises a quaternary ammonium salt formed by the reaction of a compound including a tertiary amine group and a quaternising agent; wherein the quaternising agent is selected from alkylene oxide (preferably propylene oxide), optionally in combination with an acid, chloroacetic acid or a salt thereof, methyl salicylate or dimethyl oxalate; wherein the compound including a tertiary amine group is (iv-a) a tertiary amine of formula R13R14R15N, wherein each of R13and R14is Ci to C4 alkyl, preferably methyl, and R15is an alkyl or alkenyl group having 12 to 24 carbon atoms; component (b) comprises the reaction product of a polyisobutene-substituted succinic acid or succinic anhydride and a polyethylene polyamine selected from ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethylene-heptamine and mixtures and isomers thereof; wherein polyisobutene substituent has a number average molecular weight of between 500 and 2000, preferably between 600 and 1000; and component (c) comprises the reaction product of formaldehyde, a polyethylene polyamine and a para-substituted monoalkyl phenol, preferably dodecyl phenol.

[0373] In some embodiments the diesel fuel composition comprises (a) a quaternary ammonium salt additive, (b) the reaction product of a carboxylic acid-derived acylating agent and an amine, (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol, and (g) a compound of formula (I); wherein component (a) comprises a quaternary ammonium salt formed by reacting methyl salicylate, dimethyl oxalate or propylene oxide (optionally in combination with an acid) with the reaction product of a polyisobutylene-substituted succinic anhydride having a PIB molecular weight (Mn) of 700 to 1300 and dimethylaminopropylamine; component (b) comprises the reaction product of a polyisobutenesubstituted succinic acid or succinic anhydride and a polyethylene polyamine selected from ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethylene-heptamine and mixtures and isomers thereof; wherein polyisobutene substituent has a number average molecular weight of between 500 and 2000, preferably between 600 and 1000; component (c) comprises the reaction product of formaldehyde, a polyethylene polyamine and a para-substituted monoalkyl phenol, preferably dodecyl phenol; and component (g) comprises a compound of formula (XXX): wherein:

[0374] R19, R20and R21are as defined above, or a compound of the formula (XXV) and / or (XXVI) or a mixture thereof:

[0375] (XXV) (XXVI) wherein R19and R20are as defined above, or a compound of the formula (VII): wherein R1and R17are as defined above, or a compound of the formula (VIII):

[0376] (VII) wherein R1is as defined above, or a compound of the formula (IX): wherein R1and R17are as defined above.

[0377] The one or more nitrogen containing detergents may be added to diesel fuel at any convenient place in the supply chain. For example, the additive may be added to fuel at the refinery, at a distribution terminal or after the fuel has left the distribution terminal. If the additive is added to the fuel after it has left the distribution terminal, this is termed an aftermarket application. Aftermarket applications include such circumstances as adding the additive to the fuel in the delivery tanker, directly to a customer’s bulk storage tank, or directly to the end user’s vehicle tank. Aftermarket applications may include supplying the fuel additive in small bottles suitable for direct addition to fuel storage tanks or vehicle tanks.

[0378] The present invention involves dosing into the diesel fuel composition as an additive at least one nitrogen-containing detergent. The at least one nitrogen-containing detergent may be directed dosed as a neat additive. The at least one nitrogen-containing detergent may be added as part of an additive composition. The additive composition may comprise one or more diluents or carriers and optionally one or more further fuel additives. Preferred diluents and carriers are organic compounds, preferably hydrocarbon solvents such as aromatic solvents. Suitable diluents and carriers will be known to the person skilled in the art.

[0379] Preferably the additive composition is not aqueous. Preferably the additive composition is not provided as an emulsion. Preferably the additive composition does not comprise water. Trace amounts of water may be present due to manufacturing processes but in preferred embodiments no water is deliberately added to the additive composition.

[0380] Suitably the additive composition comprises less than 10 wt% water, preferably less than 5 wt%, suitably less than 1 wt%, for example less than 0.1 wt%.

[0381] Thus in preferred embodiments the method and use of the present invention do not involve the addition of water to the diesel fuel composition.

[0382] By diesel fuel we include any fuel suitable for use in a diesel engine either for road use or nonroad use. This includes but is not limited to fuels described as diesel, marine diesel, heavy fuel oil, industrial fuel oil, etc.

[0383] The diesel fuel composition used in the present invention may comprise a petroleum-based fuel oil, especially a middle distillate fuel oil. Such distillate fuel oils generally boil within the range of from 110°C to 500°C, e.g. 150°C to 400°C. The diesel fuel may comprise atmospheric distillate or vacuum distillate, cracked gas oil, or a blend in any proportion of straight run and refinery streams such as thermally and / or catalytically cracked and hydro-cracked distillates.

[0384] The diesel fuel composition may comprise non-renewable Fischer-Tropsch fuels such as those described as GTL (gas-to-liquid) fuels, CTL (coal-to-liquid) fuels and OTL (oil sands-to-liquid).

[0385] The diesel fuel composition may comprise a renewable fuel such as a biofuel composition or biodiesel composition.

[0386] The diesel fuel composition may comprise first generation biodiesel. First generation biodiesel contains esters of, for example, vegetable oils, animal fats and used cooking fats or oils. This form of biodiesel may be obtained by transesterification of oils, for example rapeseed oil, soybean oil, canola oil, safflower oil, palm oil, corn oil, peanut oil, cotton seed oil, tallow, coconut oil, physic nut oil (Jatropha), sunflower seed oil, used cooking oils, hydrogenated vegetable oils or any mixture thereof, with an alcohol, usually a monoalcohol, usually in the presence of a catalyst. The diesel fuel composition may comprise second generation biodiesel. Second generation biodiesel is derived from renewable resources such as vegetable oils and animal fats and processed, often in the refinery, using, for example, hydroprocessing such as the H-Bio process developed by Petrobras. Second generation biodiesel may be similar in properties and quality to petroleum based fuel oil streams, for example renewable diesel produced from vegetable oils, animal fats etc. and marketed by ConocoPhillips as Renewable Diesel and by Neste as NExBTL.

[0387] The diesel fuel composition may comprise 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, but aims to exploit the whole plant (biomass) and thereby widens the feedstock base.

[0388] In some embodiments the diesel fuel composition may comprise a pyrolysis oil, for example a plastic pyrolysis oil or a biomass (wood, vegetable oil, algae) pyrolysis oil.

[0389] The diesel fuel composition may contain blends of any or all of the above diesel fuel compositions.

[0390] In some embodiments the diesel fuel composition may be a blended diesel fuel comprising biodiesel. In such blends the bio-diesel may be present in an amount of, for example up to 0.5%, up to 1 %, up to 2%, up to 3%, up to 4%, up to 5%, up to 10%, up to 20%, up to 30%, up to 40%, up to 50%, up to 60%, up to 70%, up to 80%, up to 90%, up to 95% or up to 99%.

[0391] In some embodiments the fuel composition may comprise neat biodiesel.

[0392] In some preferred embodiments the fuel composition comprises at least 5 wt% biodiesel.

[0393] In some embodiments the fuel composition may comprise GTL fuel or be a neat GTL fuel.

[0394] In some embodiments the diesel fuel composition may comprise a secondary fuel, for example ethanol. Preferably however the diesel fuel composition does not contain ethanol.

[0395] The diesel fuel composition used in the present invention may contain a relatively high sulphur content, for example greater than 0.05% by weight, such as 0.1 % or 0.2%.

[0396] However, in preferred embodiments the diesel fuel composition has a sulphur content of at most 0.05% by weight, more preferably of at most 0.035% by weight, especially of at most 0.015%. Fuels with even lower levels of sulphur are also suitable such as, fuels with less than 50 ppm sulphur by weight, preferably less than 20 ppm, for example 10 ppm or less.

[0397] The diesel fuel composition used in the present invention preferably comprises at least 5 wt% biodiesel and less than 50 ppm sulphur.

[0398] Preferably the diesel fuel composition is not an emulsion. Preferably the diesel fuel composition does not comprise water. Trace amounts of water may be present due to manufacturing processes or contamination (for example, during storage) but in preferred embodiments no water is deliberately added to the diesel fuel composition.

[0399] Suitably the diesel fuel composition comprises less than 10 wt% water, preferably less than 5 wt%, suitably less than 1 wt%, for example less than 0.1 wt%.

[0400] In some embodiments the diesel fuel composition is neat renewable diesel.

[0401] The diesel fuel composition may be suitably 100% derived from renewable sources. Such a fuel is referred to herein as a renewable diesel. A suitable renewable diesel is a renewable diesel obtained by the hydrodeoxygenation of fats and oils (the fats and oils being derived from renewable sources). For example, the renewable diesel may be a hydrotreated triglyceride oil such as a hydrogenated vegetable oil (HVO). The HVO suitably complies with EN15940 Class A. Such HVO fuels are available from Coryton and Neste.

[0402] Such renewable diesel fuels are suitably 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.

[0403] Preferably, the renewable diesel 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. Preferably the renewable diesel 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.

[0404] Preferably the renewable diesel 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.

[0405] Preferably the renewable diesel 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 mm2s-1, most preferably from 2 to 4.5 mm2s_1. Kinematic viscosity may be measured according to ASTM D445.

[0406] Preferably the renewable diesel 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.

[0407] Preferably the renewable diesel 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.

[0408] The initial boiling point, final boiling point and boiling range can be determined according to the method set out in IP 123.

[0409] In preferred embodiments the renewable diesel comprises predominately straight chain alkanes and branched alkanes.

[0410] Preferably the renewable diesel 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%.

[0411] 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.

[0412] Preferably the weight of ratio n-paraffins to i-paraffins present in the renewable diesel is from 99:1 to 1 :99, more preferably from 90:10 to 10:99, preferably from 75:25 to 25:75. Techniques for determining the ratio of n-paraffins to i-paraffins are known to the person skilled in the art and include gas chromatography. 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.

[0413] The renewable diesel may comprise greater than 4 wt%, preferably greater than 5 wt%, of C14 to C16 n-alkanes.

[0414] The renewable diesel may comprise less than 8 wt%, preferably less than 6 wt%, of C14 to C16 n-alkanes.

[0415] The renewable diesel may comprise from 4 to 8 wt%, preferably from 5 to 6 wt%, of C14 to C16 n-alkanes.

[0416] The renewable diesel may comprise greater than 5 wt%, preferably greater than 7 wt%, more preferably greater than 10 wt%, of C14 to C18 n-alkanes.

[0417] The renewable diesel may comprise less than 20 wt%, preferably less than 18 wt%, more preferably less than 16 wt%, of C14 to C18 n-alkanes.

[0418] The renewable diesel may comprise from 5 to 20 wt%, preferably from 7 to 18 wt%, more preferably from 10 to 16 wt%, of C14 to C18 n-alkanes.

[0419] The renewable diesel may comprise from 3 to 30 wt% of C6 to C24 n-alkanes (i.e. n-paraffin).

[0420] The renewable diesel suitably has an oxygen content of less than 1wt%, preferably less than 0.1wt% when measured according to EN 14078.

[0421] The renewable diesel suitably has an aromatic content of less than 5 wt%, preferably less than 1 wt%.

[0422] Preferably the renewable diesel is a hydrotreated triglyceride oil, suitably an HVO, having the contents and properties described above.

[0423] Suitably the renewable diesel complies with the standard specification set out in EN15940.

[0424] Preferably the renewable diesel is a hydrotreated triglyceride oil, suitably an HVO, having an aromatic content of less than 5 wt%, preferably less than 1 wt%.

[0425] Preferably the renewable diesel is a hydrotreated triglyceride oil, suitably an HVO, having cetane number of between 50 and 90, preferably between 55 and 90, more preferably between 60 and 85 (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).

[0426] Preferably the renewable diesel is a hydrotreated triglyceride oil, suitably an HVO, 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.

[0427] The diesel fuel composition used in the present invention suitably comprises at least 10 vol% renewable diesel as defined above, suitably at least 25 vol%, at least 50 vol% or at least 90 vol% renewable diesel, suitably wherein the renewable diesel is hydrotreated triglyceride oil, preferably HVO.

[0428] 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.

[0429] In some preferred embodiments, the fuel composition of the present invention comprises renewable diesel and one or more further components selected from biodiesel, mineral diesel and mixtures thereof.

[0430] In some embodiments the fuel composition comprises renewable diesel and at least 5 vol% biodiesel.

[0431] In some embodiments the fuel composition comprises renewable diesel and at least 20 vol% biodiesel.

[0432] In preferred embodiments the diesel fuel composition is neat (i.e. 100 vol%) renewable diesel as defined above, preferably neat hydrotreated triglyceride oil, preferably neat HVO. Such a fuel may be referred to as an R100 diesel fuel.

[0433] Various metal species may be present in the diesel fuel composition. This may be due to contamination of the fuel during manufacture, storage, transport or use or due to contamination of fuel additives. Metal species may also be added to fuels deliberately. For example, transition metals are sometimes added as fuel borne catalysts, for example to improve the performance of diesel particulate filters.

[0434] Other metal-containing species may also be present as a contaminant, for example through the corrosion of metal and metal oxide surfaces by acidic species present in the fuel or from lubricating oil. In use, fuels such as diesel fuels routinely come into contact with metal surfaces for example, in vehicle fuelling systems, fuel tanks, fuel transportation means etc. Typically, metal-containing contamination may comprise transition metals such as zinc, iron and copper; Group I or Group II metals and other metals such as lead.

[0435] In addition to metal-containing contamination which may be present in diesel fuels there are circumstances where metal-containing species may deliberately be added to the fuel. For example, as is known in the art, metal-containing fuel-borne catalyst species may be added to aid with the regeneration of particulate traps. The presence of such catalysts may also give rise to injector deposits when the fuels are used in diesel engines having high pressure fuel systems.

[0436] Metal-containing contamination, depending on its source, may be in the form of insoluble particulates or soluble compounds or complexes. Metal-containing fuel-borne catalysts are often soluble compounds or complexes or colloidal species.

[0437] In some embodiments, the diesel fuel may comprise metal-containing species comprising a fuel- borne catalyst. Preferably, the fuel borne catalyst comprises one or more metals selected from iron, cerium, platinum, manganese, Group I and Group II metals e.g., calcium and strontium. Most preferably the fuel borne catalyst comprises a metal selected from iron and cerium.

[0438] Typically, the total amount of all metal-containing species in the diesel fuel, expressed in terms of the total weight of metal in the species, is between 0.1 and 50 ppm by weight, for example between 0.1 and 20 ppm, preferably between 0.1 and 10 ppm by weight, based on the weight of the diesel fuel.

[0439] The diesel fuel compositions used in the present invention may include one or more further additives such as those which are commonly found in diesel fuels. These include, for example, antioxidants, dispersants, detergents, metal deactivating compounds, wax anti-settling agents, cold flow improvers, cetane improvers, dehazers, stabilisers, demulsifiers, antifoams, corrosion inhibitors, lubricity improvers, dyes, markers, combustion improvers, metal deactivators, odour masks, drag reducers and conductivity improvers. Examples of suitable amounts of each of these types of additives will be known to the person skilled in the art.

[0440] Suitable cetane number improvers may be selected from 02-24 alkyl nitrates and dialkyl peroxides, preferably decyl nitrate, 2-ethylhexyl nitrate and di-tert-butyl peroxides. Such cetane number improvers are suitably used at a concentration of 50-6,000 ppm, preferably at 50- 750 ppm based on the diesel fuel composition. The method and use of the present invention reduce the emission of nitrogen oxides from a diesel engine combusting a diesel fuel composition.

[0441] The diesel engine may be a direct injection diesel engine or an indirect injection diesel engine.

[0442] In some embodiments the engine may be an off road engine, for example a marine, rail or stationary engine. Stationary engines include engines for power generation and pumping.

[0443] Most preferably the engine is a direct injection diesel engine.

[0444] The additives used in the present invention have been found to be particularly effective in modern diesel engines having a high pressure fuel system.

[0445] Suitably the present invention may be used to reduce the emission of nitrogen oxide and / or nitrogen dioxide from a diesel engine having a high pressure fuel system. Suitably the diesel engine has a fuel pressure in excess of 1350 bar (1 .35 x 108Pa). It may have a pressure of up to 2000 bar (2 x 108Pa) or more.

[0446] Such diesel engines may be characterised in a number of ways.

[0447] Such engines are typically equipped with fuel injection equipment meeting or exceeding “Euro 5” emissions legislation or equivalent legislation in the US or other countries.

[0448] Such engines are typically equipped with fuel injectors having a plurality of apertures, each aperture having an inlet and an outlet.

[0449] Such engines may be characterised by apertures which are tapered such that the inlet diameter of the spray-holes is greater than the outlet diameter.

[0450] Such modern engines may be characterised by apertures having an outlet diameter of less than 500pm, preferably less than 200pm, more preferably less than 150pm, preferably less than 100pm, most preferably less than 80pm or less.

[0451] Such modern diesel engines may be characterised by apertures where an inner edge of the inlet is rounded.

[0452] Such modern diesel engines may be characterised by the injector having more than one aperture, suitably more than 2 apertures, preferably more than 4 apertures, for example 6 or more apertures. Such modern diesel engines may be characterised by an operating tip temperature in excess of 250°C.

[0453] Such modern diesel engines may be characterised by a fuel injection system which provides a fuel pressure of more than 1350 bar, preferably more than 1500 bar, more preferably more than 2000 bar.

[0454] Two non-limiting examples of such high pressure fuel systems are: the common rail injection system, in which the fuel is compressed utilizing a high-pressure pump that supplies it to the fuel injection valves through a common rail; and the unit injection system which integrates the high- pressure pump and fuel injection valve in one assembly, achieving the highest possible injection pressures exceeding 2000 bar (2 x 108Pa). In both systems, in pressurising the fuel, the fuel gets hot, often to temperatures around 100°C, or above.

[0455] Preferably, the diesel engine has fuel injection system which comprises a common rail injection system.

[0456] In common rail systems, the fuel is stored at high pressure in the central accumulator rail or separate accumulators prior to being delivered to the injectors. Often, some of the heated fuel is returned to the low pressure side of the fuel system or returned to the fuel tank. In unit injection systems the fuel is compressed within the injector in order to generate the high injection pressures. This in turn increases the temperature of the fuel.

[0457] In both systems, fuel is present in the injector body prior to injection where it is heated further due to heat from the combustion chamber. The temperature of the fuel at the tip of the injector can be as high as 250 - 350 °C.

[0458] Thus the fuel is stressed at pressures from 1350 bar (1 .35 x 108Pa) to over 2000 bar (2 x 108Pa) and temperatures from around 100°C to 350°C prior to injection, sometimes being recirculated back within the fuel system thus increasing the time for which the fuel experiences these conditions.

[0459] The present invention may also be used to reduce emissions of nitrogen oxide and / or nitrogen dioxide from a traditional diesel engine such as an indirect injection diesel engine.

[0460] The method and use of the present invention reduces the emission of nitrogen oxide and / or nitrogen dioxide on combustion of a diesel fuel composition in a diesel engine. In some embodiments the method and use reduce the emission of nitrogen oxide.

[0461] In some embodiments the method and use reduce the emission of nitrogen dioxide.

[0462] In some embodiments the method and use reduce the emission of nitrogen oxide and nitrogen dioxide.

[0463] The term “NOX“ is commonly used to refer to the combined emissions of nitrogen oxide (NO) and nitrogen dioxide (NO2). Thus the method and use may reduce the emission of NOX.

[0464] By reducing the emission of nitrogen oxide and / or nitrogen dioxide in the context of the present invention we mean that the amount of nitrogen oxide and / or nitrogen dioxide emitted from the exhaust of a diesel engine is lower when combusting a diesel fuel composition comprising as an additive at least one nitrogen-containing detergent compared with when an otherwise identical diesel fuel composition without the additive is combusted.

[0465] The amount of nitrogen oxide and / or nitrogen dioxide emitted from the engine may be measured by any suitable means. Such means will be known to the person skilled in the art. One suitable method is described in example 9.

[0466] The reduction in emissions may be measured by comparing emissions per unit volume of fuel combusted and / or by comparing emissions per unit volume of exhaust gas emitted.

[0467] By reducing the amount of nitrogen oxide and / or nitrogen dioxide emitted from the engine we mean to refer to a reduction of the nitrogen oxide and / or nitrogen dioxide which is directly emitted during combustion and not the total amount of nitrogen oxide and / or nitrogen dioxide emitted from the vehicle.

[0468] Thus the invention suitably reduces the amount of nitrogen oxide and / or nitrogen dioxide emitted from the combustion chamber.

[0469] Other features of the combustion system such as the selective catalytic reduction (SCR) unit may also have an impact on the total amount of nitrogen oxide and / or nitrogen dioxide emitted from an engine. However the invention relates in particular to the reduction of the amount of nitrogen oxide and / or nitrogen dioxide emitted from the combustion chamber.

[0470] Suitably the present invention reduces the emission of nitrogen oxide and / or nitrogen dioxide in the exhaust gas directly emitted from the engine, before it enters the post combustion system. Preferably the method and use of the present invention reduces the emission of nitrogen oxide by at least 2%, preferably at least 5%.

[0471] Preferably the method and use of the present invention reduces the emission of nitrogen dioxide by at least 2%, preferably at least 5%.

[0472] Preferably the method and use of the present invention reduces the total emissions of nitrogen oxide and nitrogen dioxide by at least 2%, preferably at least 5%.

[0473] Because the present invention reduces the levels of nitrogen oxide and / or nitrogen dioxide emitted from a diesel engine, there are lower amounts of these gases that need to be treated by the selective catalytic reduction (SCR) unit. As a result the SCR unit may need less frequent maintenance and / or the SCR additive may need topping up less frequently.

[0474] Thus the method and use of the present invention advantageously increase maintenance intervals for a vehicle fitted with a selective catalytic reduction (SCR) unit.

[0475] Further the method and use of the present invention may reduce the consumption of additive by a selective catalytic reduction (SCR) unit.

[0476] The invention will now be further described with reference to the following non-limiting examples.

[0477] Example 1

[0478] Additive A, a quaternary ammonium salt additive, was prepared as follows:

[0479] 700 g (0.7 mol) of polyisobutylene (Mn1000) was charged to a nitrogen flushed, jacketed reactor fitted with an overhead stirrer. The starting material was heated to 120 °C with stirring and nitrogen inerting was repeated. The reaction temperature was increased to 190 °C and maleic anhydride (82.4g, 0.84 mol, 1.2 eq) was charged over 1 hour. After maintaining a temperature of 190 °C for a further 1 hour, the temperature was increased to 200 - 208 °C and held in this range for 8 hours. Vacuum (< 30 mbar) was then applied for 2.5 hrs, whilst maintaining the reaction temperature, which reduced the level of residual maleic anhydride to < 0.05 wt%. The reaction mass was cooled to < 80°C then discharged from the reactor.

[0480] This material was then charged to a nitrogen flushed, jacketed reactor fitted with an overhead stirrer and heated to 120 °C. 3-(dimethylamino)propylamine (DMAPA) (1 eq relative to anhydride groups) was charged slowly, maintaining the reaction temperature between 120 - 130 °C. After stirring at 120 °C for a further 1 hr, the reaction temperature was increased to 140 °C and held for 3 hrs with concurrent distillation of water. Methyl salicylate (2.1 eq relative to anhydride groups) was added in a single portion and heating was continued at 140 °C for 10 hours. The reaction mass was diluted with Aromatic 150 solvent to provide an overall solids content of 60 wt% prior to discharging from the reactor.

[0481] Example 2

[0482] Additive B, a Mannich reaction product additive, was prepared as follows:

[0483] A 1 L reactor was charged with dodecylphenol (170.6g, 0.65 mol), ethylenediamine (30.1 g, 0.5 and Caromax 20 (123.9g). The mixture was heated to 95 °C and formaldehyde solution, 37 wt% (73.8g, 0.9 mol) charged over 1 hour. The temperature was increased to 125 °C for 3 hours and water removed. In this example the molar ratio of aldehyde (a) : amine (b) : phenol (c) was approximately 1 .8:1 :1.3.

[0484] Example 3

[0485] Additive C is a 60 wt% active ingredient solution (in aromatic solvent) of a polyisobutenyl succinimide obtained from the condensation reaction of a polyisobutenyl succinic anhydride (PIBSA) derived from polyisobutene of Mn approximately 750 with a polyethylene polyamine mixture of average composition approximating to tetraethylene pentamine. The product was obtained by mixing the PIBSA and polyethylene polyamine at 50°C under nitrogen and heating at 160°C for 5 hours with removal of water.

[0486] Example 4

[0487] Additive D, an oleyl amido propyl betaine additive, was prepared as follows:

[0488] A Lenz jacketed reactor was charged with 183.5 g (0.5 moles) oleyl amidopropyl dimethylamine (N-[3-(Dimethylamino)propyl]oleamide), 68 ml isopropylalcohol, 25.5 g (1.42 moles) water and 56.5 g (0.48 moles) sodium chloroacetate. The reaction mixture was heated to 80°C and then heated for approx. 6 hrs at 80-85°C, before being cooled and allowed to stand under N2 overnight. Following this the reaction mixture was re-heated to 60°C and charged with 300 ml of isopropylalcohol (IPA) and 67.5 g of 2-ethylhexanol. Then the heat was increased further to 90°C. This afforded the azeotropic removal of H2O and IPA and precipitation of NaCI. A 100 mbar vacuum was applied to remove the remaining water and some solvent and the resulting suspension was filtered at 75-80°C through a glass microfibre filter. 275.6g of additive D was collected, which contained 53 wt% actives. Example 5

[0489] Additive E, a quaternary ammonium compound, was prepared by the quaternization of a succinamide with propylene oxide in the absence of an additional acid using a procedure analogous to that described in preparation example 1 of US9255236 B2. The succinamide was prepared by the reaction of the polyisobutylene succinic anhydride having a PIB number average molecular weight of 1000 with dimethylaminopropylamine (DMAPA). The material obtained as a solution contained 50 wt% active.

[0490] Example 6

[0491] Additive F, a quaternary ammonium compound, was prepared by the quaternization of hexadecyldimethyl amine with 2 equivalents of propylene oxide in the presence of a the polyisobutylene succinic acid having a PIB number average molecular weight of 1000, as described in the general synthesis method and example 6 of WO2014 / 195464. The material obtained as a solution contained 60 wt% active.

[0492] Example 7

[0493] Additive G, comprising the illustrated major components was prepared as follows:

[0494] Major components: N(cocoalkyl)2

[0495] In a 500ml round bottomed flask, charged benzotriazole (26.0 g, 0.218 moles, 1 .0 eq) and A150 solvent (116.0 g) and heated to 90°C. The flask was charged the Armeen 2C (87.4 g, 0.218 moles, 1 eq [equivalent weight is 401 g / mol]) (dicocoalkylamine wherein cocoalkyl = mixture of C6-18 alkyl). Formalin (37% w / w, 0.218 moles, 1.0 eq) was then added over 5 mins and then the reaction mixture was stirred at 90°C for 2.5 hrs. The temperature in the reaction flask was increased over a period of 3 hrs to 119°C and water removed via Dean and Stark trap. When no further aqueous phase was being collected and the product was clear and bright the temperature was cooled to ambient. Collected 222.5 g of clear bright amber liquid (as 50% actives solution).

[0496] Example 8 Diesel fuel compositions were prepared comprising the following components:

[0497] Table 1 The base fuel used was an RF-06-03 diesel fuel (Haltermann Carless, UK) having the following specification:

[0498]

[0499] Example 9 Engine testing was carried out as described below to assess the performance of the nitrogen containing additives of the present invention in the reduction of the emission of NO and NOXfrom the exhausts of diesel engines.

[0500] Engine Details A Euro 6 compliant 2.0 litre, HSDI engine was connected to a test automation system and test bed fitted with an engine dynamometer. The engine was controlled by an ECU supplied by the engine manufacturer. The engine had had over 110Oh of use prior to the first test. The engine oil was changed prior to performing the first test. Modifications / Test Setup

[0501] 1 . No SCR Catalyst or associated components were present in the exhaust system.

[0502] 2. High pressure EGR cooler is artificially controlled to 40°C for the duration of the test.

[0503] 3. An FTIR was connected and the sample point is located pre-aftertreatment on the exhaust outlet of the turbocharger

[0504] Diesel fuel compositions 1 to 8 of example 9 (table 2) were tested.

[0505] Test Procedure

[0506] No cleaning of the injectors was conducted between each test run.

[0507] - Engine Start + Warm-Up

[0508] - Passive DPF Regeneration by varying the engine speed and load until the regeneration is complete. The differential pressure across the DPF is used to monitor the regeneration progress.

[0509] - Engine Stop

[0510] - Change to test fuel

[0511] - Engine restarted and warmed

[0512] - 8-Hour Steady-State Test Cycle

[0513] - 1200RPM

[0514] - 60Nm

[0515] - Engine Stop

[0516] The emissions outputs were recorded as an average over the 8h test and the results are provided in table 3. The emission of nitrogen oxide (NO) was measured as was the total emission of nitrogen oxide and nitrogen dioxide (NOX).

[0517] Table 2

Claims

Claims1 . A method of reducing the emission of nitrogen oxide and / or nitrogen dioxide from a diesel engine combusting a diesel fuel composition, the method comprising dosing into the diesel fuel composition as an additive at least one nitrogen-containing detergent.

2. The use of at least one nitrogen-containing detergent as an additive to reduce the emission of nitrogen oxide and / or nitrogen dioxide from a diesel engine combusting a diesel fuel composition.

3. A method or use according to claim 1 or claim 2 wherein the one or more nitrogen containing detergents are selected from:(a) a quaternary ammonium salt additive;(b) the reaction product of a carboxylic acid-derived acylating agent and an amine;(c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol;(d) the reaction product of a carboxylic acid-derived acylating agent and hydrazine;(e) a salt formed by the reaction of a carboxylic acid with di-n-butylamine ortri-n-butylamine;(f) the reaction product of a hydrocarbyl-substituted dicarboxylic acid or anhydride and an amine compound or salt which product comprises at least one amino triazole group; and(g) a compound of formula (I):A— L— R1(I) wherein:A is a nitrogen-containing group;L is either a bond or a linker group; andR1is an optionally substituted hydrocarbyl group; and wherein the compound has a nitrogen content of at least 4% by mass.

4. A method or use according to any preceding claim wherein the one or more nitrogen containing detergents are selected from:(a) a quaternary ammonium salt additive;(b) the reaction product of a carboxylic acid-derived acylating agent and an amine;(c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol; and(g) a compound of formula (I):A— L— R1(I) wherein:A is a nitrogen-containing group;L is either a bond or a linker group; andR1is an optionally substituted hydrocarbyl group; and wherein the compound has a nitrogen content of at least 4% by mass.

5. A method or use according to any preceding claim wherein the diesel fuel composition comprises (a) a quaternary ammonium salt additive, (b) the reaction product of a carboxylic acid- derived acylating agent and an amine and (c) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol.

6. A method or use according to any preceding claim wherein diesel fuel composition comprises a quaternary ammonium salt additive (a) which is the reaction product of a compound including a tertiary amine group and a quaternising agent; wherein the quaternising agent is selected from alkylene oxide (preferably propylene oxide), optionally in combination with an acid, chloroacetic acid or a salt thereof, methyl salicylate or dimethyl oxalate; wherein the compound including a tertiary amine group is selected from one or more of:(i-a) the reaction product of a fatty acid of formula RZCOOH in which Rzis an alkyl or alkenyl group having 12 to 24 carbon atoms, and a compound selected from N,N-dimethyl-1 ,3- diaminopropane, N,N-diethyl-1 ,3- diaminopropane, N,N-dimethylethylenediamine, N,N- diethylethylenediamine, N,N-dibutylethylenediamine, 3-(2-(dimethylamino)ethoxy) propylamine, or combinations thereof;(i-b) the reaction product of a hydrocarbyl substituted succinic acid derived acylating agent and a compound selected from N,N-dimethyl-1 ,3-diaminopropane, N , N-diethyl-1 ,3- diaminopropane, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dibutylethylenediamine, 3-(2- (dimethylamino)ethoxy) propylamine, or combinations thereof; and(iv-a) a tertiary amine of formula R13R14R15N, wherein each of R13, R14and R15is independently an alkyl group or a hydroxyalkyl group.

7. A method or use according to any preceding claim wherein diesel fuel composition comprises a quaternary ammonium salt additive (a) which is the reaction product of a compound including a tertiary amine group and a quaternising agent; wherein the quaternising agent is selected from alkylene oxide (preferably propylene oxide), optionally in combination with an acid, chloroacetic acid or a salt thereof, methyl salicylate or dimethyl oxalate; wherein the compound including a tertiary amine group is selected from one or more of:(i-a) the reaction product of a fatty acid of formula RZCOOH in which Rzis an alkyl or alkenyl group having 12 to 24 carbon atoms, and N,N-dimethyl-1 ,3-diaminopropane (DMAPA);(i-b) the reaction product of a polyisobutylene-substituted succinic anhydride having a PIB molecular weight (Mn) of 700 to 1300 and N,N-dimethyl-1 ,3-diaminopropane; and(iv-a) a tertiary amine of formula R13R14R15N, wherein each of R13and R14is Ci to C4 alkyl, preferably methyl, and R15is an alkyl or alkenyl group having 12 to 24 carbon atoms.

8. A method or use according to any preceding claim wherein diesel fuel composition comprises (b) the reaction product of a carboxylic acid-derived acylating agent and an amine which is the reaction product of a polyisobutene-substituted succinic acid or succinic anhydride and a polyethylene polyamine selected from ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine and mixtures and isomers thereof; wherein polyisobutene substituent has a number average molecular weight of between 500 and 2000, preferably between 600 and 1200.

9. A method or use according to any preceding claim wherein diesel fuel composition comprises (c) the product of a Mannich reaction between formaldehyde, a polyethylene polyamine; and a para-substituted monoalkyl phenol.

10. A method or use according to any preceding claim wherein diesel fuel composition comprises the reaction product of: p) an alkylamine having the formula NHR19R20wherein R19and R20are each independently selected from H, optionally substituted C1-20 alkyl groups or optionally substituted C1-20 alkenyl groups; q) a nitrogen-containing reagent selected from an optionally substituted triazole, tetrazole, indole, indazole or benzotriazole, and. r) formaldehyde or a source of formaldehyde.

11. A method or use according to any preceding claim which reduces the emission of nitrogen oxide.

12. A method or use according to any preceding claim which reduces the emission of nitrogen dioxide.

13. A method or use according to any preceding claim which reduces the emission of nitrogen oxide and nitrogen dioxide.

14. A method or use according to any preceding claim which reduces the emission of nitrogen oxide and / or nitrogen dioxide by at least 5%.

15. A method or use according to any preceding claim which reduces the emission of nitrogen oxide and / or nitrogen dioxide from a direct injection diesel engine.

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