WO2013114107A2

WO2013114107A2 - Improvements in or relating to fuels

Info

Publication number: WO2013114107A2
Application number: PCT/GB2013/050204
Authority: WO
Inventors: Andrea Sneddon
Original assignee: Innospec Limited
Priority date: 2012-01-30
Filing date: 2013-01-30
Publication date: 2013-08-08
Also published as: WO2013114107A3; GB201201550D0; AR090415A1

Abstract

The invention provides a fuel composition comprising: a base fuel; a copolymer of ethylene and an olefinically unsaturated compound; and a cloud point depressant additive which comprises a nitrogen-containing compound and a polysulphone; wherein the cloud point of the fuel composition is lower than it would have been in the absence of the cloud point depressant additive; and wherein the CFPP of the composition is no higher than it would have been in the absence of the cloud point depressant additive.

Description

IMPROVEMENTS IN OR RELATING TO FUELS

This invention relates to fuel additives and to their use in improving the cold temperature properties of fuels.

Fuels may require any one or more of a wide range of different chemical additives in order to deliver acceptable performance. Examples include: additives to enhance lubricity and prevent premature wear of engine parts; additives to inhibit corrosion; detergents or dispersants to keep particulate matter mobile and keep engine parts clean, and prevent sludging; additives to improve conductivity of fuels and reduce the risk of spark hazards; additives to improve the cold temperature properties of fuels, and thus improve their cold temperature operability; and additives to reduce the drag forces arising when fuels are conveyed by pipeline.

A fuel may contain several such additives, but they can interact with each other, sometimes in a way which reduces the effectiveness of an additive. This is called antagonism.

This invention relates to fuels - particularly fuels containing middle distillates, for example diesel fuels and heating oils - which require additives to improve their cold temperature properties. Further, aspects of the invention relate to the finding of antagonism between such additives, and to combating such antagonism.

Fuels containing middle distillates may be mixtures of different types of hydrocarbon (i.e. normal and branched paraffins, aromatics, olefins and other polar and non-polar compounds.) These components may be present in a range of molecular weights and carbon lengths.

As the temperature of a fuel comprising middle distillates is decreased the least soluble components present in the fuel will start to precipitate as wax crystals. These crystals consist mainly of the longer carbon chain length n-paraffins present in the fuel. The temperature at which the wax crystals first appear is known as the cloud point, and is a function of the composition of the fuel. A suitable cloud point test is described in ASTM D 5772, and in ASTM D 2500.

As the fuel is further cooled the wax crystals grow into platelets, which can block filters. The Cold Filter Plugging Point (CFPP) test of DIN EN 1 16 (also called IP 309, and ASTM D 6371) is used to measure the temperature at which the wax crystals in a middle distillate fuel will block a 45 micron filter. Subsequently the wax crystals form a network which impairs the free flow of the fuel. The temperature at which the fuel will no longer flow is known as the pour point.

Cloud point depressants are used to delay the onset of crystallisation of the wax crystals as the temperature is decreased. They have been used to enhance operability and provide economic benefits in connection to refining. To reach a cloud point specification an amount of kerosene boiling range hydrocarbons may be left in the middle distillate fraction. The use of a cloud point depressant may save up to 30% of the kerosene fraction originally required. Cold flow improvers are used in middle distillate fuels to alter the size and shape of the n- paraffin wax crystals as they form. This helps to reduce the impact of the wax crystals on filtration of the fuel. The CFPP test is used as a measure of the effectiveness of cold flow improvers. It has been found that when certain cloud point depressants are used in conjunction with certain cold flow improvers the effectiveness of the flow improver, measured by CFPP, may be impaired. An antagonistic effect of this nature has been described in the literature (Fuel, Vol 74, No12, pp1830 -1833, 1995), between a copolymer of a linear a-olefin compound with an acrylic, vinyl or maleic unsaturated compound (a cloud point depressant) and an ethylene-vinyl acetate copolymer (a cold flow improver), in terms of the ability of the latter compound to reduce the CFPP by the expected amount. It is therefore desirable that a cloud point depressant does not cause a deterioration in the CFPP performance of the cold flow improver.

The present invention involves the recognition that two classes of fuel additives known for cold temperature benefits, described below, can be antagonistic; and the finding of an additive which can combat this antagonism; and do so, in preferred embodiments, to a remarkable degree.

In accordance with a first aspect of the invention there is provided a fuel composition comprising: a base fuel; a copolymer of ethylene and an olefinically unsaturated compound; and a cloud point depressant additive which comprises a nitrogen-containing compound and a polysulphone; wherein the cloud point of the fuel composition is lower than it would have been in the absence of the cloud point depressant additive; and wherein the CFPP of the composition is no higher than it would have been in the absence of the cloud point depressant additive.

The copolymer of ethylene and an olefinically unsaturated compound is a cold flow improver, employed to lower the CFPP from that of the base fuel. For brevity in this specification the copolymer of ethylene and an olefinically unsaturated compound is also called the "CFI". In preferred embodiments the cloud point of the fuel composition is more than 1 °C lower than the cloud point of the fuel composition in the absence of the cloud point depressant additive, preferably at least 1 .2°C lower, preferably at least 1 .5°C lower, preferably at least 1 .7°C lower; preferably at least 2°C lower.

In considering the definitions of cloud point given in this specification the standard industry test ASTM D 5772 may be used.

In the definitions which follow, the term "CFI test fuel composition" is used to describe the base fuel which contains the CFI, but not the nitrogen-containing compound or polysulphone.

In preferred embodiments the base fuel and the CFI used in the fuel composition of the first aspect are such that when the CFI is added to the base fuel to provide a "CFI test fuel composition" the CFI reduces the CFPP of the fuel by at least 4°C, preferably by at least 6°C, preferably by at least 8°C.

In considering the definitions of CFPP given in this specification the standard industry test DIN EN 1 16 may be used. Preferably, the CFPP of the fuel composition is lower than it would have been in the absence of the cloud point depressant additive, preferably more than 1 °C lower; preferably at least 2°C lower, preferably at least 4°C lower; preferably at least 6°C lower.

In the definitions given above, and elsewhere in this specification, which refer to test or comparison compositions containing a CFI and/or a cloud point depressant additive, comprising a nitrogen-containing compound and a polysulphone, it is to be understood that they will involve the same fuel and the same additives (that is, the same CFI, the same nitrogen-containing compound and the same polysulphone), at the same concentrations. It will be apparent that in preferred embodiments of fuel compositions of the invention an olefinically unsaturated compound and a cloud point depressant additive achieve a cloud point and CFPP of the fuel composition which are both lower than they would be, in the absence of the cloud point depressant additive. Suitably the cloud point is more than 1 °C lower and the CFPP is more than 1 °C lower.

In accordance with a second aspect of the present invention there is provided a method of lowering the cloud point of a fuel composition containing a copolymer of ethylene and an olefinically unsaturated compound, by addition of cloud point depressant additive comprising a nitrogen-containing compound and a polysulphone, wherein the CFPP of the fuel composition is no higher than it would have been in the absence of the cloud point depressant additive. In accordance with the definitions given above, in preferred embodiments the cloud point of the fuel composition is more than 1 °C lower than the cloud point of the fuel composition in the absence of the cloud point depressant additive, preferably at least 1 .2°C lower, preferably at least 1 .5°C lower, preferably at least 1 7°C lower; preferably at least 2°C lower.

Preferably, the CFPP is lower than it would have been in the absence of the cloud point depressant additive, preferably more than 1 °C lower; preferably at least 2°C lower, for example at least 4°C lower; or at least 6°C lower.

We have found that the nitrogen-containing compound promotes a lowering of the cloud point, but that without the polysulphone, it may cause an increase in the CFPP from that of said "CFI test fuel composition"; and that a polysulphone may combat this detrimental effect.

As is well known to the person skilled in this art, fuels vary greatly in their properties and in their response to cold flow improver additives with some fuels showing very little response while other show much greater response. The finding that the nitrogen-containing compound may provide reduction in cloud point and that the combination of nitrogen-containing compound and polysulphone (whether added to the fuel together or separately) may provide the reduction in cloud point without a detrimental effect of CFPP and preferably with a further improvement in CFPP is a significant one, and one which the skilled person can make use of in providing fuels with good cloud point and CFPP properties. In some embodiments the components of the fuel composition have the following characteristic: when the nitrogen-containing compound is added to the said "CFI test fuel composition" to provide a "CFI + nitrogen-containing compound test fuel composition" the nitrogen-containing compound antagonises the CFPP-reducing effect of the CFI. In such embodiments, the addition of the nitrogen-containing compound may raise the CFPP of said "CFI test fuel composition" by at least 1 °C, or at least 2°C, or at least 4°C. In preferred embodiments the components of the fuel composition have the following characteristic: when the polysulphone is added to said "CFI + nitrogen-containing compound test fuel composition" it acts to combat any such antagonism. For example it may reduce the CFPP by more than 1 °C, or at least 2°C, or at least 4°C, or at least 6°C. In combating such antagonism it may partly remove it (such that the CFPP it achieves is improved, but is still higher than the CFPP of the "CFI test fuel composition"), or may wholly recover it, attaining the same CFPP as the "CFI test fuel composition". In especially preferred embodiments it may even achieve a lower

CFPP than the CFPP of the "CFI test fuel composition".

In accordance with a third aspect of the present invention there is provided the use of a polysulphone in a fuel composition containing a nitrogen-containing compound and a copolymer of ethylene and an olefinically unsaturated compound, in order to prevent the nitrogen-containing compound from causing deterioration in the performance of the copolymer of ethylene and an olefinically unsaturated compound.

We believe that a nitrogen-containing compound may antagonise the CFPP-reducing effect of the CFI; and yet may produce an improvement in cloud point. We have found that a polysulphone combats the antagonism and does not have any detrimental effect on the cloud point improvement.

Preferably the nitrogen-containing compound lowers the cloud point, as defined and described above.

In accordance with a fourth aspect of the present invention there is provided the use, in a fuel composition containing a copolymer of ethylene and an olefinically unsaturated compound, of: - a nitrogen-containing compound to reduce the cloud point of the fuel composition, and a polysulphone to combat any detrimental effect of the nitrogen-containing compound on the copolymer of ethylene and an olefinically unsaturated compound.

In accordance with a fifth aspect of the present invention there is provided the use of a nitrogen-containing compound and of a polysulphone to lower the cloud point without increasing the CFPP in a fuel composition containing a copolymer of ethylene and an olefinically unsaturated compound. Preferably the nitrogen-containing compound and the polysulphone lower both the cloud point, and the CFPP.

In accordance with a sixth aspect of the present invention there is provided a fuel composition comprising a base fuel and a nitrogen-containing compound, wherein the base fuel and the nitrogen-containing compound are selected such that the cloud point of the fuel composition comprising a base fuel and a nitrogen-containing compound, is lower than the cloud point of the base fuel.

In accordance with a seventh aspect of the present invention there is provided the use of a nitrogen-containing compound in a fuel composition to reduce the cloud point thereof.

In relation to the sixth or seventh aspects, it should be noted that the fuel composition may be an unadditised base fuel, or a fuel composition containing other additives. There may be further additives present for low temperature operability benefits, for example selected from a copolymer of ethylene and an olefinically unsaturated compound; and a polysulphone. There may be further additives present for other benefits, for example for fuel lubricity benefits, dispersancy or combustion benefits. It is possible that such compounds may themselves exert an effect on cloud point but a key feature of the sixth and seventh aspects is the use of a nitrogen-containing compound, which itself has the function of reducing the cloud point of the fuel.

In accordance with some embodiments of the sixth and seventh aspects the fuel composition may contain no further additive (in addition to the nitrogen-containing compound) and the nitrogen-containing compound may give the above-mentioned reduction of cloud point.

In accordance with some embodiments of the sixth and seventh aspects the fuel composition may contain further additives, none of which are present to improve low temperature performance of the fuel (in addition to the nitrogen-containing compound), and the nitrogen- containing compound may give the above-mentioned reduction of cloud point.

In accordance with some embodiments of the sixth and seventh aspects the fuel composition may contain further additives, which comprise at least one additive which is present to improve low temperature performance of the fuel (in addition to the nitrogen-containing compound), and the nitrogen-containing compound may give the above-mentioned reduction of cloud point.

In accordance with some embodiments of the sixth and seventh aspects the fuel composition preferably does not contain an oil-soluble aliphatic compound comprising at least one straight- chain or branched alkyl or alkenyl chain having at least 8 carbon atoms; the oil-soluble aliphatic compound being obtainable by reacting an aliphatic mono- or dicarboxylic acid having 4 to 300 carbon atoms or derivatives thereof, with mono- or polyamines or with alcohols. Such compounds include the reaction products of maleic anhydride with tridecylamime, and of diethylenetriamine with oleic acid. Preferably an oil-soluble aliphatic compound as defined above is not present in any aspect of the present invention. Definitions of "preferred" or "suitable" features or embodiments, whether expressed already or subsequently, are applicable to any aspect of the present invention, even if expressed in the context of one aspect, unless we expressly state otherwise. Preferred copolymers of ethylene and olefinically unsaturated compounds for use in the present invention (as defined in any aspect) are those which, in addition to ethylene, contain 1 to 23 mol %, preferably 8 to 21 mol %, especially 9 to 18 mol %, of olefinically unsaturated compounds as co-monomers. The olefinically unsaturated compounds are preferably vinyl esters, acrylic esters, methacrylic esters, alkyl vinyl ethers and/or alkenes, and the compounds mentioned may be substituted by hydroxyl groups. One or more co-monomers may be present in the polymer.

The vinyl esters are preferably those of the formula (1).

CH₂-CH-OCOR¹ (1) where R is C1 - to C30-alkyl, preferably C4- to C16-alkyl, especially C6- to C12-alkyl. In a further embodiment, the alkyl groups mentioned may be substituted by one or more hydroxyl groups.

In a further preferred embodiment, R is a branched alkyl radical or a neoalkyl radical having 7 to 1 1 carbon atoms, especially having 8, 9 or 10 carbon atoms. Particularly preferred vinyl esters derive from secondary and especially tertiary carboxylic acids whose branch is in the alpha-position to the carbonyl group. Suitable vinyl esters include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl hexanoate, vinyl heptanoate, vinyl octanoate, vinyl pivalate, vinyl 2-ethylhexanoate, vinyl laurate, vinyl stearate and Versatic esters such as vinyl neononanoate, vinyl neodecanoate, vinyl neoundecanoate. In a further preferred embodiment, these ethylene copolymers contain vinyl acetate and at least one further vinyl ester of the formula 1 where R is C4- to C30-alkyl, preferably C4- to C16-alkyl, especially C6- to C12-alkyl.

The acrylic esters are preferably those of the formula (2).

CH₂-CR²-COOR³ (2) where R² is hydrogen or methyl and R³ is C1 - to C30-alkyl, preferably C4- to C16-alkyl, especially C6- to C12-alkyl. Suitable acrylic esters include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n- and isobutyl (meth)acrylate, hexyl, octyl, 2- ethylhexyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl (meth)acrylate and mixtures of these comonomers. In a further embodiment, the alkyl groups mentioned may be substituted by one or more hydroxyl groups. An example of such an acrylic ester is hydroxyethyl methacrylate.

The alkyl vinyl ethers are preferably compounds of the formula (3).

CH₂-CH-OR⁴ (3) where R⁴ is C1 - to C30-alkyl, preferably C4- to C16-alkyl, especially C6- to C12-alkyl. Examples include methyl vinyl ether, ethyl vinyl ether, isobutyl vinyl ether. In a further embodiment, the alkyl groups mentioned may be substituted by one or more hydroxyl groups. The alkenes are preferably monounsaturated hydrocarbons having 3 to 30 carbon atoms, especially 4 to 16 carbon atoms and especially 5 to 12 carbon atoms. Suitable alkenes include propene, butene, isobutylene, pentene, hexene, 4-methylpentene, octene, diisobutylene and norbornene and derivatives thereof such as methylnorbornene and vinylnorbornene. In a further embodiment, the alkyl groups mentioned may be substituted by one or more hydroxyl groups.

Apart from ethylene, particularly preferred terpolymers contain 1 to 23 mol %, preferably 3 to 20 mol %, especially 8 to 15 mol %, of vinyl acetate, and 0.1 to 12 mol %, especially 0.2 to 5 mol %, of at least one relatively long-chain and preferably branched vinyl ester, for example vinyl 2-ethylhexanoate, vinyl neononanoate or vinyl neodecanoate, the total comonomer content of the terpolymers being preferably between 8 and 21 mol %, especially between 12 and 18 mol %. Further particularly preferred copolymers contain, in addition to ethylene and 8 to 18 mol % of vinyl esters of C2- to C12-carboxylic acids, also 0.5 to 30 mol %, preferably 0.5 to 10 mol %, of olefins such as propene, butene, isobutylene, hexene, 4-methylpentene, octene, diisobutylene and/or norbornene.

Preference is given to using mixtures of two or more of the abovementioned ethylene copolymers. More preferably, the polymers on which the mixtures are based differ in at least one characteristic. For example, they may contain different comonomers, or have different comonomer contents, molecular weights and/or degrees of branching.

Nitrogen-containing compounds for use in the present invention (as defined in any aspect) include compounds which are the reaction product of (i) a compound containing the segment - NR R² where R represents a group containing from 4 to 44 carbon atoms and R² represents a hydrogen atom or a group R , and (ii) a carboxylic acid having from 1 to 4 carboxylic acid groups or an acid anhydride or acid halide thereof.

Preferably R is a hydrocarbyl group or a polyethoxylate or polypropoxylate group.

Preferably the group R is a hydrocarbyl group. Preferably the group R is predominantly a straight chain group.

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

A hydrocarbyl group R is preferably predominantly saturated, that is, it contains no more than one carbon-to-carbon unsaturated bond for every few (for example six to ten) carbon-to- carbon single bonds present. In the case of a hydrocarbyl group R having from 4 to 10 carbon atom it may contain one unsaturated bond. In the case of a hydrocarbyl group R having from 1 1 up to 20 carbon atom it may contain up to two unsaturated bonds. In the case of a hydrocarbyl group R having from 21 up to 30 carbon atom it may contain up to three unsaturated bonds. In the case of a hydrocarbyl group R having from 31 up to 40 carbon atom it may contain up to four unsaturated bonds. In the case of a hydrocarbyl group R having from 41 up to 44 carbon atom it may contain up to five unsaturated bonds. Preferably, however, a hydrocarbyl group R is preferably a fully saturated alkyl group, preferably a fully saturated n-alkyl group.

Preferably a group R comprises from 6 to 36 carbon atoms, preferably 8 to 32, preferably 10 to 24, preferably 12 to 22, most preferably 14 to 20.

It will be appreciated that the group R will typically include moieties with a range of carbon atoms. The definitions C₄.₄₄ C ₄.₂₂ are not intended to denote that all R groups must fall within the stated range.

The group R², when present, preferably conforms to the same definitions as are given for R¹. R and R² need not be the same. Preferably, however, R and R² are the same. Preferably the species (ii) is a carboxylic acid or an acid anhydride thereof. However if an acid halide is used it is preferably an acid chloride. Suitable compounds (i) include primary, secondary, tertiary and quaternary amines. Tertiary and quaternary amines only form amine salts.

Secondary amines, of formula HNR R², are an especially preferred class of compounds (i). Examples of especially preferred secondary amines include di-octadecylamine, di-cocoamine, di-hydrogenated tallow amine and methylbehenyl amine. Amine mixtures are also suitable such as those derived from natural materials. A preferred amine is a secondary hydrogenated tallow amine, the alkyl groups of which are derived from hydrogenated tallow fat composed of approximately 3-5%wt C₁₄, 30-32%wt C₁₆, and 58-60%wt C₁₈. Quaternary amines, of formula [+NR R²R³R⁴ -An], are an especially preferred class of compounds (i). R and R² are as defined above (but R² is not hydrogen). R³ and R⁴ independently represent a C(1 -4) alkyl group, preferably propyl, ethyl or, most preferably, methyl. +NR R²(CH₃)₂ represents a preferred cation. -An represents the anion. The anion may be any suitable species but is preferably a halide, especially a chloride. Where (i) comprises a quaternary amine, the reaction conditions may be adjusted to assist the reaction between (i) and (ii). Preferably the reaction conditions are adjusted by the introduction of an auxiliary base. The auxiliary base is preferably an inorganic base, such as sodium methoxide, sodium ethoxide, or sodium hydroxide. Preferably the inorganic base is a metal alkoxide or metal hydroxide. Alternatively, the quaternary amine salt may be preformed as the corresponding basic salt, for example, a quaternary ammonium hydroxide or alkoxide.

Also preferred are mixtures of primary and secondary amines, as species (i). Also preferred are mixtures of secondary and quaternary amines, as species (ii).

Preferred carboxylic acids include carboxylic acids containing two, three or four carboxylic acid groups, and acid anhydrides and acid halides thereof.

Examples of suitable carboxylic acids and their anhydrides include aminoalkylenepolycarboxylic acids, for example nitrilotriacetic acid, propylene diamine tetraacetic acid, ethylenediamine tetraacetic acid, and carboxylic acids based on cyclic skeletons, e.g., pyromellitic acid, cyclohexane-1 ,2-dicarboxylic acid, cyclohexene-1 ,2- dicarboxylic acid, cyclopentane-1 ,2-dicarboxylic acid and naphthalene dicarboxylic acid, 1 ,4- dicarboxylic acids, and dialkyi spirobislactones. Generally, these acids have about 5 to 13 carbon atoms in the cyclic moiety. Preferred acids useful in the present invention are optionally substituted benzene dicarboxylic acids, e.g. phthalic acid, isophthalic acid, and terephthalic acid, and their acid anhydrides or acid chlorides. Optional substituents include 1 -5 substituents, preferably 1 -3 substituents, independently selected from C(1 -4)alkyl, C(1 - 4)alkoxy, halogen, C(1 -4)haloalkyl, C(1 -4)haloalkoxy, nitrile, -COOH, -CO-OC(1 -4)alkyl, and - CONR³R⁴ where R³ and R⁴ are independently selected from hydrogen and C(1 -4)alkyl. Preferred halogen atoms are fluorine, chlorine and bromine. However unsubstituted benzene carboxylic acids are preferred. Phthalic acid and its acid anhydride are particularly preferred. Preferably the molar ratio of compound (i) to acid, acid anhydride or acid halide (ii) is such that at least 50% of the acid groups (preferably at least 75%, preferably at least 90%, and most preferably 100%) are reacted in the reaction between the compounds (i) and (ii), for example to form the amide and/or the amine salt. Where compound (ii) comprises one or more free carboxylic acid groups, reaction conditions may be adjusted to allow reaction between compounds (i) and (ii), for example to form the respective amide or amine salt. The reaction conditions may be adjusted by raising reaction temperatures. The reaction conditions may be adjusted by including a dehydrating agent within the reaction mixture. The one or more carboxylic acid groups may be activated in situ ready for coupling (i) and (ii), for example, by the use of such as carbodiimides (eg. EDCI). However, where activated forms of (ii) are employed, the activated forms of (ii) are preferably preformed, for example, as acid halides or acid anhydrides. Acid anhydrides are most preferred. In the case of a preferred reaction, between a compound (i) and a dicarboxylic acid, or acid anhydride or acid halide thereof, preferably the molar ratio of compound (i) (or mixtures of compounds (i), in that situation) to acid, acid anhydride or acid halide (ii) (or mixed compounds (ii), in that situation) is at least 0.7:1 , preferably 1 :1 , preferably at least 1 .5:1 . Preferably it is up to 3:1 , preferably up to 2.5:1 . Most preferably it is in the range 1 .8:1 to 2.2:1 . A molar ratio of 2:1 , (i) to (ii) is especially preferred. Also preferred is a molar ratio of 1 :1 .

It will be understood by those skilled in the art that compound (ii) is defined as the original starting material. However, preferred products may be obtained by step-wise reactions involving reacting compound (i) with an adduct of compound (ii), particularly where (ii) has already reacted in with a compound (i) to form an intermediate. Such an intermediate may be fully isolated or partially isolated so as to allow step-wise reactions. Such an intermediate may comprise a mono-amide/mono-carboxylic acid adduct, for instance, where in a first step a first equivalent of (i) is reacted with a dicarboxylic acid, acid anhydride, or acid halide. Partial isolation may therefore be mere isolation of the reaction mixture resulting from the first step of a reaction to form the mono-amide/mono-carboxylic acid. In such circumstances, a subsequent reaction of compound (i) (optionally a different compound (i) than that used in the first step) with the mono-amide/mono-carboxylic acid adduct may yield further derivatives, for instance, a diamide or a mono-amide/ammonium carboxylate salt. Such a step-wise process provides for greater selectivity of either or both of an amide group and/or an ammonium salt, especially where the amines of said amide group and said ammonium group are different, such as when (i) essentially comprises more than one amine.

In the case of a preferred reaction, between a secondary amine as the only compound (i) and a dicarboxylic acid, or acid anhydride or acid halide thereof, preferably the molar ratio of amine (i) to acid, acid anhydride or acid halide (ii) is at least 1 :1 , preferably at least 1 .5:1 . Most preferably it is in the range 1 .8:1 to 2.2:1 . A molar ratio of 2:1 , (i) to (ii) is especially preferred.

In the case of another preferred reaction, between a quaternary ammonium salt as the only compound (i) and a dicarboxylic acid, or acid anhydride or acid halide thereof, preferably the molar ratio of quaternary ammonium salt (i) to acid, acid anhydride or acid halide (ii) is at least 1 :1 , preferably at least 1 .5:1 . Most preferably it is in the range 1 .8:1 to 2.2:1 . A molar ratio of 2:1 , (i) to (ii) is especially preferred. Preferred reaction products for use in this invention contain at least the mono-amide adduct and quaternary ammonium salt and this may be achieved by using a mixture of compounds as compound (i), preferably both a secondary amine and a quaternary ammonium compound.

Another preferred reaction employs both a secondary amine and a quaternary ammonium salt as compounds (i). Preferably the ratio of the secondary amine to the quaternary ammonium salt in the reaction mixture is 30-70% to 70-30% molar/molar, preferably 40-60% to 60-40%, and most preferably they are present in equimolar amounts. Consistent with what is stated above, therefore, this reaction employs in its most preferred embodiment equimolar amounts of the secondary amine, the quaternary ammonium salt and the acid, acid anhydride or acid halide (ii).

Preferably the reaction between the compound (i) and the carboxylic acid, acid anhydride or acid halide (ii) forms one or more amide, imide or ammonium salts, combinations of these within the same compound, and mixtures of these compounds.

Thus, in one preferred embodiment a dicarboxylic acid, acid anhydride or acid halide (ii) is reacted with a secondary amine (i), preferably in a molar ratio of 1 :2 such that one mole of the amines form an amide and one mole forms an ammonium salt. An especially preferred additive is a Ν,Ν-dialkylammonium salt of 2-N ,N -dialkylamide benzoic acid, which suitably is the reaction product of di(hydrogenated) tallow amine (i) and phthalic acid or its acid anhydride (ii); preferably at a molar ratio of 2:1 . An especially preferred additive is the reaction product of di(hydrogenated) tallow amine (i) and phthalic acid or its acid anhydride (ii); preferably at a molar ratio of 1 :1 .

Other preferred additives are the reaction products of (hydrogenated) tallow amine (i) with EDTA (ii); preferably in a molar ratio of 4:1 with removal of four moles of water or two moles of water to form respectively the tetraamide derivative or the diamide diammonium salt derivative.

Another preferred additive is the reaction product of an alkylspirobislactone (ii), for example dodecenyl-spirobislactone, with mono-tallow amine and/or di-tallow amine (i); preferably the reaction product of one mole of alkylspirobislactone, for example dodecenyl-spirobislactone with one mole of mono-tallow amine and one mole of di-tallow amine.

Another preferred additive is the reaction product of the reaction product of benzene-1 ,2,4,5- tetracarboxylic acid or its dianhydride (ii) with di(hydrogenated tallow) amine (i); preferably in a molar ratio of 1 :4. This reaction product may be termed pyromellitic tetraamide but in fact may typically be a mixture of the tetraamide, triamide/mono salt and diamide/ disalt.

A polysulphone used in this invention can be prepared by the methods known in the art (see for example, Encyclopaedia of Polymer Science and Technology Vol. 9, Interscience Publishers, page 460 et seq.) or by known processes such as those described in US 3917466, US 4416668 and US 2010/072427.

A polysulphone used in this invention is suitably a copolymer of an alkene and sulphur dioxide.

A polysulphone used in this invention is suitably of the structure -R-S0₂-R-S0₂-R-S0₂-R- where R represents an alkene-derived moiety.

Preferred alkenes are one or more linear or branched 1 -alkenes having from 2 to 36 carbon atoms. Typically, the copolymers (polysulphones) are alternating 1 :1 copolymers in which one sulphone unit generally follows one alkene unit; it is also possible for sequences of two or more alkene units to occur in small amounts. Some of the alkene monomers may be replaced by ethylenically unsaturated carboxylic acids (e.g. acrylic acid, methacrylic acid or vinylacetic acid) or ethylenically unsaturated dicarboxylic acids (e.g. maleic acid or fumaric acid) or derivatives thereof (e.g. maleic anhydride), so that the copolymer of component (A) is formed especially from 50 mol % of sulphur dioxide or sulphone units, from 40 to 50 mol % of alkene units and from 0 to 10 mol % of units from said ethylenically unsaturated carboxylic acids, ethylenically unsaturated dicarboxylic acids or derivatives thereof.

Useful branched and especially linear 1 -alkenes having from 2 to 36 carbon atoms include, for example, ethene, propene, 1 -butene, 2-butene, isobutene, 1 -pentene, 1 -hexene, 1 -heptene, 1 - octene, 1 -nonene, 1 -decene, 1 -undecene, 1 -dodecene, 1 -tridecene, 1 -tetradecene, 1 - pentadecene, 1 -hexadecene, 1 -heptadecene, 1 -octadecene, 1 -nonadecene, 1 -eicosene, 1 - heneicosene, 1 -docosene, 1 -tricosene, 1 -tetracosene or mixtures thereof. Particular preference is given to linear 1 -alkenes having from 6 to 16 carbon atoms, especially having from 8 to 14 carbon atoms, or linear 1 -alkenes having from 12 to 22 carbon atoms, especially from 14 to 20 carbon atoms, and also mixtures thereof, for example a mixture of 1 -dodecene and 1 -tetradecene. It may also be advantageous to use mixtures of low molecular weight and high molecular weight 1 -alkenes, i.e. 1 -alkene mixtures with a bimodal distribution, for example mixtures of 1 -alkenes having from 6 to 13 carbon atoms and 1 -alkenes having from 14 to 20 carbon atoms, or mixtures of 1 -alkenes having from 6 to 10 carbon atoms and 1 -alkenes having from 1 1 to 15 carbon atoms, or mixtures of 1 -alkenes having from 2 to 24 carbon atoms and a single 1 -alkene having from 4 to 10 carbon atoms. A particularly preferred alkene is 1 - decene. In one preferred embodiment, the weight average molecular weight of the polysulphone is preferably in the range from about 1 ,000 to 1 ,500,000, with the preferred range being from about 10,000 to 990,000, and the most preferred molecular weights being in the range from about 100,000 to 500,000. In another preferred embodiment, the number average molecular weight of the polysulphone is preferably in the range from 2,000 to 1 ,000,000, especially from 4,000 to 100,000, in particular from 6,000 to 25,000.

The molecular weight of a polysulphone used herein may be determined by any suitable method, for example by light scattering or by determination of the inherent viscosity as described in US 3917466 or by gel permeation chromatography.

In some preferred embodiments, the polysulphone may be provided as a constituent of a conductivity improving additive or static dissipater additive.

Suitable conductivity improving additives include those described in: US 381 1848 (polysulphone and quaternary ammonium salt), US 3917466 (polysulphone and a polyamine); US 6391070 (copolymer of an alkylvinyl monomer and a cationic vinyl monomer and polysulphone), US 2010/0072427 (polysulphone, long chain hydrocarbyl amine, oil soluble acid), US 4416668 (imides of alpha olefin maleic anhydride copolymers and polysulphones).

A particularly preferred conductivity improving additive is a composition comprising a polysulphone, a polyamine, a quaternary ammonium salt and a sulphonic acid as described in US 3917466. A preferred polysulphone is as described herein.

A preferred polyamine in the conductivity improving additive is the reaction product of epichlorohydrin with an aliphatic primary monoamine or N-aliphatic hydrocarbyl alkylene diamine.

Preferred diamines are alkyl or alkenyl diamines of the general formula:

wherein R is preferably selected from an alkyl or alkenyl straight chain group of mainly C₈ to C₁₈ (coco propylene diamine); a straight chain alkyl group of mainly C ₆ to C₂₂ (C ₆ - ₂₂ alkylpropylene diamine); a straight chain alkyl group of mainly C ₆ to C₁₈ (tallow propylene diamine). Most preferably R represents an alkyl or alkenyl straight chain of mainly C₁₈ and the amine is oleyl (vegetable oil) propylene diamine.

A preferred sulphonic acid in the conductivity improving additive is an oil-soluble sulphonic acid, preferably dodecyl benzene sulphonic acid or dinonylnapthalene sulphonic acid. A preferred quaternary ammonium compound in the conductivity improving additive has the formula:

wherein R and R² are the same or different alkyl groups having 1 to 22 carbon atoms; R³ is selected from the group consisting of alkyl groups of 1 to 22 carbon atoms and

-(CH₂CR⁵HO)_nH wherein R⁵ is hydrogen or methyl and n is 1 to 20;

and R⁴ is selected from (a) an alkyl group having 1 to 22 carbon atoms, (b) an arylalkyl group having 7 to 22 atoms, (c) -(CH₂CR₅HO)nH, (d) a group of formula: 0

-CH₂CH₂0- -OCH₂CH(OCOR⁶)CH₂OCOR⁷

0 wherein R⁶ and R⁷ are the same or different alkyl groups having 1 1 to 19 carbon atoms, and (e) R⁸C0₂ wherein R⁸ is a hydrocarbyl group having 1 to 17 carbon atoms, with the proviso that when R , R², R³ and R⁴ are all alkyl groups, at least one of them is an alkyl group having at least 8 carbon atoms;

X is an anion; z is 0 or 1 , Z is 0 when R⁴ is (d) or (e) and; y is at least 1 , y is equal to the valence of anion when z is 1 .

The skilled person can explore treat rates of the components to achieve good results; suitably, to determine the treat rates at which: the CFI gives a reduction in CFPP; the nitrogen- containing composition gives a reduction in cloud point; and any antagonism between the nitrogen-containing composition and the CFI; and whether and at what treat rate a sulphone may be present, to combat such antagonism. However the following definitions give guidance.

Preferably the concentration of the CFI in the fuel composition is at least 10 ppm, preferably at least 20 ppm, preferably at least 30 ppm, preferably at least 40 ppm.

Preferably the concentration of the CFI in the fuel composition is up to 10,000 ppm, preferably up to 2,000 ppm, preferably up to 1 ,200 ppm, preferably up to 800 ppm, preferably up to 500 ppm, preferably up to 400 ppm, preferably up to 300 ppm.

Preferably the concentration of the nitrogen-containing compound in the fuel composition is at least 1 ppm, preferably at least 10 ppm, preferably at least 20 ppm, preferably at least 25 ppm, preferably at least 30 ppm.

Preferably the concentration of the nitrogen-containing compound in the fuel composition is up to 1 ,000 ppm, preferably up to 500 ppm, preferably up to 400 ppm, preferably up to 300 ppm, preferably up to 200 ppm.

Preferably the concentration of the polysulphone in the fuel composition is at least 0.1 ppm, preferably at least 0.5 ppm, preferably at least 2 ppm, preferably at least 3 ppm, preferably at least 4 ppm, preferably at least 5 ppm. Preferably the concentration of the polysulphone in the fuel composition is up to 200 ppm, preferably up to 100 ppm, preferably up to 50 ppm.

Preferably the ratio of the nitrogen-containing compound to the CFI is in the range 1 part nitrogen-containing compound to 0.05 - 20 parts CFI, preferably 1 part nitrogen-containing compound to 0.1 - 10 parts CFI, preferably 1 part nitrogen-containing compound to 0.15 - 8 parts CFI, preferably 1 part nitrogen-containing compound to 0.15 - 3 parts CFI.

Preferably the ratio of the polysulphone to the CFI is in the range 1 part polysulphone to 1 -200 parts CFI, preferably 1 part polysulphone to 2-100 parts CFI, preferably 1 part polysulphone to 4-60 parts CFI.

Preferably the ratio of the polysulphone to the nitrogen-containing compound is in the range 1 part polysulphone to 1 -50 parts nitrogen-containing compound, preferably 1 part polysulphone to 1 -30 parts nitrogen-containing compound, preferably 1 part polysulphone to 1 -20 parts nitrogen-containing compound, preferably 1 part polysulphone to 5-10 parts nitrogen- containing compound.

Unless otherwise stated the concentrations and ratios are of active compounds, not of formulations in which they are contained.

It will be appreciated that the copolymer of ethylene and an olefinically unsaturated compound and the cloud depressant additive may be added separately or combined in an additive package or each may be added via one or more additive packages which comprise additional ingredients. Furthermore, the nitrogen-containing compound and polysulphone, when present, may be added separately or combined in one or more additive packages.

Throughout this specification, where we refer to a copolymer of ethylene and an olefinically unsaturated compound, a nitrogen-containing compound and a polysulphone, we mean to include one or more of each of these species.

Fuel

A base fuel used in the present invention may comprise or consist of a petroleum-based fuel oil, especially a middle distillate fuel oil. Such middle distillate fuel oils generally boil within the range of from 1 10°C to 500°C, e.g. 150°C to 400°C. The middle distillate fuel oil may comprise atmospheric distillate or vacuum distillate, cracked gas oil, or a blend in any proportion of straight run and refinery streams from conversion units such as thermally and/or catalytically cracked and hydro-cracked distillates. The fuel composition of the present invention may comprise or consist of 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). The fuel composition may comprise first generation biofuel. First generation biofuel contains esters of, for example, vegetable oils, animal fats and used cooking fats. This form of biofuel may be obtained by transesterification of oils, for example rapeseed oil, soybean oil, safflower oil, palm 25 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, in the presence of a catalyst.

The fuel composition may comprise second generation biofuel. Second generation biofuel is derived from renewable resources such as vegetable oils and animal fats and processed, often in the refinery, often using hydroprocessing such as the H-Bio process developed by Petrobras. Second generation biofuel may be similar in properties and quality to petroleum based fuel oil streams, for example renewable fuel produced from vegetable oils, animal fats etc. and marketed by ConocoPhillips as Renewable Diesel and by Neste as NExBTL.

The fuel composition of the present invention may comprise third generation biofuel. Third generation biofuel utilises gasification and Fischer-Tropsch technology including those described as BTL (biomass-to-liquid) fuels. Third generation biofuel does not differ widely from some second generation biofuel, but aims to exploit the whole plant (biomass) and thereby widens the feedstock base. The fuel composition may contain blends of any or all of the above fuel compositions.

In some embodiments the fuel composition of the present invention may be a blended fuel comprising biofuel, and a second fuel. In such blends the biofuel may be present in an amount of from 0.1 %, preferably from 0.4% (wt/wt). In such blends the biofuel 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% (wt/wt). The second fuel may be a petroleum-based fuel oil, especially a middle distillate fuel oil, including a non-renewable Fischer-Tropsch fuel. All such fuels may be used in embodiments of the invention.

The fuel composition of 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%, 0.5% or more. However in preferred embodiments the fuel 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.

The fuel composition of the present invention may be utilized as a fuel for locomotion in motor vehicles, ships and boats; as burner fuel in home heating and power generation and as fuel in multi purpose stationary engines. Other Additives

The fuel composition of the present invention may include one or more further additives such as those which are commonly found in the fuels of use in this invention. These include, for example, antioxidants, dispersants, detergents, cetane improvers, dehazers, stabilisers, demulsifiers, antifoams, corrosion inhibitors, lubricity improvers, dyes, markers, combustion improvers and odour masks, and further additives useful in achieving improvements in cold temperature performance; for example alkylphenol aldehyde resins, comb polymers, oil soluble polyoxyalkylene compounds and hydrogenated polymers of alkenes.

However the presence or absence of other additives is not of central importance to the present invention, which relates to the presence of (1) a copolymer of ethylene and an olefinically unsaturated compound, and (2) a nitrogen-containing compound, and (3) a polysulphone, in a fuel composition, and the interactions between them.

In accordance with a eighth aspect of the present invention there is provided the use of an additive which is the reaction product of (i) a compound containing the segment -NR R² where R represents a group containing from 4 to 44 carbon atoms and R² represents a hydrogen atom or a group R , and (ii) carboxylic acid having from 1 to 4 carboxylic acid groups or an acid anhydride or acid halide thereof, for lowering the cloud point of a fuel composition by more than 1 °C.

Suitably the salt lowers the cloud point by at least 1 .2°C, preferably at least 1 .5 °C, preferably at least 1 .7°C, and preferably by at least 2°C.

Suitably the concentration of the salt in the fuel composition is at least 1 ppm, preferably at least 10 ppm, preferably at least 20 ppm, preferably at least 25 ppm preferably at least 30 ppm.

Preferably the concentration of the salt in the fuel composition is up to 1 ,000 ppm, preferably up to 500 ppm, preferably up to 400 ppm, preferably up to 300 ppm, preferably up to 200 ppm. The invention will now be further described, by way of example, with reference to the following examples: Materials used in testing were as follows:

CFI (1 ) : a copolymer of ethylene and vinyl acetate (vinyl acetate content, approximately 13 mol%), as a solution in an aromatic solvent. Mn about 5300. CFI (2) : a copolymer of ethylene and vinyl acetate (vinyl acetate content, approximately 15 mol%), as a solution in an aromatic solvent. Mn about 4500.

Additive A : a phthalic amide salt: phthalic anhydride (7.4g) was mixed with di(hydrogenated tallow) amine (commercially available as Armeen 2HT) (50.02g) at a molar ratio of 1 :2 in Shellsol AB solvent (57.5g). The reaction mixture was heated at 65°C for approximately 6 hours.

Additive AA : EDTA tallow amide - the reaction product of EDTA with di(hydrogenated tallow) amine (Armeen 2HT) in a molar ratio of 1 :4 was prepared by heating the amine and EDTA with stirring and removal of water at 210-220°C until no further water was removed and then removing any residual water under vacuum to form the tetraamide .

Additive AB : Pyromellitic tetraamide - the reaction product of Benzene-1 ,2,4,5- tetracarboxylic dianhydride with di(hydrogenated tallow) amine (Armeen 2HT) in a molar ratio of 1 :4 was prepared using similar reaction conditions to those described in EP0272889 for Additive X of Example 1 to form a mixture of the tetraamide, triamide/mono salt and diamide/ disalt.

Additive B: a polysulphone, prepared by reaction of 1-decene and sulphur dioxide in a mole ratio of 1 :1 .5, in the presence of a peroxide free radical initiator and an alkyl mercaptan as a chain transfer agent, in toluene, under mild conditions of moderately elevated temperature, and for a moderate time. Fuels :

Fuel Characteristics

Tests were also run in two commercial low sulphur diesel fuels, Fuel C and Fuel D, both available in the European market.

Cloud point values were determined by the method of ASTM D 5772 and are reported to the nearest 0.1 °C.

CFPP values were determined by the method of DIN EN 1 16 and are reported to the nearest 1 °C.

Example Set 1 - examination of cloud point

In Fuel A

Additive A Additive B Cloud Point

(cone) (cone)

- - - 6.1 °C

187 ppm - - 8.3 °C

- 25 ppm - 6.0 °C

187 ppm 25 ppm - 8.4 °C Example Set 2 - examination of cloud point and CFPP In Fuel B

When 62 ppm of CFI (1) was used optimal results in respect of cold flow performance were obtained using 37 ppm of Additive A and 5 ppm of Additive B. A smaller benefit in cold flow performance may be expected using lower amounts of Additives A and B. Indeed, it is not to be expected that higher amounts of Additives A and B would yield further improvement, or even achieve the optimal level of performance shown above. Although the mechanisms underlying the effects shown - the loss of cold flow benefit on addition of the cloud point depressant Additive A, and the achievement of very high cold flow benefit when Additive B is also present - are not fully understood, it is possible that they could be compromised by an overdose of one or more (or all) of the components. Determining the optimum dosage rates of the additives for a given fuel are within the competence of the person skilled in the art.

Example Set 3 - examination of cloud point and CFPP

In Fuel C

CFI (1 ) Additive A Additive B Cloud Point CFPP

45 ppm - - - 3.1 °C - 14 °C

45 ppm 75 ppm 10 ppm - 3.1 °C - 23 °C

45 ppm 250 ppm 33 ppm - 5.2 °C -27 °C

Example Set 4 - examination of cloud point and CFPP

In Fuel D

CFI (2) Additive A Additive B Cloud Point CFPP

248 ppm - - - 4.5 °C - 1 1 °c

248 ppm 125 ppm 17 ppm - 5.9 °C - 16 °C Example Set 5 - examination of cloud point

In Fuel E

Example Set 6 - examination of cloud point and CFPP

In Fuel E

Example Set 7 - examination of cloud point and CFPP

In Fuel F

Example Set 8 - examination of cloud point and CFPP at a broad range of dose rates

In Fuel E

Example Set 9 - examination of cloud point and CFPP using other N-containing additives

In Fuel E

CFI (1 ) Additive AA or AB Additive B Cloud point CFPP

- - - -6.9 °C -1 1 °c

310 ppm Additive AA - 57 ppm - -7.4 °C -

310 ppm Additive AA - 57 ppm 5 ppm -7.2 °C -28 °C

310 ppm Additive AA - 1 15 ppm - -7.4 °C -

310 ppm Additive AA - 1 15 ppm 5 ppm -7.4 °C -29 °C

310 ppm Additive AB - 57 ppm - -7.4 °C -25 °C

Claims

1 . A fuel composition comprising: a base fuel; a copolymer of ethylene and an olefinically unsaturated compound; and a cloud point depressant additive which comprises a nitrogen- containing compound and a polysulphone; wherein the cloud point of the fuel composition is lower than it would have been in the absence of the cloud point depressant additive; and wherein the CFPP of the composition is no higher than it would have been in the absence of the cloud point depressant additive.

2. A fuel composition as claimed in claim 1 wherein the cloud point of the fuel composition is more than 1 °C lower than the cloud point of the fuel composition in the absence of the cloud point depressant additive.

3. A fuel composition as claimed in claim 1 or 2 wherein the CFPP is more than 1 °C lower than it would have been in the absence of the cloud point depressant additive.

4. A fuel composition as claimed in any preceding claim, wherein the components of the fuel composition have the following characteristics: - when the copolymer of ethylene and an olefinically unsaturated compound is added to the base fuel to provide a "CFI test fuel composition" the CFPP is lowered by at least 4°C; when the nitrogen-containing compound is added to the said "CFI test fuel composition" to provide a "CFI + nitrogen-containing compound test fuel composition" the CFPP is raised by more than 1 °C, from the CFPP of said "CFI test fuel composition"; when the polysulphone is added to said "CFI + nitrogen-containing compound test fuel composition" the CFPP is lowered by more than 1 °C, from the CFPP of said

"CFI + nitrogen-containing compound test fuel composition".

5. A fuel composition as claimed in any preceding claim, which has a cloud point at least 1 °C lower and a CFPP at least 1 °C lower, than they would be, absent the cloud point depressant additive.

6. A fuel composition as claimed in any preceding claim in which the copolymer of ethylene and an olefinically unsaturated compound is a copolymer of ethylene and a vinyl ester.

7. A fuel composition as claimed in any preceding claim in which the nitrogen-containing compound is the reaction product of (i) a compound containing the segment -NR R² where R represents a group containing from 4 to 44 carbon atoms and R² represents a hydrogen atom or a group R , and (ii) a carboxylic acid having from 1 to 4 carboxylic acid groups or an acid anhydride or acid halide thereof.

8. A fuel composition as claimed in claim 7, wherein the carboxylic acid is an optionally substituted benzene dicarboxylic acid, for example phthalic acid.

9. A fuel composition as claimed in any preceding claim wherein the polysulphone is a copolymer of an alkene and sulphur dioxide wherein the alkene is a linear or branched 1 - alkene having from 2 to 36 carbon atoms.

10. A fuel composition as claimed in any preceding claim, wherein the cloud point depressant additive comprises a nitrogen-containing compound and a polysulphone.

1 1 . A method of lowering the cloud point of a fuel composition containing a copolymer of ethylene and an olefinically unsaturated compound, by addition of a cloud point depressant additive comprising a nitrogen-containing compound and a polysulphone, wherein the cloud point of the fuel composition is lower then it would have been in the absence of the cloud point depressant additive; and wherein the CFPP of the composition is no higher than it would have been in the absence of the cloud point depressant additive.

12. A method as claimed in claim 1 1 , wherein the copolymer of ethylene and an olefinically unsaturated compound lowers the CFPP of the base fuel, wherein the effect is antagonised by addition of the nitrogen-containing compound, and wherein addition of the polysulphone combats the antagonism.

13. A method as claimed in claim 1 1 or claim 12 wherein the polysulphone is provided as a component of a conductivity improving additive which is a composition comprising a polysulphone, a polyamine, a quaternary ammonium salt and a sulphonic acid.

14. An additive composition comprising: a nitrogen-containing compound which is the reaction product of (i) a compound containing the segment -NR R² where R represents a group containing from 4 to 44 carbon atoms and R² represents a hydrogen atom or a group R , and (ii) a carboxylic acid having from 1 to 4 carboxylic acid groups or an acid anhydride or acid halide thereof (but which is); and a polysulphone which is a copolymer of an alkene and sulphur dioxide.

15. The use of a polysulphone in a fuel composition containing a nitrogen-containing compound and a copolymer of ethylene and an olefinically unsaturated compound, in order to prevent the nitrogen-containing compound from causing deterioration in the performance of the copolymer of ethylene and an olefinically unsaturated compound.

16. The use, in a fuel composition containing a copolymer of ethylene and an olefinically unsaturated compound, of: a nitrogen-containing compound to reduce the cloud point of the fuel composition, and a polysulphone to combat any detrimental effect of the nitrogen-containing compound on the copolymer of ethylene and an olefinically unsaturated compound.

17. The use of a nitrogen-containing compound and of a polysulphone to lower the cloud point without increasing the CFPP in a fuel composition containing a copolymer of ethylene and an olefinically unsaturated compound.

18. A fuel composition comprising a base fuel and a nitrogen-containing compound, wherein the base fuel and the nitrogen-containing compound are selected such that the cloud point of the fuel composition comprising a base fuel and a nitrogen-containing compound, is lower than the cloud point of the base fuel.

19. Use of a nitrogen-containing compound in a fuel composition to reduce the cloud point thereof.

20. The use of an additive which is the reaction product of (i) a compound containing the segment -NR R² where R represents a group containing from 4 to 44 carbon atoms and R² represents a hydrogen atom or a group R , and (ii) carboxylic acid having from 1 to 4 carboxylic acid groups or an acid anhydride or acid halide thereof, for reducing the cloud point of a fuel composition by more than 1 °C.