Additive Composition

Description

[0001] This invention relates to additive compositions, and to their use to improve the characteristics of fuel oils, especially middle distillate fuels such as diesel fuels, kerosene and jet fuel.

[0002] Environmental concerns have led to a need for fuels with reduced sulphur content, especially diesel fuel, heating oil and kerosene. However, the refining processes that produce fuels with low sulphur contents also result in a product of lower viscosity and a lower content of other components in the fuel that contribute to its lubricity, for example, polycyclic aromatics and polar compounds. Furthermore, sulphur-containing compounds in general are regarded as providing some anti-wear properties and a result of the reduction in their proportions, together with the reduction in proportions of other components providing lubricity, has been an increase in the number of reported problems in fuel pumps in diesel engines. The problems are caused by wear in, for example, cam plates, plungers, rollers, spindles and drive shafts, which may result in sudden pump failures relatively early in the life of the engine.

[0003] The problems may be expected to become worse in future because, in order to meet stricter requirements on exhaust emissions generally, higher pressure fuel systems, including in-line pumps, rotary pumps, common-rail pumps and unit injector systems, are being introduced, these being expected to have more stringent lubricity requirements than present equipment, at the same time as lower sulphur levels in fuels become more widely required.

[0004] Historically, the typical sulphur content in a diesel fuel was below 0.5% by weight. In Europe maximum sulphur levels have been reduced from 0.20% to 0.05% and in Sweden grades of fuel with levels below 0.005% (Class 2) and 0.001% (Class 1) are in use. A fuel oil composition with a sulphur level below 0.05% by weight is referred to herein as a low-sulphur fuel.

[0005] Such low-sulphur fuels may contain an additive to enhance their lubricity. These additives are of several types. In WO 94/17160, there is disclosed a low sulphur fuel comprising a carboxylic acid ester to enhance lubricity, more especially an ester in which the acid moiety contains from 2 to 50 carbon atoms and the alcohol moiety contains one or more carbon atoms. In U.S. Patent No. 3273981, a mixture of a dimer acid, for example, the dimer of linoleic acid, and a partially esterified polyhydric alcohol is described for the same purpose. In U.S. Patent No. 3287273, the use of an optionally hydrogenated dimer acid glycol ester is described. Other materials used as lubricity enhancers, or anti-wear agents as they are also termed, include a sulphurized dioleyl norbornene ester (EP-A-99595), castor oil (U.S. Patent No. 4375360 and EP-A-605857) and, in methanol-containing fuels, a variety of alcohols and acids having from 6 to 30 carbon atoms, acid and alcohol ethoxylates, mono- and di-esters, polyol esters, and olefin-carboxylic acid copolymers and vinyl alcohol polymers (also U.S. Patent No. 4375360).

[0006] EP 0 798 364 A1 describes the use of a salt formed by the reaction between a carboxylic acid and an aliphatic amine to improve inter alia, the lubricity of a diesel fuel. The amines used have hydrocarbyl groups of between 2 and 50 carbon atoms, preferably between 8 and 20 carbon atoms, with amines such as oleyl amine being exemplified.

[0007] US 6,277,158 describes a concentrate containing n-butlyamine oleate as a friction modifier for addition to motor gasoline.

[0008] US2002/0095858 relates to fuel oil compositions containing an additive formed by the reaction of a mono- or dicarboxylic acid of 6 to 50 carbon atoms with an amine having at least one branched alkyl substituent. These additives are shown to be effective lubricity enhancers for the fuel.

[0009] US 2002/0014034 describes the use of additives to improve the lubricity of a fuel oil. A suitable additive may be formed by the reaction of N, N-dibutylamine with an acid mixture consisting of 70% fatty acids and 30% resin-based acids.

[0010] A further consequence of refining processes employed to reduce diesel fuel sulphur and aromatic contents is a reduction in the electrical conductivity of the fuel. The insulating properties of low sulphur fuels represent a potential hazard to refiners, distributors and customers due to the potential for static charge accumulation and discharge. Static charges can occur during pumping and especially filtration of the fuel, the release of this charge accumulation as a spark constituting a significant risk in highly flammable environments. Such risks are minimised during fuel processing and handling through appropriate earthing of fuel lines and tanks combined with the use of anti-static additives. These anti-static additives do not prevent the accumulation of static charges but enhance their release to the earthed fuel lines and vessels thereby controlling the risk of sparking. A number of such additives are in common usage and are available commercially.

[0011] It is thus desirable to be able to improve both the lubricity and conductivity of low sulphur content fuels.

[0012] EP 1 328 609 describes combinations of either a hydrocarbyl monoamine or an N-hydrocarbyl-substituted poly(alkyleneamine) with either a fatty acid containing 8 to 24 carbon atoms or an ester thereof with an alcohol or polyol of up to 8 carbon atoms.

[0013] The present invention is based on the observation of a negative interaction between certain lubricity improving additives and certain conductivity improving additives, and the discovery of combinations of species where this negative interaction is minimised.

[0014] Thus in accordance with a first aspect, the present invention provides an additive composition comprising a lubricity enhancer and a conductivity-improving additive; wherein the lubricity enhancer comprises a salt formed by the reaction of a carboxylic acid with di-n-butylamine; and wherein the conductivity improving additive comprises the combination of:

(a) a polymeric condensation product formed by the reaction of an aliphatic aldehyde or ketone, or a reactive equivalent, with at least one ester of p-hydroxybenzoic acid with,

(b) a copolymer, terpolymer or polymer of acrylic acid or methacrylic acid or a derivative thereof.

[0015] The combination of the lubricity enhancer and the conductivity-improving additive according to the present invention is able to provide both good lubricity and good conductivity to a fuel oil composition. This is in contrast to combinations of the lubricity enhancer with other conductivity-improving additives where a significant loss in conductivity performance has been observed.

[0016] In this specification, the use of the term 'salt' to describe the product formed by the reaction of the carboxylic acid and the amine should not be taken to mean that the reaction necessarily forms a pure salt. It is presently believed that the reaction does form a salt and thus that the reaction product contains such as salt however, due to the complexity of the reaction, it is likely that other species will also be present. The term 'salt' should thus be taken to include not only the pure salt species, but also the mixture of species formed during the reaction of the carboxylic acid and the amine.

[0017] As carboxylic acid, those corresponding to the formula [R'(COOH)_x]_y , where each R' is independently a hydrocarbon group of between 2 and 45 carbon atoms, and x is an integer between 1 and 4, are suitable. Preferably, R' is a hydrocarbon group of 8 to 24 carbon atoms, more preferably, 12 to 20 carbon atoms. Preferably, x is 1 or 2, more preferably, x is 1. Preferably, y is 1, in which case the acid has a single R' group. Alternatively, the acid may be a dimer, trimer or higher oligomer acid, in which case y will be greater than 1 for example 2, 3 or 4 or more. R' is suitably an alkyl or alkenyl group which may be linear or branched. Examples of carboxylic acids which may be used in the present invention include: lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, neodecanoic acid, arachic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, melissic acid, caproleic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, coconut oil fatty acid, soy bean fatty acid, tall oil fatty acid, sunflower oil fatty acid, fish oil fatty acid, rapeseed oil fatty acid, tallow oil fatty acid and palm oil fatty acid. Mixtures of two or more acids in any proportion are also suitable. Also suitable are the anhydrides of carboxylic acids, their derivatives and mixtures thereof. In a preferred embodiment, the carboxylic acid comprises tall oil fatty acid (TOFA). It has been found that TOFA with a saturate content of less than 5% by weight is especially suitable. As is known in the art, TOFA contains small but variable amounts of rosin acids and isomers thereof. Preferably, TOFA with an abietic acid content of less than 5% by weight, for example, less than 2% by weight, is used.

[0018] In another preferred embodiment, the carboxylic acid comprises rapeseed oil fatty acid.

[0019] In another preferred embodiment, the carboxylic acid comprises soy bean fatty acid.

[0020] In another preferred embodiment, the carboxylic acid comprises sunflower oil fatty acid.

[0021] Also suitable are aromatic carboxylic acids and their alkyl derivatives as well as aromatic hydroxy acids and their alkyl derivatives. Illustrative examples include benzoic acid, salicylic acid and acids derived from such species.

[0022] Preferably, the carboxylic acid has an iodine value of at least 80g/100g, more preferably at least 100 g/100g, for example, at least 130 g/100g or at least 150 g/100g.

[0023] Particularly preferred embodiments of the present invention are thus where the lubricity enhancer comprises a salt formed by the reaction of:

Tall oil fatty acid with di-n-butylamine,

Rapeseed oil fatty acid with di-n-butylamine,

Soy bean fatty acid with di-n-butylamine, and

Sunflower oil fatty acid with di-n-butylamine.

[0024] The salt may conveniently be produced by mixing the carboxylic acid with the amine. The order in which one component is added to the other is not important. The molar ratio of the amount of acid to the amount of amine is suitably from 10:1 to 1:10, preferably from 10:1 to 1:2, more preferably from 2:1 to 1:2, for example, around 1:l. In an embodiment, a molar ratio of 1.1:1 to 1:1.1 has been found to be suitable. The reaction may be conducted at room temperature, but is preferably heated gently, for example to 40°C.

[0025] These salts are the subject of the present Applicant's co-pending application EP 05270062.2 where in addition to providing good lubricity to fuel oil compositions they were found to display particularly good low temperature properties.

Component (a)

[0026] Component (a) is a condensate species derived from an alkyl ester of p-hydroxybenzoic acid. These HydroxyBenzoate-Formaldehyde Condensates are the subject of the present Applicant's co-pending application EP 1 640 438 A and are referred to herein as HBFC.

[0027] Preferably, the at least one ester of p-hydroxybenzoic acid comprises; (i) a straight or branched chain C₁ - C₇ alkyl ester of p-hydroxybenzoic acid; (ii) a branched chain C₈ - C₁₆ alkyl ester of p-hydroxybenzoic acid, or; (iii) a mixture of long chain C₈- C₁₈ alkyl esters of p-hydroxybenzoic acid, at least one of said alkyls being branched.

[0028] Preferably, the alkyl in (i) is ethyl or n-butyl.

[0029] Preferably, the branched alkyl group in (ii) is 2-ethylhexyl or isodecyl.

[0030] Conveniently, the molar ratio of the branched ester to the other ester is in the range of 5:1 to 1:5.

[0031] Condensates of mixed esters may be used, for example mixed ester condensates of n-octyl and 2-ethylhexyl esters of p-hydroxybenzoic acid may be prepared. The ratio of the esters in the mixed condensates may be varied as required. A mixed ester condensate where the molar ratio of 2-ethylhexyl ester to n-octyl ester is 3:1 has been found to be useful. Mixed ester condensates of more than two ester monomers may also be prepared.

[0032] The number average molecular weight of the polymeric condensation products is suitably in the range of 500 to 5000, preferably 1000 to 3000, more preferably 1000 to 2000 Mn.

[0033] Other comonomers may be added to the reaction mixture of aldehyde and alkyl ester or mixture of alkyl esters. Some of the polymers described above, for example, that are based on the 2-ethylhexyl ester, are too viscous to be handled conveniently at temperatures they would be used commercially, i.e. ambient to 60°C, unless diluted with a large proportion of solvent. This problem can be overcome by replacing up to 33 mole % of the p-hydroxybenzoic ester or ester mixture used in the condensation reaction with other comonomers in order to modify the physical properties of the polymers whilst still retaining activity. The comonomers are aromatic compounds that are sufficiently reactive to take part in the condensation reaction. They include alkylated, arylated and acylated benzenes such as toluene, xylene, mesitylene, biphenyls and acetophenone. Other comonomers include hydroxy aromatic compounds such as p-hydroxybenzoic acid, acid derivatives of p-hydroxyaromatic acids such as amides and salts, other hydroxyaromatic acids, alkylphenols, naphthols, phenylphenols, acetamidophenols, alkoxyphenols and o-alkylated, o-arylated and o-acylated phenols. The hydroxy compounds should be either di- or mono- functional with regard to the condensation reaction. The hydroxy compounds that are di-functional should be substituted in the para- position whilst those that are mono-functional can be substituted in any position, e.g. 2,4-di-t-butylphenol - these will only incorporate at the end of a polymer chain.

[0034] HBFC may be prepared by the reaction between one or more aldehydes or ketones or reactive equivalents with esters of p-hydroxybenzoic acid. The term "reactive equivalent" means a material that generates an aldehyde under the conditions of the condensation reaction or a material that undergoes the required condensation reaction to produce moieties equivalent to those produced by an aldehyde. Typical reactive equivalents include oligomers or polymers of the aldehyde, acetals or aldehyde solutions.

[0035] The aldehyde may be a mono- or di- aldehyde and may contain other functional groups, such as -COOH, and these could be capable of post-reactions in the product. The aldehyde or ketone or reactive equivalent preferably contains 1-8 carbon atoms, particularly preferred are formaldehyde, acetaldehyde, propionaldehyde and butyraldehyde, most preferred is formaldehyde. Formaldehyde could be in the form of paraformaldehyde, trioxan or formalin.

[0036] HBFC may be prepared by reacting 1 molecular equivalent (M.E.) of the esters of p-hydroxybenzoic acid with about 0.5-2 M.E. of the aldehyde, preferably 0.7-1.3 M.E. and more preferably 0.8-1.2 M.E. of the aldehyde. The reaction is preferably conducted in the presence of a basic or acidic catalyst, more preferably an acidic catalyst, such as p-toluenesulphonic acid. The reaction is conveniently conducted in an inert solvent, such as Exxsol D60 (a non-aromatic, hydrocarbon solvent, having a boiling point of ~200°C), the water produced in the reaction being removed by azeotropic distillation. The reaction is typically run at a temperature of 90-200°C, preferably 100-160°C, and may be run under reduced pressure.

[0037] Conveniently, the HBFC can be prepared in a 2-step process whereby the esters of p-hydroxybenzoic acid are first prepared in the same reaction vessel that is used for the subsequent condensation reaction. Thus, the ester is prepared from the appropriate alcohol and p-hydroxybenzoic acid in an inert solvent using an acid catalyst such as p-toluenesulphonic acid, continuously removing water produced in the reaction. Formaldehyde is then added and the condensation reaction conducted as described above to give the desired HBFC.

[0038] Preferably, the solvent is a hydrocarbon solvent, such as an aromatic hydrocarbon solvent. Examples of hydrocarbon solvents include petroleum fractions such as naphtha, kerosene, diesel and heater oil; aromatic hydrocarbons such as aromatic fractions, e.g. those sold under the `SOLVESSO' tradename; alcohols and/or esters; and paraffinic hydrocarbons such as hexane and pentane and isoparaffins. The additive concentrate may also contain further additives as required. Such further additives are known in the art and include, for example the following: detergents, antioxidants (to avoid fuel degradation), corrosion inhibitors, dehazers, demulsifiers, metal deactivators, antifoaming agents, cetane improvers, co-solvents, package compatibilisers, reodourants, additives to improve the regeneration of particulate traps, middle distillate cold flow improvers and other lubricity additives.

Component (b)

[0039] The copolymers, terpolymers and polymers of acrylic acid or methacrylic acid or a derivative thereof may be branched or linear. Suitable copolymers, terpolymers or polymers of acrylic acid or methacrylic acid or derivatives thereof are those polymers of ethylenically unsaturated monomers such as methacrylic or acrylic acid esters of alcohols having about 1 to 40 carbon atoms, such as methylacrylate, ethylacrylate, n-propylacrylate, lauryl acrylate, stearyl acrylate, methylmethacrylate, ethylmethacrylate, n-propylmethacrylate, lauryl methacrylate, stearyl methacrylate, isodecylmethacrylate, 2-ethylhexylmethacrylate and the like. These copolymers, terpolymers and polymers may have number average molecular weights (Mn) of 1,000 to 10,000,000 and preferably the molecular weight range is from about 5,000 to 1,000,000, most preferably 5,000 to 100,000. A mixture of copolymers, terpolymers and polymers of acrylic acid or methacrylic acid may also be used.

[0040] In a preferred embodiment, the acrylate or methacrylate monomer or derivative thereof is copolymerized with a nitrogen-containing, amine-containing or amide-containing monomer, or includes nitrogen-containing, amine-containing or amide-containing branches. This may be achieved by providing the polymer with sites suitable for grafting, and then nitrogen-containing, amine-containing or amide-containing branches, either monomers or macromonomers, are grafted onto the main chain. Transesterification reactions or amidation reactions may also be employed to produce the same products. Preferably, the copolymer, terpolymer or polymer will contain 0.01 to 5 wt.% nitrogen, more preferably 0.02 to 1 wt.% nitrogen, even more preferably 0.04 to 0.15 wt.% nitrogen.

[0041] Examples of amine-containing monomers include: the basic amino substituted olefins such as p-(2-diethylaminoethyl) styrene; basic nitrogen-containing heterocycles having a polymerizable ethylenically unsaturated substituent, such as the vinyl pyridines or the vinyl pyrrolidones; esters of amino alcohols with unsaturated carboxylic acids such as dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, tertiary butylaminoethyl methacrylate or dimethylaminopropyl methacrylate; amides of diamines with unsaturated carboxylic acids, such as dimethylaminopropyl methacrylamide; amides of polyamines with unsaturated carboxylic acids, examples of such polyamines being ethylene diamine (EDA), diethylene triamine (DETA), triethylene tetramine (TETA), tetraethylene pentamine (TEPA), pentaethylene hexamine (PEHA), and higher polyamines, PAM (N = 7,8) and Heavy Polyamine (N>8); morpholine derivatives of unsaturated carboxylic acids, such as N-(aminopropyl)morpholine derivatives; and polymerizable unsaturated basic amines such as allyl amine.

[0042] Particularly preferred is a copolymer of a methacrylate ester of a C₈-C₁₄ alcohol with a methacrylate ester of an N,N-dialkylaminoalkyl alcohol, such as N,N dimethyl-2-aminoethanol.

[0043] In accordance with a second aspect, the present invention provides a fuel oil composition comprising a major proportion of a fuel oil and a minor proportion of an additive composition according to the first aspect.

[0044] As discussed above, it has been observed that there is a negative interaction between certain lubricity improving additives and certain conductivity improving additives. The present invention minimises this negative interaction. Accordingly, in a preferred embodiment of the second aspect, the fuel oil composition has a conductivity which is at least 50%, preferably at least 60% of the conductivity of an equivalent fuel oil composition containing the same quantity of the conductivity-improving additive, in the absence of the lubricity enhancer. In the context of this preferred embodiment it will be understood that the only difference between the fuel composition of the invention and the 'equivalent' fuel oil composition is the absence of the lubricity enhancer. It will also be understood that the percentage of conductivity retained is to be determined using identical measurement conditions, e.g. temperature, measuring apparatus, sample age etc.

[0045] Preferably, the fuel oil is e.g., 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 fuel oil may comprise atmospheric distillate or vacuum distillate, cracked gas oil, or a blend in any proportion of straight run and thermally and/or refinery streams such as catalytically cracked and hydro-cracked distillates. The most common petroleum distillate fuels are kerosene, jet fuels, diesel fuels, heating oils and heavy fuel oils. The heating oil may be a straight atmospheric distillate, or it may contain minor amounts, e.g. up to 35 wt %, of vacuum gas oil or cracked gas oil or of both.

[0046] Other examples of fuel oils include Fischer-Tropsch fuels. Fischer-Tropsch fuels, also known as FT fuels, include those described as gas-to-liquid (GTL) fuels, biomass-to-liquid (BTL) fuels and coal conversion fuels. To make such fuels, syngas (CO + H₂) is first generated and then converted to normal paraffins by a Fischer-Tropsch process. The normal paraffins may then be modified by processes such as catalytic cracking/reforming or isomerisation, hydrocracking and hydroisomerisation to yield a variety of hydrocarbons such as iso-paraffins, cyclo-paraffins and aromatic compounds. The resulting FT fuel can be used as such or in combination with other fuel components and fuel types such as those mentioned in this specification. Also suitable are fuels derived from plant or animal sources such as FAME. These may be used alone or in combination with other types of fuel.

[0047] Preferably, the fuel oil 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 50ppm sulphur by weight, preferably less than 20 ppm, for example 10ppm or less.

[0048] In accordance with a third aspect, the present invention provides the use of an additive composition according to the first aspect to improve the lubricity of a fuel oil having a sulphur content of at most 0.05% by weight, preferably at most 0.035% by weight, especially of at most 0.015%.

Treat rates

[0049] Preferably, the salt is present in the fuel oil at level of between 5 and 1000ppm by weight based on the weight of the fuel oil, more preferably between 10 and 500ppm, even more preferably between 10 and 250ppm, especially between 10 and 150ppm, for example, between 50 and 150ppm.

[0050] Preferably, the ratio of the amount of component (a) to the amount of component (b) in the additive composition is between 9:1 to 1:9, more preferably between 6:1 to 1:6, for example between 4:1 to 1:4, 3:1 to 1:3, 2:1 to 1:2 or 1:1 based on the molar amounts of active ingredient.

[0051] Suitably, the total amount of (a) and (b) present in the fuel oil is between 0.1 and 10,000ppm of active ingredient by weight based on the weight of the fuel oil, preferably between 1 and 500ppm, more preferably between 1 and 100ppm, for example, between 3 and 50ppm.

[0052] The invention will now be described by way of example only.

Preparation of the lubricity enhancer

Example 1

[0053] Tall oil fatty acid, with a saturate content of ca. 2% and a rosin acid content of ca. 1.8%, (TOFA-1) (50.0g, 173mmoles) was added to a beaker with stirring. Di-n-butylamine (22.36g, 173mmoles) was then added to the beaker. An exotherm of ca. 38.3°C was measured indicating that the two components reacted. FTIR analysis of the reaction product showed a reduction in the strong carboxylic acid peak at 1710cm^-1 compared to the starting acid, and a corresponding appearance of carboxylate antisymmetric and symmetric stretches at 1553 and 1399 cm^-1 as well as the appearance of a broad range of peaks 2300-2600cm^-1 assignable to ammonium species. This was a clear indication of the formation of a salt. The flash-point of the reaction product was 67°C.

Example 2

[0054] Example 1 was repeated using a Tall oil fatty acid with a saturate content of ca. 2% and a rosin acid content of ca. 0.8%, (TOFA-2).

HFRR testing

[0055] The salts prepared in Examples 1- 4 above were tested in two low-sulphur diesel fuels (details given in Table 1) using the High Frequency Reciprocating Rig (HFRR) test in accordance with BS EN ISO 12156-1 (2000). Results are given in Table 2. The HFRR value for untreated Fuel 1 was 664 µm, and that for untreated Fuel 2 was 518 µm.

Table 1

		Fuel 1	Fuel 2
Specification	Unit
Density	kg/m3	811.1	858.4
Kv (40°C)	cSt	1.942	2.883
Kv (20°C)	cSt	2.843	4.597
Cetane No.		58.1	41.9
Sulphur	wt%	<0.0005	0.0428

Distillation characteristics
IBP	°C	175.0	187.3
10%	°C	206.1	219.2
50%	°C	235.2	270.4
95%	°C	279.1	333.6
FBP	°C	291.8	347.3

Table 2

Example	Treat rate/ppm	HFRR in Fuel 1/µm	HFRR in Fuel 2/µm
1	50	646	385
	100	469	377
	150	438	-
2	50	648	-
	100	608	-
	150	522	-
	200	433	-
3	50	666	425
	100	451	329
4	50	654	-
	100	614	-
	150	525	-
	200	477	-
	250	414	-
	300	400	-

Preparation of Component (a)

[0056] The following synthetic schemes relate to the preparation of some HBFC compounds which may be used in the present invention. It will be understood that these examples are given merely to illustrate possible preparative routes and as such are not intended to be limiting in any way. The skilled man will be aware of other synthetic methods and will be able to extend the teachings to the preparation of other compounds, which whilst not explicitly described herein, will nonetheless be suitable for use in the present invention.

Example 3

[0057] A mixture of p-hydroxybenzoic acid (1110g), isodecanol (1397g), Exxsol D60 (670g, a non-aromatic, hydrocarbon solvent, bp ~200°C), and p-toluenesulphonic acid (43g) was heated to 160°C over 1.5 hours, slowly reducing the pressure to ~200mbar. The water produced in the reaction was continuously removed using a Dean and Stark apparatus. Heating was continued for a total of 4.5 hours and the vacuum released. The reaction mixture was then cooled to ~80°C and then to it was added 95% paraformaldehyde (216g). The mixture was kept at 80-85°C for 2 hours and then heated to 135°C. The pressure was gradually reduced to -120mbar and the water produced in the reaction was continuously removed using a Dean and Stark apparatus. Heating was continued for 5 hours and then Solvesso 150 (1500g) was added to dilute the mixture and give a product having a Mn of 1800 and a Mw of 2400.

Example 4

[0058] A mixture of p-hydroxybenzoic acid (1109g), 2-ethylhexanol (862g), n-octanol (288g), p-toluenesulphonic acid (43g) and Exxsol D60 (670g) heated to ~157°C over -30 mins, slowly reducing the pressure to ~240mbar. Water produced in the reaction was continuously removed using a Dean and Stark apparatus. Heating was continued for a total of 3.5 hours then the vacuum was released and the mixture cooled to ~80°C.

[0059] 95% Paraformaldehyde (228g) was then added and the mixture kept at 80-85°C for 2 hours followed by an hour at 95-100°C. It was then heated to 135°C and the pressure was gradually reduced to ~120mbar. Water produced in the reaction was continuously removed using a Dean and Stark apparatus. Heating was continued for a total of 5 hours. Solvesso 150 (900g) and 2,4-di-t-butylphenol (500g) were then added to the mixture as diluents to give the final product, which had a Mn of 1150 and a Mw of 1400.

Example 5

[0060] 

(i) A mixture of p-hydroxybenzoic acid (213g), 2-ethylhexanol (220g), xylene (200ml) and p-toluenesulphonic acid (2g) was refluxed at ~155°C for 10 hours and the water produced in the reaction was continuously removed using a Dean and Stark apparatus. The mixture was then evaporated under reduced pressure to give 393g of product, i.e. 2-ethylhexyl p-hydroxybenzoate.

(ii) A mixture of the above product (39.7g), 95% paraformaldehyde (4.55g), p-toluenesulphonic acid (0.35g) and heptane (60ml) was heated at 80-85°C for 2 hours. It was then refluxed at ~115°C for 9 hours and the water produced in the reaction was continuously removed using a Dean and Stark apparatus. Toluene (60ml) was then added as a diluent to give the product, which had a Mn of 1300 and a Mw of 1750.

Example 6

[0061] A mixture consisting of 2-ethylhexyl p-hydroxybenzoate (41.1g, as produced in Example 7), xylene (8.7g), 95% paraformaldehyde (5.2g), p-toluenesulphonic acid (0.4g) and octane (50ml) was heated to 80-85°C for 2 hours then refluxed at ~135°C for 4.5 hours, continuously removing the water produced in the reaction using a Dean and Stark apparatus. Toluene (40ml) was then added to dilute the product, which had a Mn of 1000 and a Mw of 1300.

Example 7

[0062] A mixture of 2-ethylhexyl p-hydroxybenzoate (37.3g, as produced in Example 7), 2,4-di-t-butylphenol (7.7g), 95% paraformaldehyde (5.65g), 0.45g p-toluenesulphonic acid and octane (25g) was heated to 80-85°C for 2 hours then refluxed at ~135°C for 5 hours. The water produced in the reaction was continuously removed using a Dean and Stark apparatus. Solvesso 150 (27g) was then added to dilute the product, which had a Mn of 1250 and a Mw of 2000.

Component (b)

Example 8

[0063] A high molecular weight (ca. 300,000) polymethacrylate containing ca. 4 wt% of dimethylaminoethylmethacrylate monomers.

Example 9

[0064] Isodecyl methacrylate dimethylaminoethylmethacrylate copolymers of ~20,000 molecular weight where the content of the aminic monomer was 1.5, 2.5 , 5.0 or 15 wt%.

Conductivity Testing

[0065] Conductivity testing was carried out using an Emcee^™ Digital Conductivity Meter (Model 1152), which has a calibrated range of 0-390 pSm^-1. The instrument is self calibrating and zeroing and was used in accordance with the user manual. All conductivity measurements were performed at room temperature on 250-300 ml of fuel in a 300 ml, tall glass beaker. The conductivity measurements were made within 2 hours of placing the fuel into the beaker, dosing it with the respective additives and mixing.

[0066] Fuel samples were prepared containing the conductivity-improving additives alone and containing both the conductivity-improving additives and the lubricity enhancer of Example 2 at 200ppm by weight. Results are given in Table 3 below. Each sample was tested as soon as it was prepared and again after standing for 7 and 14 days. Fuel 1 was used. The results are given as the percentage loss in measured conductivity between the sample containing only the conductivity-improving additive and the sample containing both the conductivity-improving additive and the lubricity enhancer.

Table 3

Conductivity additive	Treat rate / wppm	% loss after 0 days	% loss after 7 days	% loss after 14 days
A1	6	28	31	36
	12	25	29	29
	24	11	29	17
C1	1	64	69	76
	2	73	78	83
	3	78	83	85
C2	1	59	64	80
	2	67	70	68
	3	66	73	81
C3	1	54	73	77
	2	62	67	79
	3	58	66	77

[0067] Conductivity improving additive A1 was within the scope of the present invention being a 7:3 molar ratio of the HBFC of Example 3 and the copolymer of Example 9, where the amine content of the copolymer was 15%. Conductivity improving additives C1, C2 and C3 were used for comparative purposes and were respectively; Stadis^® 450, Stadis^® 425 which are products of the Octel Corporation, and AS-2010 available from DBM Chemicals.

[0068] It is clear from the data presented that a large negative interaction on fuel conductivity occurs with combinations of the lubricity enhancer and conductivity-improving additives C1, C2 and C3. On average, these combinations lose 70% or more of the conductivity they have in the absence of the lubricity enhancer. Contrastingly, conductivity-improving additive A1 is much less affected by the presence of the lubricity enhancer.

Claims

1. An additive composition comprising a lubricity enhancer and a conductivity-improving additive; wherein the lubricity enhancer comprises a salt formed by the reaction of a carboxylic acid with di-n-butylamine; and wherein the conductivity improving additive comprises the combination of:

(a) a polymeric condensation product formed by the reaction of an aliphatic aldehyde or ketone, or a reactive equivalent, with at least one ester of p-hydroxybenzoic acid with,

(b) a copolymer, terpolymer or polymer of acrylic acid or methacrylic acid or a derivative thereof.

2. An additive composition according to claim 1, wherein the carboxylic acid comprises a fatty acid or a mixture of fatty acids, preferably tall oil fatty acid, rape seed oil fatty acid, soy bean fatty acid or sunflower oil fatty acid.

3. An additive composition according to claim 1 or claim 2, wherein the at least one ester of p-hydroxybenzoic acid comprises; (i) a straight or branched chain C₁ - C₇ alkyl ester of p-hydroxybenzoic acid; (ii) a branched chain C₈- C₁₆ alkyl ester of p-hydroxybenzoic acid, or; (iii) a mixture of long chain C₈ - C₁₈ alkyl esters of p-hydroxybenzoic acid, at least one of said alkyls being branched.

4. An additive composition according to any preceding claim, wherein the copolymer, terpolymer or polymer of acrylic acid or methacrylic acid or a derivative thereof is copolymerized with a nitrogen-containing, amine-containing or amide-containing monomer; or includes nitrogen-containing, amine-containing or amide-containing branches.

5. A fuel oil composition comprising a major proportion of a fuel oil and a minor proportion of an additive composition according to any preceding claim.

6. A fuel oil composition according to claim 5, wherein the fuel oil comprises a middle distillate fuel oil having a sulphur content of at most 0.05% by weight.

7. A fuel oil composition according to claim 5 or claim 6, having a conductivity which is at least 50%, preferably at least 60% of the conductivity of an equivalent fuel oil composition containing the same quantity of the conductivity-improving additive, in the absence of the lubricity enhancer.

8. The use of an additive composition according to any of claims 1 to 4 to improve the lubricity of a fuel oil having a sulphur content of at most 0.05% by weight.