Fuel oil compositions

Abstract

 A fuel oil composition comprising a major amount of fuel oil and a polymeric additive of Mn 1,000 to less than 3,000. The polymeric additive comprises the condensation reaction product of an aliphatic aldehyde having 1 to 4 carbon atoms and a mixture of alkylphenols comprising a major amount of a monoalkylphenol with more than 10 to less than 35 mole% of a dialkylphenol. The alkyl groups of the phenol have 1 to 20 carbon atoms.

Description

[0001] This invention relates to fuel oil compositions comprising additive compositions and additive concentrates of the additive compositions for improving low temperature flow properties.

[0002] Fuel oils, whether derived from petroleum or from vegetable sources, contain components, e.g., n-alkanes, that at low temperatures tend to precipitate as large crystals or spherulites of wax in such a way as to form a gel structure which causes the fuel to lose its ability to flow. The lowest temperature at which the fuel will still flow is known as the pour point.

[0003] As the temperature of the fuel falls and approaches the pour point, difficulties arise in transporting the fuel through lines and pumps. Further, the wax crystals tend to plug fuel lines, screens, and filters at temperatures above the pour point. These problems are well recognized in the art, and various additives have been proposed, many of which are in commercial use, for depressing the pour point of fuel oils. Similarly, other additives have been proposed and are in commercial use for reducing the size and changing the shape of the wax crystals that do form. Smaller size crystals are desirable since they are less likely to clog a filter. The wax from a diesel fuel, which is primarily an alkane wax, crystallizes as platelets; certain additives inhibit this and cause the wax to adopt an acicular habit, the resulting needles being more likely to pass through a filter than are platelets. The additives may also have the effect of retaining in suspension in the fuel the crystals that have formed, the resulting reduced settling also assisting in prevention of blockages.

[0004] US 5,998,530 issued to Krull et al. on December 7, 1999 discloses alkylphenol aldehyde resins useful for improving the flowability of mineral oils and mineral oil distillates when used in combination with ethylene/vinyl ester copolymers and paraffin dispersants. The specific examples use resins prepared from nonylphenol and butlyphenol, which are monoalkyl phenols.

[0005] EP 311,452, published October 8, 1987 discloses alkyl phenol-formaldehyde condensates. EP 311,452 teaches the minimization of dialkylate products and the maximization of monoalkylates in order to achieve number average molecular weights of at least 3,000, preferably at least 7,000. We are told that preferably the alkyl phenol-formaldehyde condensates include from about 90 to 100 mole% (e.g. 95 to 100) monoalkylated phenols. EP 311,452 teaches that dialkylate molecules terminate chain growth and therefore the amount of dialkylate monomer than can be 'tolerated' is preferably 0 to 10 mole%.

[0006] The present invention is concerned with the problem of providing an improved additive composition for improving cold flow characteristics of fuel oils.

[0007] More particularly, the present invention is concerned with the problem of improving cold flow characteristics of fuel oils having a 90% - 20% boiling temperature range, as measured in accordance with ASTM D-86, of preferably from 80 to 160°C, and a final boiling point of from 330 to 390°C.

[0008] In accordance with the present invention, there has been discovered a fuel oil composition comprising a major amount of fuel oil and a low temperature flow improving amount of a polymeric additive of number average molecular weight (Mn) 1,000 to less than 3,000, preferably of Mn 1,000 to 2,500, comprising the condensation reaction product of an aliphatic aldehyde having 1 to 4 carbon atoms and a mixture of alkylphenols comprising a major amount of a monoalkylphenol with more than 10 mole% to less than 35 mole% of a monofunctional dialkylphenol, the alkyl groups of the phenols having 1 to 20, preferably 4 to 12 carbon atoms.

[0009] The condensation reaction product preferably includes 12 mole% to 33 mole%, more preferably 14 to 30 mole%, of a dialkylphenol.

[0010] The alkyl groups of the phenols preferably include 4 to 12 carbon atoms, more preferably 4 to 11 carbon atoms, and even more preferably 5 to 10 carbon atoms. The alkyl group of the monoalkylphenol is preferably branched. Preferably, at least one of the alkyl groups of the dialkylphenol is branched, more preferably, both alkyl groups of the dialkylphenol are branched. The dialkylphenol is preferably di-nonylphenol, di-t-butylphenol or a C₁₂ branched dialkylphenol.

[0011] The term "monofunctional" as used herein with reference to the dialkylphenols means that only one site is available on the phenyl ring for condensation reaction with the aldehyde. The preferred dialkylphenols for use in the invention are normally substituted with alkyls in the 2- and 4-position of the phenyl ring. As a result of the use of only such monofunctional dialkyl phenols, the molecular weight of the polymeric condensation reaction products are relatively low, on the order of Mn = 1,000 to less than 3,000, as compared with the products disclosed in EP 311,452 which are condensates prepared, for example, from trifunctional dialkylphenols having reaction sites available in the 2-, 4- and 6-position as illustrated by Formula II of EP 311,452.

[0012] The aldehyde used to prepare the condensation product is preferably formaldehyde and the condensation reaction is carried out using methods well known in the art or disclosed, for example, in U.S. Patent No. 5,998,530, using alkaline or acidic catalysts and in the presence of an organic solvent forming an azeotrope with water, such as toluene or xylene, and at temperatures of about 90 - 200°C.

[0013] The invention provides use of the additive composition defined above to improve cold flow characteristics of a fuel oil. The additive composition has been found to be particularly effective in middle distillate fuel oils having a 90% - 20% boiling temperature range, as measured in accordance with ASTM D-86, of preferably from 80 to 150°C, and a final boiling point of from 330 to 390°C.

[0014] The invention still further provides an additive concentrate comprising a solvent miscible with fuel oil and a minor proportion of the additive composition defined above.

[0015] 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 catalytically 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 may also contain vacuum gas oil or cracked gas oil or both. The fuels may also contain major or minor amounts of components derived from the Fischer-Tropsch process. Fischer-Tropsch fuels, also known as FT fuels, include those that are described as gas-to-liquid fuels, coal and/or biomass 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 and olefins 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. The above mentioned low temperature flow problem is most usually encountered with diesel fuels and with heating oils. The invention is also applicable to fuel oils containing fatty acid methyl esters derived from vegetable oils, for example, rapeseed methyl ester, either used alone or in admixture with a petroleum distillate oil.

[0016] The concentration of the additive in the oil may for example be in the range of 0.1 to 1,000 ppm of additive (active ingredient) by weight per weight of fuel, preferably 1 to 500 ppm, more preferably 1 to 100 ppm.

[0017] The additive may be incorporated into bulk oil by methods such as those known in the art. Where more than one additive component or co-additive component is to be used, such components may be incorporated into the oil together or separately in any combination.

[0018] A concentrate comprising the additive dispersed in carrier liquid (e.g. in solution) is convenient as a means of incorporating the additive. The concentrates of the present invention are convenient as a means for incorporating the additive into bulk oil such as distillate fuel, which incorporation may be done by methods known in the art. The concentrates may also contain other additives as required and preferably contain from 3 to 75 wt.%, more preferably 3 to 60 wt.%, most preferably 10 to 50 wt.% of the additives, preferably in solution in oil. Examples of carrier liquid are organic solvents including hydrocarbon solvents, for example 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 such as isodecanol and 2-ethylhexanol and/or esters; and paraffinic hydrocarbons such as hexane and pentane and isoparaffins. Alkylphenols, such as nonylphenol and 2,4-di-t-butylphenol either alone or in combination with any of the above have also been found to be particularly useful as carrier solvents. The carrier liquid must, of course, be selected having regard to its compatibility with the additive and with the fuel.

[0019] The additives of the invention may be incorporated into bulk oil by other methods such as those known in the art. If co-additives are required, they may be incorporated into the bulk oil at the same time as the additives of the invention or at a different time.

[0020] Preferably the condensate polymers of this invention are used in fuel oils in combination with one or more conventional cold flow additives as defined in (A) - (E) below.

(A) Ethylene Polymers

[0021] Each polymer may be a homopolymer or a copolymer of ethylene with another unsaturated monomer. Suitable co-monomers include hydrocarbon monomers such as propylene, n- and iso- butylenes, 1-hexene, 1-octene, methyl-1-pentene vinyl-cyclohexane and the various alpha-olefins known in the art, such as 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecane and 1-octadecene and mixtures thereof.

[0022] Preferred co-monomers are unsaturated ester or ether monomers, with ester monomers being more preferred. Preferred ethylene unsaturated ester copolymers have, in addition to units derived from ethylene, units of the formula:

        -CR¹R²-CHR³-

wherein R¹ represents hydrogen or methyl, R² represents COOR⁴, wherein R⁴ represents an alkyl group having from 1-12, preferably 1-9 carbon atoms, which is straight chain , or, if it contains 3 or more carbon atoms, branched, or R² represents OOCR⁵, wherein R⁵ represents R⁴ or H, and R³ represents H or COOR⁴.

[0023] These may comprise a copolymer of ethylene with an ethylenically unsaturated ester, or derivatives thereof. An example is a copolymer of ethylene with an ester of a saturated alcohol and an unsaturated carboxylic acid, but preferably the ester is one of an unsaturated alcohol with a saturated carboxylic acid. An ethylene-vinyl ester copolymer is advantageous; an ethylene-vinyl acetate, ethylene-vinyl propionate, ethylene-vinyl hexanoate, ethylene-vinyl 2-ethylhexanoate, ethylene-vinyl octanoate or ethylene-vinyl versatate copolymer is preferred. Preferably, the copolymer contains from 5 to 40 wt% of the vinyl ester, more preferably from 10 to 35 wt% vinyl ester. A mixture of two copolymers, for example, as described in US Patent No. 3,961,916, may be used. The Mn of the copolymer is advantageously 1,000 to 10,000. If desired, the copolymer may contain units derived from additional comonomers, e.g. a terpolymer, tetrapolymer or a higher polymer, e.g. where the additional comonomer is isobutylene or diisobutylene or a further unsaturated ester.

(B) A Comb Polymer.

[0024] Comb polymers are discussed in "Comb-Like Polymers. Structure and Properties", N. A. Platé and V. P. Shibaev, J. Poly. Sci. Macromolecular Revs., 8, p 117 to 253 (1974).

[0025] Generally, comb polymers consist of molecules in which long chain branches such as hydrocarbyl branches, optionally interrupted with one or more oxygen atoms and/or carbonyl groups, having from 6 to 30 such as 10 to 20, carbon atoms, are pendant from a polymer backbone, said branches being bonded directly or indirectly to the backbone. Examples of indirect bonding include bonding via interposed atoms or groups, which bonding can include covalent and/or electrovalent bonding such as in a salt. Generally, comb polymers are distinguished by having a minimum molar proportion of units containing such long chain branches.

[0026] As examples of preferred comb polymers there may be mentioned those containing units of the general formula

where

D represents R¹¹, COOR¹⁰, OCOR¹⁰, R¹¹COOR¹⁰ or OR¹⁰;

E represents H or D;

G represents H or D;

J represents H, R¹¹, R¹¹COOR¹⁰, or a substituted or unsubstituted aryl or heterocyclic group;

K represents H, COOR¹¹, OCOR¹¹, OR¹¹ or COOH;

L represents H, R¹¹, COOR¹¹, OCOR¹¹ or substituted or unsubstituted aryl;

R¹⁰ representing a hydrocarbyl group having 10 or more carbon atoms, and

R¹¹ representing a hydrocarbylene (divalent) group in the R¹¹COOR¹⁰ moiety and otherwise a hydrocarbyl (monovalent) group,

and m and n represent mole ratios, their sum being 1 and m being finite and being up to and including 1 and n being from zero to less than 1, preferably m being within the range of from 1.0 to 0.4 and n being in the range of from 0 to 0.6. R¹⁰ advantageously represents a hydrocarbyl group with from 10 to 30 carbon atoms, preferably 10 to 24, more preferably 10 to 18. Preferably, R¹⁰ is a linear or slightly branched alkyl group and R¹¹ advantageously represents a hydrocarbyl group with from 1 to 30 carbon atoms when monovalent, preferably with 6 or greater, more preferably 10 or greater, preferably up to 24, more preferably up to 18 carbon atoms. Preferably, R¹¹, when monovalent, is a linear or slightly branched alkyl group. When R¹¹ is divalent, it is preferably a methylene or ethylene group. By "slightly branched" is meant having a single methyl branch.

[0027] The comb polymer may contain units derived from other monomers if desired or required, examples being CO, vinyl acetate and ethylene. It is within the scope of the invention to include two or more different comb copolymers.

[0028] The comb polymers may, for example, be copolymers of maleic anhydride acid and another ethylenically unsaturated monomer, e.g. an α-olefin or an unsaturated ester, for example, vinyl acetate as described in EP-A-214,786. It is preferred but not essential that equimolar amounts of the comonomers be used although molar proportions in the range of 2 to 1 and 1 to 2 are suitable. Examples of olefins that may be copolymerized with e.g. maleic anhydride, include 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and styrene. Other examples of comb polymers include polyalkyl(meth)acrylates.

[0029] The copolymer may be esterified by any suitable technique and although preferred it is not essential that the maleic anhydride or fumaric acid be at least 50% esterified. Examples of alcohols that may be used include n-decan-1-ol, n-dodecan-1-ol, n-tetradecan-1-ol, n-hexadecan-1-ol, and n-octadecan-1-ol. The alcohols may also include up to one methyl branch per chain, for example, 2-methylpentadecan-1-ol, 2-methyltridecan-1-ol as described in EP-A-213,879. The alcohol may be a mixture of normal and single methyl branched alcohols. It is preferred to use pure alcohols rather than alcohol mixtures such as may be commercially available; if mixtures are used, the number of carbon atoms in the alkyl group is taken to be the average number of carbon atoms in the alkyl groups of the alcohol mixture; if alcohols that contain a branch at the 1 or 2 positions are used, the number of carbon atoms in the alkyl group is taken to be the number in the straight chain backbone segment of the alkyl group of the alcohol.

[0030] The copolymer may also be reacted with a primary and/or secondary amine, for example, a mono- or di-hydrogenated tallow amine.

[0031] The comb polymers may especially be fumarate or itaconate polymers and copolymers such as for example those described in European Patent Applications 153 176, 153 177, 156 577 and 225 688, and WO 91/16407. The comb polymers are preferably C₈ to C₁₂ dialkylfumarate-vinyl acetate copolymers.

[0032] Other suitable comb polymers are the polymers and copolymers of α-olefins and esterified copolymers of styrene and maleic anhydride, and esterified copolymers of styrene and fumaric acid as described in EP-A-282,342; mixtures of two or more comb polymers may be used in accordance with the invention and, as indicated above, such use may be advantageous.

[0033] Other examples of comb polymers are hydrocarbon polymers such as copolymers of at least one short chain 1-alkene and at least one long chain 1-alkene. The short chain 1-alkene is preferably a C₃-C₈ 1-alkene, more preferably a C₄-C₆ 1-alkene. The long chain 1-alkene preferably includes greater than 8 carbon atoms and at most 20 carbon atoms. The long chain 1-alkene is preferably a C₁₀-C₁₄ 1-alkene, including 1-decene, 1-dodecene and 1-tetradecene (see, for example, WO 93/19106). The comb polymer is preferably a copolymer of at least one 1-dodecene and at least one 1-butene in the ratio of 60-90 mole % 1-dodecene to 40-10 mole % 1-butene, preferably in the ratio of 75-85 mole % 1-dodecene to 25-15 mole% 1-butene. Preferably, the comb polymer is a mixture of two or more comb polymers made from a mixture of two or more 1-alkenes. Preferably, the number average molecular weight measured by Gel Permeation Chromatography against polystyrene standards of such a copolymer is, for example, up to 20,000 or up to 40,000, preferably from 4,000 to 10,000, preferably 4,000 to 6,000. The hydrocarbon copolymers may be prepared by methods known in the art, for example using a Ziegler-Natta type, Lewis acid or metallocene catalyst.

(C) Polar Nitrogen Compounds.

[0034] Such compounds are oil-soluble polar nitrogen compounds carrying one or more, preferably two or more, substituents of the formula >NR¹³, where R¹³ represents a hydrocarbyl group containing 8 to 40 atoms, which substituent or one or more of which substituents may be in the form of a cation derived therefrom. The oil soluble polar nitrogen compound is generally one capable of acting as a wax crystal growth inhibitor in fuels. It comprises, for example, one or more of the following compounds:

[0035] An amine salt and/or amide formed by reacting at least one molar proportion of a hydrocarbyl-substituted amine with a molar proportion of a hydrocarbyl acid having from 1 to 4 carboxylic acid groups or its anhydride, the substituent(s) of formula >NR¹³ being of the formula -NR¹³R¹⁴ where R¹³ is defined as above and R¹⁴ represents hydrogen or R¹³, provided that R¹³, and R¹⁴ may be the same or different, said substituents constituting part of the amine salt and/or amide groups of the compound.

[0036] Ester/amides may be used, containing 30 to 300, preferably 50 to 150, total carbon atoms. These nitrogen compounds are described in US Patent No. 4,211,534. Suitable amines are predominantly C₁₂ to C₄₀ primary, secondary, tertiary or quaternary amines or mixtures thereof but shorter chain amines may be used provided the resulting nitrogen compound is oil soluble, normally containing about 30 to 300 total carbon atoms. The nitrogen compound preferably contains at least one straight chain C₈ to C₄₀, preferably C₁₄ to C₂₄, alkyl segment.

[0037] Suitable amines include primary, secondary, tertiary or quaternary, but are preferably secondary. Tertiary and quaternary amines only form amine salts. Examples of amines include tetradecylamine, cocoamine, and hydrogenated tallow amine. Examples of 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 4% C₁₄, 31% C₁₆, and 59% C₁₈.

[0038] Examples of suitable carboxylic acids and their anhydrides for preparing the nitrogen compounds include ethylenediamine tetraacetic acid, and carboxylic acids based on cyclic skeletons, e.g., cyclohexane-1,2-dicarboxylic acid, cyclohexene-1,2-dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid and naphthalene dicarboxylic acid, and 1,4-dicarboxylic acids including dialkyl spirobislactones. Generally, these acids have about 5 to 13 carbon atoms in the cyclic moiety. Preferred acids useful in the present invention are benzene dicarboxylic acids, e.g., phthalic acid, isophthalic acid, and terephthalic acid. Phthalic acid and its anhydride are particularly preferred. The particularly preferred compound is the amide-amine salt formed by reacting 1 molar portion of phthalic anhydride with 2 molar portions of dihydrogenated tallow amine. Another preferred compound is the diamide formed by dehydrating this amide-amine salt.

[0039] Other examples are long chain alkyl or alkylene substituted dicarboxylic acid derivatives such as amine salts of monoamides of substituted succinic acids, examples of which are known in the art and described in US Patent No. 4,147,520, for example. Suitable amines may be those described above.

[0040] Other examples are condensates, for example, those described in EP-A-327427.

[0041] Other examples of polar nitrogen compounds are compounds containing a ring system carrying at least two substituents of the general formula below on the ring system

where A is a linear or branched chain aliphatic hydrocarbylene group optionally interrupted by one or more hetero atoms, and R¹⁵ and R¹⁶ are the same or different and each is independently a hydrocarbyl group containing 9 to 40 atoms optionally interrupted by one or more hetero atoms, the substituents being the same or different and the compound optionally being in the form of a salt thereof. Advantageously, A has from 1 to 20 carbon atoms and is preferably a methylene or polymethylene group. Such compounds are described in WO 93/04148 and WO9407842.

[0042] Other examples are the free amines themselves as these are also capable of acting as wax crystal growth inhibitors in fuels. Suitable amines include primary, secondary, tertiary or quaternary, but are preferably secondary. Examples of amines include tetradecylamine, cocoamine, and hydrogenated tallow amine. Examples of 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 4% C₁₄, 31% C₁₆, and 59% C₁₈.

(D) A Polyoxyalkylene Compound.

[0043] Examples are polyoxyalkylene esters, ethers, ester/ethers and mixtures thereof, particularly those containing at least one, preferably at least two, C₁₀ to C₃₀ linear alkyl groups and a polyoxyalkylene glycol group of molecular weight up to 5,000, preferably 200 to 5,000, the alkyl group in said polyoxyalkylene glycol containing from 1 to 4 carbon atoms. These materials form the subject of EP-A-0061895. Other such additives are described in United States Patent No. 4,491,455.

[0044] The preferred esters, ethers or ester/ethers are those of the general formula

        R³¹-O(D)-O-R³²

where R³¹ and R³² may be the same or different and represent

(a) n-alkyl-

(b) n-alkyl-CO-

(c) n-alkyl-O-CO(CH₂)_x- or

(d) n-alkyl-O-CO(CH₂)_x-CO-

x being, for example, 1 to 30, the alkyl group being linear and containing from 10 to 30 carbon atoms, and D representing the polyalkylene segment of the glycol in which the alkylene group has 1 to 4 carbon atoms, such as a polyoxymethylene, polyoxyethylene or polyoxytrimethylene moiety which is substantially linear; some degree of branching with lower alkyl side chains (such as in polyoxypropylene glycol) may be present but it is preferred that the glycol is substantially linear. D may also contain nitrogen.

[0045] Examples of suitable glycols are substantially linear polyethylene glycols (PEG) and polypropylene glycols (PPG) having a molecular weight of from 100 to 5,000, preferably from 200 to 2,000. Esters are preferred and fatty acids containing from 10-30 carbon atoms are useful for reacting with the glycols to form the ester additives, it being preferred to use a C₁₈-C₂₄ fatty acid, especially behenic acid. The esters may also be prepared by esterifying polyethoxylated fatty acids or polyethoxylated alcohols.

[0046] These materials may also be prepared by alkoxylation of a fatty acid ester of a polyol (e.g. ethoxylated sorbitan tristearate having the trade name TWEEN 65, which is available from Uniqema).

[0047] Polyoxyalkylene diesters, diethers, ether/esters and mixtures thereof are suitable as additives, diesters being preferred for use in narrow boiling distillates, when minor amounts of monoethers and monoesters (which are often formed in the manufacturing process) may also be present. It is preferred that a major amount of the dialkyl compound be present. In particular, stearic or behenic diesters of polyethylene glycol, polypropylene glycol or polyethylene/ polypropylene glycol mixtures are preferred.

[0048] Other examples of polyoxyalkylene compounds are those described in Japanese Patent Publication Nos. 2-51477 and 3-34790, and the esterified alkoxylated amines described in EP-A-117108 and EP-A-326356.

(E) Di-block Hydrocarbon Polymers.

[0049] These polymers may be an oil-soluble hydrogenated block diene polymers, comprising at least one crystallizable block, obtainable by ene-to-end polymerization of a linear diene, and at least one non-crystallizable block being obtainable by 1,2-configuration polymerization of a linear diene, by polymerization of a branched diene, or by a mixture of such polymerizations.

[0050] Advantageously, the block copolymer before hydrogenation comprises units derived from butadiene only, or from butadiene and at least one comonomer of the formula

        CH₂=CR¹-CR²=CH₂

wherein R¹ represents a C1 to C8 alkyl group and R² represents hydrogen or a C₁ to C₈ alkyl group. Advantageously, the total number of carbon atoms in the comonomer is 5 to 8, and the comonomer is advantageously isoprene. Advantageously, the copolymer contains at least 10% by weight of units derived from butadiene.

[0051] In addition, the additive composition may comprise one or more other conventional co-additives known in the art, such as detergents, antioxidants, corrosion inhibitors, dehazers, demulsifiers, metal deactivators, antifoaming agents, cetane improvers, co-solvents, package compatibilizers, lubricity additives and anti-static additives.

[0052] The invention will now be particularly described, by way of example only, as follows.

[0053] The cold flow improvement properties of the novel additives of this invention were evaluated in the four petroleum distillate fuels which are disclosed in Table 1 below.

Table 1

Fuel	A	B	C	D
Country	Netherlands	Netherlands	Germany	UK
Sulphur, wt.%	0.05			0.03
Density at 15°C (Kg/m3)	836.0	835.6	853.0	831.3
Cloud Point (°C)	-7	-9	-0.4	-6
CFPP (°C)	-8		-1	-9
ASTM D86 (°C)
IBP	185	169	184	155
5%	206		188	190
10%	215	202	193	202
20%	228	216	201	220
30%	240	230	216	239
40%	252	243	234	256
50%	263	256	256	270
60%	275	273	282	283
70%	289	293	308	295
80%	305	315	331	309
90%	328	339	353	326
95%	346	354	368	339
FBP	354	360	376	359

[0054] Tables 2-5 below report the results using these fuels in the Cold Filter Plugging Point (CFPP) test, the details of which are specified in the European Standard method EN116. The CFPP test is acknowledged as a standard bench test for determining fuel performance at low temperatures and, as such, has been adopted in many national fuel specifications. The results shown are the average of a number of repeated tests.

[0055] In the tables below "AFPC" is a conventional nonylphenol-formaldehyde condensation product made from a monoalkyl phenol, having a Mn of ~1500; the other compounds listed are nonylphenol-formaldehyde condensates of the invention made incorporating monofunctional di-nonylphenol or 2,6-di-t-butyl phenol. "WASA" is the reaction product of di-hydrogenated tallow amine and phthalic anhydride; "EVA-1" is an ethylene-vinyl acetate copolymer having 36 wt.% vinyl acetate; "EVA-2" is ethylene-vinyl acetate copolymer having 13 wt.% vinyl acetate; "EVE" is a mixture of an ethylene-vinyl acetate copolymer having 28 wt.% vinyl acetate and an ethylene-vinylacetate-vinyl 2-ethylhexanoate copolymer having 6 wt.% vinyl acetate and 40 wt.% vinyl 2-ethyl hexanoate; "FVA-1" is a copolymer of a mixed n-C₁₂ and n-C₁₄ alkyl fumarate and vinyl acetate; "FVA-2" is a copolymer of mixed n-C₁₄ or n-C₁₅ alkylfumarate and vinyl acetate; "FVA-3 is a copolymer of n-C₁₂ alkylfumarate and vinyl acetate; and "ppm ai" is parts per million by weight of active ingredient without regard to diluent or carrier oil.

[0056] In all the data, the condensates of the invention, i.e. condensates made from more than 10 to 35 mole% of diakyl phenol, exhibit improvements over the condensate made from a monoakyl phenol.

Table 2

Fuel A
Compound	Treat Rate (ppm ai)					CFPP (°C)
	Compound	WASA	FVA-1	EVA-1	EVA-2
APFC	25	25	50	75	25	-26
APFC containing 14 mole% di-	25	25	50	75	25	-29
nonylphenol, Mn ~1700

Table 3

Fuel B (Already treated with an MDFI)
Compound	Treat Rate (ppm ai)			CFPP (°C)
	Compound	WASA	FVA-1
APFC	25	25	50	-22
APFC containing 14 mole% di-nonylphenol, Mn ~1700	25	25	50	-30

Table 4

Fuel C
Compound	Treat Rate (ppm ai)				CFPP (°C)
	Compound	FVA-3	WASA	EVE
APFC	27	11	43	200	-15.5
APFC containing 30 mole% di-nonylphenol, Mn ~1700	27	11	43	200	-18
APFC containing 20 mole% di-nonylphenol, Mn ~2200	27	11	43	200	-20

Table 5

Fuel D
Compound	Treat Rate (ppm ai)				CFPP (°C)
	Compound	WASA	EVA-1	EVA-2
APFC	100	100	174	26	-23
APFC containing 14 mole% di-nonylphenol, Mn ~1700	100	100	174	26	-27
APFC containing 25 mole% di-nonylphenol, Mn ~1400	100	100	174	26	-25
APFC containing 14 mole% 2,6-di-t-butylphenol, Mn ~1600	100	100	174	26	-26

Claims

1. A fuel oil composition comprising a fuel oil and a polymeric additive of Mn 1,000 to less than 3,000, preferably of Mn 1,000 to 2,500, comprising the condensation reaction product of an aliphatic aldehyde having 1 to 4 carbon atoms and a mixture of alkylphenols comprising a major amount of a monoalkylphenol and more than 10 mole% to less than 35 mole%, preferably 12 mole% to 33 mole%, of a dialkylphenol, the alkyl groups of the phenol having 1 to 20 carbon atoms.

2. The composition of claim 1, wherein the alkyl group of the phenols has 4 to 12 carbon atoms, preferably 4 to 11 carbon atoms, even more preferably 5 to 10 carbon atoms.

3. The composition of claim 1 or claim 2, wherein the alkyl group of the monoalkylphenol is branched, and wherein at least one of the alkyl groups of the dialkylphenol is branched, more preferably, both alkyl groups of the dialkylphenol are branched.

4. The composition of any preceding claim, wherein the dialkylphenol is di-nonylphenol, di-t-butylphenol or a C₁₂ branched dialkylphenol.

5. The composition of any preceding claim, wherein there is present about 14 - 30 mole% of the dialkylphenol.

6. The composition of any preceding claim, wherein the aldehyde is formaldehyde.

7. The composition as claimed in any one of the preceding claims, further comprising at least one additional cold flow additive; the additional cold flow additive preferably being selected from:

(i) ethylene polymer;

(ii) comb polymer;

(iii) polar nitrogen compound;

(iv) polyoxyalkylene compound; and/or

(v) di-block hydrocarbon polymer.

8. An additive concentrate comprising a carrier liquid and 3 - 75 wt.% of the polymeric additive as defined in any one of the preceding claims.

9. Use of the polymeric additive as defmed in any one of claims 1 to 6 to improve the low temperature flow properties of a fuel oil.

10. A method of improving the low temperature flow properties of a fuel oil, the method including the step of adding the polymeric additive as defined in any one of claims 1 to 6 to the fuel oil.