FUEL OIL COMPOSITIONS

Abstract: Chemical markers are used as additives in a fuel oil composition to improve the composition's filterability at temperatures above its Cloud Point.

Description: FUEL OIL COMPOSITIONS This invention relates, inter alia, to additives useful in improving the filterability of fuel oil compositions. The art describes the problem of decreased fuel oil filterability at low temperatures and a solution thereto by use of chemical additives. A known class of such additives comprises ethylene-vinyl ester copolymers (EVECs), for example ethylene vinyl acetate copolymers (EVACs). These additives may themselves be blends of two or more different polymers. An additional problem of impaired filterability of fuel oil compositions at temperatures above cloud point has become apparent, being discussed in "Poor diesel fuel quality: a British Rail experience" by D. Smith published in the Institute of Petroleum's "Petroleum Review" of February 1990, page 80 et seq. which article is hereinafter referred to as "the D. Smith article" and is incorporated by reference herein. This problem appears to be independent of fuel oil low temperature filterability, being observed in oils which nevertheless meet their required CFPP and cloud point specifications. In the D. Smith article, the problem has been identified as one of filter clogging, a particular instance being attributed to the presence on the filter of undissolved flow improver additive originally added to improve the low temperature filterability of the fuel oil. Other insoluble matter, for example suspended particles, or organic matter of microbial origin, has also been implicated in such filter clogging. The effects of this filterability problem are seen particularly in fuel oil combustion units containing fine-mesh filters, where the fuel starvation resulting from filter clogging may lead to unit failure. Thus there exists a continuing need for fuel oil compositions possessing improved filterability at temperatures above their cloud points. There especially exists the need for reducing the tendency of low temperature flow improvers, when present in such compositions, to clog filters at temperatures above the cloud point. This need is particularly prevalent where the addition of such flow improvers is performed under physical conditions potentiating their incomplete dissolution in the fuel oil. Surprisingly, it has been found according to this invention that certain additives, when present in a fuel oil composition comprising base fuel oil and preferably at least one low temperature flow-improver, reduce the tendency for filter clogging at temperatures above the composition cloud point. Thus, one aspect of the invention is the use of a chemical marker that is detectable either by conversion to a colorimetrically identifiable tautomeric form thereof or by conversion to a colorimetrically identifiable reaction product thereof, for improving the filterability at temperatures above its cloud point of a fuel oil composition comprising a major proportion of a fuel oil . In a prefered form of the use, the fuel oil composition also comprises one or more low temperature flow improving additives for the fuel oil selected from one or more of an ethylene copolymer; a comb polymer; a polar, organic nitrogen-containing compound; a hydrocarbon polymer; a sulphur-carboxy compound; a hydrocarbylated aromatic compound; and a linear compound. The use of the additive in accordance with the invention appears particularly advantageous with those low temperature flow improvers showing inherently poor solubility in fuel oils. The features of the invention will now be discussed in further detail as follows: THE CHEMICAL MARKERS Examples of these are known in the art. See, for example US-A-4,209,302; US-A- 4,735,631 ; EP-A-509,818; and EP-A-609,591. They are chemical compounds that are dissolved in a liquid to be identified and which are then subsequently detected by an appropriate colorimetric test. Such tests may be quantitative or qualitative and are known in the art. The present invention envisages two classes of chemical marker: one where identification is effected by a chemical reaction which converts the marker to a coiorimetrically detectable product; and the other where the marker is capable of existing in two or more tautomeric forms, at least one of which forms is colorimetrically detectable. In the latter, which is preferred, identification is effected by changing conditions to convert the marker from a non-detectable tautomeric form to a detectable tautomeric form. A preferred chemical marker is an organic base capable of existing in the following tautomeric forms: a non-ionic form; and one or more ionic tautomeric forms such as an ammonium ion, an oxonium ion and a carbonium ion. A specific example is 'Rhodamine Base B" which is capable of existing in the following tautomeric forms: Ion LOW TEMPERATURE FLOW IMPROVING ADDITIVES These are discussed in more detail as follows. Ethylene Copolymers Ethylene copolymer flow improvers e.g. ethylene unsaturated ester copolymer flow improvers, have a polymethylene backbone divided into segments by hydrocarbyl side chains interrupted by one or more oxygen atoms and/or carbonyl groups. More especially, the copolymer may comprise an ethylene copolymer having, in addition to units derived from ethylene, units of the formula -CR5R6-CHR7- wherein R^ represents hydrogen or a methyl group; R^ represents a -OOCR 8 or -COOR 8 group wherein R 8 represents hydrogen or a C*ι to C28. preferably C-| to C-|6, more preferably C-| to Cg, straight or branched chain alkyl group; and R? represents hydrogen or a -COOR 8 or -OOCR 8 group. 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 an unsaturated carboxylic acid such as ethylene - acrylates (eg. ethylene -2- ethylhexylacrylate), but the ester is preferably one of an unsaturated alcohol with a saturated carboxylic acid such as described in GB-A-1,263,152. An ethylene-vinyl ester copolymer is advantageous; an ethylene-vinyl acetate, ethylene vinyl propionate, ethylene-vinyl hexanoate, ethylene 2-ethylhexanoate, or ethylene- - 1> - vinyl octanoate copolymer is preferred. Preferably, the copolymers contain from 1 to 25 such as less than 25, e.g. 1 to 20, mole % of the vinyl ester, more preferably from 3 to 15 mole % vinyl ester. They may also be in the form of mixtures of two copolymers such as those described in US-A-3,961 ,916 and EP-A-113,581. Preferably, number average molecular weight, as measured by vapour phase osmometry, of the copolymer is 1 ,000 to 10,000, more preferably 1 ,000 to 5,000. If desired, the copolymers may be derived from additional comonomers, e.g. they may be terpolymers or tetrapolymers or higher polymers, for example where the additional comonomer is isobutylene or diisobutylene or another ester giving rise to different units of the above formula and wherein the above-mentioned mole %'s of ester relate to total ester. Also, the copolymers may include small proportions of chain transfer agents and/or molecular weight modifiers (eg acetaldehyde or propionaldehyde) that may be used in the polymerisation process to make the copolymer. The copolymers may be made by direct polymerisation of comonomers. Such copolymers may also be made by transesterification, or by hydrolysis and re- esterification, of an ethylene unsaturated ester copolymer to give a different ethylene unsaturated ester copolymer. For example, ethylene vinyl hexanoate and ethylene vinyl octanoate copolymers may be made in this way, eg. from an ethylene vinyl acetate copolymer. The copolymers may, for example, have 15 or fewer, preferably 10 or fewer, more preferably 6 or fewer, most preferably 2 to 5, methyl terminating side branches per 100 methylene groups, as measured by nuclear magnetic resonance, other than methyl groups on a comonomer ester and other than terminal methyl groups. The copolymers may have a polydispersity of 1 to 6 preferably 2 to 4, polydispersity being the ratio of weight average molecular weight to number average molecular weight both as measured by Gel Permeation Chromatography using polystyrene standards. COMB POLYMERS Comb polymers are discussed in "Comb-Like Polymers. Structure and Properties", N. A. Plate and V. P. Shibaev, J. Poly. Sci. Macromolecular Revs., 8, p 117 to 253 (1974). 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 30, 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. Advantageously, the comb polymer is a homopolymer having, or a copolymer at least 25 and preferably at least 40, more preferably at least 50, molar per cent of the units of which have, side chains containing at least 6 such as at least 8, and preferably at least 10, atoms, selected from for example carbon, nitrogen and oxygen, in a linear chain or a chain containing a small amount of branching such as a single methyl branch. As examples of preferred comb polymers there may be mentioned those containing units of the general formula where D represents R 1 , COOR 1 1 , OCOR 1 1 , R 12 COOR 1 or OR 1 ; E represents H, D or R 12 ; G represents H or D; J represents H, R 12 , R 12 COOR 1 , or a substituted or unsubstituted aryl or heterocyclic group; or K represents H, COOR 12 , OCOR 12 , OR 12 or COOH; L represents H, R 2 , COOR 12 , OCOR 12 or substituted or unsubstituted aryl; R 1 1 representing a hydrocarbyl group having 10 or more carbon atoms, and R 12 representing a hydrocarbyl group being divalent in the 1 COOR 1 1 group and otherwise being monovalent, 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, n being in the range of from 0 to 0.6. R 1 1 advantageously represents a hydrocarbyl group with from 10 to 30 carbon atoms, preferably 10 to 24, more preferably 10 to 18. Preferably, R 1 1 is a linear or slightly branched alkyl group and R 12 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, R 12 - when monovalent, is a linear or slightly branched alkyl group. When R 12 is divalent, it is preferably a methylene or ethylene group. By "slightly branched" is meant having a single methyl branch. 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. The comb polymers may, for example, be copolymers of maleic anhydride or fumaric 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 polymer include methacrylates and acrylates. 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 which 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, 1-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 commerically 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. 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. Particularly preferred fumarate comb polymers are copolymers of alkyl fumarates and vinyl acetate, in which the alkyl groups have from 12 to 20 carbon atoms, more especially polymers in which the alkyl groups have 14 carbon atoms or in which the alkyl groups are a mixture of C14/C16 alkyl groups, made, for example, by solution copolymerizing an equimolar mixture of fumaric acid and vinyl acetate and reacting the resulting copolymer with the alcohol or mixture of alcohols, which are preferably straight chain alcohols. When the mixture is used it is advantageously a 1 :1 by weight mixture of normal C14 and C16 alcohols. Furthermore, mixtures of the C14 ester with the mixed C14/C16 ester may advantageously be used. In such mixtures, the ratio of C14 to C14/C16 is advantageously in the range of from 1 :1 to 4:1 , preferably 2:1 to 7:2, and most preferably about 3:1 , by weight. The particularly preferred fumarate comb polymers may. for example, have a number average molecular weight in the range of 1 ,000 to 100,000, preferably 1 ,000 to 50,000, as measured by Vapour Phase Osmometry (VPO). 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. Other examples of comb polymers are hydrocarbon polymers such as copolymers of ethylene and at least one α-olefin, preferably the α-olefin having at most 20 carbon atoms, examples being n-octene-1 , iso octene-1 , n-decene-1 and n- dodecene-1. n-tetradecene-1 and n-hexadecene-1 (for example, as described in WO9319106 Preferably, the number average molecular weight measured by Gel Permeation Chromatography against polystyrene standards of such a copolymer is for example, up to 30,000 or up to 40,000. The hydrocarbon copolymers may be prepared by methods known in the art, for example using a Ziegler type catalyst. Such hydrocarbon polymers may for example have an isotacticity of 75% or greater. Ethylene copolymer flow improvers e.g. ethylene unsaturated ester copolymer flow improvers, have a polymethylene backbone divided into segments by oxy hydrocarbon side chains. More especially, the copolymer may comprise an ethylene copolymer having, in addition to units derived from ethylene, units of the formula -CR 5 R 6 -CHR 7 - wherein R 8 represents hydrogen or a methyl group; R5 represents a -OOCR 8 or -COOR 8 group wherein R 8 represents hydrogen or a Ci to C28. preferably C-j to Cg, straight or branched chain alkyl group, provided that R 8 does not represent hydrogen when R^ represents -COOR 8 ; and h?7 is hydrogen or -COOR 8 . 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 an unsaturated carboxylic acid, but the ester is preferably 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, or ethylene-vinyl octanoate copolymer is preferred. Preferably, the copolymers contain from 1 to 25, e.g. 1 to 20, mole % of the vinyl ester, more preferably from 3 to 15 mole % vinyl ester. They may also be in the form of mixtures of two copolymers such as those described in US Patent 3,961 ,916. Preferably, number average molecular weight, as measured by vapour phase osmometry, of the copolymer is 1 ,000 to 10,000, more preferably 1 ,000 to 5,000. If desired, the copolymers may be derived from additional comonomers, e.g. they may be terpolymers or tetrapolymers or higher polymers, for example where the additional comonomer is isobutylene or diisobutylene. The copolymers may be made by direct polymerisation of comonomers. Such copolymers may also be made by transesterification, or by hydrolysis and re- esterification, of an ethylene unsaturated ester copolymer to give a different ethylene unsaturated ester copolymer. For example, ethylene vinyl hexanoate and ethylene vinyl octanoate copolymers may be made in this way, eg. from an ethylene vinyl acetate copolymer. LINEAR COMPOUNDS Such compounds comprise a compound in which at least one substantially linear alkyl group having 10 to 30 carbon atoms is connected to a non-polymeric organic residue to provide at least one linear chain of atoms that includes the carbon atoms of said alkyl groups and one or more non-terminal oxygen atoms. By "substantially linear" is meant that the alkyl group is preferably straight chain, but that essentially straight chain alkyl groups having a small degree of branching such as in the form of a single methyl group may be used. Preferably, the compound has a least two of said alkyl groups when the linear chain may include the carbon atoms of more than one of said alkyl groups. When the compound has at least three of said alkyl groups, there may be more than one of such linear chains, which chains may overlap. The linear chain or chains may provide part of a linking group between any two such alkyl groups in the compound. The oxygen atom or atoms are preferably directly interposed between carbon atoms in the chain and may, for example, be provided in the form of a mono- or poly-oxyalkylene group, said oxyalkylene group preferably having 2 to 4 carbon atoms, examples being oxyethylene and oxypropylene. As indicated the chain or chains include carbon and oxygen atoms. They may also include other hetero-atoms such as nitrogen atoms. The compound may be an ester where the alkyl groups are connected to the remainder of the compound as -O-CO n alkyl, or -CO-O n alkyl groups, in the former the alkyl groups being derived from an acid and the remainder of the compound being derived from a polyhydric alcohol and in the latter the alkyl groups being derived from an alcohol and the remainder of the compound being derived from a polycarboxylic acid. Also, the compound may be an ester where the alkyl groups are connected to the remainder of the compound as — O — n — alkyl groups. The compound may be both an ester and an ether or it may contain different ester groups. Examples include polyoxyaikylene esters, ethers, ester/ethers and mixtures thereof, particularly those containing at least one, preferably at least two, C-jrj to C30 linear alkyl groups and a polyoxyaikylene glycol group of molecular weight up to 5,000, preferably 200 to 5,000, the alkylene group in said polyoxyaikylene glycol containing from 1 to 4 carbon atoms, as described in EP-A-61 895 and in U.S. Patent No. 4,491 ,455. The preferred esters, ethers or ester/ethers which may be used may be structurally depicted by the formula R 28 OBOR 24 where R 28 and R 4 are the same or different and may be (a) n-alkyl- (b) n-alkyl-CO- (c) n-alkyl-OCO-(CH2)n- (d) n-alkyl-OCO-(CH2) n CO- n being, for example, 1 to 34, the alkyl group being linear and containing from 10 to 30 carbon atoms, and B representing the polyalkylene segment of the glycol in which the alkylene group has from 1 to 4 carbon atoms, for example, 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 tolerated but it is preferred that the glycol should be substantially linear. B may also contain nitrogen. Suitable glycols generally are substantially linear polyethylene glycols (PEG) and polypropylene glycols (PPG) having a molecular weight of about 100 to 5,000, preferably about 200 to 2,000. Esters are preferred and fatty acids containing from 10 to 30 carbon atoms are useful for reacting with the giycols to form the ester additives, it being preferred to use C-jg to C24 fatty acid, especially behenic acid. The esters may also be prepared by esterifying polyethoxylated fatty acids or polyethoxylated alcohols. Polyoxyaikylene diesters, diethers, ether/esters and mixtures thereof are suitable as additives, diesters being preferred when the petroleum based component is a narrow boiling distillate, when minor amounts of monoethers and monoesters (which are often formed in the manufacturing process) may also be present. It is important for active performance that a major amount of the dialkyi compound is present. In particular, stearic or behenic diesters of polyethylene glycol, polypropylene glycol or polyethylene/polypropylene glycol mixtures are preferred. Examples of other compounds in this general category are those described in Japanese Patent Publication Nos. 2-51477 and 3-34790, and EP-A-117,108 and EP-A-326,356, and cyclic esterified ethoxylates such as described in EP-A- ' 356,256. HYDROCARBON POLYMERS These have one or more polymethylene backbones, optionally divided into segments by short chain length hydrocarbyl groups, i.e. of 5 or less carbon atoms. Examples are those represented by the following general formula ( ■ CTT - CHτ}γ (CHU - CHU}^ — where T represents H or R 1 ; U represents H, T or substituted or unsubstituted aryl; and R 1 represents a hydrocarbyl group having up to 5 carbon atoms. and v and w represent mole ratios, v being within the range 1.0 to 0.0, w being within the range 0.0 to 1.0. Preferably, R 1 is a straight or branched chain alkyl group. These polymers may be made directly from ethylenically unsaturated monomers or indirectly by hydrogenating the polymer made from monomers such as isoprene and butadiene. Preferred hydrocarbon polymers are copolymers of ethylene and at least one α- olefin. Examples of such olefins are propylene, 1-butene, isobutene, and 2, 4, 4- trimethylpent-2 -ene. The copolymer may also comprise small amounts, e.g. up to 10% by weight of other copolymerizable monomers, for example olefins other than α-olefins, and non-conjugated dienes. The preferred copolymer is an ethylene- propylene copolymer. It is within the scope of the invention to include two or more different ethylene-α-olefin copolymers of this type. The number average molecular weight of the ethylene-α-olefin copolymer is less than 150,000, as measured by gel permeation chromatography (GPC) relative to polystyrene standards. For some applications, it is advantageously at least 60,000 and preferably at least 80,000. Functionally no upper limit arises but difficulties of mixing result from increased viscosity at molecular weights above about 150,000, and preferred molecular weight ranges are from 60,000 and 80,000 to 120,000. For other applications, it is below 30,000, preferably below 15, 000 such as below 10,000 or below 6,000. Also, the copolymers may have an isotacticity of 75% or greater. Advantageously, the copolymer has a molar ethylene content between 50 and 85 per cent. More advantageously, the ethylene content is within the range of from 55 to 80%, and preferably it is in the range from 55 to 75%; more preferably from 60 to 70%, and most preferably 65 to 70%. Examples of ethylene-α-olefin copolymers are ethylene-propylene copolymers with a molar ethylene content of from 60 to 75% and a number average molecular weight in the range 60,000 to 120,000, especially preferred copolymers are ethylene-propylene copolymers with an ethylene content of from 62 to 71 % and a molecular weight from 80,000 to 100,000. The copolymers may be prepared by any of the methods known in the art, for example using a Ziegler type catalyst. Advantageously, the polymers are substantially amorphous, since highly crystalline polymers are relatively insoluble in fuel oil at low temperatures. SULPHUR-CARBOXY COMPOUNDS Examples are those described in EP-A-0,261 ,957 which describes the use of compounds of the general formula A X R 1 B Υ — R R 1 and R 2 are alkyl, alkoxyalkyl or polyalkoxyalkyl containing at least 10 carbon atoms in the main chain; R 8 is hydrocarbyl and each R 8 may be the same or different and R 4 is absent or is Ci to C5 alkylene and in A \ C B' the carbon-carbon (C-C) bond is either a) ethylenically unsaturated when A and B may be alkyl, alkenyl or substituted hydrocarbyl groups or b) part of a cyclic structure which may be aromatic, polynuclear aromatic or cyclo-aliphatic, it is preferred that X-R 1 and Y-R 2 between them contain at least three alkyl, alkoxyalkyl or polyalkoxyalkyl groups. Multicomponent additive systems may be used and the ratios of additives to be used will depend on the fuel to be treated. POLAR, ORGANIC NITROGEN-CONTAINING COMPOUNDS Such compounds comprise an oil-soluble polar nitrogen compound carrying one or more, preferably two or more, substituents of the formula =NR 1 , where R represents a hydrocarbyl group containing 8 to 40 carbon 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 either ionic or non- ionic and is capable of acting as a wax crystal growth inhibitor in fuels. It comprises for example one or more of the compounds (i) to (iii) as follows: (i) 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 1 to 4 carboxylic acid groups or its anhydride, the substituent(s) of formula =NR 1 being of the formula -NR 1 R 2 where R 1 is defined as above and R 2 represents hydrogen or R 1 , provided that R 1 and R 2 may be the same or different, said substituents constituting part of the amine salt and/or amide groups of the compound. Ester/amides may be used containing 30 to 300, preferably 50 to 150 total carbon atoms. These nitrogen compounds are described in US Patent 4 211 534. Suitable amines are usually long chain C12-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 and therefore normally contains about 30 to 300 total carbon atoms. The nitrogen compound preferably contains at least one straight chain Cβ to C40, preferably C14 to C24, alkyl segment. Suitable amines include primary, secondary, tertiary or quaternary, but preferably are secondary. Tertiary and quaternary amines can only form amine salts. Examples of amines include tetradecyl amine, cocoamine, and hydrogenated tallow amine. Examples of secondary amines include dioctacedyl amine and methyl-behenyl amine. Amine mixtures are also suitable such as those derived from natural materials. A preferred amine is a secondary hydrogenated tallow amine of the formula HNR 1 R 2 wherein R 1 and R 2 are alkyl groups derived from hydrogenated tallow fat composed of approximately 4% C14, 31% C16, 59% C18 Examples of suitable carboxylic acids and their anhydrides for preparing the nitrogen compounds include 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 dialkyi spirobislactone. Generally, these acids have about 5-13 carbon atoms in the cyclic moiety. Preferred acids useful in the present invention are benzene dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid. Phthalic acid or its anhydride is particularly preferred. The particularly preferred compound is the amide-amine salt formed by - lb - 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. 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-A-4 147 520, for example. Suitable amines may be those described above. Other examples are condensates such as described in EP-A-327,423. (ii) A chemical compound comprising or including a cyclic ring system, the compound carrying at least two substituents of the general formula (I) below on the ring system -A-NR1R2 (I) where A is an aliphatic hydrocarbyl group that is optionally interrupted by one or more hetero atoms and that is straight chain or branched, and R 1 and R 2 are the same or different and each is independently a hydrocarbyl group containing 9 to 40 carbon 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. Preferably, A has from 1 to 20 carbon atoms and is preferably a methylene or polymethylene group. As used in this specification the term "hydrocarbyl" refers to a group having a carbon atom directly attached to the rest of the molecule and having a hydrocarbon or predominantly hydrocarbon character. Examples include hydrocarbon groups, including aliphatic (e.g. alkyl or alkenyl), alicyclic (e.g. cycloalkyl or cycloalkenyl), aromatic, and alicyclic-substituted aromatic, and aromatic-substituted aliphatic and alicyclic groups. Aliphatic groups are advantageously saturated. These groups may contain non-hydrocarbon substituents provided their presence does not alter the predominantly hydrocarbon character of the group. Examples include keto, halo, hydroxy, nitro, cyano, alkoxy and acyl. If the hydrocarbyl group is substituted, a single (mono) substituent is preferred. Examples of substituted hydrocarbyl groups include 2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl, 2-ketopropyl, ethoxyethyl, and propoxypropyl. The groups may also or alternatively contain atoms other than carbon in a chain or ring otherwise composed of carbon atoms. Suitable hetero atoms include, for example, nitrogen, sulphur, and, preferably, oxygen. The cyclic ring system may include homocyclic, heterocyclic, or fused polycyclic assemblies, or a system where two or more such cyclic assemblies are joined to one another and in which the cyclic assemblies may be the same or different. Where there are two or more such cyclic assemblies, the substituents of the general formula (I) may be on the same or different assemblies, preferably on the same assembly. Preferably, the or each cyclic assembly is aromatic, more preferably a benzene ring. Most preferably, the cyclic ring system is a single benzene ring when it is preferred that the substituents are in the ortho or meta positions, which benzene ring may be optionally further substituted. The ring atoms in the cyclic assembly or assemblies are preferably carbon atoms but may for example include one or more ring N, S or O atom, in which case or cases the compound is a heterocyclic compound. Examples of such polycyclic assemblies include (a) condensed benzene structures such as naphthalene, anthracene, phenanthrene, and pyrene; (b) condensed ring structures where none of or not all of the rings are benzene such as azulene, indene, hydroindene, fluorene, and diphenylene oxides: (c) rings joined "end-on" such as diphenyl; (d) heterocyclic compounds such as quinoline, indole, 2:3 dihydroindole, benzofuran, coumarin, isocoumarin, benzothiophen, carbazole and thiodiphenylamine; (e) non-aromatic or partially saturated ring systems such as decalin (i.e. decahydronaphthalene), a-pinene, cardinene, and bornylene; and (f) three-dimensional structures such as norbornene, bicycloheptane (i.e. norbornane), bicyclooctane, and bicyclooctene. Each hydrocarbyl group constituting R 1 and R 2 in the invention (Formula I) may for example be an alkyl or alkylene group or a mono- or poly-alkoxyalkyl group. Preferably, each hydrocarbyl group is a straight chain alkyl group. The number of carbon atoms in each hydrocarbyl group is preferably 16 to 40, more preferably 16 to 24. Also, it is preferred that the cyclic system is substituted with only two substituents of the general formula (I) and that A is a methylene group. Examples of salts of the chemical compounds are the acetate and the hydrochloride. The compounds may conveniently be made by reducing the corresponding amide which may be made by reacting a secondary amine with the appropriate acid chloride; and (iii) A condensate of long chain primary or secondary amine with a carboxylic acid-containing polymer. Specific examples include polymers such as described in GB-A-2,121 ,807, FR-A-2,592,387 and DE-A-3,941 ,561 ; and also esters of telemer acid and alkanoloamines such as described in US-A-4,639,256; and the reaction product of an amine containing a branched carboxylic acid ester, an episode and a mono- carboxylic acid polyester such as described in US-A4,631 ,071. HYDROCARBYLATED AROMATICS These materials are condensates comprising aromatic and hydrocarbyl parts. The aromatic part is conveniently an aromatic hydrocarbon which may be unsubstituted or substituted with, for example, non-hydrocarbon substitutents. Such aromatic hydrocarbon preferably contains a maximum of these substituent groups and/or three condensed rings, and is preferably naphthalene. The hydrocarbyl part is a hydrogen and carbon containing part connected to the rest of the molecule by a carbon atom. It may be saturated or unsaturated, and straight or branched, and may contain one or more hetero-atoms provided they do not substantially affect the hydrocarbyl nature of the part. Preferably the hydrocarbyl part is an alkyl part, conveniently having more than 8 carbon atoms. FUEL OIL The fuel oil may be a hydrocarbon fuel such as a petroleum-based fuel oil, for example kerosene or distillate fuel oil, suitably a middle distillate fuel oil, i.e. a fuel oil obtained in refining crude oil as the fraction between the lighter kerosene and jet fuels fraction and the heavier fuel oil fraction. Such distillate fuel oils generally boil within the range of about 100°C to about 500°C, e.g. 150° to about 400°C, for example, those having a relatively high Final Boiling Point of above 360°C. (ASTM D-86) The fuel oil can comprise atmospheric distillate or vacuum distillate, or 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 it may contain minor amounts, e.g. up to 35 wt%, of vacuum gas oil or cracked gas oils or of both. Heating oils may be made of a blend of virgin distillate, e.g. gas oil, naphtha, etc and cracked distillates, e.g. catalytic cycle stock. A representative specification for a diesel fuel includes a minimum flash point of 38°C and a 90% distillation point between 262 and 380°C (see ASTM Designations D-396 and D-975). Also, the fuel oil may be an animal or vegetable oil, or a petroleum based oil as described above in combination with an animal or vegetable oil. The concentration of the one or more low temperature flow improving additives in the oil may for example be in the range of 1 to 5,000 ppm of additive (active ingredient) by weight per weight of fuel, for example 10 to 5,000 ppm such as 10 to 2000 ppm (active ingredient) by weight per weight of fuel, preferably 25 to 500 ppm, more preferably 100 to 200 ppm. The concentration of the marker in the oil may for example be in the range of up to 10 ppm, such as 0.1 to 5 ppm, proportions being in ppm (active ingredient) by weight per weight of fuel. CONCENTRATE Concentrates are convenient as a means for incorporating the marker and/or the low temperature flow improving additives into bulk fuel oil such as distillate fuel, which incorporation may be done by methods known in the art. The concentrates may also contain other co-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; alkanols and paraffinic hydrocarbons such as hexane and pentane and isoparaffins. The carrier liquid must, of course, be selected having regard to its compatibility with the additive and with the fuel. The marker and low temperature flow improving additives, when present, may be incorporated in the same concentrate, or into different concentrates.They may also be incorporated into bulk fuel oil by other methods such as those known in the art. The marker may be incorporated into the bulk fuel oil at the same time as the low temperature flow improving additives or at a different time. CO-ADDITIVES The marker and low temperature flow improving additives may also be used in combination with one or more co-additives such as known in the art, for example the following: detergents, antioxidants, corrosion inhibitors, dehazers, demulsifiers, metal deactivators, antifoaming agents, cetane improvers, cosolvents, package compatibilisers, and lubricity additives and antistatic additives. EXAMPLE The following examples illustrate the invention. Materials Additives a mixture of two additives in the weigh weight ratio of 3:1 , the first additive comprising an ethylene-vinyl acetate copolymer of number average molecular weight 5000 as measured by GPC (Gel Permeation Chromatography) and containing 13.5% by weight of vinyl acetate, and the second additive comprising an ethylene-vinyl acetate copolymer of number average molecular weight 3300 as measured by GPC and containing 36% by weight of vinyl acetate. Rhodamine Base B Fuel A middle distillate fuel having the following characteristics: Kinematic Viscosity (at 20°C) 3.526 cst Density (at 15°C) 0.8270 g/ml D-86 Distillation characteristics (°C) 50% 252.3 90% 326.0 FBP * 359.8 Final Boiling Point Test Methods a) The measurement of the filterability of fuel oil compositions at temperatures above their cloud point was done using the British Rail Average Differential Time (hereinafter ADT) filterability test, this test being described in the D. Smith article incorporated by reference herein, and to which the reader is directed. In summary, the ADT test measures the filter-blocking tendency of a fuel oil conditioned for 24 hours at a temperature of +3°C, i.e. 5°C above the maximum fuel oil cloud point permitted under British Standards Institution: British Standard Specification for Fuel Oils for oil engines and burners for non-marine use, B.S. 2869 (Part 2, 1988). The conditioning temperature of 5°C above cloud point is considered to accurately reflect the temperature regime experienced in the field by fuel oils prior to incursion of filter blocking problems. It is also considered sufficiently above fuel oil cloud point - and the onset of low temperature flowability problems - to be representative of the general problem of impaired filterability at temperatures above cloud point, and particularly representative of this problem at temperatures of up to 10°C above cloud point. The results of the above test are reported in terms of the ADT, this figure being calculated from the test results as follows: T3 - T1 ADT xl OO T2 T-j , T2, T3 being the time periods over which respective aliquots of 50 ml fuel oil pass through the GFA 2 (1.6μm) filter. Testing in the D. Smith article has indicated that an ADT exceeding 15 correlates with impaired fuel oil filterability in particular railway locomotive fuel systems. More generally, higher ADT values characterise fuels having an increased tendency to give filter blocking problems. b) The filterability of fuel oil compositions at temperatures above their cloud point was also done using the Institute of Petroleum's Standard designated "IP 387/90" and entitled "Determination of filter blocking tendency of gas oils and distillate diesel fuels." In summary, a sample of the fuel composition to be tested is passed at a constant rate of flow through a glass fibre filter medium; the pressure drop across the filter is monitored, and the volume of fuel passing the filter medium within a prescribed pressure drop is measured. The filter blocking tendency of a fuel composition can be described as the pressure drop across the filter medium for 300 ml of fuel to pass at a rate of 20 ml/min. Reference is to be made to the above-mentioned Standard for further information. Test Procedure a) The test was carried out using untreated fuel (Experiment 1); fuel treated with the above-identified ethylene-vinyl acetate copolymer additive (200 ppm w/w) (Experiment 2); and fuel treated with a combination of said copolymer additive (200 ppm w/w) and Rhodamine Base B (0.2 ppm w/w) (Experiment 3). b) The procedure was carried out on untreated fuel; fuel treated with the above-specified copolymer additive; fuel treated with Rhodamine Base B; and fuel treated with a combination of the copolymer and Rhodamine Base B. Results a) Experiment T-i ϊ-2 is ADT Pass/Fail 1 109 115 119 4.34 Pass 2 171 200 240 17.25 Fail 3 161 160 188 8.43 Pass The results show that low temperature flow improvers clog filters at temperatures above fuel composition cloud point (as indicated by increased ADT values), even under ideal blending conditions. They further show that the additional presence of a chemical marker, according to the present invention reduces the magnitude of this deleterious effect. b) Fuel Composition* Result Pass/Fail Base 9.7 psi Pass + Copolymer (200) 8 mins Fail + Rhodamine Base B (0.2) 4.4 psi Pass + Rhodamine Base B (5) 3.7 psi Pass + Copolymer (200) + 4.4 psi Pass Rhodamine Base B (0.2) + Copolymer (200) + 8.4 psi Pass Rhodamine Base B (5) * additive concentrations are given in parentheses in ppm (w/w) The results indicate that the marker improves filterability (as indicated by lower pressure drop values across the filter) both of base fuel and of fuel treated with the low tempertaurte flow improving additive. This latter additive again gave significant filter blocking problems when used alone.

Claims: Claims: 1. The use for improving the filterability at temperatures above its cloud point, of a fuel oil composition comprising a major proportion of a fuel oil , of a chemical marker that is detectable either by conversion to a colorimetrically identifiable tautomeric form thereof or by conversion to a colorimetrically identifiable reaction product thereof. 2. The use of claim 1 wherein the chemical marker is capable of existing in one or more of the following tautomeric forms: an ammonium ion, an oxonium ion, and a carbonium ion. 3. The use of claim 1 , wherein the fuel oil composition also comprises one or more low temperature flow improving additives for the fuel oil selected from one or more of an ethylene copolymer; a comb polymer; a polar, organic nitrogen-con taining compound; a hydrocarbon polymer; a sulphur-carboxy compound; a hydrocarbylated aromatic compound; and a linear compound. 4. The use of any preceding claim, wherein the chemical marker is Rhodamine Base B.

Inventors: CAPROTTI RINALDO, TANNER TRACY, CAPROTTI, RINALDO, TANNER, TRACY
Applicants: EXXON CHEMICAL LTD, EXXON CHEMICAL PATENTS INC, EXXON CHEMICAL LIMITED, EXXON CHEMICAL PATENTS INC.
Application year: 1996
Main classification: C10L1
IPC codes: C10L1