DE69326754T2 - ADDITIVES FOR OILS - Google Patents

Abstract

One or more additives are used to modify the wax crystal growth properties of oils derived from animal or vegetable material.

Description

This invention relates to the use of wax crystal modifying additives in oils obtained from animal or vegetable material or both, or derivatives thereof.

Oils obtained from animal or vegetable material are mainly metabolites comprising triglycerides of monocarboxylic acids, e.g. acids with 10 to 25 carbon atoms, and the form

in which R is an aliphatic radical having 10 to 25 carbon atoms which may be saturated or unsaturated.

Generally, such oils contain glycerides of a number of acids, the number and type of which vary with the source of the oil, and they may additionally contain phosphoglycerides. Such oils can be obtained by methods known in the art.

Examples of derivatives of such oils are alkyl esters such as methyl esters of fatty acids from vegetable or animal oils. Such esters can be produced by transesterification.

References within this description to oils derived from animal or vegetable material therefore include references to oils obtained from the animal or vegetable material or both, as well as derivatives thereof.

US-A-2 610 915 describes glyceride oils to which a small amount of oil-soluble Polymerization product of esters with vinyl or substituted vinyl group according to the general formula

in which X is a hydrogen atom and alkyl or aromatic hydrocarbon group and Y is -C-CO-R or -COOR, in which R is a monovalent hydrocarbon radical or an ether derivative thereof having more than 4 carbon atoms.

FR-A-2 492 402 describes fuel compositions containing one or more fatty acid esters of animal and vegetable origin, represented by the general formula

R¹-COO-R²

wherein R¹ contains 5 to 23 carbon atoms, is a substantially linear saturated or unsaturated aliphatic radical and R² contains 1 to 12 carbon atoms and is a linear or branched, saturated or unsaturated aliphatic radical. Such fuel compositions are described as being particularly suitable for use in diesel engines, and have a cetane index range generally equivalent to that of conventional diesel fuels derived from mineral oils.

The usefulness of such fatty acid ester compositions as diesel fuels is, however, limited by their low temperature properties. DE-A-40 40 317 discloses that such fuels can solidify at temperatures below -5°C in feed lines due to insufficient filterability and describes a process for improving low temperature filterability involving the addition of short chain methyl esters of fatty acids and selected polymeric materials, namely polymeric esters or copolymers of esters of acrylic and/or methacrylic acids derived from alcohols having 1 to 22 carbon atoms.

The low temperature properties of petroleum-based oils, i.e. mineral oils and their derivatives such as crude oil, lubricating oil and fuel oil, for example middle distillate fuel oil, are well documented in the art. Similarly, the use of additives to modify the paraffin crystal structure of these mineral oils and derivatives thereof is known. Examples of such additives and their use are described in US-A-3 048 479, GB-A-1 263 152, US-A-3 961 916, US-A-4 211 534, EP-A-153 176 and EP-A-153 177. They are sometimes referred to as "cold flow additives". "Chemicals in the Oil Industry", a collection of papers edited by P. H. Ogden, documenting the progress of a symposium organized by the Royal Society of Chemistry and held at the University of Manchester on 22 and 23 March 1983, describes on page 112 how certain alkylated regions of the molecular structure of such additives are thought to resemble the linear saturated hydrocarbon chains of the heavier n-alkane molecules (paraffin wax) that are naturally present as minor constituents of these oils. Furthermore, because of these structural similarities, such additives are thought to interfere in some way with the crystallization of the n-alkanes into platelet-like crystals such as precipitate out of solution in oil at low temperatures. The additives modify the size and shape (form) of paraffin crystals and reduce the cohesive forces between the crystals and between the wax and the oil in such a way that the oil remains flowable at lower temperatures and passes through coarse filters.

In contrast to mineral oils and derivatives thereof, the low temperature properties of oils according to the invention, which are oils consisting essentially of alkyl esters of fatty acids derived from animal or vegetable oils or both, are predominantly controlled by the precipitation of higher molecular weight fatty acid esters which are present as major constituents. By way of example only, the major components of rapeseed oil methyl ester are illustrated below. Predominant rapeseed oil methyl ester components: Oleic acid derivative Linoleic acid derivative Linolenic acid derivative Erucic acid derivative

In general, such unsaturated fatty acid derivatives predominate over their saturated analogues, although the exact proportions of individual components within a particular oil may vary as a result of seasonal variations in the constituent fatty acids within the raw material or as a result of the particular process by which they are obtained.

This predominance of ethylenically unsaturated fatty acid esters produces oils with a crystallization behavior that differs from that of the mineral oils mentioned, whereby it is assumed that the difference in crystal morphologies between these two classes of oil results from the different structural configurations of the hydrocarbon chains of precipitating n-alkanes or unsaturated fatty acid esters.

It has now surprisingly been found that, despite their apparent lack of structural similarity to ethylenically unsaturated hydrocarbon chains, certain additives which are effective as wax crystal modifiers in mineral oils and derivatives thereof are also effective as wax crystal modifiers in oils consisting essentially of alkyl esters of fatty acids derived from animal or vegetable oils or both.

According to its first aspect, the invention is therefore a composition comprising a major proportion of oil consisting essentially of alkyl esters of fatty acids derived from vegetable or animal oils or both, mixed with a minor proportion of mineral oil cold flow improver comprising one or more of the following:

(i) comb polymer which is a copolymer of maleic anhydride or fumaric acid and another ethylenically unsaturated monomer, which copolymer may be esterified, or polymer or copolymer of α-olefin, or fumarate or itaconate polymer or copolymer,

(ii) polyoxyalkylene esters, esters/ethers or a mixture of the same,

(iii) ethylene/unsaturated ester copolymer,

(iv) polar, organic, nitrogen-containing wax crystal growth inhibitor,

(v) hydrocarbon polymer,

(vi) sulphur carboxy compounds and

(vii) aromatic pour point depressant containing hydrocarbon radicals

provided that the composition does not comprise mixtures of polymeric esters or copolymers of esters of acrylic and/or methacrylic acid derived from alcohols having 1 to 22 carbon atoms.

According to the second aspect, the invention is the use of mineral oil cold flow additive for modifying the wax crystal growth properties of oil consisting essentially of alkyl esters of fatty acids derived from vegetable or animal oils or both, wherein the additive comprises one or more of the following

(i) comb polymer, the copolymer of maleic anhydride or fumaric acid and another ethylenically unsaturated monomer, which copolymer may be esterified, or Polymer or copolymer of α-olefin, or fumarate or itaconate polymer or copolymer,

(ii) polyoxyalkylene esters, esters/ethers or a mixture of the same,

(iii) ethylene/unsaturated ester copolymer,

(iv) polar, organic, nitrogen-containing wax crystal growth inhibitor,

(v) hydrocarbon polymer,

(vi) sulphur carboxy compounds and

(vii) aromatic pour point depressant containing hydrocarbon radicals

provided that the additive does not comprise mixtures of polymeric esters or copolymers of esters of acrylic and/or methacrylic acid derived from alcohols having 1 to 22 carbon atoms.

According to a third aspect, the invention is a process for modifying the wax crystal growth properties of oil consisting essentially of alkyl esters of fatty acids derived from vegetable or animal oils or both, which comprises mixing with the additive as defined in the second aspect.

The features of the invention will now be discussed in further detail.

Oils

Examples of oils derived from animal or vegetable material are rapeseed oil, coriander oil, soybean oil, cottonseed oil, sunflower oil, castor oil, olive oil, peanut oil, corn oil, almond oil, palm kernel oil, coconut oil, mustard seed oil, beef tallow and fish oils. Other examples include oils derived from wheat, jute, sesame, shea nut, arachis oil and linseed oil and can be derived from these by methods known in the art. Rapeseed oil, which is a mixture of fatty acids partially esterified with glycerin, is preferred because it is available in large quantities and is easily obtained by pressing rapeseed.

The following are suitable as lower alkyl esters of fatty acids, for example as commercially available mixtures: the ethyl, propyl, butyl and especially methyl esters of fatty acids with 12 to 22 carbon atoms, for example of lauric acid, myristic acid, palminic acid, palmitoleic acid, stearic acid, oleic acid, elaidic acid, petroselinic acid, ricinoleic acid, eleostearic acid, linoleic acid, linolenic acid, eicosanoic acid, gadoleic acid, docosanoic acid or erucic acid, which have an iodine number of 50 to 150, in particular 90 to 125. Mixtures with particularly advantageous properties are those which mainly, i.e. at least 50% by weight, contain methyl esters of fatty acids with 16 to 22 carbon atoms and 1, 2 or 3 double bonds. The preferred lower alkyl esters of fatty acids are the methyl esters of oleic acid, linoleic acid, linolenic acid and erucic acid.

Commercially available mixtures of the type mentioned are obtained, for example, by splitting and esterifying animal and vegetable fats and oils by transesterifying them with lower aliphatic alcohols. To produce lower alkyl esters of fatty acids, it is advantageous to start with fats and oils with a high iodine number, such as sunflower oil, rapeseed oil, coriander oil, castor oil, soybean oil, cottonseed oil, peanut oil or beef tallow. Lower alkyl esters of fatty acids based on a new type of rapeseed oil, the fatty acid component of which is derived to more than 80% by weight from unsaturated fatty acids with 18 carbon atoms, are preferred.

Particularly preferred are oils according to the invention which can be used as biofuels. Biofuels, ie fuels derived from animal or vegetable material, are considered to be less harmful to the environment when burned and are obtained from a renewable source. It has been reported that less carbon dioxide is formed when burned than by an equivalent amount of petroleum distillate fuel, e.g. diesel fuel, and that very little sulphur dioxide is formed. Certain derivatives of vegetable oil, e.g. those obtained by saponification and re-esterification with a monohydric alkyl alcohol can be used as a substitute for diesel fuel. It has recently been reported that blends of rapeseed esters, for example rapeseed oil methyl ester (RME), with petroleum distillate fuels in ratios of, for example, 10:90 (by volume) will be commercially available in the near future.

Thus, a biofuel is an oil obtained from plant or animal material or both, or a derivative thereof, which can be used as a fuel.

Although many of the above oils can be used as biofuels, vegetable oil derivatives are preferred, with particularly preferred biofuels being alkyl ester derivatives of rapeseed oil, cottonseed oil, soybean oil, sunflower oil, olive oil or palm oil, with rapeseed oil methyl ester being particularly preferred.

The concentration of the additive in the oil can, for example, be in the range of 1 to 10,000 ppm by weight of additive (active ingredient) based on the weight of the fuel, for example 10 to 5,000 ppm by weight, such as 10 to 2,000 ppm by weight (active ingredient) based on the weight of the fuel, preferably 25 to 500 ppm, in particular 100 to 200 ppm.

The additive or additives should be soluble in the oil to the extent of at least 1000 ppm by weight per part by weight of oil at ambient temperature. However, near the cloud point of the oil, at least some of the additive may separate from the solution to modify the wax crystals that form.

The additive may be incorporated into bulk oil according to methods known in the art. If 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.

A concentrate comprising the additive dispersed in a liquid carrier material (e.g. in solution) is convenient as a means for incorporating the additive. The concentrates of the invention are convenient as a means for incorporating the additive into bulk oil such as distillate fuel, which incorporation may be carried out by methods known in the art. The concentrates may also contain other additives as required and preferably contain from 3 to 75% by weight, especially from 3 to 6% by weight, most preferably from 10 to 50% by weight 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 heating oil, aromatic hydrocarbons such as aromatic fractions, e.g. those sold under the trade name "SOLVESSO", and paraffinic hydrocarbons such as hexane and pentane and isoparaffins. The carrier liquid must of course be selected with regard to its compatibility with the additive and with the fuel.

The additives of the invention can be introduced into bulk oil by other methods known in the art. If coadditives are required, they can be introduced into the bulk oil at the same time as the additives of the invention, or at another time.

Additive

Preferred additives according to the various aspects of the present invention are described below.

(i) Comb polymers

Comb polymers are polymers in which hydrocarbon groups are arranged pendant from a polymer backbone and are discussed in "Comb-Like Polymers. Structure and Properties", N. A. Plate and V. P. Shibaev, J. Poly. Sci. Macromolecular Revs., 8, pp. 117 to 253 (1974).

Advantageously, the comb polymer is a homopolymer with side chains containing at least 6 and preferably at least 10 carbon atoms, or a copolymer with at least 25 and preferably at least 40, in particular at least 50 mol.% of the units having side chains with at least 6 and preferably at least 10 atoms.

The comb polymer may contain units derived from other monomers as desired or required. It is within the scope of the invention to include two or more different comb polymers.

These comb polymers may, for example, be copolymers of maleic anhydride or fumaric acid and another ethylenically unsaturated monomer, e.g. an α-olefin or unsaturated ester, e.g. vinyl acetate. It is preferred, although not necessary, that equivalent amounts of the comonomers are used, although molar proportions in the range of 2:1 to 1:2 are suitable. Examples of olefins which can be copolymerized with, e.g. maleic anhydride include 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene and 1-octadecene.

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 or 2-methyltridecan-1-ol. The alcohol may be a mixture of n-alcohols and alcohols having a single methyl branch. It is preferred to use pure alcohols rather than the commercially available alcohol mixtures, however if mixtures are used.

The comb polymers can in particular be fumarate or itaconate polymers and copolymers, such as those described in EP-A-153 176, EP-A-153 177, EP-A-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 12 to 20 carbon atoms, in particular polymers in which the alkyl groups have 14 carbon atoms or in which the alkyl groups are a mixture of C₁₄/C₁₆ alkyl groups, which can be prepared, 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. fetch which are preferably straight chain alcohols. When the mixture is used, it is advantageously a 1:1 (w:w) mixture of nC₁₄ and nC₁₆ alcohols. In addition, mixtures of C₁₄ esters with the mixed C₁₄/C₁₆ ester can advantageously be used. In such mixtures, the ratio of C₁₄ to C₁₄/C₁₆ is advantageously in the range of 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 are those having a number average molecular weight in the range of 1,000 to 100,000, preferably 1,000 to 30,000, as measured by vapor phase osmometry.

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. Mixtures of two or more comb polymers can be used in accordance with the invention and, as previously stated, this use can be advantageous.

(ii) Polyoxyalkylene compounds

Examples are polyoxyalkylene esters, ethers, ester/ethers and mixtures thereof, especially those containing at least one, preferably at least two linear saturated C₁₀ to C₃₀ alkyl groups and a polyoxyalkylene glycol group having a molecular weight of up to 5000, preferably 200 to 5000, where the alkyl group in the polyoxyalkylene glycol contains 1 to 4 carbon atoms. These materials form the subject of EP-A-0 061 895. Other such additives are described in US-A-4 491 455.

The preferred esters, ethers or ester/ethers that can be used can be represented in their structure by the formula

R-O-(A)-O-R²

in which R and R² are equal or different and

(a) n-alkyl,

where n is, for example, 1 to 30, the alkyl group is linear and saturated and contains 10 to 30 carbon atoms and A represents the polyoxyalkylene 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 branching with lower alkyl side chains (as in polyoxypropylene glycol) may be present, but it is preferred that the glycol be substantially linear. A may also contain nitrogen.

Examples of suitable glycols are essentially linear polyethylene glycols (PEG) and polypropylene glycols (PPG) having a molecular weight of about 100 to 5000, preferably about 200 to 2000. Esters are preferred and fatty acids containing 10 to 30 carbon atoms are useful for reacting with the glycols to form the ester additives, it being preferred to use a C18 to C24 fatty acid, particularly behenic acid. The esters can also be prepared by esterification of polyethoxylated fatty acids or polyethoxylated alcohols.

Polyoxyalkylene diesters, diethers, ethers/esters and mixtures thereof are suitable as additives, with diesters being preferred for use in narrow-boiling distillates when Small amounts of monoethers and monoesters (often formed in the manufacturing process) may also be present. It is important for additive performance that a larger amount of the dialkyl compound is present. In particular, stearic or behenic diesters of polyethylene glycol, polypropylene glycol or polyethylene/polypropylene glycol blends are preferred.

Other examples of polyoxyalkylene compounds are those described in Japanese Patent Publications Nos. 2-51477 and 3-34790 (both to Sanyo) and the esterified alkoxylated amines described in EP-A-117 108 and EP-A-326 356 (both to Nippon Oil and Fats).

(iii) Ethylene/unsaturated ester copolymers

Ethylene copolymer flow improvers have a polymethylene backbone divided into segments by oxyhydrocarbon side chains, i.e. ethylene/unsaturated ester copolymer cold flow improver. The unsaturated monomers copolymerizable with ethylene to form the copolymers include unsaturated mono- and diesters having the general formula

in which R¹ is hydrogen or a methyl group, R² is a -OOCR⁴ or -COOR⁴ group, where R⁴ is hydrogen or a straight-chain or branched C₁- to C₂₈₈, preferably C₁- to C₁₆, especially C₁- to C₈₃ alkyl group, with the proviso that R⁴ is not hydrogen when R² is -COOR⁴, and R³ is hydrogen or -COOR⁴.

The monomer includes, when R² and R³ are hydrogen and R¹ is -OOCR⁴, vinyl alcohol esters of C₁-C₂₉, preferably C₁-C₅ monocarboxylic acids and preferably C₂-C₂₉, more preferably C₁-C₅ monocarboxylic acids, most preferably C₂-C₅ monocarboxylic acids. Examples of vinyl esters reacted with ethylene include vinyl acetate, vinyl propionate and vinyl butylate or isobutyrate, with vinyl acetate and vinyl propionate being preferred. Preferably the copolymers contain from 5 to 40% by weight of the vinyl ester, especially from 10 to 35% by weight of the vinyl ester. They may also be in the form of mixtures of two copolymers such as those described in US-A-3,961,916. Preferably the number average molecular weight of the copolymer as measured by vapor phase osmometry is from 1,000 to 10,000, especially from 1,000 to 5,000. If desired the copolymer may be derived from additional comonomers, e.g. they may be terpolymers or tetrapolymers or higher polymers, for example the additional comonomer being isobutylene or diisobutylene.

Such copolymers can also be prepared by transesterification or by hydrolysis and re-esterification of ethylene/unsaturated ester copolymer to give another ethylene/unsaturated ester copolymer. For example, ethylene/vinyl hexanoate and ethylene/vinyl octanoate copolymers can be prepared in this way, e.g. from an ethylene/vinyl acetate copolymer.

(iv) Polar organic nitrogen-containing compounds

The oil-soluble polar nitrogen compound is either ionic or non-ionic and is capable of acting as a wax crystal growth modifier in fuels. It comprises, for example, one or more of the compounds (a) to (c) as follows:

(a) Amine salt and/or amide formed by reacting at least a molar proportion of hydrocarbon-substituted amine with a molar proportion of hydrocarbon acid having 1 to 4 carboxylic acid groups or its anhydride.

Esters/amides with a total of 30 to 300, preferably 50 to 150 carbon atoms can be used. These nitrogen compounds are described in US-A-4 211 534. Suitable amines are usually long-chain C₁₂ to C₄₀ primary, secondary, tertiary or quaternary amines or mixtures thereof, However, shorter chain amines may be used provided that the resulting nitrogen compound is oil soluble and therefore normally contains about 30 to 300 carbon atoms in total. The nitrogen compound preferably contains at least one straight chain C₈- to C₄₀-, preferably C₁₄- to C₂₄-alkyl segment.

Suitable amines include primary, secondary, tertiary or quaternary, but preferably secondary. Tertiary and quaternary amines can only form amine salts. Examples of amines include tetradecylamine, coco-amine and hydrogenated tallow amine. Examples of secondary amines include dioctadecylamine and methylbehenylamine. Amine mixtures are also suitable, such as those derived from natural materials. A preferred amine is a secondary hydrogenated tallow amine having the formula HNR¹R², in which R¹ and R² are alkyl groups derived from hydrogenated tallow fat and composed of approximately 4 wt% C₁₄, 3.1 wt% C₁₆ and 59 wt% 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 naphthalenedicarboxylic 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 benzenedicarboxylic acids such as phthalic acid, isophthalic acid and terephthalic acid. Phthalic acid or its anhydride is especially preferred. The especially preferred compound is the amide/amine salt prepared by reacting one molar proportion of phthalic anhydride with 2 molar proportions of di(hydrogenated tallow)amine. Another preferred compound is the diamide prepared 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 are described, for example, in US-A-4 147 520. Suitable amines may be those described above.

Other examples are condensates as described in EP-A-327 423.

(b) A chemical compound comprising or including a cyclic ring system, wherein the compound has at least two substituents having the following general formula (I)

-A-NR¹R² (I)

on the ring system, in which A is an aliphatic hydrocarbon group, optionally interrupted by one or more heteroatoms and is straight-chain or branched, and R¹ and R² are the same or different and each independently is a hydrocarbon group having 9 to 40 carbon atoms, optionally interrupted by one or more heteroatoms, where the substituents are the same or different and the compound is optionally in the form of its salt.

Preferably, A has 1 to 20 carbon atoms and is preferably a methylene or polymethylene group.

The term "hydrocarbon" as used in the specification refers to a group having a carbon atom directly attached to the remainder of the molecule and having 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 preferably saturated. These groups may contain non-hydrocarbon substituents provided that their presence does not alter the predominantly hydrocarbon character of the group. Examples include keto, halogen, hydroxy, nitro, cyano, alkoxy and acyl. When the hydrocarbon group is substituted, a single (mono) substituent is preferred.

Examples of substituted hydrocarbon 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 heteroatoms include, for example, nitrogen, sulfur and, preferably, oxygen.

The cyclic ring system may include homocyclic, heterocyclic or fused polycyclic structures or a system in which two or more such cyclic structures are linked together and in which the cyclic structures may be the same or different. When two or more such cyclic structures are present, the substituents of general formula (I) may be on the same or different structures, preferably on the same structure. Preferably the or each cyclic structure is aromatic, especially a benzene ring. Most preferably the cyclic ring system is a single benzene ring, it being preferred that the substituents are in ortho or meta positions, the benzene ring may optionally be further substituted.

The ring atoms in the cyclic structure or structures are preferably carbon atoms, but may include, for example, one or more N, S or O atoms in the ring, in which case or cases the compound is a heterocyclic compound.

Examples of such multinuclear structures include :

(i) condensed benzene structures such as naphthalene, anthracene, phenanthrene and pyrene,

(ii) fused ring structures in which none or not all of the rings are benzene, such as azulene, indene, hydroindene, fluorene and diphenylene oxides,

(iii) end-to-end connected rings such as diphenyl,

(iv) heterocyclic compounds such as quinoline, indole, 2,3-dihydroindole, benzofuran, coumarin, isocoumarin, benzothiophene, carbazole and thiodiphenylamine,

(v) non-aromatic or partially saturated ring systems such as decalin (i.e. decahydronaphthalene), α-pinene, cardinene and bornylene, and

(vi) three-dimensional structures such as norbornene, bicycloheptane (i.e. norbornane), bicyclooctane and bicyclooctene.

Each hydrocarbon group forming R¹ and R² in the invention (formula I) may, for example, be an alkyl or alkylene group or mono- or polyalkoxyalkyl group. Preferably, each hydrocarbon group is a straight-chain alkyl group. The number of carbon atoms in each hydrocarbon group is preferably 16 to 40, especially 16 to 24.

It is also preferred that the cyclic system is substituted with only two substituents having the general formula (I) and that A is a methylene group.

Examples of salts of chemical compounds are acetate and hydrochloride.

The compounds may be conveniently prepared by reducing the corresponding amide, which is prepared by reacting a secondary amine with the corresponding acid chloride, and

(c) Condensate of long chain primary or secondary amine with carboxylic acid containing polymer.

Specific examples include polymers as described in GB-A-2 121 807, FR-A-2 592 387 and DE-A-39 41 561, and also esters of telomer acid and alkanolamines as described in US-A-4 639 256, reaction product of long chain epoxide and amine which may optionally have been further reacted with polycarboxylic acid, and the reaction product of amine containing branched carboxylic acid ester, epoxy and monocarboxylic acid polyester as described in US-A-4 631 071.

Hydrocarbon polymers

Examples are those with the following general formula:

in the

T = H or R¹ is

U = H, T or Aryl

R¹ is a C₁ to C₃₀ hydrocarbon, and v and w represent molar ratios, where v is in the range of 1.0 to 0.0 and w is in the range of 0.0 to 1.0.

These polymers can be prepared directly from ethylenically unsaturated monomers or indirectly by hydrogenating the polymer prepared from monomers such as isoprene and butadiene.

Preferred hydrocarbon polymers are copolymers of ethylene and at least one α-olefin having a number average molecular weight of at least 30,000. Preferably the α-olefin has at most 20 carbon atoms. Examples of such olefins are propylene, 1-butene, isobutene, n-octene-1, isooctene-1, n-decene-1 and n-dodecene-1. The copolymer may also contain 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, as shown above, at least 30,000 as measured by gel permeation chromatography (GPC) relative to polystyrene standards, advantageously at least 60,000 and preferably at least 80,000. Functionally there is no upper limit, but mixing problems result due to increased viscosity at molecular weights above about 150,000, and preferred molecular weight ranges are 60,000 and 80,000 to 120,000.

Advantageously, the copolymer has a molar ethylene content between 50 and 85%. Particularly advantageously, the ethylene content is in the range of 57 to 80% and preferably in the range of 58 to 73%, in particular 62 to 71% and most preferably 65 to 70%.

Preferred ethylene/α-olefin copolymers are ethylene/propylene copolymers with a molar ethylene content of 62 to 71% and an average molecular weight (number average) in the range of 60,000 to 120,000, particularly preferred copolymers are ethylene/propylene copolymers with an ethylene content of 62 to 71% and a molecular weight of 80,000 to 100,000.

The copolymers can be prepared by any of the methods known in the art, for example using a Ziegler-type catalyst. Advantageously, the polymers are essentially amorphous, since highly crystalline polymers are relatively insoluble in fuel oil at low temperatures.

The additive composition may also comprise a further ethylene/α-olefin copolymer, advantageously having a number average molecular weight of at most 7500, advantageously 1000 to 6000 and preferably 2000 to 5000, as measured by vapor phase osmometry. Suitable α-olefins are as indicated above or styrene, with propylene again being preferred. Advantageously, the ethylene content is 60 to 77 mole percent, although in ethylene/propylene copolymers up to 86 mole percent ethylene may advantageously be used.

Examples of hydrocarbon polymers are described in WO-A-91/11488.

Sulfur carboxy compounds

Examples are those described in EP-A-0 261 957, which describes the use of compounds having the general formula

describes in which

-Y-R² is -SO₃(-)(+)NR³₃R², -SO₃(-)(+)HNR³₂R², -SO₃(-)(+)H₂NR³R², -SO₃(-)(+)H₃NR², -SO₃(-)(+)NR³R² or -SO₃R² and

-X-R¹ -Y-R² or -CONR³R¹, -CO₂(-)(+)NR³₃R¹, -CO₂(-)(+)HNR³₂R¹, -R⁴-COOR₁, -NR³COR¹, -R⁴OR¹, -R⁴OCOR¹, -R⁴R¹, -N(COR³)R¹ or Z(-)(+)NR³₃R¹ where -Z(-) is SO₃(-) or -CO₂(-).

R¹ and R² are alkyl, alkoxyalkyl or polyalkoxyalkyl with at least 10 carbon atoms in the main chain,

R³ is hydrocarbon, where each R³ may be the same or different, and

R⁴ is absent or is C₁- to C₅-alkylene, and in

the carbon-carbon bond (C-C) is either a) ethylenically unsaturated, when A and B can be alkyl, alkenyl or substituted hydrocarbon groups, or b) is part of a cyclic structure which can be aromatic, polynuclear aromatic or cycloaliphatic. It is preferred that X-R¹ and Y-R² contain at least three alkyl, alkoxyalkyl or polyalkoxyalkyl groups between them.

(vii) Aromatics with hydrocarbon residues

These materials are condensates comprising aromatic and hydrocarbon moieties. The aromatic moiety is conveniently an aromatic hydrocarbon which is unsub or substituted with, for example, non-hydrocarbon substituents.

Such an aromatic hydrocarbon preferably contains a maximum of these substituent groups and/or three condensed rings and is preferably naphthalene. The hydrocarbon moiety is a hydrogen and carbon containing moiety which is bonded to the rest of the molecule via a carbon atom. It may be saturated or unsaturated and straight-chain or branched and may contain one or more heteroatoms provided that they do not significantly affect the hydrocarbon character of the moiety. Preferably the hydrocarbon moiety is an alkyl moiety, suitably having more than 8 carbon atoms. The molecular weight of such condensates may, for example, be in the range of 2000 to 200,000, such as 2000 to 20,000, preferably 2000 to 8000.

Examples are known in the art, mainly as lubricating oil pour point depressants and as dewaxing aids as previously mentioned. They can be prepared, for example, by condensing halogenated wax with aromatic hydrocarbon. Specifically, the condensation can be a Friedel-Krafts condensation in which the halogenated wax contains 15 to 60, e.g. 16 to 50, carbon atoms, has a melting point of about 200 to 400°C and has been chlorinated to 5 to 25 wt% chlorine, e.g. 10 to 18 wt%.

Another way to produce similar condensates can be from olefins and the aromatic hydrocarbons.

Multi-component additive systems can be used and the ratios of additives to be used depend on the fuel being treated.

Examples

The invention will now be specifically described, by way of example only, as follows.

example 1 Additive

The following additives were used:

A: Ethylene/vinyl acetate copolymer having a vinyl acetate concentration of about 37 wt.% and a number average molecular weight of about 2700.

B: A 3:1 (wt:wt) blend of Additive A above and an ethylene/vinyl acetate copolymer having a vinyl acetate concentration of about 13.5 wt% and a number average molecular weight of about 5,000.

C: Mixture containing the same compounds as B, but the w:w ratio is 13:1.

Number average molecular weights are measured by vapor phase osmometry (VPO).

test

Additives A, B and C were each dissolved in samples of the same rapeseed methyl ester fuel and the cold filter plugging point (CFPP) was measured according to the procedure described in detail in "Journal of the Institute of Petroleum", Volume 52, No. 510, June 1966, pages 173 to 285. The CFPP is a measure of filterability.

The results are shown in the table below:

In comparison, the CFPP of the untreated fuel was -9ºC. It can therefore be seen that additives A, B and C each improved the filterability of the fuel as measured by the CFPP test.

Claims (11)

1. A composition comprising a major proportion of oil consisting essentially of alkyl esters of fatty acids derived from vegetable or animal oils or both, mixed with a minor proportion of mineral oil cold flow improver containing one or more of the following: (i) comb polymer which is a copolymer of maleic anhydride or fumaric acid and another ethylenically unsaturated monomer, which copolymer may be esterified, or a polymer or copolymer of α-olefin, or a fumarate or itaconate polymer or copolymer, (ii) polyoxyalkylene esters, esters/ethers or a mixture thereof, (iii) ethylene/unsaturated ester copolymer, (iv) polar, organic, nitrogen-containing paraffin crystal growth inhibitor, (v) hydrocarbon polymer, (vi) sulphur carboxy compounds and (vii) aromatic pour point depressant containing hydrocarbon radicals provided that the composition does not comprise mixtures of polymeric esters or copolymers of esters of acrylic and/or methacrylic acid derived from alcohols having 1 to 22 carbon atoms. 2. Composition according to claim 1, wherein the polyoxyalkylene ester, ester/ether or mixture thereof (ii) is represented by the formula R-O-(A)-O-R² is defined in which R and R² are equal or different and (a) n-alkyl, wherein n is 1 to 30, the alkyl group is linear and saturated and contains 10 to 30 carbon atoms, and A is a polyoxyalkylene segment having a molecular weight of 100 to 5000 in which the alkylene group has 1 to 4 carbon atoms. 3. Composition according to claim 1, in which the polar, organic, nitrogen-containing paraffin crystal growth inhibitor is an amine salt and/or amide which has been formed by reacting at least one molar proportion of hydrocarbon-substituted amine with a molar proportion of hydrocarbon acid with 1 to 4 carboxylic acid groups or its anhydride, preferably a benzenedicarboxylic acid or its anhydride. 4. A composition according to claim 1, wherein the comb polymer is (i) a copolymer of alkyl fumarate and vinyl acetate in which the alkyl groups have 12 to 20 carbon atoms, or an esterified copolymer of styrene and maleic anhydride or an esterified copolymer of styrene and fumaric acid. 5. Composition according to one of the preceding claims, in which the alkyl esters of fatty acids are the ethyl, propyl, butyl and in particular methyl esters of fatty acids having 12 to 22 carbon atoms. 6. A composition according to claim 5, wherein the alkyl esters are the methyl esters of oleic acid, linoleic acid and erucic acid. 7. A composition according to claim 1, wherein the oil is rapeseed oil methyl ester. 8. Composition according to one of the preceding claims, in which the alkyl esters of fatty acids have been prepared by transesterification of animal or vegetable oils. 9. A composition according to any preceding claim, wherein the additive comprises an ethylene/vinyl ester copolymer (iii) or mixture of copolymers thereof. 10. Use of mineral oil cold flow additive for modifying the wax crystal growth properties of oil consisting essentially of alkyl esters of fatty acids derived from vegetable or animal oils or both, wherein the additive comprises one or more of the following: (i) comb polymer which is a copolymer of maleic anhydride or fumaric acid and another ethylenically unsaturated monomer, which copolymer may be esterified, or a polymer or copolymer of α-olefin, or a fumarate or itaconate polymer or copolymer, (ii) polyoxyalkylene esters, esters/ethers or a mixture thereof, (iii) ethylene/unsaturated ester copolymer, (iv) polar, organic, nitrogen-containing paraffin crystal growth inhibitor, (v) hydrocarbon polymer, (vi) sulphur carboxy compounds and (vii) aromatic pour point depressant containing hydrocarbon radicals provided that the additive does not comprise mixtures of polymeric esters or copolymers of esters of acrylic and/or methacrylic acid derived from alcohols having 1 to 22 carbon atoms. 11. A process for modifying the wax crystal growth properties of oil consisting essentially of alkyl esters of fatty acids derived from vegetable or animal oils or both, which comprises mixing with the additive as defined in claim 1, with the proviso that the additive does not comprise mixtures of polymeric esters or copolymers of esters of acrylic and/or methacrylic acid derived from alcohols having 1 to 22 carbon atoms.