DE69317614T2 - Gasoline composition - Google Patents

Abstract

The invention provides a gasoline composition comprising a major amount of a gasoline suitable for use in spark-ignition engines, a minor amount of a polyalphaolefin having a viscosity at 100 DEG C in the range 2 x 10<-><6> to 2 x 10<-><5> m<2>/s (2 to 20 centistokes), being a hydrogenated oligomer containing 18 to 80 carbon atoms derived from at least one alphaolefinic monomer containing from 8 to 16 carbon atoms, and a minor amount of a polyoxyalkylene compound selected from glycols, mono- and diethers thereof, having number average molecular weight (Mn) in the range 400 to 3000, the weight ratio polyalphaolefin: polyoxyalkylene compound being in the range 1:10 to 10:1; a concentrate for the preparation of such gasoline composition and a method of operating a spark-ignition engine using such gasoline composition.

Description

The present invention relates to gasoline compositions containing a major amount of a gasoline suitable for use in spark-ignition engines and a minor amount of at least one additive, as well as to additive concentrates suitable for addition to gasoline to prepare such gasoline compositions.

EP-A-290 088 describes gasoline compositions containing a major amount of a gasoline suitable for use in spark-ignition engines and a minor amount of a polyalphaolefin having a viscosity at 100°C of 2x10-6 to 2x10-5 m2/s (2 to 20 centistokes), preferably a hydrogenated oligomer having 18 to 80 carbon atoms derived from an α-olefinic monomer having 8 to 12 carbon atoms, and optionally minor amounts of an oil-soluble aliphatic polyamine and/or an alkali metal or alkaline earth metal salt of a succinic acid derivative having a polyolefin substituent on at least one of its carbon atoms and/or a polyolefin derived from a C2 to C6 monomer and has a number average molecular weight (Mn) of 500 to 1500.

US Patent 3,901,665 describes liquid hydrocarbon fuel compositions characterized by improved anti-icing and improved carburetor cleanliness, comprising

A. a major quantity of a liquid hydrocarbon fuel containing hydrocarbons boiling in the petrol range and, based on the weight of that fuel,

B. about 0.01 to about 0.06 wt. % of a 3- or 4-carbon olefin, preferably polyisobutylene, having a molecular weight of about 400 to about 1400, preferably about 400 to about 900, and

C. from about 0.008 to about 0.016 wt.% of a polyoxyalkylene compound having the formula

wherein R is alkyl having 1 to 20 carbon atoms, preferably 10 to 18 carbon atoms and x has an average value of 4 to 20; and additive compositions consisting essentially of B and C.

U.S. Patent 3,658,494 discloses fuel compositions containing a major amount of at least one normally liquid fuel and a minor amount of an additive combination soluble in said fuel, said additive combination comprising (a) at least one oxy compound which is a monoether of a glycol or polyglycol and (b) at least one fuel soluble dispersant selected from the class consisting of esters, amides, imides, amidines and amine salts of at least one substantially saturated carboxylic acid characterized by the presence in the acyl radical thereof of at least 30 aliphatic carbon atoms, the weight ratio of oxy compound to dispersant being from about 0.1:1 to about 1:0.1, but preferably from 0.1:1 to about 2.5:1. In the examples, the oxy compounds used are ethylene glycol mono-n-butyl ether, dipropylene glycol monomethyl ether, triethylene glycol monoethyl ether and ethylene glycol monophenyl ether.

EP-A-384 605 describes a motor fuel composition comprising a mixture of hydrocarbons boiling in the petrol boiling range and additionally (i) the reaction product of a defined hydrocarbyl-substituted dibasic acid with a defined polyoxyalkylene diamine, (ii) a polymer component which is a polyolefin polymer, a copolymer or the corresponding aminated or hydrogenated polymer or copolymer or mixtures thereof, of a C₂₋₁₀ hydrocarbon, which polyolefin polymer or copolymer has a molecular weight in the range 500 to 10,000; (iii) a polyalkylene glycol having a molecular weight in the range 500 to 2,000; and (iv) a lubricating oil. With respect to (ii) it is stated (page 9, lines 39,40) that in general the olefin monomers, from which the polyolefin polymer component is prepared are preferably C₂-6 unsaturated hydrocarbons. The polyalkylene glycol (iii) is said (page 10, lines 39,40) to be preferably selected from the group consisting of polyethylene glycol, polypropylene glycol and polybutylene glycol.

EP-A-526 129 (published February 3, 1993) describes a fuel additive concentrate for combating octane demand increase in internal combustion engines comprising the reaction product of (i) polyamine and (ii) at least one acyclic hydrocarbyl substituted succinic acylating agent and a non-hydrotreated poly-α-olefin. While EP-A-526 129 further and more specifically provides a fuel composition comprising an amount of a gasoline boiling range hydrocarbon or hydrocarbon oxygenate mixtures or oxygenates and a small but effective amount of (a) a fuel additive comprising the reaction product of (i) polyamine and (ii) at least one acyclic hydrocarbyl substituted succinic acylating agent; (b) a non-hydrotreated poly-α-olefin having a volatility of about 50% or less as determined by a test method described therein; (c) and optionally (A) a mineral oil having a viscosity index of less than about 90 and a volatility of 50% or less as determined by a test method described therein; (B) an antioxidant, or (C) a demulsifier, or (D) an aromatic hydrocarbon solvent, or (E) a corrosion inhibitor, or any combination of any two, three, four or all five of components (A), (B), (C), (D) and (E), it is clearly an essential feature that the present polyα-olefin be a non-hydrotreated poly-α-olefin. The demulsifier (c) includes polyoxyalkylene glycols and oxyalkylated phenolic resins, and particularly mixtures thereof.

Surprisingly, it has now been found that gasolines containing combinations of particular poly-α-olefins and particular polyoxyalkylene glycol derivatives can surprisingly provide improved engine performance, expressed in terms of a beneficial combination of minimized engine intake system deposits and minimized valve sticking.

According to the present invention there is provided a gasoline composition comprising a major amount of a gasoline suitable for use in spark-ignition engines, an amount of a poly-α-olefin having a viscosity at 10,000 in the range 2x10⁻⁶ to 2x10⁻⁵ m²/s (2 to 20 centistokes), which is a hydrogenated oligomer having 18 to 80 carbon atoms, derived from at least one α-olefinic monomer having 8 to 16 carbon atoms, and comprises an amount of a polyoxyalkylene compound selected from glycols, mono- and diethers thereof having a number average molecular weight (Mn) in the range 400 to 3000, the weight ratio poly-α-olefin:polyoxyalkylene compound being in the range 1:10 to 10:1 and the amount of poly-α-olefin and polyoxyalkylene compound together being in the range 100 to 1500 parts per million by weight, based on the total composition.

The poly-α-olefins used in the gasoline compositions of the invention are predominantly trimers, tetramers and pentamers and the synthesis of such materials is described in Campen et.al., "Growing use of synlubes", Hydrocarbon Processing February 1982, pages 75 to 82. The poly-α-olefin is preferably derived from an α-olefinic monomer having 8 to 12 carbon atoms. Poly-α-olefins derived from decene-1 have been found to be very effective. The poly-α-olefin preferably has a viscosity at 10,000 in the range 6x10-6 to 1x10-5 m2/s (6 to 10 centistokes). A poly-α-olefin with a viscosity at 100ºC of 8x10⊃min;⊃6; m²/s (8 centistokes) has been found to be particularly effective.

The polyoxyalkylene compound can be represented by the formula

wherein R¹ and R² independently represent hydrogen atoms or hydrocarbyl groups, preferably C₁₋₄₀-hydrocarbyl groups, for example alkyl, cycloalkyl, phenyl or alkylphenyl groups, each R independently represents an alkylene group, preferably a C₂₋₈-alkylene group and n represents a such that Mn of the polyoxyalkylene compound is in the range 400 to 3000, preferably 700 to 2000, more preferably 1000 to 1500.

Preferably, R¹ is a C₈₋₂₀-alkyl group and R² is a hydrogen atom. R¹ is preferably a C₁₀₋₁₈-alkyl group, more preferably a C₁₂₋₁₅-alkyl group. The residue R¹ can easily be a mixture of C₁₂₋₁₅-alkyl groups.

In formula I, the groups R are preferably 1,2-alkylene groups.

Preferably, each R group independently represents a C2-4 alkylene group, for example an ethylene or 1,2-propylene group. Very effective results have been obtained using polyalkylene compounds wherein each R group represents a 1,2-propylene group.

The poly-α-olefin and the polyoxyalkylene compound may advantageously be present together in the gasoline composition in an amount of 100 to 1200 parts per million by weight, preferably 100 to 600 parts per million by weight, more preferably 150 to 500 parts per million by weight, based on the total composition.

The weight ratio of poly-α-olefin:polyoxyalkylene compound in the gasoline composition is preferably in the range 1:8 to 8:1, more preferably 1:5 to 5:1. Weight ratios in the range 1:4 to 4:1 have been found to be very effective.

The gasoline compositions of the present invention also desirably contain a small amount of at least one hydrocarbon-soluble ashless dispersant. The compounds useful as ashless dispersants are generally characterized by a "polar" group attached to a relatively high molecular weight hydrocarbon chain. The "polar" group generally contains one or more of the elements nitrogen, oxygen and phosphorus. The solubilizing chains generally have a higher molecular weight than those chains associated with the metal types are used; but in some cases they can be quite similar.

In general, any of the ashless dispersants known in the art for use in lubricants and fuels can be employed in the gasoline compositions of the present invention.

In one embodiment of the present invention, the dispersant is selected from the group consisting of

(i) at least one hydrocarbyl-substituted amine, wherein the hydrocarbyl substituent is substantially aliphatic and contains at least 8 carbon atoms;

(ii) at least one acylated nitrogen-containing compound having a hydrocarbon-based substituent of at least 10 aliphatic carbon atoms, prepared by reacting a carboxylic acid acylating agent with at least one amino compound containing at least one -NH- group, which acylating agent is linked to the amino compound via an imido, amido, amidine or acyloxyammonium linkage;

(iii) at least one nitrogen-containing condensate of a phenol or aldehyde with an amino compound having at least one -NH- group;

(iv) at least one ester of a substituted carboxylic acid;

(v) at least one polymeric dispersant;

(vi) at least one hydrocarbon-substituted phenolic dispersant; and

(vii) at least one fuel-soluble alkoxylated derivative of an alcohol, phenol or amine.

The hydrocarbyl-substituted amines used in the gasoline compositions of the present invention are well known to those skilled in the art and are described in several patents. These include U.S. Patents 3,275,5541, 3,438,757, 3,454,555, 3,565 804, 3,755,433 and 3,822,209. These patents describe suitable hydrocarbyl-substituted amines for use in the present invention, including their method of preparation.

A typical hydrocarbyl-substituted amine has the general formula

wherein A is hydrogen, 1 is a hydrocarbyl group having 1 to 10 carbon atoms or a hydroxyhydrocarbyl group having 1 to 10 carbon atoms; X is hydrogen, a hydrocarbyl group having 1 to 10 carbon atoms or a hydroxyhydrocarbyl group having 1 to 10 carbon atoms, and together with A and N can form a ring of 5 to 6 ring members and up to 12 carbon atoms; U is an alkylene group having 2 to 10 carbon atoms, any hydrocarbons required to accommodate the trivalent nitrogens being included herewith, R³ is an aliphatic hydrocarbon having 30 to 400 carbon atoms; Q is a piperazine structure; a is an integer from 0 to 10; b is an integer from 0 to 1; a+2b is an integer from 1 to 10; c is an integer from 1 to 5 and on average is in the range from 1 to 4, and is equal to or less than the number of nitrogen atoms in the molecule; x is an integer from 0 or 1, y is an integer from or 1; and x+y is 1.

When interpreting this formula, it is important to note that the R³ and H atoms are bonded to the unsatisfied nitrogen valencies within the brackets of the formula. The formula thus includes, for example, sub-generic formulas in which the R³ radical is bonded to terminal nitrogen atoms and isomeric sub-generic formulas in which the radical is bonded to non-terminal nitrogen atoms. Nitrogen atoms not bonded to an R³ radical can carry a hydrogen or an AXN substituent.

The hydrocarbyl-substituted amines useful in the present invention and encompassed by the above formula II include monoamines such as poly(propylene)amine, N,N-dimethyl-n-poly(ethylene/propylene)amine (molar ratio of monomers 50:50), poly(isobutene)amine, N,N-di(hydroxyethyl)-N-poly(isobutene)amine, poly(isobutene/1-butene/2-butene)amine (molar ratio of monomers 50:25:25), N-(2-hydroxyethyl)-N-poly(isobutene)amine, N-(2-hydroxypropyl)-N-poly(isobutene)amine, N-poly(1-butene)aniline and N-poly-(isobutene)morpholine; and polyamines such as N-poly(isobutene)ethylenediamine, N-poly(propylene)trimethylenediamine, N-poly(1-butene)diethylenetriamine, N',N'-poly(isobutene)tetraethylenepentamine, N,N-dimethyl-N'-poly(propylene)amine and 1,3-propylenediamine.

The hydrocarbyl-substituted amines useful in the gasoline compositions of the invention also include certain N-aminohydrocarbylmorpholines having the general formula:

R³N(A)UM (III),

wherein R³ represents an aliphatic hydrocarbon group having 30 to 400 carbon atoms, A represents hydrogen, a hydrocarbyl group having 1 to 10 carbon atoms, or a hydroxyhydrocarbyl group having 1 to 10 carbon atoms, U represents an alkylene group having 2 to 10 carbon atoms, and M is a morpholine structure. These hydrocarbyl-substituted aminohydrocarbylmorpholines, as well as the polyamines described by formula (II), are among the typical hydrocarbyl-substituted amines used in preparing the compositions of the present invention.

A number of acylated nitrogen-containing compounds having a hydrocarbon-based substituent with at least 10 aliphatic carbon atoms, which are prepared by reacting a carboxylic acid acylating agent with an amino compound, are known to those skilled in the art. The acylating agent is linked to the amino compound via an imido, amido, amidine or acyloxyammonium linkage. The hydrocarbon-based substituent with at least 10 aliphatic carbon atoms can be present either in the part of the molecule derived from the carboxylic acid acylating agent or in the part of the molecule derived from the amino compound. Preferably, however, it is present in the acylating agent part. The acylating agent can range from formic acid and its acylating derivatives to acylating agents with high molecular weight aliphatic Substituents of up to 5000, 10000 or 20000 carbon atoms. The amino compounds can range from ammonia itself to amines with aliphatic substituents of up to 30 carbon atoms.

A typical class of acylated nitrogen-containing compounds useful in the compositions of the present invention are those obtained by reacting an acylating agent having an aliphatic substituent of at least 10 carbon atoms and a nitrogen compound characterized by the presence of at least one -NH group. Typically, the acylating agent will be a mono- or polycarboxylic acid (or a reactive equivalent thereof) such as a substituted succinic acid or propionic acid, and the amino compound will be a polyamine or a mixture of polyamines, most typically a mixture of ethylene polyamines. The amine may also be a hydroxyalkyl-substituted polyamine. The aliphatic substituent in such acylating agents has on average at least 30 or 50 and up to 400 carbon atoms.

Exemplary hydrocarbon-based substituent groups containing at least ten aliphatic carbon atoms are n-decyl, n-dodecyl, tetrapropenyl, n-octadecyl, oleyl, chlorooctadecyl and triicontanyl. In general, the hydrocarbon-based substituents are prepared from homo- or interpolymers (e.g., copolymers, terpolymers) of mono- and diolefins having 2 to 10 carbon atoms, such as ethylene, propylene, butene-1, isobutene, butadiene, isoprene, 1-hexene and 1-octene. Typically, these olefins are 1-monoolefins. The substituent can also be derived from the halogenated (e.g., chlorinated or brominated) analogues of such homo- or interpolymers. However, the substituent may be derived from other sources such as monomeric, high molecular weight alkenes (for example 1-tetracontene) and chlorinated analogues and hydrochlorinated analogues thereof, from aliphatic petroleum fractions, in particular paraffin waxes and cracked and chlorinated analogues and hydrochlorinated analogues thereof, from white oils, synthetic alkenes such as those produced by the Ziegler-Natta process (for example poly(ethylene) greases) and from other sources known to those skilled in the art. Any unsaturation in the substituents can be reduced or eliminated by hydrogenation according to methods known in the art.

The term "hydrocarbon-based" as used in this specification refers to a group having a carbon atom directly attached to the remainder of the molecule and having a predominantly hydrocarbon character in the context of the present invention. Hydrocarbon-based groups may therefore contain up to one non-hydrocarbon group for every 10 carbon atoms, provided that this non-hydrocarbon group does not appreciably alter the predominantly hydrocarbon character of the group. Such groups are known to those skilled in the art and include, for example, hydroxyl, halogen (especially chlorine and fluorine), alkoxy, alkylmercapto and alkylsulfoxy groups. Typically, however, the hydrocarbon-based substituents are pure hydrocarbyls and do not contain any such non-hydrocarbyl groups.

The hydrocarbon-based substituents are essentially saturated, i.e. they contain no more than one unsaturated carbon-carbon bond for every 10 carbon-carbon single bonds present. Typically they contain no more than one non-aromatic unsaturated carbon-carbon bond for every 50 carbon-carbon bonds present.

The hydrocarbon-based substituents are also essentially aliphatic in nature, i.e. they contain no more than one nonaliphatic radical (cycloalkyl, cycloalkenyl or aromatic group) having 6 or fewer carbon atoms for every 10 carbon atoms in the substituent. Usually, however, the substituents contain no more than one such nonaliphatic group for every 50 carbon atoms, and in many cases they contain no nonaliphatic group at all; i.e., the typical substituents are purely aliphatic. Typically, these purely aliphatic substituents are alkyl or alkene groups.

Specific examples of the substantially saturated hydrocarbon-based substituents having an average of more than 30 carbon atoms are the following: a mixture of poly(ethylene/propylene) groups having 35 to 70 carbon atoms, a mixture of oxidatively or mechanically degraded poly(ethylene/propylene) groups having 35 to 70 carbon atoms, a mixture of poly(propylene-1-hexene) groups having 80 to 150 carbon atoms, and a mixture of polyisobutene groups having an average of 50 to 75 carbon atoms.

A preferred source of the substituents are polyisobutenes obtained by polymerizing a C4 refinery stream having a butene content of 35 to 75 wt.% and an isobutene content of 30 to 60 wt.% in the presence of a Lewis acid catalyst such as aluminum trichloride or boron trifluoride. These polyisobutenes contain predominantly (more than 80% of the total repeat units) of repeat isobutene units having the configuration:

-C(CH₃)₂CH₂-.

Examples of amino compounds suitable for the preparation of these acylated compounds are the following:

(1) Polyalkylenepolyamines with the general formula:

(R&sup4;)&sub2;N[P-N(R&sup4;)]mR&sup4; (IV),

wherein each R4 is independently hydrogen, a hydrocarbyl group or a hydroxy-substituted hydrocarbyl group having up to 30 carbon atoms, provided that at least one R4 is hydrogen, m is an integer from 1 to 10 and P is a C1-18 alkylene group;

(2) hydroxyalkyl substituted polyamines, wherein the polyamines are as described above;

(3) heterocyclic substituted polyamines, wherein the polyamines are as described above and the heterocyclic substituent is derived from, for example, piperazine, imidazoline, pyrimidine or morpholine; and

(4) aromatic polyamines with the general formula:

Ar(NR⁴)z (V),

wherein Ar represents an aromatic nucleus having 6 to 20 carbon atoms, each R⁴ is as defined above and z has a value of 2 to 8.

Specific examples of polyalkylenepolyamines of formula IV are ethylenediamine, tetra(ethylene)pentamine, tri(trimethylene)tetramine and 1,2-propylenediamine.

Specific examples of hydroxyalkyl-substituted polyamines include (N-(2-hydroxyethyl)ethylenediamine, N,N'-bis-(2-hydroxyethyl)ethylenediamine and N-(3-hydroxybutyl)tetramethylenediamine.

Specific examples of heterocyclic substituted polyamines are N-2-aminoethylpiperazine, N-2- and N-3-aminopropylmorpholine, N-3-(dimethylamino)propylpiperazine, 2-heptyl-3-(2-aminopropyl)imidazoline, 1,4-bis(2-aminoethyl)piperazine, 1-(2-hydroxyethyl)piperazine and 2-heptadecyl-1-(2-hydroxyethyl)imidazoline.

Specific examples of aromatic polyamines are the various isomeric phenylenediamines and the various isomeric naphthalenediamines.

Numerous patents have described suitable acylated nitrogen compounds, including U.S. Patents 3,172,892, 3,219,666, 3,272,746, 3,310,492, 3,341,542, 3,444,170, 3,455,831, 3,455,832, 3,576,7431, 3,630,904, 3,632,51t, 3,804,763 and 4,234,435. A typical acylated nitrogen-containing compound of this class is that prepared by reacting a polyisobutene-substituted succinic anhydride acylating agent, wherein the polyisobutene substituent has from 50 to 400 carbon atoms, with a mixture of ethylene polyamines having from 3 to 7 amino nitrogen atoms per ethylene polyamine. Another type of acylated nitrogen compound belonging to this class is that obtained by reacting the above-mentioned alkylene amines with the above-mentioned substituted succinic acids or anhydrides and with aliphatic monocarboxylic acids having 2 to 22 carbon atoms. In these types of acylated nitrogen compounds, the molar ratio of succinic acid to monocarboxylic acid is in the range of 1:0.1 to 1:1. Typical monocarboxylic acids are formic acid, acetic acid, dodecanoic acid, butyric acid, oleic acid, stearic acid, the commercial mixture of stearic acid isomers known as isostearic acid, and toluic acid. Such materials are described in more detail in U.S. Patents 3,216,936 and 3,250,715.

Yet another type of acylated nitrogen compound useful in the gasoline compositions of the invention is the product of reacting a monocarboxylic fatty acid having 12 to 30 carbon atoms with the aforementioned alkylene amines, typically ethylene, propylene or trimethylene polyamines having 2 to 8 amino groups, and mixtures thereof. The monocarboxylic fatty acids are generally mixtures of straight and branched chain carboxylic fatty acids having 12 to 30 carbon atoms. A widely used type of acylated nitrogen compound is prepared by reacting the aforementioned alkylene polyamines with a mixture of fatty acids comprising 5 to 30 mole percent straight chain fatty acids and 70 to 95 mole percent branched chain fatty acids. Among the commercially available mixtures are those commonly referred to in the trade as isostearic acid. These mixtures are produced as a by-product of the dimerization of unsaturated fatty acids, as described in U.S. Patents 2,812,342 and 3,260,671.

The branched chain fatty acids may also include those in which the branching is not alkyl in nature, as in phenyl and cyclohexyl stearic acid and in the chlorostearic acids. Branched chain carboxylic acid/alkylene polyamine products have been described, for example, in U.S. Patents 3,110,673, 3,251,853, 3,326,801, 3,337,459, 3,405,064, 3,429,674, 3,468,639 and 3,857,791.

The phenol/aldehyde/amino compound condensates useful as dispersants in the gasoline compositions of the invention include those commonly known as Mannich condensates In general, these are obtained by simultaneously or sequentially reacting at least one compound having active hydrogen, such as a hydrocarbon-substituted phenol (for example an alkylphenol wherein the alkyl groups have on average at least 12 to 400, preferably 30 to 400 carbon atoms), with at least one hydrogen atom bonded to an aromatic carbon, with at least one aldehyde or aldehyde-providing material (typically a formaldehyde precursor) and with at least one amino or polyamino compound bearing at least one NH group. The amino compounds include primary or secondary monoamines having hydrocarbon substituents having 1 to 30 carbon atoms or having hydroxyl-substituted hydrocarbon substituents having 1 to 30 carbon atoms. Another type of typical amino compounds are the polyamines described in connection with the discussion of acylated nitrogen-containing compounds.

Exemplary monoamines include methylethylamine, methyloctadecylamine, aniline, diethylamine, diethanolamine, and dipropylamine. The following patents contain extensive information on Mannich condensates: US Patents 2,459,112, 3,413,347, 3,558,743, 2,962,442, 3,442,808, 3,586,629, 2,984,550, 3,448,047, 3,591,598, 3,036,003, 3,454,4971 3,600,372, 3,166,516, 3,459,661, 3,634,515, 3,236,770, 3,461,172, 3,649,229, 3,355,270, 3,493,520, 3 697 574, 3 368 972 and 3 539 633.

Condensates prepared from sulfur-containing reactants may also be employed in the gasoline compositions of the present invention. Such sulfur-containing condensates are described in U.S. Patents 3,368,972, 3,649,229, 3,600,372, 3,649,659 and 3,741,894. These patents also disclose sulfur-containing Mannich condensates. Generally, the condensates used to prepare compositions of the present invention are prepared from a phenol bearing an alkyl substituent having from 6 to 400 carbon atoms, more typically from 30 to 250 carbon atoms. These typical condensates are prepared from formaldehyde or a C2-7 aliphatic aldehyde and an amino compound such as those described in in the preparation of the acylated nitrogen-containing compounds described above.

These preferred condensates are prepared by reacting one molar proportion of phenol compound with 1 or 2 molar proportions of alkene and 1 to 5 equivalent proportions of amino compound (one equivalent of amino compound is its molecular weight divided by the number of =NH groups present). The conditions under which such condensation reactions are carried out are well known to those skilled in the art.

A particularly preferred class of nitrogen-containing condensation products for use in the gasoline compositions of the present invention are those products prepared by (1) reacting at least one hydroxyaromatic compound containing an aliphatic-based or cycloaliphatic-based substituent having at least 30 carbon atoms and up to 400 carbon atoms with a lower aliphatic C1-7 aldehyde or a reversible polymer thereof in the presence of an alkaline reagent such as an alkali metal hydroxide at a temperature of up to 150°C; (2) substantially neutralizing the intermediate reaction mixture so formed; and (3) reacting the neutralized intermediate with at least one compound containing an amino group having at least one -NH group.

More preferably, these condensates are prepared from (a) phenols bearing a hydrocarbon-based substituent having from 30 to 250 carbon atoms, which substituent is derived from a polymer of propylene, 1-butene, 2-butene or isobutene, and (b) formaldehyde or a reversible polymer thereof (e.g. trioxane, paraformaldehyde) or a functional equivalent thereof (e.g. methylol) and (c) an alkylene polyamine such as ethylene polyamines having from 2 to 10 nitrogen atoms.

The esters useful as dispersants in the gasoline compositions of the invention are derivatives of substituted carboxylic acids wherein the substituent is a substantially aliphatic, substantially saturated hydrocarbon-based group containing at least 30, preferably at least 50 and up to 750 aliphatic carbon atoms. The term "hydrocarbon-based group" as used herein refers to a group having a carbon atom directly attached to the remainder of the molecule and having a predominantly hydrocarbon character within the scope of the present invention. Such groups include the following:

(1) Hydrocarbon groups; i.e. aliphatic groups, aromatically and alicyclic substituted aliphatic groups and the like, of the type known to the person skilled in the art,

(2) substituted hydrocarbon groups; i.e. groups containing non-hydrocarbon substituents which, in the context of the present invention, do not alter the predominantly hydrocarbon character of the group. Suitable substituents will be known to those skilled in the art; examples are halogen, nitro, hydroxy, alkoxy, carbalkoxy and alkylthio.

(3) Hetero groups; i.e. groups which, although predominantly hydrocarbon in character in the context of the present invention, contain atoms other than carbon present in a chain or ring which is otherwise composed of carbon atoms. Suitable hetero atoms will be known to those skilled in the art and include, for example, nitrogen, oxygen and sulfur. Generally, there will be no more than about 3 substituents or hetero atoms, and preferably no more than one substituent or hetero atom for every 10 carbon atoms in the hydrocarbon-based group.

The substituted carboxylic acids are normally prepared by the alkylation of an unsaturated acid or derivative thereof, such as an anhydride, with a source of the desired hydrocarbon-based group. Suitable unsaturated acids and their derivatives include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, itaconic anhydride, citraconic acid, citraconic anhydride, mesaconic acid, glutaconic acid, chloromaleic acid, aconitic acid, crotonic acid, methylcrotonic acid, sorbic acid, 3-hexenoic acid, 10-decenoic acid and 2-pentene-1,3-tricarboxylic acid. Particularly preferred are the unsaturated dicarboxylic acids and their derivatives, in particular maleic acid, fumaric acid and maleic anhydride.

Suitable alkylating agents include polymers and interpolymers of polymerizable olefin monomers having from 2 to 10, usually from 2 to 6, carbon atoms, and derivatives thereof containing polar substituents. Such polymers are substantially saturated (i.e., they contain no more than about 5% olefinic linkages) and substantially aliphatic (i.e., they contain at least 80%, and preferably at least 95%, by weight of units derived from aliphatic monoolefins). Exemplary monomers that can be used to prepare such polymers are ethylene, propylene, 1-butene, 2-butene, isobutene, 1-octene, and 1-decene. Any unsaturated units can be derived from conjugated dienes such as 1,3-butadiene and isoprene; from non-conjugated dienes such as 1,4-hexadiene, 1,4-cyclohexadiene, 5-ethylidene-2-norbornene and 1,6-octadiene; and from trienes such as 1-isopropylidene-3a,4,7,7a-tetrahydroindene, 1-isopropylidene-dicyclopentadiene and 2-(2-methylene-4-methyl-3-pentenyl) [2.2.1]-bicyclo-5-heptene.

A first preferred class of polymers includes those of terminated olefins such as propylene, 1-butene, isobutene and 1-hexene. Especially preferred within this class are polybutenes having predominantly isobutene units. A second preferred class includes terpolymers of ethylene, a C3-8 alpha-monoolefin and a polyene selected from the group consisting of nonconjugated dienes, which are especially preferred, and trienes. Illustrative of these terpolymers is "Ortholeum 2052" manufactured by E.I. Dupont de Nemours & Company, which is a terpolymer containing about 48 mole % ethylene groups, 48 mole % propylene groups and 4 mole % 1,4-hexadiene groups and has an inherent viscosity of 1.35 (8.2 grams of polymer in 10 ml of carbon tetrachloride at 3000).

Processes for the preparation of substituted carboxylic acids and their derivatives are well known in the art and do not require not be described in detail. Reference is made, for example, to US patents 3,272,746, 3,522,179 and 4,234,435. The molar ratio of polymer to unsaturated acid or its derivative can be equal to, greater than or less than 1, depending on the type of product desired.

The esters are those of the substituted carboxylic acids described above with hydroxy compounds, which can be aliphatic compounds such as monohydric and polyhydric alcohols, or aromatic compounds such as phenols and naphthols. Examples of aromatic hydroxy compounds include phenol, beta-naphthol, alpha-naphthol, cresol, resorcinol, catechol, p,p'-dihydroxybiphenyl, 2-chlorophenol, 2,4-dibutylphenol, propene tetramer substituted phenol, didodecylphenol, 4,4'-methylenebisphenol, α-decyl-β-naphthol, polyisobutene (molecular weight 1000) substituted phenol, condensation product of heptylphenol with formaldehyde, condensation product of octylphenol with acetone, di(hydroxyphenyl)oxide, di(hydroxyphenyl)sulfide, di(hydroxyphenyl)disulfide and 4-cyclohexylphenol. Phenol and alkylated phenols with up to three alkyl substituents are preferred. Each of the alkyl substituents may contain 100 or more carbon atoms.

The aliphatic alcohols from which the esters can be derived preferably contain up to 40 aliphatic carbon atoms. They can be monohydric alcohols such as methanol, ethanol, isooctanol, dodecanol, cyclohexanol, cyclopentanol, behenyl alcohol, hexatriacontanol, neopentyl alcohol, isobutyl alcohol, benzyl alcohol, β-phenylethyl alcohol, 2-methylcyclohexanol, β-chloroethanol, monomethyl ether of ethylene glycol, monobutyl ether of ethylene glycol, monopropyl ether of diethylene glycol, monodecyl ether of triethylene glycol, monooleate of ethylene glycol, monostearate of diethylene glycol, sec-pentyl alcohol, tert-butyl alcohol, 5-bromo-dodecanol, nitrooctadecanol and dioleate of glycerin. The polyhydric alcohols preferably contain two to 10 hydroxy radicals. They are exemplified by ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, dibutylene glycol, tributylene glycol and other alkylene glycols in which the alkylene radical has 2 to 8 carbon atoms. Other suitable polyhydric alcohols include glycerin, glycerin monooleate, glycerin monostearate, glycerin monomethyl ether, pentaerythritol, 9,10-dihydroxystearic acid, 9,10-dihydroxystearic acid methyl ester, 1,2-butanediol, 2,3-hexanediol, 2,4-hexanediol, pentacol, erythritol, arabitol, sorbitol, mannitol, 1,2-cyclohexanediol and xylene glycol. Carbohydrates such as sugars, starches and cellulose can also provide esters suitable for this invention. The carbohydrates can be illustrated by glucose, fructose, sucrose, rhamnose, mannose, glyceraldehyde and galactose.

A particularly preferred class of polyhydric alcohols are those compounds containing at least three hydroxy radicals, some of which are esterified with a monocarboxylic acid having 8 to 30 carbon atoms, such as octanoic acid, oleic acid, stearic acid, linoleic acid, dodecanoic acid or tall oil acid. Examples of such partially esterified polyhydric alcohols are the monooleate of sorbitol, distearate of sorbitol, monooleate of glycerin, monostearate of glycerin, didodecanoate of erythritol.

The esters may also be derived from unsaturated alcohols such as allyl alcohol, cinnamyl alcohol, propagyl alcohol, 1-cyclohexen-3-ol and oleyl alcohol. Yet another class of alcohols capable of forming the esters useful in the present invention comprises the ether alcohols and amino alcohols, including, for example, the oxyalkylene-, oxyarylene-, aminoalkylene- and aminoarylene-substituted alcohols having one or more oxyalkylene, oxyarylene, aminoalkylene or aminoarylene radicals. These are exemplified by cellosolve, carbitol, phenoxyethanol, heptylphenyl(oxypropylene)6-H, octyl(oxyethylene)30-H, phenyl(oxyoctylene)2-H, mono(heptylphenyloxypropylene) substituted glycerin, poly(styrene oxide), aminoethanol, 3-aminoethylpentanol, di(hydroxyethyl)amine, p-aminophenol, tri(hydroxypropyl)amine, N-hydroxyethylethylenediamine and N,N,N',N'-tetrahydroxytrimethylenediamine. For the most part, ether alcohols containing up to about 150 cycloalkylene radicals, where the alkylene radical contains 1 to 8 carbon atoms, are preferred.

The esters may be diesters of succinic acid or acid esters, i.e. partially esterified polyhydric alcohols or phenols, i.e. esters having free alcoholic hydroxyl radicals. Mixtures of the esters illustrated above are also considered to be within the scope of the invention.

The succinic esters can be prepared by one of several methods. The preferred method because of its simplicity and the superior properties of the esters obtained thereby comprises reacting a suitable alcohol or phenol with a substantially hydrocarbon-substituted succinic anhydride. The esterification is usually carried out at a temperature above about 10,000, preferably between 15,000 and 30,000.

The water formed as a by-product is separated by distillation during the esterification reaction. A solvent may be used during the esterification reaction to facilitate mixing and temperature control. It also facilitates the separation of water from the reaction mixture. Suitable solvents include xylene, toluene, diphenyl ether, chlorobenzene and mineral oil.

A modification of the above process involves replacing the substituted succinic anhydride with the corresponding succinic acid. However, succinic acids readily undergo dehydration at temperatures above about 10,000° and are therefore converted to their anhydrides, which are then esterified by reaction with the alcohol reactant. In this respect, succinic acids appear to be the essential equivalent of their anhydrides in the processes.

The relative proportions of succinic reactant and epoxy reactant to be employed depend to a large extent on the nature of the desired product and on the number of hydroxyl groups present in the molecule of the hydroxy reactant. For example, the formation of a half ester of a succinic acid, i.e. in which only one of the two acid residues is esterified, requires the use of 1 mole of a monohydric alcohol for each mole of substituted succinic reactant, whereas the formation of a diester of a Succinic acid requires the use of 2 moles of alcohol for each mole of acid. On the other hand, one mole of a hexahydric alcohol can react with up to 6 moles of succinic acid to form an ester in which each of the 6 hydroxyl groups of the alcohol is esterified with one of the two acid groups of the succinic acid. The maximum ratio of succinic acid to be used with a polyhydric alcohol is therefore determined by the number of hydroxyl groups present in the molecule of the hydroxy reactant. For the purposes of this invention, esters obtained by reacting equimolar amounts of the succinic acid reactant with the hydroxy reactant have been found to have superior properties and are therefore preferred. In some cases it is advantageous to carry out the esterification in the presence of a catalyst such as sulfuric acid, pyridine hydrochloride, hydrochloric acid, benzenesulfonic acid, para-toluenesulfonic acid, phosphoric acid or other known esterification catalyst. The amount of catalyst in the reaction can be as low as 0.01% (based on the weight of the reaction mixture), more commonly from 0.1 to 5%.

Alternatively, the succinic esters can be obtained by reacting a substituted succinic acid or anhydride with an epoxide or a mixture of epoxide and water. This reaction is similar to that in which the acid or anhydride is reacted with a glycol. For example, the product can be prepared by reacting a substituted succinic acid with one mole of ethylene oxide. Similarly, the product can be obtained by reacting a substituted succinic acid with 2 moles of ethylene oxide. Other epoxides that are commonly available for use in such a reaction include, for example, propylene oxide, styrene oxide, 1,2-butylene oxide, 2,3-butylene oxide, epichlorohydrin, cyclohexene oxide, 1,2-octylene oxide, epoxidized soybean oil, methyl 9,10-epoxystearate, and butadiene monoepoxide. Most of the epoxides are the alkylene oxides in which the alkylene radical has 2 to 8 carbon atoms; or the epoxidized fatty acid esters in which the fatty acid radical has up to 30 carbon atoms and the ester radical is derived from a lower alcohol with up to 8 carbon atoms.

Instead of succinic acid or anhydride, a lactone acid or a substituted succinic acid halide can be used in the processes discussed above. Such acid halides can be acid dibromides, acid dichlorides, acid monochlorides and acid monobromides. The substituted succinic anhydrides and acids can be prepared, for example, by reacting maleic anhydride with a high molecular weight olefin or a halogenated hydrocarbon such as obtained by the chlorination of an olefin polymer described above. The reaction merely requires heating the reactants to a temperature of preferably 100°C to 250°C. The product from such a reaction is an alkenyl succinic anhydride. The alkenyl group can be hydrogenated to an alkyl group. The anhydride can be hydrolyzed to the corresponding acid by treatment with water or steam. Another method suitable for producing succinic acids or anhydrides involves reacting itaconic acid or the anhydride with an olefin or a chlorinated hydrocarbon at a temperature usually in the range of 100°C to 250°C. The succinic acid halides can be produced by reacting the acids or their anhydrides with a halogenating agent such as phosphorus tribromide, phosphorus pentachloride or thionyl chloride. These and other methods for producing succinic acid compounds are generally known in the art and do not need to be explained in detail here.

Other methods of preparing esters useful in the gasoline compositions of the present invention are available. For example, the esters can be obtained by reacting maleic acid or the anhydride with an alcohol as previously set forth to form a mono- or diester of maleic acid and then reacting that ester with an olefin or a chlorinated hydrocarbon as previously discussed. They can also be obtained by first esterifying itaconic anhydride or the acid and then reacting the ester intermediate with an olefin or a chlorinated hydrocarbon under conditions similar to those previously described.

Many different types of polymeric dispersants have been suggested as being suitable for lubricating oil formulations, and such polymeric dispersants are useful in the gasoline compositions of the present invention. Often, such additives have been indicated to be useful in lubricant formulations as viscosity index improvers with dispersing properties. The polymeric dispersants are generally polymers or copolymers that have a long carbon chain and contain "polar" groups to provide the dispersing properties. Examples of polar groups include amino, amido, imino, imido, hydroxyl and ether groups. For example, the polymeric dispersants can be copolymers of methacrylates or acrylates containing additional polar groups, ethylene/propylene copolymers containing polar groups, or vinyl acetate/fumaric acid ester copolymers. Many such polymeric dispersants have been described in the prior art, for example in U.S. Patents 4,402,844, 3,356,763 and 3,891,721.

Some polymeric dispersants can be prepared by grafting polar monomers onto polyolefin backbones. For example, U.S. Patents 3,687,849 and 3,687,905 describe the use of maleic anhydride as a grafting monomer for a polyolefin backbone. Maleic acid or the anhydride is particularly desirable as a grafting monomer because this monomer is relatively inexpensive and provides an economical way to incorporate dispersing nitrogen compounds into polymers by further reacting the carboxyl groups of the maleic acid or anhydride with, for example, nitrogen compounds or hydroxy compounds. U.S. Patent 4,160,739 describes graft copolymers obtained by grafting a system comprising maleic acid or its anhydride and at least one other different monomer which is copolymerizable therewith by addition, wherein the grafted monomer system is post-reacted with a polyamine. The monomers copolymerizable with maleic acid or maleic anhydride are any α,β-monoethylenically unsaturated monomers that are sufficiently soluble in the reaction medium, and are reactive with maleic acid or its anhydride, so that considerably larger amounts of maleic acid or its anhydride can be incorporated into the grafted polymer product. Suitable monomers therefore include the esters, amides and nitriles of acrylic and methacrylic acid and monomers which do not contain free acid groups. The incorporation of heterocyclic monomers into graft polymers is described by the process which comprises a first step of grafting an alkyl ester of acrylic acid or methacrylic acid, alone or in combination with styrene, onto a backbone copolymer which is a hydrogenated block copolymer of styrene and a conjugated diene having 4 to 6 carbon atoms to form a first graft polymer. In the second step, a polymerizable heterocyclic monomer, alone or in combination with a hydrophobizing vinyl ester, is copolymerized onto the first graft copolymer to form a second graft copolymer.

Other patents describing graft polymers useful as dispersants in the gasoline compositions of the present invention include U.S. Patents 3,243,481, 3,475,514, 3,723,575, 4,026,167, 4,085,055, 4,181,618 and 4,476,283.

Another class of polymeric dispersants useful in the gasoline compositions of the invention are the so-called "star" polymers and copolymers. Such polymers are described, for example, in U.S. Patents 4,346,193, 4,141,847, 4,358,565, 4,409,120 and 4,077,893.

The hydrocarbon-substituted phenolic dispersants useful in the gasoline compositions of the present invention include the hydrocarbon-substituted phenolic compounds wherein the hydrocarbon substituents have sufficient molecular weight to render the phenolic compound soluble in the fuel. Generally, the hydrocarbon substituent will be a substantially saturated hydrocarbon-based group of at least 30 carbon atoms. The phenolic compounds can be generally represented by the following formula:

(R⁵)e-Ar¹- (OH)f (VI)

wherein R⁵ is a substantially saturated hydrocarbon-based substituent having an average of 30 to 400 aliphatic carbon atoms, and e and f are each 1, 2 or 3. Ar¹ is an aromatic radical such as a benzene nucleus, naphthalene nucleus or linked benzene nuclei. Optionally, the above phenates represented by the formula VI may contain other substituents such as lower alkyl, lower alkoxy, nitro, amino and halogen groups. Preferred examples of optional substituents are the nitro and amino groups.

The substantially saturated hydrocarbon-based group R5 in formula VI can contain up to 750 aliphatic carbon atoms, although it usually exhibits a maximum of 400 carbon atoms on average. In some cases, R5 has a minimum of 50 carbon atoms. As indicated, the phenolic compounds can contain more than one R5 group for each aromatic nucleus in the aromatic radical R1.

In general, the hydrocarbon-based R5 groups are derived from homo- or interpolymers (e.g. copolymers, terpolymers) of mono- and diolefins having 2 to 10 carbon atoms, such as ethylene, propylene, butene-1, isobutene, butadiene, isoprene, 1-hexene and 1-octene. Typically, these olefins are 1-monoolefins. The R5 groups can also be derived from the halogenated (e.g. chlorinated or brominated) analogues of such homo- or interpolymers. The R5 groups may, however, be derived from other sources, such as monomeric high molecular weight alkenes (e.g. 1-tetracontene) and chlorinated analogues and hydrochlorinated analogues thereof, aliphatic petroleum fractions, in particular paraffin waxes and cracked and chlorinated analogues and hydrochlorinated analogues thereof, white oils, synthetic alkenes such as those obtained by the Ziegler-Natta process (e.g. poly(ethylene) greases) and other sources known to those skilled in the art. Any unsaturation in the R5 groups may be reduced or eliminated by hydrogenation according to methods known in the art prior to the nitration step described below.

Specific examples of the substantially saturated hydrocarbon-based groups R5 are the following: a tetracontanyl group, a henpentacontanyl group, a mixture of poly(ethylene/propylene) groups having 35 to 70 carbon atoms, a mixture of oxidatively or mechanically degraded poly(ethylene/propylene) groups having 35 to 70 carbon atoms, a mixture of poly(propylene/1-hexene) groups having 80 to 150 carbon atoms, a mixture of polyisobutene groups having 20 to 32 carbon atoms, and a mixture of polyisobutene groups having an average of 50 to 75 carbon atoms.

A preferred source of the R5 groups are polyisobutenes, which are obtained by polymerizing a C4 refinery stream containing 35 to 75 wt.% butene and 30 to 60 wt.% isobutene in the presence of a Lewis acid catalyst such as aluminum trichloride or boron trifluoride. These polyisobutenes contain predominantly (more than 80% of the total repeat units) repeating isobutene units having the configuration:

-C(CH₃)₂CH₂-.

The linkage of the hydrocarbon-based group R5 to the aromatic radical Ar1 can be accomplished by a number of methods known to those skilled in the art. In a preferred embodiment, the phenolic dispersants useful in the gasoline compositions of the present invention are hydrocarbon-substituted nitrophenols as represented by Formula VI, wherein the optional substituent consists of one or more nitro groups. The nitrophenols can conveniently be prepared by nitrating corresponding phenols, and typically the nitrophenols are formed by nitrating alkylphenols bearing an alkyl group having at least 30 and preferably at least 50 carbon atoms. The preparation of a number of hydrocarbon-substituted nitrophenols useful in the gasoline compositions of the present invention is described in U.S. Patent 4,347,148.

In another preferred embodiment, the hydrocarbon-substituted phenolic dispersants useful in the present invention are hydrocarbon-substituted aminophenols as represented by formula VI, wherein the optional substituent consists of one or more amino groups. These aminophenols can be conveniently prepared by nitrating a corresponding aromatic hydroxy compound as described above and then reducing the nitro groups to amino groups. Typically, the suitable aminophenols are formed by nitrating and reducing alkylphenols bearing an alkyl or alkenyl group of at least 30 and preferably at least 50 carbon atoms. The preparation of numerous hydrocarbon-substituted aminophenols useful as dispersants in the present invention is described in U.S. Patent 4,320,021.

Also suitable as dispersants in the gasoline compositions of the present invention are fuel-soluble alkoxylated derivatives of alcohols, phenols and amines. A wide variety of such derivatives can be used as long as the derivatives are soluble in the fuel. More preferably, the derivatives should be insoluble in water in addition to being fuel-soluble. In a preferred embodiment, the fuel-soluble alkoxylated derivatives suitable as dispersants are thus characterized by an HLB value of 1 to 13.

As is known to those skilled in the art, the fuel solubility and water insolubility properties of the alkoxylated derivatives can be controlled by the selection of the alcohol, phenol or amine, by the choice of the particular alkoxy reactant, and by the choice of the amount of alkoxy reactant reacted with the alcohol, phenol or amine. Accordingly, the alcohols used to prepare the alkoxylated derivatives are hydrocarbon-based alcohols, whereas the amines are hydrocarbyl-substituted amines, as described above. The phenols can be phenols or hydrocarbon-substituted phenols, and the hydrocarbon substituent can contain as little as 1 carbon atom.

The alkoxylated derivatives are obtained by reacting the alcohol, phenol or amine with an epoxide or a mixture of an epoxide with water. For example, the derivative can be prepared by reacting the alcohol, phenol or amine with an equimolar amount or with an excess of ethylene oxide. Other epoxides that can be reacted with the alcohol, phenol or amine include, for example, propylene oxide, styrene oxide, 1,2-butylene oxide, 2,3-butylene oxide, epichlorohydrin, cyclohexene oxide and 1,2-octylene oxide. Preferably, the epoxides are alkylene oxides in which the alkylene group has 2 to 8 carbon atoms. As previously mentioned, it is desirable and preferred that the amount of alkylene oxide reacted with the alcohol, phenol or amine is insufficient to render the derivative water soluble.

The following are examples of commercially available alkylene oxide derivatives that can be used as dispersants in the gasoline compositions of the present invention: Ethomeen S/12, tertiary amine-ethylene oxide condensation products of primary fatty amines (HLB, 4.15; Armak Industries); and Plurafac A-24, an oxyethylated straight chain alcohol available from BASF Wyandotte Industries (HLB 5.0). Other suitable fuel-soluble alkoxylated derivatives of alcohols, phenols and amines will be readily apparent to those skilled in the art.

In a particularly preferred embodiment, the gasoline composition of the invention may contain, in addition to the poly-α-olefin and the polyoxyalkylene compound, as an ashless dispersant, a small amount of a polyolefin-substituted succinimide derivative, wherein the polyolefin has a Mn in the range 800 to 5000, preferably 1000 to 5000, more preferably at least 1750, 1800 or 1850 and at most 4000, 3500, 3000 or 2500. The amine from which the succinimide is preferably a C1-30 amine, in particular a C4-12 amine containing 3 to 7 nitrogen atoms, for example diethylenetriamine, triethylenetetramine, tetramethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, tripropylenetetramine and mixtures of any 2 or more representatives thereof.

Preferably, the hydrocarbon-soluble, ashless dispersant is present in an amount of 30 to 500 parts per million, more preferably 100 to 300 parts per million, by weight of the total composition.

The gasoline composition may additionally comprise (for example as an alternative to the inclusion of a succinimide derivative) an oil-soluble polyamine as described in EP-A-290 088, or an N-substituted carbamate as described in EP-A-414 963, in each case in similar amounts to those described therein.

The gasoline composition may further comprise, as a flame retardant, an alkali metal or an alkaline earth metal salt of a succinic acid derivative as described in EP-A-290 088 in similar amounts to those described therein.

Apart from the components already described above, the gasoline composition may also contain other additives. For example, it may contain a lead compound as an anti-knock additive, and accordingly the gasoline composition according to the present invention comprises both leaded and unleaded gasoline. The gasoline composition may also contain antioxidants such as phenolic compounds, for example 2,6-di-tert-butylphenyl, or phenylenediamines, for example N,N'-di-sec-butylp-phenylenediamine, or anti-knock additives other than lead compounds, or polyetheramino additives, for example as described in US Patent 4,477,261 and in EP-A-151 621.

The gasoline composition according to the invention comprises a major amount of a gasoline (base fuel) suitable for use in spark-ignition engines. This includes hydrocarbon-based fuels boiling substantially in the gasoline boiling range of 30 to 230°C. These base fuels may contain mixtures of saturated, olefinic and aromatic hydrocarbons. They may be derived from straight-run gasoline, synthetically produced hydrocarbon mixtures, thermally or catalytically cracked hydrocarbon feedstocks, hydrocracked petroleum fractions or catalytically converted hydrocarbons. The octane number of the base fuel is not critical and is generally above 65. In gasoline, hydrocarbons can be replaced up to significant amounts by alcohols, ethers, ketones or esters. Of course, it is desirable that basic fuels are essentially free of water, since water can make uniform combustion difficult.

The poly-α-olefin and the polyoxyalkylene compound may be conveniently added as a mixture with other selected additives. A convenient method of preparing the gasoline composition is therefore to prepare a concentrate of the poly-α-olefin and the polyoxyalkylene compound together with the other additives and then add this concentrate to the gasoline in the amount required to produce the required final concentrations of the additives.

The invention accordingly provides a concentrate suitable for addition to gasoline which comprises a gasoline compatible diluent, a poly-α-olefin as described above, a polyoxyalkylene compound as described above, the weight ratio of poly-α-olefin:polyoxyalkylene compound being in the range of 1:10 to 10:1, and optionally also containing at least one hydrocarbon soluble, ashless dispersant.

Advantageously, the poly-α-olefin and the polyoxyalkylene compound are present together in an amount in the range of 20 to 80 wt.% and the ashless dispersant, if present, is present in an amount in the range of 5 to 30 wt.%, all percentages being calculated on a diluent basis.

Suitable petrol-compatible diluents include hydrocarbons, for example heptane, alcohols or ethers such as methanol, ethanol, propanol, 2-butoxyethanol or methyl tert-butyl ether. Preferably, the diluent is an aromatic hydrocarbon solvent such as toluene, xylene, mixtures thereof or mixtures of toluene or xylene with an alcohol. The solvent is preferably toluene. Optionally, the concentrate may contain an anti-turbidity agent, in particular an ethoxylated alkylphenol-formaldehyde resin of Polyether type. The anti-turbidity agent, if used, may conveniently be present in the concentrate in an amount of 0.01 to 2% by weight, calculated on the basis of the diluent.

In another aspect, the invention provides a method of operating a spark-ignition internal combustion engine, which comprises introducing a gasoline composition according to the invention into the combustion chambers of said engines.

The invention will be better understood by the following illustrative examples. In the examples, various additives are listed as follows:

(a) "PHGE" is a polyoxypropylene glycol hemiether (monoether) prepared using a mixture of C12-15 alcohols as initiator and having a Mn in the range of 1200 to 1500 and a kinematic viscosity in the range of 72 to 82 mm2/s at 4000 according to ASTM D445, available under the trade name "SAP 949" from member companies of the Royal Dutch/Shell group;

(b) "PAO" means a polyalphaolefin which is a hydrogenated oligomer of decene-1 having a viscosity at 10,000 of 8x10-6 m2/s (8 centistokes);

(c) "PMP" is a 40% (w/w) solution in xylene of polyisobutylene succinimide prepared by reacting a polyisobutylene having a number average molecular weight (Mn) of 2470 (determined by quantitative reaction with ozone) with maleic anhydride, followed by reacting the polyisobutylene succinic anhydride product formed with a mixture of tetraethylenepentamine, pentaethylenehexamine and hexamethyleneheptamine (molar ratio 1:2:1) in a molar ratio anhydride:amine of 2:1.

In the examples below, the amounts of PMP are given as amounts of solution and where amounts of xylene are given, these do not include the xylene contained in the 40% (w/w) solutions of PMP.

In the examples, additive concentrates were prepared by taking samples of PMP and stirring at 20ºC the PAO amounts (and additional xylene) were added, followed by addition of the PGHE amounts. These additive concentrates were then sampled into gasoline formulations with stirring in amounts to give the desired concentrations of the components. This is actual industry practice and it is important that both the additive concentrates are completely stable and that the gasolines containing the additives perform well in terms of engine cleanliness and valve stick prevention.

EXAMPLES 1 to 8

Additive concentrates according to the invention and comparative examples were prepared as described above and stored for 6 weeks at 20°C and at -20°C, after which stability was evaluated visually. The results are shown in Table I. Table I

+ Storage only at 20ºC

As can be easily seen, the additive concentrates of the invention containing both PHGE and PAO had good storage stability, whereas the comparative examples containing only PHGE had insufficient stability.

EXAMPLES 9 and 10

For the evaluation of intake valve cleanliness, a standard VW Polo petrol car equipped with a four-cylinder single carburettor engine of 1.043 l displacement was used in a standard road test (Volkswagen Polo road test).

Prior to testing, the intake parts and combustion chambers were cleaned and new pre-weighed intake valves and new spark plugs were fitted to the engine, a new oil filter was fitted and the engine was filled with fresh engine oil. A small wind deflector was fitted to the roof of the test vehicle to increase air resistance and thus increase engine load. The fuel tank was drained and filled with the test petrol composition before starting a 5000 km test distance. Test cycles of 37 minutes were followed, in which the vehicle was operated in 4th gear at 4500 rpm (105 km/h) for 30 minutes and then idled for 7 minutes. 12 cycles per day were carried out for 8 consecutive days to cover the 5000 km test distance. At the end of the test, the intake valves were removed and weighed to determine the average weight of intake valve deposits.

The gasoline compositions according to the invention were compared with comparative tests carried out using unleaded gasoline (95 ULG) containing no additives (base gasoline) or containing PMP and either PHGE and PAO. The results are shown in Table II below. Table II

The data in Table II show that in those cases (Examples 9 and 10) where the additive oil contains a combination of PHGE and PAO, the weight of the deposits on the intake valves is significantly and surprisingly lower than in the case where the corresponding amount of additive oil consists exclusively of one of PHGE and PAO.

EXAMPLES 11 to 23

A standard Opel Ascona 1.6 petrol car, fitted with a standard 4-cylinder 1.6-litre Type 16SH engine, was used to evaluate valve sticking following a standard test method.

The test method involved driving the vehicle using a test petrol composition on normal city roads for a total distance of 130 km on a moderate demand cycle (maximum speed 50 km/h). The vehicle was then kept overnight at -20ºC and the maximum compression pressure in each cylinder was measured and the average of the four values was calculated. The higher the pressure value, the better the result.

Similarly to Table II, the compositions of the white spirit compositions and the results obtained are given in Table III below, wherein the "additive oil" consisted of PHGE and/or PAO. Table III

It will be apparent to those skilled in the art that the concentrations given above represent three times the normal commercial concentrations in order to increase the rigor of the test.

The above results show that when the additive oil is a combination of PHGE and PAO, the compression pressure result is very good, always significantly better than PHGE alone, significantly better than would be expected for intermediate values between those expected for PHGE alone and PAO alone, and generally comparable and sometimes even better than the values for PAO alone.

EXAMPLES 24 to 47

The effect of gasoline composition on deposits in the engine intake system was determined using the Induction System Deposit Simulator (ISD) test. In this test procedure, a gasoline composition was fed to a spray nozzle from which it was sprayed in a flat spray pattern onto the surface of an aluminum tube heated to 250ºC. The base gasoline used contained thermally cracked gasoline to promote deposit formation. Under the test conditions, such base gasolines alone form a central carbonaceous deposit on the tube surface. Cleanliness enhancers prevent deposits in the central area and produce an annular deposit on the tube. The formation of residues is evaluated visually according to the following scheme:

0 - clean

1-2 - almost clean

3-4 - slightly coked

5-6 - moderately coked

7-8 - moderate to heavy coking

9-10 - heavily coked

over 10 - very heavily coked

Similar to Table III, the results of the ISD test are given in Table IV below. Table IV Table IV (continued)

The results in Table IV show that when the additive oil is a combination of PHGE and PAO, the ISD rating is generally good, always better than PAO alone, significantly better than would be expected for average values between those for PHGE alone and PAO alone, and generally comparable to the values for PHGE alone.

In summary, additive concentrates containing both PHGE and PAO had good storage stability compared to similar concentrates containing PHGE but no PAO; lower intake valve deposits were observed for gasolines containing the additive oil in the form of a combination of PHGE and PAO compared to those in which the additive oil consisted of PHGE or PAO alone; prevention of valve sticking, as demonstrated by compression pressure determination, was significantly better for combinations of PHGE and PAO than for PHGE alone and was generally comparable to PAO alone; and prevention of deposit formation, as demonstrated by the IDS test, was significantly better for combinations of PHGE and PAO than for PAO alone and was generally comparable to PHGE alone.

Claims (14)

1. A gasoline composition containing as a major component of a gasoline suitable for use in spark-ignition engines, an amount of a polyalphaolefin having a viscosity at 10,000 in the range of 2x10⁻⁶ to 2x10⁻⁵ m²/s (2 to 20 centistokes), which is a hydrogenated oligomer having 18 to 80 carbon atoms derived from at least one alpha-olefinic monomer containing 8 to 16 carbon atoms, and an amount of a polyoxyalkylene compound selected from glycols, mono- and diethers thereof having a number average molecular weight (Mn) of 400 to 3,000, the weight ratio of polyalphaolefin: polyoxyalkylene compound being in the range 1:10 to 10:1 and the amount of polyalphaolefin and polyoxyalkylene compound together being in the range 100 to 1,500 parts per million by weight, based on the total composition. 2. The composition of claim 1, wherein the polyalphaolefin is derived from an alphaolefinic monomer having 8 to 12 carbon atoms. 3. A composition according to claim 1 or 2, wherein the polyalphaolefin has a viscosity at 100°C in the range of 6x10⁻⁶ to 1x10⁻⁵ m²/s (6 to 10 centistokes). 4. Composition according to one of claims 1 to 3, wherein the polyoxyalkylene compound has the formula R¹-O-(R-O )n-R² (I) wherein R¹ and R² independently represent hydrogen atoms or C₁₋₄hydrocarbyl groups, each R independently represents a C₂-₈alkylene group, and n is a number such that the Mn of the polyoxyalkylene compound is in the range of 700 to 2,000. 5. A composition according to claim 4, wherein R¹ represents a C₈₋₂₀ alkyl group and R² represents a hydrogen atom. 6. A composition according to claim 4 or 5, wherein each R independently represents a C₂₋₄alkylene group. 7. A composition according to any one of claims 1 to 6, wherein the polyalphaolefin and the polyoxyalkylene compound are present together in an amount of 100 to 1,200 parts per million by weight, based on the total composition. 8. A composition according to any one of claims 1 to 7, which additionally contains a small amount of at least one hydrocarbon-soluble ashless dispersant. 9. The composition of claim 8, wherein the dispersant comprises a polyolefin substituted succinimide derivative, wherein the polyolefin has a Mn in the range of 800 to 5,000. 10. A composition according to claim 8 or 9, wherein the ashless dispersant is present in an amount ranging from 30 to 500 parts per million by weight based on the total composition. 11. A composition according to any one of claims 1 to 10, wherein the weight ratio of polyalphaolefin: polyoxyalkylene compound is in the range 1:5 to 5:1. 12. A concentrate suitable for addition to gasoline which comprises a gasoline compatible diluent, a polyalphaolefin as defined in claim 1, a polyoxyalkylene compound as defined in claim 1, wherein the weight ratio polyalphaolefin:polyoxyalkylene compound is in the range 1:10 to 10:1, and optionally also at least one hydrocarbon-soluble ashless dispersant. 13. A concentrate according to claim 12, wherein the polyalphaolefin and the polyoxyalkylene compound are together present in an amount in the range of 20 to 80% by weight and the ashless dispersant, if present, is present in an amount in the range of 5 to 30 wt.%, all percentages being based on the diluent. 14. A method for operating a spark-ignited internal combustion engine, which comprises introducing a gasoline composition according to one of claims 1 to 11 into the combustion chambers of said engine.