GB2164352A

GB2164352A - Lubricant additive for use with alcohol fuels

Info

Publication number: GB2164352A
Application number: GB08505261A
Authority: GB
Inventors: Leroy Schieler
Original assignee: BankAmerica Corp; Bank of America Corp
Current assignee: Bank of America Corp
Priority date: 1984-09-17
Filing date: 1985-02-28
Publication date: 1986-03-19
Also published as: JPS6173798A; GB8505261D0; AU3877485A; SE8501187D0; SE8501187L; NO851045L; GB2164352B; DE3509407A1; IN163879B; FR2570387A1; BR8500777A

Abstract

A lubricant additive for use with engines burning alcohol fuels comprises a major amount of a polyalkylene glycol of an alkene having 2 to 3 carbons, a minor amount of an aliphatic amine, a cycloaliphatic amine, or a mixture of both, and a minor amount of a phosphoric acid ester. The amine component may include an aromatic primary amine, an aromatic secondary amino or both. A preferred composition comprises 94-98.5 wt. % of said polyalkylene glycol, 1.0 to 4.0 wt. % of said amine, and 0.5-2.0 wt. % of said phosphoric acid ester.

Description

SPECIFICATION Lubricant additive for use with alcohol fuels The present invention is directed to an additive formulation for use with conventional automotive lubricants to produce a lubricant suitable for internal combustion engines burning alcohol fuels, such as methanol or ethanol.

Commonly used automotive lubricants are not effective in alcohol burning engines as evidenced by excessive engine wear and progressively increasing rates of lubricant consumption. One reason for this is the large difference in chemical reactivity of the combustion products from gasoline and alcohol automotive fuel systems. In an alcohol fuel system, a number of lubricant degradation reactions occur which are not encountered in the gasoline fuel system. These chemical reactions cause the increased corrosiveness of alcohol fuels. For instance, methanol readily oxidizes to form formaldehyde and formic acid. This reaction is represented by Equation 1.

CH3OH# > HCHO > HCOOH (1) (methanol) (formaldehyde) (formic acid) Most vehicles using methanol fuel suffer from excessive upper-cylinder corrosion and bearing wear resulting from the formic acid produced by methanol combustion. Formic acid reacts with the conventional automotive lubricant's organic amine additives which function as antioxidants, corrosion inhibitors, and anti-wear agents. The amine additives neutralize the formic acid. However, the conventional additives seem unable to adequately neutralize the amount of formic acid formed in methanol combustion.

These reactions are represented in Equations 2 and 3.

RNH2 + 2HCOOH neutralization , RNH2-2HCOOH (2) (primary) (formic amine) acid) R2NH + HCOOH neutralization R2NH.HCOOH (3) (secondary (formic amine) acid) Formaldehyde is highly reactive with phenolic and glycol additives. Formaldehyde reacts with the phenols which are used as antioxidants and with the polymers containing hydroxyl groups which are used as ashless dispersants. These reactions take place under acidic conditions and increase as the organic amine additives are depleted by reaction with formic acid. These formaldehyde reactions, represented by Equation (4), contribute significantly to oil degradation in a methanol fuel system.

ROH + HCHO acid catalyzed aldol condensation ROCH2OR (4) (phenol (formaldehyde) or glycol) There is a need for a lubricant additive which minimizes the oxidation of methanol to formaldehyde and formic acid and minimizes excessive formaldehyde and formic acid reactions in order to prolong the life of lubricant additives which are depleted rapidly by reaction with formaldehyde and formic acid.

Similarly, there is a need for a lubricant additive which minimizes the oxidation of ethanol to acetaldehyde and acetic acid and minimizes excessive reactions of those components.

Another significant problem in an alcohol fuel system is that zinc dialkyldithiophosphate, a major multifunctional additive in most conventional lubricants, readily transesterifies and thereby loses many of its anti-wear properties. The transesterification reaction involves the interchange of an alcohol alkyl group, such as methanol or ethanol, with an existing ester, such as zinc dialkyldithiophosphate, to form a new ester. A transesterification reaction is represented in Equation 5.

RPOO(OH)R' + CH3OH acid catalyzed ,RPOO(OH)CH3 + R'OH (5) (existing (methanol) (new ester) ester) The transesterification reaction is acid catalyzed and therefore occurs after the amine base additives in the lubricant are depleted by reaction with aldehydes and acids formed in the combustion process. Transesterification is not a major mechanism of oil degradation in hydrocarbon fuel systems but is a primary mechanism of oil degradation in methanol and other alcohol fuel systems. For instance, when methanol and ethanol are blended with gasoline, the magnitude of the transesterification reaction is proportional to the amount of alcohol in the mixture.

Another cause of increased corrosiveness in an alcohol burning engine is the increased solubility of carbon dioxide in the alcohol. For instance, carbon dioxide is much more soluble in methanol than in water. Both water and methanol are usually present in the cooler parts of the crankcase as products of combustion. The water reacts with the fuel combustion products, such as SO2, NO2, and CO2 to form the corresponding acids, sulfuric acid, nitric acid, and carbonic acid, as represented in Equations 6, 7, and 8.

SO3 t H2O > H2SO4 (6) (sulfuric acid) NO2 + H2O- aHNO3 (7) (nitric acid) CO2 + H2O#H2CO3 (8) (carbonic acid) These acids reacting with metals in the engine are one of the major causes of corrosion in an internal combustion engine. The lubricants commonly used in a hydrocarbon fuel system effectively neutralize these acids with basic additives such as organic amines and alkaline metal compounds. However, carbonic acid levels are significantly higher in a methanol or other alcohol fuel system than in a gasoline fuel system due to the increased solubility of CO2 in alcohols. The same may be true of nitric acid formed from NO2 combustion products.Absorption of carbon dioxide appears to be an important reason for the unexpectedly high corrosiveness of alcohol fuels.

Lubricant analysis indicates that corrosion inhibitors composed of sulfonates, naphthenates or other alkaline metal salts are extensively depleted by reaction with carbonic acid, resulting in the precipitation of insoluble carbonates of the alkaline metals. The precipitation reaction is represented in Equations 9 and 10.

(RSO3)2Ba + H2CQ; )BaCO3 t 2RSO 2H (9) (RSO2)2Ca + H2CO3e aCaCO3 + 2RSO 3H (10) This precipitation reaction competes with the neutralization of carbonic acid by organic amines. Although the neutralization is faster and more likely to occur, the reaction with alkaline metal salts increases as the organic amines are depleted. Thus, there is a need for a lubricant additive wherein depletion of the organic amine additives due to neutralization of formic acid or acetic acid and carbonic acid occurs less rapidly, thus decreasing the likelihood that alkaline metal salts will be depleted by the precipitation reactions represented in Equations 9 and 10.

The present invention sets out to provide a lubricant additive for use in an alcohol fuel burning internal combustion engine which provides protection against corrosive and engine wear effects caused by alcohol.

The present invention provides a lubricant additive which can be added to conve-ntional automotive lubricants to produce a lubricant suitable for use in a methanol or ethanol burning engine, comprising a major amount of a polyalkylene glycol of an alkene having 2 to 3 carbons, a minor amount of an ali- phatic amine, a cycloaliphatic amine, or both optionally together with an aromatic orimary or secondary amine or both, and a minor amount of a phosphoric acid ester. Preferably, the lubricant additive of the present invention contains about 94 to 98.5 wt. % of a polyalkylene glycol of an alkene having 2 to 3 carbons, about 1 to 4 wt MO of an alkiphatic amine, a cycloaliphatic amine, or both, and about 0.5 to 2 wt % of a phosphoric acid ester.The amine portion of the lubricant additive of the present invention may also include an aromatic primary amine, an aromatic secondary amine, or both.

Preferred polyalkylene glycols include polypropylene glycol, polyisopropylene glycol, and polyethylene glycol.

A more preferred polyalkylene glycol is a polypropylene glycol having a molecular weight of about 2000 grams/mole (hereinafter polypropylene glycol 2000).

The amine component of the lubricant additive of the present invention can be an aliphatic amine, a cycloaliphatic amine, or a mixture of an aliphatic and a cycloaliphatic amine. Preferably, the amine component is an aliphatic amine; a cycloaliphatic amine; a mixture of an aliphatic amine and a cycloaliphatic amine; or a mixture of an aliphatic amine, a cycloaliphatic amine or both with an aromatic primary amine, an aromatic secondary amine, or both. An aliphatic amine alone is the more preferred amine component.

Preferred aromatic primary amines for mixing with the aliphatic or cycloaliphatic amine include ortho-, meta-, and para-phenylenediamine, ortho-, meta- and paratoluidine, aniline, xylidine, naphthylamine, benzylamine, toluenediamine, and naphthalenediamine. A more preferred primary aromatic amine is ortho-phenylenediamine. Preferred aromatic secondary amines for mixing with the aliphatic or cycloaliphatic amine include N-phenyl-2-naphthylamine, phenyl-#-naphthylamine, phenyl-#-naphthyl-amine, tolylnaphthylamine, diphenylamine, ditolylamine, phenyltolylamine, 4,4'-diaminodiphenylamine, and Nmethylaniline. A more preferred aromatic secondary amine is N-phenyl-2-naphthylamine.

Preferred aliphatic amines for use in the lubricant additive of the present invention are aliphatic amines having 10 to 30 carbon atoms. A more preferred aliphatic amine has 12 to 30 carbon atoms. The most preferred aliphatic amine is octadecylamine. Preferred cycloaliphatic amines include cyclohexylamine and methylcyclohexylamine.

Preferred phosphoric acid esters, include ortho-, meta-, or para-tricresylphosphate, dibutylphenylphosphate, tributyl-phosphate, tri-2-ethyl-hexylphosphate, trioctylphosphate, diphenyl ortho-phosphonate, dicresyl ortho-phosphonate, trilauryl ortho-phosphonate, and tristearyl ortho-phosphonate. A more preferred phosphoric acid ester is orthotricresylphosphate.

A preferred composition of the present invention comprises about 94 to 98.5 wt. % polypropylene glycol 2000, about 1 to 4 wt. % of octadecylamine, and about 0.5 to 2 wt. % of ortho-tricresylphosphate.

All of the above compounds are commercially available. The lubricant additive of the present invention is made by blending together a major amount of a polyalkylene glycol of an alkene having 2 to 3 carbons, a minor amount of an aliphatic amine, a cycloaliphatic amine, or both, and a minor amount of a phosphoric acid ester. Preferably, the lubricant additive of the present invention is prepared by blending together about 94 to 98.5 wt. % of said polyalkylene glycol, about 1 to 4 wt. % of said amine, and about 0.5 to 2 wt. % of said phosphoric acid ester. An aromatic primary amine, an aromatic secondary amine, or both, may be added to the amine portion of the lubricant additive.

There is also provided a lubricant composition comprising an additive of the invention. The additive per se may be combined with the lubricant to obtain the resultant composition or the individual ingredients thereof, alone or in combination, may be mixed with the lubricant to produce the desired composition and the present invention includes the compositions however prepared.

The invention further includes a method of preparing a lubricant composition comprising mixing together a lubricant and, as an additive, a polyalkylene glycol of an alkene having 2 to 3 carbon atoms, a phosphoric acid ester and an amine, the amine being an aliphatic amine; a cycloaliphatic amine; a mixture of an aliphatic and a cycloaliphatic amine; or a mixture of an aliphatic amine, a cycloaliphatic amine or both and an aromatic primary amine, an aromatic secondary amine or both, the polyalkylene glycol being a major amount of the additive in the lubricant composition, and the phosphoric acid ester and the amine each being a minor amount of the additive in the lubricant composition.Of course, the order in which the lubricant and each additive ingredient are mixed together is not of significance and the additive ingredients may be combined with the lubricant in combination and/or singly.

The lubricant additive of the present invention can suitably be used by adding approximately one pint (0.473 litre) of the lubricant additive to a 5 quart (4.73 litre) oil change. The lubricant additive of the present invention may provide effective protection against corrosive and engine wear effects caused by methanol or ethanol for oil change intervals of more than 4000 miles and in some cases up to 6000 miles (6437 and 9656 km).

The polyalkylene glycol, preferably polypropylene glycol, functions as a methanol or ethanol solubilizer, a non-ash dispersant and a scavenger for aldehydes. A solubilizer of this type is required to dissolve the large amounts of methanol or ethanol introduced into the lubricant during the combustion process. The polyalkylene glycol solubilizes the methanol or ethanol thereby preventing dry spots on the upper cylinder and bearing surfaces. In the absence of glycol, methanol or ethanol is insoluble in hydrocarbon lubricants and dry spots can occur. In addition, a polyalkylene glycol contains hydroxyl groups which react with the aldehydes formed by the oxidation of methanol or ethanol. The reaction product of a polyalkylene glycol and formaldehyde or acetaldehyde is also a good solvent for methanol or ethanol and continues to function as a methanol or ethanol solubilizer.

The amine component functions as a base number additive to neutralize formic or acetic and carbonic acids formed by the oxidation of methanol or ethanol and by the reaction of water and carbon dioxide, respectively. The amine component also functions as an antioxidant, minimizing the oxidation of methanol or ethanol to their respective aldehydes and acids.

The presence of larger amounts (about 1 to 4 wt. %) of organic amines in preferred embodiments of the present invention, as compared to the amount generally contained in conventional lubricant additives (about 0.25 wt. %), minimizes depletion of alkaline metal salts, such as naphthenates and sulfonates. The alkaline metal salts are depleted when they react with carbonic acid to form insoluble carbonates, competing with the neutralization of carbonic acid. The neutralization reaction is faster and more likely to occur, but the precipitation reaction becomes a problem when the organic amines become depleted.

With more organic amines present, more carbonic acid is neutralized and there is less carbonic acid available to react with the alkaline metal salts.

The phosphoric acid ester, preferably ortho-tricresylphosphate, functions as in anti-wear agent and when used with methanol or ethanol fuel it is superior to the conventional anti-wear agent, zinc dialkyldi thiophosphate. Zinc dialkyldithiophosphate is almost universally used in automotive lubricants for gasoline burning engines but loses its anti-wear properties rapidly in methanol or ethanol burning engines because it readily transesterifies with the alcohols.

A lubricant additive can be evaluated based on the amounts of wear elements, such as iron, lead, and copper, detected in an oil sample by spectrochemical analysis after the engine has been driven a certain number of miles after an oil change. These metals or wear elements show up in the lubricant as a result of excessive corrosion of or failure of certain engine components made of that metal as well as normal mechanical wear.

Table 1 sets forth criteria for evaluation of lubricant wear element data. The primary and secondary source in the engine of each wear element is given as well as the average amount in ppm's of each wear element which would be found in the oil at the "break-in" point and at the "post break-in" point. Engine wear levels during the break-in period tend to be relatively high. After the engine has been broken in, the wear levels reach a plateau, remaining stable for about 50,000 miles (80,467 km), depending on the par ticular vehicle and degree of maintenance. The "break-in" point for an average engine is generally in the 0 to 10,000 mile (16,093 km) range. The evaluation criteria found in Table 1 will be used to evaluate the data set forth in Examples 1 through 4.

Base number is a measure of the oil detergent action and its ability to inhibit corrosion. New automotive oils commonly have a base number of 4 to 5. For any oil, a reading of 1 or less indicates a dangerous depletion of additive reserves. A base number of 2 is generally considered to provide an adequate margin of protection in a gasoline burning engine.

TABLE 1 Criteria for Evaluation of Lubricant Wear Element Data Evaluation Criteria, ppm Source Break-In Post Break-In Wear Element Average Excessive Average Excessive Primary Secondary Iron (Fe) 200-400 400 10-100 200 cylinder block, wall crank shaft, wrist pins, rings, valves, oil pump, fuel tank Molybdenum 2-4 5 0-2 3 cylinder block, (Mo) wall crank shaft, wrist pins, rings, valves, oil pump, fuel tank Lead (Pb) 100-300 300 5-100 150 bearings flashing, TEL in fuel Copper (Cu) 50-150 150 5-75 100 bearings bushings, wrist pins, cam, valve, train, thrust washers, oil pump Tin (Sn) 20-50 50 1-10 15 bearings flashing Chromium (Cr) 2-10 10 1-5 5 rings crank shaft exhaust valves Nickel (Ni) 3-5 5 1-2 4 valves, rings crankshaft Aluminum (Al) 30-100 100 1-15 30 pistons, aluminum blocks Example 1 An oil sample comprising a conventional automotive lubricant and 10 wt. % of the lubricant additive of the present invention, comprising about 97 wt. % polypropylene glycol 2000, about 1.0 wt. % n-octadecylamine, about 1.0 wt. % N-phenyl-2-naphthylamine, and about 1.0 wt. % ortho-tricresylphosphate, was taken from the crankcase in methanol fueled engine C which had been driven the equivalent of 20,551 miles (33,073 km) with an oil change at 3942 miles (6344 km) prior thereto.

The sample had a total base number of 3.36. Spectrochemical analysis revealed that the following amounts of wear elements were present in the oil sample; 75 ppm iron, 27 ppm lead, 25 ppm copper, 1 ppm chromium, 9 ppm aluminum, 3 ppm nickel, and 11 ppm tin. The engine had been driven the equivalent of 20,551 miles (33,073 km) which is "post break-in" mileage. Thus, the sample will be evaluated using "post break-in" criteria from Table 1.

The base number of 3.36 was well above 2 which is considered an adequate base number, indicating that the amines meta-octadecylamine and N-phenyl-2-napthylamine, had not been depleted and were still available for neutralizing formic and carbonic acids and preventing oxidation of methanol to formaldehyde and formic acid.

Referring to Table 1, the iron, lead, copper and chromium content in the sample was within the average and acceptable content range for those wear elements at "post break-in" mileage. The aluminum content of 9 ppm was more than average but much less than 30 ppm, which is considered an excessive amount at "post break-in" mileage. The nickel content of 3 ppm was more than average but much less than 4 ppm which was considered an excessive amount at "post break-in" mileage. The tine content of 11 ppm was more than average but much less than 15 ppm which is considered an excessive amount at "post break-in" mileage.

The data provided by Example 1 illustrates that the lubricant additive of the present invention effectively minimizes corrosion and engine wear caused by methanol containing fuel.

Example 2 An oil sample comprising a conventional automotive lubricant and 10 wt. % of the lubricant additive of the present invention, comprising about 98 wt. % polypropylene glycol 2000, about 1.0 wt. % n-hexadecylamine, and about 1.0 wt. % ortho-tricresylphosphate, was taken from the crankcase in methanol fueled engine B which had been driven the equivalent of 46,153 miles (74,276 km) with an oil change at about 3,421 miles (5505 km) prior thereto.

The sample had a total base number of 2.91. Spectrochemical analysis revealed that the following amounts of wear elements were present in the sample: 87.7 ppm iron, 67 ppm lead, 96 ppm copper, 12 ppm chromium, 12 ppm aluminum, 4 ppm nickel, and 11 ppm tin. The engine had been driven the equivalent of 46,153 miles (74,276 km) which is "post-break-in" mileage. Thus, the sample will be evaluated using "post break-in" criteria from Table 1.

The base number of 2.91 was well above what is considered an adequate base number (base number 2), indicating that the amine component, n-hexadecylamine, had not been depleted and was still available for neutralizing formic and carbonic acids and preventing oxidation of methanol to formaldehyde and formic acid.

Referring to Table 1, the iron, lead, copper, and aluminum content was within the average and acceptable content range for those wear elements at "post break-in" mileage. The chromium and nickel content were above average due to the fact that engine B's rings and valves were in poor condition. Rings and valves are primary sources of wear elements chromium and nickel, thus explaining the higher than average content of those wear elements in the oil sample.

The low amounts of the major wear elements, iron, lead, and copper, as well as the above average base number, indicate that the lubricant additive of the present invention effectively minimizes corrosion and engine wear caused by methanol containing fuel.

Example 3 An oil sample comprising a conventional automotive lubricant and 10 wt. % of the lubricant additive of the present invention, comprising about 98.0 wt. % polypropyl- ene glycol 2000, about 1.0 wt. % n-octadecylamine, and about 1.0 wt. % ortho-tricresylphosphate, was taken from the crankcase in methanol fueled engine D which had been driven the equivalent of 73,395 miles (118,117 km) with an oil change at about 4,375 miles (7041 km) prior thereto.

The sample had a total base number of 2.46. Spectrochemical analysis revealed that the following amounts of wear elements were present in the sample: 73 ppm iron, 20 ppm lead, 64 ppm copper, 2 ppm chromium, 11 ppm aluminum, 2ppm nickel, and 0 ppm tin. The mileage was "post break-in" mileage and thus the sample will be evaluated using "post break-in" criteria from Table 1.

The base number of 2.46 is well above the adequate base number of 2, indicating that the amine component, n-octadecylamine, had not been depleted and was still available for neutralizing formic acid and carbonic acid and preventing oxidation of methanol to formaldehyde and formic acid.

Referring to Table 1, the iron, lead, copper, chromium, aluminum and nickel content were within the average and acceptable range for those wear elements at "post break-in" mileage. The tin content was below the average content range for tin.

The data in Example 3 demonstrates that the lubricant additive of the present invention is effective in minimizing corrosion and engine wear caused by methanol containing fuel.

Example 4 An oil sample comprising a conventional automotive lubricant and 10 wt. % of the lubricant additive of the present invention described in Example 3, was taken from the crankcase in methanol fueled engine D which had been driven the equivalent of 76,636 miles (123,334 km) with an oil change at about 4,164 miles (6701 km) prior thereto.

The sample had a total base number of 3.30. Spectrochemical analysis revealed that the following amounts of wear elements were present in the sample: 50 ppm iron, 10 ppm lead, 56 ppm copper, 2 ppm chromium, 7 ppm aluminum, 0 ppm nickel, and 0 ppm tin.

The base number of 3.30 was well above the adequate base number of 2, indicating that the amine component, n-octadecylamine, had not been depleted and was still available for neutralizing formic and carbonic acids and preventing oxidation of methanol to formaldehyde and formic acid.

Referring to Table 1, the iron, lead, copper, chromium, and aluminum content were all within the average and acceptable range for these wear elements at "post break-in" mileage. The nickel and tin content were below average.

The data provided by Example 4 demonstrates that the lubricant additive of the present invention is effective in minimizing engine wear and corrosion caused by methanol containing fuel.

Claims

1. A lubricant additive for use with alcohol fuels, comprising a major amount of a polyalkylene glycol of an alkene having 2 to 3 carbons, a minor amount of a phosphoric acid ester, and a minor amount of an amine, wherein the amine is an aliphatic amine; a cycloaliphatic amine; a mixture of an aliphatic and a cycloaliphatic amine; or a mixture of an aliphatic amine, a cycloaliphatic amine or both and an aromatic primary amine, an aromatic secondary amine or both.

2. A lubricant additive according to claim 1, wherein the polyalkylene glycol content is 94 to 98.5 wt %, the amine content is 1 to 4 wt % and the phosphoric acid ester content is 0.5 to 2 wt %.

3. A lubricant additive according to claim 2, wherein the polyalkylene glycol content is 97 to 98.5 wt %, the amine content is 1 to 2 wt %, and the phosphoric acid ester content is 0.5 to 1 wt %.

4. A lubricant additive according to any one of the preceding claims, wherein the amine is an aliphatic amine.

5. A lubricant additive according to any one of claims 1 to 3, wherein the amine is a mixture of an aliphatic amine and a cycloaliphatic amine.

6. A lubricant additive according to any one of claims 1 to 3 or 5, wherein the cycloaliphatic amine is cyclohexylamine or methylcyclohexylamine.

7. A lubricant additive according to any one of claims 1 to 3, wherein the amine is a mixture of an aliphatic amine and an aromatic primary amine, an aromatic secondary amine or a mixture of both.

8. A lubricant additive according to any one of claims 1 to 3 or 6 wherein the aromatic primary amine is ortho-phenylenediamine, meta-phenylenediamine, para-phenylenediamine, ortho-toluidine, meta-toluidine, para-toluidine, aniline, xylidine, naphthylamine, benzylamine, toluenediamine or naphthalenediamine.

9. A lubricant additive according to claim 8, wherein the aromatic primary amine is ortho-phenylenediamine.

10. A lubricant additive according to any one of claims 1 to 3 or 6 to 9, wherein the aromatic secondary amine is N-phenyl-2-naphthylamine, phenyl-a-napthylamine, phenyl-(3-naphthylamine, tolynaphthy- lamine, diphenylamine, ditolylamine, phenyltolylamine, 4,4'-diaminodiphenylamine, or N-methylaniline.

11. A lubricant additive according to claim 10, wherein the aromatic secondary amine is N-phenyl-2naphthylamine.

12. A lubricant additive according to any one of the preceding claims, wherein the aliphatic amine is an aliphatic amine having 10 to 30 carbon atoms.

13. A lubricant additive according to claim 11, wherein the aliphatic amine is octadecylamine or hexy Idecylamine.

14. A lubricant additive according to any one of the preceding claims, wherein the polyalkylene glycol is polypropylene glycol, polyisopropylene glycol, or polyethylene glycol.

15. A lubricant additive according to claim 14, wherein the polyalkylene glycol is polypropylene glycol.

16. A lubricant additive according to claim 15, wherein the polypropylene glycol has a molecular weight of about 2000 grams/mole.

17. A lubricant additive according to any one of the preceding claims, wherein the phosphoric acid ester is ortho-tricresylphosphate, meta-tricresylphosphate, para-tricresylphosphate, dibutylphenylphosphate, tributylphosphate, tri-2-ethylhexylphosphate, trioctylphosphate, diphenyl ortho-phosphonate, dicresyl ortho-phosphonate, trilauryl ortho-phosphonate, or tristearyl ortho-phosphonate.

18. A lubricant additive according to claim 17, wherein the phosphoric acid ester is ortho-tricresylphosphate.

19. A lubricant additive substantially as hereinbefore described in any one of Examples 1 to 3.

20. A lubricant composition comprising a lubricant additive as claimed in any one of the preceding claims.

21. A method of preparing a lubricant composition comprising mixing together a lubricant and, as an additive, a polyalkylene glycol of an alkene having 2 to 3 carbon atoms, a phosphoric acid ester and an amine, the amine being an aliphatic amine; a cycloaliphatic amine; a mixture of an aliphatic and a cycloaliphatic amine; or a mixture of an aliphatic amine, a cycloaliphatic amine or both and an aromatic primary amine, an aromatic secondary amine or both, the polyalkylene glycol being a major amount of the additive in the lubricant composition, and the phosphoric acid ester and the amine each being a minor amount of the additive in the lubricant composition.

22. Method according to claim 21 wherein the additive is as defined in any one of claims 1 to 19.