US2795547A - Lubricating oil compositions - Google Patents

Description

LUBRICATING OIL COR POSITIONS OliverLHarie, Berkeley, and John R. Thomas, Albany, Cahf., .assignors to California Research Corporation, San Francisco, Calif., a corporation of Delaware No Drawing. Application June 29, 1954, Seriai No. 440,250

2 Claims. (Cl. 252--49.6)

This invention relates to novel lubricant compositions. More particularly, the invention is concerned with novel lubricating oil compositions having improved oxidation and corrosion inhibiting properties.

Lubricating oils generally have a tendency to deteriorate due to oxidation and form decomposition products which are corrosive to metals. Since lubricating oils in use today almost invariably come into contact with metal surfaces, the problem of overcoming oxidation and corrosion is considered to be one of major importance. Operating conditions encountered in modern internal combustion engines in which these oils are commonly employed involve increased temperatures, higher speeds and reduced clearances which tend to promote decomposition and the formation of corrosive products. Furthermore, these engines generally employ alloy metal bearings which, besides their possible catalytic effect on the decomposition 'of the hydrocarbon type mineral lubricating oils, are easily corroded and this, in turn, has seriously accentuated the oxidation and corrosion problems in mineral lubricating oils.

Inhibitors have been added to lubricating oils to improve their resistance to decomposition and avoid corrosivity. Mineral lubricating oils for internal combustion engines, due to the severity of their service, have also been compounded with additional agents such as wear inhibitors, sludge inhibitors and detergents to loosen and suspend products of decomposition and counteract their effect. Unfortunately, many of these agents may adversely affect the efficiency of the oxidation and corrosion inhibitors and it is a problem to find inhibitors which will function in combination with them. Furthermore, some of the most effective oxidation and corrosion inhibitors contain active sulfur and are, therefore, extremely corrosive to silver and similar metals which are subject to attack by active sulfur. These types of metals, although once not so widely used in contact with lubricating oils and therefore considered to constitute only a minor problem, are being increasingly employed today. Particularly in certain important classes of internal conbustion engines as, for example, marine and rai.road diesel engines, silver metal-containing bearings are more and more common and the problem of providing proper lubrication for them is one of major importance.

It is, therefore, a general object of this invention to provide lubricating oil compositions having improved antioxidant and anticorrosion properties.

A more particular object of the invention is to provide lubricating oil compositions which are noncorrosive to silver and similar metals.

Another more particular object is the provision of mineral lubricating oil compositions in which the tendency to corrode alloy bearings of internal combustion engines has been inhibited.

A further and somewhat related object is to provide compounded mineral lubricating oil compositions having improved anticorrosion properties without adversely afiect- Patented June 11,1957

ing the stabilizing, deterging and lubricating qualities of the hydrocarbon oil composition.

Another and still more particular object of the invention is the provision of mineral lubricating oil compositions which are noncorrosive to silver metal-containing bearings of the type employed in railroad diesel engines.

Additional objects of the invention will become apparent from the description and claims which follow.

In the accomplishment of the above objects, it has been found that compositions comprising an oil of lubricating viscosity and a complex of a metal compound selected from the group consisting of acids, oxides and salts of boron with a metal chelating agent having two functional groups, not more than one of which is a hydroxyl radical, in vicinal or beta position to one another on the carbon skeleton of a hydrocarbon linkage have greatly enhanced anticorrosion properties. It has also been found that, in particular, compositions comprising a compounded mineral lubricating oil for internal combustion engines which is normally corrosive to alloy bearings and such chelates are substantially noncorrosive.

The metal chelating agent referred to above is the accepted terminology for a definite and well-known class of chemical compounds. Such compounds have been heretofore described in many published texts including the recent book entitled Chemistry of the Metal Chelate Compounds by Martell and Calvin which was published by Prentice-Hall, Inc. of New York in 1952. For present purposes the more suitable compounds of this class are members of the group consisting of dithiols, diamines, mercapto alcohols, amino alcohols, amino thiols, dicarboxylic acids, hydroxycarboxylic acids, mercaptocarboxylic acids, aminocarboxylic acids, beta-diketones, beta-keto carboxylic acid esters, dimercapto benzenes, mercaptohydroxy benzenes, diamino benzenes, aminohydroxy benzenes, aminomercapto benzenes, hydroxycarboxy benzenes, aminocarboxy benzenes, and mercaptocarboxy benzenes having the two functional groups in vicinal or beta position to one another on the carbon skeleton.

The normal tendency of oils to become oxidized and corrosive is definitely inhibited in the improved compositions of the invention. Metal surfaces in general are not corroded by contact with these compositions and internal combustion engine alloy bearings, in particular, are remarkably benefited. Bearings of silver and similar metals which, as stated above are increasingly important due to their present expanded use in marine and railroad diesel engines, are not corroded by these compositions whereas conventional oxidation inhibited oils have severely pitted and corroded such bearings. The advantages of these improvements are obtained in the compositions of this invention without loss of stability or detergency in the composition.

The complexes of the lubricating oil compositions according to this invention are prepared by the reaction of a mixture of the acid, oxide or salt of boron and chelating agent. The mixtures are ordinarily heated to accelerate the reaction. Although the nature of the reaction is not definitely known, it is believed that two of the functional groups of a single ketocarboxylic acid ester, dithiol, dicarboxylic acid, etc. react with the acid to form what is commonly termed a metal chelate compound. These compounds are characterized by a claw type of structure in which one or more rings of similar or unlike structure due to the use of mixed chelating agents are formed including the boron.

The preferred chelates of the above type are oil-soluble and the chelating agents are usually selected so as to impart oil solubility to the complex or chelate. Chelating agents containing from 2 to 18 carbon atoms are usually suitable since the less oil-soluble chelates may be used in combination with dispersants such as alkaline earth metal petroleum sulfonates or oil-solubilizing agents such as glycols and other polyhydric alcohols as well as ethers thereof. Those containing from 6 to carbon atoms in the carbon skeleton are preferred since they impart an optimum degree of oil solubility to the chelate or complex.

Examples of suitable chelating agents within the above- 7 described class include vicinaland beta-dithiols such as ethylene mercaptan and 1,3-propanedithiol; vicinaland beta-mercapto alcohols such as beta-mercaptoethanol, 3- mercapto-l-propanol; vicinaland beta-diamines such as ethylenediamine and propylenediamine; vicinaland betaamino alcohols such as ethanolamine and S-amino-lpropanol; vicinaland beta-aminothiols such as thioethanolamine and 3-amine-l-mercaptopropane; vicinaland beta-dicarboxylic acids such as oxalic acid and malonic acid; vicinaland beta-hydroxy carboxylic acids such as glycolic acid and beta-hydroxybutyric acid; vicinaland beta-mercapto carboxylic' acids such as thioglycolic acid and beta-mercaptobutyric acid; vicinaland beta-amino carboxylic acids such as glycine and beta-aminobutyric acid; beta-diketones such as acetylacetone and benzoylacetone; beta-ketocarboxylic acid esters such as ethyl acetoacetate; etc. The foregoing compounds are characterized by normal or branched carbon skeletons. They may have substituted in various positions along the carbon skeleton, aromatic and substituted aromatic rings; hydroxy, alkoxy, and aryloxy radicals; sulfhydryl, alkylthioether, arylthioether, alkylthioester, and arylthioester groups; acyl, aroyl thioacyl and thioaroyl radicals; amino, alkylamino, arylamino, acylamido and aroylamido radicals; and nitro, halogen and sulfato groups. However, preferred chelating agents of the aforementioned type for present purposes are those having an aliphatic hydrocarbon group between the two functional groups.

Also suitable as chelating agents are various carbocyclic or aromatic chelating agents including dimercaptoaromatic compounds such as thiocatechol; vicinal-mercaptohydroxy aromatic compounds such as monothiocatechol or mercaptohydroxy benzene; vicinal-diarninoaromatic compounds such as o-phenylenediamine; vicinal-aminohydroxyaromatic compounds such as o-aminophenol; vicinalaminomercaptoaromatic compounds such as o-aminothiophenol; vicinal-hydroxycarboxyaromatic compounds such as salicylic acid; vicinal-aminocarboxyaromatic compounds such as o-aminobenzoic acid; vicinal-mercaptocar boxyaromatic compounds such as o.-mercaptobenzoic acid; etc. The aforementioned carbocyclicor aromatic chelating agents may have various ring substituents including aromatic and substituted aromatic rings; hydroxy, alkoxy, and aryloxy radicals; sulfhydryl, alkylthioether, arylthioether, alkylthioester, and arylthioester groups; acyl, aroyl, thioacyl and'thioaroyl radicals; amino, alkylamino, arylamino, acylamido, and aroylarnido radicals; and nitro, halogen and sulfate groups. For present purposes those aromatic chelating agents having the two functional groups on a benzene ring or an alkyl benzene containing from 2 to 18 carbon atoms in the alkyl group are preferred .since the chelates of the above-described metals prepared with them possess the most satisfactory oil-solubility characteristics.

For present purposes the chelating agents most preferred out of the above-described classes are the beta-ketocarboxylic acid esters of from 4 to 18 and. preferably 4 to 10 aliphatic carbon atoms. Illustrative chelating agents of this particular group are ethyl acetoacetate, ethyl acetobutyrate, acetoacetic acid, pyruvic acid, etc. These chelating agents give complexes of the previously described types which are superior corrosion and/ or oxidation inhibitors in the lubricating oil compositions of the invention.

Although it is convenient for the sake of illustration in the above description of the invention torefer to the reaction of an acid of the boron with the various chelating agents or mixtures thereof to form the complexes for the lubricating oil compositions, other compounds of boron such as the oxides and salts mentioned above may also be employed to provide similar chelates. Suitable boron compounds include boric anhydride, boron trichloride and other similar acting reagents.

The complex of boron described above is present in the compositions of the invention in an amount at least suflicient to inhibit corrosion or oxidation. Small amounts, usually from about 0.01 to about 5.0 percent by Weight based on the oil, are efiective. Proportions ranging from about 0.05 to about 1.0 percent are preferred in most lubricating oil compositions. Concentrates containing larger proportions, up to 50 percent, either in solution or suspension, are particularly suitable in compounding operations.

Any of the well-known types of oils of lubricating viscosity are suitable base oils for the compositions of the invention. They include hydrocarbon or mineral lubricating oils of naphthenic, paraflinic, and mixedfnaphthenic and paraffinic types. They may be refined by any of the conventional methods such as solvent refining and acid refining. Synthetic hydrocarbon oils of the alkylene polymer type or those derived from coal and shale may also be employed. Alkylene oxide polymers and their derivatives such as the propylene oxide polymers and their ethyl esters and acetyl derivatives. in which the terminal hydroxyl groups have been modified are also suitable. Synthetic oils of the dicarboxylic acid ester type including dibutyl adipate, di-Z-ethylhexyl sebacate, di-n-hexyl fumaric polymer, dilauryl azelate, and the like may be used. Alkyl benzene types of synthetic oils such as tetradecyl benzene, etc. are also included. Liquid esters of acids of phosphorus including tricresyl phosphate, diethyl esters of decane phosphonic acid, and the like may also be employed. Also suitable are the polysiloxane oils of the type of polyalkyl, polyaryl, polyalkoxy and polyaryloxy siloxanes such as polymethyl siloxane, polymethylphenyl siloxane and polymethoxyphenoxy siloxane and silicate ester oil-s such as tetraalkyl and tetraaryl silicates of the tetra-Z-ethylhexyl silicate and tetra-p-tert.-butylphenyl silicate types.

In a preferred embodiment of the invention, as mentioned above, the complexes are employed in combina- .the case of the other, straight oils of lubricating viscosity,

a major proportion of the lubricating oil normally corrosive to metals and/or subject to oxidation and a small amount, suflicient to inhibit said corrosion and/ or oxidation, of the complex provides a remarkably improved composition. These compounded oils customarily contain detergents such as the oil-soluble petroleum sulfomates and stabilizers such as the metal alkyl phenates. Other agents such as oiliness agents, viscosity index improvers, pour point depressants, blooming agents, peptiz- ,ing agents, etc. may also be present.

In further illustration of the invention, the following examples are submitted showing the preparation of representative complexes and evaluation of their eifectiveness as corrosion inhibitors and antioxidants in oil composition. Unless otherwise specified the proportions given in these examples are on a Weight basis.

EXAMPLE A mixture of two moles of ethyl acetoacetate and one mole of boric acid in 300 milliliters of benzene is charged to a glass reaction flask equipped with stirring mechanism, reflux condenser and water separation trap. The mixture is refluxed with continuous water separation until it becomes homogenous. The product containing the boron ethyl acetoacetate formed in the reaction is then concentrated to a colorless viscous liquid by evaporation of the benzene and used as a concentrate in blending test oils.

The effectiveness of the lubricating oil compositions of the invention is demonstrated by the Copper-Lead Strip Percent by weight Iron 0.008 Lead 0.004 Copper 0.002 Manganese 0.0005 Chromium 0.004

In the tests the reference oil is a compounded oil which consists of a solvent refined SAE 40 mineral lubricating oil base having a viscosity index of 60 and containing millimoles per kilogram of neutral calcium petroleum sulfonate and millimoles per kilogram of calcium alkyl phenate, sulfurized. The results of the test are shown in the following table. The concentrations of complex employed are given in rnillimoles of boron per kilogram of oil or percent by weight of the composition.

Table I COPPER-LEAD STRIP CORROSION TEST As shown by the above test data, the reference mineral lubricating oil composition alone gives copper-lead strip Weight losses due to corrosion of over 250 milligrams in the 20-hour period. By way of distinction, compositions in accordance with this invention containing the same mineral lubricating oil base and a complex of the previously described type give as little as 2.0 milligrams for the same period. This shows that the compositions of the present invention are effectively inhibited against oxidation and/or corrosion characteristics due to the oxidative deterioration of the oil.

Compositions which comprise a major portion of a compounded oil of lubricating viscosity having a base reserve and a minor portion at least sufiicient to enhance the resistance of said oil against base depletion due to oxidation of a complex of the above type constitute another embodiment of this invention. Such base reserve oils contain additives such as basic alkaline earth metal sulfonates, alkaline earth metal alkyl phenates, alkaline earth metal salts of hydroxy phenyl sulfides and disulfides, etc. in amounts to give the composition a pH on the alkaline side, i. e., 10 or so. Ordinarily, 0.01 to 10.0% is sufiicient. The proportions of boric acid complex apply here as mentioned above.

In the Navy propulsion load test described in MIL-P- 17269 (Ships) July 17, 1952, the compositions of the invention are evaluated as diesel engine lubricating oils under severe operating conditions. The tests are run in a General Motors 4-cylinder diesel engine using one percent sulfur fuel. Copper-lead bearings are employed. The tests are run at a constant speed of 1800 R. P. M. under 2. load of brake horsepower per cylinder. The

crankcase temperature is 250 F. The present test is run continuously to simulate railroad diesel engine performance unlike the standard Navy test procedure which permits regular 4-hour shutdown periods. Sea water was also excluded for the same reason. The reference oil, as before, is a solvent refined SAE 40 mineral lubricating oil base having a viscosity index of and containing 10 mM/kg. of neutral calcium petroleum sulfonate and 20 mM/kg. of calcium alkyl phenate, sulfurized. Test results are as follows:

Table II Weight Loss mgsJW hole Bearing (Hours) Oil Reference oil 70 830 2, 000 2.0% boron ethyl acetoacetate in reference oil. 31 50 In the Navy propulsion load test results shown above, the bearing weight loss due to corrosion by the reference oil, a conventional heavy duty compounded oil, was extremely high. Such an oil would be impossible to use for any prolonged period of time without shutdown. By way of distinction, the lubricating oil composition of the invention containing borate complexes gives remarkably low corrosion losses after as much as 150 hours of continuous operation. Greatly extended periods of uninterrupted operations of diesel engines are thus possible with these improved oils.

The nature of the. improved lubricating oil compositions of the invention and their effectiveness should be readily apparent from the many'illustrations, given above. Oxidation and corrosivity in the compositions are definitely inhibited to a very substantial degree. Particularly corrodible metals such as engine alloy bearings of copper, lead, and the like, as well as bearings of silver, are not adversely affected. This is indeed remarkable since the problem of devising lubricant compositions uniformly noncorrosive to both types of bearing metals has long confronted workers in the art. The advantages of these improvements are obtained without loss of other desirable properties of the lubricant compositions.

Although the compositions of the invention have been primarily described as crankcase lubricants for internal combustion engines, they are also useful as turbine oils, hydraulic fluids, instrument oils, constituent oils in grease manufacture, ice-machine oils, and the like.

We claim:

1. A lubricant composition comprising an oil of lubricating viscosity and boron ethyl acetoacetate in an amount sufficient to inhibit corrosion.

2. A lubricant composition comprising a mineral lubricating oil for internal combustion engines which is normally corrosive to alloy bearings and from about 0.01 to about 5.0 percent by weight based on the oil of boron ethyl acetoacetate.

References Cited in the file of this patent UNITED STATES PATENTS 2,144,654 Guthmann et al J an. 24, 1939 2,161,184 McKone et al June 6, 1939 2,305,627 Lincoln et al Dec. 22, 1942 2,465,296 Swiss Mar. 22, 1949