US2452320A - Oxidation-inhibited lubricating compositions - Google Patents

Description

Patented Oct.- 26,

OXIDATION -INHIBITED LUBRICATIN G COMPOSITIONS Herman D. Kluge and JohnA. Patterson, Wappingers Falls, N. Y

., asslgnors to The Texas Company, New York, N. Y., a corporation of Delaware No Drawing. Application November 30, 1945, Serial No. 632,106. In Canada December 2, 1944 7'Clalms. 1.

This invention relates to an improved lubricating composition possessing enhanced oxidationresistant properties, and particularly to lubricating compositions containing the combination of an oxidation inhibitor and an oil-miscible dicarboxylic acid.

This is a. continuation-in-part of copending application, Serial No. 519,812, filed Jan. 26, 1944,"

now abandoned.

The hydrocarbon oils used in lubricating compositions are usually subject to deterioration caused by heat and aeration resulting from the conditions of operation of the lubricant. This deterioration or-oxidation causes the formation of acidic and sludge-like bodies which attack the bearing metals and deposit carbonaceous films on the surfaces to be lubricated. The resistance of the hydrocarbon oil and/or lubrtating composition to deterioration or oxidation is a measure of the lubricating value of the oil or composition in service and is a definite criterion of the service life' of the lubricant. This resistance has been materially increased by the incorporation of small amounts of so-called oxidation inhibitors which, in eifect, retard or minimize the formation of the acidic and sludge-like bodies in the oil for an extended period of time, depending upon the type of inhibitor. 1

However, increased demands on the performance of mechanical equipment have necessitated an improvement in the lubricants with which the equipment is lubricated in such a manner as to provide safe lubrication over longer service periods and undermore stringent operating conditions. This problem of improving a, lubricant so as to increase the service life cannot be solved by the simple expedient of increasing the amount of oxidation inhibitor in the lubricant since'the majority of inhibitors possess an optimum concentration above which no further improvement in resistance is noted. Also, the further incorporation of a second oxidation inhibitor does not necessarily improve the oxidation-resistant properties since it is recognized that these types of inhibitors are not generally compatible with one another, and as a rule do not cooperate to produce an additive eifect.

It has been found that, by incorporating a small amount of an oil-miscible dicarboxylic acid in a lubricating composition which is inhibited against oxidation in the presence of water, or by incorporating a combination of an oil-miscible dicarboxylic acid and an oxidation inhibitor possessing anti-oxidant properties in the presence of water into a lubricating composition, a lubricant is obtained whose oxidatiomresistant properties are materially greater than those resulting from the oxidation inhibitor alone.

Although the invention is broadly applicable to all oxidation inhibitors capable of functioning as such in the presence of water, it is particularly applied to the oxidation inhibitors falling within the classification of diamino diaryl alkanes together with substituted derivatives thereof. In general, the oxidation inhibitors which function as such in the presence of waterare those which are usually water insoluble and resistant to hydrolysis or decomposition in the presence of water.

As previously mentioned, the inhibitors generally possess an optimumconcentration when incorporated in hydrocarbon oils or lubricating compositions, and this optimum concentration is dependent upon the type of inhibitor, the type of .'base oil, and the conditions of operation of the lubricant. These concentrations usually vary within the range of Mil-5.0% by weight and, in most instances, between 0.12.0% by weight;

According to the invention it has been discovered that the combination of an oil-miscible dicarboxylic acid and an oxidation inhibitor, preferably a diaminodiaryl alkane, when incorporated in a mineral lubricating oil provides a lubricating composition whose resistance to oxidation is materially greater than that obtained by the addition of the oxidation inhibitor itself.

It is to be understood that the sequence of incorporation of the inhibitor and dicarboxylic acid is not a limitation of the invention and de-.

pends only upon the practical aspects of the compounding ofthe lubricant. In other words, aconcentrate of the combination of the dicarboxylic acid and inhibitor may be incorporated in the base oil or the dicarboxylic acid may be separately incorporated in a previously prepared oxidation-inhibited lubricant.

The oil-miscible dicarboxylic acids of the invention may be any aliphatic dicarboxylic acid which contains at least 10 carbon atoms in the molecule and at least one carbon atom between the carboxyl groups.

All dicarboxylic acids are subject to classification in either of two groups: (1) dicarboxylic acids which possess a fixed configuration; and

(2) dicarboxylicacids which exist in stereo-isomeric form. For the purposes of the present invention it has been found preferable to select an oil-miscible dicarboxylic acid whose carboxyl groups are in a plane symmetrical configuration. Typical examples of the types of acids falling 'droxide in 200 cos. of water within this preferred classification are the alkyl maleic acids, alkyl succinic acids. and alkyl citraconic acids.

The amounts in which the dlcarboxylic acids are incorporated in an oxidation-inhibited lubricating composition, or combined with an oxidation inhibitor and then incorporated in a lubricant, will 'vary in accordance with the type of inhibitor and the lubricating oil to which they are added. In general, the dicarboxylic acid is incorporated in-the lubricating oil in amounts ranging between 0.005%- In certain types of oil whose specifications include a maximum neutralization number, such as in turbine oil, the amounts of the acid incorporated will necessarily have to be quite small. However, in the other lubricating oils or compositions where the neutralization number is not a serious factor and performance is the sole consideration, greater amounts of the acid may be employed.

As an example of the type of dicarboxylic acids contemplated by the invention, the following description of and test data on alkyl maleic acid are presented.

The preparation of the alkyl maleic acids is carried out by condensation of maleic acid anhydride with an olefin or mixtures thereof, either straight or branched chain which contains an average of at least 6 carbon atoms and preferably 10 or more. These olefins may be obtained from any of the usual sources, such as vapor phase cracking of petroleum oil or wax, or the polymerization of lower molecular weight olefins. This condensation reaction, followed by hydrolysis, produces dicarboxylic acids which mayexist as an alkyl maleic acid, an alkenyl succinic acid, or mixtures thereof. In order to simplify the description of the acids produced by this reaction, reference will be made throughout the specification and claims to 'alkyl maleic acids.

The oxidation-resistant properties of the lubricating compositions prepared in accordance with the invention are illustrated by oxidation tests conducted on a lubricating oil containing an alkyl maleic acidand a representative diamino diaryl alkane. The alkyl maleic acid used in the oxidation test was prepared asiollows:

Two hundred ninety-seven grams of a poly"- mer gasoline distillate, boiling point 392-450" F., and,68.7 grams of maleic acid anhydride were heated with stirring at 356 F. for five hours. After cooling the reaction mixture to room temperature, a solution of 80 grams of sodium bywas introduced. The mixture was heated for one hour at a gentle reflux and thereafter cooled and filtered. The filtered solid was then dissolved in alcohol and water, filtered and evaporated on a steam bath. The residue was acidified with dilute hydrochloric acid, extracted with benzene, and the benzene solution washed with water until the aqueous layer was neutral to litmus. The benzene solution was then filtered and the solvent removed by heating on the steam bath. Neutralization No. 209.9.

The oxidation test employed herein is recognized as theproposed ASTM oxidation test for turbine oils.

In this test 300 cos. of the oil sample are introduced to an oxidation cell in which is suspended spiral coils of iron and cODper wire, and 60 ccs. of distilled water are added. Oxygen is introduced through a fritted glass outlet into the oxidation cell at the rate -of 3 liters'per hour.

and 3.0% by weight.

The oxidation cell is suspended in a heated oil bath and the temperature in the oxidation cell is 485-515 SaYbolt Universal at F.

Oxidation test Hrs. to 2.0 Neut. No. Reference 011 65-72 Reference oil #0.1% tetramethyidiamino diphenyl methane 174-200 Reference 011 #0.1% alkyl maleic acid 230-250 Reference oil 410.1% tetramethyldiamino diphenyl methane #01 alkyl maleic acid 830 It may be seen from the results obtained that the oxidation-resistant properties of an oil containing recognized oxidation inhibitors are substantially improveCLby the addition of an oilmiscible dicarboxylic acid such as an alkyl maleic acid.

Additional test results have indicated that oils inhibited with other well-known oxidation inhib itors falling within the general classification of diamino diaryi alkanes may also be improved by the incorporation of an oil-miscible dicarboxylic acid, and particularly one whose carboxyl groups are arranged in a plane symmetrical configurar tion, as, for instance, alkyl maleic acid. The

following are a few of the specific oxidation inhibitors whose resistant properties may be improved in accordance with the present invention:

Tetraethyldiamino diphenyl methane Diisoamyldiamino diphenyl methane Tetraamyldiamino diphenyl methane Dlmethyldiamino diphenyl nethane Tetramethyldiamino diphenyi ethane Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and therefore only such limitations should-be imposed as are indicated in the appended olaims.

We claim:

1. A lubricating composition comprising a mineral lubricating oil as the major constituent, about 0.005-3.0% by weight of an oilmiscible alkyl maleic acid having at least 10 carbon atoms in the molecule, and about 0.0l-5.0% by weight of an alkyl substituted diamino diphenyl alkane, wherein the said alkyl substituent contains from 1 to 5 carbon atoms and the said alkane is selected from the group consisting of methane and ethane.

2. A lubricating composition according to claim 1, wherein the alkyl maleic acid is a hydrolyzed condensation product of maleic acid anhydride with an olefin containing at least 6 carbon atoms in the molecule.

3. A lubricating composition according to claim 2, wherein the said alkyl substituted diamino diphenyi alkane is a polyalkyl diamino diphenyl methane.

4. A lubricating composition according to claim 3, wherein the said polyalkyi diamino diphenyl methane is tetramethyi diamino diphenyi methane.

having superioranti-oxidant properties in the presence of water 5. A lubricating composition resistant to ondation in the presence of water comprising a hydrocarbon oil normally subject to oxidation as the major constituent, about 0.005-3.0% by weight of an oil-miscible aliphatic dicarboxylic acid having at least 10 carbon atoms in the molecule and whose carboxyl groups are in a plane symmetrical configuration, said acid consistin of the elements carbon, hydrogen and oxygen and being free from ether linkages, and about 0.01-5.0% by weight of an alkyl substituted diamino diphenyl alkane, wherein the said alkyl substituent group contains from 1 to 5 carbon atoms and the said alkane is selected from the group consisting of methane and ethane, said dicarboxylic acid and said alkane compound flle of this patent:

being of such character and used in such proporeating composition of an alkyl substituted diamino diphenyl methane, and about 0.005-3.0% by weight of an oil-miscible dic'arboxyl ic acid having at least 10 carbon atoms in themolecule and a plane symmetrical configuration.

' HERMAN D. KIiUGE.

JOHN A. PATTERSON.

REFERENCES CITED I The following references are of record in the UNITED STATES PATENTS Number Name Date 1,789,302 Calcott Jan. 20, 1931 1,988,299 Clark Jan. 15, 1935 2,019,336 Clark Oct. 29, 1935 2,097,162 Musselman Oct. 26, 1937 2,133,734 Moser Oct. 18, 1938 2,151,300 Moran Mar. 21, 1939 2,224,158 Marks Dec. 10, 1940 2,225,533 Dewey Dec. 17, 1940 2,344,016 Anderson Mar. 14, 1944 2,346,356 Burk Apr. 11, 1944 2,351,347 Luten June 13, 1944 2,354,252 Fraser July 25, 1944 2,366,074 Wasson Dec. 26, 1944 2,371,142 Barnum et a1. Mar. 13, 1945 2,375,222 Griflin et al. May 8, 1945