US2998385A

US2998385A - Aluminum soap thickened lubricating oil

Info

Publication number: US2998385A
Application number: US827696A
Authority: US
Inventors: Leslie U Franklin; Julius C Gebhart
Original assignee: Gulf Oil Corp
Current assignee: Gulf Oil Corp
Priority date: 1959-07-17
Filing date: 1959-07-17
Publication date: 1961-08-29
Anticipated expiration: 1978-08-29

Description

Patented Aug. 29., 1961 ice 2,998,385 SOAP 'IHKIILKENED LUBRICATING This invention relates to a lubricating composition and more particularly to an aluminum soap thickened oil having improved viscosity storage stability.

Mineral lubricating oils thickened with an aluminum soap such as aluminum oleatc, aluminum stearate or aluminum naphthenate because of their resistance to oxidation have replaced in many instances lubricating oils having similar viscosities made from vegetable or animal oils. Aluminum soap thickened oils of semi-fluid consistency which have a stringy or tacky nature are known as mineral castor oils or castor machine oils. While the mineral castor oils have met with some success in lubricating fast moving heavy equipment, difliculty has been encountered with some of the prior art compositions in that the exact increase in viscosity for a given amount of aluminum soap is uncertain and the viscosity immediately following the preparation of the composition is no indication of what the viscosity will be after prolonged periods of quiescent storage. There is generally a marked change in the viscosity of such lubricants upon aging. As a result, such aluminum soap thickened oils of the prior art unless put into immediate service after being prepared do not possess the lubricating qualities which they had immediately following their preparation.

We have discovered that an aluminum soap thickened oil having improved viscosity storage stability can be obtained by incorporating in an oil the aluminum soaps of a plurality of soap-forming acids consisting of stearic acid, naphthenic acid and a branched-chain saturated fatty acid containing 8 carbon atoms. The improved lubricating composition of our invention therefore comprises a uniform dispersion of aluminum stearate, aluminum naphthenate and an aluminum soap of a branched-chain saturated fatty acid of 8 carbon atoms in a lubricating oil. We have found that the viscosity storage stability of a thickened lubricating oil containing suitable proportions of aluminum stearate, aluminum naphthenate and an aluminum soap of a branched-chain saturated fatty acids of 8 carbon atoms is markedly increased over the storage stability of otherwise identical compositions which contain only two of the three aluminum soaps.

The lubricating oil ingredient of the compositions provided by this invention may be any oil of lubricating grade. The lubricating oil, for example, may be a refined or semi-refined paraflinic-, naphthenicor asphalt-base oil having a viscosity of about 50 to about 4000 SUS at 100 F. If desired a blend of oils of suitable viscosity may be employed instead of a single oil by means of which any desired viscosity within the range of about 50 to about 4000 SUS at 100 F. may be secured. In the preparation of mineral castor oils or castor machine oils, we prefer to employ an oil having a viscosity between about 100 SUS and 500 SUS at 100 F. We do not wish to limit the invention in this regard, however, since the combination of aluminum'soaps are suitable for thickening an oil regardless of its initial viscosity. The oil content of the compositions prepared according to this invention comprises about 95.0 to about 99.0 percent by weight 01,. the total composition. The particular oil or oil blend as well as the exact amount of oil employed depends upon the characteristics desired in the final composition.

The stearic acid which can be employed in preparing the aluminum stearate for use in the compositions of the invention can be either a substantially pure product or it can be a commercial stearic acid which may contain substantial amounts of palmitic acid and minor amounts of myristic, oleic, arachidic and behenic acids. In producing the aluminum soap of stearic acid, any suitable saponification procedure can be employed. The saponification should be to such an extent that the product is predominantly aluminum t-ri-stearate or a mixture of aluminum diand tri-stearates wherein the t-ri-stearate predominates. We have found, for example, that if the saponification product is aluminum di-stearate or a mixture in which the aluminum di-stearate predominates, the grease produced therefrom does not possess the desired stability against change in viscosity on aging. The amount of aluminum stearate employed may vary depending upon the particular stearate employed and upon the properties desired in the final lubricating composition. In general, however, the aluminum stearate comprises about 0.3 to about 2.0 percent by weight of the total composition.

The naphthenic acid which can be employed as the starting material to produce aluminum naphthenate is a cycloparatfinic compound containing at least one carboxylic acid group per molecule. The cycloparafiinic compounds in the naphthenic acids generally have boiling points ranging from about 200 to about 350 C. and molecular weights within the range of about 128 to about 480. Specific compounds within the class referred to as naphthenic acids include, for example, methylcyclopentane carboxylic acid, dimet-hylcyclopentane carboxylic acid, methylcyclohexyl carboxylic acid, methylcyclohexyl acetic acid, etc. Commercially available mixtures can be used to produce an aluminum naphthenate for use in accordance with the invention. The commercially available mixtures may comprise the cycloparaflinic carboxylic acids containing from. 6 to 12 carbon atoms. However, higher molecular weight naphthenic acids, i.e., those containing more than 12 carbon atoms including those having double naphthenic rings can be used in preparing the aluminum naphthenate. In producing the aluminum naphthenate any suitable saponifying procedure can be employed. The amount of aluminum naphthenate employed may vary depending upon the particular naphthenic acid employed and upon the properties desired in the final lubricating composition. In general, however, the aluminum naphthenate comprises about 0.03 to about 0.3 percent by weight of the total composition. The aluminum naphthenate is advantageously prepared and used in the form of a mineral oil concentrate. Thus, if a concentrate is prepared which contains from 30 to 35 percent by weight of aluminum naphthenate, the amount of such concentrate which we prefer in'the ultimate composition comprises about 0.1 to about 1.0 percent by weight of the total composition. a

The saturated fatty acid containing 8 carbon atoms which is employed in preparing the third essential aluminum soap in accordance with the invention is a branchedchain acid. Thus, the C acid is a branched-chain saturated monocarboxylic acid, such as, for example, 2-

ethyl-hexanoic acid or an isooctyl acid or acid mixture obtained by oxidation of an isooctyl alcohol or mixture of isooctyl alcohols which in turn may have been obtained according to the OX0 process. Any suitable procedure for obtaining the aluminum soap of the 7 3. branched-chain saturated fatty acid containing 8 carbon atoms can be employed. We prefer aluminum di-Z-ethylhexanoate or a mixture wherein aluminum di-Z-ethylhexanoate predominates. The aluminum soap of the branched-chain saturated fatty acid of 8 carbon atoms can be used in varying amounts depending upon the particular soap employed and upon the properties desired in the final lubricating composition. In general, however, the aluminum soap of the branched-chain saturated fatty acid of 8 carbon atoms comprises about 0.3 to about 2.0 percent by weight of the total composition.

The aluminum soaps which we employ co-operate with each other to give a composition having particularly desirable properties. The aluminum soap of the C acid, for example, imparts the desired stringiness and tackiness to the composition. The aluminum stearate has a solubilizing effect on the aluminum soap of the C acid enabling the latter to give an optimum stringiness and tackiness. The aluminum naphthenate co-operates with the other aluminum soaps to give a desired viscosity and stabilizes the viscosity thus obtained against change with age. We have found that aluminum naphthenate is effective as a stabilizer only when the other two aluminum soaps are present in the proper ratios. None of the aluminum soaps will form stable gels alone. The total soap content of the composition comprises about 1 to about 5 percent by weight. While some latitude is permissible with respect to the relative proportions of the various constituents, we have obtained a particularly useful and storage stable composition when the amount of the aluminum soap of the C acid comprises about one and one-third times the amount of aluminum stearate and the amount of aluminum naphthenate is about onesixth the amount of the aluminum stearate. Thus, a preferred ratio of the aluminum soaps of stearic, naphthenic and C acids is 6:1:8, respectively. The relative ratios of the various aluminum soaps may vary within the following limits:

aluminum aluminum to 12:1 aluminum While, as indicated above, some degree of variation is permitted, it is essential that the aluminum naphthenate be employed within certain definite ratios to obtain a composition having the specific properties and characteristics desired. For example, in preparing a mineral castor oil if the proportion of the aluminum soap of naphthenic acid to the aluminum soaps of either stearic or C acids is less than about one-twelfth, the viscosity of the composition is not stable on aging. If, on the other hand, the proportion of the aluminum soap of naphthenic acid to the aluminum soap of the C acid is more than about one-sixth, there is a tendency for the gel structure of the composition to be broken down and also for the stringiness and tackiness to be reduced.

In preparing the compositions of the present invention, various compounding and blending procedures can be used in either a batch or a continuous process. For example, the aluminum soaps can be prepared separately and then blended into the lubricating oil or the soaps can be prepared in admixture with each other from a mixture of the corresponding naphthenic and fatty acids followed by blending the mixture of aluminum soaps into the oil. The soaps can be added to the oil as such or they can be utilized in the form of oil concentrates. The use of an aluminum soap in the form of an oil concentrate is desirable in that it facilitates the blending procedure. According to one embodiment, six parts by weight of aluminum tri-stearate in the form of a powder, eight parts by weight of aluminum di-2-ethyl-hexanoate in the form of a powder and three parts by weight of an oil concentrate containing 30 to 35 percent aluminum naphthenate are placed in a suitable mixing vessel. To

stearatezaluminum naphthenate 2:1 to 12:1

six parts of the mixture thus formed are then added about 30 parts of lubricating oil. The slurry thus formed is then mixed at a temperature below 100 F. for a period of about 30 minutes or until the slurry is smooth and free from lumps. To the homogeneous mixture thus obtained are then added 64 parts of oil while the mixing at a temperature below 100 F. is continued. When a substantially homogeneous mixture is obtained the contents of the vessel are heated to about 300 F. with continued stirring for an additional period of about 30 minutes or until a uniform blend is obtained. Then while continuing to stir the contents of the kettle the composition is cooled to about 150 F. after which additional oil is incorporated into the composition to obtain the desired final viscosity. A lubricant prepared from a lubricating oil having a viscosity of about 300 SUS at 100 F. and about 1.5 percent of the aluminum soaps prepared according to the above procedure typically has a viscosity at 77 F. of about 40 to 80 seconds as measured by the Convis method. The Convis method is the same as the Saybolt Universal method for determining viscosity except that 0.64 pound per square inch of weight is placed on top of the oil column in the inner pocket and the Convis value is defined as the efllux time in seconds at 77 F. for 10 milliliters of sample to emerge from the bottom of the tube.

Examples of formulations of grease compositions of the present invention are illustrated by Examples I to IV in the following table:

Examples Composition, percent by weight I II III IV Mineral oil (300 SUS at F.) 98. 50 98. 50 98. 50 98.50 Aluminum tri-stearate 0.38 0.67 0.53 0.43 Aluminum naphthenate concentrate I1 0. 38 0.17 0. 26 0.22 Aluminum di-2-ethyl-hexanoate 0. 74 0.66 0. 71 0.85

B The concentrate is a light lubricating oil which contains about 30 to 35 percent by weight of aluminum naphthenate.

Typical characteristics of the aluminum soaps used in preparing compositions illustrating the invention are as follows:

35 percent by weight of aluminum naphthenate.

When the lubricating composition of Example III was aged at room temperature for five months the viscosity remained substantially unchanged as evidenced by the following viscosity data.

Convis Vis- Composition of Example III cosity at 77 Initially 61 After 3 Weeks... 58 After 4 weeks. 66 After 5 months 63 When compositions were prepared containing only two of the aluminum soaps, i.e., Examples V to VIII, the viscosity of the composition changed considerably as compared with a composition of the invention (Example IX) after aging for only three weeks as shown by the following data.

The concentrate is a light lubricating oil which contains about 30 to 36 percent by weight of aluminum naphthenate. Compositions containing only aluminum tri-stearate and aluminum naphthenate are not listed in the above comparison inasmuch as We have found that compositions containing only the aluminum tri-stearate and aluminum naphthenate do not possess the stringy and tacky characteristics required of mineral castor oils.

From the comparative data shown in the above table it is indeed surprising to note the marked improvement with respect to the viscosity storage stability of the composition (Example IX) containing all three of the aluminum soaps. It will be observed that the compositions containing only two of the aluminum soaps (Examples V to VIII).a1'e considerably less stable to aging as evidenced by the marked change in viscosity after quiescent storage for only three Weeks.

As disclosed hereinabove, aluminum di-stearate is not an equivalent of aluminum tri-stearate in the grease composition of the present invention. For example, a grease composition was prepared comprising 98.5 percent of a mineral oil having a viscosity of 300 SUS at 100 F., 0.38 percent of aluminum di-stearate, 0.38 percent of aluminum naphthenate concentrate (30%) and 0.74 percent of aluminum di-2-ethyl-hexanoate. This composition containing the aluminum di-stearate had an initial Convis viscosity of 63. The viscosity of the composition after aging for three weeks Was 42. In contrast, it Will be noted that the viscosity of the composition of Example III remained substantially unchanged even after aging for 5 months.

The thickened lubricating oils of the instant invention are useful in lubricating fast moving cutting machinery including power saws and the like. Lubricants which have been thickened to the consistency of a grease can be used to lubricate ball and roller bearings, automobile chassis, water pumps, springs, steering gears, pipe threads, and the like. The lubricating compositions of the invention can contain other additives including a filler, an anti-oxidant, an extreme pressure agent, a corrosion and rust inhibitor, a metal deactivator, a dye and the like, without departing from the spirit or scope thereof.

While our invention has been described with reference to various specific examples and embodiments it will be understood that the invention is not limited to such eX- amples and embodiments and may be variously practiced within the scope of the claims hereinafter made.

We claim:

1. A lubricating composition comprising a uniform dispersion of about 0.3 to about 2.0 percent by weight of aluminum tri-stearate, about 0.03 to about 0.3 percent by Weight of aluminum naphthenate and about 0.3 to about 2.0 percent by Weight of an aluminum soap of a branched-chain saturated fatty acid containing 8 carbon atoms in a mineral oil whereinthe relative ratios of the aluminum soaps are aluminum tri-stearatezaluminum soap of C fatty acid about 1:1 to about 1:3; aluminum soap of C fatty acid:aluminum naphthenate about 6:1 to about 12:1; and aluminum tri-stearatezaluminum naphthenate about 2:1 to about 12:1.

2. A lubricating composition comprising a uniform dispersion of aluminum ti-stearate, aluminum naphthenate and an aluminum soap of a branched-chain saturated fatty acid containing 8 carbon atoms in a mineral oil wherein the total soap content comprises about 1.0 to about 5.0 percent by weight of the composition and the relative ratios of the aluminum soaps are aluminum tri-stearate: aluminum soap of C fatty acid about 1:1 to about 1:3; aluminum soap of C fatty acid:aluminum naphthenate about 6:1 to about 12:1 and aluminum tri-stearatezaluminum naphthenate about 2:1 to about 12:1.

3. A lubricating composition comprising a uniform dispersion of about 0.3 to about 2.0 percent by weight of aluminum tri-stearate, about 0.03 to about 0.3 percent by Weight of aluminum naphthenate and about 0.3 to about 2.0 percent by weight of aluminum di-Z-ethyl-hexanoate in a mineral oil wherein the ratio of aluminum tristearatezaluminum naphthenate:aluminum di-Z-ethyl-hexanoate is 6:128.

4. A lubricating composition comprising a uniform dispersion of about 0.3 to about 2.0 percent by weight of aluminum tri-stearate, about 0.1 to about 1.0 percent by weight of a 30 to 35 percent by weight mineral oil concentrate of alumintun naphthenate and about 0.3 to 2.0 percent by weight of aluminum di-2-ethyl-hexanoate in a mineral oil wherein the ratio of aluminum tri-stearate: aluminum naphthenate concentrate:aluminum di-2-ethylhexanoate is 6:3:8.

References Cited in the file of this patent UNITED STATES PATENTS 2,264,353 Zimmer et al Dec. 2, 1941 2,365,037 Zimmer et al Dec. 12, 1944 2,628,195 Allison et al Feb. 10, 1953

Claims

1. A LUBRICATING COMPOSITION COMPRISING A UNIFORM DISPERSION OF ABOUT 0.3 TO ABOUT 2.0 PERCENT BY WEIGHT OF ALUMINUM TRI-STEARATE, ABOUT 0.03 TO ABOUT 0.3 PERCENT BY WEIGHT OF ALUMINUM NAPHTHENATE AND ABOUT 0.3 TO ABOUT 2.0 PERCENT BY WEIGHT OF AN ALUMINUM SOAP OF A BRANCHED-CHAIN SATURATED FATTY ACID CONTAINING 8 CARBON ATOMS IN A MINERAL OIL WHEREIN THE RELATIVE RATIOS OF THE ALUMINUM SOAPS ARE ALUMINUM TRI-STEARATE:ALUMINUM SOAP OF C8 FATTY ACID ABOUT 1:1 TO ABOUT 1:3, ALUMINUM SOAP OF C8 FATTY ACID:ALUMINUM NAPHTHENATE ABOUT 6:1 TO ABOUT 12:1, AND ALUMINUM TRI-STEARATE:ALUMINUM NAPHTHENATE ABOUT 2:1 TO ABOUT 12:1.