US3389085A - Lubricants containing mixed metal salts of mono- and polybasic acids - Google Patents

Description

United States Patent 01 lice 3,339,085 Patented June 18, 1968 3,389,085 LUBRICANTS CONTAINING MIXED METAL SALTS F MONO- AND POLYBASEC AClDS Arnold J. Morway, Clark, NJ., assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Mar. 31, 1964, Ser. No. 356,035 3 Claims. (Cl. 252-41) This invention relates to lubricants comprising lubricating oil containing alkali metal mixed salts of fatty acids and certain polybasic acid materials, as additives or as thickeners.

In its preferred form, the invention relates to lubricating greases suitable for lubrication of anti-friction bearings, comprising lubricating oil thickened with alkali metal mixed salts of monobasic acid, which is preferably a mixture of low molecular weight fatty acid and higher molecular weight fatty acid, and a polybasic acid which can be phosphoric acid or low molecular weight dicarboxylic acid.

The greases of the invention differ from previously known, related alkali metal high temperature bearing greases wherein the thickener is a mixed salt of low molecular weight fatty acid, e.g. acetic acid, and higher molecular weight fatty acid, e.-g. C to C fatty acid. Thus, in contrast to said previously known greases, the greases of the invention do not become excessively fluid at elevated temperatures, or become excessively rubbery or fibrous at elevated temperatures, due to phase changes in the soapthickening structure.

In general, other advantages of the greases of the invention include: anti-wear properties, high dropping points, excellent structural stability at both low and high rates of shear, good lubrication lives, and in the case of lithium salts, the greases have good water insolubility and ability to retain their structural stability when water is emulsified into the grease.

The mixed-salt systems of the invention are best made to contain alkali metal salt of 0.05 to 6.0, preferably 0.1 to 4.0 molar hydrogen equivalents of low molecular weight C to C fatty acid per molar hydrogen equivalent of polybasic acid. These systems will usually also contain salt of 0.2 to 3.0, preferably 0.2 to 2 molar hydrogen equivalents of higher molecular weight fatty acid, e.g. C to C fatty acid, per molar hydrogen equivalent of said polybasic acid. Greases can be thus prepared having a total content of said alkali metal salts of 5.0 to 40.0 weight percent, preferably to 35 weight percent, based on the total weight of the grease. These greases in turn can be diluted with additional oil to form fluid lubricants which have antiwear properties containing about 0.1 to 5.0 of the mixed salt.

Suitable low molecular weight fatty acids include C to C fatty acid such as acetic, propionic, butyric acid, etc. Acetic acid or its anhydride is preferred.

The higher molecular weight fatty acid includes C to C naturally-occurring or synthetic, substituted or unsubstituted, saturated or unsaturated, mixed or unmixed fatty acids. Preferred acids will have 16 to 24 carbon per molecule. Examples of such acids include myristic, palmitic, stearic, IZ-hydroxy, stearic, arachidic, oleic, rincinoleic, hydrogenated fish oil, tallow acids, etc.

The low molecular weight polybasic of the invention is selected from the group consisting of phosphoric acid which can be either in its ortho, pyro, or meta form, and C to C saturated aliphatic dicarboxylic acid such as oxalic, malonic, succinic, glutaric or adipic. The corresponding acid anhydrides, where they exist, can also be used, eg. succinic anhydride.

The alkali metal component of the mixed thickeners is lithium, or mixtures of lithium and sodium.

The lubricating oil used in the compositions of the invention may be either a mineral lubricating oil or a synthetic lubricating oil. Synthetic lubricating oils which may be used include esters or dibasic acids (eg di-2-ethylhexyl sebacate), ester of glycols (e.g. C Oxo acid diester of tetraethylene glycol), complex esters (e.g. the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2- ethylhexanoic acid), halocarbon oils, alkyl silicates, sulfite esters, mercaptals, formals, polyglycol type synthetic oils, etc., or mixtures of any of the above in any proportions. If the salts are formed in situ in the oil, then this in situ reaction is frequently best carried out in a mineral oil, since many synthetic oils will tend to decompose or hydrolyze during the salt formation. However, the salts once formed, can be used in lubricants containing the synthetic oils noted above.

Various other additives may also be added to the lubricating composition (e.g. 0.1 to 10.0 weight percent) of detergents such as calcium petroleum sulfonate; oxidation inhibitors such as phenyl-alpha-naphthylamine; corrosion inhibitors, such as sodium nitrite and sorbitan monooleate; dyes; other grease thickeners, and the like.

The lubricants of the invention can be prepared in a number of different ways. Various specific techniques will be observed in the following examples. In general, these techniques involve neutralizing all the acids in at least a portion of the oil, with aqueous alkali metal base, followed by homogenization to remove lumps, then heating to about 300 to 550 F., preferably 400 to 500 F. to dehydrate the composition. The higher temperature of 400 to 500 F. seems to form some sort of a complex which results in the formation of a mixed salt material having greater thickening effect and better load and BF. properties than the lower dehydration temperatures. After dehydration, the grease can be cooled, any additives can be added, and the grease can be homogenized again. If a lubricating fluid is desired, the grease is simply diluted by mixing with additional lubricating oil.

The invention Will be further understood by reference to the following examples wherein all parts are by weight and wherein stirring was carried out throughout the grease making procedure in order to obtain a more uniform product.

EXAMPLE I 71.9 parts of a mineral lubricating oil having a viscosity of 60 SUS. at 210 F. and 15 parts of Hydrofol Acid 51 were added to a fire-heated kettle and heated to 130 F., while stirring, to disperse the acid in the oil. Then, 3 parts of glacial acetic acid were added to the kettle followed by the addition of 6.1 parts of lithium hydroxide monohydrate (LiOH-H O) in the form of an aqueous solution consisting of 20 wt. percent lithium hydroxide results in a faster and more complete neutralization than if dry lithium hydroxide was used. Then the mixture in the kettle was stirred for 15 more minutes, after which 3.0 parts of oxalic acid (dry) was added to the kettle. Heat was applied to the kettle and the temperature of the kettle contents raised to 210 F., while stirring. At this point, the wet grease was homogenized by passage from the kettle through a Charlotte mill having an opening of 0.010 inch and then returning to the kettle. This homogenization removed all lumps and specks of salt from the grease and aided in completing the saponification. The temperature was then increased to 450 F., which temperature was maintained for 0.5 hour, to dehydrate the grease and form the desired grease structure. Heating was then discontinued and the grease was allowed to cool, while stirring to prevent crust formation, until the temperature dropped to 250 F. At this point, one part of phenyl-alpha-naphthylamine was added as an antioxidant. The grease was allowed to further cool to F. whereupon it was again homogenized by passage through the Charlotte mill to form the finished grease.

Hydrofol Acid 51 is a commercial fatty acid made by hydrogenating fish oil and has an average chain length of about 18 carbon atoms and is similar to stearic acid in its degree of unsaturation.

The homogenizing step while the grease is still in the wet stage, i.e. there is still a lot of water in the grease, is important in obtaining a homogeneous final product. In the wet stage, the various salts are hydrated and can be smoothed out by homogenization. On the other hand, if the small lumps of salt are not removed by homogenization at this point, but instead are heated to high temperatures and dehydrated, subsequent milling will not remove these lumps which have now hardened. The resulting grease would therefore be grainy and give poorer lubrication d-ue to the presence of the hardened lumps. Furthermore, the presence of these hard lumps reduces the amount of salt available for thickening so as to result in a softer grease due to the poorer utilization of the thickener.

EXAMPLE II This grease was prepared in a manner similar to that of the grease of Example I except that a different proportion of materials was used.

EXAMPLE III 15 parts of Hydrofol Acid 51 and 71.9 parts of mineral lubricating oil were added to a gas-fired kettle and warmed to 130 F. while mixing to melt the acid into the oil. Then, 4.3 parts of lithium hydroxide monohydrate were added to the kettle in the form of a 20 wt. percent aqueous solution. Next, 3.0 parts of glacial acetic acid were added. The amount of lithium hydroxide monohydrate was just sufiicient to neutralize the Hydrofol Acid 51 and the glacial acetic acid. The kettle contents were then stirred for /2 hour, after which was added 3 parts of oxalic acid crystals (dry) and 1.8 parts of sodium hydroxide (to neutralize the oxalic acid) in the form of a 40% aqueous solution, i.e. 40 wt. percent sodium hydroxide and 60 wt. percent water. The resulting mixture was then heated to 200 F. and passed through a Charlotte mill having an opening of 0.008 inch and recycling back into the kettle until all lumps were removed from the grease. The composition was then heated to a temperature of about 430 which was maintained for about 0.5 hour to totally dehydrate the grease. The grease was cooled to 250 F., with stirring, where one part of phenyl-alphanaphthylamine was mixed into the grease. The grease was next cooled with stirring to 120 F. and then homogenized by passage through the Charlottle mill to form the finished grease.

EXAMPLE IV parts of Hydrofol Acid 51 and 76.9 parts of mineral lubricating oil was added to a fire-heated kettle and warmed to 130 F. while mixing. 2.9 parts of lithium hydroxide monohydrate in the form of a 20 wt. percent aqueous solution was then added followed by the addition of 2 parts of glacial acetic acid. The lithium hydroxide was used up in neutralizing the Hydrofoil Acid 51 and glacial acetic acid. The resulting mixture was stirred for V2 hour following which 2 parts of dry oxalic acid crystals and 1.2 parts of sodium hydroxide (to neutralize the oxalic acid and form sodium oxalate) in the form of a 40% aqueous solution were also added. The resulting mixture was then heated to 200 F., cycled through the Charlotte mill (0.010 inch opening) until smooth, dehydrated at 430 to 440 F. for about 0.5 hour, and cooled to 250 P. where 1 part of phenyl-alpha-naphthylamine was added, all while stirring. Then, 4 parts of an oil dispersion consisting of 2 parts of finely divided sodium nitrite as an anti-rust additive and 2 parts of mineral lubricating oil was added to the grease. The grease was then homogenized by again passing through the Charlotte mill to form the finished grease. The sodium nitrite used above was a commercial grade that had been ball milled in the mineral oil in a 50/50 weight concentration.

EXAMPLE V 15 parts of Hydrofol Acid 51 and 70.7 parts of mineral lubricating oil were added to a fire-heated kettle and mixed while gently heating to 130 F. 7.3 parts of lithium hydroxide monohydrate (20% aqueou solution) was added, following which the mixture was stirred for /2 hour. Then, a blend consisting of 3 parts of wt. percent orthophosphoric acid dissolved in 3 parts of glacial acetic acid was slowly added to the kettle and reacted. This reaction raised the temperature of the kettle contents to 175 F. The warm grease was then cycled through the Charlottle mill (0.0l0 inch opening) and then back to the kettle until a smooth homogeneous composition was obtained. Heating was then initiated and the temperature of the composition raised to 450 F. which temperature was maintained for about 0.5 hour in order to form the complex salt and totally dehydrate the grease. After this, heating was discontinued and the grease cooled to 250 F. while stirring, at which point 1 part of phenylalpha-naphthylamine was added. The grease was then further cooled to F. while stirring, where it was homogenized in a Morehouse mill to form the finished grease.

EXAMPLE VI A grease was prepared in the same manner as that of Example V except that different proportions of acetic acid and orthophosphoric acid were used.

Composition A A grease was prepared in the same manner as the grease of Example VI except that no acetic acid was used.

Composition B 76.8 parts of mineral lubricating oil and 15 parts of Hydrofol Acid 51 were added to a fire-heated kettle and stirred while heating to 130 F. Then 4.3 parts of lithium hydroxide monohydrate in the form of a 20 wt. percent aqueous solution, were added to the mixture, followed immediately by the addition of 3 parts of glacial acetic acid. The composition was then mixed for 30 minutes, after which the wet grease, which had a temperature of about 140 F., was cycled through a Morehouse mill having an 0.003" opening and then passed back to the kettle until all lumps and small specks had been eliminated. The smooth, wet, milled grease was then heated to a temperature of about 440 R, which was maintained for about 0.5 hour in order to dehydrate the mixture. Heating was then discontinued and the grease allowed to cool to 250 P. where 1 part of phenyl-alphanaphthylamine was added as an oxidation inhibitor. The grease was then cooled to F., homogenized in said Morehouse mill to form a finished grease.

Composition C 10 parts of IZ-hydroxy stearic acid was charged to a fire-heated kettle along with 87.5 parts of mineral lubricating oil and mixed while heating to F. Then, 1.5 parts of lithium hydroxide monohydrate was added in the form of a 20 wt. percent aqueous solution. Heating was then initiated and the composition was heated to a temperature of 390 F. which was maintained for about 0.5 hour whereby the entire composition was dehydrated. The composition was then cooled to 250 R, where 1 part of phenyl-alpha-naphthylamine was added as an oxidation inhibitor. The composition was then cooled to 120 F. and then homogenized in a Morehouse mill after which it was packaged.

Composition D 15 parts of Hydrofol Acid 51 and 72 parts of mineral lubricating oil was added to the kettle and warmed to 130 F. After this, 2.3 parts of lithium hydroxide monohydrate was added in the form of a aqueous solution. This mixture was then stirred for about 0.5 hour in order to react the lithium hydroxide monohydrate with the Hydrofol Acid 51. Next, 3 parts of glacial acetic acid and 3 parts of dry oxalic acid was added to the 5 composition, followed by the addition of 3.7 parts of sodium hydroxide in the form of an aqueous solution containing wt. percent NaOH. The last addition neutralized the acetic acid and oxalic acid with the sodium hydroxide. The grease was then heated to 200 F., cycled through the Charlotte mill until smooth, dehydrated at 10 The formulations and properties of lubricants of the 20 preceding examples and compositions are summarized in the following table:

appearance by being smooth and homogeneous. These greases were structurally stable as illustrated by their small change in penetration upon working. These greases were water-insoluble and had excellent lubricating properties as illustrated by the Wheel Bearing Test, and their long Lubrication Life at elevated temperatures. These results were surprising since prior attempts to use oxalic acid in grease making have not been too successful be cause of the inability of obtaining smooth non-grainy structures, which would have good structural stability. In addition, the greases of Examples I and II were tested for temperature rise in a ball-bearing. In this test, a 204 mm. steel ball bearing is packed with 3.0 grams of grease, then operated at 10,000 rpm. while its temperature is measured by thermocouples placed on the outer bearing race. In this test, using the grease of Example I, the temperature increased 20 F. above the room temperature of F. in about twenty minutes and then quickly dropped to a steady state condition of F. This shows that the grease of Example I was a good channeling grease which quickly formed a channel for the rapidly rotating steel balls. This channeling property TABLE Examples Composition (Wt. percent):

Hydroiol Acid 51. 15.0

Hydroxystearie Acid" Orthophosphoric Acid LiO H'H2O-....

34 1. ac Mole eq. ratio'acetic acid/polybasic acid... lll 1/1 l/l 1/1 .5/1 .11/1. Properties:

Appearance Excellent...- Excellent...- Excellent...- Excel1ent Excellent Excellent. Dropping Point, F 425 400 450 430 450+ 440. ASTM Penetration, 77 F. mm./10.

Unworked 200 280 210 204 200 283 Woiked 60 stroke 220 285 215 Worked 10,000 strokes 215 310 200 Water Solubility (B oiling water).

Norma I-Iotiman Oxidation, p.s.1. drop in oxygen pressure in 500 hours.

Wheel Bearing Test Slump Leakage, grams Lubigatli on Life, Hours 10,000 r.p.m

Insoluble...- llnsolublem. Insolub e Pass....

Pass Pass Pass Pass Pass. 0N8 slump... 10

slump... None. .0 0.0 1.0.

Composition A B C D Composition (Wt. Percent):

Hydroiol Ac d 51 Oxalic Acid Hydroxystearic Acid.--

Orthophosphoric Acid- OH-H Sodium Hydroxide Phenyl-naphthylamine... NaNO; Mineral lubricating oil, 60 SUS. at 210 F Mole eq. ratio-higher fatty acid/polybasic acid.

Mole eq. ratio-acetic acid/polybasic acid -I- Properties:

Appearance Excellent Fair Exccllent...-... Fluldizes and grainy. Dropping Point, F 450 395 340 ASTM Penetration, 77 F. 111111.110:

Uuworked 295 240 190 Worked 60 strokes 315..

Worked 10,000 strokes 358... Water Solubility Insoluble Norma Hoflman Oxidation, p.s.i. drop in oxygen] pressure in 500 hours. 2.5 Wheel Bearing Test:

Slump Pass Leakage, grams None Lubrication Life, Hours 10,000 r.p.m.:

*NLGI-ABE C Spindle Test.

As demonstrated by Examples I and II, and as shown in the preceding table, greases were made from oxalic acid is important since it reduces the power consumption which would otherwise be wasted by the churning of a nonas the polybasic acid, which greases had an excellent 75 channeling grease. The grease of Example II was also 7 a channeling grease, although not as good as the grease of Example I. Example II showed an initial temperature rise of 40 F. above the room temperature of 75 F. in about twenty minutes and then dropped off to a steady state condition of 100 F.

Examples III and IV illustrate how good mixed sodiumlithium complex greases can be prepared using oxalic acid. The good properties of these greases were unexpected, since not only is lithium used to make a good complex grease, but the sodium oxalate which is formed is known as a water soluble salt having no grease forming properties of its own. The grease of Example IV, which contained sodium nitrite as a rust-inhibitor successfully passed the CRC-L4l Rust Test by showing no rust. Examples V and VI illustrate the use of orthophosphoric acid as the polybasic acid in forming a good grease.

Compositions A, B, and C represent prior art type of formulations, while Composition D demonstrates the necessity for coneutralizing all acids at once when using lithium and sodium bases. Specifically, Composition A shows that without the acetic acid that the lubricant is not quite as good with regard to structural stability, i.e. resistance to mechanical working, and lubrication life at 300 F. as the greases of the examples.

Composition B shows that without the polybasic acid that the structural stability was poor. For example, the ASTM penetration increased from 260 when worked 60 strokes to 375 mm./ 10 when worked 10,000 strokes thus showing considerable breakdown in grease structure upon mechanical Working.

Composition C shows that without using the acetic acid or low molecular weight polybasic acid, that the grease had a low dropping point.

Composition D shows that upon using the mixed sodium and lithium combination, that if the sodium salt of both acetic and oxalic acid is formed, a poor grease results. On the other hand, Examples III and IV show that by using the sodium only to neutralize the oxalic acid, that a good grease results, thereby demonstrating the desirability of avoiding reacting sodium with the monocarboxylic acids present.

Using some sodium as in Examples III and IV, permits a less expensive grease which will have good high temperature lubrication life and which generally will not interfere too much with the water insolubility of the grease as long as most of the metal content of the thickener is lithium.

What is claimed is:

1. A lubricating grease comprising a major amount of mineral lubricating oil and about 15 to 35 weight percent of lithium salts of acetic acid, C to C fatty acid, and oxalic acid, wherein the mole equivalent ratio of said acetic acid to said oxalic acid is about 0.1:1 to 4:1, and wherein the mole equivalent ratio of said C to C fatty acid to said oxalic acid is about 0.2:1 to 2:1.

2. A lubricating grease comprising a major amount of mineral lubricating oil and about 15 to 35 weight percent of a salt mixture consisting of lithium salts of acetic acid, and C to C fatty acid and sodium salt of oxalic acid, wherein the mole equivalent ratio of said acetic acid to said oxalic acid is about 0.1:1 to 4:1 and wherein the mole equivalent ratio of said C to C fatty acid to said oxalic acid is about 0.2:1 to 2:1.

3. A method of preparing the lubricating grease of claim 2, which comprises neutralizing said acetic acid and said C to C fatty acid with an aqueous solution of lithium hydroxide in at least a portion of said oil, then adding said oxalic acid and sodium hydroxide in order to form sodium oxalate, then milling the composition to form a homogeneous mass, then dehydrating by heating to 300 to 550 F. and cooling to form said grease.

References Cited UNITED STATES PATENTS 2,861,043 11/1958 Morway et al. 252-21 2,880,174 3/1959 Morway et a1 252-41 X 2,898,296 8/1959 Pattenden et al 252-41 X 2,908,645 10/1959 Morway 252- 2,923,682 2/1960 Morway 252-327 2,967,151 1/1961 Morway 252-18 X 2,988,507 6/1961 Norton et al 252-42.1 3,033,787 5/1962 Morway et al 252-59 X 3,214,376 10/1965 Morway 252-18 3,223,624 12/1965 Morway et al 252-41 X 3,223,633 12/1965 Morway et al 252-41 X DANIEL E. WYMAN, Primary Examiner.

I. VAUGHN, Assistant Examiner.

Claims (1)

1. A LUBRICATING GREASE COMPRISING A MAJOR AMOUNT OF MINERAL LUBRICATING OIL AND ABOUT 15 TO 35 WEIGHT PERCENT OF LITHIUM SALTS OF ACETIC ACID, C18 TO C24 FATTY ACID, AND OXALIC ACID, WHEREIN THE MOLE EQUIVALENT RATIO OF SAID ACETIC ACID TO SAID OXALIC ACID IS ABOUT 0.1:1 TO 4:1, AND WHEREIN THE MOLE EQUIVALENT RATION OF SAID C16 TO C24 FATTY ACID TO SAID OXALIC ACID IS ABOUT 0.2:1 TO 2:1.