US3042615A

US3042615A - Greases thickened with lithium soaps and calcium soaps of fatty acids containing 12-14 carbon atoms

Info

Publication number: US3042615A
Application number: US6858A
Authority: US
Inventors: Leslie U Franklin; Julius C Gebhart
Original assignee: Gulf Oil Corp
Current assignee: Gulf Oil Corp
Priority date: 1960-02-05
Filing date: 1960-02-05
Publication date: 1962-07-03
Anticipated expiration: 1979-07-03

Description

nite. fates This invention relates to a lubricating composition and more particularly to a lithium base grease having improved mechanical and chemical characteristics.

Lithium soaps such as, for example, lithium soaps of the higher fatty acids including palmitic, stearic, l2- hydroxy stearic, oleic, linoleic, linolenic, arachidic, arachidonic, behenic, and the like, or fatty acid compositions which consist essentially of a mixture of the higher fatty acids as, for example, those derived from tallow, fish oils or castor oil, have obtained widespread use as gelling agents for mineral oils in the preparation of lubrieating greasesfor the particular properties which these soaps impart to such greases. Among the desirable properties characteristic of some of such greases, especially those containing substantial proportions of a soap of -12-hydroxy stearic acid are their high heat resistance, buttery texture and moderate resistance to loss by Water leaching. In view of these desirable characteristics, the lithium base greases containing the soap of 12-hydroxy stearic acid with minor amounts of other lithium soaps have been widely used in industry and automotive services for lubricating parts which are exposed to atmospheric conditions. While lithium base greases have met with some success in lubricating surfaces exposed to atmospheric conditions, their use as an all-purpose lubricant has been hampered because they do not possess all of the properties required of such lubricants. In particular, the lithium base greases have not had the desired mechanical and chemical stability in the presence of water which is required of all purpose lubricants.

We have discovered that a lithium base grease having improved mechanical and chemical characteristics in the presence of water can beobtained by incorporatng therein a small amount of a calcium soap of a saturated fatty acid having from 12 to 14 carbon atoms. The improved lubricating composition of our invention therefore comprises a mineral lubricating oil thickened to the consistency of a grease with a lithium soap of a fatty acid having at least 16 carbon atoms and a calcium soap of a saturated fatty acid having from 12 to 14 carbon atoms. We have found, for example, that the mechanical and the chemical characteristics of a lubricating oil thickened to the consistency of a grease with a lithium soap of tallow and a calcium soap of lauric and myristic acids is markedly improved over the corresponding characteristics of a lithium base grease which contains no such calcium soap. Among the improved mechanical and chemical characterstics exhibited by the composition of the invention are a high ASTM dropping point, good bearing retention, resistance to failure under load, resistance to change in consistency with working in the presence or absence of Water, and a smooth buttery texture. Also, good resistance to corrosion and oxidation can be imparted by use of the usual inhibitors.

The mineral oil ingredient employed in preparing the grease composition of the invention may be any of the hydrocarbon oils of lubricating grade customarily used in compounding greases. The oil may be a refined or semi-refined paratiinic-, naphthenio, or asphaltic-base oil having a viscosity of about 50 to about 4000 SUS at 100 F. However, a lithium base grease having maximum shear stability for a given amount of soap is usually obtained with a naphthenic oil. 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 producing a multipurpose lubricant, it is generally preferred to employ an oil having a viscosity within the range of about 300 to about 1000 SUS at 100 F. We do not Wish to limit the invention in this regard, however, since any lithium base grease prepared from a saturated fatty acid having at least 16 carbon atoms regardless of the viscosity of the oil used in its preparation can be improved according to the in vention by incorporating therein a small amount of a calcium soap of a saturated fatty acid having from 12 to 14 carbon atoms. The oil content of the composition prepared according to this invention comprises about to about 98 percent by weight of 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 finished grease.

The higher fatty acid material Which is employed in preparing the lithium soap for use in a composition of the invention can be either a substantially pure fatty acid or a mixture of fatty acids or their glycerides such as those obtained from various fatty oils such as cottonseed oil, rapeseed oil, animal oils, fish oils, and the like. The fatty acids can be either saturated or unsaturated or mixtures thereof. However, we prefer to employ beef tallow or hydrogenated castor oil or a mixture of these glyc- .erides. In some instances it is desirable to hydrogenate the fatty acid mixture in order to increase the saturation of the acids in the mixture. Thus, the fatty acids may be those derived from hydrogenated oils of vegetable, animal and marine extraction. Hydrogenated fish oil fatty acids, hydrogenated tallow fatty acids and, in general,- any hydrogenated animal or vegetable oil which contains a fatty acid having at least about 16 carbon atoms can be used. In producing the lithium soap any suitable saponifying procedure can be employed. The amount of the lithium soap employed should be sufficient to thicken the oil to the consistency of a grease. The optimum amount of lithium soap in any particular instance will vary depending upon the particular fatty acid employed in producing the soap, the particular lubricating oil and upon the properties desired in the final lubricating composition. For greases of the type employed in the lubrication of automobile chassis and Wheel bearings, i.e., No. 2 National Lubricating Grease Institute (NLG'I) grade greases, the lithium soap content of the grease comprises about 5 to about 12 percent by weight of the total composition. For NLGI grades of softer or harder consistencies, however, the lithium soap can comprise about 1.7 to about 17 percent by weight of the total composition.

The calcium soap which is used in the composition of the invention is the Soup of a saturated fatty acid having from 12 to 14 carbon atoms. 1 The fatty acid can be either a pure acid or a mixture of the fatty acids of naturally-occurring vegetable oils in which the predominant fatty acid is either lauric or myristic acid or a mixture in which lauric and myristic acids predominate. Examples of the naturally-occurring oils which can be used include coconut oil, babassu oil and palm kernel oil. The number of carbon atoms in the fatty acid used in preparing the calcium soap is critical. We have found, for example, that the calcium soaps of acids containing less than 12 and more than 14 carbon atoms When-used in conjuction with a lithium soap of C to C fatty acids do not produce greases having the desirable characteristics which can be obtained with the calcium soaps of the cium soap, any suitable saponifying procedure can be em- 3 ployed. The calcium soap may be used in varying amounts depending upon the properties desired in the final lubricating composition. In general, however, the calcium soap comprises about 0.3 to about 8 percent by weight of the total composition or about 15 to about 33 percent by weight of the total soaps of the composition.

The total soap content of a composition of the invention comprises about 2 to about 25 percent by weight of the composition. While some latitude is permissible with respect .to the relative proportions of the lithium and calcium soaps, we have obtained a particularly desirable composition when the amount of the calcium soap comprises about 20 percent by weight of the total soaps. In general, the mol ratios of the lithium soap to the calcium soap may vary between about 10:1 and about 3.5:1, the preferred ratio being Within the range of about 6 mols of lithium soap to 1 mol of the calcium soap to about 8 mols of the lithium soap to 1 mol of the calcium soap.

-When the amount of the lithium soap is increased beyond a 10:1 mol ratio, the advantages obtained by the incorporation of the calcium soap are materially reduced. Also, when the calcium soap is decreased so that the ratio of lithium to calcium soap is below a 3.5:1 mol ratio, the composition does not have the properties desired for an all-purpose lubricant.

In preparing the composition of the present invention, various compounding and blending procedures can be used in either a-batch or a continuous process. According to a preferred embodiment, however, a preformed calcium soap grease is blended with a preformed lithium soap grease. Thus, a preferred embodiment comprises blending a calcium soap grease containing about 25 to about 50 percent by Weight of soap with a lithium soap grease containing about 18 to about 20 percent by weight of lithium soap at a temperature of about 350 F. The blend thus formed is stirred and milled while cooling to about 300 P. Then while continuing to stir and mill, additional oil is incorporated into the composition while the temperature falls from 300 to 250 F. The addition of oil is continued until a composition having the desired consistency is obtained. If desired, conventional grease additives can be incorporated into the composition at this point.

are placed in a suitable saponification vessel such as an autoclave. Saponification is effected under a pressure of about 40 to about 60 pounds per square inch gauge for one hour at about 340 to about 350 F. At the end of the saponification period, the pressure in the vessel is reduced to atmospheric pressure. While the pressure is being reduced, the contents of the vessel are heated to a temperature of about 400 F. Thereafter an additional 12 parts by weight of the mineral oil are added to the composition in the autoclave while cooling to about 375 F. The contents of the autoclave are then discharged to a grease kettle which has been preheated so that the lithium soap-containing composition in the grease kettle has a temperature of about 350 F. To the lithium soap composition in the grease kettle are then added about parts by weightof a calcium soap grease having a soap content of about 50 percent by weight. The mixture of lithium and calcium soap greases in the grease kettle is stirred and milled while cooling to about 300 F. in about 30 minutes. Homogenization of the lithium and calcium soap grease is accomplished by circulating the grease between the grease kettle and a grease mill. Circulation is continued until the composition is smooth and free from lumps. While circulating the composition between the grease kettle and the mill, additional oil is added to obtain a composition having a desired consistency. The

temperature during the entire period of homogenization is reduced from about 350 to about 250 F.

The preparation of a calcium soap grease having a soap content of about 50 percent by weight for incorporation into a lithium soap grease as described above is typically prepared by saponifying 37 parts by weight of myristic acid in 40 parts by weight of a mineral oil having a viscosity of 500 SUS at F. and 58 SUS at 210 F. with 6.7 parts by weight of calcium hydroxide and 17 parts by .weight of water at a pressure of about 60 to about 70 pounds per square inch gauge and a temperature of about 320-to about 330 F. When saponification is substantially complete the pressure is reduced to atmospheric pressure and dehydration is thereafter effected by heating at a temperature of about 330 to about 340 F. The calcium soap grease thus obtained is then added to the lithium soap grease and further processed in accordance with the procedure described above.

Typical characteristics of the lithium soap grease, the calcium soap grease and a blend thereof obtained in accordance with the above procedure are shown in Tables 1 and 2.

Table 1 Lithium Calcium tallow plus Characteristics Lithium myristate calcium tallow grease grease 1 myristate grease blend 1 Soup content, percent by weig t. 9.7 50.0 12.5. Dropping point F 339 324. P netration, ASTM D 217:

Unworked 283 269. Worked:

60 strokes 308 287. 1 10,000 strokes 348 292. Water resistance (grease plus 10% water), penetration, ASTM D 217:

Worked 100,000 strokes--. 450+ 315. Increase over original 60 142+ 28.

stroke penetration test. Wheel bearing performance test, ASTM D 1263, 660 r.p.m., 220. F., 6 hr.

Leakage to hub cap, g. Leakage to collector, g. Deposits on bearingsurface Oil separation test, Fed. meth. 321.1 (mod), percent by weight, 50 hr., 212 F. Color Light brown. Light brown. Texture- Fibrous Buttery.

1 Hard and brittle if allowed to cool to ambient temperature (77 F.) but very fluid at temperatures above 300 F.

2 The grease blend comprises 7.0 mols of lithium soap to 1.0 mol oiealcium soap.

" Table 2 Calcium. Lithium Characteristics Lithium laurate tallow caltallow grease grease 1 cium laurate grease blend 3 Soap content, percent by 9.7 50.0".-. 15.0

weight. Dropping point, F 339 325. Penetration, ASTM D 217:

Unworkerl 28 288. Worked: 60 Strokes 308 296. 10,000 strokes 348 303. Water resistance (grease 10% water), penetration, ASTM D 217:

Worked 100,000 strokes- Increase over original 60 stroke penetration test. Wheel bearing performance test ASTM D 1263, 660 r.p.m., 220 F., 6 hr.:

Leakage to hub cap, g Leakage to collector, g Deposits on bearing surce. Oil separation test, Fed. meth. 321.1 (mod), percent by weight, 50 hr., 212 F. I 13.8 Color Light brown. Light brown. Texture Fibrous Buttery.

2 The grease blend comprises 6.2 mols of lithium soap to 1.0 mol. of calcium soap.

From the comparative data shown in the above Tables 1 and 2 it is indeed surprising to note the marked improvement in the characteristics of the composition containing both the lithium and calcium soaps.

In order to show the importance of using a calcium with about 1.7 to about 17 percent by Weight of a lithium soap of a fatty acid having from 16 to 22 carbon atoms and about 0.3 to about 8 percent by weight of a calcium soap of a saturated fatty acid having from 12 to 14 carbon atoms.

5 soap of a C or C saturated fatty acid or a mixture in 2. A lubricating composition comprising a mineral which the C and C saturated fatty acids predominate, lubricating oil thickened to the consistency of a grease comparative compositions containing calcium soaps of with a uniform dispersion of a lithium soap of a fatty C to C saturated fatty acids in combination with the acid having from 16 to 22 carbon atoms and a calcium lithium soap of tallow were made and tested. The formusoap of a saturated fatty acid having from 12 to 14 carlation of the compositions and their respective characbon atoms wherein the total soap content comprises teristics are shown in Table 3. about 2 to about 25 percent by weight of the composition Table 3 I II III IV V VI VII VIII IX x XI XII Composition, percent by weight:

Mineral oil (500 SUS, 100 F.) Glycerine from fats- Calcium caprylate (94+ Calcium laurate (95+%) Calcium myristate 94+%) Calcium palmitate (95+%) Calcium stearate (95+%) Calcium soap of- 12-hydroxy stearic acid 1 Hydrogenated tallow fatty acids Hydrogenated fish oil fatty acids Hydrogenated 0 -0 fatty acids Coconut oil 5 Coconut oil fatty acids (distilled) Tallow Characteristics:

Dropping point, F r Penetration, ASIM D 217 worked:

60 strokes 10,000 strokes. Water resistance (gr penetration, AS'IM D 217:

Worked 100,000 strokes- Increase over original 60 stroke penetration test NOTE .--The following table contains the footnotes for Table 3.

Number of carbon atoms Fat or fatty acid Cu u 018 (12- hydroxy) l l2-hydroxy stearic acid 2 Hydrogenated tallow fatty acids 3 Hydrogenated fish Oll fatty acid:

Hydrogenated C r-C22 fatty acids 5 Coconut oil 6 Coconut oil fatty acids (distilled) 1 Tallow It will be noted from Table 3 that only those lithium soap compositions containing a calcium soap selected from the group consisting of calcium laurate, calcium myristate and mixtures predominating in calcium laurate and calcium myristate, i.e., compositions II, III, X and XI gave the smallest increase in worked penetration.

The lubricating composition of the present invention in addition to being useful in general industry is also useful in lubricating ball and roller bearings, wheel bearings, water pumps, universal joints, automobile chassis, aircraft, and the like. The lubricating composition 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 examples and embodiments and may be variously practiced within the scope of the claims hereinafter made.

We claim:

1. A lubricating composition comprising a mineral lubricating oil thickened to the consistency of a grease and the molar ratio of the lithium soa-p to the calcium soap is between about 3.5:] and about 10:1.

3. A lubricating composition comprising a mineral lubricating oil thickened to the consistency of a grease with a lithium soap of tallow and a calcium soap of lauric acid wherein the molar ratio of lithium soap to calcium soap is between about 3.5:1 and about 10: 1.

4. A lubricating composition comprising a mineral lubricating oil thickened to the consistency of a grease with a lithium soap of tallow and a calcium soap of myristic aci-d wherein the molar ratio of lithium soap to calcium soap is between about 3.521 and about 10:1.

5. A lubricating composition comprising a mineral lubricating oil thickened to the consistency of a grease with a lithium soap of tallow and a calcium soap of a fatty acid mixture which predominates in la'uric and myristic acids wherein the molar ratio of lithium soap to calcium soap is between about 3.5 :1 and about 10:1.

Brunstrum et al Jan. 21, 1941 OHalloran June 9, 1953 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION a tent N0. 3,042,615 July 3, 1962 Leslie U. Franklin et a1.

It is hereby certified that error appears in the above numbered patant requiring correction and that the said Letters Patent should read as corrected below.

Column 4, Table 2, last column, and opposite the haracteristic "Oil separation 'test, Fed. meth. 321.1 (mod.) ercent by weight, 50 hr. 212 F.", the value "2.2" should e inserted.

Signed and sealed this 16th day of October 1962.

EA L) est:

NEST w swmaa DAVID LADD eating Officer Commissioner of Patents

Claims

1. A LUBRICATING COMPOSITION COMPRISING A MINERAL LUBRICATING OIL THICKNESS TO THE CONSISTENCY OF A GREASE WITH ABOUT 1.7 TO ABOUT 17 PERCENT BY WEIGHT OF A LITHIUM SOAP OF A FATTY ACID HAVING FROM 6 TO 22 CARBON ATOMS AND ABOUT 0.3 TO ABOUT 8 PERCENT BY WEIGHT OF A CALCIUM SOAP OF A SATURATED FATTY ACID HAVING FROM 12 TO 14 CARBON ATOMS.