US3318807A - Lubricating greases containing finely divided inorganic metal salts and method of preparation therefor - Google Patents

Description

United States Patent Ofifice 3,318,807 Patented! May 9, 1967 3,318,807 LUBRICATING GREASES CQNTATNING FINELY DIVIDED INORGANIC METAL SALTS AND METHQD F PREPARATHUN THEREFUR Joseph F. Lyons, Poughheepsie, and Norman R. Odell, Wappingers Falls, N.Y., assignors to Texaco, Inc, New York, N.Y., a corporation of Delaware No Drawing. Filed May 13, 1963, Ser. No. 230,159 2 Claims. (Cl. 252-18) This invention relates to improvements in grease manufacture. More particularly, it relates to lithium soap thickened greases and to an improved method of making them.

In accordance with this invention, lubricating greases containing a lithium soap as at least the principal thickening agent are prepared starting with an inexpensive lithium salt as the precursor of the base employed in the saponification in place of the relatively expensive commercial lithium hydroxide. The invention contemplates particularly employing the naturally occurring dilithium sodium phosphate as the starting material and reacting this material with an alkalaine earth metal hydroxide in aqueous solution in the initial step of the grease making process. The reaction takes place with the formation of a mixture of lithium and sodium hydroxides and alkaline earth metal phosphate suspended therein in finely-divided form. We have found that this reaction product is employed very successfully as the saponifying agent in grease preparations with the productions of greases of very satisfactory lubricating properties and with a substantial saving in production costs. We have further found that greases of i very superior extreme pressure properties are obtained by employing this saponifying agent in the production of greases from fatty acid glycerides as the saponifiable material, apparently due to some synergistic effect between the metal phosphate and the glycer-ine released in the saponification reaction.

The greases to which this invention relates particularly comprise a lubricating oil as the chief component containing a grease forming amount of a fatty acid soap comprising at least a major amount of a lithium fatty acid soap and a minor amount of alkaline earth metal phosphate. Ordinarily, the soap will be present in an amount from about to about 25 percent by weight, although somewhat smaller or larger amounts may be employed if desired. The alkaline earth metal phosphate is ordinarily present in an amount corresponding to about 1:6 mole ratio respectively with the soap, resulting from the reaction of a lithium phosphate with alkaline earth metal hydroxide, although additional finely-divided alkaline earth metal phosphate may be added if desired up to about 3 percent by weight of the grease composition. In the grease compositions resulting from the preferred meth 0d of our invention, the soap comprises lithium and sodium soaps in a 2:1 mole ratio. Greases comprising the particularly preferred embodiment of our invention contain about 0.5-3 percent by weight of alkaline earth metal phosphate and 0.22 percent by weight of glycerol.

Saponifiable materials employed in the production of these greases are higher fatty acids and hydroXy-substituted higher faty acids containing about to 32 carbon atoms, preferably from about 16 to about 22 carbon atoms, and the glycerides or other esters of such acids. Particularly suitable materials are substantially saturated hydroxy fatty acids containing 12 or more carbon atoms and 1 or more hydroxyl radicals separated from the carboxyl group by at least 1 carbon atom, and the glycerides and lower alkyl esters thereof. The saponifiable materials employed in carrying out the grease preparation by the preferred method of our invention comprise at least a substantial proportion of fatty acid glycerides, sufiicient to provide an amount of glyceride in the finished grease within the range set forth hereinabove.

In addition to the higher fatty acid materials described above, it is desirable in some cases to employ a minor proportion of lower fatty acid material in the saponification mixture, such as a fatty acid containing from 1 to about 10 carbon atoms per molecule, and most suitably from 1 to about 6 carbon atoms per molecule, the glycerides and other esters of such acids. A material of this character may be employed in the saponificaiton in an amount resulting in a lower fatty acid salt content in the finished grease from about 1 to about 10 percent by weight, preferably corresponding to a mol ratio with the higher fatty acid soap of about 5:1 to about 20:1 respectively. The lower fatty acid materials may be employed with particular advantage in greases containing glycer-.

ides, as a means of increasing the dropping points where a high dropping point grease is desired. An alternative procedure which may be preferred in some cases comprises employing a preformed metal salt of a low molecular weight acid of the character described above. The preformed salt may be added to the grease mixture at any stage of the grease making process, most suitably before the grease mixture has cooled below the maximum temperature employed in the process.

The lubricating oils forming the major constituent of these compositions may be any oils of lubricating characteristics which are suitable for use in lubricating compositions generally. Such oils include the conventional mineral lubricating oils having Saybolt Universal viscosities in the range from about seconds at F. to about 225 seconds at 210 R, which may be either naphthenic or paraffmic in type or blends comprising both naphthenic and paraffinic oils. The preferred lubricating oils are those having Saybolt Universal viscosities in the range from about 300 seconds at 100 F. to about 100 seconds at 210 R, which may be blends of lighter and heavier oils in the lubricating oil viscosity range. Synthetic lubricatingoils, which may be preferred in preparing greases having special properties required for special types of lubricating service, include oils prepared by cracking and polymerizing products of the Fischer-Tropsch process and the like as well as other synthetic oleaginous compounds such as polyethers, polyesters, silicone oils, etc. having viscosities within the lubricating oil viscosity range. Sutable polyether include particularly polyalkylene glycols such as polyethylene glycol. Suitable polyesters include the aliphatic dicarboxylic acid diesters, such as di-2-ethylhexyl sebacate, di(secondary amyl) sebacate, di-Z-ethylhexyl azelate, di-iso-octyl adipate, etc. The sulfur analogs of the polyalkylene esters and polyesters are also suitable. A particularly suitable class of dicarboxylic acid ester oils are those disclosed by 'R. T. Sanderson in US. 2,628,974, obtained by reacting dibasic aliphatic acids with glycols and end blocking the reaction products with monohydric aliphatic alcohols and monocarboxylic aliphatic acids. Silicone polymer oils may also be employed, preferably having viscosities in the range from about 7-0 to 900 seconds Saybolt Universal at 100 F. Suitable compounds of this type include dimethyl silicone polymer, diethyl silicone polymer, methyl cyclohexyl silicone polymer, diphenyl silicone polymer, methylethyl silicone polymer, methyltolyl silicone polymer, etc.

Additives of the types ordinarily employed in lubricating compositions may. be employed in these greases, such as oxidation inhibitors, corrosion inhibitors, tackiness agents, such as various high polymeric materials, ex-

treme pressure agents, etc. Oxidation inhibitors which may be employed include particularly those of the amine type, such as phenylalphanaphthylamine, diphenylparaphenyldiamine, tetramethyldiaminodiphenyl methane, and bis(2-hydroxy-3-t-butyl-5-methylphenyl) methane. A compound of this class may be suitably employed in an amount from about 0.2 percent to about 3.0 percent by weight, and preferably from about 0.2 to about 2.0 percent by Weight of the composition. A particularly suitable class of compounds for use in these greases as corrosion inhibitors are the alkaline earth metal sulfonates, particularly the overbased metal sulfonates wherein the metal to sulfur content is from 1.1 to 2 times that of the normal metal salt, as disclosed in US. 2,610,946. Such compounds may be prepared from the mahagony sulfon'ates or from sulfurized alkyl aromatic compounds Wherein the alkyl groups contain at least 8 carbon atoms. They may be employed either in the basic or the CO neutralized form, obtained by treating the basic metal sulfonate with CO until at least a substantial decrease in alkalinity is obtained. The grease composition may vary advantageously contain a compound of this class in an amount from about 0.2 to about 5.0 percent by Weight, and most suitably from about 0.5 to about 3.0 percent by weight. Another class of additives which are very advantageously employed in these greases are lead naphthenates, particularly those obtained from the lower molecular weight naphthenic acids, having molecular weights in about the range 120-235, as disclosed in US. 3,003,- 962. A compound of this class is suitably employed in an amount within the range from about 0.2 to 5.0 percent, and preferably from about 0.5 to 3.0 percent by Weight of the composition.

The preparation of these greases may be carried out by any convenient method involving saponification in situ in at least a portion of the lubricating oil employed in the finished grease, employing in the saponification step a saponifiable material as described hereinabove and a reaction product obtained by reacting a lithium phosphate salt in aqueous solution with an alkaline earth metal hydroxide. Very advantageously, the reaction between the phosphate aslt and the alkaline earth metal hydroxide is carried out in the presence of a portion of the lubricating oil employed in the grease also, and at least a portion of the water removed by evaporation prior to the saponification step. Following the saponification, the grease mixture is heated at a higher temperature to dehydrate the grease mixture and to condition the soap. The grease preparation is carried out very conveniently by the so-called low temperature process, wherein the grease mixture is heated at a maximum temperature below the melting point of the soap, although the high temperature process wherein the grease mixture is heated above the metling point of the soap may also be employed if desired. In the low temperature method the additional lubricating oil contained in the grease is added during the cooling step. In the high temperature process, the additional lubricating oil employed in the grease may be added either during the cooling step or before the grease mixtuer is heated to the maximum temperature.

The following examples are illustrative of the method of our invention and of a preferred grease composition obtained thereby.

EXAMPLE I The method of this invention was employed in the preparation of a grease having the following calculated composition in percent by weight:

Lithium 12-hydroxystearate 6.6 Sodium 12-hydroxystearate 3.8 Excess LiOH 0.2 Calcium phosphate 1.8 Additives 2.0 Lubricating oil Remainder The lubricating oil was a blend in about a 5.621 ratio 4 by weight respectively of a refined naphthenic distillate oil having a Saybolt Universal viscosity at 100 F. of about 178 seconds and a refined residual oil from a mixed base crude having a Saybolt Universal viscosity at 210 5 F. of about 105 seconds.

The grease preparation was carried out in the following manner: A metal base solution was first prepared by introducing 800 grams of water, 33.3 grams of dilithium sodium phosphate and 26.4 grams of lime into a grease kettle and heating for 3 hours at 180-190 F. The metal base solution thus obtained was employed in the saponification by adding 300 grams of the lubricating oil, 201.3 grams of saponifiable material, and 37.8 grams of 10 percent lithium hydroxide solution to the grease kettle and heating for 2 hours at 186-189 F. The saponifiable material employed was the methyl ester of 12- hydroxystearic acid, having a saponification number of 179, a neutralization number of 5.7, a hydroxy number of 169 and an iodine number of 3.3. The grease mixture obtained by the saponification was further heated to 334 F. to dehydrate and an additional 1355.0 grams of lubricating oil added. The mixture was then heated to 400 F. and maintained at that temperature for 10 minutes While it was circulated by means of a gear pump through a shear valve at 40 pounds per square inch pressure drop. The grease mixture was thereafter allowed to cool and drawn at 323 F. During the cooling, 20 grams of phenylalphanaphthylamine and 20 grams of an amine rust inhibitor were added.

The product obtained as described above was a smooth, glossy, N.L.G.I. No. 1 grade grease having a very desirable combination of lubricating properties as shown by the following test results:

Penetration, ASTM, 77 F.:

Unworked 328 Worked, strokes 339 Worked, 100,000 strokes 350 Dropping Point, ASTM, F. 391 ASTM Bomb Oxidation Test:

hr. -210 F.) lb. pressure drop 6 Dynamic Water Resistance Test, percent loss 2.5 Mean Hertz Load, kg. 24 Four Ball One Hour Wear Test, scar diameter,

mm. (40 kg.) 0.483 CRC Bearing Protection Test, rating 1 (Pass) The low wear obtained with the above grease represented by a scar diameter of only 0.483 mm. at 40 kg. load in the Four Ball One Hour Wear Test was substantially equivalent to that of a grease thickened with 10.4 percent of lithium 12-hydroxystearate and containing no inorganic material, showing that no increased wear was obtained due to the presence of the calcium phosphate.

EXAMPLE II The method of this invention was employed in the preparation of a grease having the following calculated composition in percent by weight:

0 Lithium 12-hydroxystearate 7.1 Sodium 12-hydroxystearate 4.1 Lithium stearte 2.4

Sodium stearate 1.4 Calcium phosphate 1.1

5 Glycerine 0.7 Additives 2.5 Lubricating oil Remainder The lubricating oil employed in the grease was a mixture in a 3:1 ratio by weight respectively of di-Z-ethylhexyl 0 sebacate and a refined naphthenic distillate oil having a Saybolt Universal viscosity of 178 seconds at 100 F.

The grease preparation was carried out in the following manner: A metal base solution was first formed by intnoducing 1200 grams of the naphthenic oil, 1000 5 grams of water, 117.5 grams of lime and 274.2 grams of dilithium sodium phosphate into a grease kettle and heating the mixture for 3 hours at 185-192 F. The resulting mixture was employed in the saponification by introducing 1209.0 grams of hydrogenated caster oil into the grease kettle following by heating for 3 hours at 186187 F. and then introducing 384.0 grams of triple pressed stearic acid into the kettle followed by heating for an additional hour at 183-187 F. The grease mixture thus obtained was then heated further for 3 hours at 3l6-320 F. to dehydrate. The heating was then discontinued and the grease mixture cooled to 298 F. with the addition of 895.0 grams of the naphthenic distillate oil and then further cooled to about 216 F. with the addition of 14.44 pounds of the synthetic ester oil. Additives were then introduced comprising 53.6 grams of a basic barium sulfonate, 102.2 grams of lead naphthenate and 53.6 grams of phenylaphanaphthylamine. The barium sulfonate was a commercial product obtained by neutralizing a tri-wax substituted benzene with excess barium oxide over that required to form the normal metal salt, the reaction product being employed in the form of a 50 percent concentrate in lubicating oil. Typical analyses of this product show a barium content of 5.0 percent, a sulfur content of 1.2 percent and a chlorine content of 0.1 percent. The lead naphthenate was also a commercial product, containing 29.5-30.5 percent of lead and having a Saybolt Universal viscosity at 210 F. of 400600 seconds. The grease was finely drawn at 200 F. and finished by milling with 4 passes through a Premier Colloid mill set at 0.002 inch clearance.

The above grease was a buttery N.L.G.I. No. 2 grade grease of slightly grainy texture having very superior extreme pressure properties in combination with other desirable lubricating properties as shown by the following test results:

Penetration, ASTM, 77 F.:

Unworked 201 Worked, 60 strokes 295 Dropping Point, ASTM, F. 281 ASTM Bomb Oxidation Test (100 hr. 210 F.) lb.

pressure drop 2 Dynamic Water Resistance Test, percent loss 7.5 Mean Hertz Load, kg. 52 CRC Bearing Protection Test, rating 2 (Pass) In comparison with the 52 kg. Mean Hertz Load test of the above grease, a load of 29 kg. in this test was carried by a lithium soap thickened grease without the calcium phosphate, prepared in the same manner and from the same materials except that the saponification was carried out in the conventional manner employing lithium hydroxide alone as the saponifying agent.

Greases having high dropping points up to 500 F. or above, in addition to the superior extreme pressure properties and other advantages shown above are obtained by employing lower fatty acid metal salts such as calcium acetate in the above composition in amounts from about 1 to about percent by weight.

While our invention has been described with particular reference to the production of lithium base greases, wherein it affords a special advantage in permitting the use of less expensive starting materials as described hereinabove, it is obvious that the method of grease preparation comprising the step of decomposing a metal salt to form the desired metal base together with a water-insoluble inorganic salt in very finely-divided form has application in grease making process generally where it is desired to incorporate such a metal salt in the composition either as a filler or for some other purpose. Greases which may be prepared by this method are principally alkali metal soap thickened greases containing insoluble alkaline earth and polyvalent metal sulfates, borates, carbonates, etc., in addition to the metal phosphates as. discussed hereinabove. In addition, our invention contemplates employing the combination of alkaline earth metal phosphates and glycerol in soap thickened greases generally, particularly greases thickened with alkali metal soaps, to produce greases having the high extreme pressure properties obtainable by this additive combination.

The preparation of mixed 'base greases containing finely-divided alkaline earth metal sulfates employing in the saponification step a mixture of alkali metal and trivalent metal hydroxides and alkaline earth metal sulfate obtained by treating an alum in aqueous solution with an alkaline earth metal hydroxide is disclosed and claimed in copending co-owned application Serial No. 280,156 now Patent No. 3,259,573 of N. R. Odell, filed of even date herewith.

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 claims.

We claim:

1. In a method of preparing a lithium soap thickened grease comprising the steps of saponifying a saponifiable material selected from the group consisting of fatty acids, hydroxy-substituted fatty acids, fatty acid glycerides and fatty acid esters, said fatty acid moiety containing about 10 to 32 carbon atoms therein with a saponifying agent comprising a mixture of lithium hydroxide and sodium hydroxide in the presence of at least a portion of the lubricating oil contained in the grease, heating at a higher temperature to dehydrate the resulting grease mixture and to condition the soap, cooling and adding any additional lubricating oil contained in the said grease, the improvement which comprises reacting at a maximum temperature of about 192 F. dilithium sodium phosphate in aqueous solution with calcium hydroxide to form calcium phosphate, lithium hydnoxide and sodium hydroxide, and employing the reaction product thus obtaind to react with the said saponifiable material in the saponification step.

2. The method of claim 1 wherein the said reaction between said dilithium sodium phosphate and said calcium hydroxide is carried out in at least a portion of the lubricating oil employed in the grease.

References Cited by the Examiner UNITED STATES PATENTS 2,397,956 4/1946 Fraser 252-41 X 2,513,680 7/1950 Schott et al. 252-40.7 2,548,037 4/1951 Minnick et al. 23-89 X 2,807,583 9/1957 Bratz et al. 252-18 2,820,762 1/1958 King 252-18 2,842,494 7/ 1958 Butcosk 252-41 X 2,846,391 8/1958 Morway 252-18 2,931,703 4/1960 Reader 23-184 X 2,948,679 8/1960 Rees et al. 252-25 X 2,967,151 1/1961 Morway 252-18 X 3,111,381 11/1963 Panzer et al. 252-25 X DANIEL E. WYMAN, Primary Examiner.

I. VAUGHN, Assistant Examiner.

Claims (1)

1. IN A METHOD OF PREPARING A LITHIUM SOAP THICKENED GREASE COMPRISING THE STEPS OF SAPONIFYING A SAPONIFIABLE MATERIAL SELECTED FROM THE GROUP CONSISTING OF FATTY ACIDS, HYDROXY-SUBSTITUTED FATTY ACIDS, FATTY ACID GLYCERIDES AND FATTY ACID ESTERS, SAID FATTY ACID MOIETY CONTAINING ABOUT 10 TO 32 CARBON ATOMS THEREIN WITH A SAPONIFYING AGENT COMPRISING A MIXTURE OF LITHIUM HYDROXIDE AND SODIUM HYDROXIDE IN THE PRESENCE OF AT LEAST A PORTION OF THE LUBRICATING OIL CONTAINED IN THE GREASE, HEATING AT A HIGHER TEMPERATURE TO DEHYDRATE THE RESULTING GREASE MIXTURE AND TO CONDITION THE SOAP, COOLING AND ADDING ANY ADDITIONAL LUBRICATING OIL CONTAINED IN THE SAID GREASE, THE IMPROVEMENT WHICH COMPRISES REACTING AT A MAXIMUM TEMPERATURE OF ABOUT 192*F. DILITHIUM SODIUM PHOSPHATE IN AQUEOUS SOLUTION WITH CALCIUM HYDROXIDE TO FORM CALCIUM PHOSPHATE, LITHIUM HYDROXIDE AND SODIUM HYDROXIDE, AND EMPLOYING THE REACTION PRODUCT THUS OBTAIND TO REACT WITH THE SAID SAPONIFIABLE MATERIAL IN THE SAPONIFICATION STEP.