US2702792A - Aluminum distearate composition and greases prepared therefrom - Google Patents

Description

ALUMINUM DISTEARATE COMPOSITION AND GREASES PREPARED THEREFROM No Drawing. Application November 28, 1951, Serial No. 258,747

3 Claims. (Cl. 252-35) This invention relates to aluminum soaps and grease compositions containing the same. More particularly, it relates to new and improved aluminum salts of higher fatty acids, which are known in the trade as grease grade aluminum stearates, and to grease compositions of im proved gel strength prepared therewith Greases composed of hydrocarbon oils thickened with aluminum soaps are well known. The aluminum salts of higher fatty acids used for this purpose are known in the trade as aluminum stearates, even though the fatty acids from which they are prepared are not all stearic acid. Thus, for example, hydrogenated fish oil fatty acids having the following compositions are used:

Hydrogenated tallow acids and other similar higher fatty acid mixtures are also used in the manufacture of grease grade aluminum stearates, and aluminum soaps thereof are included within the scope of the present invention.

Aluminum stearate is manufactured commercially by reacting a water solution of the sodium soap of a commercial fatty acid with a solution of an aluminum salt, generally the sulfate. The resulting slurry of insoluble aluminum stearate is filtered, washed, dried, and ground to uniform particle size.

In general, stearates with aluminum to fatty acid ratios corresponding to the distearate have proved most effective in the preparation of lubricating greases. Ordinarily, these aluminum soaps are added to hydrocarbon mineral oils in the ratio of about 4% to 12% or more of the soap to 96% to 88% hydrocarbon oil, respectively. Hydrocarbon lubricating oils having Saybolt 'viscosities within the range of 100-120 seconds at 210 F. are frequently used. The grease is compounded by heating the mixture of oil and aluminum soap until maximum dispersion of the soap in the oil is obtained. The grease is then cooled under controlled conditions during which the optimum gel structure is built up in the grease.

We have found that the gel-forming power of aluminum distearate, as defined above, in hydrocarbon oils, can be greatly improved by forming aluminum distearate anhydride therein. Our present invention is directed, therefore, to aluminum distearate anhydride, to grease grade aluminum distearate containingsubstantial quantities (i. e., 1% by weight or more) of aluminum distearate anhydride therein, and to methods for the production of these improved products.

The aluminum distearate anhydrides of this invention are characterized by the substantial absence of chemically combined water and are not to be confused with the dehydrated soaps of the prior art in which only physically present water has been removed.

The formation of our new compounds is shown by the following equation:

O O 120 110 CR O O 0 2 AI-OH Al-O-Al H20 0 O 0 R0; R0; ;CR 0 O O atent 2,702,792 Patented Feb. 22, 1955 0 OH O Al Al-OH O RC O OH AlO-Al +H2O O O RC; 012

wherein R is the same.

The aluminum distearate anhydrides, as defined above, are prepared by the dehydration of the corresponding aluminum distearates. This dehydration, we have found, can be effected by heating the previously dried aluminum distearate with agitation at temperatures of 160-180" C. or higher for a length of time suflicient to remove all of the chemically combined water, and thus to produce the anhydride. The aluminum distearate anhydrides so obtained are white solids that are soluble or dispersible in aliphatic hydrocarbons such as kerosene, lubricating oils and the like.

We have also found, however, as another important feature of our invention, that an increase in the gelforming power of aluminum distearates is obtainable by only partial conversion thereof to aluminum distearate anhydride. The advantage of this discovery is, of course, that considerably less drastic heating conditions are required to effect the partial dehydration. Thus, for example, we have found that substantial quantities of aluminum distearate anhydride, ranging from 1% to about 15-25%, can be formed by heating aluminum distearate under dehydrating conditions for a suitable time, usually within about 1-5 hours, at a temperature of at least 160 0, when stagnant heating conditions are used. We have also found, however, that the same degree of dehydration can be effected at much lower temperatures, which may be as low as C., if the aluminum distearate is heated in a current of drying gas such as hot air or hot products of combustion.

Any suitable type of equipment may be used to carry out the process of our invention. Where stagnant heating is employed, i. e., where the aluminum distearate is simply heated with agitation to drive out water, an indirect-fired kiln or a jacketed kettle provided with internal agitation may be used. When a current of hot air or other drying gas is employed, we prefer to use a belt dryer or a tray dryer in which a current of the drying gas is passed continuously over the aluminum distearate in finely divided form. Other similar equipment will readily suggest itself to those experienced in the art of drying solids, and may be employed.

The invention will be further illustrated by the following specific examples, which describe specific embodiments thereof, but to which it is not limited.

Example 1 An aluminum soap was prepared from hydrogenated fish oil fatty acids by the method previously described; i. e., by adding aluminum sulfate solution to a water solution of the sodium soap of the acids at 70 C., washing the resulting precipitate free from sodium sulfate, and drying in a current of hot air on a belt dryer. The dried soap contained 1.0% moisture and 8.74% A: and was composed essentially of aluminum distearate.

Samples of this soap were heated for 90 minutes in open containers suspended in oil baths at varying temperatures. Where necessary, the heated material was ground and screened to 40 mesh. Greases containing of the soaps were then made in a hydrocarbon lubricating oil having a viscosity of 300 at 100 F. and tested with the penetrometer both in unworked condition and after working for 60 strokes. The test results are shown in the following table, in which penetrations are in tenths of a millimeter.

These results show clearly the increase in gel strength that follows the formation of increasing amounts of aluminum distearate anhydride in the aluminum soap composition as progressively higher heating temperatures are used. Tests made by heating samples of the same soap at 160 C. for increasing times show a much slower increase in gel strength; thus, for example, a grease prepared with the same quantity of the same hydrocarbon oil, but using a soap heated at 160 C. for 2 /2 hours showed a penetration of 152 unworked and 250 worked. It is evident, therefore, that the anhydride is not formed by the stagnant heating of aluminum distearate soaps at temperatures much below 160 C. At temperatures above 160 C., however, the anhydride formation is quite rapid Example 2 We have also found that aluminum distearate anhydride can be formed at temperatures considerably below 160 C. when a stream of hot drying gases is employed. Hot air or hot combustion products of hydrocarbon oil or natural gas may be used for this purpose.

Samples of the washed precipitate of Example 1 were extruded into strings which were caught on perforated trays. These were placed in an oven arranged to blow hot air downwardly through the stearate and were dried and dehydrated under the conditions shown in the table below. The samples were then made into 10% dispcrsions in the hydrocarbon oil of Example 1 and greases were made and tested as described in that example and alsolafter working for 1000 strokes with the following resu ts:

These figures show that substantial quantities of the anhydride, sufficient to increase materially the gel strength of greases and believed to range from about 5% to 25% of the weight of the soap, are obtainable when aluminum distearate is dried in a current of hot gases at temperatures of -135 C. Comparison of the penetrations with those of Example 1 will show that the results are comparable with those obtained by heating the soap in a stagnant atmosphere at C. for 1 /2 hours.

From the foregoing it will be seen that the present invention, in efiect, substitutes a new type of grease grade aluminum stearate for those previously employed, with a resulting increase in the gel strength of the grease. It will be evident that a smaller proportion of the new aluminum stearate may be employed, as compared with the quantities of ordinary aluminum stearates, when an increase in gel strength is not of importance. It will also be evident that the new aluminum distearate anhydride may be used in admixture with ordinary aluminum distearate or other metallic soaps if desired. It will be understood, therefore, that a variety of grease compositions may be prepared by those skilled in the art within the scope of the appended claims.

What I claim is:

1. Aluminum distearate anhydride.

2. A grease grade aluminum distearate of improved gel-forming power in hydrocarbon oils, said aluminum distearate having a substantial content of aluminum distearate anhydride therein.

3. A grease composition comprising a major proportion of a hydrocarbon lubricating oil and a minor quantity within the range of about 4% to 12% by weight of an aluminum distearate having a substantial content of aluminum distearate anhydride therein.

References Cited in the file of this patent UNITED STATES PATENTS 2,211,139 Licata Aug. 13, 1940 2,297,183 Fabian et al Sept. 29, 1942 2,359,946 Sudholz et al. Oct. 10, 1944 2,447,064 Gebhart et al. Aug. 17, 1948 2,555,104 Ashley et al. May 29, 1951 OTHER REFERENCES Metallic Soaps, Raw Materials for Research and Incllislstlr yl pub. Metasap Chem. Co., 1940, pages 3, 4 and

Claims (1)

1. 3. A GREASE COMPOSITION COMPRISING A MAJOR PROPORTION OF A HYDROCARBON LUBRICATING OIL AND A MINOR QUANTITY WITHIN THE RANGE OF ABOUT 4% TO 12% BY WEIGHT OF AN ALUMINUM DISTEARATE HAVING A SUBSTANTIAL CONTENT OF ALUMINUM DISTEARATE ANHYDRIDE THEREIN.