US3475336A - Low free alkali procedure for making greases - Google Patents

Description

United States Patent M 3,475,336 LOW FREE ALKALI PROCEDURE FOR MAKING GREASES Edward A. Cross, Beaumont, Tex., assignor to Texaco Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed July 18, 1966, Ser. No. 565,742 Int. Cl. C10m 5/14, 7/20 US. Cl. 25241 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the preparation of a grease composition. More specifically, this invention relates to the preparation of a lithium soap based grease containing appreciable amounts of unsaturated fatty components.

The preparation of lithium soap thickened greases is broadly old and many processes have been taught for preparing lithium greases. These processes can generally be broken down into two categories, the melt procedures and the non-melt procedures. The melt procedures involve, generally speaking, heating a mixture of saponifiable material and saponifying agent usually with a suitable mineral oil to a temperature above the melting point of the soap to be formed and then quenching the grease forming mixture to a temperature below the solution temperature of the lithium soap formed. This top temperature is usually sufficient to vaporize any water present. Additional lubricating oil is added to adjust the final ratio of soap to the lubricating oil in the final grease composition. The non-melt procedures generally involve heating the saponifying agent, e.g., lithium hydroxide and the saponifiable material usually 12-hydroxystearic acid in oil at temperatures lower than the melting point of the soap to be formed, dehydrating under conditions whereby melting of the soap does not occur and cooling. In both of these cases the grease composition is milled. Newer procedures to obtain the proper consistency of the grease involves during the process passing the mixture of soap and lubricating oil through a shear valve having a pressure drop across the valve of between say 20 and 200 p.s.i.

Many saponifiable materials have been suggested for use in the preparation of lithium soap based greases. These include in particular saturated aliphatic fatty acids of which 12-hydroxystearic acid is a prime example. Also used are the methyl ester of 12-hyroxystearic acid and its glyceride. It has also been suggested to use stearic acid itself, but high ratios of hydroxyznon-hydroxy acids are usually required for completely suitable lithium soap greases. Some researchers have even suggested the inclusion of unsaturated fatty acids to prepare lithium soap thickened greases either alone or in admixture with a saturated fatty acid, its ester or glyceride. Attempts heretofore to prepare greases which contain appreciable quantities of an unsaturated fatty acid have failed. For this reason, it is generally conceded in the grease art that the presence of unsaturated fatty acid in saponifiable material mixtures for lithium soap thickened greases provides an inferior product, particularly with respect to 3,475,336 Patented Oct. 28, 1969 the yield as determined by the standard ASTM penetra tion tests (D2l7-48). For this reason, purchasers of fatty acid materials for use in grease manufacture have generally purchased hydrogenated castor oil having an iodine value below 7, preferably in the range of 3 to 4. An iodine value of 7 would be tantamount to a mixture of lZ-hydroxystearic acid of 92%, the balance being the unsaturated counterpart, ricinoleic acid. This is considered to be a stringent limitation on the economics of grease manufacture since highly hydrogenated castor oil is substantially more expensive than mildly hydrogenated castor oil which contains appreciable unsaturates. It has long been considered that the most desirable grease from an economic standpoint would have a high unsaturated content, the higher the less expensive.

It is an object of this invention, therefore, to prepare a grease composition containing appreciable unsaturates from say hydrogenated castor oil having an iodine value greater than 7.

It is another object of this invention, therefore, to provide a process for preparing such a grease composition which does not entail any additional procedures than those heretofore employed for the manufacture of lithium soap thickened greases.

It is still another object of this invention to prepare a lithium soap thickened grease wherein the unsaturated fatty acid content is substantially the same as the saturated fatty acid content.

These and other objects of this invention will become apparent from the following complete description of my invention and appended claims.

Broadly, this invention contemplates a process for preparing a lithium soa thickened grease which comprises saponifying a mixture of a saturated hydroxy fatty material in the C C range and unsaturated hydroxy fatty material in the C C range with a lithium base saponifying agent, the unsaturated fatty material being present in the mixture between 10 and by weight, in the presence of lubricating oil, dehydrating the saponification mixture by heating the mixture under conditions of temperature and pressure sufficient to vaporize substantially all of the water in the grease mixture, cooling the grease mixture, shearing the grease mixture and maintaining the amount of free alkali in the finished grease, calculated as lithium hydroxide, not above 0.05%

Methods for preparing a lithium soap based grease according to the process of this invention include the melt procedure of USP 2,916,452 wherein the mixture of saturated fatty material and unsaturated fatty material, as above described, is mixed with a suitable oleaginous material, e.g., mineral oil and heated together with at least a stoichiometric amount of lithium base saponifying agent above transition temperature of the soap and then cooled through the transition temperature at an average rate below about 25 F. per minute preferably below about 15 F. per minute and while quenching with additional oleaginous liquid at a rate from about 0.001 to about 0.05 gallon per minute of quench oil per pound of grease concentrate. The quenching can begin before the grease mixture has cooled substantially below the solution temperature of the soap and preferably while the mixture is at a temperature above the solution temperature of the soap. It is preferred furthermore when using this melt'procedure that the quenching be carried out during the cooling to at least about 25 F. below the solution temperature of the soap. In the instant case when preparing a grease thickened with a mixture of a lithium-saturated fatty acid soap and a lithium-unsaturated fatty acid soap the quenching is begun while the grease concentrate is at a temperature above the melting point of the soap which, depending upon the amount of unsaturated soap utilized in the saponifiable material mixture is in the range of about 385-420 F. The cooled grease mixture is then milled with shearing and any additional lubricating oil to adjust for the proper penetration can be added at this stage.

The grease composition prepared according to the instant invention can be prepared utilizing the manipulative steps disclosed in USP 3,242,082. In such case, a grease concentrate containing a mixture of saponifiable saturated fatty material and saponifiable unsaturated fatty material are introduced together with lithium base saponifying agent in the presence of a portion of lubricating oil into a vessel and this grease mixture is heated to a temperature sufiicient to cause saponification but below the melting point of the soap mixture until dehydration occurs to eliminate substantially all of the water in the grease mixture. The mixture is then cooled with the addition of the remainder of lubricating oil employed in the finished grease. While performing these general steps, a minor stream of the grease mixture is withdrawn from a maintained agitated body during the heating step and recirculated through a recycle line to the grease mixture via a shear valve operating with a pressure drop across the valve of say -200 p.s.i. to shear the withdrawn minor grease mixture stream. A minor stream of the grease mixture is also withdrawn during the cooling step and recycled through a shear valve operating at a pressure drop across the valve of about -125 p.s.i. and the cooled minor stream is returned to the maintained major portion of the grease mixture.

In still another method by which the saponification, dehydration, cooling and shearing steps can be performed a mixture of ricinoleic acid and 12-hydroxystearic acid or other mixtures of unsaturated fatty acid and saturated fatty acid in the C C range as set forth above in say 50-50 weight percent is introduced into a tubular zone together with lithium hydroxide and a minor amount of a suitable lubricating oil. The grease concentrate is passed through the tubular zone under turbulent conditions and the temperature and pressure in the zone is sufiicient to to promote saponification of the fatty acid material. A minor stream of the grease mixture is continuously withdrawn and recirculated from the bottom of the tubular zone to the top of the tubular zone. A portion of the grease mixture is continuously withdrawn from the tubular zone and introduced to a dehydration vessel maintained under temperature and pressure sufiicient to vaporize substantially all of the water present in the grease concentrate but at a temperature lower than the melting point of the soap. A minor stream of grease mixture is continuously withdrawn from the dehydration vessel and recycled back to the dehydration vessel via a shear valve operating at a pressure drop across the valve of about 20-200 p.s.i. Continuously, there is withdrawn from the dehydration zone an amount of grease concentrate which is passed into a cooler at which point additional lubricating oil can be added to adjust the final amount of lubricating oil into the grease mixture. The cooler can be operated also by withdrawing a minor stream of the grease mixture and recycling it through a shear valve operating at a pressure drop acros the valve of 20-200 p.s.i. It should be noted also that the process can be operated by use of additional lubricating oil introduced at the inlet to the dehydration zone. The cooler can be any cooler normally used including one containing a water jacket for recirculation of cold water to cool the grease mixture down to final temperature.

Any of the foregoing techniques can be employed as none is especially critical. In fact, all manipulative procedures heretofore known for lithium-fatty acid soap thickened greases can be employed providing the free alkali content, calculated as lithium hydroxide, in the finished grease does not exceed the maximum amount of 0.05%. I have found that this maximum concentration of free alkali is extremely critical for preparing lithium soap thickened greases containing substantial quantities of unsaturated fatty acid constituents. I find that by controlling the amount of free alkali in the finished grease that I can provide a grease from a mixture of fatty acids having high unsaturated fatty acid content in the range of 10 to 75% by weight, based on the total weight of the fatty acid constituents. This grease is equally as good as those heretofore prepared from highly hydrogenated castor oil with iodine value as low as 3-4. I prefer that the free lithium hydroxide concentration in the finished grease composition be not more than 0.033%. Amounts of free lithium hydroxide in the finished grease in excess of 0.05% produce a grease which has such an inferior penetration (and hence inferior yield) that it is too soft to test.

Suitable soap forming hydroxy fatty acid materials for the saturated fatty acid component in the mixture of saponifiable materials which can be employed in the production of lithium hydroxy fatty acid greases are essentially saturated hydroxy fatty acids containing twelve or more carbon atoms and one or more hydroxyl groups separated from the carboxylic acid groups by at least one carbon atom, the glycerides of such acids, the lower alkyl esters of such acids and mixtures thereof.

Preferably the acid contains about 16 to 22 carbon atoms. Such materials can be obtained from naturally occurring glycerides by hydrolysis, by hydrogenation of ricinoleic acid or castor oil or otherwise by processes such as the catalytic oxidation of hydrocarbon oils and waxes which have been extracted and fractionated to desired molecular range. Particularly suitable materials of this character are hydrogenated castor oil, 12-hydroxystearic acid, and the methyl ester of l2-hydroxystearic acid.

It is particularly desirable from an economic standpoint in furnishing the materials for use as the saponifiable material that a mildly hydrogenated castor oil be used. The mildly hydrogenated castor oil such as one having a 50-50 mixture of l2-hydroxystearic acid and ricinoleic acid is one of the most inexpensive methods of providing a suitable mixture for use in this invention. It is necessary that the unsaturated fatty material in this saponifiable material mixture be present in weight percent between 10 and 75 most preferably within the range of 35 to 60%. If the amount of unsaturated fatty material component is greater than 75% by weight, the saponifiable material will be unsuitable to prepare a grease of the order described below in the examples.

The term lithium base material as used herein refers to lithium compounds which saponify fatty material. Included within this definition are lithium hydroxide and lithium oxide. Preferably, lithium hydroxide is used in the process of the invention.

Suitable oleaginous liquids which can be employed for forming the grease concentrate or quenching in the case of a melt-quench procedure as in the examples, are the conventional mineral lubricating oils, the synthetic lubricating oils prepared by cracking and polymerizing products of the Fisher-Tropsch process and the like as well as other synthetic oleaginous compounds such as polyesters, polyethers, etc., within the lubricating oil viscosity range. Such synthetic oleaginous compounds, including mixtures thereof, can be substituted in whole or in part by conventional mineral lubricating oils. Examples of these compounds are aliphatic dicarboxylic acid diesters such as di-2-ethylhexyl sebacate, di-sec.-amyl sebacate, di-Z-ethylhexyl azelate, di-iso-octyl adipate, etc. Suitable mineral oils are those having Saybolt Universal viscosities in the range from about to 2000 seconds at 100 F. and can be either naphthenic, paraifinic, aromatic, or asphaltic, in type, or blends of any of these. Preferably it is either naphthenic or paraffinic. When the saponification is carried out in the presence of a portion of the oil included in the grease, an oil which is not hydrolyzed under saponification conditions is preferably employed for this purpose, most suitably a mineral oil fraction.

The greases produced in accordance with this invention can contain various additives of the usual type such as corrosion inhibitors, oxidation inhibitors, extreme pressure agents, antiwear agents, and so forth. Preferably, they contain an oxidation inhibitor, which can suitably be an oxidation inhibitor of the amine type such as diphenylamine, N-phenyl-alpha-naphthyl-amine or N,N,N',

-tetramethyldiaminodiphenylmethane. Compounds of this type can be added either before or during the cooling down process either in the case of a melt procedure or in the instance wherein the saponification and dehydration step are performed at temperatures not in excess of the melting point of the soap. These compounds are preferably added while the temperature of the greases is between 300 F. and about 100 F., suitably during a cooling down step.

In order to more fully illustrate the nature of my invention and the manner of practicing the same, the following examples are presented.

EXAMPLES A series of lithium soap based greases were prepared employing as the base oil a mineral lubricating oil having an SUS viscosity at 100 F. of about 457, comprising an approximate 1:1 blend of a refined wax distillate oil having a viscosity index of about 96 and an SUS viscosity of 182 at 100 F. and a refined parafiinic residual oil having a viscosity index of about 80 and an SUS viscosity of about 103 at 210 F. obtained by furfural refining, clay, and acid treating and solvent dewaxing a Manvel residual oil. The fatty material employed was a mixture of 12-hydroxystearic acid and ricinoleic acid in the amounts shown in the table below.

The greases were prepared in 200 and 300 pound laboratory batches, employing a 300 pound capacity Dowtherm heated kettle. The grease mixture was obtained by saponifying a mixture of fatty acid material with lithium hydroxide in the form of an approximately aqueous solution in the presence of about of the lubricating oil employed in the grease. The saponification was carried out at a temperature of about 160-220 F. for about 1 hour, and the mass dehydrated by heating for an additional hour at about 270-300" F. Following the dehydration additional oil was added and the mixture heated to about 395405 F. until the soap appeared to be completely melted. Stirring of the kettle contents was carried out continuously during the preparation of the grease mixture and the subsequent cooling process.

Grease mixtures obtained as described above were cooled down in the kettle to about 200-250 F. by circulating cold Dowtherm eutectic mixture through the kettle jacket and by quenching with additional lubricating oil comprising from about V to about A; of the total lubricating oil contained in the grease, the temperature of the quench oil being in about the 75l30 F. range. Good greases were obtained when the grease mixture was cooled at a rate below about 25 F. per minute in about the 400-35 0 F. range with quenching with rates below about 0.05 gallon of quench oil per minute per pound of original grease mixture employing as the quench oil the blend described above as well as the distillate oil and the heavier residual oil components of the blend. By quenching at still lower rates .very substantially improved yields are obtained, optimum yields .being obtained by quenching at rates below about 0.02 gallon of quench oil per minute per pound of original grease mixture and cooling at rates of about 3-15 F. per minute in about the 400-350 F. range. At cooling rates below about 3 F. per minute in this range the yield begins to deteriorate and fall off more rapidly at rates below about 2 F. per minute as taught in U.S. 2,916,452. Poor greases are obtained when the free alkali content in the finished grease calculated as lithium hydroxide, exceeds 0.05% by weight, based on the total weight of the grease.

TABLE Run 12-hydroxystearie acid, wt. percent... 90 90 90 90 Ricinoieie Acid, wt. percent 10 10 10 10 10 Free Alkali, as LiOH percent 0.033 0. 033 1 0. 1 0. 15 0. 054 Top Temperature Used, F 390 400 400 400 400 Appearance of Grease (2) (2) z a a Wkd. Pene on Milled Grease (ASTM l Free fatty acid.

2 Smooth.

3 Grainy soup.

4 Too soft.

The iodine value for Run 1 was 12.6 (calculated basis the iodine value of acids used, i.e. 90% l2-hydroxystearic acid at iodine value of 4 and 10% ricinoleic acid at iodine value of 90). The mixture contained minor amounts of other unsaturated fatty materials. The grease prepared in Runs 1 through 3 inclusive had especially good properties with respect to the penetration on the milled grease. It should be noted that the results obtained for these greases are substantially better than the results obtained in Runs 4 and 5 wherein the free alkali content of the finished grease calculated as lithium hydroxide was in excess of 0.05%. Note particularly in Run 5 that even a slight increase in the free lithium hydroxide content in the finished grease produces a grainy, soupy grease which is too soft to test when milled. Hence it can be readily seen from this table that it is critical when preparing a lithium soap thickened grease containing an appreciable amount of unsaturated fatty acid in the saponifiable material to have a concentration of lithium hydroxide in the grease such that the free alkali calculated as lithium hydroxide in the finished grease is below 0.05%.

Accordingly, it seems from the foregoing that I have provided a significantly useful process for preparing a grease and a useful grease. My process can be performed very economically using manipulative procedures heretofore known and taking advantage of low cost unsaturated fatty acid materials for use in a mixture with saturated fatty acid materials in the grease making process. '1 provide this process without any sacrifice in grease properties and I provide the grease industry with a method for obtaining the grease at substantially less cost than heretofore entailed.

The terms and expressions which have been employed are used as terms of descriptions and not of limitation, as there is no intention, in the use of such terms and expressions, of excluding any equivalent of the features shown and described or portions thereof, but it is recognized the various modifications are possible within the scope of the invention claimed. It should be realized, therefore, that minor amounts of nonhydroxy containing saturated fatty acids can be used in place of l2-hydroxystearic acid such as stearic acid itself in amounts up to say 25% of the total weight of the saponifiable material.

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.

I claim:

1. A method of preparing a lithium soap-thickened grease composition wherein a saponification mixture of lithium base saponifying agent and a saponifiable hydroxy fatty material is saponified in the presence of at least part of the lubricating oil in the finished grease, the saponified mixture is heated to an elevated temperature to dehydrate the said mixture, and the dehydrated mixture is cooled by adding the balance of the additional oil in the finished grease, the improvement which comprises maintaining the free alkali content of said grease' composition, calculated as lithium hydroxide, at a value not above 0.05% by weight of the finished grease, and wherein the saponifiable hydroxy fatty material is a mixture selected from the group consisting of 90-25% by weight of a saturated hydroxy fatty acid and 10-75% by weight of an unsaturated hydroxy fatty acid, the glycerides and methyl esters of said hydroxy fatty acids.

2. Method as claimed in claim 1 wherein the free alkali content of said grease composition, calculated as lithium hydroxide, is not above 0.03% by Weight.

3. A method as claimed in claim 1 wherein the saponifiable hydroxy fatty material is a mixture of about 90% by weight of 12-hydr0xystearic acid and about 10% by weight of ricinoleic acid.

4. A method as claimed in claim 1 wherein the saponifiable hydroxy fatty material is a mixture of about 50% by weight of 12-hydroxystearic acid and about 50% by weight of ricinoleic acid.

5. A lithium soap thickened grease composition comprising as the thickening agent a mixture of from about 90-25% by weight of lithium soap of 12-hydroxystearic acid and from about 10-75% by weight of lithium soap of ricinoleic acid in a mineral lubricating oil having a 20 vscosity of from 100 to 2000 seconds SUS, at 100 F., said grease composition having a free alkali content,

calculated as lithium hydroxide, not above 0.05% by weight of the composition.

6. A grease composition as claimed in claim 5 wherein the saponifiable hydroxy fatty material is a mixture of about 90% by weight of 12-hydroxystearic acid and about 10% by weight of ricinoleic acid.

7. A grease composition as claimed in claim 5 wherein the free alkali content is not above about 0.03% by weight calculated as lithium hydroxide.

References Cited UNITED STATES PATENTS 2,614,076 10/1952 Moore et al. 252-41 2,651,616 9/1953 Mathews et al. 25241 3,117,087 1/1964 McCormick et al. 2524l 3,242,082 3/1966 Badgett ct al. I5241 3,242,086 3/1966 Dowden et al. 252-41 DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner