US3428562A - Process for preparing a grease composition containing synthetic oil as the sole lubricating oil component - Google Patents

Description

United States Patent 3,428,562 PROCESS FOR PREPARING A GREASE COMPOSI- TION CONTAINING SYNTHETIC OIL AS THE SOLE LUBRICATING OIL COMPONENT Roy L. Crouch and Paul A. Cook, Nederland, Tex., as-

signors to Texaco Inc., New York, N .Y., a corporation of Delaware No Drawing. Filed Nov. 4, 1966, Ser. No. 591,978 U.S. Cl. 252-42 8 Claims Int. Cl. C10m /14 ABSTRACT OF THE DISCLOSURE The present invention is directed to a process for the preparation of a lithium soap thickened grease composition containing a synthetic oil as the sole lubricating oil component by saponifying a saponifiable fatty material with a lithium saponifying agent in water at a temperature of 160-200 F., adding 23-41% by weight of synthetic lubricating oil based on the oil component of the finished grease, heating the resulting mixture at a rate of 0.7 F. or more per minute to 380- 450" F. while adding 3056% by weight of additional synthetic lubricating oil based on the oil component of the finished grease, maintaining the heated mixture at 380-450 F. while adding any additional synthetic oil and shearing the mixture.

This invention relates to a process for preparing a lubricating grease composition containing synthetic oil as the sole lubricating oil component. More particularly, this invention relates to a process for preparing a grease composition containing synthetic oil as the sole lubricating oil component which process can be performed in one vessel providing a grease which satisfies military specifications G23827A.

Greases containing mineral-ester type synthetic lubricants thickened with say a lithium soap have been used extensively in low temperature application, particularly in aircraft. However, the operating range or more specifically the low temperature limit at which the greases are operable is restricted by the mineral oil components. One reason for retaining the mineral oil component in the grease composition is to provide a medium, during manufacture, in which the soap precursors, i.e. alkaline and acidic materials can be reacted. Generally, ester type synthetic lubricants cannot be used for this purpose because these materials tend to react with the alkaline material. The mineral oil component is eliminated by the procedure of our invention more fully described below thereby allowing the preparation of lithium-soap thickened greases that contain an all-synthetic base, e.g., ester type synthetic lubricants.

The aforementioned low temperature greases containing mineral-ester-type synthetic base oils thickened with say a lithium soap are commonplace in the grease industry. The usual method for preparing such greases is to first make a soap base in situ by reacting lithium hydroxide monohydrate with a fatty material such as 12- hydroxystearic acid, in a mineral oil-water medium. The ester type synthetic lubricant is then added to the neutral soap base. Ester-type synthetic lubricants cannot be included in the soap preparation step because these would react with the lithium hydroxide. Hence, a 100% synthetic grease could not heretofore be prepared by the commonly used process.

It is an object of this invention, therefore, to provide a process for preparing a grease containing synthetic oil as the sole lubricating oil component.

It is another object of this invention, therefore, to provide such a process for preparing a grease composition containing synthetic oil as the sole lubricating oil component which process can be performed in a single, simple, open grease kettle and does not necessitate the use of a preformed soap.

It is still another object of this invention to provide a grease composition containing synthetic oil as the sole lubricating oil component which grease passes all of the usual tests for greases of like kind including the tests under U.S. military specification MIL-G-23827A.

These and other objects of our invention will become apparent in the following more complete description of our invention and appended claims.

Broadly, this invention contemplates a method for preparing a lithium soap thickened grease containing synthetic lubricating oil as the sole lubricating oil component which comprises saponifying a saponifiable fatty material with a lithium saponifying agent in water at a temperature of between 160 and 200 F., adding between 23.0 and 41.0 weight percent synthetic lubricating oil based on the total weight of the synthetic lubricating oil component in the finished grease while the saponification mixture is at a temperature between and 200 F. heating the mixture at a rate of at least 0.7 F. per minute to a top temperature of between 380 and 450 F. while adding additional lubricating oil in an amount between 30.0 and 56.0 weight percent based on the total weight of the synthetic lubricating oil component, maintaining the temperature of the mixture between 380 and 450 F. for between 0 and 30 minutes, cooling the mixture while adding any balance of synthetic lubricating oil and shearing the mixture. The so-prepared grease is preferably milled to the proper consistency thereafter.

In a particularly desirable embodiment of this invention, lithium hydroxide monohydrate and 12-hydroxystearic acid are charged into a grease kettle containing water in a weight ratio of water to lithium hydroxide monohydrate of between 7:1 and 15:1, most preferably 7:1, maintained at a temperature between and 200 F., most preferably 160 180 F. while the lubricating oil is added at those same temperatures. The weight ratio of the synthetic oil added to the soap is preferably in the range of 2:1 to 5:1, most preferably 2:1. The mixture containing soap formed in situ is heated to a temperature within the range of 160-400 F. while a second charge of synthetic lubricaing oil is added, preferably at a temperature of between 160 and 365 F. The weight ratio of the synthetic oil to the soap added in the second oil addition is preferably in the range of 5:1-16z1, most preferably 6.4:1. The mixture is then brought to a top temperature within the range of 380-400 F., preferably, 390395 F. It is maintained at this temperature for a period of between 0 minutes and 30 minutes, preferably 15 minutes. The total time for the saponification and dehydration step preferably takes between 0.5 and 1.5 hours most preferably about 1 hour. The ingredients at a top temperature are then cooled, preferably at a rate of between 2.0 and 2.6 F. per minute while additional lubricating oil is added at a rate of between about 0.1 and 0.5 pound per minute per 100 pounds of finished grease. During this cooling step it is preferred that a portion of the grease composition be withdrawn from the maintained agitated body and recycled back to the vessel via a grease pump and a shear valve operating with a pressure drop across the valve of between 0 and 100 p.s.i.g. preferably 60 p.s.i.g., the recirculation rate of the grease being between 0.5 and 3.0 gallons per minute per 100 pounds of finished grease, preferably about 2.0 gallons per minute. The grease mixture is cooled to a temperature in the range of about 210-160 F., preferably ZOO-180 F. at which temperature any additives such as coloring agents, extreme pressure agents, corrosion inhibitors, oxidation inhibitors, etc. can be added. The grease is then finished by milling one pass through a colloid mill. It is preferred that the finished grease have a lithium soap content of between 6.0 and 15.0 weight percent based on the total weight of the grease composition, preferably 9.8% by weight. It is also preferred that the free fatty acid content be between 0.0 and 0.1% by weight, preferably 0.0% by weight and the free alkali content calculated as lithium hydroxide be between 0.0 and 0.1%, most preferably 0.06% by weight.

The saponifiable fatty materials employed in the production of soaps for the present invention are the esters of 12-hydroxystearic acid, preferably the lower alkyl, e.g. up to about 8 carbon atoms, esters of 12-hydroxystearic acid, such as the methyl ester of the glyceride. We can also utilize 12-hydroxystearic acid itself as well as other hydroxy fatty acids preferably containing 16 to 22 carbon atoms. Such materials can be obtained from naturally occurring glycerides by hydroxylation of fatty acids, 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 the desired molecular range. Particularly suitable materials of the character utilized in the present invention are hydrogenated castor oil, 12-hydroxystearic acid and the methyl ester of 12-hydroxystearic acid. In addition to these we can utilize some fatty acids containing unsaturated fatty acids such as ricinoleic acid as well as non-hydroxy containing fatty acids, e.g. stearic acid.

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

The synthetic lubricating oils which can be used in accordance with our invention are those generally 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, polyethylene glycols within the lubricating oil viscosity range. Generally, these synthetic lubricating oils are those known to have lubricating properties and can be used as a plasticizer. They include compounds such as di-2-ethylhexyl sebacate, di-sec.-amyl sebacate, di-Z-ethylhexyl azelate, di-isooctyl adipate, di-octyl-p-hthalate, di-2-ethylhexyl phthalate, di-isooctyl azelate, di-octyl azelate, dipropylene glycol dipelargonate, isodecyl pelargonate, etc. Suitable synthetic lubricating oils employed in this invention are those having Saybolt Universal viscosities in the range from about 40 to 2,000 seconds at 100 F.

In order to more fully illustrate the nature of the invention and the manner of practicing the same, the following examples are presented. These examples include the best mode contemplated by us of carrying out our invention.

EXAMPLE I 10.9 pounds of distilled water and 1.56 pounds of lithium hydroxide monohydrate were charged into a grease kettle to which was added 9.8 pounds of 12-hydroxystearic acid after the temperature of the mixture of water and lithium hydroxide monohydrate was raised to 160 F. The mixture was then heated and stirred at 160- 180 F. for 1 hour. It was maintained at this temperature while 20.0 pounds of di-2-ethylhexyl azelate were added through a swing line into the top of the kettle at a rate of 0.35 pound per minute. The first few pounds of oil were added in shots. The grease mixture was then heated to a top temperature of about 390 F. while there was added at the rate of 0.35 pound per minute 41.08 pounds of di-2-ethylhexyl azelate. When the temperature reached 390 F. all of the di-2-ethylhexy1 azelate had been added. The mixture was maintained at a temperature of 390- 400 F. for minutes. It was then cooled by circulating cold oil through the jacket surrounding the vessel. A minor stream of the grease mixture was withdrawn from the maintained agitated body at a rate of 2 gallons per minute and recirculated via a grease pump and shear value operating with a pressure drop across the valve of 60 p.s.i.g. When the temperature of the grease mixture reached 325 F. there was added at a rate of 0.35 pound per minute 20.36 pounds of di-2-isooctyl adipate via the swing line and cooling of the mixture continued. There was subsequently added 1.0 pound of N-phenyl-alphanaphthylamine, 2.0 pounds pale lead naphthenate and 6.0 pounds of tricresyl phosphate.

EXAMPLE II Into a grease vessel was charged 10.9 pounds distilled water and 1.5 pounds lithium hydroxide monohydrate.

The mixture was then stirred to break up any lumps present and was heated to F. at which temperature 9.8 pounds of l2-hydroxystearate acid were added. The mixture was held at 160'180 F. for 1 hour with the kettle cover over the vessel. While the mixture was held at this temperature 20 pounds of di-Z-ethylhexyl azelate were added via a swing line into the top of the kettle at a rate of about 0.35 pound per minute with the addition of the oil at first being in shots until soap formation began. The mixture was then heated to 390 F. as quickly as possible while 43.7 pounds of di-Z-ethylhcxyl azelate were added to the mixture. When the temperature reached about 390 F. all of the di-2-ethylhexyl azelate had been added. The mixture was maintained at a temperature of 390-395 F. for 15 minutes. It was then cooled by passing cold oils through the jacket surrounding the vessel and a minor stream of the mixture was withdrawn and recirculated at a recirculation rate of 2 gallons per minute via a grease pump and a shear valve operating with a pressure drop across the valve of about 60 p.s.i.g. When the temperature was decreased to 325 F. there was added to the mixture 21.25 pounds of di-isooctyl adipate at a rate of 0.35 pound per minute through the swing line. The grease mixture continued to cool until it reached a temperature of about 300 F. When all of the di-2-ethylhexyl adipate had been added 1.0 pound of Manvel Residuum was added. When the temperature decreased to a temperature of between 180-200" F. 1 pound of phenyl alphanaphthylamine, 2 pounds of pale lead naphthenate, 1.0 pound of an extreme pressure anti-wear agent and 46 grams of 2,5-bis(octyldithio) thiadiazole copper corrosion inhibitor was added. The mixture was then stirred for 45 minutes.

EXAMPLE III 13.1 pounds of distilled water and 1.88 pounds of lithium hydroxide monohydrate were charged into a grease kettle and stirred to break up any lumps. The kettle contents were heated to 160 F. and 11.8 pounds of IZ-hydroxystearic acid were added. The kettle was covered and held at a temperature of 160-180" F. for one hour without any venting. After that the kettle sides were scraped down and 24.0 pounds of di-Z-ethylhexyl azelate were added to the mixture in the grease kettle at a rate of 0.35 pound per minute. The di-Z-ethylhexyl azelate was added via a swing line positioned over the kettle. The temperature of the mixture in the grease kettle was maintained within the range of 160180 F. while the di-Z-ethylhexyl azelate was added. After it was added, the kettle sides were again scraped and all of the synthetic oil was worked in. The kettle was then heated and 57.0 pounds additional of di-2-ethylhexyl azelate was added at a rate of 0.35 pound per minute through the same swing line. The temperature of the grease mixture was increased to 390 F. It took about 4.2 hours to reach that temperature. When the mixture in the grease kettle reached 390 F. all of the di-2- ethylhexyl azelate added during this heating operation was in the kettle. The mixture in the grease kettle was held at a temperature in the range of 390-395 F. for

about minutes. It was then cooled by circulating cold oil through the jacket surrounding the grease kettle. While cooling, a minor stream of the grease mixture was withdrawn from the maintained agitated body at a rate of 2 gallons per minute. This minor stream was recirculated via a grease pump and shear valve operating with a pressure drop across the valve of 60 p.s.i.g. When the temperature of the grease mixture reached 325 F., 27.0 pounds of additional di-Z-ethylhexyl azelate was added at a rate of 0.35 pound per minute via the swing line as the mixture continued to cool. Cooling ceased when the temperature decreased to 300. F. at which point all of the di-Z-ethylhexyl azelate had been added during the cooling operation. A 30 pound sample was withdrawn at this point for test purposes. The balance 15 consisting of about 90 pounds was treated with addition of about 0.95 pound Manvel Residuum. When the of N-phenyl-alphanaphthylamine was added followed grease composition cooled to 180-200 F. 0.95 pound by 1.9 pounds of lead naphthenate for use as a rust inhibitor-extreme pressure agent, 0.95 pound of an extreme pressure anti-wear agent containing approximately 4.7% antimony, 10.6% chlorine, 8.05% sulfur marketed under the designation Vanlube 641 by R. T. Vanderbilt, Inc. and 43 grams of 2,5-bis(octyldithio) thiadiazole, used as a copper corrosion inhibitor. The resultant mixture was stirred for 45 minutes. When the grease composition had cooled to 160-180 F., the grease was passed through a Charlotte mill having a clearance of 0.003 inch.

Test 1 Into a grease vessel was charged 13.1 pounds of distilled water and 1.88 pounds of lithium hydroxide monohydrate. The mixture was stirred to break up any clumps and to it was added 12.2 pounds of a solvent neutral oil and the mixture was heated to 120 F. at which temperature was added 11.8 pounds of 12- hydroxystearic acid. The resultant mixture was heated to a temperature between 180 and 200 F. and held at that temperature for 1 hour. While at that temperature 12.0 pounds of di-Z-ethylhexyl sebacate were added at a rate of 0.35 pound per minute through a swing line at the top of the kettle while maintaining the tempera ture at 180-200 F. The oil addition ceased and the kettle sides were scraped. The heating was resumed and 35.9 pounds of di-Z-ethylhexyl sebacate were added at a rate of 0.35 pound per minute through the swing line. The mixture was heated to 390 F. as quickly as possible and when it reached that temperature all of the di- Z-ethylhexyl sebacate had been added. It was held, at a temperature of 390-395" F. for 15 minutes. At the end of 15 minutes jacket cooling commenced together with recirculation of a minor stream of the grease mixture from the maintained agitated body at a rate of 2 gallons per minute. The grease was withdrawn and passed through a grease pump and a shear valve operating with a pressure drop across the valve of p.s.i.g. Recirculation and shearing continued until the temperature reached 325 F. at which point 47.9' pounds of an ester-type synthetic oil marketed by Drew Chemical Corporation under the designation Drew Synthetic Lubricant NA-3705 was added. The exact chemical composition of this ester is not known. The ester was added at a. rate of 0.35 pound per minute with continued cooling of the maintained grease mixture. Cooling stopped when the temperature decreased to 300 F. When all of the Drew ester had entered the system the mixture was stirred for 30 minutes. To the mixture was added 1 pound of Vanlube 641 (an extreme-pressure. anti-wear agent containing approximately 4.7% antimony, 10.6% chlorine, 8.05% sulfur marketed by R. T. Vanderbilt, Inc.), 2.0 pounds of pale lead naphthenate and 0.10 pound 2,5-bis(octyldithio) thiadiazole. Comparative results of the grease as prepared by Examples I, II and III and the grease prepared by Test 1 are set forth below.

TABLE I Example I Example II Example III Test 1 MIL-G-23827A Specifications TG Number Contains Percent Synthetic Greases Miielral 1 Composition, calculated, Wt. percent:

Lithium 12-hydroxystearate 9. 10 9. 8 10. 00 10.0 Solvent Neutral Oil 9. 5 Di-2-ethylhexyl azelate 61. 38 Di-isooctyl adipate 20. 46 Di-2-ethylhexyl se Drew Ester N A-3705 Free Alkali at LiOH 0. 06 Additives: Mauve] Baqirilmm Phenylalphanaphthylamine 1. 00 Tricresyl Phosphate 6. 00 Vanlube 6 Pale Lead Naphthenate 2. 00 2, 5-bis(octyldithio) fhinnimnlp Tests:

Penetratlons ASTM D217-48:

k d 288 285 288 285 200 min.

297 290 294 288 2703l0. 348 325 336 333 375 max. Dropping Point, F 380 356 385 372 325 min. Oil Evaporation:

22 hrs/210, percent 0. 78 l 1 0.80 0. 59 2. 0 max. 22 hrs./250, percent 1.6 1 7 1. 4 2. 0 Dinamic Water Resistance at 100 F., percent 8.5 5 6 8. 3 4 2 20. 0 max.

058. Btiflfltb Oxidation at 210 F., Pressure Drop er 100 Hours 0 0 0 1 10 max. 500 Hours 5 5 3 15 max. Rust Preventative Propertles Pass 1 Pass 1 Pass 1 Pass 1 Pass 1 or 2. Mean Hertz Loan, Kg 40. 4 41.6 37. 6 42. 5 30.0 min. High Temperature Performance, Hours at 250 F 1, 182+ *1, 508 *1,233+ 751 1,000 min. Low Temperature Torque at 100 F., gm.-cm:

Start 4, 425 5, 192 4, 307 8, 238 10,000 max. Runnim7 502 443 354 1, 032 1,000 max. Bomb Copper Corrosion, 20 Hours/210 F.: Slight color change, not Appearance 01- green or dark brown,

Grease Pass Pass Pass Pass allowed. No appreci- Strip Pass Pass Pass Pass able strain allowed. Pressure Drop, p.s.Lg 0 0 0 0 1.0 max. Navy Gear Wear, Brass on Stainless Steel, mg.

loss/1, 000 cycles:

51b.lnari 1.13 1. 22 1.60 1. 39 2. 5 max. 10 lb. load. 2. 47 2.24 3.84 4. 77 3. 5 max.

See footnotes at end of table.

TABLE IContinued Example I Example II Example III Test 1 MIL-G-23827A Specifications Dirt Count, Particles/1111.:

Above 25 microns 1 0 0 1,000 max Above 75 microns 0 0 0 1 None. Oil Separation, 30 Hours/212 F 3.8 2.1 2. 9 2.0 5.0 max *Indicates test terminated before failure.

From the foregoing it is readily seen that we have provided a significantly useful process for preparing a soap based grease composition containing synthetic lubricating oil as the sole lubricating oil component. It is most apparent that our process provides a highly useful and satisfactory grease which from Table I can be seen surpasses a grease containing mineral oil and satisfies all of the qualifications of a grease as set forth in military specification MILG23827A. It is also apparent that our process can be performed easily using readily available standard equipment and does not necessitate utilization of extremely high temperatures, pressures or other commercially undesirable process parameters. Our process uses only the simple compounds, provides a need, i.e. a grease composition containing no natural oil therein.

The terms and expressions which have been employed herein are used as terms of description and not as limitation as there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that many modifications are possible within the scope of the invention claimed.

What is claimed is:

1. A method for preparing a lithium soap thickened grease containing synthetic lubricating oil as the sole lubricating oil component which comprises saponifying a saponifiable fatty material with a lithium saponifying agent in water at a temperature of between 160 and 200 F., adding between 23.0 and 41.0 weight percent synthetic lubricating oil based on the total weight of the lubricat ing oil component in the finished grease while the saponification mixture is at a temperature of between 150 and 200 F., heating the mixture at a rate of at least 07 F. per minute to a top temperature of between 380 and 450 F. while adding additional lubricating oil in an amount between 30.0 and 56.0 weight percent based on the total weight of the synthetic lubricating oil component, maintaining the temperature of the mixture between 380 and 450 F. for between 0 and 30 minutes, cooling the mixture while adding any balance of synthetic lubricating oil and shearing the mixture.

2. A process according to claim 1 wherein the lithium saponifying agent is lithium hydroxide monohydrate and is present in the saponification mixture such that the weight ratio of water: lithium hydroxide monohydrate is between 7:1 and 15:1 the temperature of the saponification mixture is between 160 and 200 F. while the initial portion of lubricating oil is added, the weight ratio of lubricating oil: soap after the initial oil addition is in the range of 2:1 and 5:1, the saponification mixture is heated to a temperature within the range of 160-400 F., while a second portion of synthetic lubricating oil is added at a temperature of between 160 and 365 F., the weight ratio of the synthetic oil added during the second oil addition to the soap is in the range of 5:1-16z1, the mixture is brought to a top temperature in the range of 390 395 F. and maintained at this temperature for a period of between 0 and 30 minutes and the mixture is cooled at a rate of between 2.0 and 2.6 F. per minute while the balance of lubricating oil in the grease composition is added at a rate of between about 0.1 and 0.5 pound per minute per pounds of finished grease.

3. A method according to claim 2 wherein the Weight ratio of water to lithium hydroxide monohydrate is 7:1, the weight ratio of synthetic oil initially added to the soap is 2:1, the weight ratio of synthetic oil to the soap added in the second oil addition is 6.4:1, the total time for saponification and dehydration is between 0.5 and 1.5 hours and the ingredients are cooled while a portion of the grease composition is withdrawn from a maintained agitated body and recycled back to the agitated body via a shear valve operating with a pressure drop across the valve of between 0 and 100 p.s.i.g.

4. A method according to claim 3 wherein the total time for saponification and dehydration is about 1 hour and the recirculation rate of the withdrawn portion of the grease composition is between 0.5 and 3.0 gallons per minute per 100 pounds of finished grease.

5. A process according to claim 3 wherein the recirculation rate is about 2.0 gallons per minute per 100 pounds of finished grease.

6. A process according to claim 2 wherein the saponifiable fatty material is 12-hydroxystearate acid and the free fatty acid content in the finished grease is between 0.0 and 0.1% by weight and the free alkali content, calculated as lithium hydroxide, is between 0.0 and 0.1% by weight.

7. A process according to claim 2 wherein the synthetic lubricating oil is di-Z-ethylhexyl azelate.

8. A process according to claim 2 wherein the synthetic lubricating oil is a mixture of di-2-ethylhexyl adipate and di-2-ethylhexyl azelate.

References Cited UNITED STATES PATENTS 2,847,382 8/1958 Erwin et 'al. 2524l 3,117,087 1/1964 McCormick et al. 252-4l 3,242,082 3/1966 Badgett et a1. 252-41 3,242,083 3/1966 Crookshank et al. 252-41 3,242,086 3/1966 Dowden et a1 25241 DANIEL E. WYMAN, Primary Examiner.

I. VAUGHN, Assistant Examiner.

U.S. Cl. X.R. 25256