US2598154A - Process for making grease - Google Patents

Description

G. C. BAILEY ETAL PROCESS FOR MAKING GREASE May 27, 1952 2 SHEETSr-SHEET 1 Filed Aug. 21, 1947 ATTORNEYS M y 7, 1952 G. c. BAILEY ET AL PROCESS FOR MAKING GREASE 2 SHEETS-SHEET 2 Filed Aug. 21, 194'? on a 0n H at mm d 2 s Q g IL l lnu .6 mm N0 INVENTOR. 'G .c BAI LEY ATTORNEYS Patented May 27, 1952 raoosss FOR MAKINGQGREASE" Grant 0.;Bailey, Royal Oak, Mica, andWilliani B; Whitney;Bartlesvilla; Okla, assignors to ,v Phillips Petroleum Company, a corporationof;

Delaware I Application August 21, 1947, Serial N0.--769,858

9 Claims.

This invention relates, to an improved lubricant. In one of itsmore specific aspects it relates to a lubricating grease, and to methods of preparing such a grease, havinga greaterconsistency and a higher resistance to bleeding when prepared by rapid cooling and severe workingthanby methods common inthe art.

Grease making, according to the prior art, usuallyconsists of heating, in a large kettle, a mixture of saponifiable oiland an aqueous solutionof .a metalhydroxide in the presence of a mineral oil. During this heating, which requires fromB to. 24 hours, a soapis formed most of the water is boiled'ofi, and the soap becomes dispersed in the mineraloil to form grease which is usually diluted and gradually cooled bylthe slow incorporation of more oil. During the heating and blending process, the kettlecontent must be continually stirred to maintain intimate contact of the saponifiable oil and the aqueous alkali to prevent scorching and secure a uniform product. During a considerable portion of this time the mixture is a stiff pasteelike mass-the stirring of which consumes much power and requires the attention of a skilled grease maker. This method requires large floor spaceand expensive specialized equipment. The operation also lacks flexibility as small batches cannot conveniently nor cheaply be turned outin large kettles nor production changed fromon type of grease to another in a short period of time. Use. of large kettle equipment usuallymeans thata large, inventory of finished products is carried on hand.

There have been numerous continuous processes for making grease described in the patent literature, but most Of the workers have beeninterested in using the continuous process for saponifying the fatty oil and therefore use a temperature of about 200? F. to about 300 F. for a period of from 8 to 24 hours. Although the literature pertaining to greases contains many references relating to their preparation and which references-usually contain directions for cooling and milling -(working) th directions which have been recorded refer to greaseswhich on cooling, or oncoming-and slig-ht-working, give a homogeneous grease-like structure; The statements concerning cooling are often contradictory andunsaponified fat, unsaponifiable portions of fat,-

free fatty acid, high molecular weight alcohol, wool fat, pitch, high molecular weight amides, glycols, and the like. Theart is very careful to teach that certain combinations of soapand oils alone are very difficult if not impossible to secure and to maintainin stable combination, and that stabilizing substances must be present to prevent syneresis, which in extreme cases forms an oilsoaked granular mass of soap; in liquidoil, The,

fact that this breakdown of the structure occurs for many combinations of soap when heated in oil and cooled. rapidly, under thev heating and cooling conditions disclosed in 1 our procedure hereafter described, has been repeatedly demonstrated by us. Previous reports of I improvements in grease properties by rapid coolinghavebeeninexact as to what has been meant by rapid cooling. This has usually been stated as pouring out in pans to cool. The. depth is usually stated as about 4 inches and the cooling, medium is air at room temperature, although one reference specifies layers having a depth between and inch at room temperature. Chill rolls and scrapers have been reported but the coolingisnot uniform nor rapid for the material considered as a whole.

One object of our invention-is to providea rapid and economic process forv producing greases of improved qualities.

Another object of our, invention isv to provide a method for. producing. an improved grease utilizing any one. of several metallsoap bases or combinationsof such bases;

Still another object ofour invention is to,pro-;

vide a process for producing greasesof improved,

qualities by the method of extremely rapid cooling and severe working.

Afurther objectiof our. invention is to provide an improved method for producing a grease,,- with or without an additive ,designed to impart strength to thegel. structure, whichhas increased consistency and resistanceto bleeding,

Other objects and advantages of our invention will be apparent from the accompanying description and discussion.-

Rapid cooling of a soap-oil mixture tends toen-v courage the formation of. granular masses in liquid oil and especially sowhen, suchoil issubstantially saturated with the soap at the elevated temperature. Aslthe initialstage in producing a superior grease, we have found that it is-lde-h sirable to encourage by rapid cooling the formation of a mass consisting of a hard; gelwhich breaks into lumps or crumbleswith or without the exudation of vmuch free; oil. grease-likemass is then severely milled (worked) to-bringit to a grease-like texturer The severe milling; process-.produces -a result which is.,.-un-

expected and contrary to that of the known art. Instead of producing a grease which continues to soften on extended working, it produces a grease which, during a process of severe working, usually increases in consistency and always tends to reach a degree of consistency that remains substantially constant. These greases thus produced have only a slight tendency to bleed. The reasons for these phenomena are unknown but appear to be in the inter-relation of the metal and the fatty acid used to form the soap and in the degree of mutual solubility of the oil and soap. By rapid cooling we mean that the mixture of soap and oil should be cooled to the desired temperature within a period of from about 1 to about 600 seconds, preferably between about 10 and about 300 seconds.

An important application of the above described process is the production of a grease from a mixture comprising a stiffening agent, such as a metal soap, and oil of such a nature that the soap does not dissolve when heated in an open vessel, even when heated to a temperature just below the thermal decomposition point of the ingredients, but stratifies into a lower layer of soap with a minor proportion of oil and an upper layer of oil containing a minor proportion of soap which separate phases cannot be homogenized by mild agitation. On cooling, a dense gel results from the lower layer and a soft gel from r the upper layer. On milling the two portions together, a grease of excellent quality as to the low loss of consistency is produced, on extended working, which has only a slight tendency to bleed.

In heating the soap-oil mixture it is only necessary to heat it to a point at which the soap begins to ball up in the oil during the stirring. That balling will usually begin to occur in the vicinity of about 365 F. It is not however preferred to cool from that point because the mixture which is formed is relatively difiicult to work. In the preferred method of our process We continue to heat, with stirring while adding soap to the soapoil mixture, beyond the point at which balling of the soap takes place and until the entire mixture is substantially liquefied and preferably till the oil and soap are miscible. In this manner the oil may be substantially saturated at some temperature between 365 F. and the decomposition temperature. Cooling of the mixture may be started at or above the saturation temperature. Heating is carried out quite rapidly so as not to injure the ingredients of the mixture. The critical temperature, on heating, is that temperature at which thermal decomposition may occur. Precaution should be taken to avoid burning or scorching of the mixture. Our process may be utilized in either open or closed vessels.

We have found that in many cases two greases of identical composition which have been heated similarly, but one of which has been subjected to the customary method of slow cooling and the other to the method of rapid cooling used in our invention, show markedly different characteristics. The one cooled slowly will be softer, more homogeneous and will not have as great a resistance to change of consistency on extended working nor as great a resistance to bleeding.

We have further found that this invention is not limited to the improvement of greases of compositions now known such as a hydrocarbon oil with sodium stearate, lithium laurate, aluminum laurate, aluminum tristearate, aluminum distearate, or aluminum monostearate, but by its application greases may be prepared which have hitherto not been possible. For example, all attempts to obtain a smooth grease by rapid cooling of solutions of anhydrous barium stearate in high viscosity index mineral oil have failed to make a smooth stable grease whereas by the method of rapid cooling of the heated mass to form a gel which synerizes, a good smooth grease was obtained by subsequent severe working. Similar results were obtained with calcium oleate, magnesium stearate and calcium stearate. Good results may be obtained with combinations of these soap bases and oils but we have found that greases made from combinations of soap bases do not ordinarily give a product which is as resistant to penetration as monosoap base greases.

It has been found advantageous to substantially match the metal and the fatty acid radical so as to make the best soap and grease. Sodium soaps have been found to produce the best grease when sodium hydroxide is combined with a fatty acid radical falling within the Cid-C20 range and preferably with a C18 acid radical. The best lithium greases are made when a fatty acid radical in the Clo-C14 range and preferably a C12 acid radical is used.

The stiffening agent used in this invention is generally a soap. Such a soap is a salt of a fatty acid. The fatty acid used in making the soap should be relatively pure. Another important factor in producing such greases is that the stiffening agent should generally be substantially neutral so that it contains substantially no free fatty acid. A grease produced from such a neutral stiffening agent or soap produced from a relatively pure fatty acid will, when combined with an oil as herein described, form a gel which in turn will form a grease having excellent characteristics when it has been worked to substantially constant consistency. By the term relatively pure fatty acid radical we mean one of substantially the same carbon content per molecule, e. g. C18. If a mixture of fatty acids is used they should be so close together in structure as to be nearly the same. Thus in making a sodium soap it is desirable to use a fatty acid radical having 18 carbon atoms per molecule. This gives a much better grease than one prepared from a soap in which the fatty acid was a mixture of C14 to C22 fatty acids which had an average molecular weight equivalent to 18 carbon atoms per molecule. Fatty acid radicals differing by as much as two carbon atoms, for example C18 and C16, or C18 and C20, may be used together and produce very satisfactory soaps, for they fall within the exception pointed out above in that they are bordering or adjoining structures and will not alter the soap structure materially.

The temperature below which the grease must be cooled is that at which solidifying from a liquid to a gel, which is definite and possibly related to the crystalline or colliodal structure of the soap, occurs. We do not, however, limit the rapid cooling to any specified temperature. The limit constitutes only those conditions which will produce a hard gel from a. solution substantially saturated under the conditions above described. This gel usually breaks or crumbles to an oil soaked mass on crushing and may be worked to a consistent grease by severe milling or working. The temperature at which gelling of most greases will generally begin to take place usually falls between about 330 F. and about 400 F. depending upon the type grease. The time of cooling,

as has been pointed out above, is short, usually within a period of between and 300 seconds, and the milling is equivalent to several thousand strokes of an ASTM grease worker (Precision Scientific Motorm'atic model) as described in ASTM Test D-217-44T. By working severely we mean that the gel is worked an equivalent of from about 2,000 to about 100,000 strokes of an ASTM grease worker. The exact number of strokes to be used is that number which will give the greatest consistency to the finished grease.

In a preferred process of our invention, the soap is added to lubricating oil and heated rapidly with stirring. The soap passes through the stages of being merely suspended, then becoming sticky and agglomerated, then changing to a stringy, viscous mass and finally turning to a :substantially homogeneous non-viscous liquid 01 dispersion. When this stage has been reached, usually between 390 F. and about 485 F., the mixture is cooled rapidly to form. a hard gel which cracks, breaks, or crumbles and requires severe milling or working for a short time to produce a smooth grease. During this milling process many greases tend to reach a constant penetra-bility, which penetrability is substantially maintained for several hundred thousand strokes of the ASTM worker. Though we prefer that the gel formed be sufliciently hard that it may be cracked, broken or crumbled, gels which are to some degree softer may be severely worked with beneficial effect.

In one modification of our process, we use a soap-oil-diluent mixture, rapidly heat to a temperature between about 355 F. and about 540 F. and cool rapidly to about 285 F. As diagrammatically shown in Figure I of the drawing, diluent, soap and oil are delivered to mixing chamber I through lines 2, 3 and 4 respectively. The materials are mixed and kept in suspension to form a substantially uniform suspension in the mixing chamber. The soap is any substantially pure fatty acid salt which is suitable for grease making. The oil is any lubricating oil suitable for grease making and which is substantially matched with said soap. The diluent is a low or medium boiling liquid which may or may not be miscible with the oil. Suitable diluents would be butane or other low or medium boiling hydrocarbon or hydrocarbon derivatives such as chlorinated hydrocarbons, ethers, esters, ketones, alcohols, alkyl halides, aldehydes, or amines. The ratio of diluent to soap-oil combination should be such that on suddenly reduced pressure and evaporation of the diluent, the latent heat of vaporization absorbed by the diluent shall pro duce the desired cooling eiiect described below. Mixing chamber I must be of sufficient strength to withstand the vapor pressure of the diluent at operating temperature. By metering pump 1, the mixture is forced into the heating section 8 where the mixture is rapidly heated, during agitation, to a temperature between approximately 355 F. and 540 F. The mixture changes on heating from a suspension of soap in the oildiluent mixture to substantially a liquid dispersion of soap in the oil-diluent mixture. This liquid is forced through an expansion valve 9 into expansion chamber 10 which is maintained at a pressure low enough to insure that substantiallyall the diluent is flash evaporated, with the result that'the soap-oil residue is cooled below the gelling temperature of the soap. A satisfactory temperature to which sodium stearate may be cooled is to about 285 F. or below. Theexpansion chamber may be maintained at a'pressure above, below; or at atmospheric pressure, depending on the boiling point of the diluent used. Baflie plate l3 prevents grease from entering the exhaust with the vaporized diluent. The vapors are led through cooler M where they maybe cooled and collected in condensation chamber [5. The diluent is recycled through line IE to line 2. The residue of soap and oil is passed through grease worker I], where it is worked severely, into storage l8, from which it is re moved by screw conveyer 2|, through filter 22 and delivered toa container filling machine (not shown) through line 23.

Another modified embodiment of our invention is diagrammatically illustrated in Figure II ,of the drawing. Lubricating oil is passed through line Bl into heater 62 and thence into hot oil surge tank 63. Lubricating oil is also passed from line 6| through line 64 into soap mixing. tank 65 where it is mixed with soap which is supplied through line 68. The cold soap-in-oil slurry from soap mixing tank 65 is discharged through line 69 into mixing tank 10 simultaneously with the discharge of the hot oil from surge tank 63 through line 13. The hot oil is in such proportions relative to the soap-in-oil slurry that there is only a slight drop in temperature. The soap is readily dispersed in the hot oil to form a liquid mixture. The resulting soap-in-oil dispersion is discharged continuously into cooling tank 14, which continuously receives cool oil from cooler 15. The cooling tank contents are agitated to mix quickly the hot'soap dispersion with the cool oil in the tank. The low temperature of cooling tank 14 is maintained by the inflow of cool oil from cooler 15. The soap, on cooling below its gelling temperature, separates as lumps of soap gel. The gel-oil mixture is discharged to a separator 18 consisting of a centrifuge or a screen sieve and the gel is separated from the oil. The free oil is recycled through cooler 15 to cooling tank 14 while any excess oil in the recycle system is returned to line 6|. The gel lumps are charged to grease mill (9 where they are mixed with the desired amount of oil from compounding oil storage 80. It is obvious that a modification may be made in this system whereby a desired amount of oil may be retained with the gel passing from separator 18 rather than adding it from storage and oil from another source passed through cooler 15 to cooling tank 14. The finished grease is discharged from grease mill 19 through line 8| to storage or packaging machine. The hardness of the finished grease can be increased by removing greater amounts of oil from the gel before milling while a softer grease may be prepared by adding greater amounts of oil before milling.

Three difierent oils were used in the production of the greases of our Examples I and II. The three oils are denoted as A, B, and C. having the following properties.

aawiaa (mixture comprising-80 weightper jcent mineral ,oiLA' and .20 weight .per centsodium stearate were "heated tobetween .about1'392" F. and about 485 TF. One portion or "the mixture was 'then allowed to cool slowlyto room temperature'within a'i eriodfof aboutifitoiliohours. .Thesecon'd portion was cooledby. fpouring'it'into a pan in which we layer was "about 5 inch thick, and the pan wa'sfthen set'in cold water. This portion cgell'ed lin about '2' minutes. 1A portion of the: slowly cooled .portion was severlyworked .or milled in ajgrease worker. as :wasthe rapidly cooled grease. These greases were then-tested with a penetrometer as described in ASTMTest 'D-21'7-44Tfbut modified so as to usea micropenetrator needle, fplung'er; "and cup, as describedbytKaufmangFinn and Harrington in industrial and Engineering iChem'istry, -.analytica1 edition 115108-1110 (1939). Bleeding-tests'were' made as describedwith Armystrokes. The :unworked penetration of the =ra idly cooled grease was "not of significan'ce as'the productwas-a:non-homogeneous mixture-of soap and :oil. Thus, 'thro'ugh the "working *ran'ge' of 10,000 to 100,000 strokes, the rapidly 'cooled grease "had :ma'intaineda *more satisfactory consistency :than the'.slowlyrccoled grease.

Example .IH

such tests are "recorded -in Table'IV.

Table IV Soap - Penotmtion a[ter'90,000 Additional 1 Strokes Soap Content WVeight per eanti M illing Strokes :Penetro- Coolixi a lion Rate j (A) a (C) Y'Nae'stearate .w =Li-laurate Nastearatan Li-laurate (A) plus (B) :Rcpid 10,000 .do... 10,000 Q v10,000

.50% each in the mixture.

Example -I-V Sodium stearatewas added to lubricating oil 'A to make '20 weight per cent soapin'the'o'il. This wasdiluted with octane-in the ratio-ofone part soap-oil mixture to six parts of octane. The

Table II materials weremixedand passedmnder pressure. 40 through a heated section where the temperature mailman Bleeding was raised to about-410 F. The liquid was disoomm -ram "Weight charged through an evacuated container andthe Strokes W vaporized octane removed. The residue was a mixture oflsoap'lumps and oil which on milling slow"; none 42 313 13.3 DI dUC'Bd -21. grease of excellent quality. The no 3g 3 2 'hardness o'f the finished grease can be increased r p by removing apart-of the-oil before milling or 4 Z H the hardness-decreased by the-incorporati'onof Em-amp more oil. Severalother greaseswere prepared-using difo0 A EzmmpleV ferentsoap bases in con unction with different oils; Penetration'testswere madeas in'Example Sodium stearate zw'as mixed with'oil *A and L-The efiect-of producing a grease by "our heatedtoiabout 465F. The soap wasdispersed method is' clearly indicated by data cont'ainedin in the oil to:-form.ailiquicl mixture. This mixture thex'ffilrgwing t 51 I was pouredintooil A which was :at about 250 Table HI Soap Penetration Content O Cooling Milling 'Penetraaiter 00,000 soap Weight iRate Strokes hon Additional per cent Strokes .kletrlrsteorate .20 A Slow none 202 Do 20 x ".00." 10,000 :151 202 1. 0" A LRapid 10 ,000 89 150 20 -]3 do. v10,000 133 100 20 0 do... 10,000 '102 100 The-data in Table III show that an aluminum F. 'Thesoap solidified 'to'atransparen't gel and stearate grease, which had been prepared'by 7n floated in the-oil, in lumps. 'The "temperature methods employing slow cooling, had penetrations of 50, 151; and 202 in unworked, after being worked 10,000 strokes, and after being worked 10 0;000 s'trokes, respectively. A grease similar in all resjpectsexcept2rapidly-cooled had a penetraafter mixing thetwo oilstogether'was about 285 F. The "excessoil'was drained oiiand the soap and a por'tionof theoil was-worked severely to a grease which had a low loss jofcon'sistency-on extended working *and only a slight tendency to tiorrofimly 18$! at -1 Gallic-strokes and -159at '100;000- bleed.

It may be desired to include some additives to give a finished grease certain otherwise unobtainable desirable characteristics. These additives may be added at any time during the process, but we prefer to add them after the mixture has gelled and while the gel is being worked. In that manner the structure of the gel is not affected in its formation.

In the past when hard soap cakes or lumps have appeared in the soap-oil mixture after heating and during the cooling step it has been the practice to throw such mixtures away as it was believed they were not suitable for th making of finished greases.

By the method of our invention we utilize such mixtures as those which were previously believed worthless, and gain from them a hard, even-textured, superior grease.

For those skilled in the art it will be obvious that many alterations may be made in the process of manufacture without change in the principle and the scope of our invention.

We claim:

1. A process for manufacturing a grease from an oil and a metallic soap which comprises the steps of forming a mixture comprising a metallic soap with a hydrocarbon lubricating oil, heating said mixture with agitation to substantially disperse the soap in the oil, chilling suddenly to form a hard friable gel in some free oil, separating said gel from a portion of said free oil, and working said gel and remaining free oil to a state of substantially constant consistency.

2. A process for manufacturing a grease from an oil and a metallic soap which comprises the steps of forming a mixture comprising said metallic soap, containing substantially no free acid. with a hydrocarbon lubricating oil, heating to a temperature between about 365 F. and the decomposition temperature of said mixture while agitating said mixture during said heating, chilling said mixture to form a hard fracturable gel in some free oil within from about seconds to about 300- seconds, separating said gel from a portion of said free oil, and working said gel and remaining free oil to a smooth grease texture.

3. The process of claim 2 wherein said lubricating oil is substantially saturated with said metallic soap at a temperature within the hea ing range specified. 1-

4. A process for manufacturing a grease from an oil and a metallic soap which comprises the steps of forming a mixture comprising said metallic soap containing substantially no free acid, a hydrocarbon lubricating oil and a low boiling diluent, heating said mixture to a temperature between about 355 F. and about 540 F. while agitating said mixture during said heating, flash evaporating said diluent to form a hard fracturable gel residue in some free oil within from about 10- seconds to about 300 seconds, separating said gel from said free oil, and working said gel to a smooth grease texture.

5. The process of claim 4, wherein said gel is separated from only a portion of said oil.

6. A process for manufacturing a grease from an oil and a metallic soap which comprises the steps of forming a mixture comprising said metallic soap, containing substantially no free acid, and a hydrocarbon lubricating oil, heating said mixture to a. temperature between about 365 F. and the decomposition temperature of said 10 mixture by means of adding heated oil thereto while agitating, chilling said mixture to form a hard fracturable gel in some free oil within from about 10 seconds to about 300 seconds, separating said gel from said free oil, and working said gel to a state of substantially constant consistency.

7. A process for manufacturing a grease from an oil and a metallic soap which comprises the steps of forming a mixture comprising said metallic soap, containing substantially no free acid, and a hydrocarbon lubricating oil, heating said mixture to a temperature between about 365 F. and the decomposition temperature of said mixture by means of adding heated oil thereto while agitating, chilling said mixture to form a hard friable gel in some free oil within from about 10 seconds to about 300 seconds by means of suddenly mixing said mixture with a cold oil, separating said gel from a portion of said free oil. and working said gel and oil to a smooth grease texture.

8. A process for manufacturing an improved grease from an oil and a stifiening agent which stifiening agent is formed by the combination of lithium hydroxide and a fatty acid in the 010-014 range and in which stiifening agent free acid has been substantially neutralized, which process comprises the steps of forming a mixture of a hydrocarbon lubricating oil and said stiifening agent, mixing said mixture while heating to a temperature between 365 F. and the decomposition temperature of the ingredients so as to disperse the stiffening agent in the oil, chilling said mixture to form a hard friable gel in some free oil within from 1 second to about 600 seconds, and working said gel to a state of substantially constant consistency.

9. A process for manufacturing an improved grease from an oil and a stifiening agent which stiffening agent is formed by the combination of lithium hydroxide and a fatty acid in the Clo-C14 range and in which stiffening agent free acid has been substantially neutralized, which process comprises the steps of forming a mixture of a hydrocarbon lubricating oil and said stifiening agent, mixing said mixture while heating to a temperature between 365 F. and the decomposition temperature of the ingredients so as to disperse the stiffening agent in the oil, chilling said mixture to form a hard fracturable gel in some free oil within from 10 seconds to about 300 seconds, and working said gel to a smooth grease texture.

GRANT C. BAILEY. WILLIAM B. WHITNEY.

REFERENCES CITED The following references are of record in the file of this patent:

tinuous Production of Grease, article in Industrial and Eng. Chem., vol. 30, pp. 506 and 507, Apr. 1947.

Claims (1)

1. A PROCESS FOR MANUFACTURING A GREASE FROM AN OIL AND A METALLIC SOAP WHICH COMPRISES THE STEPS OF FORMING A MIXTURE COMPRISING A METALLIC SOAP WITH A HYDROCARBON LUBRICATING OIL, HEATING SAID MIXTURE WITH AGITATION TO SUBSTANTIALLY DISPERSE THE SOAP IN THE OIL, CHILLING SUDDENLY TO FORM A HARD FRIABLE GEL IN SOME FREE OIL, SEPARATING SAID GEL FROM A PORTION OF SAID FREE OIL, AND WORKING SAID GEL AND REMAINING FREE OIL TO A STATE OF SUBSTANTIALLY CONSTANT CONSISTENCY.

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