US2876198A - Method of grease manufacture with combined oil quench and recycle cooling - Google Patents

Description

March 3, 1959 R p. GIVENS ET AL METHOD OF GREASE MANUFACTURE WITH COMBINED I OIL QUENCH AND RECYCLE COOLING Filed March 15. 1955 HIV/(w 7 [:Hfi 4n,

2 M n n /6 i "Z7 Ks rrLE Y 3.3 H54 7 fiCfi/A/VQEK 34 70 PACKAQE ('0 aL/N' 35 36 W4 7'EE /Z PUMPS United States Patent METHOD OF GREASE MANUFACTURE WITH COMBINED OIL QUENCH AND RECYCLE COOLING Richard 'C. Givens and Herbert J. Pitman, Port Arthur, Tex., assignors to The Texas Company, New York, N. Y., a corporation of Delaware Application March 15, 1955, Serial No. 494,441

11 Claims. (Cl. 252-41) This invention relates to improvements in the manufacture of lubricating greases. More particularly, it relates to an improved process for the manufacture of greases containing lithium soaps of hydroxy fatty acids.

It is well recognized in the grease making art that the method of cooling employed is frequently a very important factor bearing upon both the quality and yield of the grease produced. This is particularly true in the case of short fiber greases, such as lithium soap greases, which are conventionally prepared by the inconvenient method of pan cooling in very thin layers in order to obtain products of satisfactory smoothness. When greases of this type are cooled by the usual methods, such as by cooling down in the kettle with stirring, grainy and unsatisfactory products are obtained and in very poor yields. Methods which have been proposed involving rapidly cooling with agitation, as by quenching or by single pass of the grease mixture through a heat exchanger, have been generally unsatisfactory either from the standpoint of quality or yield, and involve the difiiculty of obtaining extremely rapid mixing or heat transfer in a large bulk of grease.

An improved method of grease manufacture, comprising recycle cooling, is described in copending application Serial No. 365,076, filed June 30, 1953, now U. S. Patent No. 2,830,022, of Roy F. Nelson, Richard C. Givens and Herbert J. Pitman. According to this method, the grease mixture is cooled while it is passing through the transition stage from a temperature above the melting point of the soap until a grease consistency is obtained by continuously cooling a minor stream of the grease at a relatively rapid rate and returning it to the main agitated body of the grease which is thereby cooled at a relatively slow rate. This cooling method has a very pronounced effect upon the gelation process, as shown by the fact that the results obtained are strikingly different from those obtained by merely cooling the grease down in the kettle with stirring or other agitation at the same or even much higher cooling rates without recycle cooling. Nelson et al. have found that lithium 12-hydroxystearate greases may be produced in this manner having excellent texture and stability, being fully equivalent in this respect to the pan cooled products, and in much higher yields than are obtainable by methods involving shock cooling the body of grease mixture either statically or with agitation.

We have now found that a further improvement in grease manufacture is unexpectedly obtained by employing quenching of the hot grease mixture in conjunction with recycle cooling. By this means, higher yields and other advantages have been obtained than are obtainable by the recycle cooling method employed separately, while the other advantages of the latter method, such as convenience and flexibility and superior quality of the product, are fully retained. This result is entirely unpredictable, and does not depend merely upon obtaining higher cooling rates'by the combined cooling methods, since the yield advantages are obtained at cooling rates no ice higher, or even lower, than those employed with the re cycle cooling method alone.

In accordance with our invention, a concentrate of a soap in a suitable oleaginous liquid in a molten homogeneous state at a temperature above the melting point of the soap is cooled down until a grease consistency is obtained by quenching with additional oleaginous liquid and by continuously withdrawing a minor stream from a maintained agitated body of the grease mixture and recycling it through a cooler. The quenching is carried out while the grease mixture is at a temperature above the melting point of the soap, preferably while the grease mixture is cooled from a temperature above the melting point of the soap down to a temperature not substantially higher than the melting point of the soap, such as a temperature within about 5 F. of the melting point of the soap, and most suitably to a temperature below the melting point of the soap. The recycle cooling is carried out from a temperature above the melting point of the soap until a grease consistency is obtained, i. e., until at least substantial gelling has occurred. According to the preferred procedure, the quenching and the recycle cooling are begun substantially simultaneously at a temperature above the melting point of the soap, the quenching being carried out until the temperature of the grease mixture has been reduced at least to about the melting point of the soap, and the recycling being carried.

out until the temperature hasbeen reduced substantially below the melting point of the soap, suitably to a temperature at least about 20 F. below the melting point of the soap. In the production of a lithium 12-hydroxystearate grease, the quenching is carried out while the grease mixture is in a molten homogeneous condition at a temperature above about 385 F., preferably until the mixture is at a temperature below 385 F.,-and the recycle cooling is initiated while the grease mixture is in a molten homogeneous condition at a temperature of at least about 385 F. and is continued until at least substantial gelling has occurred, preferably until the mixture has been cooled at least at about 365 F.

The term melting point of the soap as employed herein refers to the melting point of the soap in the concentrate rather than in the dry state, and this may vary somewhat for different concentrates of the same soap, due to the effect of the lubricating oil environment. The term molten homogeneous mass with reference to the grease mixture is employed in the ordinary sense of no phase separation which is visible to the naked eye.

Fig. 1 is a diagrammatic illustration of one form of apparatus suitable for making grease according to the method of this invention.

Referring in detail to Fig. 1, numeral 1 represents a jacketed grease kettle equipped with stirrer 2 and adapted to be heated at elevated temperatures above about 400 F. A grease mixture, comprising a slurry of a soap and an oleaginous liquid, obtained either by introducing a preformed soap and an oleaginous liquid into the kettle or by saponification in situ, is heated in the kettle at an elevated temperature above the melting point of the soap for a sufficient time to obtain a com pletely homogeneous mixture of soap and oil. When the slurry is obtained by saponification in situ, a soapforming fatty material is charged into the kettle together with a portion of the oleaginous material included in the grease and a solution of a suitable basic material introduced from tank 3 by way of line 4. The contents of the kettle are then heated with stirring until saponification is complete and for a further period at a somewhat higher temperature to accomplish dehydration. The mixture is then heated at a still higher temperature if necessary in order to obtain a moltenhomogeneous mixture.

'Hwhot grease mixture, obtained as described above, is" quenched by introducing quench oil from tank 5 by line-6 containing metering pump 7, while the grease mixture is in a molten homogeneous condition at a temperature-above themeltingpoint ofthe soap; Thequench oil is at a temperature substantially lower than. that of thegrease-mixtureg preferably at least about 200 F. lower than the temperature of the mixture. The amount ofquench oil employed is preferably such that it comprises a-minor portionof the oleaginous liquid contained in the finished grease, such'as about 5-25 by weight the total oil'contained in the grease, although it may be desirableto-employ higher amounts in some cases. The grease mixture is stirred or otherwse agitated strongly during the'introduction of the quench oil.

*Additional cooling of the grease mixture is obtained by recycling through heat exchanger 10, which may be any suitable-heat exchanger which affords the necessary amount of cooling, such as a conventional shell andtube exchanger. The grease mixture passes to heat exchanger 10 through" lines 12 and 14, containing valves 11 and 1 3, pump and line 16, and is returnedto kettle 1 byway of line 18. Circulation through heat exchanger 10 is begunwhile the grease is at a temperature above its gelation temperature; i. e., while it is still completely in a molten or homogeneous state, and is continued until a" grease consistency is obtained. In some cases the circulation is advantageously continued for a considerably longer period, and if desired it may be continued until the grease is at a sufficiently low temperature for milling, orfor packaging directly where milling is not employed. Stirring of the kettle contentsis preferably employed during-the recycling in order to maintain a'strongagitation of the grease mixture. Additional cooling may be obtained if desired by passing Water or other cooling liquid through the kettle jacket. However, such additional cooling is ordinarily not required, and where cold water or other liquid iscirculated through the kettle jacket, this is preferably not started until the grease structure has been established, in order to avoid graininess and loss in yield. Heating may also be applied to the kettle if desired in order to suitably control the rate of cooling of the grease;

Any additives employed in the grease, such as oxidation' inhibitors, corrosion inhibitors, etc., may be added suitably during the cooling down process, when the temperature of the grease is in the range between the melting point of the additive and its decomposition or volatilizationtemperature.

when the greaseis to be finished by milling, it is cooled in kettle 1, preferably to about 200 F. or lower, and then passed to mill 22, through lines 12 and 24, containing valves 11 and 23, pump 25 and line 27. From mill 22; the grease; may pass byway of line 31 to kettle 30 for further cooling and for mixing with additional lubricating oil if desired in order to adjust the penetration and soap. content. From kettle 30 the grease passes to packaging by way of line 34, valve 33, pump 351ar1d line36.

The method of this invention maybe employed advant'ag'eously-in grease manufacture generally, such as for example inthe manufacture of greases thickened with soapsof-sodiirm, potassium, lithium, calcium, barium, strontium, aluminum or lead, or mixtures of such soaps. Iris-especially valuable in the manufacture of short fiber greases, such as lithium base greases, where close controlfof the gelation process is critical for obtaining optimum quality and yields. The production of greases thickened with lithium soaps of hydroxy fatty acids is regarded as a particularly important application of the invention because of the increasing commercial importance: of suchgreases and: the large amount of difficulty which-.thas been experienced in their. manufacture.

Suitably soap-forming; hydroxy fatty acid materials whichzmay be employed inithe production of the lithium hydroxy fatty acid greases are essentially saturated hydroxy fattyacids containing'twelve'or more carbon atoms and one or more hydroxyl radicals separated from the carboxyl group by at least one carbon atom, the glycerides of such acids, and the lower alkyl esters of such acids. Preferably the acid contains about sixteen to about twentytwo carbon atoms. Such materials may 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 catalytic oxidation of hydrocarbon oils. and waxes which have been extracted and fractionated to the desired molecular range. Particularly suitable materials of. this character are hydrogenated castor oil, l2-hydroxystearic acid and the methyl ester of 12-hydroxystearic acid.

The oleaginous liquids employed in the greases produced by the method of this invention may be any suitable oils of lubricating characteristics, including the conventional mineral lubricating oils, the synthetic lubricating oils prepared by cracking and polymerizing products of the Fischer-Tropsch process and the like, as Well asother synthetic oleaginous compounds suchas polyesters, polyethers, etc., within the lubricating oil viscosity range. Such synthetic oleaginous compounds, including mixtures thereof, may be substituted in whole or in part'forthe conventional mineral lubricating oils. Examples of thesecompounds are the aliphatic dicarboxylic acid di-esters, such as di-Z-ethyl hexyl sebacate, di(secondary amyl) sebacate, di-Z-ethyl hexyl azelate, di-isooctyl adipate, etc. Suitable mineral oils are those having viscosities inv the range from about to 2,000 seconds Saybolt Universal at 100 F., and may be either naphthenic or paraflinic in type, or blends of the two. 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 the saponification conditions is preferably employed for this purpose, most suitably a mineral oil fraction.

The greases may also contain various additives of the usual type such as corrosion inhibitors, oxidation inhibitors, antiwear agents, and so forth. Preferably, they contain an oxidation inhibitor, which may suitably be an oxidation inhibitor of the amine type, such as diphenylamine, phenyl alpha naphthylamine or tetramethyl diamino diphenyl methane. Compounds of this type may be added either before or during the cooling down process. They are preferably added while the temperature of the grease is between about 300 F. and about 180 F.

The preparation of lithium 12-hydroxystearate greases is carried out in the following manner. A mixture of lithium 12-hydroxystearate and a suitable oleaginous liquid, obtained either by mixing together preformed soap and oil or by saponification in situ, is heated to a temperature above about 385 R, such as from about 390 F. to about 420 F., for a sufficient time to melt the soap, and the molten homogeneous mixture thus obtained is cooled by quenching at a temperature above about 385 F., preferably from about 400 F. to about 385 F. or lower, and recycle cooling from a temperature of at least about 385 F. to below 385 F. and until substantial gelling has occurred, preferably to about 365 F. or lower. Most advantageously, the recycling is continued. until the mixture has been cooled at least to 350" F. According to, the preferred procedure, the grease mixture is heated to about 395 F. to 405 F., and the cooling begun immediately, or with not more than about 5 or 1.0. minutes holding time at. that temperature, by simultaneously quenching and recycle cooling, until the. temperature of the mixture has been reduced. to below 385 F., the recycling being continued until the.v temperature of the mixture is about 365 F. or lower. The method of cooling below about 350 F. is not critical, although. it is usually desirable to con- .with the results obtained by recycle cooling alone.

tinue the recycling until the grease has cooled to about The following examples describe in detail the manufacture of lithium 12-hydroxystearate greases by the method of this invention, and illustrate the improved results obtainable bythls method in comparison with those obtained by recycle cooling alone.

EXAMPLE 1 H 2 A series of lithium l2 -hydroxystearate greases Twas prepared, employing as the base oil a 1952805 by weight blend of a refined wax distillate oil and a refined parafiinic residual oil, obtained by furfural refining, .clay

and acid treating and solvent dewaxing a Manvel residual oil. Inspection tests on this blend were as followsii.

The fatty acid material employed was the methyl ester of 12-hydroxystearic acid, obtained by the hydrogena- -tion of ricinoleic acid in methyl alcohol solution, and

sold commercially under the trade name of Paricin-l. This material has a saponification number of 189, a neutralization number of 2.6, an iodine number of 3.8, a hydroxyl number of 181.5 and a melting point of 625 C.

The greases were preparedzboth in laboratory batches, employing a conventional jacketed, 140 pound capacity laboratory kettle, and .in regular plant manufacture.-

In carrying out these preparations, a grease concentrate was obtained in the form of a molten homogeneous mass by saponifying the fatty acid material with the calculated amount of lithium hydroxide in the form of a 10% aqueous solution in the presence of about one half ofthe total amount of lubricating oil present in the finished grease at about 180-200 F. for one hour, dehydrating the saponification mass at about 300320 F., adding additional lubricating oil and heating the grease mixture to about 390-410 F. to melt the soap. Cooling of the hot grease concentrate thus obtained was carried out by quenching with the remainder of the lubricating oil,

amounting to about 8% to about 16% of the total amount present in the finished grease, and by circulating arecycle stream of the grease mixture through an external water-cooled exchanger at a rate such that the ratio of Typical inspection tests'on this blend are as follows:

the volume-of grease recycled 'perminute to the total continued until the grease was at about 200 F. The

grease was finished by milling in a colloid mill at 0.003- 0.006 inch clearance. Greases of excellent appearance and quality were obtained in high yields under these conditions ataverage cooling rates inthe 400-350 F. range from about 3 F. per minute to about 15 F. per minute.

obtained by the combination of quenching and recycle cooling. 4

Table I below shows the results obtained in typical preparations carried out as described above in comparison The estimated soap content for a 280 penetration grease was obtained by allowing 1% of soap for 20 points of difference in penetration.

.izasji; Li bl i Grease No l 2 3 SoarhContent, percent:

etore Quench 7.84..... 8.60. 6.12. After Quench 7.90 5.60. Final 7.85 5.57. Estimated for 280 worked pene. 9.30..... 6.70 6.50.- Cooling Method Recycle. Quench+ Quench+ Recycle. Recycle. Conditions of Quenching:

Temperature begun, F 400 400. Amount of quench 011, percent 9.1 8.9.

of total 011. Rateotquenching,gal./mln./lb. 0.0102-.." 0.0098;

finished grease. I Time, minutes 1.08 1.13. Conditions of Recycle Cooling:

Temperature begun, F 400 400 400. Recycle rate, volume recycled] 1.6 1.7 1.7.

minute/total volume. Cooling Rate, F./Minute:

400350 F. range 7.0. 400-300" F. range.-- 6.7. 300-200 F. range....' 4.2. Tests on Milled Product:

Free alkali (as LiOH); percent. 0.14. Free gatty acld (as oielc), per- None.

cen I Penetration, ASTM, at 77 F.

Unworked... 298 252 293. vWorked 310 262 298. Appearance of Product Smooth- Smooth-.. Smooth.

EXAMPLE 2 A second series. of -lithium 12-hydroxystearate greases was prepared employing as the base oil a blend of refined distillate .oils-consistingpf 15% by weight of .a medium viscosity paraffinicoil, 3.5 ,by weight, of a high viscosity naphthenicoil and by weight of a light paraffinic oil.

' v Blend Gravity, API' 25.4 Flash, CIC," F. q 440 Fire, COCIJ," F. 480 VisjcosityjSUS, at'100 F.".. 477 ViscosityQSUS, at 210? F. f.' 57.3 Viscosity index t 66.8 'Pour, F. 5

The fatty acid material employed was a commercial 12- hydroxystearic acid, sold under the trade name of Hydrofol Acids 200. Typical inspection tests on this material include an acid number of 172, asaponification number of 205, an iodine number of 4 anda hydroxyl number of 95. l

The preparation of the grease mixtures was carried out as described in Example 1. Greases of excellent quality were obtained when the mixtures were cooled by the combination quench and recycle procedure, with very by recycle cooling alone. I

The following table" shows' the improvement in yield obtained by employing the combination of quenching and recycle cooling over that obtained by employing recycle cooling alone in plant manufacture. The figures given are the average of several batches, wherein the only difference in' the preparation was the cooling method employed. v

T a l COMPARISON OF COMBINATIQN QUENCHING AND BE- CYCLE COOLING wr'rrr RECYCLE COOLING ALONE The following table gives more detailed information on "Tests on MllledProduct:

Work Appearance of Product the conditions employedniiddhe results obtained in representativepreparations of this{ greasev in plant manufacture.

Table-III Grease No 1 i 2 3 Soap Content, percent:

Before Quench glitter Quench.

Final Estimated for 280 worked pene. 8.58.-... 6.9 6.3. Cooling Method 'Recycle Quench+ .Queuch+ Recycle. Recycle. Conditions of Quenching:

Temperature begun, F 3 Temperature ended, F 366. Amount of quehchoilypercentz 16.2.

of total 011. Rate of quenehing,'gal.]1nin./lb.:- 0.0065. l 0.0065.

finished grease.

Temperature of quench 011, F Time, minutes Conditions of Recycle Cooling:

Temperature'begim, F..-.. Temperature ended. F Recycled rate, volume recycled/ 'minJtotalvol. I 'Iime, minut'es Cooling Rate, FJMinute:

400-350 F., range- 5.3 3.0 (406- 11.2 (39s- 40mm F rt-tinge a1 1.3 (377- 58 (see a 300 F 300 F) Penetration, ASTM, at 77 F Unworked Smooth- 278. Smooth.

'As shown bythetables',very considerable improvements .in yield,' amounting 'tosavings ofas much as- 3% of soap for a 280'worked penetration grease, we're obtained by employing- -quenchingiin -iconjunction with recyclecooling.

In. addition, the greases obtained were fully equivalent in I appearance and lubricating properties tosthose obtained l by recycle cooling'alone,"an'dgenerally superior in this respect to those obtainedby' 'other'cooling methods.

Obviouslymauy'niodifications 'and variations of the invention,ashereinbeforeset forth, may be'made without departing'from'the"spirit"and scope thereof and, there- "fore, 'only'suchdimitationsshouldbe imposed as are in- 'dicated "in the appended claims.

We-claim: v1. The method of -greasemanufacture which comprises,providing"a-molten-homogeneous mixture of a lithium-hydroxy fatty-acid isoap andan oleaginous liquid in grease forming proportions at an elevated temperature above the melting point of the soap, and controllingthe crystallization of thewsaid soap during cooling by con- I tinuously'withdrawing a stream of relatively small volume from a -maintained agitated body'of the said mixture and passing the said stream through an external cooler backstothe said I maintained body "of themixture while the said mixture is cooled from a temperature above the meltingpointcof the soap to a temperature below .themelting-point of the-soapand until substantial gelling .hasoccurred,andsimultaneously quenching the said :mix-

ture at-a temperatureabove the melting point of thesoap by introducing a relatively-cool oil comprising a minor proportion of the total-oleagiuous component of the finished grease 2. The method of claim-1 --wherein the quenching is continued until the mixture is at a temperature below the melting point ofthe. soap.

3. The method of claim' 1 wherein a substantial amount of the'cooling above the melting point of the said soap is 'obtained by the oil quenching and a substantial amount of the cooling below the melting point of the said soap is obtained by the recycle cooling.

'4. Themethodof claim 1 whereinthe said oleagiuous liquid is a mineral oil having a viscosity within the lubricating oil viscosity range. I

5. The -method of preparinga grease containing 'as --the thickening agenta lithium soap of a soap-forming hydroxy fattyacid material which comprises providing a molten homogeneous mixture of said lithium soap and an oleagiuous liquidat a temperature of about 390420 F., and controlling'the crystallization of the said soap during cooling'by quenching said mixture to a temperature below about 385F., by introducing a relatively cool oil comprising a minor proportion of the total oleagiuous component of the finished grease, and continuously with drawing a stream of relatively small volume from a maintained agitated body of the'said mixture and recycling it through an external cooler back to the said maintained body of the mixture while the said mixture is being cooled from a'temperature above about 385 F. until a grease consistency is obtained.

6. The method of claim 5 whereinthe recycling is carried out while the mixture is cooled from about 390 F.

to about 365 F.

7. The method of claim5 wherein the quench oil comprises about 5% to about 25% of the total oil in the finished grease.

8. The method of claimS wherein the said mixture is cooled in'the range from 400 F. to 350F at a rate'between about -3 F. and about 15 F. per minute'by means of the quenching and recycle cooling.

9. Themethod of claim 5 wherein the lithium soap 'is lithium l2-hydroxystearate.

10. The method of preparing a grease thickenedjwith .lithium JZ-hydrQxy'stea'rate which comprises providing being cooled from a temperature above about 385 F.

down to about 365 B, said mixture being cooled in the 4O0 350 F. range at a rate between about 3 F. and about 15 F. per minute by means'of the said quenching and the recycle cooling.

11. The method of claim 10 wherein the quenching and recycle cooling are begun substantially simultaneously while the said mixture is at a temperature of about 395-405 F.

References Cited in the file of this patent UNITED STATES "PATENTS 2,374,966 Zimmer et al. May 1, 1945 2,380,893 Zimmer et a1 July 31, 1945 2,588,556 Moore et al Mar. 11, 1952 2,648,634 Moore Aug. 11, 1953 2,651,616 Matthews et al. Sept. 8, 1953 2,652,365 Moore et a1 Sept. 15, 1953 2,652,366 Joneset a1. Sept. 15,1953 2,830,022 Nelson et a1 Apr. 8, 1958 OTHER REFERENCES Manufacture and Application of Lubricating Greases, Boner, Reinhold Pub. Co., N. Y. (1954), p. 454.

Claims (1)

1. THE METHOD OF GREASE MANUFACTURE WHICH COMPRISES PROVIDING A MOLTEN HOMOGENEOUS MIXTURE OF A LITHIUM HYDROXY FATTY ACID SOAP AND AN OLEAGINOUS LIQUID IN GREASE FORMING PROPORTIONS AT AN ELEVATED TEMPERATURE ABOVE THE MELTING POINT OF THE SOAP, AND CONTROLLING THE CRYSTALLIZATION OF THE SAID SOAP DURING COOLING BY CONTINUOUSLY WITHDRAWING A STREAM OF RELATIVELY SMALL VOLUME FROM A MAINTAINED AGITATED BODY OF THE SAID MIXTURE AND PASSING THE SAID STREAM THROUGH AN EXTERNAL COOLER BACK TO THE SAID MAINTAINED BODY OF THE MIXTURE WHILE THE SAID MIXTURE IS COOLED FROM A TEMPERATURE ABOVE THE MELTING POINT OF THE SOAP TO A TEMPERATURE BELOW THE MELTING POINT OF THE SOAP AND UNTIL SUBSTANTIAL GELLING HAS OCCURRED, AND SIMULTANEOUSLY QUENCHING THE SAID MIXTURE AT A TEMPERATURE ABOVE THE MELTING POINT OF THE SOAP BY INTRODUCING A RELATIVELY COOL OIL COMPRISING A MINOR PROPORTION OF THE TOTAL OLEAGINOUS COMPONENT OF THE FINISHED GREASE.

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