US2801976A - Lubricating greases containing alkali fusion products of polysaccharides - Google Patents

Description

LUBRICATING GREASES CONTAINING ALKALI FUSION PRODUCTS F POLYSACCHARIDES Arnold J. Morway, Rahway, and Jeflrey H. Bartlett, Westfield, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application December 11, 1952, Serial No. 325,444

12 Claims. (Cl. 252-42) The present invention relates to an improved method of preparing lubricating greases and to grease compositions produced by this method. More specifically, the inven tion pertains to improvements in the manufacture of grease thickeners and to greases containing such thickeners. In its broadest aspect, the invention provides for making grease thickeners by a process involving fusing polysaccharides with caustic alkali, producing a metal salt from the acid so formed and incorporating this metal salt into a lubricating oil in grease-making proportions. In a preferred embodiment of the invention, the fusion is carried out in a lubricating oil in the presence of pre- I formed soaps and salts of other carboxylic acids.

Lubricating greases normally consist of lubricating oils thickened by alkali and alkaline earth metal soaps or other thickeners to a solid or semi-solid consistency. The soaps may be prepared by the neutralization of high molecular weight fatty acids or by the saponification of fats which is usually carried out in a portion of the oil to be thickened. Saponifi-cation of fats has been the preferred grease-making method heretofore chiefly because greases produced in the absence of glycerine or similar materials have tendenciesto become crumbly, to sweat oil and to break down into soft granular masses of reduced lubricating value. frequently employed in combination with the glycerides for various purposes, such as improvements in structure of the grease, its high temperature characteristics, etc.

The present invention pertains to highly valuable, stable lubricating greases in which the high molecular weight fatty acids are replaced or at least supplemented by a new grease-making material. that such greases may be prepared by incorporating into lubricating oils a grease thickener containing a material obtained by fusing polysaccharides with alkali, particularly caustic soda or potash at temperatures between 400 and 600 F., usually between about 480 and 580 F., for a time sufficient to form the alkali metal salt of the acid produced by fusion of reactive hydroxyl groups.

Previous work on the reaction of cellulose with sodium hydroxide indicates that at relatively low temperatures of about 100-150 F. the cellulose tends to swell and forms an addition product with the metal hydroxide. At elevated temperatures of, say, about 400-500 F. a variety of decomposition products result. In accordancewith the preferred embodiment of this invention the cellulose is reacted in combination with the alkali metal soap of a high molecular weight organic acid and a low molecular weight organic acid salt in the presence of an inert liquid diluent, resulting in new and previously unknown reactions. While some decomposition of the polysaccharides does occur, the majority of the alkali metal hydroxide reacts with the polysaccharide and forms salts by fusion with one or more reactive hydroxyl groups. The exact mechanism of reaction is not completely understood at this time, however, products having highly desirable qualities are obtained.

The discovery of the utility of alkali fusion of poly- More recently, fatty acids are, being It has now been found saccharides for grease-making greatly increases the wealth of rawmaterials available for grease production. Here tofore, ester-type fats, oils or high molecular weight fatty acids have been used in the manufacture of soap-thickeued greases and these starting'materials have been be lieved almost indispensable for the purpose. All these materials have numerous other industrial uses, a situation conducive to the development of shortagesforcing frequent variations in grease-making procedures and grease characteristics.

considerably.

Two factors further contribute to the value of poly-L saccharides as grease-making materials. In the first place,

their use introduces no complication into the grease-making procedure. The greases may be produced essentially in a single process step in which the polysaccharide is fused with alkali in the lubricating oil base at greasemaking conditions, although at somewhat higher temper atures. At the conclusion of the fusion process a finished grease is obtained.

Secondly, little water is formed during the reaction so When carrying out the alkali fusion in the lubricating oil itself so as to form the grease thickening salt in situ in accordance with the preferred embodiment of the invention, it has been observed that the alkali has a strong tendency to settle out of the reaction mixture to the bottom of the reactor in the form of a cake which does not fully participate in the reaction; Highly efiicient stirring or agitation will counteract this tendeny. However, in

many cases more efficient stirring is required than may be obtained in conventional grease kettles and special equipment would have to be used. i

It has now further been found that the settling tendency of the alkali in the lubricating oil-alcohol mixture is negli gible when a suflicient amount of a solid suspending agent is present in the reaction mixture. Most desirable suspending agents are those which serve simultaneously as grease thickeners, such as soaps of high molecular weight fatty acids, silica gel, carbon black, bentones, Attapulgus clay modifications, etc.

Soaps, particularly sodium soaps of high molecular weight fatty acids, are preferred for this purpose. However, the melting points of most of these soaps in lubricating oil is rather low, usually below 400 F. Thus, at the high reaction or fusion temperatures these soaps are liquid when used as such and do not entirely counteract the settling tendency of the alkali. This difliculty may be overcome in accordance with a specific embodiment of the invention by using the salt, preferably the: alkali metal salt, of a low molecular weight acid in addition to the high molecular weight fatty acid soap. In this manner, soap-salt complexes are formed which melt well above 500 F. and thus form an excellent suspending agent.

These soaps or soap-salt complexes are preferablysequent fusion which takes place at considerably higher temperatures. High molecular weight acids useful for this purpose include hydrogenated fish oil acids, C12C2z naturally occurring acids of animal or vegetable origin,

etc. These acids may be used in amounts ranging from Patented Aug. 6, 1951-" The discovery of an entirely new and large class of suitable raw materials cases this situation mono basic acid esters mayube .used in -placecof the .free.

acids inacorrespondingproportions In-thiscase, the.- alcohol portions of the esters.are convertedintoacids and the. corresponding soaps by .alkali fusion. If esters of lowmolecular weight alcohols areused, 1 elevated pressures may be. employed to prevent volatilization-of the alcohols.- Of=course, esters ofnon-volatile lowmoleculan weight alcohols, such aspolyhydroxy-alcohol esters, e... g.- sorbitol acetate, glycol acetate, etc. may be used. The high molecular weighttype of acids or their esters used for this purpose may-also be prepared by alkali fusion of Oxo products.

Soaps of high molecular weight fatty acids and;par.- ticularlysoap-salt complexesof the type specified maybe incorporatedin-the.-greases-of=- the present invention-'- to improve hi gir -temperature or other characteristics-seven if no suspending agentsarerequired. Thus,;it has beenfound that the use of salts derived from-polysaccharides as the solegrease-thickenersoften'tend toberrelatively less stable tomechanical working andhave dropping points below 400 1 whichmay. be undesirable, HoW-. ever, when thesepolysaccharide salts are-mixedwith straight chain soaps derived from fatty acids, thisis largely-eliminated or modified to an extent that-is desirable for certain purposes.

In accordance with a specific modification of this embodiment of the invention cellulose acetate is employed to produce the major portion of the salt thickener, preferably in' the presence of other high molecular weight fatty acids. Since the cellulose molecule contains a numberof hydroxyl groups it'readily reacts with acetic anhydride in the presence of 'a trace of-H2SO4 to form the tri-acetate CsH'105(OC.CI-I3)3. On hydrolysis and fusion of the cellulose acetate with alkali the cellulose salt product described above is formed along with alkali metal acetate. This combination ofthe alkali metal salts of'cellulose (formed by fusion of" the OH group- 4 ings)- and the alkali metal acetate may be employed as a thickener for lubricating grease. Other polysaccharides may replace cellulose'and-other low molecular Weight aliphatic acids may be used in place of acetic acid in this modification of "the invention.

The 'salts formed'by alkali fusion of polysaccharides in the presence of other fatty acid'soaps consistently yield excellent smooth greases. Other conventional thickeners, antioxidants, corrosion inhibitors, tackiness agents, load-carrying compounds, viscosity index improvers, oiliness agents, and the like may be added prior, during and/or after the fusion process as will be apparent to thoseskilled in the art.

The base oil used as menstruum during the fusion process should be a mineral lubricating oil. After the fusion is completed, synthetic lubricating oils, such as a dibasic acid ester (e. g. di-Z-ethyl' hexyl sebacate, adipate, etc.),polyglycol type synthetic oils, esters of dibasic acids and polyhydric alcohols, etc., as well as alkyl silicates, carbonates, formals, acetals, etc., may be used alone or in addition to mineral lubricating oil to bring the grease to the desired consistency. The oil base preferably comprises about 50 to about 95% of the total weight of the finished grease.

As. indicated above, the process of the. invention may be carried out in two stages. When so operating, the polysaccharide to be fused may beaddedover a period of several hours, say 3 hours to a molten mixture of alkali and mineral oil, preferably a heavy oil, maintained at fusion temperatures of, say, about 530f580 F. The

Esters. of the high. and/or low. molecular; weight. acids, particularly thoseacontaining.

proportion of alkali used may amount to about -50 wt.

percent, preferably about -40, Wt. percent, of the polysaccharide, calculated as NaOH. When all the polysaccharide has been added, heating may be continued at these temperatures to complete the reaction.

The salts so prepared may then be introduced into a lubricating oil base stock. Other high and/ or low molecular weight fatty acids as wellas other. grease additives may be added and the. mixture may be converted into a greaseby the addition of at least suflicient caustic alkali to neutralize the acids present. Conventional grease-making conditions including temperatures of about 350-500 F. may be used in this stage. The salts derived from the polysacch-aride by alkali fusion should form at least 20 weight percent and preferably about weight percent of the greasethickener or about 2.020 weight percent of the finished grease. The remainder of the grease thickener is preferably made up by a suitable soap-salt complex ofthe type described above. The proportion of salt derived from polysaccharide to soaps andsaltsaderived from other acids may be about 1:4-to 4:1 and preferably is about 1:1.

In order to .prepare a grease by alkali fusion in situ in accordance with a more desirable embodiment of the invention, the grease-making procedure may be quite generally as follows. A mineral lubricating oilbase is mixed with the polysaccharide and -al kali, preferably in aqueous solution, at temperatures not substantially exceeding 100 F. The mixture is heated to about 280 320" F. When dehydration iscomplete the temperature is raised to about 480--580- F., preferably about 530 to 570 F; Heating at these temperatures is continued until the desired conversion has been obtained, which is usually the case after about 0.5-5 hours. The reaction mixture is quenched or allowed to cool and then be diluted with further amounts of lubricating oil to the desired grease consistency.

A similar procedure is employed when the polysaccharide is subjected to alkali fusion in situ in the presence of suspendingagents, such as soaps of high molecular weight fatty acids or complexes of such soaps with low molecular weight fatty acid salts in accordance with the preferred embodiment of'the invention. In this case,

all-the acidsf needed to form the suspending agents are added to the, mixture of polysaccharide, alkali and min eral oil; Sufiicient caustic -alkali is us ed to neutralize these acids andto supply additional alkali amounting, to about 10-50 wt. percent, preferably about 25-40 wt. percent of'the polysaccharide used (calculated as NaOH).

Thecaustic alkali is preferably employed in the form.

of an aqueous solution of about 15-30%. The mixture is heatedat asaponification temperature of about 300400 Fauntiltheacids are converted to soaps and salts and all the water is volatilized. Alkali fusion is then carried out substantially as described above, except that less violent stirring is required.

The invention willbe best, understood by reference to the following specific examples which represent preferred modifications of the invention.

Blend of naphthenic typemineral oils having a viscosity of 50 S. S. U. at 2l0 F 68.50

H ydrogenated fish oil acids corresponding to commercial stearicacidun degree of saturation.

{West yirginia Pulp, &, Paper Companyfs Polycel RCB- A200 which is over pure alpha cellulose.

Preparation-The cellulose and a aqueous solution of sodium hydroxide were charged to a fire heated grease kettle while cooling to 100 F. After intimate mixing, 50% of the mineral oil was charged, followed by the Hydrofol acids 54 and the acetic acid. Heating was initiated and after dehydration at 300 F. the balance of the mineral oil was added and the temperature raised to 560 F. and held above 550 F. for one hour. Some discoloration and tarry odor was noted. However, a sample showed no presence of carbonized products and was of excellent smooth structure on cooling. After heating, the grease Was cooled while agitating to 250 F. where the phenyl alpha-naphthylamine was added and further cooled to 180 F. The time of cooling to 180 F. required 65 minutes. A portion of ten grams washomogenized at high rates of shear.

When working in accordance with Example I, i. e., employing the product as described in Example I as a base, other synthetic oils of desirable qualities may be addedto the grease. These synthetic oils may be formals, simple esters, diesters, complex esters, etc. Of course, other cellulose products may be used. For example, dissolving viscose containing about 97% alpha cellulose is a highly desirable starting material.

EXAMPLE II Weight Ingredients: percent Product of Example I 50.00

Highly Refined High V. I. Paraflinic Type Mineral Oil-Viscosity at 210 F. 45 S. U. S-.. 50.00

Preparatin.-The unhomogenized product of Example I was diluted 100% with a more oxidation resistant, higher viscosity index, less volatile mineral oil base and additional phenyl alpha-naphthylamine was added. After intimately mixing, the product was homogenized at high rates of shear to form an excellent smooth grease of desired consistency.

Properties.After homogenization:

Penetrations, 77 F., mm./ 10:

Unworked 217. Worked 60 strokes 242. Worked 60,000 strokes 285. Dropping point, F. 420.

Water Washing test, percent loss..- 10.

Norma Hoffman oxidation hours to p. s. i. Drop in Oz pressure 142.

Appearance Excellent smooth uniform grease.

AFBMA 1 Test:

80 F Excellent bearing lubricating char- 150 F acteristics. No tendency to fiuidize 250 F and leak through bearing seals.

standard Anti-Friction Bearing Manufacturers Association Test.

EXAMPLE III Weight Ingredients: percent Cellulose acetate 14.00 5 Hydrofol acids 54 10.00 Sodium hydroxide a... 6.50 Phenyl alpha-naphthylamine 1.00 Blend of naphthenic type mineral oil distillates 1 having a viscosity of 50 S. S. U. at 210 F 68.50

Cellulose acetate obtained from Hercules Powder Company Grade LL-l Relatively low molecular weight; 250 centipoises viscosity.

Preparatiorn -The cellulose acetate (powder), mineral oil and the Hydrofol acids 54 were charged to a fire heated grease kettle and the mixtures warmed to 150 F. V The sodium hydroxide as a 40% aqueous solution was then charged and the mass slowly heated. (Dehydrating took place during this period to 500 F.) Heating was then continued as follows:

Time of day: Temperature, F. 11:30 500 11:55 a. -1 595 12:05 i 550 12:30 510 1:10 2 250 1315 3 200 1 Shut 0ft heat. 1 I Added phenyl alpha-naphthylamine. Stirring discontinued.

The product was then passed through a Gaulin Homogenizer for homogenization at high rates of shear. Properties: r

Free Alkalinity, percent (as NaOH) 0.07

Penetrations, 77 F. mm./10:

Unworked 155 Worked 60 strokes 137 1 Worked 100,000. strokes r 210 Dropping point, F 500+ Water washing, percent loss None Copper corrosion (3 hrs. at 210 F.) None Norma Hoffman Oxidation Test, hours to 5 p. s. i. drop in Oz pressure EXAMPLE IV The product of Example III was cut backto a lower thickener concentration by dilution with a less volatile, more oxidation stable, higher viscosity index mineral oil, than that employed in its manufacture. This mixed product was then hardened by Gaulin homogenization.

Weight Ingredients: percent Cellulose acetate 7.00 Hydrofol acids 53 5.00 55 Sodium hydroxide 3.25 Phenyl alpha-naphthylamine 0.50 Blend of naphthenic-type mineral oil: Distillates having a viscosity of 50 S. S. U. at

50 S. S. U. at 210 F. 34.25 0 Highly refined high V .I. paraflinic-type mineral oil, viscosity at 210 F. at 45 S. U. S. 50.00

Properties:

Free alkalinity, percent (as NaOH) 0.03 Penetrations, 77 F. mm./10:

Unworked 259 Worked 60 strokes 273 Worked 100,000 strokes 352 Dropping point, F. 420 Water washing test, percent loss 10 Norma Hoifman Oxidation Test, hours to 5 p. s. i. drop in Oz pressure 175 The invention is not limited to the specific figures of the foregoing examples. The relative proportions of the grease constituents may be varied within the limits indicated above to obtain greases of difierent consistency and varying characteristics.

Whatis claimed is:

1. A lubricating grease comprising a major proportion of a mineral lubricating oil and grease-making proportions of agrease thickener containing a substantial proportion of an alkali metal salt of a low molecular weight aliphatic acidand at least about 20% by weight based on total thickener of an alkali metal salt of a high molecular weightcarboxylic acid, said salts being produced by the saponification and alkali fusionat a temperature of about 4003 600 F. of an ester ofiapolysaccharide having at least about 24 carbon atoms per molecule with said low molecular weight acid.

2. A lubricating grease comprising a major proportion of a mineral lubricating oil and a grease-making proportion of agrease thickener containing at least about 30 to 50 Wt. percent f an alkali metalsalt produced by alkali fusion of a polysaccharide, having at least about 24 carbon atoms per molecule, at a temperature of about 400 to 600 F. until said alkali metal salt is formed; the remain der of said thickener being made up of a material selected from the group consisting of an alkali metal soap of a high. molecular weight straight chain fatty acid and an alkali metal soap-salt complex of a high molecular weight fatty acid and a low molecular weight fatty acid 3. The grease of claim 2 wherein said material is a complex of a high molecular weight fatty acid alkalirnetal soap with a low molecular weight fatty acid alkali metal salt.

4. The process of .preparing a lubricating grease which comprises heating cellulose acetate with sodium hydroxide in a mineral lubricating oil to a temperature of about 400 to 600 F. for a time sufiicient to form sodium acetate and to convert the cellulose freed thereby into a high molecular Weight sodium salt and cooling the product, the total amount of said sodium acetate and salt being sufficient to give the cooled product grease structure.

5. The lubricating grease of claim 2 wherein said polysaccharide is selected from the group consisting of cellulose, iiemicellulose and starch.

6. The lubricating grease 'of.clairn 2 wherein said polysaccharide is cellulose. i I

7. A process for preparing lubricating grease compositions which comprises admixing mineral lubricating oil, a high molecular weight carboxylic acid having from about 12 to 22 carbon atoms per molecule, a low molecular weightcarboxylic acid'having from about 1 to 5' carbon atoms per molecule, a polysaccharide having at leastabout 24 carbon atoms per molecule and a suflicient amount of sodium hydroxide for neutralization and alkali fusion, dehydrating the mixture to a temperature within the range ofabout 280 to 320 F.,'continuing heating to a temperature'of about 530 to 570 F. and then cooling to obtain said lubricating grease composition.

'8. The process of claim 7 wherein said polysaccharide is selected from the group consisting of cellulose, hemicellulose and starch."

9. The. process of claim 7 wherein about 2 to 30 wt. percent of hydrogenated fish oil acids is employed as the high molecular weight carboxylic acid and about 1 to 10 Wt. percent of acetic acid is employed as the low molecular Weight carboxylic acid.

10. The process of claim 7 wherein said polysaccharide is employed in sufiicient amount so that the salt derived therefrorn constitutes from about 2 to 20 wt. percentof the fipished grease, and the amount of sodium hydroxide employed is about 25 to 40 wt.percent of the 12. The process of preparing a lubricating grease corn position whicli'comprises admixing cellulose acetate, mineral: lubricating oil, a high molecular weight carboxylic acid having'from about 12 to 22 carbon atoms per mole cule and sodium hydroxide, heating said mixture to a temperature of about 480 to 600 F. for a time sufiicient to form a soap-salt complex comprising sodium acetate and the soap" at said high'rnolecular weight carboxylic acid and to 'conver't' cellulose freed from said cellulose acetate into a'high'molecular Weight sodium salt and then cooling to obtainsaid 'lubricatinggrease composition.

References Cited in the file of this patent UNITED STATES. PATENTS

Claims (1)

1. A LUBRICATING GREASE COMPRISING A MAJOR PROPORTION OF A MINERAL LUBRICATING OIL AND GREASE-MAKING PROPORTIONS OF A GREASE THICKENER CONTAINING A SUBSTANTIAL PROPORTION OF AN ALKALI SALT OF A LOW MOLECULAR WEIGHT ALIPHATIC ACID AND AT LEAST ABOUT 20% BY WEIGHT BASED ON TOTAL THICKENER OF AN ALKKALI METAL SALT OF A HIGH MOLECUALR WEIGHT CARBOXYLIC ACID, SAID SALTS BEING PRODUCED BY THE SAPONIFICATION AND ALKALI FUSION AT A TEMPERATURE OF ABOUT 400*-600* F. OF AN ESTER OF A POLYSACCHARIDE HAVING AT LEAST ABOUT 24 CARBON ATOMS PER MOLECULE WITH SAID LOW MOLECULAR WEIGHT ACID.