US2590786A - Grease - Google Patents

Description

Patented Mar. 25, 1952 GREASE John Walter Nelson, Hammond, Ind., assignor to Sinclair Refining Company, New York, N. Y.,

a corporation of Maine No Drawing. Application May 19, 1950, Serial No. 163,078

1 Claim.

This invention relates-to the manufacture of novel grease compositions based upon certain synthetic microcrystalline wax acids of extremely high molecular weight which have special capacity for imparting properties of value to greases.

In my copending application, Serial No. 157,177 filed April 20, 1950, there are disclosed certain new microcrystalline wax acids of synthetic origin. These acids have an unusually high molecular weight, containing more than eighteen carbon atoms per molecule, and ranging up to forty and more. The acids are prepared by oxidizing microcrystalline waxes having 34 to 55 carbon atoms per molecule in the presence of a stoichiometric excess of oxygen and about 0.1 to 4.0% by weight of an oxidation catalyst at a temperature in excess of about 100 C. for a period of time suiiicient to effect substantially complete conversion. The pure 018+ wax acids are then separated from the reaction mixture, as by Washing and distillation. The acids are essentially monocarboxylic and are characterized by extreme insolubility in water.

I have discovered that the free high molecular weight microcrystalline wax acids can be used to thicken lubricating oils and that the thickened oils have particular value as greases. Greases formed by use of the free wax acids possess highly favorable lubricating properties and good stability. They have excellent resistance to oxidation and valuable rust preventative properties by forming protective films on metal surfaces when dispersed in oil. The greases resist bleeding and have improved capacity for functioning in the presence of water due to their low ionization constants, so

that dissociation does not occur to any significant 1 degree and hence corrosion is almost impossible.

In addition, the use of the acids in grease com positions has the special advantage in that readily available low-cost materials of petroleum origin are provided in place of the conventional natural fats and oils that must be saponified by expensive basic materials such as lithium hydroxide.

To the best of my knowledge, free organic acids have not been suggested for thickening lubricating oils and have not been used heretofore as primary grease constituents. Small amounts of free acids sometimes are added to or left in grease compositions for other purposes, but in general the entire emphasis of grease makers has been upon the use of soaps and upon the production of netral compositions or compositions having substantial base numbers. Acids are corrosive, and with conventional greases corrosion and oxygen instability occur upon hydrolysis of the soaps to form the free acids. Surprisingly, however,

2 1 greases based upon my high weight microcrystalline wax acids are stable and actually have valuable rust preventative properties.

Further, the 018+ synthetic microcrystalline wax acids I use have unusual properties compared to other organic acids. The unusual chain lengths of the molecules result in extreme water insolubility. My wax acids are also marked by very low ionization constants. As a result, they do not dissociate significantly in the presence of water so that corrosion of metal surfaces cannot occur. The wax acid molecules are polar but extremely insoluble in water. In oil dispersion, they form protective films on metal surfaces and impart rust preventative properties to the oil or grease. The microcrystalline acids also have the valuable property of being able to form an interlacing structure with oils that is readily susceptible to gelation. This accounts for the good thickening properties of the acids and is advantageous in forming heavy lubricating compositions that are able to withstand high pressures.

' The amount of microcrystalline wax acids employed in forming the grease will depend upon the desired consistency and operating specifications. Generally, amounts in the range approximating one per cent or so to fifty per cent by weight on the finished composition are highly satisfactory. Amounts less than about one per cent by weight of the wax acids afiord only slight advantage from the use of the acid material, while amounts in excess of about 50 per cent by weight do not improve performance to a degree that is warranted by the additional higher cost of manufacture. In particular, about 10 per cent to 25 per cent by weight is especially advantageous considering utility and economy of preparation. In addition to depending principally upon the use for Which the grease is intended, the actual wax acid mixture employed, the lubricating oil base and any other substance that might be added to make the finished grease also will have effect on the amount of acid added. In this regard, the wax acids may be used in an acid mixture of wide range, such as C19 to C 0 and higher, or from a narrow fraction, such as acids in the range of C19 to C23. The wide range mixture is especially advantageous since highly satisfactory greases are obtained from acids that are economically prepared.

The grease compositions according to my invention are generally prepared by adding the microcrystalline wax acid to a lubricating oil stock, thoroughly mixing the components and cooling. Advantageously, the acid material is 3 heated to a temperature slightly above its melting point, the lubricating oil added and the mixture vigorously stirred while slowly cooling.

By way of example, a suitable microcrystalline wax acid for grease manufacture is obtained by oxidizing to complete conversion C34 to C55 microcrystalline waxes, washing the reaction product with hydrochloric acid and water and flash distilling the washed product at about 575 F. under 1 to 2 mm. of pressure for the overhead. The acid so prepared has a saponification number of about 110 to 115 and a petrolatum melting point of 130 to 135 F. It is then heated to a temperature slightly above its melting point in the usual iron grease kettle equipped with mechanical agitators. Enough mineral oil of suitable viscosity is slowly added, accompanied by agitation, to form the desired grease composition. The mixture is thoroughly agitated for dispersion of the acid in the oil. Any other substances may be added before cooling, such as graphite or talc, to' adapt the product to a specific use such as for the lubrication of heavy machinery, after which the mixture is again thoroughly agitated. The product so formed may then be deaerated under vacuum and is finally cooled. Such a finished grease composition may contain about to of the microcrystalline wax acid of saponification number 110-115 blended with a lubricating oil comprising a heavy mineral oil of 1100-1400 seconds S. U. V. at 100 F. (80 sec. at 210 F.), having a gravity of about 23 to 25 A. P. I. and a maximum pour point of about 10 F.

Suitable materials or substances may be compounded into the grease to affect its structure or properties in any desirable way. Generally, the principal constituent in amount of the finished grease will be a suitable lubricating oil stock. For instance, lighter greases may contain a major proportion of a lubricating oil stock with S. U. V.s in the range from about 100 to 200 seconds at 100 F. Heavier greases may contain oils having a S. U. V. of 300seconds and more at 100 F. Usually the lubricating oil stock is a mineral oil, although other oils ma be employed. Where especially severe loads are to be carried, graphite, mica or talc may be added in suitable amounts, as in the lubrication of heavy machinery. In addition, the consistency of the grease, its color, odor and other special properties may be altered by the addition of such substances. These substances may be added before or after preparation of the grease but are advantageously compounded while the grease is being made,

thereby insuring uniformity of final product.

The grease compositions of the present invention may also contain any of the conventional soaps ordinarily employed in such lubricants. For instance, the fatty acid soaps of aluminum, sodium. lithium, barium, lead, strontium, calcium, magnesium, tin, nickel, cobalt, chromium and manganese are illustrative. Mixtures of these soaps may likewise be employed. Or soaps of the Cl8+ microcrystalline wax acids themselves be added, as disclosed in the copending applica tion to me and John W. Teter, Serial No. 163,076, filed May 19, 1950. However, these soaps, such as the lithium soap, are more expensive to prepare since they involve saponification of the acids with a basic material.

The Wax acids I use in compounding the improved greases according to the present invention are, as I have related, of unusually high molecular weight, containing more than eighteen carbon atoms per molecule and usually in excess of 24 carbon atoms per molecule and ranging up to forty and more. They are essentially monocarboxylic, have saponification numbers of about 200 and less and are characterized by extreme insolubility in water. Their special utility in greases is aided by their capacity to form an interlacing structure with oils and solvents readily susceptible to gelation. Besides the carboxylic roup, the acids may contain other groups such as lactonic groups or inner esters and the hydroxy, ketone, ether, aldehyde, ethylene, and acyl groups. The acids have low ionization constants (high Ks. p.). They are insoluble in cold alcohol, although will dissolve in hot acetone or benzene. The acids have a relatively low melting point and, in appearance, are white to amber in color and are hard and smooth to the touch.

The synthetic microcrystalline wax acids can be prepared by oxidizing microcrystalline waxes having 34 to 55 carbon atoms per molecule in the presence of a stoichiometric excess of oxygen and about 0.1 to 4.0% by weight of an oxidation catalyst at a temperature in excess of about C. for a period of time suificient to effect substantially complete conversion of the wax to acids. The wax acids having more than 18 carbon atoms per molecule are then separated from the reacted mixture, as by distillation. For example, a microcrystalline wax derived from a Texas crude and containing 34 to 55 carbon atoms per molecule is oxidized with air in the presence of potassium permanganate. The reaction is carried out at about C. to C. with to 225 liters of air per kilogram of wax per hour using about 1.0 to 2.0% by weight of potassium permanganate. The reaction is continued until conversion is essentially complete, for instance, until the reaction mixture has a saponification number of at least about 100 and. usually. 200 to 500. The high molecular weight acids, higher than Cm, are then separated from the reaction mixture which contains certain small amounts of organic and inorganic materials. This may be accomplished by washing with water and/or an inorganic acid for the removal of inorganic materials such as catalyst, and then subjecting the mixture to distillation in a flash still under reduced pressure for elimination of any lower acids and other organic substances.

In the preparation of the high molecular weight wax acids, microcrystalline waxes containing about 34 to 55 carbon atoms per molecule are oxidized. The Car to C55 microcrystalline waxes are derived frorn'higher boiling petroleum distillates and residues such as lubricating oil fractions. The waxes appear to be largely composed of molecules especially characterized by slight branchings in the carbon chain. This structure may be contrasted to crystalline wax molecules which are essentially straight chain. Generally, the branching in the microcrystalline wax molecule is at random along the chain, each branch appearing to contain an average of about three carbon atoms. The micrdcrystalline wax to be oxidized may be composed of molecules containing very similar or identical numbers of carbon atoms. Generally however, the Wax will be made up of mixtures of molecules over the range of 34 to 55 carbon atoms as well as having molecules of varying structure. The waxes may be oxidized in the pure or impure state, although elimination of contaminating substances prior to reaction tends toward better product quality. For instance, a C34 to C55 microcrystalline wax obtained from a Texas crude may be purified for reaction by contact at elevated temperatures with aluminum chloride for a short period of time in the usual procedure well known in the art.

The reaction is carried out in the presence of 0.1 to 4.0 per cent by weight on the wax of an oxidation catalyst. Satisfactory catalysts include those dispersable in microcrystalline wax such as manganese salts, ammonium vanadate and potassium permanganate. The use of potassium permanganate, present in amount of about 0.1 to 1.25 per cent by weight on the wax, is particularly advantageous as respects a shorter reaction period and improved product quality. In any event, less than about 0.1% of the catalyst results in inordinately prolonged oxidation periods while amounts greater than about 4% tend to oxidation products heterogeneous, inconsistent and stringy in appearance and poor in color. Oxidation catalyst promoters or sensitizers may be employed to accelerate the reaction rate even more. For example, sodium carbonate, manganese palmitate or other manganese salts, may be added in small amounts as accelerators, for instance, in amounts generally equal to or less than the quantity of the oxidation catalyst employed. The oxidation catalyst is advantageously added to the microcrystalline wax prior to commencement of the oxidation. In addition, it is advantageous to add the catalyst to the wax in aqueous solution and to remove the solvent by evaporation. For instance, potassium permanganate may be added as a 15-20% by weight solution. The water is removed prior to reaction by applying heat, say by heating the mixtureto 145-150 C., or air or oxygen may be added and the solvent water removed in the course of the reaction. Additional catalyst may be added later, that is, during the reaction, to step up the oxidation rate.

By adding to the reaction mixture as a seed acid composition derived from a prior run, reaction time may be reduced as much as 50% and is usually at least to 20% less, without any sacrifice in product quality or in reaction yield, over the use of the catalyst alone under similar conditions of reaction. For example, a microcrystalline wax derived from a Texas crude and containing 34 to 55 carbon atoms per molecule is oxidized in the presence of potassium permanganate and 0.1 to 1.25% by weight of seed having a saponification number of about 200 to 300. The reaction is carried out at about 110 C. with 150 to 225 liters of air per kilogram of wax per hour using 1.0 to 2.0% by weight of potassium permanganate. The reaction is continued until conversion is essentially complete, for instance, until the reaction mixture has a saponification number of at least 100, and usually, 200 to 400, and

the higher acids are then separated out.

About 0.1 to 4.0% by weight on the wax of the acid composition prepared in a prior run is added. Although the seed may be added before or after commencement of the oxidation reaction or before or after the addition of catalyst, a highly favorable reaction rate consistent with good product quality and yield is obtained by first adding the seed to the wax, then adding the catalyst in aqueous solution and commencing oxidation. After the catalyst is added, the oxidizing gas may be added at reaction conditions. If the catalyst is added in aqueous solution, the solvent water may be removed by evaporation before reaction, as by heating to 145 to 150 (3., if desired. Also, as is the case with the catalyst, additional seed may be added during the course of the renecessary for minimum reaction periods.

ill)

rate also.

action to step up the oxidation rate. In any event, particularly advantageous reaction rates are obtained when about 1.0 to 2.0% .by weight of catalyst is employed and a similar amount of seed. The reaction will not go by adding the seed alone, that is, without at the same time employing the oxidation catalyst. The seed has a saponification number in the range of about 100 to 500, contains in substantial amount wax acid molecules having upwards of eighteen carbon atoms, and has low solubility in water.

The wax acids are formed by oxidation of the reaction mixture in the presence of oxygen, either in pure form or. in admixture with inert diluents, say as air. The oxygen is added in at least the stoichiometric amount for a period of time suiTicient to effect complete conversion. Advantageously, the oxygen is used in considable excess of the stoichiometric quantity which reduces time yet results in a very favorable product. It is preferable to add oxygen, considered as substantially pure oxygen, in amounts in the range approximating 30 to 50 liters per kilogram of wax per hour. An amount of about 35 to liters per hour of oxygen per kilogram of Wax is particularly advantageous. In any event, amounts less than about 30 liters per hour of oxygen per kilogram of wax tend to unattractively long reaction periods while excessive quantities, i. e. over liters per hour, are not necessary and are wasteful. The use of pure oxygen or diluted oxygen such as air does not noticeably affect product quality, although a higher oxygen concentration does improve reaction time. Good dispersion of the oxygen into the mixture undergoing reaction is For instance, oxygen contact and dispersion may be improved by introducing the oxygen into the reaction mass and by constant agitation of this mass during reaction.

Considerable latitude is afiorded in oxidation temperature, although the thermal environment should be in excess of about C. for the period of the reaction. Temperatures in the range approximating 100 to 150 C. are preferred. Oxidation temperatures between about 100 to C. afiord particularly favorable results, with a minimum of side product and carbon oxide formation and with maximum oxygen absorption. The reaction vessel may be cooled when necessary to maintain the desired temperature range since the reaction after commencement is exothermic in nature.

The reacted mixture is oxidized until the C34. to C55 microcrystalline wax has been completely converted into essentially acids. During the course of the reaction, water and volatile acidic matter is given off in small quantities. Generally, the degree of conversion is determined by the saponification number and the length of time required for complete conversion depends in large measure upon the quantity of oxygen available to the wax undergoing reaction and the accompanying thermal environment. However, the catalyst and seed employed, their proportions and even the exact nature of the wax appear to figure in the reaction Usually, the microcrystalline wax is oxidized until the reaction mixture has a saponification number of at least 100, and advantageously to saponification numbers of 200 to 300.

or more. saponification numbers of the solid reaction product as high as 300 to 400 are not uncommon and indicate a high degree of or However, the prolonged period of After substantially complete conversion has beenLefiected, the reaction mass essentially. comprises'a mixture of wax acidsucontaining aisub- 'stantial portion of 'monocarboxylic acids having more than .18 carbon .atoms per molecule. The mixture also contains :certain small quantities of other organic and inorganic matter .such .as'unreacted wax, lower molecular weight acids and catalyst f material. may be obtained in pure form by washingthe solid mixture free of inorganic materials :with waterzand/oran. inorganic acid,.such :as hydrochloric acid,.and then distilling the mixture to .separateout the .higher acids. theacidmixture. is first washed by adding 'wa- I ter '5. and :hydrochloric .:acid. .The .resulting mass is .stirred and permitted to .settle. water layer which separates out is removed. .The productmaybe washed again :as-withawattergalone, the .waterremoved after :another set- "tling period .and rthe product blown with .air ".to evaporate anyremaining water. The washed product isthen distilleditoremovethe substan- The. 018 plus acids For example,

.The acidtially pure C18 plus .wax acids. Thismay be accomplished by flash distillation in the pres- .enceiof steam or under high vacuum,'or by molecular distillation, in :the usual manner. For instance, employing flashrdistillation, the charge lated increasing incrementsof-distillation temperature, successively higher .molecular weight fractions over Ciaare taken .ofias desired. For

instance, the higher molecular weighfxacids may be separatedinto a number of fractions, such .asinto a.lower fraction containing C19 to-Cza ;fatty acids, having saponification numbers in :therange of vabout'195 to 155; .anintermediate fraction containing (324-170 C34 acids, :having saponification numbers in the range of 154 ..to 110 and a high fraction containing C35 and higher acids, havinga saponification number of about 109 and lower.

In place ofthe distillationprocedure.for separating out-the pure 018+ wax acids from the crude reaction product, the pure acids may be recovered by extracting the reaction product with aselective organic solvent selected from the class consisting of the saturated-hydrocarbons containing three "to twelve carbon atoms .per molecule. Propane, butane, isopentane andsnpentane are exemplary of suchsolvents. This improvement is disclosed in my copending application Serial No. 169,215, filed June 20, 1950.

-I claim:

A grease composition consisting essentially of a lubricating oil thickened by a mixture of high molecular weight microcrystalline wax acids 1 produced by substantially complete oxidation of microcrystalline Wax containing 34 to 55 carbon atoms permolecule which is characterized byxextreme Water insolubilityand by a saponi- "fication'number .less than about 200 and which predominates'in monocarboxylic acids havingan apparent chain length exceeding eighteen carbon atoms per molecule.

JOHN WALTER NELSON.

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

UNITED. STATES PATENTS Number Name Date 1,904,065 Mackenzie Apr.'18, 1933 2,029,619 James .Feb. 4, 1936 2,043,923 Burwell June 9, 1936 2,137,494 vJolley Nov. 22, 1938 2,361,547 Jenkins Oct. 31, 1944 OTHER REFERENCES Warths The Chemistry and Technology .of Waxes, 1947, pages 242 and 252.