US2590801A - Grease composition - Google Patents

Description

Patented Mar. 25, 1952 GREASE COMPOSITION John W. Teter, Chicago, Ill., and John Walter Nelson, Hammond, Ind., assignors to Sinclair Refining Company, New York, N. Y a corporation of Maine No Drawing.

Application May 19, 1950,

Serial No. 163,076

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

In the copending application of John Walter Nelson, Serial No. 157,177, filed April 20, 1950, there are disclosed certain new wax acids of synthetic origin. These acids have an unusually high molecular weight, containing more than eighteen carbon atoms per molecule and, usually, in excess of twenty-four 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 sufficient to effect substantially complete conversion. The pure C1s+ 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.

We have found that lubricating oils can be thickened with soaps of the high molecular weight microcrystalline wax acids to the cons'istencies of very useful greases. Greases so formed possess highly favorable lubricating properties and good stability. .They have excellent resistance to oxidation and valuable rust preventative properties. The greases resist bleeding and have improved capacity for functioning in the presence of water due to the significantly reduced water solubility resulting from very long hydrocarbon chains that make up the microcrystalline wax acids. In addition, the use of the acids in preparing such grease compositions 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.

The essential ingredients of the novel grease compositions of our invention are the soaps of the high molecular weight synthetic microcrystalline wax acids. The actual amount 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 satisfactory. Amounts less than about 1 per cent by weight of the soaps afford only slight advantage from their addition, while amounts in excess of about '50 per cent by weight do not improve performance to a degree that is warranted by the 2 Claims. (01. 252-s2) additional higher cost of manufacture. In particular, about 5 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 metal soap employed. the molecular weight of the microcrystalline wax acids from which it is derived, the lubricating oil base and any other substances that might be added to make the finished grease also will have effect on the amount of soap added. The soaps may be derived from an acid mixture of wide range, such as C19 to C40 and higher, or from narrow fractions, 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 are prepared with microcrystalline. wax acid soaps of any of the metals ordinarily used in compounding soap base greases. C1s+ microcrystalline wax acid soaps of aluminum, sodium, lithium, barium, lead, strontium, calcium, magnesium, tin, nickel, cobalt, chromium and manganese are illustrative. The lithium soaps of the wax acids have especially good utility due to their excellent stability on mechanical working and other favorable properties, although all the soaps have definite value in greases. Mixtures of diiierent soaps of the wax acids can be used to form mixed soap base greases, such as suitable blends of the lithium and sodium soaps. Also mixtures containing conventional soaps, such {as the soaps obtained from natural fats and oils, may be used with the wax acid soaps. For instance, equal portions or the soaps of tallow, and the synthetic acids form excellent grease compositions. Tallow is a low cost material so that employment of it with a microcrystalline wax acid soap is economically attractive when tallow is in ready supply. Thus, the grease compositions of our invention ofier the additional advantage of allowing free substitution of the soaps of natural and other fatty materials while still providing the benefits deriving from the use of the microcrystalline wax acid soaps.

The grease compositions are prepared in conventional manner. The soap may be initially formed and the oil base added to it, or the soap can be formed in situ by saponifying the acid material while in the oil.

For instance, a lithium soap grease may be prepared by first saponifying a microcrystalline wax acid mixture with lithium hydroxide monohydrate. A suitable wax acid mixture, as for lar devices. under vacuum and is finally cooled. By way of example one obtained by oxidizing to complete conversion C34 to C55 microcrystalline wax, washing the reaction product with hydrochloric acid and water and flash distilling the washed product at about 575 F. under 1-2 mm. of pressure for the overhead, which has a saponification number of about 110-115 and a petrolatum melting point of 130-135 F., is heated to a temperature slightly above its melting point in an iron kettle equipped with mechanical agitators. While the heated acid mixture is undergoing agitation sufficient lithium hydroxide monohydrate in aqueous solution is added to just neutralize the acid material. Advantageously, the lithium hydroxide is added at a temperature over about 150 F. and is dissolved in enough water so as to keep it completely in solution at the boiling point. A small quantity of a mineral oil may also be added so as to inhibit foaming during reaction and to promote ease of handling. The mixture is then reacted, while undergoing agitation,

,at a temperature of about 300 F. for a period of time necessary for complete reaction and dehydration. After reaction the reaction mixture comprising the lithium soap is partially cooled and enough mineral oil of suitable viscosity is blended with the soap to form the desired grease composition. The mixture is then additionally agitated while still warm. In order to prepare a grease of good texture and for thorough dispersion of its components the composition may be passed through a colloid mill or other simi- The grease may then be deaerated specific example, the finished grease composition may contain about 5 to 25% of the lithium soaps of the microcrystalline wax acids blended with a lubricating oil comprising a heavy mineral oil of 1100-1400 seconds S. U. V. at 100 F.

(80 seconds at 210 F.) having a gravity of about 23 to 25 API and a maximum pour point of about F. I

When the grease is prepared by saponifying the microcrystalline wax acids in the presence of the oil, a heavy sponge of fibrous structure results. 'Such greases are called fiber greases.

Preparation involves adding the acid and saponifying materials to the oil, reacting the entire mixture at elevated temperatures with accompanying agitation and then cooling the mixture.

Suitable materials or substances may be compounded into the grease to affect its structure or properties in any desirable way. Generally, the

principal constituent of the finished grease in amount will be a suitable lubricating oilstock. 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 an S. U. V. of 300 seconds and more at 100 F. Usually the lubricating oil stock is a mineral oil, although other oils may 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 maybe 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 wax acids we use in compounding the improved'greases according to our invention are,

4 as we 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. Besides the carboxylic group, the acids may contain other groups such as lactcnic 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 highly satisfactory nature of the novel grease compositions according to our invention appear to reside largely in the unique structure and characteristics of the synthetic microcrystalline wax acids. In particular, the long chain length, water insolubility and the interlacing structure formed with oils that are susceptible to gellation are very useful in manufacturing the greases. In addition, it our belief that these wax acids possess certain of the favorable properties that characterize 12-hydroxy-stearic acid, such as perhaps location of a hydroxy radical in the carbon chain although we have not been able to ascertain this positively. The hydroxy group, among other things, apparently tends to prevent granulation of and oil seepage from the finished grease.

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 andabcut,0.l to 4.0% by weight of an oxidation catalyst at a temperature in excess of about C. for a period of time sufficient 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 impurities. 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.

carbon atoms.

"structuremay 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 microcrystalline wax to be oxidized maybe composed of molecules contaming very similar or identical numbers of 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 Car 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 inelude those dispensable in microcrystalline wax such as maganese salts, ammonium vanadate and potassium permanganate. The use of potassium permanganate, present in amount of about 0.1 to 1.25 per cent by eigon 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 pg'oducts heterogeneous, inconsistent and stringy in appearance and poor in color. Oxidation catalyst promoters or sensitizers ma 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. 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 -20%'by Weight solution. The water. is removed prior to reaction by applying heat, say by heating the mixture to 1 15-1550 0., 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 10 to 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 as to 55 carbon atoms per molecule is oxidized in the presence of potassium permanganate and 0.1 to 1.5% 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 con version 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% bywe'i'ght on the'wax of the acid composition prepared in a prior run is added. Although the seedmay 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 catalyst in aqueous solution and commencing oxidation. After the catalyst is added, the oxidizing gas. may be added at reaction conditions. Ifthe catalyst is added in aqueous solution, the solvent water may be re moved by evaporation before reaction, as by heating to 145 to 150 C., if desired. Also, as is the case with the catalyst, additional seed may be added during the course of the reactionto 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 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 or he reaction mixture in the presence of oxygen, either in pure form or in admixture with inert diluents, say as air. The oxygeniis added in at least the stoichiometric amount for a period of time sufficient to effect complete conversion. Ad vantageously, the oxygen is used in considerable excess of the stoichiometric quantity which re duces time yet results inf-a very favorable prod uct. It is preferable to add oxygen, considered as substantially pure oxygen, in amounts in the iii range approximating 30 to 50 liters pe1"'lilo: grain of wax per hour. An amount of about 2-5 to 6:5 liters per hour of oxygen per kilogram of wax 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. 6., over 50 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 necessary for minimum reaction periods. 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 to C. afford 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 rate also. 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 complete conversion as well as a greater degree of cleavage. However, theprolonged period of oxidation is generally at least 30 to 40 hours and reaction time as long as 200 to 300 hours are encountered.

After substantially complete conversion has been effected, the reaction mass essentially comprises a mixture of Wax acids containing a substantial 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 andcatalyst material. The C18 plus acids may beobtained in pure form by washing the solid mixture free of inorganic materials with water and/or an. inorganic acid, such as hydrochloric acid, and then distilling the mixture to separate out the higher acids. For example, the acid mixture is first washed by adding water and hydrochloric acid. The acid-water layer which separates out is removed. The product may be washed again as with water alone, the water removed after another settling period and the product blown with air to evaporate any remaining water. The washed product is then distilled to remove the substantially pure Cm plus wax acids. This. may be accomplished by flash distillation in the presence of steam or under high vacuum, or by molecular distillation, in the usual manner. For instance, employing flash distillation, the charge stock is preheated and distilled at elevated temperatures under low pressure, advantageously as low as practicable, e. g., 1.5 to S-millimeters of mercury. By distilling at temperatures in the range of 150 to 300 C. the lower acids in the reaction mixture are taken oii first.

By then flash distilling over about 300 0., and

in regulated increasing increments of distillation temperature, successively higher molecular weight fractions over Cm are taken ofi as desired. For instance, the higher molecular weight acids may be separated into a number of fractions, such as into a lower fraction containing C19 to C23 wax acids, having saponification numbers in the range of about 195 to 155; an intermediate iraction containing Cu to C34 acids, having saponification numbers in the range of 154 to and a high fraction containing C35 and higher acids, having a saponification number of about 109 and lower.

In place of the distillation procedure for separating the pure 018+ wax acids from the crude reaction product, the pure acids may be recovered by extracting the reaction product with a selective organic solvent selected from the class consisting of the saturated hydrocarbons containing three to twelve carbon atoms per molecule. Propane, butane, iso-pentane and n-pentane are exemplary of such solvents. This improvement is disclosed in the copending application of John Walter Nelson, Serial No. 169,215, filed June 20, 1950.

We claim:

1. A grease composition comprising a lubricating oil thickened by the soaps of a high molecular weight microcrystalline wax acid mixture produced by substantially complete oxidation of microcrystalline wax containing 34 to 55 carbon atoms per molecule which is characterized by extreme water insolubility and by a saponification number less than about 200 and which predominates in monocarboxylic acids having an apparent chain length exceeding eighteen carbon atoms per molecule.

2. A grease composition'according to claim 1 wherein the soaps of a microcrystalline wax acid mixtureare in admixture with soaps of other organic acids.

JOHN WALTER. NELSON. JOHN W. TETER.

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

UNITED STATES PATENTS Number Name Date 2,029,619 James Feb. 4, 1936 2,043,923 Burwell June 9, 1936 2,119,940 Carr June '7, 1938 OTHER REFERENCES Warths book, The Chemistry and Technology of Waxes," pp. 242 and 252, 1947.

Claims (1)

1. A GREASE COMPOSITION COMPRISING A LUBRICATING OIL THICKENED BY THE SOAPS OF A HIGH MOLECULAR WEIGHT MICROCRYSTALLINE WAX ACID MIXTURE PRODUCED BY SUBSTANTIALLY COMPLETE OXIDATION OF MICROCRYSTALLINE WAX CONTAINING 34 TO 55 CARBON ATOMS PER MOLECULE WHICH IS CHARACTERIZED BY EXTREME WATER INSOLUBILITY AND BY A SAPONIFICATION NUMBER IN MONOCARBOXYLIC ACIDS WHERE PREDOMINATES IN MONOCARBOXYLIC ACIDS EIGHTEEN CARBON ATOMS PER MOLECULE.