US2417428A - Lubricating composition - Google Patents

Description

Fatentecl 18, 194? OFFICE LUBRICATING COMPOSITION Lester W. McLennan, El Cerrito, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California No Drawing. Application September 19, 1946, Serial No. 697,911

16 Claims.

This invention relates to lubricating composi tions containing metal soap complex" and processes for their production and is a continuationin-part of my copending applications, Serial Nos. 586,028, 586,029 and 586,030, which in turn are continuations-in-part of my prior application, Serial No. 469,894; Serial No. 588,719 which is a continuation-in-part of my prior application Serial No. 473 217 and Serial No. 589,941.

The object of the invention is to obtain all the benefits in such lubricants and greases as are peculiar to metal soap complexes. Such complexes produce stable greases which have excellent melting point and penetration characteristics, do not require hydration, have exceptional resistance to deterioration by the action of heat and by the action of moisture, including boiling water, and generally have unusual thickening effects on lubricating oils, even at relatively low concentrations. An especialy important fact is that in general stable greases are formed with high viscosity oils of both paraflinic and naphthenic types. Another object of this invention is to provide processes for the manufacture of basic metal soap lubricants.

By the term metal soap complex as used in this application, it is meant to include products which are substantially neutral or substantially free from readily titratable excess alkalinity, at least beyond a relatively small amount; and in which the ratio of equivalents of combined metal to equivalents of saponified higher molecular weight organic acids is greater than 1.1 to 1 and preferably is greater than about 1.2 to 1. De-

pending upon the particular saponifiable material, saponification reagent and upon the characteristics of the mineral oil employed, it is preferred that this ratio be between about 1.2 to 1 and 2 to l but it may be as high as 3 to 1 or even as high as 4 to 1.

By the term normal metal soap as used in this application, it is meant to include those products which result when one equivalentof a metal hydroxide or other basically reacting metal compound is reacted with one equivalent of a saponifiable material to form a soap, said soap being the normal metal salt of the higher molecular weight organic acid, present as such or derivable by saponification from thesaponifiable material.

By the terms saponification reagent, base, basic metal compound or basically reacting metal com pound used herein, it is meant to include the various oxides, hydroxides and/or hydrated oxides of those metals which will form salts or soaps with fatty acids, such as stearic acid, oleic acid, etc.

Among others the terms saponification reagent, base, basic metal compound or basically reacting metal compound will include the oxides, hydroxides and/or hydrated oxides of the "strongly basic metals, namely, the alkali metals, i. e., lithium, sodium and potassium and the alkaline earth metals, i. e., calcium, strontium and barium and the weakly basic metals, such as the metals of the right hand column of group II of the periodic table, i. e., beryllium, magnesium, zinc and cadmium, the metals of the right hand column of group III, i. e., aluminum, indium and gallium, the metals of the right hand column of group IV, i. e., lead, tin and germanium, the metals of the left hand column of group VI, i. e., chromium and molybdenum and the metals of the iron group of group VIII, i. e., iron, cobalt and nickel. The periodic table referred to is that form of Mendeleeffs periodic arrangement of the elements shown in Handbook of Chemistry and Physics, 25th edition, 1941-1942, pages 308-309.

Examples of saponifiable materials containing higher molecular weight organic acids present as such or readily derivable therefrom by saponification include fats such as tallow, lard oil, hog fat, horse fat, etc., higher molecular weight organic acids such as stearic acid, oleic acid, the higher molecular weight acids resulting from the oxidation of petroleum fractions (for example, parafiin wax and mineral oil), rosin and related products, higher molecular weight naphthenic acids, sulfom'c acids, etc., and saponifiable waxes such as beeswax, sperm oil, degras, etc.

The present invention resides in lubricating compositions, especially greases, which contain metal soap complexes which are substantially neutral or substantially free from readily titratable excess alkalinity. While the invention may be extended to freely fluid lubricants, such as Diesel engine lubricating oils containing small proportions of metal soap complexes, it includes more particularly the use of such metal soap complexes in proportions to thicken lubricating oils appreciably for the purpose of producing liquid greases or solid greases of varying consistencies. More articularly, the invention resides in mineral oil lubricants containing thickening proportions of metal soap complexes where the ratio of equivalents of combined metal to equivalents of saponified higher molecular weight organic acids is between about 1.2 and 2, although it extends to the upper limit above indicated, 1. e., 4 to 1, and may be as low as 1.1 to 1. Especially stable metal soap complex greases have been found to have a ratio within the range of 1.3 to 1 and 1.9 to 1. The invention also comprises the method oi! making such lubricants.-

The invention also includes the use of metal soap complexes to produce lubricants employinghigh viscosity mineral oils, ,e. g., 50 or 70 S. A. E.

grade or even bright stocks as well as lower visconditions it is possible to react one equivalent weight of a saponifiable material (as determined by its saponlflcation number) with more than about 1.1 and up to about twice the equivalent.

weight (or even up to a ratio of 4, as above in-' dicated) of a saponiflcation reagent such as a basically reacting metal compound, for example,

a metal hydroxide .or hydrate, at elevated temperatures in the presence of oxygen and preferably in the presence of a polar solvent such as water, to produce a material which is substan-- tially neutral or free from readily titratable excess alkalinity. Similarly it is possible to react 1 equivalent weight of a normal soap with more than about 0.1 and up to about 2 equivalents, or

even as high as 3 equivalents of a'basically reacting metal compound to produce a material which is with strontium hydroxide. Thi complex has a diflerent solubility in oil than normal strontium soap alone but still contains the strontium hydroxide in a readily titratable form.v It is probable, therefore, that the material actually undergoing oxidation is the normal metal soap-metal hydroxide complex.

One of the principal oxidation products which results when one equivalent of a fat, saponifiable wax, or a higher molecular weight saponifiable organic acid is reacted with about 1.1 or more equivalents of a basically reacting metal compound under the conditions as disclosed in the present invention and illustrated in the subsequent examples, is acetic acid present in the final product as metal acetate. In addition, appreciable amounts of carbon dioxide and relatively smaller amounts of other low molecular weight carboxylic acids, such as formic acid, propionic acid, oxalic acid, etc.,,also. appear to be formed and are present in the final product as the corsubstantially neutral or free from readily titrat-f able excess alkalinity. This reaction is carried as described herein.

In preparing greases the above-described-reae 40 tion may be carried-out in the presence of a part or all of themineralbii be employed injthe final productzunderdahese'eonditions the mineral out inthegres'ence of oxygen and will preferably be carriedout in the'presence of a n'elar solvent;

responding metal salts.- of oxidation coming within the scope of the present invention, metal carbonatemay be the principal salt formed and may be preferred for certain combinations of mineral oil and saponifiable materials. V

I have also discoveredthat metal soap complex greases having some of the desirable prop erties of metal soap complex'greases formed by reacting, for example, 2.0 equivalents of a basically reacting metal compound with one equivalent of a fat, saponifiable wax, 'or a higher molecular weight saponiiiablaorganic acid, can be ob-- tained'by-mixin'g one-moi of the normal metal of the same fat, saponifiable wax, or higher molecular weight saponifiable organic acid with lubricating (oil, adding one. moi of an aqueous solution of: metal acetate and then heating to an elevated. t

a perature to eiTect dehydration and "dispersion in. the lubricating oil. Also, greases,

even more closely resembling those obtained by reacting about 2.0 equivalents, of a basically reoil appears toserve essentially as an inert dil'uent. On the other hand, the 'saponifiiablema terial can be reacted withthe saponiflcation, re-

agent in the absence of mineral oil thereby form ing a "concentra which can be subsequently compounded with mineral oil to form a grease.

The purposes of the polar solvent, oxygen and excess saponification reagent will become evident in the following disclosure.

Although I do'not wish to be limited by the theories advanced herein, the net reaction which appears to occur and which results in the formation of the improved greases forming the subject of this invention is the oxidation of a portion of the saponiflable material and reaction of the excess saponiflcation reagent with the acidic products formed. It is likely that the initial reaction which occurs is the formation of a normal metal soap by the saponification of the saponifiable material with an equivalent amount of the basically reacting metal compound. Subsequently, a portion of the normal soap which may be in the formof a soap-base complex is oxidized by oxygen and the excess basically reacting metal compound present combines with the acidic materials formed. The character of the oxidation reaction which occurs is undoubtedly influenced by the presence of the excess basically reacting metal compound and by the presence of a polar solvent, such as water or glycerine. In this connection evidence has been obtained indicating that in the presence of a polar solvent such as water, normal strontium soap forms a complex lactin's' metal compound itn e equivalent r r a fat, 's'aponifiable wax, or higher molecular weight --Isaponifiable organic acidyand having substan- "tially all of the desirable characteristics of those vgreases have beenobtaine d by combining v one "mol of a normal metal soap'ofthe same fat, sa. ponifiable ,wax, or higher molecular weight saponifiable organic acid with 0.5 mol of metal acetate and 0.5 mol of metal carbonate and dispersing the resultant product in lubricating'oil.

I have also discovered that metal soap complex greases can be formed, not only by the addition of normal metal soap and metal acetate to a lubricating oil or normal metal soap, metal acetate, and metalcarbonate to lubricating oil, but also by compounding normal metal soap, lubricating oil, and a variety of other metal salts.

Metal salts which are useful for the foregoing purpose include preferably the simple reaction products resulting from the combination of one equivalent of a metal oxide orhydroxide, with one equivalent of a mineral acid or of an organic acid of relatively low molecular weight. However, I may also employ acidic or basic salts in which one equivalent of metal oxide or hydroxide has been reacted with more or less than one equivalent of a mineral acid or acid anhydride such as sulfuric acid, hydrochloric acid, orthophosphoric acid, pyrophosphoric acid, sulfurous acid, carbonic acid, boric acid, thiosulfuric acid, etc., S02, S03, 002, etc. I-may also employ metal salts of organic acids of relatively Under some conditions low molecular weight which are relatively insoluble in lubricating oil. As examples may be cited the metal salts of monocarboxylic and polycarboxylic acids containing less than about '7 carbon atoms per molecule, such as formic, acetic, propionic, valeric, oxalic, malonic, succinic, etc., acids, the low molecular weight alkyl and aryl sulfonic acids, the low molecular weight substituted carboxylic acids, such as glyceric, glycolic, thioglycolic, etc., acids, the low molecular weight phenolic and thiophenolic compounds such as phenol, cresol, thiophenol, etc.

In the case of greases coming within the scope of the present invention, I prefer to employ a complex of a normal metal soap with a metal carbonate -or with a metal salt of a monocarboxylic acid having less than about 7, carbon atoms or a mixture of any two or more of such complexes, either as such or in admixture with normal metal soap. In the case of greases to be used under acidic conditions, such as are encountered in the canning industry, it may be desirable to employ a complex of a normal metal soap with a metal oxide, or hydroxide in conjunction with the preferred complexes listed above. It is also within the scope of my invention to incorporate an alkaline-type filler, such as zinc oxide in the finished grease in order to overcome the efiects of any acid liquors with which the greases may come in contact. In accordance with the present invention of using as lubricants metal soap complexes compounded in mineral oil, I prefer to employ more than 0.1 equivalents and preferably more than 0.2 equivalents and desirably between 0.3 and 0.9 equivalents and as high as 2.0 equivalents or even as much as 3.0 equivalents of a metal salt in conjunction with one equivalent of a normal metal soap as the metal soap complex to be compounded with mineral oil to form the lubricants of the present invention.

It is not meant to intimate that any given metal salt is the full equivalent of any other metal salt of the same or different metal for modifying the characteristics of a dispersion of normal metal soap in lubricating oil. In fact, the complexes of various metal salts with a given normal metal soap vary over a wide range as regards their respective solubilities in a given mineral lubricating oil. For example, a normal metal stearate-metal carbonate complex is more solu ble in a given mineral oil than is a normal metal stearate-metal formate complex. Likewise, the latter' complex appears to be more soluble than one formed from normal metal stearate and metal acetate. Complexes of a given normal metal soap with certain metal salts will possess just the proper characteristics to form with a specific mineral oil a grease of the improved properties described herein. Other complexes of the same normal metal soap with different metal salts will be either too soluble or insufliciently soluble to form desirable greases in the given mineral oil. In the latter case it is possible and desirable to form excellent greases coming within the scope of the present invention by mixing a complex which is too soluble in the specific mineral oil with one possessing inadequate solubility. The exact proportions of the two complexes will depend upon the relative solubilities of the two complexes and can be readily determined by one skilled in the grease-making art.

It has also been noted that even though the final grease is to be substantially anhydrous, a product of improved characteristicscanoften be obtained by adding a small amount of water, for example, in the range of 0.1 to 3.0% by weight or even as high as 10% by weight of the grease charge at a suitable temperature and subsequently increasing the temperature to effect substantially complete dehydration. The grease may be at a temperature of about 210 F. or less when such Water additions are made, although temperatures as high as 230 F. or even as high as 300 F. or higher may be used, and subsequent dehydration has been accomplished by heating to temperatures in the neighborhood of 250 F. or higher when necessary. With certain saponification reagents the greases produced by the processes of the present invention have a granular appearance, but by employing the hydration-dehydration technic, products of smooth buttery texture are obtained often accompanied by an increase in consistency and melting point. Fur-- ther improvements in grease texture can likewise usually be obtained by working the grease at temperatures below about 200 F. and preferably below about F. prior to final packaging.

Normally in reacting a saponifiable material with an excess of a basically reacting metal compound the extent of the oxidation reaction is controlled so as to produce a final grease which is substantially neutral or free from readily titratable excess alkalinity, that is, one having a free acid or free alkali content less than about the equivalent of 5.0 mg. KOH per gram of soap present. In other Words, the oxidation is so controlled that it results in the formation of at least about 0.1 equivalent of acidic oxidation products and preferably about 0.2 to 1.0 equivalent of acidic oxidation products or even as high as about 3.0 equivalents of acidic oxidation products. The

progress of the oxidation reaction can be followedby periodically titrating to determine the proportion of metal hydroxide present in the reacting mass, which was not combined with acidic oxidation products and when this has reached the desired value, the oxidation may be arrested such as by rapidly cooling to a temperature below about 250 F. to 300 F, While it is preferred that the soaps in greases of this invention be substantially neutral, they may contain a small amount of free acidity or alkalinity. The finished grease may have a free alkali content calculated as metal hydroxide as high as about 0.5% by weight of grease or a free acid content equivalent to about 2.0 mg. K0 per gram of grease. A grease having a free acid content may be obtained by either continuing the oxidation to produce an excess of acidic reaction products over that required to neutralize the free metal hydroxide or the oxidation reaction can be stopped at an earlier stage, such as while free metal hydroxide is still prescut, and fatty acid or other acidic materials added in sufficient quantity to give a grease of the desired free acid content. In order to obtain a free alkali content the oxidation can be stopped at an intermediate point or it can be continued to produce a substantially neutral oreven acidic soap and the desired excess of .free hasically reacting metal compound then added.

Usually the hydration-dehydration technique to produce a final substantially anhydrous grease is most effective on a slightly acidic grease. Subsequently the grease can be adjusted to the desired acidity or alkalinity by the addition of metal hydroxide or acid, as the case may be. In a similar manner metal soap complex greases prepared by compounding normal metal soaps with metal salts can be rendered acidic or alkaline as de- 7 i sired by adding fatty acids or other acidic materials or metal hydroxide or otherbasically reacting metal compounds, as the case may be.

Free alkalinity is measured in accordance with A. S. T. M. method of test No. D-128-40, section temperatures favor the formation of metal: salts of low molecular .weightcarboxylic acids'so that 18, except that titration is conducted in the cold and the titration is made directly with standard HCl solution rather than byadding an excess of HCl solution and then back titrating with alcoholic'potassium hydroxide solution; Free acidity is measured in accordance with A. S. T. M. method of test No. D-128-40, section 20. Briefly, the methods of test employed are as follows:

A 10 gram sample of the grease is weighed to the nearest tenth of a gram into a 250 ml. Erlenmeyer flask. To the flask is then added 75 ml. of petroleum ether and 50 ml. of 95% alcohol containing phenolphthalein indicator, which has been previously made neutral as indicated by the phenolphthalein indicator. The flask is stoppered and shaken vigorously in the cold until the grease has completely disintegrated and no lumps remain. The solution is then allowed to settle and free alkali or free acid, as observed by the color of the alcoholic layer, is titrated carefully in the cold to the phenolphthalein end point with 0.5 normal H] or alcoholic KO H, as required. Free alkalinity is calculated in terms of metal hydroxide; free acidity in terms of oleic acid or acetic acid. Free alkalinity and free acidity may also be expressed in terms of equivalent mg. of KOH per gram of grease or soap as desired.

Since the formation of metal soap complexes from a fat, saponifiable wax or higher molecular weight saponifiable organic, acid and an excess of a basically reacting metal compound involves an oxidation reaction, it is necessary that this reaction be conducted in the presenceof air or other oxygen-containing gas. The oxidation may be eifected in open kettles at ordinary atmospheric pressure in which case air or oxygen may be blown into the kettle charge or the charge may be aerated by agitation designed to incorporate sufficient amounts of air into the kettle charge to effect the desired oxidation. The open kettle method is generally employed in those instances in which the ingredients selected have an affinity for the polar solvent and can retain the required proportions of polar solvent to promote the desired reactions at the temperatures employed. In

some instances, however, and particularly when the reactions are slow or when the reacting mass will not retain suflicient polar solvent, the saponification and the oxidation may be conducted under superatmospheric pressure in a closed ket-' tie to which the necessary polar solvent and oxygen or oxygen-containing gases are supplied. 0peration in a closed vessel generally permits closer control of the oxidation reaction because in this case the evaporation. of polar solvent can be prevented and the quantity of oxygen employed can be closely regulated. Moreover, the use of superatmospheric pressures, such as are obtainable in closed kettles, generally permits a reduction in the temperature required to efiect the desired oxidation.

The oxidation is conducted preferably at temperaturesbetween about 300 F. and 550 F., however, the particular temperature employed in any given case will depend upon other conditions, such as pressure, the particular saponiflcation reagent and saponifiable material employed and upon the amount and character of the mineral oil employed. In general, the higher temperatures favor the formation of metal carbonate and lower it is possible by control of temperature to vary the relative proportions .of soap-carbonate and s0aI carboxylate complexes in the oxidation product.

indicated herein'above, in order-for the desired'oxidation' reaction and nonnal metal soapmetal salt complex formation'to proceed within the preferred temperature range it is desirable.

that at least a small percentageof a polar sol-. vent, in the neighborhood of at least about 0.1%

by weight of the reacting mass, be present. Further, it appears that preferably this polar solvent should be water, although under some conditions and particularly in the case of oxidizing alkali metal soaps in the presence of alkali metal hydroxide the oxidation and complex formation proceeds more readily in the presence of amixture of water and glycerine, water and glycol, or

with some hydroxy or polyhydroxy organic compound, such as ethyl alcohol, diethylene glycol, etc. Preferably the proportion of polar solvent present should be in the range of 0.5% to 4.0% by weight of the reacting mass, but under some conditions smaller quantities, such as about 0.1% and higher quantities, such as about 10% can be used. As an indication of the desirability of having at least a small percentage of a polar solvent present, I have observed in the case of certain an- I hydrous normal strontium soaps that when mixed with anhydrous strontium hydroxide and heated in the presence of oxygen at a temperature of 350 F. to 500 F. for three hours and the'mixture subsequently analyzed, it was found that little or no reaction had occurred and substantially all of the strontium hydroxidecould be recovered unchanged. Further, if the same mixtures containing an added 0.5% of water were heated in a closed kettle under the same conditions'but with oxygen excluded, little or no reaction was observed to take place. However,

when the same mixture containing 0.5% of added water was heated for three hours in contact with" air or oxygen and at a temperature of 350" F. to

500 F., the resulting product contained normalstrontium soap along with strontium carbonate and the strontium salts of organic acidic oxidation products, and a corresponding amount. of the strontium hydroxide had disappeared.

One of the preferred methods of forming metal soap complex lubricants from a normal metal soap, a metal salt, and mineral oil is to dissolve the normal metal soap in all or only a portion of the mineral oil to be used and subsequently add a solution or a dispersion of the desired metal salt or metal salts in a polar solvent, intimately mix and then while continuing the mixing boil oil. or evaporate all or a portion of the polar solvent. Additional oil can be added during or after the removal of the polar solvent, if desired. The normal metal soap can be preformed or it can be made in the presence or absence of the mineral oil by reacting a saponifiable material with a basically reacting metal compound, by methods known to those skilled in the art.

Another preferred method of forming a metal soap complex lubricant from a normal metal soap, a metal salt, or salts, and mineral oil is to dissolve the desired normal metal soap in mineral oil or form the normal soap from the desired saponifiable material and a basically reacting metal compound in the presence of all or a part of the desired mineral oil. Subsequently, a complex is formed between the normal metalsoap and metal oxide or hydroxide, added in an amount equivalent to the amount of salt which it is desired to complex with the normal metal soap, in the manner described in the preceding paragraph, except that the polar solvent