Method of preparing finely divided solid metal salts

United States Patent Office

3,178,367

Patented Apr. 13, 1965 iZa

3,178,367

METHOD OF PREPARING FINELY DIVIDED SOLID METAL SALTS

Alan S. Dubin, Cincinnati, Ohio, and Jerome Panzer, Roselle Park, N.J., assignors to Esso Research and En- 5 gineering Company, a corporation of Delaware

No Drawing. Filed Jsme 12, 1961, Ser. No. 126,401

Claims. (Cl. 252—17)

This invention relates to a method of preparing finely divided solid metal salts. Particularly, the invention re- ¹⁰lates to a method of preparing finely divided metal salts of inorganic mineral acids and C₂ to C₄ fatty acids.

Metal salts such as calcium acetate, trisodium phosphate, calcium sulfate, sodium nitrite, etc. are very desirable in the preparation of fluid lubricants and lubricating greases. Such salts impart to oil, extreme pressure, antiwear, rust prevention, oxidation inhibition and other desirable properties, depending upon the particular salt used. Because of the insolubility in oil of metal salts of low molecular weight fatty acids and inorganic acid salts, it had been generally necessary to use either surfactants or, more frequently, salts and soaps of higher fatty acids (e.g., C₇ to C₃₀ fatty acids), as suspending agents to maintain the salt of the invention dispersed in the lubricating oil. Also because preformed commercial salts are rather coarse, when directly dispersed in the lubricating oil, the resulting composition is gritty and has poor structural stability. Because of this, it has become the usual commercial practice to form the salt in situ in the lubricating ,,θ oil by neutralization of acid with a metal base in the presence of a dispersing agent, e.g., a soap of a higher fatty acid.

This in situ preparation has several disadvantages. Specifically, it requires long heating periods and very precise control of manufacturing variables to achieve the proper particle size distribution. Furthermore, an exactly neutral product is difficult to achieve in large-scale preparations. For example, if an excess of metal base is used, the free alkali will tend to react with carbon dioxide from the air to form a carbonate, which will usually tend to make the lubricant gritty and to form a crust upon storage. On the other hand, an excess of acid will usually impair the structural stability of the lubricant to give it a false hardness (in the case of greases), which 4.5 then disappears upon working or upon exposure to shearing stresses. This latter phenomenon is believed to be caused by hydrogen bonding of the free acid, which bonds break upon shearing. If the manufacturing is not very carefully controlled, the particle size of part, or all, of the _g0salt may be too large. This, in turn, may make the grease gritty, give rise to sedimentation of fluid lubricants, or reduce the thickening effect or antiwear properties of the salt as compared with a similar lubricant containing a more finely divided salt. 55

It has now been found that it is possible to prepare metal salts of exceedingly fine particle size (e.g., 2 microns or less) from the preformed, coarse commercial salts. These salts, which have an exceedingly fine particle size, may be then dispersed or absorbed in a base oil or can be passed directly in to the base oil. By utilizing these novel techniques, the long heating times and control previously found necessary for the in situ formation of salts can be avoided and much finer particle size obtained.

Briefly, the technique of the invention involves dissolving the metal salt in an aqueous or polar solvent and adding such solution to a second solvent which is completely miscible with the first solvent. However, while the salt is soluble in the first solvent, the salt is insoluble in the combination or mixture of the two solvents. While it is known to form finely divided metal salts by in situ neutralization in a medium in which the reactants are soluble and .the resulting product is insoluble, it is believed new to use a technique to obtain such finely divided metal salts where the preformed salt is soluble in one solvent but insoluble in a combination of two solvents.

If the finely divided metal salt remains in contact for a long enough time with the solvent mixture (in one component of which it is very soluble), particle growth will occur. This particle growth can be minimized by selection of appropriate solvents, proportions of solvents, and conditions of contact between the solvent and oil phases. Using a relatively large proportion of the solvent in which the salt is insoluble results in rapid nucleation of small crystals. Rapid transfer of the salt particles from the solvent phase to the oil phase followed by rapid separation of the solvent phase from the oil prevents particle growth. The particular conditions necessary to ensure small particle size will be readily apparent to one skilled in the art.

An additional feature of this invention resides in the use of protective colloids in the solvent mixture. The protective colloid forms a coating around the tiny salt particles as soon as they are precipitated. This coating effectively curbs any tendency towards further particle growth. An advantage in using protective colloids is that rapid transfer from the solvent phase to the oil phase is not so important to insure a small particle size. Thus, the salt particles coated with a protective colloid may be stored without increased particle sizes resulting. Protective colloids are desirably utilized in proportions of from .01 to 10, e.g., 1 to 5 wt. percent based on the weight of the salt. Protective colloids are well known in the colloidal art and include such materials as gelatin, carboxymethylcellulose, silica gel, organic surfactants which are insoluble in the solvent phase, and the like.

In general, there are two distinct approaches which can be utilized in order to carry out the process of the invention so as to obtain finely divided metal salts in a hydrocarbon oil medium. In the first approach a gel, or sol, is formed initially and then contacted with a base oil which contains a surfactant. The finely divided thickener particles are then incorporated into the oil phase. The second basic technique is to add the metal salt dissolved in the first solvent to the second solvent which has been already added to the oil base and a surfactant. After formation of the finely divided particles, the mixture is distilled, preferably under vacuum, and the first solvent and second solvent come off, usually together as an azeotropic mixture. The finely divided solid metal salt is left dispersed in the base oil to form a greaselike mass.

The metal component of the salts of the invention may be any metal. However, for lubricant manufacture the metal will preferably be an alkali metal including sodium, lithium, and potassium or an alkaline earth metal such as calcium, strontium, or barium. Metals such as iron and aluminum are also used in lubricants.

Suitable acid reactants for forming the salt include C₂to C₄ fatty acids such as acetic, propionic, butyric acids and anhydrides; as well as inorganic mineral acids such as phosphoric, hydrochloric, nitric, sulfuric, etc.

The base reactants include hydroxides, carbonates, and oxides as well as various organic bases which will react with the aforesaid acids to form the desired salts. Among these latter bases are: alkoxides such as NaOCH_s and LiOC₂H₅; quaternary ammonium compounds such as (CH₃)₄NOH; and other nitrogen bases such as hydrazine and guanidine. Salts produced from the above reactants include calcium acetate, sodium chloride, trisodium phosphate, etc.

Solvents should be selected so that the first solvent is one in which the metal salt is soluble, preferably greater

3,178,367 than 15% by weight at the temperature of mixing. The second solvent is one which, when admixed with the first solvent, produces a solvent mixture or blend in which the metal salt is extremely insoluble, preferably less than 1% by weight at the temperature of mixing. The metal 5 salt may be soluble per se in the second solvent. However, the important considerations are that the metal salt is insoluble in the combination of two solvents and that the two solvents are miscible with each other. Suitable solvents include water, alcohols, ketones, pyridine, di- 10 oxane, and other solvents. The appropriate selection of first and second solvents depends on the specific metal salt to be used and on their mutual miscibility. If an aerogel is to be formed of the salt the combination of solvents preferably should form an azeotropic mixture and should 15 be volatile and have a critical point of less than 700° F., preferably less than 500° F. An aerogel is a gel in which the continuous phase is air (in contrast to a gel in oil in which oil is the continuous phase). The most essential requirement for the solvent mixture is that it 20 show no solubility for the metal salt and desirably should be inserted and, as stated above, in the case of aerogels be volatile and have a low critical temperature.

Surfactants which may be used in the techniques of the invention are those which preferably are soluble or 25 dispersible in the solvent mixture and oil and which will effectively maintain the salt dispersed in lubricating oil. Examples of such surfactants include simple metal salts of C₇ to C₃₀ fatty acids, especially the alkali metal and the alkaline earth metal salts. Specific examples of such 30 surfactant salts include calcium stearate, calcium laurate, lithium oleate, barium myristate, etc. Other surfactants that may be used include nonionic and ionic surface active agents which are commercially available under trade names of Pluronics, Ethomeens, Ethomids, Ethofats, etc. 35

Other effective surfactants are mono and dialkylolamides of C₉ to C₂i fatty acids. These materials have the general formula:

^{0 R}' an

II I ⁴⁰

R—C—N—R0H wherein R is a C₈ to C₂₈ alkyl group of a saturated fatty acid, R' is hydrogen or —ROH. and R is a C₂ to C_o, ^e-g-> C₂ to C₃, aliphatic saturated hydrocarbon radical. The hydroxyl group will generally be attached to the ter- 45 minal carbon atom, although it may be attached to other carbon atoms of the R hydrocarbon group. Specific examples of such materials include N,N-di-(2-hydroxyethyl) lauramide; N-2-hydroxyethyl lauramide; N-6-hydroxyhexyl stearamide and N,N-di(3-hydroxypropyl) laur- 50 amide.

Particularly effective surfactants are alkyl phenoxy polyoxy ethylene alcohols and ethers of the general formula:

<img file="US3178367A_D0001.tif" />

wherein R, R' and R are hydrogen or Ci to Ci₂ alkyl ₆₀groups and n is about 5 to 30. Various compounds of this type are obtainable from the General Aniline and Film Company as members of the Igepal series.

Lubricating oil compositions that can be prepared with the salts of the invention will contain about 2 to 50, 55 preferably 3 to 35 wt. percent of salt dispersed in oil. The oil can be either mineral oil or a synthetic oil. Generally, about 0.03 to 10 and preferably 0.05 to 5 wt. percent, based on the weight of salt, of surfactant will also be present. 79

Various other additive materials may also be included in the compositions of the invention in amounts of about 0.1 to 10.0 wt. percent based on the total weight of the composition. Examples of such additives include oxidation inhibitors such as phenyl-alpha-naphthylamine, tacki- 75 ness improvers such as polyisobutylene, corrosion inhibitors such as sorbitan monooleate, sodium nitrite and lanolin, dyes, VJ. improvers, thickeners, and the like.

The final lubricant can be homogenized in a Morehouse mill, a Gaulin homogenizer, etc. If a fluid lubricant is desired, it is generally more convenient to first form a concentrate and then dilute it with additional oil to form the final product.

The invention will be further understood by the following examples.

Example 1

To a beaker containing 400 ml. of a 15% aqueous solution of calcium acetate, the percent being a weight percent and based on the weight of the water, were added 200 ml. of acetone.' A “mixed solvent” gel precipitated immediately. Into this gel mass was poured a solution of 5 gms. of a surface active composition comprising 36 wt. percent of P₂S₅ treated polybutene, 32 wt. percent of a high alkalinity nonylphenol sulfide and 32 wt. percent of a high alkalinity Ca sulfonate in 200 gms. of a naphtenic refined mineral oil having a viscosity of 40 SUS at 210° F. After being stirred for a few minutes, the mixture was poured into a separatory funnel and the water and acetone layer was allowed to settle and was drawn off. The oil was then poured into a beaker and heated until all the entrained water and acetone had been driven off. A dark, stable semifluid mass resulted. This mass showed no precipitation of calcium acetate at the end of three days. Electron micrographs showed that 65% of the particles were less than l/x in size.

Example II

The procedure of Example I was repeated exactly except that methanol was employed in lieu of acetone, heptane was employed in lieu of the refined mineral oil having a viscosity of 40 SUS, and oleic acid was employed as the surface active agent. The result was a transparent, fluid sol which showed no calcium acetate precipitation at the end of three days. Electron micrographs showed that 90% of the particles had a particle size less than 0.2/z.

Example III

Four pints of pyridine were placed in the bowl of a Hobart mixer and heated to boiling, that is, 150° C. An aqueous solution of calcium acetate (144 gms. of calcium (AcO)₂-0.8H₂O) in 475 gms. of water was added dropwise from a separatory funnel over a period of about 4 hours. Fresh pyridine was added when necessary to replace that which boiled off. About 12 pints of pyridine were required. After all the calcium acetate had been added, a transparent, viscous, semifluid gel was obtained. This gel was dissolved in a solution of 50 gms. of Wecoline AAC fatty acid (which is a mixture of about 28 wt. percent caprylic, about 46 wt. percent capric and about 26 wt. percent lauric acids derived from coconut fatty acids) in 757 gms. of a refined mineral lubricating oil having viscosity of 55 SUS at 210° F. While the mixture was agitated in the Hobart mixer which was heated with a heating mantle, the pyridine was stripped off. The highest temperature attained was 435° F. The grease obtained was milled twice in a three-roll paint mill. The grease had a neutralization number of 0.02% expressed as sodium hydroxide and contained 3.63 wt. percent calcium based on the total grease. This grease was examined through an electron microscope and it was found that 93% of the particles were less than 1μ; the rest ranged from 1 to 5 μ.

Example IV

Into a two-liter, four-necked flask were placed 600 ml. of pyridine, 180 ml. of dioctyl azelate and 6 ml. of a commercial surface active agent obtainable from General Aniline and Film as Igepal CO-530. This is an alkyl

3,178,367 phenoxy polyoxyethylene ether of the nature mentioned above wherein n—6, R is a Cg alkyl group, R' is hydrogen and R is a C₂ alkyl group. While this mixture was agitated vigorously, 60 ml. of a saturated aqueous calcium acetate solution was rapidly added. A clear, viscous 5 liquid resulted which was heated under a vacuum of 100 mm of mercury to about 140° F. at which temperature water began distilling. The temperature was gradually raised to about 180° F. and 500 ml. of water and pyridine were removed. The resulting greaselike mass was then 10 removed from the flask and heated in a dish on a hot plate to drive off the remainder of the pyridine. The resulting product was a stable, translucent grease from which there was no oil separation after a two-week period. This grease was examined under an electron IS microscope and was found to have a particle size of about 0.2-5 micron.

Example V

In order to illustrate the use of a protective colloid in the preparation of finely divided metal salts the following preparation was carried out. To a solution of 10 grams of analytical reagent grade calcium acetate halfhydrate and 0.2 gram of gelatin in 100¹ ml. of distilled water there was added all at once 300 ml. of acetone. A gel formed which was filtered through a Buchner funnel. The solid which was recovered was divided into two equal portions which were labeled Portion A and Portion B. Portion A was dried in air at ambient temperature. Por- _3Qtion B was dried at 210° F. Both portions were examined by means of X-ray diffraction patterns which revealed that Portion A was composed of calcium acetate monohydrate and that Portion B was composed of calcium acetate half-hydrate. An analysis by electron micro- ₃₅graphs revealed that both Portions A and B had over 90% of particles less than 1μ in length. The balance of particles were 1-10μ in length.

Example VI

Example V was repeated exactly except without gelatin. Electron micrographs showed that in both of the resulting fractions no particles were smaller than 1μ and that 75% of the particles were longer than 10//.

Example VII ⁴⁵

The four fractions from Examples V and VI were dispersed in a naphthenic mineral oil having a viscosity of 55 SUS at 210° F. (3 parts Ca acetate plus 7 parts oil). The gelatin treated solid formed smooth dispersions which go were homogeneous for at least 10 days. The untreated solids formed gritty dispersions from which the oil and solids separated within one day. This example illustrates the fact that when a protective colloid is used the particles need not be rapidly incorporated in an oil to 55 insure small particle size.

Example VIII

500 g. of pyridine were added to a solution of 140 g.

Ca acetate half-hydrate in 637 g. water. The resulting ⁶⁰colloidal sol was immediately extracted at a temperature of 160° F. with a mixture of 560 g. naphthenic mineral oil (50 SUS at 210° F.), 125 g. aromatic extracts (125 SUS at 210° R.), 38 g. aromatic resins (2600 SUS at 100° F.), and 45 g. Wecoline AAC fatty acids. The phases were separated and the oil phase was heated with stirring in a Hobart mixer to 390° F. The resulting grease was milled in a 3-roll paint mill.

The product was analyzed and found to have 2.48% „θ by weight of calcium and a sulfated ash of 8.59% by weight. The neutralization number was 0.05 wt. percent as NaOH. Electron micrographs showed that 94% of the particles were smaller than 1μ and the rest were from 1 to 5μ. 73

Example IX

The procedural technique of Example VIII was repeated with the following components. 600 g. of pyridine were added to a solution of 133 g. Ca acetate half-hydrate in 582 g. water. The resulting clear sol was extracted with a mixture of 757 g. naphthenic mineral oil (50 SUS at 210° F.) and 50 g. Wecoline AAC fatty acids and the mixture heated to 100° C. After separation of the phases, the oil phase was heated to 390° F. and formed a translucent grease. An analysis showed 2.19% Ca by weight. The neutralization number was 0.05% by weight as NaOH.

Example X

A solution of 12 g. Ca acetate half-hydrate in 38 g. water had 50 g. of pyridine added to it. The clear sol formed was extracted with a mixture of 5 g. oleic acid in 40 g. naphthenic mineral oil (40 SUS at 210° F.). The phases were separated and the oil phase heated to 350° F. to drive off all the water and pyridine. The final product contained 8.75% calcium acetate half-hydrate and was a smooth, translucent grease.

In Example I, the polybutene had a molecular weight of 1100 and was treated with 15 wt. percent P₂S₅; the high alkalinity nonyl phenol sulfide was a barium nonyl phenol sulfide; the high alkalinity Ca sulfonate was prepared as follows. The sulfonic acid portion of the sulfonate was prepared by alkylating benzene with polypropylene, said sulfonic acid portion having an average molecular weight of about 440. The high alkalinity sulfonate was prepared by reacting netural barium sulfonate with additional barium hydroxide followed by bubbling carbon dioxide through the sulfonate to neutralize it. The “high alkalinity” nonyl phenol sulfide was obtained by reacting metal base in excess of that required for simple neutralization with the nonyl phenol sulfide to form an alkaline product which was then blown with carbon dioxide to neutralize it.