Metallic Soaps for Thickening Mineral Oils C. J. BONER Battenfeld Grease & Oil Corporation, Kansas City, Mo.
Eighteen metals were combined with two fatty acids of different titer to form metallic soaps. T h e s e s o a p s were heated to the same temperature with two mineral oils and cooled to find whether grease resulted. Grease was formed with soaps from nine of the metals. These nine, with the exception of aluminum, were divalent or gave divalent compounds. Soaps of the metals with the lowest atomic weights produced greases of best transparency. In general, soaps of the more basic metals produced the s o f t e s t g r e a s e s . Water as an emulsifier was not required except in the case of calcium and strontium soaps. The consistency was heaviest and the dropping point highest in greases made from the highest titer acid. Behavior of the metallic soaps in both napht henic and paraffin-base oils with a Saybolt viscosity of 100 at 100" F. was similar.
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T
HE metallic soaps used in grease manufacture are limited, in the main, to those of aluminum, calcium, lead, and zinc. Although sodium soaps are largely used, they are not generally classified as metallic soaps. There is a possibility that some theory can be developed, similar to that for driers used in paints and varnishes (d), as to why metallic soaps thicken mineral oils. With this object in view, a number of metallic soaps were made and tested for their ability to change the consistency of mineral oils.
Selection of Fatty Acids and Metals FATTYACIDS. Practical c o n s i d e r a t i o n s led to the selection of fatty acids which were predominantly saturated. E x p e r i e n c e has
determined that the most desirable calcium-base greases result from the use of a mixture of oleic, palmitic, and stearic acids of a titer of 32 t o 44. Acids of lower titer give soft greases, and with higher titer smoothness is sacrificed. Similarly, in the manufacture of greases with aluminum soaps, aluminum stearate provides the greatest thickening whereas the oleat8e tends to give a more fluid grease. Likewise, lead stearate gives a grease of much heavier body than the oleate or naphthenate. Thus the acids used-namely, double-pressed stearic acid and lard fatty acids-fall in the classification of those largely used in practice. METALS. Since all but a very small fraction of lubricating greases are manufactured from aluminum, calcium, lead, and sodium, the first three of
SOAPS TABLEI. PROPERTIES OF METALLIC Metal in Washed Ash, yo 4.01 4.02 18.71 19.96 16.23 15.15 10.82 10.78 6.80 6.79
Cadmium H T Cadmium LT Calcium H T Calcium LT Cerium H T Cerium LT
Titer of Acids 52.13 38.05 52.13 38.05 52.13 38.05 52.13 38.05 52.13 38.05
Chromium H T
52.13
6.82
0.14
Chromium LT
38.05
6.00
0.36
Cobalt H T Cobalt LT
52.13 38.05
8.45 8.23
0.29 0.42
Copper H T Copper L T Iron H T Iron LT
52.13 38.05
10.05 9.05
0.26 0.45
52.13 38.05
7.45 5.86
0.70
Lead H T Lead L T Magnesium H T Magnesium LT Manganese H T Manganese L T Mercury H T Nickel H T
52.13 38.05
Nickel LT Silver H T Strontium H T Strontium LT Tin H T Tin LT Zinc H T Zinc LT
Metallic Soap5 Aluminum H T Aluminum L T Barium H T Barium LT
Soluble Ash, yo 0.21 0.37 Not detd. Not detd. Not detd. Not detd. 0.11 0.24 0.16 0.58
0.00
22.33 Not detd. 22.20 Not detd.
52.13 4 . 1 8 38.05 4.36 52.13 8.81 38.05 8 . 5 5 52.13 20 09
0.01 0.17 0.13 0.70
52.13
9.13
0.37
38.05 52.13 52.13 38.05 52.13 38.05 52.13 38.05
8.99 15.86 23.60 23.49 16.58 16.50 11.60 11.50
0.02
..
.. .. ..
0.10 0.31 0.10 0.18
Appearance of Metallio Soaps Fluffy white powder Cream powder, fuses about 220° F. White powder Cream powder White powder Cream powder White fluffy powder Cream powder Light yeIlow dense powder Yellow mass, fuses about below 200' F. Blue-green powder, fuses about 210' F. Dark green mass, fuses below 200' F. Purple powder Brownish purple mass, fuses below 200' F. Fluffy blue-green powder Green mass, fuses below 200' F. Fluffy red-brown powder Dark red-brown mass, fuses below 180° F. White powder Cream powder, fuses about 200' F. White fluffy powder White powder, fuses about 210' F. Cream powder, pink tinge Brown mass, fuses below 200' F. White powder Light green powder, fuses about 210' F. Dark green, fuses below 200' F. White powder White powder Cream powder, fuses about 220° F. Cream powder, fuses below 220" F. Yellow mass, fuses below 180' F. White powder White powder
H T soaps made from double-pressed stearic acid; LT soaps from lard fatty acids. 58
INDUSTRIAL AND ENGINEERING CHEMISTRY
JANUARY, 1937
59
OF METALLIC SOAPDISPERSIOXSIN MINERALOILS^ TABLE11. CHARACTERISTICS
10% of Soap Heated to 260° F. in Oil with Viscosity of 100 at looo F.
10% of Soap Heated to 230° F. in Oils as Before; 0.5% Water Added, Stirring until Mixture Cooled to 200° E'. 7 7
Soap Aluminum H T Aluminum LT Barium H T Barium LT Cadmium H T Cadmium LT Calcium H T Calcium LT Cerium HT Cerium LT Chromium H T Chromium L T Cobalt H T Cobalt LT Copper H T Copper LT Cron H T Iron L T Lead H T Lead L T Magnesium H T Magnesium L T Manganese H T Manganese LT Mercury H T Nickel H T Nickel LT Strontium H T Strontium LT Silver H T Tin H T Tin LT Zinc H T Zinc LT a
Naphthenic oil
Naphthenic oil
, -
Naphthenic oil Paraffin oil Clear firm gel Not as clear or as Not as clear or as Clear firm gel firm as dry mixfirm as dry mixture ture Clear rubbery gel Clear rubbery gel Same Same Clear rubbery gel Clear rubbery gel Under no conditions was a homogeneous mixture obtained even a t 330' F. where soap fused to a clear mass No homoneneous mixture obtained in any instance Opaque firm gel Opaque firm gel Soft gel syneresis Soft gel syneresis Opaque firm gel Opaque G m gel Opaque semi-fluid Opaque semi-fluid Soap in lower 75% Soap in lower half Semi-fluid synere- Semi-fluid syneresis sis of oil of oil Most of soap sepa- Most of soap sepaOpaque gel Most of soap sepa- Most of soap sepa- Opaque gel rated rated rated rated Most of soap sepa- Most of soap sepaOpaque gel Opaque gel Solid soap structure throughout but rated rated oil could be poured from this Most of soap sepa- Most of soap sepaSoap separated Soap separated in Soap separated in Soap separated rated rated lower 65% of oil lower 90% of oil Most of soap sepa- Most of soap sepaSoap separated Soap separated Soap separated Soap separated rated rated Soap separated Soap separated Soap separated Soap separated, oil Soap separated, oil Soap separated colored colored Soap separated Soap separated Soap separated Soap separated, oil Soap separated, oil Soap separated co1ored colored Firm gel Firm gel Nonuniform gel Firm gel, translu- Firm gel, translu- Nonuniform gel cent cent Livery gel Livery gel Nonuniform gel Livery gel, trans- Livery gel, trans- Nonuniform gel lucent lucent Soap separated Soap separated Soap separated Soap separated, oil Soap separated, oil Soap separated colored colored Soap separated Soap separated Soap separated Soap separated, oil Soap separated, oil Soap separated colored colored Soap separated Soap separated Soap separated Soap separated, oil Soap separated, oil Soap separated colored colored Soap separated Soap separated Soap separated Soap separated, oil Soap separated, oil Soap separated colored colored Firm mass Firm mass Firm mass Opaque firm mass, Opaque firm mass, Firm mass softens on worksoftens on working ing Semi-fluid Semi-fluid Semi-fluid Soap suspended Semi-fluid synere- Semi-fluid mass would sis barely flow Firm gel Firm gel Soft gel Clear firm gel Soft gel Clear firm gel Viscous liquid Viscous liquid Cloudy liquid Clear viscous liquid Clear viscous liquid Cloudy liquid Soap separated Soap separated Soap separated Soap separated Soap separated Soap separated Soap separated Soap separated Soap separated Soap separated, oil Soap separated, oil Soap separated colored colored Firm mass Firm mass, opaque Firm mass, opaque Firm mass, some Firm mass, some Firm mass free Hg free Hg Firm gel Firm gel, cloudy Firm gel Firm gel, translu- Firm gel, translu- Firm gel, cloudy cent cent Viscous liquid Cloudy liquid Viscous liquid Viscous liquid clear Viscous liauid clear Cloudy liquid Soap separated Fluid, no separa- Fluid, no- separa- Opaque firm mass Opaque firm mass Soap separated tion tion Soap separated Opaque firm mass Opaque fbm mass Soap separated Soap separated Soap separated Soap separated Soap separated, Soap separated Soap separated, Soap separated Soap separated some free silver some free silver Mixtures did not clear a t 260° F. but soap remained suspended Mixtures did not clear a t 260° F. but soap remained suspended Soap separated Soap separated Soap separated Soap separated Mass becoming semi-fluid when touched Soap separated Soap separated Soap separated Soap separated Soap separated Soap separated Clear firm gel
Paraffin oil
+
10% of Soap 0.570 of Stearic Acid Heated in Oils as Before to 260° F.
Paraffin oil
Clear firm gel
After heating, the mixtures were cooled slowly to room temperature in 12 hours.
these metals were used, together with others which have similar characteristics or occur in like groups in the periodic table.
Experimental Procedure Soaps were made by double decomposition as outlined by Whitemore and Lauro (8). One hundred grams of fatty acids were used in the manufacture of each lot of soap which was thoroughly washed; but with the resulting bulk of soap it was difficult to free the product entirely from water-soluble impurities. Although such impurities may influence the thickening action of the metallic soaps in mineral oils, com-
The observations were made after 24 hours.
mercial experience shows that they do not prevent a grease structure. For example, commercial aluminum stearate on the market today contains water-soluble material, and, as long as this is under one per cent, grease structure is not greatly affected. I n Table I the soaps are listed together with some of their properties. When incorporating the metallic soaps in mineral oils, consideration was given the factors which experience has shown to affect grease structure most-namely, (a) different mineral oils, (b) rate of cooling of the grease, ( G ) emulsifying or suspending agents. The procedures for thickening oils are detailed in Table 11.
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VOL. 29, NO. L
TABLE 111. PROPERTIES OF LUBRICATINQ GREASES MADEFROM METALLIC SOAPS Metallic Soap
Appearance of Grease
Consistencya Unworked
Dropping Pointb oc.
Syneresis after 30 Days
Comments
(OF.)
Aluminum stearatec Aluminum, low titer0 Cadmium stearate= Cadmium, low titerC Calcium stearated Calcium, low titerd Cobalt stearateC Cobalt, low titerC
Light brown, clear Dark brown, clear Light brown, opaque Semi-fluid, opaque Cream, opaque Cream, opaque Purple, translucent Purple, translucent
205 270 200 Too soft 260 290 180 Too soft
83 (181) 70 (158) 85 (185) Too soft 95 (203) 92 (198) 75 (167) Too soft
Lead stearatec Magnesium stearate“ Magnesium, low titer“
Light yellow, opaque Yellow, clear Yellow, clear
130 265 Too soft
83 (181) 75 (167) Too soft
Nickel stearatec Nickel, low titerC Mercury stearateC
Green, translucent Green, clear Cream, opaque
230 Too soft 260
65 (149) Too soft 107 (225)
None None None None None None None About 5% free oil None None
...
... ... ... ...
...
Same characteristics in both dry and moist mixtures
... ...
Clear viscous liquid, 225 Saybolt viscosity a t 100’ F.
...
None
...
...
Rubbery nature
About 3 Yofree oil None None
Clear liquid, 150 Saybolt viscosity a t 100’ F. Grainy appearance
...
Strontium stearated Cream, opaque 260 102 (216) Strontium, low titerd Yellow, opaque 275 77 (171) A. S. T. M. method D 217, 33 T. * Holde, “The Examination of Hydrocarbon Oils and oi Saponifiable Fats and Waxes,” tr. by Mueller, p. 189, New York, John Wiley k Sons, 1915. Grease made by heating 10% of dry soap in oil 100 viscosity (at 100’ F.) t o 260” F. and cooling slowly. Grease made by heating 10% of dry soap in oil of 100 viscosity (at 100” F.) t o 230’ F., then adding 0.5% water and stirring the mixture until the temperature dropped to 200’ F.
Discussion of Results Of eighteen metals combined with fatty acids, nine gave metallic soaps which, in turn, produced lubricating greases that were worthy of consideration. Although the entire metal field was not covered, indications are that divalent combinations furnish the most promising and satisfactory bases for lubricating greases. Five of the metals-magnesium, calcium, strontium, cadmium, and mercury-in group I1 of Mendeleeff’s periodic arrangement of the elements, are divalent. Three others-cobalt, lead, and nickel-form divalent compounds. The remaining metal, aluminum, according to McBain and McClatchie (7), does not furnish a trivalent soap but rather a mono- or divalent. Further, Licata (6) says: “It is believed by some that the value of aluminum stearate as a suspension agent depends on its free stearic acid content. Various types of aluminum stearate are made. The type with a high stearic acid content forms thin gels. The low stearic acid type forms thick gels.” Faragher and associates (3) go so far as to state that aluminum monooleate gives a much heavier body in mineral oil than either the dioleate or trioleate. Referring to Table 11, soaps of four metals-aluminum, cobalt, magnesium, and nickel-gave greases which were clear or translucent; the soaps of cadmium, calcium, lead, mercury, and strontium gave opaque greases. The first four are metals of comparatively low atomic weight and thus the metal content of their soaps is low; probably, therefore, a low percentage of metal in soaps used in lubricating greases will tend to give a more transparent or translucent grease structure. Study of the consistencies of greases obtained (Table 111), indicates that the more basic the metal the softer the consistency of the thickened mineral oil. Likewise, the greases made from soaps containing high-titer acids were always heavier in consistency than the low-titer combinations. I n view of these results, the statements of two authors may be of interest. Klimont (6) is of the opinion that the solubility of the metallic soaps depends on the melting point of the concerned fatty acids. Licata (6) states: “While the fatty acid radical to a large extent governs the physical properties of a metallic soap, the metallic fraction determines the chemical
...
properties. I n general it can be said that solubility decreases from naphthenates, linoleates, oleates, palmitates to stearates, which are least soluble. Aluminum stearate seems to be the exception to this rule.” I n the series of metals reported on here no greater difficulty was experienced in obtaining greases with stearic acid soaps than with lard fatty acid soaps. Only with calcium and strontium soaps was water necessary to hold the soap in suspension. With most other soaps, 0.5 per cent of water tended to break down the structure. This result does not entirely agree with Fischer (4) who found that water-combining ability in metallic soap gels depended on the metallic radical decreasing from magnesium, calcium, mercury, and lead to barium. On all greases made, the dropping point was highest with fatty acid combinations of the highest titer. Soaps which formed a grease in naphthenic-base oil would also give a grease in paraffin-base oil. The latter produces a little less opaque grease, but the difference in consistency was not appreciable. This paper covers preliminary data on this question, and further work will be undertaken.
Literature Cited (1) Braun, “Die Metallseifen,” Leipzig, Otto Spamer, 1932.
(2) Elm, IND.ENQ.CHEM..26, 386 (1934). (3) Faragher, Henry, and Gruse, U. S. Patent 1,550,608 (Aug. 18, 1925). (4) Fischer, McLaughlin, and Hooker, Kolloidchem. Beihefte, 15, 1 (1922). ( 5 ) Klimont, J. prakt. Chem., 109, 265-72 (1925). (6) Licata, “Metallic Soaps, Their Uses and Properties,” Metasap Chemical Co., 1935. (7) McBain and McClatchie, J . Am. Chem. SOC.,54, 3266-8 (1932), (8) Whitemore and Lauro, IND.ENQ.CHEM.,22, 646-9 (1930). RECEIVEDMay 7, 1936. Presented before the Division of Petroleum Chemistry at the 91st Meeting of the Ameriortn Chemical Society, Kansas City, Mo., April 13 to 17, 1936.
