Patented- Oct. 14, 1941 UNITED STAT LUBRICATING on. coMrosi'rIoN Franz Rudolf Moser man, Amsterdam,
and Albert Johannes Dijks- Netherlands, assignors to Shell Development Company,
Calif.,' a corporation of Delaware No. Drawing.
Application November 27, 1939,
Serial No. 306,330. In the Netherlands December 5, 1938 1' Claim. .(Cl; 2525-35) tion engines,- such as high speedDiesel engines,
aviation gasoline engines, etc., which due to their high power output, operate at relatively high temperatures, piston rings have a tendency to become stuck in the grooves. Lacquer and/or carbon formation appear to be the principal reasons for this occurrence. The addition of small amounts of certain oil-soluble carboxylic acid salts, such as polyvalent metal salts of fatty acids and n'aphthenic acids, is known to reduce the ring sticking tendencies. The addition of small amounts of the foregoing salts or soaps, however, has one or more of the following disadvantages: The newer type bearings containing cadmium .are corroded especially by the soaps of naphthenic and aliphatic acids. The soaps break down under the high temperatures obtained in lubricationand, thereupon, the oil loses its effectiveness. Certain of the above salts cause gelatinization in the lubricants, while others settle out of the lubricating oil during use.
Now, in accordance with our invention, we have found that polyvalent metal salts of aromatic monocarboxylic acids in which the carboxylic acid radical is directly attached to the ring and,
more particularly, the basic salts of these acids when added to mineral oils in suitable quantities produce effective anti-ring sticking lubricants which are'relatively free from the above disadvantages. I
The salts of the aromatic acids employed may i be those of mononuclear aromatic acids, such as benzoic acid, or polynuclear, such as naphthoic or anthracene carboxylic acid. These acids are all thermally very stable.
Especially valuable are 'polyvalent' metal salts of the aromatic monocarboxylic acids and of these magnesium, calcium, strontium, barium, zinc, nickel, manganese, lead, copper, cobalt, and aluminum appear to be the most active. To be, effective as ring sticking inhibitors the salts should be soluble in the lubricating oil.
While many of the salts of these simple aromatic carboxylic acids are little soluble in mineral oils, similar salts of the corresponding alkylated acids are usually much more soluble. Thus, preferred acids contains one or several alkyl radicals, having preferably not more than six carbon atoms. Longer alkyl chains, though suitable from the point of view of enhancing solubility, tend to be thermally unstable. ing action of alkyl radicals are the following: Calcium naphthoate is practically insoluble in mineral lubricating oils, while the calcium salt of diamyl naphthoic acid is readily soluble.
Zinc benzoate dissolves in a furfural-reflned Venezuelan distillate to the extent of about .03%. Methyl benzoate of zinc dissolves to about 1%. The solubility of the zinc salt of para-tertiary butyl benzoic acid is about 1.5% and that of ditertiary butyl benzoic acid 2%. A
If desired, the aromatic acids may also conta' polar substitution radicals, i. e. radicals containing elements other than C and H, such as hydroxy, alkoxy, aroxy, hydrosulfide, amino, imino, halogen, etc., radicals. While, in general, these polar radicals raise the solubility to a' lesser extent than alkyl radicals, and often depress, rather than enhance it, they frequently are. advantageous in further reducing corrosiveness. The effect .of' halogen on solubility is illustrated by para-chlorbenzoic acid or para-brombenzoic acid, the zinc salts of which are soluble to the extent of about .5%. Very useful and comparatively easily prepared aromatic carboxylic acids are those prepared from alkyl phenols by the addition of CO2 (Kolbe reaction). Alkyl phenols are obtainable by extraction of coal tar distillates or cracked petroleum distillates with aqueous alkali and acidification of the aqueous extract. An example of a salt of an acid of this type is the zinc salt of thymotinic acid which is quite soluble even in V. I. lubricating oil and displays excellent anti-ring stickingproperties.
, Further, as an aid to solubility, we have found that if the salts are added to the lubricating oil at an elevated temperature in the range of 250 C. to 350 0., the dissolution of the' salt in the oil is rendered much easier. Once they have been dissolved at elevated temperature, the solutions thus obtained tend to remain substantially stable also at normal temperature. The addition of high boiling oxygenated solvents, such as high boiling alcohols, esters, for example, butyl stearate, amyl rlcinoleate, etc., may be added further to improve solubility and stability of folutifins of the salts of this invention in lubricatng o s. v
Examples of the solubiliz- Although we prefer to use about .5 to 1.5% of the salts in our lubricating oil, suitable amounts may be varied from approximately 2% to 2.5%. Amounts in excess-of this limit tend to cause undue increase in viscosity as well as jelling of the oil.
Crankcase lubricating oils containing salts of monocarboxylic aromatic acids may also have 'present other compounding ingredients, such as oxidation inhibitors, pour-point depressors, blooming agents and extreme pressure agents, preferably those containing at least one of the elements phosphorus, sulfur or chlorine.
The following examples further illustrate our invention:
About .8% by weight of the zinc salt of paratertiary butyl'benzoic acid was dissolved in a furfural-refined Venezuelan lubricating oil distillate at about 280 C. The resulting lubricating oil composition was found to be suitable for internal lubrication of Diesel engines, materially retarding ring sticking and to have the advantage of being very little corrosive to bearing metals containing cadmium.
About 1%.by weight of the zinc salt of diiscpropyl salicyclic acid was dissolved in a highly refined mineral lubricating oil at a temperature of about 200 C. When using the lubricating oil composition thus prepared in Diesel engines or aviation gasoline engines, piston ring sticking did not occur, whilst corrosion of bearing metals