US2320392A - Anti-ring-sticking lubricant - Google Patents

Description

Patented June 1, 1943 ANTI-RING-STICKING LUBRICANT Ellis R. White, Albany, Calif., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application January 13, 1941, Serial No. 374,201

11 Claims.

This invention is related to improved lubricating oils, and more particularly deals with mineral lubricating oils containing dissolved therein small amounts of oil-soluble metal salts capable of reducing ringsticking tendencies of the oil.

It is well known that in Diesel engines in particular, piston rings have a tendency to become stuck due to an accumulation of coke in the ring grooves. It is also known that the addition of oil-soluble detergents to the lubricating oil does in many instances reduce or even prevent such ringsticking. The class of detergents most active for this purpose are oil-soluble metal salts of carboxylic and sulfonic acids, such as soaps of fatty acids, chlorinated fatty acids, aromatic fatty acids, naphthenic acids, rosin acids, paraffin carboxylic acids (produced by oxidation of paraffin wax), mahogany acids, alkyl derivatives of benzoic or hydroxy benzoic acids and many others. Salts of polyvalent metals are in general most active, e. g., of Mg, Ca, Sr, Ba, Zn, Cd. Al, Sn, Sb, Cr, Mn, Co, Ni, etc.

The addition of oil-soluble salts to lubricating oils in effective amounts, e. g., in amounts ranging from about 25% to 5.0%, however, introduces at the same time a number of difficlllties, one of the most serious of which is bearing corrosion. Another is formation of hard coke. and still another is scratching of the top land of the piston.

The problem of corrosion seems to be very involved, corrosion apparently proceeding by at least one of several possible mechanisms with the effect that under some conditions an oil coniaining adissolved salt may be non-corrosive and even a corrosion preventive, whereas under other conditions it may cause serious corrosion. Thus some oils containing a dissolved salt are initially corrosive, while others are initially noncorrosive but acquire induced corrosiveness, i. e., turn corrosive upon use under ordinary lubricating conditions as are encountered in internal combustion engines. In some instances corrosion has been reduced, though not usually altogether overcome, by the addition of various secondary dopes, such as anti-oxidants, anti-corrosives, etc. In this connection, it should be observed that in some instances the addition of secondary dopes has an effect contrary to what one should expect, 1. e., cases are known in which, for example, a lubricating oil containing the combination of an oil-soluble salt and a proven commercial anti-corrosive are more corrosive than the same oil containing the salt alone.

Among the detergents most valuable for antiringsticking purposes are the aliphatic carboxylic acids, e. g., fatty acids, aromatic fatty acids, naphthenic acids, paraflln carboxyl acids, rosin acids, etc. However, they all suffer from the common disadvantage of relatively high corrosiveness which may be initially active or be induced upon use.

It is a. purpose of this invention to produce relatively non-corrosive lubricating oils suitable for internal combustion engines containing dissolved a detergent soap. It is another purpose to produce improved oil-soluble salts of aliphatic acids, which salts, when dissolved in mineral lubricating oils, combine an extraordinary degree of detergency with but little corrosiveness.

I have discovered that the corrosiveness of oilsoluble salts of aliphatic, alicyclic, aromatic carboxylic acids can be reduced materially and in many instances be suppressed to relatively harmless proportions by attaching an amino radical onto the carbon atom in the alpha position to the carboxyl radical. Thus the acids suitable for my purpose are amino acetic acid derivatives having the general formula COOK so des red. the R radicals may contain relatively propyl, butyl, amyl, hexyl, allyl, etc., primary or secondary amines, petroleum bases (particularly from straight run petroleum oils), piperidine,

Any of the metals heretofore known to be suitable for anti-ringsticking purposes may be used. From the point of view of detergent eflect, the polyvalent metals, Mg, Ca, Ba, Zn, Al, Sn, Cr and Co are preferred. On the other hand, salts of metals having a strong tendency to form complex compounds, such as Cu, Ag, Ni, Co, Mn, Cr, etc., because of their preference to form chelates, are the least corrosive, as'will be explained hereinafter. Either normal or basic salts or their mixtures may be used.

As already stated. salts of the alpha amino acids are less corrosive than the same salts of corresponding acids not containing the amino radical, or containing an amino radical in a position other than the alpha position. While I do not wish to be bound by my theory, I believe that the following is explanation for the improved behavior. It appears that at least one of the mechanisms by which corrosion proceeds is directly related to the electrical conductivity of the oil. Most oil-soluble salts, such as those heretofore used for imparting detergency to lubricating oils are slightly ionized in hydrocarbon oil solution, as a result of which the oil becomes conductive. However, salts of acids having a threevalent nitrogen in alpha position to the carboxyl radical exist in two forms which are in equilibrium with each other, namely, the chelate (inner ring) and the non-chelate forms. The latter ionizes, but the former does not. Thus the equilibrium may be illustrated as follows:

If a chelate form is the preferred one, relatively few ions can form, and the corrosion is accordingly reduced. Simultaneously, however, one would expect a similar reduction in detergent properties, because, as far as known, it is the ionized portion of the salt which is responsible for the detergent effect. However, the alpha amines do not show the expected detergency loss, and, on the contrary, often are materially better in this property than the same or similar salts of the corresponding acids not having the alpha amino radical.

This is believed to be due to the fact that certain definite but small amounts of ionized detergent salts displa y substantially as great dispersive action as larger amounts, while the corrosive property is more nearly proportional to the amounts of ions present. Thus, from the point of view of detergency of the oil, it is only necessary to have in the oil at any one time the minimum amounts of active ions which are just suiiicient to disperse whatever sludge or sludgelike materials happen to be'contained in the oil at that moment. As the dispersion proceeds, these minimum amounts are used up and the oil would be left unprotected, unless new active ions are introduced. Due to the presence of relatively large amounts of inactive detergent salts, effective quantities of these ions are quickly restored, and thus continued detergency of the oil is assured.

Concerning the equilibrium between the chelate and the non-chelate forms of the normal and basic salts, it appears that in the case of the normal salt the chelate is preferred, whereas in the basic salt the ionized form predominates. As a result, it has been found that the normal salts of the alpha amino acids are even less corrosive than the basic ones, whereas it was heretofore believed necessary that to suppress corrosiveness one must employ the basic salts.

The above peculiar reversal of the rate of corrosiveness as affected by alkalinity in the case of the alpha amino salts is of considerable importance. One of the main causes. for the type of corrosiveness which is induced upon use of the oils containing detergent salts is believed to reside in a gradual reduction of the alkalinity of the salt with a commensurate decrease in the pH value due to oxidation. In the case of the alpha amino salts, however, the transition from the basic to the normal salt has just the opposite effect, corrosion decreasing for reasons pointed out above, rather than increasing.

In the normal salts of some of the alpha amino acids the equilibrium in favor ofthe chelates is so pronounced that an amount of detergentactive ions may be formed less than the minimum required for truly satisfactory detergency. In such cases it may be desirable to use a mixture of normal and basic salts so as to result in an oil solution containing the required minimum amount of ions; or a mixture of a normal alpha amino carboxylic acid salt with a detergent salt which is not subject to chelate formation, such as an ordinary oil-soluble naphthenate, sulfonate, aromatic fatty acid salt, paraiiln wax carboxylic acid salt, etc., may be employed.

a The following example serves to illustrate my invention: Stearic acid was halogenated by the Hell Volhard Zelinsky reaction under conditions to insure complete conversion of all the stearic acid to the corresponding alpha halo acid halide. The resulting product was hydrolyzed with warm water, and the halo acid thereby obtained was dried by solution in isopentane and subsequent crystallization. The alpha brom stearic acid, which had a melting point of 60 C., was then heated with two equivalents of piperidine for one The benzene layer was mixed with two equivalcnts of a thick freshly slacked lime paste and the mixture was distilled with addition of more benzene until no further water came overhead with the benzene. When dry, the residual benzene solution was filtered to remove excess lime, and the filtrate was evaporated to dryness.

The residue was a reddish yellow glassy substance which readily dissolved in hot oil.

A solution of 1.7% by weight oi this material in an SAE 30 mineral lubricating oil was produced. The resulting blended lubricating oil was tested, and is compared in the table below with two recognized detergent salts for Diesel lubricating oils for corrosiveness and detergency.

In the corrosion test a hardened steel disc is made to rotate for 20 hours under constant pressure against 3 copper lead alloy bearings. The bearing assembly rests in a welded steel cup and is covered with the o'ilto be tested. During the test the temperature of the oil is maintained at 107 C. The bearings are weighed before and after the test, the difference in the weight representing the loss sustained during the test.

The detergency is measured by filtering a suspension of carbon black under standard conditions through a column placed in a glass tube, which column consists of 1 cm. layers of a sand separated from each other by pieces of filter paper. As the oil filters through this column, the carbon black is gradually filtered out and beginning at a certain point down the column, the oil is free from suspended carbon black. This point can readily be determined by visually examining the edges of the several filter papers. Those above this point have blackened edges, while those below it remain white. By counting the number of blackened papers, a direct measure for the detergency is obtained. Under the conditions of the test straight lubricating oils have detergency numbers of 1-2. The presence of 1-2% of a good detergent normally raises it to 6-8, and in exceptional cases to 9 or 10.

In addition to the detergents of this invention, the lubricating oils may contain conventional oxidation inhibitors or retarders, anti-corrosives, extreme pressure agents, particularly those containing at least one of the elements S, Cl and P in relatively stable form, so as not to cause corrosion, blooming agents, dyes, etc. The amounts of the detergent required to retard or prevent ringsticking normally varies betwen about 25% and and preferably from 175% to 2.5% by weight of the oil.

I claim as my invention:

1; Lubricating oil comprising mineral lubricating oil containing dissolved from .25%-5.0% of an oil-soluble polyvalent metal salt of an alpha amino acetic acid which is resistant to oxidation under normal lubricating conditions in internal combustion engines.

2. Lubricating oil comprising mineral lubricating oil containing dissolved a small amount of an oil-soluble salt combining a polyvalent metal with an alpha amino acetic acid which is resistant to oxidation under normal lubricating conditions in internal combustion engines.

3. Lubricating oil comprising a mineral lubricating oil containing dissolved a small amount of an oil-soluble polyvalent metal salt of an alpha amino acetic acid which is resistant to oxidation under normal lubricating conditions in internal combustion engines, the amino radical of said acid being a secondary amino radical.

4. Lubricating oil comprising a mineral lubricating oil containing dissolved a small amount of an oil-soluble polyvalent salt of an alpha amino acetic acid which is resistant to oxidation under normal lubricating conditions in internal combustion engines, the amino radical of said acid being a tertiary amino radical.

5.'Lubricating oil comprising a mineral lubricating oil containing dissolved a small amount of an oil-soluble mixture of basic and normal polyvalent metal salts of an alpha amino acetic acid which is resistant to oxidation under normal lubricating conditions in internal combustion engines.

6. Lubricating oil comprising a mineral lubricating oil containing dissolved a small amount 0! an oil-soluble mixture of a detergent salt not subject to chelate formation and of a polyvalent metal salt of an alpha amino acetic acid which is resistant to oxidation under normal lubricating conditions in internal combustion engines.

7. Lubricating oil comprising a mineral lubricating oil containing dissolved from .25 to 5.0% of an oil-soluble polyvalent metal salt of a monocarboxylic acid having not more than one olefinic double bond and having the formula wherein R1 to R4 are hydrogen or hydrocarbon radicals, at least one being a hydrocarbon radical, the total number of carbon atoms in said radicals being at least 16 said salt being further characterized by being resistant to oxidation under normal lubricating conditions in internal combustion engines.

8. Lubricating oil comprising a mineral lubricating oil containing dissolved a small amount of an oil-soluble polyvalent metal salt of an alpha amino fatty acid having at least 16 carbon atoms and not more than one olefinic double bond, and having attached to the amino group at least one hydrocarbon radical.

9. Lubricating oil comprising a mineral lubricating oil containing dissolved a small amount of an oil-soluble polyvalent metal salt of an alpha amino naphthenic acid having attached to the amino group at least one hydrocarbon radical said salt being further characterized by being resistant to oxidation under normal lubricating conditions in internal combustionengines.

l0. Lubricating oil comprising a mineral lubricating oil containing dissolved a small amount of an oil-soluble polyvalent salt of an alpha amino parafiin wax monocarboxylic acid having attached to the amino group at least one hydrocarbon radical said salt being further characterized by being resistant to oxidation under normal lubricating conditions in internal combustion engines.

11. Lubricating oil comprising a mineral lubricating oil containing dissolved a small amount ofcalcium alpha piperidino stearate.

ELLIS R. WHITE.