US2707173A - Stabilized mineral oil lubricant compositions - Google Patents

Description

United States Patent STABILIZED MINERAL OIL LUBRICANT COMPOSITIONS Troy L. Cantrell, Lansdowne, and Herschel G. Smith, Wallingford, Pa., assignors to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application June 17, 1949, Serial N- 99,889

1 Claim. (Cl. 252-515) This invention relates to stabilized mineral oil lubricant compositions, and more particularly, it relates to mineral oil lubricants which have been stabilized against oxidative deterioration. More specifically, this invention is concerned with improvements in mineral lubricant compositions containing addition agents of the type disclosed inv the copending application of Smith, Cantrell and Peters, Serial No. 66,585, filed December 21, 1948, now U. S. Patent No. 2,511,747, and assigned to the same assignee as the present application.

Plain mineral lubricating oils often prove unsatisfactory in the lubrication of internal combustion engines of all types, particularly when severe operating conditions are encountered, because of the oxidative deterioration of the oil with the attendant deposition on the engine surfaces of varnish, gum or sludge. Furthermore, many lubricating oil compositions which may be satisfactory for the lubrication of other mechanisms have been found wholly unsuitable for use as turbine oils.

The formation of varnishes, gums and sludges on engine surfaces is generally ascribed, at least in part, to oxidation effects on mineral lubricating oils. The problem of oxidation is further aggravated in turbinue oils because in normal use turbine oils become rapidly contaminated with water.

While the type of additive disclosed and claimed-in copending application, Serial No. 66,585, confers a remarkably eifective oxidation stability on mineral lubricating oils, the oils in use sometimes acquire a dark color, albeit their oxidation stability remains generally unimpaired. This darkening in color, although insignificant from the standpoint of oxidation stability, is important from the standpoint of the consumer, because to him, the darkening in color during use of the oil would normally be indicative of degradation, whether or not that is the fact. It would be advantageous, therefore, to provide mineral lubricating oils which remain light in color even after extended periods of use.

The principal object of this invention, then, is to provide mineral oil lubricant compositions which, in addition to being stabilized against oxida'tive deterioration, will not materially be darkened in color during use. Other objects willbe apparent from the following detailed description.

These objects are accomplished by the present invention which resides in the provision of a mineral lubricating oil containing (1) 2,6-ditertiarybutyl-4-methyl phenol and a non-resinous condensation product of N- dimethylaniline and formaldehyde, the mol ratio of formaldehyde to N-dimethylaniline ranging from 0.5 :1 to 10:1 and the condensation of said product having been carried out in the presence of an activatedclay catalyst at a temperature not in excess of 350 F. to condense together the two reactants.

We have found that when a mineral lubricating oil is stabilized against oxidative deterioration by the use of both of the additives set forth herein, darkening of the mineral lubricating oil in use is materially retarded. We have also found that the two additives unexpectedly synergize each other; that is, the antioxidant life of a mineral oil containing both additives is greater than the sum of the antioxidant effects obtained from the use of the individual additives alone.

As disclosed in U. S. Patent No. 2,265,582, 2,6-ditertiarybutyl-4-methyl phenol is by itself a good antioxidant. As disclosed in copending application Serial No. 66,585, the non-resinous N-dimethyaniline-formaldehyde condensation product prepared in the presence of an activated clay is in itself an excellent antioxidant, it being generally more potent than 2,G-ditertiarybutyl-4-methyl phenol, particularly under service conditions involving high temperatures. Our invention resides in using both of these antioxidants in one mineral lubricating oil to obtain as new and unexpected results the stabilization of the color of the oil during use and a synergistic effect on the oxidation stability of the oil.

As disclosed in copending application Serial No. 66,585, the non-resinous N-dimethylaniline-formaldehyde condensation product is prepared by heating the reactants in the presence of an activated clay catalyst at a temperature not in excess of 350 F. to condense together the two reactants. If the temperature of 350 F. is exceeded to any substantial extent, the condensation product formed tends to be resinous and insoluble. The preferred temperature for the condensation ranges from to 300 F. The proportions of the reactants used to prepare the condensation product vary over a relatively wide range. As a lower limit the mol ratio of formaldehyde to N- dimethylaniline should not be less than 0.5 1. However, it is preferred to employ larger amounts of formaldehyde relative to the N-dimethylaniline since more potent antioxidants are obtained thereby. Accordingly, the mol ratio of formaldehyde to N-dimethylaniline may be as high as 10:1. Ordinarily it is preferred to use from 5 to 10 per cent by weight of an activated clay catalyst based on the total weight of the reactants. However, smaller amounts, as low as 1 per cent by weight, and larger amounts, as high as 20 per cent by weight, can be used; but larger amounts than about 10 per cent by weight are ordinarily not necessary. Contrary to what may be expected from the nature of the reactants, highly condensed, insoluble resinous products are not obtained. On the contrary, when the above reactants are condensed in ac cordance with the copending application above referred to, there are obtained light-colored condensation products which are non-resinous and which are readily soluble in mineral oils.

In lieu of formaldehyde in the condensation reaction, any formaldehyde-yielding compound can be used, such as paraformaldehyde, dioxymethylene and trioxymethylene. In such case, the amount of formaldehyde-yielding compound used is based on the equivalent number of mols of formaldehyde yielded within the range of proportions of formaldehyde set forth hereinabove. Accordingly, as used in the appended claims, the term formaldehyde is intended to include formaldehyde-yielding compounds as well as formaldehyde itself.

Various activated clays are employed in the preparation of the N-dimethylaniline-formaldehyde condensation products. Such materials are well known in the art and comprise a natural clay, such as bentonite, fullers earth, floridin and smectite, which has been acid treated in order to activate the clay. These materials are described in U. S. Patent No. 1,898,165, for example.

In preparing the N-dirnethylaniline-formaldehyde condensation product, the reactants and catalyst are placed in a reaction vessel which is then closed and the mixture is heated with agitation until all of the formaldehyde or formaldehyde-yielding compound has been consumed. At this time, the water which is formed as a result of the condensation is removed, preferably under vacuum, and the dehydrated condensation product is then filtered to remove the activated clay catalyst. If it is desired, the condensation product may be prepared in a concentrate in a mineral lubricating oil which may then be diluted with additional oil to the final concentration desired. These condensation products are liquids or crystalline solids and contain in combination the reactants employed in their preparation. As shown in the copending application hereinabove referred to, the use of an activated clay as a catalyst is essential in the preparation of the condensation products; otherwise black, insoluble, resinous condensation products are obtained and the antioxidant potency of the product is adversely affected.

The other agent, 2,6-ditertiarybutyl-4-methyl phenol, which we employ in the lubricant of this invention, may be obtained from any suitable source. One method of preparing 2,6-ditertiarybutyl-4-methyl phenol is disclosed in U. S. Patent No. 2,265,582 and comprises alkylating para cresol with isobutylene until no more isobutylene reacts with the para cresol.

For the purposes of the present invention, the N-dimethylaniline-formaldehyde condensation product and 2,6-ditertiarybutyl-4-methyl phenol are added to mineral lubricating oils in minor amounts, say in a total amount of both additives of from 0.01 to 1.0 per cent by weight on the mineral oil, sufficient to inhibit oxidative deterioration of the oil. Larger amounts of our additives may be used if desired, but it is ordinarily unnecessary to do so. Within the total amounts of both additives set forth herein, each additive may range from 20 to 80 per cent by weight of the total, i. e., in a weight ratio of from 1:4 to 4:1. Stated in another way, in order to obtain the desired results as to retardation of darkening in color, at least 20 per cent by weight of the total additives should be 2,6-ditertiarybutyl-4-methyl phenol; and in order to obtain the beneficial effects of the condensation product in prolonging oxidation stability, at least 20 per cent by weight of the total additives should be the N-dimethylaniline-formaldehyde condensation product. The synergistic effects of the additives on each other with respect to antioxidant potency are also limited by the foregoing, but are obtained over the whole range of proportions of total additive disclosed herein.

The following examples are illustrative of our invention. The oxidation test referred to is a standard test designated ASTM D 943-47 T. Briefly, the test comprises subjecting the oil sample to oxygen at a temperature of 95 C. (203 F.) presence of water and an ironcopper catalyst, and determining the time required to build up a neutralization number of 2. The flow of oxygen is maintained at 3 liters per hour. The remarkably effective stability to oxidation of the mineral oil lubricant compositions containing our new addition agents, the color improvements and the synergistic effects are illustrated by the results shown in the following examples:

Example I .A portion of turbine oil stock was treated with 0.2 per cent by weight of (A) 2,6-ditertiarybutyl-4- methyl phenol, and another portion of this stock was treated with 0.2 per cent by weight of (B) the condensation product of 1 mol of N-dimethylaniline and 2 mols of formaldehyde, prepared in the presence of 10 per cent by weight of Filtrol (activated clay) as set forth in the above-identified copending application. A third portion was treated with both 0.2 per cent by weight of (A) 2,6- ditertiarylbutyl-4-rnethyl phenol and 0.2 per cent by weight of (B) the condensation product of N-dimethylaniline and formaldehyde. The base oil, the oil blended with (A), the oil blended with (B), and the oil blended with both (A) and (B) exhibited the following properties:

Bisle Base Base 1 on on @53 Base 0911' 0911' ing taintam- O11 0.2% mg mg of (A) 0.2% 0.2% and of (A) of (B) 02% of (B) Gravity, API 28. 5 28. 4 28. 4 28. 3 Viscosity, SUV, 100 F (110 (111 010 612 Flash, 00, F 490 190 490 490 Four, F +5 +5 +5 +5 Color, NPA 2. 5 2. 5 2. 5 2. 5 Oxidation Test, ASTM D943-47T:

Time Oxidized, Hrs 210 400 1, 200 2,000 Neutralization No 2.0 2.0 2. 2.0 Expected Time Oxidized, Hrs... 1, 000 Increase Over Expected Time Oxidized, Hrs 400 Color of Oil After 14 Day dation Test, NPA 5.0 2. 4. 5 2.

Example II.-A portion of turbine oil stock was treated with 0.1 per cent by weight of (A) 2,6-ditertiarybutyl-4-methyl phenol, and another portion of this stock was treated with 0.1 per cent by weight of (B) the condensation product of 2 mols of N-dimethylaniline and 3 mols of formaldehyde prepared as described in the above identified copending application. A third portion was treated with both 0.1 per cent by Weight of (A) 2,6- ditertiarybutyl-4-methyl phenol and 0.1 per cent; by

weight of (B) the condensation product of N-dimethylaniline and formaldehyde. The base oil, the oil blended with (A), the oil blended with (B), and the oil blended with both (A) and (B) showed the following results:

Brsle Base Base 1 on on $32: Base ing aintam- O11 0.1% mg mg of (A) 0.1% 0.1% and of (A) of (B) of (B) C0101, NPA l. 5 l. 5 1 5 1. 5 Oxidation Test, ASTM D9 Time Oxidized, Hrs. 195 280 650 1, 800 Neutralization No 2.0 2.0 2.0 2.0 Expected Time Oxidized, Hrsm. 930 Increased Over Expected Time Oxidized, Hrs 870 Color of Oil After 14 Days Oxidation Test, NPA 5. 0 2.0 4. 5 2.0

Example III.A portion of turbine oil stock was treated with 0.3 per cent by weight of (A) 2,6-ditertiarybutyl-4-methyl phenol, and another portion of this stock was treated with 0.3 per cent by weight of (B) the condensation product of 2 mols of N-dimethylaniline and 1 mol of formaldehyde prepared as described in the aboveidentified copending application. A third portion was treated with both 0.3 per cent by weight of (A) 2,6-ditertiarybutyl-4-methyl phenol and 0.3 per cent by weight of (B) the condensation product of N-dimethylaniline and formaldehyde. The base oil, the oil blended with (A), the oil blended with (B), and the oil blended with both (A) and (B) showed the following results:

Example IV.A portion of turbine oil stock was treated with 0.1 per cent by weight of (A) 2,6-ditertiarybutylt-methyl phenol, and another portion of this stock was treated with 0.2 per cent by weight of (B) the condensation product of 2 mols of N-dimethylaniline and 3 mols of formaldehyde prepared as described in the above-identified copending application. A third portion was treated with both 0.1 per cent by weight of (A) 2,6-ditertiarybutyl-4-methyl phenol and 0.2 per cent by weight of (B) the condensation product of N-dimethylaniline and formaldehyde. The base oil, the oil blended with (A), the oil blended with (B), and the oil blended with both (A) and (B) showed the following results:

Bgsle Base Base 1 on on Base 9 0911' ing amtam- Oil 0.1% mg mg of (A) 0.1% 0.2% and of (A) of (B) 0.2%

Gravity, API 28.8 28. 7 28. 7 28.8 Viscosity, SU", F 303 301 302 303 Oxidation Test, ASTM D943-47T:

Time Oxidized, Hrs 1, 530 Neutralization No 2.0 Expected Time Oxidized, H 1,165 Increase Over Expected Time Oxidized, Hrs 365 Color of 011 After 14 Days Oxidation Test, NPA 8.0 2.0 8.0 2.0

The preceding examples clearly illustrate the remarkable properties of our new mineral oil lubricant composi; tions. The color tests made during oxidation show that the base oil and the oil containing the N-dimethylanilineformaldehyde condensation products alone turned dark during oxidation, while the oil containing both additives, in accordance with the present invention, retained its pristine color. The color test referred to is described in ASTM Standards on Petroleum Products and Lubricants, November 1948, pages 105-109 (ASTM D 155- 45 T). A National Petroleum Association (NPA) color number of 2 designates an oil slightly darker than cream white, namely extra pale. Also significant is the fact that while the lubricating oil containing the N-dimethylaniline-formaldehyde condensation products alone turned dark during oxidation, only a relatively small amount of 2,6-ditertiarybutyl-4-methyl phenol need be added to give an NPA color of 2.

In addition to color improvement, the above examples clearly show the unexpected synergistic efiect with respect to antioxidant potency obtained in accordance with the present invention. In preceding Example I, for instance, the lubricating oil containing the combination of additives was much more stable to oxidation than oils containing the additives separately. The oil containing only 2,6-ditertiarybutyl-4-methyl phenol had an antioxidant life of 400 hours. The oil containing only the N-dimethylaniline-formaldehyde condensation product had an antioxidant life of 1200 hours. It would be expected, therefore, that an oil containing both additives would have an antioxidant life of about 1600 hours. However, the test shows that the improved oil of this invention had an antioxidant life of 2000 hours, indicating an unexpected synergistic effect.

The above examples also show the remarkable oxidation stability imparted to mineral oil lubricant compositions by the use of the addition agents described. Mineral oil lubricant compositions containing these addition abents are therefore eminently suited for use where the operating conditions are extremely severe, as in Diesel,

tank and truck engines, and in the lubrication of steam turbines. Furthermore, the beneficial effects of our invention may be applied to all types of lubricating oil basekstocks, that is, parafiinic, naphthenic and mixed base stoc s.

If desired, other known addition agents may be incorporated into lubricant compositions prepared in accordance with our invention. For example, pour point depressants, extreme-pressure agents, and the like may be added. Resort may be had to such modifications and variations as fall within the spirit of the invention and the scope of the appended claim.

We claim:

A lubricant composition comprising a major amount of a mineral lubricating oil and minor amounts, in a total of from 0.01 to 1 per cent by weight of said oil, of: (1) 2,6-ditertiarybutyl-4-methyl phenol; and (2) a nonresinous condensation product of 1 mol of N-dimethylaniline and 2 mols of formaldehyde, the condensation of said product having been carried out in the presence of an activated clay catalyst at a temperature not in excess of 350 F. to condense together the two reactants; the amounts of (1) and (2) with respect to each other being in a weight ratio ranging from 1:4 to 4:1.

References Cited in the file of this patent UNITED STATES PATENTS 2,202,825 Brandes June 4, 1940 2,225,533 Dewey Dec. 17, 1940 2,375,168 Hardman May 1, 1945 2,410,652 Grifiin Nov. 5, 1946 2,440,530 Yates Apr. 27, 1948 2.511,747 Smith et al. June 13, 1950 OTHER REFERENCES Kalichevsky, Lubricating Oil Additives, Petroleum Refiner, September 1940, pages and 86.

Georgi, Motor Oils and Engine Lubrication, Rein hold Pub. Co., 1950, pages 27 and 28. i