US2167273A - Stabilized mineral oil - Google Patents

Description

Patented July 25, 1939 STABILHZED M'HNERAL' on.

Elmer William Cook, New York, N. Y., assignor to Tide Water Associated Oil Company, Bayonne, N. 3., a corporation of Delaware No Drawing. Application December 4, 1936, .Serial No. 114,136

'7 Claims.

The useful service life of mineral oils, in re-- spect both of the character and rapidity of deterioration, is influenced. by the service conditions obtaining during use. In some instances, as in the lubrication of internal combustion engines, high temperatures prevail and thin films of the oil are in continued and renewed contact with'hot metal surfaces. Strongly oxidizing atmospheres may be encountered in other services where operatingtemperatures are the Same or may be lower. In the lubrication of steam turbines, the oil temperature is relatively low but contacted metal surfaces or other operating conditions may catalyze, promote or permit acid or sludge formation with eventual emulsification due to the presence of water. For transformer, cable wrapping or other electrical services, the foregoing or other factors may tend to occasion deterioration. I

Petroleum hydrocarbons oils may be improved in some respects by refining methods effective to remove or convert, at least in part, certain deterioration inducing constituents vnormally present therein. Refining with chemicals frequently is employed, as by extraction with selective solventsoi the character of phenol, liquid sulfur dioxide, 'nitro-benzine, furfural, and others well known in the art as well as combinations thereof, by clay filtration, or by moderate treatment with sulfuric acid of less than fuming acid strength. More drastic refining, as by treatment with fuming sulfuric acid, may be resorted to when it is desired to produce highly refined viscous hydrocarbon oils the so-called technical white oils) from which substantially all, asphaltic constituents have been removed. The refined products, however, still are to an undesirable degree susceptible to oxidation, polymerization, or other chemical phenomena to which may be attributed observed impairment of the oil resulting from or indicated by acid, gum, and sludge formation, coior degradation, inordinate viscosity increase, or other evidence of deterioration.

Accordingly, it has been proposed to further improve the service life of various mineral hydrocarbon oils, and in particular lubricating or like oils of petroleum origin, by the incorporation therewith of substances or compounds having an inhibiting or retarding action in one or another respect upon the deterioration of the oil. Many suggestions heretofore have been made in this direction and a, number of compounds advanced for trial as inhibitors some of which in greater or less degree have proved effective. Discrepancies in results have been noted, however, both as to the relative inhibiting effect of a given com pound with'difierent oils in overcoming a parvalue of an inhibitor in one oil environment from its effect in another. Thus, many compounds effective as anti-gum forming agents for cracked gasoline may be wholly without eiiect in petroleum lubricating oils. Again, certain inhibitors of value in preventing deterioration of very highly refined turbine oils (the so-called technical white oils) have proved quite inefi'ective in respect of inhibiting action in less highly refined turbine oils.

The action of inhibitors, particularly in mineral hydrocarbon oil environments, appears, therefore, to be in a sense specific not only for certain reactions but further with respect to the character of the oil, the nature and extent of the refining to which it has been subjected, and the service for which it is intended. The present invention is concerned with and provides compounds of proven inhibiting action; but it is deemed undesirable and of little practical value to attempt or rely upon any prescribed theory in explanation of observed efiects or results.

In its broad aspect, the present invention relates to the use of inhibitors which I have discovered to be of marked utility in preventing the deterioration of viscous or relatively viscous petroleum oils (as contrasted with the less viscous or non-viscous distillate petroleum products such as gasoline and kerosene).

More specifically, an important object of the invention is to provide effective .lnhibitors for lubricating and like oils of petroleum origin; which oils have been subjected in greater or less degree to conventional methods of refining other than drastic treatment of the character resorted to for the production of water white viscous mineral oils (viz, technical white oils as prepared by extended treatment with heavy fuming sulfuric acid).

A further object of the invention is to provide, for the indicated use, inhibitors selected from those compounds of a di-arylamine designation conforming to'the general molecular structure R-NH-R' wherein both R and R. are polycyclic or condensed aromatic rings and wherein the molecular arrangement is anti-symmetrical.

It is likewise an object of the invention to improve, and to provide improved, lubricating oils by incorporating therewith small amounts of the compounds which I have discovered to be of effective inhibiting action.

Other objects and advantages will appear from the following description of the invention and the illustrative examples presented hereinafter in order that the invention may be more particularly ascertained. 7

Various tests have been devised and are available by which a comparative evaluation of oils with respect to deterioration thereof in service may be obtained in a relatively short period of time. Some of these tests are of longer duration than others, but have the advantage of affording a perhaps more reliable laboratory criterion by which to judge the relative value of various inhibitors than extremely accelerated tests.

One such relatively prolonged test, which has proved of particular convenience in, although not limited to, the evaluation of oils intended for such service as the lubrication of steam turbines, is the familiar Funk test. In this test, a measured quantity of oil and water (ordinarily 8 gallons of oil and 0.8 gallon of distilled water) is continuously circulated through a cast iron chamber under conditions of violent agitation, the oil being maintained at a temperature of 200 F. and air being passed continuously through the Bii as it circulates and re-circulates through the chamber. The length of time required to form 1% (by volume) of sludge and emulsion as measured in a centrifuged sample is the criterion by which the relative service life of the oil is measured.

Illustrative of inhibitors according to the invention is the compound alpha beta di-naphthyl amine which is an anti-symmetrical di-aryl amine having the structural formula:

which compound has given unusually beneficial results by way of inhibiting deterioration of mineral hydrocarbon lubricating oil. This is demonstrated inone instance by the following test data resulting from comparative Funk machine runs. There is likewise demonstrated the distinction, in regard to inhibiting effectiveness, between anti-symmetrical compounds, such as the aforementioned, and related symmetrical compounds such as beta beta di-naphthyl amine. The runs were made with a turbine oil, produced from an East Texas crude petroleum, which oil had been refined by solvent extraction with liquid sulfur dioxide and had a viscosity at F. of

Saybolt seconds.

. Time to form 1% Inhibitor:

* (No evidence of sludge and emulsion formation at 2500 hours.)

A particular advantage of inhibitors according to the invention resides in the extremely small proportions necessary to effect very substantial inhibiting or stabilizing of the oil in respect of deterioration thereof. This is aptly demonstrated by the foregoing data wherein 0.05% of alpha beta di-naphthyl amine is shown to occasion a remarkable increase in the Funk life of the oil in question. It will be understood, of course, that larger or smaller proportions of inhibitor may be used as deemed desirable but in general it is contemplated that the practice of the invention will entail the use of amounts of the order of less than 1% and, in the interests of economy, less than 0.1%. My investigations indicate that the potency of inhibitors, of ,the character of alpha beta di-naphthyl amine, is such that proportions in the range of 0.005% to 0.05% will in many cases be entirely satisfactory.

The compounds which I have discovered to be of value as inhibitors for lubricating and like petroleum oils are readily soluble in the oil in proportions well in excess of the range indicated above as giving effective stabilizing action. The invention may be practiced, therefore, either by the direct addition of inhibitor to oil in the desired inhibiting proportion or, as may in many instances be preferable, by preparing a concentrated solution comprising several percent of inhibitor in oil and then adding a suitable amount of such concentrate to bulk quantities of oil.

Inhibitors within the contemplated scope and practice of the invention include not only the straight di-aryl amines of anti-symmetrical structure wherein both aryl groups are polycyclic aromatic rings, but also derivatives thereof comprising such di-aryl amines wherein one or more hydrogen atoms on one or both of the arcmatic nuclei is replaced by a substituent group. The substituting group may, for example, be one selected from the class of aryl, alkyl, amino, aryloxy and alkyloxy radicals, but it is important to avoid the presence of substituents which would occasion undue decrease in oil solubility, increase in water solubility, particularly if the inhibitor is to be used in turbine oil or like service where the presence of water is a service factor), or otherwise detracts from the useful effectiveness at the inhibitor.

The importance of an anti-symmetrical structure or molecular arrangement in inhibitors of the invention has been referred to. Ample evidence of'this is afforded by the illustrative Funk test reported herein, where the data includes results with a symmetrical di-naphthyl amine for comparison with those attending the use of an anti-symmetrical compound. The marked novelty and utility of the latter is apparent.

The use of inhibitors of the character of alpha beta'di-naphthyl amine and derivatives thereof according'to the invention is not confined to the specific oil designated in the foregoing example. 75

Other mineral hydrocarbon oils of lubricating oil character may be stabilized against deterioration by the incorporation therewith of these inhibiting compounds. Thus, the inhibitors of the invention may be applied to the stabilization of oils having greater or less viscosity than 150 seconds Saybolt at 100 F.; and to such oils as refined by various methods alternative to extraction with liquid sulfur dioxide. However, the use of these inhibitors in technical white oils derived from petroleum as by drastic refining with fuming sulfuric acid forms no part of the present invention; nor does the present invention contemplate as within its intended scope or practice the use of these compounds as inhibitors of gum formation in cracked gasoline.

Evidence of the broad utility of inhibitors according to the invention in its intended field of service is afforded by the results of another test method wherein internal combustion engine lubricants comprise the oil environment in which the inhibitors function. This test, described below, is one devised in recent years to demonstrate both the tendency of motor oils to deteriorate per se and their tendency to occasion corrosion of bearing surfaces in internal combustion engines wherein the bearings are formed of, or surfaced with, cadmium-silver, cadmiumnickel, copper-lead and like alloys. The two said tendencies may or may not be related, little being known concerning the nature of the corrosive action or its causes. It has been observed that motor oils derived from selected crudes predominantly parafiinic in origin, as well as those oils from these or other crudes which have been improved by treatment with selective solvents, exhibit a marked tendency toward corrosion of the bearings in question, although by other tokens the lubricant is of superior quality and is not corrosive toward bearing surfaces formed of Babbitt metal. It is possible that the high bearing surface temperatures existing under service conditions with the newer bearingsformed of cadmium-silver and like alloys may be a factor in occasioning the observed deleterious effect of motor oils thereupon.

The aforementioned test, by which a comparative evaluation of motor oils may be obtained in the laboratory, is conducted as follows. A group of bearings, ordinarily including at least one each of several of the newer bearing metal alloys (viz: cadmium-silver, cadmium-nickel and copper-lead) is supported in a chamber in which air may circulate, and the bearing surfaces are exposed for a period of 22 hours to a stream of oil sprayed under pressure continuously upon the corrodible area. The oil is maintained at a temperature of 335 F. and the spray is so directed as to disperse the oil over the surfaces of the bearings. Means are provided for re-circulating the sprayed oil so that a given quantity is used for a given test, thus simulating service conditions in an engine. The measure of corrosion is taken as the loss in weight of the bearing per unit of exposed corrodible surface. Coincidently, a measure of oil deterioration per se is obtained by observing or determining the neutralization number of the oil after a test run as well as such factors as the increase in viscosity and carbon residue.

The test method described above is carried out in the familiar Underwood corrosion apparatus supplied by the Scientific Instrument Company of Detroit, Michigan, in accordance with General Motors specifications.

-a viscosity at 210 F. of 54 Saybolt seconds, and

a carbon residue of 0.39%. It comprised a blend of solvent refined Pennsylvania neutral oil with conventionally produced Pennsylvania bright stock. A sample of this oil was submitted to test according to a procedure as hereinbefore outlined wherein cadmium-silver, cadmium-nickel and copper-lead bearings were used. The loss in weight per square decimeter due to corrosion was as follows for the respective bearings:

' Grams Cadmium-silver -1 6.7 Cadmium-nickel 3 .8 Copper-lead 1.0

The used oil after the run showed a 47% increase in the Saybolt viscosity at 210 R, an increase in carbon residue from 0.39 to 3.41, and a neutralization number of 4.5 milligrams KOH per gram of oil.

There was then incorporated with a fresh supply of the foregoing motor oil an inhibitor according to the invention comprising alpha beta di-naphthyl amine in the amount of 0.2% by weight, and this inhibitor containing oil subjected to test according to the indicated procedure. The results indicated a complete suppression of bearing corrosion, no loss in weight for any of the three types of bearing being observed. Regarding deterioration of the oil itself, substantial benefit resulted from the presence of the inhibitor, the increase in viscosity at 210 F.

' being but 9% instead of 4'7 for the oil without inhibitor, the carbon residue increasing only to 1.27, and the used oil showing a neutralization number of 1.1 milligrams KOH per gram of oil as. compared with 4.5 in the blank run.

Further investigations utilizing the foregoing motor oil test for the evaluation of inhibitors according to the invention emphasized the marked superiority of anti-symmetrical compounds over those of a symmetrical arrangement. Thus, when 0.2% by weight of alpha alpha di-naphthyl amine was used in place of 0.2% by weight of alpha beta di-naphthyl amine, bearing corrosion losses as follows were observed:

Grams Cadmium-silver; 6.4 Cadmium-nickel 8.0 Copper-lead 0.5

Coniparing the abovewith the corrosion lossesinduced by the oil without inhibitor, it will be noted that the cadmium-silver bearing underwent substantially the same degree of corrosion, and that while the corrosion of the copper-lead bearing appeared to be somewhat retarded, the symmetrical compound actually accelerated in marked degree the corrosion of the cadmiumnickel bearing. The carbon residue of the used oil in this run was 3.07, very nearly as high as that of the used oil in the run without innibitor; and a neutralization number of 6.94 milligrams KOH per gram of used oil indicated an accelerated deterioration of the oil itself.

The assembled evidence of all of the foregoing data and results obtained in the several comparative tests demonstrates the advantages attendingthe use of inhibitors comprising anti-symmetrical diarylamines wherein both aryl groups are condensed rings.

I claim:

1. Mineral oil composition comprising a viscous hydrocarbon oil normally tending to deteriorate in service and having incorporated therewith deterioration inhibiting proportions of an anti-symmetrical di-aryl amine wherein both aryl groups are polycyclic or substituted polycyclic aromatic rings.

2. Mineral oil composition comprising a viscous hydrocarbon oil normally tending to deteriorate in service and having incorporated therewith deterioration inhibiting proportions of an anti-symmetrical di-aryl amine wherein both aryl groups are polycyclic-aromatic rings.

3. Mineral oil composition comprising a viscous hydrocarbon oil normally tending to deteriorate in service and having incorporated therewith deterioration inhibiting proportions of alpha beta di-naphthyl amine.

4. Refined turbine oil, normally tending toward acid, sludgeor emulsion formation in service, having incorporated therewith inhibiting proportions of an anti-symmetrical di-aryl amine 5. Refined turbine oil, normally tending toward acid, sludge or emulsion formation in service,

' having incorporatedtherewith inhibiting proportions of alpha beta di-naphthyl amine.

6. Mineral oil composition, comprising a hydrocarbon lubricating oil of motor oil character normally tending to corrode the type of bearing metal exemplified by cadmium-silver, cadmiumnickel and copper-lead alloys when continuously applied to the surface thereof for an extended period of time at an oil temperature of 335 F., and an anti-symmetrical di-aryl amine wherein both aryl groups are polycyclic aromatic rings incorporated with said oil in corrosion inhibiting proportions. p

7. Mineral oil composition, comprising a hydrocarbon lubricating oil of motor oil character normally tending'to corrode the type of bearing metal exemplified by cadmium-silver, cadmium nickel and copper-lead alloys when continuously applied to the surface thereof for an extended period of time at an oil temperature of 335 F., and alpha beta di-naphthyl amine incorporated with said oil in corrosion inhibiting proportions.

ELMER WILLIAM COOK.