US2269282A

US2269282A - Mineral oil composition

Info

Publication number: US2269282A
Application number: US276616A
Authority: US
Inventors: Robert C Moran; Darwin E Badertscher; Henry G Berger
Original assignee: Socony Vacuum Oil Co Inc
Current assignee: ExxonMobil Oil Corp
Priority date: 1939-05-31
Filing date: 1939-05-31
Publication date: 1942-01-06
Anticipated expiration: 1959-01-06

Description

Fat-ented jan. 6, 1942 ED STATES OFFER MINERAL 0E COIVIPOSITHON ration oi New York No Drawing. Application May 31,

Serial No. 276,616

9 Claims.

This invention is concerned with the stabilization of viscous mineral oil fractions against the harmful effects of oxidation or deterioration with use by means of an oxidation inhibitor or an antioxidant. The invention is more specifically related to the improvement or stabilization of such mineral oil fractions by the use of novel compounds, or a novel class of compounds, which when admixed with a viscous mineral oil in minor proportions will prevent or delay undesirable changes taking place in the oil.

As is well known to those familiar with the art, substantially all the various fractions obtained from mineral oils and refined for their various uses are susceptible to oxidation; The susceptibility of an oil fraction to oxidation and the manner in which oxidation manifests itself within the oil varies with the type and degree of refinement to which the oil has been subjected and with the conditions under which it is used or tested. In other words, the products formed in an oil fraction as a result of oxidation and the degree to which they are formed. depends upon the extent to which the various unstable constituents or constituents which may act as oxidation catalysts have been removed by refining operations, and also upon the conditions of use.

A highly refined viscous oil, for example, which is one that has been refined by treatment with fuming sulfuric acid or other means or combinations such as A1Cl3, solvents and acids (or with large quantities of concentrated sulfuric acid), tends to form relatively large amounts of acidic constituents when subjected to oxidizing conditions. The presence of a catalytic material such as copper does not appear to affect appreciably the oxidation of highly refined oils and such oils are less prone to the formation of colored bodies or of insoluble sludge. The formation of acidic bodies, however, is highly undesirable for most applications of these oils. For example, when used as an insulating or cooling oil in elec-' trical equipment such as transformers or capacitors an increase in acidic bodies tends to lower the dielectric strength of the oil and has other harmful eifects which are undesirable. The acids are corrosive to metals and thus reduce the useful life of the oils as lubricants or for other purposes in which they come in contact with metals,

and the acidic materials are also injurious in textile lubricants and in spray oils.

Moderately refined oils, which are normally oils that have been refined by treatment with only moderate amounts of sulfuric acid, or other refining agents, tend to form relatively small amounts of acidic oxidation products as compared with highly refined oils, but they undergo material color depreciation and form considerable amounts of sludge. The changes taking place in these oils are appreciably accelerated by the presence of metal catalysts such as copper. Sufiicient acid is generally formed to cause some reduction in the dielectric strength of these oils, but the principal objection to them is their tendency to deposit sludge which interferes with heat transfer in transformers and turbines and also causes plugging of oil feed lines in lubricating systems.

"Solvent-refined oils in general which have been prepared by treatment with selective solvents, such as chlorex, phenol, furfural, etc., resemble the moderately refined acid-treated oils in that their oxidation is accelerated by the presence of metals such as copper and further in that it is attended by substantial color depreciation and sludge formation. Acid formation is usually greater than in the case of moderately acidrefined oils, but considerably less than with highly refined oils. -Both sludge and acid formation lower their value for many purposes, such as electrical insulation, lubrication, etc. Also, solvent-refined oils have found extensive use as lubricants for internal combustion engines because of their high viscosity index, but under the conditions of use encountered in crankc'ases such oils develop constituents which are corrosive toward certain metal bearings such as the cadmiumsilver bearing, etc., which are sometimes used.

It is to be understood that this classification of oils as highly refined, moderately refined and solvent-refined is by no means limiting and that there can exist oils whose refining and blending has been such as to make them intermediate in properties betweenthe types set up. Thus, response to inhibitors may be said to depend entirely upon the type of oxidation and end products of oxidation of'an oil, which in turn depends largely upon the degree of refining this oil has had. Further, the degree of refining required to produce these types of oils varies with the crude source so that any one refining procedure may produce either a highly refined oil or a moderately refined oil, depending upon the crude source. Pennsylvania type oils, for example, require much less refining to produce highly refined oils than the Coastal type of oils.

The use of oxidation inhibitors for the purpose of stabilizing a viscous mineral oil fraction against the deleterious effects of oxidation discussed above is well known. Since the action of the problem of their development is a difiicult one and is evidently influenced to a large degree by the oxidizable constituents which are in the.

oil following a particular refining treatment. Thus, a particular inhibitor or class of inhibitors may be effective to stabilize a highly refined oil oil against acid formation while the same inhibitor may have no appreciable effect upon acid, color or sludge formation in a moderately refined oil and vice versa. This same inhibitor may or may not be effective in inhibiting acid, sludge and color formation in a solvent-refined oil and may or may not be effective to inhibit the corrosive action of a solvent-refined oil toward metals such as used in cadmium-silver bearings.

This invention is particularly concerned with the inhibition of oxidation in highly refined oils of the type used in transformers, turbines, and the like through the use of a novel class of compounds to be hereinafter described. The compounds contemplated herein do not appear to be effective negative catalysts toward the oxidation of moderately refined or solvent-refined oils of the turbine oil type, but they are effective to inhibit the corrosive action of solvent-refined motor oils toward alloy metals, such as cadmiumsilver alloy bearings, under conditions encountered in crankcase use.

This invention is predicated upon the discovery that a group of organic compounds which we may broadly classify as thiazane and its N-substituted derivatives are effective to inhibit the deleterious effects of oxidation upon certain types of viscous mineral oils.

More specifically, the addition agents or antioxidants contemplated by this invention are members of the specific class of thiazanes known as the thiomorpholines, which are characterized by the general formula ,in which R represents a radical selected from the group consisting of hydrogen, alkyl, aryl, and alkaryl radicals or groups. When R. in the above formula is hydrogen the compound is thiomorpholine, the remaining compounds comprehended by the formula beingbroadly classified herein as N-substituted derivatives of thiomorpholine or N- substituted thiomorpholines.

To demonstrate the effectiveness of these thiomorpholine compounds as antioxidants for viscous mineral oils, N-amyl thiomorpholine was preparedby the procedure of Lawson and Reid, Journal American Chemical Society 47, 2828 (1925), using the crude material after topping off any amylamine which might have been present.

The following examples in which the N-amyl, thiomorpholine was used as a representative compound within the class, illustrate the effectiveness of these compounds as anti-oxidants or oxidation inhibitors for viscous mineral oils.

hours.

aacaasa these inhibiting materials is apparently catalytic,

EXAMPLE I Highly refined oil The oil employed in this test was of the highly refined type used in transformers and the like which had been obtained from a Coastal distillate by successive treatment with 40 lbs. per bbl. of 98 per cent sulfuric acidand 180 lbs. per bbl. of 103 per cent Oleum, followed by neutralization, washing and clay percolation. It had a specific gravity of 0.871, a flash point of 310 F. and a Saybolt viscosity of 69 seconds at'100 F.

The test used, known as the modified German tar test, involved heating a 150 gram sample of the oil at a temperature of 120 C. while bubbling oxygen gas through the oil for a period of The quantity of acidic oxidation products thus formed in the oil was determined by titration with standard alkali and the results recorded in terms of neutralization number (N. N.) which represents the milligrams of KOH required to neutralize the acid in one gram of oil. The results obtained with the oil alone and with the same oil inhibited with N-ampl thiomorpholine are given in Table I below:

EXAMPLE II Solvent refined motor oil The oil used in this test was a motor oil obtained by refining with chlorex a Pennsylvania -neutral stock and a Pennsylvania residual stock and blending to produce an oil of the following properties: specific gravity 0.872; flash point 435 F., Saybolt viscosity 318 seconds at F.

The test involved immersing a 6 gram section of a cadmium-silver bearing in a 30 gram sample of the oil, heating the oil to a temperature of C., and bubbling air therethrough against the surface of the bearing for a period of 22 hours. Two specimens from the same bearing were tested simultaneously, one in the oil alone and the other in the oil containing the inhibitor, the comparative weight loss of the bearing specimens indicates the extent to which corrosion has been retarded by the thiomorpholine. The results of this test are given in Table II below:

Table II ()il Weight loss JUN/[grams Oilalonc 543,0 0il+0.25}1,N-amyl Lhiorriurpholinc. v 2.0

It will be understood that a suitable solvent such as benzol, toluol and related hydrocarbons; carbon tetrachloride etc. may be employed if desired to facilitate solution of the improving agent in the oil; also that the compounds contemplated herein may be used in varying amounts depending upon the oil fraction, conditions of use, etc., but for the purposes contemplated herein it will be found that in general the use of thiazanes in proportions ranging from about 0.10% to about 5.0% will give satisfactory results.

It is to be further understood that the terms highly refined, and solven refined as used herein have reference to oils corresponding substantially in their manner of deterioration and inhibitor response to the examples given hereinabove and are not necessarily restricted to an oil obtained by particular refining operation. As has been previously pointed out, the final characteristics in an oil fractlolliare efiected by the crude from which the oil is obtained as well as by the refining treatment. For example, an oil of the -.,highly refined type may be obtained from a selected crude by a refining treatment which with another crude stock would yield a moderately refined" oil.

We claim:

1. An improved mineral oil composition comprising a viscous mineral oil fraction having in admixture therewith in minor proportion, sufiicient to inhibit the deleterious efiects of oxidation on said oil, a compound having the general formula:

H2 H2 -0 s\-- /N-R (1-0 H: H: v in which R represents a radical selected from the group consisting of alkyl, aryl and alkaryl hydrocarbon groups.

2. An improved mineral oil composition comprising a viscous mineral oil fraction selected from the group consisting of highly refined oils and solvent refined motor oils having in admixture therewith a minor proportion, suflicient to inhibit the deleterious efiects of oxidation on said oil, a compound having the general formula:

H7 H: c-c s N--lt in which R represents a radical selected from the group consisting of alkyl, aryl and alkaryl hydrocarbon groups. I

3. A highly refined viscous mineral oil fraction having an N- substituted thiomorpholine in admixture therewith in minor proportion sufficient to inhibit the deleterious efiect of oxidation on said 011. V

4. A highly refined viscous mineral oil fraction rosive to alloy bearings, typified by cadmiumsilver bearings, under conditions of use .encoun-,

tered in the operation of an internal combustion engine, said oil having in admixture therewith a minor proportion, sufficient to inhibit said corrosive action, of a compound having the general formula V in m H2 H2 in which R represents a radical selected from the group consisting of alkyl, aryl and alkaryl hydrocarbon groups.

7. A viscous mineral oil fraction normally corrosive to alloy bearings, typified by cadmiumsilver bearings, under conditions of use encountered in the operation of an internal combustion engine, said oil having an N- substituted thiomorpholine in-admixture therewith in minor proportion sufiicient to inhibit said corrosive action.

8. A viscous mineral oil fraction normally corrosive to alloy bearings, typified by cadmiumsilver bearings, under conditions of use encountered in the operation of an internal combustion engine, said oil having N-amyl thiomorpholine in admixture therewith in a minor amount sufficient to inhibit said corrosive action.

9. A viscous mineral oil fraction normally corrosive to alloy bearings, typified by cadmiumsilver bearings, under conditions of use encounteredin the operation of an internal combustion engine, said oil having about 0.25% N-amyl thiomorpholine in admixture therewith to inhibit said corrosive action.

ROBERT C. MORAN. DARWIN E. BADER'I'SCHER. HENRY G. BERGER.