US2218283A - Stabilized mineral oil composition - Google Patents

Description

1 Patented a. 15, 1940 v 1 'UNITED -STATES PATENT OFFICE; my 2,21s,2s3f j i .c STABILIZED INERAnon. ooMrosrrIon Everett W. Fuller, Woodbury, N. J.,-assignor to. I

.Socony-Vacuum Oil Company, Incorporated, 7 7 e NewYork,N.rY.,acorporationofNewYoi-kh V No Drawing. Application March 8,1939, -SerialNo.260,'5 17 j, s V

6 Claims'. (01. 252-47) I I This invention is concemed'with the stabiliza tion of viscous mineral oil fractions'against the I harmful effects of oxidation or deterioration with use by means of an oxidation inhibitor, or an. 6 "antioxidant. The invention is more specifically relatedto the improvement orstabilization of such mineral oil'fractions by the use of novel I compounds, or a novel class of compounds, which V when admixed with a viscous mineral oil in minor proportions will, preventor'dela'y 'unde-' I sirable' changes taking placein. the oil.

As is well known to those familiar with the art, substantially allthev'arious fractions obtainedfrom mineral oils and refined for'their various usesare susceptible to oxidation. The

susceptibility of an oil fraction to oxidation and the manner in whichoxidation manifests itself within the oil varies with the type and degree of refinement to whichthe oil has been subjected and with the conditions'und'er which it is used or I 1 tested.. In other words-the products formed in.

"an oil fraction as/a result of-oxidationand the' degree to which they are formed depends upon the extent to which the various unstableconstituents or constituents'which may act as oxidation. catalysts. have been removed by refining operations, and also upon the conditions o fuse. A highly refined viscous oil, I for example, which is one that has been refined by treatment I 80 with fuming'sulfuric acid or other means or combinations such as AlCla, solvents and acids (or with large quantities of concentrated sulfuric acid), tends to form relatively large amounts of.

. acidic constituents whensubjected to oxidizing conditions. The presence'of catalytic materials 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 4 acidic bodies, however, is highly undesirable=for most applications of these oils. For example. when used as an insulating orcooling oil in electrical equipment such as .transformers'or capacitors an increase in acidic bodies tends to lower'the div: 5 electric strength of the oil'and has-other harmful efiects which are undesirable. The acids are cor- 'rosive 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 lubri- V cants and in spray oils. 7

Moderatelyrefined oils, which are normally. 7

oils that have been refinedby treatment with only moderate amounts of sulfuric acid, or other refining agents; tend to form relatively small refinedoils, but considerably less than with highly refinedoils. Both sludge and acid formation;--

- lower theirfvalue for many purposes, such 'aSj25i amounts of acidic oxidation productsaas-com vpared with highly refined oils, but they undergo imaterial color'depreciation and form considerable amounts of sludge. The changes taking place in V V 7 these oilsare appreciably accelerated by the 6 presence of.meta1 catalysts-such as copper, 'Suffi-" cient acid is'generally formed to cause some re-' duction inthedielectric strength of these 0115';

but the. principal objection 'to the'm is their 7 I tendency to deposit sludgewhich interfers with 10 p a heat transfer in transformers and turbines and also causes plugging 'of oil feed lines in lubricating V v systemssolvent refined oils: in general which have been prepared by treatment with selectivesol- 16,

vents, such as chlorex, phenol, furfural; etc.; resemble the moderately refined acid-treated oils in i .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 20 sludge formation. 'Acid formation is usually greater than in the case of moderatelyacidhas been such as to make them intermediate in properties between'the types set up- Thus, respouse to inhibitors may be said to depend em; tirely on 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 5 so that any one refining procedure may produce either a highly refined oil ora moderatelyrefined oil, depending upon the crude source. .Pennsylvania type oils,'for example; requireimuch less refining to produce highly refined oils than 50 the Coastal type of oils. r r V V J The use of oxidation inhibitors for the purpose 5 of stabilizing a viscous-mineral oil fraction against a the deleterious efiects of oxidation'discussed above is'wellk'nown 'Sincethe action ofthe'seinhibiting i (Ber. 24, 1403).

2 materials is apparently catalytic the problem of their development is a difiicult one and is evident- 1y 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 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 verse. This same inhibitor may or may not be effective in inhibiting acid, sludge and color formation in a solvent-refined oil and mayor 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 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 eifective negative catalysts toward the oxidation of moderately refined or solvent-refined oils of the turbine oil type, but I have found that certain of the compounds belonging to the general class contemplated herein are efiective to inhibit corrosive action of solvent-refined motor oils toward alloy metals, such as cadmium-silver alloy bearings, under conditions encountered in crankcase use.

My invention is predicated upon the discovery that a class of organic compounds which may be broadly termed mercapto benzo thiazoles and their derivatives are effective negative catalysts toward the oxidation of viscous mineral oils of the highly refined type.

The mercapto benzo tives thereof contemplated as oxidation inhibitors for the mineral oil blends contemplated herein may be represented by the general formula:

wherein R. represents hydrogen, an alkyl group or an aryl gro p, and X-represents hydrogen or the radical Compounds of the general type characterized by Formula A in which X represents hydrogen are the mercapto benzo thiazoles, such a compound in which R also represents hydrogen being l-mercapto benzo thiazole. Compounds of the type characterized by Formula A where X represents the radical A are benzo thiazyl disulfldes, such last-mentionedv compounds being oxidation products of the corresponding mercapto benzo thiazoles.

The mercapto benzo thiazoles can be prepared by heating an azobenzene with carbon disulfide On treating a solution of a in highly refined oils tar test, involved heating a thiazoles and the derivaindicated by general mercapto benzo thiazole with an oxidizing agent, such as potassium dichromate, the corresponding benzo thiazyl disulfide is obtained (same reference). Other methods for preparing these compounds are given in the literature.

The following examples illustrate the effectiveness of the class of compounds contemplated herein as oxidation inhibitors for viscous mineral oils by certain specific compounds within the class.

Exmms 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 treatments with 40 lbs. per bbl. of 98 per cent sulfuric acid and 180 lbs. per bbl. of 103 per cent oleum, followed by neutralization, washing and clay percolation. It has 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 150 gram sample of the oil at a temperature of 120 C. while bubbling oxygen gas through the oil for a period of '10 hours. The quantity of acidic'oxidatlon products formed was determined by: (a) extracting the oil with alcoholic soda, neutralizing the extract, and then weighing the precipitated material, which is calculated as per cent acidic tar; and (b) by titrating the acids formed in the oil with alcoholic KOH and expressing the result as the neutralization number (N. N.) which represents the milligrams of KOH required to neutralize the acid in one gram of oil.

The results of this test, using representative compounds of the type contemplated by this invention, are listed in Tables I and 11 below. In Table I the compounds used are of the type Formula A above, where R is hydrogen. In Table II the compounds are of the type represented by general Formula A, wherein at least one R represents an alkyl group or an aryl group and the remaining Rs represent hydrogen.

Table I Acidic Oil tar Percent 01] alarm 15 Oil-+03% mercapto benzo thiazole 0. 02 Oil saturated (0.02- l-%) with benzo thiazyl dixulflde-----. 0. (I!

a Table II Oil N. N.

Oil alone... 25. Oil+ .10 methyl mercapto benzo thiazole 0. 01 Oili m phenyl mercapto benzo thiazole. 0. 02 Oil .l0 diEniethyl benzo thiazyl) disulflde... 0. 01 Oil+ .l0% dl phenyl benzo thiazyl) disulflde-.- 0. 01

From the foregoing results it will be seen that both the unsubstituted and the substituted mercapto benzo thiazoles and their corresponding oxidation products, the benzo thiazyl disulfides, are effective inhibitors of acid formation in oils of the highly refined type:

VEXAMPLI II Solvent-refined motor oil The substituted mercapto benzo thiazoles and their corresponding disulfldes were also found to be of measurable effectiveness in inhibiting the corrosive action of solvent-refined motor ofl toward alloy metals of the type used in cadmiumsiiver bearings. The oil used in this test was one obtained by separately refining Pennsylvania neutral and residuum stocks with chlorex and blending to give an oil of the following properties:

specific gravity 0.872; flash point 435 F., and,

Saybolt viscosity of 318 seconds at 100 F.

The test used involved immersing a fi-gram section of a cadmium-silver bearing of the type used in connecting rods in. a. 30-gram sample of the oil, heating the oil to a temperature of 175 C.

and bubbling air therethrough against the surface of the bearing for a period of 22 hours. Two

specimens from the samebearing were tested simultaneously, one in the oil alone and the other in "oil containing the inhibitor. I

In Table III below the losses in weight of the respective metal specimens in the oil alone and the oil containing the inhibitor are listed in the 7 columns headed Not. inh." and Inh., respectively, such losses being a measure of corrosiveness of the oil or oil blend toward the alloy of f the test specimen.

Table III Loss in weight (mgs.) Inhibitor Amount Not. inh. Inh.

I Methyl mercapto benzo thiazole... 25% 78 28 Phenyl mercapto benzo thiazole 25% 78 40 Di(methyl benzo thiazyl) disulfide. 25% 73 12 Di(phenyl benzo thiazyl) disulfide 25% 73 52 It will be understood that a suitable, solvent such as benzene 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 has been found that the use of these compounds in amounts 7 ranging from about 0.01 per cent to about 0.5 per cent will give satisfactory results.

It is to be further understood that the terms highly refined and solvent-refined as used herein have reference to oils corresponding substantially in their manner of deterioration and 7 inhibitor response to the examples given and are prising a highly refined viscous oil of the type 15,

used in turbines,.transformers, and the like having in admixture therewith a minor proportion, suflicient to substantially inhibit the deleterious 'eifects of oxidation on said oil, of a. mercapto benzo thiazole. I 2. An improved mineral oil composition comprising a solvent-refined viscous mineral oil fraction having in admixture therewith a minor proportion, sufi'icient to substantially inhibit the deleterious effects of oxidation on said oil, of a mercapto benzo thiazolein which the arylnucleus has at least one substituent selected from the group consisting of alkyl and aryl hydrocarbon groups.

3. A viscous mineral oil fraction containing from about'0.01 per cent to about 0.5 per cent of a mercapto benzo thiazole. V

4. A highly refined viscous mineralfoil fraction normally tending to develop acidic. products under oxidizing conditions and in admixture therewith a minor proportion of l-mercapto benzo thiazole, suflicient to substantially inhibit the development of said acidic oxidation products.

5. A highly refined viscous mineral oil fraction normallytending to developacidic products under oxidizing conditions and in admixture therewith a minor proportion of methyl mercapto benzo thiazole, sufficient to substantially inhibit the .development of said acidic oxidation products;

6. A highly refined viscous mineral oil fraction 'normally tending to develop acidicproducts under oxidizing conditions and in admixture therewith a minor proportion of phenyl mercapto benzo thiazole, sufiicient to substantially inhibit the development of said acidic oxidation products. EVERETT W. FUILER.