US3414519A - Corrosion inhibitor - Google Patents

Description

United States Patent 3,414,519 CORROSION INHIBITOR Eric Beynon, Sulfern, N.Y., assignor to Union Carbide Corporation, a corporation of New York No Drawing. Continuation of application Ser. No.

471,495,, June 21, 1965. This application July 7,

1967, Ser. No. 659,263

7 Claims. (Cl. 25275) ABSTRACT OF THE DISCLOSURE For use in an aqueous cooling liquid for an internal combustion engine containing a water-miscible alcohol as the principal non-aqueous ingredient, a combination of corrosion inhibitors consisting of, based on the alcohol present, from about 0.7 to about 10 weight percent of a borate of an alkali or an alkaline earth metal, from about 0.007 to about 4 weight percent of a nitrite of an alkali or an alkaline earth metal, from about 0.007 to about 4 weight percent of benzotriazole and/ or a related compound, and from about 0.1 to about weight percent of an oil inhibitor which is a polar-type oil.

This application is a continuation of application Ser. No. 471,495, filed on June 21, 1965, now abandoned, which is a continuation-in-part of application Ser. No. 311,494, filed on Sept. 25, 1963, now abandoned. Application Ser. No. 311,494, supra, is in turn a continuation-inpart of application Serial No. 129,849, filed on Aug. 7, 1961, now abandoned.

The invention relates in general to a novel combination of corrosion inhibitors for use in the cooling system of an internal combustion engine, and also refers to an antifreeze composition and a summer inhibitor formulation which contain this combination of corrosion inhibitors.

Generally, water is the accepted heat exchange medium for the cooling systems of internal combustion engines primarily due to its good heat transferability, availability, and low cost. Since many internal combustion engines are exposed to temperatures lower than 32 F., however, antifreeze compositions which depress the freezing point of water are widely used. These antifreeze compositions usually contain a water-miscible alcohol such as methanol or ethylene glycol. Ethylene glycol, propylene glycol, diethylene glycol, and other polyhydroxy alcohols are generally referred to as permanent antifreezes since their relatively high boiling points minimize vaporization of the alcohol from the cooling system.

These alcohols are not considered as being inherently corrosive toward the metals usually found in cooling systems. During use, however, a heat exchange medium comprising an aqueous solution of at least one of these alcohols is usually exposed to elevated temperatures and to aeration. Under these conditions, ii has been found that chemical degradation of the antifreeze material does take place, and the degradation products can impart a corrosive quality to the solution. This, in turn, can cause the solution to corrode the metallic paths in which it flows, an obviously undesirable result.

The general solution to this problem has been to add various substances to the antifreeze composition which tend to retard corrosion of the metallic paths. Moreover, it has been found in recent years that various combinations of these substances seem to function cooperatively, thereby inhibiting corrosion better than the same substances used singly or in combination with other compounds. The reason for this cooperative performance is not fully understood.

The magnitude of the problem becomes more apparent when one considers the amazingly large number of metals 3,414,519 Patented Dec. 3, 1968 ice found in the cooling systems of modern internal combustion engines and other devices. These metals include aluminum, its alloys, cast iron, steel, brass, copper, and various solders, some of which contain tin and lead.

Obviously, the selection of the proper additives, and frequently as important, the proper quantities of these additives for the inhibition of corrosion of not only one of these metals, but of all of these metals, is a very difiicult task. Moreover, the modern trend of employing components made of aluminum and its alloys in internal combustion engines enlarges the problem even more. The difficulty of inhibiting the corrosion of a metal as high as aluminum in oxidation potential should be apparent.

Since corrosion can be caused by a number of factors other than corrosive products of alcohols, such as galvanic action, for example, it is also desirable to add corrosion inhibiting substances to the cooling system of an internal combustion engine during summer use. If the procedure is followed to supplement the protection afforded by antifreeze compositions containing corrosion inhibitors, corrosion in the cooling system of an internal combustion engine can be held to a minimum.

The primary object of the invention, therefore, is to provide a novel combination of corrosion inhibitors suitable for use in the cooling system of an internal combustion engine.

Another object of the invention is to provide a corrosion inhibitor formulation suitable for aqueous dilution in the cooling system of an internal combustion engine.

Another object is to provide a novel antifreeze composition suitable for aqueous dilution in the cooling system of an internal combustion engine.

The foregoing objects are achieved by a water-miscible alcohol containing a combination of corrosion inhibitors which comprises from about 0.7 to about 10 weight percent of a borate of an alkali or an alkaline earth metal, from about 0.007 to about 4 weight percent of a nitrite of an alkali or an alkaline earth metal, from about 0.007 to about 4 weight percent of benzotriazole and/or a related compound, and from about 0.1 to about 20 weight percent of an oil inhibitor which is a polar-type oil. These percentages are expressed in terms of weight percent of the alcohol.

Hereinabove and in the ensuing discussion and in the claims the amount of borate present in a given composition is recited on basis of the anhydrous borate. Either the anhydrous or the hydrated borate can be employed in compounding the formulations, however. Alternatively the borate can be produced in situ by reacting boric acid with the corresponding alkali or alkaline earth metal hydroxide.

During use the above water-soluble alcohol containing the corrosion inhibitor combination can be diluted with water. The dilution is usually in the range from about 2 to about 16 parts by weight of water to one part by weight of the alcohol, depending on the contemplated end use.

The preferred antifreeze composition comprises at least one water-miscible polyhydroxy alcohol as a freezing point depressant and contains as an anticorrosive agent between about 0.1 and about 3 percent oil inhibitor as defined herein, between about 1 and about 5 percent borate, between about 0.01 and about 2 percent nitrite, and between about 0.01 and about 2 percent benzotriazole and/ or related compound, the percentages being in weight percent of the alcohol. During use one part by weight of the composition is diluted with from about 2 to about 5 parts by weight of water.

The preferred concentrated summer inhibitor composition comprises at least one water-miscible polyhydroxy alcohol, and as an anticorrosive agent about 0.7 to about 10 percent borate, about 0.007 to about 4 percent nitrite,

about 0.007 to about 4 percent benzotriazole and/or related compound, and about 0.7 to about 20 percent oil inhibitor, the percentages "being in weight percent of the alcohol. During use one part by weight of the composition is diluted with from about 8 to about 16 parts by weight of water.

The oil inhibitor which forms a part of the inhibitor combination of the invention is water-insoluble and is not emulsified within the formulation but is present as a separate phase within the water-miscible alcohol which separates out even after vigorous shaking or stirring of the composition.

The oil inhibitor is made up of a polar-type oil. Oils of this type generally comprise a mineral oil base to which is added a polar organic material such as the alkali and alkaline earth salts of carboxylic acids having from about 10 to about 20 carbon atoms, a sulfonated derivative of an animal, vegetable, or mineral oil, and the like. Sulfonated derivatives of synthetic oils are included within the aforementioned classification. For the purposes of the present invention both the mineral oil base and the polar molecules must be present. The polar additive alone will not give corrosion inhibition. Similarly, no protection will be afforded by the mineral oil alone.

The polar-type oils having a pour point below about F., a flash point above about 300 F., and a viscosity from about 100 to about 400 Saybolt Universal seconds (SUS) at 100 F. are preferred.

The mineral oil base makes up the major portion of the polar-type oil. Preferably about 60 to about 95 percent by weight of the mineral oil and about 40 to about percent by weight of the polar organic additive are present.

The mineral oil base can be a high-boiling fraction from petroleum oil. Preferred for this purpose are the paraffin-base and the naphthene-base high-boiling hydrocarbon oils.

Broadly the polar organic material or additive to the mineral oil base is an amphipathic molecule which absorbs on the metal surfaces of the cooling system as a hydrophobic, oleophilic layer and anchors thereto a substantially uniform layer of the mineral oil. The term amphipathic as used herein and in the appended claims refers to a molecule possessing an unsymmetrical duality of affinity, one end being water-attracting and the other being water-repelling. Typical amphipathic additives are the alkali metal salts of carboxylic acids containing from about to about 20 carbon atoms such as the sodium salt of capric acid, the sodium salt of palmitic acid, the potassium salt of stearic acid, the lithium salt of lauric acid, and the like; also the alkaline earth metal salts of carboxylic acids containing from about 10 to about 20 carbon atoms such as the calcium salt of stearic acid, the barium salt of myristic acid, the magnesium salt of arachidic acid, and the like.

Still other amphipathic additives are the sulfonated derivatives of the various oils enumerated above and having a molecular weight of at least about 400. The sulfonated derivative of an oil is an oil which contains either a sulfate group [(OSO M], a sulfonate group [(SO M], or both wherein M represents an alkali or alkaline earth metal and n represents the valence of M. The sulfonated derivatives are prepared in general by reacting sulfuric acid with an oil and then neutralizing the resulting product with an alkaline material such as sodium hydroxide, sodium carbonate, sodium bicarbonate, calcium carbonate, barium carbonate, and the like. If the oil initially contains hydroxyl or olefinic groups, the sulfonated derivative, in general, will contain sulfate groups. On the other hand, if no hydroxyl or olefinic groups are initially present, the sulfonated derivative will contain sulfonate groups.

Examples of preferred sulfonated derivatives of animal and vegetable oils include the sulfate-group containing castor, cottonseed, corn, peanut, coconut, tallow oils, and the like. Other preferred additives are the sulfonated derivatives of petroleum fractions such as mahogany oil, for example. This oil usually contains sulfonate groups and is prepared by reacting sulfuric acid with petroleum oil and thereafter neutralizing the reaction product.

Preferred sulfonated derivatives of synthetic oils are the alkylarene sulfonates such as sodium eicosylbenzene sulfonate, barium eicosylbenzene sulfonate, sodium didodecylbenzene sulfonate, sodium hexadecylnaphthalene sulfonate, barium dinonylnaphthalene sulfonate, and the like. The alkyl portion of the alkylarene sulfonate usually contains from about 15 to about 25 carbon atoms and the arene portion usually is either benzene or naphthalene.

It has also been found that improved corrosion protection can be obtained frequently by including with the oil inhibitor an alkaline earth compound such as barium carbonate, calcium carbonate, or the like, in an amount ranging from zero up to about 10 percent by weight of the oil inhibitor. The alkaline earth compound can be either dissolved or highly dispersed in the oil inhibitor.

The three remaining inhibitor ingredients which form the inhibitor combination of the invention with the oil inhibitor include a borate of an alkali or alkaline earth metal, a nitrite of an alkali or alkaline earth metal, and benzotriazole and/or a related compound. These four ingredients, when mixed together as an anticorrosive agent, provide improved, cooperative corrosion inhibition in the cooling system of an internal combustion engine.

Illustrative alkali metal borates are sodium metaborate, sodium tetraborate, potassium tetraborate, the lithium borates, and the like.

Illustrative alkaline earth metal borates are the magnesium borates, the calcium borates, the strontium borates, and the barium borates.

Illustrative alkali metal nitrites are sodium nitrite, potassium nitrite, and lithium nitrite.

Illustrative alkaline earth metal nitrites are calcium nitrite, barium nitrite, and the like.

The benzotriazole and related compounds which form a part of the inhibitor formulation conform to the general wherein X can be nitrogen, aminomethylidyne ECNH methylidyne (ECN), benzylidyne (ECC H or guanidinomethylidyne /NH ECNHC R can be a hydrogen or an alkyl group, or an alkali metal when X is nitrogen, and R" can be a hydrogen or an alkyl, preferably a lower alkyl group. Common names of some of these compounds are benzotriazole, sodium benzotriazole, potassium benzotriazole, N-methyl benzotriazole, N-ethyl benzotriazole, bcnzimidazole, guanidino bcnzimidazole, 2-phenyl bcnzimidazole, tolyltriazole, propyl benzotriazole, sodium tolyltriazole, and the like.

The preferred antifreeze composition of the invention basically comprises a water-miscible polyhydroxy alcohol as a freezing point depressant. Ethylene glycol, propylene glycol, diethylene glycol, and the like may be mentioned as polyhydroxy alcohols suitable for this purpose. In general, the polyhydroxy alcohol will contain from 2 to 6 carbons.

Since commercially sold antifreeze compositions usually contain about 93 percent by weight alcohol, the antifreeze compositions described herein will contain about this amount, but it will be understood by those skilled in the art that a smaller percentage of alcohol in the antifreeze merely aifects the quantity necessary to depress the freezing point of a given amount of water and does not affect the function of the antifreeze. Antifreeze compositions sold commercially for use in internal combustion engines are usually diluted with Water until an alcohol concentration between 25% and 68% by volume (preferably between 33% and 40%) is obtained in the cooling system.

It has been found that improved overall corrosion protection can be obtained if the weight ratio of nitrite to benzotriazole or equivalent in the inhibitor is limited to between about 0.2 and about 1 part benzotriazole or equivalent to 1 part nitrite. The improvement obtained is illustrated in Table I, which shows the weight losses of several metal specimens during standard corrosion tests. The tests consisted of placing the specimens in a corrosive solution maintained at 80 C. and aerating the solution at a rate of 850 milliliters per minute. The corrosive solution consisted of about 33 percent by volume antifreeze in corrosive water containing about 100 parts per million each of chloride, bicarbonate, and sulfate ions. The antifreeze was prepared by forming a mixture of about 2.14 percent by weight boric acid, about 0.77 percent by weight calcium hydroxide, and the remainder ethylene glycol, and adding 1% by weight oil inhibitor consisting of 80% by weight mineral oil and 20% by weight sulfated triglycerides to form an inhibited antifreeze. To this composition were added the various amounts of sodium nitrite and benzotriazole listed in Table I.

TABLE I.CORROSION INHIBITING EFFECTS OF BENZO- TRIAZOLE AND SODIUM NITRITE l Solder Spot Rating: 6=excellent, 0=very poor.

In another experiment specimens were placed in a corrosive solution for about 200 hours. The corrosive solution consisted of about 33 percent by volume ethylene glycol in corrosive water which contained about 100 parts per million each of chloride, bicarbonate, and sulfate ions. The solution was maintained at about 80 C. and was aerated at a rate of about 850 milliliters per minute.

The corrosion inhibitors added were tolyltriazole, sodium nitrite, a polar-type oil, and a calcium or sodium borate. The borate was added in an amount sufiicicnt to give a predetermined reserve alkalinity. The latter is de- The experimental results are shown in Table II below. All concentrations are given in terms of weight percent relative to the amount of ethylene glycol present.

TABLE II.CORROSION INHIBITING EFFECT OF TOLYLTRIAZOLE Weight Loss, mg,/9 111. of specimen Inhibitor and Concentration Fe Al Brass Cu Mg SS 1 No inhibitor 631 63 94 49 101 4 Tolyltriazole, 0.05 wt. percent". 103 32 16 13 118 5 Tolyltriazole, 0.05 wt. percent. NtlNOg, 0.01 wt. percent Calcium Borate, reserve alkalinity 75, Oil A, 1 wt. percent 2 6 20 16 24 6 Tolyltriazole, 0.05 wt. percent NaNOz, 0.2 wt. percent Sodium Bot-ates, reserve alkalinity 80, Oil B, 2 wt. percent 3 5 20 10 23 6 From the data in the foregoing table it is readily apparent that the corrosion inhibitor compositions within the purview of this invention are extremely effective in the reduction of corrosion.

Corrosion tests were conducted in glass containers according to A.S.T.M. Method D-1384. In these tests, specimens of the metals usually found in automotive cooling systems are totally immersed for 336 hours in a solution containing the antifreeze composition. The solution is maintaind at a temperature of 160:5 F. and is aerated at the rate of 100:10 milliliters per minute. The corrosive properties of the solution containing the antifreeze are evaluated by the weight losses incurred by the specimens during the test. The weight loss of each metal is determined on three separate test runs, and the average weight loss is the final evaluation of the corrosive properties of the antifreeze, thereby evaluating in reverse the effectiveness of corrosion inhibitors in the antifreeze.

Water containing 100 parts per million each of chloride, sulfate, and bicarbonate ions was mixed with several antifreeze com-positions to form a series of test solutions containing 33% by volume antifreeze. The antifreeze compositions contained about 93% ethylene glycol and included the corrosive inhibitors shown in Table II, the balance being water. Oil A in the inhibitor formulations comprised by weight about percent mineral oil, about 10 percent sulfated cottonseed oil, about 6 percent methyl ester of tallow, and about five percent coconut oil, the balance consisting substantially of other related vegetable oils. Oil B comprises by weight about mineral oil, about 20 percent barium eicosylbenzenesulfonate, and about 5 percent barium carbonate. The results of tests run in accordance with'the above test method are shown in Table III.

TABLE III.-CORROSION TEST RESULTS OF INHIBITOR OF INVENTION AND INHIBITOR OF PRIOR ART Average Weight Loss in Mg. per 4 in. Specimen Test Corrosion Inhibitor Formula, Wt. percent of Antifreeze Composition Solution Cast Cast Steel Brass Solder Copper Iron Aluminum Inhibitor formula of commercially successful antifreeze 52 154 4 7 31 7 1.4% Calcium Borate, 1.0% Oil A, 0.2% Sodium Nitrite, 0.1% Benzotriazole, 0 5 2 6 5 7 1.9% Calcium Borate, 1.0% Oil A, 0.2% Sodium Nitrite, 0.1% Benzotriazole. 1 6 l 3 14 3 1.4% Calcium Borate, 1.0% Oil A, 0.2% Sodium Nitrite, 0.1% Benzimidazole... 1 3 2 3 12 3 1.9% Calcium Borate, 1.0% Oil A, 0.00% Sodium Nitrite, 0.00% Benzotriazole 0 103 1 4 28 5 F 1.9%1 Calcium Borate, 1.0% Oil A, 0.025% Sodium Nitrite, 0.025% Benzotria- 0 5 1 3 27 4 zo e. G 1.9% Calcium Borate, 1.0% OilA, 0.10% Sodium Nitrite, 0.025% Benzotriazole 0 5 2 2 8 4 H 1.9% Calcium Borate, 1.0% Oil B, 0.10% Sodium Nitrite, 0.025% Benzotriazole. 0 9 1 0 6 1 2.6% Sodium Borate, 2.0% Oil B, 0.200% Sodium Nitrite, 0.05% Benzotriazole. 1 0 1 2 1 2 J 2.6% Sodium Borate, 2.0% Oil B, 0.200% Potassium Nitrite, 0.05% Benzotria 0 0 0 0 2 0 z e. K 2.6%1 Sodium Borate, 2.0% Oil B, 0.200% Calcium Nitrite, 0.05% Benzotria- 0 0 0 0 0 0 zo e. L 2.6% Sodium Borate, 2.0% Oil B, 0.200% Barium Nitrite, 0.05% Benzotria- 0 0 0 0 0 0 fined as milliliters of 0.1 N HCl solution required to neutralize milliliters of the above corrosive solution after the addition of the calcium or sodium borate.

Test Solution A was composed of an aqueous solution of a commercially successful glycol antifreeze of the 75 prior art, one which has maintained an outstanding sales record because of its excellent quality. The weight losses listed in Table III, however, show conclusively that the inhibitor combination of the invention provides a very impressive reduction in corrosion, especially with respect to aluminum and to cast iron.

Summer inhibitor formulations are usually diluted more than antifreeze compositions when put in a cooling system. The summer inhibitor formulation described herein is suitable for about eightfold to about sixteenfold dilution in cooling water, and preferably comprises about 82 percent by weight solvent made up of about 67 percent by weight ethylene glycol and about 15 percent by weight water. Based on the ethylene glycol present the inhibitor concentrations are about 6 percent by weight sodium tetraborate, about 3 percent by weight sodium nitrite, about 1.5 percent by weight benzotriazole, and about 13.5 percent by weight oil inhibitor consisting of a paratfin oil and a mixture of barium and sodium alkylarenesulfonates in a weight ratio of about 4: 1, respectively. The composition can also include an antifoaming agent and suitable dyes. This formulation provides the same corrosion protection as described with respect to the antifreeze compositions of the invention.

It will be apparent from the above test results that the novel corrosion inhibiting combination of ingredients in accordance with the invention provides a marked improvement in corrosion protection over the best of the prior art. The improved protection is believed particularly significant in view of the recent trend toward the use of cast aluminum internal combustion engines, and aluminum components with internal combustion engines having ferrous metal engine blocks.

The foregoing discussion and the examples are illustrative. Still other variations within the scope of this invention will readily present themselves to the skilled artisan.

What is claimed is:

1. An aqueous cooling liquid for an internal combustion engine containing a water-miscible alcohol as the principal non-aqueous ingredient and a combination of corrosion inhibitors consisting essentially of, based on the alcohol present, from about 0.7 to about 10 weight percent of a borate of an alkali or an alkaline earth metal; from about 0.007 to about 4 weight percent of a nitrite of an alkali or an alkaline earth metal; from about 0.007 to about 4 weight percent of at least one compound having the general formula NR /l\|I RI! N wherein R is a member of the grouping consisting of a hydrogen, an alkyl group and an alkali metal and R" is a member of the grouping consisting of a hydrogen and an alkyl group; and from about 0.1 to about 20 weight percent of an oil inhibitor present as a separate phase; said oil inhibitor having a pour point below about F., a flash point above about 300 F., and a viscosity from about 100 to about 400 Saybolt Universal seconds at 100 F. and consisting essentially of from about 60 to about 95 weight percent of a paraffin-base or naphthene-base hydrocarbon oil and from about 40 to about weight percent of a polar organic additive which is an amphipathic material selected from the grouping consisting of a sulfonated derivative of animal oil, a sulfonated derivative of vegetable oil, and a sulfonated derivative of mineral oil.

2. The aqueous cooling liquid in accordance with claim 1 wherein the oil inhibitor also contains from 0 to about percent by weight of the inhibitor a carbonate of an alkali metal or an alkaline earth metal.

3. An antifreeze composition for an internal combustion engine containing a water-miscible polyhydroxy alcohol as the principal non-aqueous ingredient and a contbination of corrosion inhibitors consisting essentially of, based on the alcohol present, from about 1 to about 5 weight percent of a borate of an alkali or an alkaline earth metal; from about 0.01 to about 2 weight percent of a nitrite of an alkali or an alkaline earth metal; from about 0.01 to about 2 weight percent of at least one compound having the general formula wherein R is a member of the grouping consisting of a hydrogen, an alkyl group and an alkali metal, and R is a member of the grouping consisting of a hydrogen and an alkyl group; and from about 0.1 to about 3 weight percent of an oil inhibitor present as a separate phase; said oil inhibitor having a pour point below about 0 F., a fiash point above about 300 F., and a viscosity from about 100 to about 400 Saybolt Universal seconds at 100 F. arid consisting essentially of from about 60 to about weight percent of a paraffin-base or naphthene-base hydrocarbon oil and from about 40 to about 5 weight percent of a polar organic additive which is an amphipathic material selected from the grouping consisting of a sulfonated derivative of animal oil, a sulfonated derivative of vegetable oil, and a sulfonated derivative of mineral oil.

4. The antifreeze composition in accordance with claim 3 wherein the oil inhibitor also contains from 0 to about 10 percent by weight of the inhibitor a carbonate of an alkali metal or an alkaline earth metal.

5. An aqueous summer coolant composition for an internal combustion engine containing a water-miscible polyhydroxy alcohol as the principal non-aqueous ingredient and a combination of corrosion inhibitors consisting essentially of, based on the alcohol present, from about 0.7 to about 10 weight percent of a borate of an alkali or an alkaline earth metal; from about 0.007 to about 4 weight percent of a nitrite of an alkali or an alkaline earth metal; from about 0.007 to about 4 weight percent of at least one compound having the general formula wherein R is a member of the grouping consisting of a hydrogen, an alkyl group, and an alkali metal, and R" is a member of the grouping consisting of a hydrogen and an alkyl group; and from about 0.7 to about 20 weight percent of an oil inhibitor present as a separate phase; said oil inhibitor having a pour point below about 0 R, a fiash point above about 300 F. and a viscosity from about to about 400 Saybolt Universal seconds at 100 F. and consisting essentially of from about 60 to about 95 weight percent of a paraffin-base or naphthene base hydrocarbon oil and from about 40 to about 5 weight percent of a polar organic additive which is an amphipathic material selected from the grouping consisting of a sulfonated derivative of animal oil, a sulfonated derivative of vegetable oil, and a sulfonated derivative of mineral oil.

6. The aqueous summer coolant composition in accoidance with claim 5 wherein the oil inhibitor also contains from zero to about 10 percent by weight of the inhibitor an alkaline earth metal carbonate.

7. An aqueous cooling liquid for an internal combustion engine containing a water-miscible alcohol as the principal non-aqueous ingredient and a combination of corrosion inhibitors consisting essentially of, based on the alcohol present, from about 0.7 to about 10 weight percent of a borate of an alkali or an alkaline earth metal; from about 0.007 to about 4 weight percent of a nitrite of an alkali or an alkaline earth metal; from about 0.007 to about 4 weight percent of benzotriazole; and from about 0.1 to about 20 weight percent of an oil inhibitor present as a separate phase; said oil inhibitor having a pour point below about 0 F., a flash point above about 300 F., and a viscosity from about 100 to about 400 Saybolt Universal seconds and consisting essentially of from about 60 to about 95 weight percent of a paraffin-base or naphthene base hydrocarbon oil and from about 40 to about 5 weight percent of a polar organic additive which is an amphipathic material selected from the grouping consisting of a sulfonated derivative of animal oil, a sulfonated deriva tive of vegetable oil, and a sulfonated derivative of mineral oil.

References Cited UNITED STATES PATENTS 2,007,243 7/1935 Downing et a1 252388 2,803,603 8/1957 Meighen.

FOREIGN PATENTS 624,410 7/ 1961 Canada.

LEON D. ROSDOL, Primary Examiner. S. D. SCHWARTZ, Assistant Examiner.