US2999813A

US2999813A - Lubricant comprising a sulfurized mineral oil and a polyvalent metal dithiocarbamate

Info

Publication number: US2999813A
Application number: US628980A
Authority: US
Inventors: Richard C Givens; Melvin R Hefty
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1956-12-18
Filing date: 1956-12-18
Publication date: 1961-09-12
Anticipated expiration: 1978-09-12

Description

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Tex., assignors to Texaco Inc., a corporation of Delaware No Drawing. Filed Dec. 18, 1956, Ser. No. 628,980

9 Claims. (Cl. 252-316) This invention relates to improved lubricating compositions comprising a sulfurized mineral lubricating oil, and more particularly to extreme pressure lubricants of the lead-sulfur type, containing polyvalent metal dithiocarbamates.

Major users of industrial gear lubricants have adopted more severe specification requirements during the past few years, calling among other things for greatly improved resistance to thickening at elevated temperatures in the presence of air in long time tests. This requirement has been ditficult to meet in otherwise very superior gear lubricants, particularly in the heavier grades of the better gear lubricants, wherein parafiinic residual oils are employed in order to obtain the desired viscosity characteristics and other advantages.

in accordance with this invention, very superior extreme pressure lubricants having the combination of properties required to meet the more severe requirements are obtained by employing as the base oil a stably sulfurized lubricating oil and in combination therein a minor but substantial amount of a lead soap, a minor amount of a sulfurized fatty oil and a minor amount of a polyvalent metal dithiocarbamate. We have found that a combination of superior properties is obtained in these compositions which is not obtainable in other lead-sulfur gear lubricants of the prior art. They have a considerable advantage over lead-sulfur gear lubricants of the usual type in that they contain only a very small amount of sulfur in the active form, and they thereby avoid the sludging and other difficulties associated with high contents of loosely bound, reactive sulfur. In addition, they provide the desired combination of high load bearing properties, represented by OK Timken values of at least about 45, and the very superior resistance to thickening required to give a 15 percent maximum viscosity increase by the extreme pressure oil oxidation by bubbling dry air method, hereinafter referred to as the extreme pressure oil oxidation test, specified in the United States Steel Lubricants Testing Laboratory No. 220 Lubricant Performance Requirements for Extreme Pressure Oil.

The stably sulfurized lubricating oils employed in these compositions are obtained by heating mineral lubricating oils with sulfur for a long time until the sulfurized products are substantially non-corrosive to metals. In this reaction, upon the prolonged heating, the reactive sulfur groups which are formed in the first stage of the reaction disappear and substantial thickening of the oil The product is therefore a material of very different character from the corrosive sulfurized oils ordinarily employed in lubricant compositions of this type which are obtained by heating the oils with sulfur for a short time only. The stably sulfurized mineral lubricating oil may be obtained by heating a suitable mineral lubricating oil with about 1 to 5 percent of sulfur at a temperature above about 350 F. and preferably at about 400 F. to 500 F. for several hours, so as to obtain a reaction product which is substantially non-corrosive to copper in the copper strip corrosion test at 212 F. The quantity of sulfur employed is calculated to give about 0.3 to about 1.5 percent, and preferably from about 0.5 to 1.2 percent, of sulfur in the oil. The lubricating oils employed in the sulfurization may be distillate or rates Patent 0 Patented Sept. 12, 1961 ice The sulfurized fatty oil may be any of the sulfurized natural or synthetically obtained fatty materials which have been employed heretofore as lubricant additives of the active sulfur type, such as may be obtained, for

example, by sulfurizing lard oil, sperm oil, corn oil, or the like. A particularly suitable material of this character is sulfurized lard oil containing from about 5 to 12 percent of the sulfur, obtained by heating lard oil with about 10 to 15 percent of sulfur at a temperature about 300 F. and preferably at about 350-400 F., for

a suificient time to obtain a homogeneous product.

About 0.5 to 5 percent, and preferably about 1 to 3 percent, by weight of this sulfurized oil may be employed in the lubricating composition.

The polyvalent metal dithiocarbamates employed are salts of organic substituted dithiocarbamic acids as described, for example, in U.S. 2,400,106. They are preferably polyvalent metal salts of N-aliphatic hydrocarbon substituted dithiocarbamic acids containing sufiicient aliphatic carbon atoms to impart oil solubility to the molecule, and most advantageously those wherein each nitrogen is substituted by aliphatic hydrocarbon groups containing about 4 to 20 carbon atoms. Suitable polyvalent metals include, for example, the alkaline earth metals, zinc, cadmium, magnesium, tin, aluminum and iron. Metals of the group II subgroup consisting of magnesium, cadmium and zinc are especially suitable. As examples of this preferred group of compounds may be mentioned zinc dibutyl dithiocarbamate, zinc diamyl dithiocarbamate, zinc di(2-ethylhexyl) dithiocarbamate, cadmium dibutyl dithiocarbamate, cadmium dioctyl dithiocarbamate, cadmium octyl-butyl dithiocarbamate, magnesium dibutyl dithiocarbamate, magnesium dioctyl dithiocarbamate, zinc petroleum base dithiocarbamates. and cadmium dicetyl dithiocarbamate. Especially desirable compounds of this class are zinc dibutyl dithiocarbamate, zinc diamyl dithiocarbamate, and cadmium dibutyl dithiocarbamate, which are commercially available materials. The polyvalent metal dithiocarbamate is usually employed in amounts of about 0.2-5 percent by weight, although somewhat larger or smaller amounts may be employed if desired, such as from about 0.1 to about 10 percent by weight.

The high stability against oxidative thickening in the extreme pressure oil oxidation test obtained in these compositions is surprising, since compositions comprising these stably sulfurized mineral oils have not been inhibited in this test by numerous other oxidation inhibitors of various types, including some of the most generally effective oxidation inhibitors commonly employed in lubricating compositions. In addition, the dithiocarbamates are of generally inferior oxidation inhibiting effectiveness in mineral lubricating oils of the ordinary types in the usual tests. The following table shows, for example, the effect of zinc dibutyl dithiocarbamate in an unsulfurized mineral lubricating oil in the Penn State oxidation test, as compared with the efiect of a common oxidation inhibitor of a different type. The Penn State oxidation test is a well-known test employed for determining the oxidation resistance oflubricating compositions, and is carried out by circulating oxygen in a closed system thrpugh a 2.50

gram sample of the test oil in a glass tube at a rate of liters per hour for 40 hours while the oil is maintained at 338 F. The lubricating oil employed was a refined paralfinic distillate oil having a viscosity of 3-28 seconds SU at 100 F. (kinematic viscosity of 71.0). The table also shows the strong pro-oxidant effect of. lead naphthenate upon. the same mineral lubricating oil in this test.

As shown by the above table, the unsulfurized mineral luubricating oil containing zinc dibutyl dithiocarbamate had thickened only slightly less than the base oil alone after 40 hours at 338 F. The composition containing zinc dibutyl dithiocarbamate had a characteristic high initial oxidation resistance in this test, an oxygen absorption curve of the test showing -a long induction period of about 18 hours, followed by a very rapid increase in oxygen absorption so that at the end of the 40 hour period the oxygen absorption had almost equaled that of the uninhibited oil.

In contrast with the failure of the polyvalent metal dithiocarbamates to inhibit other types of mineral lubri cating oils over long periods of time, as shown by the above test, the compounds of this class are extremely eflective in inhibiting the stably sulfurized mineral lubrieating oils employed in the lubricating compositions of this invention even in the presence of. strong pro-oxidants such as, lead naphthenate.

Thefollowing examples are given for the purpose of further disclosing the invention.

Example I A gear lubricant representative of a preferred embodiment of this invention was preparedv comprising a sulifurized mineral lubricating oil containing 7.5 percent of lead naphthenate, 2.0 percent of sulfurized lard oil and zinc dibutyl dithiocarbamate in amounts of both 0.5 and 1. percent by weight. The composition also contained 50 parts per million of an antifoam compound, which. was a 1.0 percent by weight solution of a dimethyl silicone polymer in kerosene.

The sulfurized mineral oil employed was a blend of sulfurized heavy parafinic residual oil and a sulfurized light. paraffinic distillate oil. The sulfurized. heavy residua'l oil was obtained by heating a residual oil having a viscosity of 381 seconds Saybolt Universal at 21.0 F. forabout 4.5 hours at 440 F. with 2.0 percent sulfur; and finally steaming in a vacuum tower to remove hydrogen sulfide. The product. had a viscosity of 457 seconds Saybolt Universal at 210 F. and contained 0.92 percent sulfur. The light parafiinic distillate oil was a fraction having a viscosity of about 168 seconds Saybolt Universal at 100 F., and was sulfurized. in the form of a 476 seconds viscosity blend with a minor portion of the heavy residual oil described. above by heating the blend for about 8 hours at 445 F. with 2.8 percent sulfur, and. finally steaming in. a vacuum tower to remove hydrogen. sulfide. The product had a viscosity of 591 seconds Saybolt Universal at 100 F. and contained 0.73 percent sulfur. Both oils were substantially non-corrosive to copper in the copper strip corrosion test at. 212 F. The. sulfurized stocks were: each mixed with 2.16 percent by weight. of sulfurized lard oil, based on the weight of the blend,. and; then; blended. together in aboutv a 31.5:55 byweight ratio of heavy to'light oil.

The sulfurizedlard oilemployed was obtained by heat. ing a No. I lard oil at about 300 F. for 4 hours while powdereds'ulfur. was added in a proportion of 33 pounds of powdered sulfur per barrel to 170 barrels of lard oil, then heating for 8 hours longer at 300-405 F. and finally steaming in a vacuum tower to remove hydrogen sulfide. The product contained 7.09 percent of sulfur and had a viscosity of 217 seconds Saybolt Universal at 210 F.

The zinc dibutyl dithiocarbamate employed was commercial product sold by the R. T. Vanderbilt Company under the name Butyl Zimate. Typical tests on this material show a melting point of 106 C., a sulfur content of 28.25 percent. and zinc content of 14.3 percent.

The lubricant was prepared by mixing the above mate rials in the proportions indicated in an ordinary grease kettle for about 3 hours while the temperature was maintained at about 160200 F., and drawing at about F.

The following table shows the results obtained upon this lubricant in the extreme pressure oil oxidation test, together with comparative data upon the same composition without the zinc dibutyl dithiocarbamate and also upon the composition containing various other inhibitors of diiferent types in place of the zinc dithiocarbamate. This test is carried out by circulating 10 liters of dry air continuously through a 300 ml. sample of the test oil in a: glass tube fora period of 13 days (312 hours) while the temperature of the test oil is maintained at about 200 F 207 F. The viscosity of the oil, at 210 F. is determined both-beforeand after the test.

TABLE II Viscosity Goncenincrease, Inhibitor tration SUS at percent 210 F percent Nona. r 18. 6 Phenyl-alpha-naphthylamine; 0. 5 21. 4 N,N,N,N tetramethyldiamino diphenylmethane 0. 5 22. O N,Ndisalicylidene-l,Z-diaminopropene 0. 5 17. 5 2,6-ditertiary butyl-4-methyl phenol 0. 5 18. 6 Diphenylamine 0. 5 21. 9 0. 5 21. 6 0. 5 21. 0 Ditertiary butyl-paracresol 0. 5 17. 4 Vanlube 26 1 1. 0 17. l Calco 2246 1. 0 30. 3 Zinc dibutyl dlthiocarbama 0. 5 11.7 Zinc dibutyl dithiocarbamate- 1. 0 6. 6

1 Commercial oxidation inhibitors otnnlmown composition.

As shown by the above table, thickening of the composition comprising the stably sulfurized mineral lubricating oil was inhibited to well below the required 15 percent maximum in the extreme pressure oil oxidation test by means of 0.5 percent of the polyvalent metal dithiocarbamate, and a still further inhibiting efiect was obtained by increasing the amount of polyvalent metal dithiocarbamate to 1.0 percent. In very striking contrast to the inhibiting effectiveness obtained by means of this compound, the other compounds of various types which are commonly employed as antioxidants in lubricating compositions were almost entirely ineffective or even increased the amount of thickening in this test.

In addition to the high stability against oxidative thickening as shown by the above table, this composition had high load bearing properties and other advantages, as shown by the following inspection tests obtained upon the composition containing 1.0 percent of zinc dibutyl dithiocarbamate:

Viscosity, SUS, at 210 F 125.7

Example II TABLE III Zinc dibutyl Viscosity dithiocarbaincrease, SUS, mate, percent at 210 F., by weight percent As shown by the above table, the composition based on the sulfurized paraffinic residual oil alone was also inhibited to the required degree by employing higher proportions of the polyvalent metal dithiocarbamate.

While the combination of stably sulfurized mineral lubricating oil and polyvalent metal dithiocarbamate is employed with particular advantage in the production of superior gear lubricants of the lead-sulfur type as described above, the use of this combination of stably sulfurized mineral lubricating oil and polyvalent metal dithiocarbamate in other lubricating compositions is also contemplated, and it may be employed either alone or together with other additives of various types wherever superior resistance to oxidation and other special properties are desired. Other extreme pressure agents which may be employed in these compositions include particularly phosphorus acid esters, such as tricresyl phosphate, other heavy metal soaps, and other active sulfur compounds, such as dibenzyl disulfide, diphenol disulfide, dioctyl sulfide, dicyclohexyl disulfide, sulfurized cyclohexene, sulfurized terpinolene, sulfurized oleyl alcohol, etc. Additives of other types, including other oxidation inhibitors, particularly those of the amine type, such as diphenylamine, diphenyl-para-phenylene diamine, etc., corrosion inhibitors, anti-foam agents, etc., may also be employed.

Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made Without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A lubricating composition consisting essentially of a stably sulfurized mineral lubricating oil in major proportion containing about 0.3 to 1.5 percent by weight of combined stable sulfur, about 5-20 percent by weight of a lead soap selected from the group consisting of lead naphthenates and lead soaps of fatty acids containing at least 8 carbon atoms per molecule, about 0.55 percent by weight of a sulfurized fatty oil, and about 0.1 to 10 percent by weight of an oil soluble polyvalent metal dithiocarbamate, wherein the said polyvalent metal is chosen from the group consisting of alkaline earth metals, cadmium and zinc, said stably sulfurized mineral lubricating oil being obtained by heating a mineral lubricating oil with sulfur at a temperature above about 350 F. until a sulfurized product is obtained wherein the sulfur is present substantially entirely in a form which is nonreactive with copper in the copper strip corrosion test at 212 F.

2. The lubricating composition of claim 1 wherein the said oil-soluble polyvalent metal dithiocarbamate is chosen from the group consisting of magnesium, cadmium, and zinc salts of N-aliphatic hydrocarbon substituted dithiocarbamate acids containing from about 8 to 40 aliphatic carbon atoms.

3. A lubricating composition consisting essentially of a stably sulfurized mineral lubricating oil in major proportion containing about 0.5 to 1.5 percent by weight of combined stable sulfur, about 0.5 to 5 percent by weight of an oil-soluble zinc dithiocarbamate, about 5-20 percent by weight of a lead soap selected from the group consisting of lead naphthenates and lead soaps of fatty acids containing at least 8 carbon atoms per molecule and about 0.5 to 5 percent by weight of a sulfurized fatty oil, said stably sul-furized mineral lubricating oil being obtained by heating a mineral lubricating oil with sulfur at a temperature above about 350 F. until a sulfuri'zed product is obtained wherein the sulfur is present substantially entirely in a form which is nonreactive with copper in the copper strip corrosion test at 212 F.

4. The lubricating composition of claim 3 wherein the said lead soap is lead naphthenate.

5. The lubricating composition of claim 3 wherein the said sulfurized fatty oil is sulfurized lard oil containing about 5-12 percent by weight of sulfur.

6. A lubricating composition consisting essentially of a stably sulfurized mineral lubricating oil containing about 0.5 to 1.5 percent of combined stable sulfur, about 0.5 to 5 percent by weight of an oil soluble Zinc dialkyl dithiocarbamate wherein the said alkyl groups each contains from about 4 to 20 carbon atoms, about 7 to 15 percent by weight of lead naphthenate and about 1 to 3 percent by weight of sulfurized lard oil containing about 5 to 12 percent of sulfur, said stably sulfurized mineral lubricating oil being obtained by heating a mineral lubricating oil with sulfur at a temperature above about 350 F. until a sulfurized product is obtained wherein the sulfur is present substantially entirely in a form which is nonreactive with copper in the copper strip corrosion test at 212 F.

7. The lubricating composition of claim 6 wherein the said oil soluble zinc dithiocarbamate is zinc dibutyl dithiocarbamate.

8. The lubricating composition of claim 6 wherein the said stably sulfurized mineral lubricating oil is a sulfurized parafiinic oil.

9. The lubricating composition of claim 6 wherein the said stably sulfurized mineral lubricating oil comprises at least about 50 percent by weight of a sulfurized paraffinie residual oil.

References Cited in the file of this patent UNITED STATES PATENTS 2,142,916 Parkhurst Jan. 3, 1939 2,212,189 Brunstrum Aug. 20, 1940 2,246,282 Zimmer et al. June 17, 1941 2,265,851 Matheson Dec. 9, 1941 2,400,106 Denison et al May 14, 1946 2,629,694 Woods et a1 Feb. 22, 1953 2,813,076 Edelman et al Nov. 12, 1957 2,820,011 Mahoney et al. Jan. 14, 1958 2,836,561 Elliott et al May 27, 1958 OTHER REFERENCES Kalichevsky et al.: Petroleum Refining with Chemicals, Elservier Pub. Go, January 1956 (pages 590 and 597).

Claims

1. A LUBRICATING COMPOSITION CONSISTING ESSENTIALLY OF A STABLY SULFURIZED MINERAL LUBRICATING OIL IN MAJOR PROPORTION CONTAINING ABOUT 0.3 TO 1.5 PERCENT BY WEIGHT OF COMBINED STABLE SULFUR, ABOUT 5-20 PERCENT BY WEIGHT OF A LEAD SOAP SELECTED FROM THE GROUP CONSISTING OF LEAD NAPHTHENATES AND LEAD SOAPS OF FATTY ACIDS CONTAINING AT LEAST 8 CARBON ATOMS PER MOLECULE, ABOUT 0.5-5 PERCENT BY WEIGHT OF A SULFURIZED FATTY OIL, AND ABOUT 0.1 TO 10 PERCENT BY WEIGHT OF AN OIL SOLUBLE POLYVALENT METAL DITHIOCARBAMATE, WHEREIN THE SAID POLYVALENT METAL IS CHOSEN FROM THE GROUP CONSISTING OF ALKALINE EARTH METALS, CADMIUM AND ZINC, SAID STABLY SULFURIZED MINERAL LUBRICATING OIL BEING OBTAINED BY HEATING A MINERAL LUBRICATING OIL WITH SULFUR AT A TEMPERATURE ABOVE ABOUT 350*F. UNTIL A SULFURIZED PRODUCT IS OBTAINED WHEREIN THE SULFUR IS PRESENT SUBSTANTIALLY ENTIRELY IN A FORM WHICH IS NONREACTIVE WITH COPPER IN THE COPPER STRIP CORROSION TEST AT 212*F.