US2929778A - Corrosion resistant sulfurized-phosphorized extreme pressure lubricant - Google Patents

Description

nited States ate t CORROSION RESISTANT SULFURIZED-PHOS- PHORIZED EXTREME PRESSURE LUBRICANT Allan A. Manteufiel, Crystal Lake, George W. Ayers, Chicago, and William D. Gilson, Crystal Lake, 11L, assignors to The Pure Oil Company, Chicago, 111., a corporation of Ohio Application September 13, 1956 Serial No. 609,543

7 Claims. (Cl. 252-44) No Drawing.

ing compositions as E.P. lubricant additives is Wellknown):

Each type of additive has-its advantagesand;dis'advair tages. The halogen-containing additives, while: capable of imparting high load-carrying characteristics. to oils, have the disadvantage of being corrosive and hydrolyzing in service to formobjectionable acids. The ability of sulfur to impart high load-carrying characteristics to a lubricating oil is dependent on the activity of the sulfur, which in turn is dependent on the tightness with which it is chemically bound in a compound. Elemental or loosely bound sulfur, while imparting high load-carrying characteristics, is too corrosive to be allowed to remain in an automotive differential or other gear assembly over a long period of time. The same is true of the phosphorus sulfides. On the other hand, sulfur and phosphorus sulfides when tightly bound chemically to organic compounds such as fatty acids, fatty esters, fatty alcohols and terpenes, impart excellent load-carrying characteristics to a lubricating oil and are substantially non-corrosive. However, additives of this type will not give the desired protection against wear to new gears during the initial break-in period.

An object of this invention-his to'provide artextreme' pressure lubricant. Anotherobject of this invention is to provide a composition which can be added to mineral and other lubricating oils to impart thereto extreme press'ure characteristics. A further object of the invention is to provide a lubricant which will protect gears against wear during the initial break-in period and during the subsequent running life of the gears. Still another object of the invention is to provide a composition which can be added to mineral oil and other types of lubricants to enable such lubricants to satisfactorily lubricate automotive gears during the initial break-in period and during the subsequent running life thereof. A still further object of the invention is to provide an extreme pressure lubricant which will satisfactorily lubricate gear assemblies during the initial break-in period and during the subsequent running life thereof without causing undue corrosion of the gear elements. Still another object is to provide a method for making the aforesaid compositions and lubricants.

Other objects of the invention will become manifest from the following detailed description of the invention.

In co-pending application Serial No. 606,585 there is disclosed a lubricating oil composed of a major portion of mineral lubricating oil, sulfurized and phosphorized fatty material and free sulfur or sulfur-liberating compound, with or without materials which will accelerate the chemical fixation of the free sulfur, namely, naphthenate salts and ammonium or amine salts of sulfonic acids. We have discovered that the conversion of the active sulfur to a non-corrosive form can be accelerated by incorporating in the oil a small amount of an organic phosphite or trithiophosphite (also called a phosphorotrithioitc). The accelerators used in accordance with our invention may be represented by the general formula (RS) P (phosphorotrithioites) and (RO) P (phosphites) in which the R may be an alkyl, aryl or alkylaryl radical. As specific examples of compounds falling within the scope of this invention may be mentioned triethyl phosphorotrithioite, diethyl hydrogen phosphite, and tricresyl phosphite. Any alkyl, aryl or alkylaryl phosphite or phosphorotrithioite may be used which is sutficiently 'soluble in the finished oil so that it does not precipitate out during storage.

The phosphites and phosphorotrithioites are effective for rendering sulfur non-corrosive, either in the presence or absence of naphthenate salts. In order to improve the anti-weld properties of lubricants in accordance with our invention, we preferrto. incorporate into the lubricant Glenda; naphthenatecsaltisnclnas lead naphthenate. The

sulfurized-phosphorized fatty material, sulfur: and lead naphthenate cooperate to provide the required anti-weld properties to the lubricant during the break-in period and the sulfurized-phosphorized fatty material in conjunction with dibenzyl'disulfide imparts the required load-carrying properties to the oil during operation subsequent to the break-in period.

As sulfurized and phosphorized compositions which are effective for the purpose of our invention we prefer sulfurized and phosphorized fatty bodies such as those made in accordance with Whittier et al., Patent 2,211,306. As therein disclosed, such sulfurized and phosphorized fatty bodies are prepared by sulfurizing a fatty material such as vegetable, animal, or marine oils and waxes, including but not limited to wool grease, cotton seed, castor, rape seed, sperm and lard oils, and synthetic esters of high molecular weight, mono-unsaturated fatty acids (C C such as glyceryl trioleate, propylene glycol dioleate and butylene glycol dioleate, at a temperature of approximately 330-340 F. with elemental sulfur until a satisfactory'copperstrip test is obtained, and then phosphorizing' the sulfurized material with a phosphorus sulfide, preferably phosphorus sesquisulfide,

at a temperature of about 220-230" Fluntil'a satisfactorycopper strip is obtained.

Instead of following the process set forth in the aforesaid Whittier et al. patent, the initial sulfurization step may be terminated prior to the time a satisfactory copper strip test is obtained, that is, when the copper strip shows a tan color, and then phosphorized with a phosphorus sulfide for a sufficiently long period of time to more firmly bind the su'fur and phosphorus. This method is particularly effective where higher amounts of phosphorus sescguisulfide within the limits of those disclosed in the aforesaid patent are used in the phosphorization step. As a specinc example, lard oil was mixed with 7.5% of sulfur and then was stirred with constant agitation in a kettle at a temperature of 325-340 F. Heating was continued for approximately four hours, at which time the copper strip gave a tan color upon immersion in a sample of the product at 300 F. for one minute. The mixture was then rapidly cooled to approximately 220 F., 0.8% by weight of phosphorus sesquisulfide was slowly added in finely divided form, and the reaction was allowed to continue at 220-230" F. for a period of eight hours, after which the mixture was rapidly cooled to F. and thereafter allowed to cool to room temperature. The final product contained 7.85% sulfur and 0.45% phos- 3 phorus by weight and gave a tan color on the strip test at 220 F. for one minute.

In preparing sulfurized-phosphorized fatty materials in accordance with the method just described, the fatty material may be reacted with about 5 to of sulfur in the first stage and with from about 0.4 to 5% of phosphorus sesquisulfide or equivalent amount of other phosphorus sulfide in the second stage. This method of preparing sulfurized-phosphorized fatty materials, in which sulfur is not tightly bound in the first stage and relatively large amounts of phosphorus sulfide are reacted in the second stage, is disclosed and claimed in co-pending application of P. R. Chapman and A. Manteuffel, Serial No. 553,419.

Instead of using elemental sulfur in conjunction with the sulfurized-phosphorized fatty material, we may add to the oil an unstable sulfur compound which will release elemental sulfur as, for example, dibenzyl trisulfide or other alkyl, aryl or arylalkyl poly'sulfides containing three or more sulfur atoms in the molecule. A phosphorus sulfide such asphosphorus sesquisulfide suspended or dissolved in the mineral oil will also function to provide the anti-weld properties for which the elemental sulfur is added. If desired, both sulfur and a phosphorus sulfide such as phosphorus sesquisulfide may be used in combination within the limits of the amounts specified above for sulfur. If a sulfur-liberating compound is used, it should be added in amounts sufficient to liberate the desired amount of sulfur.

In preparing gear oils in accordance with our invention, the sulfur or active sulfur-containing compound is dissolved in a portion or all of the mineral oil at a temperature of about 270290 F. After the addition of the sulfur or active-sulfur compound is complete, the temperature of the oil is reduced to about 200 F. before adding the sulfurized-phosphorized fatty material. It is important to reduce the temperature to this level to avoid immediate or rapid reaction, inactivation, or absorption of the sulfur into a substantially less active form. A suitable temperature for admixture of the sulfur-containing oil and the sulfurized-phosphorized fatty body is about l60200 F.

The manner of mixing the several constituents together or the order in which they are admixed is not important, provided temperatures are properly adjusted to a level which will permit solution of the additives in the oil within a reasonable period of time without causing substantial reaction between the active sulfur and the sulfurizedcopper fur compound to sulfurized-phosphorized fatty material is too high, the sulfur will not be completely absorbed and the corrosive condition of the gear oil will continue for an indefinite period of time with resultant harmful wear of the gear parts. The amount of sulfur which can be chemically absorbed is determined by the amount of the sulfurized-phosphorized fatty material and phosphite or phosphorotrithioite present and also by the amount of sulfur bound in the sulfurized-phosphorized material. A sulfurized-phosphorized material containing a relatively low amount of bound sulfur, as, for example, 5% by weight, enables the use of a larger amount of free sulfur or active sulfur-containing material than does a sulfurized-phosphorized material containing a higher amount as, for example, 10% of bound sulfur. In general, we have found that an amount of sulfur or equivaent active sulfur-containing compound between 1 and 50% of the ,quantity of sulfurized-phosphorized fatty material is cfphosphorized fatty material. The sulfurized-phosphorized fatty material, dibenzyl disulfide, naphthenate salt and phosphite or phosphorotrithioite, as well as other additives such as pour point depressors, V.I. improvers and antifoam agents, may be added separately to the oil or may be admixed together and added as an admixture. They may be dissolved directly in the oil in which the sulfur or active-sulfur compound which has been previously dissolved, or they may be admixed with a portion of the oil to which the sulfur or active-sulfur compound has not been added and this portion added to the portion containing the sulfur or active-sulfur compound. We prefer to add dibenzyl disulfide or equivalent disulfide as disclosed in claims in Reissue Patent 22,911, in order to improve the load-carrying properties of the oil. We also, preferably, incorporate in the finished lubricant a sufficient amount of aromatic extract obtained in the solvent extraction of mineral lubricating oil fractions by means of phenol, furfural, nitrobenzene and equivalent solvents in order to prevent precipitation.

In order to realize the benefits of our invention, it is necessary to adjust the proportions of sulfurized-phosphorized fatty material and sulfur, or activesulfur compound, so that the active sulfur is absorbed or chemically bound by the sulfurized-phosphorized material and does not remain in the oil in a corrosive form over a long period of time. If the ratio of sulfur or active-sulfective in providing initial anti-weld characteristics to the oil during the break-in period and of being subsequently absorbed or reacted with the sulfurized-phosphorized fatty material to a substantially non-corrosive state. We prefer an amount of sulfur equivalent to about 3 to 10% by weight of the sulfurized-phosphorized fatty material.

The amount of free sulfur or active sulfur-containing material to be added will be determined to some extent by the nature of the gears to be lubricated. For example. in the case of phosphate-coated gears the number of miles required for breaking them in is probably not more than and may be as low as 25 to 50. In such cases, therefore, it may be desirable to incorporate smaller amounts of sulfur so that the sulfur will be bound in an inactive or non-corrosive form within a short period of time, probably not more than 24 hours. On the other hand, green gears," that is, gears which are not precoated, are usually considered to be broken in after 500 miles of recommended driving speed. In such cases, sufficient sulfur should be present so that it will not be completely bound before the end of the period required to drive 500 miles, which on an average may be approximately one week.

The amount of sulfur required in the oil to furnish anti-weld protection during the necessary period of breakin can be approximated by subjecting an oil blend maintained at approximately 200' F. for the requisite period of time to the copper strip test. performed by immersing a clean copper strip for three minutes in a sample of the oil maintained at a temperature of 210 F. The appearance of the strip after this test provides an indication of the amount of corrosion which occurred and hence the extent to which the active sulfur has been bound in a non-active form. If the color of the strip remains clear and bright it is indicative of the fact that the sulfur has been tightly bound chemically and is in non-corrosive form. As the color of the strip progresses through light orange, orange. light brown, medium brown, mottled brown and brown-black, it indicates that the oil is more and more corrosive.

In order to demonstrate the effectiveness of compositions made in accordance with our invention, a number of blends were prepared and subjected to the copper strip corrosion test. The blends tested and the corrosion tests on each blend are given in the following table. Blends were made by dissolving free sulfur in approximately half of the total mineral oil, previously blended, at a temperature of 270-290 F. with stirring. The total mineral oil consisted of a blend of mineral oil, bright stock and solvent extract. These three constitutents were blended together to give the desired finished viscosity and V.I. The extract oil was used to insure complete compatibility of the additives, particularly sulfurized-phosphorized lard oil, in the finished oil andto inhibit precipitation.

After the sulfur had been dissolved in a portion of the mineral oil, the remainder of the oil was added, resulting in cooling of the'solution'to below 200 F. sulfurizedphosphorized la'rd oil, dibenzyl disulfide','lead naphthenate and phosphite or phosphorotrithioite were then added as indicated in the specific blends. During the addition of these additives, the oil was at a temperature between 160 F. and 200 F. The temperature was maintained below 200 F. to avoid premature inactivation of the sulfur.

Portions of the blends were heated in an oil bath to 200 F. and samples were subjected to the three-minute copper strip test at 210 F. after reaching bath temperature and thereafter at intervals of one hour, two hours, twenty-four hours, and one Week. The temperature of 200 F. was selected as representing the average temperature to which gear oils are subjected in service. The sulfurized and phosphorized lard oil used in the blends given in the ensuing table was made by heating 91.7 parts by weight of lard oil to 285, plus or minus F., and then dusting in slowly, with agitation, 7.5 parts by weight of sulfur. After the addition of the sulfur the temperature was raised to 335, plus or minus 5 F., and held at that level for four hours. At the completion of the heating period a copper strip was immersed in the bath for three minutes and was only lightly tarnished. The temperature of the reaction mixture was then lowered to 220, plus or minus 5 F., and 0.8 part by weight of phosphorus sesquisulfide was slowly added. This temand the desired rate of sulfur inactivation.

1o phosphorized lard oil may vary between approximately 0.1 and 5% by weight of the gear oil blend. The amount of phosphorotrithioite and/or phosphite required to accelerate the reaction will be dependent on the particular compound chosen, the amount of active sulfur present In general, amounts between 0.1 and 5% of the total gear oil blend are effective.

The amount of solvent extract in the blend may vary from 0 to 100% of the mineral oil portion, depending upon the desired V.I. and the compatibility characteristics of the finished blend. In general, amounts from 5 to 30% will prevent precipitation and at the same time give an oil with a commercially desirable V.I. The solvent extract used in the blends reported in the foregoing table had the following characteristics:

perature level was maintained for eight hours with con- Gravity 1"'ALEL)"L .w. 13.2 tinuons me'chanical agitation of the reaction "mixture: At. Flash"(C.OICl, 'F.) 550 the end of this period a copper strip immersed in the Fire (C.O.Cl, F.) 6,40 bath at 220 F. for three minutes gave a pink coating, in- S.U.S. viscosity at 100 F. 34,000 dicating that the reaction was completed. The final .prod- S.U.S. viscosityat"150 F. 2,824 not contained 7.85% sulfur and.0.45% phosphorus by" S.U.S. viscosity at 210 F 404 weight. Viscosity index 17 From an examination of the table, the following con- Pour point F.) +65 clusions can be drawn: (1) Blend 1 demonstrates that in Total sulfur (percent) 2.39 the absence of a phosphite or phosphorotrithioite the Neutralization number (ASTM D974) 2.8 blend still contained corrosive sulfur after being main- Conradson carbon residue 4.2

Table I Blend No. Composition in parts by weight of gear oil Neutral Oil, 200 SUS viscosity at 46.7 46.7 46.7.

100 F., 90 V.I. Bright stock, 160-170 SUS viscosity at 212 F.. 90 V.I. Solvent Extract ulf e ur Sulfurized-phosphorized rd Lead naphthen ate (3ll-00Fb):

Triethyl phosphorotrithioite.

Diethyl hydrogen phosphite Tricre=yl phosphite Viscosity:

at 100 F. at 130 F at 210 F. Viscosity Index.. 3 Minute Cu Strip Test:

Upon reaching bath temperature (approx. hour). After 1 hr. at 200 F After 2 hr. at 200 F.. After 24 hr. at 200 F After 1 week at 200 F.

clear and bright;

orange--. orange. clear and bright. clear and bright.

Light orange tained for one week at 200 F; (2) blend 2 demonstrates that the addition of 2% of triethyl phosphorotrithioite to blend 1 rendered the sulfur non-corrosive after the blend was maintained at 200 F. for two hours; ('3) blend 3 demonstrates that with the addition of only 1% of triethyl phosphorotrithioite the blend was slightly corrosive after one week; (4) diethyl hydrogen phosphite in the amount of 1.3% was effective in rendering the blend non-corrosive after one week, as was also true of 3.3% of tricresyl phosphite.

As was previously pointed out, the phosphorotrithioites and the phosphites are effective for inactivating corrosive sulfur in the absence of naphthenate salt. However, naphthenates such as ammonium, sodium, calcium, lead,

Any solvent extract of high aromaticity (above obtained by extraction of mineral lubricating oil fractions with solvents selective for separating paraflinic from aromatic hydrocarbons may be used in place of the specific extract used in preparing the blends given in the material which has been reacted with 5 to 10% by weight of sulfur and then with 0.4 to 5% by weight of phosphorous sesquisuliide until the product is substantially non-corrosive as measured by the copper strip test, from 0.1 to 5% of sulfur, about 0.5 to 2% by weight of may be added to the blend to help accelerate the removal dibenzyl disulfide, and a material from the group consisting of oil soluble alkyl, aryl and arylalkyl-phosphites and phosphorotrithioites in an amount of about 0.5 to 4% by weight.

2. A lubricant composition consisting essentially of mineral lubricating oil, from 5 to 20% by weight of lard oil which has been reacted with 5- to 10% by weight of sulfur and then with 0.4 to 5% by weight of phosphorus sesquisulfide until the product is substantially non-corrosive as measured by the copper strip test, from 0.1 to 5% of sulfur, about 0.5 to 2% by weightof dibenzyl disulfide, and a material from the group consisting of alkyl, aryl and arylalkyl phosphites and phosphorotrithioites in an amount of about 0.5 to 4% by weight.

3. Lubricant composition in accordance with claim 2 containing about 0.1 to 5% by weight of lead naphthenate.

4. Lubricant composition in accordance with claim 3 containing sufficient highly aromatic solvent extract from the extraction of mineral lubricating oil to substantially prevent precipitation. i

5. Lubricant composition in accordance with claim 4 in which the material is triethyl phosphorotrithioite.

6. Lubricant composition in accordance with claim 4 in which the material is diethyi hydrogen phosphite.

7. Lubricant composition in accordance with claim 4 in which the material is tricresyl phosphite.

References Cited in the file of this patent UNITED STATES PATENTS 2,160,577 Maag May 30, 1939 2,212,899 Flaxman Aug. 27, 1940 2,382,115 Stucker Aug. 14, 1945 2,391,311 Helmore Dec. 18, 1945 2,422,630 Musselman June 17, 1947 2,432,095 Frey Dec. 9, 1947 2,560,542 Bartleson July 17, 1951 2,580,005 Cyphers Dec. 25, 1951 2,629,721 Sunde Feb. 24, 1953 2,764,547 Fields Sept. 25, 1956 FOREIGN PATENTS Canada Ian. 17, 1950

Claims (2)

1. 2. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF MINERAL LUBRICATING OIL, FROM 2 TO 20% BY WEIGHT OF LARD OIL WHICH HAS BEEN REACTED WITH 5 TO 10% BY WEIGHT OF SULFUR AND THEN WITH 0.4 TO 5% BY WEIGHT OF PHOSPHORUS SESQUISULFIDE UNTIL THE PRODUCT IS SUBSTANTIALLY NON-CORROSIVE AS MEASURED BY THE COPPER STRIP TEST, FROM 0.1 TO 5% OF SULFUR, ABOUT 0.5 TO 2% BY WEIGHT OF DIBENZYL DISULFIDE, AND A METERIAL FROM THE GROUP CONSISTING OF ALKYL, ARYL AND ARYLAKYL PHOSPHITES AND PHOSPHOROTRITHIOITES IN AN AMOUNT OF ABOUT 0.5 TO 4% BY WEIGHT.
2. 3. LUBRICANT COMPOSITION IN ACCORDANCE WITH CLAIM 2 CONTAINING ABOUT 0.1 TO 5% BY WEIGHT OF LEAD NAPHTHENATE.