US2839471A - Extreme pressure lubricants - Google Patents

Description

EXTREME PRESSURE LUBRICANTS Robert W. Scott, West'field, and Fred B. Fischl Springfield, N. 3., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application May 17, 1955 Serial No. 509,093

1 Claim. (Cl. 252-334) The present invention relates to additives for use in extreme pressure gear oils and the like. It relates particularly to phosphorus-. and sulfur-containing compositions designed to enhance the load carrying capacity of lubrieating oils, greases, and the like, employed where unit loads are exceptionally high as for example in automotive differential units and hypoid gearing. The invention pertains also to an improved method for preparing such additives and to lubricants containing theminappropriate proportions.

The present application is a continuatiomin-part of Serial No. 239,012, filed July 27, 1951, by the present applicams, and now abandoned.

The prior art recognizes the fact that lubricants containing phosphorus and sulfur, among other things, are capable of carrying higher unit loads without failure of the lubricating film than are lubricants which do not contain these elements. For example, certain hydrocarbon oils, such as the bright stock lubricating oil. and related mineral lubricating oil base stocks, may be treated at relatively high temperatures with various phosphorus sulfides, especially P 3 although P 5 P 8 and P 8 and others may also be used. Treatment is continued long enough to add substantial phosphorus. The resulting reaction products have been further treated with a reactive olefinic hydrocarbon which stabilizes the phosphorus sulfide treated oil, reducing or eliminating its corrosiveness toward copper, for example, and substantially reducing the tendency to evolve H 5 and thereby improving the odor of the products.

it is known that phospho-sulfurized oils which have been treated with a reactive olefin have improved anticorrosive properties and improved stability against evolution of H S under storage conditions or when used in lubricants. It has been found, however, that the compounded lubricants containing such oils are not entirely satisfactory in many cases from the standpoint of stability against sludge formation during storage. Although treatment or" the phospho-sulfurized oil with large amounts of reactive olefin may in some cases improve the sludge forming characteristics of a lubricant containing the treated additive, such treatment frequently impairs the extreme pressure performance of the lubricant.

has been found that finished lubricants including the reactive olefin-treated phospho-sulfurized oils of the above character are effectively stabilized by including in the composition from trace to extremely small quantities of both an oil-soluble aromatic hydrocarbon sulfonate and an oil-soluble kaline earth metal salt of an alkyl phenol sulfide. it has further been found that the use of only one the two latter-mentioned materials in the extreme pressure additive has substantially no effect on the stability of the finished lubricant. However, by using both a sulfonate and a phenol sulfide salt in proper combinations, a synergistic improvement in stability against sludge formation is obtained. Furthermore, gear oils and the like of excellent performance characteristics are obtained by using relatively small concentrations of reactive olefin in the itd States Patent() 2,339,47l Patented June 17, 1958 2 treatment of the phospho-sulfurized oil and combining therewith small amounts of the sulfonate and phenol sulfidc heretofore mentioned.

According to the present invention, a mineral lubricating oil base stock of about 56 to 250 S. S. U. viscosity at 210 F.,.or of higher viscosity, is treated with a substantial proportion of a phosphorus sulfide at an elevated temperature. Tl e proportions or: the phosphorus sulfide may vary from as little as 5 to as much as 25%, the preferred range being around 10 to 20% of the phosphorus sulfide based on the weight of the oil. The treating temperature employed is in the range of 375 to 475 F., preferably in the range of 406 to 430 F. The oil obviously must be of such type, including viscosity and boiling point, that it remains stable during the treatment. The time of treatment may vary somewhat, from as little as 1 hour to as much as 20 hours or more, but it is preferably continued for several hours, for example 10 hours or so and until the oil has a phosphorus content of 2 to 3% or more by Weight and a sulfur content of 5% or more by weight. The phosphorus content may be as high as 5 or 6% and the sulfur content as high as 10 to 12%, but treatment should not be extended to the point that the material becomes insoluble in the gear oil base stock in which it is to be used. Ordinarily the upper limit is about 5 to 6% for the phosphorus content and about 9 to 11% for sulfur. This phosphorus content, in particular, is higher than in most prior art practices.

Particularly suitable lubricating oil base stocks for the phospho-sulfurization are bright stocks having for examplc a viscosity at 210 F. in therange from about to 250 Saybolt seconds. They may be refined, for example,

. by deasphalting, dewaxing, acid-treating, clay-treating, etc.

In any case, however, the oils selected should be treated at high temperatures for extended periods so as to obtain a high phosphorus content. The phosphorus content desired is several times, and may be as much as 10 to 15 times, as high as in common prior art additives of this type.

The odor of the bright stock, treated in the manner described, is highly objectionable because there is usually a spontaneous evolution of H S gas, showing a fairly high degree of instability in the reaction product. In order to eliminate this instability, which is evidenced also in a high degree of eorrosivity toward copper, the reaction product of the oil and phosphorus sulfide is further treated.

The further treatment which stabilizes the phosphorus and sulfur-containing oil consists in reacting the material with suitable proportions, of about 2 to 39 weight percent on the total material of a suitably active olefinic hydrocarbon. By suitably active is meant that the olefinic material has the property of reacting with loosely bound sulfur in the phospho-sulfurized oil in order to stabilize the composition against subsequent H S evolution.

The preferred olefinic hydrocarbon materials to be reacted with the phospho-sulfurized material includes the terpenes, such as turpentine, dipentene, alpha-pinene, terpinene, terpineol, and the like and such olefinic hydrocarbons as isobutylene, diisobutylene and the more reactive of the analogous aliphatic and cycloaliphatic materials.

In particular, a product sold commercially as Dipentene consisting primarily of a mixture of true dipentene with its isomers and minor proportions of related products, is used in proportions of about 2 to 30% by weight based on the material to be treated, the ingredients being mixed together and heated at a suitable temperature until the product is stabilized. Preferred proportions are 5 to 15% by weight, particularly about 8 to 12% by weight. Stability is indicated by reduced evolution of H S gas at ordinary temperatures and at moderately elevated temperatures such gas and upon the degree of stability desired. More broadly, the time required for soaking may be as little as one-quarter of an hour to as much as 20 hours. When the higher temperature range for treatment, e. g. up to 400 F, is employed, the soaking time is, of course, quite short. For a moderate soaking temperature, such as in the range of 200 to 300 F., a longer soaking time obviously is necessary.

' An essential component of the compositions of this invention is an oil-soluble aromatic hydrocarbon sul fonate. This may be an alkali or alkaline earth salt, including the lithium, sodium, potassium, calcium, strontium, and barium salts of the hydrocarbon sulfonates prepared by the treatment of petroleum oils with strong sulfuric acid followed, for example, by treatment with a base of the metal. The alkali or alkaline earth metal sulfonates are most commonly used, but petroleum sulfonates of other metals may be used if they are soluble in the lubricant in the small concentrations required in the practice of the present invention. Synthetic sulfonates may also be employed in this invention, such as the alkali and alkaline earth metal salts (e. g. sodium, calcium, etc.) of sulfonicacids produced by sulfonating alkyl aromatic hydrocarbons such as alkylated benzene (e. g. benzene alkylated with polypropylene). Mixtures of the various sulfonates may be employed if desired. Preferably the sodium and calcium sulfonates are used. The most effective sulfonates are those having relatively high molecular weights such as from about 400 for monovalent to about 1100 for divalent salts. The sulfonates are generally added to the treated phospho-sulfurized additive in concentrations ranging from 0.02 to 1.0 weight percent with preferred concentrations ranging from 0.05 to 0.3 weight percent.

The alkaline earth metal salts of alkyl phenol sulfides also comprise an essential ingredient of the present composition. The alkaline earth metals include calcium, barium, strontium, and magnesium. The presence of at least one alkyl group in the benzene nucleus is usually necessary to impart oil solubility to the compound. The alkyl group may contain from 4 to 12 or more carbon atoms and may be straight chain or branched. From one to four sulfur atoms may interconnect benzene nuclei. The sulfide may contain only one alkaline earth metal or may have a mixture of at least two alkaline earth metals in the same molecule. Barium is generally the preferred metal, calcium being second choice, as a rule. A particularly preferred alkaline earth metal alkyl phenol sulfide is a mixed barium-calcium alkyl phenol sulfide having a weight ratio of barium to calcium in the range of about 4:1 to 1:4, preferably about 2:1 to 1:2. The salts of the alkyl phenol sulfides are well known to the art as detergents and sludge dispersers for lubricants. Methods of preparing such salts are described in U. S. 2,362,291, which discloses the preparation of barium salts; U. S. 2,362,292, which discloses the preparation of magnesium salts; U. S. 2,362,289, which discloses the preparation of calcium salts; and U. S. 2,362,292, which discloses methods of preparing mixed alkaline earth salts containing two different alkaline earth metals. It is seen that a wide variety of alkyl phenol sulfide salts may be employed in the practice of the present invention.

The concentration of the alkyl phenol sulfide salt is usually in the range of 0.05 to 2.0%, preferably in the range of about 0.1 to 1.0%, by weight based on the treated phospho-sulfurized oil. The weight ratio of sulfonate to alkyl phenol sulfide salt is preferably in the range of 1:1 to 1:3. The desired amounts of sulfonate and phenol sulfide salt may be added to the phosphosulfurized oil prior to treatment with the reactive olefin, or these materials may be added to the olefin-treated material before compounding in the finished lubricant. If desired the sulfonate and sulfide may be added to the finished lubricant which has been compounded with the treated phospho-sulfurized additive.

The treated phospho-sulfurized additive may be used in various proportions in lubricating oils depending upon the specific application. In the lubrication of automotive hypoid gears, 21 concentration of about 5 to 20 weight percent, preferably 8 to 10%, based on the total lubricant is generally required for satisfactory operation. It is thus seen that based on the finished lubricant only extremely small quantities of the sulfonate and phenol sulfide are required to impart effective protection against sludge formation. For example, only about 0.002 to 0.1 weight percent, preferably 0.005 to 0.03 weight percent, of sulfonate and 0.005 to 0.2 weight percent, preferably 0.01 to 0.1 weight percent, of alkyl phenol sulfide salt, based on the total composition, are needed for stabilization purposes. To the extent that the additive is soluble, concentrations in mineral oil containing up to 50% or more of the additive may be prepared for subsequent dilution.

The phosphorus sulfide-treated oil, stabilized by the addition of the compounds described above, is a potent extreme pressure additive which is substantially free from the objectionable odor of sulfur and sulfur-containing volatile materials, is not corrosive to copper at normal operating temperatures, and stabilizes the compounded oil against sludge formation. The finished material, however, contains a relatively very large proportion of phosphorus,

e. g. 2% or more and at least 5% sulfur. These elements,

as incorporated by the procedure of the present invention, are sufiiciently active to give the necessary film protection under conditions of extreme pressure. When the ordinary lubricating film fails, the instantaneous temperature rise at the point of contact causes formation of a phosphide or sulfide film on the metal surfaces to preserve them from mutual injury due to welding and/ or abrasion.

The invention will be further illustrated by reference to specific examples.

EXAMPLE I A deasphalted, dewaxed, acidand clay-treated Panhandle bright stock having an S. S. U. viscosity of 170 at 210 F. was treated in a nitrogen atmosphere with 17.5 weight percent, based on the oil, of P 8 for 10 hours at a temperature of 425 F. The product was then filtered.

Additive A was prepared by treating the above phosphosulfun'zed oil with 10 weight percent of commercial dipentene at a temperature of 380 F. with stirring for 1.0 hour. Commercial dipentene contains 31% dipentene, 39% terpinolene, 6% alphapinene, 10% para-cymene, 7% alpha terpeneol, 5% A2,4(8)-p-methadiene, and 2% residue. The material was then cooled to room temperature while blowing with nitrogen.

Additive B was prepared in the same way as additive A except that 20 weight percent of commercial dipentene was used in the treating step.

Additive C was prepared in the same way as additive A except that 0.17 weight percent of oil-soluble, sodium petroleum sulfonate having a molecular weight of about 500 and 0.67 weight percent of barium tert.-octyl phenol sulfide were added along with the dipentene to the phospho-sulfurized oil before the treating step.

Additive D was prepared in the same manner as additive A, and, after the dipentene treating step, identical concentrations of the same sulfonate and phenol sulfide used in making additive C were blended into additive D at F. temperature.

Additive E was prepared in accordance with the procedure used in making additive A except that 1.0 weight percent of barium tert.-octyl phenol sulfide was present during the treating step.

Additive F was prepared by the procedure used in making additive A except that 0.5 weight percent of oilsoluble, sodium petroleum sulfonate having a molecular weight of about 500 was present during the treating step.

The various additives contained in the range of 3.0 to 3.6 weight percent phosphorus and 6.3 to 7.3 weight percent sulfur. The additives were stable with respect to H 8 evolution.

The various additives were then blended in 10 weight percent concentrations, based on the total oil, in an oil blend of parafiinic and coastal stocks to make an SAE 90 gear oil. The blends were then placed in storage at a temperature of 140 F. Thermal storage stability was determined as the number of days the blend remained in storage before no more than a trace of sludge was produced. Results of the storage stability tests are shown in Table I.

Treatment of the phospho-sulfurized oil with only 10% dipentene produced an additive that rendered the oil blend unstable. Treatment with dipentene gave a blended oil having substantially the same stability as the oil containing no additive. The use of small concentrations of either sodium sulfonate or phenol sulfide salt in the 10% dipentene-treated material did not improve the storage stability of the oil, whereas the addition of both of these materials, either before or after dipentene treatment, resulted in an extreme pressure additive that did not impair finished oil storage stability.

EXAMPLE II SAE 90 gear lubricants were formulated by blending 10 weight percent, based on the finished oil, of additive B in one case and of additive C in another case, with an oil base stock containing a refined Mid-Continent residuum and a Mid-Continent acid-treated distillate oil. Both finished blends were tested for full scale gear performance by the high speed-low torque axle test, CRC-L-19, and the high torque-low speed axle test, CRC-L-ZO, in accordance with U. S. Ordnance Specification MIL-L- 2105. The oil base stock without additives of course does not pass either one of these tests. The performance of the gear oil containing additive C was quite satisfactory; however, the oil containing additive B was not entirely satisfactory for these severe tests. Although treatment of the phospbo-sulfurized additive with relatively large amounts of reactive olefin tends to improve the stability of the finished gear oil, the gear performance of the oil is weakened thereby. On the other hand, inclusion of very small amounts of petroleum sulfonate and alkyl phenol sulfide salt in the lubricant containing phospho-sulfurized additive treated with a relatively small amount of reactive olefin gave a gear oil of good stability without impairing its gear performance.

EXAMPLE III Phospho-sulfurized oils prepared substantially in accordance with the procedure described in Example I were treated with 10 weight percent commercial dipentene by two different procedures. In one series of treats, the additives were prepared by dipentene treatment at a soaking temperature of 380 F.. for one hour both with and without the sodium sulfonate and phenol sulfide (used in preparing additive C) being present. Another series of treats was carried out by 10% dipentene treatment at a temperature of 250 F. for a soaking time of two hours both with and without the sulfonate and phenol sulfide. The :treated products contained 3.6 weight percent phosphorus and 6.6 Weight percent sulfur. The treated additives were blended in 10 Weight percent concentrations in the base stock of Example II and the resulting blends were tested for storage stability at 140 F. Results of the test follow:

Sodium Barium Sulfonatc tert.-0ctyl Thermal Temperature of Dipentene in Oil Phenol Storage Treatment, F. Blend, Sulfide in Stability Weight Oil Blend, at, 140 F.,

Percent Weight Days Percent EXAMPLE IV Two additional additive compositions of the present invention were prepared as follows:

ADDITIVE G The following composition was formulated and then heated for one hour at 350 F., the resultant product being additive G:

Component: Wt. percent Phospho-sulfurized oil 1 89.5 Commercial dipentene 9.5 Ca-Ba alkyl phenol sulfide cone. 0.67 Sodium sulfonate cone. 0.33

1 Same as that described in first paragraph of Example I.

An oil concentrate containing as the active ingredient 40 wt. percent of calciu1n-barium tert. octyl phenol sulfide (wt. ratio of Ba/Ca: about 1.2).

An oil concentrate containing as the active ingredient about 50 wt. percent of oil-soluble synthetic sodium sulfonate (molecular weightzabout 470; prepared from sulfonic acids produced by sulfonating alkyl benzene obtained by alkylating benzene with polypropylene).

ADDITIVE H The following composition was formulated and then heated for one hour at 350 F., the resultant product being additive H:

1 Same as used in the preparation of additive G.

An oil concentrate containing as the active ingredient about 30 wt. percent of oil-soluble synthetic calcium sulfonatc (molecular weightzabout 950; prepared from sulfonic acids produced by sulfonating alkyl benzene obtained by nlkylating benzene with polypropylene).

Each of the two above-described additives was then blended in 10 wt. percent concentration, based on the total composition, in an oil blend of .parafiinic and coastal stocks to make two separate SAE gear oil compositions, one containing 10 wt. percent of additive G and the other containing 10 wt. percent of additive H. Both of these two compositions were then placed in storage in an oven at a temperature of F. There was no trace of sludge in either of the two compositions after storage at 140 F. for ten days, after which the test was V 7 discontinued. These results show that additives G and H had excellent thermal stability in oil blends.

Since stability of the lubricant in storage as well as under actual operating conditions is of considerable importance, the compounding of the lubricant in accordance with the present invention is necessary to achieve the versatility of stabilization needed under various conditions. Not only is treatment of the phospho-sulfuriz ed additive with controlled quantities of reactive olefin essential to prevent H S evolution and to avoid impaired lubricant quality, but also the inclusion in the finished lubricant of stabilizing amounts of both su-lfonate and alkyl phenol sulfide salt is essential to produce a thermally stable finished oil that will not precipitate objectionable quantities of insoluble sludge on storage or It will be obvious to the skilled workman that other additives in addition to the extreme pressure and stabilizin additives mentioned heretofore may be used in the finished lubricant. Such additives include thickeners, viscosity index improvers, oxidation inhibitors, metal deactivators, pour point depressants and the like.

What is claimed is:

A storage-stable gear oil composition comprising: a major proportion of a mineral lubricating oil and 10 'wt. percent of a treated phosphosulfurized additive; said additive being formed by reacting a deasphalted bright stock having an SSU viscosity of 170 at 210 F. with 17.5 wt. percent of phosphorus pentasulfide at 425 F. for about 10 hours, then reacting the phosphosulfurized material so obtained for one hour at 350-380 F. simultaneously with (1) about 9.5-l0 wt. percent of commercial dipentene, (2) 0.67 wt. percent of a wt. percent concentrate in oil of a calcium-barium tertiary octophenol sulfide having a barium/calcium ratio of about 1.2, and (3) 0.33 wt. percent of a sulfonate concentrate selected from the group consisting of a wt. percent concentrate in-oil of a sodium sulfonate having a molecular weight of about 470 and prepared from a sulfonated polypropylene alkylated benzene, and a 30 wt. percent concentrate in oil of a calcium sulfonate having a molecular weight of about 950 and prepared from a sulfonated po1ypropylene alkylated benzene.

References Cited in the file of this patent UNITED STATES PATENTS 2,379,453 Noland July 3, 1945 2,421,004 Berger et al. May 27, 1947 2,606,872 Gasser et al. Aug. 12, 1952 2,640,053 Hill et al. May 26, 1953