US2945810A

US2945810A - Lubricating oil compositions containing bi-metal dithiophosphates

Info

Publication number: US2945810A
Application number: US631464A
Authority: US
Inventors: James H Walker
Original assignee: California Research LLC
Current assignee: California Research LLC
Priority date: 1956-12-31
Filing date: 1956-12-31
Publication date: 1960-07-19
Anticipated expiration: 1977-07-19

Description

LUBRICATING OIL COMPOSITIONS CONTAINING BI-METAL DITHIOPHOSPHATES James-H. Walker, Richmond, Calif., assignor to California Research Corporation, San Francisco, Calif., a corporation of Delaware No Drawing. Filed Dec. 31, 1956, Ser. No. 631,464 3 Claims. (Cl. 252-325 This invention :pertains to lubricating oil compositions which are particularly beneficial to use where silver wearing surfaces are concerned.v

In particular, lubricating oil compositions of. thisinvention are resistant to oxidation .and noncorrosive to silver wearing surfaces, as well as to the conventional metal alloy surfaces. Such lubricating oil compositions contain particular bi-metal saltsof dithiophosphoric acids.

Generally, oils of lubricating viscosity are now subjected to higher temperatures and greater conditions of wear than those which vexistedonly a relatively few years ago. Such changes in lubricating requirements are due primarily to the many advances which have occurred in the design of automotive equipment. For example, diesel engines used in railway service arenow equipped with bearings lined with pure silver metal. Also, many auto- United States Patent lice 2,945,810 Patented July .19, 1960 Thus, the oxidation and silver corrosion resistant oilcompure silver.

By the use of the particular bi-metal dithiophosphates of this invention, oxidation-resistant lubricants noncor- Iosive to silver have been obtained. The "particular reasons underlying the effectiveness of these particular dithiophosphates herein as inhibitors for lubricating oil compositions. is .not :known'.

'As used herein, the .term' bi-metal salts :of .dithiophos tpjhoric acids means :the product which is obtained by reacting'an :al'kaline'earth metal oxide or hydroxide with a metal salt of an ester of dithiophosphoric acid, the

metals being dissimilar.

The metal salts of esters of dithiophosp'horic acids of the prior'art which .r'eact withalkaline earth metal oxides mobiles have valve lifters which are subject to such high loads that the bearing surfaces operate under conditions approaching boundary lubrication. Thus, new requirements have been imposedonlubricating oils so that oils which were satisfactoryjust a few years ago are now inadequate for proper lubrication.

Metal salts of thiophosphoric acids, particularly alkaline earth metal and zinc salts of alkyl or alk'ylaryl dithiophosphoric acids, have long been used as additives for lubricating oils. These salts have been extremely efiective in inhibiting oxidation of oils and corrosion of alloy bearings. In more recent years, dithiophosphate salts were found to have another useful property, that of imparting extreme-pressure properties to oils. Because of these favorable characteristics, dithiophosphate salts have been outstanding among lubricating oil additives.

Even though the salts .of dithiophosphoric acids have such virtues as listed hereinabove, these salts have not been used universally because of one serious drawback; that is, such salts cause severe corrosion of silver in engines employing silver wearing surfaces. This attack of silver is believed due to the sulfur of the dithiophosphates. This sulfur attack on silver has often, been so severe in railroad diesel engines as to render these engines unfit for service after a comparatively short period of operation. In attempts to take advantage of the oxidation and corrosion inhibiting properties of the thiophosphate salts, the petroleum industry has spenta great deal of effort to overcome the deficiency with regard to silver. Although silver protective agents have been developed to minimize this sulfur attack by the thiophosphate salts,

isueh additives have not beenentirely satisfactory.

and hydroxides to :form the new bi-metal basic dithiophosphates herein are represented by the following formula:

RO-P-s- M droxidereactants, used in the formation of :the bi-metal dithiophosphates. At least one of the metals of the -bimetal dithiophospha-tes is an alkaline earth metal.

The R radicals and the R radicals can be derived from straight chain or branched chain alcohols containing at least 8 carbon atoms, .or alkylphenols wherein the alkyl radicals .contain a total of at least 6 carbon atoms; for example, n-octanol, Z-ethylhexanol, 2-propylpentanol, decanol, undecanol, vdodecanol, hexadecanol, octadecanol, vdipropylphenol, hexylphenol, dibutylphenol, decylpheno'l, dodeeylphenol, hexadecylphenol, octadecylphenol, dioctylphenol, 2-phenylhexanol, etc.

Examples of esters of dithiophosphon'c acids which are reacted with the alkaline earth metal oxides or hydroxides are dioctyl dithiophosphoric acid; octyldecyl dithiophosphoric acid; didecyl dithiophosphoric acid; didodecyl di-th iophosphorio acidydihexadecyl dithiophosphoric acid; dioctadecyl dithiophosphoric acid; di(decylphenyl) dithiophosphoric acid; di(am-ylphenyl)- di-thiophosphoric acid; di (dodecylphenyl) d-ithiophosphoric acid, etc.

Improved oil solubility of the resulting bi-metal dithiophosphate is obtained when the alkaline earth metal oxide (or hydroxide) reactant is a barium oxide (or hydroxide), the metal salt of dithiophosphoric acid is a zinc salt of esters of dithiophosphoric acid, and wherein each of the ester radicals (i.e., the R and R of the formula hereinabove) are derived from alcohols or alkylphenols containing not less than 12, carbon atoms, and not more than 25 carbon atoms (i.e., it is preferred that the total number of carbon atoms in the ester radicals-is 24 to 50).

M is a metal For purposes of simplification, the metal of the alkaline earth metal oxide and hydroxide reactants will be termed secondary metal, and the metal of the. dithiophosphate reactant will be termed primary dithiophos phate metal. 7

The particular bi-metal salts of esters of dithiophosphoric acids with which I am concerned have molecular weights of such magnitude as to indicate the formation 'of complex polymeric type compounds. Molecular weight data for these compounds, as determined by sedimentation rates in an ultracentrifuge, show that the molecular Weights are in the range of 150,000 to 550,000.

Suitable base oils include a wide variety of lubricating oils such as naphthenic base, paraffin base, and mixed base mineral oils; synthetic oils, e.g., alkylene polymers, such as polymers of propylene, butylene, etc., and mixtures thereof; alkylene oxide type polymers; dicarboxylic acid esters; liquid esters of phosphorus and silicon; and alkyl aromatic hydfocarbdns;

The above base oils may be used individually as such or in various combinations (wherever miscible or whenever made so by the use of mutual solvents).

The bi-metal salts of esters of dithiophosphoric acids are used in lubricating oils in amounts sufliicient to inhibit oxidation thereof; that is, amounts of 0.25% to 20%, by weight, preferably from 1.5% to 10% by Weight. Stated in other terms, the amounts of these bi-metal dithiophosphates may be expressed as millimols per kilogram" of finished oil, based on the phosphorus content. That is, the amountof bi-metal dithiophosphate is ex- Expressed in such terms, the amount of bi-metal salts of esters of dithiophosphoric acids used in lubricating oils can be from 1 millimol to 50 millimols of phosphorus per kilogram of finished oil, preferably from 4 millimols to 25 millimols.

In the preparation of the bi-metal salts of esters of dithiophosphoric acids, the simple neutral metal salts of esters of dithiophosphoric acids of the prior art can be prepared by methods known heretofore. For example, a mixture of the desired alcohol or alkylphenol and phosphorus pentasulfide is reacted with or without a solvent (e.g., petroleum naphtha) at 100 F. to 200 F. until the dithiophosphoric acid is formed. The crude acid mixture is then filtered to remove unreacted phosphorus pentasulfide, after which the resulting acid is neutralized with a metal oxide (e.g., zinc oxide) to form the metal dithiophosphate. Such simple metal salts of esters of dithiophosphoric acids can also be prepared by reacting the dithiophosphoric acid with sodium hydroxide to form the sodium salt, then precipitating the desired metal salt from a solution of the sodium salt by the addition of a metal chloride (e.g., zinc chloride or calcium chloride).

The bi-metal salts of esters of dithiophosphoric acids (e.g., barium-zinc diester dithiophosphates) are prepared by reacting a metal diester dithiophosphate with an alkaline earth metal oxide (or hydroxide) in a solvent (e.g., a lubricating oil), followed by heating to a temperature ranging from 200 F. to 450 F. (preferably from 250 F. to 375 F.), and filtering the resulting admixture. The following examples illustrate the preparation of lubricating oil compositions of this invention.

EXAMPLE 1 A mixture of 5 pounds (0.032 pound mol) of barium oxide (92% purity) and 125 pounds (0.0625 pound mol) of a zinc di(alkylphenyl) dithiophosphate (wherein the alkyl radical is derived from propylene polymers having an average of 12 carbon atoms) containing 3.27% zinc, 3.0% phosphorus, and 5.78% sulfur, was incorporated in a California solvent-refined paraflin base oil having a viscosity of about 140 SSU at 100 F. The whole mixture was heated in a kettle with agitation at 300-310 F. for a period of 1.4 hours. 79 pounds (0.245 pound mol) of barium hydroxide octahydrate (98% purity) was then .pressed as millimols of phosphorus per kilogram of oil.

as silver corrosion inhibitors.

'2,945,s1o p I e v acharged at the rate of 20 pounds per hour while the temperature was maintained at 300 F. to 310 F. The barium to-zinc mol ratio of this charge was 4.43 to 1.0. The pH of the charge (determined in a solvent consisting of 40%, by volume, of ethyl alcohol; 40% ethyl ether; and 20% water) increased from 4 to 13+. The whole mixture was agitated at 300 F. for another hour, with nitrogen flowing through the bottom of the kettle to remove residual moisture. This was followed by a final drying period of 30 minutes at 300 F. under a vacuum of 25 inches of mercury. To this mixture was added 5 pounds of Celite filter aid, after which the mixture was cooled to 250 F. and filtered.

The resulting product analyzed 1.76% zinc, 16.73% barium, 1.63% phosphorus, and 3.26% sulfur. The mol ratios based on zinc, as one, were as follows: barium, 4.52; phosphorus, 1.95; and sulfur, 3.78. The viscosity was 3838 SSU at F., and SSU at 210 F.

The barium-Zinc dialkylphenyl dithiophosphate product thus formed Was isolated from the lubricating oil concentrate as follows: 100 grams of a lubricating oil solution of the concentrate was dissolved in 100 ml. of benzene. 300 ml. of CP acetone was added to precipitate out the compound. The solid fraction precipitating out was separated and redissolved in 100 ml. of benzene and reprecipitated with 300 ml. of CP acetone.

Table I hereinbelow sets forth the analysis of the reprecipitated solid, again using the zinc content as the base for determining the molratio.

Table II hereinbelow presents data showing the effectiveness of the bi-metal dithiophosphates of this invention The silver strip test which was used is described as follows:

A silver metal strip having the dimensions of 2 /2 inches by inch by inch was first cleaned with a wire brush until the strip was highly polished. The strip was weighed and the weight recorded. This highly polished silver strip was then placed in a 600 ml. beaker in such a manner that the strip was completely immersed when 300 grams of the oil being tested was poured into the beaker. The oil was stirred at a temperature of 300 F. for 20 hours, at which time the silver strip was removed and cleaned, first with chloroform, then with petroleum ether. The appearance of the strip was noted. Those strips which had been severely attacked were quite black. The tested silver strip was washed in 15% aqueous solution of potassium cyanide for about 5 minutes to remove the sulfide film adhering to the strip. After the strip had been washed with potassium cyanide and dried, it was weighed. The difference in weight of the original strip and the strip after the potassium cyanide wash was noted and recorded as the weight loss due to corrosion.

The base oil of the compositions was a 60 V1. SAE 30 California base oil.

The amounts of the several components of the oil compositions are set forth in terms of millimols of additive per kilogram of finished oil, as determined by the metal content. For example, when a calcium sulfonate is expressed as being present in an amount of 10 millimols per kilogram, it is meant that the sulfonate was present in such an amount that the calcium content was 10 millimols per kilogram of finished oil.

ml. of test oil contained in a 400 ml. beaker.

Table II Tabllll" Gomponents/mM./kg. Oil N o.- 1 Oil No. 2 Additive (mM./kg.) StripqCozroston V 6S 3 M01 Base 011: 5 Ratio, Calcium Petroleum Sultnate 7 7 No Barium/ Copper- Suliurired OalcrumAlkylphenate l6 16 Zinc Bi-metal Sul- Phe- Lead Strip Silver Zinc Di(al kylphenyl) Dithiophosphate .4.... 6 Dithio fonate nafe- Strip Barium-Zinc-Basie Di(alkylphenyl) Dithiophosphate 1 phosphate u 1 3 ''6 A B Silver Strip Loss, mgs 145 r 1.11 e 7 is. T as so 1 The alkyl radicals contained an average of 12 carbon atoms. 3.0 6 7 13. 0 2 67 1 6 mM./kg. as determined by the zinc present. 3. 7 1 0.5 104 I 3; v 10 4' 8,1 1 Thus,.1t is readily seen thatlubricatmg o1l compos1t1ons 4.1 6 7 i 16 1L8 7 Y 4.1 10 7 4;? L5 6:]. contalmng small amounts of bi-metal salts of.d1esters of 1 10 7 72 5 5 dithiophosphoric acids are practically non-corrosive to I 22 j 6 4 4' 5 7 7 9' 107 8 43 s1 ver. 4. 5 1o 9 10 12" Y 6 Table III herembelow presents further data. showing 23 11 1 8 V 4. 5 12 7 15 7 the efiectiveness of bi-metal dithiophosphates as oxidation 10 4 i 37 v 5 inhibitors and as silver corrosion inhibitors in lubricating oil compositions.

The base oil, the test conditions, etc., which were used are described as follows:

With-'the'exception of Examples 1 and 2 (wherein the base oil was SAE the base-oil in each instance was a 60'V.I. SAE California base: oil.

The bi-metal dithiophosphates were prepared (unless otherwise noted) according to the process described in Examplel hereinabove, by reacting barium oxide and barium hydroxide. with a zinc di(alkylphenyl-) dithiophosphate, wherein the alkyl radical was obtained from polypropylenes containingan average of 1-2 carbon atoms.

The sulfonate was a calcium petroleum sulfonate wherein the petroleum radical was obtained from a California paraifin base oil having a viscosity of 480 SSU at: 100 F.

The. phenate was asulfurized calcium alkylphenate wherein the alkyl radical was obtained. frompolypropylenes having an average of 12 carbon atoms.

The copper-lead strip corrosion test A was run as follows: A polished copper-lead strip (obtained from a commercial bearing) was weighed and immersed in 300 The test oil wasmaintained at 295 F. under a pressure of one atmosphere of air and vigorously stirred with a mechanical stirrer. After 2 hours, a catalyst was added to provide the following. catalytic metals (all percentages being by weight):

The test was continued for 20 hours, after which the copper-lead strip was removed, rubbedvigorously with a soft: cloth, and weighed to. determine the weight loss. The copper-lead corrosion strip test- B was run as follows: A polished copper-lead strip (obtained from a commercial bearing) was weighed and immersed in 300 ml. of test oil contained in a 400 ml. beaker. The test oil was maintained at 340 F. under a pressure of one atmosphere of air and vigorously stirred with a mechanical stirrer. After 2 hours, the following catalyst was added to provide the following catalytic metals (all per centages being by weight):

The test was continued for 20 hours, after which the copper-lead strip was removed, rubbed vigorously with a soft cloth, and weighed to determine the net weight loss.

- lirepared frombarium oxide onl'y. 0.1% of asulturizeddiparaflfin sulfide. As noted from the above data, the -bi-metal' dithioa phosphates are particularly efiective. aslubricating oil additives; when the mol: ratio of the secondary metal to the. primary dithiophosphate metal is. from about 3.7 to 1 to about 4:6 to 1 (=i:e.,.ha's:avaluefrom13;7 to 4.6); TableIV hereinbelow sets-forth data obtained ina the Chevrolet L-.-4 engine test, further show-ingthe effectivenessofthe-bi-metal basic salts of diesters of dithiophosphoric' acids. as oxidation-corrosion inhibitors.

In.the L-4 engine test, corrosion characteristics of: the oilzwere determined :ina; Chevrolet standardo-cylinder enginein a typicallaboratoryinstallation. Weighed copperlead test. bearings and new piston rings. were installed. The test was run at a constant engine speed of 3150 r.p.m. under a load of 30 brake horsepower for a total of 36 hours subsequent to a run-in period of 8 hours. The

outlet temperature of the jacket coolant was 200 F: and the oil sump temperature was 280 F. At the conclusion of the test, the engine was disassembled and inspected for varnish and sludge deposits,. and the various parts were rated on a cleanliness scaleof 0. to 10,. 10 being perfectly clean. The bearings were weighed to determine the weight loss per whole bearing due to cor rosion. This L-4 engine test is more fully described in the CRC Handbook, 1946 edition, Coordinating Research Council, New York, N.Y.

compounded oil (A) was a 60 V1. SAE 30' California (base oil containing 7 mM./kg. of neutral calcium petroleum sulfonate and 0.1% by weight of a sulfurized diparaflin. sulfide.

Table. IV

Oil. I Weight Loss,.mg.

' per Whole Bearing (1) (;A) Greaterthan-500'. (2) Oil (A)+l0 mM./kg. Barium-zinc Di(alky1- .50.

phenyl) Dithiophosphatc.

1 The alkyl radicals were derived from polypropylenes containing an average of 12 carbon atoms. The barium/zine mol ratio was 4.4/1.

Table V hereinbelow presents data obtained from a test wherein the oil was subjected to severe conditions of operation. These data were obtained by the Navy Propulsion Load Tes-t described in MIL-P-17273 (Ships, 15 July 1952). The tests were run in a General Motors 4-cylinder diesel engine using 1% sulfur fuel. Copperlead bearings and pure silver bearings were employed. The tests were run at a constant speed of 1800 r.p.m. under a load of 30 brake horsepower per cylinder for 300 hours. The crankcase temperature was maintained at 250 F. The test was run continuously to simulate railroad diesel engine performance, unlike the. standard Navy test procedure, which permits regular four-hour shutdown periods. Sea water was also excluded for the Table V Weight Loss Copper- Oil Lead Bearing, mg. per Whole Hearing (2) Oil (A)+12 mM./kg. Barium-Zinc Di (alkylphenyl) Dithiophosphate Greater than 2,500. 11.

1 The aikyl radicals were derived from polypropylenes containing an average of 12 carbon atoms. The barium/7.11.10 mol ratio was 4.5/1.

The oxidation stability of the oils compounded with the bi-metal diester dithiophosphates of the present invention was determined by the following procedure. Oxidation tests were carried out in an apparatus of the type described by Dornte in Industrial & Engineering Chemistry, vol. 28, p. 26 (1936). Oxygen at atmospheric pressure was passed through the oil, maintained at 340 F., a fine fritted glass filter being employed in the bottom of the absorption cell to disperse the gas stream into very fine bubbles. The amount of oxygen absorbed was measured, and the time in hours required for 100 grams of oil to absorb 1200 cc.- of oxygen (S.T.P.) called the induction period, was noted. These test data are reported in Table VI, hereinbelow, wherein the compounded oil (B) is a 60 V.I. SAE 30 California base oil containing 7 mM./kg. calcium petroleum sulfonate and 0.25% by weight of a sulfurized diparaffin sulfide. In order to compare the two oils in the table below at approximately the same base level, a calcium salt of an alkylphenol was added to the oil containing the conventional zinc thiophosphate.

Table VI Induction Oil Period (Hours) (1) (EH-6 mM./kg. Zinc Di(alkylphenyl) Dithiophosphate +1G mMJkg. of a Calcium Alkylphenate 2. 5 (2) (EH-6 mM./kg. basic Barium-Zinc Di(alky1phenyl) Dlthiophosphate 5.6

1 Alkyl radicals derived from polypropylene having an average of 12 carbon atoms.

i Barium-to-zlnc mol ratio 4.1/1.

a Allryl radical derived from propylene polymers having an average of 12 carbon atoms. 7

Although the compositions of the present invention have been described above as being primarily useful as internal combustion engine lubricants, the additives herein are suitable for use in gear lubricants, ice machine oils, instrument oils, constituent oils for grease manufacture, turbine oils, and the like.

In addition to the additives noted hereinabove, the lubricating oils of this invention may contain other oxidation inhibitors, grease thickening agents, color correctors, extreme pressure agents, oiliness agents, gel modifiers, etc.

I claim:

1. A lubricating oil composition comprising a major proportion of a mineral lubricating oil, and from about 0.25% to about 20%, by weight, of a bi-metal salt of a dithiophosphoric acid, wherein said bi-metal salt is prepared by reacting barium oxide with a zinc salt of a diester of dithiophosphoric acid of the formula:

wherein R and R are hydrocarbon radicals containing a total of from 12 to carbon atoms, wherein the mol ratio of said barium to said zinc has a value from 3.9 to 4.6, said bi-metal salt having a molecular weight in the range of 150,000 to 550,000.

2. The lubricating oil composition of claim 1, wherein R and R are alkylphenyl radicals, wherein said alkyl radicals are derived from polypropylenes having an average of 12 carbon atoms.

3. A lubricating oil composition comprising a major proportion of a mineral lubricating oil, and from about 1.5% to about 10%, by weight, of a bi-metal salt of a dithiophosphoric acid, wherein said bi-metal salt is prepared by reacting barium oxide with a zinc salt of a diester of dithiophosphoric acid of the formula:

i Ro-r-S- Zn wherein R and R are alkylphenyl radicals having alkyl radicals derived from polypropylenes having an average of 12 carbon atoms, wherein the mol ratio of said barium to said zinc has a value from 3.9 to 4.6, and said bi-metal salt has a molecular weight in the range of 150,000 to 550,000.

References Cited in the file of this patent UNITED STATES PATENTS 2,441,587 Musselman May 18, 1948 2,713,557 Lowe July 19, 1955 FOREIGN PATENTS 717,039 Great Britain Oct. 20, 1954 723,133 Great Britain Feb. 2, 1955

Claims

1. A LUBRICATING OIL COMPRISING A MAJOR PROPORTION OF A MINERAL LUBRICATING OIL, AND FROM ABOUT 0.25% TO ABOUT 20%, BY WEIGHT, OF A BI-METAL SALT OF A DITHIOPHOSPHORIC ACID, WHEREIN SAID BI-METAL SALT IS PREPARED BY REACTING BARIU, OXIDE WITH A ZINC SALT OF A DIESTER OF DITHIOPHOSPHORIC ACID OF THE FORMULA: