LUBRICATING OIL COMPOSITION FOR INHIBITING RUST FORMATION

Abstract: A lubricating oil composition comprising a lubricating oil basestock and a minor synergistic rust inhibiting amount of an additive comprising (a) rust inhibitor capable of reducing the interfacial tension between the oil and water in the oil from 1 to about 4 mN/m, and (b) a rust inhibitor containing a succinic acid derivative and a partially esterified alkyl succinic acid derivative having C2 to C10 alkyl groups, wherein the weight ratio of (b) to (a) is between 0 and 1:1.

Description: Lubricating Oil Composition For Inhibiting Rust Formation BACKGROUND OF THE INVENTION 1. Field of the Invention This invention concerns the use of a synergistic combination of two rust inhibitors to inhibit rust formation in lubricating oils. 2. Description of Related Art Many lubricating oils require the presence of rust inhibi¬ tors to inhibit or prevent rust formation, which often occurs due to water contacting a metal surface. However, we have found that a synergistic combination of rust inhibitors is particularly effective in preventing rust in lubricating oils. SUMMARY OF THE INVENTION In one embodiment, this invention concerns a lubricating oil capable of inhibiting rust formation which comprises a major amount of a lubricating oil basestock and a minor synergistic rust inhibiting amount of an additive combination comprising: (a) a rust inhibitor capable of reducing the interfacial tension between the oil and water in the oil to from about 1 to about 4 mN/m, and (b) a rust inhibitor containing a succinic acid derivative of the formula (Rl)2 - C-COOH (R2)2 - C-COOH and partially esterified alkyl succinic acid of the formula where Ri, 2, and R3 may be the same or different and are each an al yl group containing from about 2 to about 10 carbon atoms, wherein the weight ratio of (b) to (a) is greater than zero and less than 1:1. In another embodiment, this invention concerns a method for inhibiting rust formation in an internal combustion engine by lubricating the engine with the oil described above. DETAILED DESCRIPTION OF THE INVENTION This invention requires a major amount of a lubricating oil basestock and a minor synergistic rust inhibiting amount of a combina¬ tion of two oil soluble rust inhibitors. The lubricating oil basestock can be derived from natural lubricating oils, synthetic lubricating oils, or mixtures thereof. Suitable lubricating oil basestocks also include basestocks obtained by isomerization of synthetic wax and slack wax, as well as hydro- crackate basestocks produced by hydrocracking (rather than solvent extracting) the aromatic and polar components of the crude. In general, the lubricating oil basestock will have a kinematic viscosity ranging from about 5 to about 10,000 cSt at 40°C, although typical appl cations will require an oil having a viscosity ranging from about 10 to about 1,000 cSt at 40°C. Natural lubricating oils include animal oils, vegetable oils (e.g., castor oil and lard oil), petroleum oils, mineral oils, and oils derived from coal or shale. Synthetic oils include hydrocarbon oils and halo-substituted hydrocarbon oils such as polymerized and interpolymerized olefins (e.g. polybutylenes, polypropylenes, propylene-isobutylene copolymers, chlorinated polybutylenes, poly(l-hexenes), poly(l-octenes), poly(l- decenes), etc., and mixtures thereof); al ylbenzenes (e.g. dodecyl- benzenes, tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)ben¬ zene, etc.); polyphenyls (e.g. biphenyls, terphenyls, alkylated polyphenyls, etc.); alkylated diphenyl ethers, alkylated diphenyl sulfides, as well as their derivatives, analogs, and homologs thereof; and the like. Synthetic lubricating oils also include alkylene oxide polymers, interpoly ers, copolymers and derivatives thereof wherein the terminal hydroxyl groups have been modified by esterification, etherification, etc. This class of synthetic oils is exemplified by polyoxyalkylene polymers prepared by polymerization of ethylene oxide or propylene oxide; the alkyl and aryl ethers of these polyoxyalkylene polymers (e.g., methyl-polyisopropylene glycol ether having an average molecular weight of 1000, diphenyl ether of polyethylene glycol having a molecular weight of 500-1000, diethyl ether of polypropylene glycol having a molecular weight of 1000-1500); and mono- and poly- car- boxylic esters thereof (e.g., the acetic acid esters, mixed C3-C8 fatty acid esters, and C13 oxo acid diester of tetraethylene glycol). Another suitable class of synthetic lubricating oils com¬ prises the esters of dicarboxylic acids (e.g., phthalic acid, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebasic acid, fu aric acid, adipic acid, linoleic acid dimer, alonic acid, alkylmalonic acids, alkenyl malonic acids, etc.) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether, propylene glycol, etc.). Specific examples of these esters include dibutyl adipate, di (2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyl diester of linoleic acid dimer, and the complex ester formed reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2-ethyl exanoic acid, and the like. Esters useful as synthetic oils also include those made from C5 to C12 monocarboxylic acids and polyols and polyol ethers such as neopentyl glycol, trimethylolpropane, pentaerythritol , dipentaeryl- thritol, tripentaerythri ol, and the like. Silicon-based oils (such as the polyalkyl-, polyaryl-, polyalkoxy-, or polyaryloxy-siloxane oils and silicate oils) comprise another useful class of synthetic lubricating oils. These oils include tetra-ethyl silicate, tetraisopropyl silicate, tetra-(2- ethylhexyl) silicate, tetra-(4-methyl-2-ethylhexyl) silicate, tetra(p- tert-butyphenyl) silicate, hexa-(4-methyl-2-pentoxy)-disiloxane, poly(methyl)-siloxanes and poly(methylphenyl) siloxanes, and the like. Other synthetic lubricating oils include liquid esters of phosphorus- containing acids [e.g., tricresyl phosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid), polymeric tetrahydrofurans, polyalphaolefins, and the like. The lubricating oil may be derived from unrefined, refined, rerefined oils, or mixtures thereof. Unrefined oils are obtained directly from a natural source or synthetic source (e.g., coal, shale, or tar sands bitumen) without further purification or treatment. Examples of unrefined oils include a shale oil obtained directly from a retorting operation, a petroleum oil obtained directly from distil¬ lation, or an ester oil obtained directly from an esterification process, each of which is then used without further treatment. Refined oils are similar to the unrefined oils except that refined oils have been treated in one or more purification steps to improve one or more properties. Suitable purification techniques include distillation, hydrotreating, dewaxing, solvent extraction, acid or base extraction, filtration, and percolation, all of which are known to those skilled in the art. Rerefined oils are obtained by treating used oils in processes similar to those used to obtain the refined oils. These rerefined oils are also known as reclaimed or reprocessed oils and often are additionally processed by techniques for removal of spent additives and oil breakdown products. One of the oil soluble rust inhibitors used in this inven¬ tion (inhibitor A) must be capable of reducing the interfacial tension between the oil and water in the oil to from about 1 to about 4, preferably to from about 1.5 to about 2.5, mN/m, as measured by ASTM Test Method D971-82. The other oil soluble rust inhibitor (inhibitor B) prefer¬ ably contains a major amount (preferably at least 70 wt.%) of a succinic acid derivative of the formula (Rl)2 - C-COOH (R2)2 - C-COOH and a minor amount (preferably less than 30 wt.%) of a partially esterified alkyl succinic acid of the formula where R], R2, and R3 are each an alkyl group. The alkyl group may be linear or branched, with linear being preferred. If there are too few carbon atoms in each of R\ , R2, and R3, the inhibitor will be very soluble but cannot absorb on the metal surface to prevent rust. In contrast, if there are too many carbon atoms in each of Rj, R2, and R3, the inhibitor will not be sufficiently oil soluble. Accordingly, to ensure that Ri, R2, and R3 can be oil soluble and impart rust inhibition to the lubricating oil, Rj, R2, and R3 should each contain from about 2 to about 10, preferably from about 3 to about 5, and most preferably from about 3 to about 4, carbon atoms. Rj, R2, and R3 may be the same or different and saturated or unsaturated. Most prefer¬ ably, Ri and R2 will each be CH3 - CH = CH. The amount of the additive combination added need only be an amount that is necessary to impart rust inhibition performance to the oil; i.e.. a rust inhibiting amount. Broadly speaking, this corres¬ ponds to using at least about 0.03 wt.% of the combination. However, the minimum amount .required will vary with the particular feedstock. For example, high viscosity basestocks such as 1400 Neutral or higher base oils will require at least 0.1 wt.% or more, while most other lower viscosity basestocks (such as 150 to 600 Neutral) require at least 0.03-0.04 wt.%. Although not necessary, an amount of the combination in excess of the minimum amount required could be used if desired. The relative amount of the two inhibitors used is important. To pass the ASTM D665B rust test, the weight ratio of inhibitor B to inhibitor A should be greater than zero and less than 1:1. As shown in the following examples, rust inhibitors suitable for use in this invention are commercially available. As such, so is their method of preparation. If desired, other additives known in the art may be added to the lubricating base oil. Such additives include dispersants, anti- wear agents, antioxidants, corrosion inhibitors, detergents, pour point depressants, extreme pressure additives, viscosity index im¬ provers, friction modifiers, and the like. These additives are typically disclosed, for example, in "Lubricant Additives" by C. V, S alhear and R. Kennedy Smith, 1967, pp. 1-11 and in U.S. Patent 4,105,571, the disclosures of which are incorporated herein by refer¬ ence. A lubricating oil containing the synergistic rust inhibitor combination described above can be used in essentially any application where rust inhibition is required. Thus, as used herein, "lubricating oil" (or "lubricating oil composition") is meant to include automotive crankcase lubricating oils, industrial oils, gear oils, transmission oils, and the like. In addition, the lubricating oil composition of this invention can be used in the lubrication system of essentially any internal combustion engine, including automobile and truck engines, two-cycle engines, aviation piston engines, marine and railroad engines, and the like. Also contemplated are lubricating oils for gas-fired engines, alcohol (e.g. ethanol) powered engines, stationary powered engines, turbines, and the like. This invention may be further understood by reference to the following examples, which include a preferred embodiment of the invention. In the examples, the rust protection was measured using ASTM Test Method D665B, the disclosure of which is incorporated herein by reference. Example 1 - Properties of Base Oils Tested The properties of the nine base oils tested in the following examples are shown in Table 1. (1) A polyalphaolefin synthetic base oil obtained by polymerizing a Cχo monomer to form a mixture of three components: Cio trimer (C30), C10 tetramer (C40), and C10 penta er (C50). (2) A slack wax isomerate, which is the lubes fraction remaining following dewaxing the isomerate formed from isomerizing slack wax. (3) A white oil obtained by high pressure hydrogenation to saturate aro atics and remove essential¬ ly any sulfur and nitrogen from conventional base oils. (4) A conventional 150 Neutral NMP extracted base oil which is then solvent dewaxed and hydro- finished. (5) A conventional 150 Neutral phenol extracted base oil which is then solvent dewaxed and hydro- finished. (6) A conventional 150 Neutral NMP extracted base oil which is then solvent dewaxed and hydro- finished. (7) A conventional 600 Neutral NMP extracted base oil which is then solvent dewaxed and hydro- finished. (8) A conventional 600 Neutral phenol extracted base oil which is then solvent dewaxed and hydro- finished. (9) A conventional 1400 Neutral phenol extracted base oil which is then solvent dewaxed and hydro- finished. Example 2 - Rust Protection of Various Base Oils Using Lz 859 Rust protection tests were performed on the base oils of Example 1 containing various concentrations of Lz 859, commercial rust inhibitor available from The Lubrizol Corporation. This inhibitor is a mixture of about 74.5 wt.% unreacted tetrapropenyl succinic acid of the formula (CH3 - CH = CH)2 C - COOH I (1) (CH3 - CH = CH)2 C - COOH and about 25.5 wt.% of a partially esterified alkyl succinic acid of the formula (CH3 - CH = CH)2 C - COOH I • (2) (CH3 - CH = CH)2 C - C00(CH2)3 - OH which is obtained by reacting (1) with H0-(CH2)3-0H. The results of these tests are shown in Table 2 below. Table 2 The data in Table 2 show that only base oils D and G pass the rust test using 0.03 wt.% of Lz 859. At a concentration of 0.05 wt.%, base oils D-H (i.e. conventional base oils -- those containing less than about 95% wt.% saturates) passed the test. Only base oils A.-C (i.e . . non-conventional base oils -- those containing at least about 95 wt.% saturates) and base oil I (a high viscosity conventional base oil) failed the rust test. However, base oil C passed when the concentration of Lz 859 was increased to 0.1 wt.%. Oils A, B, and I still did not pass at concentrations up to 0.15 wt.%. Example 3 - Rust Protection of Various Base Oils Using Mobilad C603 Rust protection tests were performed on the base oils of Example 1 containing various concentrations of Mobilad C603, a commer¬ cial rust inhibitor available from Mobil Chemical Company. This inhibitor is a succinic anhydride amine solution that can reduce the interfacial tension between oil and water in the oil to from about 1 to about 4, preferably to from about 1.5 to about 2.5, mN/m, as measured by ASTM Test Method D971-82, the disclosure of which is incorporated herein by reference. The results of these tests are shown in Table 3 below. Table 3 The data in Table 3 show that Mobilad C603 can prevent rust formation in all of the base oils tested, but at significantly in¬ creased concentrations relative to the amounts required using Lz 859. For example, as shown in Table 2, Lz 859 can prevent rust formation in oils D-H at a concentration from 0.03-0.05 wt.%, but was ineffective in oils A, B, and I at higher concentrations. Example 4 - Synergism Between Mobilad C603 and Lz 859 Prevents Rust Mobilad C603 and Lz 859 were blended in a 1:1 weight ratio to determine the minimum concentration required to pass the rust test using several base oils described in Example 1. The results of these tests are shown in Table 4 below. Table 4 (1) Not tested because lower concentration passed. (2) Borderline failure. (3) Not tested because failed at a higher concentration. The data in Tables 2-4 show that a synergism between the two rust inhibitors allows obtaining rust protection at a lower concentra¬ tion of the mixture than can be obtained at higher concentration of each inhibitor alone. For example, oils E and H require 0.05 wt.% of Lz 859 (see Table 2) to pass the rust test, but only 0.03 wt.% to pass using a blend of Lz 859 and Mobilad C603 in a 1:1 weight ratio. Similarly, oils A-C normally require from 0.1 to 0.15 wt.% Mobilad C603 to pass, but did so using 0.03-0.05 wt.% of the blend. Example 5 - Weight Ratio of Lz 859 to Mobilad C603 Important The rust performance of different weight ratios of Lz 859 and Mobilad C603 in Oil B were determined at the same total concentra¬ tion (0.03 wt.%). The results of these tests are shown in Table 5 below. Tabl e 5 Lz 859/Mobilad C603 Ratio, wt.% Concentration wt.% Rust T R 100:0(1) 95:5 90:10 80:20 70:30 60:40 50:50 40:60 30:70 20:80 10:90 0:100(2) (1) Failed at 0.15 wt.% Lz 859. (2) Minimum of 0.06 wt.% required to pass. The data in Table 5 show that the weight ratio of Lz 859 to Mobilad C603 must be greater than zero and less than 1:1 for effective rust performance.

Claims: CLAIMS: 1. A lubricating oil which comprises a major amount of a lubricating oil basestock and a minor synergistic rust inhibiting amount of an additive combination comprising (a) a rust inhibitor capable of reducing the interfacial tension between the oil and water in the oil to from about 1 to about 4 mN/m, and (b) a rust inhibitor containing a succinic acid derivative of the formula (Rl)2 - C-COOH (R2)2 - C-COOH and partially esterified alkyl succinic acid of the formul where Rj, R2, and R3 may be the same or different and are each an alkyl group containing from about 2 to about 10 carbon atoms, wherein the weight ratio of (b) to (a) is greater than zero and less than 1:1. 2. The oil of claim 1 wherein any one of Rj . , R , and R3 contains from about 3 to about 6 carbon atoms. 3. The oil of claim 1 wherein Ri, R , and R3 are linear. 4. The oil of claim 3 wherein Ri and R2 are unsaturated. 5. The oil of claim 1 wherein (b) contains a major amount of the succinic acid derivative and a minor amount of the partially esterified alkyl succinic acid. 6. The oil of claim 5 wherein (b) contains at least 70 wt.% of the succinic acid derivative. 7. The oil of claim 6 wherein the succinic acid derivative in (b) is tetrapropenyl succinic acid. 8. The oil of claim 1 wherein at least 0.03 wt.% of the combination is present therein. 9. A method for inhibiting the formation of rust in an internal combustion engine which comprises lubricating the engine with the oil of claim 1.

Inventors: ASSELIN ANDRE E, PILLON LILIANNA Z, REID LLOYD E, ASSELIN, ANDRE, E., PILLON, LILIANNA, Z., REID, LLOYD, E.
Applicants: EXXON RESEARCH ENGINEERING CO, EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1992
Main classification: C10M129
IPC codes: C10M141, C10N30