Patent Application
20080132434
This application relates to vegetable oil lubricating compositions with improved thermal and oxidative stability, corrosion resistance, and antiwear pressure properties. The application also relates to an additive composition to improve thermal and oxidative stability, corrosion resistance, and antiwear properties of vegetable oil based lubricants.
Vegetable oils are biodegradable and unlike petroleum based lubricants, vegetable oils are derived from renewable resources. These characteristics make them excellent base stocks for the formulation of environmentally friendly lubricants. However, one major limitation of vegetable oils is their poor resistance to oxidative and thermal breakdown even in the presence of oxidation and corrosion inhibitors.
In U.S. Pat. No. 4,880,551, there are provided synergistic antioxidant compositions containing (a) 1-[di(4-octylphenyl)aminomethyl]tolutriazole and (b) 2,6-di-t-butyl-4-secbutylphenol, 2,6-di-t-butyl-methylphenol, and butylated phenol mixture. Another aspect of that disclosure concerns a lubricating composition comprising a major portion of mineral oil or synthetic lubricating oil, fluid or grease and 0.1 to 5.0 percent of aforementioned antioxidant composition. However, U.S. Pat. No. 4,880,551 does not consider lubricating compositions based on vegetable oils which are neither mineral nor synthetic in nature.
U.S. Pat. No. 4,880,551 also states that lubricating compositions may further contain extreme pressure agents and antiwear additives among other additives types. Work presented herein confirms that the antioxidant combination in U.S. Pat. No. 4,880,551 is very effective in providing thermal and oxidative stability and corrosion resistance to vegetable oil. However, the addition of phosphorus based or phosphorus/sulfur based ashless antiwear additives were antagonistic on these properties with the surprising exception of triphenylphosphorothionate (TPPT). In addition, antiwear protection provided by TPPT used at the inventive concentration exceeded that of other antiwear additives.
U.S. Pat. No. 5,538,654 discloses lubricating compositions comprised of (A) major amount of a genetically modified vegetable oil and minor amounts of (B) phenolic antioxidant and (C) TPPT in which (A):(B):(C) weight ratio are (94-99.9):(0.05-5):(0.05-1). However, the reference teaches that the upper limit for TPPT is 1%; and therefore does not foresee that the use of TPPT at 1.5 or higher weight percent would improve antiwear protection, or that 1-[di(phenyl)aminomethyl]tolutriazole acts synergistically with TPPT to achieve the desired antiwear protection, as well as acting to prevent detrimental effects on thermal stability and corrosion properties.
Thus, the present invention relates to lubricant compositions comprising a major amount of vegetable oil, and minor amounts of TPPT, phenolic antioxidant, 1-[di(phenyl)aminomethyl]tolutriazole, and ashless rust inhibitor. The invention also relates to an additive composition comprising TPPT, phenolic antioxidants, phenyl amino derivatives of benzo- or tolutriazole, and ashless rust inhibitor, which affords excellent thermal and oxidative stability, corrosion resistance, and antiwear properties when used in combination with vegetable oil based lubricant compositions. In one embodiment of the invention, the additive composition and the lubricating composition containing same are free or substantially free of phosphorus- or sulfur-based ashless antiwear additives, such as ashless dialkyldithiophosphate and amine phosphate antiwear additives, with the exception of TPPT.
The invention relates to a lubricant composition comprising the following components, all in weight %:
In a preferred embodiment of the invention, the lubricant composition comprises:
(a) at about 1.5 percent,
(b) at about 0.3-1 percent,
(c) at about 0.125-0.25 percent,
(d) at about 0.1 percent.
The invention also discloses an additive composition for use in vegetable oils. The additive composition is comprised of the following compounds:
Vegetable oil lubricating compositions with improved thermal and oxidative stability, corrosion resistance, and antiwear pressure properties are described in invention herein. The application also relates to an additive composition to improve thermal and oxidative stability, corrosion resistance, and antiwear properties of vegetable oil based lubricants.
Vegetable Oil
Vegetable oils of this invention are triglyceride mixtures:
Vegetable oils can be genetically or chemically modified to reduce polyunsaturation that reduces resistance to oxidative and thermal breakdown. In reducing polyunsaturation, the oleic acid content of vegetable oils is increased to levels above 60 weight percent. For lubricating applications, vegetable oils with high oleic contents (>60 mass percent) are preferred.
Triphenylphosphorothionate (TPPT)
TPPT is phosphorus/sulfur based compound with the following chemical structure:
Hindered Phenolic Antioxidants
wherein R1 and R2 are independent aliphatic groups that contain 1 to 12 carbons and R3 is hydrogen or aliphatic or alkoxy group containing 1 to 12 carbons. Preferably, R1 and R2 are tert-butyl groups and R3 is hydrogen or methyl groups.
Methylenebis phenols are of the formula:
wherein R4 is independent aliphatic group that contain 1 to 18 carbons and n is an integer from 0 to 3 or mixture of alkyl phenol and methylene bridged phenol. Preferred compound is 2,2′-methylenebis-(6-tert-butyl-4-methylphenol).
The formula for esters of beta (3,5 di-tert-4-hydroxylphenyl) propionic acid is the following:
wherein esters are produced from monohydric and polyhydric alcohols. Preferred alcohol is iso-octyl alcohol or R5 is branched C8 alkyl group.
Tolutriazole Derivatives
Tolutriazole derivatives of the invention prepared in known fashion from tolutriazole, formaldehyde and diphenyl amines by means of Mannich reaction and are the following formula:
wherein R6, R7, R8 and R9 are independently hydrogen or alkyl and styryl groups that contain 2 to 9 carbons. Preferred compound is 1-[di(4-octylphenyl)aminomethyl]tolutriazole wherein R6, and R9 are octyl groups and R7, and R8 are hydrogen.
Ashless Rust Inhibitor
Ashless rust inhibitors of this invention are alkyl succinic half ester acids:
wherein R10, R11, R12, and R13 are hydrogen and/or alkyl groups, at least one of R10, R11, R12, and R13 is always an alkyl group, and R14 is always an aliphatic group. For R10, R11, R12, and R13, alkyl groups are polybutyl moiety, fatty acids, isoaliphatic acids (e.g., 8-methyloctadecanoic acid). For R14, alkyl group contains 2 to 6 carbons or is alkoxy group. Commercial examples are VANLUBE® RI-A lubricant additive (alkyl succinic acid half ester derivative), and LUBRIZOL® 859 additive.
Test methods used in this invention to evaluate thermal stability, corrosion resistance, oxidative stability, and wear properties of vegetable oil based lubricating compositions were the following:
1. modified Cincinnati Milicron (CM) Test
2. Pressure Differential Scanning Calorimetry (PDSC), ASTM D 6186
3. 4-Ball Wear, ASTM D 4172
Modified Cincinnati Milacron measures thermal stability and corrosive properties of lubricating fluids. In this procedure, a copper and iron rod are kept in contact with each other under surface of 40 milliliters of test oil in beaker for 7 days at a constant temperature of 135° C. Upon completion, percent change in total acid number (TAN), and viscosity of the test oil is determined and copper and iron rods are rated for corrosion on scale of 1 to 10 with 1 being no corrosion.
PDSC is an instrumental technique that measures the oxidation stability of oils by detecting exothermic release of energy that occurs when oils succumb to autooxidation. For this invention, test oils were held 130° C. under 500 psi of oxygen pressure. The length of time required to reach autooxidation is a measure of oxidation resistance and is known as oxidation induction time.
Four-Ball Wear Test was conducted according to standard procedure described in ASTM D4172. In this test method, one ball is rotated on three evenly spaced static balls while the four balls are completely submerged under the test oil. The tests for this invention were conducted at a rotation speed of 1200 rpm under a load of 40 kg for a hour at 75° C. The scar diameter of three static balls is measured and averaged for the final result. An acceptable result for this test is an average wear scar that is less 0.4 mm in diameter.
Lubricating compositions were prepared using high oleic content Canola oil. Canola oil was tested without the addition of TPPT and with the addition of the phenolic antioxidant, tolutriazole derivative and ashless rust inhibitor of the invention. As expected, the addition of the additives led to significant improvement in thermal stability, oxidative stability and corrosion properties with no improvement in wear resistance. The addition of ashless antiwear additives such amine phosphates described in U.S. Pat. Nos. 4,701,273, 5,538,654 and 6,046,144, dialkyldithiophosphate esters described in U.S. Pat. No. 6,046,144 and phosphate esters improved wear resistance but for the most part did not lower wear scars to acceptable result of 0.4 mm or lower. More importantly, the more effective antiwear additives were detrimental to thermal stability and corrosion properties as summarized in Table 1.
To Canola oil composition containing phenolic antioxidant, tolutriazole derivative and ashless rust inhibitor was added different concentrations of triphenylphosphorothionate (TPPT) antiwear additive. Unlike other ashless antiwear, TPPT did not negatively affect thermal stability and corrosion properties and more surprisingly, acceptable wear scars were obtained at TPPT concentrations of about 1.5 weight % as summarized in Table 2. Of more surprising significant consequence is experiment 15, which shows that acceptable wear scar, oxidative stability, thermal stability and corrosion properties are not achievable if the tolutriazole derivative is removed from the composition.
1Vanlube ® RI-A is dodecenyl half ester rust inhibitor.
| Number | Date | Country | |
|---|---|---|---|
| 60867847 | Nov 2006 | US |
