Lubricating oil antioxidant, preparation method thereof and lubricating oil composition

Abstract

The invention discloses a lubricating oil antioxidant, a preparation method thereof and a lubricating oil composition. The lubricating oil antioxidant is prepared by carrying out alkylation reaction on diarylamine and alkyl-substituted 1, 2-dihydroquinoline under the action of a catalyst. The prepared alkyl diarylamine antioxidant is added into lubricating oil according to a certain proportion to form a lubricating oil composition, the oxidative decomposition of the lubricating oil can be inhibited, the oxidation induction period of the lubricating oil is remarkably prolonged, and the performance of the alkyl diarylamine antioxidant is superior to that of a commercially available lubricating oil composition.

Description

Technical Field

[0001] The present invention belongs to the field of fine chemicals, and in particular relates to a lubricating oil antioxidant, a preparation method thereof, and a lubricating oil composition. Background Art

[0002] Contact between lubricating oil and metal surfaces within the engine can lead to the deposition of metal-containing particles into the oil. These particles can act as oxidation catalysts, accelerating oil degradation. It is generally believed that the elevated temperatures common in engines and other operating machinery also accelerate lubricating oil oxidation.

[0003] Lubricant oil oxidation can adversely affect the oil's physical and chemical properties and weaken its ability to protect engine components. For example, oxidation increases the oil's acidity, accelerating wear and corrosion of engine components. Oxidation also produces sludge and film, which can clog oil circulation channels. Furthermore, oxidation increases oil viscosity, interfering with oil circulation and filtration systems. To prevent these adverse effects, oil-soluble antioxidants are often added to lubricants to inhibit oxidation, increase lubricity, and regulate viscosity fluctuations caused by temperature changes.

[0004] In view of the above reasons, it is of great significance in the art to provide a lubricating oil antioxidant to provide better protection for lubricating oil base oil and prevent it from oxidative damage. Summary of the Invention

[0005] In order to achieve the above-mentioned object, the present invention provides a lubricating oil antioxidant, a preparation method thereof, and a lubricating oil composition.

[0006] The technical solution adopted in the present invention is:

[0007] A lubricating oil antioxidant is prepared by alkylation reaction of diarylamine and alkyl-substituted 1,2-dihydroquinoline in the presence of a catalyst.

[0008] Furthermore, the alkyl-substituted 1,2-dihydroquinoline is at least one of 2,2,4-trimethyl-1,2-dihydroquinoline, 2-methyl-2,4-diethyl-1,2-dihydroquinoline, 2,2,4,6-tetramethyl-1,2-dihydroquinoline, 2,2,4,7-tetramethyl-1,2-dihydroquinoline and 6,6'-bis(2,2,4-trimethyl-1,2-dihydroquinoline).

[0009] Furthermore, the purity of 2,2,4-trimethyl-1,2-dihydroquinoline is 60-100%. Most processes for manufacturing TMDQ produce a product mixture containing approximately 30% to approximately 50% TMDQ monomer. Simple distillation of this product can provide TMDQ monomer with a purity between 83% and 92%. Rectification of the product obtained from simple distillation can provide TMDQ monomer with a purity greater than approximately 92%.

[0010] Furthermore, the diarylamine is at least one of diphenylamine, phenyl-α-naphthylamine, dimethylaniline, amphetamine, dinaphthylamine, 4-phenyldiphenylamine, p-hydroxydiphenylamine, p-aminodiphenylamine and isopropoxydiphenylamine.

[0011] Furthermore, the catalyst is at least one of hydrogen chloride, phosphoric acid, sulfuric acid, zinc chloride, aluminum chloride, aluminum bromide, ferric chloride, boron trifluoride, hydrofluoric acid, tin chloride, acid-leached clay and iodine.

[0012] The preparation method of any one of the above-mentioned lubricating oil antioxidants comprises the following steps:

[0013] (1) Add diphenylamine to the reactor, add the catalyst after nitrogen purge, and heat until the diphenylamine melts;

[0014] (2) heating the melt to 80-140° C. under stirring, then adding alkyl-substituted 1,2-dihydroquinoline and reacting for 0.5-6 hours. After the reaction is completed, cooling and adding a solvent;

[0015] (3) Separate and remove the aqueous layer, then add alkali solution to neutralize the reactant, and wash with hot water;

[0016] (4) The washed product is distilled and dried under normal pressure, and then the excess diphenylamine and volatile organic compounds are removed by distillation under vacuum, and the product is filtered.

[0017] Furthermore, the solvent is xylene.

[0018] Furthermore, the molar ratio of the alkyl-substituted 1,2-dihydroquinoline to the diarylamine is (1.5-0.4):1, and the molar ratio of the diarylamine to the acidic catalyst is (15.6-1.8):1.

[0019] The reaction of the alkyl-substituted 1,2-dihydroquinoline and the diarylamine of the present invention is carried out in the presence of an acidic condensation catalyst. A typical example of such a catalyst is the Friedel-Crafts catalyst familiar to those skilled in the art. A diarylamine (e.g., diphenylamine) is melted with an acidic catalyst (e.g., aluminum chloride), and the alkyl-substituted 1,2-dihydroquinoline (e.g., TMDQ) is then added to the melt. The relative proportions of the reactants can vary widely, with a preferred molar ratio of the alkyl-substituted 1,2-dihydroquinoline to the diarylamine being from about 3:2 to about 1:2.5, more preferably from about 5:4 to about 1:2. The molar ratio of the diarylamine to the acidic catalyst can range from about 94:6 to about 65:35, and most preferably from about 91:9 to about 82:18. The alkyl-substituted 1,2-dihydroquinoline can be added to the melt over a period of about 30 to 180 minutes, preferably about 45 to 120 minutes. The reaction temperature can be between 80 and 140°C, preferably between 105 and 125°C. After the reaction is complete, the mixture is washed with water, neutralized with a dilute alkaline solution such as ammonium hydroxide, sodium hydroxide, or potassium hydroxide, and then washed again with water. Unreacted volatiles, including excess diphenylamine, are removed by vacuum distillation.

[0020] The composition of the resulting reaction products will vary depending on the reactants, reaction conditions, and stoichiometric ratios employed. For example, the reaction can include various products resulting from the alkylation of diarylamines with alkyl-substituted 1,2-dihydroquinoline units. Diarylamines can be alkylated with any of a variety of combinations of alkyl-substituted 1,2-dihydroquinolines, including monomers, dimers, trimers, tetramers, and higher polymers.

[0021] A lubricating oil composition comprising any one of the above-mentioned lubricating oil antioxidants.

[0022] Furthermore, the weight percentage of the lubricating oil antioxidant in the lubricating oil composition is 0.01 to 5%.

[0023] The reaction product prepared by the present invention is added to a lubricating oil base to provide a lubricating oil composition having excellent antioxidant properties. In the practice of the present invention, various natural and synthetic lubricating oil bases can be used, such as hydrocarbon oils, synthetic oils, and kerosene. These lubricating oil bases include crankcase lubricants for spark-ignition and compression-ignition internal combustion engines, including automobile and truck engines, two-cycle engines, aviation piston engines, marine and railway diesel engines, etc. The lubricating oil base can also be used in gas engines, stationary power engines, and turbines. The same effect can be achieved by adding the antioxidant composition of the present invention to automatic transmission fluids, drive shaft lubricants, gear lubricants, metalworking lubricants, hydraulic oils, and other lubricating grease compositions.

[0024] Natural oils include solvent refined or acid refined paraffinic, naphthenic, aromatic or paraffinic-naphthenic mineral lubricating oils. Oils having lubricating properties extracted from coal or shale are also useful base oils.

[0025] Synthetic lubricating oils include hydrocarbon oils and halogenated hydrocarbon oils, such as polymerized and interpolymerized olefins (e.g., polybutene, polypropylene, propylene-isobutylene copolymer, chlorinated polybutene, etc.), alkylbenzenes (e.g., dodecylbenzene, tetradecylbenzene, dinonylbenzene, di-(2-ethylhexyl)benzene, etc.), and polyphenols (e.g., biphenyl, terphenyl, etc.). Synthetic lubricating oils are composed of alkylene oxide polymers and copolymers, and their derivatives, whose terminal hydroxyl groups have been modified by esterification, etherification, etc. Typical examples include lubricating oils prepared by polymerizing ethylene oxide or propylene oxide, as well as the alkyl and aryl ethers of these polyoxyethylene polymers (e.g., methyl polyisopropylene glycol ether with an average molecular weight of 1000, polyethylene glycol diphenyl ether with a molecular weight of 500-1000, polypropylene glycol diethyl ether with a molecular weight of 1000-1500, etc.), or their mono- and polycarboxylic acid esters, such as acetates or mixed C3-C8 fatty acid esters. Another class of suitable synthetic lubricating oils includes esters of dicarboxylic acids (e.g., phthalic acid, succinic acid, maleic acid, azelaic acid, octanoic acid, sebacic acid, fumaric acid, adipic acid, linoleic acid dimer, etc.) with various alcohols (e.g., butanol, hexanol, dodecyl alcohol, 2-ethylhexanol, pentaerythritol, etc.). Specific examples of these esters include dibutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctyl olefinate, diisodecyl olefinate, dioctyl phthalate, didecyl phthalate, di-n-octyl sebacate, 2-ethylhexyl diester of linoleic acid dimer, complex esters formed by reacting 1 mole of sebacic acid with 2 moles of tetraethylene glycol and 4 moles of 2-ethylhexanoic acid, and the like. Silicone-based oils, such as polyalkyl, polyaryl, polyalkoxy or polyaryloxysiloxane oils and silicate oils, constitute another class of useful synthetic lubricating oils (e.g., tetraethyl silicate, tetraisopropyl silicate, tetra-(2-ethylhexyl)-silicate, tetra-(4-methyl-2-tetraethyl)-silicate, tetra-(p-tert-butylphenyl)-silicate, hexyl-(4-methyl-2-pentyloxy)-disiloxane, poly(methyl)-siloxane, poly(methylphenyl)-siloxane, etc.). Other synthetic lubricating oils include liquid esters of phosphoric acid (e.g., trimethyl phosphate, trioctyl phosphate, diethyl decanephosphonate, etc.), polymerized tetrahydrofuran, etc.

[0026] The lubricating oil base oil can be used alone or mixed under miscible conditions. The viscosity of the lubricating oil base oil is generally in the range of about 50-5000 c.p., preferably about 100-1500 c.p.

[0027] The lubricating oil composition of the present invention can be prepared by adding about 0.01-5, preferably about 0.05-1, weight percent of the reaction product to a lubricating oil basestock. The amount of reaction product used will vary depending on the type of lubricating oil basestock used, the performance level of the reaction product, and the presence of other additives in the lubricating oil basestock. In addition to the antioxidant component herein, other additives may be added to the lubricating oil basestock to improve its performance without adversely affecting its stability. Such additives include corrosion and rust inhibitors, defoamers, viscosity index improvers, friction modifiers, pour point improvers, antiwear and extreme pressure agents, metal deactivators, dispersants, detergents, and the like.

[0028] In many cases, it is advantageous to form a concentrate of the reaction product to provide a convenient method of handling and transporting the antioxidant for subsequent dilution and use. The concentration of the reaction product in the concentrate may be from about 10 to 90, preferably from about 20 to 50, weight percent.

[0029] The present invention provides the following beneficial effects: An antioxidant is prepared by condensing an alkyl-substituted 1,2-dihydroquinoline with a diarylamine in the presence of an acidic catalyst. This antioxidant is then added to a lubricating oil base to produce a lubricating oil composition with excellent antioxidant properties. This lubricating oil composition exhibits enhanced antioxidant capacity compared to lubricating oil compositions without the antioxidant, and also compared to commercially available lubricating oil compositions containing antioxidants other than the reaction product of the present invention. DETAILED DESCRIPTION

[0030] Example 1

[0031] In a one-liter reactor equipped with a stirrer, a thermometer, and an addition funnel, 275 g of diphenylamine was added, the reactor was purged with a nitrogen stream, and then 27.5 g of aluminum trichloride as a catalyst was added; the temperature was increased until the diphenylamine melted, stirring was initiated, and then further heated to 115°C; over 90 minutes, 260 g of 2,2,4-trimethyl-1,2-dihydroquinoline (95% purity as determined by gas chromatography) was added to the reactor; the reactants were then heat treated at 140°C for 4 hours, and the reactor temperature was lowered to 90°C; hot water was slowly added with stirring, followed by 200 ml of xylene; the aqueous layer was removed by separation, and the reactants were neutralized with dilute sodium hydroxide and washed with hot water.

[0032] The product obtained above was dried by distillation at atmospheric pressure, and then volatile organic compounds including excess diphenylamine were removed by vacuum distillation. The product was filtered while hot to obtain 305 g of a dark amber glassy product. This reaction product is hereinafter referred to as antioxidant component A.

[0033] Example 2

[0034] To a 2-liter reactor equipped with a stirrer, a thermometer, and an addition funnel was added 486 g of diphenylamine. The container was purged with a nitrogen stream, followed by the addition of 48.6 g of aluminum chloride as a catalyst. The reaction mixture was heated until the diphenylamine melted, and the temperature was then further increased to 115°C. Over 110 minutes, 565 g of 2,2,4-trimethyl-1,2-dihydroquinoline (78% purity according to gas chromatography) was added to the reactor. The reactants were then reacted at 115°C for 4 hours, after which the reactor temperature was lowered to 90°C. Hot water was slowly added with stirring, followed by 400 ml of xylene. The aqueous layer was removed by separation, and the reactants were neutralized with dilute sodium hydroxide, followed by two hot water washes.

[0035] The above product was dried by distillation under normal pressure, and then light components including excess diphenylamine were removed by vacuum distillation. The product was filtered while hot to obtain 582 grams of reaction product, which we call antioxidant component B.

[0036] Example 3

[0037] The preparation method of this embodiment is the same as that of Example 1, except that 2,2,4-trimethyl-1,2-dihydroquinoline uses TMDQ monomer with a purity of 84%.

[0038] Example 4

[0039] The preparation method of this embodiment is the same as that of Example 2, except that 2,2,4-trimethyl-1,2-dihydroquinoline uses TMDQ monomer with a purity of 91%.

[0040] Example 5-29

[0041] Antioxidant components A, B, C, and D were added individually to SG-grade engine oils at the levels shown in Table 1. The oils contained the standard additive package except for the supplemental antioxidants.

[0042] Comparative Example 1-2

[0043] In addition, two commercially available antioxidants, Irganox L57 (Ciba Geigy Corp.) and Vanlube SL (RT Vanderbilt Corp.), were added to the same SG-grade motor oil, respectively, and are referred to herein as antioxidant components E and F. Irganox L57 is a mixture of butylated and octylated diphenylamines, and Vanlube SL is a mixture of octylated and styrenated diphenylamines.

[0044] The SG-grade engine oils of Examples 5-29 and Comparative Examples 1-2 were tested for oxidation stability using the standard Thin Film Oxygen Uptake Test (TFOUT). The oil samples were heated to 160°C in an oxygen-pressurized aerosol bomb container along with a small amount of liquid metal catalyst and partially oxidized fuel. Induction time was measured from the start of the test to the onset of a noticeable pressure loss. An increase in induction time indicates enhanced oxidation stability. Three SG-grade engine oil samples without antioxidants (referred to herein as blanks) were also tested. The test results are shown in Table 1 below.

[0045] Table 1 Oxidation stability evaluation results of Examples 2-29 and Comparative Examples 1-2

[0046]

[0047]

[0048]

[0049] As can be seen in Table 1, the addition of the antioxidant compositions of the present invention, such as Antioxidants AD, to an engine oil containing standard additives (excluding the supplemental antioxidant), significantly increased the induction time of the lubricating oil composition relative to a control sample without the addition of the antioxidant. The test data also demonstrates that the antioxidant compositions of the present invention provide superior antioxidant protection compared to commercially available antioxidants E and F. Furthermore, the data demonstrates that even with a small amount of the antioxidants of the present invention, the same level of antioxidant protection as with larger amounts of commercially available antioxidants can be achieved.

[0050] Example 30

[0051] The antioxidant component A obtained in Example 1 was added to industrial turbine oil containing all necessary additives except the antioxidant. The added amount of the antioxidant component A was 0.5 wt %.

[0052] Comparative Examples 3-8

[0053] A commercial antioxidant was added to the same industrial turbine oil as in Example 30 at an amount of 0.5 wt%.

[0054] The oxidative stability of the industrial turbine oils of Example 30 and Comparative Examples 3-8 was evaluated using the rotating oxygen bomb method (RBOT). The test was conducted as follows:

[0055] 50 grams of lubricating oil (containing 0.5% antioxidant base, except for Comparative Example 3), 5 grams of water, and 3 meters of copper wire were placed in a glass beaker inside a steel reactor. The steel reactor was pressurized to 0.6 MPa with oxygen, sealed, and placed in a 150°C water bath. The system pressure increased as the temperature rose. As the lubricating oil components began to oxidize, the system pressure decreased as the oxygen was consumed. When the oxygen was completely consumed, the pressure in the closed system dropped. The test endpoint was when the pressure was 0.15-0.6 MPa lower than the maximum pressure reached. The test results are shown in Table 2.

[0056] Table 2 Oxidation stability test data of Example 30 and Comparative Examples 3-8

[0057] Antioxidant composition Oxidation induction period (minutes) Example 30 Antioxidant composition A 3725 Comparative Example 3 No antioxidants 22 Comparative Example 4 Phenylnaphthylamine 1593 Comparative Example 5 Butyloctyl diphenylamine mixture 740 Comparative Example 6 Octylphenylnaphthylamine 2046 Comparative Example 7 Dinonyldiphenylamine 417 Comparative Example 8 Nonyldiethyldiphenylamine 145

[0058] The results in Table 2 clearly show that the antioxidants of the present invention provide superior antioxidant protection for the lubricating oil (Example 30) relative to commercially available antioxidants (Comparative Examples 4-8). Furthermore, a small amount of the antioxidants of the present invention can achieve the same effect as a large amount of commercially available antioxidants.

[0059] Examples 31-34

[0060] The antioxidant component A obtained in Example 1 was added to base oils I and II, respectively. Base oil I is a mineral oil-based heavy-duty diesel engine oil containing all necessary additives, except for the supplemental antioxidant. Base oil II is a mineral oil-based marine diesel engine oil containing all necessary additives, except for the supplemental antioxidant. The amount of antioxidant component A added was 0.5 wt%.

[0061] Comparative Examples 9-16

[0062] Commercially available antioxidants were added to the same base oils I and II as in Examples 31-34, respectively, with an addition amount of 0.5 wt%.

[0063] The oxidation stability of the diesel engine oils of Examples 31-34 and Comparative Examples 9-16 was evaluated using the Caterpillar Micro Oxidation Test (CMOT). The test results are shown in Table 3.

[0064] CMOT involves heating a sample of a formulated heavy-duty diesel engine oil containing 0.5 weight percent antioxidant at 230°C. At specified intervals, the weight percent of deposits is measured. The data is plotted against time to determine the induction time. This time correlates to the point at which deposits in the oil begin to increase dramatically.

[0065] Table 3 Oxidation stability test data of Examples 31-34 and Comparative Examples 9-16

[0066]

[0067]

[0068] The above data show that the antioxidants of the present invention produced longer induction times than the antioxidants of Comparative Examples 9 to 16 in all cases except Example 31. These data demonstrate that the antioxidants of the present invention are superior to currently commercially used antioxidants.

[0069] The data in Tables 1, 2 and 3 clearly show that the lubricating oil composition of the present invention has a stronger antioxidant capacity than a lubricating oil composition without added antioxidant, and also has a stronger antioxidant capacity than a commercial lubricating oil composition containing an antioxidant other than the reaction product of the present invention.

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications are also within the scope of protection of the present invention.

Claims

1. A lubricating oil antioxidant, characterized in that: It is prepared by alkylation reaction of diarylamine and alkyl-substituted 1,2-dihydroquinoline in the presence of a catalyst.

2. A lubricating oil antioxidant according to claim 1, characterized in that: The alkyl-substituted 1,2-dihydroquinoline is at least one of 2,2,4-trimethyl-1,2-dihydroquinoline, 2-methyl-2,4-diethyl-1,2-dihydroquinoline, 2,2,4,6-tetramethyl-1,2-dihydroquinoline, 2,2,4,7-tetramethyl-1,2-dihydroquinoline and 6,6'-bis(2,2,4-trimethyl-1,2-dihydroquinoline).

3. A lubricating oil antioxidant according to claim 2, characterized in that: The purity of 2,2,4-trimethyl-1,2-dihydroquinoline is 60-100%.

4. The lubricating oil antioxidant according to claim 1, characterized in that: The diarylamine is at least one of diphenylamine, phenyl-α-naphthylamine, xylidine, amphetamine, dinaphthylamine, 4-phenyldiphenylamine, p-hydroxydiphenylamine, p-aminodiphenylamine and isopropoxydiphenylamine.

5. The lubricating oil antioxidant according to claim 1, characterized in that: The catalyst is at least one of hydrogen chloride, phosphoric acid, sulfuric acid, zinc chloride, aluminum chloride, aluminum bromide, ferric chloride, boron trifluoride, hydrofluoric acid, tin chloride, acid-leached clay and iodine.

6. The method for preparing the lubricating oil antioxidant according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Add diphenylamine into a reactor, add a catalyst after nitrogen purging, and heat until the diphenylamine melts; (2) heating the melt to 80-140° C. under stirring, then adding alkyl-substituted 1,2-dihydroquinoline, reacting for 0.5-6 hours, and after the reaction is completed, cooling and adding a solvent; (3) separating and removing the water layer, then adding alkali solution to neutralize the reactant, and washing with hot water; (4) The washed product is distilled and dried under normal pressure, and then the excess diphenylamine and volatile organic matter are removed by distillation under vacuum, and the product is filtered.

7. A lubricating oil antioxidant according to claim 6, characterized in that: The solvent is xylene.

8. The preparation method according to claim 6, characterized in that: The molar ratio of the alkyl-substituted 1,2-dihydroquinoline to the diarylamine is (1.5-0.4):1, and the molar ratio of the diarylamine to the acidic catalyst is (15.6-1.8):

1.

9. A lubricating oil composition, characterized in that: The lubricating oil antioxidant comprises the lubricating oil antioxidant according to any one of claims 1 to 5.

10. A lubricating oil composition according to claim 9, characterized in that: The weight percentage of the lubricating oil antioxidant in the lubricating oil composition is 0.01-5%.

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