High-temperature-resistant antioxidant lubricating oil and preparation method thereof

Abstract

The application relates to a high-temperature-resistant antioxidant lubricating oil and a preparation method thereof, and belongs to the technical field of lubricating oils. A bentonite imidazole composite particle grafted antioxidant and an alkyl imidazole phosphate ionic liquid complex system are constructed to achieve a double-antioxidation effect. MoS2 nanosheets in the bentonite imidazole composite particle are exposed to sufficient S vacancies after low-temperature ultrasonic crushing, form stable covalent grafting with the mercapto group of 2-mercaptobenzimidazole, avoid the defects that traditional small-molecule antioxidants are easy to volatilize and migrate, meanwhile, the alkyl imidazole phosphate ionic liquid forms a dynamic balance in base oil, continuously releases a nitrogen-containing cation component, cooperates with the grafted antioxidant to capture free radicals generated at high temperature, interrupts the oxidation chain reaction, on the process, the composite bentonite prepared by a solvothermal method provides a stable carrier for the antioxidant component, a freeze-drying process retains the porous structure and active sites of the material, improves the initial oxidation temperature of the lubricating oil, and effectively adapts to high-temperature long-time operation conditions.

Description

Technical Field

[0001] This invention belongs to the field of lubricating oil technology, and relates to a high-temperature resistant and antioxidant lubricating oil and its preparation method. Background Technology

[0002] With the rapid development of industries such as chemical, energy, aerospace, and metallurgy, the operating conditions of core mechanical equipment such as compressors, vertical mill roller bearings, and high-temperature valves are becoming increasingly demanding. These equipment often operate in high-temperature, high-pressure, and highly oxidizing environments exceeding 100°C and require continuous 24-hour operation, placing extremely high demands on the high-temperature resistance and oxidation resistance of lubricating oils. Currently, the lubricating oils widely used in industry are mainly formulated with mineral oil, polyalphaolefin (PAO), and ester oils as base oils, combined with conventional antioxidants. However, their high-temperature oxidation resistance has significant limitations.

[0003] Chinese invention patent application CN116855300A discloses a high-temperature resistant industrial lubricating oil and its preparation method, comprising the following raw materials in parts by weight: hydrogenated base oil, synthetic base oil, high-temperature resistant composite microcapsules, carbon nanotubes, trihydroxybenzoic acid, sulfonate, surfactant, antioxidant, and dispersant. By introducing specially formulated high-temperature resistant composite microcapsules into the conventional components of the lubricating oil, an adhesion effect can be generated on the surface of mechanical metals, forming a microcapsule layer. The silicone oil encapsulated inside is slowly released, forming an effective boundary lubrication film on the surface of mechanical metals, which significantly reduces the coefficient of friction and wear rate of the mechanical metal surface. This effectively reduces the heat generation during friction and lowers the ambient temperature of the mechanical metal. At the same time, in conjunction with carbon nanotubes, the lubricating oil has good thermal conductivity, which can further improve its high-temperature resistance.

[0004] The above-mentioned technical solutions achieve antioxidant function by adding a single antioxidant. Traditional small molecule antioxidants are volatile and easily migrate, making it difficult for them to remain in the lubricating oil for a long time under high-temperature conditions, resulting in a rapid decline in antioxidant effect. Furthermore, antioxidants do not have a synergistic effect with other components (such as microcapsules and carbon nanotubes), and cannot effectively interrupt the free radical chain reaction at high temperatures. This makes the lubricating oil prone to oxidation and deterioration after long-term high-temperature operation, limiting its applicability under extreme conditions. Summary of the Invention

[0005] The purpose of this invention is to provide a high-temperature resistant and antioxidant lubricating oil and its preparation method. By constructing a synergistic system of bentonite imidazole composite microparticles, alkyl imidazole phosphate ionic liquid and pentaerythritol ester base oil, the lubricating oil's high-temperature resistance, antioxidant properties, friction reduction, and extreme pressure performance are improved, making it suitable for extreme working conditions and solving the problem of easy failure of traditional lubricating oils.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing a high-temperature resistant and antioxidant lubricating oil includes the following steps:

[0008] Step 1: The bentonite is modified by inserting a cationic surfactant into the interlayer of bentonite through ion exchange. Then, MoS2 nanosheets are synthesized using ammonium molybdate tetrahydrate as the molybdenum source and thiourea as the sulfur source and anchored in the interlayer or surface of the bentonite to obtain composite bentonite. 2-Mercaptobenzimidazole is grafted onto the MoS2 nanosheets in the composite bentonite to obtain bentonite imidazole composite microparticles.

[0009] Step 2: Grafting octanoic acid, isooctanoic acid, and decanoic acid onto pentaerythritol via esterification to obtain pentaerythritol ester base oil.

[0010] Step 3: Using 2-n-undecylimidazole as the cation and bis(2-ethylhexyl) phosphate as the anion, an alkylimidazolium phosphate ionic liquid was synthesized.

[0011] Step 4: Mix the bentonite imidazole composite microparticles, alkyl imidazole phosphate ionic liquid and pentaerythritol ester base oil evenly to obtain a high-temperature resistant and antioxidant lubricating oil.

[0012] Furthermore, the specific preparation process of composite bentonite is as follows:

[0013] Bentonite, cationic surfactant, anhydrous ethanol and deionized water were added to a high-pressure reactor and stirred until homogeneous. Ammonium molybdate tetrahydrate and thiourea were then added. The mixture was reacted at 180-190℃ and 300-500 r / min for 24-26 h. After cooling, filtration, washing, and freeze-drying, composite bentonite was obtained.

[0014] Furthermore, the ratio of bentonite, cationic surfactant, anhydrous ethanol, deionized water, ammonium molybdate tetrahydrate, and thiourea is 47.0-57.0g: 16.5-20.5g: 2-2.2L: 4-4.5L: 70.6-90.6g: 152-190g.

[0015] Furthermore, the cationic surfactant is any one of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, and 2-n-undecylimidazole.

[0016] Furthermore, the specific preparation process of the bentonite imidazole composite microparticles is as follows:

[0017] Composite bentonite, 2-mercaptobenzimidazole and isopropanol were added to a reaction vessel and ultrasonically crushed at 0-5℃ for 5-6 hours. Then, the mixture was stirred at 60-65℃ for 48-50 hours. After the reaction was completed, the mixture was naturally cooled to room temperature, centrifuged, and the supernatant was washed and dried to obtain bentonite-imidazolium composite microparticles.

[0018] Furthermore, the ratio of compound bentonite, 2-mercaptobenzimidazole and isopropanol is 3.0-4.0g: 300-400mL: 1.2-1.5L.

[0019] Furthermore, the specific preparation process of pentaerythritol ester base oil is as follows:

[0020] Pentaerythritol, octanoic acid, isooctanoic acid, decanoic acid, and a solid acid catalyst were added to a three-necked reactor equipped with a water separator. A water-removing agent was added to the water separator. The esterification reaction was carried out at 210-220℃ and 300-400 r / min for 8-10 hours. The mixture was then vacuum distilled to obtain pentaerythritol ester base oil.

[0021] Furthermore, the mass ratio of pentaerythritol, octanoic acid, isooctanoic acid, decanoic acid, and solid acid catalyst is 648-700:144-150:1009-1209:1840-1940:34-46.

[0022] Furthermore, the water-removing agent is one of toluene and petroleum ether.

[0023] Furthermore, the specific preparation process of the alkylimidazolium phosphate ionic liquid is as follows:

[0024] Add 2-n-undecylimidazole and anhydrous ethanol to a reaction vessel and stir for 30-40 min. Slowly add bis(2-ethylhexyl) phosphate and stir for 24-26 h. Rotary evaporate and dry to obtain alkylimidazolium phosphate ionic liquid.

[0025] Furthermore, the ratio of 2-n-undecylimidazole, anhydrous ethanol, and bis(2-ethylhexyl) phosphate is 7.28-9.28 g : 100-140 mL : 6.44-8.44 g.

[0026] Furthermore, the mass ratio of bentonite imidazole composite microparticles, alkyl imidazole phosphate ionic liquid, and pentaerythritol ester base oil is 0.4-0.6:2-3:100-120.

[0027] The present invention also provides a high-temperature resistant and antioxidant lubricating oil, which is obtained by ultrasonically dispersing and mixing the above-mentioned bentonite imidazole composite microparticles, alkyl imidazole phosphate ionic liquid and pentaerythritol ester base oil, and vacuum degassing at 40-50°C for 30-40 minutes.

[0028] The beneficial effects of this invention are:

[0029] 1. This invention achieves a dual antioxidant effect by constructing a compound system of bentonite imidazole composite microparticles grafted with antioxidants and alkyl imidazole phosphate ionic liquids. After low-temperature ultrasonic fragmentation, the MoS2 nanosheets in the bentonite imidazole composite microparticles expose sufficient S vacancies, which form stable covalent grafts with the thiol groups of 2-mercaptobenzimidazole, avoiding the defects of traditional small molecule antioxidants such as easy volatility and migration. At the same time, the alkyl imidazole phosphate ionic liquid forms a dynamic equilibrium in the base oil, continuously releasing nitrogen-containing cationic components, which synergistically capture free radicals generated at high temperatures with the grafted antioxidants, interrupting the oxidation chain reaction. In terms of process, the composite bentonite prepared by the solvothermal method provides a stable carrier for the antioxidant components, and the freeze-drying process preserves the porous structure and active sites of the material, increasing the initial oxidation temperature of the lubricating oil and effectively adapting to high-temperature long-term operation conditions.

[0030] 2. In this invention, the layered structure of bentonite in the bentonite-imidazolium composite microparticles is modified with cationic surfactants, which increases the interlayer spacing and weakens the interlayer van der Waals forces. This allows for the formation of a physical lubrication layer with low slip resistance at the friction interface. The phosphate anions of the alkyl imidazolium phosphate ionic liquid can undergo tribochemical reactions with the metal surface to generate a dense friction film containing phosphorus, oxygen, and metal, enhancing extreme pressure bearing capacity. The polarity of the ester groups in the pentaerythritol ester base oil can be adsorbed onto the metal surface to form a stable oil film, playing a synergistic lubricating role. In addition, the intercalation modification of the cationic surfactants not only increases the interlayer spacing of bentonite but also assists in the uniform anchoring of MoS2 nanosheets, preventing agglomeration. This results in improved extreme pressure performance and friction reduction and anti-wear effects of the lubricating oil.

[0031] 3. The polyol ester structure of the pentaerythritol ester base oil in this invention has excellent thermal oxidation stability, low ether bond content, and is not easily broken at high temperatures. The inorganic bentonite in the composite bentonite acts as a skeleton support, which can inhibit the aggregation and loss of MoS2 nanosheets at high temperatures. The alkyl imidazole phosphate ionic liquid itself has a high thermal decomposition temperature and good compatibility with the base oil. It will not produce destructive impurities due to high-temperature decomposition. The solvothermal reaction ensures that MoS2 and bentonite are firmly bonded, thereby increasing the thermal decomposition temperature of the lubricating oil. Detailed Implementation

[0032] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, features and effects of the present invention, in conjunction with preferred embodiments, is provided below.

[0033] Example 1: This example provides a high-temperature resistant and antioxidant lubricating oil, prepared through the following steps:

[0034] S1: 52.0 g bentonite, 18.5 g cetyltrimethylammonium bromide, 2.1 L anhydrous ethanol and 4.25 L deionized water were added to a high-pressure reactor and stirred at 22 °C and 400 r / min for 35 min. Then, 80.6 g ammonium molybdate tetrahydrate and 171 g thiourea were added and stirred for another 25 min. The mixture was then reacted at 185 °C and 400 r / min for 25 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, filtered, and the precipitate was washed four times alternately with deionized water and anhydrous ethanol. The precipitate was then freeze-dried for 49 h to obtain composite bentonite.

[0035] Hexadecyltrimethylammonium bromide is fully inserted into the interlayer of bentonite to complete organic modification, expanding the interlayer spacing and improving surface loading activity. Then, a molybdenum source and a sulfur source are uniformly dispersed in the modified bentonite system. During the reaction, the sulfur source decomposes with water to produce H2S. H2S reacts with the molybdenum source precursor (MoO4). 2- The reaction generates MoS2 nanosheets, which grow, aggregate, interlock, and stack to form a stable spherical structure. Simultaneously, the organically modified bentonite, through interlayer forces and surface adsorption, uniformly anchors MoS2 within the interlayer or on the surface. At lower reaction temperatures, MoO4... 2- When the reaction is not complete during the conversion to Mo-S bonds, O atoms are incorporated into the interlayer framework of MoS2. On the one hand, this expands the interlayer spacing, weakens the interlayer van der Waals forces, and improves the tribological properties; on the other hand, it causes crystal structure disorder and generates S vacancies, providing conditions for subsequent vacancy grafting of organic antioxidants.

[0036] S2: 3.5g of composite bentonite, 350mL of 2-mercaptobenzimidazole and 1.3L of isopropanol were added to the reaction vessel and ultrasonically crushed at 2℃ for 5.5h. Then, the mixture was stirred at 62℃ for 49h to promote the covalent bonding between the thiol group of 2-mercaptobenzimidazole and the S vacancy on the surface of MoS2. After the reaction was completed, the mixture was naturally cooled to room temperature and centrifuged at 1100r / min for 12min. The supernatant was collected and washed 4 times with anhydrous ethanol by centrifugation. The precipitate was dried at 62℃ for 11h, ground and sieved to obtain bentonite-imidazolium composite microparticles with a particle size of 3-5μm.

[0037] MoS2 nanoparticles rich in S vacancies in composite bentonite are fully exfoliated by ultrasonic crushing at low temperature, exposing more surface S vacancies, while avoiding high-temperature side reactions of the thiol group (-SH) of 2-mercaptobenzimidazole. Upon further heating, thermodynamics is used to drive the thiol group in the 2-mercaptobenzimidazole molecule to form a stable covalent bond with the S vacancies on the MoS2 surface, thus grafting 2-mercaptobenzimidazole onto the MoS2 surface.

[0038] S3: 674g pentaerythritol, 147g octanoic acid, 1109g isooctanoic acid, 1890g decanoic acid and 40g solid acid catalyst were sequentially added to a three-necked reactor equipped with a water separator. 70mL toluene was added to the water separator as a water-removing agent to promote the separation of water in the reaction system. The esterification reaction was carried out at 215℃ and 350r / min for 9h. After the reaction was completed, the remaining fatty acids in the reaction system were removed by vacuum distillation at -0.095MPa for 2.5h to obtain pentaerythritol ester base oil.

[0039] Under the catalysis of a solid acid catalyst, the hydroxyl groups in pentaerythritol molecules undergo dehydration condensation esterification with the carboxyl groups in octanoic acid, isooctanoic acid, and decanoic acid molecules. Toluene in the water separator can promptly separate the water generated in the reaction, break the esterification reaction equilibrium, and promote the reaction to proceed in the forward direction, forming pentaerythritol ester base oil with a polyol ester structure.

[0040] S4: Add 8.28 g of 2-n-undecylimidazole and 120 mL of anhydrous ethanol to the reactor and stir for 35 min at 22 °C and 350 r / min. Slowly add 7.44 g of bis(2-ethylhexyl) phosphate at a dropping rate of 1 mL / min and stir for 25 h at 22 °C. Remove the remaining ethanol by rotary evaporation and vacuum dry for 25 h at 72 °C and -0.09 MPa to obtain alkylimidazolium phosphate ionic liquid.

[0041] Using anhydrous ethanol as solvent and 2-n-undecylimidazole as a nitrogen-containing cation precursor, a stable ion pair is formed with bis(2-ethylhexyl) phosphate through a proton transfer reaction. Continuous stirring ensures that the proton transfer reaction proceeds fully and avoids incomplete local reactions.

[0042] S5: Add 0.5g of bentonite imidazole composite microparticles, 2.5g of alkyl imidazole phosphate ionic liquid and 110g of pentaerythritol ester base oil to the reaction vessel, ultrasonically disperse for 50min, adjust the vacuum degree of the system to -0.09MPa, and degas under vacuum at 45℃ for 35min to remove residual bubbles in the system, and obtain a high-temperature resistant and antioxidant lubricating oil.

[0043] Example 2: This example provides a high-temperature resistant and antioxidant lubricating oil, prepared through the following steps:

[0044] S1: 47.0g bentonite, 16.5g hexadecyltrimethylammonium bromide, 2L anhydrous ethanol and 4L deionized water were added to a high-pressure reactor and stirred for 30min at 20℃ and 300r / min. 70.6g ammonium molybdate tetrahydrate and 152g thiourea were added and stirred for another 20min. The mixture was then reacted at 180℃ and 300r / min for 24h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, filtered, and the precipitate was washed three times alternately with deionized water and anhydrous ethanol. The precipitate was then freeze-dried for 48h to obtain composite bentonite.

[0045] S2: Add 3.0g of composite bentonite, 300mL of 2-mercaptobenzimidazole and 1.2L of isopropanol to the reaction vessel, sonicate for 5h at 0℃, and then stir at 60℃ for 48h to promote the covalent bonding of the thiol group of 2-mercaptobenzimidazole with the S vacancy on the surface of MoS2. After the reaction is completed, cool naturally to room temperature, centrifuge at 1000r / min for 10min, collect the supernatant, wash the supernatant three times with anhydrous ethanol, centrifuge again, dry the precipitate at 60℃ for 10h, grind and sieve to obtain bentonite-imidazolium composite microparticles with a particle size of 3-5μm.

[0046] S3: 648g pentaerythritol, 144g octanoic acid, 1009g isooctanoic acid, 1840g decanoic acid and 34g solid acid catalyst were sequentially added to a three-necked reactor equipped with a water separator. 60mL of toluene was added to the water separator as a water-removing agent to promote the separation of water in the reaction system. The esterification reaction was carried out at 210℃ and 300r / min for 8h. After the reaction was completed, the remaining fatty acids in the reaction system were removed by vacuum distillation at -0.095MPa for 2h to obtain pentaerythritol ester base oil.

[0047] S4: 7.28 g of 2-n-undecylimidazole and 100 mL of anhydrous ethanol were added to the reaction vessel and stirred at 20 °C and 300 r / min for 30 min. 6.44 g of bis(2-ethylhexyl) phosphate was slowly added at a dropping rate of 1 mL / min and stirred at 20 °C for 24 h. The remaining ethanol was removed by rotary evaporation and the mixture was vacuum dried at 70 °C and -0.095 MPa for 24 h to obtain alkylimidazolium phosphate ionic liquid.

[0048] S5: Add 0.4g of bentonite imidazole composite microparticles, 2g of alkyl imidazole phosphate ionic liquid and 100g of pentaerythritol ester base oil to the reactor, ultrasonically disperse for 45min, adjust the vacuum degree of the system to -0.09MPa, and degas under vacuum at 40℃ for 30min to remove residual bubbles in the system, and obtain a high-temperature resistant and antioxidant lubricating oil.

[0049] Example 3: This example provides a high-temperature resistant and antioxidant lubricating oil, prepared through the following steps:

[0050] S1: 57.0 g bentonite, 20.5 g cetyltrimethylammonium bromide, 2.2 L anhydrous ethanol and 4.5 L deionized water were added to a high-pressure reactor and stirred at 25 °C and 500 r / min for 40 min. Then, 90.6 g ammonium molybdate tetrahydrate and 190 g thiourea were added and stirred for another 30 min. The mixture was then reacted at 190 °C and 500 r / min for 26 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, filtered, and the precipitate was washed 5 times alternately with deionized water and anhydrous ethanol. The precipitate was then freeze-dried for 50 h to obtain composite bentonite.

[0051] S2: Add 4.0g of composite bentonite, 400mL of 2-mercaptobenzimidazole and 1.5L of isopropanol to the reaction vessel, sonicate at 5℃ for 6h, and then stir at 65℃ for 50h to promote the covalent bonding of the thiol group of 2-mercaptobenzimidazole with the S vacancy on the surface of MoS2. After the reaction is completed, cool naturally to room temperature, centrifuge at 1200r / min for 15min, collect the supernatant, wash the supernatant with anhydrous ethanol 5 times by centrifugation, centrifuge again, dry the precipitate at 65℃ for 12h, grind and sieve to obtain bentonite-imidazolium composite microparticles with a particle size of 3-5μm.

[0052] S3: 700g pentaerythritol, 150g octanoic acid, 1209g isooctanoic acid, 1940g decanoic acid and 46g solid acid catalyst were sequentially added to a three-necked reactor equipped with a water separator. 80mL toluene was added to the water separator as a water-removing agent to promote the separation of water in the reaction system. The esterification reaction was carried out at 220℃ and 400r / min for 10h. After the reaction was completed, the remaining fatty acids in the reaction system were removed by vacuum distillation at -0.095MPa for 3h to obtain pentaerythritol ester base oil.

[0053] S4: 9.28 g of 2-n-undecylimidazole and 140 mL of anhydrous ethanol were added to the reaction vessel and stirred at 25 °C and 400 r / min for 40 min. 8.44 g of bis(2-ethylhexyl) phosphate was slowly added at a dropping rate of 1 mL / min and stirred at 25 °C for 26 h. The remaining ethanol was removed by rotary evaporation and the mixture was vacuum dried at 75 °C and -0.085 MPa for 26 h to obtain alkylimidazolium phosphate ionic liquid.

[0054] S5: Add 0.6g of bentonite imidazole composite microparticles, 3g of alkyl imidazole phosphate ionic liquid and 120g of pentaerythritol ester base oil to the reaction vessel, ultrasonically disperse for 55min, adjust the vacuum degree of the system to -0.09MPa, and degas under vacuum at 50℃ for 40min to remove residual bubbles in the system, and obtain a high-temperature resistant and antioxidant lubricating oil.

[0055] Example 4: This example provides a high-temperature resistant and antioxidant lubricating oil. The difference from Example 1 is that hexadecyltrimethylammonium chloride is used instead of hexadecyltrimethylammonium bromide in step S1.

[0056] Example 5: This example provides a high-temperature resistant and antioxidant lubricating oil. The difference from Example 1 is that octadecyltrimethylammonium chloride is used instead of hexadecyltrimethylammonium bromide in step S1.

[0057] Example 6: This example provides a high-temperature resistant and antioxidant lubricating oil. The difference from Example 1 is that 2-n-undecylimidazole is used instead of hexadecyltrimethylammonium bromide in step S1.

[0058] Comparative Example 1: This comparative example provides a high-temperature resistant and antioxidant lubricating oil, which differs from Example 1 in that the alkyl imidazole phosphate ionic liquid is removed in step S5.

[0059] Comparative Example 2: This comparative example provides a high-temperature resistant and antioxidant lubricating oil. The difference from Example 1 is that the bentonite imidazole composite particles are removed in step S5.

[0060] Comparative Example 3: This comparative example provides a high-temperature resistant and antioxidant lubricating oil. The difference from Example 1 is that PAG46 base oil is used instead of pentaerythritol ester base oil in step S5.

[0061] The specific specifications and sources of the raw materials used in the above embodiments and comparative examples are as follows:

[0062] Bentonite: Purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0063] Cetyltrimethylammonium bromide: purity ≥99.0%, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0064] Ammonium molybdate tetrahydrate: purity ≥99.0%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0065] Thiourea: purity ≥99.0%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0066] 2-Mercaptobenzimidazole: purity ≥98%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0067] Isopropanol: purity ≥99.8%, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0068] Pentaerythritol: analytical grade, purchased from Guangdong Xiyuan Chemical Co., Ltd.

[0069] Caprylic acid: 99.0% purity, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0070] Isooctanoic acid: 99.0% purity, purchased from Jinan Yuno Chemical Co., Ltd.

[0071] n-Cephalic acid: 99.0% purity, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0072] Solid acid catalyst: HND-260 solid acid catalyst, 99.0% purity, purchased from Wuhan Lanabai Pharmaceutical Chemical Co., Ltd.

[0073] 2-Undecylimidazole: Purity ≥96%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0074] Bis(2-ethylhexyl) phosphate: 98% purity, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0075] The high-temperature resistant and antioxidant lubricating oils prepared in Examples 1-6 and Comparative Examples 1-3 were subjected to performance tests:

[0076] Antioxidant performance testing: The initial oxidation temperature (OOT) and oxidation induction period (OIT) of lubricating oils were evaluated according to ASTM D6186-08 using differential pressure scanning calorimetry (PDSC, DSC 204 HP, NETZSCH). For OOT and OIT tests, 3.00 ± 0.2 mg of test oil was added to an aluminum pot, and the pressure was maintained at 3.5 ± 0.2 MPa. For the OOT test, the lubricating oil samples were heated at a rate of 10 °C / min, with an oxygen flow rate of 100 mL / min, from room temperature to 310 °C. For the OIT test, the lubricating oil samples were first heated from room temperature to 210 °C at a rate of 100 °C / min. The oxygen flow rate was set to 100 mL / min for 2 hours. The OOT and OIT results of the test oils were analyzed using PDSC software.

[0077] Thermal stability test: The thermal stability of the three composite materials and their mass change during heating were tested using a thermogravimetric analyzer (TGA-101, Shanghai Jiezhun Instrument Equipment Co., Ltd.). The test conditions were as follows: nitrogen atmosphere was filled into the chamber at a rate of 130 mL / min, and the temperature was increased from room temperature to 800℃ at a rate of 10℃ / min.

[0078] Lubrication performance testing: The tribological properties of ester-based oils were tested using a four-ball friction and wear tester. Both upper and lower test balls were made of GCr15 bearing steel, with a diameter of 12.7 mm, a surface roughness of 0.025 μm, and a hardness of HRC 60-63. The test temperatures were 75, 150, or 200℃, the rotation speed was 1200 r / min, the load was 392 N, and the test time was 60 min, to investigate the tribological properties of different lubricating oil samples under different conditions. The lubrication performance test was repeated at least three times.

[0079] Extreme pressure performance testing: The extreme pressure performance of the lubricating oil was evaluated using a four-ball tester according to ASTM D2783-98 standard. The test was conducted at room temperature at 1450 r / min for 10 s, including the maximum non-seizure load (PB) and the minimum sintering load (PD). The extreme pressure performance test was repeated at least 3 times.

[0080] The test results are shown in the table below:

[0081] Table 1 Performance Test Overview

[0082] project Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 Oxidation start temperature (OOT) / °C 272.3 268.5 275.1 276.8 279.5 283.2 221.7 249.2 225.3 Oxidation induction period (OIT, 210℃) / min 82 78 85 87 91 95 45 80 52 Thermal decomposition temperature (T5% weight loss) / ℃ 312.5 308.7 316.8 318.4 322.6 325.3 285.9 290.2 230.7 Coefficient of friction at 150℃ (392N, 60min) 0.070 0.071 0.068 0.067 0.063 0.065 0.078 0.089 0.086 150℃ wear scar diameter / mm 0.35 0.37 0.34 0.33 0.31 0.32 0.39 0.60 0.48 Maximum non-seize load (PB) / N 856 832 874 889 905 923 728 841 753 Minimum sintering load (PD) / N 1920 1885 1950 1980 2050 2100 1505 1860 1620

[0083] As shown in Table 1, the initial oxidation temperature and oxidation induction period of Examples 1-6 were higher than those of Comparative Examples 1-3, indicating that Examples 1-6 had better antioxidant performance. This may be because Examples 1-6 simultaneously contained bentonite imidazole composite microparticles and alkyl imidazole phosphate ionic liquid, forming a synergistic antioxidant system. The S vacancy of MoS2 in the bentonite imidazole composite microparticles was grafted with 2-mercaptobenzimidazole. Its mercapto and benzimidazole ring can capture free radicals at high temperatures, and the antioxidant is less volatile and has improved thermal stability after grafting. The alkyl imidazole phosphate ionic liquid can release cationic components through dynamic equilibrium, further scavenging free radicals and delaying the oxidation of base oil. At the same time, the polyol ester structure of pentaerythritol ester base oil itself has better thermal oxidation stability than PAG46 base oil in Comparative Example 3. However, Comparative Example 1 lacked alkyl imidazole phosphate ionic liquid and relied only on the antioxidant effect of bentonite imidazole composite microparticles, which had limited effect. Comparative Example 3 had a weak synergistic antioxidant ability with additives due to the incompatible base oil type, so its antioxidant performance was significantly reduced.

[0084] As shown in Table 1, the thermal decomposition temperatures of Examples 1-6 are higher than those of Comparative Examples 1-3, indicating that Examples 1-6 have better high-temperature resistance. This may be because the pentaerythritol ester base oils of Examples 1-6 have a polyol ester structure, and the synergistic effect of the ester group and long alkyl chain in the molecule makes them more thermally stable. The bentonite in the bentonite imidazole composite microparticles is a layered inorganic carrier with excellent thermal stability and can serve as a skeleton to support MoS2 nanosheets, inhibiting the aggregation and loss of components at high temperatures. The alkyl imidazole phosphate ionic liquid itself has a high thermal decomposition temperature and good compatibility with pentaerythritol ester base oil, and will not produce destructive impurities due to high-temperature decomposition.

[0085] As shown in Table 1, the coefficient of friction at 150℃ of Examples 1-6 is lower than that of Comparative Examples 2 and 3, and the wear scar diameter is smaller than that of Comparative Examples 2 and 3. The maximum non-seize load and minimum sintering load of Examples 1-6 are higher than those of Comparative Examples 1 and 3, indicating that Examples 1-6 have better lubrication performance. This may be because the bentonite imidazole composite microparticles in Examples 1-6 play a core role in reducing friction and wear. The interlayer spacing of the layered structure of MoS2 is expanded after modification, resulting in low interlayer sliding resistance, which can form a physical lubrication layer at the friction interface. At the same time, the phosphate anions of the alkyl imidazole phosphate ionic liquid can undergo tribochemical reactions with the metal surface to generate a dense friction film containing phosphorus-oxygen-metal, which enhances the extreme pressure bearing capacity. The polarity of the ester group of the pentaerythritol ester base oil can be adsorbed on the metal surface to form an oil film. Together with the bentonite imidazole composite microparticles and the alkyl imidazole phosphate ionic liquid, they synergistically construct a dual system of physical lubrication and chemical protection.

[0086] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0087] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a high-temperature resistant and antioxidant lubricating oil, characterized in that, Step 1: The cationic surfactant is inserted into the interlayer of bentonite by ion exchange for modification. Then, MoS2 nanosheets are synthesized using ammonium molybdate tetrahydrate as molybdenum source and thiourea as sulfur source and anchored in the interlayer or surface of bentonite to obtain composite bentonite. 2-mercaptobenzimidazole is grafted onto the MoS2 nanosheets in the composite bentonite to obtain bentonite imidazole composite microparticles. Step 2: Grafting octanoic acid, isooctanoic acid, and decanoic acid onto pentaerythritol via esterification to obtain pentaerythritol ester base oil; Step 3: Using 2-n-undecylimidazole as the cation and bis(2-ethylhexyl) phosphate as the anion, an alkylimidazolium phosphate ionic liquid was synthesized. Step 4: Mix the bentonite imidazole composite microparticles, alkyl imidazole phosphate ionic liquid and pentaerythritol ester base oil evenly to obtain a high-temperature resistant and antioxidant lubricating oil.

2. The method for preparing a high-temperature resistant and antioxidant lubricating oil according to claim 1, characterized in that, The specific preparation process of the composite bentonite mentioned in step one is as follows: Bentonite, cationic surfactant, anhydrous ethanol and deionized water were added to a high-pressure reactor and stirred until homogeneous. Ammonium molybdate tetrahydrate and thiourea were then added. The mixture was reacted at 180-190℃ and 300-500 r / min for 24-26 h. After cooling, filtration, washing, and freeze-drying, composite bentonite was obtained.

3. The method for preparing a high-temperature resistant and antioxidant lubricating oil according to claim 2, characterized in that, The ratio of bentonite, cationic surfactant, anhydrous ethanol, deionized water, ammonium molybdate tetrahydrate, and thiourea is 47.0-57.0g: 16.5-20.5g: 2-2.2L: 4-4.5L: 70.6-90.6g: 152-190g; The cationic surfactant is any one of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, and 2-n-undecylimidazole.

4. The method for preparing a high-temperature resistant and antioxidant lubricating oil according to claim 1, characterized in that, The specific preparation process of the bentonite imidazole composite microparticles mentioned in step one is as follows: Composite bentonite, 2-mercaptobenzimidazole and isopropanol were added to a reaction vessel and ultrasonically crushed at 0-5℃ for 5-6 hours. Then, the mixture was stirred at 60-65℃ for 48-50 hours. After the reaction was completed, the mixture was naturally cooled to room temperature, centrifuged, and the supernatant was washed and dried to obtain bentonite-imidazolium composite microparticles.

5. The method for preparing a high-temperature resistant and antioxidant lubricating oil according to claim 4, characterized in that, The ratio of the composite bentonite, 2-mercaptobenzimidazole and isopropanol is 3.0-4.0g: 300-400mL: 1.2-1.5L.

6. The method for preparing a high-temperature resistant and antioxidant lubricating oil according to claim 1, characterized in that, The specific preparation process of the pentaerythritol ester base oil mentioned in step two is as follows: Pentaerythritol, octanoic acid, isooctanoic acid, decanoic acid, and a solid acid catalyst were added to a three-necked reactor equipped with a water separator. A water-removing agent was added to the water separator. The esterification reaction was carried out at 210-220℃ and 300-400 r / min for 8-10 hours. The mixture was then vacuum distilled to obtain pentaerythritol ester base oil.

7. The method for preparing a high-temperature resistant and antioxidant lubricating oil according to claim 6, characterized in that, The mass ratio of pentaerythritol, octanoic acid, isooctanoic acid, decanoic acid and solid acid catalyst is 648-700:144-150:1009-1209:1840-1940:34-46; The water-removing agent is one of toluene and petroleum ether.

8. The method for preparing a high-temperature resistant and antioxidant lubricating oil according to claim 1, characterized in that, The specific preparation process of the alkylimidazolium phosphate ionic liquid in step three is as follows: 2-n-undecylimidazole and anhydrous ethanol were added to a reaction vessel and stirred for 30-40 min. Bis(2-ethylhexyl) phosphate was slowly added and stirred for 24-26 h. The mixture was then rotary evaporated and dried to obtain alkylimidazolium phosphate ionic liquid. The ratio of 2-n-undecylimidazole, anhydrous ethanol and bis(2-ethylhexyl) phosphate is 7.28-9.28 g : 100-140 mL : 6.44-8.44 g.

9. The method for preparing a high-temperature resistant and antioxidant lubricating oil according to claim 1, characterized in that, The mass ratio of bentonite imidazole composite microparticles, alkyl imidazole phosphate ionic liquid and pentaerythritol ester base oil in step four is 0.4-0.6:2-3:100-120.

10. A high-temperature resistant and antioxidant lubricating oil, characterized in that, It is prepared by any one of the preparation methods of the high-temperature resistant and antioxidant lubricating oil according to any one of claims 1-9.