Ester anti-wear agent, preparation method and application

Abstract

The invention relates to the technical field of wear resistance of methanol fuel, in particular to an ester anti-wear agent, a preparation method and application, the molecular structural formula of the ester anti-wear agent is R-(OCH2CH2OCH2CH2O)-R, and R is C4-C8 branched chain alkyl. The ester anti-wear agent shows excellent environmental adaptability and functional compatibility through the synergistic effect of an ester-alkyl binary structure. The introduction of branched chain alkyl further optimizes the molecular spatial configuration, C4-C8 branched chain alkyl reduces intermolecular internal friction through a steric hindrance effect, and the branched chain structure can be embedded into micro pits in the surface of a friction pair to form a physical adsorption film, so that the boundary lubricating property is enhanced. Oxygen atoms in the ester group have strong electronegativity and can chemically react with the surface of a friction pair at high friction temperature to generate a chemical protective film containing oxides, and the chemical protective film can bear instantaneous high pressure, effectively prevent direct contact of the metal friction pair and reduce the wear rate; the problems that in the prior art, an anti-wear agent is high in viscosity and poor in lubricating performance are solved.

Description

Technical Field

[0001] This invention relates to the field of methanol fuel anti-wear technology, specifically to an ester anti-wear agent, its preparation method, and its application. Background Technology

[0002] With the profound restructuring of the global energy landscape and the increasingly urgent need for environmental protection, energy transition has become an irreversible trend. Traditional fossil fuels, such as coal and oil, have revealed numerous problems during their long-term large-scale development and utilization, including limited reserves, uneven distribution, and the generation of large amounts of pollutants during combustion. These problems not only pose a potential threat to global energy security but also cause serious damage to the ecological environment, triggering a series of severe challenges such as global warming and air pollution. Therefore, seeking clean and sustainable alternative energy sources has become a common focus for countries around the world.

[0003] Methanol fuel, as a highly promising clean energy source, is gradually gaining attention. Methanol has a wide range of sources, as it can be produced from various raw materials such as coal, natural gas, and biomass. Meanwhile, the pollutant emissions produced during methanol combustion are relatively low. Compared with traditional gasoline and diesel, its emissions of hydrocarbons, carbon monoxide, and particulate matter are significantly reduced, helping to improve air quality and alleviate urban smog. Furthermore, methanol has a high octane rating and good anti-knock properties, making it suitable for use in high-compression engines, improving engine thermal efficiency and further enhancing energy utilization efficiency.

[0004] With continuous technological advancements, methanol fuel is showing increasingly promising applications in transportation, industrial boilers, and power generation. In transportation, methanol-fueled vehicles are becoming a research hotspot, with many automakers investing heavily in their R&D and production. Some regions have also established methanol refueling stations and other infrastructure, facilitating the promotion and application of methanol vehicles. In industrial boilers, methanol, as a clean fuel to replace coal, can effectively reduce boiler emissions and achieve a green transformation in industrial production. In power generation, methanol fuel cell technology is constantly developing, providing new solutions for distributed energy systems. However, methanol's low viscosity makes it difficult to form an effective lubricating film in precision components such as fuel pumps and injectors. Furthermore, methanol is corrosive to metal parts, damaging the oil film on the cylinder walls and leading to abnormal wear of the cylinder wall and piston ring friction pair, making them prone to seizure failure.

[0005] In improving the lubrication performance of methanol fuel, traditional mineral oil-based anti-wear agents were a commonly used early technology. These anti-wear agents use mineral oil as the base oil and add various additives to improve their lubrication performance, thus reducing wear on precision engine components to some extent. Their working principle mainly involves using additives to form a lubricating film on the friction surface, reducing the coefficient of friction and thus reducing wear. However, traditional mineral oil-based anti-wear agents have some inherent defects, such as high viscosity and poor low-temperature fluidity. High viscosity makes it difficult for the anti-wear agent to flow at low temperatures, preventing it from reaching the friction surface in time to form an effective lubricating film, thereby affecting the lubrication effect. Poor low-temperature fluidity also increases engine wear during cold starts, reducing engine lifespan. Furthermore, the interfacial tension between methanol and lubricating oil is significantly lower than that of the base oil, posing a risk of oil film rupture; the stable emulsion formed by methanol and lubricating oil at -20°C will increase the wear of the friction pair several times over.

[0006] With the continuous development of technology, modified methanol fuel technology has gradually become a research hotspot. Among them, phosphorus-containing anti-wear agents have received widespread attention due to their excellent lubrication performance. Phosphorus-containing anti-wear agents can undergo chemical reactions on friction surfaces to generate a chemical reaction film with good lubrication properties, effectively reducing friction and wear. However, methanol has a contamination effect on lubricating oil, affecting its performance and service life. Carbamate additives have good extreme pressure properties and can provide reliable lubrication protection for engines under high temperature and high pressure conditions. However, carbamate additives are prone to crystallization and precipitation at low temperatures, leading to blockage of the fuel supply system, affecting the normal fuel supply of the engine, and even causing engine failure. Boronates, due to their unique chemical structure, can also improve the lubricity of methanol fuel and reduce wear on engine parts. However, boronates have poor hydrolytic stability and cannot meet storage cycle requirements. They are prone to hydrolysis during storage, reducing their lubrication performance and increasing usage costs and risks. Therefore, developing a new anti-wear system that combines good lubricity, low viscosity, economical processing, and environmental friendliness has become a key path to overcome the technological bottlenecks of methanol fuel. Summary of the Invention

[0007] To address the problems of high viscosity and poor lubrication performance of existing anti-wear agents, this invention provides an ester anti-wear agent, its preparation method, and its application.

[0008] To achieve the above objectives, the present invention employs the following technical solution: The present invention provides an ester anti-wear agent, wherein the molecular structure of the ester anti-wear agent is: R-(OCH2CH2OCH2CH2O)-R, wherein R is a C4-C8 branched alkyl group.

[0009] Optionally, R is n-hexyl or 2,2-dimethylbutyl.

[0010] The preparation method of the ester anti-wear agent described above includes: A mixed reaction solution was prepared using diethylene glycol, C4-C8 carboxylic acids, p-toluenesulfonic acid monohydrate, and cyclohexane; The mixed reaction solution was heated and phase separation was performed. The organic phase was taken to obtain the ester anti-wear agent.

[0011] Optionally, the molar ratio of diethylene glycol to C4-C8 carboxylic acid is 1:(2.0-2.5).

[0012] Optionally, the amount of p-toluenesulfonic acid monohydrate added is 1%-2% of the total mass of the mixed reaction solution.

[0013] Optionally, the ratio of cyclohexane to diethylene glycol is (60-80 mL): (17-19.15 g).

[0014] Optionally, the temperature at which the mixed reaction solution is heated is 110-130°C.

[0015] Optionally, a saturated sodium chloride solution can be used to perform phase separation on the heated mixed reaction solution.

[0016] The application of the aforementioned ester anti-wear agents in methanol fuel modification technology.

[0017] In the application of this ester anti-wear agent in methanol fuel modification technology, the mass concentration of the ester anti-wear agent in methanol fuel is 0.5-2%.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention provides an ester anti-wear agent with the molecular structure R-(OCH2CH2OCH2CH2O)-R, where R is a C4-C8 branched alkyl group. This ester anti-wear agent exhibits excellent environmental adaptability and functional compatibility through the synergistic effect of its ester-alkyl binary structure. The introduction of the branched alkyl group further optimizes the molecular spatial configuration. The C4-C8 branched alkyl group reduces intermolecular friction through steric hindrance, and its branched structure can embed into micro-pits on the surface of the friction pair, forming a physical adsorption film and enhancing boundary lubrication performance. The oxygen atom in the ester group has strong electronegativity and can chemically react with the surface of the friction pair at high frictional temperatures to generate an oxide-containing chemical protective film. This chemical protective film can withstand instantaneous high pressure, effectively preventing direct contact between metal friction pairs and reducing wear rate. Under low-temperature and low-load conditions, the formation of the physical adsorption film plays a dominant role, rapidly forming basic protection. Under high temperature and high load conditions, the chemical reaction film replaces the detached physical adsorption film, building a continuous and stable lubrication barrier for the friction pair. This fundamentally solves the three major problems of poor lubricity of methanol fuel, contamination of lubricating oil by traditional anti-wear agents, and insufficient low-temperature fluidity. It provides an efficient, environmentally friendly, and low-cost lubrication solution for methanol fuel engines, diesel vehicles, and industrial equipment, and has the potential for large-scale industrial application.

[0019] R is either n-hexyl or 2,2-dimethylbutyl. The n-hexyl group has a straight-chain structure with tightly packed molecules, resulting in an oil film with high shear stability. Furthermore, the straight-chain structure maintains oil film continuity more easily at high temperatures, making it suitable for continuous high-temperature operating conditions (such as turbocharged engines). In addition, the n-hexyl group has a moderate carbon chain length, providing good low-temperature fluidity. During cold starts, the straight-chain structure can penetrate the metal surface more quickly, shortening the lubrication lag time. The 2,2-dimethylbutyl group has a branched structure, which can reduce intermolecular friction through steric hindrance. Simultaneously, its branches can embed into micro-pits on the metal surface, forming a physical adsorption film, effectively shortening the cold-start lubrication lag time, making it more suitable for frequent cold-start scenarios.

[0020] This invention also provides a method for preparing the ester anti-wear agent as described above. This method involves preparing a mixed reaction solution using diethylene glycol, C4-C8 carboxylic acids, p-toluenesulfonic acid monohydrate, and cyclohexane. The mixed reaction solution is then heated, and phase separation is performed to obtain the organic phase, thus yielding the ester anti-wear agent. Diethylene glycol, as a long-chain diol, has a dihydroxyl structure that can undergo esterification with C4-C8 carboxylic acids to form diester-based anti-wear molecules. This structure significantly enhances the adsorption capacity of the molecules on the metal surface, forming a dense protective film through chemisorption, reducing direct contact between friction pairs, and thereby lowering the wear rate. This method uses p-toluenesulfonic acid monohydrate as a highly efficient organic acid catalyst to accelerate the esterification reaction, reducing water accumulation during the reaction, avoiding reverse reactions, and increasing the esterification yield. Cyclohexane is used as a dehydrating agent to continuously remove the water generated during heating, shifting the chemical equilibrium towards esterification and ensuring thorough subsequent phase separation.

[0021] The application of the aforementioned ester anti-wear agent in methanol fuel modification technology demonstrates that, during application, when the mass concentration of the ester anti-wear agent in methanol fuel is 0.5–2%, the ester anti-wear agent exhibits good miscibility with both methanol and gasoline, allowing it to be uniformly dispersed in the fuel, preventing stratification or sedimentation, and ensuring long-term storage stability. Furthermore, due to its low viscosity, good fluidity, and good lubricity, the ester anti-wear agent significantly improves the lubricity, anti-wear properties, and overall performance of methanol fuel, while also considering economic efficiency and environmental friendliness, thus promoting the large-scale application of methanol fuel in transportation, industry, and civilian sectors. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the preparation method of an ester anti-wear agent according to the present invention.

[0023] Figure 2 is a comparison of the 1H NMR spectrum of the ester anti-wear agent prepared in Example 1 of the present invention; wherein, a is a comparison of the theoretical and actual 1H NMR spectrum of diethylene glycol di(2,2-dimethylbutyric acid) ester, and bf is the chemical shift of the hydrogen atom peaks of different groups and the multiple peak analysis diagram.

[0024] Figure 3 is a comparison of the 1H NMR spectrum of the ester anti-wear agent prepared in Example 2 of the present invention; where a is a comparison of the theoretical and actual 1H NMR spectrum of diethylene glycol di(hexanoic acid) ester, and bg is the chemical shift of the hydrogen atom peaks of different groups and the multiple peak analysis diagram.

[0025] Figure 4 The figures show a comparison of the average friction coefficient and friction volume of the ester anti-wear agents prepared in Examples 1 and 2 of the present invention with methanol at different mass fractions; wherein, a is a comparison of the average friction coefficient and friction volume of the diethylene glycol di(2,2-dimethylbutyric acid) ester mixed with methanol, and b is a comparison of the average friction coefficient and friction volume of the diethylene glycol di(hexanoic acid) ester mixed with methanol. Detailed Implementation

[0026] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0027] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0028] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0029] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0030] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0031] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0032] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0033] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0034] The present invention provides an ester anti-wear agent, wherein the molecular structure of the ester anti-wear agent is: R-(OCH2CH2OCH2CH2O)-R, wherein R is a C4-C8 branched alkyl group.

[0035] Preferably, R is n-hexyl or 2,2-dimethylbutyl.

[0036] When R is a positive hexyl group, its structural formula is: ; When R is 2,2-dimethylbutyl, its structural formula is: .

[0037] When the number of carbon atoms in a branched alkyl group is small, the shorter branch length makes it difficult to effectively entangle with other molecular chains, allowing the molecular chains to slide more easily and thus increasing fluidity. However, longer branches are more prone to entanglement with surrounding chains, leading to increased viscosity and decreased fluidity. Longer branches exhibit significantly better mechanical strength and oxidation resistance than shorter branches. Methanol anti-wear agents need to possess both viscosity and strength to address the low viscosity of methanol and improve its anti-friction properties. Therefore, R is selected from the C6 groups of n-hexyl and 2,2-dimethylbutyl as branches, achieving an effective balance between fluidity, lubricity, and mechanical strength.

[0038] This ester-based anti-wear agent exhibits excellent environmental adaptability and functional compatibility through the synergistic effect of its ester-alkyl binary structure. The introduction of branched alkyl groups further optimizes the molecular spatial configuration. C4-C8 branched alkyl groups reduce intermolecular friction through steric hindrance, while their branched structure can embed into micro-pits on the friction pair surface, forming a physical adsorption film and enhancing boundary lubrication performance. The oxygen atoms in the ester group have strong electronegativity and can chemically react with the friction pair surface at high frictional temperatures to generate an oxide-containing chemical protective film. This chemical protective film can withstand instantaneous high pressure, effectively preventing direct contact between metal friction pairs and reducing wear rate. Under low-temperature and low-load conditions, the formation of the physical adsorption film dominates, quickly forming basic protection. Under high-temperature and high-load conditions, the chemically reacted film replaces the detached physical adsorption film, constructing a continuous and stable lubrication barrier for the friction pair. This fundamentally solves the three major problems of poor lubricity of methanol fuel, contamination of lubricating oil by traditional anti-wear agents, and insufficient low-temperature fluidity. It provides an efficient, environmentally friendly, and low-cost lubrication solution for methanol fuel engines, diesel vehicles, and industrial equipment, and has the potential for large-scale industrial application.

[0039] See Figure 1The present invention also provides a method for preparing the ester anti-wear agent as described above, characterized in that it comprises: S1: A mixed reaction solution is prepared using diethylene glycol, C4-C8 carboxylic acids, p-toluenesulfonic acid monohydrate, and cyclohexane; wherein the molar ratio of diethylene glycol to C4-C8 carboxylic acids is 1:(2.0-2.5), the amount of p-toluenesulfonic acid monohydrate added is 1%-2% of the total mass of the mixed reaction solution, and the ratio of cyclohexane to diethylene glycol is (60-80mL):(17-19.15g). The specific method is as follows: Diethylene glycol was mixed with C4-C8 carboxylic acids, and p-toluenesulfonic acid monohydrate and cyclohexane were added. The mixture was stirred to obtain a mixed reaction solution.

[0040] S2: The mixed reaction solution is heated and phase separation is performed. The organic phase is collected to obtain the ester anti-wear agent, specifically: Heat the mixed reaction solution to 110-130℃ and react for 4-5 hours; After the reaction is complete, pour the mixed reaction solution into a separatory funnel, add saturated sodium bicarbonate solution and mix thoroughly to neutralize the excess C4-C8 carboxylic acids in the mixture; After neutralizing the excess C4-C8 carboxylic acid, add saturated sodium chloride solution to separate the organic phase from the solution phase. Take the upper organic phase and repeat the addition of saturated sodium chloride solution several times until no more bubbles are generated. Keep the final upper organic phase. Ethyl acetate and anhydrous sodium sulfate were added to the final upper organic phase to remove excess water, and the anhydrous sodium sulfate was filtered out to obtain the filtered organic phase. The filtered organic phase was subjected to vacuum rotary evaporation to remove any possible residues such as ethyl acetate, cyclohexane, and water. Further vacuum distillation was then performed to remove water and other residues, yielding the ester anti-wear agent.

[0041] This method uses diethylene glycol as a long-chain diol. Its dihydroxy structure can undergo esterification with C4-C8 carboxylic acids to form diester-based anti-wear molecules. This structure significantly enhances the adsorption capacity of the molecules on the metal surface, forming a dense protective film through chemisorption, reducing direct contact between friction pairs, and thus lowering the wear rate. The method employs p-toluenesulfonic acid monohydrate as a highly efficient organic acid catalyst to accelerate the esterification reaction, reducing water accumulation during the reaction, avoiding reverse reactions, and increasing the esterification yield. Cyclohexane is used as a dehydrating agent to continuously remove water generated during heating, shifting the chemical equilibrium towards esterification and ensuring thorough subsequent phase separation.

[0042] This method achieves low-cost manufacturing of high-performance products through optimized raw material selection and process route design. Using industrial-grade carboxylic acids and diethylene glycol of varying chain lengths as raw materials, combined with continuous production processes and a highly efficient catalyst system, production costs are significantly reduced. Notably, at the current international advanced level, the ester viscosity index has exceeded 240, and the thermal decomposition temperature exceeds 300℃. Diethylene glycol di(2,2-dimethylbutyric acid) ester, as a novel ester base oil, exhibits a viscosity index (130-160) and thermal stability (thermal decomposition temperature 250-300℃) at a mid-to-high level, particularly excelling in lubricity, environmental friendliness, and additive compatibility. While the viscosity index (120-140) of diethylene glycol di(hexanoic acid) ester is at a mid-to-low level, it is still higher than that of traditional mineral oils (viscosity index 90-100). Furthermore, the thermal decomposition temperature of diethylene glycol di(hexanoic acid) ester is 240-260℃, while that of traditional mineral oils is 200-250℃. Therefore, diethylene glycol di(hexanoate) ester has superior viscosity index and thermal stability compared to traditional mineral oil lubricants. It also excels particularly in low-temperature fluidity and environmental friendliness.

[0043] Example 1 raw material: Diethylene glycol (Shanghai Aladdin, 99%, molecular weight 106.12) 2,2-Dimethylbutyric acid (Shanghai Aladdin, 98%, molecular weight 116.16) p-Toluenesulfonic acid monohydrate (Shanghai Aladdin, 99%) Cyclohexane (Shanghai Aladdin, 99%) The ester anti-wear agent (diethylene glycol di(2,2-dimethylbutyrate) ester) was prepared by the following steps: Add 0.16 mol (17 g) of diethylene glycol and 0.43 mol (50 g) of 2,2-dimethylbutyric acid to a 500 mL round-bottom flask; Add 0.003 mol (0.6 g) of p-toluenesulfonic acid monohydrate and 60 mL of cyclohexane to a round-bottom flask. Place a magnetic stirrer in the mixture. Install a water separator and a spherical condenser on the round-bottom flask, with a receiving beaker placed at the bottom of the condenser. Heat the mixture to 120 °C and maintain the temperature for 4 h, monitoring the reaction for completeness using micro-thin-layer chromatography. After the reaction is complete, pour the resulting mixture into a separatory funnel, add saturated sodium bicarbonate solution, and gently shake to neutralize the excess 2,2-dimethylbutyric acid in the mixture. Repeat this process several times until no more bubbles are generated. Then, add saturated sodium chloride solution to break the emulsion and finally retain the upper organic phase mixture. Subsequently, the upper organic phase mixture was taken and an appropriate amount of ethyl acetate was added. The mixture was dried with anhydrous sodium sulfate and filtered. The filtered organic phase mixture was then subjected to vacuum rotary evaporation to remove any possible residues such as ethyl acetate, cyclohexane, and water. The remaining liquid was further distilled under reduced pressure with the aid of a vacuum pump to remove any possible residues such as water, yielding crude diethylene glycol di(2,2-dimethylbutyric acid) ester, which is a yellow oily liquid and serves as the ester anti-wear agent.

[0044] Referring to Figure 2, the horizontal axis (ppm) of the 1H NMR spectrum represents the chemical shift, indicating the positional differences of hydrogen atoms in a magnetic field. The vertical axis of the 1H NMR spectrum represents the NMR peak signal intensity, reflecting the absorption intensity of the hydrogen nucleus under specific magnetic field conditions. The structural characterization is as follows: 1H NMR spectrum ( 1 H NMR, DMSO): δ 4.27-4.22 (m, 4H, -COOCH2-); δ 3.76-3.69 (m, 4H, -CH2-O-); δ 1.63-1.56 (m, 4H, -CH2-); δ 1.19–1.18 (m, 12H, branched alkyl); δ 0.92-0.84 (m, 6H, -CH3).

[0045] To further illustrate the beneficial effects of the present invention, the anti-wear performance of the diethylene glycol di(2,2-dimethylbutyric acid) ester anti-wear agent obtained in this embodiment in methanol fuel was verified.

[0046] Test sample preparation: Single-agent test group: The diethylene glycol di(2,2-dimethylbutyric acid) ester synthesized in this example was mixed with methanol (water ≤0.5wt%, sulfur ≤10ppm) at mass ratios of 0.5%, 1% and 2% respectively to form a homogeneous solution.

[0047] Control group: pure methanol.

[0048] Test method: RETC's multi-functional friction and wear machine Test parameters: load 20N, frequency 10 Hz, time 10 min, ambient temperature 25℃ Test parameters: Wear volume (mm) 3 Average coefficient of friction The test results of the single-agent anti-wear performance are shown in the table below. Figure 4 As shown:

[0049] The data above shows that the wear volume of 0.5% diethylene glycol di(2,2-dimethylbutyrate) ester + 99.5% methanol is reduced by about 42.4189% compared to that of alcohol, and its anti-wear performance is significantly better than that of other samples.

[0050] Example 2 raw material: Diethylene glycol (Shanghai Aladdin, 99%, molecular weight 106.12) Hexanoic acid (Shanghai Aladdin, 98%, molecular weight 116.16) p-Toluenesulfonic acid monohydrate (Shanghai Aladdin, 99%) Cyclohexane (Shanghai Aladdin, 99%) The ester anti-wear agent (diethylene glycol di(n-hexanoate) ester) was prepared by the following steps: Add 0.18 mol (19.15 g) of diethylene glycol and 0.52 mol (60 g) of hexanoic acid to a 500 mL round-bottom flask; Add 0.003 mol (0.6 g) of p-toluenesulfonic acid monohydrate and 70 mL of cyclohexane to a round-bottom flask. Place a magnetic stirrer in the mixture. Install a water separator and a spherical condenser on the round-bottom flask, with a receiving beaker placed at the bottom of the condenser. Heat the mixture to 120 °C and maintain the temperature for 4 h, monitoring the reaction for completeness using micro-thin-layer chromatography. After the reaction is complete, pour the resulting mixture into a separatory funnel, add saturated sodium bicarbonate solution, and gently shake to neutralize the excess hexanoic acid in the mixture. Repeat this process several times until no more bubbles are generated. Then, add saturated sodium chloride solution to break the emulsion and finally retain the upper organic phase mixture. Subsequently, the organic phase mixture was taken and an appropriate amount of ethyl acetate was added. The mixture was dried with anhydrous sodium sulfate, filtered, and then subjected to vacuum rotary evaporation to remove any possible residues such as ethyl acetate, cyclohexane, and water. The remaining liquid was further distilled under reduced pressure with the aid of a vacuum pump to remove any remaining water. Finally, crude diethylene glycol di(n-hexanoic acid) ester was obtained, appearing as a yellow oily liquid.

[0051] Referring to Figure 3, the horizontal axis (ppm) of the proton NMR spectrum represents the chemical shift, indicating the positional differences of hydrogen atoms in a magnetic field. The vertical axis of the proton NMR spectrum represents the NMR peak signal intensity, reflecting the absorption intensity of the hydrogen nucleus under specific magnetic field conditions. The structural characterization is as follows: 1H NMR spectrum ( 1 H NMR, DMSO): δ 4.30-4.26 (m, 4H, -COOCH2-); δ 3.76-3.73 (m, 4H, -CH2-O-CH2-); δ 2.39-2.36 (m, 4H, -COOCH2-); δ 1.71-1.64 (m, 4H, -CH2-); δ 1.47-1.28 (m, 8H, -CH2-) δ 0.95-0.92 (m, 6H, -CH3).

[0052] To further illustrate the beneficial effects of the present invention, the anti-wear performance of the diethylene glycol di(n-hexanoic acid) ester anti-wear agent prepared in this embodiment was verified in methanol fuel.

[0053] Single-agent test group: The synthesized diethylene glycol di(hexanoic acid) ester was mixed with methanol (water ≤ 0.5 wt%, sulfur ≤ 10 ppm) at mass ratios of 0.5%, 1% and 2% respectively to form a homogeneous solution.

[0054] Control group: pure methanol Test method: RETC's multi-functional friction and wear machine Test parameters: load 20N, frequency 10Hz, time 10min, ambient temperature 25℃ Test parameters: Wear volume (mm) 3 Average coefficient of friction The test results of the single-agent anti-wear performance are shown in the table below. Figure 4 As shown:

[0055] The data above shows that the wear volume of 1% diethylene glycol di(hexanoic acid) ester + 99% methanol is reduced by about 28.0236% compared with pure methanol, and its anti-wear performance is significantly better than other samples.

[0056] Example 3 raw material: Diethylene glycol (Shanghai Aladdin, 99%, molecular weight 106.12) 2,2-Dimethylbutyric acid (Shanghai Aladdin, 98%, molecular weight 116.16) p-Toluenesulfonic acid monohydrate (Shanghai Aladdin, 99%) Cyclohexane (Shanghai Aladdin, 99%) The ester anti-wear agent (diethylene glycol di(2,2-dimethylbutyrate) ester) was prepared by the following steps: Add 0.16 mol (17 g) of diethylene glycol and 0.43 mol (50 g) of 2,2-dimethylbutyric acid to a 500 mL round-bottom flask; Add 0.003 mol (0.6 g) of p-toluenesulfonic acid monohydrate and 80 mL of cyclohexane to a round-bottom flask. Place a magnetic stirrer in the mixture. Install a water separator and a spherical condenser on the round-bottom flask, with a receiving beaker placed at the bottom of the condenser. Heat the mixture to 110 °C and maintain the temperature for 5 h, monitoring the reaction for completeness using micro-thin-layer chromatography. After the reaction is complete, pour the resulting mixture into a separatory funnel, add saturated sodium bicarbonate solution, and gently shake to neutralize the excess 2,2-dimethylbutyric acid in the mixture. Repeat this process several times until no more bubbles are generated. Then, add saturated sodium chloride solution to break the emulsion and finally retain the upper organic phase mixture. Subsequently, the upper organic phase mixture was taken and an appropriate amount of ethyl acetate was added. The mixture was dried with anhydrous sodium sulfate and filtered. The filtered organic phase mixture was then subjected to vacuum rotary evaporation to remove any possible residues such as ethyl acetate, cyclohexane, and water. The remaining liquid was further distilled under reduced pressure with the aid of a vacuum pump to remove any possible residues such as water, yielding crude diethylene glycol di(2,2-dimethylbutyric acid) ester, which is a yellow oily liquid and serves as the ester anti-wear agent.

[0057] Example 4 raw material: Diethylene glycol (Shanghai Aladdin, 99%, molecular weight 106.12) Hexanoic acid (Shanghai Aladdin, 98%, molecular weight 116.16) p-Toluenesulfonic acid monohydrate (Shanghai Aladdin, 99%) Cyclohexane (Shanghai Aladdin, 99%) The ester anti-wear agent (diethylene glycol di(n-hexanoate) ester) was prepared by the following steps: Add 0.18 mol (19.15 g) of diethylene glycol and 0.52 mol (60 g) of hexanoic acid to a 500 mL round-bottom flask; Add 0.003 mol (0.6 g) of p-toluenesulfonic acid monohydrate and 80 mL of cyclohexane to a round-bottom flask. Place a magnetic stirrer in the mixture. Install a water separator and a spherical condenser on the round-bottom flask, with a receiving beaker placed at the bottom of the condenser. Heat the mixture to 130 °C and maintain the temperature for 4 h, monitoring the reaction for completeness using micro-thin-layer chromatography. After the reaction is complete, pour the resulting mixture into a separatory funnel, add saturated sodium bicarbonate solution, and gently shake to neutralize the excess hexanoic acid in the mixture. Repeat this process several times until no more bubbles are generated. Then, add saturated sodium chloride solution to break the emulsion and finally retain the upper organic phase mixture. Subsequently, the organic phase mixture was taken and an appropriate amount of ethyl acetate was added. The mixture was dried with anhydrous sodium sulfate, filtered, and then subjected to vacuum rotary evaporation to remove any possible residues such as ethyl acetate, cyclohexane, and water. The remaining liquid was further distilled under reduced pressure with the aid of a vacuum pump to remove any remaining water. Finally, crude diethylene glycol di(n-hexanoic acid) ester was obtained, appearing as a yellow oily liquid.

[0058] The application of the aforementioned ester anti-wear agent in methanol fuel modification technology demonstrates that, during application, when the mass concentration of the ester anti-wear agent in methanol fuel is 0.5–2%, the ester anti-wear agent exhibits good miscibility with both methanol and gasoline, allowing it to be uniformly dispersed in the fuel, preventing stratification or sedimentation, and ensuring long-term storage stability. Furthermore, due to its low viscosity, good fluidity, and good lubricity, the ester anti-wear agent significantly improves the lubricity, anti-wear properties, and overall performance of methanol fuel, while also considering economic efficiency and environmental friendliness, thus promoting the large-scale application of methanol fuel in transportation, industry, and civilian sectors.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. An ester-based anti-wear agent, characterized in that, The molecular structure of the ester anti-wear agent is: R-(OCH2CH2OCH2CH2O)-R, where R is a C4-C8 branched alkyl group.

2. The ester anti-wear agent according to claim 1, characterized in that, R is n-hexyl or 2,2-dimethylbutyl.

3. The method for preparing the ester anti-wear agent as described in claim 1 or 2, characterized in that, include: A mixed reaction solution was prepared using diethylene glycol, C4-C8 carboxylic acids, p-toluenesulfonic acid monohydrate, and cyclohexane; The mixed reaction solution was heated and phase separation was performed. The organic phase was taken to obtain the ester anti-wear agent.

4. The method for preparing the ester anti-wear agent according to claim 3, characterized in that, The molar ratio of diethylene glycol to C4-C8 carboxylic acids is 1:(2.0-2.5).

5. The method for preparing the ester anti-wear agent according to claim 3, characterized in that, The amount of p-toluenesulfonic acid monohydrate added is 1%-2% of the total mass of the mixed reaction solution.

6. The method for preparing the ester anti-wear agent according to claim 3, characterized in that, The ratio of cyclohexane to diethylene glycol is (60-80 mL): (17-19.15 g).

7. The method for preparing the ester anti-wear agent according to claim 3, characterized in that, The temperature at which the mixed reaction solution is heated is 110-130℃.

8. The method for preparing the ester anti-wear agent according to claim 3, characterized in that, A saturated sodium chloride solution was used to separate the phases of the heated mixed reaction solution.

9. The application of the ester anti-wear agent according to claim 1 in methanol fuel modification technology.

10. The application of the ester anti-wear agent according to claim 9 in methanol fuel modification technology, characterized in that, The mass concentration of ester anti-wear agent in methanol fuel is 0.5-2%.

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