Complex ester-based hydraulic oil and preparation method thereof

Abstract

The invention discloses composite ester-based hydraulic oil and a preparation method thereof, and belongs to the technical field of hydraulic oil preparation. The hydraulic oil based on the complex ester comprises the following components: pentaerythritol synthetic ester, polysebacic acid glycol ester, a viscosity-temperature performance regulator, an ash-free antioxidant, a bio-based anti-wear agent and a nano modifier. Wherein the pentaerythritol synthetic ester is a mixed ester obtained by carrying out a reaction on a mixture of 2-ethylhexanoic acid, 3, 5-dimethylhexanoic acid and 4-methyloctanoic acid and pentaerythritol, and the pentaerythritol synthetic ester is a mixture of 2-ethylhexanoic acid, 3, 5-dimethylhexanoic acid and 4-methyloctanoic acid; the viscosity-temperature performance regulator is a grafted copolymer obtained by grafting poly (N-isopropylacrylamide) to a poly (ethylene sebacate) molecular chain through an ester exchange reaction. The product prepared by the method disclosed by the invention can effectively solve the contradiction between the environmental protection performance and the comprehensive performance of the traditional hydraulic oil through the synergistic effect of the components, has the characteristics of high biodegradation rate and good oxidation resistance and hydrolytic stability, and can keep excellent performance in both low-temperature and high-temperature environments.

Description

Technical Field

[0001] This invention belongs to the field of hydraulic oil preparation technology, specifically relating to a hydraulic oil based on a composite ester and its preparation method. Background Technology

[0002] Hydraulic oil, as the working medium for transmitting power and signals in hydraulic systems, is widely used in many fields such as industry, transportation, and aerospace. With increasing environmental awareness and increasingly stringent environmental regulations, higher requirements are being placed on the environmental performance of hydraulic oil.

[0003] Traditional mineral-based hydraulic oils are refined from petroleum, and their main components are various hydrocarbon compounds. These hydraulic oils have advantages such as low cost and stable performance, and have dominated the market for a long time. However, mineral-based hydraulic oils have a serious drawback: poor biodegradability, with a biodegradability rate typically less than 30%. This means that when mineral-based hydraulic oil leaks during use and flows into soil or water bodies, it is difficult for it to be decomposed by microorganisms in the natural environment, causing long-term pollution of soil and water bodies, severely damaging the ecological environment, and failing to meet the increasingly stringent environmental regulations.

[0004] To address the environmental concerns associated with mineral-based hydraulic oils, synthetic ester-based hydraulic oils have emerged. These oils are prepared through chemical synthesis and possess good biodegradability. However, they also have some inherent drawbacks. Firstly, their antioxidant properties are insufficient. During long-term operation of a hydraulic system, the hydraulic oil comes into contact with oxygen in the air. Under conditions of high temperature, high pressure, and metal catalysts, oxidation reactions easily occur, generating acidic substances, colloids, and precipitates. These substances corrode metal components in the hydraulic system, clog filters and valves, and affect the normal operation of the system. Secondly, synthetic ester-based hydraulic oils have poor hydrolytic stability. In humid environments, water molecules readily react with ester molecules, causing ester bonds to break and generating acids and alcohols. This also reduces the performance of the hydraulic oil and shortens its service life. Typically, the service life of synthetic ester-based hydraulic oils is less than 5000 hours. Frequent oil changes not only increase operating costs but may also affect the normal operation of equipment.

[0005] Furthermore, most existing environmentally friendly hydraulic oils use single esters, such as pentaerythritol esters. While pentaerythritol esters offer certain performance advantages, single esters struggle to balance low-temperature fluidity and high-temperature anti-wear properties. At low temperatures, the viscosity of the hydraulic oil increases dramatically, leading to decreased fluidity and affecting the start-up and response speed of the hydraulic system. At high temperatures, the oil film strength decreases, failing to effectively protect the friction surfaces between metal parts, thus exacerbating wear.

[0006] In summary, both traditional mineral-based hydraulic oils and existing synthetic ester-based hydraulic oils have their own shortcomings. Developing a new type of hydraulic oil and its preparation method that not only has good environmental performance, but also excellent oxidation resistance, hydrolytic stability, and can balance low-temperature fluidity and high-temperature anti-wear properties is of great practical significance. Summary of the Invention

[0007] To address the problems of existing hydraulic oils, such as poor biodegradability, insufficient oxidation resistance, poor hydrolytic stability, and difficulty in simultaneously achieving low-temperature fluidity and high-temperature anti-wear properties, the inventors propose the following solutions:

[0008] A hydraulic oil based on a complex ester comprises the following components: pentaerythritol synthetic ester, polyethylene sebacic acid ester, viscosity-temperature modifier, ashless antioxidant, bio-based anti-wear agent, and nano-modifier. This hydraulic oil uses a complex ester obtained by esterification of a C8-C12 branched fatty acid mixture with pentaerythritol as the base oil. The fatty acid mixture is obtained by mixing 2-ethylhexanoic acid, 3,5-dimethylhexanoic acid, and 4-methyloctanoic acid in a certain proportion. 2-Ethylhexanoic acid, with its good branched structure, imparts good low-temperature performance and solubility to the complex ester; 3,5-dimethylhexanoic acid, with its unique molecular structure, helps improve the thermal stability and antioxidant properties of the complex ester; and 4-methyloctanoic acid allows the synthetic ester to maintain a high viscosity index while possessing better lubrication performance. The complex ester obtained by esterification of the above-mentioned fatty acid mixture with pentaerythritol exhibits a high viscosity index, and the viscosity change of the hydraulic oil is relatively small with temperature variations, ensuring stable operation of the hydraulic system under different temperature environments. Meanwhile, this composite ester also has good thermal stability. Under high temperature conditions, its molecular structure can remain relatively stable and is not prone to decomposition or polymerization reactions, thereby extending the service life of hydraulic oil.

[0009] In this solution, a polyester component—polyethylene sebacic acid (PEG)—is incorporated into the hydraulic oil. In low-temperature environments, PEG lowers the pour point of the hydraulic oil, allowing it to maintain good flowability even at lower temperatures. This ensures the hydraulic system can start smoothly and operate normally in cold weather or low-temperature working environments. Furthermore, PEG enhances the hydraulic oil's resistance to hydrolysis, effectively resisting the damage to ester bonds by water molecules and improving its stability in humid environments.

[0010] In this solution, a viscosity-temperature modifier is introduced into the hydraulic oil. Specifically, it is a graft copolymer obtained by grafting poly(N-isopropylacrylamide) onto the molecular chain of polyethylene sebacic acid via transesterification. In this graft copolymer molecular chain, poly(N-isopropylacrylamide) has a low critical dissolution temperature. When the ambient temperature is below the critical dissolution temperature, its molecular chain segments are hydrophilic and extended, having little impact on the viscosity of the base oil. When the temperature exceeds the critical dissolution temperature, the molecular chain segments hydrophobically shrink and form micromicelles, increasing the intermolecular forces within the oil and thus inhibiting a sharp decrease in viscosity at high temperatures. Based on these characteristics, this viscosity-temperature modifier can maintain the viscosity-temperature index of the base oil over a wide temperature range, avoiding the problems of insufficient high-temperature viscosity and excessively high low-temperature viscosity in traditional base oils. In addition, the flexible backbone (i.e., the polyethylene sebacic acid ester molecular chain) in this viscosity-temperature performance regulator has good compatibility with pentaerythritol ester and polyethylene sebacic acid ester. The grafted poly(N-isopropylacrylamide) segments can form a network-like dispersion structure in the oil, enhancing the elasticity and shear resistance of the oil film.

[0011] In this solution, the hydraulic oil uses an ashless antioxidant, specifically a compound of alkylated diphenylamine and natural tocopherol. Alkylated diphenylamine possesses highly efficient antioxidant properties, capable of capturing free radicals generated during hydraulic oil oxidation, interrupting the oxidation chain reaction, and thus slowing down the oxidation process. Natural tocopherol not only has its own antioxidant capacity but also exhibits a synergistic effect with alkylated diphenylamine, further enhancing the antioxidant effect. By precisely controlling the compounding ratio of the two, the antioxidant performance is ensured while avoiding adverse effects on other properties of the hydraulic oil due to excessive additives, thereby significantly extending the oxidation life of the hydraulic oil.

[0012] In this solution, epoxidized soybean oil derivatives are used as anti-wear agents, which not only meet the anti-wear requirements but also comply with environmental protection requirements. A nano-modifier, namely modified nano-zinc oxide particles, is added. Due to their extremely small size, nanoparticles possess unique physicochemical properties. The surface-modified zinc dioxide nanoparticles can be uniformly dispersed in the hydraulic oil. Under extreme pressure conditions, the nanoparticles can fill the microscopic pits on the metal surface, making the friction surface smoother, enhancing the oil film's load-bearing capacity, and thus improving the extreme pressure performance of the hydraulic oil.

[0013] Based on the above-mentioned solutions to the problems, this invention specifically proposes a hydraulic oil based on a composite ester, comprising the following components: pentaerythritol synthetic ester, polyethylene sebacic acid ester, viscosity-temperature performance modifier, ashless antioxidant, bio-based anti-wear agent, and nano-modifier. The pentaerythritol synthetic ester is characterized in that it is a mixed ester obtained by reacting a mixture of 2-ethylhexanoic acid, 3,5-dimethylhexanoic acid, and 4-methyloctanoic acid with pentaerythritol; the viscosity-temperature performance modifier is a graft copolymer obtained by grafting poly(N-isopropylacrylamide) onto the polyethylene sebacic acid ester molecular chain via transesterification; the ashless antioxidant is a mixture of N,N′-di-sec-butyl-p-phenylenediamine and natural tocopherol; the bio-based anti-wear agent is an epoxidized soybean oil derivative; and the nano-modifier is modified nano-zinc oxide particles.

[0014] Furthermore, the pentaerythritol synthetic ester is prepared by the following method: 2-ethylhexanoic acid, 3,5-dimethylhexanoic acid, and 4-methyloctanoic acid are mixed in a ratio of 2:2:1 to obtain a fatty acid mixture; the above fatty acid mixture and pentaerythritol are added to a reaction vessel equipped with a stirrer, thermometer, and reflux condenser at a molar ratio of 4.5:1, and 0.5%-1% of p-toluenesulfonic acid by mass of the total reactants is added as a catalyst; stirring is started and the temperature is slowly raised to 180-220°C, and the reaction is carried out for 4-6 hours, and water is removed by a water separator; after the reaction is completed, the temperature is cooled to about 100°C, neutralized to neutral with saturated sodium carbonate solution, impurities are removed by washing with water, and unreacted substances are removed by vacuum distillation to obtain the pentaerythritol synthetic ester.

[0015] Furthermore, the viscosity-temperature modifier is prepared by the following method: poly(N-isopropylacrylamide) and poly(ethylene sebacic acid) are mixed at a molar ratio of 1:5, and 0.3% sodium methoxide by mass of the total reactants is added as a catalyst. The transesterification reaction is carried out at 180°C under nitrogen protection for 4 hours. The main chain of this graft copolymer is poly(ethylene sebacic acid), and the side chains are poly(N-isopropylacrylamide). The main chain and side chains are connected by ester bonds (-OC(=O)-). The chemical expression of the repeating unit in the graft copolymer molecular chain is "-[OC(=O)-(CH2)8-C(=O)-O-CH2-CH2-]". m -OC(=O)-[CH2-CH(CONH-CH(CH3)2)] n -”, where m and n represent the number of repeating units in the main chain, which is affected by the grafting rate.

[0016] Furthermore, the mass ratio of N,N′-di-sec-butyl-p-phenylenediamine to natural tocopherol in the ashless antioxidant is 3:1.

[0017] Furthermore, the natural tocopherol mixture is a mixture of α-tocopherol and γ-tocopherol in a weight ratio of 1:1.

[0018] Furthermore, a hydraulic oil based on a composite ester is composed of the following components in weight percentage: 45-50% pentaerythritol synthetic ester, 35-40% polyethylene sebacic acid ester, 6-8% viscosity-temperature modifier, 5-8% ashless antioxidant, 4-6% bio-based anti-wear agent, and 0.5-1% nano-modifier.

[0019] Furthermore, a preferred embodiment of a composite ester-based hydraulic oil comprises the following components in weight percentage: 45% pentaerythritol synthetic ester, 38% polyethylene sebacic acid ester, 7% viscosity-temperature modifier, 5.5% ashless antioxidant, 4% bio-based anti-wear agent, and 0.5% nano-modifier.

[0020] Furthermore, the present invention also provides a method for preparing hydraulic oil based on composite esters, comprising the following steps:

[0021] S1 base oil premix: First, add pentaerythritol synthetic ester to the blending reactor, start stirring at 50 rpm; slowly add polyethylene sebacic acid ester, and at the same time raise the temperature to 60℃; gradually increase the stirring speed to 150 rpm and maintain it for 30 min;

[0022] S2 Additive Addition: Divide the viscosity-temperature performance regulator into 4 equal parts, add each part to the mixing reactor at 10-minute intervals, and gradually raise the temperature to 70°C while increasing the stirring speed to 200 rpm and maintaining it for 1 hour. During this period, take samples every 15 minutes to observe the transparency.

[0023] S3 antioxidant and anti-wear agent addition: Cool to 60℃, first add N,N′-di-sec-butyl-p-phenylenediamine and natural tocopherol to the mixing reactor, stir for 30 min; then add epoxidized soybean oil derivative, stir for 45 min;

[0024] S4 nano-modifier dispersion: Slowly add the ultrasonically pre-dispersed modified nano zinc oxide particles into the mixing reactor, while simultaneously turning on the high shear disperser at a linear velocity of 20 m / s and maintaining the temperature at 60℃ for 1 hour;

[0025] S5 Post-processing: The mixture obtained in step S4 is degassed at 50℃ / 1kPa vacuum for 1h, filtered through a 0.1μm ceramic membrane, allowed to stand for 24h, and the supernatant is taken to obtain the finished product.

[0026] Through the above-mentioned solution, the present invention can effectively resolve the contradiction between the environmental performance and overall performance of traditional hydraulic oil, and prepare a new type of hydraulic oil with high biodegradability, good antioxidant and hydrolytic stability, and excellent performance under both low and high temperature environments, as well as its preparation method, to meet the increasingly stringent requirements of modern industry for hydraulic oil. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] A hydraulic oil based on a complex ester is prepared using the following steps:

[0030] (1) Preparation of pentaerythritol synthetic ester. 2-Ethylhexanoic acid, 3,5-dimethylhexanoic acid, and 4-methyloctanoic acid were mixed in a ratio of 2:2:1 to obtain a fatty acid mixture. This fatty acid mixture was then added to pentaerythritol at a molar ratio of 4.5:1 into a reactor equipped with a stirrer, thermometer, and reflux condenser. Simultaneously, 0.5%-1% of p-toluenesulfonic acid (by mass of the total reactants) was added as a catalyst. Stirring was started, and the temperature was slowly increased to 180-220°C. The reaction was carried out for 4-6 hours, and water was removed using a water separator. After the reaction was complete, the mixture was cooled to approximately 100°C, neutralized with a saturated sodium carbonate solution, washed with water to remove impurities, and then subjected to vacuum distillation to remove unreacted substances, yielding the pentaerythritol synthetic ester.

[0031] (2) Preparation of viscosity-temperature modifier. Poly(N-isopropylacrylamide) and polyethylene sebacate were mixed at a molar ratio of 1:5, and sodium methoxide (0.3% by mass of total reactants) was added as a catalyst. The transesterification reaction was carried out at 180°C under nitrogen protection for 4 hours to obtain the viscosity-temperature modifier.

[0032] (3) Prepare raw materials according to the following mass percentage composition: 45-50% pentaerythritol synthetic ester, 35-40% polyethylene sebacic acid ester, 6-8% viscosity-temperature performance regulator, 5-8% ashless antioxidant, 4-6% bio-based anti-wear agent, and 0.5-1% nano-modifier.

[0033] (4) Preparation of finished products. S1 Base oil premixing: First, add pentaerythritol synthetic ester to the blending reactor, start stirring at 50 rpm; slowly add polyethylene sebacic acid ester, and simultaneously raise the temperature to 60℃; gradually increase the stirring speed to 150 rpm and maintain for 30 min; S2 Additive addition: Divide the viscosity-temperature performance regulator into 4 equal portions, add each portion to the blending reactor at 10 min intervals, and simultaneously gradually raise the temperature to 70℃, and increase the stirring speed to 200 rpm and maintain for 1 h, taking samples every 15 min to observe the transparency; S3 Antioxidant and anti-wear agent addition: cool to 60℃. At 0℃, N,N′-di-sec-butyl-p-phenylenediamine and natural tocopherol were first added to the mixing reactor and stirred for 30 min; then epoxidized soybean oil derivative was added and stirred for 45 min; S4 Nano-modifier dispersion: The ultrasonically pre-dispersed modified nano zinc oxide particles were slowly added to the mixing reactor, and a high-shear disperser was turned on at a linear velocity of 20 m / s and a temperature of 60℃ for 1 h; S5 Post-treatment: The mixture obtained in step S4 was degassed at 50℃ / 1 kPa vacuum for 1 h, filtered with a 0.1 μm ceramic membrane, allowed to stand for 24 h, and the supernatant was taken to obtain the finished product.

[0034] Example 2

[0035] Based on the preparation method of Example 1, a hydraulic oil sample based on a composite ester was prepared using the following proportions of raw materials: 450g of pentaerythritol synthetic ester, 380g of polyethylene sebacic acid ester, 70g of viscosity-temperature performance regulator, 55g of ashless antioxidant, 40g of bio-based anti-wear agent, and 5g of nano-modifier.

[0036] Example 3

[0037] Under the same experimental conditions, the viscosity index, pour point, rotating bomb oxidant, and HTHS viscosity of the hydraulic oil sample prepared in Example 2 (Group A) and a commercially available hydraulic oil product (Group B) were tested.

[0038] In this comparative experiment, the testing of each technical indicator was conducted using the following methods.

[0039] Viscosity and viscosity index test: The viscosity index (VI) data are obtained by referring to the methods of standards GB / T265 and GB / T1995.

[0040] Low-temperature flowability test: Pour point data are obtained by referring to the method in standard GB / T3535.

[0041] Oxidation stability test: The rotating oxygen bomb data were obtained by referring to the method of standard SH / T0193.

[0042] Hydrolysis stability test: Hydrolysis stability data were obtained by referring to the method of standard SH / T0301.

[0043] Wear resistance test: The wear scar diameter data were obtained by referring to the method of standard SH / T0189.

[0044] Based on the above methods, the test results of various technical indicators of the samples in Group A and Group B are shown in the table below:

[0045]

[0046] The data comparison above shows that the hydraulic oil based on composite ester prepared by the method of this invention, represented by Group A samples, has certain advantages over similar products on the market in terms of low-temperature adaptability, anti-wear properties, and oxidation life.

[0047] 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, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A hydraulic oil based on a composite ester, comprising the following components: pentaerythritol synthetic ester, polyethylene sebacic acid ester, viscosity-temperature modifier, ashless antioxidant, bio-based anti-wear agent, and nano-modifier, characterized in that, The pentaerythritol synthetic ester is a mixed ester obtained by reacting a mixture of 2-ethylhexanoic acid, 3,5-dimethylhexanoic acid, and 4-methyloctanoic acid with pentaerythritol; the viscosity-temperature modifier is a graft copolymer obtained by grafting poly(N-isopropylacrylamide) onto the molecular chain of polyethylene sebacate via transesterification; the ashless antioxidant is a mixture of N,N′-di-sec-butyl-p-phenylenediamine and natural tocopherol; the bio-based anti-wear agent is an epoxidized soybean oil derivative; and the nano-modifier is modified nano-zinc oxide particles.

2. The hydraulic oil based on a composite ester according to claim 1, characterized in that, The pentaerythritol synthetic ester is prepared by the following method: 2-ethylhexanoic acid, 3,5-dimethylhexanoic acid, and 4-methyloctanoic acid are mixed in a ratio of 2:2:1 to obtain a fatty acid mixture; the above fatty acid mixture and pentaerythritol are added to a reaction vessel equipped with a stirrer, thermometer, and reflux condenser at a molar ratio of 4.5:1, and 0.5%-1% of p-toluenesulfonic acid by mass of the total reactants is added as a catalyst; stirring is started and the temperature is slowly raised to 180-220°C, and the reaction is carried out for 4-6 hours, and water is removed by a water separator; after the reaction is completed, the temperature is cooled to about 100°C, neutralized to neutral with saturated sodium carbonate solution, impurities are removed by washing with water, and unreacted substances are removed by vacuum distillation to obtain the pentaerythritol synthetic ester.

3. The hydraulic oil based on a composite ester according to claim 1, characterized in that, The viscosity-temperature modifier is prepared by the following method: poly(N-isopropylacrylamide) and poly(ethylene sebacate) are mixed at a molar ratio of 1:5, and sodium methoxide (0.3% by mass of total reactants) is added as a catalyst. The transesterification reaction is carried out at 180°C under nitrogen protection for 4 hours.

4. The hydraulic oil based on a composite ester according to claim 1, characterized in that, The mass ratio of N,N′-di-sec-butyl-p-phenylenediamine to natural tocopherol in the ashless antioxidant is 3:

1.

5. The hydraulic oil based on a composite ester according to claim 1, characterized in that, The natural tocopherol mixture is a mixture of α-tocopherol and γ-tocopherol in a weight ratio of 1:

1.

6. The hydraulic oil based on a composite ester according to claim 1, characterized in that, It is composed of the following components by weight percentage: 45-50% pentaerythritol synthetic ester, 35-40% polyethylene sebacic acid ester, 6-8% viscosity-temperature modifier, 5-8% ashless antioxidant, 4-6% bio-based anti-wear agent, and 0.5-1% nano-modifier.

7. The hydraulic oil based on a composite ester according to claim 1, characterized in that, It is composed of the following components by weight percentage: 45% pentaerythritol synthetic ester, 38% polyethylene sebacic acid ester, 7% viscosity-temperature modifier, 5.5% ashless antioxidant, 4% bio-based anti-wear agent, and 0.5% nano-modifier.

8. A method for preparing any one of the composite ester-based hydraulic oils according to claims 1-7, comprising the following steps: S1 base oil premix: First, add pentaerythritol synthetic ester to the blending reactor, start stirring at 50 rpm; slowly add polyethylene sebacic acid ester, and at the same time raise the temperature to 60℃; gradually increase the stirring speed to 150 rpm and maintain it for 30 min; S2 Additive Addition: Divide the viscosity-temperature performance regulator into 4 equal parts, add each part to the mixing reactor at 10-minute intervals, and gradually raise the temperature to 70°C while increasing the stirring speed to 200 rpm and maintaining it for 1 hour. During this period, take samples every 15 minutes to observe the transparency. S3 antioxidant and anti-wear agent addition: Cool to 60℃, first add N,N′-di-sec-butyl-p-phenylenediamine and natural tocopherol to the mixing reactor, stir for 30 min; then add epoxidized soybean oil derivative, stir for 45 min; S4 nano-modifier dispersion: Slowly add the ultrasonically pre-dispersed modified nano zinc oxide particles into the mixing reactor, while simultaneously turning on the high shear disperser at a linear velocity of 20 m / s and maintaining the temperature at 60℃ for 1 hour; S5 Post-processing: The mixture obtained in step S4 is degassed at 50℃ / 1kPa vacuum for 1h, filtered through a 0.1μm ceramic membrane, allowed to stand for 24h, and the supernatant is taken to obtain the finished product.

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