Highly antioxidant complex ester insulating oil and its synthesis method

Abstract

The application discloses a kind of high antioxidation composite ester insulating oil and synthesis method thereof, it is related to synthetic ester insulating oil technical field.The synthesis method includes the following steps: with neopentyl glycol and gallic acid as reactant under the action of catalyst, first esterification reaction is carried out, and intermediate is obtained;With the intermediate, n-octanoic acid and n-decanoic acid as reactant under the action of catalyst, vacuum esterification reaction is carried out, and the high antioxidation composite ester insulating oil is obtained.The product prepared by specific step-by-step reaction process and raw material selection in the application, while realizing very low viscosity (40 ℃ kinematic viscosity is as low as 8.16 mm 2 s ‑1 )Simultaneously, very high initial oxidation temperature (as high as 272.8 ℃) and very low dielectric loss (as low as 0.0026) are obtained, and the "low viscosity-high antioxidation-low dielectric loss" is realized.

Description

Technical Field

[0001] This invention relates to the field of synthetic ester insulating oil technology, and in particular to a high-antioxidant composite ester insulating oil and its synthesis method. Background Technology

[0002] Power transformers operate in high electric fields and high temperatures for extended periods. The insulating oil must not only dissipate heat rapidly through convection within narrow oil channels, but also resist the synergistic aging caused by multiple factors such as oxygen, water, and metal catalysts. Traditional approaches often compromise one aspect for another: reducing viscosity to improve fluidity results in a smaller molecular weight, making the oil more susceptible to oxidation; while introducing various antioxidants can slow down the rise in acid value, it also leads to increased dielectric loss, sludge precipitation, and the maintenance burden caused by continuous consumption. This makes it difficult to achieve both "low viscosity" and "high oxidation resistance" in a single oil product, becoming the core bottleneck restricting the comprehensive replacement of mineral oil by synthetic ester insulating oil.

[0003] Chinese patent CN107903985A discloses a synthetic ester-based traction transformer oil composition and its preparation method. This patent uses a mixture of pentaerythritol and C4-C10 branched and straight-chain acids to prepare a pentaerythritol mixed ester as a base oil, and physically adds hindered phenolic antioxidants such as di-tert-butyl-p-cresol, 2,6-di-tert-butyl-4-methylphenol, and 4,4-methylene-bis-2,6-di-tert-butylphenol (addition amount 0.25-0.4 parts) to prepare the synthetic ester-based traction transformer oil. Although this scheme uses a pentaerythritol tetraester framework, the antioxidants are physically added and dispersed in the base oil without forming chemical bonds with the base oil molecules. Long-term operation poses a risk of antioxidant migration, volatilization, and loss. Furthermore, the pentaerythritol tetraester framework has a high kinematic viscosity at 40°C (typically >20 mm² / s), resulting in insufficient low-temperature fluidity.

[0004] CN105294441A discloses a method for synthesizing the antioxidant octapentaerythritol ester [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]. This patent uses tripentaerythritol as the backbone and performs a first-step esterification reaction with 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid to prepare an octafunctional hindered phenolic antioxidant. Although this method achieves the chemical bonding of multifunctional hindered phenols, the tripentaerythritol octapentaerythritol ester backbone has a very large molecular weight and higher viscosity. Furthermore, this patent primarily uses it as an antioxidant additive rather than as a base oil for insulating oils, and does not address the systematic optimization of dielectric properties, low-temperature fluidity, and oxidation stability for transformer insulating oil applications.

[0005] In summary, existing technologies consistently face a dilemma between achieving both viscosity and antioxidant properties: while reducing molecular weight leads to lower viscosity, it simultaneously weakens steric hindrance and bond energy, making the oil more susceptible to oxidation; while introducing antioxidant groups or adding external antioxidants can delay oxidation, the increased molecular volume, residual polar impurities, or precipitation of by-reaction salts result in increased viscosity and dielectric loss (dielectric loss factor generally exceeding 3%), making it difficult to achieve a long-term balance between "low viscosity, high antioxidant properties, and low dielectric loss." This fails to meet the requirements of various relevant standards for synthetic ester insulating oils, becoming a fundamental obstacle to the large-scale replacement of mineral oils with synthetic ester insulating oils. Secondly, in addition to the above problems, existing synthetic ester insulating oil synthesis methods also suffer from unfriendly process environments. Epoxy-ring-opening or acyl chloride-esterification routes require the use of hazardous reagents such as peracetic acid and phosphorus trichloride, resulting in the discharge of large amounts of saline wastewater; moreover, hindered phenolic antioxidant groups lose their tert-butyl groups at around 160℃, exhibiting insufficient thermal stability and rapidly losing their antioxidant capacity. Summary of the Invention

[0006] In response to the structural contradiction in existing technologies where "reducing viscosity inevitably leads to loss of antioxidant properties, and increasing antioxidant properties inevitably leads to increased viscosity," as well as common problems such as process hazards, reagent contamination, easy decomposition of antioxidant groups at high temperatures, and excessive dielectric loss sensitivity, this invention provides a high-antioxidant composite ester insulating oil and its synthesis method. The synthesis method of this invention is a green, high-antioxidant composite ester insulating oil synthesis method. This invention can simultaneously achieve low viscosity, high initial oxidation temperature, and low dielectric loss without the need for external antioxidants. High-performance insulating oil that meets the requirements of transformer use can be prepared through the synthesis method of this invention.

[0007] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of the present invention is a method for synthesizing a high antioxidant composite ester insulating oil, comprising the following steps: using neopentyl glycol and gallic acid as reactants to carry out a first-step esterification reaction under the action of a catalyst to obtain an intermediate; using the intermediate, n-octanoic acid and n-decanoic acid as reactants to carry out a reduced-pressure esterification reaction under the action of a catalyst to obtain the high antioxidant composite ester insulating oil.

[0008] Furthermore, the neopentyl glycol (structural formula: Gallic acid (structural formula: The molar ratio of the octanoic acid and the decanoic acid is 1:2:0.1~6:0.1~6.

[0009] Furthermore, the first step of the esterification reaction includes: mixing neopentyl glycol, gallic acid, catalyst 1 and solvent, and refluxing at 120 °C.

[0010] Furthermore, the reflux reaction time at 120 °C is 3~8 h.

[0011] Further, the steps of the reduced pressure esterification reaction include: adding triethylamine to the reaction solution containing the intermediate obtained in the first step esterification reaction for neutralization reaction; adding catalyst 2, octanoic acid and decanoic acid to the reaction solution after neutralization reaction, and refluxing the reaction under the conditions of 65°C and vacuum degree ≤ -0.09 MPa.

[0012] Furthermore, the reflux reaction time was 3~8h under the conditions of 65℃ and vacuum degree ≤-0.09 MPa.

[0013] Furthermore, before adding triethylamine to the reaction solution containing the intermediate obtained in the first step of the esterification reaction for neutralization, the method further includes a step of cooling the reaction solution containing the intermediate obtained in the first step of the esterification reaction to room temperature.

[0014] Furthermore, the catalyst 1 comprises p-toluenesulfonic acid.

[0015] Furthermore, the catalyst 2 comprises 4-dimethylaminopyridine (DMAP).

[0016] Furthermore, the solvent includes methyl isobutyl ketone.

[0017] Furthermore, the first step of the esterification reaction is carried out under nitrogen protection.

[0018] Furthermore, the molar ratio of the catalyst 1 to the triethylamine is 1:1.0~1.5.

[0019] Furthermore, the neutralization reaction was carried out at room temperature for 15 minutes.

[0020] The purpose of adding triethylamine is to neutralize the residual strong acid catalyst p-toluenesulfonic acid from the first step, terminate acid catalysis, protect the catalytic activity of the second-step catalyst DMAP, and provide an alkaline environment for the second-step reaction, thus promoting the forward reaction.

[0021] Furthermore, after the reduced pressure esterification reaction is completed, the process also includes steps of reduced pressure distillation, alkali refining, water washing, adsorption, and drying.

[0022] The purpose of vacuum distillation is to remove unreacted low-boiling-point acids and neopentyl glycol; the purpose of alkali refining and water washing is to remove unreacted high-boiling-point acids; and the purpose of adsorption and drying is to remove polar impurities and moisture.

[0023] After vacuum distillation, fatty acids and a small amount of gallic acid still remain in the product, which need to be removed by alkali refining and water washing.

[0024] Furthermore, the alkali refining step includes: adding sodium bicarbonate solution to the high antioxidant composite ester insulating oil after vacuum distillation, stirring at 50 °C for 10 min, and then allowing it to stand and separate the liquids.

[0025] Furthermore, the mass concentration of the sodium bicarbonate solution is 10-30%.

[0026] Furthermore, the mass ratio of the high-antioxidant composite ester insulating oil obtained after vacuum distillation to the sodium bicarbonate solution is 1:2.

[0027] Furthermore, the water washing step includes: mixing the alkali-refined high antioxidant composite ester insulating oil with water at a volume ratio of 1:2, stirring at 50 °C for 10 min, and then allowing it to stand and separate.

[0028] Furthermore, the adsorption specifically involves using a compound adsorbent to adsorb the water-washed high-antioxidant composite ester insulating oil. The components of the compound adsorbent include activated clay, alkaline alumina, silica gel, and 4Å molecular sieve.

[0029] Because sodium bicarbonate is not sufficiently alkaline, the oil remains weakly acidic after alkali refining and water washing, and contains residual water and ionic impurities, resulting in high dielectric loss. Therefore, further adsorption treatment is necessary after alkali refining and water washing. However, a single adsorbent is often ineffective in adsorption treatment. Therefore, this invention selects a combination of multiple adsorbents, specifically using activated clay as the main adsorbent, combined with alkaline alumina to lower the acid value, along with silica gel as an adsorbent and 4Å molecular sieve as a desiccant. These components work synergistically to better remove polar impurities and water.

[0030] Furthermore, the mass ratio of activated clay, alkaline alumina, silica gel and 4Å molecular sieve in the compound adsorbent is (6~8):(2~6):(1~3):(1~3).

[0031] Further, the adsorption step includes: adding a compound adsorbent to the water-washed high antioxidant composite ester insulating oil, stirring at 50 °C for 1 h, and then filtering to obtain the adsorbed high antioxidant composite ester insulating oil.

[0032] Furthermore, the mass ratio of the water-washed high-antioxidant composite ester insulating oil to the composite adsorbent is 1:0.3~0.6.

[0033] The reaction mechanism of the synthesis method of this invention is as follows: Because the phenolic hydroxyl groups on gallic acid, a reactant in this invention, have low reactivity, reacting it with octanoic acid and decanoic acid in a one-pot reaction with neopentyl glycol to prepare the composite ester insulating oil would be difficult. Therefore, neopentyl glycol needs to react with gallic acid to generate an intermediate, which then reacts with octanoic acid and decanoic acid to generate the composite ester insulating ester of this invention. Since both neopentyl glycol and gallic acid are solids, the reaction can be carried out by heating and melting or solvent dissolution. Due to their high melting points, solvent dissolution is chosen. Gallic acid is insoluble in benzene and its homologues, as well as in common organic solvents such as dichloromethane and chloroform. Suitable solvents for dissolving gallic acid and neopentyl glycol include a series of oxygen-containing organic solvents such as diethyl ether, ethanol, acetone, and glycerol. Considering that alcohols will react with gallic acid, and that diethyl ether and acetone have too low boiling points, methyl isobutyl ketone, which is low in toxicity, environmentally friendly, and has a suitable boiling point (117~118℃), is used as the solvent. In addition, since the antioxidant groups in gallic acid and intermediates are easily oxidized, it is necessary to remove oxygen from the reaction vessel as much as possible. Available methods include vacuum depressurization esterification or inert gas protection. In vacuum depressurization esterification, the temperature should not be too high in order to avoid solvent evaporation, while too low a temperature will make the reaction rate very slow. Therefore, nitrogen protection is adopted to achieve a suitable reaction temperature to generate intermediates.

[0034] The intermediate reacts with octanoic acid and decanoic acid under catalytic conditions to dehydrate and form an ester. This reaction is reversible. To promote the reaction in the forward direction, the water produced can be separated from the reaction system. Since water has a relatively low boiling point among the main reaction products, vacuum esterification is employed. By reducing the pressure of the reaction system, the boiling point of water is lowered, allowing water to be separated from the reaction system more quickly. This promotes the esterification process, increasing the reaction rate and yield.

[0035] The second technical solution of the present invention: a high antioxidant composite ester insulating oil prepared according to the above-mentioned synthesis method of high antioxidant composite ester insulating oil.

[0036] This invention has the following technical advantages: This invention discloses a method for synthesizing a high-antioxidant composite ester insulating oil. Gallic acid, neopentyl glycol, n-octanoic acid, and n-decanoic acid, all possessing multiple antioxidant groups, are used as raw materials. The high-antioxidant composite ester insulating oil is synthesized through a stepwise reaction. Furthermore, this invention explores the product yield of the composite ester insulating oil under different synthesis processes (reactant ratio, triethylamine dosage, and compound adsorbent ratio). Simultaneously, the acid value, antioxidant properties, kinematic viscosity at 40°C, and dielectric properties of the composite ester insulating oil were tested, yielding an extremely low viscosity (kinematic viscosity as low as 8.16 mm at 40°C). 2 s -1This high-antioxidant composite ester insulating oil, characterized by its extremely high initial oxidation temperature (up to 272.8 ℃) and extremely low dielectric loss (as low as 0.0026), achieves a balance of multiple properties for synthetic ester insulating oil, namely "low viscosity, high oxidation resistance, and low dielectric loss".

[0037] Compared with the prior art, the specific advantages of the present invention are as follows: 1. This invention utilizes natural gallic acid and covalently bonds the antioxidant units of gallic acid to the base oil molecules, thereby reducing the risk of antioxidant migration, volatilization and loss in insulating oil and thus improving the service life of the oil.

[0038] 2. In the molecular structure of the composite ester insulating oil of the present invention, neopentyl glycol provides a rigid quaternary carbon central skeleton, endowing the molecule with high thermal stability and resistance to thermal decomposition; octanoic acid and decanoic acid provide flexible short-chain saturated alkyl groups, which can disrupt molecular crystallinity and improve low-temperature fluidity. The two form a rigid-flexible complementary structure in the molecular structure, achieving a synergistic enhancement of high-temperature stability and low-temperature fluidity.

[0039] 3. The main raw materials of this invention (gallic acid, bio-based neopentyl glycol, octanoic acid, and decanoic acid) are all renewable plant raw materials. The composite ester insulating oil of this invention has a high biodegradability rate and meets the environmental protection requirements of synthetic ester insulating oil.

[0040] 4. Compared with commercial mineral oil insulating oil GB 2536, natural ester Cargill, and MIDEL 7131 synthetic ester, the high antioxidant composite ester insulating oil of the present invention has lower viscosity, stronger antioxidant capacity, and longer service life. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a schematic flowchart illustrating the synthesis process of the high antioxidant composite ester insulating oil in this invention. Figure 2 This is a schematic diagram of the reaction apparatus for the first step of the esterification reaction in this invention; Figure 3 This is a schematic diagram of the reaction apparatus for the reduced pressure esterification reaction in this invention; Figure 4 The molecular weight distribution diagram of the high antioxidant composite ester insulating oil prepared in Example 1; Figure 5This is a comparison of the infrared spectra of the first step product (i.e., the intermediate) in Example 1 and the high-antioxidant composite ester insulating oil product. Detailed Implementation

[0043] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0044] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0045] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0046] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0047] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0048] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0049] Unless otherwise specified, room temperature or ambient temperature in the following embodiments and comparative examples of the present invention refers to 20-30°C.

[0050] The raw materials or materials used in the following embodiments and comparative examples of this invention, including octanoic acid, decanoic acid, gallic acid (3,4,5-trihydroxybenzoic acid), neopentyl glycol, p-toluenesulfonic acid (PTSA), methyl isobutyl ketone, triethylamine, 4-dimethylaminopyridine (DMAP), sodium bicarbonate (NaHCO3), ultrapure water, activated clay, alkaline alumina, silica gel, 4Å molecular sieve, and hydrophilic polytetrafluoroethylene (PTFE) microporous filter membranes, are all commercially available products. All reagents used in the experiments were of analytical or chemical purity. The experimental instruments, including a digital display constant temperature magnetic stirrer, oil bath, circulating water vacuum pump, and vacuum drying oven, are all common instruments in the art.

[0051] The following embodiments of the present invention provide a schematic diagram of the process for synthesizing the crude product of high antioxidant composite ester insulating oil. Figure 1 As shown.

[0052] Before synthesizing the composite ester insulating oil, the raw materials in the following embodiments and comparative examples of the present invention need to be pretreated, as follows: Neopentyl glycol was vacuum dried at 80 °C for 2 h and then cooled to room temperature for later use. Gallic acid was vacuum dried at 60 °C for 4 h and then cooled to room temperature for later use. Take octanoic acid and decanoic acid, mix them in a certain proportion, and degas them at 90 °C for 30 min to obtain mixed fatty acids. Cool them to room temperature for later use. Methyl isobutyl ketone: Take freshly opened methyl isobutyl ketone and add an excess of molecular sieve for water absorption treatment; Triethylamine: Take freshly opened triethylamine and add an excess of molecular sieve for water absorption treatment; DMAP: Take freshly opened DMAP and add an excess of molecular sieve for water absorption treatment.

[0053] Example 1 A method for synthesizing a high-antioxidant composite ester insulating oil, comprising the following steps: (1) The first step of esterification reaction (carried out under nitrogen protection and atmospheric pressure, the schematic diagram of the reaction apparatus is shown below) Figure 2 (As shown) Under nitrogen protection, 0.1 mol of pretreated neopentyl glycol, 0.2 mol of gallic acid, 0.01 mol of p-toluenesulfonic acid, and 500 mL of methyl isobutyl ketone were added to a 1 L three-necked flask. A constant-pressure dropping funnel was connected to the three-necked flask, with 2 / 3 of its volume filled with 4Å molecular sieve as a desiccant. A spherical condenser (for reflux) was then connected to the top of the funnel. The magnetic stirrer was turned on, and the reaction system was gradually heated to 120 °C and refluxed at 120 °C for 4 h until the reactants were completely reacted. TLC (thin-layer chromatography) showed that the gallic acid starting material spot disappeared, yielding a light brown transparent solution (i.e., the reaction solution containing the intermediate).

[0054] In this step, the 4Å molecular sieve in the dropping funnel should be in excess (to 2 / 3 of its volume) as a desiccant; otherwise, the molecular sieve may absorb water and turn into a mud-like substance that falls into the reaction system, increasing the difficulty of subsequent purification. Before the reaction, nitrogen gas should be purged to purge the air from the entire system to avoid the risk of oxidation of gallic acid and intermediates during the reaction. Since the reaction phenomena are not easy to observe, it is necessary to monitor the disappearance of the reactant spots on a TLC plate to determine that the reaction is basically over.

[0055] After the first step of esterification is completed, nitrogen gas must be continuously introduced until the reaction liquid is cooled before proceeding with the subsequent reduced pressure esterification reaction. Otherwise, the oil may be oxidized when exposed to air at higher temperatures, and the reaction liquid may boil violently due to the presence of solvent when vacuuming at higher temperatures.

[0056] (2) Reduced pressure esterification reaction (see schematic diagram of the reaction apparatus as shown) Figure 3 (As shown) After the reaction solution cools to room temperature, add pretreated triethylamine (0.01 mol) and stir for 15 minutes. After 15 minutes, quickly assemble a new apparatus, connecting the distillation head, spherical condenser, glass stopper, rubber stopper, thermometer, receiving bottle, and buffer bottle to the three-necked flask in sequence, lubricating and sealing the ground glass joints with vacuum grease. Close the safety valve of the buffer bottle and open the other vacuum valve, connecting it to a circulating water vacuum pump. Turn on the vacuum pump and, after the vacuum pressure gauge reading stabilizes, observe whether the pressure inside the system remains constant below -0.09 MPa. After the airtightness check is complete, turn off the vacuum pump. Add the catalyst DMAP (0.1 mol) and mixed fatty acids (0.3 mol octanoic acid and 0.3 mol decanoic acid) to the three-necked flask, and turn on magnetic stirring until the reactants are uniformly mixed. Then turn on the vacuum pump and evacuate to -0.09 MPa. Then gradually raise the temperature to 65°C and reflux the reaction until no obvious liquid droplets are generated in the condenser and no obvious bubbles are generated in the reaction liquid. The reaction can then be stopped (specifically 5 hours in this embodiment) to obtain the crude product of high antioxidant composite ester insulating oil (i.e., crude oil).

[0057] (3) Vacuum distillation (the purpose is to remove acid) Maintaining a vacuum, the temperature was raised to 90 °C and distilled for 1 h to recover excess fatty acids and the reaction solvent methyl isobutyl ketone, yielding a high-antioxidant composite ester insulating oil after vacuum distillation.

[0058] (4) Refined 1) Alkali refining: Take a 10% NaHCO3 solution, heat the NaHCO3 solution and the high antioxidant composite ester insulating oil after vacuum distillation to 50 ℃ respectively, and then mix the two in a volume ratio of 2:1 (that is, the volume of NaHCO3 solution is twice the volume of the high antioxidant composite ester insulating oil after vacuum distillation), and stir at 50 ℃ for 10 min. Then pour the mixture into a separatory funnel, shake it thoroughly, and let it stand to separate the liquids to obtain the alkali-refined high antioxidant composite ester insulating oil.

[0059] 2) Water washing: The high antioxidant composite ester insulating oil after alkali refining is heated at 50 ℃, and then ultrapure water at 50 ℃ is added (the volume of ultrapure water is twice the volume of the high antioxidant composite ester insulating oil after alkali refining). The mixture is stirred at 50 ℃ for 10 min, and then the mixture is poured into a separatory funnel. After thorough shaking, the mixture is allowed to stand and separate to obtain the water-washed high antioxidant composite ester insulating oil.

[0060] 3) Adsorption: A compound adsorbent (composed of 24 parts by mass of activated clay, 18 parts by mass of alkaline alumina, 9 parts by mass of silica gel, and 9 parts by mass of 4Å molecular sieve, with a mass ratio of 1:0.5 between the water-washed high antioxidant composite ester insulating oil and the compound adsorbent) was added to the water-washed high antioxidant composite ester insulating oil. The mixture was stirred at 50 °C for 1 h. The solution was then poured into a sand core funnel and the compound adsorbent was removed by vacuum filtration using a 0.1 μm hydrophilic polytetrafluoroethylene microporous membrane to obtain the adsorbed high antioxidant composite ester insulating oil.

[0061] 4) Drying: After adsorption treatment, a small amount of moisture remains in the insulating oil, which needs to be dried. Specifically, the adsorbed high antioxidant composite ester insulating oil is vacuum dried at 90 ℃ for 48 h to obtain 98.9 g of light yellow finished product (i.e., refined high antioxidant composite ester insulating oil).

[0062] Figure 4 The molecular weight distribution diagram of the high antioxidant composite ester insulating oil prepared in this embodiment shows that the product is a composite ester insulating oil, with a molecular weight of about 1275 g / mol being the most abundant component in the composite ester insulating oil.

[0063] Figure 5 The image shows a comparison of the infrared spectra of the reaction intermediate (i.e., the first step product) and the high-antioxidant composite ester insulating oil product in this embodiment. It can be seen that there are no phenolic hydroxyl groups in the product.

[0064] Example 2 Same as Example 1, except that the amount of triethylamine added in step (2) is 0.012 mol.

[0065] Example 3 Same as Example 1, except that the amount of triethylamine added in step (2) is 0.015 mol.

[0066] Example 4 Same as Example 1, except that the mixed fatty acids added in step (2) consist of 0.1 mol of octanoic acid and 0.5 mol of decanoic acid.

[0067] Example 5 Same as Example 1, except that the mixed fatty acids added in step (2) consist of 0.5 mol of octanoic acid and 0.1 mol of decanoic acid.

[0068] Example 6 Same as Example 1, except that in the adsorption process of step (4), the added compound adsorbent is a mixture of 24 parts by mass of activated clay, 15 parts by mass of alkaline alumina, 9 parts by mass of silica gel, and 9 parts by mass of 4Å molecular sieve.

[0069] Example 7 Same as Example 1, except that in the adsorption process of step (4), the added compound adsorbent is a mixture of 24 parts by mass of activated clay, 6 parts by mass of alkaline alumina, 9 parts by mass of silica gel, and 9 parts by mass of 4Å molecular sieve.

[0070] Comparative Example 1 Commercial oil-mineral insulating oil GB 2536 was used as Comparative Example 1.

[0071] Comparative Example 2 Natural ester Cargill was used as comparative example 2.

[0072] Comparative Example 3 MIDEL 7131 was used to synthesize an ester as Comparative Example 3.

[0073] Comparative Example 4 Same as Example 1, except that in the adsorption process of step (4), the added compound adsorbent is a mixture of 24 parts by mass of activated clay, 6 parts by mass of alkaline alumina, and 18 parts by mass of silica gel.

[0074] Comparative Example 5 Same as Example 1, except that in the adsorption process of step (4), the added compound adsorbent is a mixture of 24 parts by mass of activated clay, 6 parts by mass of alkaline alumina, and 18 parts by mass of 4Å molecular sieve.

[0075] Comparative Example 6 Same as Example 1, except that gallic acid is replaced in equimolar amounts with salicylic acid (structural formula: The molar amounts of octanoic acid and decanoic acid in the mixed fatty acids were adjusted to 0.1 mol.

[0076] The final products from the above examples and comparative examples were tested for acid value, initial oxidation temperature, kinematic viscosity at 40 °C, and dielectric loss. The acid value was determined according to GB / T 41633.3-2022, the kinematic viscosity at 40 °C was determined according to GB / T 265-1988, the dielectric loss factor (90 °C) was determined according to GB / T 5654-2007, and the initial oxidation temperature (OIT) was determined according to DL / T1977-2019 (DSC). The data are summarized in Table 1.

[0077] Table 1 Note: " / " indicates that this indicator is not involved in this ratio.

[0078] As can be seen from Table 1, the overall performance of the oils in Examples 1 to 7 is greatly improved compared with Comparative Examples 1 to 3. This indicates that the high-oxidation-resistant composite ester insulating oil of the present invention has lower viscosity, stronger oxidation resistance, and longer service life compared with commercial mineral insulating oil GB 2536, natural ester Cargill, and MIDEL 7131 synthetic ester.

[0079] As shown in Table 1, the product yields of Examples 1 to 7 ranged from 76.1% to 80.6%, with acid values ​​all below 0.03 and dielectric losses below 0.005, indicating that the process route can achieve good reaction and post-treatment effects. Meanwhile, the acid values ​​and dielectric losses of Examples 6 and 7 were higher than those of Examples 1 to 5, indicating that the adsorption effect was optimal when the mass ratio of activated clay, alkaline alumina, silica gel, and 4Å molecular sieve in the compound adsorbent was 24:18:9:9.

[0080] As can be seen from Table 1, Example 1 has advantages in acid value and dielectric loss data of oil compared with Comparative Examples 4 to 5, indicating that each component in the compound adsorbent has an impact on the acid value and dielectric loss of the oil, and the synergistic effect of each component achieves the best effect of reducing acid value and dielectric loss.

[0081] As shown in Table 1, the kinematic viscosity of the products at 40 °C in Examples 1 to 7 is between 8.18 and 8.22 mm. 2 The viscosity is between [value] / s, significantly lower than the kinematic viscosity (typically >20 mm) of the pentaerythritol tetraester backbone product at 40°C as described in patent publication CN107903985A.2 / s), indicating that the introduction of flexible saturated alkyl groups into the molecular structure of the present invention can effectively improve low-temperature fluidity; at the same time, no antioxidants are added to the insulating oil system of the present invention, but the antioxidant units of gallic acid are covalently bonded to the base oil molecules, which has a significant promoting effect on reducing the viscosity of the oil.

[0082] As can also be seen from Table 1, in Examples 1 to 7, the initial oxidation temperature of the products is above 270°C, which has the advantage of antioxidant stability. This may be because in the molecular structure of the composite ester insulating oil of the present invention, neopentyl glycol provides a rigid quaternary carbon central skeleton, which improves the thermal decomposition resistance of the product molecules and thus increases the initial oxidation temperature of the product.

[0083] Table 1 also shows that, compared with Comparative Example 6, gallic acid (containing three hydroxyl groups) was replaced with salicylic acid (containing one hydroxyl group) which was covalently bonded to the base oil molecule (forming an antioxidant unit). The initial oxidation temperature of the product dropped sharply, indicating that the three hydroxyl groups of gallic acid played a key role in improving the antioxidant performance of the composite ester insulating oil obtained after the reaction. The addition of gallic acid reduced the risk of antioxidant migration, volatilization and loss in the insulating oil, thereby improving the service life of the oil.

[0084] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for synthesizing a high-antioxidant composite ester insulating oil, characterized in that, Includes the following steps: The first step of esterification was carried out using neopentyl glycol and gallic acid as reactants in the presence of a catalyst to obtain an intermediate. The intermediate, octanoic acid, and decanoic acid were used as reactants in a reduced-pressure esterification reaction under the action of a catalyst to obtain the high-antioxidant composite ester insulating oil.

2. The method for synthesizing the high-antioxidant composite ester insulating oil as described in claim 1, characterized in that, The molar ratio of neopentyl glycol, gallic acid, octanoic acid and decanoic acid is 1:2:0.1~6:0.1~6.

3. The method for synthesizing the high antioxidant composite ester insulating oil as described in claim 1, characterized in that, The first step of the esterification reaction includes: mixing neopentyl glycol, gallic acid, catalyst 1 and solvent, and refluxing at 120 °C; The steps of the vacuum esterification reaction include: adding triethylamine to the reaction solution containing the intermediate obtained in the first step esterification reaction for neutralization reaction; adding catalyst 2, octanoic acid and decanoic acid to the reaction solution after neutralization reaction, and refluxing the reaction under the conditions of 65°C and vacuum degree ≤ -0.09 MPa.

4. The method for synthesizing the high antioxidant composite ester insulating oil as described in claim 3, characterized in that, The catalyst 1 includes p-toluenesulfonic acid; And / or, the catalyst 2 comprises 4-dimethylaminopyridine; And / or, the solvent includes methyl isobutyl ketone; And / or, the first step of the esterification reaction is carried out under nitrogen protection.

5. The method for synthesizing the high antioxidant composite ester insulating oil as described in claim 3, characterized in that, The molar ratio of catalyst 1 to triethylamine is 1:1.0~1.

5.

6. The method for synthesizing the high antioxidant composite ester insulating oil as described in claim 1, characterized in that, After the vacuum esterification reaction is completed, the process also includes vacuum distillation, alkali refining, water washing, adsorption, and drying.

7. The method for synthesizing the high antioxidant composite ester insulating oil as described in claim 6, characterized in that, The alkali refining step includes: adding sodium bicarbonate solution to the high antioxidant composite ester insulating oil after vacuum distillation, stirring at 50 °C for 10 min, and then allowing it to stand and separate the liquids.

8. The method for synthesizing the high antioxidant composite ester insulating oil as described in claim 6, characterized in that, The adsorption specifically involves using a compound adsorbent to adsorb the water-washed high-antioxidant composite ester insulating oil. The components of the compound adsorbent include activated clay, alkaline alumina, silica gel, and 4Å molecular sieve.

9. The method for synthesizing the high antioxidant composite ester insulating oil as described in claim 8, characterized in that, The mass ratio of activated clay, alkaline alumina, silica gel and 4Å molecular sieve in the compound adsorbent is (6~8):(2~6):(1~3):(1~3).

10. A high-antioxidant composite ester insulating oil prepared by the synthesis method of the high-antioxidant composite ester insulating oil according to any one of claims 1-9.

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