Bisphenol amine type antioxidant as well as preparation method and application thereof

Abstract

The invention discloses a bisphenol amine antioxidant as well as a preparation method and application thereof, and relates to the field of antioxidants. The chemical structural formula of the antioxidant is # imgabs0. The preparation method comprises the following steps: heating alkylated 1, 2-benzenediol and a formaldehyde aqueous solution for reaction to produce an intermediate; and then carrying out condensation reaction with p-phenylenediamine to synthesize the bisphenol amine type antioxidant. Phenol and amine groups are introduced into the molecular structure of the bisphenol amine antioxidant, the phenol group provides strong free radical capturing ability, the amine group promotes the antioxidant process through hydrogen supply, and the bisphenol amine antioxidant can play a stable antioxidant effect at a high temperature. The antioxidant can effectively capture free radicals generated in the oxidation process in natural ester insulating oil, inhibits the oxidation reaction of oil products, has antioxidant stability at high temperature, effectively prolongs the service life of the oil products, and has significant industrial application potential and market prospects.

Description

Technical Field

[0001] The invention relates to the field of antioxidants, and in particular to a bisphenolamine antioxidant and a preparation method and application thereof. Background Art

[0002] In the long-term operation of transformers, affected by factors such as temperature, electric field, moisture and oxygen, the internal oil-paper insulation system gradually ages, and the generated moisture will be absorbed by the insulation paper, increasing the moisture content, resulting in a decrease in insulation performance and even shortening the life of the transformer. Practice has shown that adding antioxidants to transformer oil can slow down the aging rate of the oil during operation and extend the service life of the oil. This method has the advantages of simple operation, no need for special equipment, less maintenance workload, and good anti-deterioration effect.

[0003] At present, the maintenance measure of adding antioxidant 2,6-di-tert-butyl-p-cresol (T501) to transformer oil has been widely adopted, and a lot of operating experience has been accumulated. In recent years, with the continuous upgrading of the capacity and load of the transmission system, the internal voltage level and operating temperature of the transformer have continued to increase, requiring the transformer oil to still have good oxidation stability under high temperature conditions. At present, for important transformers operating at high temperatures, a larger dose of T501 (mass fraction 0.3%) is usually used to extend the life of the oil. However, studies have shown that the higher the temperature, the faster the oxidation rate of the oil. Under long-term high-temperature operating conditions, the antioxidant performance of T501 is significantly reduced, and it may even decompose, which accelerates the aging of the oil paper.

[0004] Therefore, it is necessary to conduct in-depth research on the antioxidant mechanism of transformer insulating oil, develop new high molecular weight antioxidants, reduce its volatility and migration, and improve hydrolysis resistance, thermal stability and material compatibility, so as to achieve stronger antioxidant effect. Summary of the invention

[0005] The invention provides a bisphenolamine antioxidant and a preparation method and application thereof. The bisphenolamine antioxidant has phenol and amine groups, can improve the antioxidant and heat resistance stability at the same time, and can achieve stable antioxidant capacity under high temperature conditions and extend the service life by adding it into natural ester insulating oil.

[0006] In order to solve the above technical problems, one of the purposes of the present invention is to provide a bisphenol amine antioxidant, the chemical structural formula of the bisphenol amine antioxidant is

[0007] In order to solve the above technical problems, the second object of the present invention provides a method for preparing a bisphenol amine antioxidant, comprising the following steps:

[0008] (1) After the alkylated 1,2-benzenediol and solvent A are mixed and dissolved, a formaldehyde aqueous solution is slowly added dropwise, followed by heating and stirring for reaction, washing and neutralization, and then separating and purifying the product to obtain an intermediate;

[0009] The alkylated 1,2-benzenediol has the general structural formula: Wherein, R is an alkyl group or a halogenated alkyl group;

[0010] (2) The intermediate and p-phenylenediamine are mixed and dissolved with solvent B, a catalyst is added, heated for reaction, washed and neutralized, and then the product is separated and purified to obtain a bisphenol amine antioxidant.

[0011] By adopting the above scheme, a bisphenolamine structure is introduced into the molecule of the bisphenolamine antioxidant of the present application, which can improve the antioxidant ability and high temperature stability. First, 1,2-benzenediol is alkylated to introduce an alkyl functional group to enhance its lipophilicity and antioxidant properties. Then, the modified 1,2-benzenediol is reacted with p-phenylenediamine through a Mannich condensation reaction to synthesize the bisphenolamine antioxidant. Heating is used to assist the reaction, and a trifluoroboron chloride catalyst is introduced during the reaction to promote the efficient reaction. The reaction rate and product purity are effectively improved, and the production efficiency and economic benefits are improved. The antioxidant can be widely used in natural ester insulating oil and other occasions requiring efficient antioxidant protection, and has significant industrial application potential and market prospects.

[0012] As a preferred embodiment, in step (1), the method for preparing alkylated 1,2-benzenediol comprises the following steps: dissolving 1,2-benzenediol, alkyl halide and alkali in solvent C, heating for reaction, washing and neutralizing, and separating and purifying the product to obtain alkylated 1,2-benzenediol.

[0013] As a preferred embodiment, in the method for preparing alkylated 1,2-benzenediol, the molar ratio of 1,2-benzenediol to alkyl halide is 2:(1-2).

[0014] As a preferred embodiment, in the method for preparing alkylated 1,2-benzenediol, alkali is added to adjust the pH of the system to 9-11.

[0015] As a preferred embodiment, in the method for preparing alkylated 1,2-benzenediol, the solvent C is methanol.

[0016] As a preferred embodiment, in the method for preparing alkylated 1,2-benzenediol, the heating reaction temperature is 60-80° C. and the reaction time is 1-2 h.

[0017] As a preferred embodiment, in the method for preparing alkylated 1,2-benzenediol, separation and purification are performed by adding ethyl acetate to the reaction mixture, extracting and combining the organic phases, drying the organic layer with anhydrous sodium sulfate, filtering and removing the solvent by rotary evaporation.

[0018] As a preferred embodiment, in the method for preparing alkylated 1,2-benzenediol, the alkyl halide is methyl chloride, and the structural formula of the alkylated 1,2-benzenediol is

[0019] As a preferred embodiment, in step (1), 5-10 mL of a 30 wt%-40 wt% formaldehyde aqueous solution is added to every 0.1 mol of the alkylated 1,2-diphenol.

[0020] As a preferred embodiment, in step (1), the heating and stirring reaction temperature is 40-60°C and the time is 2-4h.

[0021] As a preferred embodiment, in step (1), the solvent A is methanol.

[0022] As a preferred embodiment, in step (1), separation and purification is performed by adding ethyl acetate to the reaction mixture, extracting and combining the organic phases, drying the organic layer with anhydrous sodium sulfate, filtering and removing the solvent by rotary evaporation.

[0023] As a preferred embodiment, in step (2), the molar ratio of the intermediate to p-phenylenediamine is (1-2): (1-2);

[0024] As a preferred embodiment, in step (2), the catalyst is boron trifluorochloride.

[0025] As a preferred embodiment, in step (2), 0.2-0.5 g of catalyst is added for every 0.05 mol of the intermediate.

[0026] As a preferred embodiment, in step (2), the solvent B is methanol.

[0027] As a preferred embodiment, in step (2), the heating reaction temperature is 80-100°C and the time is 50-70 minutes.

[0028] As a preferred embodiment, in step (2), the heating reaction is carried out in a nitrogen atmosphere.

[0029] As a preferred embodiment, in step (2), separation and purification are performed by adding ethyl acetate to the reaction mixture, extracting and combining the organic phases, drying the organic layer with anhydrous sodium sulfate, filtering and removing the solvent by rotary evaporation, and purifying by recrystallization.

[0030] In order to solve the above technical problems, the third object of the present invention is to provide a natural ester insulating oil containing 0.08wt%-0.12wt% of a bisphenol amine antioxidant.

[0031] By adopting the above scheme, the bisphenolamine structure is introduced into the molecule of the bisphenolamine antioxidant of the present application, combining the antioxidant ability of phenols and the stability enhancement effect of amines. The phenolic group has a strong free radical capture ability, while the amine group can promote the extension of the antioxidant process through hydrogen supply. Therefore, the bisphenolamine antioxidant can more effectively capture the free radicals generated during the oxidation process in natural ester insulating oil, inhibit the oxidation reaction of oil products, and delay the increase of acid value. The molecular structure stability of the bisphenolamine antioxidant is relatively strong, and it can better resist decomposition at high temperatures. Compared with traditional antioxidants, the multifunctional group structure of the bisphenolamine antioxidant improves its thermal stability at high temperatures. Secondly, the phenol structure is alkylated and modified to improve the lipophilicity of the antioxidant, so that its solubility and dispersibility in natural ester insulating oil are greatly improved, avoiding the problem of antioxidant deposition or precipitation in oil products, thereby extending the service life of natural ester insulating oil.

[0032] As a preferred solution, it includes 0.08wt%-0.12wt% bisphenolamine antioxidant, 95-99.92wt% natural ester and 0wt%-5wt% functional additive, wherein the functional additive is at least one of a preservative, an antifoaming agent and an anti-emulsifier.

[0033] As a preferred embodiment, the natural ester is FR3 natural ester.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The bisphenol amine antioxidant of the present application introduces a bisphenol amine structure containing phenols and amines. The phenol group provides a strong free radical capture ability, and the amine group promotes the antioxidant process by hydrogen donation. It can also exert a stable antioxidant effect under high temperature conditions. It has excellent compatibility with natural ester insulating oil. After addition, it can effectively inhibit the oxidation reaction in natural ester insulating oil, delay the increase of acid value, and thus extend the service life of the oil. It has significant industrial application potential and market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 : A schematic diagram of the synthesis route of a bisphenolamine antioxidant in Preparation Example 1 of the present invention;

[0037] Figure 2 : A hydrogen nuclear magnetic resonance spectrum of a bisphenol amine antioxidant in Preparation Example 1 of the present invention;

[0038] Figure 3 : It is a statistical chart of the acid value of the insulating oil of the embodiment of the present invention and the comparative example changing with the aging test time;

[0039] Figure 4 : It is a statistical chart of the dielectric loss factor of the insulating oil of the embodiment of the present invention and the comparative example changing with the aging test time. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0042] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0043] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0044] As used herein:

[0045] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0046] The conjunction "consisting of excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed-ended so that it does not include materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0047] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood to specifically invent all ranges formed by any pairing of any upper range limit or preferred value with any lower range limit or preferred value, regardless of whether the range is invented separately. When a numerical range is described in this article, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0048] In these examples, parts and percentages are by mass unless otherwise indicated.

[0049] "Parts by mass" refers to the basic unit of measurement that indicates the proportional relationship of the masses of multiple components. 1 part can represent any unit mass. It should not be misunderstood that, unlike the number of parts by mass, the sum of the parts by mass of all components is not limited to 100 parts.

[0050] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0051] In the description of the present invention, it is necessary to understand that the terms "up", "down", "left", "right", "top", "bottom", etc., indicating directions or positional relationships, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0052] In order to further illustrate the present invention, the present invention is described in detail below in conjunction with the examples, but they should not be construed as limiting the scope of protection of the present invention. Raw materials used in the following examples and comparative examples of the present application, unless otherwise specified, can be obtained from commercial sources, and the same raw materials are used in parallel experiments.

[0053] Preparation Example 1

[0054] A bisphenolamine antioxidant, its chemical structural formula is Its synthetic route is Figure 1 As shown, the preparation steps include:

[0055] (1) Add 0.2 mol 1,2-benzenediol and 0.1 mol chloroform into a dry reaction bottle, add 120 mL of methanol solution, and add 20% sodium hydroxide to adjust the pH of the system to 10, heat to the reaction temperature of 70°C, maintain the reaction for 1.5 hours, then wash the reaction mixture with water to neutralize the excess alkali, pour the reaction mixture into 100 mL ethyl acetate solvent, separate the layers through a separatory funnel, extract and separate the organic layer with ethyl acetate, dry the organic layer with anhydrous sodium sulfate, filter and remove the solvent by rotary evaporation to obtain alkylated 1,2-benzenediol;

[0056] (2) Add 0.1 mol of alkylated 1,2-benzenediol to a dry round-bottom flask, and add 100 mL of anhydrous methanol as a solvent, turn on magnetic stirring at a stirring speed of 400 rpm to completely dissolve the alkylated 1,2-benzenediol, slowly drop 7.75 mL of a 37 wt% formaldehyde aqueous solution, keep stirring during the dropwise addition process and control the temperature at room temperature, install a reflux condenser after the dropwise addition is completed, slowly heat to 50° C., continue stirring to react for 3 h, cool to room temperature after the reaction is completed, add water for washing, stand in a separatory funnel to separate the organic phase, extract the aqueous phase with ethyl acetate three times, combine the organic phases, then dry with anhydrous sodium sulfate, filter and evaporate the organic solvent on a rotary evaporator to obtain an intermediate;

[0057] (3) Add 0.05 mol of the intermediate and 0.05 mol of p-phenylenediamine to a dry round-bottom flask, and add 50 mL of anhydrous methanol, turn on magnetic stirring at a stirring speed of 400 rpm to completely dissolve the solid matter, slowly add 0.3 g of trifluoroboron chloride catalyst under nitrogen protection, put the round-bottom flask into a microwave synthesizer, set the reaction temperature to 90° C., and the reaction time to 60 min. After the reaction is completed, cool to room temperature, pour in a large amount of cold water for dilution and neutralization, extract the reaction mixture with ethyl acetate several times, combine the organic phases, wash the organic phases with deionized water three times to remove excess impurities, dry the organic phases with anhydrous sodium sulfate, filter and remove the solvent by rotary evaporation to obtain a crude product, and purify the crude product by recrystallization to obtain a bisphenolamine antioxidant.

[0058] Example 1

[0059] A natural ester insulating oil, comprising 0.1wt% of the bisphenolamine antioxidant of Preparation Example 1 and the balance of natural ester, wherein the natural ester is Cargill The preparation method of natural ester comprises the following steps: adding 0.1% by mass of bisphenolamine insulating oil antioxidant to natural ester vacuum dried for 24 hours, magnetically stirring at 60°C for 2 hours, and then ultrasonically oscillating for 2 hours to obtain natural ester insulating oil.

[0060] Comparative Example 1

[0061] A natural ester insulating oil, wherein each step of the preparation method and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that the content of the bisphenol amine antioxidant in Preparation Example 1 is 0.05w%.

[0062] Comparative Example 2

[0063] A natural ester insulating oil, wherein each step of the preparation method and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that the bisphenol amine antioxidant in Preparation Example 1 is replaced by an equal amount of 2,6-di-tert-butyl-p-cresol.

[0064] Comparative Example 3

[0065] A natural ester insulating oil, wherein each step of the preparation method and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that the content of the bisphenol amine antioxidant in Preparation Example 1 is 0.3w%.

[0066] Comparative Example 4

[0067] A natural ester insulating oil, wherein each step of the preparation method and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that the content of the bisphenol amine antioxidant in Preparation Example 1 is 0.2w%.

[0068] Comparative Example 5

[0069] A natural ester insulating oil, wherein each step of the preparation method and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that the amount of bisphenol amine antioxidant added in Preparation Example 1 is 0.

[0070] Performance testing

[0071] 1. The bisphenol amine antioxidant prepared in Preparation Example 1 was tested by nuclear magnetic resonance hydrogen spectrum. The results of nuclear magnetic resonance hydrogen spectrum are as follows: Figure 2 As shown, it can be seen that the signal at δ = 9.96 ppm is the nuclear magnetic resonance signal of the phenolic hydroxyl (-OH) proton, the signal at δ = 6.78 ppm is the nuclear magnetic resonance signal of the secondary amine (-NH-) hydrogen connecting the two phenolamine structures, the signal at δ = 3.77 ppm belongs to the proton in the methoxy -OCH3 group, and the signal at δ = 4.52 ppm is the nuclear magnetic resonance signal of the primary amine (-NH2) proton.

[0072] 2. The insulating oils of the embodiments and comparative examples were subjected to aging tests. 200 g of insulating oil were weighed and placed in a 120° C. thermostat for 7 days, 14 days, 21 days and 28 days of thermal aging to accelerate the oxidation rate of the insulating oil. After the aging test, the acid value and dielectric loss factor of the insulating oil before and after aging were tested. The acid value was tested according to the IEC 62021.3 standard, and the dielectric loss factor was tested according to the IEC 60247 standard. The test results are shown in Tables 1 and 2. Figure 3-4 shown.

[0073] Table 1 - Acid value and dielectric loss factor results of insulating oil before and after aging test of examples and comparative examples

[0074]

[0075]

[0076] During the oxidation process of transformer oil, cyclopentane acid and low molecular weight fatty acids will be produced. These acidic products are not only corrosive to the metal materials in the transformer, but also destroy the cellulose macromolecular structure in the insulating paper. Therefore, the acid value in the oil is one of the important indicators to measure the degree of deterioration of transformer oil.

[0077] As shown in Table 1 and Figure 1 As shown, with the extension of aging time, the acid value of the insulating oil in the examples and comparative examples shows a trend of slowly rising and then rapidly rising. After adding bisphenolamine antioxidant to Example 1, it contains phenolic and amine groups. The phenolic structure captures free radicals by providing active hydrogen atoms, effectively interrupting the oxidation chain reaction; while the amine structure enhances the stability of the antioxidant, and the antioxidant and high temperature resistance are improved. Compared with the blank control group of comparative example 4, the acid value dropped by more than half after 28 days, indicating that in a high temperature aging environment of 120°C, the bisphenolamine antioxidant has excellent antioxidant performance for natural ester insulating oil, which can meet the long-term antioxidant requirements in high temperature environments.

[0078] As shown in Table 1 and Figure 1As shown, in Comparative Example 2, the natural ester insulating oil was added with 2,6-di-tert-butyl-p-cresol antioxidant component, and the acid value was maintained at a low level within 14 days before aging, and the acid value increased rapidly after 14 days, indicating that 2,6-di-tert-butyl-p-cresol has a certain antioxidant effect on the insulating oil in the early stage of aging, which mainly delays the oxidation process by removing alkyl radicals and peroxy radicals produced by thermal decomposition of active alkanes in the oil. However, with the increase of aging, the oxidation reaction is accelerated, and 2,6-di-tert-butyl-p-cresol is gradually exhausted, resulting in a rapid increase in the acid value in the later stage. In contrast, in Example 1, the acid ester value of the bisphenol amine antioxidant added with the same mass fraction remains at a relatively low level after 28 days of high-temperature aging. This is because the phenol structure in the bisphenol amine antioxidant captures free radicals by providing active hydrogen atoms, effectively interrupting the oxidation chain reaction, while the amine structure enhances the stability of the antioxidant, making it show a more lasting effect in the anti-oxidation process. The synergistic effect of the two significantly improves the antioxidant efficiency of the antioxidant, and can effectively inhibit the generation of free radicals during the aging process of the insulating oil, delaying the intensification of the oxidation reaction; secondly, the phenol structure is alkylated to improve the lipophilicity of the antioxidant, greatly improving its solubility and dispersibility in natural ester insulating oil, avoiding the problem of antioxidant deposition or precipitation in the oil product. The molecular structure stability of the bisphenol amine antioxidant is strong, and it can better resist decomposition at high temperatures. Compared with traditional 2,6-di-tert-butyl-p-cresol, the bisphenol amine antioxidant has higher thermal stability under high temperature conditions.

[0079] As shown in Table 1 and Figure 2 As shown, the dielectric loss factor of the natural ester insulating oil of the embodiment and the comparative example increases with the extension of the aging time. After aging for 14 days, the dielectric loss factor of the oil samples of Example 1 with 0.1wt% added and Comparative Example 1 with 0.05wt% added bisphenol amine type antioxidant are relatively close, while the dielectric loss factor of the oil samples of Comparative Examples 3-4 with 0.2wt%-0.3wt% added polyphenol type antioxidant is higher. This is because the bisphenol amine type antioxidant itself is a polar substance, and a higher addition amount will lead to an increase in the dielectric loss factor of the oil. In addition, the addition amount of bisphenolamine antioxidant in Example 1 and Comparative Examples 1, 3-4 is 0.05wt%-0.3wt%, and the dielectric loss factor of the oil samples is lower than that of the oil sample with 1wt% 2,6-di-tert-butyl-p-cresol added in Comparative Example 2. This is because the single phenol structure of the bisphenolamine oxidant does not significantly improve the polarization characteristics of the insulating oil, and the bisphenolamine antioxidant not only has a hindered phenol group, but also contains an amine group. This bifunctional structure can more effectively capture free radicals, slow down the generation of polarized molecules, and inhibit the increase in dielectric loss of oil products. In general, adding 0.1wt% of bisphenolamine antioxidant to natural ester can effectively improve the antioxidant capacity of oil products while maintaining good electrical properties.

[0080] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A bisphenolamine antioxidant, characterized in that The chemical structural formula of the bisphenol amine antioxidant is 2. A method for preparing a bisphenol amine antioxidant as claimed in claim 1, characterized in that: The following steps are involved: (1) After the alkylated 1,2-benzenediol and solvent A are mixed and dissolved, a formaldehyde aqueous solution is slowly added dropwise. Then, the reaction is heated and stirred, and after washing and neutralization, the product is separated and purified to obtain an intermediate; The alkylated 1,2-benzenediol has the general structural formula: Wherein, R is an alkyl group or a halogenated alkyl group; (2) The intermediate and p-phenylenediamine are mixed and dissolved with solvent B, a catalyst is added, heated for reaction, washed and neutralized, and then the product is separated and purified to obtain a bisphenol amine antioxidant.

3. The method for preparing a bisphenol amine antioxidant as claimed in claim 1, characterized in that: In step (1), the method for preparing alkylated 1,2-benzenediol comprises the following steps: dissolving 1,2-benzenediol, alkyl halide and alkali in solvent C, heating for reaction, washing and neutralizing, and separating and purifying the product to obtain alkylated 1,2-benzenediol.

4. The method for preparing a bisphenol amine antioxidant as claimed in claim 3, wherein: In the method for preparing alkylated 1,2-benzenediol, the molar ratio of the 1,2-benzenediol to the alkyl halide is 2:(1-2); and / or, in the method for preparing alkylated 1,2-benzenediol, adding alkali to adjust the pH of the system to 9-11; and / or, in the method for preparing alkylated 1,2-benzenediol, the solvent C is methanol; and / or, in the method for preparing alkylated 1,2-benzenediol, the heating reaction temperature is 60-80° C. and the time is 1-2 h; And / or, in the method for preparing alkylated 1,2-benzenediol, separation and purification are performed by adding ethyl acetate to the reaction mixture, extracting and combining the organic phases, drying the organic layer with anhydrous sodium sulfate, filtering and removing the solvent by rotary evaporation.

5. The method for preparing a bisphenolamine antioxidant as claimed in claim 3, characterized in that: In the method for preparing alkylated 1,2-benzenediol, the alkyl halide is methyl chloride, and the structural formula of the alkylated 1,2-benzenediol is 6. The method for preparing a bisphenol amine antioxidant as claimed in claim 1, characterized in that: In step (1), 5-10 mL of a 30 wt%-40 wt% formaldehyde aqueous solution is added to every 0.1 mol of the alkylated 1,2-diphenol; And / or, in step (1), the heating and stirring reaction temperature is 40-60°C and the time is 2-4h; And / or, in step (1), the solvent A is methanol; And / or, in step (1), separation and purification is performed by adding ethyl acetate to the reaction mixture, extracting and combining the organic phases, drying the organic layer with anhydrous sodium sulfate, filtering and removing the solvent by rotary evaporation.

7. The method for preparing a bisphenolamine antioxidant as claimed in claim 1, characterized in that: In step (2), the molar ratio of the intermediate to p-phenylenediamine is (1-2): (1-2); and / or, in step (2), the catalyst is boron trifluorochloride; and / or, in step (2), adding 0.2-0.5 g of catalyst per 0.05 mol of the intermediate; and / or, in step (2), the solvent B is methanol; And / or, in step (2), the heating reaction temperature is 80-100° C. and the time is 50-70 min; and / or, in step (2), the heating reaction is carried out in a nitrogen atmosphere; And / or, in step (2), separation and purification are performed by adding ethyl acetate to the reaction mixture, extracting and combining the organic phases, drying the organic layer with anhydrous sodium sulfate, filtering and removing the solvent by rotary evaporation, and purifying by recrystallization.

8. A natural ester insulating oil, characterized in that: Contains 0.08wt%-0.12wt% of the bisphenolamine antioxidant as claimed in claim 1.

9. A natural ester insulating oil as claimed in claim 8, characterized in that: The invention comprises 0.8wt%-0.12wt% of a bisphenolamine antioxidant, 95wt%-99.92wt% of a natural ester and 0wt%-5wt% of a functional auxiliary agent, wherein the functional auxiliary agent is at least one of a preservative, an antifoaming agent and an anti-emulsifier.

10. The natural ester insulating oil according to claim 9, characterized in that: The natural ester is FR3 natural ester.

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