Synthetic ester insulating oil based on collaborative regulation of alkyl chain length grading and star-comb composite branching and preparation method of synthetic ester insulating oil

Abstract

The invention discloses synthetic ester insulating oil based on alkyl chain length grading and star-comb composite branching cooperative regulation and a preparation method, and relates to the technical field of electrical equipment insulating materials. The preparation method comprises the following steps: esterifying polyhydric alcohol and C8-C12 gradient mixed fatty acid to obtain a gradient main chain ester intermediate; performing vacuum grafting on the intermediate and branched chain acid to obtain star branched ester; carrying out ester exchange on the star-shaped branched ester and branched-chain alcohol to obtain star-shaped-comb-shaped composite branched ester; and compounding the composite branched ester with an additive to obtain a finished product. The insulating oil solves the problem that low pour point and low-temperature viscosity of a traditional oil product cannot be considered at the same time, extremely low-temperature adaptability, insulating performance and thermal stability are improved, the insulating oil is adaptive to alpine regions and direct-current power transmission equipment, raw materials are easy to obtain, the process is environment-friendly, traditional mineral insulating oil can be replaced, and the cost is low. And a key technical support is provided for stable operation of power equipment in an extreme environment.

Description

Technical Field

[0001] This invention relates to the field of electrical equipment insulation materials technology, and in particular to synthetic ester insulating oils and their preparation methods based on the synergistic regulation of alkyl chain length hierarchies and star-comb composite branching. Background Technology

[0002] As power systems develop towards higher voltage, larger capacity, and adaptability to extreme environments, the performance requirements for insulating oil, as the core insulation and heat dissipation medium for power equipment, are becoming increasingly stringent.

[0003] While traditional mineral insulating oils possess good dielectric strength and thermal stability, their poor biodegradability, insufficient low-temperature fluidity (pour points are generally above -30℃), and fire hazards make them unsuitable for meeting the comprehensive requirements of low-temperature start-up, environmental friendliness, and safety in high-altitude and cold regions (such as polar regions and plateaus) and DC transmission equipment. In recent years, synthetic ester insulating oils have been considered an important alternative to mineral oils due to their biodegradability, high flash point (>300℃), and excellent thermal oxidation stability. However, significant challenges remain in controlling their pour point at extreme low temperatures.

[0004] The primary problem with existing synthetic ester oils is the inherent contradiction between molecular structure and pour point: although short-chain esters (such as some pentaerythritol esters) can lower the pour point to below -50°C, the increased molecular rigidity leads to a sharp increase in viscosity at low temperatures, which in turn worsens the fluidity; although long-chain or branched esters can improve viscosity-temperature characteristics, the disordered distribution of branches can easily reduce molecular stacking resistance, causing the pour point to rise back to above -40°C. Meanwhile, existing technologies mostly use single methods such as fixed chain length or random branching to control the pour point, neglecting the synergistic effect of alkyl chain length gradation (such as differentiated design of main chain / side chain) and branch spatial configuration (such as symmetric / asymmetric branching, optimization of branch position). This results in difficulty in achieving both low-temperature fluidity and thermal stability, and serious inadequacy in adaptability to extreme environments: power equipment in high-altitude and cold regions requires insulating oil to maintain fluidity below -60℃, but the lowest pour point of existing synthetic ester oils is only -60℃, and this requires the use of pour point depressants. Pour point depressants may not only introduce impurities but also degrade dielectric properties. In addition, in DC transmission equipment, traditional ester oils are prone to space charge accumulation under long-term electric field stress due to insufficient matching between molecular polarity and steric hindrance, which accelerates insulation aging.

[0005] In summary, existing technologies cannot achieve synergistic optimization of the pour point, viscosity-temperature characteristics, dielectric properties, and thermal stability of synthetic ester insulating oils through precise molecular-level design. There is an urgent need for a design and preparation method for synthetic ester insulating oils based on precise molecular topology design. Summary of the Invention

[0006] The purpose of this invention is to provide a synthetic ester insulating oil and its preparation method based on the synergistic regulation of alkyl chain length gradation and star-comb composite branching, so as to solve the problems existing in the prior art.

[0007] To achieve the above objectives, the present invention provides the following solution: This invention provides a method for preparing synthetic ester insulating oil, comprising the following steps: (1) Main chain construction: Under a protective atmosphere, polyols and C8-C12 gradient mixed fatty acids were esterified under the action of a catalyst. The acid value was monitored to ≤2.5 mg KOH / g to obtain ester intermediates with gradient main chains. (2) Construction of star-shaped branched chain: The ester intermediate with gradient main chain is mixed with branched acid, a catalyst is added, and grafting reaction is carried out under vacuum. The acid value is monitored to ≤1.2 mg KOH / g to obtain star-shaped branched ester; (3) Comb-like branched chain construction: The star-shaped branched ester is mixed with a branched alcohol and transesterification is carried out under the action of a catalyst. The conversion rate of the branched alcohol is monitored to be ≥95% to obtain a star-shaped-comb-like composite branched ester. (4) Compounding: The composite branched ester and additives are mixed evenly to obtain the synthetic ester insulating oil; In step (1), the polyol is selected from pentaerythritol or trimethylolpropane; In step (1), the C8-C12 gradient mixed fatty acid is a mixture of C8 fatty acid, C10 fatty acid and C12 fatty acid in a molar ratio of 4:3:3; In step (2), the molar ratio of the ester intermediate with a gradient main chain to the branched acid is 1:4; In step (2), the branched acid is selected from isooctanoic acid or neopentanoic acid; In step (3), the branched alcohol is selected from 2-ethylhexanol or 3,5-dimethylheptanol; In step (3), the molar ratio of the star-shaped branched ester to the branched alcohol is 1:3; The catalyst in step (1) is p-toluenesulfonic acid or concentrated sulfuric acid; the catalyst in step (2) is selected from tetrabutyl titanate or stannous oxide; the catalyst in step (3) is a Ziegler-type catalyst.

[0008] Further, in step (1), the temperature of the esterification reaction is 150-170℃ and the time is 5-7h; in step (2), the temperature of the grafting reaction is 175-185℃ and the time is 4-5h; in step (3), the temperature of the transesterification reaction is 200-220℃ and the time is 3-4h.

[0009] Furthermore, the esterification reaction is carried out in a segmented heating manner, first pre-esterifying at 150℃ for 2 hours, and then heating to 160-170℃ to continue the reaction for 4 hours.

[0010] Furthermore, in step (3), during the transesterification reaction, the main chain is grafted with side chains at intervals of 2-4 carbon atoms.

[0011] In the transesterification reaction of this invention, side chains are grafted onto the main chain at regular intervals of 2-4 carbon atoms. This is achieved through a synergistic mechanism of directed catalysis, structural adaptation, and parameter control. The specific mechanism is as follows: First, a directed reaction system is constructed by using a Ziegler-type catalyst. This type of catalyst has site-selective catalytic activity for the reaction between ester and hydroxyl groups, preferentially recognizing and activating ester group sites with 2-4 carbon atom intervals on the main chain, reducing the reactivity of non-target ester groups, and inhibiting random branch grafting from a catalytic perspective, thus laying the foundation for regular grafting. Second, based on the structural characteristics of the main chain carbon chain, branched alcohols with matching molecular structures (such as 2-ethylhexanol and 3,5-dimethylheptanol) are selected. Their hydroxyl active centers have a higher compatibility with the steric hindrance and electronic effects of the specific interval ester groups on the main chain, enabling them to bind directionally through intermolecular interactions and undergo transesterification, further enhancing the tendency of the side chains to graft at the target interval positions. Simultaneously, by controlling the reaction temperature to 200-220℃ and the reaction time to 3-4 hours... The reaction time is controlled to maintain the reaction system within a moderate reaction rate range. This avoids insufficient grafting efficiency caused by slow reactions at low temperatures, and also prevents disordered stacking of branches caused by fast reactions at high temperatures. This ensures that the main chain is stably grafted with branches at preset intervals, ultimately forming a well-structured comb-like branched structure. This provides molecular structural support for the synergistic optimization of the low-temperature fluidity and dielectric properties of insulating oil.

[0012] Furthermore, the additives include one or more of antioxidants, charge inhibitors, light stabilizers, and defoamers.

[0013] Furthermore, the amount of the additive used is 0.01-0.2% of the total mass of the system.

[0014] Further, the antioxidant in step (4) includes di-tert-butyl-p-cresol; the charge inhibitor includes benzotriazole; the light stabilizer includes hindered amine light stabilizers; and the defoamer includes siloxane defoamers.

[0015] The additives are mixed at a temperature of 60-70℃ for 1-2 hours, and can be dispersed by ultrasonic treatment at a frequency of 35-45 kHz for 20-40 minutes.

[0016] The second technical solution of this invention provides a synthetic ester insulating oil obtained by the above preparation method. This insulating oil has a pour point ≤ -62℃, a kinematic viscosity ≤ 3500 mm² / s at -30℃, a dielectric strength ≥ 65 kV / 2.5mm, an oxidation life ≥ 800 h, a biodegradability rate ≥ 90%, a flash point ≥ 240℃, and an ignition point ≥ 350℃.

[0017] In the insulating oil molecular structure of this invention, the gradient main chain is composed of C8-C12 carbon chains, the star-shaped branches are isooctyl or neopentyl, and the comb-shaped branches are ethyl or methyl, forming a molecular topology structure of gradient main chain-star-shaped branches-comb-shaped branches working together.

[0018] Figure 1 is a schematic diagram of the molecular topology of star-comb composite branched ester synthesized with pentaerythritol as the core alcohol. The core design is based on the synergistic construction of the star branched region (R1) and the comb branched region (R2) of pentaerythritol tetraester. In the star-shaped branched region, pentaerythritol tetraester is the core, with its four ester groups connected to a gradient backbone of C8:C10:C12 = 4:3:3. The ends of the backbone are further grafted with C4-C6 isomer branches (such as isooctyl branches, with the structural formula CH2-CH(CH2CH2CH2CH2CH(CH2CH3))). This difference in backbone length and branch isomerization disrupts molecular symmetry, forming a composite structure of rigid framework and flexible ends. In the comb-shaped branched region, the main chain is a straight C6-C8 chain, with short C2-C4 branches (such as ethyl branches, with the structural formula -CH(CH2CH3)-) grafted every 2-3 carbon atoms. This spatial distribution of branches increases the free volume between molecules, further blocking the molecular crystallization pathway at low temperatures. The overall molecular topology is synergistically regulated through multi-level control of gradient chain length, asymmetric branching, and polar directional distribution, achieving a balance and optimization of low-temperature fluidity, thermal stability, and insulation properties.

[0019] The third technical solution of this invention is to provide the application of the above-mentioned low pour point synthetic ester insulating oil in power equipment.

[0020] The power equipment includes transformers, reactors, and high-voltage capacitors, and is particularly suitable for power equipment in cold regions and DC transmission scenarios.

[0021] This invention, through the synergistic regulation of alkyl chain length gradation (main chain / side chain gradient length design) and branch configuration (such as star-shaped branching and comb-shaped branching), can not only break the molecular crystallization trend to optimize low-temperature performance, but also utilize the steric hindrance of the branched chain to suppress charge migration to adapt to DC scenarios. Ultimately, it provides theoretical guidance and engineering solutions for the development of high-performance insulating oils for extreme environments.

[0022] This invention innovatively employs a gradient main chain design, effectively breaking the tendency of molecular crystallization. Simultaneously, by combining this with steric hindrance control through a composite branched configuration, it completely eliminates the inherent contradiction of the incompatibility between low pour point and low-temperature viscosity at the molecular level. This design significantly improves the extreme low-temperature adaptability of insulating oil, enabling it to maintain a stable flow state even in frigid environments, successfully solving the technical problems of low-temperature solidification and deterioration of fluidity in traditional oils. At the same time, through the directional design and polarity distribution optimization of the branched chains, the insulating performance and charge suppression capability of the insulating oil are greatly enhanced, effectively reducing space charge accumulation and lowering the risk of insulation aging under long-term electric field effects, providing a solid guarantee for the safe and stable operation of high-voltage and DC transmission equipment.

[0023] This invention, by flexibly adjusting the types of polyols, branched raw materials, and compounding ratios, can achieve precise performance matching for different application scenarios. It is suitable for power equipment in extremely cold regions and can also meet the stringent insulation stability requirements of special operating conditions such as DC power transmission. Regarding long-term service reliability, the composite branched structure and functional additives work synergistically to significantly improve the thermal oxidation stability and anti-aging ability of the insulating oil, effectively reducing sludge formation and extending oil life and equipment maintenance cycles. Simultaneously, it ensures performance stability over a wide temperature range, avoiding adverse effects of temperature fluctuations on insulation and heat dissipation functions.

[0024] Furthermore, the technical solution of this invention fully considers both industrial feasibility and environmental safety requirements: the raw materials used are readily available, the process parameters are precise and controllable, and the production process is green and environmentally friendly; the product has excellent biodegradability and high safety performance, and can replace traditional mineral insulating oil to achieve the green transformation of the industry, which fully meets the core needs of the current power industry to develop towards high voltage, large capacity, extreme environmental adaptability and environmental protection.

[0025] This invention constructs a gradient main chain-composite branching molecular design, providing a high-performance insulating oil solution with balanced performance, wide adaptability to various scenarios, and engineering scalability, providing key technical support for the stable operation of power equipment in extreme environments.

[0026] The present invention discloses the following technical effects: This invention overcomes the technical bottleneck of traditional synthetic ester insulating oils, which cannot simultaneously achieve low pour point and low-temperature viscosity, by synergistically regulating gradient main chain design and star-comb composite branching configuration. It significantly improves the adaptability to extreme low temperatures and can maintain stable flow even in frigid environments, thus completely solving the problems of low-temperature solidification and deterioration of fluidity in traditional oils.

[0027] This invention employs branched-chain directional design and polarity distribution optimization to enhance the insulation performance and charge suppression capability of synthetic ester insulating oil, reduce space charge accumulation, and mitigate the risk of insulation aging during long-term operation of high-voltage and DC transmission equipment, ensuring equipment safety and stability. The synergistic effect of the composite branched structure and functional additives improves thermal oxidation stability and anti-aging capabilities, reduces sludge formation, extends oil life and equipment maintenance cycles, and ensures stable performance over a wide temperature range, preventing temperature fluctuations from affecting insulation and heat dissipation functions.

[0028] The raw materials used in this invention are readily available and the process is controllable. The production is green and environmentally friendly, and the product has both high biodegradability and safety. It can replace traditional mineral insulating oil to promote the green transformation of the industry, meet the development needs of the power system, and construct a new "gradient main chain-composite branching" molecular design to provide a high-performance insulating oil solution with balanced performance and wide application scenarios. Attached Figure Description

[0029] 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.

[0030] Figure 1 This is a schematic diagram of the topological structure of the star-shaped-comb-shaped composite branched ester molecule synthesized using pentaerythritol as the core alcohol in this invention.

[0031] Figure 2 shows a comparison curve of the kinematic viscosity of Example 1 and Comparative Example 1 as a function of temperature.

[0032] Figure 3 The curves show the difference in space charge migration suppression effect between Example 1 and Comparative Example 1 as a function of temperature. Detailed Implementation

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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 readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0037] 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.

[0038] 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.

[0039] The key points that need to be paid attention to during the preparation process of this invention are as follows: (1) Main chain gradient ratio control: The mixed molar ratio of C8, C10 and C12 fatty acids must be strictly controlled within ≤±5%; if the ratio deviation exceeds this range, the pour point of the insulating oil will increase significantly, directly affecting the core performance of low temperature fluidity.

[0040] (2) Process parameter tolerance control: The esterification reaction temperature is allowed to fluctuate by ±5℃, and the reaction time is allowed to fluctuate by ±1 hour. These can be flexibly adjusted within this tolerance range. The vacuum degree of the molecular distillation process must be strictly controlled to ≤15 Pa to avoid thermal decomposition of the product under high temperature conditions and to ensure that the dielectric properties and thermal stability of the insulating oil are not affected.

[0041] Example 1: Preparation of star-shaped-comb-shaped composite branched ester insulating oil This embodiment provides a star-shaped-comb-shaped composite branched ester insulating oil, and the preparation steps are as follows: (1) Synthesis of tetraester intermediate: 1 mol pentaerythritol was used as the core alcohol and reacted with a gradient mixture of straight-chain fatty acids, wherein the straight-chain fatty acids were a mixture of 4 mol octanoic acid, 3 mol decanoic acid and 3 mol dodecanoic acid (lauric acid); 0.5% of p-toluenesulfonic acid was added to the above mixed raw materials as a catalyst, and the reaction system was heated to 160℃ under a nitrogen protective atmosphere and stirred continuously for 6 hours for esterification. The acid value of the system was monitored in real time during the reaction. When the acid value dropped to ≤2 mg KOH / g, the reaction was stopped to obtain the tetraester intermediate (a mixed straight-chain total ester formed by pentaerythritol and octanoic acid / decanoic acid / dodecanoic acid).

[0042] (2) Construction of star-shaped branched structure: 4 mol of isooctanoic acid was added to the tetraester intermediate obtained in step (1), and 0.3% of tetrabutyl titanate was added as a catalyst. The vacuum degree of the reaction system was controlled at 0.05 MPa, and the temperature was raised to 180℃ and the reaction was continued for 4 hours. During the reaction, the generated water was continuously removed. When the acid value of the system was further reduced to ≤1 mgKOH / g, the reaction was terminated. At this time, the product formed a star-shaped branched ester characterized by a C8-C12 gradient main chain and isooctyl side chain, thus completing the construction of the star-shaped branched structure and obtaining a star-shaped mixed ester in which some straight-chain acyl groups were replaced by isooctyl groups.

[0043] (3) Construction of comb-like branched structure: The star-shaped branched ester obtained in step (2) was mixed with 2-ethylhexanol at a molar ratio of 1:3. Ziegler catalyst accounting for 0.2% of the total mass of the system was added. The reaction temperature was raised to 220℃ and the transesterification reaction was carried out for 3 hours. The conversion rate of 2-ethylhexanol was monitored in real time by gas chromatography (GC). The reaction was stopped when the conversion rate reached ≥95%. At this time, the product formed a star-shaped-comb-like composite branched ester with C8 main chain spaced and grafted with ethyl branches.

[0044] (4) Product Refining and Compounding: The star-shaped-comb-shaped composite branched ester product obtained in step (3) is placed in a molecular distillation apparatus and subjected to molecular distillation at 180°C and a vacuum of ≤10 Pa to remove unreacted raw materials and low-boiling-point impurities from the system. After distillation, 0.1% of di-tert-butyl-p-cresol (antioxidant) and 0.05% of benzotriazole (charge inhibitor) by mass of the total system are added to the refined product. The mixture is stirred at 60°C for 1 hour to ensure uniform dispersion of the additives. Finally, trace solid impurities are removed by filtration to obtain transparent star-shaped-comb-shaped composite branched ester insulating oil.

[0045] Targeted performance tests were conducted on the synthetic ester insulating oil prepared in this embodiment. All tests were performed in accordance with the corresponding standards and specifications. The specific results are as follows: the pour point was determined according to GB / T 3535 standard, and the result was -62℃; the kinematic viscosity at -30℃ was determined according to GB / T 265 standard, and the value was 3200 mm² / s; the dielectric strength was tested according to GB / T 507 standard, reaching 66 kV / 2.5mm; and the oxidation life was evaluated according to IEC 61125 (Method C) standard, reaching 820 h.

[0046] This synthetic ester insulating oil exhibits excellent performance across all indicators, fully meeting the core requirements of power equipment in high-altitude and cold regions for low-temperature fluidity and long-term operational stability.

[0047] Example 2: Preparation of Gradient Main-Chain Neopentyl Branched Insulating Oil This embodiment provides a gradient main chain-neoptiyl branched insulating oil, and the specific steps are as follows: (1) Gradient esterification reaction: 1 mol of trimethylolpropane was used as the core polyol and mixed with straight-chain fatty acids in a certain proportion, wherein the straight-chain fatty acids included 4 mol of octanoic acid, 3 mol of decanoic acid, and 3 mol of dodecanoic acid (lauric acid) to form a raw material system with a gradient distribution of carbon chain length. 0.6% of concentrated sulfuric acid was added to the mixed system as a catalyst, and the esterification reaction was promoted by a segmented heating mode: the system was first heated to 150℃ for pre-esterification for 2 hours to initially activate the reactivity of hydroxyl and carboxyl groups and reduce the by-products of subsequent high-temperature reactions; after the pre-esterification was completed, the temperature was raised to 170℃ and the reaction was continued for 4 hours to further promote the esterification process. The acid value of the system was monitored in real time during the reaction. When the acid value dropped to ≤2.5 mgKOH / g, the reaction was stopped to obtain an ester intermediate with a gradient main chain of C8-C10-C12.

[0048] (2) Branch optimization (construction of star-shaped neopentyl side chains): 1.5 mol of neopentyl acid and 5% of 4A molecular sieve (to adsorb water generated in the reaction) were added to the gradient main chain ester intermediate obtained in step (1); 0.4% of stannous oxide was added as a catalyst. After evacuating the reaction system, the temperature was raised to 180℃ and the reaction was carried out for 5 hours. The acid value of the system was continuously monitored. When the acid value dropped to ≤1.2 mg KOH / g, the reaction was terminated. At this time, the product formed a star-shaped branched structure with the gradient main chain as the backbone and neopentyl as the side chain, thus completing the directional construction of the star-shaped branch.

[0049] (3) Comb-like chain regulation (constructing a comb-like structure with spaced methyl branches): Take the star-shaped branched ester product 3,5-dimethylheptanol obtained in step (2) and mix them evenly in a molar ratio of 1:3. Add 0.3% of Ziegler-type catalyst in total mass of the system. Raise the reaction temperature to 200℃ and keep the reaction at this temperature for 4 hours. By directionally catalyzing the transesterification reaction with the catalyst, control the grafting of a methyl branch every 3 carbon atoms between each main chain segment, and finally form a comb-like topology with gradient main chain and spaced methyl branches, further optimizing the free volume between molecules and low-temperature fluidity.

[0050] (4) Post-processing: The product obtained in step (3) is placed in a molecular distillation apparatus and molecular distilled at 170°C and a vacuum of ≤15Pa to remove unreacted neopentanoic acid, 3,5-dimethylheptanol and low-boiling impurities from the system; after distillation, a transparent gradient main chain and neopentyl branched insulating oil is obtained.

[0051] Targeted performance tests were conducted on the synthetic ester insulating oil prepared in this embodiment. All tests were performed in accordance with the corresponding standards and specifications. The specific results are as follows: the pour point was determined according to GB / T 3535 standard, and the result was -63.1℃; the kinematic viscosity at -30℃ was determined according to GB / T 265 standard, and the value was 3345mm² / s; the dielectric strength was tested according to GB / T 507 standard, reaching 66 kV / 2.5mm; and the oxidation life was evaluated according to IEC 61125 (Method C) standard, reaching 805 h.

[0052] This synthetic ester insulating oil exhibits excellent performance across all indicators, fully meeting the core requirements of power equipment in high-altitude and cold regions for low-temperature fluidity and long-term operational stability.

[0053] Example 3 Preparation of a wide-temperature-range insulating oil compound system This embodiment builds upon the advantages of the single-system approach of Example 1 (star-shaped-comb-shaped composite branched ester) and Example 2 (gradient main chain-neopentyl branched ester), further optimizing the wide temperature range adaptability and overall performance of the insulating oil through a synergistic additive enhancement method using basic ester compounding. The specific steps are as follows: (1) Basic ester mixing: Take the star-comb composite branched ester (60 wt%) prepared in step (3) of Example 1 and the product (40 wt%) prepared in step (2) of Example 2 in a mass percentage ratio of 6:4, and add them together to a reaction vessel equipped with a stirring device; raise the system temperature to 70°C and stir continuously at a stable rate for 1 hour. This temperature and stirring conditions can promote the full fusion of ester molecules with two different topologies, forming a complementary and synergistic molecular network of star-comb branches + gradient main chain - neopentyl branches.

[0054] (2) Additive enhancement: Two functional additives were added to the basic ester mixture obtained in step (1) in sequence: first, a hindered amine light stabilizer (model Tinuvin 770) accounting for 0.05% of the total mass of the system was added, followed by a siloxane defoamer accounting for 0.01% of the total mass; after the additives were added, the mixture was ultrasonically treated at a frequency of 40 kHz for 30 minutes to ensure that the two additives were uniformly dispersed in the ester system by ultrasonic vibration.

[0055] Targeted performance tests were conducted on the synthetic ester insulating oil prepared in this embodiment. All tests were performed in accordance with the corresponding standards and specifications. The specific results are as follows: the pour point was determined according to GB / T 3535 standard, and the result was -62.3℃; the kinematic viscosity at -30℃ was determined according to GB / T 265 standard, and the value was 3150 mm² / s; the dielectric strength was tested according to GB / T 507 standard, reaching 67 kV / 2.5mm; and the oxidation life was evaluated according to IEC 61125 (Method C) standard, reaching 830 h.

[0056] Comparative Example 1 This comparative example provides a traditional homogeneous linear ester insulating oil, and the preparation steps are as follows: Using 1 mol pentaerythritol as the core alcohol, it was mixed with 10 mol dodecanoic acid (lauric acid). No gradient carbon chain design or branching control step was adopted. The mixture was heated to 180℃ and reacted continuously for 8 hours using a one-step esterification process. After the reaction was completed, a traditional homogeneous straight-chain ester insulating oil was directly obtained.

[0057] The product performance was tested using the same testing standards as in Example 1. The overall performance of this traditional insulating oil was significantly inferior to that of the products in Examples 1-3 of this invention: the pour point was only -48℃; the kinematic viscosity at -30℃ was as high as 4228 mm² / s, with extremely poor low-temperature fluidity; the dielectric strength was 62 kV / 2.5mm, indicating insufficient insulation performance; and the oxidation life was only 580 h, indicating poor long-term stability.

[0058] Figure 2 shows the comparison curves of kinematic viscosity as a function of temperature for Example 1 and Comparative Example 1. As can be seen from the figure, as the temperature gradually increases from -30℃ to 40℃, the kinematic viscosity of both media shows a significant decreasing trend, and the effect of temperature on viscosity exhibits obvious segmented characteristics: below 0℃, the viscosity is more sensitive to temperature changes, and in the range of -30℃ to -20℃, the viscosity drops sharply from the order of 10³ mm² / s to the order of 10² mm² / s; above 0℃ to 40℃, the viscosity decreasing trend becomes more gradual, and by room temperature (20℃) it has dropped to below about 10² mm² / s, and at 40℃ it further drops to the level of tens of mm² / s.

[0059] This viscosity-temperature relationship conforms to the classic Arrhenius model or the Vogel–Fulcher–Tammann model, reflecting both the restricted molecular motion of synthetic ester-based oils at low temperatures and highlighting the optimizing effect of the modified components on low-temperature fluidity. Notably, throughout the entire test temperature range, the kinematic viscosity of Example 1 was significantly lower than that of Comparative Example 1. Specifically, at -30°C, the kinematic viscosity of Example 1 was 3200 mm² / s, while that of the Comparative Example was as high as 4200 mm² / s, fully demonstrating the improving effect of the present invention on the low-temperature fluidity of insulating oil.

[0060] Figure 3 The figure shows a comparison of the space charge migration suppression effect of Example 1 and Comparative Example 1 as a function of temperature. As can be seen from the figure, the volume charge density of both media monotonically decreases as the temperature increases from -60°C to 60°C: from 10 at -60°C... -5 The value is on the order of C / m³, gradually decreasing to 10 at 60℃. -6 The volumetric charge density is on the order of C / m³. Throughout the entire test temperature range, Example 1 consistently maintained a lower level of space charge accumulation than Comparative Example 1. For example, at –60°C, the volumetric charge densities of both were approximately 5.0 × 10⁻⁶. -5 C / m³ and 7.0×10 -5 C / m³; approximately 1.5 × 10⁻² at –20℃. -5 C / m³ and 3.5×10 -5 C / m³, with a maximum suppression efficiency of approximately 57%.

[0061] The core reason for this temperature-dependent suppression effect is that the polar modified component introduced in Example 1 forms a higher density and deeper energy level charge trap in the synthetic ester oil system, which can efficiently capture free charges during carrier migration. At low temperature, the increased oil viscosity further restricts carrier diffusion, so that the trap effect and viscosity restriction form a dual synergistic mechanism, and the suppression effect is particularly significant. As the temperature rises, the thermal activation ability of carriers is enhanced and the oil viscosity decreases, and some trap effects are weakened. Although the difference in charge density between the two narrows, Example 1 still shows excellent space charge migration suppression ability.

[0062] 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 preparing a synthetic ester insulating oil, characterized in that, Includes the following steps: (1) Main chain construction: Under a protective atmosphere, polyols and C8-C12 gradient mixed fatty acids were esterified under the action of a catalyst. The acid value was monitored to ≤2.5 mg KOH / g to obtain ester intermediates with gradient main chains. (2) Construction of star-shaped branched chain: The ester intermediate with gradient main chain is mixed with branched acid, a catalyst is added, and grafting reaction is carried out under vacuum. The acid value is monitored to ≤1.2 mg KOH / g to obtain star-shaped branched ester; (3) Comb-like branched chain construction: The star-shaped branched ester is mixed with a branched alcohol and transesterification is carried out under the action of a catalyst. The conversion rate of the branched alcohol is monitored to be ≥95% to obtain a star-shaped-comb-like composite branched ester. (4) Compounding: The star-shaped-comb-shaped composite branched ester and the additives are mixed evenly to obtain the synthetic ester insulating oil; In step (1), the polyol is selected from pentaerythritol or trimethylolpropane; In step (1), the C8-C12 gradient mixed fatty acid is a mixture of C8 fatty acid, C10 fatty acid and C12 fatty acid in a molar ratio of 4:3:3; In step (2), the molar ratio of the ester intermediate with a gradient main chain to the branched acid is 1:4; In step (2), the branched acid is selected from isooctanoic acid or neopentanoic acid; In step (3), the branched alcohol is selected from 2-ethylhexanol or 3,5-dimethylheptanol; In step (3), the molar ratio of the star-shaped branched ester to the branched alcohol is 1:3; The catalyst in step (1) is p-toluenesulfonic acid or concentrated sulfuric acid; the catalyst in step (2) is selected from tetrabutyl titanate or stannous oxide; the catalyst in step (3) is a Ziegler-type catalyst.

2. The preparation method according to claim 1, characterized in that, In step (1), the esterification reaction is carried out at a temperature of 150-170℃ for 5-7 hours; in step (2), the grafting reaction is carried out at a temperature of 175-185℃ for 4-5 hours; in step (3), the transesterification reaction is carried out at a temperature of 200-220℃ for 3-4 hours.

3. The preparation method according to claim 2, characterized in that, The esterification reaction was carried out in a segmented heating manner, first pre-esterifying at 150℃ for 2 hours, and then heating to 160-170℃ to continue the reaction for 4 hours.

4. The preparation method according to claim 1, characterized in that, The additives include one or more of antioxidants, charge inhibitors, light stabilizers, and defoamers.

5. The preparation method according to claim 4, characterized in that, The antioxidant mentioned in step (4) includes di-tert-butyl-p-cresol; the charge inhibitor includes benzotriazole; the light stabilizer includes hindered amine light stabilizers; and the defoamer includes siloxane defoamers.

6. A synthetic ester insulating oil obtained by any one of the preparation methods described in claims 1-5.

7. The application of the synthetic ester insulating oil as described in claim 6 in power equipment.

Images