Electrical equipment insulating liquid and preparation method thereof

Abstract

The invention discloses an electrical equipment insulating liquid and a preparation method thereof, and belongs to the technical field of insulating liquid preparation, the preparation method comprises the following steps: sequentially adding trimethylolpropane, caprylic acid, capric acid and oleic acid into a reaction container, then adding toluenesulfonic acid as a catalyst, and carrying out an esterification reaction to obtain a substrate after the esterification reaction; removing the unreacted substrate from the substrate after the esterification reaction by using a vacuum distillation method to obtain a distilled product; and naturally cooling the distilled product, carrying out alkali refining treatment by using a sodium hydroxide solution, washing by using ultrapure water to remove sodium salt in the alkali refining process, adsorbing by using an adsorbent to remove moisture and polar impurities, carrying out vacuum drying, and finally filtering by using a filter membrane to generate the trimethylolpropane caprylic / capric trioleate insulating liquid. The problem of low ignition point of the trimethylolpropane ester insulating liquid can be solved, and the insulating liquid has excellent electrical performance and is suitable for electrical equipment such as transformers.

Description

Technical Field

[0001] The invention relates to an insulating liquid for electrical equipment and a preparation method thereof, belonging to the technical field of insulating liquid preparation. Background Art

[0002] At present, the global power grid is in a critical period of transformation to a cleaner, smarter and more powerful version. This trend is driving the continuous development of excellent insulation systems. As a key component of the power grid, power transformers undertake the important task of transmitting and distributing electric energy. Their reliability is an important guarantee for the safe and stable operation of the power system. If the power transformer is compared to the heart of the power system, then the insulating oil is equivalent to the blood flowing inside the transformer, playing a vital role in the safe and stable operation of the transformer.

[0003] Since 1887, mineral oil has been widely used as an insulating medium due to its good performance and relatively low cost. However, mineral oil has a low flash point and poor degradation ability, which will cause resource depletion and increase greenhouse gas emissions, making it difficult to use in high-safety situations such as offshore wind power. In the context of my country's promotion of the "dual carbon" goal, mineral insulating oil is obviously difficult to meet the requirements of safety, green and sustainable development. Therefore, the use of a new liquid insulation mechanism that is non-toxic, environmentally friendly and biodegradable has become a natural choice to replace mineral oil.

[0004] In recent years, ester-based insulating oils have been widely studied due to their excellent natural degradability and high flash point and other physical and chemical properties. For example, sunflower oil, rapeseed oil, linseed oil and soybean oil have been tested for transformer oil applications and are gradually considered to be promising candidates for large transformers. However, they are extremely easy to oxidize, which will shorten the service life of the transformer. These shortcomings limit its sustainable application in transformers, so there is an urgent need to find an antioxidant, economical and environmentally friendly raw material to produce insulating oil. In the prior art, antioxidant trimethylolpropane ester insulating liquid is synthesized using ester exchange technology, and trimethylolpropane is esterified with a short-chain acid. The ester-based insulating oil prepared above has a low flash point and is difficult to be applied to electrical equipment such as transformers. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide an electrical equipment insulating liquid and a preparation method thereof, which can overcome the problem of low ignition point of trimethylolpropane ester insulating liquid, has excellent electrical properties, and is suitable for electrical equipment such as transformers.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] In a first aspect, the present invention provides a method for preparing an insulating liquid for electrical equipment, comprising the following steps:

[0008] Adding trimethylolpropane, octanoic acid, decanoic acid and oleic acid into a reaction container in sequence, and then adding toluenesulfonic acid as a catalyst to carry out an esterification reaction under low pressure conditions to obtain a substrate after the esterification reaction;

[0009] The substrate after the esterification reaction is subjected to vacuum distillation to remove unreacted substrate to obtain a distilled product;

[0010] The distilled product is naturally cooled and then alkali-refined with sodium hydroxide solution, then washed with ultrapure water to remove the sodium salt in the alkali-refining process, then adsorbed with an adsorbent to remove moisture and polar impurities, then vacuum dried, and finally filtered with a membrane to produce trimethylolpropane octanoic acid decanoic acid triester insulating liquid.

[0011] The initial temperature of the esterification reaction is 55~65°C. After each reaction of 1~1.5 h, the temperature is increased by 10~15°C. After increasing to 148~152°C, the reaction is continued for 1~2 h.

[0012] The stirring speed of the esterification reaction is 280~320 rpm, and the pressure of the esterification reaction is 1~3 kPa.

[0013] The amount of p-toluenesulfonic acid added is 1.0~1.4 wt% of the total mass of the reaction substrate.

[0014] The molar ratio of the sum of caprylic acid, capric acid and oleic acid to trimethylolpropane is 3.1-3.3:1, the molar ratio of the sum of caprylic acid and capric acid to oleic acid is 8:2-2:8, and the molar ratio of n-caprylic acid to n-decanoic acid is 4:5-4:7.

[0015] The distillation temperature is 158~160℃ and the distillation time is 2.5~3.5h.

[0016] The adsorbent is composed of basic alumina, 3A molecular sieve, silica gel and activated clay in a mass ratio of 1:1:1:1. The amount of the adsorbent added is 4-6wt% of the generated substrate, and the adsorption time is 50-70min.

[0017] The vacuum drying conditions are 90~110 Pa and 70~80℃ for 30~40h.

[0018] The filter membrane used was 0.25 μm.

[0019] In a second aspect, the present invention provides an insulating liquid for electrical equipment: the insulating liquid is prepared by the insulating liquid preparation method for electrical equipment.

[0020] Beneficial effects of the invention: The invention provides a method for preparing an insulating liquid for electrical equipment, which uses trimethylolpropane, octanoic acid, decanoic acid and oleic acid as raw materials, introduces long-chain fatty acids (oleic acid) into trimethylolpropane molecules through ester exchange technology, and adjusts the viscosity, flash point, pour point and other physical and chemical properties of triester oil by adjusting the proportion of oleic acid. The generated polyol ester changes the chemical structure of trimethylolpropane, which not only overcomes the problem of low ignition point of trimethylolpropane, but also does not excessively increase the viscosity of the oil, thereby improving the stability and high-voltage resistance of the insulating oil, and is suitable for electrical equipment such as transformers;

[0021] The method of the present invention uses p-toluenesulfonic acid (TsOH) as a catalyst, which has higher catalytic efficiency than traditional catalysts (strong acid and strong base), can promote esterification reaction at lower reaction temperature and pressure, significantly improve the conversion rate of reactants, and reduce the residue of unreacted substances. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention is a reaction device for preparing trimethylolpropane octanoic acid decanoic acid triester;

[0023] Figure 2 This is a flow chart of purifying trimethylolpropane octanoic acid oleic acid triester insulating liquid of the present invention;

[0024] Figure 3 This is the synthesis reaction formula used in the synthesis of trimethylolpropane octanoic acid decanoic acid triester of the present invention;

[0025] Figure 4 It is a physical picture of the preparation of trimethylolpropane octanoic acid and decanoic acid triester of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the protection scope of the present invention.

[0027] Example 1

[0028] The present invention provides a method for preparing an insulating liquid for electrical equipment, comprising the following steps:

[0029] Step 1: add trimethylolpropane, octanoic acid, decanoic acid and oleic acid to a three-necked flask in sequence. The molar ratio of the sum of octanoic acid, decanoic acid and oleic acid to trimethylolpropane is 3.2:1, the molar ratio of the sum of octanoic acid and decanoic acid to oleic acid is 8:2, and the molar ratio of n-octanoic acid to n-decanoic acid is 4:6. Toluenesulfonic acid is then added as a catalyst, and the amount of p-toluenesulfonic acid added is 1.2 wt% of the total mass of the reaction substrate. Then, an esterification reaction is carried out under low pressure conditions. The esterification reaction device is as follows: Figure 1As shown, install the three-necked flask in an oil bath, heat it to 60°C first, and stir the mixture with a magnetic stirrer to keep the reaction uniform. The stirring speed of the esterification reaction is 280-320 rpm, then start the vacuum system, and use a circulating water vacuum pump to adjust the vacuum degree of the reaction system to about 3 kPa. During the reaction, sample the acid value of the reactants regularly to monitor the progress of the reaction. After each reaction for 1 h, increase the temperature by 10-15°C, and continue the reaction for 1-2 h after increasing to 150°C to obtain the substrate after the esterification reaction, generating trimethylolpropane octanoic acid triester and water. The synthetic reaction formula is as follows Figure 3 shown.

[0030] Step 2: After the esterification reaction, the substrate is subjected to vacuum distillation to remove the unreacted substrate, mainly to remove the unreacted acid, to obtain a distilled product. Specifically, the circulating water vacuum pump is replaced with an oil vacuum pump, the pressure in the three-necked flask is further reduced, and the flask is heated to a distillation temperature of 160° C. for 3.0 h.

[0031] Step three, such as Figure 2 As shown, the product after distillation is naturally cooled to 60°C (the oil pump and vacuum pump continue to work during the cooling process), and then alkali-refined with sodium hydroxide solution, and then washed with ultrapure water to remove the sodium salt in the alkali refining process, and then adsorbed with an adsorbent to remove moisture and polar impurities. The adsorbent is composed of alkaline alumina, 3A molecular sieve, silica gel, and activated white clay in a mass ratio of 1:1:1:1. The amount of adsorbent added is 5wt% of the generated substrate, and the adsorption time is 60min. Then vacuum drying is performed, and the vacuum drying conditions are drying at 100 Pa and 75°C for 36h. Finally, membrane filtration is performed to generate trimethylolpropane octanoic acid oleic acid triester insulating liquid, wherein the filter membrane is a 0.25 μm filter membrane.

[0032] The final insulating liquid for electrical equipment prepared in this embodiment is shown in the following figure. Figure 4 The physical and chemical properties are shown in Table 1.

[0033] Table 1 Physical and chemical properties of trimethylolpropane octanoic acid decanoic acid triester insulating liquid with oleic acid accounting for 20%

[0034]

[0035] Example 2

[0036] The present invention provides a method for preparing an insulating liquid for electrical equipment, comprising the following steps:

[0037] Step 1: add trimethylolpropane, octanoic acid, decanoic acid and oleic acid to a three-necked flask in sequence. The molar ratio of the sum of octanoic acid, decanoic acid and oleic acid to trimethylolpropane is 3.2:1, the molar ratio of the sum of octanoic acid and decanoic acid to oleic acid is 6:4, and the molar ratio of n-octanoic acid to n-decanoic acid is 4:6. Toluenesulfonic acid is then added as a catalyst, and the amount of p-toluenesulfonic acid added is 1.2 wt% of the total mass of the reaction substrate. Then, an esterification reaction is carried out under low pressure conditions. The esterification reaction device is as follows: Figure 1 As shown, install the three-necked flask in an oil bath, heat it to 60°C first, and stir the mixture with a magnetic stirrer to keep the reaction uniform. The stirring speed of the esterification reaction is 280-320 rpm, then start the vacuum system, and use a circulating water vacuum pump to adjust the vacuum degree of the reaction system to about 3 kPa. During the reaction, sample the acid value of the reactants regularly to monitor the progress of the reaction. After each reaction for 1 h, increase the temperature by 10-15°C, and continue the reaction for 1-2 h after increasing to 150°C to obtain the substrate after the esterification reaction, generating trimethylolpropane octanoic acid triester and water. The synthetic reaction formula is as follows Figure 3 shown.

[0038] Step 2: After the esterification reaction, the substrate is subjected to vacuum distillation to remove the unreacted substrate, mainly to remove the unreacted acid, to obtain a distilled product. Specifically, the circulating water vacuum pump is replaced with an oil vacuum pump, the pressure in the three-necked flask is further reduced, and the flask is heated to a distillation temperature of 160° C. for 3.0 h.

[0039] Step three, such as Figure 2 As shown, the product after distillation is naturally cooled to 60°C (the oil pump and vacuum pump continue to work during the cooling process), and then alkali-refined with sodium hydroxide solution, and then washed with ultrapure water to remove the sodium salt in the alkali refining process, and then adsorbed with an adsorbent to remove moisture and polar impurities. The adsorbent is composed of alkaline alumina, 3A molecular sieve, silica gel, and activated white clay in a mass ratio of 1:1:1:1. The amount of adsorbent added is 5wt% of the generated substrate, and the adsorption time is 60min. Then vacuum drying is performed, and the vacuum drying conditions are drying at 100 Pa and 75°C for 36h. Finally, membrane filtration is performed to generate trimethylolpropane octanoic acid oleic acid triester insulating liquid, wherein the filter membrane is a 0.25 μm filter membrane.

[0040] The test performance of the final electrical equipment insulating liquid prepared in this embodiment is shown in Table 2.

[0041] Table 2 Physical and chemical properties of trimethylolpropane octanoic acid triester oleate insulating liquid with oleic acid accounting for 40%

[0042]

[0043] Example 3

[0044] The present invention provides a method for preparing an insulating liquid for electrical equipment, comprising the following steps:

[0045] Step 1: add trimethylolpropane, octanoic acid, decanoic acid and oleic acid to a three-necked flask in sequence. The molar ratio of the sum of octanoic acid, decanoic acid and oleic acid to trimethylolpropane is 3.2:1, the molar ratio of the sum of octanoic acid and decanoic acid to oleic acid is 4:6, and the molar ratio of n-octanoic acid to n-decanoic acid is 4:6. Toluenesulfonic acid is then added as a catalyst, and the amount of p-toluenesulfonic acid added is 1.2 wt% of the total mass of the reaction substrate. Then, an esterification reaction is carried out under low pressure conditions. The esterification reaction device is as follows: Figure 1 As shown, install the three-necked flask in an oil bath, heat it to 60°C first, and stir the mixture with a magnetic stirrer to keep the reaction uniform. The stirring speed of the esterification reaction is 280-320 rpm, then start the vacuum system, and use a circulating water vacuum pump to adjust the vacuum degree of the reaction system to about 3 kPa. During the reaction, sample the acid value of the reactants regularly to monitor the progress of the reaction. After each reaction for 1 h, increase the temperature by 10-15°C, and continue the reaction for 1-2 h after increasing to 150°C to obtain the substrate after the esterification reaction, generating trimethylolpropane octanoic acid triester and water. The synthetic reaction formula is as follows Figure 3 shown.

[0046] Step 2: After the esterification reaction, the substrate is subjected to vacuum distillation to remove the unreacted substrate, mainly to remove the unreacted acid, to obtain a distilled product. Specifically, the circulating water vacuum pump is replaced with an oil vacuum pump, the pressure in the three-necked flask is further reduced, and the flask is heated to a distillation temperature of 160° C. for 3.0 h.

[0047] Step three, such as Figure 2 As shown, the product after distillation is naturally cooled to 60°C (the oil pump and vacuum pump continue to work during the cooling process), and then alkali-refined with sodium hydroxide solution, and then washed with ultrapure water to remove the sodium salt in the alkali refining process, and then adsorbed with an adsorbent to remove moisture and polar impurities. The adsorbent is composed of alkaline alumina, 3A molecular sieve, silica gel, and activated white clay in a mass ratio of 1:1:1:1. The amount of adsorbent added is 5wt% of the generated substrate, and the adsorption time is 60min. Then vacuum drying is performed, and the vacuum drying conditions are drying at 100 Pa and 75°C for 36h. Finally, membrane filtration is performed to generate trimethylolpropane octanoic acid oleic acid triester insulating liquid, wherein the filter membrane is a 0.25 μm filter membrane.

[0048] The test performance of the final electrical equipment insulating liquid prepared in this embodiment is as shown in 3.

[0049] Table 3 Physical and chemical properties of trimethylolpropane octanoic acid triester with oleic acid accounting for 60%

[0050]

[0051] Example 4

[0052] The present invention provides a method for preparing an insulating liquid for electrical equipment, comprising the following steps:

[0053] Step 1: add trimethylolpropane, octanoic acid, decanoic acid and oleic acid to a three-necked flask in sequence. The molar ratio of the sum of octanoic acid, decanoic acid and oleic acid to trimethylolpropane is 3.2:1, the molar ratio of the sum of octanoic acid and decanoic acid to oleic acid is 2:8, and the molar ratio of n-octanoic acid to n-decanoic acid is 4:6. Toluenesulfonic acid is then added as a catalyst, and the amount of p-toluenesulfonic acid added is 1.2 wt% of the total mass of the reaction substrate. Then, an esterification reaction is carried out under low pressure conditions. The esterification reaction device is as follows: Figure 1 As shown, install the three-necked flask in an oil bath, heat it to 60°C first, and stir the mixture with a magnetic stirrer to keep the reaction uniform. The stirring speed of the esterification reaction is 280-320 rpm, then start the vacuum system, and use a circulating water vacuum pump to adjust the vacuum degree of the reaction system to about 3 kPa. During the reaction, sample the acid value of the reactants regularly to monitor the progress of the reaction. After each reaction for 1 h, increase the temperature by 10-15°C, and continue the reaction for 1-2 h after increasing to 150°C to obtain the substrate after the esterification reaction, generating trimethylolpropane octanoic acid triester and water. The synthetic reaction formula is as follows Figure 3 shown.

[0054] Step 2: After the esterification reaction, the substrate is subjected to vacuum distillation to remove the unreacted substrate, mainly to remove the unreacted acid, to obtain a distilled product. Specifically, the circulating water vacuum pump is replaced with an oil vacuum pump, the pressure in the three-necked flask is further reduced, and the flask is heated to a distillation temperature of 160° C. for 3.0 h.

[0055] Step three, such as Figure 2 As shown, the product after distillation is naturally cooled to 60°C (the oil pump and vacuum pump continue to work during the cooling process), and then alkali-refined with sodium hydroxide solution, and then washed with ultrapure water to remove the sodium salt in the alkali refining process, and then adsorbed with an adsorbent to remove moisture and polar impurities. The adsorbent is composed of alkaline alumina, 3A molecular sieve, silica gel, and activated white clay in a mass ratio of 1:1:1:1. The amount of adsorbent added is 5wt% of the generated substrate, and the adsorption time is 60min. Then vacuum drying is performed, and the vacuum drying conditions are drying at 100 Pa and 75°C for 36h. Finally, membrane filtration is performed to generate trimethylolpropane octanoic acid oleic acid triester insulating liquid, wherein the filter membrane is a 0.25μm filter membrane.

[0056] The test performance of the final electrical equipment insulating liquid prepared in this embodiment is shown in Table 4.

[0057] Table 4 Physical and chemical properties of trimethylolpropane octanoic acid decanoate triester with oleic acid accounting for 80%

[0058]

[0059] Example 5

[0060] The present invention provides a method for preparing an insulating liquid for electrical equipment, comprising the following steps:

[0061] Step 1: add trimethylolpropane, octanoic acid, decanoic acid and oleic acid to a three-necked flask in sequence. The molar ratio of the sum of octanoic acid, decanoic acid and oleic acid to trimethylolpropane is 3.1:1, the molar ratio of the sum of octanoic acid and decanoic acid to oleic acid is 8:2, and the molar ratio of n-octanoic acid to n-decanoic acid is 4:6. Toluenesulfonic acid is then added as a catalyst, and the amount of p-toluenesulfonic acid added is 1.4 wt% of the total mass of the reaction substrate. Then, an esterification reaction is carried out under low pressure conditions. The esterification reaction device is as follows: Figure 1 As shown, install the three-necked flask in an oil bath, heat it to 60°C first, and stir the mixture with a magnetic stirrer to keep the reaction uniform. The stirring speed of the esterification reaction is 280 rpm, then start the vacuum system, and use a circulating water vacuum pump to adjust the vacuum degree of the reaction system to about 3 kPa. During the reaction, sample the acid value of the reactants regularly to monitor the progress of the reaction. After each reaction for 1 h, increase the temperature by 10~15°C, and continue the reaction for 1~2 h after increasing to 148°C to obtain the substrate after the esterification reaction, generating trimethylolpropane octanoic acid triester and water. The synthetic reaction formula is as follows Figure 3 shown.

[0062] Step 2: After the esterification reaction, the substrate is subjected to vacuum distillation to remove the unreacted substrate, mainly to remove the unreacted acid, to obtain a distilled product. Specifically, the circulating water vacuum pump is replaced with an oil vacuum pump, the pressure in the three-necked flask is further reduced, and the flask is heated to a distillation temperature of 160° C. for 2.5 hours.

[0063] Step three, such as Figure 2 As shown, the product after distillation is naturally cooled to 60°C (the oil pump and vacuum pump continue to work during the cooling process), and then alkali-refined with sodium hydroxide solution, and then washed with ultrapure water to remove the sodium salt in the alkali refining process, and then adsorbed with an adsorbent to remove moisture and polar impurities. The adsorbent is composed of alkaline alumina, 3A molecular sieve, silica gel, and activated white clay in a mass ratio of 1:1:1:1. The amount of adsorbent added is 6wt% of the generated substrate, and the adsorption time is 50min. Then vacuum drying is performed, and the vacuum drying conditions are drying at 110 Pa and 70°C for 40h. Finally, membrane filtration is performed to generate trimethylolpropane octanoic acid oleic acid triester insulating liquid, wherein the filter membrane is a 0.25μm filter membrane.

[0064] Example 6

[0065] The present invention provides a method for preparing an insulating liquid for electrical equipment, comprising the following steps:

[0066] Step 1: add trimethylolpropane, octanoic acid, decanoic acid and oleic acid to a three-necked flask in sequence. The molar ratio of the sum of octanoic acid, decanoic acid and oleic acid to trimethylolpropane is 3.3:1, the molar ratio of the sum of octanoic acid and decanoic acid to oleic acid is 8:2, and the molar ratio of n-octanoic acid to n-decanoic acid is 4:6. Toluenesulfonic acid is then added as a catalyst, and the amount of p-toluenesulfonic acid added is 1.0 wt% of the total mass of the reaction substrate. Then, an esterification reaction is carried out under low pressure conditions. The esterification reaction device is as follows: Figure 1 As shown, install the three-necked flask in an oil bath, heat it to 60°C first, and stir the mixture with a magnetic stirrer to keep the reaction uniform. The stirring speed of the esterification reaction is 320 rpm, then start the vacuum system, and use a circulating water vacuum pump to adjust the vacuum degree of the reaction system to about 1 kPa. During the reaction, sample the acid value of the reactants regularly to monitor the progress of the reaction. After each reaction for 1 h, increase the temperature by 10~15°C, and continue the reaction for 1~2 h after increasing to 152°C to obtain the substrate after the esterification reaction, generating trimethylolpropane octanoic acid triester and water. The synthetic reaction formula is as follows: Figure 3 shown.

[0067] Step 2: After the esterification reaction, the substrate is subjected to vacuum distillation to remove the unreacted substrate, mainly to remove the unreacted acid, to obtain a distilled product. Specifically, the circulating water vacuum pump is replaced with an oil vacuum pump, the pressure in the three-necked flask is further reduced, and the flask is heated to a distillation temperature of 158° C. for 3.0 h.

[0068] Step three, such as Figure 2 As shown, the product after distillation is naturally cooled to 60°C (the oil pump and vacuum pump continue to work during the cooling process), and then alkali-refined with sodium hydroxide solution, and then washed with ultrapure water to remove the sodium salt in the alkali refining process, and then adsorbed with an adsorbent to remove moisture and polar impurities. The adsorbent is composed of alkaline alumina, 3A molecular sieve, silica gel, and activated white clay in a mass ratio of 1:1:1:1. The amount of adsorbent added is 4wt% of the generated substrate, and the adsorption time is 70min. Then vacuum drying is performed, and the vacuum drying conditions are drying at 90Pa and 80°C for 30h, and finally membrane filtration is performed to generate trimethylolpropane octanoic acid oleic acid triester insulating liquid, wherein the filter membrane is a 0.25μm filter membrane.

[0069] Comparative Example 1

[0070] This embodiment is the same as embodiment 1, except that no oil acid is added. The physical and chemical properties of the finally generated trimethylolpropane octanedioic acid triester are shown in Figure 5.

[0071] Table 5 Physical and chemical properties of trimethylolpropane octanoate triester

[0072]

[0073] Comparative Example 2

[0074] This embodiment is the same as embodiment 1, except that oleic acid is added. The physical and chemical properties of the finally generated trimethylolpropane oleate triester are shown in Figure 5.

[0075] Table 6 Physical and chemical properties of trimethylolpropane oleate triester

[0076]

[0077] Comparing the physical and chemical properties of the products of the embodiment of the present invention with those of comparative example 1, it can be seen that the present invention introduces oleic acid on the basis of octanolic acid, which can reduce the ignition point of the insulating liquid. However, as the proportion of oleic acid increases, the kinematic viscosity also increases. In actual use, embodiment 1 is used as the optimal embodiment. In addition, comparing the physical and chemical properties of the products of the embodiment of the present invention with those of comparative example 2, it can be seen that although the ignition point of single oleic acid is high, the kinematic viscosity is also high, and it is not suitable for direct use in the preparation of insulating liquid. The present invention introduces long-chain fatty acids (oleic acid) into trimethylolpropane molecules. By adjusting the proportion of oleic acid, the viscosity, flash point, pour point and other physical and chemical properties of triester oil can be adjusted. The generated polyol ester changes the chemical structure of trimethylolpropane, which not only overcomes the problem of low ignition point of trimethylolpropane, but also does not excessively increase the viscosity of the oil product, improves the stability and high-voltage resistance of the insulating oil, and is suitable for electrical equipment such as transformers.

[0078] The above are only preferred embodiments of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing an insulating liquid for electrical equipment, characterized in that: The following steps are involved: Adding trimethylolpropane, octanoic acid, decanoic acid and oleic acid into a reaction container in sequence, and then adding toluenesulfonic acid as a catalyst to carry out an esterification reaction under low pressure conditions to obtain a substrate after the esterification reaction; Using vacuum distillation to remove unreacted substrate from the substrate after the esterification reaction to obtain a distilled product; The distilled product is naturally cooled and then alkali-refined with sodium hydroxide solution, then washed with ultrapure water to remove the sodium salt in the alkali-refining process, then adsorbed with an adsorbent to remove moisture and polar impurities, then vacuum dried, and finally filtered with a membrane to produce trimethylolpropane octanoic acid decanoic acid triester insulating liquid.

2. The method for preparing insulating liquid for electrical equipment according to claim 1, characterized in that: The initial temperature of the esterification reaction is 55~65°C. After each reaction of 1~1.5 h, the temperature is increased by 10~15°C. After increasing to 148~152°C, the reaction is continued for 1~2 h.

3. The method for preparing insulating liquid for electrical equipment according to claim 1, characterized in that: The stirring speed of the esterification reaction is 280~320 rpm, and the pressure of the esterification reaction is 1~3 kPa.

4. The method for preparing insulating liquid for electrical equipment according to claim 1, characterized in that: The amount of p-toluenesulfonic acid added is 1.0~1.4 wt% of the total mass of the reaction substrate.

5. The method for preparing insulating liquid for electrical equipment according to claim 1, characterized in that: The molar ratio of the sum of caprylic acid, capric acid and oleic acid to trimethylolpropane is 3.1-3.3:1, the molar ratio of the sum of caprylic acid and capric acid to oleic acid is 8:2-2:8, and the molar ratio of n-caprylic acid to n-decanoic acid is 4:5-4:

7.

6. The method for preparing insulating liquid for electrical equipment according to claim 1, characterized in that: The distillation temperature is 158~160℃ and the distillation time is 2.5~3.5h.

7. The method for preparing insulating liquid for electrical equipment according to claim 1, characterized in that: The adsorbent is composed of basic alumina, 3A molecular sieve, silica gel and activated clay in a mass ratio of 1:1:1:

1. The amount of the adsorbent added is 4-6wt% of the generated substrate, and the adsorption time is 50-70min.

8. The method for preparing insulating liquid for electrical equipment according to claim 1, characterized in that: The vacuum drying conditions are 90~110 Pa and 70~80℃ for 30~40h.

9. The method for preparing insulating liquid for electrical equipment according to claim 1, characterized in that: The filter membrane used was 0.25 μm.

10. An insulating liquid for electrical equipment, characterized in that: The insulating liquid for electrical equipment is prepared by the method for preparing the insulating liquid for electrical equipment according to any one of claims 1 to 9.

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