Natural ester insulating oil and preparation method thereof

Abstract

The invention provides natural ester insulating oil, and relates to the field of insulating oil. The modified vegetable oil comprises the following components in percentage by mass: 95-98% of modified vegetable oil, 0.05-0.5% of an antioxidant and the balance of other additives. According to the insulating oil provided by the invention, the vegetable oil is used as a basic raw material and is matched with the antioxidant and other additives, and natural ester provided by the vegetable oil has higher moisture absorption capacity and can delay aging of insulating paper; low toxicity causes little harm to ecology and human bodies; high temperature resistance: when a cellulose insulating material is matched, higher operating temperature is allowed. And the ignition point is high (generally higher than 300 DEG C), so that the fire risk is reduced, and the safety is improved.

Description

Technical Field

[0001] The present invention relates to the field of insulating oils, and in particular, to a natural ester insulating oil and a preparation method thereof. Background Art

[0002] Insulating oil is an important liquid insulating medium in oil-immersed transformers, mainly playing roles such as insulation, heat dissipation, and arc quenching. The performance of insulating oil determines the environmental protection characteristics, fire prevention ability of the transformer, and affects its service life.

[0003] Insulating oils can be classified into mineral oils and synthetic oils according to types. Mineral insulating oils include naphthenic mineral insulating oils, paraffinic mineral insulating oils, etc., and synthetic insulating oils include silicone oils, synthetic esters, and vegetable insulating oils, etc. To accelerate the development and utilization of biomass energy, natural ester insulating oil is one of the development directions of biomass resources. Secondly, natural ester insulating oil can effectively solve the air pollution problem generated during the recycling and treatment of waste mineral insulating oil.

[0004] However, at present, the antioxidant property of natural ester insulating oil on the market is poor. Summary of the Invention

[0005] An object of the present invention is to provide a natural ester insulating oil, which has the advantages of good antioxidant stability, low cost, and environmental protection and no pollution.

[0006] Another object of the present invention is to provide a preparation method of a natural ester insulating oil, in which the antioxidant is uniformly dispersed and the stability of the insulating oil is good.

[0007] The present invention solves its technical problems by adopting the following technical solutions.

[0008] On the one hand, an embodiment of the present invention provides a natural ester insulating oil, including the following raw materials:

[0009] 95 - 98% of modified vegetable oil, 0.05 - 0.5% of antioxidant, and the balance is other additives.

[0010] In some embodiments of the present invention, the antioxidant is one or a mixture of more of butylated hydroxyanisole, dibutylhydroxytoluene, tert-butylhydroquinone, and rosemary extract.

[0011] In some embodiments of the present invention, the other additives are one or more of citric acid, vitamin E, tea polyphenols, antistatic agents, corrosion inhibitors, pour point depressants, and passivators.

[0012] In some embodiments of the present invention, the modified vegetable oil is prepared by the following method:

[0013] Mix vegetable oil with alcohol, and under the action of an acid or enzyme catalyst, transesterification occurs to produce fatty acid esters and glycerol; after the reaction is completed, separate, wash, dry, decolorize, filter, and separate to obtain the modified vegetable oil.

[0014] In some embodiments of the present invention, the vegetable oil is one of soybean oil, rapeseed oil, palm kernel oil, and coconut oil.

[0015] In some embodiments of the present invention, the decolorization includes: heating the dried product to 80 - 90 °C, stirring under a vacuum of -0.08 to -0.1 MPa for 10 - 20 minutes to ensure that the moisture content is < 0.05%; adding an adsorbent and stirring at 60 - 100 rpm for 20 - 30 minutes, and drying at 120 °C for 2 hours to remove the moisture.

[0016] In some embodiments of the present invention, the reaction temperature for adding an acid catalyst is 80 - 120 °C, the reaction time is 4 - 8 h, and the vacuum degree of the reaction system is -0.05 to -0.08 MPa.

[0017] In some embodiments of the present invention, the reaction temperature for adding an enzyme catalyst is 40 - 60 °C, the reaction time is 12 - 24 h, and the vacuum degree of the reaction system is -0.05 to -0.08 MPa.

[0018] On the other hand, in the embodiments of the present invention, a method for preparing a natural ester insulating oil is provided, including the following steps:

[0019] Heat the modified vegetable oil to 60 - 70 °C;

[0020] Mix the antioxidant and other additives with a solvent separately and uniformly, and then drop them into the modified vegetable oil and disperse them evenly;

[0021] Vacuum remove the solvent and filter to obtain the natural ester insulating oil.

[0022] In some embodiments of the present invention, the temperature for vacuum removing the solvent is ≤ 80 °C, and the vacuum degree is ≤ 3 kPa.

[0023] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0024] The insulating oil provided by the present invention uses vegetable oil as the basic raw material, combined with an antioxidant and other additives. The natural ester provided by the vegetable oil has a stronger moisture absorption capacity, which can delay the aging of insulating paper; it has low toxicity and little harm to the ecology and human body; it is high-temperature resistant: when combined with cellulose insulating materials, it allows a higher operating temperature. It has a high flash point (usually > 300 °C): reducing the fire risk and enhancing safety. Brief Description of the Drawings

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0026] Figure 1 It is a schematic flow chart for the preparation of the natural ester insulating oil according to the embodiments of the present invention;

[0027] Figure 2 It is a comparison chart of the water content of insulating paper. Specific embodiments

[0028] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0029] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to specific embodiments.

[0030] The embodiments of the present invention provide a natural ester insulating oil, which includes the following raw materials:

[0031] 95 - 98% of modified vegetable oil, 0.05 - 0.5% of antioxidant, and the balance is other additives.

[0032] The main molecule of vegetable oil is triglyceride, which contains an ester bond in the molecule. Its molecular structure is more asymmetric than that of mineral oil, and its molecular polarity is greater than that of mineral oil; it contains C = C double bonds in the molecule; its molecular weight is much larger than that of mineral insulating oil. The content of triglyceride in primary vegetable oil is high. Therefore, using primary vegetable oil as the source of triglyceride, its raw materials are extensive and the price is low, which can effectively reduce the production cost of insulating oil.

[0033] In some embodiments of the present invention, the antioxidant is one or a mixture of butylated hydroxyanisole, dibutylhydroxytoluene, tert-butylhydroquinone, rosemary extract, etc. The above antioxidants are all food-grade, with high safety and no toxic side effects.

[0034] In some embodiments of the present invention, the other additives are one or more of citric acid, vitamin E, tea polyphenols, antistatic agents, corrosion inhibitors, pour point depressants, and metal deactivators. Citric acid, vitamin E, and tea polyphenols can act synergistically with antioxidants. Citric acid can reduce the growth rate of the acid value of insulating oil by 60%, improving the antioxidant property of the insulating oil. Vitamin E can act synergistically with antioxidants to scavenge free radicals, and the dielectric strength of the insulating oil is increased by 5%-8%; rosemary extract and tea polyphenols act together, and the oxidation stability of the insulating oil can reach 300-400 hours.

[0035] The metal deactivator is benzotriazole (BTA). The corrosion inhibitor is a phosphate ester compound. The pour point depressant is polymethacrylate.

[0036] In some embodiments of the present invention, the modified vegetable oil is prepared by the following method:

[0037] Mix the vegetable oil with alcohol, and under the action of an acid or enzyme catalyst, carry out a transesterification reaction to generate fatty acid esters and glycerol; after the reaction is completed, separate, wash, dry, decolorize, filter, and separate to obtain the modified vegetable oil.

[0038] In some embodiments of the present invention, the vegetable oil is one of soybean oil, rapeseed oil, palm kernel oil, and coconut oil.

[0039] In some embodiments of the present invention, the decolorization includes: heating the dried product to 80-90 °C, stirring for 10-20 minutes under a vacuum of -0.08 to -0.1 MPa to ensure that the moisture content < 0.05%; adding an adsorbent and stirring at 60-100 rpm for 20-30 minutes, and drying at 120 °C for 2 hours to remove the moisture.

[0040] In some embodiments of the present invention, the reaction temperature for adding an acid catalyst is 80-120 °C, the reaction time is 4-8 h, and the vacuum degree of the reaction system is -0.05 to -0.08 MPa.

[0041] In some embodiments of the present invention, the reaction temperature for adding an enzyme catalyst is 40-60 °C, the reaction time is 12-24 h, and the vacuum degree of the reaction system is -0.05 to -0.08 MPa.

[0042] On the other hand, in the embodiments of the present invention, a method for preparing a natural ester insulating oil is provided, including the following steps:

[0043] Heat the modified vegetable oil to 60-70 °C;

[0044] Mix the antioxidant and other additives with a solvent respectively and uniformly, and then drop them into the modified vegetable oil and disperse them uniformly;

[0045] The natural ester insulating oil is obtained by vacuum solvent removal and filtration.

[0046] In some embodiments of the present invention, the temperature for vacuum solvent removal is ≤80 °C and the vacuum degree is ≤3 kPa.

[0047] The features and performance of the present invention are further described in detail below in conjunction with embodiments.

[0048] Example 1

[0049] 1. Refine soybean oil by the following method to obtain modified soybean oil:

[0050] (1) Esterification reaction: Put soybean oil and ethanol into the reaction kettle at a molar ratio of 1:6, add an acidic catalyst, stir and mix evenly, control the temperature in the reaction kettle at 110 ± 2 °C, the vacuum degree at -0.08 MPa, and continuously discharge the product: water. React for 8 h. Acid value detection: Terminate the reaction when the acid value drops to <1 mg KOH / g. Refractive index monitoring: Consider the reaction completed when the refractive index is stable;

[0051] (2) Separation and purification

[0052] Glycerol separation: After the reaction, glycerol will precipitate at the bottom as a by-product and is separated by a separation device.

[0053] Washing: Wash the fatty acid ester with warm water to remove residual catalyst and other impurities.

[0054] Drying: Dry the washed fatty acid ester to remove moisture.

[0055] (3) Refining and filtration

[0056] Heat the fatty acid ester to 90 ± 2 °C, stir for 20 minutes under -0.1 MPa vacuum to ensure the moisture is <0.05%. Add activated clay, stir for 30 minutes at 100 rpm, and dry at 120 °C for 2 hours to remove moisture.

[0057] Filtration separation: Precoat filtration (for plate and frame filter press), precoat a layer of diatomite on the filter cloth surface (thickness 1 - 2 mm). Recycle the oil until the filter cake is formed to ensure smooth filtration.

[0058] Formal filtration: Pressure: 0.2 MPa. Transparency requirement of the filtered oil: No visible suspended matter.

[0059] 2. Prepare the natural ester insulating oil of this example according to the following ratio and method:

[0060] Modified soybean oil 98%, antioxidant 0.1%, pour point depressant (polymethacrylate) 1.9%.

[0061] Heat the refined modified soybean oil mentioned above to 60 ± 5 °C and continuously stir (rotation speed 300 rpm).

[0062] Dissolve the antioxidant TBHQ (tert-butylhydroquinone) in a small amount of ethanol (solvent dosage ≤ 1%), slowly add it dropwise to the modified soybean oil, and stir for 1 hour until homogeneous. Then add the pour point depressant and stir evenly. Subsequently, carry out vacuum removal of the residual solvent (temperature ≤ 80 °C, vacuum degree ≤ 3 kPa), filter, and the natural ester insulating oil is obtained.

[0063] Example 2

[0064] Prepare the natural ester insulating oil of this example according to the following ratio and method:

[0065] 98% of the modified soybean oil prepared in Example 1, 0.1% antioxidant, 0.05% citric acid, 1.85% pour point depressant (polymethacrylate).

[0066] Mix the citric acid evenly with the modified soybean oil. Then dissolve the antioxidant TBHQ (tert-butylhydroquinone) in a small amount of ethanol (solvent dosage ≤ 1%), slowly add it dropwise to the modified soybean oil, and stir for 1 hour until homogeneous. Then add the pour point depressant and stir evenly. Subsequently, carry out vacuum removal of the residual solvent (temperature ≤ 80 °C, vacuum degree ≤ 3 kPa), filter, and the natural ester insulating oil is obtained.

[0067] Example 3

[0068] Prepare the natural ester insulating oil of this example according to the following ratio and method:

[0069] 98% of the modified soybean oil prepared in Example 1, 0.1% antioxidant, 0.3% rosemary extract, 0.1% tea polyphenols, 1.5% pour point depressant (polymethacrylate).

[0070] Dissolve the rosemary extract and tea polyphenols in propylene glycol (solvent dosage 2% - 3%). Add the mixed solution to the modified soybean oil at 50 °C and disperse ultrasonically (20 kHz, 30 minutes). Centrifuge to remove the undispersed particles and filter. The natural ester insulating oil is obtained.

[0071] Example 4

[0072] The difference from Example 1 is that the natural ester insulating oil is prepared according to the following ratio:

[0073] 95% modified soybean oil, 0.5% antioxidant, 4.5% pour point depressant (polymethacrylate)

[0074] All the remaining preparation steps are the same as those in Example 1.

[0075] Example 5

[0076] It is different from Example 2 in that the citric acid in Example 2 is replaced by tea polyphenols, and the remaining preparation methods are the same as those in Example 2.

[0077] Example 6

[0078] It is different from Example 1 in that the antioxidant in Example 1 is replaced by butylated hydroxyanisole, and the remaining preparation methods are the same as those in Example 1.

[0079] Example 7

[0080] It is different from Example 1 in that the antioxidant in Example 1 is replaced by dibutylhydroxytoluene, and the remaining preparation methods are the same as those in Example 1.

[0081] Example 8

[0082] It is different from Example 1 in that the soybean oil in Example 1 is replaced by rapeseed oil, and the remaining preparation methods are the same as those in Example 1.

[0083] Example 9

[0084] 1. Refine soybean oil according to the following method to obtain modified soybean oil:

[0085] (1) Esterification reaction: Put soybean oil and ethanol into the reaction kettle at a molar ratio of 1:6, add an acidic catalyst, stir and mix evenly, control the temperature in the reaction kettle at 80 ± 2 °C, the vacuum degree at -0.05 MPa, and continuously discharge the product: water, react for 8 h, and stop the reaction when the acid value is detected: the acid value drops to <1 mg KOH / g. Refractive index monitoring: The reaction is considered complete when the refractive index is stable;

[0086] (2) Separation and purification

[0087] Glycerol separation: After the reaction, glycerol will precipitate at the bottom as a by-product and be separated by a separation device.

[0088] Washing: Wash the fatty acid ester with warm water to remove the residual catalyst and other impurities.

[0089] Drying: Dry the washed fatty acid ester to remove moisture.

[0090] (3) Refining and filtration

[0091] Heat the fatty acid ester to 80 ± 2 °C, stir for 10 minutes under -0.08 vacuum to ensure that the moisture content is <0.05%. Add activated clay, stir at 100 rpm for 20 minutes, and dry at 120 °C for 2 hours to remove moisture.

[0092] Filtration and separation: Pre - coating filtration (for plate - frame filter presses), diatomaceous earth is pre - coated on the surface of the filter cloth (with a thickness of 1 - 2 mm). Recirculate the oil until the filter cake is formed to ensure smooth filtration.

[0093] Formal filtration: Pressure: 0.2 MPa. Requirement for the transparency of the filtered oil product: No visible suspended matter.

[0094] Experimental examples

[0095] Taking the natural ester insulating oils and modified soybean oils of Examples 1 - 3 as objects, the oxidation induction period, acid value, and dielectric strength were tested, and the results are shown in Table 1.

[0096] Table 1 Performance of each insulating oil

[0097]

[0098] It can be concluded from Table 1 that for the natural ester insulating oils of Examples 1 - 3, the initial acid value control: The base oils of all schemes have been pretreated (de - acidification), and the initial acid value ≤ 0.05 mg KOH / g, meeting the insulating oil standard (such as the acid value requirement in IEC 62770 is < 0.1 mg KOH / g). Acid value increase after oxidation: Example 1 (TBHQ): The acid value increases the slowest, with the best antioxidant effect; Example 2 (synergistic formulation): Citric acid enhances the antioxidant efficiency by chelating metal ions, and the acid value control is better than that of single TBHQ; Example 3 (natural antioxidant): The acid value increases relatively fast, but it has outstanding environmental friendliness and is suitable for scenarios sensitive to toxicity. Change in dielectric strength: Excessive antioxidant or poor dispersion may lead to a decrease in dielectric strength (such as undissolved TBHQ particles); The synergistic formulation of Example 2 has the best dielectric strength retention after oxidation due to its better antioxidant effect; The natural antioxidant of Example 3 may have a slightly lower dielectric strength due to the residue of polar components.

[0099] Regarding the flash point, in the example of 0.1% TBHQ, TBHQ is a phenolic antioxidant and has no negative impact on the flash point; The high - purity transesterification product reduces volatile components. In the example of 0.1% TBHQ + citric acid, citric acid may slightly increase polar components, but the impact is not significant; The flash point still remains high. In the example of 0.3% rosemary + 0.1% tea polyphenols, the rosemary extract contains a small amount of volatile terpenoids, which may slightly reduce the flash point.

[0100] Immerse the dried insulating paper in oil samples (mineral oil, natural ester insulating oil of Example 1), place the samples in a constant - temperature oven, set at 150 °C, with an aging time gradient. After aging, take out the oil - paper samples and let them stand and cool to room temperature. Use a syringe to extract the oil sample, avoid contact with air, and immediately conduct a moisture test. Obtain the change law of the water content of mineral oil and natural ester during high - temperature aging. Analyze the water absorption differences of insulating paper in different oil media. The results are asFigure 2 as shown. Moisture saturation : natural ester = 1057 ppm, mineral oil = 60 ppm. The water absorption capacity of natural ester is 16 times that of mineral oil. The moisture balance effect can delay the aging of insulating paper by transferring moisture from the insulating paper to the insulating liquid.

[0101] In summary, the insulating oil provided by the embodiments of the present invention uses vegetable oil as the basic raw material, combined with antioxidants and other additives, and the natural ester provided by the vegetable oil has a stronger moisture absorption capacity.

[0102] On the other hand, the natural ester insulating oil provided by the present invention has: (1) low toxicity, little harm to the ecosystem and human body; (2) high temperature resistance: when combined with cellulose insulating materials, it allows a higher operating temperature. (3) high flash point (usually > 300 °C): reducing the fire risk and improving safety, as shown in Table 1. The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

Claims

1. A natural ester insulating oil, characterized in that, By mass fraction, it includes the following raw materials: Modified vegetable oil 95 - 98%, antioxidant 0.05 - 0.5%, and the balance is other additives.

2. The natural ester insulating oil according to claim 1, characterized in that, The antioxidant is one or a mixture of butylated hydroxyanisole, dibutylhydroxytoluene, tert-butylhydroquinone, rosemary extract, etc.

3. The natural ester insulating oil according to claim 1, wherein, The other additives are one or more of citric acid, vitamin E, tea polyphenols, antistatic agent, anti-corrosion agent, pour point depressant, passivator, etc.

4. The natural ester insulating oil according to claim 1, characterized in that, The modified vegetable oil is prepared by the following method: Mix the vegetable oil with alcohol, and under the action of an acid or enzyme catalyst, carry out a transesterification reaction to generate fatty acid esters and glycerol; after the reaction is completed, separate, wash, dry, decolorize, filter, and separate to obtain the modified vegetable oil.

5. The natural ester insulating oil according to claim 4, characterized in that, The vegetable oil is one of soybean oil, rapeseed oil, palm kernel oil, coconut oil.

6. The natural ester insulating oil according to claim 4, characterized in that The decolorization includes: heating the dried product to 80 - 90 °C, stirring for 10 - 20 minutes under a vacuum of -0.08 to -0.1 MPa to ensure that the moisture content < 0.05%; adding an adsorbent and stirring at 60 - 100 rpm for 20 - 30 minutes, and drying at 120 °C for 2 hours to remove moisture.

7. The natural ester insulating oil according to claim 4, characterized in that, The reaction temperature for adding an acid catalyst is 80 - 120 °C, the reaction time is 4 - 8 h, and the vacuum degree of the reaction system is -0.05 to -0.08 MPa.

8. The natural ester insulating oil according to claim 4, wherein, The reaction temperature for adding an enzyme catalyst is 40 - 60 °C, the reaction time is 12 - 24 h, and the vacuum degree of the reaction system is -0.05 to -0.08 MPa.

9. A preparation method of a natural ester insulating oil according to any one of claims 1-8, characterized in that, It includes the following steps: Heat the modified vegetable oil to 60 - 70 °C; Mix the antioxidant and other additives with a solvent evenly respectively, and then drop them into the modified vegetable oil and disperse evenly; Vacuum remove the solvent and filter to obtain the natural ester insulating oil.

10. The preparation method of the natural ester insulating oil according to claim 9, characterized in that, The temperature for vacuum removing the solvent ≤ 80 °C, and the vacuum degree ≤ 3 kPa.

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