Cottonseed vegetable insulating oil and preparation method thereof

Abstract

The invention provides cottonseed vegetable insulating oil and a preparation method thereof.The preparation method comprises the following steps that S1, cottonseed is extracted to obtain cottonseed mixed oil, and the cottonseed mixed oil is degummed to obtain a first oil sample; s2, performing alkali refining on the first oil sample to obtain a second oil sample; s3, performing ultraviolet radiation on the second oil sample, applying a static magnetic field, and adding an adsorbent to obtain a third oil sample; s4, performing low-temperature crystallization fractionation on the third oil sample; and S5, adding a nano additive, uniformly mixing, and dehydrating and degassing to obtain the cottonseed vegetable insulating oil. The prepared cottonseed plant insulating oil has the advantages of obviously reduced acid value, extremely low dielectric loss, high refining rate, excellent breakdown voltage and low-temperature performance, high use safety and suitability for transformers of various voltage grades.

Description

Technical Field

[0001] This invention relates to the field of cottonseed plant insulating oil technology, and more particularly to a cottonseed plant insulating oil and its preparation method. Background Technology

[0002] For a long time, the issue of cottonseed disposal has constrained the further development of the cotton industry. Large quantities of cottonseed remain underutilized, resulting not only in resource waste but also a failure to generate corresponding economic value.

[0003] As an environmentally friendly and renewable energy product, plant-based insulating oil has significant advantages such as low carbon emissions, environmental friendliness, and the ability to replace traditional petroleum-based insulating oil.

[0004] With increasingly stringent environmental regulations and the green transformation of power equipment, natural ester insulating oils are gradually replacing mineral insulating oils due to their advantages such as biodegradability, high flash point, and low toxicity. Cottonseed oil, as a potential raw material, is rich in unsaturated fatty acids and natural antioxidants, possessing good electrical insulation potential. However, unrefined crude cottonseed oil contains a large amount of free fatty acids, gossypol, phospholipids, and colloids, leading to defects such as low refining efficiency, high acid value, excessive dielectric loss factor, and poor low-temperature fluidity when directly applied to insulating oils, severely restricting its industrial application. Summary of the Invention

[0005] In view of this, the present invention proposes a cottonseed plant insulating oil and its preparation method. The prepared cottonseed plant insulating oil has a significantly reduced acid value, extremely low dielectric loss, high refining rate, excellent breakdown voltage and low temperature performance, high safety in use, and is suitable for transformers of various voltage levels.

[0006] The technical solution of this invention is implemented as follows: In a first aspect, the present invention provides a method for preparing cottonseed plant insulating oil, comprising the following steps: Step S1: Extract cottonseed to obtain cottonseed mixed oil, and degumm the cottonseed mixed oil to obtain the first oil sample; Step S2: The first oil sample is subjected to alkali refining to obtain a second oil sample; Step S3: Irradiate the second oil sample with ultraviolet light, apply a static magnetic field, add adsorbent and mix well to obtain the third oil sample; Step S4: Perform low-temperature crystallization fractionation on the third oil sample; Step S5: Add nano-additives, mix well, and dehydrate and degas to obtain cottonseed plant insulating oil.

[0007] Based on the above technical solution, the cottonseed is further pretreated, which includes the following steps: separating the cottonseed hulls and kernels by using a hulling machine and a multi-stage stepped sieve; softening the cottonseed kernels with steam at 50°C; mechanically pressing the cottonseed kernels; and finally, hot air drying to obtain cottonseed meal with a moisture content of less than 3%.

[0008] Based on the above technical solution, the extraction further includes extracting the above cottonseed meal by low-temperature physical spiral pressing to obtain a solid-liquid mixture of crude cottonseed oil and crushed cottonseed kernels, then adding n-hexane and carrying out the extraction reaction at 60°C for 2-4 hours, followed by vacuum filtration in an evaporator to obtain cottonseed mixed oil. The mass ratio of n-hexane to the solid-liquid mixture is (0.8~1.1):1.

[0009] Based on the above technical solutions, the degumming further includes adding phosphoric acid or citric acid to the cottonseed oil mixture, mixing it well, and then adding water for washing.

[0010] Based on the above technical solutions, the alkaline agent used in the alkali refining process further includes sodium hydroxide, sodium silicate, sodium bentonite, and activated carbon. The mass ratio of sodium hydroxide, sodium silicate, sodium bentonite, and activated carbon is (6~8):(1~2):(3~5):(0.2~0.5). The mass ratio of alkali agent to cottonseed oil mixture is (5%~10%): 1.

[0011] After extraction, filtration, degumming, and alkali refining, the resulting mixed oil has low viscosity and density, facilitating uniform mixing. This process neutralizes free fatty acids while removing free gossypol. Gossypol binds with soapstock and precipitates, which is then removed through settling. This reduces protein denaturation in cottonseed oil caused by high-temperature evaporation and solvent impregnation. Denatured proteins remaining in the oil can be toxic, and this process also reduces oxidation and degradation of electrical properties caused by high temperatures. This invention uses sodium hydroxide to alkalize sodium-based bentonite, enhancing its activity and contact with free fatty acids, resulting in a more complete reaction and faster removal of impurities, thus improving the oil refining rate. Simultaneously, ultrasonic-assisted alkali refining lowers the refining temperature, ensures uniform mixing, reduces the loss of neutral oil caused by high temperatures, further improving the refining rate. Furthermore, ultrasonic treatment alters the molecular structure and crystallization kinetics of the vegetable oil, lowering the pour point.

[0012] Alkali refining is a crucial step in vegetable oil refining. This invention uses alkali to neutralize free fatty acids in crude oil, generating fatty acid salts (soap residue), while simultaneously adsorbing impurities such as phospholipids, pigments, and proteins, achieving deacidification and preliminary purification. This process directly affects the acid value, color, stability, and refining yield of the oil, making it a core step determining the quality of the finished oil. Cottonseed oil has a large fluctuation in free fatty acid content (1-5%), and using NaOH alone can easily lead to localized over-alkaliening; secondly, cotton soap easily coats neutral oil. The combined use of sodium silicate can precisely control the depth of the saponification reaction, avoiding localized over-alkaliening leading to neutral oil saponification, and reducing neutral oil hydrolysis better preserves the natural antioxidant tocopherol in cottonseed oil, thus reducing neutral oil loss and refining consumption during alkali refining. Furthermore, the generated silica colloid has a high specific surface area, which can coat free fatty acid soap particles. The silica soap has stronger adsorption capacity, removing more pigments and impurities. The addition of sodium bentonite and activated carbon further accelerates impurity removal, making the alkali refining process a combination of chemical refining and adsorption refining. The interlayer structure of bentonite enhances the sedimentation of soapstock through ion exchange adsorption of sodium soap and non-hydrated phospholipids, accelerating solid-liquid separation and improving centrifugation efficiency. This reduces the extensive water washing process required in traditional alkali refining, minimizing losses and increasing the overall refining rate. The addition of activated carbon, with its large specific surface area and porous structure, effectively captures pigments and odors in cottonseed oil. In summary, the combined use of these four substances rapidly settles soapstock through saponification, neutralization, and adsorption, reducing losses from neutral oil and water washing, while also reducing the number of washes. Compared to conventional methods involving multiple washes until the wastewater is clear, this method reduces waste and improves the refining rate. The intermittent ultrasonic-assisted alkali refining process not only helps the system mix more evenly but also generates vibrations at the molecular level during refining, producing repeated compression and stretching forces and releasing more energy, thereby breaking the molecular bonds between structures. As the ultrasonic treatment time varies, the energy input brings thermal and vibrational energy. The vibrational energy is converted into energy to form molecular cavitation. This energy conversion, along with the resulting microfluidics and vibrations, leads to molecular dislocations. Due to the change in molecular composition, the pour point temperature of the cottonseed oil sample decreases compared to its initial value.

[0013] Based on the above technical solution, the alkali refining further includes the following steps: maintaining the temperature of the first oil sample at 60°C, adding alkali agent using the spray alkali addition method, stirring, and simultaneously applying ultrasound at a frequency of 20~40kHz and a power of 300w.

[0014] Based on the above technical solutions, the adsorbent further includes magnesium silicate, basic alumina, and amylopectin; The mass ratio of magnesium silicate, basic alumina, and amylopectin is (2~5):(3~5):(1~2); the mass ratio of the adsorbent to the second oil sample is (2%~5%):1.

[0015] Magnesium silicate micropores exhibit strong adsorption for polar pigment molecules such as gossypol, mechanically trapping colloids and large molecular oxidized polymers. The alkaline sites of basic alumina react with carboxylic acids to neutralize the acidic environment and attack the electronic system of chromophores such as conjugated alkenes through nucleophilic reactions, degrading them into colorless small molecules, which are then more easily adsorbed by magnesium silicate micropores. Meanwhile, amylopectin encapsulates the adsorbed pigment molecules through hydroxyl groups, preventing re-aggregation and maintaining the low color stability of the system.

[0016] When exposed to ultraviolet light, the energy of 254 nm UV photons is absorbed by oxygen molecules, causing the ground-state triplet oxygen to transition to the more oxidizing excited-state singlet oxygen. This activates the aldehyde group in gossypol, breaking the carbon-hydrogen bond and forming a stable carboxyl group with the oxygen atom in the oxygen molecule. This makes it easier for the weakly basic adsorbent to capture the carboxyl group, further removing gossypol during the adsorption process. Meanwhile, the magnetic field can induce free radicals in glycerides to shift from disordered thermal motion to spin-oriented alignment, promoting easier bimolecular collisions and recombination to form inactive dimers. Through synergistic adsorption using ultraviolet light and a magnetic field, not only is the gossypol content in cottonseed oil reduced directionally, but some free radicals in the oil are also deactivated, prolonging the oxidation induction period of cottonseed oil and reducing the increased polarity loss caused by traditional antioxidants.

[0017] Based on the above technical solution, the second oil sample is further heated before ultraviolet irradiation. The wavelength of the ultraviolet irradiation is 254nm, the time is 10~30min, and the magnetic induction intensity of the static magnetic field is 0.5~1T.

[0018] Based on the above technical solution, the heating further includes heating the second oil sample to 70°C.

[0019] Based on the above technical solution, after adding the adsorbent, the mixture is stirred at a speed of 60~70 r / min for 3 hours, and then vacuum adsorption filtration is performed with a vacuum degree of 30~50 kPa.

[0020] Based on the above technical solution, further, step S5 includes adding a nano-additive to the oil sample obtained in step S4 at 70°C. The nano-additive includes any one of nano-silica modified with a silane coupling agent, boron nitride, or iron tetroxide. The mass ratio of the nano-additive to the oil sample obtained in step S4 is (0.01%~0.3%):1.

[0021] By adding different nanoparticles modified with siloxane, the compatibility between nanoparticles and oil is enhanced by connecting the nanoparticles with siloxane. Furthermore, the silanol groups can adsorb acid molecules in the oil due to their strong surface electrostatic potential and form hydrogen bonds with them, thus slowing down the hydrolysis of ester molecules by acids. The nanoparticles inhibit the expansion of discharge channels and stabilize the dispersion of charges through their own electron trapping effect, thereby improving the dielectric properties of the oil.

[0022] Based on the above technical solutions, the silane coupling agent further includes any one of KH550 (γ-aminopropyltriethoxysilane), KH560 (γ-glycidoxypropyltrimethoxysilane), and KH570 (γ-methacryloyloxypropyltrimethoxysilane).

[0023] Based on the above technical solutions, the particle size of nano-silica, boron nitride, or iron oxide is further improved to be 50~500nm.

[0024] Based on the above technical solutions, the preparation method of the nano-additive further includes the following steps: Take 0.2-0.5 g of nano-silica, boron nitride, or iron oxide and add it to 200 mL of 75 wt% ethanol aqueous solution. Disperse the solution by ultrasonication to form a suspension. Then add 0.2-0.5 mL of silane coupling agent to the suspension. Stir and condense the solution in an oil bath at 70℃-100℃ for 8-24 h. After the solution cools, filter out the precipitate and dry it to obtain the nano-additive.

[0025] Based on the above technical solution, the low-temperature crystallization and fractionation method further includes: lowering the third oil sample from room temperature to 0°C at a rate of 0.5°C / min, then lowering it to -10°C at a rate of 2°C / h, maintaining the temperature for crystallization for 6-18h, and centrifuging.

[0026] Cottonseed oil has a relatively high pour point compared to other oils, resulting in poor low-temperature performance. It contains a high content of saturated fatty acid palmitic acid (usually around 26%). Removing the high-melting-point palmitic acid through low-temperature crystallization and fractionation can further improve the low-temperature performance of cottonseed oil, thereby increasing the pour point and low-temperature viscosity of the oil. This makes it better suited to cold weather conditions that may be encountered during use and expands its application range in extremely cold regions.

[0027] Based on the above technical solutions, the dehydration and degassing method further includes: vacuum drying with a vacuum degree of 50~80kPa.

[0028] Secondly, the present invention also provides a cottonseed plant insulating oil prepared by the above method. Compared with the prior art, the present invention has the following beneficial effects: This invention provides a cottonseed plant insulating oil and its preparation method. The prepared cottonseed plant insulating oil has a significantly reduced acid value, extremely low dielectric loss, high refining rate, excellent breakdown voltage and low temperature performance, and high safety in use. It is suitable for transformers of various voltage levels. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1 This embodiment provides a cottonseed plant insulating oil, wherein the alkali agent includes sodium hydroxide, sodium silicate, sodium bentonite and activated carbon in a mass ratio of 6:2:3:0.3, and the mass ratio of alkali agent to cottonseed mixed oil is 8%:1.

[0031] The adsorbent consists of magnesium silicate, basic alumina, and amylopectin in a mass ratio of 3:3:2, and the mass ratio of the adsorbent to the second oil sample is 3%:1.

[0032] Its preparation method includes the following steps: S1. Physical Separation: Pre-treatment of cottonseed involves separating the husks and kernels using a hulling machine and a multi-stage stepped sieve. After softening with steam at 50°C, the cottonseed kernels are mechanically crushed. Finally, hot air drying is used to obtain cottonseed meal with a moisture content of less than 3%.

[0033] S2. Extracting crude oil: The cottonseed meal from step S1 is extracted by low-temperature physical screw pressing to obtain virgin cottonseed crude oil and a solid-liquid mixture formed by crushed cottonseed kernels. Hexane at a mass ratio of 1:1 and the above solid-liquid mixture were added and extracted at 60°C. The mixture was then vacuum filtered through an evaporator to obtain cottonseed oil.

[0034] S3. Degumming: Keep the temperature of the cottonseed mixed oil obtained in step S2 at 60℃, add citric acid with a concentration of 80wt% and a weight of 0.1% of the cottonseed mixed oil, and mix thoroughly at a speed of 40 r / min. Then add distilled water with a weight of 5% of the cottonseed mixed oil for washing. After washing for 0.5h, let it stand for 1h to release the lower layer of waste, and then distill and dehydrate for 0.5h to obtain the first oil sample.

[0035] S4. Ultrasonic Alkali Refining: The first oil sample was kept at 60℃, and alkali was added using a spray alkali addition method. The stirring speed was 65 r / min for 30 min. During this process, intermittent ultrasonication (frequency 30 kHz, power 300 W, pulse mode 5s on 5s off) was applied. The sample was kept at this temperature and allowed to stand for 5 h to allow the soap residue to settle and separate. Then, the oil was washed with hot water at the same temperature as the oil to remove residual alkali and soap. The amount of water was 8% of the weight of the cottonseed oil mixture. The stirring speed during washing was 20 r / min. After washing, the lower layer of liquid was drained, leaving the oil sample. The oil sample was transferred to a centrifuge for rapid centrifugation at 800 r / min to obtain the second oil sample.

[0036] S5. UV-Magnetic Field Synergistic Decolorization: The second oil sample was heated to 70℃ and irradiated with UV light (254nm, 30min). Adsorbent was added in combination with a static magnetic field (0.8T). The stirring speed was 65r / min. After stirring for 3h, vacuum adsorption filtration was performed with a vacuum degree of 40kPa to obtain the third oil sample.

[0037] S6. Low-temperature crystallization fractionation: The third oil sample was lowered from room temperature to 0℃ at a rate of 0.5℃ / min, and then lowered to -10℃ at a rate of 2℃ / h. The sample was kept at this temperature for 12h for crystallization. The high pour point solid esters were removed by centrifugation.

[0038] S7. Adding nano-additives and dehydration / degassing: At 70°C, nano-silica modified with 0.1% by mass of silane coupling agent in the oil sample obtained in step S6 is mixed and then vacuum dried at a vacuum degree of 60 kPa to obtain cottonseed plant insulating oil.

[0039] Example 2 This embodiment provides a cottonseed plant insulating oil, wherein the alkali agent includes sodium hydroxide, sodium silicate, sodium bentonite and activated carbon in a mass ratio of 8:1:5:0.2, and the mass ratio of alkali agent to cottonseed mixed oil is 5%:1.

[0040] The adsorbent consists of magnesium silicate, basic alumina, and amylopectin in a mass ratio of 2:5:1, and the mass ratio of the adsorbent to the second oil sample is 2%:1.

[0041] Its preparation method includes the following steps: S1. Physical Separation: Pre-treatment of cottonseed involves separating the husks and kernels using a hulling machine and a multi-stage stepped sieve. After softening with steam at 50°C, the cottonseed kernels are mechanically crushed. Finally, hot air drying is used to obtain cottonseed meal with a moisture content of less than 3%.

[0042] S2. Extracting crude oil: The cottonseed meal from step S1 is extracted by low-temperature physical screw pressing to obtain virgin cottonseed crude oil and a solid-liquid mixture formed by crushed cottonseed kernels. Hexane at a mass ratio of 0.8:1 and the above solid-liquid mixture were added and extracted at 60°C. The mixture was then vacuum filtered through an evaporator to obtain cottonseed oil.

[0043] S3. Degumming: Keep the temperature of the cottonseed mixed oil obtained in step S2 at 60℃, add 0.05% phosphoric acid with a concentration of 80% by weight of the cottonseed mixed oil, and mix thoroughly at a speed of 30 r / min. Then add 5% distilled water by weight of the cottonseed mixed oil for washing. After washing for 0.5h, let it stand for 1h to release the lower layer of waste, and then distill and dehydrate for 0.5h to obtain the first oil sample.

[0044] S4. Ultrasonic Alkali Refining: The first oil sample was kept at 60℃, and alkali was added using a spray alkali addition method. The stirring speed was 65 r / min for 30 min. During this process, intermittent ultrasonication (frequency 20 kHz, power 300 W, pulse mode 10 s on 5 s off) was applied. The sample was kept at this temperature and allowed to stand for 3 h to allow the soap residue to settle and separate. Then, the oil was washed with hot water at the same temperature as the oil to remove residual alkali and soap. The amount of water was 5% of the weight of the cottonseed oil mixture. The stirring speed during washing was 10 r / min. After washing, the lower layer of liquid was drained, leaving the oil sample. The oil sample was transferred to a centrifuge for rapid centrifugation at 500 r / min to obtain the second oil sample.

[0045] S5. UV-Magnetic Field Synergistic Decolorization: The second oil sample was heated to 70℃ and irradiated with UV light (254nm, 10min). Adsorbent was added in combination with a static magnetic field (0.5T). The stirring speed was 60r / min. After stirring for 3h, vacuum adsorption filtration was performed with a vacuum degree of 30kPa to obtain the third oil sample.

[0046] S6. Low-temperature crystallization fractionation: The third oil sample was lowered from room temperature to 0℃ at a rate of 0.5℃ / min, and then lowered to -10℃ at a rate of 2℃ / h. The sample was kept at this temperature for 6 hours to crystallize. The high pour point solid esters were removed by centrifugation.

[0047] S7. Adding nano-additives and dehydration / degassing: Add 0.01% by mass of silane coupling agent-modified boron nitride to the oil sample obtained in step S6 at 70℃, mix well, and then vacuum dry at a vacuum degree of 50 kPa to obtain cottonseed plant insulating oil.

[0048] Example 3 This embodiment provides a cottonseed plant insulating oil, wherein the alkali agent includes sodium hydroxide, sodium silicate, sodium bentonite and activated carbon in a mass ratio of 7:1.5:4:0.5, and the mass ratio of alkali agent to cottonseed mixed oil is 10%:1.

[0049] The adsorbent consists of magnesium silicate, basic alumina, and amylopectin in a mass ratio of 5:4:1.5, and the mass ratio of the adsorbent to the second oil sample is 5%:1.

[0050] Its preparation method includes the following steps: S1. Physical Separation: Pre-treatment of cottonseed involves separating the husks and kernels using a hulling machine and a multi-stage stepped sieve. After softening with steam at 50°C, the cottonseed kernels are mechanically crushed. Finally, hot air drying is used to obtain cottonseed meal with a moisture content of less than 3%.

[0051] S2. Extracting crude oil: The cottonseed meal from step S1 is extracted by low-temperature physical screw pressing to obtain virgin cottonseed crude oil and a solid-liquid mixture formed by crushed cottonseed kernels. Hexane at a mass ratio of 1.1:1 and the above solid-liquid mixture were added and extracted at 60°C. The mixture was then vacuum filtered through an evaporator to obtain cottonseed oil.

[0052] S3. Degumming: Keep the temperature of the cottonseed mixed oil obtained in step S2 at 60℃, add phosphoric acid with a concentration of 80% and a weight of 0.3% of the cottonseed mixed oil, and mix thoroughly at a speed of 50 r / min. Then add distilled water with a weight of 8% of the cottonseed mixed oil for washing. After washing for 0.5h, let it stand for 1h to release the lower layer of waste, and then distill and dehydrate for 0.5h to obtain the first oil sample.

[0053] S4. Ultrasonic Alkali Refining: The first oil sample was kept at 60℃, and alkali was added using a spray alkali addition method. The stirring speed was 70 r / min for 30 min. During this process, it was ultrasonically treated (frequency 40 kHz, power 300 W, 30 min). The sample was kept at this temperature and allowed to stand for 6 h to allow the soap residue to settle and separate. Then, it was washed with hot water at the same temperature as the oil to remove residual alkali and soap. The amount of water was 8% of the weight of the cottonseed oil mixture. The stirring speed during washing was 30 r / min. After washing, the lower layer of liquid was drained, leaving the oil sample. The oil sample was transferred to a centrifuge for rapid centrifugation at 1000 r / min to obtain the second oil sample.

[0054] S5. UV-Magnetic Field Synergistic Decolorization: The second oil sample was heated to 70℃ and irradiated with UV light (254nm, 20min). Adsorbent was added in combination with a static magnetic field (1T). The stirring speed was 70r / min. After stirring for 3h, vacuum adsorption filtration was performed with a vacuum degree of 50kPa to obtain the third oil sample.

[0055] S6. Low-temperature crystallization fractionation: The third oil sample was lowered from room temperature to 0℃ at a rate of 0.5℃ / min, and then lowered to -10℃ at a rate of 2℃ / h. The sample was kept at this temperature for 18h to crystallize. High pour point solid esters were removed by centrifugation.

[0056] S7. Adding nano-additives and dehydration / degassing: At 70°C, add 0.3% by mass of silane coupling agent-modified iron(III) oxide to the oil sample obtained in step S6, mix well, and then vacuum dry at a vacuum degree of 80 kPa to obtain cottonseed plant insulating oil.

[0057] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example is not subject to ultraviolet irradiation.

[0058] Comparative Example 2 The difference between this comparative example and Example 1 is that no static magnetic field is applied in this comparative example.

[0059] Comparative Example 3 The difference between this comparative example and Example 1 is that this comparative example does not undergo ultraviolet irradiation or apply a static magnetic field.

[0060] Comparative Example 4 The difference between this comparative example and Example 1 is that the adsorbent includes magnesium silicate, basic alumina and amylopectin in a mass ratio of 10:3:2.

[0061] Comparative Example 5 The difference between this comparative example and Example 1 is that the adsorbent includes magnesium silicate, basic alumina and amylopectin in a mass ratio of 0.1:3:2.

[0062] Comparative Example 6 The difference between this comparative example and Example 1 is that this comparative example does not contain sodium silicate.

[0063] Comparative Example 7 The difference between this comparative example and Example 1 is that the alkali agent in this comparative example includes sodium hydroxide, sodium silicate, sodium bentonite and activated carbon in a mass ratio of 6:11:3:0.3.

[0064] Comparative Example 8 The difference between this comparative example and Example 1 is that the alkali agent in this comparative example includes sodium hydroxide, sodium silicate, sodium bentonite and activated carbon in a mass ratio of 6:0.1:3:0.3.

[0065] Comparative Example 9 The difference between this comparative example and Example 1 is that phosphoric acid is not added during the degumming process of this comparative example, and the same mass of water is added for washing.

[0066] Comparative Example 10 The difference between this comparative example and Example 1 is that this comparative example does not involve ultrasonic treatment during the alkali refining process.

[0067] Performance testing The cottonseed plant insulating oils prepared in Examples 1-3 and Comparative Examples 1-9 were tested for performance according to the following standards, and the test results are shown in Table 1 below.

[0068] Breakdown voltage: GB / T 507; Acid value: IEC 62021-3; Dielectric loss: GB / T 5654; Refining rate: calculated as (mass of cottonseed insulating oil / mass of crude cottonseed oil) × 100%; Pour point: GB / T3535.

[0069] Table 1 Test results of cottonseed insulating oil performance

[0070] As shown in Table 1, the cottonseed plant insulating oil prepared by this invention exhibits excellent performance across various indicators. The significantly reduced acid value not only effectively removes acidic substances from the oil but also demonstrates the excellent oxidative stability of the cottonseed plant insulating oil, inhibiting the generation of acidic substances through reactive free radical reactions and extending equipment lifespan. The extremely low dielectric loss factor indicates that the insulation performance and energy loss control of the cottonseed plant insulating oil of this invention reach industry-leading levels, making it suitable for transformers of various voltage levels. The refining rate is increased to over 93%, reflecting the high efficiency and economy of the preparation method of this invention. Furthermore, the breakdown voltage of this invention is also excellent, ensuring high safety in use. The pour point can reach as low as -30℃, demonstrating excellent low-temperature performance.

[0071] As can be seen from the comparison between Example 1 and Comparative Example 1, without ultraviolet irradiation, the aldehyde groups in gossypol were not activated, resulting in limited adsorption effect of the adsorbent. The residual gossypol in the oil sample led to a higher acid value.

[0072] As can be seen from the comparison between Example 1 and Comparative Example 2, the free radicals in the ester without a magnetic field exhibit disordered thermal motion. Compared with the inactive dimers formed by the magnetic field, the molecules are smaller and the thermal motion is more intense, resulting in increased dielectric loss.

[0073] A comparison of Example 1 and Comparative Example 3 shows that without the addition of ultraviolet light and a magnetic field, the adsorption effect is limited when relying solely on the adsorbent for adsorption. The oil contains a large amount of gossypol and small molecule free radicals, resulting in higher acid value and dielectric loss.

[0074] As can be seen from the comparison between Example 1 and Comparative Example 4, although the excessive addition of magnesium silicate improves the performance of oil products, it significantly reduces the refining rate.

[0075] A comparison of Example 1 and Comparative Example 5 shows that the addition of a very small amount of magnesium silicate leads to an imbalance in the proportions of the components in the adsorbent, resulting in poor dielectric loss control.

[0076] As can be seen from the comparison between Example 1 and Comparative Example 6, the only alkali agent in alkali refining is the strong alkali NaOH, which easily leads to local over-alkaliening, resulting in saponification of neutral oil and a significant decrease in refining rate.

[0077] A comparison of Example 1 and Comparative Example 7 shows that in the alkali refining process, the ratio of strong alkali to weak alkali is too high, resulting in insufficient overall alkali refining reaction and poor electrical and physical properties of the insulating oil.

[0078] A comparison of Example 1 and Comparative Example 8 shows that in the alkali refining process, the amount of weak alkali added in the strong-weak alkali ratio is too small, which limits the effect of controlling the depth of saponification reaction and results in a low refining rate, although it is still higher than the refining rate without the addition of weak alkali.

[0079] As can be seen from the comparison between Example 1 and Comparative Example 9, hydration degumming is effective for easily hydrated α-phospholipids, but its effect on removing β-phospholipids is generally limited. There are more impurities in the oil. Acidification degumming is more effective in removing impurities and is beneficial for subsequent alkali refining.

[0080] As can be seen from the comparison between Example 1 and Comparative Example 10, ultrasound not only achieves more uniform mixing, but also induces molecular dislocations through molecular vibrational energy. Due to the change in molecular composition, the pour point temperature of the cottonseed oil sample decreased compared to its initial value.

[0081] In summary, this invention provides a cottonseed plant insulating oil and its preparation method. The prepared cottonseed plant insulating oil has a significantly reduced acid value, extremely low dielectric loss, high refining rate, excellent breakdown voltage and low-temperature performance, and high safety in use, making it suitable for transformers of various voltage levels.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing cottonseed plant insulating oil, characterized in that, Includes the following steps: Step S1: Extract cottonseed to obtain cottonseed mixed oil, and degumm the cottonseed mixed oil to obtain the first oil sample; Step S2: The first oil sample is subjected to alkali refining to obtain a second oil sample; Step S3: Irradiate the second oil sample with ultraviolet light, apply a static magnetic field, and add an adsorbent to obtain the third oil sample; Step S4: Perform low-temperature crystallization fractionation on the third oil sample; Step S5: Add nano-additives, mix well, and dehydrate and degas to obtain cottonseed plant insulating oil.

2. The method for preparing cottonseed plant insulating oil as described in claim 1, characterized in that, The alkaline agents used in the alkali refining process include sodium hydroxide, sodium silicate, sodium bentonite, and activated carbon. The mass ratio of sodium hydroxide, sodium silicate, sodium bentonite, and activated carbon is (6~8):(1~2):(3~5):(0.2~0.5). The mass ratio of alkali agent to cottonseed oil mixture is (5%~10%):

1.

3. The method for preparing cottonseed plant insulating oil as described in claim 1, characterized in that, The alkali refining process includes the following steps: maintaining the temperature of the first oil sample at 60°C, adding alkali agent using a spray alkali addition method, stirring, and simultaneously applying ultrasound at a frequency of 20~40kHz and a power of 300W.

4. The method for preparing cottonseed plant insulating oil as described in claim 1, characterized in that, The adsorbent includes magnesium silicate, basic alumina, and amylopectin; The mass ratio of magnesium silicate, basic alumina, and amylopectin is (2~5):(3~5):(1~2); the mass ratio of the adsorbent to the second oil sample is (2%~5%):

1.

5. The method for preparing cottonseed plant insulating oil as described in claim 1, characterized in that, The second oil sample was heated before ultraviolet irradiation. The wavelength of the ultraviolet irradiation was 254 nm, the time was 10 to 30 minutes, and the magnetic induction intensity of the static magnetic field was 0.5 to 1 T.

6. The method for preparing cottonseed plant insulating oil as described in claim 1, characterized in that, Step S5 includes adding a nano-additive to the oil sample obtained in step S4 at 70°C. The nano-additive includes any one of nano-silica modified with a silane coupling agent, boron nitride, or iron oxide. The mass ratio of the nano-additive to the oil sample obtained in step S4 is (0.01%~0.3%):

1.

7. The method for preparing cottonseed plant insulating oil as described in claim 1, characterized in that, The low-temperature crystallization fractionation method includes: lowering the third oil sample from room temperature to 0℃ at a rate of 0.5℃ / min, then lowering it to -10℃ at a rate of 2℃ / h, maintaining the temperature for crystallization for 6-18h, and centrifuging.

8. The method for preparing cottonseed plant insulating oil as described in claim 1, characterized in that, The dehydration and degassing method includes: vacuum drying, with a vacuum degree of 50~80kPa.

9. The cottonseed plant insulating oil prepared by the method according to any one of claims 1 to 8.

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