Preparation process of high oxidation stability plant insulating oil
By integrating palladium-nickel bimetallic catalysts with activated carbon, selective hydrogenation is used to remove linolenic acid from vegetable oils, solving the problems of oxidation stability and low-temperature fluidity, and achieving efficient preparation of vegetable insulating oil with high oxidation stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WUHAN ZD NEW MATERIALS CO LTD
- Filing Date
- 2026-04-01
- Publication Date
- 2026-07-10
AI Technical Summary
Existing technologies struggle to significantly improve the oxidation stability and low-temperature fluidity of vegetable insulating oils while maintaining high refining yields. Traditional methods suffer from cumbersome processes and poor selectivity.
A highly oxidatively stable vegetable insulating oil was prepared by using an integrated process combining a palladium-nickel bimetallic catalyst and activated carbon to selectively hydrogenate linolenic acid from vegetable oil and adding antioxidants and pour point depressants.
It significantly reduces linolenic acid content, improves oxidative stability, maintains good low-temperature fluidity, simplifies the process, and is suitable for large-scale production.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of vegetable insulating oil refining technology, and in particular to a preparation process for a vegetable insulating oil with high oxidation stability. Background Technology
[0002] Vegetable-based insulating oils, as biodegradable, high-ignition-point, and environmentally friendly liquid dielectrics, have the potential to replace traditional mineral insulating oils in power equipment such as transformers. However, their widespread application faces a key bottleneck: the unsaturated fatty acids abundant in vegetable oils, especially polyunsaturated components such as linolenic acid, are highly susceptible to oxidation reactions under the influence of heat, oxygen, and metal ions. This leads to increased acid value, increased dielectric loss, and precipitation, severely impacting the long-term insulation reliability and service life of electrical equipment.
[0003] Currently, the conventional method for improving the stability of vegetable insulating oils is through multi-step physicochemical refining, including degumming, deacidification, decolorization, and deodorization. While these traditional processes can remove some impurities, they are relatively cumbersome and have limited ability to specifically remove key unstable components such as linolenic acid. Therefore, it is difficult to significantly and fundamentally improve the oxidative stability of the oil while maintaining a high refining yield, and the results are not ideal.
[0004] In addition, some technologies have attempted to use hydrogenation to saturate double bonds in oils to improve stability. However, commonly used hydrogenation catalysts (such as Raney nickel) often lack selectivity, easily leading to oversaturation of other unsaturated fatty acids while reducing linolenic acid content. This deep hydrogenation significantly increases the saturation of the oil, resulting in a marked increase in its pour point and deterioration in low-temperature fluidity, failing to meet the low-temperature performance requirements of insulating oils in cold regions. Therefore, developing a highly efficient refining process that can selectively remove easily oxidized components while maintaining good low-temperature fluidity has become a pressing technical challenge in this field. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention provides a process for preparing a vegetable insulating oil with high oxidation stability. This process aims to efficiently remove easily oxidized linolenic acid from the oil and improve its low-temperature fluidity through optimized catalysts and integrated processes, thereby obtaining a vegetable insulating oil with excellent overall performance and high oxidation stability.
[0006] The technical solution of this invention is implemented as follows:
[0007] In a first aspect, the present invention provides a process for preparing a highly oxidatively stable vegetable insulating oil, comprising the following steps:
[0008] S1. A precursor solution is prepared by mixing palladium salt, nickel salt and polyethylene glycol, then mixing with alkaline clay, and then subjecting the mixture to impregnation, heating and stirring, drying and reaction under hydrogen atmosphere to obtain an alkaline clay-supported palladium-nickel bimetallic catalyst.
[0009] S2. Mix vegetable oil, palladium-nickel bimetallic catalyst supported on alkaline clay obtained in step S1, and activated carbon, and pass hydrogen gas through them to react. After the reaction, filter to obtain hydrogenated refined oil.
[0010] S3. Add antioxidants and pour point depressants to the hydrogenated refined oil obtained in step S2 to obtain the plant insulating oil.
[0011] Based on the above technical solutions, preferably, in step S1, the palladium salt includes palladium chloride (PdCl2); the nickel salt includes nickel nitrate (Ni(NO3)2·6H2O); and the polyethylene glycol (PEG) is added as a surfactant and reducing agent at an amount of 10%-20% of the total mass of the palladium salt and nickel salt.
[0012] More preferably, in step S1, the molar ratio of palladium to nickel in the palladium-nickel bimetallic catalyst is 1:3-1:5. The palladium-nickel alloy nanoparticles provide highly active hydrogenation sites, enabling selective hydrogenation of linolenic acid, reducing the linolenic acid content to below 2%, decreasing the formation of trans acids, and significantly improving the oxidative stability of vegetable insulating oil while ensuring low-temperature performance.
[0013] Furthermore, palladium-nickel alloying forms bimetallic nanoparticles, generating significant electronic and geometric synergies. Electronic synergy: d electrons from nickel transfer to palladium, forming electron-rich palladium centers, lowering the H2 dissociation barrier and increasing the hydrogenation reaction rate; changes in electronic structure regulate the adsorption strength of unsaturated fatty acid double bonds, avoiding excessive hydrogenation due to over-adsorption; nickel preferentially adsorbs impurities in the oil (forming NiP and NiS), protecting palladium active sites from poisoning. Geometric synergy: The difference in atomic radii between palladium and nickel (Pd: 137 pm, Ni: 124 pm) leads to lattice strain, generating more low-coordination active sites; lattice distortion regulates the spacing between active sites, facilitating the selective adsorption of long-chain molecules such as linolenic acid. The synergy of both reduces only the two conjugated double bonds of linolenic acid (converting it into monounsaturated fatty acids), resulting in a hydrogenation rate of ≤5% for oleic acid (C18:1), avoiding excessive hydrogenation that leads to an increase in the pour point.
[0014] Further preferably, in step S1, a palladium-nickel precursor solution is first prepared by dissolving palladium and nickel salts in deionized water, followed by adding polyethylene glycol and stirring until completely dissolved. This precursor solution is then placed in a reaction vessel with alkaline clay, impregnated at room temperature for 2 hours, and then heated and stirred at 60 °C for 4 hours to complete the loading. The loaded solid is then dried at 120 °C for 8 hours. Finally, the dried material is transferred to a tube furnace, where air is replaced under a nitrogen atmosphere, and then switched to a hydrogen atmosphere. The specific reaction conditions under the hydrogen atmosphere are: heating to 400-600 °C at a heating rate of 2-5 °C / min, and holding at this temperature for 2-6 hours.
[0015] More preferably, in step S1, the loading of the palladium-nickel bimetallic compound relative to the alkaline clay is 3.3-3.5 wt%. The alkaline sites of the alkaline clay can neutralize (deacidify) the free fatty acids in crude oil and saponify (degumme) the phospholipids. The loaded palladium-nickel bimetallic active component achieves selective hydrogenation of linolenic acid through synergistic effects (electronic effects, adsorption-catalytic coupling), and the carrier properties of the alkaline clay can enhance the stability of the bimetallic active component.
[0016] More preferably, in step S2, the mass ratio of the palladium-nickel bimetallic catalyst supported on alkaline clay to activated carbon is 1:1-4:1, and the total amount of the catalyst and activated carbon mixture added is 2-8% of the mass of the vegetable oil. The high specific surface area of the activated carbon can synergistically adsorb soap residue, pigments, and oxidized impurities (decolorization) generated during the degumming and deacidification process. Simultaneously, the complementary porous structures of the two supports are beneficial for mass transfer, and the adsorption effect of the activated carbon can protect the metal active centers from activity decay caused by the adsorption of impurities.
[0017] More preferably, in step S2, the reaction is carried out under vacuum conditions, with a vacuum degree of 30-50 mmHg, a reaction temperature of 80-90℃, a reaction time of 50-70 minutes, hydrogen gas is continuously introduced and stirred, and the hydrogenated refined oil is obtained by filtration after the reaction is completed.
[0018] More preferably, in step S2, the vegetable oil includes rapeseed oil, soybean oil, or perilla seed oil.
[0019] More preferably, in step S3, the antioxidant is at least one of butylated hydroxytoluene, tert-butylhydroquinone, or propyl gallate, and the amount added is 0.2wt%-0.5wt% of the mass of the hydrogenated refined oil. The antioxidant delays the oxidative aging of the insulating oil by providing hydrogen atoms to react with free radicals generated in the insulating oil under the catalysis of heat, light, or metal ions, thereby interrupting the chain reaction of free radicals.
[0020] More preferably, in step S3, the pour point depressant is polymethyl methacrylate, and the amount added is 0.5wt%-2wt% of the mass of the hydrogenated refined oil. The pour point depressant improves the flow properties of the oil at low temperatures, that is, it improves the pour point.
[0021] In a second aspect, the present invention provides a highly oxidatively stable vegetable insulating oil, which is prepared by any of the preparation methods described in the first aspect above.
[0022] The present invention has the following advantages over the prior art:
[0023] (1) Significantly improved oxidation stability: Through the specific Pd-Ni bimetallic catalyst and process of this invention, the linolenic acid content in vegetable oil can be selectively and efficiently reduced to an extremely low level (less than 2%), fundamentally eliminating the main source of instability. As shown in the data of the examples in Table 2, the increase in acid value and dielectric loss factor of the resulting insulating oil after oxidation is much lower than that of oils that are not hydrogenated or treated with conventional catalysts.
[0024] (2) Excellent overall performance: While improving oxidation stability, the process also ensures good low-temperature fluidity (pour point can reach below -18℃) by adding PMMA pour point depressant, which solves the problem of excessively high pour point caused by traditional deep hydrogenation. The product has excellent initial electrical properties (dielectric loss, acid value) and high refining yield (>97%).
[0025] (3) High efficiency and specificity of catalyst: The Pd-Ni / alkaline clay catalyst exhibits high catalytic activity and selectivity at relatively low temperatures (80-90℃). Compared with pure nickel catalyst, its hydrogenation efficiency and selectivity are significantly improved; compared with traditional Raney nickel, it has less impact on the product pour point.
[0026] (4) High process integration: The catalyst preparation, selective hydrogenation and refining performance regulation steps are coupled into a continuous process to achieve process synergy and performance optimization. The process is reasonable, easy to operate, and suitable for large-scale production of environmentally friendly high-performance plant insulating oil. Detailed Implementation
[0027] 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.
[0028] Table 1: Material Source Description Table
[0029]
[0030] Example 1
[0031] S1. Weigh 0.44 g palladium chloride and 2.91 g nickel nitrate hexahydrate (corresponding to a palladium-nickel molar ratio of 1:4) and dissolve them in 100 mL of deionized water. Then, add 0.5 g polyethylene glycol and stir until completely dissolved to obtain a clear precursor solution. Add 100 mL of the precursor solution and 25 g of alkaline clay to the reactor. First, impregnate at room temperature for 2 hours, then heat and stir continuously at 60 °C for 4 hours to fully load the active component onto the support (the loading of the palladium-nickel bimetallic active component in this catalyst is approximately 3.4 wt%). Transfer the loaded solid material to a drying oven and dry at 120 °C for 8 hours to completely remove moisture. Place the dried material in a tube furnace, first purging with nitrogen to remove air from the system, then switching to a hydrogen atmosphere. Under a hydrogen atmosphere, program the temperature to 500 °C at a heating rate of 3 °C / min and maintain this temperature for 4 hours for reduction. After the reaction is complete, the mixture is naturally cooled to room temperature to obtain the desired alkaline clay-supported palladium-nickel bimetallic catalyst.
[0032] S2. Using soybean oil as the raw material, 1000g of soybean oil was added to a reaction vessel and heated to 85°C under a vacuum of 40mmHg. Then, a mixture of the palladium-nickel bimetallic catalyst and activated carbon prepared in step S1 (with a mass ratio of catalyst to activated carbon of 3:1) was added, the total amount of which was 5% (50g) of the oil mass. Under the conditions of maintaining vacuum and temperature, hydrogen gas was continuously introduced into the reaction system and the reaction was stirred for 1 hour. After the reaction was completed, the mixture was filtered while hot to separate the solids and obtain hydrogenated refined oil.
[0033] S3. Add 3g of butylated hydroxytoluene as an antioxidant and 10g of polymethyl methacrylate as a pour point depressant to the above-mentioned hydrogenated refined oil, and stir and mix evenly at 70°C to obtain the final product of vegetable insulating oil with high oxidation stability.
[0034] Example 2
[0035] S1. Weigh 0.55g palladium chloride and 2.73g nickel nitrate hexahydrate (corresponding to a palladium-nickel molar ratio of 1:3) and dissolve them in 100mL deionized water. Then, add 0.33g polyethylene glycol and stir until completely dissolved to obtain a clear precursor solution. Add 100mL of the precursor solution and 25g of alkaline clay to the reactor. First, impregnate at room temperature for 2 hours, then heat and stir continuously at 60℃ for 4 hours to fully load the active component onto the support (the loading of the palladium-nickel bimetallic active component in this catalyst is approximately 3.5wt%). Transfer the loaded solid material to a drying oven and dry at 120℃ for 8 hours to completely remove moisture. Place the dried material in a tube furnace, first purging with nitrogen to remove air from the system, then switching to a hydrogen atmosphere. Under a hydrogen atmosphere, program the temperature to 400℃ at a heating rate of 2℃ / min and hold at this temperature for 2 hours for reduction. After the reaction is complete, the mixture is naturally cooled to room temperature to obtain the desired alkaline clay-supported palladium-nickel bimetallic catalyst.
[0036] S2. Rapeseed oil was selected as the raw material. 1000g of rapeseed oil was added to a reaction vessel and heated to 80℃ under a vacuum of 30mmHg. Then, a mixture of the palladium-nickel bimetallic catalyst and activated carbon prepared in step S1 (with a mass ratio of catalyst to activated carbon of 1:1) was added. The total amount of this mixture added was 2% (i.e., 20g) of the oil mass. Under the conditions of maintaining vacuum and temperature, hydrogen gas was continuously introduced into the reaction system and the reaction was stirred for 50 minutes. After the reaction was completed, the mixture was filtered while hot to separate the solids and obtain hydrogenated refined oil.
[0037] S3. Add 2g of tert-butylhydroquinone as an antioxidant and 5g of polymethyl methacrylate as a pour point depressant to the above-mentioned hydrogenated refined oil, and stir and mix evenly at 70°C to obtain the final product of vegetable insulating oil with high oxidation stability.
[0038] Example 3
[0039] S1. Weigh 0.37g palladium chloride and 3.03g nickel nitrate hexahydrate (corresponding to a palladium-nickel molar ratio of 1:5) and dissolve them in 100mL deionized water. Then, add 0.68g polyethylene glycol and stir until completely dissolved to obtain a clear precursor solution. Add 100mL of the precursor solution and 25g of alkaline clay to the reactor. First, impregnate at room temperature for 2 hours, then heat and stir continuously at 60℃ for 4 hours to fully load the active component onto the support (the loading of the palladium-nickel bimetallic active component in this catalyst is approximately 3.3wt%). Transfer the loaded solid material to a drying oven and dry at 120℃ for 8 hours to completely remove moisture. Place the dried material in a tube furnace, first purging with nitrogen to remove air from the system, then switching to a hydrogen atmosphere. Under a hydrogen atmosphere, program the temperature to 500℃ at a heating rate of 3℃ / min and maintain this temperature for 4 hours for reduction. After the reaction is complete, the mixture is naturally cooled to room temperature to obtain the desired alkaline clay-supported palladium-nickel bimetallic catalyst.
[0040] S2. Using soybean oil as the raw material, 1000g of soybean oil was added to a reaction vessel and heated to 90°C under a vacuum of 50mmHg. Then, a mixture consisting of the palladium-nickel bimetallic catalyst obtained in step S1 and activated carbon (with a mass ratio of catalyst to activated carbon of 4:1) was added. The total amount of this mixture added was 8% (i.e., 80g) of the oil mass. Under the conditions of maintaining vacuum and temperature, hydrogen gas was continuously introduced into the reaction system, and the reaction was stirred for 70 minutes. After the reaction was completed, the mixture was filtered while hot to separate the solids and obtain hydrogenated refined oil.
[0041] S3. Add 5g of butylated hydroxytoluene as an antioxidant and 20g of polymethyl methacrylate as a pour point depressant to the above-mentioned hydrogenated refined oil, and stir and mix evenly at 70°C to obtain the final product of vegetable insulating oil with high oxidation stability.
[0042] Comparative Example 4-5
[0043] Unlike Example 1, the total amount of the mixture consisting of palladium-nickel bimetallic catalyst and activated carbon added was 1% and 9% of the oil mass, respectively. The remaining steps were the same as in Example 1, and will not be repeated here.
[0044] Comparative Example 6
[0045] Compared to Example 1, the traditional step-by-step hydrogenation process involves the following steps:
[0046] Degumming: Heat 1000g of soybean oil to 60℃, add 2g of 0.2% phosphoric acid aqueous solution (by weight of oil), stir for 30 minutes, let stand to separate into layers, and remove the lower layer of gum; Deacidification: Heat the degummed oil to 70℃, add 50g of 10% sodium hydroxide solution (by weight), stir for 30 minutes, let stand to separate into layers, and remove the lower layer of soapberry; Washing: Keep the deacidified oil at 70℃, add 200g of hot water (90℃), stir for 15 minutes, let stand to separate into layers, remove the lower layer of wastewater, and repeat the washing process twice; Adsorption and Decolorization: Heat the washed oil to 65℃, add a mixture of 18.2g of activated clay and 1.8g of activated carbon (the ratio of activated clay to activated carbon is 10:1), stir for 1 hour, and filter to obtain refined oil.
[0047] The subsequent steps are the same as steps S2 and S3 in Example 1, and will not be repeated here.
[0048] Comparative Example 7
[0049] Unlike Example 1, only 3.63g of nickel nitrate hexahydrate was added in the preparation of the catalyst, and no palladium salt was added. The remaining steps were the same as in Example 1, and will not be repeated here.
[0050] Comparative Example 8
[0051] Unlike Example 1, only 2.22g of palladium chloride was added in the preparation of the catalyst, and no nickel salt was added. The remaining steps were the same as in Example 1, and will not be repeated here.
[0052] Comparative Examples 9-10
[0053] Unlike Example 1, the molar ratios of palladium and nickel were 4:1 (1.77g palladium chloride and 0.73g nickel nitrate hexahydrate) and 1:9 (0.22g palladium chloride and 3.27g nickel nitrate hexahydrate), respectively. The remaining steps were the same as in Example 1 and will not be repeated here.
[0054] The above embodiments and comparative examples were tested according to the following standards: pour point: GB / T 3535; media loss factor: GB / T 5654; acid value: IEC 62021-3; oxidative stability test: performed according to Appendix B of DL / T 1811; linolenic acid content: GB5009.168-2016.
[0055] Table 2: Performance Data of Examples and Comparative Examples
[0056]
[0057] As shown in Table 2, the insulating oils prepared using the process of this invention (Examples 1-3) all exhibited significantly reduced content of the key unstable component, linolenic acid, to below 2%, while maintaining an excellent pour point between -21°C and -15°C. This demonstrates that the palladium-nickel bimetallic catalyst can selectively hydrogenate linolenic acid without deeply saturating oleic acid (C18:1), fundamentally solving the problem of increased pour point caused by traditional deep hydrogenation.
[0058] The comparative data from Comparative Examples 7 and 8 further demonstrate the necessity of palladium-nickel alloying. Pure nickel catalysts exhibit poor catalytic efficiency and selectivity, requiring higher temperatures to achieve the same catalytic efficiency. This may lead to a catalytic pathway that favors further hydrogenation of oleic acid (C18:1) into the unwanted stearic acid (C18:0), increasing saturation and raising the pour point. Additionally, trace impurities in the oil can easily poison and deactivate the nickel catalyst. Pure palladium catalysts, due to their high surface energy at high temperatures, are prone to agglomeration, forming large particles that reduce the number of active sites and thus lower catalytic efficiency. Furthermore, the cost difference between palladium-based and nickel-based catalysts is approximately 30 times, making them uneconomical for production.
[0059] Compared to the traditional stepwise refining process (Comparative Example 6), the integrated process of this invention significantly increases the refining yield from 91.2% to over 97% while achieving similar linolenic acid content and pour point, and simplifies the operation process. Furthermore, data from Comparative Examples 4 and 5 show that there is an optimal range for the addition amount of the catalyst and activated carbon mixture (2-8% of the oil mass). While too low an addition amount is beneficial for low-temperature fluidity, it results in incomplete removal of linolenic acid; too high an addition amount leads to decreased selectivity, resulting in excessively high linolenic acid residue, which severely affects the performance after oxidation.
[0060] The data from Comparative Examples 9 and 10 show that at a palladium-nickel molar ratio of 4:1, the excessively high Pd content leads to an increase in nanoparticle size or partial agglomeration, weakening the strong synergistic interaction between Pd and Ni, resulting in a decrease in selectivity, and the higher cost is not economical for production. At a palladium-nickel molar ratio of 1:9, under the high Ni ratio, the excessively low Pd content cannot fully utilize the advantages of high activity, resulting in a decrease in overall catalytic efficiency and a significant weakening of the synergistic effect. This causes the selective hydrogenation of linolenic acid to be partially transformed into over-hydrogenation of oleic acid, further increasing the saturation of the oil and deteriorating the pour point.
[0061] 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 preparation process for a highly oxidatively stable vegetable insulating oil, characterized in that, Includes the following steps: S1. A precursor solution is prepared by mixing palladium salt, nickel salt and polyethylene glycol, then mixing with alkaline clay, and then subjecting the mixture to impregnation, heating and stirring, drying and reaction under hydrogen atmosphere to obtain an alkaline clay-supported palladium-nickel bimetallic catalyst. S2. Mix vegetable oil, palladium-nickel bimetallic catalyst supported on alkaline clay obtained in step S1, and activated carbon, and pass hydrogen gas through them to react. After the reaction, filter to obtain hydrogenated refined oil. S3. Add antioxidants and pour point depressants to the hydrogenated refined oil obtained in step S2 to obtain the vegetable insulating oil; In step S1, the molar ratio of palladium to nickel in the alkaline clay-supported palladium-nickel bimetallic catalyst is 1:3-1:
5. In step S2, the mass ratio of the alkaline clay-supported palladium-nickel bimetallic catalyst to activated carbon is 1:1-4:1, and the total amount of the catalyst and activated carbon mixture added is 2-8% of the mass of vegetable oil.
2. The preparation process according to claim 1, characterized in that, In step S1, the specific conditions for the reaction under a hydrogen atmosphere are: heating to 400-600°C at a heating rate of 2-5°C / min, and holding at that temperature for 2-6 hours.
3. The preparation process according to claim 1, characterized in that, In step S1, the loading of the palladium-nickel bimetal relative to the alkaline clay is 3.3-3.5 wt%.
4. The preparation process according to claim 1, characterized in that, In step S2, the reaction is carried out under vacuum conditions, with a vacuum degree of 30-50 mmHg, a reaction temperature of 80-90℃, and a reaction time of 50-70 minutes.
5. The preparation process according to claim 1, characterized in that, In step S2, the vegetable oil includes rapeseed oil, soybean oil, or perilla seed oil.
6. The preparation process according to claim 1, characterized in that, In step S3, the antioxidant is at least one of butylated hydroxytoluene, tert-butylhydroquinone, or propyl gallate, and the amount added is 0.2wt%-0.5wt% of the mass of the hydrogenated refined oil.
7. The preparation process according to claim 1, characterized in that, In step S3, the pour point depressant is polymethyl methacrylate, and the amount added is 0.5wt%-2wt% of the mass of the hydrogenated refined oil.