Slow-release antioxidant as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of insulating oil, and provides a slow-release antioxidant as well as a preparation method and application thereof, the preparation method comprises the following steps: (1) mixing octadecyl trimethyl ammonium bromide, 2, 6-butylated hydroxytoluene, tetraethoxysilane, water and ammonia water, and reacting to obtain the antioxidant; and (2) in a protective atmosphere, mixing the antioxidant, ethanol, water and gamma-mercaptopropyltriethoxysilane, and carrying out a reaction so as to obtain the slow-release antioxidant. The slow-release antioxidant suitable for the synthetic ester insulating oil is prepared through a physical coating means and oleophylic modification, has excellent solubility, can effectively inhibit the increase of the acid value of the synthetic ester insulating oil, delays the oxidation process of the synthetic ester insulating oil, and remarkably prolongs the service life of the insulating oil. Meanwhile, through a slow release mechanism, the antioxidant can prolong the antioxidant effect of the antioxidant, improve the antioxidant stability in long-time operation and meet the higher antioxidant requirement of high-performance equipment such as a transformer for the insulating oil.

Description

Technical Field

[0001] The invention relates to the technical field of insulating oil, and in particular to a slow-release antioxidant and a preparation method and application thereof. Background Art

[0002] During the long-term operation of the transformer, the internal oil-paper insulation system gradually ages due to the influence of external factors such as temperature, electric field, moisture and oxygen. The moisture generated during the aging process is absorbed by the insulating paper, resulting in an increase in its water content, which in turn reduces the insulation performance, affects the operating stability of the transformer, and even shortens its service life. In addition, the acidic substances generated by the insulating oil under oxidation will accelerate the corrosion of metal parts and catalyze the further oxidation of the oil, resulting in the formation of sludge. The deposition of sludge may cause local overheating or short circuit, seriously threatening the safe operation of the transformer. In the prior art, although the insulation performance of the insulating oil can be improved to a certain extent by degassing, filtering or replacing the insulating oil, the interaction between the aging products and the insulating material will still aggravate the aging of the insulation system. Therefore, the insulating oil not only needs to have good insulation performance, but also must have strong antioxidant ability. Adding antioxidants has become a common means to improve the performance of insulating oil. However, in actual applications, the existing antioxidants still have problems such as being easily ineffective under high temperature and long-term operation conditions, and it is difficult to continuously inhibit the oxidation reaction of the insulating oil, and the decomposition products of some antioxidants may have a negative impact on the insulating oil, accelerating the degradation of the oil. As the power grid continues to increase its requirements for transformer stability and service life, the limitations of existing antioxidants can no longer meet the stringent application requirements. Therefore, developing an antioxidant with excellent long-term effectiveness and stability has become a key technical issue in dealing with complex operating environments and extending the life of transformers. Summary of the invention

[0003] The purpose of the present invention is to overcome the problems in the prior art and provide a sustained-release antioxidant and a preparation method and application thereof.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a method for preparing a sustained-release antioxidant, comprising the following steps:

[0006] (1) mixing octadecyltrimethylammonium bromide, 2,6-di-tert-butyl-p-cresol, ethyl orthosilicate, water and ammonia water to react to obtain an antioxidant;

[0007] (2) In a protective atmosphere, an antioxidant, ethanol, water and γ-mercaptopropyltriethoxysilane are mixed and reacted to obtain the sustained-release antioxidant.

[0008] Preferably, in step (1), the mass ratio of octadecyltrimethylammonium bromide, 2,6-di-tert-butyl-p-cresol and tetraethyl orthosilicate is 1-2:15-20:3.5-4.

[0009] Preferably, the mass ratio of octadecyltrimethylammonium bromide, water and aqueous ammonia in step (1) is 1-2:80-120:0.1-0.5;

[0010] The mass fraction of the ammonia water is 25-28%.

[0011] Preferably, the reaction temperature in step (1) is 20-30°C and the reaction time is 20-30h.

[0012] Preferably, the mass volume ratio of the antioxidant, ethanol, water and γ-mercaptopropyltriethoxysilane in step (2) is 5-15 g: 300-400 mL: 30-40 mL: 10-20 mL.

[0013] Preferably, the pH of the system after mixing in step (2) is 3-4.

[0014] Preferably, the mixing temperature in step (2) is 20 to 30° C. and the mixing time is 10 to 15 hours.

[0015] Preferably, the reaction temperature in step (2) is 50-70° C. and the reaction time is 10-15 h.

[0016] The invention also provides the sustained-release antioxidant prepared by the preparation method of the sustained-release antioxidant.

[0017] The invention also provides application of the slow-release antioxidant in synthetic ester insulating oil.

[0018] The present invention provides a method for preparing a sustained-release antioxidant, comprising the following steps: (1) mixing octadecyltrimethylammonium bromide, 2,6-di-tert-butyl-p-cresol, ethyl orthosilicate, water and ammonia water to react to obtain an antioxidant; (2) mixing the antioxidant, ethanol, water and γ-mercaptopropyltriethoxysilane in a protective atmosphere to react to obtain the sustained-release antioxidant.

[0019] The present invention is based on 2,6-di-tert-butyl-p-cresol and coated with TiO 2Particles. When the composite antioxidant is added to the synthetic ester insulating oil, 2,6-di-tert-butyl-p-cresol slowly diffuses into the oil through the pores of the coating material, maintaining the antioxidant concentration within a stable range. As the insulating oil oxidizes, the antioxidant is gradually consumed, and the 2,6-di-tert-butyl-p-cresol in the coating material will continue to diffuse to replenish the consumed antioxidant. In addition, the by-products generated by the oxidation of the oil are also adsorbed by the coating material through the pores, thereby effectively delaying the increase in the viscosity and acid value of the synthetic ester insulating oil. By lipophilic modification of the composite antioxidant, on the one hand, the dispersibility of the antioxidant in the synthetic ester insulating oil is improved, the problem of particle aggregation is reduced, and the efficiency of the antioxidant is improved; on the other hand, the isocyanate group in γ-isocyanatopropyltriethoxysilane can react with the hydroxyl group or other active groups in the synthetic ester oil, enhancing the stability and heat resistance of the system, while significantly improving the antioxidant and anti-aging properties. In summary, the antioxidant prepared by the present invention achieves an effective improvement in the antioxidant capacity of the synthetic ester insulating oil through the dual mechanisms of slow release and adsorption.

[0020] The invention uses physical coating and lipophilic modification to prepare a slow-release antioxidant suitable for synthetic ester insulating oil, which has excellent solubility, can effectively inhibit the increase of the acid value of the synthetic ester insulating oil, delay its oxidation process, and significantly extend the service life of the insulating oil. At the same time, through the slow-release mechanism, the antioxidant of the invention can extend its own antioxidant effect, improve the antioxidant stability during long-term operation, and meet the higher antioxidant requirements of high-performance equipment such as transformers for insulating oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The graph showing the change of oleic acid value of the synthetic ester insulating oil of Example 1 and Comparative Examples 1 to 3 with aging time;

[0022] Figure 2 This is a graph showing the change in peroxide value of the synthetic ester insulating oil of Example 1 and Comparative Examples 1 to 3 with aging time. DETAILED DESCRIPTION

[0023] The present invention provides a method for preparing a sustained-release antioxidant, comprising the following steps:

[0024] (1) mixing octadecyltrimethylammonium bromide, 2,6-di-tert-butyl-p-cresol, ethyl orthosilicate, water and ammonia water to react to obtain an antioxidant;

[0025] (2) In a protective atmosphere, an antioxidant, ethanol, water and γ-mercaptopropyltriethoxysilane are mixed and reacted to obtain the sustained-release antioxidant.

[0026] In the present invention, the mass ratio of octadecyltrimethylammonium bromide, 2,6-di-tert-butyl-p-cresol and tetraethyl orthosilicate in step (1) is preferably 1-2:15-20:3.5-4, more preferably 1.2-1.8:16-19:3.6-3.9, and more preferably 1.4-1.6:17-18:3.7-3.8.

[0027] In the present invention, the mass ratio of octadecyltrimethylammonium bromide, water and aqueous ammonia in step (1) is preferably 1-2: 80-120: 0.1-0.5, more preferably 1.2-1.8: 85-115: 0.15-0.45, and more preferably 1.4-1.6: 90-110: 0.2-0.3.

[0028] In the present invention, the mass fraction of the aqueous ammonia is preferably 25 to 28%, more preferably 25.5 to 27.5%, and even more preferably 26 to 27%.

[0029] In the present invention, octadecyltrimethylammonium bromide and water are first mixed, and the stirring time of the mixing is preferably 10 to 20 minutes, more preferably 12 to 18 minutes, and more preferably 14 to 16 minutes; then 2,6-di-tert-butyl-p-cresol is added and stirred, and the stirring time is preferably 20 to 40 minutes, more preferably 25 to 35 minutes, and more preferably 26 to 34 minutes; then tetraethyl orthosilicate and ammonia water are added to react.

[0030] In the present invention, the reaction temperature in step (1) is preferably 20-30°C, more preferably 22-28°C, more preferably 24-26°C; the reaction time is preferably 20-30h, more preferably 22-28h, more preferably 24-26h.

[0031] In the present invention, after the reaction in step (1) is completed, centrifugation is performed and ethanol is used for washing to obtain an antioxidant.

[0032] In the present invention, the mass volume ratio of the antioxidant, ethanol, water and γ-mercaptopropyltriethoxysilane in step (2) is preferably 5-15 g: 300-400 mL: 30-40 mL: 10-20 mL, more preferably 6-14 g: 320-380 mL: 32-38 mL: 12-18 mL, and more preferably 8-12 g: 340-360 mL: 34-36 mL: 14-16 mL.

[0033] In the present invention, antioxidant, ethanol and water are mixed, and the stirring speed of the mixing is preferably 200-400 rpm, more preferably 250-350 rpm, and more preferably 280-320 rpm; hydrochloric acid solution is added dropwise during the stirring process to adjust the pH.

[0034] In the present invention, the pH of the system after mixing in step (2) is preferably 3 to 4, more preferably 3.2 to 3.8, and even more preferably 3.4 to 3.6.

[0035] In the present invention, after the pH is adjusted, γ-mercaptopropyltriethoxysilane is added and mixed.

[0036] In the present invention, the mixing temperature in step (2) is preferably 20-30°C, more preferably 22-28°C, and more preferably 24-26°C; the mixing time is preferably 10-15h, more preferably 11-14h, and more preferably 12-13h.

[0037] In the present invention, the protective atmosphere in step (2) is preferably nitrogen or argon.

[0038] In the present invention, the reaction temperature in step (2) is preferably 50-70°C, more preferably 55-65°C, more preferably 58-62°C; the reaction time is preferably 10-15h, more preferably 11-14h, more preferably 12-13h.

[0039] In the present invention, after the reaction in step (2) is completed, the product is filtered and washed alternately with ethanol and water until it is neutral; the washed and purified product is dried, and the drying temperature is preferably 60-100°C, more preferably 65-95°C, and more preferably 70-90°C; the drying time is preferably 10-15h, more preferably 11-14h, and more preferably 12-13h; and after drying, a sustained-release antioxidant is obtained.

[0040] The invention also provides the sustained-release antioxidant prepared by the preparation method of the sustained-release antioxidant.

[0041] The invention also provides application of the slow-release antioxidant in synthetic ester insulating oil.

[0042] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0043] Example 1

[0044] Take 1.2g of octadecyltrimethylammonium bromide and 100g of water, mix them and stir for 10min to mix thoroughly; then add 18.75g of 2,6-di-tert-butyl-p-cresol and continue stirring for 30min to mix it evenly in the solution, add 3.75g of ethyl orthosilicate and 0.25g of 26% ammonia water in sequence, stir the mixture at 25°C for 24h, centrifuge it, and wash it with ethanol to obtain an antioxidant.

[0045] 10 g of antioxidant, 350 mL of ethanol and 35 mL of water were mixed, and hydrochloric acid solution was added dropwise at 300 rpm to adjust the pH to 3.5; then 15 mL of γ-mercaptopropyltriethoxysilane was added and stirred at 25 °C for 12 h; then the mixture was reacted at 60 °C in a nitrogen atmosphere for 12 h; after the reaction, the product was filtered and washed alternately with ethanol and water until neutral, and then the product was dried under vacuum at 80 °C for 12 h to obtain a sustained-release antioxidant, which was recorded as T501@SiO 2 .

[0046] The slow-release antioxidant prepared in this example was added to the synthetic ester insulating oil in an amount of 0.3 wt %, and then the synthetic ester insulating oil was vacuum dried for 48 h.

[0047] Comparative Example 1

[0048] The difference between Comparative Example 1 and Example 1 is that the amount of the slow-release antioxidant added to the synthetic ester insulating oil is 0.1 wt %.

[0049] Comparative Example 2

[0050] The difference between Comparative Example 2 and Example 1 is that the amount of the slow-release antioxidant added to the synthetic ester insulating oil is 0.5 wt %.

[0051] Comparative Example 3

[0052] The difference between Comparative Example 3 and Example 1 is that 2,6-di-tert-butyl-p-cresol (T501) is added to the synthetic ester insulating oil, and the added amount is still 0.3 wt %.

[0053] 200 g of the synthetic ester insulating oil prepared in Example 1 and Comparative Examples 1 to 3 were weighed and placed in a 120°C constant temperature box for 7, 14, 21, and 28 days of thermal aging to accelerate the oxidation rate of the synthetic ester insulating oil. The acid value and peroxide value of the insulating oil before and after aging, as well as the power frequency breakdown voltage after aging, were measured.

[0054] The changes of oleic acid value of synthetic ester insulating oil before and after aging are as follows: Figure 1 As shown in the figure, it can be seen that in the early stage of aging, the inhibitory effect of adding antioxidants on the acid value of insulating oil is more obvious, among which adding 0.3wt% T501@SiO 2 The acid value of synthetic ester insulating oil is relatively the lowest. However, with the increase of aging time, the addition of 0.1wt% T501@SiO 2 The acid value of the synthesized ester showed a significant upward trend. 2 Still maintain the lowest acid value level. Compared with the same addition amount of T501@SiO 2Compared with pure T501, the inhibitory effects of the two are similar in the early stage of aging, but in the later stage of aging, T501@SiO 2 The inhibitory effect on acid value is more obvious. This is mainly attributed to the SiO 2 The formed coating structure can slowly release T501, maintain its effective concentration in the insulating oil, and ensure the continuous antioxidant effect. Therefore, from the perspective of acid value control, adding 0.3wt% T501@SiO 2 Synthetic ester insulating oils exhibit the best antioxidant properties.

[0055] The changes of peroxide value of synthetic ester insulating oil before and after aging are as follows: Figure 2 As shown in Figure 2, the peroxide value in the oil gradually decreases with the increase of antioxidant content. Especially in the late aging period, adding 0.1wt% T501@SiO 2 The peroxide value of the oil increased significantly, which may be due to the fact that the generation rate of peroxyl radicals in the oil during aging exceeded the ability of T501 to reduce peroxyl radicals. 2 The oil has a more significant inhibitory effect on the peroxide value, further illustrating its advantage in delaying the oxidation process.

[0056] Example 1 and Comparative Examples 1 to 3 The power frequency breakdown voltage of the synthetic ester insulating oil after the aging experiment is completed is shown in Table 1.

[0057] Table 1 Power frequency breakdown voltage after aging test

[0058]

[0059] From the data in Table 1, it can be seen that adding 0.3wt% T501@SiO 2 The synthetic ester insulating oil still maintains a high breakdown voltage value after aging for 28 days, which is significantly better than the oil added with T501. This may be because T501@SiO 2 The coating structure not only has a certain adsorption effect, and can absorb part of the moisture and tiny impurities in the oil during the aging process, but also because it is modified with γ-isocyanatepropyltriethoxysilane, the isocyanate groups it carries can react with hydroxyl groups or other active groups in the synthetic ester, further enhancing its antioxidant and anti-aging properties.

[0060] As can be seen from the above examples, the slow-release antioxidant suitable for synthetic ester insulating oil is prepared by physical coating and lipophilic modification, has excellent solubility, can effectively inhibit the increase of the acid value of synthetic ester insulating oil, delay its oxidation process, and significantly extend the service life of insulating oil. At the same time, through the slow-release mechanism, the antioxidant of the present invention can extend its own antioxidant effect, improve the antioxidant stability during long-term operation, and meet the higher antioxidant requirements of high-performance equipment such as transformers for insulating oil.

[0061] The above is only a preferred embodiment 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 principle 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 a sustained-release antioxidant, characterized in that: It includes the following steps: (1) mixing octadecyltrimethylammonium bromide, 2,6-di-tert-butyl-p-cresol, ethyl orthosilicate, water and ammonia water to react to obtain an antioxidant; (2) In a protective atmosphere, an antioxidant, ethanol, water and γ-mercaptopropyltriethoxysilane are mixed and reacted to obtain the sustained-release antioxidant.

2. The method for preparing a sustained-release antioxidant according to claim 1, characterized in that: The mass ratio of octadecyltrimethylammonium bromide, 2,6-di-tert-butyl-p-cresol and tetraethyl orthosilicate in step (1) is 1-2:15-20:3.5-4.

3. The method for preparing a sustained-release antioxidant as claimed in claim 2, characterized in that: The mass ratio of octadecyltrimethylammonium bromide, water and aqueous ammonia in step (1) is 1-2:80-120:0.1-0.5; The mass fraction of the ammonia water is 25-28%.

4. The method for preparing a sustained-release antioxidant as claimed in claim 3, characterized in that: The reaction temperature in step (1) is 20-30° C. and the reaction time is 20-30 h.

5. The method for preparing a sustained-release antioxidant as claimed in claim 4, characterized in that: The mass volume ratio of the antioxidant, ethanol, water and γ-mercaptopropyltriethoxysilane in step (2) is 5-15 g: 300-400 mL: 30-40 mL: 10-20 mL.

6. The method for preparing a sustained-release antioxidant as claimed in claim 5, characterized in that: The pH of the system after mixing in step (2) is 3-4.

7. The method for preparing a sustained-release antioxidant as claimed in claim 6, characterized in that: The mixing temperature in step (2) is 20-30° C. and the mixing time is 10-15 hours.

8. The method for preparing a sustained-release antioxidant as claimed in claim 7, characterized in that: The reaction temperature in step (2) is 50-70° C. and the reaction time is 10-15 h.

9. The sustained-release antioxidant prepared by the method for preparing a sustained-release antioxidant according to any one of claims 1 to 8.

10. Use of the slow-release antioxidant according to claim 9 in synthetic ester insulating oil.

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