Regeneration method of zinc oxide catalyst for transformer waste oil treatment

Abstract

The invention discloses a regeneration method of a zinc oxide catalyst for transformer waste oil treatment, which comprises the following steps: (1) eluting and drying an inactivated zinc oxide catalyst by using an eluent to obtain an eluted and dried zinc oxide catalyst; and (2) performing partial selenium activation on the eluted and dried zinc oxide catalyst in a tube furnace filled with selenium powder in an argon atmosphere. The regeneration method disclosed by the invention has a good regeneration effect on the zinc oxide catalyst for treating the waste oil of the transformer, and is high in environmental protection property and low in cost.

Description

Technical Field

[0001] This invention belongs to the field of catalyst regeneration technology, and more specifically, relates to a method for regenerating zinc oxide catalyst for transformer waste oil treatment. Background Technology

[0002] As a core piece of equipment in the power system, the operational stability of transformers directly affects the safety of the power grid. Transformer insulating oil plays a dual role: serving as a cooling medium to regulate temperature and as an insulating medium to ensure electrical safety. This special liquid, primarily composed of mineral oil, is a non-renewable petrochemical resource and typically possesses excellent insulating properties. However, during long-term operation, transformer oil's insulating properties deteriorate due to thermal stress, electrochemical reactions, and oxidation, generating various organic impurities. These aging products not only reduce the oil's own insulating properties but also interact with internal transformer materials, forming conductive impurities that can ultimately lead to serious equipment failures. Therefore, it is necessary to periodically purify transformer insulating oil by removing impurities, water, and color. Common purification methods include adsorption, catalytic hydrogenation, and extraction. Recent research has found that photodegradation can also degrade organic impurities in waste transformer oil, achieving decolorization, impurity removal, and improved electrical properties.

[0003] Zinc oxide has attracted widespread attention in the field of photodegradation due to its ideal band structure and excellent electron transport properties. During the photodegradation of organic matter, when a zinc oxide catalyst receives ultraviolet light with a wavelength of 365 nm, electrons in its valence band are excited to transition to the conduction band, forming free electrons (ek). - At the same time, it leaves holes in the valence band (h) +These free electrons and holes migrate to the catalyst surface and react with adsorbed oxygen (O2), water molecules (H2O), or hydroxide ions (OH-) to generate highly active hydroxyl radicals (·OH). Organic impurities in transformer waste oil are effectively degraded through direct oxidation by hydroxyl radicals or oxidation by holes. As described above, the photodegradation process occurs on or near the surface of zinc oxide. However, if intermediate products accumulated on the catalyst surface do not leave in time, they will gradually accumulate and block surface active sites, leading to a decrease in the catalytic activity of zinc oxide or even complete loss of its photodegradation ability. Therefore, the regeneration process of deactivated catalysts is crucial. It not only allows for catalyst recycling, reducing the regeneration cost of photodegradation, but also reduces waste generation and mitigates environmental pollution. However, current regeneration methods mainly target catalysts in aqueous systems, while methods for regenerating oil-based catalysts are still lacking. Furthermore, existing regeneration methods still generate acidic elution wastewater, which can easily cause environmental pollution. Summary of the Invention

[0004] The purpose of this invention is to provide a method for regenerating zinc oxide catalysts for transformer waste oil treatment. The regeneration method of this invention re-exposes the active sites on the catalyst surface by elution with an eluent, and then activates the active sites of the catalyst by selenium activation. During the activation process, difficult-to-clean organic impurities are removed by high-temperature calcination, and the activity of photodegradation is restored.

[0005] To achieve the above objectives, the present invention provides a method for regenerating zinc oxide catalyst used in transformer waste oil treatment, the regeneration method comprising:

[0006] (1) The deactivated zinc oxide catalyst was eluted and dried with an eluent to obtain the eluted and dried zinc oxide catalyst;

[0007] (2) Under an argon atmosphere, the eluted and dried zinc oxide catalyst is partially activated by selenium in a tube furnace containing selenium powder.

[0008] According to the present invention, preferably, the eluent comprises: nonylphenol polyoxyethylene ether, sodium fatty alcohol polyoxyethylene ether sulfate, potassium tripolyphosphate, N-methylcarboxymethylmorpholine bis(trifluoromethanesulfonyl)imide and water;

[0009] Relative to 500 mL of water, the amount of nonylphenol polyoxyethylene ether used is 15-25 g, the amount of fatty alcohol polyoxyethylene ether sodium sulfate is 25-35 g, the amount of potassium tripolyphosphate is 35-45 g, and the amount of N-methylcarboxymethylmorpholine bis(trifluoromethanesulfonyl)imide is 10-20 g.

[0010] In this invention, by formulating an oil-removing eluent, the hydrophilic / hydrophobic conversion mechanism of a temperature-responsive ionic liquid is utilized to efficiently remove oily impurities from the catalyst surface, thereby re-exposing its active sites.

[0011] In this invention, the nonionic surfactant nonylphenol polyoxyethylene ether has good emulsifying and penetrating abilities, as well as excellent detergency and cleaning effects, making it suitable for removing oily impurities. The anionic surfactant sodium fatty alcohol polyoxyethylene ether sulfate has good degreasing properties and biodegradability. The auxiliary agent potassium tripolyphosphate can improve the cleaning effect of the eluent and has good solubility and stability in water. N-methylcarboxymethylmorpholine bis(trifluoromethanesulfonyl)imide is a temperature-responsive ionic liquid. Below 75°C, it is hydrophobic and can quickly and similarly dissolve oily substances on the surface of deactivated catalysts to achieve the effect of elution and oil removal. When the temperature rises above 75°C, the ionic liquid becomes hydrophilic, and the oily substances will combine with traditional surfactants in a homogeneous phase. After the temperature returns to room temperature, the oily substances can be separated from the ionic liquid, completing the regeneration and reuse of the ionic liquid.

[0012] In this invention, the oil-removing performance of the eluent is optimized by adjusting the ratio of nonionic and anionic surfactants, and the chelating metal removal ability of the eluent is optimized by adding a suitable potassium tripolyphosphate adjuvant. Through the selection and optimization of the types and components of the eluent surfactants, adjuvants, and temperature-responsive ionic liquids, a suitable eluent formulation is obtained, giving it excellent oil-removing and regeneration capabilities.

[0013] According to the present invention, preferably, the preparation method of the eluent includes the following steps: mixing the nonylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether sodium sulfate, potassium tripolyphosphate and water evenly, then adding the N-methylcarboxymethylmorpholine bis(trifluoromethanesulfonyl)imide, mixing evenly to obtain the eluent.

[0014] In this invention, more preferably, the preparation method of the eluent includes the following steps: adding the nonylphenol polyoxyethylene ether to water, stirring and mixing evenly, adding sodium fatty alcohol polyoxyethylene ether sulfate, stirring and mixing evenly, adding potassium tripolyphosphate, stirring and mixing evenly, and finally adding the N-methylcarboxymethylmorpholine bis(trifluoromethanesulfonyl)imide, stirring and mixing evenly to obtain the eluent.

[0015] According to the present invention, preferably, in step (1), the elution is performed 1-2 times, each time first eluting at 56-65°C for 40-90 minutes, and then eluting at 76-85°C for 40-90 minutes.

[0016] According to the present invention, preferably, in step (2): in the tube furnace, two ceramic crucibles are arranged in sequence in the direction of argon gas inlet, selenium powder is placed in the ceramic crucible closer to the direction of argon gas inlet, and the zinc oxide catalyst after washing and drying is placed in the other ceramic crucible.

[0017] According to the present invention, preferably, the amount of selenium powder used is 0.1-0.5g relative to 1g of deactivated zinc oxide.

[0018] According to the present invention, preferably, in step (2), the flow rate of the argon gas is 50-200 mL / min.

[0019] According to the present invention, preferably, in step (2), the partial selenium activation temperature is 400-500℃ and the time is 30-90min.

[0020] In this invention, calcination is used to provide high-temperature conditions for partial selenium activation.

[0021] In this invention, the catalyst undergoes a high-temperature activation process after elution. Selenium powder is converted into divalent selenium ions in an argon atmosphere for partial selenium-oriented activation. Simultaneously, the deeply attached organic matter is oxidized and removed at the high temperature of partial selenium-oriented activation. To avoid changes in the crystal structure and morphology of zinc oxide caused by high temperature and gas environment, the calcination activation temperature and time of partial selenium-oriented activation need to be optimized to improve the activity of the regenerated catalyst.

[0022] In this invention, the regeneration process differs significantly from the aqueous solution system used in traditional photodegradation processes. The large amount of transformer oil adhering to the catalyst surface significantly increases the difficulty of catalyst regeneration. Therefore, this invention aims to use a combination of various surfactants and temperature-responsive ionic liquid extraction to form a highly efficient and reliable eluent. This eluent effectively removes oily impurities from the catalyst surface and interior, re-exposing the active sites on the catalyst surface. The performance of the eluent is optimized through ratio control. Secondly, high-temperature calcination under an argon atmosphere is used to deeply remove difficult-to-remove organic impurities. Simultaneously, partial selenium-directed activation of selenium powder is used to activate the active sites of the catalyst, restoring the activity from photodegradation. This invention couples the above two processes through a rational connection, forming a continuously operable regeneration method for zinc oxide catalysts used in waste oil treatment.

[0023] In this invention, the regeneration method has low cost. Specifically, the cost of the eluent used for the elution and regeneration of the zinc oxide catalyst is approximately RMB 0.48 / kg. Adding the labor, water, electricity, and fixed asset losses during the eluent manufacturing process (RMB 0.13 / kg), the cost of the eluted catalyst is RMB 610 / ton. Adding the subsequent roasting and activation cost of RMB 1700 / ton, the total cost is RMB 2310 / ton. As shown in Table 1, the cost of the new catalyst is RMB 20,000 / ton, far exceeding the cost of the elution-activation coupled regeneration technology. Using a water washing-roasting process for regeneration requires extending the roasting time to 4 hours to remove more residual organic impurities, significantly increasing costs. Therefore, the elution-activation process for regeneration is more economical.

[0024] Table 1 Comparison of Economic Benefits

[0025] project New catalyst Washing-roasting Elution-Activation Cost (RMB / ton) 20000 4500 2310

[0026] The regeneration method of the present invention has good environmental benefits. Specifically, the activation time of the catalyst after elution is shorter than that after water washing (only 30-90 min of calcination is required), and the amount of waste gas emissions is significantly reduced, resulting in obvious environmental benefits.

[0027] The technical solution of the present invention has the following beneficial effects:

[0028] The regeneration method of the present invention has a good regeneration effect on zinc oxide catalyst used for transformer waste oil treatment, and is environmentally friendly and low in cost.

[0029] The regeneration method of the present invention not only improves the recycling rate and frequency of catalyst use, but also reduces waste generation and environmental pollution, thus having significant economic and social benefits.

[0030] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0031] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0032] Figure 1 Images of zinc oxide catalysts before and after regeneration are shown; where a is zinc oxide before photodegradation treatment, b is zinc oxide after photodegradation and deactivation followed by the treatment in the examples, and c is zinc oxide after photodegradation and deactivation followed by the treatment in the comparative examples.

[0033] Figure 2A calcination image of the catalyst after treatment in step (2) of Example 3 according to the present invention is shown.

[0034] Figure 3 A calcination image of the catalyst after treatment in comparative step (2) according to Test Example 3 of the present invention is shown.

[0035] Figure 4 The X-ray photoelectron spectrum of Zn in zinc oxide according to Test Example 4 of the present invention is shown.

[0036] Figure 5 The X-ray photoelectron spectrum of O in zinc oxide according to Test Example 4 of the present invention is shown.

[0037] Figure 4 and Figure 5 In this context, Intensity represents peak intensity, and Binding energy represents bond energy. Detailed Implementation

[0038] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0039] The present invention is further illustrated by the following examples:

[0040] In the following embodiments, comparative examples, and test cases:

[0041] The deactivated zinc oxide catalyst used was zinc oxide that had undergone photodegradation reaction in the waste oil of transformers from Xiaogan Power Supply Bureau using ultraviolet light with a wavelength of 365nm and a power of 100W for 24 hours.

[0042] In the examples: the nonylphenol polyoxyethylene ether, sodium fatty alcohol polyoxyethylene ether sulfate, and potassium tripolyphosphate used were all purchased from Sinopharm Group Co., Ltd.

[0043] The selenium powder used was purchased from Sinopharm Group Co., Ltd.

[0044] The preparation method of the N-methylcarboxymethylmorpholine bis(trifluoromethanesulfonyl)imide used is as follows:

[0045] Using equimolar amounts of N-methylmorpholine and ethyl chloroform as raw materials, the reaction was carried out in dichloromethane with stirring in an ice bath for 48 h. The resulting solid was then washed three times with diethyl ether to remove unreacted compounds, and hydrolyzed by reflux at 90 °C for 7 h with 37% hydrochloric acid aqueous solution. The chloride precursor was obtained by recrystallization in a mixture of acetonitrile and methanol (1:1 volume ratio), and then dissolved in 50 mL of a lithium bis(trifluoromethanesulfonyl)amide aqueous solution (the content of lithium bis(trifluoromethanesulfonyl)amide aqueous solution was half the molar amount of N-methylmorpholine). The reaction was stirred at 25 °C for 24 h, and the mixture was separated into layers to obtain the final product, N-methylcarboxymethylmorpholine bis(trifluoromethanesulfonyl)imide.

[0046] In the following test cases:

[0047] The acid value of transformer oil was determined by colorimetric titration in the national standard GB / T 41633.2-2022, "Determination of Acid Value of Insulating Liquids".

[0048] The dielectric loss value of transformer oil was determined using the national standard GB / T 5654.

[0049] The breakdown voltage of transformer oil was determined using the national standard GB / T 507-2002.

[0050] The sulfur content in transformer oil was determined using the industry standard SH / T0253-1992, the method for determining total sulfur content in petroleum products (electromagnetic method).

[0051] The water content was determined using a Karl Fischer micro-water analyzer.

[0052] Example

[0053] Preparation of eluent: Add 500 mL of deionized water as the base solvent to a 1 L container, gradually add 20 g of nonylphenol polyoxyethylene ether, stir and mix for 30 min, add 30 g of fatty alcohol polyoxyethylene ether sodium sulfate, stir and mix for 30 min, add 40 g of potassium tripolyphosphate, stir and mix for 10 min to fully dissolve it, and finally add 15 g of N-methylcarboxymethylmorpholine bis(trifluoromethanesulfonyl)imide, stir and mix for 30 min to form a self-made eluent that is uniformly mixed and has stable composition.

[0054] This embodiment provides a method for regenerating zinc oxide catalyst used in transformer waste oil treatment, as detailed below:

[0055] (1) Place 3g of deactivated zinc oxide catalyst into 200mL of the above eluent, stir at 60℃ for 1h, and then stir at 80℃ for 1h.

[0056] (2) After filtration, add 100 mL of the above eluent, stir at 60°C for 1 h, then stir at 80°C for 1 h; after filtration, dry at 120°C for 40 min to obtain the eluted and dried zinc oxide catalyst.

[0057] (3) In a tube furnace connected to an argon cylinder, two ceramic crucibles are sequentially placed in the direction of argon gas inflow, and these two ceramic crucibles are located in the middle of the tube furnace; 0.5g of selenium powder is placed in the ceramic crucible closer to the direction of argon gas inflow, and the above-mentioned eluted and dried zinc oxide catalyst is placed in the other ceramic crucible; first, the air in the tube furnace is purged by vacuuming, and then argon gas is introduced at a rate of 150mL / min, and the temperature is increased at a rate of 5℃ / min until it reaches 450℃. Then, under an argon gas flow rate of 150mL / min, the furnace is calcined at 450℃ for 1h to partially activate the selenium. After cooling, the treated catalyst (e.g.) is obtained. Figure 1 (As shown).

[0058] The state of the catalyst after the above steps is shown in Table 2.

[0059] Comparative Example

[0060] This comparative example provides a method for regenerating zinc oxide catalyst for transformer waste oil treatment, as detailed below:

[0061] (1) Place 3g of deactivated zinc oxide catalyst into 200mL of boiling water and stir for 2h;

[0062] (2) After filtration, stir in 100 mL of boiling water for 2 h; after filtration, dry at 120 °C for 40 min to obtain the eluted and dried catalyst;

[0063] (3) The eluted and dried catalyst is placed in a tube furnace, and then heated at a rate of 5°C / min to 450°C. After heating, it is calcined at 450°C for 4 hours. After cooling, the treated catalyst is obtained (e.g., Figure 1 (As shown).

[0064] The state of the catalyst after the above steps is shown in Table 2.

[0065] Table 2 Comparison of different regeneration schemes

[0066]

[0067]

[0068] Test Example 1

[0069] Photodegradation experiments were conducted on the zinc oxide catalysts treated in the above examples and comparative examples to degrade transformer waste oil. The degraded oil was then subjected to electrical and physicochemical property tests. Specifically, 0.1 kg of the catalysts treated in the comparative and examples were added to a device containing 1 kg of transformer waste oil from Xiaogan Power Supply Bureau. The waste oil was then photodegraded using ultraviolet light at a wavelength of 365 nm and a power of 100 W for 24 hours. Samples were taken after 24 hours of irradiation for testing, and the results are shown in Table 3.

[0070] Table 3 Comparison of Regeneration Effects of Different Regeneration Schemes

[0071]

[0072] As can be seen from the results in Table 3, the catalyst regenerated by the eluent can reduce the dielectric loss of deteriorated transformer oil to the national standard value.

[0073] Test Example 2

[0074] The deactivated zinc oxide catalyst was subjected to three consecutive regeneration cycle tests. Specifically, the process was as follows: (1) The deactivated zinc oxide catalyst was regenerated according to the method described in the above embodiment, and then 0.1 kg of the catalyst treated according to the embodiment was added to a device containing 1 kg of transformer waste oil from Xiaogan Power Supply Bureau. The waste oil was then photodegraded for 24 h using ultraviolet light with a wavelength of 365 nm and a wavelength of 100 W; (2) The deactivated zinc oxide catalyst after the previous photodegradation for 24 h was regenerated according to the method described in the above embodiment, and then 0.1 kg of the catalyst treated according to the embodiment was added to a device containing 1 kg of transformer waste oil from Xiaogan Power Supply Bureau. The waste oil was then photodegraded for 24 h using ultraviolet light with a wavelength of 365 nm and a wavelength of 100 W; (3) Step (2) was repeated once. The recycling capacity of the regeneration method of the present invention was determined by testing parameters such as dielectric loss and acid value of the oil sample after photodegradation.

[0075] Table 4. Changes in dielectric loss of catalyst-treated waste oil after regeneration cycle

[0076]

[0077] As shown in Table 4, although the dielectric loss value of the transformer oil sample was significantly lower than that before regeneration, the dielectric loss value of the zinc oxide after the third "elution-activation" treatment for photodegradation of waste oil increased with the number of regeneration cycles. Secondly, the acid value of the oil sample remained essentially unchanged after photodegradation. Therefore, the regeneration cycle experiment results indicate that this technology can significantly restore the catalytic activity of the catalyst, but performance degradation is inevitable.

[0078] Test Example 3

[0079] To verify the difference in catalyst elution effects between water washing and self-made eluent treatment, the catalysts treated in the comparative example step (2) and the example step (2) were calcined at 450°C in a muffle furnace. It was found that the water washing method generates and emits a large amount of polluting gases during the subsequent high-temperature calcination regeneration stage. Figure 3 This increases environmental remediation costs, while catalysts treated with self-made eluents do not release polluting gases under high-temperature conditions. Figure 2 The results indicate that the catalyst surface treated by the elution method has fewer organic impurities. Therefore, the self-made eluent can achieve efficient cleaning of zinc oxide catalysts used for transformer waste oil treatment, and can effectively remove oily impurities from the surface of deactivated catalysts, while water washing cannot completely remove oily impurities from the catalyst surface.

[0080] Test Example 4

[0081] X-ray photoelectron spectroscopy (XPS) characterization analysis was performed on zinc oxide that had not undergone photodegradation treatment (i.e., original zinc oxide) and zinc oxide that had been deactivated and treated according to the examples. The analysis revealed that the energy peak positions of Zn and O elements were basically consistent between the original zinc oxide and the activated zinc oxide (zinc oxide treated according to the examples) (see...). Figure 4 and 5 Furthermore, the energy intensities of different peaks are basically consistent, indicating that the regeneration method of the present invention can restore the original structural characteristics of the material and restore the photodegradation ability of zinc oxide.

[0082] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for regenerating zinc oxide catalyst used in transformer waste oil treatment, characterized in that, The regeneration method includes: (1) The deactivated zinc oxide catalyst was eluted and dried with an eluent to obtain the eluted and dried zinc oxide catalyst; (2) Under an argon atmosphere, the eluted and dried zinc oxide catalyst is partially activated by selenium in a tube furnace containing selenium powder.

2. The regeneration method according to claim 1, wherein, The eluent comprises: nonylphenol polyoxyethylene ether, sodium fatty alcohol polyoxyethylene ether sulfate, potassium tripolyphosphate, N-methylcarboxymethylmorpholine bis(trifluoromethanesulfonyl)imide, and water; Relative to 500 mL of water, the amount of nonylphenol polyoxyethylene ether used is 15-25 g, the amount of fatty alcohol polyoxyethylene ether sodium sulfate is 25-35 g, the amount of potassium tripolyphosphate is 35-45 g, and the amount of N-methylcarboxymethylmorpholine bis(trifluoromethanesulfonyl)imide is 10-20 g.

3. The regeneration method according to claim 2, wherein, The preparation method of the eluent includes the following steps: mixing the nonylphenol polyoxyethylene ether, sodium fatty alcohol polyoxyethylene ether sulfate, potassium tripolyphosphate and water evenly, then adding the N-methylcarboxymethylmorpholine bis(trifluoromethanesulfonyl)imide, mixing evenly to obtain the eluent.

4. The regeneration method according to claim 1, wherein, In step (1), the elution is performed 1-2 times, each time first eluting at 56-65℃ for 40-90 minutes, and then eluting at 76-85℃ for 40-90 minutes.

5. The regeneration method according to claim 1, wherein, In step (2): In the tubular furnace, two ceramic crucibles are arranged in sequence in the direction of argon gas inlet. Selenium powder is placed in the ceramic crucible closer to the direction of argon gas inlet, and the zinc oxide catalyst after washing and drying is placed in the other ceramic crucible.

6. The regeneration method according to claim 1, wherein, The amount of selenium powder used is 0.1-0.5g relative to 1g of deactivated zinc oxide.

7. The regeneration method according to claim 1, wherein, In step (2), the flow rate of the argon gas is 50-200 mL / min.

8. The regeneration method according to claim 1, wherein, In step (2), the partial selenium activation temperature is 400-500℃ and the time is 30-90min.

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