Regeneration method for recycling waste transformer oil

Abstract

The invention discloses a regeneration method for waste transformer oil recovery, which comprises the following steps: 1, pretreatment: preheating waste transformer oil to 50-70 DEG C, and filtering to obtain pretreated waste transformer oil; and 2, regeneration treatment: adding a composite regenerant into the pretreated waste transformer oil in the step 1, and carrying out mechanical stirring, ultrasonic treatment and solid-liquid separation to obtain regenerated transformer oil. The composite regenerant is a chitosan porous material loaded with hydrophobic modified nano aluminum nitride and nano silicon dioxide, the mass ratio of the nano aluminum nitride to the nano silicon dioxide is (1-2): 1, and the total mass of the nano aluminum nitride and the nano silicon dioxide accounts for 5%-20% of the mass of the composite regenerant. The composite regenerant disclosed by the method can realize synergistic adsorption of aging products such as acidic substances, moisture and colloid in the waste transformer oil, and the process has the advantages of greenness, high efficiency, excellent regenerated oil performance, low cost and no secondary pollution.

Description

Technical Field

[0001] This invention belongs to the field of regenerated transformer oil technology, specifically relating to a composite regenerator based on nanoparticles and chitosan, its preparation method, and its application. Background Technology

[0002] Transformer oil, as the "blood" of the power system, plays a crucial role in insulation, heat dissipation, and arc extinguishing. However, during long-term operation, transformer oil undergoes aging reactions due to multiple factors such as oxygen, moisture, electric fields, high temperatures, and metal catalysts. This process generates low-molecular-weight organic acids, alcohols, aldehydes, ketones, and other polar oxygen-containing compounds, which further condense to form gums, asphaltenes, and sludge. Simultaneously, impurities such as water, carbon particles, and metal shavings dissolve and suspend in the oil. These aging products lead to an increase in the acid value and a decrease in dielectric properties of the transformer oil (such as a decrease in breakdown voltage and an increase in the dielectric loss factor). Directly discarding the large quantities of waste transformer oil not only wastes resources but also poses a severe environmental disposal challenge due to its hazardous waste classification (HW08). Therefore, regenerating and recycling it to restore its performance and achieve circular utilization has significant economic and environmental benefits.

[0003] Currently, the regeneration methods for waste transformer oil are mainly divided into physical methods (such as filtration, centrifugation, and vacuum dehydration and degassing) and chemical methods (such as sulfuric acid-clay refining and solvent refining). Among these, the traditional "sulfuric acid-clay" process was once widely used, but it has insurmountable drawbacks: sulfuric acid reacts with impurities in the oil during treatment to generate large amounts of difficult-to-treat acid sludge, which is classified as hazardous waste; simultaneously, the process consumes a large amount of bleaching clay, generating waste bleaching clay solid waste, causing secondary pollution; the process is lengthy, energy-intensive, and carries safety risks associated with strong acid operation. This contradicts the current advocacy of green and low-carbon development concepts.

[0004] To overcome the drawbacks of traditional methods, adsorption purification has become a research hotspot due to its relatively simple operation and mild conditions. Compared with conventional adsorbents such as activated clay, bentonite, sepiolite, and diatomaceous earth, chitosan exhibits superior adsorption selectivity for polar degradation products, especially acidic substances. Furthermore, Liaoning Province, located in a coastal area, has abundant shrimp and crab shells, which are a primary source of chitosan.

[0005] On the other hand, with the development of nanotechnology, nanomaterials (such as nano-silica, nano-zinc oxide, and nano-aluminum nitride) exhibit adsorption activity and potential catalytic performance far exceeding that of traditional materials due to their extremely high specific surface area, abundant surface atoms, and unsaturated bonds. However, directly applying nanoparticles to transformer oil systems with high viscosity faces two major technical bottlenecks: First, nanoparticles have a large specific surface area and high surface energy, making them prone to agglomeration in oil, which significantly reduces their effective adsorption area and efficiency; second, after processing, due to the extremely small particle size of nanoparticles, separation and recovery are extremely difficult, usually requiring harsh conditions such as high-speed centrifugation (e.g., above 8000 r / min), which is not only energy-intensive but also prone to incomplete separation, resulting in nanoparticles remaining in the regenerated oil, introducing new insulation hazards, and even potentially causing partial discharge by entering the transformer winding gap with the oil.

[0006] CN 118931636A discloses a method for regenerating and recovering transformer oil. This method uses a porous inorganic particle composite chitosan as the adsorbent material, wherein the chitosan is an acid-resistant modified chitosan prepared by bacterial cellulose cross-linking modification. The porous inorganic particles include at least one of attapulgite, diatomaceous earth, or bentonite. This technical solution does not disclose the use of nanoscale inorganic particles as the composite component, nor does it perform hydrophobic modification treatment on the inorganic particles. This results in limited adsorption efficiency, easy agglomeration of nanoparticles, and difficulty in separation, making it difficult to achieve deep purification of aging products in waste transformer oil.

[0007] Therefore, there is a significant contradiction and gap in existing technologies: highly efficient nanomaterials face challenges in application and separation, while easily manipulated macroscopic adsorbents are limited by insufficient purification depth. How to organically combine the advantages of both to design a regenerator and supporting process that can achieve deep and rapid purification, is easy to separate and recover, and is even recyclable, has become a pressing technical challenge in this field. Summary of the Invention

[0008] To address the technical bottlenecks in the regeneration and treatment of waste transformer oil, a nanoparticle-chitosan adsorption and purification method was designed. Through the preparation and application of composite regenerators, efficient and green recycling can be achieved.

[0009] According to one aspect of the present invention, a regeneration method for recovering waste transformer oil is provided, comprising the following steps: Step 1, Pretreatment: Preheat the waste transformer oil to 50~70℃, filter it, and obtain pretreated waste transformer oil; Step 2, Regeneration treatment: Add the composite regenerator to the pretreated waste transformer oil described in Step 1, mechanically stir, ultrasonically treat, and separate the solid and liquid to obtain regenerated transformer oil; The composite regenerator is a chitosan porous material loaded with hydrophobically modified nano-aluminum nitride and nano-silica, wherein the mass ratio of nano-aluminum nitride to nano-silica is 1~2:1, and the total mass of the two accounts for 5%-20% of the mass of the composite regenerator.

[0010] Based on the above technical solution, the acid value of the waste transformer oil in step 1 is 0.106~1.2mgKOH / g, and the breakdown voltage is 24~31kV; The amount of the composite additive added is 1% to 5% of the pretreated waste transformer oil; The conditions for mechanical stirring are as follows: The temperature of the mechanical stirring is 60~80℃; The mechanical stirring speed is 800~1200 r / min; The mechanical stirring time is 40-80 minutes; The conditions for the ultrasonic treatment are as follows: The power of the ultrasonic treatment is 200~400W; The ultrasonic treatment time is 15-30 minutes.

[0011] Based on the above technical solution, the solid-liquid treatment is static sedimentation or low-speed centrifugation; When the solid-liquid treatment is static precipitation, allow it to settle at 60~70℃ for 60~90 min; When the solid-liquid treatment is performed by low-speed centrifugation, centrifuge at a speed of 3000~5000 r / min for 20~40 min.

[0012] Based on the above technical solution, the preparation method of the composite regenerator in step 2 includes the following steps: dissolving chitosan in dilute acetic acid solution to form a slurry, adding hydrophobically modified nano-aluminum nitride and nano-silica, stirring and mixing, vacuum freeze-drying to form a porous solid framework, crushing and sieving to obtain the composite regenerator.

[0013] Based on the above technical solution, the modified nano-aluminum nitride and nano-silica used in the hydrophobically modified nano-aluminum nitride and nano-silica are hexadecyltrimethoxysilane. The modification process includes: dispersing nano-aluminum nitride in isopropanol, adding the modifier at 50~60℃, and reacting in a water bath for 120~180 min to obtain the modified nano-aluminum nitride. Nano-silica was dispersed in a mixed solution of ethanol and ammonia, and a modifier was added at 50-60°C. The mixture was then reacted in an oil bath for 180-240 minutes to obtain modified nano-silica.

[0014] Based on the above technical solution, the mass-to-volume ratio of the nano-aluminum nitride to isopropanol is 1~3g:50~100ml; The mass ratio of the nano-aluminum nitride to the modifier is 10~20:1~3; The mass-to-volume ratio of the nano-silica to ethanol is 2~5g:80~150ml; The mass ratio of the nano-silica to the modifier is 15~25:2~4.

[0015] Based on the above technical solution, the concentration of dilute acetic acid in the slurry is 1%~3%; The concentration of chitosan in the slurry is 5%~10%; The mass ratio of chitosan, hydrophobically modified nano-aluminum nitride, and nano-silica is 70~90:5~15:3~10.

[0016] Based on the above technical solution, the stirring and mixing conditions are as follows: the stirring and mixing time is 60~120min; The stirring speed is 500~800 r / min; The freeze-drying conditions are as follows: The freeze-drying temperature is -40~-20℃; The freeze-drying time is 24-48 hours.

[0017] Beneficial effects The composite regenerator disclosed in this invention achieves synergistic adsorption by incorporating nanomaterials, which possess high specific surface area and targeted adsorption, along with the three-dimensional network structure of chitosan. Hydrophobic modification of nano-aluminum nitride and nano-silica reduces nanoparticle aggregation, improving dispersibility and adsorption efficiency. Furthermore, the chitosan matrix facilitates separation and recycling, reducing energy consumption and the risk of secondary pollution. The technical solution disclosed in this invention is simple in process and low in cost, significantly improving regenerated oleic acid value, moisture content, and other indicators, meeting reuse standards. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the preparation process of the composite regenerant described in Example 1 of the present invention. Detailed Implementation

[0019] To make the objectives and technical solutions of this invention clearer, the following embodiments are provided for further explanation. However, the scope of protection of this invention is not limited to these embodiments; the embodiments are merely for illustrative purposes. Those skilled in the art should understand that any changes or equivalent substitutions that do not depart from the concept of this invention are included within the scope of protection of this invention.

[0020] Unless otherwise specified, all reagents and raw materials used in this invention were obtained through purchase. Chitosan was purchased from Sinopharm Group; nano-aluminum nitride was purchased from Shanghai Maclean Company with a particle size of 2-5 μm; and nano-silica was purchased from Shanghai Maclean Company with a particle size of 30-50 nm.

[0021] Preparation Example 1 Step 1, preparation of chitosan slurry: Weigh 80g of chitosan and dissolve it in 1000ml of 2% dilute acetic acid solution to form a uniform slurry; Step 2, hydrophobic modification of nano-aluminum nitride: Dissolve 10g of nano-aluminum nitride in 500ml of isopropanol, add 1g of hexadecyltrimethoxysilane at 55℃, and react in a water bath for 150min to obtain hydrophobically modified nano-aluminum nitride (HDMS modified). Step 3, hydrophobic modification of nano-silica: 8g of nano-silica was dispersed in 800ml of a mixed solution of ethanol and ammonia (volume ratio of ethanol to ammonia was 1:3, and mass fraction of ammonia was 30%). 2g of hexadecyltrimethoxysilane was added at 75℃, and the mixture was reacted in a water bath for 200min to obtain hydrophobically modified nano-silica (HDMS modified). Step 4: Following a 1:1 mass ratio of nano-aluminum nitride to nano-silica, add 5g of the hydrophobically modified nano-aluminum nitride obtained in Step 2 and 5g of the hydrophobically modified nano-silica obtained in Step 3 to 500ml of the slurry obtained in Step 1. Mechanically stir at 600r / min for 90min, then freeze-dry under vacuum at -30℃ for 36h to form a porous solid framework. Crush and pass through a 100-mesh sieve to obtain granular composite regenerant. See [link to detailed preparation process] for more information. Figure 1 .

[0022] Preparation Example 2 The difference from Preparation Example 1 is that the mass ratio of nano-aluminum nitride to nano-silica in step 4 is 2:1. Specifically, 6g of hydrophobically modified nano-aluminum nitride obtained in step 2 and 3g of hydrophobically modified nano-silica obtained in step 3 are added to 500ml of the slurry obtained in step 1, mechanically stirred at 600r / min for 90min, and then vacuum freeze-dried at -30℃ for 36h to form a porous solid framework. The solid is then crushed and passed through a 100-mesh sieve. The remaining steps are consistent with Preparation Example 1 to obtain a granular composite regenerant.

[0023] Comparative Example 1 The difference from Preparation Example 1 is that steps 2 and 3 are not required. In addition, the nano-aluminum nitride and nano-silica in step 4 are replaced with 10g of attapulgite, which is directly added to 500ml of the slurry obtained in step 1 and dried at 80℃ for 12h to obtain a conventional regenerator.

[0024] Application Example 1 Step 1, Pretreatment: Waste transformer oil with an acid value of 0.2 mg KOH / g and a breakdown voltage of 28.76 kV is preheated at 60°C for 2 hours and then coarsely filtered through a 200-mesh filter to remove mechanical impurities, thus obtaining pretreated waste transformer oil. Step 2, regeneration treatment: Add 30g of the granular regenerator prepared in Preparation Example 1 (addition amount is 3%) to 1000ml of the pretreated waste transformer oil described in Step 1, and mechanically stir at 1000r / min at 70℃ for 60min, while simultaneously performing ultrasonic treatment (power is 300W, 70℃, 20min) to promote the adsorption of aging products. Let it stand at 65℃ for 80min to settle, and collect the supernatant, which is the regenerated transformer oil. The properties of the regenerated transformer oil are shown in Table 1.

[0025] Application Example 2 The difference from Application Example 1 is that the amount of granular regenerant added in step 2 is different. Specifically, 50g of the granular regenerant prepared in Preparation Example 1 (addition amount of 5%) is added to 1000ml of the pretreated waste transformer oil described in step 1. The remaining steps are the same as in Application Example 1 to obtain regenerated transformer oil. The performance of the regenerated transformer oil is shown in Table 1.

[0026] Application Example 3 The difference from Application Example 1 is that the static settling in step 3 is replaced by low-speed centrifugation, specifically centrifugation at 4000 r / min for 30 min. The remaining steps are the same as in Application Example 1, and the regenerated transformer oil is obtained. The properties of the regenerated transformer oil are shown in Table 1.

[0027] Application Example 4 The granular regenerant in Example 1 is recycled by filtering and collecting the regenerant after static settling, washing it three times with anhydrous ethanol, and then vacuum drying it at 80°C for 2 hours to obtain the recycled composite regenerant.

[0028] Application Example 5 The recovered composite regenerant obtained in Application Example 4 was used for transformer oil regeneration. The regeneration process was consistent with that in Application Example 1, and regenerated transformer oil was obtained. The properties of the regenerated transformer oil are shown in Table 1.

[0029] Comparative Example 2 The conventional regenerant prepared in Comparative Example 1 was used to regenerate waste transformer oil. The regeneration process was as follows: 30g of conventional composite regenerant was added to 1000ml of waste transformer oil pretreated in Application Example 1, and the mixture was mechanically stirred at 1000r / min at 70℃ for 60min without ultrasonic treatment. The regenerant was recovered by high-speed centrifugation at 8000r / min for 60min, and the supernatant was collected to obtain regenerated transformer oil. The properties of the regenerated transformer oil are shown in Table 1.

[0030] Table 1 shows the performance of regenerated transformer oil.

[0031] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A regeneration method for recovering waste transformer oil, characterized in that, Includes the following steps: Step 1, Pretreatment: Preheat the waste transformer oil to 50~70℃, filter it, and obtain pretreated waste transformer oil; Step 2, Regeneration treatment: Add the composite regenerator to the pretreated waste transformer oil described in Step 1, mechanically stir, ultrasonically treat, and separate the solid and liquid to obtain regenerated transformer oil; The composite regenerator is a chitosan porous material loaded with hydrophobically modified nano-aluminum nitride and nano-silica, wherein the mass ratio of nano-aluminum nitride to nano-silica is 1~2:1, and the total mass of the two accounts for 5%~20% of the mass of the composite regenerator.

2. The regeneration method according to claim 1, characterized in that, The waste transformer oil mentioned in step 1 has an acid value of 0.106~0.2mgKOH / g and a breakdown voltage of 24~31kV; The amount of the composite additive added is 1% to 5% of the pretreated waste transformer oil; The conditions for magnetic stirring are as follows: The temperature of the mechanical stirring is 60~80℃; The mechanical stirring speed is 800~1200 r / min; The mechanical stirring time is 40-80 minutes; The conditions for the ultrasonic treatment are as follows: The power of the ultrasonic treatment is 200~400W; The ultrasonic treatment time is 15-30 minutes.

3. The regeneration method according to claim 1, characterized in that, The solid-liquid treatment is either static sedimentation or low-speed centrifugation. When the solid-liquid treatment is static precipitation, allow it to settle at 60~70℃ for 60~90 min; When the solid-liquid treatment is performed by low-speed centrifugation, centrifuge at a speed of 3000~5000 r / min for 20~40 min.

4. The regeneration method according to claim 1, characterized in that, The preparation method of the composite regenerator in step 2 includes the following steps: dissolving chitosan in dilute acetic acid solution to form a slurry, adding hydrophobically modified nano-aluminum nitride and nano-silica, stirring and mixing, vacuum freeze-drying to form a porous solid framework, crushing and sieving to obtain the composite regenerator.

5. The regeneration method according to claim 4, characterized in that, The hydrophobically modified nano-aluminum nitride and nano-silica used hexadecyltrimethoxysilane as the modifier. The modification process includes: dispersing nano-aluminum nitride in isopropanol, adding the modifier at 50~60℃, and reacting in a water bath for 120~180 min to obtain the modified nano-aluminum nitride. Nano-silica was dispersed in a mixed solution of ethanol and ammonia, and a modifier was added at 50-60°C. The mixture was then reacted in a water bath for 180-240 minutes to obtain modified nano-silica.

6. The regeneration method according to claim 4, characterized in that, The mass-to-volume ratio of the nano-aluminum nitride to isopropanol is 1~3g:50~100ml; The mass ratio of the nano-aluminum nitride to the modifier is 10~20:1~3; The mass-to-volume ratio of the nano-silica to ethanol is 2~5g:80~100ml; The mass ratio of the nano-silica to the modifier is 15~25:2~4; The ethanol and ammonia solution has a mass ratio of 1:3 and ammonia content of 30%.

7. The regeneration method according to claim 4, characterized in that, The concentration of dilute acetic acid in the slurry is 1% to 3%; The concentration of chitosan in the slurry is 5%~10%; The mass ratio of chitosan, hydrophobically modified nano-aluminum nitride, and nano-silica is 70~90:5~15:3~10.

8. The regeneration method according to claim 4, characterized in that, The mixing conditions are as follows: the mixing time is 60~120 min; The stirring speed is 500~800 r / min; The freeze-drying conditions are as follows: The freeze-drying temperature is -40~-20℃; The freeze-drying time is 24-48 hours.

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