Process for producing transformer base oil, transformer base oil and transformer oil

Abstract

The application provides a transformer base oil production process, a transformer base oil and a transformer oil, and particularly relates to the technical field of mineral oil production. The transformer base oil production process is characterized by the following steps: mixing raw oil and hydrogen to obtain refined generated oil; and fractionating the refined generated oil to obtain the transformer base oil. The raw oil comprises solvent-extracted oil and / or tire pyrolysis oil. The production process selectively removes non-ideal components such as aromatic hydrocarbons and nitrides through refining, while retaining the naphthenic structure to the maximum extent; and then cutting the target fraction through fractionation. The production process has the advantages of simple process, high value of resources and environmental friendliness. The transformer base oil prepared by the production process avoids the disposal cost of waste white clay and the energy consumption of furfural recovery, and has a lower comprehensive production cost. The transformer oil prepared by using the transformer base oil also has a reduced cost, which reduces the operation and maintenance cost of the transformer and improves the economy and reliability of power grid operation.

Description

Technical Field

[0001] This invention relates to the technical field of mineral oil production, and in particular to a production process for transformer base oil, transformer base oil, and transformer oil. Background Technology

[0002] Transformer oil base oil is a key functional material for ensuring the safe operation of power equipment, requiring excellent insulation, cooling properties, oxidation stability, and an ultra-low pour point. Currently, the industry mainly relies on naphthenic second-line or reduced-line distillate oils, as they are naturally rich in naphthenes, have good low-temperature fluidity, and do not require deep dewaxing to meet specifications. However, naphthenic crude oil accounts for less than 5% of global crude oil reserves, and my country's recoverable resources are particularly limited, facing long-term pressure from supply shortages and rising costs.

[0003] Meanwhile, solvent extract oils and emerging tire pyrolysis oils, both byproducts of refineries, share common characteristics of high aromatics, high cycloalkanes, extremely low alkanes, and ultra-low pour points, theoretically possessing the basic component advantages for producing high-quality transformer oils. However, due to their high content of nitrogen, sulfur, gum, and polycyclic aromatic hydrocarbons, conventional refining methods are difficult to utilize effectively: although traditional furfural-clay refining can remove aromatics and decolorize, clay regeneration is difficult, waste disposal costs are high, and deep dearomatization before hydrogenation easily leads to the loss of ideal cycloalkanes, resulting in product yields generally below 85%; although a combined process of hydrogenation, hydrodewaxing, and supplementary refining can improve quality, it requires multiple reactors in series, a complex high-pressure hydrodewaxing system, and strict catalyst gradation requirements, significantly increasing investment and operating costs. Furthermore, the hydrodewaxing process is accompanied by the splitting of light components, further reducing the yield of heavy base oils.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a production process for transformer base oil, transformer base oil, and transformer oil, aiming to solve at least one of the above-mentioned technical problems in the prior art.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: The first aspect of the present invention provides a production process for transformer base oil, wherein a raw material oil and hydrogen are mixed and refined to obtain a refined product oil; the refined product oil is fractionated to obtain the transformer base oil; wherein the raw material oil includes solvent-extracted oil and / or tire pyrolysis oil.

[0007] Furthermore, the volume ratio of the hydrogen to the feedstock oil is 600~1300:1.

[0008] Preferably, in the purification process, the hydrogen partial pressure is >8.0 MPa.

[0009] Preferably, the refining reaction temperature is 300~370℃, and the volume hourly space velocity is 0.2~1.0 h⁻¹. -1 .

[0010] Furthermore, the fractionation is carried out within a fractionation column.

[0011] Preferably, the fractionation is vacuum fractionation.

[0012] Preferably, the top pressure of the fractionation column is 0.07~0.09MPa and the temperature is 50~70℃.

[0013] Preferably, the bottom temperature of the fractionation column is 270~310℃.

[0014] Preferably, the feed temperature of the fractionation tower is 220~240℃.

[0015] Furthermore, the feedstock oil contains 1-6 wt% alkanes, 20-40 wt% cycloalkanes, and 40-90 wt% aromatics, with a pour point < -40°C.

[0016] Furthermore, the catalyst used in the refining process includes at least one of tungsten-nickel hydrogenation catalyst, molybdenum-nickel hydrogenation catalyst, and molybdenum-tungsten-nickel hydrogenation catalyst, preferably a tungsten-nickel hydrogenation catalyst.

[0017] The second aspect of the present invention provides a transformer base oil, which is prepared using the production process described in the first aspect.

[0018] A third aspect of the present invention provides a transformer oil comprising 0.25-0.35 wt% antioxidant, with the balance being the transformer base oil.

[0019] Furthermore, the antioxidants include aromatic amine antioxidants and / or hindered phenolic antioxidants.

[0020] Furthermore, the transformer oil has a breakdown voltage > 50kV and a kinematic viscosity < 1800 mm³ at -30℃. 2 / s, cycloalkane carbon content C N Value > 61%.

[0021] Furthermore, the total acid value of the transformer oil after an oxidation stability test at 120°C for 500 hours is <0.6 mg KOH / g.

[0022] Preferably, the transformer oil contains less than 0.3% sludge.

[0023] Preferably, the dielectric loss factor of the transformer oil is <0.05 at 90°C.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects: The production process provided by this invention first involves refining to selectively remove non-ideal components such as aromatics and nitrogen compounds, while preserving the cycloalkane structure to the maximum extent possible; then, the target fraction is obtained through fractionation. This production process combines simplicity, high resource utilization, and environmental friendliness. The transformer base oil prepared by this process avoids the costs of waste clay disposal and the energy consumption of furfural recovery, resulting in a lower overall production cost; the cost of transformer oil prepared using this transformer base oil is also reduced, lowering transformer operation and maintenance costs and improving the economy and reliability of power grid operation. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0026] In the following, the terms “comprising,” “having,” and their cognates, which may be used in various embodiments of the invention, are intended only to indicate a particular feature, number, step, operation, element, component, or combination thereof, and should not be construed as excluding, firstly, the presence of one or more other features, numbers, steps, operations, elements, components, or combinations thereof, or adding the possibility of one or more features, numbers, steps, operations, elements, components, or combinations thereof.

[0027] The first aspect of the present invention provides a production process for transformer base oil, wherein a raw material oil and hydrogen are mixed and refined to obtain a refined product oil; the refined product oil is fractionated to obtain the transformer base oil; wherein the raw material oil includes solvent-extracted oil and / or tire pyrolysis oil.

[0028] Furthermore, the volume ratio of the hydrogen to the feedstock oil is 600~1300:1.

[0029] Typically, but not limitingly, the volume ratio of the hydrogen to the feedstock oil can be, for example, 600:1, 700:1, 800:1, 900:1, 1000:1, 1100:1, 1200:1 or 1300:1, or any ratio in the range of 600 to 1300:1.

[0030] Preferably, in the refining process, a hydrogen partial pressure > 8.0 MPa is beneficial for enhancing the deep hydrogenation saturation of heteroatom compounds such as aromatics and nitrides, especially for polycyclic aromatics and basic nitrides, thereby improving the refining depth and cycloalkanes retention rate, and ensuring the oxidation stability and dielectric loss factor of the base oil. However, when the hydrogen partial pressure is < 8.0 MPa, the removal of heteroatoms is insufficient, which can easily lead to an increase in the acid value of the transformer oil, an increase in sludge precipitation, and an excessive dielectric loss factor. Although the risk of ring-opening by cycloalkanes hydrogenation is reduced, insufficient refining depth leads to a decrease in the conversion rate of aromatics to cycloalkanes by hydrogenation, thereby reducing the oxidation stability of the product and the solubility of sludge.

[0031] Typically, but not limitingly, in the purification process, the hydrogen partial pressure can be, for example, a value greater than 8.0 MPa such as 8.1 MPa, 9 MPa, 10.0 MPa, 13 MPa, or 15 MPa, or any pressure value within the range greater than 8.0 MPa.

[0032] Preferably, the refining reaction temperature is 300~370℃, and the volume hourly space velocity is 0.2~1.0 h⁻¹. -1 During the refining process, aromatics are hydrogenated to saturation, nitrogen / sulfur compounds are hydrogenated to remove them, gums are cracked, and some polycyclic aromatic hydrocarbons undergo deep saturation reactions. At the same time, under optimal conditions, the ring-opening of cycloalkanes and the cracking of alkanes are suppressed to achieve selective purification and avoid excessive hydrogenation.

[0033] Typical, but not limiting, the purification reaction temperature can be, for example, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, or 370°C, or any value within the range of 300°C to 370°C; the volume hourly space velocity can be, for example, 0.2 h⁻¹. -1 0.4h -1 0.5h -1 0.6h -1 0.8h -1 or 1.0h -1 It can also be 0.2~1.0h -1 Any value within the range.

[0034] Furthermore, the fractionation is carried out within a fractionation column.

[0035] Preferably, the fractionation is vacuum fractionation. Under reduced system pressure, by controlling the temperature gradient at the top / bottom of the column, the target fraction corresponding to the transformer base oil distillation range in the refined product oil is cut and enriched according to the difference in relative volatility of each component, while removing light impurity distillate oil.

[0036] Preferably, the top pressure of the fractionation column is 0.07~0.09MPa and the temperature is 50~70℃.

[0037] Typically, but not limitingly, the top pressure of the fractionation column can be, for example, 0.07 MPa, 0.075 MPa, 0.08 MPa, 0.085 MPa or 0.09 MPa, or any value in the range of 0.07 to 0.09 MPa; the top temperature can be, for example, 50°C, 55°C, 60°C, 65°C or 70°C, or any value in the range of 50 to 70°C.

[0038] Preferably, the bottom temperature of the fractionation column is 270~310℃.

[0039] Typically, but not limitingly, the bottom temperature of the fractionation column can be, for example, 270°C, 280°C, 290°C, 300°C, or 310°C, or any value within the range of 270°C to 310°C.

[0040] Preferably, the feed temperature of the fractionation tower is 220~240℃.

[0041] Typically, but not limitingly, the feed temperature of the fractionation tower can be, for example, 220°C, 225°C, 230°C, 235°C, or 240°C, or any value within the range of 220°C to 240°C.

[0042] Furthermore, the feedstock oil contains 1-6 wt% alkanes, 20-40 wt% cycloalkanes, and 40-90 wt% aromatics, with a pour point < -40°C. The feedstock oil used in this invention is naturally rich in cycloalkanes and isoalkanes, and contains almost no n-chain alkanes, thus possessing excellent ultra-low pour point properties and structural potential as a transformer base oil.

[0043] This invention does not specifically limit the origin and grade of solvent-extracted oil and tire pyrolysis oil in the feedstock. Any solvent-extracted oil and tire pyrolysis oil that meets the above-mentioned aromatic content and pour point can be used to produce transformer base oil using the production process provided by this invention.

[0044] Typically, but not limitingly, the aromatic content in the feedstock oil may be, for example, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, or 90 wt%, or any value within the range of 40 to 90 wt%.

[0045] In some embodiments of the present invention, the solvent extraction oil may be a naphthenic secondary solvent extraction oil, such as CNOOC Suizhong 36-1 secondary solvent extraction oil and CNOOC Qinhuangdao 32-6 secondary solvent extraction oil.

[0046] In some embodiments of the present invention, the tire pyrolysis oil may be, for example, tire pyrolysis oil provided by Jinan Hengyu, tire pyrolysis oil provided by Shandong Kaiyuan Runfeng, or tire pyrolysis oil provided by Jinan Youbang Xingyuan.

[0047] Furthermore, the catalyst used in the refining process includes at least one of tungsten-nickel hydrogenation catalyst, molybdenum-nickel hydrogenation catalyst, and molybdenum-tungsten-nickel hydrogenation catalyst, preferably a tungsten-nickel hydrogenation catalyst.

[0048] The second aspect of the present invention provides a transformer base oil, which is prepared using the production process described in the first aspect.

[0049] A third aspect of the present invention provides a transformer oil comprising 0.25-0.35 wt% antioxidant, with the balance being the transformer base oil.

[0050] Typically, but not limitingly, the antioxidant content can be, for example, 0.25 wt%, 0.28 wt%, 0.30 wt%, 0.32 wt%, or 0.35 wt%, or any value in the range of 0.25 to 0.35 wt%, and the remaining components are the transformer base oil described above.

[0051] Furthermore, the antioxidants include aromatic amine antioxidants and / or hindered phenolic antioxidants.

[0052] Furthermore, the transformer oil has a breakdown voltage > 50kV and a kinematic viscosity < 1800 mm³ at -30℃. 2 / s, cycloalkane carbon content C N Value > 61%.

[0053] Furthermore, the total acid value of the transformer oil after an oxidation stability test at 120°C for 500 hours is <0.6 mg KOH / g.

[0054] Preferably, the transformer oil contains less than 0.3% sludge.

[0055] Preferably, the dielectric loss factor of the transformer oil is <0.05 at 90°C.

[0056] The production process provided by this invention first involves refining to selectively remove non-ideal components such as aromatics and nitrogen compounds, while preserving the cycloalkane structure to the maximum extent possible; then, the target fraction is obtained through fractionation. This production process combines simplicity, high resource utilization, and environmental friendliness. The transformer base oil prepared by this process avoids the costs of waste clay disposal and the energy consumption of furfural recovery, resulting in a lower overall production cost; the cost of transformer oil prepared using this transformer base oil is also reduced, lowering transformer operation and maintenance costs and improving the economy and reliability of power grid operation.

[0057] The present invention is further illustrated below with specific embodiments and comparative examples. However, it should be understood that these embodiments are merely for illustrative purposes and should not be construed as limiting the invention in any way. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of the present invention were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0058] The physicochemical properties of the feed oils used in the following examples and comparative examples are shown in Table 1.

[0059] Table 1

[0060] Tungsten-nickel type hydrogenation catalyst: purchased from CNOOC Chemical and New Materials Research Institute, grade ZQC-25 hydrogenation catalyst; Molybdenum-nickel type hydrogenation catalyst: purchased from CNOOC Chemical and New Materials Research Institute, grade ZQC-26 hydrogenation catalyst; Molybdenum-cobalt type hydrogenation catalyst: purchased from CNOOC Chemical and New Materials Research Institute, grade ZQC-27 hydrogenation catalyst.

[0061] Example 1 This embodiment provides a transformer oil, using solvent-extracted oil from the CNOOC Suizhong 36-1 reduced voltage line II as raw material. The specific production process is as follows: 1. The feedstock oil is mixed with hydrogen and then introduced into a fixed-bed hydrotreating pilot plant packed with a tungsten-nickel type hydrotreating catalyst ZQC-25 for refining reaction; wherein the reaction temperature is 350℃, the hydrogen-to-oil volume ratio is 1000:1, the system hydrogen partial pressure is 15.0 MPa, and the volume hourly space velocity is 0.5 h⁻¹. -1 .

[0062] 2. The refined oil obtained from the reaction is fed into a vacuum distillation tower for fractionation. The operating conditions are: top pressure 0.08 MPa, top temperature 60℃, bottom temperature 290℃, and feed temperature 230℃. The target fraction is collected to obtain transformer base oil.

[0063] 3. Take the base oil obtained above, add 0.30wt% of 2,6-di-tert-butyl-p-cresol (BHT), and stir evenly at 60℃ for 30 minutes to obtain the finished transformer oil.

[0064] Example 2 This embodiment provides a transformer oil. The difference from Embodiment 1 is that the refining reaction temperature is 330°C. The rest of the production process is the same as that in Embodiment 1, and will not be described again here.

[0065] Example 3 This embodiment provides a transformer oil that differs from Embodiment 1 in that the feedstock oil is replaced with Shandong Kaiyuan Runfeng Tire Cracked Oil. The refining reaction temperature is 360°C, and during the refining reaction, the system hydrogen partial pressure is 16.0 MPa and the volume hourly space velocity is 0.3 h⁻¹. -1 The remaining production processes are the same as in Example 1, and will not be repeated here.

[0066] Example 4 This embodiment provides a transformer oil. The difference from Embodiment 1 is that the catalyst ZQC-25 is replaced with ZQC-26. The rest of the production process is the same as in Embodiment 1, and will not be described again here.

[0067] Example 5 This embodiment provides a transformer oil. The difference from Embodiment 1 is that the catalyst ZQC-25 is replaced with ZQC-27. The rest of the production process is the same as in Embodiment 1, and will not be described again here.

[0068] Example 6 This embodiment provides a transformer oil. Unlike embodiment 1, the system hydrogen partial pressure is 6.0 MPa. The rest of the production process is the same as that in embodiment 1, and will not be described again here.

[0069] Example 7 This embodiment provides a transformer oil. The difference from Embodiment 1 is that the hydrogen partial pressure of the system is 8.0 MPa. The rest of the production process is the same as that of Embodiment 1, and will not be described again here.

[0070] Example 8 This embodiment provides a transformer oil, using solvent-extracted oil from the CNOOC Suizhong 36-1 reduced voltage line II as raw material. The specific production process is as follows: 1. Same as the steps in Example 1.

[0071] 2. The refined oil obtained from the reaction enters a fractionation tower for fractionation. The operating conditions are: tower top pressure 0.1 MPa, tower top temperature 60℃, tower bottom temperature 220℃, and feed temperature 230℃. The target fraction is collected to obtain transformer base oil.

[0072] 3. Same as the steps in Example 1.

[0073] Comparative Example 1 This comparative example provides a transformer oil using solvent-extracted oil from CNOOC Suizhong 36-1 reduced-temperature distillation line as raw material. It is first mixed with furfural (solvent-to-oil ratio 0.8:1) at 60℃ for extraction. After separating the furfural phase, the furfural-free oil is then treated with 10 wt% activated clay at 120℃ for 30 min, and filtered to obtain refined oil. Finally, it is fractionated at atmospheric pressure to obtain the target fraction of transformer base oil. The obtained base oil is then mixed with 0.30 wt% of 2,6-di-tert-butyl-p-cresol (BHT) and stirred evenly at 60℃ for 30 min to obtain the finished transformer oil.

[0074] Comparative Example 2 This comparative example provides a transformer oil using solvent-extracted oil from the CNOOC Suizhong 36-1 reduced voltage reduction line II as raw material. The specific production process is as follows: 1. The feedstock oil is mixed with hydrogen and then introduced into a fixed-bed hydrotreating pilot plant packed with a tungsten-nickel type hydrotreating catalyst ZQC-25 for refining reaction; wherein the reaction temperature is 390℃, the hydrogen-to-oil volume ratio is 1000:1, the system hydrogen partial pressure is 15.0 MPa, and the volume hourly space velocity is 0.1 h⁻¹. -1 .

[0075] 2. Same as the steps in Example 1.

[0076] 3. Same as the steps in Example 1.

[0077] Comparative Example 3 This comparative example provides a transformer oil using paraffin-based atmospheric third-line distillate oil as raw material. The remaining production processes are the same as in Example 1, and will not be repeated here.

[0078] Comparative Example 4 This comparative example provides a transformer oil that differs from Example 1 in that step 2 is omitted, and the refined oil obtained from the reaction is directly used as the transformer base oil. The remaining production processes are the same as in Example 1, and will not be described again here.

[0079] Test Example 1 The transformer oils obtained in the examples and comparative examples were subjected to the following tests: (1) Yield (relative to blended oil), % (2) Density at 20℃, g / cm³ 3 Tested according to GB / T1884; (3) Pour point, °C: Tested in accordance with GB / T3535; (4) Kinematic viscosity at -30℃ / 40℃, mm 2 / s: Tested according to GB / T1884; (5) Breakdown voltage, kV: Tested in accordance with GB / T507; (6) 90℃ dielectric loss factor: tested according to GB / T5654; (7) Oxidation stability: Tested according to SH / T0811; (8) Closed-cup flash point, °C: Tested according to GB / T261; (9) Acid value, mgKOH / g: Tested according to GB / T7304.

[0080] The results are summarized in Tables 2, 3, and 4.

[0081] Table 2

[0082] Table 3

[0083] As can be seen from Tables 2 and 3, the transformer oils prepared in Examples 1-5 all meet or significantly exceed the key indicators of the national standard GB2536–2011: the breakdown voltage is stably maintained at 51-53 kV, and the kinematic viscosity at -30℃ is strictly controlled at 1675-1763 mm. 2 Within the range of / s, the dielectric loss factor at 90℃ is as low as 0.0003-0.0007, and after the oxidation stability test at 120℃ / 500 h, the total acid value is 0.35-0.47 mg KOH / g, and the sludge content is only 0.028-0.18%, which fully confirms the inventive concept of this process to retain the cycloalkane structure to the maximum extent while deeply removing non-ideal components such as aromatics and nitrides. Example 6 reveals that insufficient hydrogenation saturation under low pressure leads to the residue of large molecular polar impurities.

[0084] In Example 7, the hydrogen partial pressure was precisely controlled at 8.0 MPa, exhibiting a significant critical effect: its dielectric loss factor was exactly 0.005, the acid value after oxidation jumped to 2.13 mg KOH / g, and the sludge content reached 1.16%. Compared with 15.0 MPa in Example 1, this confirms that a hydrogen partial pressure below 8.0 MPa will lead to insufficient removal of heteroatoms, thereby causing insulation degradation and accelerated oxidation.

[0085] Example 8 reduced the low temperature and vacuum of the vacuum distillation tower, resulting in insufficient extraction of light components, a significant decrease in the closed-cup flash point, and an abnormal increase in kinematic viscosity at -30°C. Although the yield was slightly higher and the medium loss factor was still good, the key safety indicator - the flash point - failed to meet the standard, indicating that its distillation process deviated from the core concept of this invention and could not reliably obtain qualified transformer base oil.

[0086] Comparative Example 1 uses the traditional furfural-clay refining process, with a yield of only 76.2%, and the breakdown voltage, acid value, and sludge all exceed the standards. Comparative Example 2, due to excessive hydrogenation, has a breakdown voltage as high as 57 kV, but the yield drops to 81.3% and the closed-cup flash point is only 137℃.

[0087] Comparative Example 3 used a paraffin-based feedstock with a pour point as high as +36°C, directly negating its potential as a base oil for ultra-low temperature transformer oil. Although the yield of Comparative Example 4 increased to 98.9%, the lack of fractionation resulted in the inability to effectively separate light and heavy components, leading to a decrease in the closed-cup flash point, an abnormally low kinematic viscosity at -30°C, a deterioration in the dielectric loss factor, and a decline in oxidation stability.

[0088] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A production process for transformer base oil, characterized in that, The feedstock oil and hydrogen are mixed and refined to obtain a refined product oil; the refined product oil is fractionated to obtain the transformer base oil; The feedstock oil includes solvent-extracted oil and / or tire pyrolysis oil.

2. The production process according to claim 1, characterized in that, The volume ratio of hydrogen to the feedstock oil is 600~1300:1; Preferably, in the purification process, the hydrogen partial pressure is >8.0 MPa; Preferably, the refining reaction temperature is 300~370℃, and the volume hourly space velocity is 0.2~1.0 h⁻¹. -1 .

3. The production process according to claim 1, characterized in that, The fractionation is carried out inside a fractionation column; Preferably, the fractionation is vacuum fractionation; Preferably, the top pressure of the fractionation column is 0.07~0.09MPa and the temperature is 50~70℃; Preferably, the bottom temperature of the fractionation column is 270~310℃; Preferably, the feed temperature of the fractionation tower is 220~240℃.

4. The production process according to any one of claims 1 to 3, characterized in that, The feedstock oil contains 1-6 wt% alkanes, 20-40 wt% cycloalkanes, and 40-90 wt% aromatics, with a pour point < -40°C.

5. The production process according to any one of claims 1 to 3, characterized in that, The catalyst used in the refining process includes at least one of tungsten-nickel hydrogenation catalyst, molybdenum-nickel hydrogenation catalyst, and molybdenum-tungsten-nickel hydrogenation catalyst, preferably a tungsten-nickel hydrogenation catalyst.

6. A transformer base oil, characterized in that, It is prepared using the production process described in any one of claims 1 to 5.

7. A transformer oil, characterized in that, It includes 0.25~0.35wt% antioxidant, with the balance being the transformer base oil as described in claim 6.

8. The transformer oil according to claim 7, characterized in that, The antioxidants include aromatic amine antioxidants and / or hindered phenolic antioxidants.

9. The transformer oil according to claim 7, characterized in that, Breakdown voltage > 50kV, kinematic viscosity < 1800mm at -30℃ 2 / s, cycloalkane carbon content C N Value > 61%.

10. The transformer oil according to any one of claims 7 to 9, characterized in that, The total acid value after 500 hours of oxidation stability test at 120℃ is <0.6 mg KOH / g; Preferably, the transformer oil contains less than 0.3% sludge. Preferably, the dielectric loss factor of the transformer oil is <0.05 at 90°C.

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