Manufacturing method for recycled insulating oil

Abstract

To provide a manufacturing method for a recycled insulating oil that exhibits an oxidation stability equivalent to that of new oil.SOLUTION: A manufacturing method for a recycled insulating oil includes the following steps (1) and (2). Step (1): Treating deteriorated insulating oil with clay. Step (2): Mixing a treated oil obtained in Step (1) with a mineral oil containing 200 ppm.mass to 2,500 ppm.mass of sulfur.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing recycled insulating oil. [Background technology]

[0002] Electrical insulating oil is used as an insulating material in oil-filled electrical equipment, such as oil-filled capacitors, oil-filled cables, oil-filled transformers, and oil-filled circuit breakers. In recent years, from the perspective of environmental considerations, IEC60296, the international standard for electrical insulating oil quality, has been revised overseas, and virgin insulating oil and insulating oil obtained by recycling used insulating oil (hereinafter referred to as "recycled insulating oil") are now treated equally, with no distinction in quality. Known methods for regenerating used insulating oil include mechanical methods such as filtration and centrifugation, adsorption methods, and chemical treatment methods. For example, Non-Patent Document 1 describes that by subjecting used insulating oil to a two-stage regeneration process using a percolation method with activated clay, it is possible to obtain recycled insulating oil that has properties similar to those of new oil, although its oxidation stability is inferior to that of new oil. It also describes that adding an antioxidant to the recycled insulating oil significantly improves its oxidation stability. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] "Adsorption Regeneration Treatment and Stability of Degraded Insulating Oil," Proceedings of the 42nd Insulating Oil Subcommittee Research Presentation Meeting, Japan Petroleum Institute, No. 8, 2022 Summary of the Invention [Problem to be solved by the invention]

[0004] However, Non-Patent Document 1 does not fully consider how to improve the oxidation stability of the recycled insulating oil itself to a level equivalent to that of new oil.

[0005] Therefore, an object of the present invention is to provide a method for producing recycled insulating oil that exhibits oxidation stability equivalent to that of new oil. [Means for solving the problem]

[0006] According to the present invention, the following [1] is provided. [1] A method for producing recycled insulating oil, comprising the following steps (1) and (2): Step (1): The process of treating deteriorated insulating oil with clay. Step (2): A step of mixing the treated oil obtained in the step (1) with a mineral oil having a sulfur content of 200 ppm by mass to 2,500 ppm by mass. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a method for producing recycled insulating oil that exhibits oxidation stability equivalent to that of new oil. DETAILED DESCRIPTION OF THE INVENTION

[0008] The upper and lower limits of the ranges described herein can be combined in any way. For example, if the ranges are "A to B" and "C to D," the ranges "A to D" and "C to B" are also included in the scope of the present invention. Furthermore, unless otherwise specified, the numerical range "lower limit to upper limit" described in this specification means that the range is equal to or greater than the lower limit and equal to or less than the upper limit. In this specification, the numerical values ​​in the examples are numerical values ​​that can be used as upper or lower limit values.

[0009] [Manufacturing method for recycled insulating oil] The method for producing recycled insulating oil of this embodiment includes the following steps (1) and (2). Step (1): The process of treating deteriorated insulating oil with clay. Step (2): A step of mixing the treated oil obtained in the step (1) with a mineral oil having a sulfur content of 200 ppm by mass to 2,500 ppm by mass.

[0010] The present inventors have conducted extensive research to solve the above problems. As a result, it was found that the above problems could be solved by mixing mineral oil with treated oil obtained by treating deteriorated insulating oil with clay. Each step will be described in detail below.

[0011] <Process (1)> In step (1), the deteriorated insulating oil is treated with clay.

[0012] (deteriorated insulating oil) The deteriorated insulating oil provided in step (1) is a used insulating oil that has been used for a certain period of time and deteriorated, and typically satisfies the following condition (A). (A) an acid value of 0.001 mgKOH / g or more and 1.0 mgKOH / g or less (preferably 0.50 mgKOH / g or less, more preferably 0.20 mgKOH / g or less, and even more preferably 0.05 mgKOH / g or less); In this specification, the acid value of deteriorated insulating oil means a value measured in accordance with JIS K 2501-7:2003.

[0013] The deteriorated insulating oil provided in step (1) typically has a sulfur content of 20 mass ppm to 100 mass ppm based on the total amount of the deteriorated insulating oil. In this specification, the sulfur content refers to a value measured in accordance with JIS K 2541-2:2013 "Crude oil and petroleum products - Sulfur content test method - Microcoulometric oxidation method."

[0014] Furthermore, it is preferred that the deteriorated insulating oil provided in step (1) typically satisfy the following physical properties. ·40℃ kinematic viscosity: preferably 8mm 2 / s~13mm 2 / s, more preferably 8 mm 2 / s~12mm 2 / s, more preferably 8 mm 2 / s~11mm 2 / s, even more preferably 8 mm 2 / s~10mm 2 / s ·100℃ kinematic viscosity: preferably 2mm2 / s~5mm 2 / s, more preferably 2 mm 2 / s~4mm 2 / s, more preferably 2 mm 2 / s~3mm 2 / s Density (15°C): preferably 0.8600 g / cm 3 ~0.9100g / cm 3 , more preferably 0.8600 g / cm 3 ~0.8900g / cm 3 , and more preferably 0.8600 g / cm 3 ~0.8700g / cm 3 Flash point (PM): preferably 140°C or higher Pour point: preferably -20°C or lower, more preferably -30°C or lower, and even more preferably -35°C or lower

[0015] (Clay treatment) The clay treatment can be carried out by a conventionally known method, such as a clay refining method used as a final finishing step for lubricating oils, such as a percolation method or a contact method.

[0016] The amount of white clay used is not particularly limited, but from the viewpoint of preventing excessive use of white clay while making it easier to improve the oxidation stability of the recycled insulating oil produced, the amount is preferably 6 parts by mass or less, more preferably 0.5 to 6 parts by mass, even more preferably 3 to 6 parts by mass, and even more preferably 5 parts by mass per 100 parts by mass of deteriorated insulating oil.

[0017] The temperature in the clay treatment (the temperature of the deteriorated insulating oil) is not particularly limited, but is typically 50 to 80°C.

[0018] The time required for the clay treatment (contact time between the deteriorated insulating oil and the clay) is set appropriately depending on the amount of deteriorated insulating oil, the amount of clay used, and the temperature during the clay treatment, and is not particularly limited, but is typically 30 minutes to 3 hours.

[0019] <Process (2)> In step (2), the treated oil obtained in step (1) is mixed with a mineral oil having a sulfur content of 200 ppm by mass to 2,500 ppm by mass. The treated oil obtained in step (1) has inferior oxidation stability compared to new oil (non-recycled insulating oil). Therefore, in step (2), the treated oil obtained in step (1) is mixed with mineral oil having a sulfur content of 200 mass ppm to 2,500 mass ppm. This makes it possible to produce recycled insulating oil with excellent oxidation stability.

[0020] (mineral oil) The mineral oil contains 200 ppm by mass to 2,500 ppm by mass of sulfur. As the mineral oil, preferably, mineral oil containing a large amount of sulfur (hereinafter also referred to as "high sulfur mineral oil") is used. The sulfur content contained in mineral oil is derived from crude oil. From the viewpoint of further improving the oxidation stability of the produced recycled insulating oil, the sulfur content of the mineral oil is preferably 200 ppm by mass to 2,000 ppm by mass, more preferably 200 ppm by mass to 1,500 ppm by mass, even more preferably 200 ppm by mass to 1,000 ppm by mass, still more preferably 200 ppm by mass to 600 ppm by mass, and even more preferably 300 ppm by mass to 600 ppm by mass. Here, the mineral oil may be a paraffinic mineral oil or a naphthenic mineral oil, but from the viewpoint of easily adjusting the pour point of the recycled insulating oil to a low level, a high sulfur mineral oil (α) described below is preferred.

[0021] -High sulfur mineral oil (α)- The high sulfur mineral oil (α) preferably satisfies the following requirements (α1) to (α3). ·Requirement (α1): %C by ring analysis (ndM method) A However, it is 3.5 or higher. Requirement (α2): %C by ring analysis (ndM method) N is 50.0 or more. Requirement (α3): The sulfur content is 200 ppm by mass or more and 600 ppm by mass or less, based on the total amount of high-sulfur mineral oil (α). The sulfur content specified in requirement (α3) is preferably 250 ppm by mass or more and 600 ppm by mass or less, more preferably 250 ppm by mass or more and 400 ppm by mass or less, and even more preferably 300 ppm by mass to 350 ppm by mass, based on the total amount of high sulfur mineral oil (α).

[0022] The high sulfur mineral oil (α) can be obtained, for example, by subjecting a distillate obtained by distilling naphthenic crude oil under normal vacuum to solvent extraction. In addition to solvent extraction, the high sulfur mineral oil (α) may also be produced by an appropriate combination of conventionally known refining processes such as dewaxing, deasphalting, hydrofinishing, alkali treatment, and clay treatment. The high sulfur mineral oil (α) may be used alone or in combination of two or more kinds.

[0023] The high-sulfur mineral oil (α) can be subjected to solvent extraction to remove excess aromatics and sulfur compounds (and nitrogen compounds) derived from the distillate oil while leaving a moderate amount of sulfur compounds that can function as antioxidants. Therefore, an appropriate amount of sulfur remains, making it easy to use as the mineral oil in step (2).

[0024] In addition, the input ratio [(S) / (R)] of furfural (S) to raffinate (R, raw material base oil) during solvent extraction treatment is preferably 1.00 or more, more preferably 1.50 or more, and even more preferably 1.75 or more, in terms of volume ratio, from the viewpoint of facilitating the removal of excess sulfur content, etc. In addition, from the viewpoint of preventing excessive removal of sulfur content and aromatic content, it is preferably less than 2.50, more preferably 2.30 or less, and even more preferably 2.25 or less. The upper and lower limits of these numerical ranges can be combined arbitrarily. Specifically, the range is preferably 1.00 or more and less than 2.50, more preferably 1.50 or more and 2.30 or less, and even more preferably 1.70 or more and 2.25 or less.

[0025] Here, the high sulfur mineral oil (α) preferably has the following physical properties: Pour point Preferably it is below -50°C, more preferably below -55°C. Aniline point The temperature is preferably 65.0°C to 71.0°C, more preferably 65.5°C to 70.5°C, and even more preferably 66.0°C to 70.0°C. %C A The range is preferably 4.0 to 12.5, more preferably 4.5 to 11.5, and even more preferably 4.7 to 11.0. %C N It is preferably 52.0 to 62.0, more preferably 53.0 to 61.0, and even more preferably 54.0 to 60.0. %C p It is preferably 30.0 to 45.0, more preferably 31.0 to 42.0, and even more preferably 32.0 to 40.0. ·40℃ kinematic viscosity Preferably 8.40mm 2 / s~10.00mm 2 / s, more preferably 8.45 mm 2 / s~9.50mm 2 / s, more preferably 8.50 mm 2 / s~9.30mm 2 / s. ·Kinematic viscosity at 100℃ Preferably 2.00mm 2 / s~2.50mm 2 / s, more preferably 2.05 mm 2 / s~2.45mm 2 / s, more preferably 2.10 mm 2 / s~2.40mm 2 / s. ·Viscosity index It is preferably 20 to 37, more preferably 23 to 36, and even more preferably 25 to 35. ·Density (15℃) Preferably 0.8960 g / cm 3 ~0.9150g / cm 3 , more preferably 0.8970 g / cm 3 ~0.9100g / cm 3 is. ·flash point The temperature is preferably 140°C to 160°C, more preferably 143°C to 155°C, and even more preferably 145°C to 150°C.

[0026] (Mixing ratio of treated oil and mineral oil) The mixing ratio of the treated oil obtained in step (1) to the mineral oil [treated oil / mineral oil] is not particularly limited, but from the viewpoint of facilitating the production of recycled insulating oil with excellent oxidation stability, the mass ratio is preferably 80 / 20 to 97 / 3, more preferably 85 / 15 to 96 / 4, and even more preferably 90 / 10 to 95 / 5.

[0027] <Process (3)> The method for producing recycled insulating oil of this embodiment may include the above steps (1) and (2), but from the viewpoint of making it easier to improve the performance of the recycled insulating oil, it is preferable to include the following step (3). Step (3): A step of dehydrating the mixed oil obtained in step (2). The dehydration method is not particularly limited, and any conventionally known method for dehydrating electrical insulating oils can be appropriately employed, such as clay treatment, vacuum degassing, activated alumina filtration, etc. Here, from the viewpoint of facilitating the production of recycled insulating oil having excellent oxidation stability, the treatment in step (3) is preferably a white clay treatment. That is, in the method for producing recycled insulating oil of this embodiment, it is preferable to carry out a white clay treatment in step (1) (hereinafter also referred to as a "first white clay treatment") and a white clay treatment in step (3) (hereinafter also referred to as a "second white clay treatment"). By carrying out the second clay treatment in step (3), not only water but also furfural and trace polar components can be removed, making it easier to further improve the performance as an electrical insulating oil.

[0028] (White clay treatment (second white clay treatment)) As described in detail in step (1), the second clay treatment can be carried out by a conventional method, such as the clay refining method used as a final finishing step for lubricating oils. Examples of the clay refining method include the percolation method and the contact method.

[0029] The amount of clay used in the second clay treatment is not particularly limited, but from the viewpoint of preventing excessive use of clay while making it easier to improve the oxidation stability of the recycled insulating oil produced, the amount is preferably 0.5 parts by mass or more, more preferably 0.5 to 6 parts by mass, even more preferably 0.5 to 2 parts by mass, and even more preferably 1 part by mass per 100 parts by mass of the mixed oil.

[0030] Here, from the viewpoint of further improving the oxidation stability of the produced recycled insulating oil, the clay concentration in the first clay treatment is preferably higher than the clay concentration in the second clay treatment. From the same viewpoint, it is more preferable that the clay concentration in the first clay treatment is 6 parts by mass or less per 100 parts by mass of the deteriorated insulating oil, and that the clay concentration in the second clay treatment is 0.5 parts by mass or more per 100 parts by mass of the mixed oil. From the same viewpoint, it is more preferable that the clay concentration in the first clay treatment is 3 to 6 parts by mass per 100 parts by mass of the deteriorated insulating oil, and that the clay concentration in the second clay treatment is 0.5 to 2 parts by mass per 100 parts by mass of the mixed oil. From the same viewpoint, it is even more preferable that the clay concentration in the first clay treatment is 5 parts by mass per 100 parts by mass of the deteriorated insulating oil, and that the clay concentration in the second clay treatment is 1 part by mass per 100 parts by mass of the mixed oil.

[0031] The temperature in the second clay treatment (the temperature of the deteriorated insulating oil) is not particularly limited, but is typically 50 to 80°C, similar to the first clay treatment.

[0032] The time required for the second clay treatment (contact time between the deteriorated insulating oil and the clay) is set appropriately depending on the amount of deteriorated insulating oil, the amount of clay used, and the temperature in the clay treatment, and is not particularly limited, but is typically 30 minutes to 3 hours, as with the first clay treatment.

[0033] <Additives> In the manufacturing method of this embodiment, an antioxidant may be blended in accordance with the specifications of the electrical insulating oil. Specifically, one or more antioxidants selected from the group consisting of phenol-based antioxidants (e.g., 2,6-di-tert-butyl-p-cresol), amine-based antioxidants, molybdenum amine-based antioxidants, and sulfur-based antioxidants may be blended in. In addition, depending on the specifications of the electrical insulating oil, one or more additives selected from metal deactivators, pour point depressants, rust inhibitors and flow antistatic agents (for example, benzotriazole-based compounds that function as both rust inhibitors and flow antistatic agents) may be further blended as other additives. The timing for adding these additives is preferably after step (3).

[0034] [Physical properties of recycled insulating oil obtained by the manufacturing method of this embodiment] The recycled insulating oil obtained by the production method of this embodiment preferably satisfies the following physical properties.

[0035] <Dielectric loss tangent> The recycled insulating oil obtained by the manufacturing method of this embodiment preferably has a dielectric loss tangent of 0.10% or less, more preferably 0.07% or less, and even more preferably 0.05% or less, as measured by the method described in the examples below.

[0036] <Volume resistivity> The recycled insulating oil obtained by the manufacturing method of this embodiment preferably has a volume resistivity of 1.0 TΩm or more, more preferably 10 TΩm or more, and even more preferably 20 TΩm or more, as measured by the method described in the examples below.

[0037] <Acid value after oxidation stability test> The recycled insulating oil obtained by the manufacturing method of this embodiment has an acid value after an oxidation stability test measured by the method described in the examples below of preferably 0.40 mgKOH / g or less, more preferably 0.35 mgKOH / g or less, and even more preferably 0.30 mgKOH / g or less.

[0038] <Amount of sludge after oxidation stability test> The recycled insulating oil obtained by the manufacturing method of this embodiment has a sludge amount after an oxidation stability test measured by the method described in the Examples below of preferably 0.60 mass % or less, more preferably 0.40 mass % or less, even more preferably 0.20 mass % or less, still more preferably 0.15 mass % or less, and even more preferably 0.10 mass % or less.

[0039] [One aspect of the present invention provided] According to one aspect of the present invention, the following [1] to [8] are provided. [1] A method for producing recycled insulating oil, comprising the following steps (1) and (2): Step (1): The process of treating deteriorated insulating oil with clay. Step (2): A step of mixing the treated oil obtained in the step (1) with a mineral oil having a sulfur content of 200 ppm by mass to 2,500 ppm by mass. [2] The method for producing the recycled insulating oil according to [1] above further comprises the following step (3): Step (3): A step of subjecting the mixed oil obtained in step (2) to a dehydration treatment. [3] The dehydration treatment in the step (3) is a clay treatment, The method for producing recycled insulating oil according to [2] above, wherein the concentration of the white clay in the white clay treatment in the step (1) is higher than the concentration of the white clay in the white clay treatment in the step (3). [4] The concentration of the clay in the clay treatment in the step (1) is 6 parts by mass or less with respect to 100 parts by mass of the deteriorated insulating oil, The method for producing recycled insulating oil according to [3] above, wherein the concentration of the clay in the clay treatment in step (3) is 0.5 parts by mass or more per 100 parts by mass of the mixed oil. [5] The concentration of the clay in the clay treatment in the step (1) is 3 parts by mass to 6 parts by mass with respect to 100 parts by mass of the deteriorated insulating oil, The method for producing recycled insulating oil according to the above [3] or [4], wherein the concentration of the clay in the clay treatment in the step (3) is 0.5 to 2 parts by mass per 100 parts by mass of the mixed oil. [6] The method for producing recycled insulating oil according to any one of [1] to [5] above, wherein the mixing ratio of the treated oil and the mineral oil [treated oil / mineral oil] in step (2) is 80 / 20 to 97 / 3 by mass. [7] The method for producing recycled insulating oil according to any one of [1] to [6] above, wherein in step (2), the mixing ratio of the treated oil to the mineral oil [treated oil / mineral oil] is 90 / 10 to 95 / 5 by mass. [8] The method for producing recycled insulating oil according to any one of the above [1] to [7], wherein the mineral oil has a sulfur content of 200 ppm by mass to 600 ppm by mass. [Example]

[0040] The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

[0041] [Methods for measuring various physical properties] The various physical properties of the base oil and recycled insulating oil used in each example and comparative example were measured according to the procedures shown below. (1) Kinematic viscosity and viscosity index The kinematic viscosity at 40°C, the kinematic viscosity at 100°C, and the viscosity index were measured and calculated in accordance with JIS K2283:2000. (2) Density (15℃) Measurements were performed in accordance with JIS K 2249-1:2011 (Crude oil and petroleum products - Determination of density - Part 1: Vibration method). (3) Refractive index (15°C) Measurement was carried out in accordance with JIS K 0062:1992. (4) Molecular weight (Mw), aromatic content (%C A ), naphthene content (%C N ), and paraffin content (%C P ) Calculation was performed by ring analysis (ndM method) in accordance with ASTM D3238:1995. (5) Sulfur content Measurements were performed in accordance with JIS K 2541-2:2013 "Crude oil and petroleum products - Sulfur content test method - Microcoulometric oxidation method." (6) Acid value Measurement was carried out in accordance with JIS K 2501-7:2003. (7) ASTM color, Saybolt color ASTM color was measured in accordance with JIS K 2580:2003. The Saybolt color was measured in accordance with JIS K2580:2003. (8) Flash point Measurement was performed using the Pensky-Martens closed-loop method (PM) in accordance with JIS K2265-3:2007. (9) Pour point Measurements were made in accordance with JIS K 2269:1987 (Test method for pour point and cloud point of crude oil and petroleum products). (10) Aniline point Measurements were performed in accordance with JIS K 2256:2013. (11) Dielectric tangent Measurement was carried out at 80°C in accordance with JIS C2101. (12) Volume resistivity Measurement was carried out at 80°C in accordance with JIS C2101.

[0042] [Preparing deteriorated insulating oil] A 2L Transformer G (manufactured by Idemitsu Kosan Co., Ltd.) and a copper wire coil (diameter φ1 mm × length 90 cm) were placed in a 4L metal can with an open top, and forcibly aged in an oven at 120°C for 120 hours to prepare aged insulating oil (1). In addition, 2 L of Transformer G (manufactured by Idemitsu Kosan Co., Ltd.) and a copper wire coil (diameter φ1 mm × length 90 cm) were placed in a 4 L metal can with an open top and forcibly aged in an oven at 120°C for 288 hours to prepare aged insulating oil (2).

[0043] Table 1 shows various physical properties of Transformer G (abbreviated as "Trans G" in the table), Deteriorated Insulating Oil (1), and Deteriorated Insulating Oil (2). In Table 1, "-" indicates that the measurement was not performed.

[0044] [Table 1]

[0045] [Preparing mineral oil] As the mineral oil (1), a paraffin-based solvent refined oil was prepared. Furthermore, a hydrorefined naphthenic crude oil was prepared as a comparative mineral oil. Furthermore, mineral oils (2) and (3) were produced according to the following Production Examples 1 and 2.

[0046] <Production Example 1: Production of Mineral Oil (2)> The distillate obtained by distilling naphthenic crude oil under normal vacuum was subjected to solvent extraction and then to adsorption treatment to remove furfural that had been mixed in during the solvent extraction, thereby obtaining mineral oil (2). In the solvent extraction treatment, the input ratio of furfural (S) to distillate oil (R) [(S) / (R)] was set to 2.0 by volume. The mineral oil (2) corresponds to the high sulfur mineral oil (α).

[0047] <Production Example 2: Production of Mineral Oil (3)> The distillate obtained by distilling naphthenic crude oil under normal vacuum was subjected to solvent extraction and then to adsorption treatment to remove furfural that had been mixed in during the solvent extraction, thereby obtaining mineral oil (3). In the solvent extraction treatment, the input ratio of furfural (S) to distillate oil (R) [(S) / (R)] was set to 0.8 by volume. The mineral oil (3) corresponds to the high sulfur mineral oil (α).

[0048] Table 2 shows the physical properties of mineral oils (1) to (3) and the comparative mineral oil. In Table 2, "-" indicates that the measurement was not performed.

[0049] [Table 2]

[0050] [Examples 1 to 5, Comparative Examples 1 to 3] Recycled insulating oils of Examples 1 to 5 and Comparative Examples 1 to 3 were produced according to the procedures described below, and the evaluations described below were carried out.

[0051] <Comparative Example 1> 5 parts by mass of white clay was added to 100 parts by mass of deteriorated insulating oil (1) to perform a white clay treatment, thereby obtaining treated oil (1). The white clay treatment was carried out by adding the white clay to the deteriorated insulating oil (1), heating it with a heater, and turning off the heater after confirming that the temperature of the deteriorated insulating oil (1) had reached 80°C, followed by stirring for 10 minutes. The mixture was then filtered using filter paper, and the filtrate was designated as treated oil (1). In the following explanation, the white clay treatment carried out on the mixed oil was also carried out in the same manner.

[0052] <Comparative Example 2> The deteriorated insulating oil (2) was subjected to a clay treatment under the same conditions as in Comparative Example 1 to obtain treated oil (2).

[0053] Example 1 95 parts by mass of the treated oil (1) obtained in Comparative Example 1 was mixed with 5 parts by mass of mineral oil (2), and then 1 part by mass of clay was added to 100 parts by mass of the mixed oil to perform clay treatment, thereby obtaining recycled insulating oil (1).

[0054] <Example 2> 90 parts by mass of the treated oil (1) obtained in Comparative Example 1 was mixed with 10 parts by mass of mineral oil (2), and then 1 part by mass of clay was added to 100 parts by mass of the mixed oil to perform clay treatment, thereby obtaining recycled insulating oil (2).

[0055] Example 3 95 parts by mass of the treated oil (1) obtained in Comparative Example 1 was mixed with 5 parts by mass of mineral oil (1), and then 1 part by mass of clay was added to 100 parts by mass of the mixed oil to perform clay treatment, thereby obtaining recycled insulating oil (3).

[0056] Example 4 95 parts by mass of the treated oil (2) obtained in Comparative Example 2 was mixed with 5 parts by mass of mineral oil (2), and then 1 part by mass of clay was added to 100 parts by mass of the mixed oil to perform clay treatment, thereby obtaining recycled insulating oil (4).

[0057] <Example 5> 95 parts by mass of the treated oil (2) obtained in Comparative Example 2 was mixed with 5 parts by mass of mineral oil (3), and then 1 part by mass of clay was added to 100 parts by mass of the mixed oil to perform clay treatment, thereby obtaining recycled insulating oil (5).

[0058] <Comparative Example 3> After mixing 95 parts by mass of the treated oil (1) obtained in Comparative Example 1 with 5 parts by mass of a comparative mineral oil, 1 part by mass of clay was added to 100 parts by mass of the mixed oil to perform clay treatment, thereby obtaining recycled insulating oil (1').

[0059] <Evaluation> Various physical properties of the recycled insulating oils (1) to (5) of Examples 1 to 5, the treated oils (1) and (2) of Comparative Examples 1 and 2, and the recycled insulating oil (1') of Comparative Example 3 were measured. In addition, the acid values ​​of the recycled insulating oils (1) to (5) of Examples 1 to 5, the treated oils (1) and (2) of Comparative Examples 1 and 2, the recycled insulating oil (1') of Comparative Example 3, Transformer G, the deteriorated insulating oil (1), and the deteriorated insulating oil (2) were measured after conducting an oxidation stability test under the following test conditions in accordance with JIS C2101:2010. Test conditions: 120°C, 72 hours The acid value after the oxidation stability test was measured in accordance with JIS K 2501-7:2003. Those having an acid value of 0.40 mgKOH / g or less were judged to be acceptable. For the recycled insulating oils (1) to (5) of Examples 1 to 5, the oxidation stability test was carried out under the above test conditions, and then the amount of sludge was measured. The results are shown in Table 3.

[0060] [Table 3]

[0061] From Table 3, we can see the following: As in Comparative Examples 1 and 2, it is clear that the oxidation stability of the recycled insulating oil (treated oil) is insufficient when 5 parts by mass of clay treatment is performed for 100 parts by mass of deteriorated insulating oil. It is also clear that when a comparative mineral oil having a sulfur content of less than 200 mass ppm is mixed as in Comparative Example 3, the oxidation stability of the recycled insulating oil is insufficient. In contrast to these, it is clear that the recycled insulating oil obtained by treating deteriorated insulating oil with clay and then mixing it with mineral oil, as in Examples 1 to 5, has excellent oxidation stability.

Claims

1. A method for producing recycled insulating oil, comprising the following steps (1) and (2): Step (1): A step of treating deteriorated insulating oil with clay Step (2): Mixing the treated oil obtained in step (1) with a mineral oil having a sulfur content of 200 ppm by mass to 2,500 ppm by mass.

2. The method for producing recycled insulating oil according to claim 1, further comprising the following step (3): Step (3): A step of dehydrating the mixed oil obtained in step (2).

3. The dehydration treatment in the step (3) is a clay treatment, 3. The method for producing recycled insulating oil according to claim 2, wherein the concentration of the clay in the clay treatment in the step (1) is higher than the concentration of the clay in the clay treatment in the step (3).

4. The concentration of the clay in the clay treatment in the step (1) is 6 parts by mass or less relative to 100 parts by mass of the deteriorated insulating oil, 4. The method for producing recycled insulating oil according to claim 3, wherein the concentration of the clay in the clay treatment in the step (3) is 0.5 parts by mass or more relative to 100 parts by mass of the mixed oil.

5. The concentration of the clay in the clay treatment in the step (1) is 3 parts by mass to 6 parts by mass with respect to 100 parts by mass of the deteriorated insulating oil, The method for producing recycled insulating oil according to claim 3 or 4, wherein the concentration of the clay in the clay treatment in the step (3) is 0.5 parts by mass to 2 parts by mass per 100 parts by mass of the mixed oil.

6. The method for producing recycled insulating oil according to any one of claims 1 to 5, wherein the mixing ratio of the treated oil and the mineral oil [treated oil / mineral oil] in the step (2) is 80 / 20 to 97 / 3 by mass.

7. The method for producing recycled insulating oil according to any one of claims 1 to 6, wherein the mixing ratio of the treated oil and the mineral oil [treated oil / mineral oil] in the step (2) is 90 / 10 to 95 / 5 by mass.

8. The method for producing recycled insulating oil according to any one of claims 1 to 7, wherein the sulfur content of the mineral oil is 200 ppm by mass to 600 ppm by mass.

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