Desulfurization method

Abstract

The present invention provides the use of a solid aid comprising a reducing agent for reducing the active sulfur content in an oil and / or reducing the dielectric loss factor of an oil, wherein: (i) the oil is contacted with (a) a solid aid comprising the reducing agent and (b) a liquid aid suitable for dispersing the solid aid; (ii) contacting the oil with a solid substrate having the reducing agent on its surface; or (iii) the oil is an ester and is in contact with a particulate adsorbent carrier having the reducing agent on its surface.

Description

Technical Field

[0001] This invention relates to a desulfurization method, based on the fact that certain forms of reducing agents can be used to reduce the amount of sulfur in insulating oil and remove reactive sulfur in a very efficient manner. This has particular applications in the field of transformer oil regeneration.

[0002] More specifically, the present invention provides a method for reducing the total sulfur content in mineral insulating liquids and synthetic ester insulating liquids used in power transformers and removing S8, S4, S5, S6, S7, thiols, monosulfides and / or disulfides, oxidized sulfur compounds, typically sulfoxides, sulfones, and sulfur-containing oxyacids. The present invention also provides desulfurized insulating oils obtained or available by the method described herein, as well as compositions and apparatus for the desulfurization method of the present invention, and methods for preparing these compositions. Background Technology

[0003] Sulfur compounds present in oil, such as S8, monosulfides, disulfides, oxidized sulfur compounds, typically sulfur oxides, thiols, and sulfur oxyacids, can cause corrosion of metal components made of metals such as silver and copper. Therefore, power transformers often have components made of silver and / or copper, and the corrosiveness of insulating liquids such as mineral oils and esters to these components is a problem in the power industry as it can lead to transformer failure. In addition, known methods for regenerating used mineral insulating oil include one method using alumina- and aluminum silicate-based adsorbents in online systems. During the reactivation of the adsorbent using high-temperature combustion technology, S8, S2, S4, S5, S6, S7, hydrogen sulfide, and thiols may form as byproducts. Therefore, these regeneration methods can lead to corrosion by S8, S2, S4, S5, S6, S7, hydrogen sulfide, and thiols.

[0004] Methods for desulfurizing such oils are known. For example, WO2018190741 describes a method in which mineral oil is circulated through a stainless steel column containing a synthetic adsorbent made by depositing silver and ammonium ions on annealed silica. This method can remove sulfur from the oil and also remove amine derivatives of toluenetriazole. However, it would obviously be very beneficial to design a desulfurization method that improves upon efficiency and / or the degree of desulfurization as well as the overall cost of the method. Summary of the Invention

[0005] This invention provides the use of a solid additive containing a reducing agent for reducing the active sulfur content in oil and / or reducing the dielectric loss factor of oil, wherein: (i) Contacting the oil with (a) a solid additive containing the reducing agent and (b) a liquid additive suitable for dispersing the solid additive; (ii) Contacting the oil with a solid substrate having a reducing agent on its surface; or (iii) The oil is an ester and is in contact with a particulate adsorbent carrier having a reducing agent on its surface.

[0006] This invention also provides the use of a reducing agent solid additive for reducing the active sulfur content and / or reducing the dielectric loss factor, oil acidity, and particulate matter in oils (especially insulating oils, such as mineral insulating oils or ester insulating oils), while increasing interfacial tension, wherein: (i) Contacting the oil with (a) a solid additive containing a reducing agent and (b) a liquid additive suitable for dispersing the solid additive; (ii) Contacting the oil with a solid substrate having a reducing agent on its surface; or (iii) The oil is an ester and is in contact with a particulate adsorbent carrier having a reducing agent on its surface.

[0007] The reducing agents defined in options (i), (ii), and (iii) above have been shown to be very effective in reducing the active sulfur content in oil and / or reducing the dielectric loss factor and / or reducing the acidity and / or reducing the particle level and / or increasing the interfacial tension, and are particularly suitable for regenerated transformer oils that may contain various types of active sulfur compounds and lose their insulating properties over time during use (active sulfur is also referred to here as reactive sulfur). The reducing agent in option (iii) has been found to have unexpected effectiveness in cases where the oil is an ester.

[0008] In a first embodiment, the inventors of the present invention devised a novel method for removing S8 from oils such as mineral insulating oils and esters (especially mineral oils), employing a selective liquid-liquid-solid method. Therefore, the present invention provides a means to reduce power transformer failures caused by the presence of S8.

[0009] This method is a selective desulfurization process that utilizes liquid-liquid-solid phase chemical reactions to effectively and specifically remove S8. Surprisingly, this method achieves highly efficient selective removal of S8. This invention solves the problem of providing a desulfurization method that improves both efficiency and desulfurization extent.

[0010] The method of the first embodiment of the present invention can effectively and highly selectively remove S8, thereby preventing the corrosion reaction originally caused by S8. This method can be used to provide post-treated oil that meets the physical, chemical, and electrical standards that oils used in power transformers must satisfy. Therefore, it enables the regeneration of corrosive mineral insulating oils and their reuse as insulating oils in power transformers. Furthermore, a single dispersant as defined according to the present invention can be used to perform this regeneration process multiple times. The ability to recycle the dispersant in this way offers significant advantages in terms of efficiency, cost, waste reduction, and the environment.

[0011] Furthermore, corrosive mineral insulating oils can quickly become non-corrosive, for example, within 60 to 90 minutes. This method can also be used to remove aged products from mineral insulating oils, further improving their regeneration. Another advantage is the low metal-to-oil ratio used in this method, making the entire process highly economical and efficient. Relatedly, readily available and inexpensive reagents can be used as starting materials, further enhancing the cost-effectiveness of the method.

[0012] In a second embodiment, the inventors devised a new method for reducing total sulfur content, more specifically total active sulfur content, and removing sulfur, more specifically S8, S7, S6, S5, S4 disulfides and / or sulfoxides, sulfones and sulfur oxyacids, from oils such as mineral insulating oils and synthetic ester insulating liquids. This method may employ silver-plated coils made of iron, steel, aluminum or copper, having a silver plating layer of 0.005 to 0.05 mm, as shown in Figure 6 (silver-plated wire of copper, iron or aluminum, 8-10 mm in diameter, 5-15 m in length, with a silver plating layer of 0.005 to 0.05 mm).

[0013] In another embodiment, the silver-plated coil is wound around a heating cylinder made of silver-plated copper, iron, or steel.

[0014] The surface area of ​​available silver can be varied to suit the quality of the oil and the concentration of total active sulfur in the oil. Silver-plated coils are placed in a batch reactor, which may or may not include a silver-plated heating cylinder. Figure 6A The silver-plated coils are placed in the batch reactor in two different possible arrangements: one is a single silver-plated coil ( Figure 6 Another type is a silver-plated coil wound around a cylindrical silver-plated heating element. Figure 6B ).

[0015] One to four silver-plated coils are fixed to the lid of the batch reactor. The silver-plated coils can be wound around the heating cylinder or placed individually 40 cm from the top of the reactor and immersed in the oil. Figure 7 , 7A(7B, 7C). The specific range of the ratio of silver-plated surface to total oil mass in the batch reactor is from 0.0025 to 0.01m. 2 Between / kg.

[0016] Place one to three silver-plated coils (see Figure 8A Inserted into a tubular reactor made of stainless steel, 80-130cm in length and 28-40cm in diameter (see...) Figure 8 and 8B The reactor, made of steel, has a diameter of 700-900 cm. 3 The preheater chamber of the working fluid volume (see working fluid volume) Figure 9 It can be connected to a tubular reactor or a batch reactor to enable continuous flow of oil between the tubular reactor and the preheater or between tubular or batch reactors.

[0017] Silver-plated coils, with or without heating cylinders, are heated at specific temperatures within two different ranges, depending on the flash point of the oil being processed, the concentration and type of sulfur-reactive substances in the oil, and the required reaction time. The lower temperature range, from 100°C to 140°C, is typically suitable for mineral oils; the higher temperature range, from 160°C to 200°C, is typically suitable for synthetic ester insulating liquids.

[0018] Silver-plated coils are immersed in oil in batch reactors and tubular reactors.

[0019] The batch reactor filled with oil is heated to a temperature of 100°C-120°C.

[0020] The oil in the tubular reactor is heated by a silver-plated coil and a preheater connected to the tubular reactor.

[0021] Therefore, the second embodiment of the present invention provides a means for mitigating power transformer failures caused by the presence of reactive sulfur, namely S8, S7, S6, S4 disulfides and sulfur oxide compounds, typically sulfoxides, sulfones and sulfur oxyacids.

[0022] This method is a desulfurization process that reduces the total sulfur content and the total reactive sulfur content by utilizing the solid-state reaction of silver with sulfur compounds such as S8 disulfide and oxidized sulfur compounds, typically sulfoxides, sulfones, and sulfur oxyacids. Surprisingly, this method has been found to selectively remove S8, S7, S6, and S4 disulfides and sulfoxides, sulfones, and sulfur oxyacids in a highly efficient manner, thereby achieving efficient desulfurization in mineral and synthetic ester insulating liquids. A second embodiment of the invention addresses the problem of providing a desulfurization method that offers improvements in efficiency and the degree of desulfurization in mineral and synthetic ester insulating liquids.

[0023] The method of the second embodiment of the present invention effectively reduces the total reactive sulfur content and removes S8, S7, S6, S4, as well as sulfoxides, sulfones, and sulfur oxyacids, thereby avoiding the corrosion reactions that would normally result from sulfur compounds such as S8, S7, S6, S4 disulfides and sulfur oxides (typically sulfur oxides). Furthermore, according to the second embodiment of the present invention, the single reagent described herein can be used to perform this treatment process multiple times (after mechanical removal of deposited sulfides by grinding). The absence of chemicals and waste materials offers significant advantages in terms of efficiency, cost, and environment.

[0024] Furthermore, corrosive mineral insulating oils can be rapidly converted to non-corrosive forms, for example, within 30 to 360 minutes, but longer (one to three days) if necessary. Another advantage is the low metal-to-oil ratio used in this method, making the entire process highly economical and efficient. Relatedly, the readily available and reusable materials further enhance the cost-effectiveness of this method.

[0025] In a third embodiment, the inventors of the present invention have designed a new method for reducing the content of reactive sulfur in the form of thiols, disulfides, sulfoxides, sulfones, sulfur oxyacids, etc., and / or reducing the dielectric loss factor of ester oils. The method includes contacting the ester oil with a particulate adsorbent carrier having a reducing agent on its surface.

[0026] This third approach is particularly suitable for removing elemental sulfur and disulfides that may be present in ester oils at a wide concentration range, while simultaneously achieving a lower dielectric loss factor in the treated oil—an important oil characteristic for further use in power transformers. An exemplary method for preparing a particulate adsorbent carrier with a reducing agent on its surface is described below, wherein the adsorbent is based on silica and doped with silver and ammonium ions. This exemplary method comprises three steps: 1 - Annealing the adsorbent carrier composed of silica; 2 - Deposition of silver ions onto an adsorbent support using an aqueous solution of silver nitrate to remove sulfur compounds that are corrosive to silver; and 3 - An aqueous solution of ammonium hydroxide is deposited on the adsorbent support to neutralize acidic byproducts after removing sulfur compounds from the adsorbent.

[0027] Steps 2 and 3 are critical because the deposition of specific components produces adsorbents that are highly efficient and selective in removing corrosive parts.

[0028] As an illustration of how a particulate adsorbent carrier with a reducing agent on its surface can be used to treat ester oils in the method of the present invention, it can be used in a method comprising the following steps: circulating the ester oil through a stainless steel column filled with a bed of a particulate adsorbent carrier having a reducing agent on its surface at a mass of 2-10% relative to the oil at a pressure of 1000-2000 L / h at an operating temperature of 80°C to 90°C, so that effective diffusion conditions of reactive sulfur substances at the active sites of the adsorbent can be achieved due to the high viscosity of the ester oil. In the case of removing high concentrations of reactive sulfur compounds (up to 50 mg / kg S8, up to 200 mg / kg dibenzyl disulfide, sulfones, sulfoxides, and sulfur oxyacids) from the oil, treatment can be carried out in a narrow temperature range of 85°C to 90°C, possibly using a two-stage method, i.e., using two portions of fresh adsorbent, wherein the amount of the maximum adsorbent relative to the oil is up to 10% by mass. The high efficiency stems from the binding of silver ions to the adsorbent carrier, specifically the acidic sites with -Si-OH bonds. These sites react with reactive sulfur compounds and molecules, effectively removing them from the oil. Ammonium hydroxide effectively neutralizes the acidic byproducts of sulfur compound chemisorption on the adsorbent. This adsorbent can be placed in oil treatment plants or in stainless steel towers / columns connected to transformers. Figure 19 The oil is packed in a bed of oil, allowing it to circulate continuously between the tower / column and the power transformer (online, i.e., while the transformer is operating).

[0029] These methods are capable of removing reactive corrosive sulfur compounds, especially high concentrations of elemental sulfur up to 50 mg / kg and disulfides up to 200 mg / kg, determined by testing the oil according to: IEC 62697 Part 1 (quantification of dibenzyl disulfide compounds), IEC TR 62697 Part 3 (quantification of octetral sulfur molecules - S8), and ASTM D 1275-15 (silver sheet corrosion test).

[0030] The common feature of these three implementation methods is that they remove elemental sulfur (S8) from insulating oils, especially synthetic ester oils, by applying processes and methods that include heterogeneous chemical reactions between the liquid and solid phases at the interface, thus obtaining an oil that is non-corrosive to silver. Attached Figure Description

[0031] Figure 1 is a chromatogram showing the S8 content in mineral insulating oil before, during and after treatment using the method of the present invention (see Example 1).

[0032] Figure 2 is a chromatogram showing the S8 content in mineral insulating oil before and after treatment using the method of the present invention (see Embodiment 1).

[0033] Figure 3 is a chromatogram showing the S8 content in mineral insulating oil before and after treatment using a method not described in this invention (see Embodiment 1A).

[0034] Figure 4A shows a silver plate that had been in contact with corrosive oil before treatment, according to the DIN 51353 oil corrosion test, and contains a typical S8 content.

[0035] Figure 4B shows an undetectable amount of S8 in a silver plate that has been in contact with a non-corrosive oil after treatment, according to the DIN 51353 oil corrosion test.

[0036] Figure 5A shows a copper plate that has been in contact with a non-corrosive oil after treatment, according to the DIN 51353 oil corrosion test.

[0037] Figure 5B shows a silver plate that has been in contact with a non-corrosive oil after treatment, according to the DIN 51353 oil corrosion test.

[0038] Figure 6 is a schematic diagram of a silver-plated coil used in a batch reactor.

[0039] Figure 6A is a schematic diagram of a silver-plated heating cylinder.

[0040] Figure 6B is a schematic diagram of a silver-plated coil wound around a heating cylinder for use in a batch reactor.

[0041] Figure 7 is a front view of an intermittent reactor with installed silver-plated coils.

[0042] Figure 7A is a side view of an intermittent reactor equipped with silver-plated coils.

[0043] Figure 7B is a side view of an intermittent reactor equipped with silver-plated coils wound around a silver-plated heating cylinder.

[0044] Figure 7C is a front view of an intermittent reactor equipped with silver-plated coils wound around a silver-plated heating cylinder.

[0045] Figure 8 is a schematic diagram of a silver-plated coil used in a tubular reactor.

[0046] Figure 8A is a schematic diagram of a tubular reactor.

[0047] Figure 8B is a schematic diagram of a tubular reactor with silver-plated coils.

[0048] Figure 9 is a schematic diagram of a modular reactor system including a preheater, a tubular reactor equipped with silver-plated coils, and a batch reactor, wherein there is continuous flow between the preheater and the tubular reactor, and between the tubular reactor and the batch reactor.

[0049] Figure 10 is a chromatogram showing the S8 content of the synthetic ester insulating liquid containing 7.6 ppm S8 before treatment, and the S8 chromatogram during and after treatment by the method of the present invention (see Example 7).

[0050] Figure 11A shows the results of the ASTM D 1275-15 silver corrosion test performed on the synthetic ester oil before treatment (see Example 8).

[0051] Figure 11B shows the results of the ASTM D 1275-15 silver corrosion test performed on the synthetic ester oil after treatment (see Example 8).

[0052] Figure 12A shows the results of the ASTM D 1275-15 silver foil corrosion test of the synthetic ester oil before treatment—with additional tests including sulfur oxide compounds and low total sulfur content (see Example 8).

[0053] Figure 12B shows the results of the ASTM D 1275-15 silver foil corrosion test on the treated synthetic ester oil—with additional tests including sulfur oxide compounds and low total sulfur content (see Example 8).

[0054] Figure 13 is a chromatogram showing the S8 content of a synthetic ester insulating liquid containing 7.6 ppm S8 and a low oil-to-silver surface ratio before, during and after treatment using the method of the present invention (see Example 9).

[0055] Figure 14A shows the results of the ASTM D 1275-15 silver foil corrosion test on the synthetic ester oil before treatment (see Example 9).

[0056] Figure 14B shows the results of the ASTM D 1275-15 silver foil corrosion test on the treated synthetic ester oil (see Example 9).

[0057] Figure 15 The chromatogram shows the S8 content in the synthetic ester oil before, during and after treatment using the method of the present invention (see Example 10).

[0058] Figure 16 The chromatogram shows the S8 content in the synthetic ester oil before, during and after treatment using the method of the present invention (see Example 10).

[0059] Figure 17 shows the chromatograms of mineral oil containing 7.6 ppm S8 before, during and after treatment (see Example 11).

[0060] Figure 18A shows the results of the silver foil corrosion test of the mineral oil before treatment, according to DIN 51353.

[0061] Figure 18B shows the results of the silver foil corrosion test of the treated mineral oil according to DIN 51353.

[0062] Figure 19 is a schematic diagram of a stainless steel tower for a third embodiment of the present invention, having a length (L) to diameter (D) ratio of 2.3 to 3, and comprising a particulate adsorbent carrier (which has a reducing agent on its surface).

[0063] Detailed Description of the First Embodiment This invention provides the use of a solid additive containing a reducing agent for reducing the active sulfur content in an oil and / or reducing the dielectric loss factor and acidity of the oil, while also increasing the interfacial tension, wherein the oil is contacted with (a) a solid additive containing a reducing agent and (b) a liquid additive suitable for dispersing the solid additive. Preferred aspects of this use correspond to those aspects described below related to the method of the first embodiment.

[0064] The present invention (in a first embodiment) provides a method for reducing the S8 content in an oil containing S8, the method comprising contacting the oil with (a) a solid additive containing a reducing agent and (b) a liquid additive suitable for dispersing the solid additive.

[0065] The reducing agent preferably comprises one or more metals. Preferably, the one or more metals are selected from copper, iron, zinc, aluminum, nickel, and tin. More preferably, the reducing agent comprises copper. Most preferably, the reducing agent is copper.

[0066] The solid additive is preferably contained in solid carrier particles having a reducing agent on their surface (and most preferably consists of solid carrier particles having a reducing agent on their surface). This does not require that all the reducing agent be present only on the surface of the solid carrier particles, but at least some of the reducing agent needs to be on their surface. Preferably, most (more than 50%) of the reducing agent is on the surface of the solid carrier particles, and more preferably, substantially all of the reducing agent is present on the surface of the solid carrier particles.

[0067] Preferably, the solid carrier particles are in the form of granules or powder. There are no particular limitations on the size of the solid carrier particles, which can be appropriately adjusted to control the reaction rate; smaller particle sizes (e.g., using powder instead of granules) can increase the reaction rate (this applies to desulfurization reactions and—if / when appropriate—the reduction of copper salts to copper during the preparation of the dispersions described herein). The solid carrier particles preferably contain at least some particles with a particle size of 4.00 mm or less, more preferably 2.00 mm or less. Preferably, the majority (>50% by weight) of the solid carrier particles, more preferably >80% by weight, and even more preferably still >90% by weight, have a particle size of 4.00 mm or less, more preferably 2.00 mm or less. Typically, all solid carrier particles have a particle size of 4.00 mm or less, more preferably 2.00 mm or less. Particles meeting these size requirements can be obtained using standard-sized sieves and are readily available commercially. Aside from natural physical limitations, there is no specific lower limit to the size of solid carrier particles—the presence of relatively small particles is not a problem. Typically, the proportion of solid carrier particles with a size ≤88 μm is <50% by weight, preferably <20% by weight, and more preferably <10% by weight. These particles can also be identified using standard-sized sieves.

[0068] Solid carrier particles typically contain iron and / or zinc. In this embodiment, the particles may further contain one or more salts of iron and / or zinc, preferably one or more salts selected from sulfates, nitrates, chlorides, and bromides. Typically, the solid carrier particles are iron and / or zinc particles, which may optionally have a certain proportion of iron and / or zinc oxide (e.g., sulfates, nitrates, chlorides, and bromides). (Oxidized iron and / or zinc are typically present in a preferred manner of preparation of the solid additive—as described below, which can be prepared, for example, by adding iron and / or zinc particles to a copper salt solution, such that the iron and / or zinc reduce the copper, thereby forming elemental copper and a certain proportion of corresponding oxidized iron and / or zinc on the particle surface.) The liquid additive is preferably a polymer, more preferably a polyether, and even more preferably polyethylene glycol. While the number-average molecular weight (Mn) of the polymer is not particularly limited, it is somewhat restricted in practical applications due to the requirement that the reagent be liquid under the conditions of use. Suitable polymers are commercially available. The polymer preferably has a number-average molecular weight (Mn) of at least 300 g / mol, more preferably at least 350 g / mol. The polymer preferably has an Mn of no more than 800 g / mol, more preferably no more than 600 g / mol, more preferably still no more than 550 g / mol, and even more preferably still no more than 500 g / mol. A typical range is 300 to 600 g / mol, with 350 to 550 g / mol being more preferred, and 350 to 500 g / mol still more preferred. Mn can be measured by gel permeation chromatography, but it is usually unnecessary to measure Mn because suitable reagents are readily available commercially. For example, a particularly suitable reagent is the commercially available polymer PEG-400 (polyethylene glycol with 400 g / mol Mn).

[0069] The properties of the solid additives and the reducing agents contained therein, as well as the amounts of these components, can be adjusted to control the rate of the desulfurization process.

[0070] Preferably, the amount of solid additives is 0.05 to 10 by weight relative to the amount of oil.

[0071] Preferably, the amount of reducing agent is 0.01 to 2% by weight relative to the amount of oil, more preferably 0.02 to 1.5% by weight.

[0072] Preferably, the reducing agent accounts for 0.5 to 25% by weight of the solid additive.

[0073] Preferably, the amount of liquid additive is 1.5 to 40 by weight relative to the amount of oil.

[0074] In one embodiment, the method includes the step of contacting the oil with a dispersion, wherein a solid additive is dispersed in a liquid additive. Preferably, the dispersion further comprises water. However, it is not necessary to form the dispersion before contacting the oil with components (a) and (b). Therefore, in another embodiment, components (a) and (b) can be contacted with the oil separately. For example, component (b) can be added to the oil first, and then component (a) can be added separately.

[0075] The content of dispersant is preferably 1.5% to 40% by weight relative to the total amount of oil and dispersant.

[0076] The dispersant is preferably the dispersant of the present invention as described below.

[0077] In the method of the present invention, reagents (a) and (b) as described above are the only essential components. The inclusion of other components is not excluded, provided that these other components do not interfere with the desulfurization reaction. Furthermore, in some cases, the inclusion of other components may be advantageous, as this may help promote the desulfurization reaction; for example, the inclusion of a polar liquid may be helpful. Therefore, in a preferred embodiment, the method of the present invention comprises contacting oil with (a) a solid auxiliary agent containing a reducing agent, (b) a liquid reagent suitable for dispersing the solid auxiliary agent, and (c) one or more polar liquids, such as one or more polar liquids selected from water, alcohols, and polyols. Most preferably, the method of the present invention further comprises contacting the oil with water, which may optionally be combined with one or more alcohols and / or polyols. Preferred alcohols are C10 and C20. 1-3 Alcohols, such as methanol, ethanol, and propanol, with methanol being the most preferred. Preferred polyols are C10 and C20. 1-3 Diols and C 1-3 The preferred alcohol is glycerol. Typically, it is preferable not to include optional alcohol and / or polyol components (i.e., the preferred method of the invention involves contacting the oil with (a) a solid additive containing a reducing agent, (b) a liquid additive suitable for dispersing the solid additive, and (c) water). However, if a heavier liquid additive is used, for example if the liquid additive is a polymer having a relatively high Mn, such as >400, ≥500, or ≥550 Mn (e.g., polyethylene glycol), then including alcohol and / or polyols may be advantageous.

[0078] In the method of the present invention, the oil, solid additives and liquid additives are preferably subjected to stirring and / or ultrasonic treatment.

[0079] In the method of the present invention, the oil, solid additives, and liquid additives are preferably heated to a temperature of 50 to 120°C, more preferably 60 to 105°C, and still more preferably 70 to 99°C. In this case, the reaction mixture is preferably heated to these temperatures for at least 20 minutes, more preferably at least 30 minutes. The reaction mixture is preferably heated to these temperatures for up to 4 hours, more preferably up to 3 hours, and still more preferably up to 2 hours. Typically, the reaction mixture is heated to these temperatures (e.g., 50 to 120°C) for 20 minutes to 3 hours, and more typically 30 minutes to 2 hours.

[0080] Oils containing S8 can be mineral oils or ester oils. Esters can be synthetic or natural.

[0081] The oil containing S8 can be a mineral oil or a synthetic oil (e.g., an ester oil). Mineral oil is preferred.

[0082] The oil containing S8 is preferably an insulating oil for transformers, and more preferably a mineral insulating oil for transformers. Typically, it is an existing insulating transformer oil, and more typically, it is an existing mineral insulating transformer oil.

[0083] Based on the total amount of oil, the oil containing S8 preferably contains at least 2.0 mg / kg of S8, more preferably at least 5.0 mg / kg, and even more preferably at least 10.0 mg / kg.

[0084] In the method of the present invention, based on the total amount of oil, the content of S8 is preferably reduced to less than 5.0 mg / kg, more preferably less than 2.0 mg / kg, more preferably less than 1.0 mg / kg, and even more preferably less than 0.2 mg / kg.

[0085] The S8 content in the oil is preferably measured by IEC TR 62697-3 / 2018.

[0086] Once the method of the present invention is implemented, this oil (and thus having a reduced S8 content) can be separated from the other components, for example by precipitation. These other components should be present in the form of a dispersion. This dispersion may consist only of (a) and (b) (plus some copper sulfide), but may also contain other components if other reagents (e.g., water, optionally combined with alcohols and / or polyols) are used.

[0087] Therefore, the present invention also provides a method comprising: (a) Reducing the S8 content in oil containing S8 by the method described above; and (b) The oil is then separated from other components, wherein the other components are in the form of a dispersion containing solid and liquid additives.

[0088] The separated oil with reduced S8 content can be used in applications that may come into contact with components susceptible to S8 corrosion—for example, it can be used as insulating oil in transformers with such components. Simultaneously, the separated dispersion can be reused for desulfurization treatment of other oils. Therefore, the present invention also provides a method comprising: (a) The method of the present invention as defined above reduces the S8 content in oil containing S8; (b) The oil is then separated from the other components, wherein the other components are present in the form of a dispersion comprising solid and liquid additives; and (c) Using the dispersion thus obtained, reduce the S8 content in the oil containing S8 by the method defined independently above.

[0089] Certain dispersions suitable for use with the method according to the invention (comprising solid and liquid additives as defined above) are considered novel. Therefore, the invention also provides dispersions comprising water and elemental copper, wherein the water and copper are dispersed in a liquid polymer. The preferred aspects of the aforementioned liquid additives (component (b) in the method of the invention) are equally and independently applicable to the liquid polymer.

[0090] The dispersion of the present invention preferably comprises solid carrier particles having copper on their surface. Therefore, the present invention provides a dispersion comprising water and solid carrier particles having copper on their surface, wherein the water and particles are dispersed in a liquid polymer. The solid carrier particles are preferably defined in the same manner as in the method of the present invention described above.

[0091] The amount of water in the dispersion is preferably 1% to 50% by weight, more preferably 2% to 40% by weight.

[0092] The amount of liquid polymer in the dispersion is preferably 40% to 98% by weight, more preferably 45% to 97% by weight.

[0093] The amount of copper in the dispersion is preferably from 0.02% to 4.0% by weight, more preferably from 0.05% to 3.0% by weight.

[0094] When the dispersion of the present invention contains solid carrier particles having copper on their surface, the amount of solid carrier particles in the dispersion (excluding the copper on their surface) is preferably from 0.1% to 12.0% by weight, more preferably from 0.2% to 10.0% by weight.

[0095] To avoid misunderstanding, these preferred aspects of the dispersions of the present invention also apply to the dispersions used in the methods of the present invention as defined above.

[0096] The present invention also provides a method for preparing the dispersion of the present invention as defined above, the method comprising the following steps: (i) Preparation of an aqueous solution or a suspension of a copper-containing reagent, and (ii) Dispersing the solution or suspension in a liquid polymer; Wherein, if the copper-containing reagent in step (i) is characterized by copper in an oxidized form (i.e., if copper is present as a copper cation, for example, if it is obtained by adding a copper salt), then the method further includes a step between steps (i) and (ii) to reduce the copper in the copper-containing reagent. In this respect, the copper in the copper-containing reagent is reduced to form elemental copper.

[0097] Preferably, step (i) involves preparing an aqueous solution of a copper salt, such as copper sulfate. In this regard, the aqueous solution of the copper salt is preferably prepared using the following substances: (a) H2O; (b) A mixture of H2O and alcohol, wherein the alcohol is preferably C2O. 1-3 Hydrocarbons, such as methanol, ethanol, or propanol, preferably methanol; or (c) A mixture of H2O and polyols, wherein the polyol is preferably C 1-3 Diol or C 1-3 Triol, more preferably glycerol.

[0098] In a preferred aspect of the above process, the copper-containing reagent in step (i) is characterized by copper in an oxidized form (therefore the method also includes a step of reducing copper in the copper-containing reagent between steps (i) and (ii)), and the reduction reaction involves introducing one or more reducing agents into an aqueous solution or suspension, said reducing agents being selected from transition metals and post-transition metals, more preferably from elements iron, zinc, aluminum, nickel, and tin. In a further preferred aspect, the reducing agent is preferably present in the form of fine particles or powder. Furthermore, the preferred aspects of the solid carrier particles used in the method of the present invention according to the above definition also apply to the reducing agents herein. Typically, particles of a metal reducing agent are used to reduce copper in a copper-containing reagent (e.g., copper sulfate), such that elemental copper forms on the surface of these particles.

[0099] The method of this invention produces oils with beneficial properties, making them particularly suitable for use as insulating oils in transformers. Furthermore, the method is believed to impart a "fingerprint" to the oil, distinguishing it from previously known oils (even those with low S8 content). One aspect of this is that the method is thought to selectively desulfurize the oil while other components, such as aromatics, paraffins, and cycloalkanes, remain largely unchanged or unaffected. Therefore, this invention also provides oils that are obtained or available through the methods defined above.

[0100] These oils preferably have a total S8 content of ≤0.5 mg / kg (more preferably ≤0.2 mg / kg). The preferred type of oil should have a content of thiols and disulfides ≤2 mg / kg.

[0101] This type of oil preferably has a dielectric loss factor of <0.005 at 90°C.

[0102] These types of oils preferably have an acid value of <0.02 mg KOH / g.

[0103] The preferred type of oil has an oil-water interfacial tension of ≥35 mN / m.

[0104] These types of oils are preferably grown at 700 to 1300 cm. -1 The Fourier transform infrared (FT-IR) spectrum within the wavelength range is essentially the same as that of the oil before the desulfurization process.

[0105] These oils preferably have particles with a size of ≥4 μm and a quantity of ≤320 particles / ml (typically, the number of such particles ranges from >160 to ≤320 particles / ml).

[0106] These oils preferably have particles with a size of ≥6 μm and a quantity of ≤320 particles / ml (typically, the number of such particles ranges from >20 to ≤40 particles / ml).

[0107] These oils preferably have particles with a size of ≥4 μm and an amount of ≤320 particles / ml, and particles with a size of ≥6 μm and an amount of ≤40 particles / ml.

[0108] These types of oils preferably possess the following characteristics: - The total amount of thiols, sulfides and disulfides ≤2 mg / Kg; - S8 content ≤ 0.5 mg / Kg; - Dielectric loss factor at 90℃ < 0.005, - Acid value <0.02 mgKOH / g - Oil-water interfacial tension ≥35 mN / m, - Between 700 and 1300 cm -1 The FT-IR spectra in the wavelength range are essentially the same as those of the oil before the desulfurization process, and / or - The amount of particles with a size ≥ 4 μm is ≤ 320 particles / ml, and the amount of particles with a size ≥ 6 μm is ≤ 40 particles / ml.

[0109] According to the preferred aspects of the invention described above, such oils preferably have an ISO code ≤15 / 12 (refer to ISO 4406, a standard for defining particle number and size). The first number, 15, represents >160 particles / ml with a particle size of 4 μm, and up to and including 320 particles / ml. The second number, 12, represents >20 particles / ml with a particle size of 6 μm, and up to and including 40 particles / ml.

[0110] Particle size and quantity can be measured according to IEC 60970:2007.

[0111] The above-described preferred properties of the oil obtained or obtainable by this method are particularly preferred when the oil is a mineral oil. When the oil obtained or obtainable by this method is an ester oil, its preferred properties may sometimes differ.

[0112] These ester oils preferably have a total sulfur content of ≤0.5 mg / Kg (more preferably ≤0.2 mg / Kg). These ester oils preferably have a total S8 content of ≤0.5 mg / Kg (more preferably ≤0.2 mg / Kg). These ester oils preferably have a thiol and disulfide content of ≤0.2 mg / Kg.

[0113] This type of ester oil preferably has a dielectric loss factor of <0.020 at 90°C.

[0114] These ester oils preferably have an acid value of <0.03 mg KOH / g.

[0115] These ester oils preferably have an oil-water interfacial tension of ≥35 mN / m.

[0116] These ester oils preferably have particles with a size ≥ 4 μm and an amount ≤ 320 particles / ml (typically, the number of such particles ranges from > 160 to ≤ 320 particles / ml).

[0117] These ester oils preferably have particles with a size ≥6 μm and an amount ≤320 particles / ml (typically, the number of such particles ranges from >20 to ≤40 particles / ml).

[0118] Consistent with the preferred aspects described above, these ester oils preferably have an ISO code ≤15 / 12 (refer to: ISO 4406, a standard for defining particle number and size). The first digit, 15, indicates that the amount of particles with a particle size of 4 μm is >160 particles / ml and up to and includes 320 particles / ml. The second digit, 12, indicates that the amount of particles with a particle size of 6 μm is >20 particles / ml and up to and includes 40 particles / ml.

[0119] Particle size and quantity can be measured according to IEC 60970:2007.

[0120] Detailed Description of the Second Embodiment This invention provides the use of a solid additive containing a reducing agent for reducing the active sulfur content in oil, wherein the oil is in contact with a solid substrate having the reducing agent on its surface. Preferred aspects of this use correspond to those aspects related to the method of the second embodiment.

[0121] The present invention (in a second embodiment) provides a method for reducing the content of S8, S7, S6, S5, S4, disulfides and / or sulfoxides, sulfones and sulfur oxyacids in an oil containing S8, S7, S6, S5, S4, disulfides and / or sulfoxides, sulfones and sulfur oxyacids, the method comprising contacting the oil with a solid substrate having a reducing agent on its surface.

[0122] The substrate is preferably made of metal. Preferred substrates include aluminum, copper, zinc, brass, and iron. More preferred substrates are aluminum, copper, zinc, brass, and iron. The most preferred materials used are aluminum and copper. Therefore, an aluminum or copper substrate is preferred.

[0123] The reducing agent preferably comprises one or more metals. Preferably, the one or more metals are selected from silver, zinc, aluminum, nickel, and tin. More preferably, the reducing agent comprises silver. Most preferably, the reducing agent is silver.

[0124] The reducing agent is preferably a material different from the substrate. Therefore, if the substrate is aluminum, for example, the reducing agent is preferably not aluminum.

[0125] The substrate should have structural integrity, allowing it to be inserted / immersed in oil to provide the desired treatment. There are no particular restrictions on the shape of the substrate. Coil shapes can be conveniently used, but in principle, any shape providing a similar or higher surface area to volume ratio may be appropriately used.

[0126] Preferably, the solid substrate having a reducing agent on its surface is a substrate for plating the reducing agent, more preferably a metal substrate for plating the reducing agent (e.g., a metal coil for plating the reducing agent), wherein typically: - The reducing agent may be one or more selected from silver, zinc, aluminum, nickel, and tin, more preferably silver; and - The metal coil comprises or is selected from one or more of aluminum, copper, zinc, brass, iron and steel, more preferably aluminum and copper.

[0127] The dimensions and surface area of ​​the substrate (e.g., a metal coil), particularly the surface area of ​​the reducing agent on it (in contact with the oil), can be adjusted by those skilled in the art based on factors such as the desired performance level and the cost of preparing the substrate with the reducing agent on its surface. The ratio of the reducing agent's surface area to the oil mass is preferably from 0.00001 to 0.01 m². 2 / kg, more preferably 0.00005 to 0.005 m 2 / kg, more preferably 0.0001 to 0.001m 2 / kg, and more preferably 0.00015 to 0.00080m 2 / kg.

[0128] When the base is a coil, the coil preferably has a diameter of 2-20 mm, more preferably 4-15 mm, still more preferably 6-12 mm, and most preferably 8-10 mm.

[0129] When the base is a coil, the coil preferably has a length of 2-30 m, more preferably 3-25 m, still more preferably 4-20 m, and most preferably 5-15 m.

[0130] When the substrate having a reducing agent on its surface is a substrate plated with a reducing agent (more preferably a metal substrate plated with a reducing agent, such as a metal coil plated with a reducing agent, like a silver-plated metal coil), the coating preferably has a thickness of 0.0005 to 0.2 mm, more preferably 0.001 to 0.1 mm, even more preferably 0.003 to 0.08 mm, and most preferably 0.005 to 0.05 mm.

[0131] In a preferred aspect, the solid substrate comprises (and more preferably) a metal coil coated with a reducing agent, the metal coil being wound around the heater.

[0132] In a preferred aspect of the second embodiment of the invention, the oil is heated to a temperature of 100°C to 220°C.

[0133] If the oil is mineral oil, it is preferably heated to a temperature of 100°C to 160°C, more preferably 100°C to 140°C.

[0134] If the oil is an ester, it is preferable to heat it to a temperature of 160°C to 180°C, more preferably 180°C to 200°C.

[0135] Preferably, the oil needs to be heated for at least 30 minutes, more preferably 60 minutes, and most preferably 120 minutes. If necessary, a longer heating time can be used, ≤72 hours, more typically ≤48 hours, more typically ≤20 hours, and most typically not exceeding 10 hours.

[0136] A second embodiment of the invention provides a method for reducing the total sulfur content in an oil containing various forms of elemental sulfur, disulfides, sulfoxides, sulfones, and sulfur oxyacids. In insulating oils used in power transformers, operating conditions (i.e., associated temperatures and pressures) can lead to the significant presence of these substances, particularly S8. In a preferred aspect, the method involves contacting the oil with a heated silver-plated coil. More preferably, the heated silver-plated coil attracts reactive sulfur substances, namely elemental sulfur (S8, S7, S6, S4, but primarily S8), disulfides, and / or sulfoxides, sulfones, and sulfur oxyacids, to react and deposit silver sulfide on its surface.

[0137] In another preferred aspect, the reducing agent comprises one or more metals, preferably selected from zinc, aluminum, copper, and silver. More preferably, the reducing agent comprises silver. Most preferably, the reducing agent is silver.

[0138] In another preferred aspect, the solid substrate comprises (and most preferably consists of) a coil-shaped solid substrate made of aluminum, copper, zinc, brass, or iron steel (preferably aluminum or copper).

[0139] In another preferred aspect, the substrate is in the form of a coil ( Figure 6 The coil preferably comprises a conductor with a diameter of 0.8-2 cm and a length of 10 m (preferably less than or equal to 7 m, more preferably less than or equal to 3 m).

[0140] In another preferred aspect, the substrate having a reducing agent on its surface is a silver-plated coil with a diameter of 100 to 150 mm, preferably 130 mm; a length of 300 to 1000 mm, preferably 450 mm, more preferably 700 mm; and a surface area to oil mass ratio of 0.00015 to 0.0008 m². 2 / kg oil (Figure 6).

[0141] Silver-plated coils can be wound around heating cylinders made of aluminum, copper, or iron (Figure 6B), the surfaces of which can be silver-plated.

[0142] In a second embodiment of the invention, characterized by a heater, the heater may be a copper-plated and / or silver-plated heating cylinder with a surface area of ​​0.001 to 0.010 m². 2 / kg oil, preferably 0.007 m 2 / kg oil (see Figure 6A ).

[0143] This invention provides a batch reactor, a tubular reactor, or a reactor system comprising a batch reactor and a tubular reactor, wherein the batch reactor, the tubular reactor, and at least one reactor in the reactor system each comprise at least one solid substrate having a reducing agent on its surface as defined above, wherein the solid substrate having the reducing agent on its surface is located inside the reactor or is movable for installation and removal therefrom. This aspect of the invention is important for the efficient cleaning of silver-plated coils.

[0144] In a preferred embodiment, the coils are located within the batch reactor, and preferably, they are wound around a cylindrical heating element mounted, for example, in the upper region of the batch reactor (see...). Figure 8 ).

[0145] In another preferred aspect, silver-plated coils, with and without silver-plated heating cylinders, are placed in the batch reactor. Figure 8 , 8A (and 8B, 8C).

[0146] In another preferred aspect, the batch reactor (170 cm high, 90 cm in diameter) is made of 316 stainless steel. Figure 7 It is equipped with a stirrer and has a filling capacity of 600 to 900 cm³.3 The capacity of the insulating liquid ( Figure 8 C).

[0147] In another preferred aspect, the number of coils with heated copper or silver-plated cylinders immersed in the batch reactor is 2 to 4, more preferably 4; while in a preferred aspect of the tubular reactor, the number of silver-plated coils is 1 to 3, more preferably 2.

[0148] In another preferred aspect, one to three silver-plated coils are used in the tubular reactor. In this regard, the diameter of the silver-plated coils can be between 100 and 150 mm, preferably 130 mm, and the length can be between 300 and 1000 mm, preferably 450 mm, more preferably 700 mm, and the ratio of their surface area to oil mass is between 0.00015 and 0.0008 m². 2 Within the range of / kg oil ( Figure 8 ).

[0149] In another preferred aspect, the tubular reactor is made of 316 stainless steel (1500 mm in length and 280 mm in diameter) (Figure 8A).

[0150] In another preferred aspect, the silver-plated coil is placed in the middle of the cross-section of the tubular reactor (Fig. 8B).

[0151] In another preferred aspect, tubular reactors with silver-plated coils and batch reactors constitute a modular reactor system. Figure 9 A suitable tubular reactor and preheater are connected in a circulating flow loop. If necessary, the tubular reactor is connected to a batch reactor in the loop if the additional treatment requires a reaction time longer than 120 minutes. Otherwise, the tubular reactor is disconnected and / or connected to the preheater chamber in the loop, run for a certain number of cycles and time, and then reconnected to the batch reactor.

[0152] In another preferred aspect, the number of silver-plated coils, the total available silver-plated surface area, and the number of oil recirculations in the loop and return treatment can be adjusted to control the rate of desulfurization. Preferably, the total number of silver-plated coils in the batch and tubular reactors is six.

[0153] Preferably, the total silver-plated surface area is 0.005 to 0.0110 m². 2 .

[0154] The surface areas of the coil and heating cylinder are determined using the equation for the roller surface, while the length and diameter are determined using a meter stick and vernier calipers.

[0155] In another preferred aspect of the method of the second embodiment of the invention, the oil circulates in a loop between a preheater chamber and a tubular reactor with embedded silver-plated coils, and is heated from ambient temperature to a temperature ranging from 100°C to 220°C, more preferably 100°C to 140°C for mineral oils, and more preferably 160°C to 180°C, and even more preferably 180°C to 200°C for ester oils. In this regard, the oil is heated for at least 30 minutes, more preferably 60 minutes, and most preferably 120 minutes. After the above steps, the oil is stirred, preferably in a batch reactor containing four silver-plated coils and / or silver-plated coils wound around a silver-plated heating cylinder, using the same temperature described above. As an additional option, the oil may be circulated between the tubular reactor and the batch reactor for a period of time.

[0156] If the concentrations of S8, disulfide, sulfoxide, sulfone, and sulfur oxyacid are up to 5 mg / kg oil, the reaction time is preferably between 30 minutes and 360 minutes, at least 30 minutes, more preferably 60 minutes, and most preferably 120 minutes.

[0157] If the concentrations of S8, disulfides, sulfoxides, sulfones, and sulfur-containing oxyacids are higher than 5 mg / kg oil, the reaction time is preferably more than 360 minutes, up to a maximum of 2000 minutes.

[0158] Oils containing sulfur compounds, S8, S7, S6, S4 disulfides, and sulfoxides, sulfones, and sulfur oxyacids can be mineral oils or ester oils (e.g., synthetic ester oils).

[0159] Oils containing S8, S7, S6, and S4 disulfides and sulfoxides, sulfones, and sulfur-containing oxyacids are preferred insulating oils for transformers. Typically, it is a pre-existing insulating transformer oil, more typically a pre-existing mineral insulating transformer oil, and most preferably a pre-existing synthetic ester insulating oil.

[0160] Based on the total amount of oil, the sulfur-containing synthetic ester insulating oil preferably contains at least 1 mg / kg of total sulfur, more preferably at least 5.0 mg / kg of oil, and even more preferably at least 10.0 mg / kg of oil.

[0161] The sulfur-containing mineral insulating oil preferably contains a total sulfur content of at least 10 mg / kg, more preferably at least 100 mg / kg, and even more preferably at least 800 mg / kg.

[0162] In the method of the present invention, based on the total amount of oil, the total sulfur content in the synthetic ester oil should be reduced to less than 5.0 mg / kg, preferably less than 2.0 mg / kg, and more preferably ≤1.0 mg / kg.

[0163] The total sulfur content in the oil is preferably measured using ASTM D 5453.

[0164] The contents of sulfoxides and sulfones were determined using high performance liquid chromatography (HPLC), LC MS / MS, or GC / MS.

[0165] The total of thiols, disulfides and elemental sulfur was determined by automatic potentiometric titration of zinc particles (Zn) according to CIGRE A2.32 TF 3 method.

[0166] Based on the total amount of oil, the sulfur-containing oil preferably contains at least 0.2 mg / kg of S8, more preferably at least 5.0 mg / kg, and even more preferably at least 10.0 mg / kg.

[0167] In the method of the present invention, the content of S8 is preferably reduced to less than 5.0 mg / kg oil, more preferably less than 1.0 mg / kg, and even more preferably less than 0.2 mg / kg.

[0168] The S8 content in the oil is preferably measured by IEC TR 62697-3 / 2018.

[0169] Once the method of the present invention is employed, the oil (which thus has reduced levels of S8, S7, S6, S5, S4, disulfides and / or sulfoxides, sulfones and sulfur oxyacids) can be separated from a substrate having a reducing agent on its surface. And the substrate having a reducing agent on its surface can be reused (optionally, after being treated to remove sulfide deposits).

[0170] Therefore, the present invention also provides a method comprising: (a) Reducing the content of S8, S7, S6, S5, S4, disulfides and / or sulfoxides, sulfones and sulfur oxyacids in the oil by methods defined above; and (b) The oil is then separated from the solid substrate on which the reducing agent is present.

[0171] The present invention also provides a method comprising: (a) Reduce the content of S8, S7, S6, S5, S4, disulfides and / or sulfoxides, sulfones and sulfur oxyacids in the oil by the methods defined above; (b) The oil is then separated from a solid substrate having a reducing agent on its surface; and (c) Using a solid substrate thus obtained having a reducing agent on its surface, reduce the content of S8, S7, S6, S5, S4, disulfides and / or sulfoxides, sulfones and sulfur oxyacids in an oil containing S8, S7, S6, S5, S4, disulfides and / or sulfoxides, sulfones and sulfur oxyacids by the methods defined above.

[0172] The method of this invention can produce oils with beneficial properties, making them particularly suitable for use as insulating oils in transformers. Furthermore, this method is believed to impart a "fingerprint" to the oil, distinguishing it from previously known oils (even those with low S8 content). One aspect of this is that the method is thought to selectively desulfurize the oil while leaving little or no change to other components such as esters, aromatics, paraffins, and cycloalkanes. Therefore, this invention also provides oils that are obtained or available through the methods defined above.

[0173] When this oil is a synthetic ester oil, it preferably has a total sulfur content ≤0.5 mg / kg (more preferably ≤0.2 mg / kg). This type of oil preferably has an S8 content of ≤0.5 mg / kg (more preferably ≤0.2 mg / kg).

[0174] Such oils preferably have a disulfide content of ≤10 mg / kg, more preferably ≤5 mg / kg.

[0175] This type of oil preferably has a dielectric loss factor of <0.020 at 90°C, more preferably ≤0.010.

[0176] These types of oils preferably have an acid value ≤ 0.03 mg KOH / g.

[0177] The preferred type of oil has an oil-water interfacial tension of ≥30 mN / m.

[0178] These oils preferably have ≤320 particles / ml of particles with a size ≥4 μm (typically, the number of such particles is >160 to ≤320 particles / ml).

[0179] These oils preferably have ≤320 particles / ml of particles with a size ≥6 μm (typically, the number of such particles is >20 to ≤40 particles / ml).

[0180] These oils preferably have a particle size of ≥4 μm of ≤320 particles / ml and a particle size of ≥6 μm of ≤40 particles / ml.

[0181] According to the preferred aspects of the invention described above, such oils preferably have an ISO code ≤ 15 / 12 (refer to: ISO 4406, a standard for defining particle number and size). The first number, 15, represents >160 particles / ml with a particle size of 4 μm, and up to and including 320 particles / ml. The second number, 12, represents >20 particles / ml with a particle size of 6 μm, and up to and including 40 particles / ml.

[0182] Particle size and quantity can be measured according to IEC 60970:2007. The above-mentioned preferred characteristics of the oil obtained or obtainable by this method are particularly preferred when the oil is a mineral oil. When the oil obtained or obtainable by this method is an ester oil, its preferred characteristics may sometimes be different.

[0183] These ester oils preferably have a total sulfur content of ≤0.5 mg / kg (more preferably ≤0.2 mg / kg). These ester oils preferably have a total S8 content of ≤0.5 mg / kg (more preferably ≤0.2 mg / kg). These ester oils preferably have a thiol and disulfide content of ≤0.2 mg / kg.

[0184] This type of ester oil preferably has a dielectric loss factor ≤0.020 at 90°C.

[0185] These ester oils preferably have an acid value of ≤0.03 mg KOH / g.

[0186] These ester oils preferably have an oil-water interfacial tension of ≥35 mN / M.

[0187] These ester oils preferably have particles with a size ≥ 4 μm and an amount ≤ 320 particles / ml (typically, the number of such particles is > 160 to ≤ 320 particles / ml).

[0188] These ester oils preferably have particles with a size ≥6 μm and an amount ≤320 particles / ml (typically, the number of such particles is >20 to ≤40 particles / ml).

[0189] Consistent with the preferred aspects of the invention described above, these ester oils preferably have an ISO code of ≤15 / 12 (refer to: ISO 4406, standard for defining particle number and size). The first digit, 15, indicates that the amount of particles with a particle size of 4 μm is >160 particles / ml and up to and includes 320 particles / ml. The second digit, 12, indicates that the amount of particles with a particle size of 6 μm is >20 particles / ml and up to and includes 40 particles / ml.

[0190] Particle size and quantity can be measured according to IEC 60970:2007.

[0191] Detailed Description of the Third Embodiment This invention provides the use of solid additives containing reducing agents for reducing the content of reactive sulfur in oils in the form of thiols, disulfides, sulfur oxides such as sulfoxides, sulfones, and sulfur oxyacids, and / or reducing the dielectric loss factor and oleicity, wherein the oil is an ester and is in contact with a particulate adsorbent carrier having a reducing agent on its surface. Preferred aspects of this use correspond to those described below in relation to the method of the third embodiment.

[0192] The present invention (in a third embodiment) provides a method for reducing the reactive sulfur content in ester oils and / or reducing the dielectric loss factor of ester oils, the method comprising contacting the oil with a particulate adsorbent carrier having a reducing agent on its surface.

[0193] Preferably, the particulate adsorbent carrier comprises silica and / or calcium oxide. Typically, the particulate adsorbent carrier is silica-based. Preferably, the particulate adsorbent carrier has a silica content of ≥60 wt%, ≥80 wt%, ≥90 wt%, or ≥94 wt%. In each case, the silica content is capped at 100 wt%, and preferably 99 wt%. More preferably, the particulate adsorbent carrier has a silica content of 90 to 100 wt%, typically 94 to 99 wt%, and a calcium oxide content of 0 to 10 wt%, typically 1 to 6 wt%.

[0194] The reducing agent preferably comprises one or more transition metal ions, and more preferably silver ions. Most preferably, the reducing agent is silver ions. Typically, silver ions are deposited on the particulate adsorbent support by contacting the support with an aqueous silver nitrate solution. The reducing agent (typically silver ions) is preferably present in an amount of ≥1%, ≥2%, or ≥3% based on the weight of the particulate adsorbent support. The reducing agent (typically silver ions) is preferably present in an amount of ≤20%, ≤10%, or ≤6% based on the weight of the particulate adsorbent support. The reducing agent (preferably silver ions) is preferably present in an amount of 1 to 20 wt%, 2 to 10 wt%, or 3 to 6 wt% based on the weight of the particulate adsorbent support.

[0195] The particulate adsorbent support preferably also has an alkaline reagent on its surface. This helps to neutralize acidic byproducts. Suitable reagents are those containing ammonium ions, such as ammonium hydroxide. Therefore, the particulate adsorbent support preferably also has ammonium ions on its surface, and more preferably has ammonium hydroxide on its surface. Typically, the alkaline reagent is deposited on the particulate adsorbent support by contacting the support with aqueous ammonium hydroxide. The alkaline reagent (typically ammonium hydroxide) is preferably present in an amount of ≥1 wt%, ≥2 wt%, or ≥3 wt%, based on the weight of the particulate adsorbent support. The alkaline reagent (typically ammonium hydroxide) is preferably present in an amount of ≤30 wt%, ≤20%, or ≤10%, based on the weight of the particulate adsorbent support. The alkaline reagent (typically ammonium hydroxide) is preferably present in an amount of 1 to 30 wt%, 2 to 20 wt%, or 3 to 10 wt%, based on the weight of the particulate adsorbent support.

[0196] In a preferred embodiment, the particulate adsorbent carrier comprises silica and / or calcium oxide, and the reducing agent comprises silver ions; even more preferably, the particulate adsorbent carrier has ammonium ions on its surface.

[0197] In a further preferred embodiment, the particulate adsorbent carrier has a silica content of 90 to 100 wt% (typically 94 to 99 wt%) and a calcium oxide content of 0 to 10 wt% (typically 1 to 6 wt%); the reducing agent comprises silver ions present in an amount of 1 to 20 wt% (typically 3 to 6 wt%) based on the weight of the particulate adsorbent carrier; and the particulate adsorbent carrier has ammonium hydroxide on its surface present in an amount of 1 to 30 wt% (typically 3 to 10 wt%) based on the weight of the particulate adsorbent carrier.

[0198] Preferably, the particulate adsorbent carrier has a particle size of ≥50 μm, ≥100 μm, or ≥200 μm. The particle size is preferably ≤5000 μm, ≤2000 μm, or ≤1200 μm. The particle size is typically 50 to 5000 μm, 100 to 2000 μm, or 200 to 1200 μm.

[0199] Preferably, a particulate adsorbent carrier having a reducing agent on its surface is placed in a container, typically a tower-shaped container / column (preferably a stainless steel tower), and the ester oil, for example by a percolation process, passes through this carrier.

[0200] In a preferred aspect of the third embodiment of the invention, the oil is heated to a temperature of 40°C to 120°C. More preferably, it is heated to a temperature of 50°C to 100°C, and even more preferably, to 75°C to 90°C.

[0201] In a preferred embodiment, the particulate adsorbent support having a reducing agent on its surface can be prepared by a three-stage technique: a first stage of annealing the silica particulate adsorbent support; a second stage of depositing silver ions; and a third stage of depositing ammonium hydroxide. Illustrative examples are given below.

[0202] In the first stage (annealing of the adsorbent), an adsorbent based on silica (94% to 98%, particle size 200 to 1200 μm) is annealed at 150°C and atmospheric pressure for 18 to 24 hours to remove adsorbed moisture.

[0203] In the second stage (activation of the adsorbent via silver ion deposition), the annealed silica is treated with 4 to 10 wt% silver nitrate relative to the mass of the adsorbent by applying an aqueous silver nitrate solution to the adsorbent, followed by gradual evaporation of moisture from the adsorbent in the following manner: - Heating at 30°C and 40-45 mbar for 2 hours Heating at 40°C and 70-75 mbar for 2 hours - Heat at 50°C and 120-130 mbar for 2 hours, then anneal at atmospheric pressure at 120-130°C for 18-24 hours.

[0204] In the third stage (addition of ammonium hydroxide to neutralize acidic byproducts), a silver-doped silica adsorbent with the following chemical composition is used: silicon (30-40%, 20-33 atomic percent (at.%)), oxygen (60-65%, 74-80 at.%), silver (3-6%, 0.50-1.15 at.%), and calcium (0.25-0.80%, 0.10-0.40 at.%). This adsorbent is treated with an aqueous solution of ammonium hydroxide at 5-10 wt% relative to the adsorbent mass, the specific concentration depending on the concentration of corrosive compounds to be removed and the acidic byproducts to be neutralized. Subsequently, the moisture is gradually evaporated over 5 hours at atmospheric pressure in temperature increments of 0.3 °C per minute from 30 °C to 120 °C. In the second step, an additional annealing of the adsorbent is performed at 125 °C to 130 °C for 18-24 hours.

[0205] When using a particulate adsorbent carrier with a reducing agent on its surface according to the present invention (e.g., during percolation), the ester oil can be contacted with it under conditions that can be determined by a person skilled in the art. For example, the ester oil can be circulated under pressure at a temperature of 80°C to 85°C at a flow rate of 1000 to 2000 liters / hour through a stainless steel tower with a length-to-diameter ratio of 2.3 to 3, the tower being filled with a particulate adsorbent carrier with a reducing agent on its surface, thereby achieving chemisorption of active sulfur. Subsequently, the oil can be vacuum filtered at the above temperature through a 4-10 μm porous sintered glass filter, followed by an additional vacuum treatment (1 mbar) for 1 to 4 hours.

[0206] The use of a particulate adsorbent carrier with a reducing agent on its surface enables surprisingly efficient removal of thiols, disulfides, sulfur oxides (such as sulfoxides, sulfones, and sulfur oxyacids), high concentrations of reactive sulfur compounds such as elemental sulfur (S8) up to 50 mg / kg and dibenzyl disulfide up to 200 mg / kg, and a reduction in total sulfur content. It also unexpectedly and effectively reduces the dielectric loss factor of ester oils and the aluminum and iron content in the oil. The dielectric loss factor can be measured according to IEC 60247:2008 (using a Bar oil tester DPA 75C). The concentrations of aluminum, iron, copper, and silver in the oil are determined according to ASTM D 7151 or ASTM D 2622.

[0207] The total sulfur content in the oil is preferably determined according to ASTM D 5453.

[0208] The contents of sulfoxides and sulfones can be determined by HPLC, LC MS / MS or GC / MS, with GC / MS being preferred.

[0209] The total amounts of thiols, disulfides, and elemental sulfur were determined by automatic potentiometric titration according to CIGRE A2.32. TF3 method.

[0210] Once the method described in the third embodiment of the invention is implemented, this ester oil (which thus has a reduced active sulfur content and / or a reduced dielectric loss factor and acid content) can be separated from a particulate adsorbent carrier having a reducing agent on its surface. Furthermore, the particulate adsorbent carrier having a reducing agent on its surface can be used multiple times and reused (optionally, after treatment to remove sulfide deposits).

[0211] Therefore, the present invention also provides a method comprising: The methods defined above are used to reduce the active sulfur content in ester oils and / or lower the dielectric loss factor of ester oils; and The ester oil was then separated from a particulate adsorbent carrier with a reducing agent on its surface.

[0212] The present invention also provides a method comprising: The methods defined above are used to reduce the active sulfur content in ester oils and / or lower the dielectric loss factor of ester oils. The ester oil was then separated from a particulate adsorbent carrier with a reducing agent on its surface; and Using the particulate adsorbent carrier with a reducing agent on its surface obtained thereby, the active sulfur content in ester oil and / or the dielectric loss factor of ester oil are reduced by the independently defined methods described above.

[0213] The method of the third embodiment of the present invention produces an ester oil with beneficial properties, making it particularly suitable for use as an insulating oil in transformers. Furthermore, this method is believed to impart a "fingerprint" to the oil, distinguishing it from previously known oils (even those with low active sulfur content). Therefore, the present invention also provides an ester oil obtained or obtainable by the method of the third embodiment as defined above.

[0214] These ester oils preferably have a total sulfur content of ≤0.5 mg / kg (more preferably ≤0.2 mg / kg).

[0215] These ester oils preferably have a total S8 content of ≤0.5 mg / kg (more preferably ≤0.2 mg / kg).

[0216] These ester oils preferably have a content of thiols, disulfides, sulfoxides and sulfides of ≤0.2 mg / kg.

[0217] Such ester oils preferably have a dielectric loss factor of ≤0.020 at 90°C.

[0218] These ester oils preferably have an acid value of ≤0.03 mg KOH / g.

[0219] These ester oils preferably have an oil-water interfacial tension of ≥35 mN / m.

[0220] These ester oils preferably have particles with a size ≥4 μm and an amount ≤320 particles / ml (typically, the number of such particles is >160 to ≤320 particles / ml).

[0221] These ester oils preferably have particles with a size ≥6 μm and an amount ≤320 particles / ml (typically, the number of such particles is >20 to ≤40 particles / ml).

[0222] Consistent with the preferred aspects of the invention described above, these ester oils preferably have an ISO code of ≤15 / 12 (refer to: ISO 4406, a standard for defining particle number and size). The first number, 15, represents >160 particles / ml with a particle size of 4 μm, and up to and including 320 particles / ml. The second number, 12, represents >20 particles / ml with a particle size of 6 μm, and up to and including 40 particles / ml.

[0223] Particle size and quantity can be measured according to IEC 60970:2007.

[0224] definition Unless otherwise stated, non-limiting references to “copper” and “elemental copper” throughout this document refer to copper in its zero oxidation state. The same principle applies to other elements mentioned herein. (An example of the opposite meaning is the mention of “copper-containing reagent” in the method for preparing the dispersion of the present invention—as mentioned above, in this particular case, copper may optionally be in its oxidized form.) Unless otherwise stated, non-limiting references to “sulfur” and references to “elemental sulfur” in this text refer to sulfur in its zero oxidation state. The same principle applies to other elements mentioned in this text.

[0225] Unless otherwise stated, all quantities given as a percentage refer to weight.

[0226] Unless otherwise stated, the terms “reactive sulfur” or “active sulfur” can be defined as sulfur that reacts with silver in the DIN 51353 test, and sulfur that reacts with silver and copper in the ASTM D 1275-15 test.

[0227] Example Examples 1 to 6 relate to the first embodiment of the present invention described above, and Examples 7 and 9 to 11 relate to the second embodiment of the present invention described above. Example 8 relates to the third embodiment of the present invention described above.

[0228] Example 1: Treatment of corrosive oil using copper as a solid reducing agent and polyethylene glycol (PEG) as a liquid dispersant. Step (1): Preparation of a dispersion containing copper particles Add 0.6 g of copper sulfate (II) pentahydrate to a glass bottle, followed by 5 g of water. Shake the mixture for 3 minutes to dissolve the copper salt in the water. Then, add 0.6 g of zinc particles with a diameter between 0.3 and 1.5 mm to the bottle, and shake the mixture again at room temperature for 3 minutes. The reduction reaction is complete when the blue color of the solution disappears and becomes colorless or dark transparent. Next, add the mixture to a glass beaker containing 180 g of pure PEG-400 (Fisher Chemical, UK; CAS: 25322-68-3). Heat the resulting mixture and then stir at 40°C for 15 minutes to obtain a dispersion containing approximately 0.08 wt.% copper particles.

[0229] Step (2): Preparation of corrosive oil To simulate corrosive mineral insulating oil, 0.009 g of S8 was added to 600 g of waste oil from a power transformer.

[0230] Step (3): Desulfurization of corrosive oil The corrosive oil obtained from step (2) was heated to 95°C and added to the dispersion obtained in step (1). A magnetic stirrer (LLG experimental setup) was used at approximately 600 RPM to maintain the temperature in the range of 92–97°C. The reaction time was 120 minutes. The copper content in the reaction mixture, i.e., the amount of copper relative to the total weight of the dispersion and oil, was approximately 0.019 wt.%.

[0231] Following the guidelines of IEC TR 62697-3 / 2018, samples were collected at specific time intervals and measured using gas chromatography (Agilent Technologies 7890B, equipped with an ECD detector). The results are listed in Table 1A below, and... Figure 1 and Figure 2 It is also shown in China.

[0232] Table 1A: Changes in S8 content in oil over time.

[0233]

[0234] nd – Not detected.

[0235] As shown in Table 1A and Figure 1 and 2 As shown, S8 was almost completely removed after 90 minutes. After an additional 30 minutes, the content of S8 decreased further, and S8 was no longer detectable at this stage.

[0236] Step (4): Processing After completing step (3), the stirring and heating of the liquid-liquid-solid oil-dispersion mixture were stopped. This allowed the oil to separate naturally and form a top layer, while the dispersion (including solids) settled to the bottom of the container. After 20 minutes, the oil was separated from the dispersion by decantation without any cooling step, yielding desulfurized oil. The obtained oil was analyzed to evaluate its properties before and after treatment with the dispersion. The results are listed in Table 1B below. Figure 1 , Figure 2 , Figure 4A and Figure 4B middle.

[0237] Table 1B: Changes in oil properties before and after treatment.

[0238]

[0239] nd—— Not detected Since the Zn reagent used in step (1) was not 100% pure, the iron content was tested.

[0240] As shown in Table 1B and Figure 1 and 2 As shown, this treatment completely removes S8 from the oil. Furthermore, as shown in Table 1B and Figures 4A and 4B, the oil was corrosive before treatment (Figure 4A), while the oil was non-corrosive after treatment (Figure 4B). This demonstrates the present invention's ability to provide non-corrosive mineral insulating oil for previously corrosive power transformers.

[0241] The data presented in Table 1B were obtained through additional steps such as oil regeneration, drying, and degassing, which are standard procedures for oils treated with reagents. Various properties are measured as shown in the table below.

[0242]

[0243] Example 1A: Treatment of corrosive oils using copper sulfate solution and PEG as liquid dispersants (Comparative Example) To illustrate the use of copper sulfate pentahydrate (II) alone to treat corrosive oils (without the need for reduction with zinc or other reducing agents), another experiment was conducted using the same conditions and equipment as in Example 1, but without the addition of zinc in step (1). The experimental results are listed in Table 1C below, and in Figure 3 It is also shown in China.

[0244] Table 1C: Changes in S8 content in oil over time.

[0245]

[0246] As shown in Table 1C and Figure 3As shown, dispersions containing only Cu2SO4•5H2O as the active component are much less effective at removing S8 from mineral insulating oil.

[0247] Example 2: Treating corrosive oil with a higher concentration of solid reducing agent Further experiments were conducted using the same equipment as in Example 1. The procedures (including reagents and quantities) were the same as in Example 1, except for the following: Step (1) uses 32.4 g Cu2SO4•5H2O, 32.4 g zinc particles and 150 g water dispersed in 180 g pure PEG-400. The dispersion contains about 2.4 wt.% copper particles.

[0248] Step (2) Replace the waste oil with new oil (Nynas 4000x) with 0.009 g S8 added.

[0249] Step (3) is performed at a temperature between 90 and 105°C. The copper content in the reaction mixture, i.e., the amount of copper relative to the total combined weight of the dispersion and oil, is approximately 0.81 wt.%.

[0250] The results are listed in Table 2 below. Figure 5A and 5B middle.

[0251] Table 2: Changes in S8 content in oil over time.

[0252]

[0253] nd — Not detected.

[0254] The data in Table 2 show that using a higher concentration of copper relative to the total amount of dispersion and oil results in a faster rate of S8 content reduction. After 60 minutes, the S8 content in the oil had decreased to undetectable levels.

[0255] Figures 5A and 5B show that the treated oil is not corrosive to copper or silver.

[0256] Example 3: Intermittent treatment On a laboratory scale, the same equipment as in Example 1 was used to simulate an industrial-scale intermittent processing of corrosive oil containing a typical amount of S8.

[0257] Step (1): Prepare a dispersion containing copper particles as a solid reducing agent. Add 3.6 g of copper sulfate pentahydrate (II) to a glass bottle, followed by 15 g of water. Shake the mixture for 6 minutes to dissolve the copper salt in the water. Then, add 3.6 g of zinc particles with a diameter between 0.3 and 1.5 mm to the vial, and shake the mixture again at room temperature for 6 minutes. Next, add the mixture to a glass beaker containing 180 g of pure PEG-400 (Fisher Chemical, UK; CAS: 25322-68-3). Heat the resulting mixture and stir at 40°C for 15 minutes to obtain a dispersion containing approximately 0.46 wt.% copper particles.

[0258] Step (2): Preparation of corrosive oil Fifteen batches of oil containing approximately 15.4 mg S8 / kg oil were prepared in the same manner as step (2) in Example 1.

[0259] Step (3): Desulfurization of corrosive oil The corrosive oil obtained in step (2) was preheated to 95°C and added to the first dispersion obtained in step (1). A magnetic stirrer (LLG experimental setup) was used with a stirring speed of approximately 600 RPM to maintain the temperature in the range of 92 to 97°C. The amount of copper in the reaction mixture, i.e., the amount of copper relative to the total weight of the dispersion and oil, was approximately 0.11 wt.%.

[0260] Samples were collected at the end of the 90-minute period: after a 90-minute and subsequent 20-minute sedimentation process, the oil was separated from the dispersion by decantation, similar to Example 1. A new batch of corrosive oil was then added to the dispersion, and the same treatment was continued for the next 90 minutes. This process was repeated four times, until five batches had been processed.

[0261] After processing the fifth batch, the dispersion was replenished with copper particles by adding 3.6 g of copper(II) sulfate pentahydrate, 3.6 g of zinc particles, and 15 g of water to the dispersion (used five times). This process was then repeated for another five batches, bringing the total number of processed batches to 10.

[0262] After processing the tenth batch, the dispersion was replenished with copper particles by adding 3.6 g of copper(II) sulfate pentahydrate, 3.6 g of zinc particles, and 15 g of water (again, according to step (1)). This process was then repeated for another five batches, bringing the total number of processed batches to 15.

[0263] Therefore, a total of 9 kg of oil (600 g per batch, 15 batches in total) was treated using only 180 g of PEG. This clearly demonstrates the significant improvement in efficiency and environmental benefits of this invention. The PEG content relative to the oil ranged from 30 wt.% in the first batch to 2 wt.% in the last batch.

[0264] The results are listed in Table 3.

[0265] Table 3: S8 content after treatment in each batch of oil.

[0266]

[0267] nd – Not detected These results demonstrate that the dispersions used according to the present invention can be reused multiple times and still provide effective desulfurization, particularly with appropriate supplementary steps. The recyclability of such dispersions offers clear benefits in terms of environmental impact and efficiency / cost.

[0268] Example 4: Large-scale processing The following examples are intended to investigate the effectiveness of the invention on a scale larger than that of a laboratory.

[0269] 31.4 g of copper sulfate (II) pentahydrate was added to a glass beaker, followed by 400 g of water. The mixture was stirred for 6 minutes to dissolve the copper salt in the water. Then, 31.4 g of metallic iron powder was added to the beaker, and the mixture was stirred at room temperature for another 10 minutes (until the reduction reaction was complete).

[0270] Next, 7 kg of pure PEG-400 was placed in a 100L stainless steel container and mixed with 26 kg of corrosive oil preheated to 75°C containing approximately 12.7 mg S8 / kg oil. Then, a copper solution was added to the container. The temperature was maintained within the range of 75–78°C, and the mixture was stirred with a top stirrer set to approximately 750 RPM. The reaction time was 120 minutes. The amount of copper in the reaction mixture, i.e., the amount of copper relative to the total weight of the dispersion and oil, was approximately 0.023 wt.%.

[0271] Following the guidelines of IEC TR 62697-3 / 2018, samples were collected at specific time intervals and measured using gas chromatography (Agilent Technologies 7890B, equipped with an ECD detector). The results are listed in Table 4 below.

[0272] Table 4: Changes in S8 content in oil over time.

[0273]

[0274] nd – Not detected.

[0275] As shown in Table 4, S8 was completely removed (to an undetectable level) after only 90 minutes. This confirms that the method can remove the corrosiveness of mineral insulating oil on an industrial scale.

[0276] Step (4): Processing After 120 minutes, stirring and heating of the liquid-liquid-solid mixture of oil and dispersion were stopped. This allowed the oil to separate naturally and form a top layer, while the dispersion, including solids, precipitated at the bottom of the container. After 20 minutes, the oil was drained from the side outlet of the container without any cooling steps, thus obtaining desulfurized oil.

[0277] Example 5: Waterless treatment of corrosive oil using copper as a solid reducing agent and PEG as a liquid dispersant. Step (1): Preparation of a dispersion containing copper particles Add 0.6 g of copper sulfate pentahydrate (II) to a glass bottle, followed by 5 g of pure PEG-400. Shake the mixture for 3 minutes to obtain a copper salt dispersion. Next, add 0.6 g of zinc granule powder with a diameter between 0.3 and 1.5 mm to the vial, and shake the mixture at room temperature for another 10 minutes. Then, add the mixture to a glass beaker containing 175 g of pure PEG-400 (Fisher Chemical, UK; CAS: 25322-68-3). Heat the resulting mixture and stir at 40°C for 15 minutes to obtain a dispersion containing approximately 0.08 wt.% copper particles.

[0278] Step (2): Preparation of corrosive oil The corrosive oil was prepared in the same manner as step (2) in Example 1.

[0279] Step (3): Desulfurization of corrosive oil The corrosive oil obtained in step (2) was heated to 95°C and added to the dispersion obtained in step (1). The temperature was controlled in the range of 92 to 97°C by using a magnetic stirrer (LLG experimental apparatus) with a stirring speed of approximately 600 RPM. The reaction time was 120 minutes. The amount of copper in the reaction mixture, i.e., the amount of copper relative to the total combined weight of the dispersion and oil, was approximately 0.019 wt.%.

[0280] According to the manual of IEC TR 62697-3 / 2018 standard, samples were collected at specific time intervals and measured using gas chromatography (Agilent Technologies 7890B instrument equipped with an ECD detector). The results are listed in Table 5.

[0281] Table 5: Changes in S8 content in oil over time.

[0282]

[0283] As shown in Table 5, the dispersion without added water effectively removes S8 from mineral insulating oil. However, a comparison with the data in Table 1A above reveals that adding water to the dispersion produces a more effective desulfurization effect.

[0284] Step (4): Processing After completing step (3), stop stirring and heating the liquid-liquid-solid mixture of oil and dispersion. This allows the oil to separate naturally and form a top layer, while the dispersion (containing solids) settles at the bottom of the container. After 20 minutes, the oil is separated from the dispersion by decantation without any cooling step, thus obtaining desulfurized oil.

[0285] Example 6: Large-scale treatment under anhydrous conditions The following examples are intended to investigate the effectiveness of the invention under anhydrous conditions on a larger scale than in a laboratory setting.

[0286] Add 31.4 g of copper sulfate (II) pentahydrate to a glass beaker, then add 400 g of pure PEG-400. Stir the mixture for 6 minutes to obtain a dispersion of copper salt in PEG. Next, add 31.4 g of iron metal powder to the beaker and stir the mixture at room temperature for another 10 minutes.

[0287] Next, 6.6 kg of pure PEG-400 was placed in a 100 L stainless steel container and mixed with 26 kg of corrosive oil preheated to 75 °C containing approximately 12.0 mg S8 / kg oil. Then, the copper dispersion was added to the container. The temperature was maintained within the range of 75–78 °C, and the mixture was stirred with a top stirrer set to approximately 750 RPM. The reaction time was 120 minutes. The amount of copper in the reaction mixture, i.e., the amount of copper relative to the total combined weight of the dispersion and oil, was approximately 0.023 wt.%.

[0288] According to the manual of IEC TR 62697-3 / 2018 standard, the sample was collected at the end of the processing and measured using gas chromatography (Agilent Technologies 7890B, equipped with an ECD detector). The results are listed in Table 6 below.

[0289] Table 6: Changes in S8 content in oil over time.

[0290]

[0291] As shown in Table 6, desulfurization occurred. A comparison with the results when water was added (see Table 4 above) further reveals the unexpected benefits of adding water.

[0292] Step (4): Processing After 120 minutes, stop stirring and heating the liquid-liquid-solid mixture of oil and dispersion. This allows the oil to separate naturally and form a top layer, while the dispersion, including solids, settles at the bottom of the container. After 20 minutes, drain the oil from the side outlet of the container.

[0293] Example 7: Treatment of synthetic ester corrosive oil with high S8 content (Second embodiment) First processing Step (1): Desulfurize the high S8 content in the corrosive synthetic ester insulating oil. To simulate the corrosiveness of synthetic ester insulating oil, 0.0016 g of S8 was added to 213 g of synthetic ester insulating oil.

[0294] Step (2): Desulfurize the corrosive synthetic ester oil. The oil obtained in step (1) was used to heat the silver-plated plate, and a silver-plated coil was used to heat it to 200°C. The ratio of oil volume to silver surface area was 0.01 cm². 2 / g oil. Before processing, purge the oil with argon for 10 minutes.

[0295] The temperature was controlled within the range of 200±2℃. The reaction durations were 30 minutes, 60 minutes, 120 minutes, 150 minutes, 210 minutes, and 270 minutes.

[0296] According to the IEC TR 62697-3 / 2018 standard manual, samples were collected at specific time intervals and measured using gas chromatography (Agilent Technologies 7890B, equipped with an EC detector). The results are listed in Table 7 below. Figure 10 It is displayed in the middle.

[0297] Table 7: Changes in S8 content in oil over time.

[0298]

[0299] As shown in Table 7 and Figure 10 As shown, S8 was almost completely removed after 210 minutes. After an additional 60 minutes, the content of S8 decreased further, at which point S8 was detected at a trace concentration, between the detection limit and quantitation limit of this method.

[0300] Example 8: Treatment of synthetic esters containing S8 (Third embodiment) To simulate the corrosiveness of synthetic ester insulating oil, 0.0011 g of S8 was added to 213 g of synthetic ester insulating oil.

[0301] Desulfurization of corrosive synthetic ester oils was performed using a silver reducing agent incorporated into the surface of the adsorbent. The oil obtained in step (1) was treated for 10 cycles at 80°C with an adsorbent embedded with silver, the amount of which was 2% by weight of the oil. The temperature was controlled within ±2°C.

[0302] According to the manual of IEC TR 62697-3 / 2018 standard, samples were collected at specific time intervals and measured using gas chromatography (Agilent Technologies 7890B, equipped with an EC detector). The results are listed in Table 8 below and shown in Figure 11.

[0303] Table 8: Changes in S8 content in oil over time.

[0304]

[0305] Table 9: Changes in the properties of the synthesized ester oil before and after treatment.

[0306]

[0307] nd – Not detected Additional experiments including sulfur oxide compounds and low total sulfur content. Desulfurization of a corrosive synthetic ester oil with a total sulfur content of 1.9 ppm and detected sulfonyl benzazepine was performed for 10 cycles at 80 °C using a silver-embedded adsorbent, wherein the adsorbent accounted for 2% by weight of the oil. The temperature was controlled within ±2 °C.

[0308] After 10 cycles, the collected samples were measured by a GC-MS detector to determine the content of sulfonylbenzoza. The results are listed in Table 10 below and shown in Figure 12.

[0309] Table 8: Changes in sulfur content in oil after 10 treatment cycles.

[0310]

[0311] nd – Not detected Example 9: Treatment of synthetic esters containing S8 content (Second embodiment) To simulate corrosion of synthetic ester insulating oil, 0.0016 g of S8 was added to 213 g of synthetic ester insulating oil.

[0312] Desulfurization of high S8 content in corrosive synthetic ester oils using a relatively small available silver surface area. The corrosive oil obtained in step (1) was heated to 200°C using a silver-plated coil. The ratio of oil volume to silver surface area was 0.01 cm². 2 / g oil and 0.007 cm 2 / g oil. Before the reaction, purge the oil with argon for 10 minutes. Maintain the temperature within the range of 200±2℃. Reaction durations were 30, 60, 120, 150, and 210 minutes.

[0313] According to the manual of IEC TR 62697-3 / 2018 standard, samples were collected at specific time intervals and measured using gas chromatography (Agilent Technologies 7890B, equipped with an ECD detector). The results are listed in Table 11 below.

[0314] Table 11: Changes in S8 content in oil over time.

[0315]

[0316] As shown in Table 11 and Figure 13 As shown, after 210 minutes, this treatment was able to remove S8 from the oil, reaching the low end of the method's limit of quantitation. Furthermore, as shown in Figure 14A, the oil was corrosive before treatment, but no longer corrosive after treatment. Figure 14B This demonstrates the ability of the present invention to provide non-corrosive insulating oil for previously corrosive power transformers.

[0317] Example 10: Treatment of synthetic ester oil with low S8 content (Second Embodiment) Further experiments were conducted using the same equipment as in Example 9. The steps and conditions were the same as in Example 9, except for the following: Step (1): Preparation of corrosive oil To simulate the corrosive nature of synthetic ester insulating oil, 0.0003 g of S8 was added to 213 g of synthetic ester insulating oil.

[0318] According to the manual of IEC TR 62697-3 / 2018 standard, samples were collected at specific time intervals and measured using gas chromatography (Agilent Technologies 7890B, equipped with an ECD detector). The results are listed in the table below and shown in Figure 15.

[0319] Table 12: Changes in S8 content in oil over time.

[0320]

[0321] Additional experiments with low concentrations of S8 were conducted in synthetic ester oils. Step (1): Preparation of corrosive oil To simulate the corrosiveness of synthetic ester insulating oil, 0.0002 g of S8 was added to 213 g of synthetic ester insulating oil.

[0322] Samples were then collected at specific time intervals and measured using GC chromatography (Agilent Technologies 7890B, equipped with an ECD detector) in accordance with the manual of IEC TR 62697-3 / 2018 standard. The results are listed in the table below and shown in Figure 16.

[0323] The data in Table 13 indicate that a shorter contact time is required to fully convert S8 within 60 minutes.

[0324] Table 13: Changes in S8 content in oil over time.

[0325]

[0326] nd – Not detected.

[0327] Example 11: Treatment of mineral oil with high S8 content (Second embodiment) Step (1): Preparation of corrosive oil To simulate the corrosiveness of synthetic oil, 0.0003 g of S8 was added to 213 g of synthetic ester insulating oil.

[0328] Step (2): Desulfurization of corrosive mineral oil The corrosive oil obtained in step (1) was heated to 200°C using a silver-plated coil and maintained for 30 minutes, 60 minutes, and 120 minutes. The volume ratio of the oil to the surface area of ​​the silver was 0.014 cm². 2 / g oil and 0.007 cm 2 / g oil. Before the reaction, the oil was purged with argon for 10 minutes. The temperature was controlled within the range of 200±2℃. The reaction durations were 30 minutes, 60 minutes, and 120 minutes.

[0329] Oil samples were collected at specific time intervals according to the IEC TR 62697-3 / 2018 standard manual and measured using GC chromatography (Agilent Technologies 7890B, equipped with an EC detector). The measurement results are listed in Table 14 below and are also shown in Figure 17.

[0330] Table 14A: Changes in S8 content in mineral oil over time.

[0331]

[0332] nd — Not detected.

[0333] As shown in Table 14A and Figure 17 As shown, S8 was almost completely removed after 120 minutes. After an additional 30 minutes, the content of S8 decreased further, at which point S8 was below the limit of quantitation.

[0334] Step (3): Processing After completing step (3), the oil is analyzed to assess the mineral oil properties before and after treatment.

[0335] The data presented in Table 14B were obtained through additional steps such as regeneration, drying, and degassing of the oil, which are standard treatments for the oil. Various properties were measured as shown in the table.

[0336] Table 14B: Changes in mineral oil properties before and after treatment.

[0337]

[0338] The numbered clauses [1] through

[25] below correspond to the claims of the prior application for which priority is claimed in this case and define various aspects of the invention. These numbered clauses are not claims of this application. The claims of this application are further described in a separate section entitled “Claims” below.

[0339] [1] A method for reducing the S8 content in an oil containing S8, the method comprising contacting the oil with (a) a solid additive containing a reducing agent and (b) a liquid additive suitable for dispersing the solid additive.

[0340] [2] The method according to claim 1, wherein the reducing agent comprises one or more metals selected from copper, iron, zinc, aluminum, nickel and tin, and preferably the reducing agent is copper.

[0341] [3] The method according to claim 1 or 2, wherein the solid additive comprises solid carrier particles having the reducing agent on their surface.

[0342] [4] The method according to claim 3, wherein the solid carrier particles are in the form of fine particles or powder.

[0343] [5] The method according to claim 3 or 4, wherein the solid carrier particles comprise iron and / or zinc, and optionally further comprise one or more salts of iron and / or zinc, preferably one or more salts selected from sulfates, nitrates, chlorides and bromides.

[0344] [6] The method according to any one of the preceding claims, wherein the liquid additive is a polymer, preferably a polyether, and more preferably a polyethylene glycol.

[0345] [7] The method according to any one of the preceding claims, wherein the amount of the solid additive is 0.05 to 10 by weight relative to the amount of the oil.

[0346] [8] The method of any of the preceding claims comprises the steps of: contacting the oil with a dispersion, wherein the solid additive is dispersed in the liquid additive, and wherein the dispersion preferably further comprises water.

[0347] [9] The method of claim 8, wherein the amount of dispersion is 1.5 to 40 by weight relative to the total amount of oil plus dispersion.

[0348]

[10] According to the method of any of the preceding claims, wherein the oil, solid additive and liquid additive are subjected to stirring and / or ultrasonic treatment.

[0349]

[11] The method according to any one of the preceding claims, wherein the oil, solid additive and liquid additive are heated to a temperature of 50 to 120°C, preferably 60 to 105°C, more preferably 70 to 99°C.

[0350]

[12] In the method according to any of the preceding claims, the S8 content, as determined by IEC TR 62697-3 / 2018 standard, is reduced to less than 2.0 mg / kg, preferably less than 1.0 mg / kg, more preferably less than 0.2 mg / kg based on the total amount of oil.

[0351]

[13] One method includes: (a) Reducing the S8 content in oil using the method described in any one of claims 1 to 12; and (b) The oil is then separated from the other components, wherein the other components are in the form of a dispersion containing solid and liquid additives.

[0352]

[14] One method includes: (a) Reducing the S8 content in the oil by the method described in any one of claims 1 to 12; (b) The oil is then separated from the other components, wherein the other components are present in the form of a dispersion comprising the solid additive and the liquid additive; and (c) Using the dispersion thus obtained, reduce the S8 content in an oil containing S8 by a method independently defined in any one of claims 1 to 12.

[0353]

[15] A dispersion containing water and elemental copper, wherein the water and copper are dispersed in a liquid polymer, wherein the liquid polymer is preferably a polyether, more preferably a polyethylene glycol.

[0354]

[16] The dispersion according to claim 15 comprises solid carrier particles having copper on their surface.

[0355]

[17] The dispersion according to claim 16, wherein the solid carrier particles comprise iron and / or zinc, and optionally further comprise one or more salts of iron and / or zinc, more preferably one or more salts selected from sulfates, nitrates, chlorides and bromides.

[0356]

[18] The dispersion according to any one of claims 15 to 17, wherein the liquid polyether is polyethylene glycol with a number average molecular weight between 300 and 600 g / mol.

[0357]

[19] A method for preparing a dispersion as described in any one of claims 15 to 18, the method comprising the following steps: (i) Preparation of aqueous solutions or suspensions of copper-containing reagents, and (ii) Dispersing the solution or suspension in the liquid polymer; If the copper-containing reagent in step (i) is characterized by copper in an oxidized form, the method further includes a step of reducing the copper in the copper-containing reagent between steps (i) and (ii).

[0358]

[20] The method according to claim 19, wherein step (i) is to prepare an aqueous solution of a copper salt, preferably copper sulfate.

[0359]

[21] The method according to claim 20, wherein the aqueous solution of the copper salt is prepared using the following substances: (a) H2O; (b) A mixture of H2O and alcohol, wherein the preferred alcohol is a C1-3 alcohol, such as methanol, ethanol, or propanol, more preferably methanol; or (c) H2O / polyol mixture, wherein the preferred polyol is C1-3 diol or C1-3 triol, more preferably glycerol.

[0360]

[22] The method according to any one of claims 19 to 21, wherein the liquid polymer is a polyether, and preferably polyethylene glycol.

[0361]

[23] The method according to any one of claims 19 to 22, wherein the copper-containing reagent in step (i) is characterized by copper in an oxidized form, such that the method further includes a step of reducing copper in the copper-containing reagent between step (i) and step (ii), and wherein the reduction reaction involves introducing one or more reducing agents selected from transition metals and post-transition metals into an aqueous solution or suspension, more preferably selected from elements iron, zinc, aluminum, nickel and tin; Furthermore, the reducing agent is preferably in the form of fine particles or powder.

[0362]

[24] Oil obtained or available by the method as described in claim 13.

[0363]

[25] The oil according to claim 24, wherein the oil: - The total amount of thiols, sulfides, and disulfides ≤2 mg / kg; - S8 content ≤ 0.5 mg / kg; - Dielectric loss factor at 90℃ <0.005; - Acid value <0.02 mg KOH / g; - Oil-water interfacial tension ≥35 mN / m; - The FT-IR spectrum in the wavelength range of 700 to 1300 cm⁻¹ is substantially the same as that of the oil before the desulfurization process, or / and - It contains particles with a size ≥4 μm and a content ≤320 particles / ml, and particles with a size ≥6 μm and a content ≤40 particles / ml.

Claims

1. The use of solid additives containing reducing agents for reducing the active sulfur content in oil and / or reducing the dielectric loss factor of oil, wherein: (i) Contacting the oil with (a) a solid additive containing the reducing agent and (b) a liquid additive suitable for dispersing the solid additive; (ii) Contacting the oil with a solid substrate having the reducing agent on its surface; or (iii) The oil is an ester and is in contact with a particulate adsorbent carrier having the reducing agent thereon.

2. The use according to claim 1, wherein the active sulfur is provided by S8, and the oil is in contact with (a) a solid additive containing a reducing agent and (b) a liquid additive suitable for dispersing the solid additive.

3. A method for reducing the content of S8 in an oil containing S8, the method comprising contacting the oil with (a) a solid additive containing a reducing agent and (b) a liquid additive suitable for dispersing the solid additive.

4. The use according to claim 2 or the method according to claim 3, wherein the reducing agent comprises one or more metals selected from copper, iron, zinc, aluminum, nickel and tin, and preferably the reducing agent is copper.

5. The use according to claim 2 or the method according to claim 3 or 4, wherein the solid additive comprises solid carrier particles having the reducing agent on their surface, and wherein: - Preferably, the solid carrier particles are in the form of fine particles or powder; - More preferably, the solid carrier particles contain iron and / or zinc, and optionally further contain one or more salts of iron and / or zinc, preferably one or more salts selected from sulfates, nitrates, chlorides, and bromides.

6. The use according to claim 2 or the method according to any one of claims 3 to 5, wherein the liquid additive is a polymer, preferably a polyether, and more preferably polyethylene glycol.

7. The use according to claim 2 or the method according to any one of claims 3 to 6, wherein the amount of the solid additive is 0.05 to 10% by weight relative to the amount of oil, and the amount of the reducing agent is preferably 0.01 to 2% by weight relative to the amount of oil.

8. The use according to claim 2 or the method according to any one of claims 3 to 7, the method comprising the step of contacting the oil with a dispersion, wherein the solid additive is dispersed in the liquid additive, and wherein the dispersion preferably further comprises water.

9. The use according to claim 1, wherein the active sulfur is provided by S8, S7, S6, S5, S4, disulfide and / or sulfoxide, and the oil is in contact with a solid substrate having a reducing agent on its surface.

10. A method for reducing the content of S8, S7, S6, S5, S4, disulfides and / or sulfoxides in an oil containing S8, S7, S6, S5, S4, disulfides and / or sulfoxides, the method comprising contacting the oil with a solid substrate having a reducing agent on its surface.

11. The use according to claim 9 or the method according to claim 10, wherein the solid substrate is a metal coil plated with a reducing agent, and: - The reducing agent is selected from one or more of silver, zinc, aluminum, nickel, and tin, preferably silver; and - The metal coil comprises or is selected from one or more of aluminum, copper, zinc, brass, and iron steel, and is preferably selected from aluminum and copper.

12. The use according to claim 9 or the method according to claim 10 or 11, wherein the ratio of the surface area of ​​the reducing agent to the mass of the oil is 0.00015 to 0.00080 m² / kg.

13. The use according to claim 9 or the method according to any one of claims 10 to 12, wherein the solid substrate comprises a metal coil of plating reducing agent wound on a heater.

14. The use according to claim 9 or the method according to any one of claims 10 to 13, wherein the oil is a synthetic ester.

15. The use according to claim 9 or the method according to any one of claims 10 to 14, wherein the oil is in contact with the solid substrate or more than one such solid substrate in a batch reactor and / or a tubular reactor.

16. The use according to claim 1, wherein the oil is an ester and is in contact with a particulate adsorbent carrier having the reducing agent on its surface.

17. A method for reducing the active sulfur content in an ester oil and / or reducing the dielectric loss factor of the ester oil, the method comprising contacting the oil with a particulate adsorbent carrier having a reducing agent on its surface.

18. The use according to claim 16 or the method according to claim 17, wherein the particulate adsorbent carrier comprises silica and / or calcium oxide, and the reducing agent comprises silver ions; and wherein the particulate adsorbent carrier further comprises ammonium ions on its surface.

19. The use according to claim 16 or the method according to claim 17 or 18, wherein the particulate adsorbent carrier has a particle size of 200 to 1200 μm.

20. A method comprising: (a) Reducing the S8 content in the oil by the method of any one of claims 3 to 9; (b) The oil is then separated from the other components, wherein the other components are in the form of a dispersion comprising the solid additive and the liquid additive.

21. A method comprising: (a) Reducing the S8 content in the oil by the method of any one of claims 3 to 9; (b) The oil is then separated from the other components, wherein the other components are in the form of a dispersion comprising the solid additive and the liquid additive; (c) Using the method independently defined in any one of claims 3 to 9, the resulting dispersion reduces the content of S8 in an oil containing S8.

22. A dispersion comprising water and elemental copper, wherein the water and copper are dispersed in a liquid polymer; wherein the liquid polymer is preferably a polyether, more preferably polyethylene glycol.

23. The dispersion according to claim 22, wherein: (a) The dispersion comprises solid carrier particles having the copper on their surface, and preferably the solid carrier particles comprise iron and / or zinc, and optionally further comprise one or more salts of iron and / or zinc, preferably one or more salts selected from sulfates, nitrates, chlorides, bromides; and / or (b) The liquid polyether is polyethylene glycol with a number average molecular weight of 300 to 600 g / mol.

24. A method for preparing the dispersion of claim 22 or 23, the method comprising the following steps: (i) Prepare an aqueous solution or a suspension of a copper-containing reagent; (ii) Dispersing the solution or suspension in the liquid polymer; If the copper-containing reagent in step (i) is characterized by copper in an oxidized form, the method further includes a step of reducing the copper in the copper-containing reagent between steps (i) and (ii).

25. The method according to claim 24, wherein step (i) is to prepare an aqueous solution of a copper salt, preferably copper sulfate; And among them, the preferred ones are: • The aqueous solution of the copper salt is prepared using the following substances: (a) H2O; (b) A mixture of H2O and alcohol, wherein the alcohol is preferably C2O. 1-3 Alcohols, such as methanol, ethanol, or propanol, and more preferably methanol); or (c) A mixture of H2O and polyol, wherein the polyol is preferably C 1-3 Diol or C 1-3 Triols, and more preferably glycerol); • The liquid polymer is a polyether, and preferably polyethylene glycol; and / or • The copper-containing reagent in step (i) is characterized by copper in an oxidized form, such that the method further includes a step of reducing the copper in the copper-containing reagent between steps (i) and (ii); and wherein the reduction reaction involves introducing one or more reducing agents selected from transition metals and post-transition metals, more preferably selected from elements iron, zinc, aluminum, nickel and tin, into the aqueous solution or suspension; and wherein the reducing agent is preferably in the form of fine particles or powder.

26. A method comprising: (a) The method of any one of claims 10 to 15 is used to reduce the content of S8, S7, S6, S5, S4, disulfides and / or sulfoxides in the oil; (b) The oil is then separated from the solid substrate on which a reducing agent is present.

27. A method comprising: (a) The method of any one of claims 10 to 15 is used to reduce the content of S8, S7, S6, S5, S4, disulfides and / or sulfoxides in the oil; (b) The oil is then separated from the solid substrate having a reducing agent on its surface; (c) Using the method independently defined in any one of claims 10 to 15, the content of S8, S7, S6, S5, S4, disulfide and / or sulfoxide in an oil containing S8, S7, S6, S5, S4, disulfide and / or sulfoxide is reduced by a solid substrate having a reducing agent on its surface obtained therefrom.

28. A batch reactor, a tubular reactor, or a reactor system comprising a batch reactor and a tubular reactor, wherein at least one of the batch reactor, the tubular reactor, and the reactor in the reactor system comprises at least one solid substrate having a reducing agent on its surface as defined in any one of claims 10 to 15; wherein the solid substrate having a reducing agent on its surface is located inside the reactor or is movable to be disposed therein.

29. A method comprising: (a) The active sulfur content in the ester oil and / or the dielectric loss factor of the ester oil are reduced by the method of any one of claims 17 to 19; (b) The ester oil is then separated from a particulate adsorbent carrier having the reducing agent on its surface.

30. A method comprising: (a) The active sulfur content in the ester oil and / or the dielectric loss factor of the ester oil are reduced by the method of any one of claims 17 to 19; (b) The ester oil is then separated from a particulate adsorbent carrier having the reducing agent on its surface; (c) Using the method independently defined in any one of claims 17-19, the particulate adsorbent carrier having the reducing agent on its surface obtained therefrom reduces the content of active sulfur in the ester oil and / or reduces the dielectric loss factor of the ester oil.

31. An oil that is obtained or obtainable by the method of claim 16, 26 or 29.

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