Use of silane-functionalized graphene oxide for the regeneration of insulating mineral oil

Description

1 / 10 “USE OF SILAN-FUNCTIONALIZED GRAPHENE OXIDE FOR THE REGENERATION OF INSULATING MINERAL OIL”

[01] The present invention relates to the use of silane-functionalized graphene oxide (APTES - aminopropyltriethoxysilane), in particular, for use as a nanoadditive in the regeneration of insulating mineral oil.

[02] For over a hundred years, insulating mineral oil (IMO), derived from petroleum refining, has been used as an insulating fluid in transformers. Many billions of liters of oil are in use in electrical equipment worldwide, and its popularity is due to its availability and low cost. Insulating fluids used in electrical equipment exist in considerable quantities, as they are present in various equipment used in high-voltage substations. Their use is concentrated in transformers, cables, capacitors, and oil switches, but in many applications they are gradually being replaced due to the development of new products with better characteristics.

[03] These mineral oils are made by various international refining companies, each using a particular type of crude oil and refining technology. The chemical, electrical, and physical characteristics of transformer oil are, to some extent, unique to the manufacturer. To ensure that a given oil is acceptable for use, the measured values ​​for its relevant characteristics are compared with the limits defined in internationally agreed specifications for manufacturers and users of electrical equipment.

[04] The most relevant characteristic of the oil may be an intrinsic property used in the design of transformers or it may be the concentration of a specific component or impurity. In some cases, the characteristic is the response of an oil to a careful, controlled test procedure intended to simulate the actual behavior of an oil in a transformer.

[05] The amount of oil contained in transformers varies significantly with electrical load capacity. A typical unit mounted on a neighborhood pole in a distribution system is rated at 25 kVA and contains approximately 20 Petition 870250011960, dated 02 / 13 / 2025, page 8 / 22 2 / 10 gallons of mineral oil (approximately 76 liters of oil). At the other extreme, an electric power generation unit that boosts voltage for long-distance transmission can be rated at around 400 MVA and may contain over 10,000 gallons of oil (approximately 378,541 liters of oil).

[06] These oils must be highly stable and have low viscosity, because in addition to their dielectric impregnation function, they must also transmit heat. This is one of the typical problems in transformers, where the oil transfers the heat generated in the windings to the tank walls. Denser oils cannot meet these conditions. In the case of control devices, the oil must flow rapidly between the open contacts to quickly extinguish the electric arc. In cables and capacitors, the oil must also flow easily to fully impregnate the insulating paper used, thus displacing and eliminating the presence of water and air pockets in fibrous products, such as paper.

[07] In addition to low viscosity, it is important to have a high flash point to prevent fires.The aniline melting point is related to its ability to dissolve materials it comes into contact with; conversely, it should be high, as it reveals the solvent power of the aniline dye in relation to the materials it will come into contact with.

[08] Interfacial tension indicates the existence of certain polar substances dissolved in the oil that interfere with the dielectric properties and influence aging; for this reason, a high interfacial tension value is desirable. The color of the oil determines its aging; therefore, the darker the oil, the older it is.

[09] Finally, the pour point must be balanced at the ideal operating temperature of the oil and the density: between 0.850 gm-1 and 0.900 gm-1, as it impacts transmission capacity.

[10] The search for increasingly efficient materials used in electrical power transmission and distribution systems to improve their dielectric properties, reduce their size, weight and cost, is an ongoing task. In addition, the regeneration of these mineral oils constitutes an innovative line of research, with Petition 870250011960, dated 02 / 13 / 2025, page 9 / 22 3 / 10 promising potential and future. Not only due to the cost of conventional regeneration methods, but also due to the resulting environmental problems.

[11] The regeneration of insulating mineral oil is an economically and environmentally viable alternative since it is cheaper to regenerate used oil than to buy new oil. In addition, environmental legislation prohibits the improper disposal of oil as it is considered hazardous waste.

[12] In an attempt to solve these problems, the idea arose to use nanoparticles that would assist in the regeneration process of insulating mineral oil by acting as adsorbent additives.

[13] Graphene-based and graphene oxide (GO)-based materials have been extensively investigated as next-generation adsorbents. They have adsorption affinities for various classes of organic and inorganic contaminants due to their extremely large specific surface areas, chemical stabilities and long-range conjugation.

[14] The oxidation process of graphite, which results in graphite oxide, with the aid of strong oxidants, introduces functional groups such as carbonyls, epoxides, hydroxyl and carboxyl groups that may be present at the edges and / or basal planes of the graphene layers. These groups decrease the interactions between the layers, resulting in an increase in the distance between them. The greater space between the graphene sheets aids in exfoliation, leading to the formation of a monolayer or a few layers of graphene oxide. Therefore, GO is a graphene layer decorated with functional groups. These functional groups are responsible for the ease of functionalization of graphene sheets and interaction with other materials.This versatility of GO, achieved through chemical / thermal modifications, alters its properties and allows it to be applied in a wide variety of areas, such as polymer composites, photocatalysts, membranes for water purification, sensors, nanofluids, and solid-state chemistry, among others.

[15] To prepare materials with well-dispersed nanoparticles for practical applications, surface functionalization is key to stabilizing the nanoparticles. Petition 870250011960, dated 02 / 13 / 2025, page 10 / 22 4 / 10 against aggregation in oil. This process can provide several benefits, such as improved colloidal stability of nanoparticles, their self-organization, compatibility with other phases, or incorporation of organic groups for specific interaction. Firstly, surface modification includes simple functionalization of the nanoparticle surface with low molecular weight compounds, which can directly improve stability and dispersibility or can serve as an introduction of functional groups necessary for subsequent post-functionalization with low molecular weight compounds or polymers.

[16] Usually, coupling agents are used on the surface of the filler, which serve as a connection between the oil and the dispersed phase. Among the best known, the most efficient is the silane type, as it has an organic part that reacts with or is compatible with the polymer, and an inorganic part that binds to the added particles. Silanes have a generic structure composed of a silico-functional group and an organo-functional group, responsible for the bonds with the nanoparticles and with the oil, respectively. A widely used silane is aminopropyltriethoxysilane (APTES), which functionalizes the graphene oxide surface with amine groups.

[17] Therefore, the present invention aims to develop a process to facilitate the regeneration of insulating mineral oil from electrical equipment through the use of a graphene oxide-based nanoadditive functionalized with APTES.

[18] To achieve the objective described in paragraph

[017] , the present invention must follow the following steps: 1st step, separation of 1000 ml of insulating mineral oil (CAS 64742-53-6) from operating equipment, collected in accordance with ABNT NBR 8840:2021 - sampling of insulating liquids; 2nd step, carrying out physicochemical analyses such as interfacial tension and acidity content, in accordance with ABNT - NBR-10576 - insulating mineral oil for electrical equipment; 3rd step, removal of a 100 ml aliquot of oil for insertion of graphene oxide nanoparticles functionalized with APTES (according to GHASEMI, MH; IRANI, V.; TAVASOLI, A. J Natural Gas Sci Eng 74, 103110, 2020) Petition 870250011960, dated 02 / 13 / 2025, page 11 / 22 5 / 10 in percentages of 0.01, 0.02 and 0.03% (by mass); 4th step, magnetic stirring for 5 min at 600 rpm; followed by sonication for 1.5 h and magnetic stirring for 30 min at 600 rpm; 5th step, filtration on filter paper with a nominal retention of 8 microns; 6th step, carrying out the same physicochemical analyses performed in the 2nd step, after nano-additivation.

[19] For comparison purposes and to demonstrate the innovative potential of the present invention, some patents are presented below as examples of processes for preparing graphene oxide nanoparticles for the regeneration of insulating mineral oil.

[20] A search was conducted on the National Institute of Industrial Property (INPI) search portal using the keywords: mineral oil, regeneration, APTES, silane, aminopropyltriethoxysilane, graphene, graphene oxide, functionalized graphene oxide, a search with at least 2 keywords together, with “mineral oil” fixed, the only combination that returned a result was: “mineral oil” and “regeneration”. Presenting application BR 10 2012 028611 4, entitled: METHOD FOR CONTINUOUS DEHALOGENIZATION AND REGENERATION IN MINERAL OIL CONTAMINATED BY CHLORINATED ORGANIC COMPOUNDS, invention that deals with a method for decontamination under safe conditions of mineral oils contaminated by chlorinated organic compounds, working with both alkali metals and their hydrates.The invention proposes treatment carried out in a reactor composed of multiple reaction tubes that receive the contaminated mineral oil to be treated, and is provided with means to regulate the temperature inside the reaction tubes.

[21] By simplifying the search to find all patents that deal with “regeneration” and “oil”, 4 new results are obtained. However, these do not relate to oil regeneration for reuse (as proposed in this patent application), but rather to tissue regeneration (BR 13 2013 023109 5), to collagen regeneration (PI 9909670-6) or to alkylation catalyst regeneration (PI 9302357-0).

[22] A search was carried out on the Espacenet patent portal using the words Petition 870250011960, dated 02 / 13 / 2025, p. 12 / 22 6 / 10 keywords: mineral oil, regeneration, APTES, silane, aminopropyltriethoxysilane, graphene, graphene oxide, functionalized graphene oxide. Following the same search parameters used on the INPI portal, more results were found, since Espacenet searches for patents registered in more than 100 countries. Using the two main keywords, many patents were displayed, for example "oil" and "graphene" with 612 results, while "oil" and "regeneration" resulted in another 1302 patents. Thus, at least 3 descriptors were used to perform the search and obtain better filtering.

[23] Using “oil” and “regenerated” and “graphene”, 2 results are obtained. One of them presents a method for preparing regenerated engine oil with graphene, CN110484337 (A) - “PREPARATION METHOD OF GRAPHENE REGENERATED ENGINE OIL”. In this, a primary filtration of the deteriorated engine oil is carried out by heating the oil, allowing it to pass through filters with a 15-micron membrane, followed by another with a 5-micron membrane to remove impurities. Smaller impurities are removed using a flocculating agent, offering a more complete removal of impurities so that the quality of the regenerated engine oil is better. Only then is a paste prepared with graphene mixed with the oil and heated to promote the catalytic dissolution of graphene, producing graphene engine oil.

[24] The other result, CN109627797 (A) - “WASTE EDIBLE SOYBEAN OIL AND GRAPHENE OXIDE COMPOSITE REGENERATED ASPHALT AND PREPARATION METHOD THEREOF”, deals with a method for preparing a composite, using waste edible soybean oil and graphene oxide to create regenerated asphalt, an invention that has little to do with this patent application.

[25] When relating the descriptors “mineral oil” and “graphene”, a search expected to generate several patent records, only 1 (one) result was presented, US2015294753 (A1) - “DIELECTRIC MINERAL OIL CONDITIONED WITH GRAPHENE NANOFLAKES”, which refers to a composition of a dielectric mineral oil for transformers, formed of at least one dielectric mineral oil and Petition 870250011960, dated 02 / 13 / 2025, page 13 / 22 7 / 10 enhanced with graphene nanoflakes decorated with metallic / ceramic nanoparticles. Although it does not involve regeneration processes, the patent presents a way to produce dielectric paraffinic mineral oil with graphene nanoflakes with improved and stabilized thermal conductivity using oleic acid and ultrasonication.

[26] Performing a search with “mineral oil” and “silane”, no results are presented, indicating that there were no registered patents that made use of mineral oil and silane (aminopropyltriethoxysilane - APTES) in the same process.

[27] By covering the search for all types of oils using the descriptor “oil” along with the descriptor “silane”, 48 patents are registered. However, none of them are employed in oil regeneration processes, since the descriptors “regenerated” and “regeneration” do not return in a patent.

[28] Despite this, some patents involving silane functionalization and use in oil are presented, however the silane group has a wide variety of compositions, the only example of interest being the one cited: CN114605976 (A) - “POLYSULFONIC ACID SILANE COMPOSITE GRAPHENE OXIDE PLUGGING AGENT AND OIL-BASED DRILLING FLUID”, which discloses a micro-crack sealant agent from the mixture of graphene oxide functionalized with an amino base agent, in this context 3-aminopropyltriethoxysilane (APTES) together with a sulfamic acid compound producing polysulfonic acid silane, for use in an oil-based drilling fluid.

[29] When analyzing patents with “mineral oil” and “regeneration”, 59 patents are displayed, the vast majority dealing with pretreatment devices [CN215947199 (U), CN217041596 (U)], treatment systems and production lines [CN114854484 (A), CN113088371 (A)], separation devices and other methods (CN210915945 (U). In the search, none of these patents show the use of any graphite derivative, graphene or the use of APTES in the regeneration process, since no results are displayed when adding any of the following descriptors: silane, graphene, graphene oxide, APTES, aminopropyltriethoxysilane. Petition 870250011960, dated 02 / 13 / 2025, page 14 / 22 8 / 10

[30] Two registered patents can be cited as examples that show the use of solvents or release agents. CN111394123 (A) - “WASTE MINERAL OIL SOLVENT REFINING LUBRICATING OIL BASE OIL REGENERATION PROCESS”, which discloses a process for refining residual mineral oil solvent in the lubricant base oil regeneration process. The residual mineral oil goes through five stages to achieve recovery (flocculation neutralization, vacuum flash evaporation dehydration, vacuum distillation in a film evaporator, separation in a rectifier tower, solvent refining), returning two base oils and other by-products can be recovered. In this way, recovery resources are maximized, solvent is reduced along with cost, energy resources are saved and the process becomes greener.

[31] CN112251281 (A) - “WASTE MINERAL OIL REGENERATION CASTING RELEASE AGENT PRODUCTION PROCESS”, the invention describes a process for producing a release agent for the regeneration of waste mineral oil and relates to the technical field of release agent production. According to the invention, the waste mineral oil is fully recycled, offering energy savings, reducing process costs and environmental pollution. The chemical performance is stable, chemical reactions are unlikely to occur, and the wastewater obtained after cleaning can be used repeatedly. The patent presents a system with the following steps: (1) precipitation, (2) filtration, (3) agitation, (4) stacking, (5) sub-packaging, (6) storage and (7) cleaning.

[32] With the search carried out and all patents listed, it is possible to affirm that the use of silane (APTES) in the functionalization of graphene oxide as a nanoadditive in the process of regenerating insulating mineral oil is a new invention, and no record is found with the descriptors of greatest interest in the search platforms, both national (INPI) and international (Espacenet).

[33] The present invention is best exemplified by the attached Figures, which are presented as non-limiting examples.

[34] Figure 1 represents the flowchart of the process of adding insulating mineral oil from operating equipment through nanofluid synthesis Petition 870250011960, dated 02 / 13 / 2025, page 15 / 22 9 / 10 with APTES-functionalized graphene oxide, as described in paragraph

[018] .

[35] Figure 2 shows the measured Interfacial Tension values ​​according to ABNT NBR-6234:2015, for determining oil-water interfacial tension using the ring method. Measuring interfacial tension in the water-oil system aims to infer the amount of polar substances present in the oil, since such substances tend to concentrate at the system interface. The higher the concentration of polar substances, the lower the interfacial tension value. The minimum value of 40.0 dynes / cm is commonly adopted for the interfacial tension of a new oil.

[36] In Figure 2 it is possible to verify that the new oils (before going to the electrical equipment) have interfacial tension values ​​around 40 mN / m or above. After removing these oils from the equipment, a marked decrease in interfacial tension is observed and after nano-additivation with graphene oxide / APTES these values ​​increase (reaching around 40 mN / m) again. This may have occurred due to functionalization with APTES, since the amine groups act as sites for interactions with adsorbates that have anionic characteristics, and it is also possible that the nitrogen present in the amine group acts as a nucleophile for cation adsorption.

[37] Figure 3 shows the Acidity Content values ​​measured according to the ABNT NBR-14448:2013 standard, which describes the procedure for lubricating oils, petroleum products and biodiesel — determination of the acid number by the potentiometric titration method. The phenomenon of degradation or oxidation suffered by the oil due to operation at temperatures above ambient causes an increase in its acid content. Monitoring the acidity of an oil allows inferences to be made about its quality. The lower this value, the better the quality of the oil.

[38] All samples nano-additivated with graphene oxide / APTES (Figure 3) show a reduction in acidity, which improves the quality of the oil, since it is necessary for insulating oil to have a low acidity level in order to minimize electrical conductivity and metallic corrosion, and thus increase the service life of the Petition 870250011960, dated 02 / 13 / 2025, page 16 / 22 10 / 10 insulating system. The chemical functionalization of graphene can also increase interactions with organic polymers and further modify intrinsic characteristics, allowing its use in even more applications. Thus, graphene oxide / APTES may have formed inter- and intramolecular bonds with other hydroxyl groups on the surface of the nanoparticles, retaining these molecules in the filtration step, which makes the OMI less acidic. The filtration step is essential to be able to perform the analyses again without damaging the equipment. Petition 870250011960, dated 02 / 13 / 2025, page 17 / 22

Claims

1 / 2 CLAIMS 1. “USE OF SILAN-FUNCTIONALIZED GRAPHENE OXIDE FOR THE REGENERATION OF INSULATING MINERAL OIL” characterized by being an invention that corresponds to a process for nano-adding insulating mineral oil with silane-functionalized graphene oxide, comprising preparation steps for a suspension of graphite nanoparticles functionalized in insulating mineral oil for use in electrical transformers (used oil), where dispersion and filtration processes of particle agglomerates are removed by means of agitation / sonication and filtration, respectively.

2. “USE OF SILAN-FUNCTIONALIZED GRAPHENE OXIDE FOR THE REGENERATION OF INSULATING MINERAL OIL” method according to claim 1, characterized in that the used insulating mineral oil is used as the base fluid.

3. “USE OF GRAPHENE OXIDE FUNCTIONALIZED WITH SILANE FOR THE REGENERATION OF INSULATING MINERAL OIL” method according to claim 1 or 2, characterized in that the functionalization of graphene oxide is carried out with the silane APTES aminopropyltriethoxysilane.

4. “USE OF SILAN-FUNCTIONALIZED GRAPHENE OXIDE FOR THE REGENERATION OF INSULATING MINERAL OIL” method according to any one of claims 1-3, characterized in that graphene oxide is used as graphitic material in concentrations of 0.01%, 0.02% and 0.03% by mass.

5. “USE OF SILAN-FUNCTIONALIZED GRAPHENE OXIDE FOR THE REGENERATION OF INSULATING MINERAL OIL” method according to any one of claims 1-4, characterized in that the suspension of functionalized graphene oxide nanoparticles is driven by magnetic stirring followed by sonication and again magnetic stirring. Petition 870250078987, dated 04 / 09 / 2025, page 4 / 6 2 / 2 6. “USE OF SILAN-FUNCTIONALIZED GRAPHENE OXIDE FOR THE REGENERATION OF INSULATING MINERAL OIL” method according to any one of claims 1-5, characterized in that the particle agglomerates are removed after mixing by filtration through filter paper with a nominal retention of 8 microns. Petition 870250078987, dated 04 / 09 / 2025, p. 5 / 6

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