Deep purification and performance improvement method of vegetable insulating oil

Abstract

The invention relates to the technical field of insulating oil purification, and particularly discloses a deep purification and performance improvement method of vegetable insulating oil, which comprises the following steps: determining fluorination parameters through molecular dynamics simulation, carrying out surface fluorination modification on a polypropylene filter membrane, and constructing a high-coverage C-F bond layer; specific endogenous impurities such as gossypol, phospholipid and pigment in the vegetable insulating oil such as cotton seeds can be effectively removed, and the problems of oxidation acceleration, insulation performance reduction and equipment aging caused by the specific endogenous impurities are avoided; and a core technical support is provided for long-acting stable operation of the vegetable insulating oil.

Description

Technical Field

[0001] This invention relates to the field of insulating oil purification technology, specifically to a method for deep purification and performance improvement of plant-based insulating oil. Background Technology

[0002] As an environmentally friendly alternative to mineral insulating oil, vegetable insulating oil has demonstrated significant advantages in green energy transition and sustainable development of power equipment due to its renewability, excellent biodegradability, and high flash point. It has gradually become an important research direction for oil media in distribution transformers and high-voltage power systems. However, vegetable oils are derived from natural plant extracts, and their composition inevitably contains complex endogenous impurities. These impurities differ significantly from mineral oil systems in molecular structure and chemical behavior, posing a fundamental obstacle to the industrial application and long-term operational stability of vegetable insulating oils.

[0003] Key impurities in vegetable insulating oils mainly include: phenolic compounds with strong oxidative catalytic activity (such as gossypol, containing ortho-phenolic hydroxyl structures), which can initiate free radical chain reactions at room temperature, accelerating the breakage of fatty acid ester bonds and the formation of peroxides within the oil; amphoteric surfactant molecules such as phospholipids, which can accumulate at the oil-solid interface under an electric field, forming a colloidal layer that significantly reduces dielectric breakdown strength and induces electrochemical corrosion of copper and aluminum conductors; and natural pigment molecules containing conjugated double bonds and polar groups, which act as photosensitizers, absorbing ultraviolet and visible light energy and promoting the continuous accumulation of aging byproducts such as free radicals and carbonyl compounds in the oil. Furthermore, these impurities often coexist in multiple forms, including molecular, micellar, and even submicron-sized suspended phases, further exacerbating their combined impact on the physicochemical properties and insulation life of the oil.

[0004] Current mainstream technologies for refining and regenerating vegetable insulating oils still have many limitations. Physical adsorption methods (such as activated carbon and zeolite) adsorb nonpolar molecules through van der Waals forces, exhibiting a certain affinity for low-polarity impurities. However, their adsorption efficiency for polar colloidal impurities such as phospholipids is significantly insufficient (phospholipid removal rate is typically below 70%, and pigment removal rate is even less than 50%). Furthermore, adsorption materials are prone to saturation and difficult to regenerate, leading to potential secondary pollution risks and making it difficult to meet the long-term requirements of equipment for oil stability and purity.

[0005] Chemical refining methods mostly remove free fatty acids and phenolic hydroxyl impurities from oils through acid-base neutralization and saponification reactions. Although this can inhibit the oxidation reaction caused by gossypol to a certain extent, the introduced alkaline components (such as metal soaps) are prone to remain and have a negative impact on the dielectric properties of the oil, limiting the increase in breakdown voltage (usually no more than 20-30%). At the same time, it may cause chemical degradation of insulating paper and interfacial instability.

[0006] Membrane separation technology, which has developed in recent years, relies on pore size control and physical sieving mechanisms to selectively retain large molecular impurities using microfiltration / ultrafiltration membranes. Although this type of method is simple to operate and has low energy consumption, the pore sizes of existing mainstream filter membrane materials are mostly in the micrometer range, and the membrane surface generally lacks active sites. This results in extremely weak retention capacity for small molecular impurities such as gossypol with a size of only 1.5–2 nm (retention rate is usually less than 60%). At the same time, it is difficult to effectively act on colloidal phospholipids and nonpolar pigments, resulting in an intrinsic bottleneck in purification efficiency. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for deep purification and performance improvement of plant-based insulating oils. It develops a novel separation platform that combines molecular recognition functionalized surfaces, controllable charge storage characteristics, and enhanced intermolecular interactions, representing a key pathway to overcome the technological bottlenecks in deep purification of plant-based insulating oils. The invention aims to provide a highly selective, high-throughput, and oil-resistant composite membrane separation solution to address key issues such as accelerated oxidation, decreased dielectric properties, and aging of power equipment caused by various types of endogenous impurities in oils, including residual gossypol, phospholipids, and natural pigments. This solution is particularly suitable for plant-based insulating oil systems using cottonseed oil as a raw material.

[0008] This invention provides a method for deep purification and performance improvement of plant-based insulating oil, comprising the following steps: S1. Model Construction: Establish molecular models of polypropylene before and after fluorination, as well as interface models of polypropylene before and after fluorination and key impurities to be removed in plant insulating oil. Reveal the interaction mechanism between fluorinated polypropylene and key impurities in plant insulating oil from the perspective of quantum chemistry and molecular dynamics, and establish a microscopic characterization platform that relates the charge storage characteristics of the fluorinated layer and the interfacial adsorption behavior. S2. Based on the microscopic mechanism of regulating the proportion and coverage of CF bonds in the fluorinated layer under fluorination conditions, combined with the analysis of quantum mechanics and molecular dynamics of the fluorinated layer, the fluorination modification conditions are optimized, and the polypropylene filter membrane is fluorinated according to the optimized fluorination modification conditions to obtain a fluorinated polypropylene filter membrane. S3. Pressurize the vegetable insulating oil to be purified and pass it through a fluorinated polypropylene filter membrane to remove key impurities, thereby achieving deep purification and performance improvement of the vegetable insulating oil.

[0009] Furthermore, in S1, Gaussian 09 software was used to establish molecular models of polypropylene before and after fluorination, and quantum chemical calculations were performed to determine the dipole moment and polarizability. DFT, as a computational method for studying the electronic structure of multi-electron systems, is widely used in various fields such as condensed matter physics, computational materials science, and computational chemistry. This study used the DFT method to calculate the molecular structure of polypropylene before and after fluorination, and Gaussian 09 software was used for DFT simulation. For geometry optimization and frequency analysis, a B3LYP hybrid functional combined with a 6-31G(d) basis set was selected, where the polarization function can accurately describe the electronic polarization characteristics of the CF bond. The default convergence criterion was used during optimization, and the stable configuration was verified through frequency calculations. High-precision single-point energy calculations were further performed on the optimized ground-state structure to obtain more accurate electronic structure information. Through this calculation, the frontier molecular orbital energy levels and their band gaps of polypropylene before and after fluorination were systematically analyzed, and the dipole moment vector value and polarizability parameters were extracted. This is of great significance for studying the mechanism by which fluorination modification improves the electret properties of polypropylene.

[0010] Dipole moment is a physical quantity describing the degree of charge separation in a molecule. It is defined as the product of the amount of charge at the positive and negative charge centers in the molecule and the distance between them, directly affecting the polarization intensity and space charge distribution of an electret. Polarizability describes the polarization ability of a material in an electric field, directly affecting charge injection and transport in an electret. Both dipole moment and polarizability can characterize the electret properties of PP, thus reflecting the ability of PP filter membranes to filter impurities. After fluorination, the dipole moment and polarizability of PP material both changed significantly. Calculation results show that the dipole moment of fluorinated PP increased by 32.2% of its original value, and the polarizability increased by 10.5%. This change is mainly attributed to the high polarity of the CF bonds formed after the introduction of fluorine atoms. The increase in dipole moment indicates that after fluorination, the strongly polar CF bonds form dipoles, which align oriented under an external electric field, synergistically with space charge polarization, significantly improving the overall polarization intensity. The increased polarizability indicates that fluorinated PP is more likely to generate polarized charges under an external field, enhancing charge storage density and further optimizing the uniformity of charge distribution and electric field response efficiency of PP. The dipole moment-dominated polarization mechanism with deep trap synergy overcomes the contradiction between charge stability and dynamic response in traditional polypropylene electrets, indicating that surface fluorination enhances the electret properties of PP and improves the ability of PP filter membranes to filter insulating oil impurities. This provides a theoretical and practical basis for developing long-lasting, highly environmentally adaptable electrostatic filter materials.

[0011] Furthermore, in S1, Material Studio software was used to employ molecular dynamics simulations to study the interaction energies of the interface model; the interactions between the fluorinated filter membrane and gossypol, phospholipids, and pigments were investigated. Molecular dynamics simulations were based on the Forcite module and performed using the COMPASSIII force field. First, a three-dimensional amorphous structure of PP was constructed using the amorphous crystal cell module. Based on this, interface models of polypropylene before and after fluorination with gossypol, phospholipids, and pigments were constructed respectively. To obtain a reasonable initial structure, the model underwent 500,000 geometric optimization steps to ensure it reached equilibrium. To avoid local minima traps, an annealing algorithm was further used to perform six rounds of annealing on the model, with the temperature range set from 300K to 600K, to promote sufficient sampling of molecular conformations, thereby obtaining a more stable, low-energy system structure. Based on this, the system density was simulated for 200 ps under NVT and NPT conditions, with a time step set to 1 fs, until the system reached thermodynamic equilibrium. Finally, under NVT conditions, the system was further subjected to a 500 ps equilibrium simulation with a time step of 1 fs. This invention evaluated the interaction behavior between the fluorinated polypropylene filter membrane and the main impurity molecules in vegetable insulating oil using a molecular dynamics simulation system. The results showed that the filter membrane possesses significantly enhanced impurity recognition and binding capabilities at the molecular level: the interaction energy with gossypol and phospholipids is increased by approximately 40–65% compared to the unmodified polypropylene membrane, while the interaction energy with conjugated molecules of natural pigments is generally enhanced by more than 50%. This significant increase in interaction energy stems from the highly electronegative region on the fluorinated membrane surface, which induces stronger electrostatic adsorption and dipole coupling between the phenolic hydroxyl groups of gossypol and the phosphate head groups of phospholipids, while simultaneously enhancing the interfacial free energy gradient and improving the affinity and adsorption stability for polar and conjugated molecular structures. Furthermore, the nanoscale pore structure of the fluorinated membrane exhibits high molecular size matching, enabling effective confinement and physical retention of small to medium-sized impurities such as gossypol and pigments. Simultaneously, it exerts a synergistic effect of spatial trapping and electrostatic inhibition on phospholipid micelles. The aromatic structures in the conjugated pigment molecules can also interact with the fluorinated surface via π–F interactions and enhanced hydrophobicity through van der Waals adsorption, further increasing their retention probability. This synergistic effect of multiple mechanisms not only enables the fluorinated polypropylene filter membrane to achieve higher selectivity and stronger binding force for various impurities but also significantly improves the deep removal efficiency and dielectric property retention capacity during the purification process of plant-based insulating oils. This provides a theoretical basis and key material support for the preparation and application of next-generation green high-performance electrical insulating oils.

[0012] By combining quantum mechanics and analytical kinetics simulations, a microscopic characterization platform was established to correlate the charge storage characteristics of the fluorinated layer with the interfacial adsorption behavior. This platform represents the first time a complete chain of analysis has been achieved, from electronic structure (DFT) and molecular motion (MD) to macroscopic performance (experimental), overcoming the limitations of single-scale research. Through the established closed-loop optimization platform of "computation-characterization-process," a fluorinated filter membrane with both high charge storage stability and multi-mechanism synergistic adsorption function was designed, providing a theoretically driven and efficient solution for the deep purification of plant-based insulating oils. Multi-scale coupled simulations of quantum chemical calculations and molecular dynamics revealed that the increase in dipole moment is positively correlated with the CF bond ratio, while the enhancement of impurity interaction energy significantly depends on the integrity of the fluorination coverage. Therefore, the core requirements for fluorination were determined: a CF bond ratio ≥65% to ensure the required increase in dipole moment, and a fluorination coverage ≥98% to ensure the required increase in interaction energy between the fluorinated filter membrane and key impurities.

[0013] Furthermore, in S2, to achieve efficient fluorination modification of the filter membrane surface, the fluorination modification was optimized based on the microscopic mechanism of controlling the properties of the fluorinated layer under fluorination conditions, combined with the analysis of quantum mechanics and molecular dynamics of the fluorinated layer, and a precisely controlled gas-phase fluorination process was adopted. Specifically, an F2 / N2 mixed gas with a fluorine gas volume fraction of 0.8% was introduced, and the reaction was carried out in a closed reaction chamber for 60 minutes under a constant pressure of 0.25 MPa. Under these conditions, the fluorination reaction can initiate a controlled hydrogen-fluorine substitution reaction on the surface and near-surface region of the polypropylene filter membrane, forming stable carbon-fluorine (C–F) covalent bonds, thereby endowing the membrane surface with excellent chemical stability and high electronegativity. FTIR and X-ray photoelectron spectroscopy (XPS) analyses verified that the C–F bonds in the surface layer of the treated filter membrane accounted for more than 65% of the total carbon bonds, and the continuity and integrity of the surface fluorinated layer were good, with a fluorine coverage of no less than 98%, significantly superior to conventional liquid-phase or low-pressure plasma fluorination methods. This dense and highly covered fluorinated layer not only significantly enhances the filter membrane's ability to recognize polar impurity molecules, but also reconstructs the interfacial energy and charge distribution on the membrane surface at the microscale, providing a stable and controllable functional interface basis for subsequent efficient molecular sieving and selective adsorption.

[0014] Simulation results show that when the fluorine concentration exceeds 1%, fluorine radical overloading will induce polymer backbone degradation; fluorine permeation kinetics are limited when the reaction pressure is below 0.2 MPa, while side reactions are induced when the pressure is above 0.3 MPa; a reaction time shorter than 50 minutes leads to incomplete surface coverage, while a reaction time exceeding 70 minutes causes over-fluorination. By establishing a mapping network of fluorination parameters, microstructure, and performance output, the optimal combination of 0.8% F2 concentration, 0.25 MPa pressure, and 60-minute reaction time was finally determined.

[0015] In addition, the fluorinated polypropylene filter membrane was placed on a surface potential decay measurement platform to obtain the dynamic change curve of the surface potential of the tested sample. Experiments showed that after fluorination, a dense and highly polar C–F bond network structure was formed on the filter membrane surface, significantly altering its surface electron cloud density and charge distribution characteristics. This resulted in an increase in the initial surface electrostatic potential from -2653.84 V in the unmodified state to -2945.77 V, an increase of approximately 11%. This potential enhancement effect not only helps improve the filter membrane's electrostatic adsorption capacity for polar impurities (such as phospholipid head groups and phenolic hydroxyl groups) but also reflects the stronger charge trapping ability of the surface after fluorination. To evaluate its charge retention performance, the surface potential change of the filter membrane was monitored under stable environmental conditions for 24 consecutive hours. The results showed that the surface potential of the unmodified filter membrane sample rapidly decayed to 13.2% of its initial value, indicating loose charge trapping and easy leakage. In contrast, the fluorinated filter membrane sample could maintain 76% of its initial potential under the same conditions, exhibiting excellent charge stability and sustained-release characteristics. According to the potential decay curve fitting, its charge half-life is extended by approximately 7.4 times compared to the unmodified sample, indicating that the fluorinated surface has a significantly enhanced ability to capture and bind free charges. This characteristic is of great significance for practical applications: the enhanced surface potential stability not only improves the persistence of electrostatic interaction in the membrane material during impurity adsorption, but also significantly enhances the ability to electrostatically adsorb impurities, providing a long-term guarantee for the continuous and efficient removal of polar impurities in vegetable insulating oils. This result further verifies the core role of fluorination modification in improving the interfacial functionality of membrane materials, extending service life, and maintaining purification performance. The fluorinated modified polypropylene filter membrane used not only obtained a stable fluorine functional layer at the chemical structure level, but also showed a significant improvement in charge storage and surface potential maintenance capabilities.

[0016] Furthermore, the operating pressure difference in S3 was controlled at 0.2-0.8 MPa. During dynamic filtration at a pressure difference of 0.2-0.8 MPa, the fluorinated layer achieved molecular-level removal of impurities through the following synergistic mechanisms: (1) selective adsorption of gossypol by atomic-level interactions; (2) capture of phospholipid micelles by charge-matching effects; and (3) retention of pigment macromolecules by enhanced intermolecular forces (including π-F interactions). Surface potential decay experiments verified that the fluorination process significantly improved the initial surface potential (-2945.77 V, an increase of 11%) and greatly reduced the decay rate (maintaining 76% after 24 h), and extended the charge half-life by approximately 7.4 times.

[0017] After continuous fine filtration of vegetable insulating oil using a fluorinated polypropylene filter membrane, high-purity purified oil was successfully collected, and its key performance indicators were quantitatively analyzed and evaluated. Experimental data show that this purification process achieves highly efficient removal of complex impurities at multiple scales, exhibiting excellent selectivity and stability. Specifically, the removal rate of gossypol, an active phenolic substance in the oil, exceeded 98%, essentially achieving complete removal of small-molecule oxidation catalysts, fundamentally blocking the initiation conditions of subsequent free radical oxidation chain reactions, and significantly improving the oil's antioxidant capacity. Phospholipids, a key factor affecting the stability of the insulation interface and the risk of electrochemical corrosion, were removed at a rate exceeding 95%, indicating that the membrane material possesses a highly synergistic and sustained adsorption capacity for the interface recognition and physical capture mechanism of colloidal polar molecules, effectively mitigating potential insulation system hazards such as electric field concentration and conductor corrosion.

[0018] Furthermore, the fluorinated filter membrane still exhibits excellent adaptability and adsorption capacity for non-polar, complex conjugated structures, and highly photosensitive pigment impurities, with a removal rate exceeding 92%, providing crucial protection against the aging process of the oil. Thanks to the significant removal of these various impurities, the overall dielectric properties of the filtered vegetable insulating oil are greatly improved, particularly in terms of breakdown voltage, which is at least 60% higher than the average of the raw oil. This surge in breakdown voltage not only reflects a significant improvement in oil purity but also verifies the functional effect of the fluorinated filter membrane in constructing microscopic electric field stability, enhancing the reliability and safety margin of the insulation system during long-term operation under high voltage.

[0019] Furthermore, the key impurities in the plant-based insulating oil are gossypol, phospholipids, and pigments.

[0020] This invention also relates to the application of the method in the purification and performance improvement of transformer insulating oil.

[0021] The present invention also relates to cottonseed oil as the plant-based insulating oil.

[0022] The present invention has the following beneficial effects: This invention reveals the interaction mechanism between fluorinated polypropylene and key impurities (gossypol, phospholipids, and pigments) in vegetable oil from the perspectives of quantum chemistry and molecular dynamics. It also establishes a microscopic characterization platform linking the charge storage characteristics and interfacial adsorption behavior of the fluorinated layer. Based on an understanding of the microscopic mechanism by which fluorination conditions (fluorine concentration, pressure, and time) regulate the properties of the fluorinated layer (CF bond ratio, coverage, and charge trap distribution), this method achieves precise optimization of fluorination process conditions. Applying this optimized process, >98% of gossypol, >95% of phospholipids, and >92% of pigments can be efficiently removed from vegetable insulating oil, increasing the breakdown voltage of the insulating oil by ≥60% compared to the raw oil. This breaks through the adsorption limits of traditional physical filtration for small molecule dissolved and colloidal impurities, providing core technical support for the long-term stable operation of vegetable insulating oil. Furthermore, charge storage and stability are significantly improved, enhancing electret characteristics; the electrical properties of the insulating oil are significantly improved; and the method provided by this invention is highly efficient and has long-term environmental adaptability. Attached Figure Description

[0023] Figure 1 : This refers to the fluorination reaction formula in Example 3; Figure 2 Construction of the interface model in Example 3; Figure 3 Flowchart of the fluorination process of the polypropylene filter membrane in Example 3; Figure 4 Examples 2 and 3: The sealed reactor used for fluorination of polypropylene filter membranes; wherein: 1. Gas source; 2. Gas path system; 3. Gas mixing ratio regulator; 4. Vacuum pump; 5. High-temperature and high-pressure sealed reactor; 6. Dynamic micro-positive pressure distribution reaction system; 7. Temperature controller; 8. Electromagnetic heating system; 9. Raman spectroscopy monitoring system; 10. Inert gas purging system; 11. Cooling circuit system; 12. Rotating support. Figure 5 : CF ratio and coverage of the polypropylene filter membrane after fluorination in Example 3; Figure 6 The dipole moment of the polypropylene filter membrane before and after fluorination in Example 3; Figure 7 Polarization of the polypropylene filter membrane before and after fluorination in Example 3; Figure 8 Initial surface potential increase and surface potential decay rate of unfluorinated (Example 1) and fluorinated (Example 3) polypropylene filter membranes; Figure 9 Performance comparison of different purification methods; traditional purification is Example 1, and fluorinated membrane purification is Example 3. Figure 10 The effect of different purification methods on breakdown voltage; traditional purification is Example 1, and fluorinated membrane purification is Example 3. Detailed Implementation

[0024] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials used in the following examples are commercially available products.

[0025] Example 1 (Unfluorinated polypropylene filter membrane) Step 1: Raw Materials and Equipment Raw materials: Cottonseed insulating oil containing gossypol (320ppm), phospholipids (180ppm), and pigments (85ppm) (initial breakdown voltage 32kV). Filter membrane: Ordinary polypropylene filter membrane (pore size 0.45μm, thickness 120μm) Step 2: Filtering Operation The insulating oil was passed through an unfluorinated polypropylene filter membrane at a pressure difference of 0.5 MPa, with the flow rate controlled at 10 L / min.

[0026] Step 3: Performance testing is shown in Table 1. The amount of residual impurities was measured using high-performance liquid chromatography; the breakdown voltage was detected using a DC flashover device on the insulating oil; and the surface potential decay rate was measured in real-time using a potential decay meter via an electrostatic probe method.

[0027] Table 1

[0028] Conclusion: Unmodified filter membranes have low removal rates of polar impurities such as phospholipids and pigments, limited improvement in breakdown voltage, and poor charge stability of polypropylene filter membranes.

[0029] Example 2 (Fluorinated polypropylene filter membrane under unoptimized fluorination conditions) Step 1: Fluorination modification A polypropylene filter membrane (0.45 μm pore size, 120 μm thickness) was placed in a closed reaction chamber, and a 5% (v / v) F2 / N2 mixed gas (higher than the optimized concentration) was introduced. The reaction was carried out at atmospheric pressure (0.1 MPa) for 30 minutes. These conditions did not follow the optimized parameters from quantum chemical and molecular dynamics simulations.

[0030] Step 2: Performance Verification Characterization of the fluorinated layer: XPS analysis showed that the CF bond ratio was only 42.3% and the fluorine coverage was 78.6% (significantly lower than ≥65% and ≥98% under optimized conditions).

[0031] Surface potential decay: The initial surface potential was -2750.15V (3.6% higher than the unfluorinated film, far lower than the 11% of the optimized process); after 24 hours, the potential decayed to 48% of the initial value (the charge half-life was extended by about 2.1 times, compared to 7.4 times in the optimized process).

[0032] Step 3: Filtering Operation Raw materials: cottonseed insulating oil as in Example 1 (320ppm gossypol, 180ppm phospholipids, 85ppm pigment, breakdown voltage 32kV).

[0033] Operation: Filter under a pressure difference of 0.5 MPa and a flow rate of 10 L / min.

[0034] Step 4: Performance testing is shown in Table 2.

[0035] Table 2

[0036] in conclusion: Insufficient impurity removal: Due to the low coverage and insufficient bond ratio of the CF bond in the fluorinated layer, the synergistic adsorption mechanism of gossypol, phospholipids and pigments is weakened, resulting in limited improvement in electrical performance and poor charge stability.

[0037] Example 3 (Optimized fluorination conditions for fluorinated polypropylene filter membrane) Step 1: Molecular Model Construction During the fluorination reaction, a stable C–F covalent network layer is formed on the membrane surface through a chemical hydrogen-fluorine substitution reaction (see...). Figure 1 The reaction principle is illustrated to achieve high polarity modification of the material surface. Molecular models of polypropylene before and after fluorination were established using Gaussian 09 software; interface models of polypropylene before and after fluorination with gossypol, phospholipids, and pigments were established using Material Studio software. The model construction is as follows: Figure 2 As shown, the interaction mechanism between fluorinated polypropylene and key impurities (gossypol, phospholipids, and pigments) in vegetable oils was revealed from the perspectives of quantum chemistry and molecular dynamics. A microscopic characterization platform was established to correlate the charge storage characteristics and interfacial adsorption behavior of the fluorinated layer. Based on the microscopic mechanism by which fluorination conditions regulate the properties of the fluorinated layer, and combined with the analysis of the quantum mechanics and molecular dynamics of the fluorinated layer, the fluorination modification was optimized.

[0038] Based on a molecular simulation microscopic characterization platform, the electronic structure characteristics and interfacial adsorption behavior of polypropylene filter membranes under different fluorination conditions were systematically evaluated. Through multi-scale coupled simulations of quantum chemical calculations and molecular dynamics, the quantitative structure-activity relationship (QS) between the microscopic properties and macroscopic performance of the fluorinated layer was revealed: the increase in dipole moment is positively correlated with the proportion of CF bonds, while the enhancement of impurity interaction energy significantly depends on the integrity of the fluorination coverage. To balance deep fluorination and structural stability, a parameter space scanning strategy was used to optimize the modeling of key process variables. Simulation results show that when the fluorine concentration exceeds 1%, fluorine radical overloading will induce polymer backbone degradation; fluorine permeation kinetics are limited when the reaction pressure is below 0.2 MPa, while side reactions are induced when the pressure is above 0.3 MPa; reaction time less than 50 minutes leads to incomplete surface coverage, while reaction time exceeding 70 minutes causes over-fluorination. By establishing a mapping network of fluorination parameters, microstructure, and performance output, the optimal combination of 0.8% F2 concentration, 0.25 MPa pressure, and 60-minute reaction time was finally determined. This condition simultaneously meets two core requirements at the molecular scale: 1) CF bond ratio ≥ 65% to ensure a 32.2% increase in dipole moment (DFT verification); 2) fluorine coverage ≥ 98% to achieve a 40-65% increase in impurity interaction energy (MD verification), thereby achieving synergistic optimization of functionalization and structural integrity at the atomic level.

[0039] Table 3 shows a comparison of performance under different fluorination conditions.

[0040] Table 3

[0041] Condition 1 (unoptimized): 5% F2, 0.1MPa, 30min; Condition 2 (high pressure and high concentration): 10% F2, 0.4MPa, 90min; Condition 3 (pass): 5% F2, 0.1MPa, 30min; Condition 4 (pass): 5% F2, 0.1MPa, 30min.

[0042] Step 2: Fluorination modification A polypropylene filter membrane was placed in a sealed reaction chamber, and a 0.8% (v / v) F2 / N2 mixed gas was introduced at room temperature (25°C). The reaction pressure was controlled at 0.25 MPa, and the reaction lasted for 60 minutes. The fluorination process is as follows: Figure 3 As shown. Figure 4 It is a fluorination-sealed reaction vessel.

[0043] Verification showed that XPS indicated a CF bond percentage of 68.2% and a fluorine coverage of 98.5%. Figure 5 ).

[0044] Step 3, Surface Potential Decay Test: Place the fluorinated polypropylene filter membrane into the surface potential decay measurement platform to obtain the initial surface potential and dynamic change curve of the surface potential of the sample, such as... Figure 8 As shown.

[0045] Step 4, Dynamic Filtration and Flashover Test: Vegetable insulating oil containing gossypol, phospholipids, and pigments is passed through a fluorinated polypropylene filter membrane under an operating pressure difference of 0.5 MPa to remove impurities at the molecular level. The composition of the insulating oil is then analyzed, and a breakdown test is performed. Figure 9 , Figure 10 As shown.

[0046] Performance testing results are shown in Table 4.

[0047] Table 4

[0048] Conclusion: Fluorinated filter membranes achieve molecular-level removal of three types of impurities, with a breakthrough increase in breakdown voltage, and fluorinated polypropylene filter membranes exhibit strong charge.

[0049] Example 4 (Pressure filtration and optimized conditions for fluorinated polypropylene filter membrane) The polypropylene filter membrane was fluorinated under optimized fluorination conditions, and a three-stage circulating filtration system was set up at a pressure difference of 0.8 MPa and a flow rate of 15 L / min.

[0050] Performance testing results are shown in Table 5.

[0051] Table 5

[0052] Conclusion: This embodiment achieves two breakthroughs through the synergistic effect of high-pressure filtration (0.8 MPa) and an optimized fluorinated membrane (CF bond 68.5% / coverage 98.7%): 1. Molecular-level removal limit: The removal rates of gossypol, phospholipids, and pigments reached 98.8%, 96.7%, and 94.1%, respectively.

[0053] 2. Significant improvement in electrical performance: The breakdown voltage increased by 168.8% (86 kV), which is 9.4% higher than the un-voltage optimized process (Example 3).

[0054] The above embodiments describe preferred embodiments of the present invention, but the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other way. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for deep purification and performance improvement of plant-based insulating oil, characterized in that, Includes the following steps: S1. Model Construction: Establish molecular models of polypropylene before and after fluorination, as well as interface models of polypropylene before and after fluorination and key impurities to be removed in plant insulating oil. Reveal the interaction mechanism between fluorinated polypropylene and key impurities in plant insulating oil from the perspective of quantum chemistry and molecular dynamics, and establish a microscopic characterization platform that relates the charge storage characteristics of the fluorinated layer and the interfacial adsorption behavior. S2. Based on the microscopic mechanism of regulating the proportion and coverage of CF bonds in the fluorinated layer under fluorination conditions, combined with the analysis of quantum mechanics and molecular dynamics of the fluorinated layer, the fluorination modification conditions are optimized, and the polypropylene filter membrane is fluorinated according to the optimized fluorination modification conditions to obtain a fluorinated polypropylene filter membrane. S3. Pressurize the vegetable insulating oil to be purified and pass it through a fluorinated polypropylene filter membrane to remove key impurities, thereby achieving deep purification and performance improvement of the vegetable insulating oil.

2. The method according to claim 1, characterized in that: In S1, Gaussian 09 software was used to establish molecular models of polypropylene before and after fluorination, and quantum chemical calculations were performed to determine the dipole moment and polarizability.

3. The method according to claim 2, characterized in that: In S1, molecular dynamics simulations were performed using Material Studio software to study the interaction energies of the interface model; the interaction between the fluorinated filter membrane and gossypol, phospholipids, and pigments was also investigated.

4. The method according to claim 3, characterized in that: Through multi-scale coupled simulations of quantum chemical calculations and molecular dynamics, it was revealed that the increase in dipole moment is positively correlated with the proportion of CF bonds, while the enhancement of impurity interaction energy is significantly dependent on the integrity of fluorination coverage. Therefore, the core requirements for fluorination are determined: CF bond proportion ≥ 65% to ensure that the increase in dipole moment meets the requirements, and fluorination coverage ≥ 98% to ensure that the increase in interaction energy between fluorinated filter membrane and key impurities meets the requirements.

5. The method according to claim 1, characterized in that: During the fluorination modification of S2, an F2 / N2 mixed gas with a fluorine concentration of less than or equal to 1% is introduced.

6. The method according to claim 1, characterized in that: When S2 is fluorinated, the fluorination pressure is 0.2MPa~0.3MPa and the reaction time is 50min~70min.

7. The method according to claim 1, characterized in that: When pressurizing S3, the operating pressure differential is controlled between 0.2 and 0.8 MPa.

8. The method according to claim 1, characterized in that: The key impurities in the plant-based insulating oil are gossypol, phospholipids, and pigments.

9. The application of the method according to any one of claims 1 to 8 in the purification and performance improvement of transformer insulating oil.

10. The application according to claim 9, characterized in that, The plant-based insulating oil mentioned is cottonseed oil.

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