Deep deashing method of polyolefin resin, eutectic solvent and preparation method thereof

Abstract

The application provides a eutectic solvent, a preparation method thereof and a method for deep deashing of a polyolefin resin, and the eutectic solvent is a combination of a polyfluorosubstituted alcohol and an azacycloalkene, and the eutectic solvent realizes deep removal of ash (especially metal ions) in the polyolefin resin.

Description

Technical Field

[0001] This invention belongs to the field of polyolefin resin purification technology, specifically relating to a eutectic solvent and its preparation method, and a method for deep deashing of polyolefin resin. Background Technology

[0002] Currently, polypropylene capacitor manufacturing technology has matured. Isotactic polypropylene (iPP) is the mainstream capacitor film material, but its quality stability is significantly affected by the purity of raw materials. Parameters such as ash content (especially metal ions), isotacticity, crystal structure, and crystallinity can all cause problems such as capacitor breakdown voltage fluctuations and increased dielectric loss. Among these, metal ions in the ash (such as Ti, Mg, and Al) are prone to forming conductive channels under the action of a high-voltage electric field, leading to local overheating or even breakdown of the capacitor, which is a key factor affecting the reliability of ultra-high voltage equipment.

[0003] At present, organic composite solvent elution is commonly used for the purification of polypropylene resin both domestically and internationally. Its mechanism of action includes: (1) dissolving atactic polypropylene and low isotacticity components, thereby improving the overall isotacticity of the material; (2) removing silicone ester compounds and catalyst residues, thereby reducing the inorganic ash content; and (3) removing small organic molecules such as white oil and electron donors, thereby eliminating smoke and odor problems during the film-making process. However, the existing technology has significant limitations: according to literature reports and industrial practice, conventional solvent systems can only achieve a metal ion removal rate of ≤60%, and the ash content of the final product is generally ≥30 ppm, with the metal ion residue far exceeding the industry standard.

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

[0005] The primary objective of this invention is to provide a specific combination of eutectic solvents. By constructing a hydrogen-bonded donor-acceptor composite system with a specific composition, the eutectic solvent utilizes its specific coordination effect on metal ions and its ability to dissolve organic impurities to achieve deep removal of ash (especially metal ions) from polyolefin resins. This satisfies the stringent standard requirements for polypropylene used in ultra-high voltage capacitor films and provides key technical support for the localization of ultra-high voltage capacitor film materials.

[0006] The second objective of this invention is to provide a method for preparing the above-mentioned eutectic solvent, which has a simple preparation process and produces a eutectic solvent with excellent performance.

[0007] The third objective of this invention is to provide a method for deep deashing of polyolefins using the aforementioned eutectic solvent. By using the method of this invention, the total ash content can be less than 30 ppm, and the metal ion content can be less than 3 ppm, thus breaking through this technical bottleneck of deep deashing.

[0008] To achieve the above-mentioned objectives of this invention, the following technical solution is adopted: The present invention provides a eutectic solvent, which is composed of a combination of polyfluorinated substituted alcohols and nitrogen-containing heterocyclic olefins.

[0009] In the present invention, the eutectic solvent used is a combination of polyfluorinated substituted alcohols and nitrogen-containing heterocyclic olefins. This combination exhibits suitable acidity, which allows it to penetrate into the microporous structure of polyolefins for deeper processing and dissolve the metal oxides formed during the deashing process, thereby achieving the effect of removing metal oxides.

[0010] Preferably, as a further feasible option, the eutectic solvent comprises at least one of the following four substances: .

[0011] The reason for choosing one of the above four substances is that polyfluorosubstituted alcohols have stronger acidity than ordinary alcohols. Hexafluoroisopropanol was found to be effective due to its strong acidity and low viscosity, allowing it to penetrate the porous structure of polypropylene particles and effectively elute metal oxides. Additionally, nitrogen-containing heterocyclic alkenes are a class of 1,1-diamino-substituted alkenes with exocyclic carbon atoms that are both basic and nucleophilic. When combined with hexafluoroisopropanol, they further facilitate complexation with metal ions, enabling their removal from the polypropylene. Furthermore, the acidity of the polyfluorosubstituted alcohol and the basicity of the nitrogen-containing heterocyclic alkene form a loose acid-base ion pair, enhancing the capture of metal oxides.

[0012] Preferably, as a further feasible option, the eutectic solvent comprises at least two of the following three substances: .

[0013] Of course, specific experiments have shown that it is best to choose two of DES-A, DES-B, and DES-C. This is because DES-A and DES-B are relatively weaker acids, which are more conducive to removing titanium and magnesium oxides. DES-C has greater steric hindrance and stronger acidity, making it more suitable for removing aluminum oxides. If each one is used alone, it will not have a strengthening effect. Therefore, by combining any two of the above three substances, the oxides of titanium, magnesium, and aluminum can be effectively removed simultaneously.

[0014] Preferably, as a further feasible option, the eutectic solvent is a mixture of DES-A and DES-C, wherein the mass ratio of DES-A to DES-C is 1:(2-8).

[0015] Preferably, as a further feasible option, the mass ratio of DES-A to DES-C is 1:(3-6), more preferably 1:4.

[0016] Among the aforementioned DES substances, the optimal combination is a mixture of DES-A and DES-C in a specific mass ratio. During actual removal processes, polypropylene typically has the highest aluminum content, usually several times that of titanium and magnesium. Therefore, when selecting DES substances, it is necessary to use more DES-C to primarily remove aluminum oxides. However, excessive DES-C will increase the overall acidity of the solvent, leading to a decrease in the removal efficiency of titanium and magnesium. Therefore, the aforementioned ratio needs to be controlled within an optimal range. After continuous optimization, the optimal combination is a mass ratio of DES-A to DES-C of 1:4, which achieves the best removal effect.

[0017] Furthermore, existing technologies generally employ eutectic solvents such as choline chloride, betaine, glycerol, and urea. However, the removal effect of these eutectic solvents is not optimal because these substances cannot form the acidic, basic, and nucleophilic interactions described in this invention, thereby enhancing the stripping of metal oxides through complexation.

[0018] The present invention also provides a method for preparing the above-described eutectic solvent, comprising the following steps: After adding hydrogen bond acceptors and hydrogen bond donors sequentially, stir for 1-2 hours to obtain the final product.

[0019] The above preparation method is simple to operate, and the eutectic solvent prepared has excellent properties.

[0020] The method for deep deashing of polyolefin resins using the above-mentioned eutectic solvent includes the following steps: The polyolefin powder is mixed with the elution mobile phase for the first stage of elution. The polyolefin powder after the first stage of elution is mixed with the eutectic solvent and then subjected to the second stage of elution. The polyolefin powder after the second-stage elution treatment is mixed with a low-boiling-point alcohol and subjected to a third-stage elution treatment to achieve deep deashing of the polyolefin resin.

[0021] This invention employs a staged elution process: the first stage uses a low-polarity system that rapidly dissolves random and isotactic polyolefins, removing small organic molecule impurities such as white oil and electron donors; the second stage uses a low-viscosity, weakly acidic DES system that penetrates the microporous structure of polyolefins to deeply remove embedded metal ions; furthermore, the DES system, formed by a combination of a strongly acidic polyfluorinated substituted alcohol and a weakly basic nitrogen-containing heterocyclic olefin, exhibits appropriate acidity to dissolve and remove the formed metal oxides; the third stage uses a highly polar, low-boiling-point system that rapidly removes residual eluent and enables rapid drying of the polyolefin powder at lower temperatures. Preferably, as a further feasible option, the elution mobile phase comprises an alkane and a solvent, wherein the solvent is selected from one or more alcohols, amines, and ethers; Preferably, the mass ratio of the alkane to the solvent is (3-12):1; Preferably, the alkane is selected from one or more of petroleum ether, n-hexane, cyclohexane, and n-heptane; Preferably, the solvent is selected from one or more of n-propanol, isopropanol, n-butanol, isobutanol, N,N-dimethylformamide, N,N-dimethylacetamide, ethylene glycol monomethyl ether, and ethylene glycol dimethyl ether.

[0022] Preferably, the temperature of the first-stage elution process is 60-100℃, for example, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃ or 100℃; the time of the first-stage elution process is 1-2 hours, for example, 1 hour, 1.5 hours or 2 hours.

[0023] Preferably, the first-stage elution process is carried out under stirring conditions. The stirring speed is not specifically defined and can be any stirring speed known in the art; for example, the stirring speed is 200-800 rpm.

[0024] Preferably, the first-stage elution process includes the following steps: adding polyolefin powder and elution mobile phase sequentially to a washing container equipped with heating, mechanical stirring and pressure filtration, then turning on stirring and heating to 60-100°C, eluting for 1-2 hours; then removing the elution mobile phase by pressure filtration to complete the first-stage elution process.

[0025] Preferably, as a further feasible option, the mass ratio of the polyolefin powder to the eutectic solvent is 1:(0.8-2.5); for example, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, 1:2.1, 1:2.2, 1:2.3, 1:2.4 or 1:2.5.

[0026] Preferably, the temperature of the second-stage elution process is 60-100°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, or 100°C, and the time of the second-stage elution process is 1-2 hours, for example, 1 hour, 1.5 hours, or 2 hours.

[0027] Preferably, the second-stage elution process is carried out under stirring conditions. The stirring speed is not specifically defined and can be any stirring speed known in the art; for example, the stirring speed is 200-800 rpm.

[0028] Preferably, the second-stage elution process includes the following steps: adding polyolefin powder and eutectic solvent sequentially to a washing container equipped with heating, mechanical stirring and pressure filtration, then turning on stirring and heating to 60-100°C, eluting for 1-2 hours; then removing the eutectic solvent by pressure filtration to complete the second-stage elution process.

[0029] Preferably, as a further feasible option, the low-boiling alcohol is methanol and / or ethanol; Preferably, the temperature of the third-stage elution process is 40-60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C, and the time of the third-stage elution process is 0.5-1h.

[0030] Preferably, the mass of the low-boiling-point alcohol is more than 5 times the mass of the polyolefin powder, more preferably 5-10 times, for example, 5, 6, 7, 8, 9, or 10 times. When the mass of the low-boiling-point alcohol is more than 5 times the mass of the polyolefin powder, the effective removal of ash from the polyolefin powder by the low-boiling-point alcohol can be guaranteed.

[0031] Preferably, the third-stage elution process is carried out under stirring conditions. The stirring speed is not specifically defined and can be any stirring speed known in the art; for example, the stirring speed is 200-800 rpm.

[0032] Preferably, the third-stage elution process includes the following steps: adding polyolefin powder and low-boiling-point alcohol sequentially to a washing container equipped with heating, mechanical stirring and pressure filtration, then turning on stirring and heating to 40-60°C, eluting for 0.5-1 hour; then removing the low-boiling-point alcohol by pressure filtration to complete the third-stage elution process.

[0033] Preferably, after the third-stage elution process is completed, the process further includes drying the polyolefin resin, such as by heating or natural drying (e.g., hot air purging).

[0034] In summary, by employing the above-mentioned deashing method, the ash content of polyolefin resins after three-stage elution treatment can be as low as 8-25 ppm, with titanium content <1 ppm, magnesium content <3 ppm, and aluminum content <3 ppm. The eutectic solvent (DES) elution system, with its unique strong complexing ability, efficient ash removal in a single wash, solvent recyclability, mild operating conditions, and significantly improved product quality, provides a more advanced, sustainable, and economical solution for the purification of polyolefin resins. It is expected to overcome the limitations of traditional technologies and drive the development of polyolefin resin preparation technology towards higher purity and higher efficiency. Utilizing the synergistic coordination effect of DES enhances the capture capacity of metal ions, achieving a metal removal rate of up to 92%-99%. The solvent can be recycled through simple distillation; waste DES can be converted into fertilizer components through neutralization, achieving a green life cycle. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0036] To more clearly illustrate the technical solutions in this invention, the following description is provided in the form of specific embodiments.

[0037] In the following examples, the ash content was determined according to the method specified in GB / T 9345.1-2008; the metal ion content was determined according to the method specified in SH / T 1829-2020. The isotacticity test of polypropylene resin was performed according to the method specified in GB / T 2412. Each sample was tested three times, and the average value was taken.

[0038] In the following embodiments, hydrogen bond acceptors and hydrogen bond donors were added sequentially to a 25 L stainless steel reactor according to the designed molar ratio, and then stirring was started for 1.5 h to prepare stable and homogeneous low-viscosity DES for later use. The structural formulas corresponding to the prepared low-viscosity DES are as follows (DES-A, DES-B, DES-C, and DES-D are directly used to replace the specific structural formulas in the following embodiments): . Example 1

[0039] The polypropylene powder contains 3.7 ppm titanium, 26.9 ppm magnesium, 45.5 ppm aluminum, and 114.2 ppm ash.

[0040] First-stage elution: Organic solvent elution. 1.000 kg of the above polypropylene powder was placed in a 25L stainless steel reactor with a jacket and filter plate. 10.00 kg of n-hexane and 2.00 kg of isopropanol were added sequentially, and the stirrer was turned on (800 rpm) to form a homogeneous suspension. The temperature was increased to 80±1℃ at a rate of 5℃ / min using a heat transfer oil circulation heating system, and stirred at a constant temperature for 2.0 hours. The mixture was then filtered while hot under a pressure of 0.3 MPa, and the filtrate was collected for solvent recovery.

[0041] Second-stage elution: Deep desorption of the eutectic solvent. Under nitrogen protection (flow rate 0.5 L / min), 1.0 kg of the eutectic solvent DES-A was added to the reactor. The stirrer was turned on (1000 rpm) to form a homogeneous suspension. The temperature was increased to 80±1℃ at a rate of 5℃ / min using a heat transfer oil circulation heating system, and stirred at a constant temperature for 2.0 hours (stirrer linear velocity 1.2 m / s). The solution was then filtered while hot under 0.3 MPa pressure, and the filtrate was collected for solvent recovery.

[0042] Third-stage elution: alcohol purification and drying. 5.00 kg of anhydrous ethanol was added to the reactor, and the stirrer was turned on (500 rpm) to form a dispersion system. The temperature was increased to 60 ± 0.5 °C at a rate of 5 °C / min using a programmed temperature control system, and after being kept at this temperature for 0.5 hours, the mixture was filtered while hot under a pressure of 0.3 MPa. The filtrate was collected for solvent recovery. Finally, the eluted polypropylene particles were purged with hot nitrogen (80 °C, flow rate 0.8 m / s) for 1.0 hour to obtain a high-purity polypropylene sample. The test results for ash content and metal ion content are shown in Table 1. Example 2

[0043] The polypropylene powder contains 3.7 ppm titanium, 26.9 ppm magnesium, 45.5 ppm aluminum, and 114.2 ppm ash.

[0044] First-stage elution: Organic solvent elution. 1.000 kg of the above polypropylene powder was placed in a 25L stainless steel reactor with a jacket and filter plate. 3 kg of cyclohexane and 1 kg of n-butanol were added sequentially, and the stirrer was turned on (800 rpm) to form a homogeneous suspension. The temperature was increased to 80±1℃ at a rate of 5℃ / min using a heat transfer oil circulation heating system, and stirred at a constant temperature for 2.0 hours. The mixture was then filtered while hot under a pressure of 0.3 MPa, and the filtrate was collected for solvent recovery.

[0045] Second-stage elution: Deep desorption of the eutectic solvent. Under nitrogen protection (flow rate 0.5 L / min), 0.8 kg of eutectic solvents DES-A and DES-C (mass ratio 1:8) were added to the reactor. The stirrer was turned on (1000 rpm) to form a homogeneous suspension. The temperature was increased to 60±1℃ at a rate of 5℃ / min using a heat transfer oil circulation heating system, and stirred at a constant temperature for 1.0 hour (stirrer blade linear velocity 1.2 m / s). The solution was then filtered while hot under 0.3 MPa pressure, and the filtrate was collected for solvent recovery.

[0046] Third-stage elution: alcohol purification and drying. 5.00 kg of anhydrous ethanol was added to the reactor, and the stirrer was turned on (500 rpm) to form a dispersion system. The temperature was increased to 40 ± 0.5 °C at a rate of 5 °C / min using a programmed temperature control system, and after being kept at this temperature for 1 hour, the mixture was filtered while hot under a pressure of 0.3 MPa. The filtrate was collected for solvent recovery. Finally, the eluted polypropylene particles were purged with hot nitrogen (80 °C, flow rate 0.8 m / s) for 1 hour to obtain a high-purity polypropylene sample. The test results for ash content and metal ion content are shown in Table 1. Example 3

[0047] The polypropylene powder contains 3.7 ppm titanium, 26.9 ppm magnesium, 45.5 ppm aluminum, and 114.2 ppm ash.

[0048] First-stage elution: Organic solvent elution. 1,000 kg of the above polypropylene powder was placed in a 25L stainless steel reactor with a jacket and filter plate. 12 kg of petroleum ether and 1 kg of n-propanol were added sequentially, and the stirrer was turned on (800 rpm) to form a homogeneous suspension. The temperature was increased to 80±1℃ at a rate of 5℃ / min using a heat transfer oil circulation heating system, and stirred at a constant temperature for 2.0 hours. The mixture was then filtered while hot under a pressure of 0.3 MPa, and the filtrate was collected for solvent recovery.

[0049] Second-stage elution: Deep desorption of the eutectic solvent. Under nitrogen protection (flow rate 0.5 L / min), 2.5 kg of eutectic solvents DES-A and DES-C (mass ratio 1:3) were added to the reactor. The stirrer was turned on (1000 rpm) to form a homogeneous suspension. The temperature was increased to 100°C at a rate of 5°C / min using a heat transfer oil circulation heating system, and stirred at a constant temperature for 1.5 hours (stirrer blade linear velocity 1.2 m / s). The solution was then filtered while hot under 0.3 MPa pressure, and the filtrate was collected for solvent recovery.

[0050] Third-stage elution: alcohol purification and drying. 5.00 kg of anhydrous ethanol was added to the reactor, and the stirrer was turned on (500 rpm) to form a dispersion system. The temperature was increased to 50 ± 0.5 °C at a rate of 5 °C / min using a programmed temperature control system, and after being kept at this temperature for 0.8 hours, the mixture was filtered while hot under a pressure of 0.3 MPa. The filtrate was collected for solvent recovery. Finally, the eluted polypropylene particles were purged with hot nitrogen (80 °C, flow rate 0.8 m / s) for 1.0 hour to obtain a high-purity polypropylene sample. The test results for ash content and metal ion content are shown in Table 1. Example 4

[0051] The other operations are the same as in Example 1, except that the eutectic solvents DES-A and DES-C are added during the second-stage elution process, with a mass ratio of 1:2. The test results for ash content and metal ion content are shown in Table 1. Example 5

[0052] The other operations are the same as in Example 1, except that the eutectic solvents DES-A and DES-C are added during the second-stage elution process, with a mass ratio of 1:6. The test results for ash content and metal ion content are shown in Table 1. Example 6

[0053] The other operations are the same as in Example 1, except that the eutectic solvents DES-A and DES-C are added during the second-stage elution process, with a mass ratio of 1:4. The test results for ash content and metal ion content are shown in Table 1. Example 7

[0054] The other operations are the same as in Example 1, except that the eutectic solvents DES-B and DES-D are added during the second-stage elution process, with a mass ratio of 1:4. The test results for ash content and metal ion content are shown in Table 1.

[0055] Comparative Example 1 Polypropylene powder: Titanium content 3.7 ppm, magnesium content 26.9 ppm, aluminum content 45.5 ppm, ash content 114.2 ppm.

[0056] Elution protocol: Take 1.0 kg of the above polypropylene powder, add 10 kg of n-hexane and 2 kg of isopropanol, heat to 80°C, stir rapidly for 2 hours, and filter while hot to remove the eluent. Then add 5.0 kg of ethanol, heat to 60°C, stir rapidly for 0.5 hours, and filter while hot to remove low-boiling-point alcohols. After purging with air while hot for 1 hour, a high-purity polypropylene sample is obtained. The test results of ash content and metal ion content are shown in Table 1.

[0057] Table 1. Test results of ash content and metal ion content in polypropylene Blank group 114.2 3.7 26.9 45.5 97.4 Example 1 15.2 1.2 3.5 5.7 98.0 Example 2 15.5 1.1 3.2 5.4 98.0 Example 3 15.2 1.1 3.8 5.9 98.1 Example 4 10.7 0.7 2.1 4.3 98.4 Example 5 9.1 0.4 1.1 2.8 99.0 Example 6 4.0 0.1 0.2 1.5 99.5 Example 7 12.6 1.0 2.2 5.1 98.1 Comparative Example 1 42.1 1.2 13.7 25.5 97.6 As shown in Table 1, the technical solution provided by this invention can effectively remove ash and metal ions from polypropylene powder, with ash content less than 25 ppm, titanium content <1 ppm, magnesium content <3 ppm, and aluminum content <3 ppm. Therefore, the technical solution provided by this invention can effectively produce high-purity polypropylene products that meet industry standards.

[0058] Compared to the conventional elution method shown in Comparative Example 1, the technical solution provided by this invention can effectively and deeply elute metal ions, with removal rates of up to 97% for titanium, 96% for magnesium, 97% for aluminum, and 92% for ash, all significantly higher than the 60% achieved by conventional methods. Regarding the isotacticity of polypropylene, regardless of the elution method used, a portion of the atactic components in polypropylene can be eluted away. Therefore, compared to the raw polypropylene powder, the isotacticity of all washed polypropylene is improved.

[0059] In each embodiment, the one that achieves the best removal effect of ash and metal ions from polypropylene powder is... Example 6 achieved the lowest possible ash content and other metal content. Example 7, using DES-B and DES-D solvents, had a slightly worse removal effect than the combination of DES-A and DES-C. This is because, through practice, it was found that the combination of DES-A and DES-C had a better ash removal effect than other combinations. In addition, Examples 4 and 5 had slightly worse effects because the ratio of DES-A to DES-C was not controlled to the optimal level as in Example 6. However, their removal effects were still relatively better than those of the other examples.

[0060] The data in Table 1 above shows that the elution method of the present invention can improve isotacticity to a certain extent compared with the prior art. Example 8

[0061] Polypropylene powder: titanium content 18.7 ppm, magnesium content 134.3 ppm, aluminum content 237.5 ppm, ash content 551.1 ppm.

[0062] The other operations are the same as in Example 1, except that the eutectic solvents DES-A and DES-C are used, and their mass ratio is 1:4.

[0063] Comparative Example 2 The other procedures were the same as in Example 1, except that a mixture of 2.0 kg of choline chloride and glycerol (molar ratio 1:2) was added during the second-stage elution process. The test results for ash content and metal ion content are shown in Table 2.

[0064] Comparative Example 3 Polypropylene powder: titanium content 18.7 ppm, magnesium content 134.3 ppm, aluminum content 237.5 ppm, ash content 551.1 ppm.

[0065] Elution protocol: Take 1.0 kg of the above polypropylene powder, add 10 kg of n-hexane and 5 kg of isopropanol, heat to 80°C, stir rapidly for 2 hours, and filter while hot to remove the eluent. Then add 10 kg of n-hexane and 5 kg of isopropanol, heat to 80°C, stir rapidly for 2 hours, and filter while hot to remove the eluent. Add another 10 kg of n-hexane and 5 kg of isopropanol, heat to 80°C, stir rapidly for 2 hours, and filter while hot to remove the eluent. Finally, add 5.0 kg of ethanol, heat to 60°C, stir rapidly for 0.5 hours, and filter while hot to remove low-boiling-point alcohols. After purging with air while hot for 1 hour, a high-purity polypropylene sample is obtained. The test results of ash content and metal ion content are shown in Table 2.

[0066] Table 2 Test results of ash content and metal ion content of polypropylene Blank group 551.1 18.7 134.3 237.5 97.6 Example 8 9.5 1.2 1.4 4.3 98.5 Comparative Example 2 44.0 4.2 18.0 24.0 97.8 Comparative Example 3 119.0 8.1 28.9 51.8 97.8 As shown in Table 2 above, the polypropylene powder has a high ash content (e.g., greater than 500 ppm). This usually indicates that the polypropylene powder was produced due to an abnormality in the polypropylene production unit. This type of polypropylene powder reacts fully with air or water to generate stubborn ash that is difficult to remove. However, a comparison between the above-mentioned embodiments and comparative examples of the present invention shows that Embodiment 8 of the present invention still has a good ash removal effect on polypropylene powder with high ash content. Correspondingly, the effect of using some commonly used eutectic solvents in the prior art, such as Comparative Example 2, is relatively poor and cannot achieve the ideal ash removal effect. It is evident that by using the eutectic solvent with specific components of the present invention, compared with commonly used eutectic solvents in the prior art, it still has a superior deashing effect on powder with high ash content.

[0067] The data from Comparative Example 3 show that even with conventional elution methods and three elution cycles, the residual ash and metal ion content of the polypropylene powder remains high, failing to meet the requirements for downstream applications. This demonstrates that the technical solution provided by this invention achieves efficient removal of stubborn components from high-ash polypropylene powder, solving the technical problems of low removal rates and excessive residues in existing technologies, and possesses significant industrial application value.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A eutectic solvent, characterized in that, Its composition includes at least one of the following four substances: 。 2. The eutectic solvent according to claim 1, characterized in that, It is a mixture of DES-A and DES-C, with a mass ratio of DES-A to DES-C of 1:(2-8).

3. The eutectic solvent according to claim 2, characterized in that, The mass ratio of DES-A to DES-C is 1:(3-6).

4. A method for preparing a eutectic solvent as described in any one of claims 1-3, characterized in that, Includes the following steps: After adding hydrogen bond acceptors and hydrogen bond donors sequentially, stir for 1-2 hours to obtain the final product.

5. A method for deep deashing of polyolefin resins using the eutectic solvent according to any one of claims 1-3 and the eutectic solvent prepared by the preparation method according to claim 4, characterized in that, Includes the following steps: The polyolefin powder is mixed with the elution mobile phase for the first stage of elution. The polyolefin powder after the first stage of elution is mixed with the eutectic solvent and then subjected to the second stage of elution. The polyolefin powder after the second-stage elution treatment is mixed with a low-boiling-point alcohol and subjected to a third-stage elution treatment to achieve deep deashing of the polyolefin resin.

6. The method according to claim 5, characterized in that, The elution mobile phase comprises alkanes and a solvent, wherein the solvent is selected from one or more alcohols, amines, and ethers.

7. The method according to claim 5, characterized in that, The mass ratio of the polyolefin powder to the eutectic solvent is 1:(0.8-2.5).

8. The method according to claim 5, characterized in that, The temperature of the third-stage elution process is 40-60℃, and the time of the third-stage elution process is 0.5-1h.

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