A method for preparing a precipitation-resistant polyolefin material with low metal impurities

Abstract

This invention belongs to the field of polyolefin preparation and relates to a method for preparing a polyolefin material with low metal impurities and resistance to precipitation. The method includes the following steps: (1) adding polyolefin resin raw material and fatty ketone solvent into the extraction vessel of a supercritical extraction device, introducing a gaseous medium into the extraction vessel, adjusting the temperature and pressure of the extraction vessel to make the gaseous medium be in a supercritical state, and treating the polyolefin resin raw material in a supercritical fluid; the fatty ketone solvent is C3-C 10 (1) At least one of the fatty ketone solvents; (2) Cooling and depressurizing to separate the polyolefin resin raw material from the solvent phase and drying it to obtain the polyolefin material with low metal impurities and resistance to precipitation. The method provided by the present invention has high efficiency in removing metal impurities from polyolefins and simultaneously achieves the removal and control of the content of soluble polymers, which significantly improves the purity and precipitation resistance of polyolefin resins.

Description

Technical Field

[0001] This invention belongs to the field of polyolefin preparation, specifically, it relates to a method for preparing a polyolefin material with low metal impurities and resistance to precipitation. Background Technology

[0002] Polyolefin materials such as polyethylene (PE), polypropylene (PP), ethylene-α-olefin copolymers, and ethylene-cycloolefin copolymers (COC) possess excellent mechanical properties, good machinability, and outstanding chemical stability, and are widely used in agriculture, electronics, pharmaceuticals, and construction, playing an irreplaceable role in daily life. However, residual metal impurities in polyolefins can adversely affect the color, electrical properties, and optical properties of the products. Furthermore, metal ions and leached low-molecular-weight polymers may leach out during use, contaminating contact items and affecting usability. Therefore, industries with high purity requirements, such as packaging, medical devices, optical equipment, and electronics, have extremely stringent requirements for the metal and leached content of polyolefin products. Polyolefin materials with low leaching and low metal impurities are currently one of the key directions in polyolefin development and preparation.

[0003] Currently, in industry, complexation adsorption is generally used to treat polyolefin solutions to reduce metal impurities. In practice, the adsorption column containing the deashing adsorbent is typically heated to above 100°C before the polyolefin solution is injected into the column for metal complexation adsorption to remove metal ions. While this method effectively reduces metal impurities in polyolefins, it is only applicable to polyolefin solutions. Except for solution polymerization, which directly yields the polymer solution, polymers obtained through other polymerization methods require dissolution in a large amount of solvent before adsorption and deashing can be performed, making the process relatively complex. For example, CN202210909910.6 describes first impregnating or dissolving polyolefin resin in a hydrocarbon solvent, then adding an acidic reagent for further impregnation or dissolution to obtain a pretreated polyolefin mixture. A complexing agent is then added to this mixture to initiate a metal complexation reaction, followed by elution with an eluent, thereby reducing residual metal impurities in the polyolefin. This process not only fails to effectively remove low molecular weight polymers, but it is also cumbersome, consuming large amounts of solvent and time. Furthermore, it introduces multiple solvents, including hydrocarbon solvents, acidic reagents, metal complexing agents, and eluents, making the removal process complex and solvent recovery difficult. CN202210413155.2 uses the chelating agent triazine to chelate and adsorb metal ions in a polyolefin solution to form a complex. The solution containing the complex is then purified by adsorption using an adsorption column to remove metal impurities from the polyolefin. However, triazine has a high boiling point of 350℃; if elution is incomplete, it may remain in the polyolefin, making removal difficult and posing a risk of contaminating the polyolefin.

[0004] Therefore, developing new methods for preparing polyolefin materials with low leaching and low metal impurity content suitable for industrial production remains one of the urgent problems to be solved in this field.

[0005] Supercritical fluid extraction technology boasts advantages such as strong dissolving power, high efficiency, environmental friendliness, and mild operating conditions, demonstrating excellent application results in polymer purification. CN116217910A utilizes supercritical carbon dioxide fluid to extract most oligomers and tetrahydrofuran from polyesters containing 1,4-butanediol dicarboxylic acid structural units, yielding polyesters with low migration. CN1993385A describes the extraction of olefin polymers using static / flowing supercritical carbon dioxide, finding that polypropylene treated with a combination of flowing supercritical carbon dioxide extraction and static supercritical carbon dioxide treatment exhibits a significant reduction in impurities (mainly low molecular weight oligomers), making it suitable for manufacturing ultra-high purity products. However, this method uses a pressure as high as 65 MPa and does not mention changes in the metal content of the polymer. Patent CN113500053A uses 75% ethanol to purify polypropylene granules under supercritical carbon dioxide conditions, reducing the ash content in polypropylene; however, the moisture introduced during purification is difficult to remove, resulting in low drying efficiency. There is still room for further improvement in the metal impurity removal rate and soluble matter removal efficiency of the methods described in the aforementioned patents. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method for preparing polyolefin materials with low metal impurities and resistance to precipitation. This method is based on supercritical fluid extraction technology, which achieves simultaneous and efficient removal of metal impurities and soluble low molecular weight polymers from polyolefins by selecting a suitable solvent. The aliphatic ketone solvent used has the characteristics of low boiling point, strong solubility, and good diffusion volatility, leaving no more than 0.5 ppm residue in the polyolefin. This avoids the problems of complex solvent recovery and difficulty in removing high-boiling-point chelating agents in existing deashing processes. It has advantages such as simple process, easy operation, high removal efficiency, and low cost, and is applicable to polyolefin products of different forms prepared by various processes.

[0007] This invention provides a method for preparing a precipitation-resistant polyolefin material with low metal impurities, comprising the following steps:

[0008] (1) The polyolefin resin raw material and a fatty ketone solvent are added to the extraction vessel of a supercritical extraction device. A gaseous medium is introduced into the extraction vessel, and the temperature and pressure of the extraction vessel are adjusted to bring the gaseous medium into a supercritical state. The polyolefin resin raw material is then treated in a supercritical fluid. The fatty ketone solvent is C3-C4. 10 At least one of the fatty ketone solvents;

[0009] (2) Cool down and depressurize to separate the polyolefin resin raw material from the solvent phase and dry it to obtain the polyolefin material with low metal impurities and resistance to precipitation.

[0010] This invention provides a method for preparing a precipitation-resistant polyolefin material with low metal impurities. Compared with the prior art, the advantages of this invention are as follows:

[0011] (1) The method provided by the present invention has a wide range of applications and can be used for polyolefin products of different forms and different basic impurity contents prepared by various production processes.

[0012] (2) The method provided by the present invention has high efficiency in removing metal impurities from polyolefins and simultaneously achieves the removal and control of the content of soluble polymers, which significantly improves the purity and precipitation resistance of polyolefin resins.

[0013] (3) The method provided by the present invention avoids the problems of complex solvent recovery and difficulty in removing high-boiling-point chelating agents in traditional deashing processes. The fatty ketone solvents used can be easily removed and will not cause pollution to polyolefin resin.

[0014] (4) The method provided by the present invention is simple to operate, has a short process flow, and uses solvents in a recyclable manner, which will not cause pollution to the environment and is conducive to industrialization and widespread application.

[0015] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0016] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0017] This invention provides a method for preparing a precipitation-resistant polyolefin material with low metal impurities, comprising the following steps:

[0018] (1) The polyolefin resin raw material and a fatty ketone solvent are added to the extraction vessel of a supercritical extraction device. A gaseous medium is introduced into the extraction vessel, and the temperature and pressure of the extraction vessel are adjusted to bring the gaseous medium into a supercritical state. The polyolefin resin raw material is then treated in a supercritical fluid. The fatty ketone solvent is C3-C4. 10 At least one of the fatty ketone solvents;

[0019] (2) Cool down and depressurize to separate the polyolefin resin raw material from the solvent phase and dry it to obtain the polyolefin material with low metal impurities and resistance to precipitation.

[0020] According to the preparation method proposed in this invention, the prepared polyolefin resin has low metal impurities, controllable soluble content, and no risk of introducing new impurities.

[0021] According to the present invention, the fatty ketone solvent is preferably selected from at least one of acetone, butanone, dimethyl butyl ketone, methyl isopropyl ketone, methyl n-butyl ketone, methyl isobutyl ketone and cyclohexanone. More preferably, it is a fatty ketone solvent with a boiling point of 40-95°C at room temperature and atmospheric pressure, specifically selected from at least one of acetone, butanone, dimethyl butyl ketone and methyl isopropyl ketone.

[0022] The amount of the fatty ketone solvent should be as small as possible while ensuring the impurity removal effect. According to a preferred embodiment of the present invention, the mass ratio of the fatty ketone solvent to the polyolefin resin raw material is (0.5-40):1, and more preferably (2-20):1.

[0023] The method of the present invention is carried out in the presence of a supercritical fluid, and various gaseous media that provide supercritical conditions conventional in the art can be used. Preferably, the gaseous medium is at least one of carbon dioxide, ethane, propane and nitrogen dioxide, and correspondingly, the supercritical fluid is at least one of supercritical carbon dioxide, supercritical ethane, supercritical propane and supercritical nitrogen dioxide.

[0024] Once the gas medium is determined, the corresponding temperature and pressure conditions can also be determined. Specifically, the temperature of the extraction vessel is adjusted to 60-140℃ and the pressure to 5-25MPa; the treatment time of the polyolefin resin raw material in the supercritical fluid is 2-10 hours, preferably 4-8 hours.

[0025] To further enhance the diffusion and solubility of the fatty ketone solvent in the polymer network, step (1) preferably includes adding a co-solvent to the extraction vessel, i.e., using a mixed solvent, wherein the co-solvent is one of an alkane solvent and a haloalkane solvent with a boiling point of 20-90℃; preferably at least one of n-pentane, n-hexane, cyclohexane, petroleum ether, dichloromethane, trichloromethane and dichloroethane.

[0026] According to a preferred embodiment of the present invention, the mass ratio of the fatty ketone solvent to the co-solvent is (0.2-3):1, more preferably (0.3-1):1.

[0027] The method proposed in this invention is applicable to processing polyolefin resins in different states obtained by various polymerization methods, and has good universality and significant impurity removal effect.

[0028] Specifically, the resin in the polyolefin resin raw material includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene-α-olefin copolymer, ethylene-cyclic olefin copolymer, propylene-α-olefin copolymer, and propylene-cyclic olefin copolymer. The α-olefin typically refers to C3-C4. 12 olefins.

[0029] In particular, the method of the present invention is applicable to the purification of solid polyolefin resins, wherein the polyolefin resin raw material can be in any solid form, including but not limited to powder, granules, flakes, or other shapes. Furthermore, the metallic impurities contained in the polyolefin resin raw material include one or more elements selected from magnesium, aluminum, calcium, titanium, sodium, chromium, iron, and zinc.

[0030] According to the method of the present invention, after the solvent phase is separated from the polyolefin resin raw material, it can be recovered by distillation and recycled. The term "solvent phase" in this invention refers to all solvents in the system. When only fatty ketone solvents are used, the "solvent phase" refers to the fatty ketone solvents; when a mixed solvent of fatty ketone solvents and co-solvents is used, the "solvent phase" refers to the mixed solvent.

[0031] The present invention does not particularly limit the drying conditions in step (2), as long as the residual solvent phase is evaporated as cleanly as possible. Preferably, the drying conditions include vacuum drying at 90-120°C for 2-10 hours.

[0032] The method of the present invention has no significant effect on the weight of the polyolefin resin raw material. After supercritical treatment and drying, the weight of the obtained polyolefin resin is reduced by 0-2 wt% compared with that before treatment.

[0033] According to the method of the present invention, the metal impurity content of the low-metal-impurity resistant polyolefin material obtained after treatment is not more than 20 ppm, the residual amount of fatty ketone solvents is not more than 0.5 ppm, and the content of solubles is less than 0.2 wt%. The content of solubles is tested according to the standard GB / T 5009.58-2003.

[0034] Normally, the method of the present invention can reduce the impurities in polyolefin resin raw materials to the expected standard by performing it once. If necessary, the above process can be repeated 1-2 times to further reduce the content of metal impurities and soluble substances in polyolefin materials.

[0035] Compared with polyolefin resins that have only been treated once: the metal impurity content in resins treated twice will be further reduced by 0-2 ppm, and the soluble matter removal efficiency will be further improved by 0-3%; the metal impurity content in resins treated three times will be further reduced by 0-3 ppm, and the soluble matter removal efficiency will be further improved by 0-5%.

[0036] The present invention will be further described below with reference to the embodiments, but the scope of the present invention is not limited to these embodiments.

[0037] The following test methods were used in the following examples and comparative examples:

[0038] Metal content in polyolefins: After digestion, the polyolefin samples were tested using an inductively coupled plasma atomic emission spectrometer (ICP) model Agilent 8900. The tested metal elements included Li, Be, B, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Sr, Zr, Mo, Cd, In, Sn, Sb, Te, Ba, Tl, Pb, and Bi, totaling 32 elements.

[0039] The content of residual solvent components in polyolefins is determined according to the VDA277 test standard of the German Association of the Automotive Industry.

[0040] Content of soluble low molecular weight polymers in polyolefins: According to the standard test of GB / T 5009.58-2003, weigh about 2.00g of sample into a flask with a 250mL reflux condenser, add 100mL of n-hexane, connect the condenser tube, heat and reflux in an 80℃ water bath for 2h, immediately filter with rapid qualitative filter paper, wash the filter and sample with a small amount of n-hexane, combine the washings and filtrate, then put the n-hexane into a small bottle of a pre-concentrated concentrator, concentrate and recover the n-hexane, dry the residue at 100-105℃ for 2h, cool in a desiccator for 30min, and weigh.

[0041] Example 1

[0042] 5g of polyethylene granules and 40g of methyl isopropyl ketone were added to the extraction vessel of a supercritical fluid extraction apparatus. Carbon dioxide was injected, and the pressure was maintained at 12MPa. After treatment at 90℃ for 6 hours, the mixture was cooled and depressurized to separate the polyethylene from the methyl isopropyl ketone. The resulting polyethylene was then vacuum-dried at 90℃ for 5 hours. The treated polyethylene contained 12.4ppm of metal (73% metal removal efficiency), 0.11wt% of soluble matter (83% soluble matter removal efficiency), and 0.2ppm of residual methyl isopropyl ketone.

[0043] Example 2

[0044] 5g of polyethylene granules and 20g of methyl isopropyl ketone were added to the extraction vessel of a supercritical fluid extraction apparatus. Carbon dioxide was injected, and the pressure was maintained at 14MPa. After treatment at 100℃ for 4 hours, the mixture was cooled and depressurized to separate the polyethylene from the methyl isopropyl ketone. The resulting polyethylene was then vacuum dried at 90℃ for 5 hours. The treated polyethylene contained 12.9ppm of metal (72% metal removal efficiency), 0.12wt% of soluble matter (82% soluble matter removal efficiency), and 0.2ppm of residual methyl isopropyl ketone.

[0045] Example 3

[0046] The polyethylene granules treated in Example 1 were subjected to a second treatment. 5g of the treated polyethylene granules and 20g of methyl isopropyl ketone were added to the extraction vessel of a supercritical fluid extraction apparatus. Carbon dioxide was injected, and the pressure was maintained at 12MPa. After treatment at 90°C for 6 hours, the mixture was cooled and depressurized to separate the polyethylene from the methyl isopropyl ketone. The resulting polyethylene was then vacuum-dried at 90°C for 5 hours. The treated polyethylene contained 11.7 ppm of metal (75% metal removal efficiency), 0.10 wt% of soluble matter (84% soluble matter removal efficiency), and 0.2 ppm of residual methyl isopropyl ketone.

[0047] Example 4

[0048] 5g of polypropylene granules and 50g of methyl isopropyl ketone were added to the extraction vessel of a supercritical fluid extraction apparatus. Carbon dioxide was injected, and the pressure was maintained at 14MPa. After treatment at 90℃ for 5 hours, the mixture was cooled and depressurized to separate the polypropylene from the methyl isopropyl ketone. The resulting polypropylene was then vacuum dried at 90℃ for 6 hours. The metal content in the treated polypropylene was 10.4ppm, with a metal removal efficiency of 75%; the soluble matter content was 0.14wt%, with a soluble matter removal efficiency of 79%; and the residual methyl isopropyl ketone was 0.2ppm.

[0049] Example 5

[0050] 5g of polyethylene granules and 40g of acetone were added to the extraction vessel of a supercritical fluid extraction apparatus. Carbon dioxide was injected, and the pressure was maintained at 12MPa. After treatment at 90℃ for 6 hours, the mixture was cooled and depressurized to separate the polyethylene from the acetone. The resulting polyethylene was then vacuum-dried at 90℃ for 5 hours. The metal content in the treated polyethylene was 15.4ppm, with a metal removal efficiency of 67%. The soluble matter content was 0.18wt%, with a soluble matter removal efficiency of 72%. Acetone was not detected.

[0051] Example 6

[0052] 5g of polyethylene granules and 40g of dimethyl ethyl ketone (DME) were added to the extraction vessel of a supercritical fluid extraction apparatus. Carbon dioxide was injected, and the pressure was maintained at 14MPa. After treatment at 100℃ for 4 hours, the mixture was cooled and depressurized to separate the polyethylene from the DME. The resulting polyethylene was then vacuum-dried at 90℃ for 5 hours. The treated polyethylene contained 14.4 ppm of metal (69% metal removal efficiency), 0.14 wt% of soluble matter (78% soluble matter removal efficiency), and 0.1 ppm of residual DME.

[0053] Example 7

[0054] 5g of polyethylene granules, 20g of n-hexane, and 20g of methyl isopropyl ketone were added to the extraction vessel of a supercritical fluid extraction apparatus. Carbon dioxide was injected, and the pressure was maintained at 12MPa. After treatment at 90℃ for 6 hours, the mixture was cooled and depressurized to separate the polyethylene from the methyl isopropyl ketone and n-hexane. The resulting polyethylene was then vacuum-dried at 90℃ for 5 hours. The treated polyethylene contained 10.2 ppm of metal (78% metal removal efficiency), 0.10 wt% of soluble matter (85% soluble matter removal efficiency), 0.2 ppm of residual methyl isopropyl ketone, and no detectable n-hexane.

[0055] Example 8

[0056] 5g of polyethylene granules, 20g of dichloromethane, and 20g of methyl isopropyl ketone were added to the extraction vessel of a supercritical fluid extraction apparatus. Carbon dioxide was injected, and the pressure was maintained at 12MPa. After treatment at 90℃ for 6 hours, the mixture was cooled and depressurized to separate the polyethylene from the dichloromethane and methyl isopropyl ketone. The resulting polyethylene was then vacuum-dried at 90℃ for 5 hours. The treated polyethylene contained 10.9 ppm of metal (76% metal removal efficiency), 0.09 wt% of soluble matter (86% soluble matter removal efficiency), and 0.1 ppm of residual methyl isopropyl ketone. Dichloromethane was not detected.

[0057] Example 9

[0058] 5g of polyethylene granules, 20g of chloroform, and 20g of dimethyl ethyl ketone (DME) were added to the extraction vessel of a supercritical fluid extraction apparatus. Carbon dioxide was injected, and the pressure was maintained at 12MPa. After treatment at 90℃ for 6 hours, the mixture was cooled and depressurized to separate the polyethylene from the DME and chloroform. The resulting polyethylene was then vacuum-dried at 90℃ for 5 hours. The treated polyethylene contained 12.0 ppm of metal (74% metal removal efficiency), 0.08 wt% of soluble matter (88% soluble matter removal efficiency), and no chloroform or DME was detected.

[0059] Example 10

[0060] 5g of polypropylene granules, 20g of butanone (MEK), and 20g of methyl isopropyl ketone (MCO) were added to the extraction vessel of a supercritical fluid extraction apparatus. Carbon dioxide was injected, and the pressure was maintained at 12MPa. After treatment at 90℃ for 6 hours, the mixture was cooled and depressurized to separate the polypropylene from MEK and MCO. The polypropylene was then vacuum-dried at 90℃ for 5 hours. The treated polypropylene contained 9.3 ppm of metal (78% metal removal efficiency), 0.12 wt% of soluble matter (82% soluble matter removal efficiency), and 0.1 ppm of residual MCO. MEK was not detected.

[0061] Example 11

[0062] 5g of cyclic olefin copolymer granules, 10g of n-hexane, and 30g of methyl isobutyl ketone were added to the extraction vessel of a supercritical fluid extraction apparatus. Carbon dioxide was injected, and the pressure was maintained at 12MPa. After treatment at 60℃ for 6 hours, the mixture was cooled and depressurized to separate the cyclic olefin copolymer from the n-hexane and methyl isobutyl ketone. The resulting cyclic olefin copolymer was then vacuum dried at 90℃ for 5 hours. The metal content in the treated cyclic olefin copolymer was 10.1ppm, with a metal removal efficiency of 83%. The residual methyl isopropyl ketone was 0.1ppm, and n-hexane was not detected.

[0063] Example 12

[0064] 5g of polyethylene granules and 40g of methyl isopropyl ketone were added to the extraction vessel of a supercritical fluid extraction apparatus. Propane was injected, and the pressure was maintained at 6MPa. After treatment at 100℃ for 6 hours, the mixture was cooled and depressurized to separate the polyethylene from the methyl isopropyl ketone. The resulting polyethylene was then vacuum dried at 90℃ for 5 hours. The treated polyethylene contained 10.0ppm of metal (78% metal removal efficiency), 0.05wt% of soluble matter (92% soluble matter removal efficiency), and 0.2ppm of residual methyl isopropyl ketone.

[0065] Comparative Example 1

[0066] 5g of polyethylene granules and 40g of dimethyl ethyl ketone were added to a flask with a 1L reflux condenser and heated under reflux in an oil bath at 100°C for 4 hours. The mixed solution containing the resin raw materials was filtered, and the resulting polyethylene was vacuum dried at 90°C for 5 hours. The treated polyethylene contained 41.2 ppm of metal (metal removal efficiency of 10%), 0.45 wt% of soluble matter (soluble matter removal efficiency of 31%), and 0.2 ppm of residual dimethyl ethyl ketone.

[0067] Comparative Example 2

[0068] Without introducing fatty ketone solvents, 5g of polyethylene granules were directly added to the extraction vessel of a supercritical fluid extraction apparatus. Carbon dioxide was injected, and the pressure was maintained at 12MPa. After treatment at 90℃ for 6 hours, the mixture was cooled and depressurized. The resulting polyethylene was then vacuum-dried at 90℃ for 5 hours. The treated polyethylene contained 43.3ppm of metal (6% metal removal efficiency) and 0.38wt% of soluble matter (41% soluble matter removal efficiency).

[0069] Comparative Example 3

[0070] The solvent in Example 1 was replaced with ethanol. The treated polyethylene contained 28.8 ppm of metal, with a metal removal efficiency of 37%, and 0.23 wt% of soluble matter, with a soluble matter removal efficiency of 65%.

[0071] Comparative Example 4

[0072] The solvent in Example 1 was replaced with n-hexane. The treated polyethylene contained 39.6 ppm of metal, with a metal removal efficiency of 14%, and 0.12 wt% of soluble matter, with a soluble matter removal efficiency of 81%.

[0073] After treatment with the method provided by this invention, the content of metal impurities and soluble substances in different types and states of polyolefin resins were significantly reduced, and the precipitation resistance was improved. Furthermore, the aliphatic ketone solvents used left almost no residue in the resin, ensuring the high purity of the polyolefins. Compared to Example 2, Comparative Example 1 did not use supercritical fluid, and the removal effect of aliphatic ketone solvents on metal impurities and soluble substances was significantly reduced. In Comparative Example 2, the content of metal impurities and soluble substances in the polyolefin resin treated only with supercritical fluid was relatively high, indicating that aliphatic ketone solvents can promote the dissolution and extraction of metal ions and soluble substances. Comparative Example 3 used ethanol solvent, a solvent used in the prior art, and the removal effect of metal impurities and the efficiency of soluble substance removal were worse than those of the aliphatic ketone solvents of this invention. Comparative Example 4 used only a co-solvent, and the removal rate of metal impurities was significantly lower than that of Example 1.

[0074] The above examples and comparative examples verify that the preparation method of the low-metal-impurity resistant polyolefin material provided by the present invention has significant effects. Based on supercritical fluid-assisted extraction technology and combined with fatty ketone solvents, it can effectively remove metal impurities and soluble substances from various polyolefins in different states, and the solvent is almost left behind. This makes up for the shortcomings of existing deashing processes, such as narrow applicability, long process flow, complex solvent recovery, and difficulty in removing high-boiling-point chelating agents.

[0075] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

[0076] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A method for preparing a precipitation-resistant polyolefin material with low metal impurities, comprising the following steps: (1) The polyolefin resin raw material and a fatty ketone solvent are added to the extraction vessel of a supercritical extraction device. A gaseous medium is introduced into the extraction vessel, and the temperature and pressure of the extraction vessel are adjusted to bring the gaseous medium into a supercritical state. The polyolefin resin raw material is then treated in a supercritical fluid. The fatty ketone solvent is C3-C4. 10 At least one of the fatty ketone solvents; (2) Cool down and depressurize to separate the polyolefin resin raw material from the solvent phase and dry it to obtain the polyolefin material with low metal impurities and resistance to precipitation.

2. The preparation method according to claim 1, wherein, The fatty ketone solvent is selected from at least one of acetone, butanone, butanedione, methyl isopropyl ketone, methyl n-butyl ketone, methyl isobutyl ketone, and cyclohexanone; preferably selected from at least one of acetone, butanone, butanedione, and methyl isopropyl ketone.

3. The preparation method according to claim 1, wherein, The mass ratio of the fatty ketone solvent to the polyolefin resin raw material is (0.5-40):1, preferably (2-20):

1.

4. The preparation method according to claim 1, wherein, The gaseous medium is at least one of carbon dioxide, ethane, propane, and nitrogen dioxide, and correspondingly, the supercritical fluid is at least one of supercritical carbon dioxide, supercritical ethane, supercritical propane, and supercritical nitrogen dioxide.

5. The preparation method according to claim 4, wherein, Adjust the temperature of the extraction vessel to 60-140℃ and the pressure to 5-25MPa; treat the polyolefin resin raw material in supercritical fluid for 2-10 hours, preferably 4-8 hours.

6. The preparation method according to claim 1, wherein, Step (1) further includes adding a co-solvent to the extraction vessel, wherein the co-solvent is one of an alkane solvent and a haloalkane solvent with a boiling point of 20-90℃; preferably at least one of n-pentane, n-hexane, cyclohexane, petroleum ether, dichloromethane, trichloromethane and dichloroethane.

7. The preparation method according to claim 6, wherein, The mass ratio of the cosolvent to the fatty ketone solvent is (0.2-3):1, preferably (0.3-1):

1.

8. The preparation method according to claim 1, wherein, The resin in the polyolefin resin raw material includes at least one of polyethylene, polypropylene, ethylene-α-olefin copolymer, ethylene-cyclic olefin copolymer, propylene-α-olefin copolymer, and propylene-cyclic olefin copolymer.

9. The preparation method according to claim 1, wherein, The polyolefin resin raw material is solid, preferably in powder, granule, flake, or other form.

10. The preparation method according to claim 1, wherein, After the solvent phase is separated from the polyolefin resin raw material, it is recovered by distillation and reused.

11. The preparation method according to claim 1, wherein, The drying conditions include vacuum drying at 90-120°C for 2-10 hours.

12. The preparation method according to any one of claims 1-11, wherein, The low-metal-impurity, precipitation-resistant polyolefin material has a metal impurity content of no more than 20 ppm, a fatty ketone solvent residue of no more than 0.5 ppm, and a soluble content of less than 0.2 wt%. The soluble content is tested according to the standard GB / T 5009.58-2003.