Process for purification of polyolefin feedstock

Abstract

The invention relates to the field of preparation of polymer materials, and discloses a purification method of a polyolefin raw material. The method comprises the following steps: S1, carrying out first mixing on a polyolefin raw material and a good solvent to obtain a polyolefin dilute solution; wherein the dosage of the polyolefin raw material and the good solvent enables the content of polyolefin in every 100 mL of the polyolefin dilute solution to be 0.001-1 g; s2, carrying out second mixing on the polyolefin dilute solution and a precipitant; s3, carrying out third mixing on the solid-phase material in the second mixed material obtained in S2 and a dispersing agent to obtain a dispersion liquid; and S4, mixing the dispersion liquid obtained in S3 with a chelating reagent and an acidic reagent for reaction, and then separating out a solid-phase material from the reaction liquid. According to the method, polyolefin is condensed by adopting a dilute solution condensation method, so that the wrapping of the polyolefin on ash impurities such as metal compounds in the condensation process is reduced, and the mass transfer effect in the washing and deliming process is improved.

Description

Technical Field

[0001] This invention relates to the field of polymer material preparation, and more specifically, to a method for purifying polyolefin raw materials. Background Technology

[0002] With my country's economic development, the demand for high-end polyolefin materials is increasing, such as POE elastomers prepared by copolymerizing ethylene, propylene, and various α-olefins and cyclic olefins, cyclic olefin polymers (COC), linear low-density polyethylene (LLDPE), and ethylene propylene diene monomer (EPDM). These materials possess high volume resistivity, low dielectric constant, excellent optical properties, and outstanding heat and chemical resistance, making them promising for applications in electrical engineering, high-end optics, medical packaging, and medical implants. However, the residual catalyst ash content in polyolefins directly affects their appearance, dielectric, and optical properties, and can also cause degradation and reduce biocompatibility during processing, thus limiting their applications. Therefore, the removal of residual catalysts from polyolefin materials is of great significance for their high-end applications.

[0003] Currently, deashing methods for polyolefins mainly include chelation adsorption and solvent washing extraction. Compared to chelation adsorption, which requires the design and manufacture of specialized adsorbents, solvent washing extraction is simpler to operate. For example, CN107417796A discloses a deashing process that sequentially washes water-insoluble polymers with acid and alkali water to remove ash, and CN115124635A discloses a deashing process that sequentially washes polyolefins with hydrocarbon solvents, acidic reagents, chelating reagents, and elution reagents. However, in the washing process, the contact area between polyolefin particles and the detergent is very limited, and the large number of metal ions encapsulated inside the polyolefin particles are difficult to extract and wash away. Therefore, it is often necessary to first use a large amount of good solvent to swell or dissolve the polyolefin particles before washing. At the same time, in order to enhance the washing effect, multiple washings are generally required to achieve the purpose of deashing. This method has the problems of many operation steps, long time consumption, and large solvent consumption. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of limited contact area between polyolefin particles and detergents in existing technologies, making it difficult to extract and wash away the large number of metal ions encapsulated inside the polyolefin particles, resulting in poor deashing effect and complex operation steps. This invention provides a purification method for polyolefin raw materials. This method first uses a dilute solution coagulation method to coagulate the polyolefin, reducing the encapsulation of metal compounds and other ash impurities by the polyolefin during coagulation, thus improving the mass transfer effect during washing and deashing. The resulting fine polyolefin particles or loose fragments are highly dispersed and have a high specific surface area. Therefore, during further washing with acidic and chelating reagents, the detergent fully contacts the surface and interior of the polyolefin, allowing for the chelation and extraction removal of a large number of metal compounds, resulting in purified polyolefin. This method does not contaminate the initial polyolefin solvent, the detergent can be reused, reducing energy consumption for subsequent reagent separation, and is simple to operate, time-saving, easy to separate, and low in cost.

[0005] To achieve the above objectives, the present invention provides a method for purifying polyolefin raw materials, wherein the method includes the following steps:

[0006] S1. The polyolefin raw material and a good solvent are mixed for the first time to obtain a dilute polyolefin solution; wherein the amount of polyolefin raw material and good solvent used is such that the content of polyolefin in each 100 mL of dilute polyolefin solution is 0.001-1 g.

[0007] S2. Mix the dilute polyolefin solution and the precipitant for the second time;

[0008] S3. The solid material and dispersant in the second mixture obtained in S2 are mixed in a third step to obtain a dispersion.

[0009] S4. The dispersion obtained in S3 is mixed with a chelating reagent and an acidic reagent and reacted, and then the solid phase material is separated from the reaction solution.

[0010] The beneficial effects of the present invention through the above technical solution include at least the following:

[0011] This invention employs a dilute solution coagulation method to greatly reduce the encapsulation of metal compound residues during the coagulation process of polyolefins, resulting in polymer particles with a high specific surface area, thereby ensuring that the metal compound residues are mainly enriched on the surface of the polyolefin.

[0012] The polyolefin fine particles or loose debris formed by the coagulation of dilute solutions are highly dispersed and have a large specific surface area. They can fully contact the detergent in the subsequent washing and deashing process, enhance the mass transfer process, and improve the removal effect.

[0013] The present invention employs a process of coagulation followed by washing and deashing, which can avoid excessive contamination of polyolefin solvents during the washing process and reduce the difficulty of subsequent solvent separation.

[0014] The compound detergent used in this invention can be reused, avoiding the huge material consumption caused by the inability to reuse the adsorbent in the adsorption deashing method. Detailed Implementation

[0015] 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.

[0016] This invention provides a method for purifying polyolefin raw materials, wherein the method includes the following steps:

[0017] S1. The polyolefin raw material and a good solvent are mixed for the first time to obtain a dilute polyolefin solution; wherein the amount of polyolefin raw material and good solvent used is such that the content of polyolefin in each 100 mL of dilute polyolefin solution is 0.001-1 g.

[0018] S2. Mix the dilute polyolefin solution and the precipitant for the second time;

[0019] S3. The solid material and dispersant in the second mixture obtained in S2 are mixed in a third step to obtain a dispersion.

[0020] S4. The dispersion obtained in S3 is mixed with a chelating reagent and an acidic reagent and reacted, and then the solid phase material is separated from the reaction solution.

[0021] This invention utilizes a good solvent to prepare or dilute a polyolefin solution, then mixes the dilute polyolefin solution with a precipitant. The polyolefin rapidly agglomerates to form highly dispersed fine particles or loose debris with a high specific surface area. These high-specific-surface-area polyolefin fine particles or loose debris are then neutralized and mixed with a dispersant to disperse them. A chelating agent and an acidic reagent are further added. After a period of time, solid-liquid separation and drying are performed to obtain the purified polyolefin product. This method utilizes dilute solution agglomeration to obtain highly dispersed polyolefin fine particles with a very large specific surface area, significantly reducing the content of internally encapsulated metal compounds in the polyolefin. These compounds are primarily located on the surface of the polyolefin, allowing for sufficient contact with reagents during washing and deashing, improving mass transfer efficiency, and effectively removing metal ash from the polyolefin to obtain a polyolefin product with very low metal content. Simultaneously, this method does not contaminate the initial good polyolefin solvent, and the chelating and acidic reagents can be reused, reducing energy consumption for subsequent reagent separation. The entire process is simple to operate, time-efficient, easy to separate, and low in cost.

[0022] This invention does not particularly limit the type of polyolefin raw material. The method provided by this invention is applicable to any type of polyolefin raw material. In a preferred embodiment of this invention, the polyolefin raw material is selected from at least one of cyclic olefin copolymer raw materials, ethylene propylene diene monomer (EPDM) rubber raw materials, and linear low-density polyethylene raw materials.

[0023] This invention does not impose any particular restrictions on the types of good solvents and precipitants. Based on the type of polyolefin raw material, the basic principle of similar compatibility is used to select good solvents and precipitants. The selection of good solvents and precipitants should meet the following requirements: good solvents and precipitants can be miscible or have a large solubility, and the two can form a homogeneous phase, and enable polyolefins to aggregate into highly dispersed fine particles or loose debris.

[0024] According to the present invention, preferably, the good solvent is selected from at least one of toluene, cyclohexane and hexane.

[0025] According to the present invention, preferably, the precipitant is selected from ethanol and / or acetone.

[0026] In a preferred embodiment of the present invention, when the polyolefin raw material is a cyclic olefin copolymer raw material, the good solvent is toluene, and the precipitant is selected from ethanol and / or acetone; when the polyolefin raw material is ethylene propylene diene monomer (EPDM) rubber raw material, the good solvent is cyclohexane, and the precipitant is ethanol; when the polyolefin raw material is linear low-density polyethylene raw material, the good solvent is hexane, and the precipitant is acetone.

[0027] The inventors have discovered that the method provided by this invention exhibits better purification effects on cyclic olefin copolymer (COC) raw materials, ethylene propylene diene monomer (EPDM) raw materials, or linear low-density polyethylene (LLDPE) raw materials than other types of polyolefin raw materials when using preferred solvents and precipitants. The method provided by this invention is particularly effective for cyclic olefin copolymer raw materials.

[0028] In a preferred embodiment of the present invention, the cyclic olefin copolymer (COC) raw material has a weight-average molecular weight of 20,000-150,000 g / mol, a molecular weight distribution coefficient of 1.2-3, a glass transition temperature of 50-200℃, and a molar content of structural units derived from norbornene in the cyclic olefin copolymer (COC) of 30-80%. The method provided by the present invention has a better purification effect on cyclic olefin copolymer raw materials that meet these conditions.

[0029] To obtain a cyclic olefin copolymer raw material that meets the aforementioned conditions, in a preferred embodiment of the present invention, the preparation method of the cyclic olefin copolymer raw material includes: mixing ethylene and norbornene in the presence of a catalyst, a co-catalyst, and a solvent for a polymerization reaction; wherein the catalyst is a metallocene catalyst (rac-[Et(Ind)2]ZrCl2 catalyst), the co-catalyst is methylaluminoxane, and the solvent is toluene. When preparing the cyclic olefin copolymer raw material, the molar ratio of ethylene to norbornene is 1:(8-12), and the weight ratio of norbornene to toluene is 1:(7-11); the polymerization reaction temperature is 50-150℃, the pressure is 1-3 MPaG, and the time is 25-40 min; based on a volume of 1 L of the obtained mixture, the catalyst content is (5-7) × 10⁻⁶. -5 mol; the amount of catalyst is calculated as Zr, the amount of co-catalyst is calculated as Al, and the molar ratio of co-catalyst to catalyst is (1000-2000):1.

[0030] To further accelerate the formation of a stable dilute solution from the polymer, in a preferred embodiment, the first mixing in S1 is carried out under heating conditions; more preferably, the temperature of the first mixing is 40-100°C.

[0031] To promote a more thorough formation of a stable dilute solution of polyolefin, the first mixing is preferably carried out under stirring conditions, which can be done by magnetic stirring or mechanical stirring, with a stirring speed of 50-1000 rpm and a stirring time of 0.5-10 h.

[0032] In S2, the present invention does not have any particular restrictions on the second mixing method. The polyolefin dilute solution can be poured directly into the precipitant all at once, or the polyolefin dilute solution can be added to the precipitant drop by drop.

[0033] In order to further promote the rapid aggregation of polyolefins into highly dispersed fine particles or loose debris with a high specific surface area, preferably, in S2, the amount of the precipitant is such that the volume ratio of the precipitant to the dilute polyolefin solution is (1-100):1.

[0034] In S2, in order to further improve the solvent removal efficiency, in a preferred case, the temperature of the second mixing is less than or equal to the boiling point of the precipitant, and the temperature of the second mixing is preferably 20-50°C.

[0035] To further promote the rapid aggregation of polyolefins into highly dispersed fine particles or loose debris with a high specific surface area, the second mixing is preferably carried out under stirring conditions, with a stirring speed of less than or equal to 1000 rpm, preferably 100-600 rpm; and a stirring time of less than or equal to 60 min, preferably 1-30 min.

[0036] According to the present invention, after the dilute polyolefin solution and the precipitant are mixed a second time, the polyolefin agglomerates in the second mixture to form highly dispersed fine particles or loose debris with a high specific surface area. Solid-liquid separation is required, and the separated solid material, i.e., the fine particles or loose debris, is dispersed in a dispersion liquid for subsequent ash and impurity removal. The present invention does not particularly limit the method of solid-liquid separation; conventional solid-liquid separation methods in the art can be used, such as filtration.

[0037] The present invention does not impose any particular limitation on the amount of dispersion, as long as it can cover the fine polyolefin particles or loose debris. In order to make the fine particles or loose debris more fully and uniformly dispersed, so that the fine particles or loose debris in the dispersion can come into more sufficient contact with the chelating agent and acidic agent in the subsequent deashing process, preferably, in S3, the amount of the dispersant is such that the weight ratio of the dispersant to the solid material is (30-100):1.

[0038] The present invention does not impose any particular restrictions on the type of dispersant, as long as it does not dissolve polyolefins but can dissolve metal complexes formed by the reaction of deashing reagents (chelating reagents and acidic reagents) with metal compounds. The dispersant can be selected from alcohols, preferably from at least one of C1-C4 monohydric alcohols, such as methanol, ethanol, isopropanol, n-propanol and butanol.

[0039] The present invention does not impose any particular restrictions on the temperature and time of the third mixing, as long as the fine particles or loose debris can be fully and uniformly dispersed in the dispersant.

[0040] To further enhance the effect of the chelating agent on the metal compounds in the polyolefin raw material, preferably, in S4, the amount of the chelating agent is such that the molar equivalent ratio of the chelating agent to the metal compounds in the polyolefin raw material is (0.1-10):1, more preferably (1-5):1.

[0041] To further remove metal compounds from polyolefin raw materials, preferably, the volume ratio of the chelating agent to the acidic agent is (0.1-10):1, more preferably (0.5-5):1.

[0042] This invention does not impose any particular restrictions on the types of chelating reagents and acidic reagents, as long as the acidic reagents and chelating reagents can chelate and extract the metal compounds.

[0043] According to the present invention, preferably, the chelating agent is a β-dicarbonyl compound, preferably at least one of acetylacetone, benzoylacetone, dibenzoylacetone and trifluoroacetylacetone, and more preferably acetylacetone and / or benzoylacetone.

[0044] According to the present invention, the acidic reagent may be selected from inorganic acids and / or organic acids; preferably, the inorganic acid is selected from at least one of sulfuric acid, hydrochloric acid and nitric acid, and the organic acid is selected from at least one of formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid and nonanoic acid.

[0045] Furthermore, the acidic reagent is selected from at least one of sulfuric acid, hydrochloric acid, nitric acid, formic acid, and acetic acid.

[0046] This invention does not impose any particular restrictions on the method of adding chelating reagents and acidic reagents; they can be added directly or prepared as a solvent using a gel solvent. Acidic reagents and chelating reagents can be added simultaneously or sequentially.

[0047] To more effectively remove metal compounds, preferably, in S4, the reaction temperature is 50-200℃, more preferably 60-120℃; the reaction pressure is 0.1-1MPa, more preferably 0.12-0.3MPa; and the time is 0.5-12h, more preferably 0.5-5h.

[0048] To more effectively remove metal compounds, the reaction is preferably carried out under stirring at a speed of 50-1000 rpm, more preferably 400-800 rpm.

[0049] After the metal compound reacts fully with the chelating agent and the acidic reagent, the purified polyolefin product can be obtained by separating the solid phase material from the reaction solution. This invention does not particularly limit the method for separating the solid phase material from the reaction solution; conventional solid-liquid separation methods in the art can be used. Preferably, the separation method includes: filtering and drying the reaction solution. Filtration can be performed by centrifugal filtration, positive pressure filtration, or negative pressure filtration; drying can be performed by vacuum heating. In a preferred embodiment, the heating temperature is 40-100°C, and the time is 5-72 hours.

[0050] The present invention will be described in detail below through examples and comparative examples. Unless otherwise specified, the methods used in the following examples are conventional; the reagents and materials used are commercially available unless otherwise specified.

[0051] Preparation Example

[0052] This preparation example illustrates the preparation method of cyclic olefin copolymer (COC) raw materials.

[0053] Preparation of raw material solution: Preparation of toluene reaction solution for cyclic olefin polymer (COC): 10g of norbornene was dissolved in 90g of purified toluene and added to the polymerization reactor. The reactor temperature was raised to 60℃, and then high-purity ethylene (dehydrated and deoxygenated) was introduced into the reactor. The molar ratio of ethylene to norbornene was 1:10. After the pressure inside the reactor reached 1MPa, rac-[Et(Ind)2]ZrCl2 catalyst and methylaluminoxane (MAO) co-catalyst were added. Based on a total volume of 1L for norbornene, ethylene, toluene, catalyst, and co-catalyst, the catalyst dosage was 6×10⁻⁶. -5 The amount of catalyst used was calculated as Zr, and the amount of co-catalyst used was calculated as Al. The molar ratio of co-catalyst to catalyst was 2000:1. After reacting for 30 min, a COC toluene reaction solution was obtained. The COC content in 100 mL of the solution was determined to be 8 g after precipitation with ethanol. Using trichlorobenzene as solvent, the weight-average molecular weight of the obtained COC was 70,000 g / mol and the molecular weight distribution coefficient was 1.9, as determined by high-temperature GPC. NMR analysis showed that the molar content of structural units from norbornene was 50%. The glass transition temperature was determined to be 145 °C using differential scanning calorimetry.

[0054] The following examples and comparative examples illustrate the purification method of the cyclic olefin copolymer (COC) raw material obtained in the preparation examples.

[0055] Example 1

[0056] Take 10 mL of the prepared adhesive solution, add 70 mL of toluene, and dilute the adhesive solution at 500 rpm and 45°C until the COC content in 100 mL of diluted adhesive solution is 1 g. After stirring for 30 min, pour the diluted adhesive solution into 500 mL of ethanol, continue stirring at 25°C for 30 min, and then filter under negative pressure to obtain highly dispersed COC with a high specific surface area. Add ethanol (the weight ratio of ethanol to highly dispersed COC with a high specific surface area is 30:1) to the obtained COC for dispersion, and then add 2 mL of acetylacetone and 1 mL of concentrated hydrochloric acid. React at 90°C, 0.12 MPa, and 500 rpm for 1 h. The resulting polyolefin solid is filtered and dried (drying temperature 60°C, time 72 h). ICP analysis shows that the aluminum content is 18 ppm and the zirconium content is 0 ppm.

[0057] Example 2

[0058] Take 10 mL of the adhesive solution prepared in the preparation example, add 100 mL of toluene, and dilute the adhesive solution at 500 rpm and 50°C until the COC content in each 100 mL of diluted adhesive solution is 0.7 g. After stirring for 30 min, pour the diluted adhesive solution into 500 mL of ethanol, continue stirring at 25°C for 30 min, and then filter under negative pressure to obtain highly dispersed COC with a high specific surface area. Add ethanol (the weight ratio of ethanol to highly dispersed COC with a high specific surface area is 40:1) to the obtained COC for dispersion, and then add 2 mL of acetylacetone and 1 mL of nitric acid. React at 120°C, 0.15 MPa, and 500 rpm for 1 h. The resulting polyolefin solid is filtered and dried (drying temperature 60°C, time 72 h). ICP analysis shows that the aluminum content is 13 ppm and the zirconium content is 0 ppm.

[0059] Example 3

[0060] Take 10 mL of the adhesive solution prepared in the preparation example, add 200 mL of toluene, and dilute the adhesive solution at 700 rpm and 80°C until the COC content in 100 mL of diluted adhesive solution is 0.3 g. After stirring for 30 min, pour the diluted adhesive solution into 500 mL of acetone, and continue stirring at 500 rpm for 30 min at 50°C. After negative pressure filtration, highly dispersed COC with high specific surface area is obtained. Add methanol (the weight ratio of methanol to highly dispersed COC with high specific surface area is 60:1) to the obtained COC for dispersion, and then add 2 mL of benzoyl acetone and 1 mL of sulfuric acid. React at 120°C, 0.2 MPa, and 500 rpm for 1 h. The resulting polyolefin solid is filtered and dried (drying temperature 60°C, time 72 h). ICP analysis shows that the aluminum content is 12 ppm and the zirconium content is 0 ppm.

[0061] Example 4

[0062] Take 10 mL of the adhesive solution prepared in the preparation example, add 200 mL of toluene, and dilute the adhesive solution at 600 rpm and 50°C until the COC content in 100 mL of diluted adhesive solution is 0.3 g. After stirring for 30 min, pour the diluted adhesive solution into 1000 mL of ethanol without stirring, and filter directly under negative pressure to obtain highly dispersed COC with a high specific surface area. Add n-propanol to the obtained COC (the weight ratio of n-propanol to highly dispersed COC with a high specific surface area is 50:1) to disperse it, and then add 2 mL of benzoylacetone and 1 mL of acetic acid. React at 100°C, 0.15 MPa, and 500 rpm for 1 h. The resulting polyolefin solid is filtered and dried (drying temperature 60°C, time 72 h). ICP analysis shows that the aluminum content is 13 ppm and the zirconium content is 0 ppm.

[0063] Example 5

[0064] Take 10 mL of the adhesive solution prepared in the preparation example, add 200 mL of toluene, and dilute the adhesive solution at 700 rpm and 100 °C until the COC content in 100 mL of diluted adhesive solution is 0.3 g. After stirring for 30 min, pour the diluted adhesive solution into 800 mL of ethanol without stirring, and filter directly under negative pressure to obtain highly dispersed COC with a high specific surface area. Add butanol (butanol to highly dispersed COC with a high specific surface area weight ratio of 80:1) to the obtained COC for dispersion, and then add 2 mL of benzoylacetone and 1 mL of formic acid. React at 115 °C, 0.2 MPa, and 600 rpm for 1 h. The resulting polyolefin solid is filtered and dried (drying temperature 60 °C, time 72 h). ICP analysis shows that the aluminum content is 11 ppm and the zirconium content is 0 ppm.

[0065] Example 6

[0066] The cyclic olefin copolymer (COC) raw material was purified according to the method in Example 3, except that "the diluted adhesive solution was poured into 500 mL of acetone" was replaced with "the diluted adhesive solution was poured into 100 mL of acetone". A polyolefin solid was obtained, and ICP analysis revealed an aluminum content of 18 ppm and a zirconium content of 0.3 ppm.

[0067] Example 7

[0068] The cyclic olefin copolymer (COC) feedstock was purified according to the method in Example 3, except that the weight ratio of methanol to highly dispersed COC with a high specific surface area was replaced with "10:1" instead of "60:1". A polyolefin solid was obtained, and ICP analysis revealed an aluminum content of 20 ppm and a zirconium content of 0.1 ppm.

[0069] Example 8

[0070] The cyclic olefin copolymer (COC) raw material was purified according to the method in Example 3, except that "adding 0.1 mL of benzoyl acetone and 1 mL of sulfuric acid" was used instead of "adding 2 mL of benzoyl acetone and 1 mL of sulfuric acid". A polyolefin solid was obtained, and ICP analysis revealed an aluminum content of 21 ppm and a zirconium content of 0.5 ppm.

[0071] Example 9

[0072] The cyclic olefin copolymer (COC) raw material was purified according to the method in Example 3, except that "2 mL of benzoylacetone and 1 mL of sulfuric acid" were replaced with "2 mL of trifluoroacetylacetone and 1 mL of nonanoic acid". A polyolefin solid was obtained, and ICP analysis revealed an aluminum content of 25 ppm and a zirconium content of 1 ppm.

[0073] Example 10

[0074] The cyclic olefin copolymer (COC) raw material was purified according to the method in Example 3, except that after adding 2 mL of benzoylacetone and 1 mL of sulfuric acid, the reaction was carried out at 120°C, 0.2 MPa, and 50 rpm for 1 h instead of 1 h at 50°C, 0.2 MPa, and 50 rpm. A polyolefin solid was obtained, and ICP analysis revealed an aluminum content of 26 ppm and a zirconium content of 0.6 ppm.

[0075] Example 11

[0076] The linear low-density polyethylene (LLDPE) raw material was purified according to the method in Example 3. LLDPE granules (weight-average molecular weight 90,000 g / mol, molecular weight distribution coefficient 3.1, melting point 122°C) were added to hexane and heated to dissolve at 800 rpm and 60°C to obtain a diluted adhesive solution. The concentration of LLDPE in each 100 mL of the diluted adhesive solution was 0.3 g. The remaining steps were the same as in Example 3. A polyolefin solid was obtained, and ICP analysis revealed an aluminum content of 28 ppm, a magnesium content of 1.4 ppm, and a titanium content of 0 ppm.

[0077] Example 12

[0078] Isotactic polypropylene raw material was purified according to the method in Example 3. Isotactic polypropylene granules (weight-average molecular weight of 344,000 g / mol, molecular weight distribution coefficient of 5.4, isotacticity of 96.2%, melt flow index of 3.74 g / 10 min) were added to cyclohexane and heated to dissolve at 800 rpm and 60°C to obtain a diluted adhesive solution, such that the isotactic polypropylene content was 0.3 g per 100 mL of the diluted adhesive solution. The remaining steps were the same as in Example 3. A polyolefin solid was obtained, and ICP analysis revealed an aluminum content of 28 ppm, a magnesium content of 2 ppm, and a titanium content of 0 ppm.

[0079] Example 13

[0080] The cyclic olefin copolymer (COC) raw material was purified according to the method of Example 3, except that the type of COC was different. COC granules (purchased from Mitsui Chemicals, brand name APL6509T) with a weight-average molecular weight of 80,000 g / mol, a molar content of 20% from norbornene structural units, a molecular weight distribution coefficient of 2.52, and a glass transition temperature of 80°C were added to toluene and dissolved by heating at 1000 rpm and 105°C to obtain a diluted solution, such that the COC content was 0.3 g per 100 mL of the diluted solution. The remaining steps were the same as in Example 3. A polyolefin solid was obtained, and ICP analysis showed that it contained 21 ppm aluminum and 1 ppm zirconium.

[0081] Example 14

[0082] The cyclic olefin copolymer (COC) raw material was purified according to the method of Example 3, except that the types of good solvent and precipitant were different. Specifically, the method of "taking 10 mL of the adhesive solution prepared in the preparation example, adding 200 mL of naphtha to it; and pouring the diluted adhesive solution into 500 mL of methyl ethyl ketone" was used instead of "taking 10 mL of the adhesive solution prepared in the preparation example, adding 200 mL of toluene to it; and pouring the diluted adhesive solution into 500 mL of acetone". A polyolefin solid was obtained, and ICP analysis showed that it contained 26 ppm of aluminum and 1.5 ppm of zirconium.

[0083] Comparative Example 1

[0084] The cyclic olefin copolymer (COC) raw material was purified according to the method of Example 3, except that the prepared solution was not diluted with toluene, but was directly poured into acetone and filtered under negative pressure to obtain agglomerated COC. A polyolefin solid was obtained, and ICP analysis showed that it contained 1050 ppm aluminum and 15 ppm zirconium.

[0085] Comparative Example 2

[0086] The cyclic olefin copolymer (COC) raw material was purified according to the method of Example 3, except that the COC content in the diluted solution was different. Methyl dilution solution was added to the solution obtained in the preparation example until the COC content in 100 mL of the diluted solution was 4 g. Acetone was added, and the mixture was filtered under negative pressure to obtain agglomerated COC. A polyolefin solid was obtained, and ICP analysis showed that it contained 830 ppm aluminum and 8 ppm zirconium.

[0087] Comparative Example 3

[0088] Take 10 mL of the prepared adhesive solution and add 70 mL of toluene. Dilute the adhesive solution at 500 rpm and 25°C until the COC content is 1 g per 100 mL of diluted adhesive solution. After stirring for 30 min, pour the diluted adhesive solution into 500 mL of ethanol and continue stirring at 25°C for 30 min. After negative pressure filtration, highly dispersed COC with a high specific surface area is obtained. Add 50 mL of acetylacetone and 4 mL of concentrated hydrochloric acid to the obtained COC and react at 90°C, 0.12 MPa, and 500 rpm for 1 h. The resulting polyolefin solid is filtered and dried (drying temperature 60°C, time 72 h). ICP analysis shows that the aluminum content is 35 ppm and the zirconium content is 0 ppm. However, the obtained polyolefin is yellow, which is significantly different from the normal white polyolefin product. Therefore, adding only a chelating agent without a dispersant will affect the product appearance.

[0089] The results of the above examples and comparative examples show that purifying polyolefin raw materials using the method of the present invention in Examples 1-14 can increase the specific surface area of ​​polyolefins, which is beneficial for the contact between polyolefin particles and chelating reagents and acidic reagents, thereby improving the deashing effect and obtaining polyolefins with lower metal content. In Comparative Examples 1 and 2, without using a good solvent or with an unsatisfactory dilution ratio, effective metal removal could not be achieved. Although metal removal could be achieved in Comparative Example 3 without using a dispersant, it caused the polyolefin to yellow, affecting product quality.

[0090] Furthermore, Example 6 changed the volume ratio of the precipitant to the dilute polyolefin solution; Example 7 changed the weight ratio of the dispersant to the COC solid; Example 8 changed the volume ratio of the chelating reagent to the acidic reagent; Example 9 changed the types of the chelating reagent and the acidic reagent; Example 10 changed the reaction conditions after adding the chelating reagent and the acidic reagent; Examples 11-13 changed the types of polyolefin raw materials; and Example 14 changed the types of good solvent and precipitant. Compared with Examples 1-5, the metal content in the obtained polyolefin increased. This shows that when the volume ratio of the precipitant to the dilute polyolefin solution, the weight ratio of the dispersant to the COC solid, the types of good solvent and precipitant, the volume ratio of the chelating reagent to the acidic reagent, the types of chelating reagent and acidic reagent, the reaction conditions after adding the chelating reagent and the acidic reagent, and the types of polyolefin raw materials meet the preferred conditions, the purification effect of the polyolefin raw materials can be further improved.

[0091] The preferred embodiments of the present invention have been described in detail above; however, 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 suitable manner. 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.

Claims

1. A method for purifying polyolefin raw materials, characterized in that, The method includes the following steps: S1. The polyolefin raw material and a good solvent are mixed for the first time to obtain a dilute polyolefin solution; wherein the amount of polyolefin raw material and good solvent used is such that the content of polyolefin in each 100 mL of dilute polyolefin solution is 0.001-1 g. S2. Mix the dilute polyolefin solution and the precipitant for the second time; S3. The solid material and dispersant in the second mixture obtained in S2 are mixed in a third step to obtain a dispersion. S4. The dispersion obtained in S3 is mixed with a chelating reagent and an acidic reagent and reacted, and then the solid phase material is separated from the reaction solution.

2. The method according to claim 1, characterized in that, In S1, the polyolefin raw material is selected from at least one of cyclic olefin copolymer raw material, EPDM rubber raw material and linear low-density polyethylene raw material, preferably cyclic olefin copolymer raw material; Preferably, the cyclic olefin copolymer raw material has a weight-average molecular weight of 20,000-150,000 g / mol, a molecular weight distribution coefficient of 1.2-3, a glass transition temperature of 50-200℃, and a content of structural units from norbornene of 30-80 wt%; based on a volume of 100 ml of the cyclic olefin copolymer raw material, the content of the cyclic olefin copolymer in the raw material is 6-10 g. Preferably, the good solvent is selected from at least one of toluene, cyclohexane, and hexane, with toluene being the most preferred.

3. The method according to claim 1 or 2, characterized in that, In S1, the temperature of the first mixture is 40-100℃; Preferably, the first mixing is carried out under stirring conditions, with a stirring speed of 50-1000 rpm and a stirring time of 0.5-10 h.

4. The method according to any one of claims 1-3, characterized in that, In S2, the amount of the precipitant used is such that the volume ratio of the precipitant to the dilute polyolefin solution is (1-100):1; Preferably, the precipitant is selected from ethanol and / or acetone.

5. The method according to any one of claims 1-4, characterized in that, In S2, the temperature of the second mixture is less than or equal to the boiling point of the precipitant, preferably 20-50°C; Preferably, the second mixing is carried out under stirring conditions, with a stirring speed of less than or equal to 1000 rpm, preferably 100-600 rpm; and a stirring time of less than or equal to 60 min, preferably 1-30 min.

6. The method according to any one of claims 1-5, characterized in that, In S3, the amount of the dispersant used is such that the weight ratio of the dispersant to the solid material is (30-100):1; Preferably, the dispersant is selected from alcohols, and more preferably from at least one of C1-C4 monohydric alcohols.

7. The method according to any one of claims 1-6, characterized in that, In S4, the amount of the chelating agent is such that the molar equivalent ratio of the chelating agent to the metal compound in the polyolefin raw material is (0.1-10):1, preferably (1-5):1; Preferably, the volume ratio of the chelating reagent to the acidic reagent is (0.1-10):1, more preferably (0.5-5):

1.

8. The method according to any one of claims 1-7, characterized in that, The chelating agent is a β-dicarbonyl compound, preferably at least one of acetylacetone, benzoylacetone, dibenzoylacetone and trifluoroacetylacetone, and more preferably acetylacetone and / or benzoylacetone.

9. The method according to any one of claims 1-8, characterized in that, The acidic reagent is selected from inorganic acids and / or organic acids; the inorganic acid is selected from at least one of sulfuric acid, hydrochloric acid and nitric acid, and the organic acid is selected from at least one of formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid and nonanoic acid; Preferably, the acidic reagent is selected from at least one of sulfuric acid, hydrochloric acid, nitric acid, formic acid, and acetic acid.

10. The method according to any one of claims 1-9, characterized in that, In step S4, the reaction temperature is 50-200℃, preferably 60-120℃; the reaction pressure is 0.1-1MPa, preferably 0.12-0.3MPa; and the reaction time is 0.5-12h, preferably 0.5-5h. Preferably, the reaction is carried out under stirring conditions, with a stirring speed of 50-1000 rpm, more preferably 400-800 rpm.