Process for purification of polyolefins

Abstract

The invention relates to the field of preparation of polyolefin materials, and discloses a polyolefin purification method which comprises the following steps: S1, spraying and atomizing polyolefin reaction liquid to obtain atomized polyolefin reaction liquid drops; s2, performing primary devolatilization on the atomized liquid drops of the polyolefin reaction liquid through hot air flow to obtain filamentous or reticular solid polyolefin; s3, carrying out deliming on the filamentous or netted solid polyolefin; and S4, carrying out secondary devolatilization on the delimed material. According to the method, the polymer fluid can be effectively prepared into a filamentous or net-shaped solid polymer with the large specific surface area ranging from nanometer to micrometer, the polymer can make efficient contact with a detergent, the diffusion mass transfer effect is improved, and the washing and deliming effect is effectively improved.

Description

Technical Field

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

[0002] Polyolefin materials, due to their excellent mechanical strength, superior processing performance, and wide availability, have extensive applications in packaging, transportation, construction, and machinery, making them one of the most important classes of synthetic materials. With my country's economic development, the demand for high-end polyolefin materials is increasing, such as POE elastomers, cyclic olefin polymers (COC), linear low-density polyethylene (LLDPE), and ethylene propylene diene monomer (EPDM) prepared by solution polymerization copolymerization of ethylene, propylene, and various α-olefins and cyclic olefins. These materials possess high volume resistivity, low dielectric constant, excellent optical properties, and outstanding heat and chemical resistance, showing broad application prospects 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. Furthermore, residual volatiles directly affect their biosafety. Therefore, the removal of residual catalysts and volatiles from polyolefin materials is of great significance for their high-end applications.

[0003] Currently, deashing methods for polyolefin materials mainly include adsorbent adsorption and solvent swelling washing. In adsorbent adsorption, the polyolefin reaction solution is passed through an adsorbent-filled column loaded with acids, bases, and ligands, thereby adsorbing metal ions to achieve deashing. However, this method easily contaminates the solvent, leading to significant energy consumption during solvent recycling. Furthermore, these deashing adsorbents are often used in large quantities and cannot be regenerated after adsorption, resulting in high production costs. On the other hand, the non-specific adhesion of polyolefins to the adsorbent inevitably reduces production yield. Therefore, it cannot meet the low energy consumption and environmental protection requirements of industrial production. Solvent swelling washing, on the other hand, is simple to operate, typically involving washing the polyolefin in a solution containing acids, bases, or ligands to remove ash. Current methods generally involve directly washing the polyolefin particles, but the contact area between the particles and these solutions is limited. Therefore, it is often necessary to first use a large amount of good solvent to swell or dissolve the polyolefin particles before washing. To enhance the washing effect, multiple washes are usually required to achieve deashing. This method is complex, time-consuming, and not conducive to industrial production.

[0004] Furthermore, current methods for removing metal ash from polyolefins do not further address the removal of volatiles, often resulting only in polymers with low ash content, making it difficult to simultaneously produce low-volatile polyolefins. Therefore, developing a polyolefin purification process that simultaneously removes both metal ash and volatiles will promote the industrialization of high-purity polyolefin production. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of poor purification effect, low production yield and complicated operation steps in the existing technology, and to provide a purification method for polyolefins. The jet atomization method used in this method can effectively form polymer fluid into filamentous or network solid polymers with a large specific surface area of ​​nanometer to micrometer. It can come into efficient contact with detergent, improve diffusion mass transfer effect, and effectively improve washing and deashing effect. It can simultaneously achieve efficient removal of metal ash and volatile matter from polyolefins to obtain high-purity polyolefins. The operation process does not contaminate high-boiling-point polymerization solvents, the operation is continuous, and it is easy to promote industrially.

[0006] To achieve the above objectives, the present invention provides a method for purifying polyolefins, wherein the method includes the following steps:

[0007] S1. The polyolefin reaction liquid is sprayed and atomized to obtain polyolefin reaction liquid atomized droplets;

[0008] S2. The polyolefin reaction liquid is atomized into droplets by a hot gas flow and subjected to primary devolatilization to obtain filamentous or network solid polyolefins.

[0009] S3. Deashing the filamentous or mesh-like solid polyolefins;

[0010] S4. Perform secondary devolatilization on the deashed material.

[0011] The beneficial effects of the present invention through the above technical solution include at least the following:

[0012] The jet atomization method used in this invention can effectively transform polymer fluid into filamentous or network solid polymers with a large specific surface area of ​​nanometers to micrometers. These polymers can come into efficient contact with detergents, which is beneficial for diffusion and mass transfer processes and effectively improves the washing and deashing effect.

[0013] While forming filamentous or network solid polymers with extremely large specific surface areas, this method effectively removes volatiles from the polymer, achieving a combination of volatile and ash removal. This avoids solvent pollution during conventional adsorption and deashing processes, thereby reducing the huge energy consumption caused by solvent recycling and distillation.

[0014] In a preferred embodiment of the present invention, the use of a highly efficient deashing composite solvent reduces the number of washing cycles and improves deashing efficiency. A large amount of ash residue can be removed in a single washing operation, which is simple to operate, time-saving, and highly efficient. Combined with the use of a vacuum screw, the removal of polymer ash and volatile matter can be achieved simultaneously, yielding high-purity polyolefins. Attached Figure Description

[0015] Figure 1 This is a flow chart of a polyolefin purification process in a preferred embodiment of the present invention;

[0016] Figure 2 This is a schematic diagram of the structure of a dynamic collection network in a preferred embodiment of the present invention.

[0017] Explanation of reference numerals in the attached figures

[0018] 1. Polymerization reactor 2. Fluid transfer pump 3. Fluid mixing nozzle 4. Separation chamber

[0019] 5. Dynamic collection chamber; 6. Dynamic collection net; 7. Rotating shaft; 8. Scraper.

[0020] 9. Air extraction fan; 10. Cyclone separator; 11. Heater; 12. Collection silo

[0021] 13 Washing tank 14 Twin-screw extruder Detailed Implementation

[0022] 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.

[0023] This invention provides a method for purifying polyolefins, wherein the method includes the following steps:

[0024] S1. The polyolefin reaction liquid is sprayed and atomized to obtain polyolefin reaction liquid atomized droplets;

[0025] S2. The polyolefin reaction liquid is atomized into droplets by a hot gas flow and subjected to primary devolatilization to obtain filamentous or network solid polyolefins.

[0026] S3. Deashing the filamentous or mesh-like solid polyolefins;

[0027] S4. Perform secondary devolatilization on the deashed material.

[0028] The purification method provided by this invention can effectively convert polymer fluid (polyolefin reaction liquid) into filamentous or network solid polymers with a large specific surface area of ​​nanometers to micrometers. These polymers can come into efficient contact with detergents, improve diffusion and mass transfer, and effectively improve washing and deashing effects. The method can simultaneously achieve efficient removal of metal ash and volatiles from polyolefins. Furthermore, the operation process does not contaminate high-boiling-point polymerization solvents, is continuous, and is easy to promote industrially.

[0029] In a preferred embodiment of the present invention, the process of forming filamentous or network-like solid polyolefins from the polyolefin reaction liquid is carried out in a jet atomization device. In S1, the jet atomization method includes: heating the polyolefin reaction liquid obtained from solution polymerization in the polymerization reactor and mixing it with a hot carrier gas through a fluid mixing nozzle of the jet atomization device; then, spraying the mixed fluid into the separation chamber of the jet atomization device to atomize it, forming nano- to micron-sized atomized droplets with high specific area. The hot carrier gas is selected from at least one of nitrogen, carbon dioxide, and water vapor; the temperature of the hot carrier gas is 60-200°C; and the flow rate of the hot carrier gas is 1-50 m / s. 3 In S2, primary devolatilization takes place in the separation chamber of the jet atomization device. Before primary devolatilization, the separation chamber is preheated with hot air before the material enters. After the atomized droplets of the polyolefin reaction solution enter the separation chamber, the solvent in the atomized droplets is evaporated by the hot air, forming filamentous or mesh-like solid polyolefins that adhere to the surface of the dynamic collection net, thus achieving primary devolatilization. The filamentous polyolefins adhering to the dynamic collection net are scraped off by a scraper and sent to the washing tank for subsequent deashing. The distance between the scraper and the dynamic collection net is adjustable and can be adjusted according to the polymer fluid flow rate. The dynamic collection net has a porous structure, as shown in the diagram. Figure 2 As shown.

[0030] The present invention does not particularly limit the type of gas in the hot gas flow, and can be any gas conventionally used in the art for assisting in the transport of fluids. Preferably, the gas in the hot gas flow is selected from at least one of nitrogen, carbon dioxide and water vapor.

[0031] According to the present invention, preferably, the temperature of the hot airflow is 60-200°C, and / or the flow velocity of the hot airflow is 1-50 m / s. 3 / h.

[0032] The present invention does not impose any particular limitation on the content of polyolefin in the polyolefin reaction solution, and it can be a polyolefin reaction solution obtained by conventional solution polymerization. Preferably, in S1, the content of polyolefin in the polyolefin reaction solution is 5-80 wt%.

[0033] To further improve the spray atomization effect of the polyolefin reaction liquid and thus obtain a solid polymer with a larger specific surface area, preferably, the dynamic viscosity of the polyolefin reaction liquid at 150°C is less than or equal to 1000 Pa·s.

[0034] This invention does not particularly limit the type of polyolefin in the polyolefin reaction solution. The method provided by this invention is applicable to any polyolefin reaction solution. Preferably, the polyolefin in the polyolefin reaction solution is a cyclic olefin copolymer (COC). The inventors have found that the method provided by this invention has a better purification effect on COC reaction solutions than on other types of polyolefin reaction solutions.

[0035] In a preferred embodiment of the present invention, the COC in the COC reaction solution has a weight-average molecular weight of 10,000-150,000 g / mol, a molecular weight distribution coefficient of 1.2-3, a glass transition temperature of 50-200℃, a molar content of structural units from norbornene in the COC of 30-80%, and a COC content of 5-80 wt%. The method provided by the present invention has a better purification effect on COC reaction solutions that meet these conditions.

[0036] To obtain a COC reaction solution that meets the aforementioned conditions, in a preferred embodiment of the present invention, the preparation method of the COC reaction solution includes: mixing ethylene and norbornene in the presence of a main catalyst, a co-catalyst, and a solvent to carry out a polymerization reaction; wherein the main catalyst is a zirconium monoxide compound (rac-[Et(Ind)2]ZrCl2), the co-catalyst is methylaluminoxane, and the solvent is toluene. When preparing the COC reaction solution, 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 content of the main catalyst is (5-7) × 10⁻⁶. -5 mol; the amount of main catalyst is calculated as Zr, the amount of co-catalyst is calculated as Al, and the molar ratio of co-catalyst to main catalyst is (1000-2000):1.

[0037] According to the present invention, preferably, in S1, the spray atomization conditions result in an average diameter of 1-100 μm for the atomized droplets of the polyolefin reaction solution. To obtain atomized droplets with an average diameter within the preferred range, the polyolefin reaction solution is heated to 60-200°C before spray atomization.

[0038] The polyolefin reaction liquid atomized droplets utilize the heat of the hot gas flow to evaporate the solvent in the polyolefin reaction liquid atomized droplets, forming filamentous or network-like solid polyolefins, thereby achieving primary devolatilization.

[0039] According to the present invention, preferably, in S3, the deashing method includes: a) mixing filamentous or mesh-like solid polyolefin with alcohol detergent, acidic reagent, and chelating reagent and heating for a first time, separating the solid phase material from the obtained material; b) mixing the obtained solid phase material with alcohol eluent and heating for a second time, and then separating the solid phase material from the obtained material to obtain the deashed material. The solid phase material separated from the material after the first heating still contains residual acidic reagent and chelating reagent, as well as entrained ash. Heating and rinsing with alcohol eluent can further remove the residual reagent and ash.

[0040] The present invention does not have a particular limitation on the number of times the alcohol eluent is heated and rinsed. In a preferred case, the heated rinse is performed 2-4 times, that is, step b is repeated 2-4 times.

[0041] The present invention does not impose any particular restrictions on the order of adding alcohol detergent, acid reagent, and chelating reagent, as long as the ash in the solid polyolefin can be effectively removed. In a preferred case, the filamentous or mesh-like solid polyolefin is first mixed with alcohol detergent so that the alcohol detergent immerses the solid polyolefin, and then the acid reagent and chelating reagent are added.

[0042] To further improve the deashing effect on solid polyolefins, preferably, the amount of alcohol detergent used is such that the weight ratio of alcohol detergent to filamentous or network-like solid polyolefin is (10-50):1. To further improve the deashing effect on solid polyolefins, preferably, the amount of acidic reagent used is such that the weight ratio of acidic reagent to filamentous or network-like solid polyolefin is (1-25):100.

[0043] To further improve the deashing effect on solid polyolefins, preferably, the amount of chelating agent used is such that the weight ratio of acidic agent to chelating agent is 1:(0.1-10).

[0044] To further improve the deashing effect on solid polyolefins, preferably, the amount of alcohol eluent used is such that the weight ratio of alcohol eluent to filamentous or network solid polyolefin is (10-50):1. The amount of alcohol eluent used refers to the amount of alcohol eluent used in a single heating rinse.

[0045] The present invention does not particularly limit the types of alcohol detergents and alcohol eluents, which can be various monohydric alcohols or polyhydric alcohols. Preferably, the alcohol detergents and alcohol eluents are each independently selected from C1-C20 alcohols, more preferably from C1-C5 monohydric alcohols, such as at least one of methanol, ethanol, n-propanol, isopropanol, butanol and pentanol.

[0046] The present invention does not particularly limit the type of acidic reagent, which can be selected from organic acids and / or inorganic acids. Preferably, the inorganic acid is selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, perchloric acid and hypochlorous acid; the organic acid is selected from C1-C20 organic acids, more preferably from at least one of formic acid, acetic acid, oleic acid, butyric acid, isobutyric acid, benzoic acid, caprylic / capric acid, oxalic acid, citric acid, gluconic acid and benzenesulfonic acid.

[0047] The present invention does not have any particular limitation on the type of chelating agent, as long as it can chelate metal ions. Preferably, the chelating agent is a β-dicarbonyl compound, preferably selected from at least one of acetylacetone, benzoylacetone, dibenzoylacetone and trifluoroacetylacetone.

[0048] To further improve the deashing effect on solid polyolefins, preferably, the temperature of the first heating is 50-200℃ and the time is 0.5-6h.

[0049] To further improve the deashing effect on solid polyolefins, preferably, the second heating temperature is 50-200℃, and the time is 0.5-5 hours. The second heating time refers to the time of a single heating and rinsing using an alcohol-based eluent.

[0050] To deeply remove volatiles from polyolefins, solid polyolefins undergo secondary devolatilization after deashing. Preferably, in S4, the conditions for secondary devolatilization include: the secondary devolatilization is carried out in a vacuum twin-screw extruder, the temperatures of the first, second, and third chambers of the vacuum twin-screw extruder are 250-280℃, 270-310℃, and 270-320℃, respectively, and the vacuum degrees of the first, second, and third chambers of the vacuum twin-screw extruder are 0.01-0.06MPa, 0.04-0.08MPa, and 0.08-0.096MPa, respectively.

[0051] 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.

[0052] Preparation Example

[0053] Preparation of the toluene reaction solution for cyclic olefin copolymer (COC): 10g of norbornene was dissolved in 90g of purified toluene and added to a 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. The catalyst dosage was 6×10⁻⁶ based on a total volume of 1L for norbornene, ethylene, toluene, catalyst, and co-catalyst. -5The catalyst was measured in mol; the amount of catalyst was calculated as Zr, and the amount of co-catalyst was calculated as Al, with a molar ratio of co-catalyst to catalyst of 2000:1; after reacting for 30 min, a COC toluene reaction solution was obtained. Sampling was performed using inductively coupled plasma atomic emission spectrometry (ICP-AES), revealing an aluminum content of 4500 ppm and a zirconium content of 50 ppm; the COC content in the reaction solution was measured to be 5 wt% using a rotational rheometer; the dynamic viscosity of the reaction solution at 150 °C was measured to be 0.01 Pa·s using a rotational rheometer; using trichlorobenzene as a solvent, the weight-average molecular weight of COC in the reaction solution was measured by high-temperature GPC to be 70,000 g / mol, with a molecular weight distribution coefficient of 1.9; 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 (DSC).

[0054] By varying the feed amounts of ethylene and norbornene monomers and the reaction time, while keeping other reaction conditions constant, COC reaction solutions with different COC concentrations and dynamic viscosities were obtained. The resulting COC reaction solutions with COC contents of 7wt%, 8wt%, 10wt%, 15wt%, 20wt%, and 90wt% exhibited dynamic viscosities of 0.015 Pa·s, 0.04 Pa·s, 0.05 Pa·s, 0.1 Pa·s, 0.15 Pa·s, and 3500 Pa·s at 150°C, respectively; aluminum content ranged from 3000 to 5000 ppm, and zirconium content ranged from 30 to 100 ppm; the molar content of structural units derived from norbornene in the COC was... The percentages were 48%, 48%, 49%, 47%, 50%, and 53%; the weight-average molecular weights of COC were 68,000 g / mol, 72,000 g / mol, 75,000 g / mol, 73,000 g / mol, 71,000 g / mol, and 69,000 g / mol, respectively; the molecular weight distribution coefficients were 1.89, 1.93, 1.95, 2.01, 2.11, and 2.6, respectively; and the glass transition temperatures were 140℃, 137℃, 142℃, 147℃, 146℃, and 142℃, respectively.

[0055] The following examples illustrate the purification method of polyolefin reaction solution. The preparation and purification of the polyolefin reaction solution are described in... Figure 1 The process is carried out in the apparatus shown.

[0056] Examples 1-6

[0057] Purification of COC toluene reaction solution:

[0058] The COC reaction solution is pumped to a fluid mixing nozzle via a fluid delivery pump, while heated nitrogen gas is also supplied as a heat carrier gas. The mixed hot fluid is atomized through the nozzle at a certain gas velocity and injected into the separation chamber. Heated auxiliary nitrogen gas is continuously introduced into the separation chamber as a hot gas flow to achieve primary devolatilization. The resulting network solid polyolefin, after evaporation of volatiles, adheres to the surface of a porous dynamic collection net. Simultaneously, the hot gas flow continues to blow across the dynamic collection net to further promote the evaporation of volatiles. The products are collected from the dynamic collection net and the cyclone separator, respectively, yielding filamentous or network polyolefins with a specific area ranging from nanometers to micrometers.

[0059] The polyolefin collected from the silo is then sent to a washing tank. Alcohol detergent is added to immerse the polymer, followed by the addition of acidic and chelating reagents. The mixture is then heated and stirred for a certain period before being filtered. Alcohol eluent is added again to rinse the mixture three times before it is filtered out.

[0060] After discharge, the material is fed into a vacuum screw extruder for devolatilization. The screw extruder has three sections with a set temperature and vacuum level. After three stages of heating and vacuuming, the secondary devolatilization is completed, and the product is granulated and discharged.

[0061] The metal ash content of the obtained product was determined by inductively coupled plasma atomic emission spectrometry, and the volatile content was determined by headspace chromatography. The operating conditions and test results of Examples 1-6 are shown in Table 1.

[0062] Example 7

[0063] The COC reaction solution was purified according to the method in Example 1, except that the COC content in the COC reaction solution was 90 wt%. Specific operating conditions and test results are shown in Table 1.

[0064] Example 8

[0065] The linear low-density polyethylene (LLDPE) reaction solution was purified according to the method in Example 1. The preparation method of the LLDPE reaction solution was as follows: LLDPE granules (weight-average molecular weight 90,000 g / mol, molecular weight distribution coefficient 3.1, melting point 122℃) were added to hexane and heated to dissolve at 800 rpm and 60℃ for 60 min to obtain the reaction solution. The obtained LLDPE reaction solution contained 5 wt% LLDPE, 3200 ppm aluminum, and 32 ppm titanium. The dynamic viscosity of the LLDPE reaction solution at 150℃ was 0.01 Pa·s. Specific operating conditions and test results are shown in Table 1.

[0066] Example 9

[0067] The COC reaction solution was purified according to the method of Example 1, except that the content of structural units from norbornene in the COC was different. Specifically, the COC reaction solution was prepared according to the preparation example, except that the molar ratio of ethylene to norbornene was 1:2. The resulting COC reaction solution had a molar content of 15% of structural units from norbornene in the COC; the COC content was 4 wt%, the aluminum content was 4300 ppm, and the zirconium content was 42 ppm; the dynamic viscosity of the COC reaction solution at 150°C was 0.008 Pa·s; the weight-average molecular weight of the COC was 40,000 g / mol, the molecular weight distribution coefficient was 2.4, and the glass transition temperature was 65°C. Specific operating conditions and test results are shown in Table 1.

[0068] Example 10

[0069] The COC reaction solution was purified according to the method in Example 1. The difference was that after the polyolefin was fed into the washing vessel, instead of immersing the polymer in alcohol-based detergents, acidic reagents and chelating agents were directly added. Specific operating conditions and test results are shown in Table 1. As can be seen from the results in Table 1, the deashing effect was still good even without the addition of alcohol-based detergents, but the obtained COC product turned yellow.

[0070] Example 11

[0071] The COC reaction solution was purified according to the method in Example 1, except that after the polyolefin was fed into the washing vessel, 1-octanol was used as the alcohol detergent to immerse the polymer. Specific operating conditions and test results are shown in Table 1.

[0072] Example 12

[0073] The COC reaction solution was purified according to the method in Example 1, except that the average particle size of the physicochemical droplets obtained by spraying was different. Specifically, the flow rates of the hot carrier gas and the hot gas stream were set to 0.1 m / s during the spraying process. 3 The average diameter of the COC reaction solution droplets was measured to be 1500 μm per hour using optical microscopy. Specific operating conditions and test results are shown in Table 1.

[0074] Example 13

[0075] The COC reaction solution was purified according to the method in Example 1, except that the polyCOC reaction solution was heated to 50°C before atomization, resulting in an average droplet diameter of 800 μm. Specific operating conditions and test results are shown in Table 1.

[0076] Example 14

[0077] The COC reaction solution was purified according to the method in Example 1, except that the mass ratio of acidic reagent to polyolefin was 0.1:100. Specific operating conditions and test results are shown in Table 1.

[0078] Example 15

[0079] The COC reaction solution was purified according to the method in Example 1, except that the mass ratio of the acidic reagent to the chelating reagent was 1:100. Specific operating conditions and test results are shown in Table 1.

[0080] Comparative Example 1

[0081] This comparative example provides a method for purifying polyolefins. The difference between this method and the method in Example 1 is that the unsprayed polyolefin solution is directly added to an alcohol-based detergent for subsequent processing. The specific operation is as follows: A 5 wt% polyolefin solution obtained from polymerization is directly added to a washing vessel. Following the proportions in Example 1, alcohol-based detergent, acid reagent, and chelating reagent are added sequentially, followed by heating and stirring. It was observed that the polyolefin rapidly agglomerates in the vessel and cannot be removed, then transferred to a vacuum twin-screw extruder for devolatilization. The agglomerated sample is filtered, and further rinsed three times with alcohol eluent. After filtration, the vessel is opened, and the agglomerated sample is removed. Specific operating conditions and test results are shown in Table 1.

[0082] Comparative Example 2

[0083] This comparative example provides a method for purifying polyolefins. The difference between this method and the method in Example 1 lies in the addition of acidic and chelating reagents to the unsprayed polyolefin solution for deashing in solution. The specific operation is as follows: Acidic and chelating reagents are added to the unsprayed polyolefin solution according to the proportions in Example 1 for deashing. After deashing, methanol is added to precipitate the polymer, resulting in agglomerated polymer solids that cannot be further fed into a vacuum twin-screw extruder for devolatilization. Specific operating conditions and test results are shown in Table 1. As can be seen from the results in Table 1, the yield of the polymer solids precipitated after liquid-phase deashing is only 53% of the yield obtained by spraying. Although ICP-MS characterization shows an aluminum content of 15 ppm and a zirconium content of 1 ppm, its yield is far lower than that of the method in Example 1.

[0084] The aluminum and zirconium content in the product was determined by ICP-MS, and the volatile content was determined by headspace chromatography.

[0085] The formula for calculating polyolefin yield is: Polyolefin yield % = (m1 ÷ m2) × 100%.

[0086] Where m1 is the mass of the polyolefin product obtained after removing ash and volatiles from the polyolefin reaction solution; m2 is the mass of the polyolefin in the polyolefin reaction solution, which is obtained by weighing the polyolefin reaction solution after removing the solvent through rotary evaporation and vacuum drying.

[0087] Table 1

[0088]

[0089]

[0090] Table 1 (continued 1)

[0091]

[0092]

[0093] Table 1 (continued 2)

[0094]

[0095] Table 1 (continued 3)

[0096]

[0097] As shown in Table 1, the method provided by this invention in Examples 1-15 effectively removes ash and volatiles from the polyolefin reaction solution, and the polyolefin yield is relatively high. In Comparative Example 1, the unsprayed polyolefin solution was directly added to an alcohol-based detergent for subsequent processing. Compared to Examples 1-15, the ash and volatile content limits in the polyolefin product increased, and the polyolefin yield was significantly reduced. In Comparative Example 2, acidic and chelating reagents were added to the unsprayed polyolefin solution for deashing in solution. After deashing, methanol was added to precipitate the polymer, resulting in agglomerated polymer solids. Although the ash content in the polyolefin product was lower, the polyolefin yield was significantly reduced.

[0098] Furthermore, Example 7 changed the COC content in the COC reaction solution; Examples 8 and 9 changed the type of polyolefin; in Example 10, after the polyolefin was fed into the washing vessel, the polymer was not submerged with alcohol detergent, but instead, acidic reagents and chelating reagents were directly added; Example 11 changed the type of alcohol detergent; Examples 12 and 13 changed the spraying conditions; Example 14 changed the mass ratio of acidic reagent to polyolefin; and Example 15 changed the mass ratio of acidic reagent to chelating reagent. Compared with Example 1, the ash or volatile matter content in the polyolefin products obtained in Examples 7-9 and 11-15 increased; although the ash and volatile matter content in the polyolefin product obtained in Example 10 was lower, the product color turned yellow. This shows that when the spraying conditions, the COC content in the COC reaction solution, the type of polyolefin, the deashing steps, the type of alcohol detergent, and the mass ratio of acidic reagent to polyolefin meet the preferred conditions, the purification effect of polyolefin can be further improved, and the product color can be further improved.

[0099] 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 polyolefins, characterized in that, The method includes the following steps: S1. The polyolefin reaction liquid is sprayed and atomized to obtain polyolefin reaction liquid atomized droplets; S2. The polyolefin reaction liquid is atomized into droplets by a hot gas flow and subjected to primary devolatilization to obtain filamentous or network solid polyolefins. S3. Deashing the filamentous or mesh-like solid polyolefins; S4. Perform secondary devolatilization on the deashed material.

2. The purification method according to claim 1, characterized in that, The gas in the hot gas stream is selected from at least one of nitrogen, carbon dioxide, and water vapor; Preferably, the temperature of the hot airflow is 60-200°C, and / or the flow velocity of the hot airflow is 1-50 m / s. 3 / h.

3. The purification method according to claim 1 or 2, characterized in that, In S1, the polyolefin content in the polyolefin reaction solution is 5-80 wt%. Preferably, the dynamic viscosity of the polyolefin reaction solution at 150°C is less than or equal to 1000 Pa·s.

4. The purification method according to any one of claims 1-3, characterized in that, In S1, the conditions for jet atomization result in an average diameter of 1-100 μm for the atomized droplets of the polyolefin reaction liquid.

5. The purification method according to any one of claims 1-4, characterized in that, In S3, the deashing method includes: a) mixing filamentous or mesh-like solid polyolefin with alcohol detergent, acid reagent, and chelating reagent and heating for the first time, and separating the solid phase material from the obtained material; b) mixing the obtained solid phase material with alcohol eluent and heating for the second time, and then separating the solid phase material from the obtained material to obtain the deashed material.

6. The purification method according to claim 5, characterized in that, The amount of alcohol detergent used is such that the weight ratio of alcohol detergent to filamentous or network solid polyolefin is (10-50):1; Preferably, the amount of acidic reagent used is such that the weight ratio of acidic reagent to filamentous or network solid polyolefin is (1-25):100; Preferably, the amount of the chelating agent is such that the weight ratio of the acidic agent to the chelating agent is 1:(0.1-10); Preferably, the amount of alcohol eluent used is such that the weight ratio of alcohol eluent to filamentous or network solid polyolefin is (10-50):

1.

7. The purification method according to claim 5 or 6, characterized in that, The alcohol detergent and alcohol eluent are each independently selected from C1-C20 alcohols, preferably from C1-C5 monohydric alcohols.

8. The purification method according to claim 5 or 6, characterized in that, The acidic reagent is selected from organic acids and / or inorganic acids, wherein the inorganic acid is selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, perchloric acid and hypochlorous acid; the organic acid is selected from C1-C20 organic acids, preferably at least one of formic acid, acetic acid, oleic acid, butyric acid, isobutyric acid, benzoic acid, caprylic / capric acid, oxalic acid, citric acid, gluconic acid and benzenesulfonic acid; Preferably, the chelating agent is a β-dicarbonyl compound, and is preferably selected from at least one of acetylacetone, benzoylacetone, dibenzoylacetone and trifluoroacetylacetone.

9. The purification method according to any one of claims 5-8, characterized in that, The first heating temperature is 50-200℃, and the time is 0.5-6h; Preferably, the second heating temperature is 50-200℃ and the time is 0.5-5h.

10. The purification method according to any one of claims 1-9, characterized in that, In S4, the conditions for the secondary devolatilization include: the secondary devolatilization is carried out in a vacuum twin-screw extruder, the temperatures of the first, second, and third chambers of the vacuum twin-screw extruder are 250-280℃, 270-310℃, and 270-320℃, respectively, and the vacuum degrees of the first, second, and third chambers of the vacuum twin-screw extruder are 0.01-0.06MPa, 0.04-0.08MPa, and 0.08-0.096MPa, respectively.

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