Method for preparing ethylene-octylene copolymer by slurry method and ethylene-octylene copolymer

Abstract

The invention discloses a method for preparing an ethylene-octene copolymer by a slurry method. The method comprises the following steps: taking monomer ethylene and comonomer 1-octene as raw materials; the method comprises the following steps: diluting a catalyst with supercritical ethane to obtain a catalyst diluent, wherein the catalyst is a metallocene catalyst and a cocatalyst; adding the catalyst diluent, raw materials and hydrogen into a stirring reaction kettle containing supercritical ethane for polymerization reaction, wherein the temperature and the pressure of the stirring reaction kettle are controlled to be higher than the supercritical condition of ethane; after polymerization is completed, slurry discharged from the stirring reaction kettle is subjected to post-treatment, and a finished product is obtained. According to the invention, a supercritical ethane pretreatment catalyst is adopted, the supercritical ethane is used as a solvent during polymerization, and the characteristics of the supercritical solvent are combined, so that the reaction system is further optimized, the performance of the product is improved, and the prepared ethylene-octene copolymer has excellent melt index and tensile property.

Description

Technical Field

[0001] The invention relates to the field of polyethylene preparation technology, in particular to a method for preparing ethylene-octene copolymer by a slurry process and the ethylene-octene copolymer. Background Art

[0002] As an important engineering plastic, polyethylene is widely used in packaging, construction, automobile and other industries. The slurry method is a common method for preparing polyethylene. Products with different properties can be obtained by controlling the reaction conditions. However, in the production process of the traditional slurry method, the activity of the catalyst in the reaction is affected by factors such as the solvent environment, resulting in low monomer conversion rate, low reaction efficiency, and easy production of random copolymers, which affects the final physical and chemical properties of the finished product. At present, the performance of the product is mainly improved by adjusting the reaction conditions (such as temperature, pressure), the selection of the catalyst system and the monomer feed rate. How to efficiently and stably prepare polyethylene with stable molecular weight and good physical and chemical properties remains a challenge.

[0003] At present, taking ethylene as the main component and adding other α-olefins as comonomers (1-butene, 1-hexene, 1-octene) can reduce the density and crystallinity of polyolefins and expand their physical and application properties. In particular, the copolymerization of ethylene and 1-octene can obtain high-end polyolefin products, which greatly improves the application value of the products. The products have the advantages of light weight, excellent flexibility and impact resistance, and have great commercial application value. However, when ethylene and octene are copolymerized, since ethylene is gaseous and octene is liquid, the reaction activity of the two monomers is quite different, resulting in a mismatch in polymerization rate. In addition, the steric hindrance of the 1-octene comonomer is large, and the copolymerization performance of the catalyst is required to be higher. The copolymerization reaction of the two is relatively difficult, resulting in a low degree of polymerization of octene and unsatisfactory performance of the copolymer product. Therefore, further research is still needed to explore suitable polymerization process conditions. Summary of the invention

[0004] In order to solve the defects in the prior art, the present invention provides a slurry preparation method for efficiently and stably preparing ethylene octene copolymers with stable molecular weight and good physical and chemical properties.

[0005] The present invention is achieved through the following technical scheme: a method for preparing ethylene-octene copolymer by a slurry process, wherein monomer ethylene and copolymer monomer 1-octene are used as raw materials; a catalyst is diluted with supercritical ethane to obtain a catalyst dilution liquid, wherein the catalyst is a metallocene catalyst and a co-catalyst; the catalyst dilution liquid, the raw materials and hydrogen are added into a stirred reactor containing supercritical ethane to carry out a polymerization reaction, wherein the temperature and pressure of the stirred reactor are controlled to be above the supercritical conditions of ethane; after the polymerization is completed, the slurry discharged from the stirred reactor is post-treated to obtain a finished product.

[0006] As a preferred technical solution of the present invention, the metallocene catalyst is bis-indenyl methylene bridged zirconium, and the co-catalyst is aluminoxane;

[0007] The molar ratio of the metallocene catalyst to the co-catalyst is 1:50-400, preferably 1:100-200;

[0008] In the catalyst dilution solution, the concentration of the metallocene catalyst in supercritical ethane is 0.1-10 mmol / L, preferably 0.1-5 mmol / L, and more preferably 0.1-1 mmol / L.

[0009] As a preferred technical solution of the present invention, the metallocene catalyst is (Ind)2CH2ZrCl2, and the co-catalyst is methylaluminoxane and / or tetrabutylaluminoxane, preferably methylaluminoxane.

[0010] As a preferred technical solution of the present invention, in a catalyst preparation tank, the metallocene catalyst and the co-catalyst are uniformly mixed with supercritical ethane under an inert environment, and the catalyst preparation tank is maintained at a supercritical condition of ethane.

[0011] As a preferred technical solution of the present invention, ethane is continuously introduced into the stirred reactor after being purged with inert gas, and the pressure is controlled at 4.8-6Mpa, so that the stirred reactor is kept in a heated state, and the reactor is heated to 33-40°C to make ethane in a supercritical state. The bottom liquid of the stirred reactor has a total volume of 1 / 4-1 / 2 of the total volume of the stirred reactor, preferably 1 / 4-1 / 3.

[0012] As a preferred technical solution of the present invention, under stirring, catalyst dilution liquid and 1-octene are added to the stirred reactor in sequence, and finally high-pressure ethylene and hydrogen are introduced, and the pressure in the stirred reactor is controlled to be 5.6-6Mpa and the temperature is controlled to be 33-40°C to carry out polymerization reaction.

[0013] As a preferred technical solution of the present invention, the amount of the catalyst diluent added is 1-5% of the volume of the kettle bottom liquid;

[0014] and / or, the amount of 1-octene added is 5-30%, preferably 10-15%, by weight, of the ethylene;

[0015] And / or, the molar concentration of the total amount of ethylene added in the kettle bottom liquid is 1-10 mol / L, preferably 1.5-3.5 mol / L;

[0016] And / or, the amount of hydrogen added is 0.1-5% by volume of ethylene;

[0017] And / or, adding an additive accounting for 0.01-1% of the total weight of the kettle bottom liquid, wherein the additive includes polyoxyethylene.

[0018] As a preferred technical solution of the present invention, the ethylene and hydrogen are added from the bottom of the stirred reactor and enter the bottom liquid of the reactor;

[0019] And / or, a pressure relief vent is provided on the top of the stirred reactor.

[0020] As a preferred technical solution of the present invention, the post-processing step includes: moving the reaction slurry to a flash tank for product separation, sending the separated gas phase to a recovery unit, and the separated solid phase polymer entering a degassing and drying unit. The dried polymer powder is sieved and homogenized to obtain the final product.

[0021] The ethylene octene copolymer prepared by the above-mentioned method for preparing ethylene octene copolymer by a slurry process has a viscosity average molecular weight of 550,000-650,000, a molecular weight distribution of 2-3, a melt index of 0.6-0.75 g / 10 min, a tensile strength of 40-45 MPa, an elongation at break of 800-900%, and a simply supported beam impact strength of 100-115 kJ / m 2 .

[0022] The beneficial effects of the present invention are:

[0023] The present invention obtains a high-performance ethylene-octene copolymer product by copolymerizing ethylene with 1-octene having a high carbon number, thereby increasing the melt index and improving the mechanical processing performance, especially greatly increasing the tensile strength and elongation at break of the product. The present invention effectively solves the problems of polymerization difficulty, poor product performance, low degree of polymerization of octene, etc., which exist in the copolymerization of ethylene and octene, by improving the catalyst and the polymerization process.

[0024] The present invention adopts a highly active metallocene catalyst bis-indenyl methylene bridged zirconium. When configuring the catalyst, supercritical ethane fluid is used as a diluent. Before the catalyst is added to the reaction system, the low viscosity and high diffusivity of supercritical ethane are used to significantly improve the dispersibility of the catalyst and the co-catalyst, reduce the agglomeration of catalyst particles, fully expose the single active center of the metallocene catalyst, and more evenly distribute it in the reaction medium, which helps to improve the catalytic efficiency. In addition, through specific catalyst drying and preactivation steps, the activity of the catalyst is further improved, ensuring that the catalyst can quickly play a role at the beginning of the reaction, thereby improving the polymerization conversion rate of ethylene and 1-octene monomers.

[0025] In the polymerization process, the present invention controls the pressure and temperature in the reactor so that both the ethane as the solvent and the ethylene as the raw material are in a supercritical state. The supercritical special fluid can reduce the viscosity of the reaction system, reduce the shear stress, reduce the energy consumption, help improve the mass transfer and heat transfer efficiency of the reactor, accelerate the reaction process, make the ethylene monomer and the 1-octene monomer fully dispersed, and fully contact with the catalyst for reaction and polymerization, improve the reaction conversion rate, improve the performance of the product, and make the prepared polyethylene have excellent melt index and tensile strength

[0026] In addition, the supercritical ethane in the present invention can be conveniently recovered by reducing pressure after completing its function, thereby reducing energy consumption and environmental pollution during recovery, improving the environmental protection and economy of the entire process, and at the same time, product post-processing is also easier to carry out, and product separation can be achieved by only gas-solid separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The figure is a schematic diagram of the process flow of preparing ethylene-octene copolymer by the slurry process of the present invention. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of the present invention, not all. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The following is a process flow summary of the method for preparing polyethylene by the slurry process disclosed in the present invention.

[0030] 1. Preparation step: This step is before step S1.

[0031] 1.1 Drying preparation, mainly to ensure that the catalyst is dry and free of water to avoid the influence of moisture on the catalyst activity.

[0032] Place the catalyst in a drying container. Pass high-purity nitrogen into the drying container to exclude air and moisture. The nitrogen flow rate is 50-100 mL / min. Place the drying container in an oven and set the temperature to 80°C.

[0033] Dry for at least 12 hours to ensure that the catalyst is completely dry. After drying, turn off the heat and let the container cool naturally to room temperature. Transfer the dried catalyst to a desiccator and seal it for storage under nitrogen protection.

[0034] 1.2 Pre-activation mainly improves the activity of the catalyst to ensure that it can work quickly at the beginning of the reaction.

[0035] Transfer the dried catalyst to a pre-activation container. Pass a small amount of high-purity hydrogen (for example, a mixture of hydrogen and inert gas), and the concentration of hydrogen can be adjusted according to experimental needs. The flow rate is 10-50mL / min (milliliters per minute). The temperature is between 60°C and 80°C. The pre-activation time is generally 1-2 hours. After the pre-activation is completed, turn off the heating and let the container cool naturally to room temperature. Transfer the pre-activated catalyst to a dryer under nitrogen protection and seal it for storage.

[0036] Preprocessing

[0037] Ethane drying: Use molecular sieve drying column to ensure the water content is <5ppm.

[0038] Ethylene and 1-octene are refined raw materials from which oxygen, carbon monoxide, water and carbon dioxide have been removed.

[0039] 2. Reaction Stage

[0040] The embodiment of the present invention uses a 30L stirred reactor as a small test device for experiments. The reactor is made of stainless steel or corrosion-resistant material, has a volume of 30L, is ensured to withstand a pressure of more than 6MPa, and is equipped with a heat exchange jacket.

[0041] Figure 1 The process flow diagram of the present invention is as follows: gaseous ethane (or supercritical ethane directly introduced) is introduced into a stirred reactor, and the pressure and temperature in the stirred reactor are adjusted to keep the ethane in a supercritical state. The supercritical ethane is used as a reaction medium, and then a catalyst, 1-octene, ethylene, hydrogen and other reaction raw materials are added to carry out a polymerization reaction. After the reaction is completed, the product is discharged from the reactor for post-treatment to obtain the final product.

[0042] Specific process of reaction process:

[0043] S1 Ethane preparation: Ethane is continuously introduced into the reactor after nitrogen purge, and the reactor is kept heated. The reactor is heated to about 33-40°C and the pressure is controlled at 4.8-6Mpa to make the ethane in a supercritical state. Supercritical ethane is continuously accumulated in the reactor, and 10-15L is maintained as the reactor bottom liquid (supercritical ethane can also be directly introduced). A small amount of additives (such as polyoxyethylene) can also be added, and the added amount is 0.01-1% of the total weight of the reactor bottom liquid. The addition of a small amount of polyoxyethylene can change the molecular weight distribution and morphology of the polymer, and help to improve the flexibility, tensile strength and processing properties of the polymer.

[0044] Preparation of S2 catalyst dilution liquid: In a catalyst preparation tank, the bis-indenyl methylene bridged zirconium catalyst (Ind)2CH2ZrCl2, the co-catalyst MMAO and the supercritical ethane fluid are evenly mixed to form a supercritical ethane catalyst dilution liquid, wherein the molar ratio of (Ind)2CH2ZrCl2 to MMAO is 1:100-200, and the concentration of the bis-indenyl methylene bridged zirconium catalyst in supercritical ethane is 0.1-1mmol / L.

[0045] S3: Under stirring, add about 100-500 mL of the above catalyst dilution solution to the reactor, add measured 1-octene, and adjust to the set rotation speed, the stirring speed is 100-500 rpm.

[0046] S4 maintains the reactor temperature at 33-40°C and the pressure at 5.6-6Mpa, adds raw materials ethylene and hydrogen to the reactor, and adjusts the hydrogen flow rate to control the molecular weight. After the reaction is completed, the slurry is moved to the flash tank for product separation, the separated gas phase is sent to the recovery unit, and the separated solid polymer enters the degassing and drying unit. The dried polymer powder is sieved and homogenized to obtain the final product.

[0047] This embodiment adopts the batch process (which can be adjusted to a continuous process in actual industrial production), the total mass of ethylene feed is less than 1000g, the total mass of 1-octene feed is 5-30wt% of ethylene, and the hydrogen flow rate is 0.1-1mol / h. The reaction progress, including temperature, pressure and monomer consumption, is monitored. During the polymerization reaction, the temperature is maintained between 33°C and 40°C, and the pressure is maintained between 5.6MPa and 6MPa.

[0048] The following is an explanation with reference to specific embodiments to prepare different polyethylene finished products.

[0049] Example 1

[0050] S1 supercritical ethane is maintained in the reactor at 10 L as the reactor bottom liquid.

[0051] The molar ratio of (Ind)2CH2ZrCl2 to MMAO in the S2 catalyst dilution was 1:100, and the concentration of the bis-indenyl methylene bridged zirconium catalyst in supercritical ethane in a stirred reactor was 0.032 mmol / L.

[0052] S3: Add the catalyst dilution into the reactor, start stirring, and adjust the stirring speed to 200 rpm.

[0053] S4 maintains the reactor temperature at 33°C and the pressure at about 5.6 MPa, adds 624 g of ethylene and 62.4 g of 1-octene monomers, and adjusts the hydrogen flow rate to 0.1 mol / h to control the molecular weight. The reaction is continued for 2 hours to finally obtain a polyethylene product.

[0054] Example 2

[0055] S1: 10L of supercritical ethane is maintained in the reactor as the reactor bottom liquid, and 10g of polyoxyethylene is added.

[0056] The molar ratio of (Ind)2CH2ZrCl2 to MMAO in the S2 catalyst dilution was 1:150, and the concentration of the bis-indenyl methylene bridged zirconium catalyst in supercritical ethane in a stirred reactor was 0.065 mmol / L.

[0057] S3: Add the catalyst dilution into the reactor, start stirring, and adjust the stirring speed to 200 rpm.

[0058] S4 maintains the reactor temperature at 34.5°C and the pressure at about 5.7 MPa, adds 600 g of ethylene and 60 g of 1-octene monomers, and adjusts the hydrogen flow rate to 0.1 mol / h to control the molecular weight. The reaction is continued for 1 hour to finally obtain a polyethylene product.

[0059] Example 3

[0060] S1: 12L of supercritical ethane is maintained in the reactor as the reactor bottom liquid, and 15g of polyoxyethylene is added.

[0061] The molar ratio of (Ind)2CH2ZrCl2 to MMAO in the S2 catalyst dilution was 1:180, and the concentration of the bis-indenyl methylene bridged zirconium catalyst in supercritical ethane in a stirred reactor was 0.04 mmol / L.

[0062] S3: Add the catalyst dilution into the reactor, start stirring, and adjust the stirring speed to 200 rpm.

[0063] S4 maintains the reactor temperature at 39°C and the pressure at about 5.8 MPa, adds 800 g of ethylene and 120 g of 1-octene monomers, and adjusts the hydrogen flow rate to 0.1 mol / h to control the molecular weight. The reaction is continued for 2 hours to finally obtain a polyethylene product.

[0064] Example 4

[0065] S1 supercritical ethane is maintained in the reactor at 11 L as the reactor bottom liquid.

[0066] The molar ratio of (Ind)2CH2ZrCl2 to MMAO in the S2 catalyst dilution was 1:200, and the concentration of the bis-indenyl methylene bridged zirconium catalyst in supercritical ethane in a stirred reactor was 0.02 mmol / L.

[0067] S3: Add the catalyst dilution into the reactor, start stirring, and adjust the stirring speed to 200 rpm.

[0068] S4 maintains the reactor temperature at 38°C and the pressure at about 5.6 MPa, adds 700 g of ethylene and 60 g of 1-octene monomers, and adjusts the hydrogen flow rate to 0.1 mol / h to control the molecular weight. The reaction is continued for 3 hours to finally obtain a polyethylene product.

[0069] Example 5

[0070] S1: 15L of supercritical ethane is maintained in the reactor as the reactor bottom liquid, and 20g of polyoxyethylene is added.

[0071] The molar ratio of (Ind)2CH2ZrCl2 to MMAO in the S2 catalyst dilution solution was 1:120, and the concentration of the bis-indenyl methylene bridged zirconium catalyst in supercritical ethane in a stirred reactor was 0.022 mmol / L.

[0072] S3: Add the catalyst dilution into the reactor, start stirring, and adjust the stirring speed to 200 rpm.

[0073] S4 maintains the reactor temperature at 40°C and the pressure at about 5.9 MPa, adds 900 g of ethylene and 50 g of 1-octene monomers, and adjusts the hydrogen flow rate to 0.1 mol / h to control the molecular weight. The reaction is continued for 3.5 hours to finally obtain a polyethylene product.

[0074] Comparative Example 1

[0075] Compared with Example 3, no 1-octene comonomer was added, 1-octene was replaced by an equal amount of ethylene, and the remaining steps were the same as in Example 3.

[0076] Comparative Example 2

[0077] Compared with Example 3, the catalyst type was changed and the catalyst was replaced with a Ziegler-Natta catalyst (TiCl4 and triethylaluminum, Ti / Al molar ratio of 1:75, and the concentration of TiCl4 in supercritical ethane in the reactor was 0.012 mmol / L), and the remaining steps were the same as in Example 3.

[0078] Comparative Example 3

[0079] Compared with Example 3, the solvent type was changed, and ethane was replaced by an equal amount of hexane, that is, supercritical fluid ethane was not used, and the remaining steps were the same as in Example 3.

[0080] Comparative Example 4

[0081] Compared with Example 3, the supercritical state of the solvent in the reactor was changed, the temperature of the reactor was controlled at 29° C., and only ethane was kept in liquid state. The remaining steps were the same as in Example 3.

[0082] Comparative Example 5

[0083] Compared with Example 3, supercritical ethane is replaced by liquid ethane in the catalyst diluent, and the remaining steps are the same as those in Example 3.

[0084]

Finished product performance testing

[0085] (1) Molecular weight determination experiment The viscosity average molecular weight was tested according to standard GB 1632.3-2010 (α=1.49);

[0086] The molecular weight distribution (PDI) was calculated from gel permeation chromatography (GPC) testing.

[0087] Experimental procedures

[0088] Sample preparation: Grind the polyethylene sample into fine powder and ensure that the sample is evenly dispersed. Weigh 10 mg of the sample and put it into a vial for later use.

[0089] Solvent preparation: Filter tetrahydrofuran (THF) or dichloromethane (DCM) solvent to remove impurities and ensure the purity of the solvent.

[0090] Sample dissolution: Add the sample to the solvent and dissolve it in an ultrasonic cleaner to ensure that the sample is completely dissolved.

[0091] GPC analysis: Inject the dissolved sample into the GPC instrument for analysis. Use the standard polystyrene calibration curve for molecular weight calibration. Record the molecular weight distribution data, calculate the number average molecular weight (Mn) and weight average molecular weight (Mw), and finally calculate PDI.

[0092] (2) Melt index measurement experiment

[0093] Melt index is tested according to GB / T 3682.1-2018 (test conditions 190℃ / 21.6kg)

[0094] Experimental procedures

[0095] Sample preparation: Grind the polyethylene sample into fine powder and ensure that the sample is evenly dispersed. Weigh 10g of the sample and put it into a small bottle for later use.

[0096] Melt Flow Indexer Settings: Preheat the melt flow indexer to the desired test temperature of 190°C. Set the load to 21.6 kg.

[0097] Sample test: Add the sample into the barrel of the melt indexer. Heat the sample to the test temperature and keep it for a certain time to make it completely melted. Apply a load and record the mass of the sample flowing out within the specified time.

[0098] Data processing: The melt index (MFI) is calculated based on the outflow quality and time.

[0099] (3) Mechanical properties test

[0100] Simply supported beam impact strength (unit: kJ / m 2 ) The test was carried out according to the standard GB / T1043;

[0101] The tensile strength and elongation at break were tested by a universal testing machine according to GB / T528-2009. The standard specimens for mechanical property testing were injection molded by an injection molding machine. The test specimens were cut into dumbbell-shaped tensile specimens of 25 mm × 4 mm, and the stretching rate was 20 mm / min.

[0102] Each example was tested at least 5 times to ensure the reliability of the results.

[0103] The products obtained in Examples 1-5 and Comparative Examples 1-5 were tested according to the above experimental scheme. The experimental results are shown in Tables 1 and 2 for details.

[0104] Table 1 Molecular weight and melt index test data

[0105] Viscosity average molecular weight / Molecular weight distribution (PDI) Melt Index (MFI) / Example 1 57 2.4 0.63 Example 2 59 2.1 0.68 Example 3 63 2.2 0.72 Example 4 61 2.5 0.64 Example 5 62 2.7 0.67 Comparative Example 1 65 2.0 0.47 Comparative Example 2 54 5.9 0.49 Comparative Example 3 55 5.1 0.59 Comparative Example 4 59 4.6 0.56 Comparative Example 5 58 4.3 0.53

[0106] Table 2 Test data of tensile strength, elongation at break and simply supported beam impact strength

[0107] Tensile strength(MPa) Elongation at break (%) <![CDATA[Izod impact strength (kJ / m 2 )]]> Example 1 44.8 838 104 Example 2 41.3 865 109 Example 3 40.1 887 112 Example 4 44.9 826 103 Example 5 43.8 842 106 Comparative Example 1 43.3 668 89 Comparative Example 2 42.8 759 95 Comparative Example 3 44.0 737 94 Comparative Example 4 45.2 799 101 Comparative Example 5 44.8 774 99

[0108] As shown in Table 1 and Table 2, the viscosity average molecular weight of the products obtained in Examples 1 to 5 of the present invention is about 600,000 on average, the melt index is 0.6-0.75 g / 10 min, the molecular weight distribution is between 2 and 3, the tensile strength is 40-45 MPa, the elongation at break is 800-900%, and the simply supported beam impact strength is 100-115 kJ / m 2 Compared with polyethylene without adding 1-octene comonomer (Comparative Example 1), the melt index, elongation at break and simply supported beam impact strength of the product are significantly improved. When the catalyst type (Comparative Example 2), solvent type (Comparative Example 3) and supercritical process conditions (Comparative Examples 4 and 5) are changed, the uniformity, melt index, elongation at break and impact strength of the obtained product deteriorate to varying degrees. It can be seen that the supercritical ethane polymerization process of the present invention can make ethylene and 1-octene polymerize better and obtain products with better performance.

[0109] The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing ethylene-octene copolymer by a slurry process, characterized in that: The following steps are involved: The monomer ethylene and the comonomer 1-octene are used as raw materials; Diluting the catalyst with supercritical ethane to obtain a catalyst dilution solution, wherein the catalyst comprises a metallocene catalyst and a co-catalyst; Adding the catalyst dilution, raw materials and hydrogen into a stirred reactor containing supercritical ethane to carry out polymerization reaction, wherein the temperature and pressure of the stirred reactor are controlled above the supercritical condition of ethane; After the polymerization is completed, the slurry discharged from the stirred reactor is post-treated to obtain the finished product.

2. The method for preparing ethylene octene copolymer by a slurry process according to claim 1, characterized in that: The metallocene catalyst is bis-indenyl methylene bridged zirconium, and the co-catalyst is aluminoxane; The molar ratio of the metallocene catalyst to the co-catalyst is 1:50-400, preferably 1:100-200; In the catalyst dilution solution, the concentration of the metallocene catalyst in supercritical ethane is 0.1-10 mmol / L, preferably 0.1-5 mmol / L, and more preferably 0.1-1 mmol / L.

3. The method for preparing ethylene octene copolymer by a slurry process according to claim 2, characterized in that: The metallocene catalyst is (Ind)2CH2ZrCl2, and the co-catalyst is methylaluminoxane and / or tetrabutylaluminoxane, preferably methylaluminoxane.

4. The method for preparing ethylene octene copolymer by a slurry process according to claim 1, characterized in that: In the catalyst preparation tank, the metallocene catalyst and the co-catalyst are uniformly mixed with supercritical ethane under an inert environment, and the catalyst preparation tank is maintained at a supercritical condition of ethane.

5. The method for preparing ethylene octene copolymer by a slurry process according to claim 1, characterized in that: After the inert gas is purged, ethane is continuously introduced into the stirred reactor, and the pressure is controlled at 4.8-6Mpa. The stirred reactor is kept in a heated state, and the reactor is heated to 33-40°C to make ethane in a supercritical state. The bottom liquid of the stirred reactor has a total volume of 1 / 4-1 / 2 of the total volume of the stirred reactor, preferably 1 / 4-1 / 3.

6. The method for preparing ethylene octene copolymer by a slurry process according to claim 5, characterized in that: Under stirring, catalyst dilution and 1-octene are added to the stirred reactor in sequence, and finally high-pressure ethylene and hydrogen are introduced. The pressure in the stirred reactor is controlled at 5.6-6Mpa and the temperature is controlled at 33-40°C to carry out polymerization reaction.

7. The method for preparing ethylene octene copolymer by a slurry process according to claim 6, characterized in that: The amount of the catalyst diluent added is 1-5% of the volume of the kettle bottom liquid; and / or, the amount of 1-octene added is 5-30%, preferably 10-15%, by weight, of the ethylene; And / or, the molar concentration of the total amount of ethylene added in the kettle bottom liquid is 1-10 mol / L, preferably 1.5-3.5 mol / L; And / or, the amount of hydrogen added is 0.1-5% by volume of ethylene; And / or, adding an additive accounting for 0.01-1% of the total weight of the kettle bottom liquid, wherein the additive includes polyoxyethylene.

8. The method for preparing ethylene octene copolymer by a slurry process according to claim 7, characterized in that: The ethylene and hydrogen are added from the bottom of the stirred reactor and enter the bottom liquid of the reactor; And / or, a pressure relief vent is provided on the top of the stirred reactor.

9. The method for preparing ethylene octene copolymer by a slurry process according to claim 1, characterized in that: The post-processing steps include: transferring the reaction slurry to a flash tank for product separation, sending the separated gas phase to a recovery unit, and the separated solid polymer entering a degassing and drying unit. The dried polymer powder is sieved and homogenized to obtain the final product.

10. The ethylene octene copolymer prepared by the method for preparing ethylene octene copolymer by a slurry process according to any one of claims 1 to 9, characterized in that: The viscosity average molecular weight of the ethylene octene copolymer is 550,000-650,000, the molecular weight distribution is 2-3, the melt index is 0.6-0.75 g / 10 min, the tensile strength is 40-45 MPa, the elongation at break is 800-900%, and the simply supported beam impact strength is 100-115 kJ / m 2 .

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