Ethylene copolymer and preparation method thereof

Abstract

The invention provides an ethylene copolymer and a preparation method thereof. A catalyst adopted by the preparation method is a metallocene catalyst, and the metallocene catalyst comprises a carrier for the metallocene catalyst, a metallocene compound and a cocatalyst; the carrier is prepared by the following steps: placing silicon dioxide aerogel microspheres in a container for microwave treatment; hot nitrogen is introduced for purging in the microwave treatment; stopping microwave treatment, vacuumizing, and introducing normal-temperature nitrogen for purging to obtain the carrier for the metallocene catalyst; the preparation method comprises a pre-polymerization step and a copolymerization reaction step, the prepolymerization comprises the following steps: mixing a metallocene catalyst and alkyl aluminum, and introducing ethylene for prepolymerization. According to the invention, the silicon dioxide aerogel microspheres are used as the carrier to load the metallocene catalyst, so that the loading capacity of the metallocene compound is improved, the vinyl monomer can be subjected to polymerization reaction on the surface of the silicon dioxide aerogel and in internal pores, the polymerization activity of the metallocene catalyst is improved, and the activity release of the catalyst is stable.

Description

Technical Field

[0001] This invention relates to an ethylene copolymer and its preparation method, belonging to the field of polymer materials technology. Background Technology

[0002] Metallocene polyolefins possess good strength, transparency, and heat-sealing properties due to their narrow molecular weight distribution and uniform comonomer distribution. The core technology for producing metallocene polyolefins is the use of metallocene catalysts, which can be supported on various materials such as silica gel (silica), magnesium chloride, and alumina. Silica has abundant silanol groups on its surface, allowing for the loading of metallocene catalysts; therefore, silica is the most commonly used support for metallocene catalysts.

[0003] Silica exists in two forms: crystalline and amorphous. Silica used as a support for metallocene catalysts is usually amorphous silica, which is lightweight, porous, has a high specific surface area, good insulation, acid and alkali resistance, and high temperature resistance.

[0004] SiO2 aerogel is a porous amorphous material with an open pore structure. The main structure of silica aerogel is a continuous three-dimensional network structure formed by the aggregation of silicon-oxygen nanoparticles. It consists of over 90% network pores and less than 10% SiO2 framework, with the pores filled with a gaseous dispersion medium. Silica aerogel has many excellent properties, including a high surface area (500-1000 m²). 2 High porosity (80-99.8%), low density (0.003-0.8 g / cm³). 3 It has a low thermal conductivity (~0.02 W / m·K), among which the extremely low thermal conductivity is the most significant characteristic of silica aerogel microspheres.

[0005] Compared to ordinary silica gel (SiO2), a key characteristic of aerogel porous networks is their "open" nature and interconnectivity, allowing fluid to flow from one pore to another and eventually through the entire material. Aerogel microspheres have pore sizes of around 10 nanometers (nm) and contain numerous micropores, making them a typical nanoporous material with a continuous network structure and a relatively uniform distribution of internal network pores. Because the tiny pores of aerogel permeate the entire material, it exhibits excellent adsorption performance, resulting in adsorption efficiency superior to that of ordinary silica gel.

[0006] Silica aerogels are typically irregular, blocky materials, making them difficult to process into complex geometries and limiting their applications. However, preparing silica aerogels into porous network microspheres can broaden their application range. Post-processing SiO2 aerogel microspheres and using them as supports for metallocene catalysts can significantly increase the loading of active components in metallocene catalysts and alter their catalytic properties.

[0007] Metallocene catalyst supports (such as silica) typically require high-temperature activation before loading to remove trace amounts of water and some hydroxyl groups from the silica surface. CN1055184A discloses a supported catalyst active in the polymerization and copolymerization of olefinic unsaturated compounds. This catalyst comprises an organometallic aluminum derivative and a second component. This second component is obtained by reacting a magnesium compound and / or a titanium, vanadium, or chromium compound, and optionally at least one compound of a second metal selected from Al, V, Zr, Hf, Nd, and Mo, in the presence of one or more inorganic oxide aerogel microsphere porous supports. The support can be used directly without treatment or activated first, for example, by heating under reduced pressure at 165°C for 8 hours and then cooling in dry nitrogen. However, this method makes it difficult to effectively control the hydroxyl content on the support surface during activation, and the support is also difficult to heat uniformly, thus affecting catalyst performance. Furthermore, this method requires an extremely narrow pore diameter distribution on the aerogel support, with the difference between the maximum and minimum pore sizes not exceeding 50 angstroms, placing extremely high demands on the aerogel microspheres.

[0008] CN108970647A discloses a method for preparing a metallocene catalyst support. This method involves fluidizing SiO2 or modified SiO2 under nitrogen purging, heating to a constant temperature, and then gradually cooling to room temperature to obtain the metallocene catalyst support. For ordinary silica gel (SiO2), calcination under hot nitrogen purging ensures uniform heating of the silica gel support and sufficient exchange of atmospheres inside and outside the support, improving the activation effect. However, the stability of the SiO2 aerogel framework is slightly worse than that of ordinary silica gel, and high-temperature gas fluidization may cause damage to its framework. Therefore, SiO2 aerogel supports are not suitable for activation using this method.

[0009] A significant portion of metallocene polyethylene (mLLDPE) products are used in the film industry; therefore, the processing behavior of mLLDPE and the performance of film products have become a focus of current attention. Currently, films prepared from experimental mLLDPE metallocene 1-hexene-ethylene copolymer produced by the gas-phase method exhibit good mechanical properties, but suffer from issues such as numerous crystal points and insufficient brightness. During polymerization, uneven distribution of catalyst active sites or excessively high local activity can easily lead to unstable catalytic activity, incomplete and unstable polymerization, and consequently, the production of high molecular weight products or uneven distribution of comonomers.

[0010] Therefore, developing a preparation method that can improve the optical properties of metallocene polyethylene is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0011] To address the aforementioned technical problems, the present invention aims to provide an ethylene copolymer and its preparation method, wherein the film made from the ethylene copolymer has low haze.

[0012] To achieve the above objectives, the present invention provides a method for preparing ethylene copolymers, wherein the catalyst used in the preparation method includes a metallocene catalyst and a co-catalyst, and the metallocene catalyst comprises a metallocene catalyst support and a metallocene compound;

[0013] The support for the metallocene catalyst is prepared through the following steps:

[0014] Silica aerogel microspheres were placed in a container and microwaved.

[0015] During microwave processing, hot nitrogen gas is introduced into the container to purge the silica aerogel microspheres.

[0016] Stop the microwave treatment, evacuate the container, and then purge the silica aerogel microspheres with room temperature nitrogen gas to obtain the support for the metallocene catalyst.

[0017] The preparation method includes a prepolymerization step and a copolymerization reaction step; the prepolymerization step includes: mixing the metallocene catalyst and alkylaluminum, and then passing ethylene through to perform prepolymerization to obtain a prepolymer catalyst.

[0018] Microwave treatment is a type of heating that occurs from within the material, enabling rapid overall temperature rise of the system within a very short time. This rapid overall heating approach overcomes the shortcomings of traditional heating methods, such as inefficiency and uneven heating due to thermal gradients. This invention utilizes microwave-assisted activation of silica aerogel microspheres to facilitate the preparation of high-performance metallocene catalyst supports.

[0019] According to a specific embodiment of the present invention, preferably, the silica aerogel microspheres have an average particle size of 20-200 μm and a bulk density of 0.20-0.35 g / cm³. 3 The pore volume is 1.2-3.0 cm³. 3 / g, specific surface area of ​​100-1000m² 2 / g.

[0020] According to a specific embodiment of the present invention, preferably, the container is a microwave activation device, which includes a body, a first filter, and a second filter;

[0021] The main body is spindle-shaped, with a vacuum port and a nitrogen inlet at the upper and lower ends, respectively. The nitrogen inlet is connected to a hot nitrogen pipe and a room temperature nitrogen pipe.

[0022] The first filter and the second filter are disposed in the middle of the container, with a space between them for placing silica aerogel microspheres.

[0023] A schematic diagram illustrating the usage of the microwave activation device is shown below. Figure 2 As shown, during use, the silica gel microspheres to be activated are placed between the first and second filters, i.e., on the surface of the second filter, and then the microwave activation device is placed in a microwave oven for microwave treatment.

[0024] According to a specific embodiment of the present invention, preferably, the first filter screen has a mesh count of not less than 800 mesh (the sieve aperture does not exceed 18 micrometers), and / or, the second filter screen has a mesh count of not less than 800 mesh.

[0025] According to a specific embodiment of the present invention, preferably, the first filter screen is made of ceramic or quartz, and / or the second filter screen is made of ceramic or quartz.

[0026] According to a specific embodiment of the present invention, preferably, the microwave emission source used in the microwave processing has a frequency of 1000-3000MHz, more preferably 2450MHz (exciting molecules inside the material to move at 2.45 × 10⁻⁶ MHz per second). 9 The ultra-high frequency vibration and friction (repeated times) has a power of 500-1000W, preferably 850W.

[0027] According to a specific embodiment of the present invention, preferably, the microwave treatment time is 1-10 minutes.

[0028] According to a specific embodiment of the present invention, preferably, the temperature of the hot nitrogen gas is 70-150°C, and / or the purity of the hot nitrogen gas and the room temperature nitrogen gas is above 99.999% and the water content is not more than 5 ppm.

[0029] According to a specific embodiment of the present invention, preferably, the vacuuming is performed until the pressure inside the container reaches -0.05 MPa to -0.1 MPa.

[0030] According to a specific embodiment of the present invention, preferably, the hydroxyl content of the metallocene catalyst support is 2.0-5.0 mmol / g-SiO2, more preferably 2.2-3.6 mmol / g-SiO2.

[0031] According to a specific embodiment of the present invention, preferably, the comonomer comprises an α-olefin and ethylene, wherein the α-olefin is selected from one or more combinations of propylene, 1-butene, 1-pentene, 1-hexene, and 1-octene.

[0032] According to a specific embodiment of the present invention, preferably, based on the total amount of all gases in the reactor being 100%, the molar percentage of ethylene is 40-60%, the molar ratio of α-olefin to ethylene is 0.01-0.3, and the molar ratio of hydrogen to ethylene is 0.5-10.0. The reactor contains gases such as ethylene, α-olefin, hydrogen, nitrogen, and isopentane.

[0033] According to a specific embodiment of the present invention, preferably, the metallocene catalyst has a zirconium content of 0.2-0.5 wt% (more preferably 0.20-0.45 wt%) and an aluminum content of 10-25 wt% (more preferably 12-25 wt%) by mass percentage.

[0034] According to a specific embodiment of the present invention, preferably, the particle size of the metallocene catalyst is 25-210 μm, more preferably 35-105 μm.

[0035] According to a specific embodiment of the present invention, preferably, the bulk density of the metallocene catalyst is 0.3-0.6 g / cm³. 3 More preferably, it is 0.42-0.51 g / cm³. 3 .

[0036] According to a specific embodiment of the present invention, preferably, the metallocene compound has the general formula Cp. x MA y B z ,in:

[0037] Cp can be an unsubstituted cyclopentadienyl, a substituted cyclopentadienyl, an indenyl, a fluorenyl, an indenyl ligand in hydrogenated form, or a fluorenyl ligand in hydrogenated form.

[0038] M is a transition metal;

[0039] A and B are halogen atoms, hydrogen atoms, or alkyl groups, respectively;

[0040] x is an integer from 1 to 3, and y and z are integers from 0 to 3 respectively.

[0041] According to a specific embodiment of the present invention, preferably, in the above-mentioned metallocene compounds, when x equals 2 in the general formula, the Cp ligand can be bridged by polymethylene or dialkylsilane, such as by bridging with -Si(CH3)2-, -C(CH3)2-, -CH2-, -CH2-CH2-, etc.

[0042] According to a specific embodiment of the present invention, preferably, in the above-mentioned metallocene compound: when the substituents A and B are halogen atoms, y+z is equal to or less than 3, and x+y+z is equal to 4; when the substituents A and B in the general formula of the metallocene compound are alkyl groups, the substituents A and B are preferably straight-chain or branched alkyl groups containing 1-8 carbon atoms, such as methyl, ethyl, n-propyl, n-butyl, isobutyl or n-pentyl.

[0043] According to a specific embodiment of the present invention, preferably, the metallocene compound includes one or more combinations of bis(cyclopentadienyl) metal dihalides, bis(cyclopentadienyl) metal monoalkyl monohalides, bis(cyclopentadienyl) metal dialkyl compounds, and bis(indenyl) metal dihalides, wherein the metal is a group IVB metal, including titanium, zirconium, or hafnium, typically zirconium or hafnium, the alkyl group is an alkyl group with 1-6 carbons, and the halide is a chloride.

[0044] The following description uses examples to illustrate the metallocene compounds used in this invention, but is not intended to limit the invention. These metallocene compounds include di(cyclopentadienyl)zirconia dichloride, di(cyclopentadienyl)hafnium dichloride, di(cyclopentadienyl)dimethylzirconia, di(cyclopentadienyl)dimethylhafnium, di(n-butylcyclopentadienyl)zirconia dichloride, di(n-butylcyclopentadienyl)hafnium dichloride, di(n-butylcyclopentadienyl)dimethylzirconia, di(n-butylcyclopentadienyl)dimethylzirconia, di(n-butylcyclopentadienyl)zilium chloride ... (di(dimethylcyclopentadienyl)dimethylhafnium, bis(dimethylcyclopentadienyl)dimethylzirconium, bis(tetramethylcyclopentadienyl)dimethylhafnium, diindylzirconium dichloride, methylene-bridged diindylzirconium dichloride and bis(4,5,6,7-tetrahydro-1-indyl)zirconium dichloride, ethylidene-bridged di(indyl)zirconium dichloride, diindylhafnium dichloride, methylene-bridged diindylhafnium dichloride and bis(4,5,6,7-tetrahydro-1-indyl)zirconium dichloride, ethylidene-bridged di( Hafnium dichloride (indenyl), ethylene-bridged bis(indenyl)titanium dichloride, bis(4,5,6,7-tetrahydro-1-indenyl)titanium dichloride, bis(n-butylcyclopentadienyl)titanium dichloride, bis(cyclopentadienyl)titanium dichloride, dimethylsilyl-bridged bis(2-methyl-4-phenylindenyl)zirconium dichloride, dimethylsilyl-bridged bis(2-methyl-4-phenylindenyl)hafnium dichloride, dimethylsilyl-bridged bis(2-methyl-4-phenylindenyl)dimethylzirconium, dimethyl The following are examples of methylsilicon-bridged bis(2-methylindene)zirconium dichloride, bis(2-methylindene)hafnium dichloride, bis(2-methyl-benzoindene)zirconium dichloride, bis(2-methyl-benzoindene)hafnium dichloride, bis(2-methyl-benzoindene)dimethylzirconium dichloride, bis(2-methyl-benzoindene)dimethylzirconium dichloride, and methylsilicon-bridged bis(2-methyl-4-phenylindene)dimethylzirconium dichloride.

[0045] According to a specific embodiment of the present invention, preferably, the co-catalyst is selected from alkylaluminoxane compounds, and the alkylaluminoxane compounds are selected from one or more combinations of methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, butylaluminoxane, pentylaluminoxane, decylaluminoxane, modified methylaluminoxane, etc.

[0046] According to a specific embodiment of the present invention, preferably, the preparation method of the above-mentioned metallocene catalyst includes the following steps:

[0047] The metallocene catalyst is reacted by mixing a support with a solution of a co-catalyst.

[0048] After washing the solid product of the reaction, a solvent was added, followed by the addition of a metallocene compound for loading.

[0049] The loaded product was washed and desolventized to obtain the metallocene catalyst.

[0050] The reaction formulas for silanol groups with MAO and cyclohexane compounds are as follows:

[0051]

[0052] According to a specific embodiment of the present invention, preferably, in the above-mentioned method for preparing the metallocene catalyst, the temperature of the mixing reaction is -20°C to 60°C, and the time is 1-8 hours.

[0053] According to a specific embodiment of the present invention, preferably, in the above-mentioned method for preparing the metallocene catalyst, the loading temperature is 30-70°C and the time is 1-10 hours.

[0054] According to a specific embodiment of the present invention, preferably, in the above-mentioned method for preparing the metallocene catalyst, the solvent is an alkane solvent and / or an aromatic solvent, wherein the alkane solvent may be butane, hexane, heptane, cyclohexane, etc., and the aromatic solvent may be benzene, xylene, toluene, etc.

[0055] In the preparation of metallocene catalysts using silica aerogel microspheres, metallocene compounds and the co-catalyst methylaluminoxane (MAO) are primarily loaded onto the support through interaction with silanol groups on and within the aerogel surface. The type and quantity of silanol groups significantly influence the metal loading of the metallocene catalyst; excessive or insufficient hydroxyl content is detrimental to metallocene loading and ultimately affects catalyst performance. Since the silica aerogel microsphere content is mainly controlled through the activation process, achieving appropriate hydroxyl content control during silica aerogel activation while avoiding damage to its framework structure presents a crucial technical challenge.

[0056] This invention employs microwave treatment combined with vacuuming and hot nitrogen purging to enable activated silica aerogel microspheres to have an appropriate hydroxyl content, thereby facilitating the loading of metallocene compounds in metallocene catalysts and resulting in highly active metallocene catalysts.

[0057] According to a specific embodiment of the present invention, preferably, the method for preparing the ethylene copolymer includes a prepolymerization step and a copolymerization reaction step; wherein, the prepolymerization step includes:

[0058] The solvent and alkylaluminum were mixed in a reaction vessel, and the metallocene catalyst was added. The temperature was controlled to the prepolymerization temperature, and ethylene was introduced for slurry polymerization. After polymerization was completed, the ethylene feed was stopped, the temperature was lowered to room temperature, and the prepolymerization catalyst was separated. In slurry polymerization, the ethylene monomer concentration is relatively low, which is beneficial for reducing the initial polymerization activity.

[0059] According to a specific embodiment of the present invention, preferably, the solvent is an alkane solvent, which is selected from one or more combinations of butane, hexane, heptane, and cyclohexane.

[0060] According to a specific embodiment of the present invention, preferably, in the prepolymerization step, the mass ratio of the alkylaluminum to the metallocene catalyst is 8:1-32:1.

[0061] According to a specific embodiment of the present invention, preferably, the alkyl aluminum used in the prepolymerization step has the general formula AlR 3 m X 1 (3-m) In the formula R 3 For C1-C 20 Alkyl, aryl, or aralkyl; X 1 It is a halogen (e.g., F, Cl, Br, I, etc.); m is an integer 0 ≤ n ≤ 3, preferably one or a combination of two or more of trimethylaluminum, triethylaluminum, triisobutylaluminum, diethylaluminum chloride and diisobutylaluminum chloride, preferably triethylaluminum and / or triisobutylaluminum.

[0062] According to a specific embodiment of the present invention, preferably, the prepolymerization temperature is -10°C to 20°C, more preferably -5°C to 5°C.

[0063] According to a specific embodiment of the present invention, preferably, the prepolymerization time is 5-60 minutes.

[0064] During polymerization, prepolymerization enables the microcrystals within the catalyst particles to be fully activated under mild conditions, resulting in a looser catalyst particle structure and increased surface gaps. This also allows for a more complete and uniform release of the catalyst's active centers. This invention, by improving the catalyst and polymerization process, enables the comonomers to be uniformly distributed between molecular chains, reducing the differences in crystallization ability between different crystalline segments and facilitating the formation of more uniform crystal nuclei. This results in metallocene polyethylene films with lower haze and better optical properties.

[0065] During the prepolymerization process, it is necessary to control the prepolymerization rate and degree of prepolymerization of the silica aerogel microsphere-based metallocene catalyst, which is achieved by controlling reaction conditions such as prepolymerization temperature and prepolymerization time. When the prepolymerization rate of the catalyst is too fast or the degree of prepolymerization is too low, the catalyst is prone to premature breakage because the strength of the aerogel microspheres is slightly lower than that of ordinary silica, affecting the final polymer morphology and performance.

[0066] According to a specific embodiment of the present invention, the degree of prepolymerization is determined by the polymerization activity. Preferably, the activity of the prepolymerized catalyst obtained by prepolymerization is 10-50 gP / g cat·h.

[0067] According to a specific embodiment of the present invention, preferably, the copolymerization reaction step includes:

[0068] The reactor is purged with nitrogen, a prepolymer catalyst is injected, the reactor is heated to the copolymerization reaction temperature, and then comonomers and hydrogen are introduced to copolymerize and obtain the ethylene copolymer.

[0069] According to a specific embodiment of the present invention, preferably, the reactor is a gas-phase fluidized bed reactor.

[0070] According to a specific embodiment of the present invention, preferably, the copolymerization reaction is carried out at a pressure of 1.0-2.5 MPa and a temperature of 60-100°C.

[0071] The present invention also provides an ethylene copolymer, which is prepared by the above-described method for preparing ethylene copolymer.

[0072] According to a specific embodiment of the present invention, preferably, the haze of the ethylene copolymer is 3.4-5.2, and this haze is measured using a haze meter for films made of the ethylene polymer. The haze of the film is tested according to GB / T 2410-2008.

[0073] This invention utilizes silica aerogel microspheres as a support for loading metallocene catalysts. The high specific surface area and high porosity of silica aerogel as a support (compared to ordinary silica gel supports) increases the loading capacity of metallocene compounds. Ethylene monomers can polymerize on the surface and within the pores of the silica aerogel, enhancing the polymerization activity of the metallocene catalyst and stabilizing its release. Through prepolymerization and gas-phase polymerization processes, the uniformity of copolymer monomer insertion in the ethylene copolymer can be improved, enhancing the optical properties of the copolymer. Films made from this copolymer exhibit low haze.

[0074] The beneficial effects of this invention are:

[0075] (1) Compared with metallocene catalysts supported on traditional silica gel supports, the silica aerogel support has a higher specific surface area and pore volume, which can increase the loading of metallocene catalysts and thus greatly improve the activity of metallocene catalysts.

[0076] (2) Compared with metallocene catalysts supported on traditional silica gel supports, the silica aerogel support has a higher specific surface area and pore volume, which can increase the loading of metallocene catalysts and thus improve the activity of metallocene catalysts.

[0077] (3) The high porosity and pore volume of silica aerogel support are conducive to the stable release of the activity of metallocene catalyst during polymerization, and improve the insertion rate and uniformity of comonomers during copolymerization.

[0078] (4) By using microwave-assisted activation of the support, the support can be heated efficiently and uniformly, preventing the destruction of the support skeleton structure of silica aerogel microspheres at high temperature or in fluidized state, thereby obtaining high-performance metallocene catalysts.

[0079] (5) After prepolymerization, the catalyst components are uniformly aged, and the catalyst containing some highly active centers naturally decays, which can avoid the sudden release of activity of the catalyst components during subsequent polymerization, causing problems such as catalyst particle breakage and local hot spots. Attached Figure Description

[0080] Figure 1 This is a schematic diagram of the microwave activation device used in the embodiments and comparative examples.

[0081] Figure 2 This is a schematic diagram illustrating how the microwave activation device is used. Detailed Implementation

[0082] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0083] The evaluation and analysis methods for some parameters involved in the examples and comparative examples are as follows:

[0084] (1) The particle size of the support and catalyst was determined using a Mastersizer 2000 Malvern particle size analyzer.

[0085] (2) Specific surface area, pore structure and porosity were tested using a TriStar IIPlus 3.02 specific surface area and porosity analyzer from Microneritics, USA, by N2 adsorption method.

[0086] (3) The bulk density was tested using an HT1001 multi-functional powder physical property tester.

[0087] (4) The content of metal elements in the catalyst was determined using an Avio 500 inductively coupled plasma atomic emission spectrometer.

[0088] (5) The molecular weight and molecular weight distribution of the polymer were tested using a Polymer Char high-temperature gel permeation chromatograph.

[0089] (6) The haze of the film was tested using a Diffusion EEL57D haze meter from the UK, according to GB / T 2410-2008.

[0090] The structure of the microwave activation device used in the embodiments and comparative examples is as follows: Figure 1 As shown, the microwave activation device includes a main body 1, a first filter 2, and a second filter 3;

[0091] The main body 1 is spindle-shaped, with a vacuum port 4 at the top and a nitrogen inlet at the bottom. The nitrogen inlet is connected to a hot nitrogen pipe 5 and a room temperature nitrogen pipe 6 respectively.

[0092] The first filter 2 and the second filter 3 are disposed in the middle of the body 1, and there is a space between them for placing silica aerogel microspheres; the first filter 2 has a mesh size of 800 mesh, and the second filter 3 has a mesh size of 800 mesh; the first filter is made of ceramic or quartz, and the second filter is made of ceramic or quartz.

[0093] A schematic diagram illustrating the usage of the microwave activation device is shown below. Figure 2 As shown.

[0094] Example 1

[0095] This embodiment provides a method for preparing an ethylene copolymer, which includes the following steps:

[0096] (1) Preparation of SiO2 aerogel microspheres: Specifically, the following steps are included:

[0097] ① Preparation of silica sol: At room temperature, 23.3g of tetraethyl orthosilicate (TEOS), 28.4g of ethanol and 6.1g of water are stirred and mixed at 400r / min for 5 minutes. Then, 0.53g of 0.01mol / L glycolic acid solution is added dropwise and stirred for 10 minutes. At this time, the pH value of the solution is 6.2. Let it stand for 3 hours to carry out the hydrolysis reaction. Then, 2.94g of 0.3mol / L ethanol ammonia solution is added dropwise and stirred for 10 minutes. At this time, the pH value of the solution is 8.2, thus forming silica sol.

[0098] ② At room temperature, 100 mL of soybean oil and 0.57 g of octylphenol polyoxyethylene ether-10 (op-10) were mixed in a 50 mL three-necked flask to prepare an oil phase. The mixture was stirred at 300 r / min until homogeneous. Then, 20 mL of the above silica sol was added and stirred at 800 r / min until gelation occurred, thus obtaining an emulsion system.

[0099] ③ Add 100 mL of ethanol to the above emulsion system, stir and mix at 800 r / min for 10 minutes, let stand and separate the layers, and then perform solid-liquid separation (after stopping stirring and standing, the entire emulsion system is divided into three layers, from top to bottom: ethanol, alcohol gel microspheres, and oil phase, and then use a separatory funnel to separate the alcohol gel microspheres). Wash the alcohol gel microspheres once with an ethanol-water solution (ethanol and water volume ratio of 1:2), wash them three times with ethanol, and then soak them in ethanol for aging for 20 hours to obtain aged alcohol gel microspheres.

[0100] ④ The aged alcohol aerogel microspheres are subjected to supercritical drying. The supercritical drying temperature reaches 50-270℃ within 5 hours, the supercritical drying pressure is 10-18MPa, and after reaching 250-270℃, it is held for 10 minutes. Then the pressure is released, nitrogen is purged, and the material is cooled to below 50℃ before being discharged. The obtained silica aerogel microspheres are sieved using sieves of different mesh sizes to obtain silica aerogel microspheres of specific particle sizes.

[0101] From the preparation of silica aerogel microspheres, some microspheres were screened out, and the average particle size was measured to be 100 μm and the bulk density was 0.30 g / cm³. 3 Specific surface area is 500m² 2 / g, pore volume 2.0cm 3 / g.

[0102] (2) Activation of SiO2 aerogel microspheres: Place 10g of silica aerogel microspheres between the two filters of the microwave activation device, turn on the microwave oven, the frequency of the microwave source is 2450MHz, the power of the microwave oven is 850W, purge the activation device with hot nitrogen gas preheated to 100℃ for 10 minutes, then turn off the microwave oven, stop the hot nitrogen gas, evacuate the activation device to -0.1MPa through the vacuum port, and purge with room temperature nitrogen gas for 30 minutes to complete the activation; the activated carrier is stored under nitrogen protection for later use.

[0103] (3) Preparation of metallocene catalyst: Under anhydrous and oxygen-free conditions, 1 g of the above-treated silica aerogel microsphere carrier was accurately weighed, and 30 mL of toluene was added to form a suspension. Then, 10 mL of a toluene solution containing 25 mmol MAO was added, and the mixture was stirred at 60 °C for 1 hour. The solid portion was washed three times with 30 mL of toluene, and then 30 mL of toluene was added again. 0.05 g of di(cyclopentadienyl)zirconium dichloride (Cp₂ZrCl₂) was added, and the mixture was stirred at 30 °C for 5 hours. The solid portion was washed three times with 30 mL of toluene, and the mixture was vacuum-sealed for 2 hours. After drying the toluene, a catalyst with good flowability was obtained. The average particle size of the obtained catalyst was 105 μm, the aluminum content was 25 wt%, and the zirconium content was 0.35 wt%.

[0104] (4) Preparation of ethylene copolymers:

[0105] ① Prepolymerization: 2L of n-hexane and 10mL of a hexane solution of triethylaluminum (10wt%) were added to a 5L slurry polymerization reactor. After stirring for 15 minutes, 500mg of the metallocene catalyst obtained in step (3) was added. The temperature of the polymerization reactor was controlled to -5℃, ethylene was introduced, and the reaction pressure was maintained at 0.8MPa for slurry polymerization. After polymerization for 10 minutes, the ethylene feed was stopped, the temperature was lowered to room temperature, and the prepolymerization catalyst was separated from the reactor under nitrogen protection. The hexane was then dried for later use. The prepolymerization activity of the catalyst was measured to be 20gP / g·cat·h.

[0106] ② Gas-phase copolymerization: Nitrogen is used to replace the gas in the reactor, a prepolymerization catalyst is injected, the reactor is heated to the reaction temperature, and then comonomers (α-olefins and ethylene), hydrogen, nitrogen and isopentane are introduced for copolymerization; after polymerization, the polymer is devolatilized and deactivated.

[0107] The reactor pressure is controlled at 2.0 MPa and the reaction temperature is 70℃.

[0108] The molar percentage of water and oxygen in the reactor must be less than 1 ppm.

[0109] Based on the sum of the contents of nitrogen, ethylene, and isopentane, the molar percentage of nitrogen is 42%, the molar percentage of ethylene is 50%, and the molar percentage of isopentane is 8%; the molar percentage of α-olefins and hydrogen does not need to be controlled, and the same applies below.

[0110] The molar ratio of α-olefin to ethylene is 0.15, the molar ratio of hydrogen to ethylene is 4.0, and the α-olefin of the comonomer is 1-butene.

[0111] During the polymerization process, the prepolymer catalyst is continuously added to the reactor at a feed rate of 3 g / h through a catalyst feeder and injection pipe.

[0112] The polymerization results and polymer properties are shown in Table 1. A 25 μm thick film was fabricated using a molding instrument, and the haze of the film was measured.

[0113] Example 2

[0114] This embodiment provides a method for preparing an ethylene copolymer, which includes the following steps:

[0115] The preparation, activation, and metallocene catalyst preparation of silica aerogel were the same as in Example 1. From the prepared silica aerogel microspheres, some microspheres were screened, and the average particle size was measured to be 60 μm, and the bulk density was 0.30 g / cm³. 3 Specific surface area is 500m² 2 / g, pore volume 2.0cm 3 / g. The average particle size of the obtained catalyst was 64 μm, the aluminum content in the catalyst was 21 wt%, and the zirconium content in the catalyst was 0.36 wt%.

[0116] Preparation of ethylene copolymers:

[0117] ① Prepolymerization: 2L of n-hexane and 20mL of triethylaluminum in n-hexane were added to a 5L slurry polymerization reactor. After stirring for 15 minutes, 500mg of the metallocene catalyst obtained in step (3) was added. The temperature of the polymerization reactor was controlled to 5℃, ethylene was introduced, and the reaction pressure was maintained at 0.8MPa for slurry polymerization. After polymerization for 5 minutes, the ethylene feed was stopped, the temperature was lowered to room temperature, and the prepolymerization catalyst was separated from the reactor under nitrogen protection. The hexane was then dried for later use. The prepolymerization activity of the catalyst was measured to be 50gP / g·cat·h.

[0118] ② Gas-phase copolymerization: Nitrogen is used to replace the gas in the reactor, a prepolymerization catalyst is injected, the reactor is heated to the reaction temperature, and then comonomers (α-olefins and ethylene), hydrogen, nitrogen and isopentane are introduced for copolymerization; after polymerization, the polymer is devolatilized and deactivated.

[0119] The reactor pressure is controlled at 1.0 MPa and the reaction temperature is 60℃.

[0120] The molar percentage of water and oxygen in the reactor must be less than 1 ppm.

[0121] Based on the sum of the contents of nitrogen, ethylene and isopentane, the molar percentage of nitrogen is 32%, the molar percentage of ethylene is 60%, and the molar percentage of isopentane is 8%.

[0122] The molar ratio of α-olefin to ethylene is 0.10, the molar ratio of hydrogen to ethylene is 3.0, and the α-olefin of the comonomer is 1-butene;

[0123] During the polymerization process, the prepolymer catalyst is continuously added to the reactor at a feed rate of 3 g / h through a catalyst feeder and injection pipe.

[0124] The polymerization results and polymer properties are shown in Table 1. A 25 μm thick film was fabricated using a molding instrument, and the haze of the film was measured.

[0125] Example 3

[0126] This embodiment provides a method for preparing an ethylene copolymer, which includes the following steps:

[0127] The preparation, activation, and metallocene catalyst preparation of silica aerogel were the same as in Example 1. From the prepared silica aerogel microspheres, some microspheres were screened, and the average particle size was measured to be 80 μm, and the bulk density was 0.25 g / cm³. 3 Specific surface area is 300m² 2 / g, pore volume 1.6cm 3 / g. The average particle size of the obtained catalyst is 86 μm, the aluminum content in the catalyst is 15 wt%, and the zirconium content in the catalyst is 0.25 wt%.

[0128] Preparation of ethylene copolymers:

[0129] ① Prepolymerization: 2L of n-hexane and 5mL of triethylaluminum in n-hexane were added to a 5L slurry polymerization reactor. After stirring for 15 minutes, 500mg of the metallocene catalyst obtained in step (3) was added. The temperature of the polymerization reactor was controlled to 0℃, ethylene was introduced, and the reaction pressure was maintained at 0.8MPa for slurry polymerization. After polymerization for 60 minutes, the ethylene feed was stopped, the temperature was lowered to room temperature, and the prepolymerization catalyst was separated from the reactor under nitrogen protection. The hexane was then dried for later use. The prepolymerization activity of the catalyst was measured to be 30gP / g·cat·h.

[0130] ② Gas-phase copolymerization: Nitrogen is used to replace the gas in the reactor, a prepolymerization catalyst is injected, the reactor is heated to the reaction temperature, and then comonomers (α-olefins and ethylene), hydrogen, nitrogen and isopentane are introduced for copolymerization; after polymerization, the polymer is devolatilized and deactivated.

[0131] The reactor pressure is controlled at 2.5 MPa and the reaction temperature is 100℃.

[0132] The molar percentage of water and oxygen in the reactor must be less than 1 ppm.

[0133] Based on the combined content of nitrogen, ethylene, and isopentane, the molar percentage of nitrogen is 32%, the molar percentage of ethylene is 45%, and the molar percentage of isopentane is 23%.

[0134] The molar ratio of α-olefin to ethylene is 0.30, and the molar ratio of hydrogen to ethylene is 2.0.

[0135] The α-olefin of the comonomer is 1-butene;

[0136] During the polymerization process, the prepolymer catalyst is continuously added to the reactor at a feed rate of 3 g / h through a catalyst feeder and injection pipe.

[0137] The polymerization results and polymer properties are shown in Table 1. A 25 μm thick film was fabricated using a molding instrument, and the haze of the film was measured.

[0138] Example 4

[0139] This embodiment provides a method for preparing an ethylene copolymer, which includes the following steps:

[0140] (1) Preparation of SiO2 aerogel microspheres: The preparation of SiO2 aerogel microspheres was the same as in Example 1. From the prepared silica aerogel microspheres, some microspheres were screened and measured to have an average particle size of 40 μm and a bulk density of 0.28 g / cm³. 3 Specific surface area is 800m² 2 / g, pore volume 1.8cm 3 / g.

[0141] (2) The activation of SiO2 aerogel microspheres is the same as in Example 1.

[0142] (3) Preparation of metallocene catalyst: Under anhydrous and oxygen-free conditions, 1 g of the above-treated silica aerogel microsphere carrier was accurately weighed, and 30 mL of toluene was added to form a suspension. 25 mmol of MAO solution was added, and the mixture was stirred at 30 °C for 2 hours. The solid portion was washed three times with 30 mL of toluene, and then 30 mL of toluene was added again. A certain amount of dimethylsilyl-bridged bis(2-methyl-4-phenylindenyl)zirconia dichloride was added, and the mixture was stirred at 70 °C for 1 hour. The solid portion was washed three times with 30 mL of toluene. The mixture was then vacuum-sealed for 2 hours, and after the toluene was dried, a catalyst with good flowability was obtained. The average particle size of the obtained catalyst was 44 μm, the aluminum content was 20 wt%, and the zirconium content was 0.26 wt%.

[0143] (4) Preparation of ethylene copolymers:

[0144] ① Prepolymerization: 2L of n-hexane and 10mL of triethylaluminum in n-hexane were added to a 5L slurry polymerization reactor. After stirring for 15 minutes, 500mg of the metallocene catalyst obtained in step (3) was added. The temperature of the polymerization reactor was controlled to -5℃, ethylene was introduced, and the reaction pressure was maintained at 0.8MPa for slurry polymerization. After polymerization for 10 minutes, the ethylene feed was stopped, the temperature was lowered to room temperature, and the prepolymerization catalyst was separated from the reactor under nitrogen protection. The hexane was then dried for later use. The prepolymerization activity of the catalyst was measured to be 25gP / g·cat·h.

[0145] ② Gas-phase copolymerization: Nitrogen is used to replace the gas in the reactor, a prepolymerization catalyst is injected, the reactor is heated to the reaction temperature, and then comonomers (α-olefins and ethylene), hydrogen, nitrogen and isopentane are introduced for copolymerization; after polymerization, the polymer is devolatilized and deactivated.

[0146] The reactor pressure is controlled at 2.0 MPa and the reaction temperature is 70℃.

[0147] The molar percentage of water and oxygen in the reactor must be less than 1 ppm.

[0148] Based on the combined content of nitrogen, ethylene, and isopentane, the molar percentage of nitrogen is 32%, the molar percentage of ethylene is 50%, and the molar percentage of isopentane is 18%.

[0149] The molar ratio of α-olefin to ethylene is 0.15, and the molar ratio of hydrogen to ethylene is 4.0.

[0150] The α-olefin of the comonomer is 1-hexene;

[0151] During the polymerization process, the prepolymer catalyst is continuously added to the reactor at a feed rate of 3 g / h through a catalyst feeder and injection pipe.

[0152] The polymerization results and polymer properties are shown in Table 1. A 25 μm thick film was fabricated using a molding instrument, and the haze of the film was measured.

[0153] Example 5

[0154] This embodiment provides a method for preparing an ethylene copolymer, which includes the following steps:

[0155] (1) Preparation of SiO2 aerogel microspheres: The preparation of SiO2 aerogel microspheres was the same as in Example 1. From the prepared silica aerogel microspheres, some microspheres were screened and measured to have an average particle size of 30 μm and a bulk density of 0.24 g / cm³. 3 Specific surface area is 300m² 2 / g, pore volume 3.0cm 3 / g.

[0156] (2) Activation of SiO2 aerogel microspheres: Place 10g of silica aerogel microspheres between the two filters of the microwave activation device, turn on the microwave oven, the frequency of the microwave emission source is 2450MHz, the power of the microwave oven is 850W, purge the activation device with hot nitrogen gas preheated to 150℃ for 5 minutes, then turn off the microwave oven, stop the hot nitrogen gas, evacuate the activation device to -0.05MPa through the vacuum port, and then purge with room temperature nitrogen gas for 30 minutes to complete the activation; the activated carrier is stored under nitrogen protection for later use.

[0157] (3) The metallocene catalyst was prepared in the same manner as in Example 1. The average particle size of the obtained catalyst was 35 μm, the aluminum content in the catalyst was 19 wt%, and the zirconium content in the catalyst was 0.31 wt%.

[0158] (4) Preparation of ethylene copolymers:

[0159] ① Prepolymerization: 2L of n-hexane and 5mL of triethylaluminum in n-hexane were added to a 5L slurry polymerization reactor. After stirring for 15 minutes, 500mg of the metallocene catalyst obtained in step (3) was added. The temperature of the polymerization reactor was controlled to 0℃, ethylene was introduced, and the reaction pressure was maintained at 0.8MPa for slurry polymerization. After polymerization for 60 minutes, the ethylene feed was stopped, the temperature was lowered to room temperature, and the prepolymerization catalyst was separated from the reactor under nitrogen protection. The hexane was then dried for later use. The prepolymerization activity of the catalyst was measured to be 35gP / g·cat·h.

[0160] ② Gas-phase copolymerization: Nitrogen is used to replace the gas in the reactor, a prepolymerization catalyst is injected, the reactor is heated to the reaction temperature, and then comonomers (α-olefins and ethylene), hydrogen, nitrogen and isopentane are introduced for copolymerization; after polymerization, the polymer is devolatilized and deactivated.

[0161] The reactor pressure is controlled at 2.5 MPa, and the reaction temperature is 100℃.

[0162] The molar percentage of water and oxygen in the reactor must be less than 1 ppm.

[0163] Based on the combined content of nitrogen, ethylene, and isopentane, the molar percentage of nitrogen is 32%, the molar percentage of ethylene is 45%, and the molar percentage of isopentane is 23%.

[0164] The molar ratio of α-olefin to ethylene is 0.3, and the molar ratio of hydrogen to ethylene is 2.0.

[0165] The α-olefin of the comonomer is 1-octene;

[0166] During the polymerization process, the prepolymer catalyst is continuously added to the reactor at a feed rate of 3 g / h through a catalyst feeder and injection pipe.

[0167] The polymerization results and polymer properties are shown in Table 1. A 25 μm thick film was fabricated using a molding instrument, and the haze of the film was measured.

[0168] Example 6

[0169] This embodiment provides a method for preparing an ethylene copolymer, which includes the following steps:

[0170] (1) The preparation, activation, and metallocene catalyst preparation of SiO2 aerogel microspheres were the same as in Example 1. From the prepared silica aerogel microspheres, some microspheres were screened out, and the average particle size was measured to be 65 μm, and the bulk density was 0.30 g / cm³. 3 Specific surface area is 500m² 2 / g, pore volume 1.5cm 3 / g. The average particle size of the obtained catalyst was 68 μm, the aluminum content in the catalyst was 22 wt%, and the zirconium content in the catalyst was 0.27 wt%.

[0171] (2) Preparation of ethylene copolymers:

[0172] ① Prepolymerization: 2L of n-hexane and 5mL of triethylaluminum in n-hexane were added to a 5L slurry polymerization reactor. After stirring for 15 minutes, 500mg of the metallocene catalyst obtained in step (3) was added. The temperature of the polymerization reactor was controlled to -5℃, ethylene was introduced, and the reaction pressure was maintained at 0.8MPa for slurry polymerization. After polymerization for 30 minutes, the ethylene feed was stopped, the temperature was lowered to room temperature, and the prepolymerization catalyst was separated from the reactor under nitrogen protection. The hexane was then dried for later use. The prepolymerization activity of the catalyst was measured to be 10gP / g·cat·h.

[0173] ② Gas phase copolymerization: Same as Example 1.

[0174] The polymerization results and polymer properties are shown in Table 1. A 25 μm thick film was fabricated using a molding instrument, and the haze of the film was measured.

[0175] Example 7

[0176] This embodiment provides a method for preparing an ethylene copolymer, which includes the following steps:

[0177] (1) Preparation of SiO2 aerogel microspheres, activation of SiO2 aerogel microspheres, and preparation of metallocene catalysts were the same as in Example 1. From the prepared silica aerogel microspheres, some microspheres were screened out, and the average particle size was measured to be 60 μm, and the bulk density was 0.30 g / cm³. 3 Specific surface area is 500m²2 / g, pore volume 1.5cm 3 / g. The average particle size of the obtained catalyst was 68 μm, the aluminum content was 21 wt%, and the zirconium content was 0.29 wt%.

[0178] (2) Preparation of ethylene copolymers:

[0179] ① Prepolymerization: 2L of n-hexane and 5mL of triethylaluminum in n-hexane were added to a 5L slurry polymerization reactor. After stirring for 15 minutes, 500mg of the metallocene catalyst obtained in step (3) was added. The temperature of the polymerization reactor was controlled to -5℃, ethylene was introduced, and the reaction pressure was maintained at 0.8MPa for slurry polymerization. After polymerization for 60 minutes, the ethylene feed was stopped, the temperature was lowered to room temperature, and the prepolymerization catalyst was separated from the reactor under nitrogen protection. The hexane was then dried for later use. The prepolymerization activity of the catalyst was measured to be 15gP / g·cat·h.

[0180] ② Gas phase copolymerization: Same as Example 1.

[0181] The polymerization results and polymer properties are shown in Table 1. A 25 μm thick film was fabricated using a molding instrument, and the haze of the film was measured.

[0182] Example 8

[0183] This embodiment provides a method for preparing an ethylene copolymer, which includes the following steps:

[0184] (1) The preparation, activation, and metallocene catalyst preparation of SiO2 aerogel microspheres were the same as in Example 1. From the prepared silica aerogel microspheres, some microspheres were screened out, and the average particle size was measured to be 50 μm, and the bulk density was 0.35 g / cm³. 3 Specific surface area is 650m² 2 / g, pore volume 1.8cm 3 / g. The average particle size of the obtained catalyst was 54 μm, the aluminum content in the catalyst was 16 wt%, and the zirconium content in the catalyst was 0.23 wt%.

[0185] (2) Preparation of ethylene copolymers:

[0186] ① Prepolymerization: 2L of n-hexane and 5mL of triethylaluminum in n-hexane were added to a 5L slurry polymerization reactor. After stirring for 15 minutes, 500mg of the metallocene catalyst obtained in step (3) was added. The temperature of the polymerization reactor was controlled to 0℃, ethylene was introduced, and the reaction pressure was maintained at 0.8MPa for slurry polymerization. After polymerization for 100 minutes, the ethylene feed was stopped, the temperature was lowered to room temperature, and the prepolymerization catalyst was separated from the reactor under nitrogen protection. The hexane was then dried for later use. The prepolymerization activity of the catalyst was measured to be 19gP / g·cat·h.

[0187] ② Gas phase copolymerization: Same as Example 1.

[0188] The polymerization results and polymer properties are shown in Table 1. A 25 μm thick film was fabricated using a molding instrument, and the haze of the film was measured.

[0189] Comparative Example 1

[0190] This comparative example provides a method for preparing an ethylene copolymer, which includes the following steps:

[0191] (1) The preparation, activation, and metallocene catalyst preparation of SiO2 aerogel microspheres were the same as in Example 1. The average particle size of the obtained catalyst was 104 μm, the aluminum content in the catalyst was 24 wt%, and the zirconium content in the catalyst was 0.33 wt%.

[0192] (2) Preparation of ethylene copolymer: The catalyst was not prepolymerized and was directly copolymerized in the gas phase.

[0193] Gas-phase copolymerization: Nitrogen is used to replace the gas in the reactor, a metallocene catalyst is injected, the reactor is heated to the reaction temperature, and then comonomers (α-olefins and ethylene), hydrogen, nitrogen and isopentane are introduced to copolymerize; after polymerization, the polymer is devolatilized and deactivated.

[0194] The reactor pressure is controlled at 2.0 MPa and the reaction temperature is 70℃.

[0195] The molar percentage of water and oxygen in the reactor must be less than 1 ppm.

[0196] Based on the combined content of nitrogen, ethylene, and isopentane, the molar percentage of nitrogen is 42%, the molar percentage of ethylene is 50%, and the molar percentage of isopentane is 8%.

[0197] The molar ratio of α-olefin to ethylene is 0.15, and the molar ratio of hydrogen to ethylene is 4.0.

[0198] The α-olefin of the comonomer is 1-butene;

[0199] During the polymerization process, the metallocene catalyst is continuously added to the reactor at a feed rate of 3 g / h through a catalyst feeder and injection pipe.

[0200] The polymerization results and polymer properties are shown in Table 1. A 25 μm thick film was fabricated using a molding instrument, and the haze of the film was measured.

[0201] Comparative Example 2

[0202] This comparative example provides a method for preparing an ethylene copolymer, which includes the following steps:

[0203] (1) The preparation, activation, and metallocene catalyst preparation of SiO2 aerogel microspheres were the same as in Example 1. The average particle size of the obtained catalyst was 105 μm, the aluminum content in the catalyst was 22 wt%, and the zirconium content in the catalyst was 0.34 wt%.

[0204] (2) Preparation of ethylene copolymer: The catalyst is directly used for slurry copolymerization.

[0205] Add 2L of n-hexane and 10mL of triethylaluminum n-hexane solution to a 5L slurry polymerization reactor. After stirring for 15 minutes, add 500mg of the metallocene catalyst obtained in step (3). Control the temperature of the polymerization reactor to 70℃, and introduce ethylene, 1-butene and hydrogen. The molar ratio of 1-butene to ethylene is 0.15 and the molar ratio of hydrogen to ethylene is 4.0. Maintain the reaction pressure at 0.8MPa and carry out slurry polymerization. After polymerization for 60 minutes, stop the ethylene feed, cool to room temperature, and separate the polymer from the reactor.

[0206] The polymerization results and polymer properties are shown in Table 1. A 25 μm thick film was fabricated using a molding instrument, and the haze of the film was measured.

[0207] Comparative Example 3

[0208] This comparative example provides a method for preparing an ethylene copolymer, which includes the following steps:

[0209] (1) Catalyst support: Commercial silica gel support was selected, with an average particle size of 45 μm and a bulk density of 0.25 g / cm³. 3 Specific surface area 310m² 2 / g, pore volume 1.6cm 3 / g.

[0210] (2) The activation of the support, the preparation of the metallocene catalyst, and the preparation of the ethylene copolymer were carried out in the same manner as in Example 1. The prepolymerization activity of the catalyst was measured to be 45 gP / g·cat·h.

[0211] The polymerization results and polymer properties are shown in Table 1. A 25 μm thick film was fabricated using a molding instrument, and the haze of the film was measured.

[0212] Comparative Example 4

[0213] This comparative example provides a method for preparing an ethylene copolymer, which includes the following steps:

[0214] (1) Catalyst support: Commercial silica gel support was selected, with an average particle size of 45 μm and a bulk density of 0.25 g / cm³. 3 Specific surface area 310m² 2 / g, pore volume 1.6cm 3 / g.

[0215] (2) The activation of the support and the preparation method of the metallocene catalyst were the same as those in Comparative Example 1. The average particle size of the obtained catalyst was 51 μm, the aluminum content in the catalyst was 16 wt%, and the zirconium content in the catalyst was 0.20 wt%. The catalyst was not prepolymerized but directly subjected to gas-phase copolymerization, and the copolymer preparation method was the same as in Example 1.

[0216] The polymerization results and polymer properties are shown in Table 1. A 25 μm thick film was fabricated using a molding instrument, and the haze of the film was measured.

[0217] Comparative Example 5

[0218] This comparative example provides a method for preparing an ethylene copolymer, which includes the following steps:

[0219] (1) Preparation of SiO2 aerogel microspheres: Same as in Example 1.

[0220] (2) Activation of SiO2 aerogel microsphere carrier: Referring to patent CN 108970647A, silica aerogel microspheres are placed in an activator and nitrogen is introduced to make the silica aerogel microspheres fluidized; the activator is heated to 200°C and kept at that temperature for 2 hours; the temperature is then increased to 600°C and kept at that temperature for 2 hours; the temperature is then reduced to 300°C within 2 hours and then reduced to room temperature (20°C) within 2 hours, and the material is discharged for use.

[0221] (3) The preparation methods of the metallocene catalyst and the ethylene copolymer were the same as in Example 1. The average particle size of the obtained catalyst was 66 μm, the aluminum content in the catalyst was 18 wt%, and the zirconium content in the catalyst was 0.23 wt%. The prepolymerization activity of the catalyst was measured to be 40 gP / g·cat·h.

[0222] The polymerization results and polymer properties are shown in Table 1. A 25 μm thick film was fabricated using a molding instrument, and the haze of the film was measured.

[0223] The polymerization results and polymer properties are summarized in Table 1.

[0224] Table 1 Catalyst metal content, polymerization performance, and polymer properties

[0225]

[0226] A comparison of Example 1 and Comparative Examples 1 and 2 shows that the metallocene catalyst obtained by using microwave-activated silica aerogel microspheres as a carrier, followed by prepolymerization treatment, results in a higher polymer packing density, lower haze, and better optical performance in the prepared film.

[0227] A comparison of Example 1 and Comparative Example 3 shows that the metallocene catalyst obtained by using microwave-activated silica aerogel microspheres as a carrier, after undergoing a prepolymerization process, results in a film with lower haze and better optical performance.

[0228] A comparison of Example 1 and Comparative Example 4 shows that the microwave-activated treatment method for silica aerogel microsphere carriers provided by the present invention is beneficial to improving the optical properties of the polymer obtained from the catalyst.

Claims

1. A method for preparing an ethylene copolymer, wherein, The catalyst used in this preparation method is a metallocene catalyst, which includes a metallocene catalyst support, a metallocene compound, and a co-catalyst. The support for the metallocene catalyst is prepared through the following steps: Silica aerogel microspheres were placed in a container and microwaved. During microwave processing, hot nitrogen gas is introduced into the container to purge the silica aerogel microspheres. Stop the microwave treatment, evacuate the container, and then purge the silica aerogel microspheres with room temperature nitrogen gas to obtain the support for the metallocene catalyst. The preparation method includes a prepolymerization step and a copolymerization reaction step; the prepolymerization step includes: mixing the metallocene catalyst and alkylaluminum, and then passing ethylene through to perform prepolymerization to obtain a prepolymer catalyst.

2. The method for preparing the ethylene copolymer according to claim 1, wherein, The silica aerogel microspheres have an average particle size of 20-200 μm and a bulk density of 0.20-0.35 g / cm³. 3 The pore volume is 1.2-3.0 cm³. 3 / g, specific surface area of ​​100-1000m² 2 / g.

3. The method for preparing the ethylene copolymer according to claim 1, wherein, The container is a microwave activation device, which includes a main body, a first filter, and a second filter. The main body is spindle-shaped, with a vacuum port and a nitrogen inlet at the upper and lower ends, respectively. The nitrogen inlet is connected to a hot nitrogen pipe and a room temperature nitrogen pipe. The first filter and the second filter are disposed in the middle of the container, with a space between them for placing silica aerogel microspheres.

4. The method for preparing the ethylene copolymer according to claim 3, wherein, The first filter screen has a mesh count of not less than 800 mesh, and / or the second filter screen has a mesh count of not less than 800 mesh.

5. The method for preparing the ethylene copolymer according to claim 3, wherein, The first filter screen is made of ceramic or quartz, and / or the second filter screen is made of ceramic or quartz.

6. The method for preparing the ethylene copolymer according to claim 1, wherein, The microwave processing uses a microwave emission source with a frequency of 1000-3000MHz and a power of 500-1000W.

7. The method for preparing the ethylene copolymer according to claim 1, wherein, The microwave treatment time is 1-10 minutes.

8. The method for preparing the ethylene copolymer according to claim 1, wherein, The temperature of the hot nitrogen gas is 70-150℃, and / or the purity of the hot nitrogen gas and the room temperature nitrogen gas is above 99.999% and the water content is not more than 5ppm.

9. The method for preparing the ethylene copolymer according to claim 1, wherein, The vacuuming process involves evacuating the container until the pressure reaches -0.05 MPa to -0.1 MPa.

10. The method for preparing the ethylene copolymer according to claim 1, wherein, The bulk density of the metallocene catalyst is 0.3-0.6 g / cm³. 3 .

11. The method for preparing the ethylene copolymer according to claim 1, wherein, The general formula of the metallocene compound is Cp x MA y B z ,in: Cp can be an unsubstituted cyclopentadienyl, a substituted cyclopentadienyl, an indenyl, a fluorenyl, an indenyl ligand in hydrogenated form, or a fluorenyl ligand in hydrogenated form. M is a transition metal; A and B are halogen atoms, hydrogen atoms, or alkyl groups, respectively; x is an integer from 1 to 3, and y and z are integers from 0 to 3 respectively.

12. The method for preparing the ethylene copolymer according to claim 11, wherein, The metallocene compound comprises one or more of the following: di(cyclopentadienyl) metal dihalides, di(cyclopentadienyl) metal monoalkyl monohalides, di(cyclopentadienyl) metal dialkyl compounds, and di(indenyl) metal dihalides, wherein the metal is a group IVB metal, including titanium, zirconium, or hafnium, the alkyl group is an alkyl group with 1-6 carbons, and the halide is a chloride.

13. The method for preparing the ethylene copolymer according to claim 1, wherein, The cocatalyst is selected from alkylaluminoxane compounds, which are selected from one or more combinations of methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, butylaluminoxane, pentylaluminoxane, decylaluminoxane, and modified methylaluminoxane.

14. The method for preparing the ethylene copolymer according to claim 1, wherein, The prepolymerization step includes: The solvent and alkylaluminum were mixed in a reaction vessel, the metallocene catalyst was added, the temperature was controlled to the prepolymerization temperature, ethylene was introduced for slurry polymerization, the ethylene feed was stopped after polymerization was completed, the temperature was cooled to room temperature, and the prepolymer catalyst was separated.

15. The method for preparing the ethylene copolymer according to claim 1 or 14, wherein, The mass ratio of the alkylaluminum to the metallocene catalyst is 8:1 to 32:

1.

16. The method for preparing the ethylene copolymer according to claim 1, 14, or 15, wherein, The general formula of the alkylaluminum is AlR 3 m X 1 (3-m) In the formula, R 3 For C1-C 20 Alkyl, aryl, or aralkyl; X 1 is a halogen; m is an integer 0 ≤ n ≤ 3.

17. The method for preparing the ethylene copolymer according to claim 1 or 14, wherein, The activity of the prepolymer catalyst is 10-50 gP / g cat·h.

18. The method for preparing the ethylene copolymer according to claim 1 or 14, wherein, The prepolymerization temperature is -10℃ to 20℃, and the prepolymerization time is 5-60 minutes.

19. The method for preparing the ethylene copolymer according to claim 1 or 14, wherein, The copolymerization reaction steps include: The reactor is purged with nitrogen, a prepolymer catalyst is injected, the reactor is heated to the copolymerization reaction temperature, and then comonomers and hydrogen are introduced to copolymerize and obtain the ethylene copolymer.

20. The method for preparing the ethylene copolymer according to claim 19, wherein, The reactor is a gas-phase fluidized bed reactor.

21. The method for preparing the ethylene copolymer according to claim 19, wherein, The copolymerization reaction is carried out at a pressure of 1.0-2.5 MPa and a temperature of 60-100℃.

22. The method for preparing the ethylene copolymer according to claim 19, wherein, The comonomer comprises an α-olefin and ethylene, wherein the α-olefin is selected from one or more combinations of propylene, 1-butene, 1-pentene, 1-hexene, and 1-octene.

23. The method for preparing the ethylene copolymer according to claim 22, wherein, With the total amount of all gases in the reactor being 100%, the molar percentage of ethylene is 40-60%, the molar ratio of α-olefin to ethylene is 0.01-0.3, and the molar ratio of hydrogen to ethylene is 0.5-10.

0.

24. An ethylene copolymer prepared by the preparation method according to any one of claims 1-23.

25. The ethylene copolymer according to claim 24, wherein, The haze of the ethylene copolymer is 3.4-5.2.

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