Polyethylene catalyst and preparation method thereof, ethylene polymerization method and low-thermal-conductivity polyethylene resin

Abstract

The invention provides a polyethylene catalyst and a preparation method thereof, an ethylene polymerization method and low thermal conductivity polyethylene resin, the catalyst comprises post-treated large particle size SiO2 aerogel microspheres and alkyl aluminum, the particle size of the large particle size SiO2 aerogel microspheres is 100-300 [mu] m, and the particle size of the alkyl aluminum is 100-300 [mu] m. The post-treatment method comprises the following steps: placing the large-particle-size SiO2 aerogel microspheres in an inert atmosphere for atmosphere exchange treatment, then activating the large-particle-size SiO2 aerogel microspheres, and then carrying out atmosphere exchange treatment again, and the activating step comprises the following steps: placing the large-particle-size SiO2 aerogel microspheres subjected to atmosphere exchange in an activator, heating the large-particle-size SiO2 aerogel microspheres to 150-200 DEG C, and keeping the temperature constant; raising the temperature to 300-400 DEG C, and keeping the temperature constant; raising the temperature to 450-650 DEG C, and keeping the temperature constant; cooling to 300-400 DEG C, and keeping the temperature constant; cooling to 100-200 DEG C, and keeping the temperature constant; and cooling to 20-30 DEG C. When the catalyst is used for preparing a polyethylene material, low-heat-conductivity polyethylene can be obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of olefin polymerization, and specifically relates to a polyethylene catalyst, a preparation method thereof, an ethylene polymerization method, and a low thermal conductivity polyethylene resin. Background Art

[0002] Thermoplastic polyolefin materials such as polyethylene are widely used in life and production due to their excellent mechanical properties and easy processing and molding. When polyethylene is used as a heat insulation and thermal insulation material, its heat insulation performance needs to be further improved.

[0003] Patent CN109135019A invented a vulcanized low thermal conductivity polyethylene material, which includes the following raw material components: modified polyethylene, aluminum oxide / zinc oxide / silicon dioxide, and modified nanocellulose. In this method, the modified nanocellulose is prepared by reacting nanocellulose, mesoporous aluminum oxide, microcrystalline cellulose, and sodium hydroxide aqueous solution, and the modified polyethylene is prepared by ball milling polyethylene with mesoporous titanium dioxide modified fumed silica, KH-560 coupling agent, and maleic anhydride, etc.; finally, the modified polyethylene, aluminum oxide / zinc oxide / silicon dioxide, and modified nanocellulose are added to a flat vulcanizing machine according to a certain mass fraction for vulcanization molding. This technology involves processes such as hydrothermal reaction, multi-step heat treatment, multiple washing, and grinding, with complex reaction raw materials and a long preparation process.

[0004] The low thermal conductivity polyethylene material for heat preservation disclosed in Patent CN109294040A includes the following raw material components: fumed silica modified polyethylene, urea modified polyethylene, calcium oxalate modified polyethylene, and bentonite modified polyethylene. This invention uses different raw materials to modify polyethylene separately in a reaction kettle, and finally vulcanizes and forms all the modified polyethylene with a flat vulcanizing machine. This technology also requires multiple complex modification treatments for polyethylene, with a complex preparation process.

[0005] Silica has two forms: crystalline and amorphous non-crystalline. The silica used as a catalyst support is usually amorphous non-crystalline silica, which has the characteristics of light weight, porous, high specific surface area, good insulation, acid and alkali resistance, and high temperature resistance.

[0006] SiO 2 Aerogel is a porous amorphous material with an open pore structure. Silica aerogel was first prepared by Dr. Kistler of Stanford University in 1931 through the sol-gel method and supercritical drying technology. Its main structural formula is a continuous three-dimensional network structure formed by the aggregation of silicon-oxygen ultrafine particles at the nanometer scale. The structure of silica aerogel consists of network pores with a volume fraction of more than 90% and an SiO 2 skeleton of less than 10%. The pores are filled with a gaseous dispersion medium. It has many excellent properties, including a high surface area (500 - 1000m2 / g), high porosity (80-99.8%), low density (0.003-0.8g / cm 3 ), low thermal conductivity (~0.02W / m*K), among which the extremely low thermal conductivity is the most significant feature of silica aerogel microspheres.

[0007] Compared with ordinary silica gel (SiO 2 ), an important feature of the aerogel pore network is its "open" nature and interconnectivity. The fluid can flow from one hole to another and eventually pass through the entire material. The pore size of aerogel microspheres is about 10 nanometers (nm), and there are a large number of micropores. It is a typical nanoporous material with a continuous network structure, and the internal network pores are relatively evenly distributed. Since the small pore size of aerogel runs through the entire material, its adsorption performance is good, so its adsorption efficiency is better than that of ordinary silica gel. The pore size of aerogel is generally less than 50nm, which is lower than the mean free path of air molecules at normal temperature and pressure (70nm), which reduces the probability of collision between air molecules and avoids heat conduction, thus becoming a super insulating material.

[0008] SiO 2 Aerogel is used as a modifier, and low-density polyethylene is modified by a blending casting method to improve the thermal insulation performance of packaging materials and prepare packaging films with excellent thermal insulation performance (Wang Guanglin, Yang Fuxin, Chai Li, et al. Preparation and performance research of SiO_2 aerogel thermal insulation packaging materials [J]. Functional Materials, 2022, 53(02): 2087-2093). However, in order to enhance the thermal insulation performance of polyethylene and SiO_2 in this technology, 2 The compatibility of aerogel requires the use of a coupling agent to first 2 The aerogel is surface modified and then melt-blended with polyethylene.

[0009] Silica aerogel is usually an irregular block material, which is difficult to process into complex geometric shapes, and its application is subject to certain restrictions. However, preparing silica aerogel into microspheres with porous network structure can broaden its application field. 2 The high porosity of aerogel makes it an excellent catalyst carrier, and its high specific surface area can greatly increase the catalyst loading.

[0010] Patent CN1055184A discloses a supported catalyst that is active in the polymerization and copolymerization of ethylenically unsaturated compounds, comprising an organometallic derivative of aluminum and a second component which is obtained by reacting a magnesium compound and / or a titanium, vanadium or chromium compound and optionally a compound of at least one second metal selected from Al, V, Zr, Hf, Nd, Mo in the presence of one or more inorganic oxide aerogel microbead-shaped porous supports. The support can be used directly without treatment or can be used after activation. For example, after heating under reduced pressure at 165 °C for 8 hours and then cooling in dry nitrogen, it can be used. When activating the support, the temperature is relatively low, and it is difficult to ensure effective control of the hydroxyl content on the support surface, thus affecting the catalyst performance. Moreover, this invention requires an extremely narrow pore diameter distribution for the aerogel support, with the difference between the maximum and minimum pore diameters being at most 50 Å, which places extremely high requirements on the aerogel microspheres. The catalyst prepared using this support has good hydrogen regulation performance and the polymer has good rheology, but no improvement in the heat insulation performance of the polymer has been found.

[0011] Patent CN108970647A discloses a preparation method for a metallocene catalyst support. SiO 2 or modified SiO 2 is in a fluidized state under a nitrogen atmosphere, heated, kept at a constant temperature, and cooled using a gradient cooling method to room temperature to obtain a metallocene catalyst support. For ordinary silica gel (SiO 2 ), calcination in a hot nitrogen fluidized state can ensure uniform heating of the silica gel support, full exchange of the atmosphere inside and outside the support, and improve the activation effect. However, the stability of the SiO 2 aerogel framework structure is slightly worse than that of ordinary silica gel, and the high-temperature gas fluidization may cause damage to its framework. Therefore, SiO 2 aerogel is not suitable for activation by this fluidization method. Summary of the Invention

[0012] The object of the present invention is to provide a polyethylene catalyst which is used in the preparation of polyethylene materials and can obtain low-thermal-conductivity polyethylene, thereby improving the heat insulation effect of polyethylene resin.

[0013] The object of the present invention is also to provide a preparation method for a polyethylene catalyst.

[0014] The object of the present invention is also to provide an ethylene polymerization method.

[0015] The object of the present invention is also to provide a low-thermal-conductivity polyethylene resin.

[0016] To achieve the above object, the present invention provides a polyethylene catalyst, comprising post-treated large-particle-size SiO 2 aerogel microspheres and alkylaluminum, and the large-particle-size SiO 2The particle size of the aerogel microspheres is 100 - 300 μm. The post-treatment method is to first place the large-particle-size SiO 2 aerogel microspheres under an inert atmosphere for atmosphere exchange treatment, and then perform activation. After activation, atmosphere exchange treatment is performed again. The activation step includes placing the large-particle-size SiO 2 aerogel microspheres after atmosphere exchange in an activator, heating to 150 - 200 °C and keeping the temperature constant; heating to 300 - 400 °C and keeping the temperature constant; heating to 450 - 650 °C and keeping the temperature constant; cooling to 300 - 400 °C and keeping the temperature constant; cooling to 100 - 200 °C and keeping the temperature constant; cooling to 20 - 30 °C.

[0017] For the polyethylene catalyst of the present invention, the bulk density of the large-particle-size SiO 2 aerogel microspheres is 0.15 - 0.28 g / cm 3 , the pore volume is 1.5 - 3 cm 3 / g, preferably 1.8 - 2.5 g / cm 3 , the specific surface area is 300 - 1000 m 2 / g, preferably 400 - 850 m 2 / g, and the porosity is 85 - 92%.

[0018] For the polyethylene catalyst of the present invention, the atmosphere exchange treatment is to place the large-particle-size SiO 2 aerogel microspheres in a vacuum drying oven, evacuate and then introduce an inert gas, keep the pressure, the pressure for keeping the pressure is 0.01 - 0.2 MPa, and the time for keeping the pressure is 3 - 8 hours.

[0019] For the polyethylene catalyst of the present invention, 2 - 5 times of atmosphere exchange treatment are performed before activation.

[0020] For the polyethylene catalyst of the present invention, during multiple constant temperature processes, the constant temperature time is 0.5 - 2 hours.

[0021] For the polyethylene catalyst of the present invention, the general formula of the alkylaluminum is AlR 3m X 1(3-m) , where R 3 is an alkyl, aryl or aralkyl group of C 1 ~C 20 ; X 1 is a halogen; m is an integer of 0 ≦ n ≦ 3, preferably one or more of trimethylaluminum, triethylaluminum, triisobutylaluminum, monochlorodiethylaluminum and monochlorodiisobutylaluminum, more preferably triethylaluminum and / or triisobutylaluminum.

[0022] To achieve the above object, the present invention also provides a preparation method of the polyethylene catalyst as described above, which is characterized in that under an inert gas condition, the large-particle-size SiO 2After the aerogel microspheres and tetrahydrofuran are mixed evenly, an alkyl aluminum is added. After reacting at 30 - 60 °C for 1 - 5 hours, the temperature is lowered to -10 - 20 °C, and a titanium compound is added under stirring conditions. Then the temperature is raised to 30 - 60 °C and reacted for 2 - 10 hours. After washing and drying, the catalyst is obtained.

[0023] In the preparation method of the polyethylene catalyst of the present invention, for every gram of large particle size SiO 2 20 - 300 ml of tetrahydrofuran is added to the aerogel microspheres; the molar ratio of tetrahydrofuran to alkyl aluminum is 8:1 - 2:1; the addition amount of TiCl 4 is such that the molar ratio of Ti / Si is 10:1 - 50:1, preferably 15:1 - 30:1.

[0024] In the preparation method of the polyethylene catalyst of the present invention, the particle size of the catalyst is 100 - 300 μm, and the specific surface area is 300 - 800 m 2 / g, wherein the Ti content of the catalyst is 0.5 - 3 wt%, and the THF content in the catalyst is 5 - 20 wt%.

[0025] To achieve the above object, the present invention also provides an ethylene polymerization method. Under an inert gas condition, a solvent and an alkyl aluminum are added to a polymerization kettle. After stirring evenly, the above-mentioned catalyst is added. After stirring, an alkoxysilane is added and ethylene is introduced for a polymerization reaction. After the reaction ends, polyethylene is separated out, washed and dried to obtain a polyethylene resin.

[0026] In the ethylene polymerization method of the present invention, small particle size SiO 2 aerogel microspheres are added simultaneously with the solvent and the alkyl aluminum to the polymerization kettle. The added mass of the small particle size SiO 2 aerogel microspheres is 500 - 3000 times the mass of the catalyst, and the particle size of the small particle size SiO 2 aerogel microspheres is 10 - 50 μm.

[0027] In the ethylene polymerization method of the present invention, the ethylene polymerization conditions are as follows: the molar ratio of aluminum in the alkyl aluminum added during the polymerization process to titanium in the catalyst is 20:1 - 100:1, the polymerization temperature is 60 - 80 °C, and the polymerization pressure is 0.5 - 1.5 MPa.

[0028] In the ethylene polymerization method of the present invention, the alkoxysilane is one or more selected from dimethoxydimethylsilane, diethoxydimethylsilane, dimethoxydiphenylsilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, and tetraamyloxysilane, preferably diethoxydimethylsilane and tetraethoxysilane. The addition amount of the alkoxysilane and the mass ratio of the catalyst is 50:1 - 200:1.

[0029] To achieve the above object, the present invention also provides a low thermal conductivity polyethylene resin, which comprises the above-mentioned polyethylene resin and additives.

[0030] In the low thermal conductivity polyethylene resin of the present invention, the additives include an antioxidant and zinc stearate. The antioxidant includes antioxidant 1010 and antioxidant 168. The addition amount of antioxidant 1010 is 1000 - 3000 ppm of the mass of the polyethylene resin, and the addition amount of antioxidant 168 is 600 - 2000 ppm of the mass of the polyethylene resin; the addition amount of zinc stearate is 500 - 2000 ppm of the mass of the polyethylene resin.

[0031] In the low thermal conductivity polyethylene resin of the present invention, the density of the low thermal conductivity polyethylene resin is 0.890 - 0.925 g / cm 3 , and the thermal conductivity is 0.10 - 0.20 W / (m·K).

[0032] Advantages of the present invention:

[0033] (1) Using ordinary silica as a carrier to load TiCl 4 , its loading amount is relatively low and the polymerization activity is not high. The present invention uses silica aerogel with large particle size, high specific surface area and high porosity as a carrier to prepare a Z - N catalyst, which improves the loading amount of TiCl 4 , enables the catalyst to obtain appropriate ethylene polymerization activity, and ethylene monomers polymerize on the surface and inside pores of the silica aerogel, which is beneficial to reducing the density of polyethylene, increasing its porosity, and improving the heat insulation performance of polyethylene.

[0034] (2) Due to the poor stability of the skeleton structure of silica aerogel itself, the present invention activates the silica aerogel through a special post - treatment method, so that the structure of the silica aerogel is not damaged during the activation process.

[0035] (3) During the ethylene polymerization process of the present invention, small - particle - size silica aerogel microspheres can be introduced. As the polymerization reaction proceeds, the small - particle - size silica aerogel is in - situ dispersed in the polymer, achieving the goal of improving the heat insulation performance of polyethylene by silica aerogel, and finally obtaining a polyethylene with a low thermal conductivity.

[0036] The present invention uses a catalyst prepared with a silica aerogel microsphere carrier for ethylene polymerization, and realizes the uniform dispersion of SiO 2 aerogel microspheres during the ethylene polymerization process. It can avoid or reduce the post - treatment process of polyethylene and modifiers in the prior art, reduce the preparation cost, and simplify the process flow. Compared with ordinary polyethylene or polyethylene modified with conventional silica (thermal conductivity is 0.5 - 0.8 W / (m·K)), the density of the low - thermal - conductivity polyethylene obtained in the present invention is 0.890 - 0.925 g / cm3 , with a thermal conductivity of 0.10 - 0.20 W / (m·K), greatly improving the heat insulation performance of the polyethylene resin. Specific embodiments

[0037] The present invention will be specifically described below through examples. It is necessary to point out here that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above content of the present invention.

[0038] Evaluation and analysis method:

[0039] (1) The particle sizes of the carrier and the catalyst are measured using a Mastersizer 2000 Malvern particle size analyzer.

[0040] (2) The specific surface area, pore structure and porosity are tested by the nitrogen adsorption method using a TriStar II Plus 3.02 specific surface area and porosity analyzer from Microneritics, USA.

[0041] (3) The bulk density is tested using an HT1001 multi-functional powder physical property tester.

[0042] (4) The titanium (Ti) content in the catalyst is determined by spectrophotometry (722S type), and the tetrahydrofuran (THF) content in the catalyst is determined by gas chromatography (Techcomp GC7900).

[0043] (5) The thermal conductivity is measured using a TC3000E thermal conductivity meter (Xi'an Xiaxi Electronic Technology Co., Ltd.).

[0044] Example 1

[0045] (1) SiO 2 Preparation of aerogel microspheres: Refer to CN103523789 to prepare silica aerogel microspheres. Specifically:

[0046] ① Preparation of silica sol: At room temperature, 23.3 g of tetraethyl orthosilicate (TEOS), 28.4 g of ethanol and 6.1 g of water were stirred and mixed at a rotation speed of 400 r / min for 5 minutes. Then, 0.53 g of 0.01 mol / L glycolic acid solution was added dropwise thereto, and after stirring for 10 minutes, the pH value of the solution was 6.2 at this time. It was left standing for 3 hours to carry out the hydrolysis reaction, and then 2.94 g of 0.3 mol / L ethanol ammonia aqueous solution was added dropwise, and after stirring for 10 minutes, the pH value of the solution was 8.2 at this time, and silica sol was formed. 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, stirred evenly at a rotation speed of 300 r / min, and then 20 mL of the above silica sol was poured in, and stirred at a rotation speed of 800 r / min until the gel phenomenon occurred to obtain an emulsion system. ③ 100 mL of ethanol was added to the above emulsion system, stirred and mixed at a rotation speed of 800 r / min for 10 minutes, and after standing and separating layers, solid-liquid separation was carried out (after stopping stirring and standing, the whole emulsion system was divided into three layers, from top to bottom were ethanol, alcohol gel microspheres, and oil phase respectively, and then the alcohol gel microspheres could be easily separated by using a separating funnel), washed once with an ethanol aqueous solution (volume ratio of ethanol to water was 1:2), washed three times with ethanol, and then soaked in ethanol for aging for 20 hours to obtain alcohol gel microspheres. ④ The obtained alcohol gel microspheres were subjected to supercritical drying (the supercritical drying temperature reached 50-270 °C within 5 hours, the supercritical drying pressure was 10-18 MPa, and after rising to 250-270 °C, it was kept warm for 10 minutes), depressurized, purged with nitrogen and then cooled to below 50 °C for discharging. The obtained silica aerogel microspheres were screened with different mesh sieves to obtain silica aerogel microspheres with different particle sizes.

[0047] From the preparation of silica aerogel microspheres, two types of microspheres with different particle sizes were selected for standby. Among them, the large-particle-size microspheres: the average particle size was 150 μm, the bulk density was 0.20 g / cm 3 , the specific surface area was 730 m 2 / g, the pore volume was 1.8 cm 3 / g, and the porosity was 85%; the small-particle-size microspheres: the average particle size was 12 μm, the bulk density was 0.15 g / cm 3 , the specific surface area was 800 m 2 / g, the pore volume was 1.8 cm 3 / g, and the porosity was 86%.

[0048] (2) Large-particle-size SiO 2Post-treatment of aerogel microspheres: Place large-sized silica aerogel microspheres to be used in a vacuum drying oven, evacuate to vacuum, then introduce nitrogen, and maintain the pressure at 0.2 MPa for 3 hours for atmosphere exchange, repeating 2 times. Put the large-sized silica aerogel microspheres after atmosphere exchange into a muffle furnace, heat up to 150 °C and keep the temperature constant for 2 hours; heat up to 400 °C and keep the temperature constant for 0.5 hour; heat up to 650 °C and keep the temperature constant for 2 hours; cool down to 300 °C and keep the temperature constant for 1 hour; cool down to 200 °C and keep the temperature constant for 1 hour; cool down to 30 °C and discharge to obtain activated SiO 2 aerogel microsphere support. Put the activated SiO 2 aerogel microsphere support into the vacuum drying oven again, evacuate to vacuum, then introduce nitrogen, and maintain the pressure at 0.2 MPa for 3 hours. The treated large-sized SiO 2 aerogel microspheres are stored for standby in a nitrogen atmosphere.

[0049] (3) Preparation of polyethylene catalyst: Vacuum bake a 500 ml round-bottom flask and fully displace it with high-purity nitrogen. Add 2 g of large-sized SiO 2 aerogel microspheres (parameters see step (1)) and 200 ml of tetrahydrofuran (THF) into the flask. After stirring well, add 3 ml of a hexane solution of triethylaluminum with a concentration of 0.1 mol / ml (the molar ratio of THF to triethylaluminum is 8:1), and heat up to 30 °C for reaction for 5 hours. Cool down to 10 °C, and slowly add 110 ml of TiCl 4 (Ti / Si molar ratio is 30:1) under rapid stirring, and heat up to 60 °C for reaction for 5 hours. Wash with an appropriate amount of hexane for more than 3 times, and dry to obtain the catalyst.

[0050] The average particle size of the obtained catalyst is 135 μm, and the specific surface area is 745 m 2 / g. Among them, the titanium content in the catalyst is 2.1 wt%, and the THF content in the catalyst is 8.6 wt%.

[0051] (4) Ethylene polymerization and preparation of low-thermal-conductivity polyethylene: Use a 10 L slurry-phase C 2 H 4 polymerization evaluation device for polymerization. Add 5 L of n-hexane, 1.3 mL of a n-hexane solution of triethylaluminum with a concentration of 0.001 mol / ml, and 300 g of small-sized SiO 2 aerogel microspheres (parameters see step (1)) into the polymerization kettle. After stirring for 15 minutes, add 100 mg of the polyethylene catalyst obtained in step (3) (Al / Ti molar ratio is 30:1). After stirring for 5 minutes, add 5 g of diethoxydimethylsilane. Heat up to 80 °C, introduce ethylene, maintain the reaction pressure at 1 MPa, and carry out slurry polymerization. After polymerization for 1 h, stop feeding ethylene, cool down to room temperature, separate the polyethylene from the reaction kettle, wash with hexane, and dry.

[0052] After mixing 500 g of dried polyethylene resin with 0.5 g of antioxidant 1010, 0.3 g of antioxidant 168, and 0.5 g of zinc stearate evenly, they are melt-extruded by co-mixing in a twin-screw extruder. The temperatures of zones 1-7 are set at 175, 180, 185, 185, 185, 180, and 175 °C, and the rotation speed is 40 r / min; after water cooling, they are pelletized to obtain polyethylene with a low thermal conductivity coefficient.

[0053] The density of the obtained polyethylene with a low thermal conductivity coefficient is 0.910 g / cm 3 , and the thermal conductivity coefficient is 0.12 W / (m·K).

[0054] Example 2

[0055] (1) Preparation of SiO 2 aerogel microspheres is the same as in Example 1. From the preparation of silica aerogel microspheres, two types of microspheres with different particle sizes are screened for standby. Among them, the large-particle-size microspheres: the average particle size is 245 μm, the bulk density is 0.20 g / cm 3 , the specific surface area is 605 m 2 / g, the pore volume is 2.5 cm 3 / g, and the porosity is 85%; the small-particle-size microspheres: the average particle size is 50 μm, the bulk density is 0.15 g / cm 3 , the specific surface area is 800 m 2 / g, the pore volume is 1.8 cm 3 / g, and the porosity is 86%.

[0056] (2) Post-treatment of large-particle-size SiO 2 aerogel microspheres: Place the large-particle-size SiO 2 aerogel microspheres to be used in a vacuum drying oven, evacuate to vacuum, then introduce nitrogen, and keep the pressure at 0.01 MPa for 8 hours, repeating 5 times. Put the large-particle-size silica aerogel microspheres after atmosphere exchange into a muffle furnace, heat up to 200 °C, keep the temperature constant for 0.5 hour; heat up to 300 °C, keep the temperature constant for 2 hours; heat up to 450 °C, keep the temperature constant for 2 hours; cool down to 400 °C, keep the temperature constant for 1 hour; cool down to 200 °C, keep the temperature constant for 1 hour; cool down to 20 °C, and discharge to obtain activated SiO 2 aerogel microsphere carriers. Put the activated SiO 2 aerogel microsphere carriers into the vacuum drying oven again, evacuate to vacuum, then introduce nitrogen, and keep the pressure at 0.01 MPa for 8 hours. The treated large-particle-size SiO 2 aerogel microspheres are stored for standby in a nitrogen atmosphere.

[0057] (3) Preparation of polyethylene catalyst: Bake a 500 ml round-bottom flask under vacuum and replace it thoroughly with high-purity nitrogen. Add 1 g of large-particle-size SiO 2 aerogel microspheres (parameters as in step (1)) and 100 ml of tetrahydrofuran (THF) into the flask. After stirring well, add 6.2 ml of a hexane solution of triethylaluminum with a concentration of 0.1 mol / ml (the molar ratio of THF to triethylaluminum is 2:1), and raise the temperature to 40 °C and react for 2 hours. Cool down to 15 °C, and slowly add 55 ml of TiCl 4 (Ti / Si molar ratio is 30:1) under rapid stirring. Raise the temperature to 40 °C and react for 2 hours. Wash with hexane for more than 3 times, and obtain the catalyst after drying.

[0058] The average particle size of the obtained catalyst is 241 μm, and the specific surface area is 610 m 2 / g. Among them, the titanium content in the catalyst is 2.4 wt%, and the THF content in the catalyst is 9.6 wt%.

[0059] (4) Ethylene polymerization and preparation of low-thermal-conductivity polyethylene: Use a 10 L slurry-phase C 2 H 4 polymerization evaluation device for polymerization. Add 5 L of hexane, 1.5 mL of a hexane solution of triethylaluminum with a concentration of 0.001 mol / ml, and 300 g of small-particle-size SiO 2 aerogel microspheres (parameters as in step (1)) into the polymerization kettle. After stirring for 15 minutes, add 100 mg of the polyethylene catalyst obtained in step (3) (Al / Ti molar ratio is 30:1). After stirring for 5 minutes, add 5 g of diethoxydimethylsilane. Raise the temperature to 80 °C, introduce ethylene, maintain the reaction pressure at 0.5 MPa, and carry out slurry polymerization. After polymerization for 1 h, stop feeding ethylene, cool down to room temperature, separate the polyethylene from the reaction kettle, wash it with hexane, and dry it.

[0060] Take 500 g of the dried polyethylene resin, mix it evenly with 0.5 g of antioxidant 1010, 1.0 g of antioxidant 168, and 1.0 g of zinc stearate, and then carry out co-melting extrusion on a twin-screw extruder. Set the temperatures of zones 1-7 to 175, 180, 185, 185, 185, 180, 175 °C, and the rotation speed to 40 r / min; after water cooling, pelletize to obtain low-thermal-conductivity polyethylene.

[0061] The density of the obtained low-thermal-conductivity polyethylene is 0.904 g / cm 3 , and the thermal conductivity is 0.10 W / (m·K).

[0062] Example 3

[0063] (1) SiO 2The preparation of aerogel microspheres was the same as in Example 1. From the preparation of silica aerogel microspheres, two types of microspheres with different particle sizes were selected for standby. Among them, the large-particle-size microspheres had an average particle size of 102 μm, a bulk density of 0.25 g / cm 3 , a specific surface area of 400 m 2 / g, a pore volume of 2.0 cm 3 / g, and a porosity of 87%; the small-particle-size microspheres had an average particle size of 50 μm, a bulk density of 0.18 g / cm 3 , a specific surface area of 480 m 2 / g, a pore volume of 1.8 cm 3 / g, and a porosity of 86%.

[0064] (2) Post-treatment of large-particle-size SiO 2 aerogel microspheres: Place the required large-particle-size SiO 2 aerogel microspheres in a vacuum drying oven, evacuate to vacuum, then introduce nitrogen, and keep the pressure at 0.1 MPa for 5 hours. Repeat this 3 times. After the atmosphere exchange, put the large-particle-size silica aerogel microspheres into a muffle furnace, heat up to 180 °C and keep it at a constant temperature for 1 hour; heat up to 350 °C and keep it at a constant temperature for 2 hours; heat up to 550 °C and keep it at a constant temperature for 1 hour; cool down to 350 °C and keep it at a constant temperature for 1 hour; cool down to 100 °C and keep it at a constant temperature for 1 hour; cool down to 25 °C and discharge to obtain the activated SiO 2 aerogel microsphere carrier. Put the activated SiO 2 aerogel microsphere carrier into the vacuum drying oven again, evacuate to vacuum, then introduce nitrogen, and keep the pressure at 0.1 MPa for 5 hours. The treated large-particle-size SiO 2 aerogel microspheres are stored for standby in a nitrogen atmosphere.

[0065] (3) Preparation of polyethylene catalyst: Vacuum bake a 500 ml round-bottom flask and fully displace it with high-purity nitrogen. Add 2 g of large-particle-size SiO 2 aerogel microspheres (parameters as in step (1)) and 100 ml of tetrahydrofuran (THF) into the flask. After stirring well, add 6.2 ml of a 0.1 mol / ml triisobutylaluminum n-hexane solution (the molar ratio of THF to alkylaluminum is 2:1), and heat up to 60 °C and react for 1 hour. Cool down to 20 °C, and slowly add 55 ml of TiCl 4 (Ti / Si molar ratio 15:1) under rapid stirring, and heat up to 30 °C and react for 10 hours. Wash with hexane more than 3 times and dry to obtain the catalyst.

[0066] The average particle size of the obtained catalyst is 100 μm, and the specific surface area is 401 m 2 / g. Among them, the titanium content in the catalyst is 1.6 wt%, and the THF content in the catalyst is 6.1 wt%.

[0067] (4) Ethylene polymerization and preparation of low thermal conductivity polyethylene: Use a 10 L slurry-phase C 2 H 4 polymerization evaluation device for polymerization. Add 5 L of n-hexane, 0.7 mL of a n-hexane solution of triethylaluminum with a concentration of 0.001 mol / ml, and 50 g of small particle size SiO 2 aerogel microspheres (parameters are shown in step (1)) into the polymerization kettle. After stirring for 15 minutes, add 100 mg of the polyethylene catalyst obtained in step (3) (Al / Ti molar ratio is 20:1). After stirring for 5 minutes, add 20 g of diethoxydimethylsilane. Heat up to 80 °C, introduce ethylene, maintain the reaction pressure at 1.5 MPa, and carry out slurry polymerization. After polymerization for 1 h, stop feeding ethylene, cool down to room temperature, separate the polyethylene from the reaction kettle, wash it with hexane, and dry it.

[0068] Take 500 g of the dried polyethylene resin, mix it evenly with 1.5 g of antioxidant 1010, 0.3 g of antioxidant 168, and 1.0 g of zinc stearate, and then carry out melt extrusion and blending in a twin-screw extruder. Set the temperatures of zones 1-7 to 175, 180, 185, 185, 185, 180, 175 °C, and the rotation speed to 40 r / min; after passing through water cooling, pelletize to obtain low thermal conductivity polyethylene.

[0069] The density of the obtained low thermal conductivity polyethylene is 0.901 g / cm 3 , and the thermal conductivity is 0.11 W / (m·K).

[0070] Example 4

[0071] (1) Preparation of SiO 2 aerogel microspheres is the same as in Example 1. From the preparation of silica aerogel microspheres, two types of microspheres with different particle sizes are selected for standby. Among them, the large particle size microspheres: the average particle size is 200 μm, the bulk density is 0.18 g / cm 3 , the specific surface area is 850 m 2 / g, the pore volume is 1.9 cm 3 / g, and the porosity is 91%; the small particle size microspheres: the average particle size is 30 μm, the bulk density is 0.19 g / cm 3 , the specific surface area is 891 m 2 / g, the pore volume is 1.8 cm 3 / g, and the porosity is 89%.

[0072] (2) During the activation process of the large particle size SiO 2 aerogel microspheres, the constant temperature time during the heating section is 2 hours for both, and the rest of the process is the same as in Example 1.

[0073] (3) Preparation of polyethylene catalyst: Bake a 1000 ml round-bottom flask under vacuum and fully displace it with high-purity nitrogen. Add 3 g of large-particle-size SiO 2 aerogel microspheres (parameters as in step (1)) and 600 ml of tetrahydrofuran (THF) into the flask. After sufficient stirring, add 15 ml of a hexane solution of triethylaluminum with a concentration of 0.1 mol / ml (the molar ratio of THF to alkylaluminum is 5:1), and raise the temperature to 30 °C and react for 5 hours. Cool to 20 °C, and slowly add 110 ml of TiCl 4 (Ti / Si molar ratio is 20:1) while stirring rapidly, and raise the temperature to 60 °C and react for 5 hours. Wash with hexane for more than 3 times, and obtain the catalyst after drying.

[0074] The average particle size of the obtained catalyst is 183 μm, and the specific surface area is 785 m 2 / g. Among them, the titanium content in the catalyst is 1.1 wt%, and the THF content in the catalyst is 10.3 wt%.

[0075] (4) Ethylene polymerization and preparation of low-thermal-conductivity polyethylene: Use a 10 L slurry-phase C 2 H 4 polymerization evaluation device for polymerization. Add 5 L of hexane, 2.3 mL of a hexane solution of triethylaluminum with a concentration of 0.001 mol / ml, and 150 g of small-particle-size SiO 2 aerogel microspheres (parameters as in step (1)) into the polymerization kettle. After stirring for 15 minutes, add 100 mg of the polyethylene catalyst obtained in step (3) (Al / Ti molar ratio is 100:1). After stirring for 5 minutes, add 5 g of diethoxydimethylsilane. Raise the temperature to 60 °C, introduce ethylene, maintain the reaction pressure at 1 MPa, and carry out slurry polymerization. After polymerization for 1 h, stop feeding ethylene, cool to room temperature, separate the polyethylene from the reaction kettle, wash it with hexane, and dry it.

[0076] Take 500 g of the dried polyethylene resin, mix it evenly with 0.5 g of antioxidant 1010, 1.0 g of antioxidant 168, and 0.25 g of zinc stearate, and then carry out melt extrusion in a twin-screw extruder. Set the temperatures of zones 1-7 to 175, 180, 185, 185, 185, 180, 175 °C, and the rotation speed to 40 r / min; cool by passing through water and then pelletize to obtain low-thermal-conductivity polyethylene.

[0077] The density of the obtained low-thermal-conductivity polyethylene is 0.912 g / cm 3 , and the thermal conductivity is 0.17 W / (m·K).

[0078] Example 5

[0079] (1) SiO 2The preparation of the aerogel microspheres was the same as that in Example 1. From the prepared silica aerogel microspheres, large-sized microspheres were screened out: the average particle size was 300 μm, the bulk density was 0.20 g / cm 3 , the specific surface area was 703 m 2 / g, the pore volume was 1.8 cm 3 / g, and the porosity was 85%.

[0080] (2) During the activation process of the large-sized SiO 2 aerogel microspheres, the constant temperature time in the heating section was 2 hours for each, and the remaining processes were the same as those in Example 1.

[0081] (3) The preparation of the polyethylene catalyst was the same as that in Example 1. The average particle size of the obtained catalyst was 283 μm, and the specific surface area was 723 m 2 / g. Among them, the titanium content in the catalyst was 2.6 wt%, and the THF content in the catalyst was 9.1 wt%.

[0082] (4) Ethylene polymerization and preparation of low thermal conductivity polyethylene: A 10 L slurry-phase C 2 H 4 polymerization evaluation device was used for polymerization. 5 L of n-hexane and 1.6 mL of a n-hexane solution of triethylaluminum with a concentration of 0.001 mol / ml were added to the polymerization kettle. After stirring for 15 minutes, 100 mg of the polyethylene catalyst prepared in step (3) (the Al / Ti molar ratio was 30:1) was added. After stirring for 5 minutes, 5 g of diethoxydimethylsilane was added. The temperature was raised to 80 °C, and ethylene was introduced to maintain the reaction pressure at 1 MPa for slurry polymerization. After polymerization for 1 h, the ethylene feed was stopped, and the temperature was lowered to room temperature. The polyethylene was separated from the reaction kettle, washed with hexane, and dried. The extrusion granulation process of the resin was the same as that in Example 1.

[0083] The density of the obtained low thermal conductivity polyethylene was 0.925 g / cm 3 , and the thermal conductivity was 0.12 W / (m·K).

[0084] Example 6

[0085] (1) The preparation of SiO 2 aerogel microspheres was the same as that in Example 1. From the prepared silica aerogel microspheres, large-sized microspheres were screened out: the average particle size was 102 μm, the bulk density was 0.25 g / cm 3 , the specific surface area was 402 m 2 / g, the pore volume was 2.1 cm 3 / g, and the porosity was 87%.

[0086] (2) During the atmosphere exchange process of the large-sized SiO 2 aerogel microspheres, the pressure holding time was 8 hours, and during the activation process, the constant temperature time in the heating section was 2 hours for each. The remaining processes were the same as those in Example 1.

[0087] (3) The preparation of the polyethylene catalyst is the same as that in Example 1. The average particle size of the obtained catalyst is 102 μm, and the specific surface area is 401 m 2 / g. Among them, the titanium content in the catalyst is 2.1 wt%, and the THF content in the catalyst is 8.3 wt%.

[0088] (4) Ethylene polymerization and preparation of low thermal conductivity polyethylene: Use a 10L slurry-phase C 2 H 4 polymerization evaluation device for polymerization. Add 4L of n-hexane and 1.3 mL of a n-hexane solution of triethylaluminum with a concentration of 0.001 mol / ml to the polymerization kettle. After stirring for 15 minutes, add 100 mg of the polyethylene catalyst prepared in step (3) (Al / Ti molar ratio is 30:1). After stirring for 10 minutes, add 5 g of diethoxydimethylsilane. Heat up to 70 °C, introduce ethylene, maintain the reaction pressure at 1 MPa, and carry out slurry polymerization. After polymerization for 1 h, stop feeding ethylene, cool down to room temperature, separate the polyethylene from the reaction kettle, wash it with hexane, and dry it. The extrusion granulation process of the resin is the same as that in Example 1.

[0089] The density of the obtained low thermal conductivity polyethylene is 0.928 g / cm 3 , and the thermal conductivity is 0.20 W / (m·K).

[0090] Example 7

[0091] Select the large particle size SiO 2 aerogel microspheres in Example 1. The difference from Example 1 during post-treatment is only that the pressure is 0.5 Mpa and the pressure holding time is 10 h during the atmosphere exchange process of the large particle size SiO 2 aerogel microspheres. The preparation of the catalyst is the same as that in Example 1.

[0092] The average particle size of the obtained catalyst is 132 μm, and the specific surface area is 604 m 2 / g. Among them, the titanium content in the catalyst is 1.9 wt%, and the THF content in the catalyst is 8.4 wt%.

[0093] Ethylene polymerization and preparation of low thermal conductivity polyethylene are the same as in Example 1. The density of the obtained low thermal conductivity polyethylene is 0.915 g / cm 3 , and the thermal conductivity is 0.18 W / (m·K).

[0094] Comparative Example 1

[0095] Vacuum bake a 500 ml round-bottom flask and fully displace it with high-purity nitrogen. Add 2 g of ordinary SiO 2 support (average particle size is 150 μm, bulk density 0.29 g / cm 3, with a specific surface area of 318 m 2 / g, a pore volume of 1.5 cm 3 / g, and a porosity of 65%) and 200 ml of tetrahydrofuran (THF). After thorough stirring, 3 ml of a hexane solution of triethylaluminum with a concentration of 0.1 mol / ml (the molar ratio of THF to alkylaluminum is 8:1) was added. The temperature was raised to 30 °C and the reaction was carried out for 5 hours. The temperature was lowered to 10 °C, and 110 ml of TiCl 4 (Ti / Si molar ratio 30:1) was slowly added under rapid stirring. The temperature was raised to 60 °C and the reaction was carried out for 5 hours. An appropriate amount of hexane was added for washing more than 3 times, and the catalyst was obtained after drying.

[0096] The average particle size of the obtained catalyst was 143 μm, and the specific surface area was 325 m 2 / g. Among them, the titanium content in the catalyst was 0.78 wt%, and the THF content in the catalyst was 7.6 wt%.

[0097] The ethylene polymerization and the preparation of low-thermal-conductivity polyethylene were the same as in Example 1. The density of the obtained low-thermal-conductivity polyethylene was 0.931 g / cm 3 , and the thermal conductivity was 0.24 W / (m·K).

[0098] Comparative Example 2

[0099] A 500-ml round-bottom flask was vacuum baked and thoroughly replaced with high-purity nitrogen. 2 g of ordinary SiO 2 support (average particle size 144 μm, bulk density 0.28 g / cm 3 , specific surface area 318 m 2 / g, pore volume 1.5 cm 3 / g, porosity 65%) and 200 ml of tetrahydrofuran (THF) were added to the flask. After thorough stirring, 3 ml of a hexane solution of triethylaluminum with a concentration of 0.1 mol / ml (the molar ratio of THF to alkylaluminum is 8:1) was added. The temperature was raised to 30 °C and the reaction was carried out for 5 hours. The temperature was lowered to 10 °C, and 110 ml of TiCl 4 (Ti / Si molar ratio 30:1) was slowly added under rapid stirring. The temperature was raised to 60 °C and the reaction was carried out for 5 hours. An appropriate amount of hexane was added for washing more than 3 times, and the catalyst was obtained after drying.

[0100] The average particle size of the obtained catalyst was 123 μm, and the specific surface area was 324 m 2 / g. Among them, the titanium content in the catalyst was 0.82 wt%, and the THF content in the catalyst was 8.3 wt%.

[0101] Small-sized SiO 2 aerogel microspheres were not added during the ethylene polymerization process, and the remaining processes and the preparation of low-thermal-conductivity polyethylene were the same as in Example 1.

[0102] The density of the obtained low-thermal-conductivity polyethylene is 0.939 g / cm 3 , and the thermal conductivity is 0.38 W / (m·K).

[0103] Comparative Example 3

[0104] (1) Preparation of SiO 2 aerogel microspheres is the same as in Example 1. From the prepared silica aerogel microspheres, two types of microspheres with different particle sizes are screened and reserved. Among them, the large-particle-size microspheres: the average particle size is 150 μm, the bulk density is 0.20 g / cm 3 , the specific surface area is 730 m 2 / g, the pore volume is 1.8 cm 3 / g, and the porosity is 85%; the small-particle-size microspheres: the average particle size is 12 μm, the bulk density is 0.15 g / cm 3 , the specific surface area is 800 m 2 / g, the pore volume is 1.8 cm 3 / g, and the porosity is 86%.

[0105] (2) Post-treatment of large-particle-size SiO 2 aerogel microspheres: Referring to Patent CN1055184A, the silica aerogel microspheres are decompressed to -0.02 MPa and heated at 165 °C for 8 hours, and then cooled in nitrogen for standby.

[0106] (3) Preparation of the polyethylene catalyst is the same as in Example 1. The average particle size of the obtained catalyst is 131 μm, and the specific surface area is 532 m 2 / g. Among them, the titanium content in the catalyst is 2.5 wt%, and the THF content in the catalyst is 10.3 wt%.

[0107] (4) The process of ethylene polymerization and preparation of low-thermal-conductivity polyethylene is the same as in Example 1.

[0108] The density of the obtained low-thermal-conductivity polyethylene is 0.935 g / cm 3 , and the thermal conductivity is 0.310 W / (m·K).

[0109] Comparative Example 4

[0110] (1) Preparation of SiO 2 aerogel microspheres is the same as in Example 1. From the prepared silica aerogel microspheres, two types of microspheres with different particle sizes are screened and reserved. Among them, the large-particle-size microspheres: the average particle size is 150 μm, the bulk density is 0.20 g / cm 3 , the specific surface area is 730 m 2 / g, the pore volume is 1.8 cm 3 / g, and the porosity is 85%; the small-particle-size microspheres: the average particle size is 12 μm, the bulk density is 0.15 g / cm 3 , the specific surface area is 800 m2 / g, pore volume 1.8 cm 3 / g, porosity 86%.

[0111] (2) Large particle size SiO 2 Post-treatment of silica aerogel microspheres: Referring to Patent CN 108970647 A, the silica aerogel microspheres are put into an activator, and nitrogen is passed through to make the silica aerogel microspheres in a fluidized state. Heat the activator, raise the temperature to 200 °C, and keep it at a constant temperature for 2 hours; raise the temperature to 600 °C and keep it at a constant temperature for 2 hours; cool down to 300 °C within 2 hours, and then cool down to room temperature (20 °C) within another 2 hours, and discharge the material for standby.

[0112] (3) The preparation of the polyethylene catalyst is the same as in Example 1. The average particle size of the obtained catalyst is 102 μm, and the specific surface area is 522 m 2 / g, among which, the titanium content in the catalyst is 2.2 wt%, and the THF content in the catalyst is 8.9 wt%.

[0113] (4) The process of ethylene polymerization and the preparation of low thermal conductivity polyethylene are the same as in Example 1.

[0114] The density of the obtained low thermal conductivity polyethylene is 0.932 g / cm 3 , and the thermal conductivity is 0.340 W / (m·K).

[0115] Comparative Example 5

[0116] (1) SiO 2 The preparation of silica aerogel microspheres is the same as in Example 1. Two types of microspheres with different particle sizes are selected from the prepared silica aerogel microspheres for standby. Among them, the large particle size microspheres: the average particle size is 150 μm, the bulk density is 0.20 g / cm 3 , the specific surface area is 730 m 2 / g, pore volume 1.8 cm 3 / g, porosity is 85%; small particle size microspheres: the average particle size is 12 μm, the bulk density is 0.15 g / cm 3 , the specific surface area is 800 m 2 / g, pore volume 1.8 cm 3 / g, porosity 86%.

[0117] (2) Large particle size SiO 2Post-treatment of aerogel microspheres: Place large-sized silica aerogel microspheres to be used in a vacuum drying oven, evacuate to vacuum, then introduce nitrogen, and maintain the pressure at 0.2 MPa for 3 hours for atmosphere exchange, repeating 2 times. Put the large-sized silica aerogel microspheres after atmosphere exchange into a muffle furnace, heat up to 250 °C and keep the temperature constant for 2 hours; heat up to 500 °C and keep the temperature constant for 0.5 hour; cool down to 300 °C and keep the temperature constant for 1 hour; cool down to 200 °C and keep the temperature constant for 1 hour; cool down to 30 °C and discharge to obtain activated SiO 2 aerogel microsphere support. Put the activated SiO 2 aerogel microsphere support into the vacuum drying oven again, evacuate to vacuum, then introduce nitrogen, and maintain the pressure at 0.2 MPa for 3 hours. The treated large-sized SiO 2 aerogel microspheres are stored for standby in a nitrogen atmosphere.

[0118] (3) The preparation of the polyethylene catalyst is the same as in Example 1. The average particle size of the obtained catalyst is 135 μm, and the specific surface area is 648 m 2 / g, where the titanium content in the catalyst is 2.0 wt%, and the THF content in the catalyst is 8.1 wt%.

[0119] (4) The process of ethylene polymerization and the preparation of low-thermal-conductivity polyethylene are the same as in Example 1.

[0120] The density of the obtained low-thermal-conductivity polyethylene is 0.928 g / cm 3 , and the thermal conductivity is 0.32 W / (m·K).

[0121] Comparative Example 6

[0122] Ethylene polymerization and the preparation of low-thermal-conductivity polyethylene: Use a 10 L slurry-phase C 2 H 4 polymerization evaluation device for polymerization. Add 5 L of n-hexane and 2.4 mL of a triethylaluminum n-hexane solution with a concentration of 0.001 mol / ml to the polymerization kettle, stir for 15 minutes, and then add 100 mg of a commercial polyethylene catalyst (Sinopec BCS-O1 polyethylene catalyst, titanium content 2.3 wt%). After stirring for 5 minutes, add 5 g of diethoxydimethylsilane. Heat up to 80 °C, introduce ethylene, maintain the reaction pressure at 1 MPa, and carry out slurry polymerization. After polymerization for 1 h, stop the ethylene feed, cool down to room temperature, separate the polyethylene from the reaction kettle, wash it with hexane, and dry it. The process of extrusion granulation of the resin is the same as in Example 1.

[0123] The density of the obtained low-thermal-conductivity polyethylene is 0.940 g / cm 3 , and the thermal conductivity is 0.42 W / (m·K).

[0124] To better illustrate the implementation effects of the present invention, the implementation effects of Examples 1-7 and Comparative Examples 1-6 are summarized in the following table.

[0125]

[0126] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention. However, these corresponding changes and deformations should all fall within the protection scope of the claims of the present invention.

Claims

1. A polyethylene catalyst, characterized in that, Including post-treated large-particle-size SiO 2 aerogel microspheres and alkylaluminum, wherein the large-particle-size SiO 2 aerogel microspheres have a particle size of 100-300 μm. The post-treatment method is to first place the large-particle-size SiO 2 aerogel microspheres under an inert atmosphere for atmosphere exchange treatment, and then perform activation. After activation, atmosphere exchange treatment is performed again. The activation step includes placing the large-particle-size SiO 2 aerogel microspheres after atmosphere exchange in an activator, heating to 150-200 °C and keeping the temperature constant; heating to 300-400 °C and keeping the temperature constant; heating to 450-650 °C and keeping the temperature constant; cooling to 300-400 °C and keeping the temperature constant; cooling to 100-200 °C and keeping the temperature constant; cooling to 20-30 °C.

2. The polyethylene catalyst according to claim 1, characterized in that, The large particle size SiO 2 The bulk density of the aerogel microspheres is 0.15 - 0.28 g / cm 3 , the pore volume is 1.5 - 3 cm 3 / g, preferably 1.8 - 2.5 g / cm 3 , the specific surface area is 300 - 1000 m 2 / g, preferably 400 - 850 m 2 / g, and the porosity is 85 - 92%.

3. The polyethylene catalyst according to claim 1, characterized in that, The atmosphere exchange treatment is to place large-particle-size SiO 2 aerogel microspheres in a vacuum drying oven, evacuate the air, and then introduce an inert gas, maintain the pressure, the pressure for maintaining the pressure is 0.01-0.2 MPa, and the time for maintaining the pressure is 3-8 hours.

4. The polyethylene catalyst according to claim 1, characterized in that, 2 - 5 times of atmosphere exchange treatments are carried out before activation.

5. The polyethylene catalyst according to claim 1, characterized in that, During multiple constant - temperature processes, the constant - temperature time is 0.5 - 2 hours.

6. The polyethylene catalyst according to claim 1, characterized in that, The general formula of the alkylaluminum is AlR 3m X 1(3-m) , where R 3 is an alkyl, aryl or aralkyl group having C 1 to C 20 ; X 1 is a halogen; m is an integer of 0 ≦ n ≦ 3, preferably one or more of trimethylaluminum, triethylaluminum, triisobutylaluminum, monochlorodiethylaluminum and monochlorodiisobutylaluminum, more preferably triethylaluminum and / or triisobutylaluminum.

7. A preparation method of the polyethylene catalyst according to any one of claims 1 - 6, characterized in that, Under an inert gas condition, after post-treatment, large-sized SiO 2 aerogel microspheres and tetrahydrofuran are mixed evenly, then alkylaluminum is added. After reacting at 30 - 60 °C for 1 - 5 hours, the temperature is lowered to -10 - 20 °C. Under stirring conditions, a titanium compound is added, and the temperature is raised to 30 - 60 °C and reacted for 2 - 10 hours. After washing and drying, the catalyst is obtained.

8. The preparation method of the polyethylene catalyst according to claim 7, characterized in that, For every gram of large-sized SiO 2 aerogel microspheres, 20 - 300 ml of tetrahydrofuran is added; the molar ratio of tetrahydrofuran to alkyl aluminum is 8:1 - 2:1; the addition amount of TiCl 4 is such that the Ti / Si molar ratio is 10:1 - 50:1, preferably 15:1 - 30:

1.

9. The preparation method of the polyethylene catalyst according to claim 7, characterized in that, The particle size of the catalyst is 100 - 300 μm, and the specific surface area is 300 - 800 m 2 / g. Among them, the Ti content of the catalyst is 0.5 - 3 wt%, and the THF content in the catalyst is 5 - 20 wt%.

10. An ethylene polymerization method, characterized in that, Under the condition of inert gas, a solvent and an alkyl aluminum are added into a polymerization kettle, after stirring evenly, the catalyst according to any one of claims 1 - 6 is added, after stirring, an alkoxysilane is added and ethylene is introduced for polymerization reaction. After the reaction ends, polyethylene is separated out, washed and dried to obtain a polyethylene resin.

11. The ethylene polymerization method according to claim 10, characterized in that, While adding a solvent and an alkylaluminum into a polymerization kettle, add SiO aerogel microspheres with small particle sizes. 2 The added mass of the SiO aerogel microspheres with small particle sizes is 500 - 3000 times the mass of the catalyst. 2 The particle size of the SiO aerogel microspheres with small particle sizes is 10 - 50 μm. 2 ​ 12. The ethylene polymerization method according to claim 10, characterized in that, The ethylene polymerization conditions are: the molar ratio of aluminum in the alkyl aluminum added during the polymerization process to titanium in the catalyst is 20:1 - 100:1, the polymerization temperature is 60 - 80 °C, and the polymerization pressure is 0.5 - 1.5 MPa.

13. The ethylene polymerization method according to claim 10, characterized in that, The alkoxysilane is one or more selected from dimethoxydimethylsilane, diethoxydimethylsilane, dimethoxydiphenylsilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane and tetrapentyloxysilane, preferably diethoxydimethylsilane and tetraethoxysilane, and the addition amount of the alkoxysilane to the mass of the catalyst is 50:1 - 200:

1.

14. A low - thermal - conductivity polyethylene resin, characterized in that, It comprises the polyethylene resin according to any one of claims 10 - 13 and additives.

15. The low - thermal - conductivity polyethylene resin according to claim 14, characterized in that, The additives include an antioxidant and zinc stearate. The antioxidant includes antioxidant 1010 and antioxidant 168. The addition amount of antioxidant 1010 is 1000 - 3000 ppm of the mass of the polyethylene resin, the addition amount of antioxidant 168 is 600 - 2000 ppm of the mass of the polyethylene resin; the addition amount of zinc stearate is 500 - 2000 ppm of the mass of the polyethylene resin.

16. The low - thermal - conductivity polyethylene resin according to claim 14, characterized in that, The density of the low thermal conductivity polyethylene resin is 0.890 - 0.925 g / cm 3 , and the thermal conductivity is 0.10 - 0.20 W / (m·K).

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