Metallocene catalyst for ethylene polymerization and preparation method thereof

Abstract

The invention provides a preparation method of a metallocene catalyst for ethylene polymerization, which comprises the following steps: carrying out polymerization reaction on a cyano-containing olefin compound and polypropylene under the conditions of an initiator and supercritical CO2 to obtain a cyano-modified polypropylene carrier; then loading alkyl aluminoxane and alkyl magnesium halide to obtain an activated carrier; and loading a metallocene compound on the activated carrier to obtain the metallocene catalyst for ethylene polymerization. According to the method, cyan-functionalized polypropylene is grafted by using supercritical CO2, a metallocene compound, alkyl magnesium halide and an alkyl aluminoxane compound are supported by cyan-functionalized polypropylene microspheres, and double carriers can be formed between alkyl magnesium halide and the cyan-functionalized polypropylene microspheres, so that the active center of the catalyst is uniformly dispersed after being supported; the obtained catalyst is good in particle morphology and easy to regulate and control a polymerization process, and polyethylene prepared by the catalyst is wide in molecular weight distribution and easy to process and form subsequent products.

Description

Technical Field

[0001] The present invention relates to the field of supported metallocene catalysts, and particularly to a metallocene catalyst for ethylene polymerization and a preparation method thereof. Background Art

[0002] Catalysts are an important part of the polyolefin industry. They not only determine the types of monomers that can be polymerized, polymerization activity, and copolymerization efficiency, but also the molecular weight and its distribution, sequence structure, and stereoregularity of the resulting polymer mainly depend on the catalyst. Compared with traditional Ziegler-Natta catalysts, metallocene catalysts have high activity and single active centers. The polyethylene obtained has the characteristics of linear low density, regular arrangement of polyethylene molecular chains, narrow molecular weight distribution, and uniform distribution of comonomers. It has advantages such as high strength, good transparency, low initial heat-sealing temperature, few extractables, and good impact resistance compared with traditional polyethylene, so it has been widely used. However, metallocene catalysts also have their disadvantages. For example, to prevent the deactivation of catalyst bimolecules and improve their activity and selectivity, usually an excessive amount of cocatalyst is required to fully surround the metallocene molecules. At the same time, a large amount of heat is released during the polymerization process, resulting in serious fouling of the reactor, and the morphology of the obtained polyolefin particles is not good. Catalyst immobilization can overcome the disadvantages of the catalyst during the polymerization process and has an important impact on the catalyst performance.

[0003] The carrier greatly improves the catalytic activity of the catalyst and also solves the problem of ash in the catalytic product. The introduction of the carrier can improve the mechanical strength of the catalyst. In industrial slurry polymerization devices and gas-phase polymerization devices, there is an advantage of controlling the particle size and morphology of the polymer by controlling the particle size and morphology of the carrier for homogeneous catalysts. Moreover, the introduction of the carrier can make the release of the catalyst activity become gentle, avoid "explosive polymerization", and can also extend the reaction life of the catalyst. Selecting a suitable carrier can also play a role in improving the catalytic reaction activity.

[0004] Currently, the commonly used carriers are divided into two categories: inorganic carriers and organic carriers. Inorganic carriers are usually SiO 2 , molecular sieves, γ-Al 2 O 3 etc., mainly relying on surface hydroxyl groups to bond with metal compounds, and only a few carriers directly bond with metal compounds, such as MgCl 2 , mainly loading Ziegler-Natta titanium catalytic systems to form Mg-Cl-Ti bonds. SiO 2The carrier has a high specific surface area, appropriate pore volume, pore distribution, good fluidity and mechanical strength, meeting the requirements of industrial production equipment. Organic carriers include polysiloxane, cyclodextrin, polystyrene, etc. In addition to chemically bonding or coordinating with the main catalyst and cocatalyst, organic carriers can also adsorb the active components of the catalyst on their surfaces through physical or chemical adsorption, mainly because the carrier has a porous structure. The swelling property of the organic carrier can evenly distribute the active centers of the catalyst in the carrier particles, greatly increasing the number of active centers and improving the reaction activity. However, due to the swelling property of the organic carrier, the finally prepared catalyst has poor mechanical strength and is prone to fragmentation during the production process, ultimately resulting in uneven product morphology and particle size, which is not conducive to product production. The compatibility between inorganic carriers and catalysts is poor, leading to ash in the polymerization product, and there are generally acidic groups on the surface of inorganic carriers, which will inhibit the release of catalyst activity. Organic carriers bring low ash content to polymers and can solve technical problems such as fisheyes caused by inorganic carriers. By selecting active groups, the electronic environment and steric hindrance of the active centers can be controlled, and the catalyst activity can be adjusted accordingly.

[0005] As disclosed in Chinese Patent Document CN104558265B, a novel monodisperse porous styrene-divinylbenzene-ethylene glycol dimethacrylate terpolymer carrier is used. By loading the metallocene catalyst system with polar functional groups on the polymer, a metallocene catalyst supported on an organic polymer is obtained. In this scheme, the specific surface area and bulk density of the organic carrier are close to those of inorganic silica carriers, the morphology of the supported metallocene catalyst and polymer particles is good, and the catalyst activity is relatively high. However, the metallocene loading of the prepared carrier is relatively low.

[0006] Chinese Patent Document CN101440137B prepares a monodisperse porous polystyrene microsphere carrier through a two-step seed swelling method, and loads the metallocene catalyst onto the carrier to obtain a supported metallocene main catalyst, which forms a monodisperse porous organic polymer microsphere supported metallocene catalyst with a cocatalyst. Compared with the existing solid organic carriers, this supported catalyst has a larger specific surface area, which is beneficial to the loading of the catalyst and the release of active centers. This porous structure is more conducive to the gradual fragmentation of the carrier during the catalytic olefin polymerization process; compared with the post-functionalized carrier of polymer microspheres, the carrier structure with functional group monomers copolymerized during synthesis is clear, and the functional groups are evenly distributed in the carrier. However, a large amount of solvent is consumed during the preparation of the polystyrene carrier, and the pore volume and average pore diameter of the polystyrene carrier are relatively small, making it difficult to accurately control and not conducive to the loading of the metallocene catalyst.

[0007] Chinese Patent Document CN115073629A discloses a supported metallocene catalyst system, which mainly consists of an organic-inorganic composite support, a cocatalyst, and a metallocene compound. The organic-inorganic composite support is composed of an organic support copolymerized from divinylbenzene and styrene containing sulfonic acid groups and a hydrophilic TiO 2 inorganic support. The functional groups in the prepared support enable the catalyst to have higher catalytic activity by influencing the chemistry of the metal active centers; in addition, through the regulation of the support by inorganic hydrophilic nano-TiO 2 particles, the prepared support particles have a narrow particle size distribution, good fluidity and surface morphology, and a single-peak distribution and narrow dispersion particle morphology can be obtained after direct drying without post-treatment such as screening, and the surface morphology of the particles is good, and the bulk density of the support is controllable. During the olefin polymerization process, due to the replication effect, the polymer can obtain good particle morphology and higher bulk density. However, the preparation process of the catalyst support involved is complex.

[0008] Chinese Patent Document CN116410370A discloses a metallocene catalyst for ethylene polymerization and its application. The catalyst includes a support and an active component supported on the support; the active component includes a metallocene compound and an alkylaluminum compound; the support is a porous polymer microsphere modified with cyano and tertiary amino groups; the mass content of cyano in the support is 1-10%, and the mass content of tertiary amino in the support is 1-25%. The support is obtained by the polymerization reaction of a porous polymer microsphere with an olefin compound containing cyano and an olefin compound containing tertiary amino. The preparation process of the support involved in this scheme is relatively complex.

[0009] Chinese Patent Document CN109320637B discloses a supported metallocene catalyst for ethylene polymerization, comprising: a carrier, a metallocene compound supported on the carrier, and a cocatalyst. The carrier is a polymer microsphere, and the cocatalyst is an alkyl aluminum. The zirconium loading content in the catalyst is 0.1-5 wt%, the aluminum content is 10-36 wt%, and the carrier is 59-89.9 wt%. The preparation of this catalyst includes the following steps: ① Supercritical carbon dioxide-assisted loading: Add an aromatic solution of the metallocene compound to the polymer carrier, place it in a high-pressure reactor, introduce carbon dioxide, heat and pressurize until carbon dioxide reaches the supercritical state, and use supercritical carbon dioxide to swell the polymer carrier. The swelling and permeation temperature during the supercritical carbon dioxide swelling process is 31-60 °C, the swelling pressure is 7.5-12 MPa, and the swelling time is 0.5-10 hours; ② Catalyst activation: After swelling, slowly release the pressure, introduce nitrogen for replacement, and then add the cocatalyst to the swollen catalyst intermediate for catalyst activation; ③ Drying and shaping: Add a solution to the reactor, wash repeatedly, remove the solvents in steps ① and ②, and dry to obtain a highly active supported metallocene catalyst. However, the polymer obtained with this catalyst has a narrow molecular weight distribution. Summary of the Invention

[0010] In view of this, the present invention provides a preparation method of a metallocene catalyst for ethylene polymerization. This method uses supercritical CO 2 to graft cyano-functionalized polypropylene, uses the cyano-functionalized polypropylene microspheres as a carrier to load the metallocene compound, alkyl magnesium halide, and alkylaluminoxane compound. A double carrier can be formed between the alkyl magnesium halide and the cyano-functionalized polypropylene microspheres, enabling the active centers of the loaded catalyst to be evenly dispersed. The obtained catalyst has good particle morphology and is easy to control the polymerization process. Moreover, the polyethylene prepared with this catalyst has a wide molecular weight distribution and is easy to process and form subsequent products. In addition, the preparation of the cyano-functionalized polypropylene microspheres is simple and easy to implement. The entire preparation method of the metallocene catalyst for ethylene polymerization is conducive to large-scale industrial applications and can meet industrialization requirements.

[0011] To achieve the above object, the present invention adopts the following technical solutions:

[0012] A preparation method of a metallocene catalyst for ethylene polymerization, comprising the following steps:

[0013] Preparation of the carrier: A cyano-containing olefin compound and polypropylene are subjected to a polymerization reaction under the conditions of an initiator and supercritical CO 2 to obtain a cyano-modified polypropylene carrier;

[0014] Activation of the carrier: Load the alkylaluminoxane and alkyl magnesium halide on the cyano-modified polypropylene carrier to obtain an activated carrier;

[0015] Loading: The metallocene compound is loaded onto the activated support to obtain a metallocene catalyst for ethylene polymerization.

[0016] Optionally, in the method for preparing the metallocene catalyst for ethylene polymerization provided by the present invention, the grafting rate of the cyano group in the cyano-modified polypropylene support is not specifically limited. As long as a cyano functional group is introduced onto the polypropylene support and then the cyano group is bonded to the magnesium ion in the alkyl magnesium halide to form a double support. The recommended grafting rate of the cyano group in the cyano-modified polypropylene support of the present invention is 1 wt% - 10 wt%.

[0017] Optionally, in the support preparation step of the method for preparing the metallocene catalyst for ethylene polymerization provided by the present invention, during the supercritical CO 2 During the swelling process, the swelling temperature is 40 - 120 °C, the swelling pressure is 5 - 18 MPa, and the swelling time is 1 - 12 h.

[0018] Optionally, in the support preparation step of the method for preparing the metallocene catalyst for ethylene polymerization provided by the present invention, after the polymerization reaction ends, it further includes the steps of cooling the reaction system to normal temperature and pressure, extracting the obtained material to remove oligomers and solvents, and then drying. The extraction is preferably carried out in a Soxhlet extractor with acetone for 1 - 24 h; the drying is preferably carried out under vacuum at 60 - 80 °C.

[0019] Optionally, in the support activation step of the method for preparing the metallocene catalyst for ethylene polymerization provided by the present invention, the specific method of loading the alkylaluminoxane and the alkyl magnesium halide onto the cyano-modified polypropylene support is not limited, as long as the alkylaluminoxane and the alkyl magnesium halide can be loaded onto the cyano-modified polypropylene support. For example, the following method can be used:

[0020] After adding the cyano-modified polypropylene support to a solvent and mixing evenly, add the alkylaluminoxane and the alkyl magnesium halide and mix. Stir at 20 - 90 °C for 1 - 24 h, then slowly cool to room temperature and normal pressure. After separation (such as suction filtration), the obtained solid is washed with a solvent to remove the excess cocatalyst to obtain the activated support. Among them, the solvent can be selected from conventional ones in the industry, such as toluene, etc.

[0021] Optionally, in the loading step of the method for preparing the metallocene catalyst for ethylene polymerization provided by the present invention, the specific operation of loading the metallocene compound onto the activated support is not limited, as long as it can be loaded. For example, the activated support and a solvent (such as toluene, etc.) can be mixed evenly in a Schlenk-type filtration reactor, and then a prepared Cp 2 TiCl 2A toluene solution is then stirred at 20 - 90 °C for 1 - 24 h for loading, followed by suction filtration. The obtained solid is washed with toluene 1 - 3 times and then with n - hexane 1 - 2 times. After the solid is dried under vacuum, a supported metallocene catalyst is obtained and transferred to an ampoule. The whole operation is carried out under anhydrous and anaerobic conditions.

[0022] Optionally, in the loading step of the preparation method of the metallocene catalyst for ethylene polymerization provided by the present invention, the loading temperature is 20 - 90 °C and the time is 1 - 24 h.

[0023] Optionally, in the preparation method of the metallocene catalyst for ethylene polymerization provided by the present invention, the general formula of the metallocene compound is: (Cp) x TiCl y , where x is 1 or 2, y is 2 or 3, and Cp is cyclopentadienyl or a derivative of cyclopentadienyl.

[0024] Optionally, in the preparation method of the metallocene catalyst for ethylene polymerization provided by the present invention, the polypropylene is homopolypropylene, and the average particle size of the homopolypropylene is 100 - 1500 μm.

[0025] Optionally, in the preparation method of the metallocene catalyst for ethylene polymerization provided by the present invention, the cyano - containing olefin compound is acrylonitrile.

[0026] Optionally, in the preparation method of the metallocene catalyst for ethylene polymerization provided by the present invention, the alkylmagnesium halide is selected from any one of methylmagnesium chloride, ethylmagnesium chloride, propylmagnesium chloride, and methylmagnesium bromide, and preferably methylmagnesium chloride.

[0027] Optionally, in the preparation method of the metallocene catalyst for ethylene polymerization provided by the present invention, the initiator is selected from at least one of benzoyl peroxide, di - tert - butyl peroxide, di - cumyl peroxide, and azobisisobutyronitrile.

[0028] Optionally, in the preparation method of the metallocene catalyst for ethylene polymerization provided by the present invention, the alkylaluminoxane is selected from at least one of methylaluminoxane, ethyl - modified methylaluminoxane, and isobutyl - modified methylaluminoxane; preferably methylaluminoxane.

[0029] The present invention also provides a metallocene catalyst for ethylene polymerization, which is prepared by the above-mentioned preparation method. Based on the mass of the metallocene catalyst for ethylene polymerization being 100%, in terms of Al element, it is alkylaluminoxane; in terms of Mg element, it is alkylmagnesium halide; in terms of Ti element, it is metallocene compound. The content of the metallocene compound is 0.2 wt% - 1 wt%, the content of the alkylaluminoxane is 15 wt% - 20 wt%, the content of the alkylmagnesium halide is 5 wt% - 10 wt%, and the content of the cyano-modified polypropylene carrier is 69 wt% - 79.8 wt%.

[0030] Compared with the prior art, the effects of the present invention are as follows:

[0031] Beneficial effect 1: The preparation method of the metallocene catalyst for ethylene polymerization provided by the present invention first uses cyano-functionalized polypropylene microspheres as the carrier, then loads alkylaluminoxane and alkylmagnesium halide, and finally loads the metallocene compound, thereby obtaining a supported metallocene catalyst. By directly introducing cyano functional groups onto the polypropylene carrier and utilizing the bonding of cyano with magnesium ions in alkylmagnesium halide, a dual-carrier system can be formed between the alkylmagnesium halide and the cyano-modified polypropylene, which is easy to regulate the metallocene active center, thereby promoting the loading of metallocene on the carrier and improving the uniformity of metallocene loading. As a result, the polyethylene prepared using this catalyst has a larger particle size, less fine powder generation during the production process, a wide molecular weight distribution, and is easy to process and form.

[0032] In addition, the preparation of cyano-functionalized polypropylene microspheres is simple and easy to implement. Compared with the existing supported metallocene catalyst system, the polypropylene carrier has a wide source and low cost. The entire preparation method of the metallocene catalyst for ethylene polymerization is conducive to large-scale application in industrial devices, can meet the industrialization requirements, and the prepared polyethylene products have excellent properties and can be used to produce high-end pipe materials, films, blow molding and other special polyethylene materials. Specific embodiments

[0033] 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 understood 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.

[0034] For those not specifying specific experimental steps or conditions in the examples, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For the reagents or instruments not specifying the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0035] Table 1 Raw material sources

[0036]

[0037]

[0038] Example 1

[0039] This example provides a preparation method of a metallocene catalyst for ethylene polymerization, including the following steps:

[0040] Cyano-modified polypropylene support

[0041] Put 2 g of homopolypropylene (average particle size of 100 - 130 μm), acrylonitrile and 0.02 g of diisopropylbenzene peroxide into an autoclave, and introduce CO 2 After thoroughly purging the inside of the autoclave, introduce CO again 2 At the same time, raise the temperature until the temperature of the reaction kettle is 80 °C and the pressure is 12 Mpa. After swelling and permeating for 3 h under this condition, slowly release the pressure. After cooling to room temperature, discharge the reacted materials in the reaction kettle, and extract in a Soxhlet extractor with acetone for 24 h to remove the oligomers and solvents therein; finally, put the obtained solid particles into a vacuum drying oven and dry them under vacuum at 80 °C to obtain a cyano-modified polypropylene support. By infrared detection, the grafting rate of cyano in this cyano-modified polypropylene support is 4.8%.

[0042] Support activation

[0043] After vacuum drying the above cyano-modified polypropylene support at 80 °C for 12 h, take 1 g and add it to a 100 ml Schlenk-type filter reactor treated under anhydrous and anaerobic conditions, add 30 mL of toluene, and stir magnetically at 50 °C to mix evenly; then add methylmagnesium chloride and MAO respectively, stir for 12 h, then carry out suction filtration, and wash with toluene 3 times to remove the excess cocatalyst to obtain an activated support.

[0044] Loading metallocene

[0045] After vacuum drying the above activated support at 60 °C for 12 h, take 1 g and add it to a 100 ml Schlenk-type filter reactor treated under anhydrous and anaerobic conditions, add 30 mL of toluene, and stir magnetically at 50 °C to mix evenly; then add the prepared toluene solution of Cp 2 TiCl 2 (Cp is cyclopentadienyl) by syringe, stir magnetically at 50 °C for 12 h, then carry out suction filtration. The obtained solid is washed 3 times with toluene and 2 times with n-hexane. After vacuum drying the solid, a supported metallocene catalyst is obtained and transferred to an ampoule. The whole operation is carried out under anhydrous and anaerobic conditions.

[0046] Example 2

[0047] This embodiment provides a preparation method of a metallocene catalyst for ethylene polymerization, comprising the following steps:

[0048] Cyano-modified polypropylene support

[0049] Place 2 g of homopolypropylene (average particle size of 300 - 350 μm), acrylonitrile, and 0.02 g of benzoyl peroxide into an autoclave, and introduce CO 2 Replace the gas in the autoclave completely, and then introduce CO 2 Meanwhile, raise the temperature until the temperature of the reaction kettle is 40 °C and the pressure is 15 Mpa. After swelling and permeating for 12 h under this condition, slowly release the pressure. After cooling to room temperature, discharge the reacted materials in the reaction kettle, and extract with acetone in a Soxhlet extractor for 24 h to remove the oligomers and solvents therein. Finally, put the extracted solid particles into a vacuum drying oven and dry them under vacuum at 60 °C to obtain the cyano-modified polypropylene support. By infrared detection, the grafting rate of cyano groups in the cyano-modified polypropylene support is 9.3%.

[0050] Activation of the support

[0051] After vacuum drying the above cyano-modified polypropylene support at 60 °C for 12 h, take 1 g and add it to a 100 ml Schlenk-type filtration reactor treated under anhydrous and anaerobic conditions. Add 60 mL of toluene and stir magnetically at 30 °C to mix evenly; add methylmagnesium bromide and ethyl-modified methylaluminoxane respectively, stir for 24 h, then perform suction filtration, and wash with toluene 3 times to remove the excess cocatalyst to obtain the activated support.

[0052] Loading of metallocene

[0053] After vacuum drying the above activated support at 60 °C for 12 h, take 1 g and add it to a 100 ml Schlenk-type filtration reactor treated under anhydrous and anaerobic conditions. Add 60 mL of toluene and stir magnetically at 50 °C to mix evenly; then add the prepared toluene solution of Cp 2 TiCl 2 (Cp is cyclopentadienyl) by syringe. After stirring magnetically at 60 °C for 6 h, perform suction filtration. The obtained solid is washed 3 times with toluene and 2 times with n-hexane. After vacuum drying the solid, the supported metallocene catalyst is obtained and transferred to an ampoule. The whole operation is carried out under anhydrous and anaerobic conditions.

[0054] Example 3

[0055] This embodiment provides a preparation method of a metallocene catalyst for ethylene polymerization, comprising the following steps:

[0056] Cyano-modified polypropylene support

[0057] Place 2 g of homopolypropylene (average particle size 1400 - 1450 μm), acrylonitrile, and 0.02 g of di-tert-butyl peroxide in an autoclave, and introduce CO 2 Replace the gas in the autoclave completely, and then introduce CO 2 At the same time, raise the temperature until the temperature of the autoclave reaches 120 °C and the pressure is 18 Mpa. After swelling and permeating for 10 h under these conditions, slowly release the pressure. After cooling to room temperature, discharge the reacted materials in the autoclave, and extract with acetone in a Soxhlet extractor for 15 h to remove the oligomers and solvents therein. Finally, put the extracted solid particles into a vacuum drying oven and dry them under vacuum at 70 °C to obtain a cyanide-modified polypropylene support. By infrared detection, the grafting rate of cyanide in the cyanide-modified polypropylene support is 7.1%.

[0058] Activation of the support

[0059] After vacuum drying the above cyanide-modified polypropylene support at 60 °C for 12 h, take 1 g and add it to a 100 ml Schlenk-type filtration reactor treated under anhydrous and anaerobic conditions. Add 50 mL of toluene and mix evenly by magnetic stirring at 80 °C; add propylmagnesium chloride and isobutyl-modified methylaluminoxane respectively, stir for 8 h, then perform suction filtration, and wash with toluene 3 times to remove the excess cocatalyst to obtain the activated support.

[0060] Loading metallocene

[0061] After vacuum drying the above activated support at 60 °C for 12 h, take 1 g and add it to a 100 ml Schlenk-type filtration reactor treated under anhydrous and anaerobic conditions. Add 50 mL of toluene and mix evenly by magnetic stirring at 50 °C; then add the prepared toluene solution of Cp 2 TiCl 2 (Cp is cyclopentadienyl), stir magnetically at 30 °C for 20 h, then perform suction filtration. The obtained solid is washed 3 times with toluene and 2 times with n-hexane. After vacuum drying the solid, a supported metallocene catalyst is obtained and transferred to an ampoule. The whole operation is carried out under anhydrous and anaerobic conditions.

[0062] Example 4

[0063] This example provides a preparation method of a metallocene catalyst for ethylene polymerization, including the following steps:

[0064] Cyanide-modified polypropylene support

[0065] Place 2 g of homopolypropylene (average particle size 850 - 860 μm), acrylonitrile, and 0.02 g of azobisisobutyronitrile in an autoclave, and introduce CO 2 Replace the gas in the autoclave completely, and then introduce CO 2Meanwhile, raise the temperature until the temperature in the reaction kettle reaches 60 °C and the pressure reaches 5 Mpa. After swelling and permeating for 8 h under this condition, slowly release the pressure until it cools to room temperature, then discharge the reacted materials in the reaction kettle, and extract with acetone in a Soxhlet extractor for 8 h to remove the oligomers and solvents therein. Finally, put the extracted solid particles into a vacuum drying oven and dry them under vacuum at 70 °C to obtain a cyano-modified polypropylene support. By infrared detection, the grafting rate of cyano groups in the cyano-modified polypropylene support is 3.2%.

[0066] Activation of the support

[0067] After vacuum drying the above cyano-modified polypropylene support at 60 °C for 12 h, take 1 g and add it to a 100 ml Schlenk-type filtration reactor treated under anhydrous and anaerobic conditions, add 30 mL of toluene, and mix evenly by magnetic stirring at 70 °C; add ethylmagnesium chloride and MAO respectively, stir for 3 h, then perform suction filtration and wash 3 times with toluene to remove the excess cocatalyst, and obtain the activated support.

[0068] Loading metallocene

[0069] After vacuum drying the above activated support at 60 °C for 12 h, take 1 g and add it to a 100 ml Schlenk-type filtration reactor treated under anhydrous and anaerobic conditions, add 30 mL of toluene, and mix evenly by magnetic stirring at 50 °C; then add the prepared toluene solution of Cp 2 TiCl 2 (Cp is cyclopentadienyl) by syringe, stir magnetically at 80 °C for 3 h, then perform suction filtration, wash the obtained solid 3 times with toluene and 2 times with n-hexane, vacuum dry the solid, and obtain the supported metallocene catalyst, and transfer it to an ampoule. The whole operation is carried out under anhydrous and anaerobic conditions.

[0070] Example 5

[0071] This example provides a preparation method of a metallocene catalyst for ethylene polymerization, including the following steps:

[0072] Cyano-modified polypropylene support

[0073] Put 2 g of homopolypropylene (average particle size is 1100 - 1130 μm), acrylonitrile and 0.02 g of diisopropylbenzene peroxide into a high-pressure kettle, and introduce CO 2 After thoroughly displacing the inside of the kettle, introduce CO again 2Meanwhile, raise the temperature until the temperature in the reaction kettle reaches 100 °C and the pressure reaches 8 Mpa. After swelling and permeating for 6 h under this condition, slowly release the pressure. After cooling to room temperature, discharge the reacted materials in the reaction kettle, and extract with acetone in a Soxhlet extractor for 2 h to remove the oligomers and solvents therein. Finally, put the solid particles obtained after extraction into a vacuum drying oven and dry them under vacuum at 80 °C to obtain a cyano-modified polypropylene support. By infrared detection, the grafting rate of cyano groups in the cyano-modified polypropylene support is 1.5%.

[0074] Support activation

[0075] After vacuum drying the above cyano-modified polypropylene support at 80 °C for 12 h, take 1 g and add it to a 100 ml Schlenk-type filtration reactor treated under anhydrous and anaerobic conditions. Add 30 mL of toluene and mix evenly by magnetic stirring at 60 °C. Then add methylmagnesium chloride and MAO respectively, stir for 18 h, and then perform suction filtration. Wash with toluene 3 times to remove the excess cocatalyst to obtain the activated support.

[0076] Supported metallocene

[0077] After vacuum drying the above activated support at 60 °C for 12 h, take 1 g and add it to a 100 ml Schlenk-type filtration reactor treated under anhydrous and anaerobic conditions. Add 30 mL of toluene and mix evenly by magnetic stirring at 50 °C. Then add the prepared toluene solution of Cp 2 TiCl 2 (Cp is cyclopentadienyl) by syringe. After magnetic stirring at 70 °C for 15 h, perform suction filtration. Wash the obtained solid 3 times with toluene and then 2 times with n-hexane. After vacuum drying the solid, obtain the supported metallocene catalyst and transfer it to an ampoule. The whole operation is carried out under anhydrous and anaerobic conditions.

[0078] Comparative Example 1

[0079] This comparative example is similar to Example 1, except that polypropylene is not modified with cyano in this comparative example. The preparation method of the metallocene catalyst for ethylene polymerization in this comparative example is as follows:

[0080] Treatment of polypropylene support

[0081] Put 2 g of homopolypropylene (average particle size of 100 - 130 μm) into a high-pressure kettle, and introduce CO 2 Replace the air in the kettle completely, and then introduce CO 2 , raise the temperature of the reaction kettle to 80 °C and the pressure to 12 Mpa. After swelling and permeating for 3 h under this condition, slowly release the pressure. After the reaction kettle cools to room temperature, discharge the materials, put them into a vacuum drying oven and dry them under vacuum at 80 °C to obtain the swollen polypropylene support.

[0082] Support activation

[0083] After vacuum drying the above-mentioned swollen polypropylene support at 80 °C for 12 h, 1 g was taken and added to a 100 ml Schlenk-type filter reactor treated under anhydrous and anaerobic conditions. 30 mL of toluene was added, and the mixture was magnetically stirred and mixed evenly at 50 °C. Then methylmagnesium chloride and MAO were added respectively. After stirring for 12 h, suction filtration was carried out, and it was washed 3 times with toluene to remove the excess cocatalyst, obtaining the activated support.

[0084] Supported metallocene

[0085] After vacuum drying the above-mentioned activated support at 60 °C for 12 h, 1 g was taken and added to a 100 ml Schlenk-type filter reactor treated under anhydrous and anaerobic conditions. 30 mL of toluene was added, and the mixture was magnetically stirred and mixed evenly at 50 °C. Then the prepared toluene solution of Cp 2 TiCl 2 (where Cp is cyclopentadienyl) was added with a syringe. After magnetic stirring at 50 °C for 12 h, the reactor was inverted for suction filtration. After washing 3 times with toluene and then 2 times with n-hexane, the solid was vacuum dried to obtain the supported metallocene catalyst, which was transferred to an ampoule. The whole operation was carried out under anhydrous and anaerobic conditions.

[0086] Comparative Example 2

[0087] This comparative example is similar to Example 1, except that silica gel is used instead of polypropylene in this comparative example. The preparation method of the metallocene catalyst for ethylene polymerization in this comparative example is as follows:

[0088] Support activation

[0089] After vacuum drying silica gel at 80 °C for 12 h, it was added to a 100 ml Schlenk-type filter reactor treated under anhydrous and anaerobic conditions. 30 mL of toluene was added, and the mixture was magnetically stirred and mixed evenly at 50 °C. Then methylmagnesium chloride and MAO were added respectively. After stirring for 12 h, suction filtration was carried out, and it was washed 3 times with toluene to remove the excess cocatalyst, obtaining the activated support.

[0090] Supported metallocene

[0091] After vacuum drying the above-mentioned activated support at 60 °C for 12 h, 1 g was taken and added to a 100 ml Schlenk-type filter reactor treated under anhydrous and anaerobic conditions. 30 mL of toluene was added, and the mixture was magnetically stirred and mixed evenly at 50 °C. Then the prepared toluene solution of Cp 2 TiCl 2A toluene solution of (Cp is cyclopentadienyl) was magnetically stirred at 50 °C for 12 h, then filtered by suction. The obtained solid was washed three times with toluene and then twice with n-hexane. After the solid was dried under vacuum, a supported metallocene catalyst was obtained and transferred to an ampoule. The whole operation was carried out under anhydrous and anaerobic conditions.

[0092] Comparative Example 3

[0093] This comparative example is similar to Example 1, except that the supercritical carbon dioxide condition is omitted in the preparation process of the cyano-modified polypropylene support in this comparative example. The preparation method of the metallocene catalyst for ethylene polymerization in this comparative example is as follows:

[0094] Cyano-modified polypropylene support

[0095] 2 g of homopolypropylene (average particle size of 100 - 130 μm), acrylonitrile, and 0.02 g of diisopropylbenzene peroxide were placed in a reactor. Then, 2 ml of the interfacial agent xylene was added to the reactor, nitrogen was introduced, and the reaction was carried out at 80 °C for 2 h. The obtained solid particles were extracted with acetone in a Soxhlet extractor for 24 h to remove the oligomers and solvents therein. Finally, the extracted solid particles were placed in a vacuum drying oven and dried under vacuum at 80 °C to obtain a cyano-modified polypropylene support. By infrared detection, the grafting rate of cyano groups in the cyano-modified polypropylene support was 4.8%.

[0096] Support activation: Similar to Example 1, except that the above-mentioned cyano-modified polypropylene support was used in this comparative example;

[0097] Loading metallocene: Similar to Example 1, except that the above-activated support was used in this comparative example.

[0098] Comparative Example 4

[0099] This comparative example is similar to Example 1, except that in this comparative example, alkylaluminoxane, alkylmagnesium halide, and metallocene compound were loaded together. The preparation method of the metallocene catalyst for ethylene polymerization in this comparative example is as follows:

[0100] Cyano-modified polypropylene support

[0101] 2 g of homopolypropylene (average particle size of 100 - 130 μm), acrylonitrile, and 0.02 g of diisopropylbenzene peroxide were placed in an autoclave, and CO 2 After the inside of the autoclave was purged and replaced, CO was introduced again 2Meanwhile, raise the temperature until the temperature of the reaction kettle reaches 80 °C and the pressure reaches 12 Mpa. After swelling and permeating for 3 h under these conditions, slowly release the pressure. After cooling to room temperature, discharge the reacted materials in the reaction kettle, and extract with acetone in a Soxhlet extractor for 24 h to remove the oligomers and solvents therein. Finally, put the solid particles obtained after extraction into a vacuum drying oven and dry them under vacuum at 80 °C to obtain the cyano-modified polypropylene carrier. By infrared detection, the grafting rate of cyano groups in the cyano-modified polypropylene carrier is 4.8%.

[0102] Load

[0103] After vacuum drying the above cyano-modified polypropylene carrier at 80 °C for 12 h, take 1 g and add it to a 100 ml Schlenk-type filtration reactor treated under anhydrous and anaerobic conditions. Add 30 mL of toluene and stir magnetically at 50 °C to mix evenly. Then add methylmagnesium chloride and MAO respectively, and then add the prepared toluene solution of Cp 2 TiCl 2 (Cp is cyclopentadienyl) at 50 °C and stir magnetically for 12 h. Then perform suction filtration. The obtained solid is washed 3 times with toluene and 2 times with n-hexane. After vacuum drying the solid, the supported metallocene catalyst is obtained and transferred to an ampoule. The whole operation is carried out under anhydrous and anaerobic conditions.

[0104] The metallocene catalysts prepared in each example and comparative example were detected for titanium, magnesium, and aluminum elements by ICP. The specific detection results are shown in Table 2 below.

[0105] Table 2

[0106]

[0107]

[0108] Performance test

[0109] The metallocene catalysts prepared in each of the above examples and comparative examples were respectively subjected to performance tests for ethylene polymerization reaction according to the following method.

[0110] Ethylene polymerization reaction

[0111] The autoclave with a volume of 500 mL was vacuum dried at 70 °C for 30 min, and replaced three times with nitrogen and ethylene respectively. 250 mL of n-hexane was added to the autoclave, and then MAO and 5 mg of metallocene catalyst were added in sequence. Among them, the molar ratio of Al element in MAO to Ti element in the supported metallocene catalyst was 300:1. Then, the pipeline was rinsed with a small amount of hexane, stirred, and heated to 80 °C. Ethylene was introduced until the system pressure reached 1.0 MPa. After polymerization under this condition for 2 h, the pressure was released, and it was quenched with acidified ethanol under stirring, filtered, and vacuum dried to constant weight to obtain the polyethylene product. The obtained polyethylene products were respectively subjected to performance tests such as density, bulk density, and molecular weight distribution. The specific test results are shown in Table 3.

[0112] Among them, the density was tested according to the method specified in GB / T 1033.

[0113] The bulk density was tested according to the method specified in GB / T 1636-2008.

[0114] The molecular weight distribution was tested according to the GPC method.

[0115] Table 3

[0116]

[0117]

[0118] From the data in the above table, it can be seen that the metallocene catalyst for ethylene polymerization provided by the present invention is easy to regulate the metallocene active center. During the production of polyethylene prepared by this catalyst, less fine powder is generated, the molecular weight distribution is wide, and it is easy for subsequent product processing and molding.

[0119] Of course, the present invention can also 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, but these corresponding changes and deformations should all fall within the protection scope of the claims of the present invention.

Claims

1. A preparation method of a metallocene catalyst for ethylene polymerization, characterized in that, it comprises the following steps: Carrier preparation: An olefin compound containing a cyano group and polypropylene are subjected to a polymerization reaction under an initiator and supercritical CO 2 conditions to obtain a polypropylene carrier modified with a cyano group; Support activation: Loading an alkylaluminoxane and an alkylmagnesium halide on the cyano-modified polypropylene support to obtain an activated support; Loading: Loading a metallocene compound on the activated support to obtain a metallocene catalyst for ethylene polymerization.

2. The preparation method according to claim 1, characterized in that, the grafting rate of cyano groups in the cyano-modified polypropylene support is 1 wt% - 10 wt%.

3. The preparation method according to claim 1, characterized in that, In the step of preparing the carrier, the supercritical CO 2 During the swelling process, the swelling temperature is 40 - 120 °C, the swelling pressure is 5 - 18 MPa, and the swelling time is 1 - 12 h.

4. The preparation method according to claim 1, characterized in that, in the loading step, the loading temperature is 20 - 90 °C and the time is 1 - 24 h.

5. The preparation method according to claim 1, characterized in that, The general formula of the metallocene compound is: (Cp) x TiCl y , where x is 1 or 2, y is 2 or 3, and Cp is cyclopentadienyl or a derivative of cyclopentadienyl.

6. The preparation method according to claim 1, characterized in that, the polypropylene is homopolypropylene, and the average particle size of the homopolypropylene is 100 - 1500 μm.

7. The preparation method according to claim 1, characterized in that, the cyano-containing olefin compound is acrylonitrile.

8. The preparation method according to claim 1, characterized in that, the alkylmagnesium halide is selected from any one of methylmagnesium chloride, ethylmagnesium chloride, propylmagnesium chloride and methylmagnesium bromide, preferably methylmagnesium chloride.

9. The preparation method according to claim 1, characterized in that, the initiator is selected from at least one of benzoyl peroxide, di-tert-butyl peroxide, diisopropylbenzene peroxide and azobisisobutyronitrile; the alkylaluminoxane is selected from at least one of methylaluminoxane, ethyl-modified methylaluminoxane, isobutyl-modified methylaluminoxane; preferably methylaluminoxane.

10. A metallocene catalyst for ethylene polymerization prepared by the preparation method of the metallocene catalyst for ethylene polymerization according to any one of claims 1 - 9, characterized in that, taking the mass of the metallocene catalyst for ethylene polymerization as 100%, based on Al element, the alkylaluminoxane, based on Mg element, the alkylmagnesium halide, based on Ti element, the metallocene compound, the content of the metallocene compound is 0.2 wt% - 1 wt%, the content of the alkylaluminoxane is 15 wt% - 20 wt%, the content of the alkylmagnesium halide is 5 wt% - 10 wt%, and the content of the cyano-modified polypropylene support is 69 wt% - 79.8 wt%.

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