CN109320637B - Supported metallocene catalyst for ethylene polymerization and preparation method thereof - Google Patents
Supported metallocene catalyst for ethylene polymerization and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a load type metallocene catalyst for ethylene polymerization and a preparation method thereof, wherein the catalyst comprises the following components: the catalyst comprises polymer microspheres, a metallocene compound and alkyl aluminum, wherein the metallocene compound and the alkyl aluminum are loaded on the polymer microspheres, 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%; when loading, adding aromatic hydrocarbon solution of metallocene compound into polymer microsphere, using supercritical carbon dioxide to swell the polymer microsphere, then adding alkyl aluminoxane to activate catalyst, finally drying and forming. The metallocene catalyst prepared by the invention has good particle shape, high polymerization activity, stable polymerization reaction dynamics and controllable molecular weight of a polymerization product.
Description
Technical Field
The invention belongs to the field of supported metallocene catalysts, and particularly relates to a supported metallocene catalyst for ethylene polymerization and a preparation method for synthesizing the supported metallocene catalyst by treating porous polymer microspheres with supercritical carbon dioxide.
Background
Metallocene polyethylene (mPE) is the earliest metallocene polyolefin to be produced industrially, and is the metallocene polymer which has the largest yield, the fastest practical progress and the most research and development companies at present. At present, about more than ten large petrochemical companies can industrially produce metallocene products all over the world, and only a few polyolefin manufacturers such as Daqing petrochemical company, Dushan petrochemical company, Qilu petrochemical company and the like produce metallocene polyethylene products in China. In the end of 2011, the Daqing chemical research center of the China Petroleum chemical research institute carries out long-period operation work on a 50kg/hr gas phase method full-density polyethylene pilot plant for developing metallocene polyethylene pilot plant for 14 days, the continuous operation of the plant is 276 hours, and marks that the most advanced domestic polyethylene pilot plant has the strength of long-period operation of metallocene catalyst, so that technical service can be better provided for production plants.
Metallocene polyethylene is produced without leaving the metallocene catalyst. The research and development of metallocene catalysts and polyolefins in China began in the early 90 s of the last century, and research institutions and colleges for joining the work are gradually increased in recent years, wherein the research institutions and colleges mainly comprise China petrochemical research institute, petrochemical science research institute, chemical institute of Chinese academy, Beijing chemical research institute, Zhejiang university and the like. The homogeneous metallocene catalyst has many advantages and disadvantages, such as deactivation of the active center of the catalyst due to bimolecular association, so that a large amount of MAO must be added to isolate the active center, and the Al/Zr molar ratio required by the homogeneous metallocene catalyst is very high; meanwhile, when the homogeneous metallocene catalyst is used for olefin polymerization, the prepared polymer has poor form, and the polymer generated in the polymerization process seriously adheres to a kettle, thereby restricting the industrial application of the metallocene catalyst to a certain extent.
In order to overcome the above disadvantages, it has been attempted to support a metallocene catalyst on a carrier to obtain a supported metallocene catalyst. After the metallocene catalyst is loaded on the carrier, the active centers can not be close to each other, so bimolecular deactivation can not occur, the dosage of MAO can be greatly reduced, and the catalyst can basically keep the original activity under the condition of lower Al/Zr molar ratio. Moreover, the macroscopic morphology of the polyolefin catalyst carrier particles is used as a template of polymer particles in the polymerization process, and has a great influence on the activity and catalytic performance of the catalyst. The use of the supported catalyst can prevent bimolecular deactivation and reduce beta-H elimination reaction, and a polymer having a high molecular weight and a high melting point is obtained, and the polymer thus prepared is expected to have a good morphology and a large bulk density. In addition, the catalyst can be supported to release the activity of the catalyst uniformly, so that the polymerization reaction is easy to control, slurry and gas phase polymerization can be carried out, and the catalyst can be applied to the existing industrial equipment for olefin polymerization more easily.
The process for loading metallocene catalysts on a carrier generally has four processes: (1) simultaneously adding a metallocene complex and a cocatalyst (usually methylaluminoxane), reacting for a period of time, adding a carrier, and simultaneously loading the metallocene complex and the cocatalyst on the carrier during stirring; (2) the metallocene complex reacts with the carrier for a period of time, and after the metallocene complex is loaded on the carrier, the cocatalyst is added for loading; (3) after the cocatalyst and the carrier act for a period of time and are loaded on the carrier, adding the metallocene complex for loading; (4) in two reaction kettles, the metallocene complex and the cocatalyst are respectively reacted with the carrier for a period of time, and then the metallocene complex and the cocatalyst are mixed and stirred to load the metallocene complex and the cocatalyst together.
There are currently a lot of studies on The loading of Metallocene Catalysts, such as "study progress of Metallocene catalyst loading" disclosed by Putenjie et al in synthetic resins and plastics, 2018, pp.76-80, "study progress of Metallocene catalyst loading" disclosed by Co., Ltd. et al, No. 5, 2014-748, "study progress of Metallocene catalyst loading mechanism for Olefin Polymerization, such as" study strength "disclosed by Shimad. et al, No. 1, pp.76-79, Fernando Silviara et al, Macromoler Reaction Engineering, pp.139-147," The wheel of The Support in The Performance of modified Metallocene Catalysts, "and" review of Polymer processing, publication 400, cited by Long Wu et al, Polymer of transfer Catalysts, pp.2018, "review of Polymerization processes.
The supported metallocene catalyst mainly comprises a metallocene compound, aluminoxane and a carrier. The metallocene compound is composed of cyclopentadiene and its derivative, bridge chain part, central transition metal such as Zr, Hf, Ti, etc. and other substituent connected to metal. The aluminoxane is mainly used as a cocatalyst, and has high price, thereby greatly influencing the performance and the cost of the catalyst. In the supported metallocene catalyst, the aluminoxane and the metallocene compound are firmly supported on the carrier, otherwise the aluminoxane and the metallocene compound are dropped off during the polymerization process, so that the polymer has poor morphology, more polymer fine powder and even sticking to a kettle. In the prior art, the loading amounts of the alkyl aluminoxane and the metallocene compound on the carrier are not high, which leads to larger loss of the alkyl aluminoxane in the loading process and improves the cost of the loaded catalyst on the one hand, and also reduces the utilization rates of the alkyl aluminoxane and the metallocene compound on the other hand, and in addition, the catalytic activity of the catalyst is lower.
The most commonly used catalyst carriers are classified into inorganic carriers and organic polymer carriers. A commonly used inorganic support is alumina (Al)2O3) Magnesium chloride (MgCl)2) Silica gel (SiO)2) Inorganic substances with equal pore volume and specific surface area, in which SiO is used2For example, Grace 955 silica gel has been reported most extensively as carrier, for example, CN1095474C, CN1049439C, CN1157419C, US4808561, US5026797, US5763543, US5661098 all disclose SiO2A supported metallocene catalyst as a carrier.
CN 105622796 discloses a supported metallocene catalyst and a preparation method thereof. The content of Al in the catalyst is 5-20 wt%; the content of the transition metal is 0.01 to 0.3 wt%. The preparation method mainly comprises two steps, namely step A, loading alkyl aluminoxane: adding a silica gel carrier into an alkylaluminoxane solution, stirring, washing, filtering and drying to obtain a carrier loaded with alkylaluminoxane; step B, loading a metallocene compound: adding the carrier loaded with the alkyl aluminoxane into the metallocene compound slurry, stirring, washing, filtering and drying to finally prepare the loaded metallocene catalyst. The method adopts a mode of adding the carrier into the alkyl aluminoxane solution, thereby omitting the step of preparing the carrier into suspension, reducing the using amount of the solvent, simultaneously reducing the possibility of carrier aggregation by controlling the adding speed of the carrier, and improving the form of the catalyst. However, the catalyst prepared by the method is mainly used for catalyzing propylene polymerization. The ethylene polymerization has a high exotherm which is more than 2 times that of propylene polymerization, resulting in that the propylene polymerization catalyst cannot be used for catalyzing the polymerization of ethylene to obtain a high quality polyethylene product.
CN 105330766 discloses a supported metallocene catalyst loaded on a spherical montmorillonite mesoporous composite material and a preparation method thereof. The carrier is a mesoporous molecular sieve material containing montmorillonite, having a one-dimensional through channel structure and a mesoporous molecular sieve material having a hexagonal channel structure, the average particle size of the carrier is 30-60 microns, the specific surface area is 150-600 square meters/g, the pore volume is 0.5-1.5 ml/g, and the pore diameter is in trimodal distribution. The method mainly improves the activity of the supported metallocene catalyst by changing a catalyst carrier. However, the carrier used in the method is a spherical molecular sieve, and the preparation process of the carrier is complex and is not beneficial to the industrial production and application of the catalyst.
Due to SiO2、MgCl2、Al2O3The strong electrostatic interaction between the inorganic carrier and the metallocene changes the catalytic performance of the metallocene catalyst; on the other hand, the polyolefin obtained by the catalysis of the inorganic supported catalyst has residual inorganic matters; more importantly, these hard carrier particle fragments will contribute to undesirable polymer morphology and purity. In contrast, organic polymer supported metallocene catalysts provide a chemical environment similar to homogeneous catalysts. The organic support appears to have a greater "affinity" for the final polymer than does the rigid surface of the inorganic support. And the organic supports are easier to prepare, less costly, and more easily functionalized to meet specific catalytic requirements. The polyolefin catalyzed by the organic carrier metallocene catalyst has less residual inorganic impurities, the polymer form is easier to control, and the requirements of fields such as cable jackets and the like which need high insulation can be met, so the organic polymer carrier gradually enters the sight of people. The most commonly used organic polymer carriers are porous polystyrene microspheres, polyethylene powder, polysiloxane, and the like.
CN 1624005 discloses a preparation method of a solid homogeneous metallocene catalyst supported by polystyrene. The method comprises introducing cyclopentadiene groups on linear polystyrene chain, and loading metallocene into crosslinked polystyrene network by Diels-Alder crosslinking reaction between cyclopentadiene groups in the presence of metallocene. The catalyst prepared by the method is solid in appearance, a solvent can enter a polystyrene network in the polymerization process to enable the metallocene catalyst to catalyze olefin polymerization in a homogeneous environment, and a cross-linked network of a carrier can be gradually untied in the polymerization process, so that an active center originally wrapped in the carrier is gradually released, and the industrial application of the catalyst is facilitated. However, the method has the main disadvantages that: the structure of the functional group of the carrier is not clear, the distribution of the functional group in the carrier is not uniform, so that the distribution of the active center of the loaded catalyst in the polystyrene microsphere is not uniform, and the particle form of the produced polymer can not meet the industrial requirement.
CN 1257875 discloses a preparation method of a high molecular metallocene catalyst, which utilizes a metallocene catalyst with olefin functional groups to copolymerize with styrene, thereby synthesizing a self-supported high molecular metallocene catalyst with a special structure. However, the metallocene compound required in this method requires a specific structure, has a large influence on the properties of the polymer product, and can be used only for producing polyethylene having a specific structure. In addition, most of the active centers of the catalyst prepared by the method are concentrated on the surface of the carrier, the distribution of the active centers of the catalyst is not uniform, the carrier is not uniformly crushed in the polymerization process, and the produced polymer has poor particle shape and high fine powder content, so that the method is not favorable for large-scale industrial application of the catalyst.
Supercritical fluids are fluids above the critical temperature and critical pressure point. At the critical temperature and pressure, the fluid cannot be liquefied and is in a gas-liquid state regardless of the pressure, but the density of the fluid increases as the pressure increases. Supercritical fluids have densities similar to liquids and viscosities similar to gases, but have diffusion coefficients nearly 100 times greater than liquids, and have the advantage of exceptional transfer properties not comparable to other fluids. The Supercritical fluid expands rapidly (Rapid Expansion of Supercritical Solution), abbreviated as RESS preparation. The method is characterized in that the characteristics of the supercritical fluid are utilized, the supercritical fluid containing volatile substances is rapidly expanded or even vacuumized in a very short time by a specific method, the dissolving capacity of the fluid is greatly changed due to the change of pressure, so that a very large supersaturation degree is formed, and the substances are rapidly precipitated. The specific method is a method in which expansion is performed by a nozzle, a capillary, or the like, and desired ultrafine particles can be obtained due to the small size of the nozzle. According to classical nucleation theory, the greater the supersaturation, the finer the particles formed. The method for preparing the catalyst of the supported metallocene catalyst fine particles by utilizing the supercritical fluid technology such as the phyllocrine and the like provides a new method for preparing the polyolefin catalyst particles, and has important significance for the development of petrochemical industry in China and the promotion of the application of the polyolefin catalyst. However, the supercritical fluid rapid expansion method uses supercritical propane as the fluid, propane is flammable and explosive, a special nozzle is needed for carrier formation, and the regulation of the particle morphology and the particle size distribution of the catalyst are not ideal, which is not favorable for the morphological replication of the polymerization product.
Disclosure of Invention
The invention aims to provide a supported metallocene catalyst for ethylene polymerization, which aims to solve the technical problems that the existing catalyst has unsatisfactory particle morphology and particle size distribution regulation and control, and the produced polymer has poor particle morphology and cannot meet the industrial requirements.
In order to realize the purpose, the invention is realized by adopting the following technical scheme:
a supported metallocene catalyst for ethylene polymerization comprising: the catalyst comprises a carrier, a metallocene compound and a cocatalyst, wherein the carrier is a polymer microsphere, the cocatalyst is alkyl aluminum, the zirconium load content in the catalyst is 0.1-5 wt%, the aluminum content is 10-36 wt%, and the carrier is 59-89.9 wt%; when loading, adding aromatic hydrocarbon solution of metallocene compound into polymer microsphere, using supercritical carbon dioxide to swell the polymer microsphere, then adding alkyl aluminoxane to activate catalyst, finally drying and forming.
The polymer microspheres are preferably homopolymer microspheres and copolymer microspheres of monomers such as styrene, divinylbenzene, acrylonitrile or acrylamide.
Preferably, the metallocene compound has a structure represented by the following formula,
wherein R is1、R2、R3、R4、R5、R1’、R2’、R3’、R4' and R5' each independently is hydrogen or C1-C5 alkyl, M is metallic zirconium, and X is halogen.
In the present invention, the alkyl aluminum is preferably one or a mixture of two or more of trimethyl aluminum, triethyl aluminum, triisopropyl aluminum, triisobutyl aluminum, tri-n-hexyl aluminum, diethyl aluminum monochloride and methyl aluminoxane.
The second purpose of the invention is to provide a preparation method of a supported metallocene catalyst for ethylene polymerization, which utilizes supercritical carbon dioxide to process porous polymer microspheres in the preparation process, and then loads metallocene compounds and alkyl aluminoxane on the polymer microspheres, thereby effectively solving the technical problems that the catalyst prepared by the existing method has unsatisfactory particle shape and particle size distribution regulation, the produced polymer has poor particle shape and cannot meet the industrial requirements.
In order to realize the purpose, the invention is realized by adopting the following technical scheme:
a preparation method of a supported metallocene catalyst for ethylene polymerization comprises the following steps:
the supercritical carbon dioxide assists in loading: adding an aromatic hydrocarbon solution of a metallocene compound into a polymer carrier, placing the polymer carrier in a high-pressure reactor, introducing carbon dioxide, heating and pressurizing until the carbon dioxide reaches a supercritical state, and swelling the polymer carrier by using the supercritical carbon dioxide;
② catalyst activation: slowly releasing the pressure after swelling is finished, introducing nitrogen for replacement for 5-10 times, and adding a certain proportion of cocatalyst into the swollen catalyst intermediate for catalyst activation;
thirdly, drying and forming: and (3) adding a hexane solution into the reactor, repeatedly washing for 5-10 times, removing the solvent in the first step and the second step, and drying to obtain the high-activity supported metallocene catalyst.
In the present invention, the aromatic hydrocarbon solution in the step (i) is preferably one or a mixture of two or more of benzene, toluene, and xylene.
As a further preferable mode of the present invention, in the swelling process of the supercritical carbon dioxide, the swelling permeation temperature is 31 to 60 ℃, the swelling pressure is 7.5 to 12MPa, and the swelling time is 0.5 to 10 hours.
As a further preferred of the invention, the cocatalyst in the step (II) is aromatic hydrocarbon solution of aluminum alkyl; the activation reaction is stirring at 10-100 ℃, and refluxing is carried out for 1-4 hours.
As a further preferred mode of the present invention, the activation in the step (c) and the drying and forming in the step (c) are both performed under anhydrous and oxygen-free conditions.
As a further preferable mode of the present invention, the molar ratio of the amount of the alkyl aluminum to the amount of the metallocene compound added in the step (ii) is 20 to 1000.
The invention has the advantages and positive effects that:
(1) the invention utilizes supercritical carbon dioxide (CO) in the process of loading the metallocene catalyst2) The swelling effect on the porous polymer microsphere of the carrier enables the metallocene compound and the aluminoxane compound to be uniformly dispersed on the pore canal and the surface of the polymer microsphere, so that the active center of the loaded catalyst is also uniformly dispersed, the obtained catalyst has good particle shape, high polymerization activity, stable polymerization reaction dynamics and easy control of the polymerization process; and the obtained polymer particles have good shape, controllable shape, adjustable molecular weight, low fine powder content, high bulk density and better fluidity, are beneficial to large-scale application of industrial devices, and can meet the industrial requirements.
(2) The invention uses supercritical CO2 as the supercritical fluid swelling carrier method to prepare the load type metallocene catalyst, and has the following unique advantages: the surface tension of the supercritical CO2 is extremely low, and the swelling of the supercritical CO2 on the organic polymer carrier and the diffusion and permeation of the metallocene compound on the organic polymer carrier are not influenced no matter how poor the wettability of the organic polymer carrier is; secondly, the swelling capacity of the supercritical CO2 to the carrier polymer is changed along with the temperature and the pressure, the solubility of the metallocene compound in the supercritical CO2 and the swelling degree of the porous polymer microspheres are easily controlled, and the amount of the metallocene compound entering the carrier is further controlled, so that catalyst precursors meeting different requirements are prepared. ③ the plasticizing action of the supercritical CO2 can greatly improve the diffusion speed of the metallocene compound in the polymer carrier after swelling and also can improve the adsorption and dissolution degree of the metallocene compound in the polymer carrier. And fourthly, by controlling the swelling time, the metallocene compound can be in gradient distribution in the polymer carrier without influencing the morphology of the generated blend. The supercritical CO2 is a reaction medium with wide application range and environmental protection, and does not change the original properties of the metallocene compound and the carrier. And sixthly, slowly releasing pressure after swelling is finished, wherein the swollen polymer microspheres can still keep the original pore structure and performance, and the next step of load reaction and uniform distribution of the active center of the catalyst are facilitated.
Drawings
FIG. 1 is an electron micrograph of the catalyst prepared in example 1.
Detailed Description
In order to make the technical solutions and advantages of the present invention clear to those skilled in the art, the technical solutions of the present invention are described in detail below by examples and comparative examples, but are not intended to limit the scope of the present invention.
The invention provides a supported metallocene catalyst for ethylene polymerization, which comprises the following components: the catalyst comprises a carrier, a metallocene compound and a cocatalyst, wherein the metallocene compound and the cocatalyst are loaded on the carrier, 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 carrier is a polymer microsphere, the cocatalyst is alkyl aluminum, an aromatic hydrocarbon solution of a metallocene compound is added into the polymer microsphere during loading, the polymer microsphere is swelled by using supercritical carbon dioxide, then alkyl aluminoxane is added for catalyst activation, and finally drying and forming are carried out; the polymer microspheres are homopolymers and copolymer microspheres of monomers such as styrene, divinylbenzene, acrylonitrile, acrylamide and the like;
the metallocene compound has a structure represented by the following formula,
wherein R is1、R2、R3、R4、R5、R1’、R2’、R3’、R4' and R5' each independently is hydrogen or C1-C5 alkyl, M is metallic zirconium, X is halogen;
the alkyl aluminum is one or a mixture of two or more of trimethyl aluminum, triethyl aluminum, triisopropyl aluminum, triisobutyl aluminum, tri-n-hexyl aluminum, diethyl aluminum chloride or methylaluminoxane.
The invention also provides a preparation method of the supported metallocene catalyst for ethylene polymerization, which comprises the following steps of treating porous polymer microspheres by using supercritical carbon dioxide in the preparation process, and then loading the metallocene compound and alkyl aluminoxane on the polymer microspheres, wherein the preparation method specifically comprises the following steps:
a preparation method of a supported metallocene catalyst for ethylene polymerization comprises the following steps:
the supercritical carbon dioxide assists in loading: adding an aromatic hydrocarbon solution of a metallocene compound into a polymer carrier, placing the polymer carrier in a high-pressure reactor, introducing carbon dioxide, heating and pressurizing until the carbon dioxide reaches a supercritical state, and swelling the polymer carrier by using the supercritical carbon dioxide;
② catalyst activation: slowly releasing the pressure after swelling is finished, introducing nitrogen for replacement for 5-10 times, and adding a certain proportion of cocatalyst into the swollen catalyst intermediate for catalyst activation;
thirdly, drying and forming: and (3) adding a hexane solution into the reactor, repeatedly washing for 5-10 times, removing the solvent in the first step and the second step, and drying to obtain the high-activity supported metallocene catalyst.
In order to make the preparation of the supported metallocene catalyst of the present invention more clear to those skilled in the art, the present invention will be further described with reference to the following examples:
example 1
The preparation method of the supported metallocene catalyst for ethylene polymerization comprises the following steps:
the supercritical carbon dioxide assists in loading: adding 4ml of 0.1mol/l (abbreviated as 0.1M, the same below) of zirconocene dichloride toluene solution into 10g of polymer carrier (polystyrene microspheres, produced by Suzhou Zhi micro-nano technology Co., Ltd., particle size of 20 μ M), placing the mixture in a high-pressure reactor, introducing carbon dioxide, raising the swelling permeation temperature to 40 ℃, and pressurizing the swelling pressure to 10.0MPa to ensure that the carbon dioxide reaches a supercritical state, and swelling the polymer carrier by using the supercritical carbon dioxide for 4 hours;
② catalyst activation: slowly releasing the pressure after swelling is finished, cooling to room temperature, introducing nitrogen into the reactor for replacement for 5-10 times, then adding 200ml of 1M methylaluminoxane toluene solution, heating to 60 ℃, and refluxing for 1-4 hours to activate the catalyst;
thirdly, drying and forming: and adding 500ml of hexane solution into the reactor, repeatedly washing for 5-10 times, removing the solvent in the first step and the second step, and drying to obtain the high-activity supported metallocene catalyst.
The prepared catalyst is shown in the picture of an electron microscope in figure 1; the contents of chromium, magnesium and aluminum in the catalyst components and the polymerization evaluation results are shown in Table 1.
Evaluation of slurry polymerization
Heating a 2L reaction kettle to about 80 ℃, vacuumizing for 1h, replacing with dry nitrogen, and then blowing out with hydrogen. 1L of hexane is added into a polymerization kettle, 1ml (1M) of triethyl aluminum, 10ml of hexene-1 and 10mg of the catalyst are added simultaneously, then the temperature is raised to 75 ℃, 0.1MPa of hydrogen is added, ethylene is added after the hydrogenation is finished to ensure that the pressure in the kettle reaches 1.03MPa, the temperature is raised to 80 ℃, the reaction is carried out for 2 hours, the temperature is reduced, the discharging is carried out, and the slurry polymerization result is shown in Table 1.
Example 2
The catalyst component was prepared in the same manner as in example 1, except that zirconocene dichloride was replaced with bis (ethylcyclopentadiene) zirconium dichloride.
Example 3
The catalyst component was prepared in the same manner as in example 1, except that zirconocene dichloride was replaced with bis (n-butylcyclopentadienyl) zirconium dichloride.
Example 4
The catalyst component was prepared in the same manner as in example 1 except that zirconocene dichloride was replaced with bis (1-butyl-3-methylcyclopentadienyl) zirconium dichloride.
Example 5
The catalyst component was prepared in the same manner as in example 1, except that zirconocene dichloride was replaced with bis (pentamethylcyclopentadienyl) zirconium dichloride.
Example 6
The catalyst component was prepared in the same manner as in example 1, except that the swelling permeation temperature in the supercritical carbon dioxide assisted loading was decreased from 40 ℃ to 35 ℃.
Example 7
The catalyst component was prepared in the same manner as in example 1, except that the swelling permeation temperature in the supercritical carbon dioxide assisted loading was decreased from 40 ℃ to 31 ℃.
Example 8
The catalyst component was prepared in the same manner as in example 1, except that the swelling permeation temperature in the case of supporting supercritical carbon dioxide with assistance was increased from 40 ℃ to 50 ℃.
Example 9
The catalyst component was prepared in the same manner as in example 1, except that the swelling permeation temperature at the time of supporting with supercritical carbon dioxide assistance was increased from 40 ℃ to 60 ℃.
Example 10
The catalyst component was prepared in the same manner as in example 1, except that the swelling pressure at the time of assisted loading of supercritical carbon dioxide was reduced from 10.0MPa to 9.0 MPa.
Example 11
The catalyst component was prepared in the same manner as in example 1, except that the swelling pressure at the time of assisted loading of supercritical carbon dioxide was reduced from 10.0MPa to 7.5 MPa.
Example 12
The catalyst component was prepared in the same manner as in example 1 except that the swelling pressure at the time of assisted loading of supercritical carbon dioxide was changed from 10.0MPa to 11.0 MPa.
Example 13
The catalyst component was prepared in the same manner as in example 1 except that the swelling pressure at the time of assisted loading of supercritical carbon dioxide was changed from 10.0MPa to 12.0 MPa.
Example 14
The catalyst component was prepared in the same manner as in example 1, except that the swelling time in the case of supporting supercritical carbon dioxide with assistance was changed from 4.0 hours to 6.0 hours.
Example 15
The catalyst component was prepared in the same manner as in example 1, except that the swelling time in the case of supporting supercritical carbon dioxide with assistance was changed from 4.0 hours to 8.0 hours.
Example 16
The catalyst component was prepared in the same manner as in example 1, except that the swelling time in the case of the supercritical carbon dioxide assisted loading was reduced from 4.0 hours to 2.0 hours.
Example 17
The catalyst component was prepared in the same manner as in example 1 except that the 0.1M solution of zirconocene dichloride in toluene was changed from 4ml to 8 ml.
Example 18
The catalyst component was prepared in the same manner as in example 1 except that the 0.1M solution of zirconocene dichloride in toluene was changed from 4ml to 12 ml.
Example 19
The catalyst component was prepared in the same manner as in example 1 except that the 0.1M solution of zirconocene dichloride in toluene was changed from 4ml to 2 ml.
Example 20
The catalyst component was prepared in the same manner as in example 1 except that the 0.1M solution of zirconocene dichloride in toluene was changed from 4ml to 1 ml.
Example 21
The catalyst component was prepared in the same manner as in example 1 except that the amount of the 1M methylaluminoxane solution in toluene was changed from 200ml to 300 ml.
Example 22
The catalyst component was prepared in the same manner as in example 1 except that the amount of the 1M methylaluminoxane solution in toluene was changed from 200ml to 100 ml.
Example 23
The catalyst component was prepared in the same manner as in example 1 except that the 1M methylaluminoxane solution in toluene was replaced with the 1M triethylaluminum solution in toluene.
Example 24
The catalyst component was prepared in the same manner as in example 1 except that the 1M methylaluminoxane solution in toluene was changed to 1M triisobutylaluminum solution in toluene.
Comparative example 1
The preparation steps of the catalyst are as follows:
carrying metallocene compound: adding 4ml of 0.1mol/l (abbreviated as 0.1M, the same below) zirconocene dichloride toluene solution into 10g of polymer carrier (polystyrene microspheres, produced by Suzhou Zhi micro-nano technology Co., Ltd., particle size of 20 μ M), placing the mixture into a reaction kettle, adding 40ml tetrahydrofuran as a solvent into the reaction kettle, and carrying out immersion loading for 4 hours under the nitrogen protection condition;
② catalyst activation: after loading is finished, evaporating the solvent, cooling to room temperature, introducing nitrogen into the reactor for replacement for 5-10 times after drying is finished, then adding 200ml of 1M methylaluminoxane toluene solution, heating to 60 ℃, refluxing for 1-4 hours, and activating the catalyst;
thirdly, drying and forming: and adding 500ml of hexane solution into the reactor, repeatedly washing for 5-10 times, removing the solvent in the first step and the second step, and drying to obtain the high-activity supported metallocene catalyst. The contents of chromium, magnesium and aluminum in the catalyst components and the polymerization evaluation results are shown in Table 1.
The composition of the catalyst prepared in each example was determined as follows:
the Zr content and the Al content in the catalyst are measured by adopting an ICP method;
the polymerization activity was calculated according to the following formula:
wpoly ═ Q/wcat, gPolyg-1 Cat, where Wpoly is the catalyst polymerization activity, Q is the yield (g) of the polymer in 2 hours of polymerization, and wcat is the catalyst amount.
The test conditions for the polymers are as follows:
melt index MI-ASTM D1238-99.
Table 1 catalyst composition and polymerization evaluation results.
Claims (9)
1. A supported metallocene catalyst for ethylene polymerization comprising: a carrier, a metallocene compound supported on the carrier, and a cocatalyst, characterized in that: the carrier is a polymer microsphere, the cocatalyst is aluminum alkyl, the zirconium load content in the catalyst is 0.1-5 wt%, the aluminum content is 10-36 wt%, and the carrier is 59-89.9 wt%, and the preparation of the catalyst comprises the following steps:
the supercritical carbon dioxide assists in loading: adding an aromatic hydrocarbon solution of a metallocene compound into a polymer carrier, placing the polymer carrier in a high-pressure reactor, introducing carbon dioxide, heating and pressurizing until the carbon dioxide reaches a supercritical state, and swelling the polymer carrier by using the supercritical carbon dioxide; the swelling and penetrating temperature in the swelling process of the supercritical carbon dioxide is 31-60 ℃, the swelling pressure is 7.5-12MPa, and the swelling time is 0.5-10 hours;
② catalyst activation: slowly releasing pressure after swelling is finished, introducing nitrogen for replacement, and then adding a cocatalyst into the swollen catalyst intermediate for catalyst activation;
thirdly, drying and forming: adding the solution into the reactor, repeatedly washing, removing the solvent in the first step and the second step, and drying to obtain the high-activity supported metallocene catalyst.
2. The supported metallocene catalyst for ethylene polymerization according to claim 1, wherein: the polymer microspheres are homopolymer and copolymer microspheres of styrene, divinylbenzene, acrylonitrile or acrylamide monomers.
3. The supported metallocene catalyst for ethylene polymerization according to claim 1, wherein: the metallocene compound has a structure represented by the following formula,
wherein R is1、R2、R3、R4、R5、R1’、R2’、R3’、R4' and R5' each independently is hydrogen or C1-C5 alkyl, M is metallic zirconium, and X is halogen.
4. The supported metallocene catalyst for ethylene polymerization according to claim 1, wherein: the alkyl aluminum is one or a mixture of more than two of trimethyl aluminum, triethyl aluminum, triisopropyl aluminum, triisobutyl aluminum, tri-n-hexyl aluminum and diethyl aluminum chloride.
5. The method of claim 1, wherein the supported metallocene catalyst for ethylene polymerization comprises: the method specifically comprises the following steps:
the supercritical carbon dioxide assists in loading: adding an aromatic hydrocarbon solution of a metallocene compound into a polymer carrier, placing the polymer carrier in a high-pressure reactor, introducing carbon dioxide, heating and pressurizing until the carbon dioxide reaches a supercritical state, and swelling the polymer carrier by using the supercritical carbon dioxide;
② catalyst activation: slowly releasing the pressure after swelling is finished, introducing nitrogen for replacement for 5-10 times, and adding a certain proportion of cocatalyst into the swollen catalyst intermediate for catalyst activation;
thirdly, drying and forming: and (3) adding a hexane solution into the reactor, repeatedly washing for 5-10 times, removing the solvent in the first step and the second step, and drying to obtain the high-activity supported metallocene catalyst.
6. The method of claim 5, wherein the supported metallocene catalyst for ethylene polymerization comprises: the aromatic hydrocarbon solution in the step I is one or a mixture of more than two of benzene, toluene or xylene.
7. The method of claim 5, wherein the supported metallocene catalyst for ethylene polymerization comprises: the cocatalyst is aromatic hydrocarbon solution of aluminum alkyl; the activation reaction is stirring at 10-100 ℃, and refluxing is carried out for 1-4 hours.
8. The method of claim 5, wherein the supported metallocene catalyst for ethylene polymerization comprises: the activation and the drying and forming operation of the step III are carried out under the anhydrous and oxygen-free conditions.
9. The method of claim 5, wherein the supported metallocene catalyst for ethylene polymerization comprises: and the molar ratio of the addition amount of the alkyl aluminum to the addition amount of the metallocene compound is 20-1000.
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