Silica-supported metallocene polyethylene catalysts and their preparation and application

Abstract

This invention discloses a silica-supported metallocene polyethylene catalyst, its preparation, and its application. The catalyst mainly consists of a hierarchical porous silica microsphere support, methylaluminoxane, and a zirconium-centered metallocene compound. The hierarchical porous silica microspheres of this invention not only possess microporous, mesoporous, and macroporous structures, but also allow for precise control of the proportions of each pore type. The catalyst obtained after metallocene loading treatment exhibits adjustable particle size and narrow particle size distribution. The process is simple and the preparation conditions are mild, resulting in high catalytic activity and a polymer with excellent particle morphology.

Description

Technical Field

[0001] This invention relates to silica-supported metallocene polyethylene catalysts, their preparation, and applications. Background Technology

[0002] Metallocene catalysts typically refer to catalytic systems composed primarily of metallocene compounds and methylaluminoxane (MAO). Homogeneous metallocene catalysts have several drawbacks: they cannot effectively control the morphology of the polymerization products; they are not suitable for the gas-phase and slurry polymerization processes commonly used in the polyolefin industry; and they require large amounts of expensive MAO as co-catalysts, resulting in high polymer production costs. Therefore, supported metallocene catalysts have emerged. Currently, the silica supports used for supported metallocene polyolefin catalysts typically have a relatively uniform pore size distribution, with most being mesoporous silica and a few being microporous silica. The structurally uniform silica supports limit the mass transfer of monomer molecules within their pores, preventing molecules with chain segments larger than the pore size from efficiently contacting the catalyst center; for molecules with small chain segments, even if the catalytic active center can be effectively utilized, diffusion limitations cause the chain segments to remain within the single pore for too long, increasing the probability of side reactions and thus limiting the practical application of silica supports.

[0003] In recent years, significant progress has been made in the research of hierarchical porous silica materials, with a wide variety of materials being synthesized. Research focuses primarily on morphology / structure control, selection of low-cost template agents, and simplification of synthesis methods. This has led to the preparation of hierarchical porous materials with various pore morphologies, including amino-functionalized cage-like hierarchical hollow silica microspheres, radially porous mesoporous hollow silica spheres, and hexagonal structures with helical channels. The material particle sizes range from 50 nm to 800 nm, specific surface areas from 150 to 700 m² / g, and total pore volumes from 0.5 to 10 cm³ / g. However, precise control of the proportions of each pore level has not yet been achieved. Summary of the Invention

[0004] To further improve the application effect of metallocene polyethylene catalysts, the inventors made this invention. As one aspect of this invention, it relates to a silica-supported metallocene polyethylene catalyst, mainly composed of a hierarchical porous silica microsphere carrier, methylaluminoxane, and a zirconium-centered metallocene compound.

[0005] In one specific embodiment, the catalyst contains 5-30 wt% aluminum and 0.1-2 wt% zirconium. Preferably, in one embodiment, the aluminum content is 10-20 wt% and the zirconium content is 0.3-1.0 wt%.

[0006] In one specific embodiment, the hierarchical porous silica microsphere carrier includes micropores, mesopores, and macropores. In one embodiment, the volume ratios of micropores, mesopores, and macropores to the total pore volume in the hierarchical porous silica microsphere carrier are 13%-25%, 55%-80%, and 10%-18%, respectively. Preferably, the volume ratios of micropores, mesopores, and macropores to the total pore volume in the hierarchical porous silica microsphere carrier are 15%-23%, 58%-76%, and 11%-16%, respectively. More preferably, the volume ratios of micropores, mesopores, and macropores to the total pore volume in the hierarchical porous silica microsphere carrier are 16%-20%, 60%-72%, and 12%-14%, respectively.

[0007] In one specific embodiment, the sum of the volumes of all micropores, mesopores, and macropores in the hierarchical porous silica microsphere carrier is 0.5-4 cm³. 3 / g. Preferably, in one embodiment, the sum of the volumes of all micropores, mesopores, and macropores in the hierarchical porous silica microsphere carrier is 1-2.5 cm³. 3 / g.

[0008] In one specific embodiment, the specific surface area of ​​the hierarchical porous silica microsphere carrier is 100-600 m². 2 Between / g. Preferably, in one embodiment, the specific surface area of ​​the hierarchical porous silica microsphere carrier is 200-400m². 2 / g.

[0009] In one specific embodiment, the average particle size of the hierarchical porous silica microsphere carrier ranges from 5 to 200 μm. Preferably, in one embodiment, the average particle size of the hierarchical porous silica microsphere carrier ranges from 20 to 80 μm.

[0010] In one specific embodiment, the zirconium-centered metallocene compound is the compound shown in formula (1):

[0011] Cp2ZrR m X 2-m (1)

[0013] Wherein, Cp is an indole, fluorenyl, or cyclopentadienyl group with or without substituents; the two Cp groups can be the same or different; the two Cp groups can be bridged or unbridged; R is a C1-C8 alkyl group; X is a halogen; m is 0, 1, or 2.

[0014] As another aspect of the present invention, a method for preparing the silica-supported metallocene polyethylene catalyst according to any one of claims 1-14 is provided, comprising:

[0015] A. Preparation of emulsion system

[0016] (101) An acrylate monomer and a silicon precursor are co-dissolved in an organic hydrocarbon compound to form a homogeneous solution;

[0017] (102) Add a silane coupling agent to the solution of step (101);

[0018] (103) Add a polymerization initiator to the solution obtained in step (102) to obtain a mixed solution as the oil phase;

[0019] (104) Mix the oil phase obtained in step (103) with water in a certain proportion and stir;

[0020] (105) While stirring, add a certain amount of surfactant to the microemulsion obtained in step (104) to form an oil-in-water microemulsion;

[0021] (106) Heat the oil-in-water emulsion prepared in step (105) to 60-90°C and maintain the reaction for 1-10 hours to polymerize the acrylate monomers and obtain polyvinyl ester microspheres loaded with silicon precursors.

[0022] (107) The polyvinyl acetate particles loaded with silicon precursor obtained in step (106) are immersed in a hydrolysate composed of acid, alcohol and water and stirred for 2-20 hours to allow the silicon precursor to undergo a sol-gel process to generate silicon dioxide, thus obtaining polyvinyl acetate / silica hybrid particles.

[0023] (108) The polyvinyl ester / silica hybrid particles obtained in step (107) are calcined at 400-1200℃ for 2-10 hours to completely decompose the polyvinyl ester and obtain a hierarchical porous silica microsphere carrier.

[0024] B. Preparation of spherical catalysts

[0025] (201) Transfer the hierarchical porous silica microspheres to a reactor that has been fully purged with nitrogen, add toluene and methylaluminoxane, stir at 25-80°C for 1-10 hours, wash with hexane after completion, and finally dry the solid with nitrogen to obtain hierarchical porous silica microspheres loaded with methylaluminoxane.

[0026] (202) Under nitrogen protection, multi-level porous silica microspheres loaded with methylaluminoxane were added to the reactor, toluene was added, and the mixture was stirred into a slurry. The metallocene compound was dissolved in a container that had been purged with nitrogen to prepare a solution. The metallocene compound solution was slowly added dropwise to the reaction under stirring at 25-80°C. The reaction was stirred for 0.3-2 hours. After the reaction was completed, the mixture was allowed to stand, the liquid was filtered out, washed with toluene and hexane, and dried with nitrogen to obtain the supported metallocene catalyst.

[0027] In one embodiment, the acrylate monomer is an ester compound formed by acrylic acid or its homologues with a fatty alcohol or aromatic alcohol. In one embodiment, the acrylate monomer is methyl acrylate, methyl 2-methacrylate, ethyl acrylate, or ethyl 2-methacrylate.

[0028] In one specific embodiment, the silicon precursor is a silicate or silicate ester compound that can form silicon dioxide through a hydrolysis / condensation process. In one specific embodiment, the silicon precursor is sodium silicate, potassium silicate, methyl orthosilicate, or ethyl orthosilicate.

[0029] In one specific embodiment, the silane coupling agent is a compound having a Y(CH2)nSiX3 structure, wherein Y is an organic functional group that reacts with the resin, and X is a group that can be hydrolyzed to silanol. In one specific embodiment, Y is vinyl, amino, mercapto, epoxy, or methacryloxy; and X is chloro, methoxy, ethoxy, or acetoxy.

[0030] In one specific embodiment, the polymerization initiator is an ester, alkane, or acyl substance having a peroxide group. In another specific embodiment, the polymerization initiator is benzoyl peroxide, lauroyl peroxide, tert-butyl peroxide, dicumyl peroxide, tert-amyl acetate peroxide, or 1,1-bis(tert-amylperoxy)cyclohexane.

[0031] In one specific embodiment, the surfactant is an anionic surfactant, a cationic surfactant, an amphoteric surfactant, or a nonionic surfactant. In a specific embodiment, the surfactant is a dehydrated sorbitol fatty acid ester, partially hydrolyzed polyvinyl alcohol, polyoxyethylene fatty acid ester, polyoxyethylene ether, polyoxyethylene amine, polyoxyethylene amide, or polypropylene glycol.

[0032] In one specific embodiment, the proportions of each component are as follows: 100 parts by mass of acrylate, 5-200 parts of diluent, 2-100 parts of silicone precursor, 0.5-10 parts of silane coupling agent, and 0.5-10 parts of initiator. In another specific embodiment, 100 parts by mass of acrylate, 60 parts of diluent, 40 parts of silicone precursor, 3 parts of silane coupling agent, and 2 parts of initiator.

[0033] In one specific embodiment, the interaction temperature of each component in steps (101)-(105) is 0℃-50℃, preferably 15℃-35℃.

[0034] In one specific embodiment, the acid contained in the hydrolysate in step (107) is an organic or inorganic acid that does not dissolve silica. In a specific embodiment, it is preferably one or a mixture of hydrochloric acid, nitric acid, sulfuric acid, chloric acid, formic acid, acetic acid, and benzoic acid.

[0035] In one specific embodiment, the alcohol in the acid / alcohol mixture in step (107) includes one or more of methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, 2-methylpentanol, 2-ethylbutanol, heptanol, 2-ethylhexanol, octanol, and decanol.

[0036] In one specific embodiment, the heating rate in step (108) is in the range of 1℃ / min to 5℃ / min, preferably 2℃ / min.

[0037] As another aspect of the present invention, it relates to the use of the above-mentioned silica-supported metallocene polyethylene catalyst in the homopolymerization of ethylene or the copolymerization of ethylene with α-olefin CH2=CHR (wherein R is hydrogen or an alkyl or aryl group with 1 to 6 carbons).

[0038] As another aspect of the invention, it relates to the homopolymerization of ethylene or the copolymerization of ethylene with α-olefin CH2=CHR (wherein R is hydrogen or an alkyl or aryl group with 1 to 6 carbons), using the above-described silica-supported metallocene polyethylene catalyst.

[0039] This invention achieves at least the following beneficial effects:

[0040] The multi-level porous silica microspheres in this invention not only have micropore, mesopore, and macropore structures, but also allow for precise control of the proportion of each level of pore structure. The catalyst obtained after metallocene loading treatment has the characteristics of adjustable particle size and narrow particle size distribution. The process is simple and the preparation conditions are mild, resulting in high catalytic activity and a polymer with good particle morphology. Attached Figure Description

[0041] Appendix Figure 1 : Attached figure for the preparation method of multi-level silica carrier.

[0042] Appendix Figure 2 Example 5: Morphology of the multi-stage silica carrier (see attached figure).

[0043] Appendix Figure 3 : Attached figures for aperture distribution of Example 5 and Comparative Example 1. Detailed Implementation

[0044] The inventors discovered that existing supported metallocene catalysts have at least two problems: First, the catalytic activity of metallocene catalysts decreases significantly once they are supported on a silica support; second, the polymer products obtained from metallocene catalysts have a narrow molecular weight distribution, which increases the difficulty of their processing.

[0045] The inventors believe that among different pore types, micropores (<2 nm) allow the ethylene monomer to be closest to the catalytic active center, resulting in a faster reaction rate in the initial stage. Mesopores (2-50 nm) facilitate substrate diffusion more easily than micropores, and their "confining effect" regulates the monomer insertion mode and chain growth process, thus controlling the molecular weight and distribution of the product to some extent. Macropores (>50 nm) can reduce resistance to substrate diffusion in the later stages of the reaction, which is particularly important for the addition of α-olefin comonomers with larger molecular dynamic radii. Furthermore, if the supported metallocene catalyst is used in liquid-phase bulk polymerization or slurry polymerization, larger pore sizes offer advantages for liquid diffusion. Therefore, the ideal metallocene catalyst support should be silica microspheres with a multi-level pore structure of micropores-mesopores-macropores and good particle morphology.

[0046] For silica supports used in metallocene olefin polymerization, in addition to obtaining a hierarchical porous structure with different pore sizes, it is also necessary to consider issues such as the loading of methylaluminoxane and the anchoring of active metals. Therefore, it is essential to precisely control the optimal ratio of each pore level.

[0047] Based on the above understanding, the inventors made this invention.

[0048] The technical solution adopted is summarized as follows:

[0049] First, a mixed oil phase was prepared using acrylate monomers, a silicon precursor, a silane coupling agent, and a polymer initiator. The acrylate monomers were then polymerized through microemulsion preparation to obtain polyvinyl acetate microspheres supported on the silicon precursor. The obtained polyvinyl acetate particles supported on the silicon precursor were immersed in a hydrolysate composed of acid, alcohol, and water and stirred to obtain polyvinyl acetate / silica hybrid particles. These particles were calcined for 2-10 hours to obtain a hierarchical porous silica microsphere carrier. After stirring and washing with methylaluminoxane, hierarchical porous silica microspheres supported on methylaluminoxane were obtained. Under nitrogen protection, the hierarchical porous silica microspheres supported on methylaluminoxane were added to a reactor, along with toluene, and stirred to form a slurry. A metallocene compound was dissolved in a pre-purged nitrogen container to prepare a solution. Under stirring conditions, the metallocene compound solution was slowly added dropwise to the reaction mixture. The mixture was washed with toluene and hexane, and dried with nitrogen to obtain a supported metallocene catalyst.

[0050] The principle of controlling the generation and proportion of hierarchical pores in this invention is as follows: the hierarchical structure is generated through the dynamic diffusion and self-assembly of the emulsion. This mainly includes two processes: first, the emulsification process of the emulsion, which includes the dynamic release, diffusion, and consumption of surfactants; second, the deposition and solidification process of silica, which mainly includes the hydrolysis and polymerization of silanes and the self-assembly process of surfactants. The generation of hierarchical porous materials involves removing the template agent through high-temperature treatment, leaving spaces that constitute the various levels of pores. Factors affecting emulsification include stirring rate, temperature, and the type and concentration of surfactants; factors affecting silica deposition and solidification include silicon source concentration, temperature, and the proportion of hydrolysate. Hierarchical porous materials can be synthesized and pore size controlled by precisely controlling these two processes.

[0051] Higher polyacrylate synthesis temperatures and higher acid content in the hydrolysate result in a greater ratio of micropores to macropores in the synthesized hierarchical porous structure. The proportion of micropores in the macropore distribution also gradually increases, while the mesopore size slightly decreases and the pore wall thickness increases. This contributes to improving the strength of the silica material. The proportion of the hierarchical porous structure can be controlled by precisely regulating the acrylate polymerization conditions and hydrolysis process.

[0052] Comparative experiment:

[0053] Based on patent document CN110759348A, the inventors prepared a silica material with a hierarchical porous structure. However, this document does not disclose two methods for controlling the pore size ratio, which cannot meet the inventors' requirements for a hierarchical porous silica material for olefin polymerization.

[0054] Based on patent document CN101837981A, the inventors prepared a hierarchical porous mesoporous silica material. The material has a spherical morphology with a diameter of 200-800 nm; it contains two types of mesopores of different sizes: cubic mesopores with a pore size of 2.2-3.3 nm, and secondary nanopores distributed between the spherical mesopores with a pore size of 20-60 nm; the specific surface area is 171-734 m² / g, and the total pore volume is 0.65-1.15 cm³ / g. However, this patent document does not disclose methods for controlling the pore size ratio, which fails to meet the inventors' requirements for a hierarchical porous silica material for olefin polymerization.

[0055] Based on patent document CN103130229A, the inventors prepared hierarchical porous silica nanomaterials. These nanomaterials exhibit a near-spherical morphology with diameters ranging from 50 to 250 nm and a specific surface area of ​​500 to 1000 m² / g. The materials possess two distinct types of pores: mesoporous main channels with a worm-like or near-hexagonal structure and a pore size between 2 and 3 nm, and vesicle-shaped channels located at the center of the material spheres or uniformly dispersed within the spheres, with a pore size between 5 and 50 nm. These two types of pores are interconnected. The maximum pore size is less than 50 nm, classifying them as microporous-mesoporous materials without macropores. However, the patent document does not disclose methods for controlling the pore size ratio, thus failing to meet the inventors' requirements for hierarchical porous silica materials used in olefin polymerization.

[0056] Since the above experiments failed to obtain materials that meet the inventor's requirements for hierarchical porous silica materials for olefin polymerization, the inventor conducted the following experiments.

[0057] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific conditions are not specified in the examples, they are performed under conventional conditions or conditions recommended by the manufacturer. Reagents, instruments, or methods used in the embodiments of the present invention whose source is not specified are all conventional products that can be obtained commercially or from the applicant.

[0058] Table 1 shows the main raw materials and their sources used in the experiment.

[0059]

[0060]

[0061] Evaluation and analysis methods used in the embodiments of this invention:

[0062] (1) Polymerization activity was calculated using the following method:

[0063] The unit of polymerization activity is kgPE / gcat.

[0064] (2) Apparent density was tested in accordance with GB / T1636.

[0065] In this invention, micropores refer to pores with a diameter of <2nm, mesopores refer to pores with a diameter of 2-50nm, and macropores refer to pores with a diameter of >50nm.

[0066] Example 1

[0067] 1. Preparation of silica microsphere carriers:

[0068] 1) Mix 100g of monomer ethyl acrylate (EA), 300g of diluent benzene, 100g of precursor methyl orthosilicate (TMOS), 8g of coupling agent chloropropyl-terminated polydiethylsiloxane, and 1g of initiator dicumyl peroxide. Mix them evenly with mechanical stirring at 500rpm to form the oil phase.

[0069] 2) Add the oil phase to 1000 mL of deionized water and stir to form suspended microemulsion droplets. Add 10.5 g of polyvinyl alcohol as a surfactant.

[0070] 3) React at 70°C for 60 minutes to obtain polymethyl methacrylate (PMMA) polymer particles containing TEOS.

[0071] 4) Immerse PMMA particles containing TEOS in a hydrochloric acid / isopropanol mixed solution with a hydrogen chloride:water:isopropanol mass ratio of 3:7:90, so that TEOS can form silica through a sol-gel reaction.

[0072] 5) Hexane was removed by vacuum drying, and the mixture was calcined in a muffle furnace at 400℃ for 2 hours to obtain a hierarchical porous silica microsphere carrier. The average particle size of the microspheres was 94.3 μm, and the specific surface area was 78.6 m². 2 / g, pore volume 0.48m 3 / g, of which the proportions of micropores, mesopores and macropores are shown in Table 1.

[0073] 2. Metallocene catalyst support

[0074] 1) Transfer 1 gram of hierarchical porous silica microspheres to a reactor that has been fully purged with nitrogen, add 6 ml of toluene, and stir to form a suspension. Add a 10% (w / w) methylaluminoxane (MAO) toluene solution to the suspension, stir at 65°C for 4 hours, wash with hexane afterward, and finally dry the solid with nitrogen to obtain MAO-loaded hierarchical porous silica microspheres.

[0075] 2) Under nitrogen protection, 1 gram of MAO-supported hierarchical porous silica microspheres were added to the reactor, along with 10 mL of toluene, and stirred to form a slurry. In a container pre-purged with nitrogen, 40 mg of bis-n-butylcyclopentadienylzirconium dichloride (n-BuCp)₂ZrCl₂ was dissolved in 10 mL of toluene to prepare a solution. Under stirring at 65°C, the metallocene compound solution was slowly added dropwise to the reactor, and the reaction was stirred for 1 hour. After the reaction was complete, the mixture was allowed to stand, the liquid was filtered off, washed with toluene and hexane, and dried with nitrogen to obtain the supported metallocene catalyst. The catalyst contained 10.1 wt% aluminum and 0.32 wt% zirconium.

[0076] 3. Ethylene homopolymerization:

[0077] After the stainless steel reactor with a volume of 5 liters was fully purged with nitrogen, 40 mg of the above-mentioned supported metallocene catalyst and 12.0 mmol of triisobutylaluminum were added, along with 2.5 L of n-hexane as solvent. The temperature was raised to 80 °C, and polymerization was carried out at 80 °C for 2 hours. The polymerization results are shown in Table 2, and the sieving results of the polymerization products are shown in Table 3.

[0078] Example 2

[0079] 1. Preparation of silica microsphere carriers:

[0080] 1) Mix 150g of monomer methyl acrylate (MA), 120g of diluent heptane, 60g of precursor tetraethyl orthosilicate (TEOS), 15g of coupling agent vinyl-terminated polymethylphenylsiloxane, and 9g of initiator benzoyl peroxide. Mix them evenly with mechanical stirring at 500rpm to form the oil phase.

[0081] 2) Add the oil phase to 600 mL of deionized water and stir to form suspended microemulsion droplets. Add 10.5 g of polyvinyl alcohol as a surfactant.

[0082] 3) Polymethyl methacrylate (PMMA) polymer particles containing TEOS can be obtained by reacting at 70°C for 60 minutes.

[0083] 4) Immerse PMMA particles containing TEOS in a hydrochloric acid / isopropanol mixed solution with a hydrogen chloride:water:isopropanol mass ratio of 3:7:90, so that TEOS can form silica through a sol-gel reaction.

[0084] 5) Hexane was removed by vacuum drying, and the mixture was calcined in a muffle furnace at 400℃ for 2 hours to obtain silica microspheres with a hierarchical porous structure. The average particle size of the microspheres was 195.3 μm, and the specific surface area was 366.9 m². 2 / g, pore volume 2.13m³ 3 / g, of which the proportions of micropores, mesopores and macropores are shown in Table 1.

[0085] 2. Metallocene catalyst support

[0086] 1) Transfer 1 gram of hierarchical porous silica microspheres to a reactor that has been fully purged with nitrogen, add 6 ml of toluene, and stir to form a suspension. Add a 10% (w / w) methylaluminoxane (MAO) toluene solution to the suspension, stir at 65°C for 4 hours, wash with hexane afterward, and finally dry the solid with nitrogen to obtain MAO-loaded hierarchical porous silica microspheres.

[0087] 2) Under nitrogen protection, 1 gram of MAO-supported hierarchical porous silica microspheres were added to the reactor, along with 10 mL of toluene, and stirred to form a slurry. In a container pre-purged with nitrogen, 60 mg of bis-n-butylcyclopentadienylzirconium dichloride (n-BuCp)₂ZrCl₂ was dissolved in 10 mL of toluene to prepare a solution. Under stirring at 65 °C, the metallocene compound solution was slowly added dropwise to the reactor, and the reaction was stirred for 1 hour. After the reaction was complete, the mixture was allowed to stand, the liquid was filtered off, washed with toluene and hexane, and dried with nitrogen to obtain the supported metallocene catalyst. The catalyst contained 12.5 wt% aluminum and 0.84 wt% zirconium.

[0088] 3. Ethylene homopolymerization:

[0089] Same as Example 1, the polymerization results are shown in Table 2, and the sieving results of the polyethylene product are shown in Table 3.

[0090] Example 3

[0091] 1. Preparation of silica microsphere carriers:

[0092] 1) Mix 300g of monomer methyl methacrylate (MMA), 90g of diluent hexane, 120g of precursor tetraethyl orthosilicate (TEOS), 10g of coupling agent amino-terminated polydimethylsiloxane, and 20g of initiator lauroyl peroxide. Mix them evenly with mechanical stirring at 500rpm to form the oil phase.

[0093] 2) Add the oil phase to 1200 mL of deionized water and stir to form suspended microemulsion droplets. Add 10.5 g of polyvinyl alcohol as a surfactant.

[0094] 3) Polymethyl methacrylate (PMMA) polymer particles containing TEOS can be obtained by reacting at 70°C for 60 minutes.

[0095] 4) Immerse PMMA particles containing TEOS in a hydrochloric acid / isopropanol mixed solution with a hydrogen chloride:water:isopropanol mass ratio of 3:7:90, so that TEOS can form silica through a sol-gel reaction.

[0096] 5) Hexane was removed by vacuum drying, and the mixture was calcined in a muffle furnace at 400℃ for 2 hours to obtain silica microspheres with a hierarchical porous structure. The average particle size of the microspheres was 45.7 μm, and the specific surface area was 607.5 m². 2 / g, pore volume 4.07m³ 3 / g, of which the proportions of micropores, mesopores and macropores are shown in Table 1.

[0097] 2. Metallocene catalyst support

[0098] 1) Transfer 1 gram of hierarchical porous silica microspheres to a reactor that has been fully purged with nitrogen, add 6 ml of toluene, and stir to form a suspension. Add a 10% (w / w) methylaluminoxane (MAO) toluene solution to the suspension, stir at 65°C for 4 hours, wash with hexane afterward, and finally dry the solid with nitrogen to obtain MAO-loaded hierarchical porous silica microspheres.

[0099] 2) Under nitrogen protection, 1 gram of hierarchical porous silica microspheres supported on MAO were added to the reactor, along with 10 mL of toluene, and stirred to form a slurry. In a container pre-purged with nitrogen, 80 mg of bis(1,3-butylmethylcyclopentadienyl)zirconium dichloride (1,3-BuMeCp)₂ZrCl₂ was dissolved in 10 mL of toluene to prepare a solution. Under stirring at 65 °C, the metallocene compound solution was slowly added dropwise to the reactor, and the reaction was stirred for 1 hour. After the reaction was complete, the mixture was allowed to stand, the liquid was filtered off, washed with toluene and hexane, and dried with nitrogen to obtain the supported metallocene catalyst. The catalyst contained 9.4 wt% aluminum and 1.93 wt% zirconium.

[0100] 3. Ethylene homopolymerization:

[0101] Same as Example 1, the polymerization results are shown in Table 2, and the sieving results of the polyethylene product are shown in Table 3.

[0102] Example 4

[0103] 1. Preparation of silica microsphere carriers:

[0104] 1) Mix 150g of monomer methyl methacrylate (MMA), 60g of diluent hexane, 90g of precursor tetraethyl orthosilicate (TEOS), 3g of coupling agent methacryloxy-terminated polydimethylsiloxane, and 4.5g of initiator lauroyl peroxide. Mix them evenly with mechanical stirring at 500rpm to form the oil phase.

[0105] 2) Add the oil phase to 700 mL of deionized water and stir to form suspended microemulsion droplets. Add 10.5 g of polyvinyl alcohol as a surfactant.

[0106] 3) Polymethyl methacrylate (PMMA) polymer particles containing TEOS can be obtained by reacting at 70°C for 60 minutes.

[0107] 4) PMMA particles containing TEOS were immersed in a hydrochloric acid / isopropanol mixed solution with a hydrogen chloride:water:isopropanol mass ratio of 3:7:90, allowing TEOS to form silica through a sol-gel reaction. Hexane was removed by vacuum drying to obtain the silica / PMMA template agent.

[0108] 5) The silica / PMMA template agent was calcined in a muffle furnace at 400℃ for 2 hours to obtain a silica microsphere carrier with a hierarchical porous structure. The average particle size of the microspheres was 23.6 μm, and the specific surface area was 264.7 m². 2 / g, pore volume 1.86m³ 3 / g, of which the proportions of micropores, mesopores and macropores are shown in Table 1.

[0109] 2. Metallocene catalyst support

[0110] 1) Transfer 1 gram of hierarchical porous silica microspheres to a reactor that has been fully purged with nitrogen, add 6 mL of toluene, and stir to form a suspension. Add 6 mL of a 10% (w / w) methylaluminoxane (MAO) toluene solution to the suspension, stir at 65 °C for 4 hours, and then wash with hexane. Finally, dry the solid with nitrogen to obtain MAO-loaded hierarchical porous silica microspheres.

[0111] 2) Under nitrogen protection, 1 gram of MAO-supported hierarchical porous silica microspheres were added to the reactor, along with 10 mL of toluene, and stirred to form a slurry. In a container pre-purged with nitrogen, 80 mg of bis-n-butylcyclopentadienylzirconium dichloride (n-BuCp)₂ZrCl₂ was dissolved in 10 mL of toluene to prepare a solution. Under stirring at 65 °C, the metallocene compound solution was slowly added dropwise to the reactor, and the reaction was stirred for 1 hour. After the reaction was complete, the mixture was allowed to stand, the liquid was filtered off, washed with toluene and hexane, and dried with nitrogen to obtain the supported metallocene catalyst. The catalyst contained 16.3 wt% aluminum and 0.76 wt% zirconium.

[0112] 3. Ethylene homopolymerization:

[0113] Same as Example 1, the polymerization results are shown in Table 2, and the sieving results of the polyethylene product are shown in Table 3.

[0114] Example 5

[0115] 1. Preparation of silica microsphere carriers: Except for increasing the water / oil phase volume ratio of the prepared oil-in-water emulsion to 19:1, the process was the same as in Example 4. The average particle size of the microspheres was 5.2 μm, and the specific surface area was 210.9 m². 2 / g, pore volume 1.36m³ 3 / g, of which the proportions of micropores, mesopores and macropores are shown in Table 1.

[0116] 2. Catalyst synthesis: Except for the addition of 10 mg of metallocene compound, the process was the same as in Example 1. The catalyst contained 11.5 wt% aluminum and 0.13 wt% zirconium.

[0117] 3. Polymerization: Same as in Example 1. The polymerization results are shown in Table 2, and the sieving results of the polyethylene product are shown in Table 3.

[0118] Example 6

[0119] 1. Preparation of silica microsphere carriers: Except for the omission of polyvinyl alcohol during the emulsification stage and the maintenance of the oil-in-water emulsion at 90°C for 2 hours, the process was the same as in Example 4. The average particle size of the microspheres was 137.5 μm, and the specific surface area was 275.1 m². 2 / g, pore volume 0.87m 3 / g, of which the proportions of micropores, mesopores and macropores are shown in Table 1.

[0120] 2. Catalyst synthesis: Same as in Example 1. The aluminum and zirconium contents in the catalyst are shown in Table 2.

[0121] 3. Polymerization: Same as in Example 1. The polymerization results are shown in Table 2, and the sieving results of the polyethylene product are shown in Table 3.

[0122] Example 7

[0123] 1. Preparation of silica microsphere carrier: Except that the polymer microspheres containing TEOS were immersed in the hydrolysate to form an acetic acid / ethanol solution, the process was the same as in Example 4. The average particle size, specific surface area, pore volume, and the proportion of micropores, mesopores, and macropores in the microspheres are shown in Table 1.

[0124] 2. Catalyst synthesis: Same as in Example 1. The aluminum and zirconium contents in the catalyst are shown in Table 2.

[0125] 3. Polymerization: Same as in Example 1. The polymerization results are shown in Table 2, and the sieving results of the polyethylene product are shown in Table 3.

[0126] Example 8

[0127] 1. Preparation of silica microsphere carrier: Except for changing the calcination conditions of silica / PMMA template agent in the muffle furnace to 1000℃ and 1.5 hours, the process was the same as in Example 4. The average particle size, specific surface area, pore volume, and the proportion of micropores, mesopores, and macropores in the microspheres are shown in Table 1.

[0128] 2. Catalyst synthesis: Same as in Example 1. The aluminum and zirconium contents in the catalyst are shown in Table 2.

[0129] 3. Polymerization: Same as in Example 1. The polymerization results are shown in Table 2, and the sieving results of the polyethylene product are shown in Table 3.

[0130] Example 9

[0131] 1. Preparation of silica microsphere carrier: Same as in Example 4. The average particle size, specific surface area, pore volume, and the proportion of micropores, mesopores, and macropores in the microspheres are shown in Table 1.

[0132] 2. Catalyst synthesis: Except for the addition of 12 mL of 10% MAO toluene solution, the process was the same as in Example 1. The aluminum and zirconium contents in the catalyst are shown in Table 2.

[0133] 3. Polymerization: Same as in Example 1. The polymerization results are shown in Table 2, and the sieving results of the polyethylene product are shown in Table 3.

[0134] Example 10

[0135] 1. Preparation of silica microsphere carrier: Same as in Example 4. The average particle size, specific surface area, pore volume, and the proportion of micropores, mesopores, and macropores in the microspheres are shown in Table 1.

[0136] 2. Catalyst Synthesis: Except that the metallocene compound used was difluorenylzirconium dichloride, the process was the same as in Example 1. The aluminum and zirconium contents in the catalyst are shown in Table 2.

[0137] 3. Polymerization: Same as in Example 1. The polymerization results are shown in Table 2, and the sieving results of the polyethylene product are shown in Table 3.

[0138] Example 11

[0139] 1. Preparation of silica microsphere carrier: Same as in Example 4. The average particle size, specific surface area, pore volume, and the proportion of micropores, mesopores, and macropores in the microspheres are shown in Table 1.

[0140] 2. Catalyst synthesis: Except for the addition of a metallocene compound, vinyl-bridged bis(indene)ethyl zirconium dichloride, the process was the same as in Example 1. The aluminum and zirconium contents in the catalyst are shown in Table 2.

[0141] 3. Polymerization: Same as in Example 1. The polymerization results are shown in Table 2, and the sieving results of the polyethylene product are shown in Table 3.

[0142] Example 12

[0143] 1. Preparation of silica microsphere carrier: Same as in Example 4. The average particle size, specific surface area, pore volume, and the proportion of micropores, mesopores, and macropores in the microspheres are shown in Table 1.

[0144] 2. Catalyst synthesis: Same as in Example 1. The aluminum and zirconium contents in the catalyst are shown in Table 2.

[0145] 3. Ethylene / 1-hexene copolymerization:

[0146] After the stainless steel reactor with a volume of 5 liters was fully purged with N2, 40 mg of the above-mentioned supported metallocene catalyst, 12.0 mmol of triisobutylaluminum, and 50 mL of 1-hexene were added. 2.5 L of n-hexane was added as solvent, and the temperature was raised to 80 °C. Polymerization was carried out at 80 °C for 2 hours. The polymerization results are shown in Table 2, and the sieve analysis results of the polymerization products are shown in Table 3.

[0147] Example 13

[0148] 1. Carrier preparation:

[0149] 90 g of the precursor tetraethyl orthosilicate (TEOS) was added to 700 mL of deionized water, followed by the addition of a hydrochloric acid / isopropanol mixed solution. This allowed the TEOS to form silica via a sol-gel reaction. After vacuum drying, the silica was calcined in a muffle furnace at 400 °C for 2 hours to obtain silica microspheres prepared by the sol-gel method. The average particle size, specific surface area, pore volume, and the proportions of micropores, mesopores, and macropores in the microspheres are shown in Table 1.

[0150] 2. Catalyst synthesis: Same as in Example 1. The aluminum and zirconium contents in the catalyst are shown in Table 2.

[0151] 3. Polymerization: Same as in Example 1. The polymerization results are shown in Table 2, and the sieving results of the polyethylene product are shown in Table 3.

[0152] Example 14

[0153] 1. Carrier preparation: Grace 955 silica microspheres were used as the carrier. The average particle size, specific surface area, pore volume, and the proportion of micropores, mesopores, and macropores in the microspheres are shown in Table 1.

[0154] 2. Catalyst synthesis: Same as in Example 1. The aluminum and zirconium contents in the catalyst are shown in Table 2.

[0155] 3. Polymerization: Same as in Example 1. The polymerization results are shown in Table 2, and the sieving results of the polyethylene product are shown in Table 3.

[0156] Example 15

[0157] 1. Carrier preparation: SBA-15 molecular sieve microspheres were prepared as carriers according to the method described in the literature "Xie Huanling et al., Preparation and characterization of SBA-15 microspheres, Journal of Chongqing Institute of Technology (Natural Science Edition), 2008, 22(11): 57-61". The average particle size, specific surface area, pore volume and the proportion of micropores, mesopores and macropores in the microspheres are shown in Table 1.

[0158] 2. Catalyst synthesis: Same as in Example 1. The aluminum and zirconium contents in the catalyst are shown in Table 2.

[0159] 3. Polymerization: Same as in Example 1. The polymerization results are shown in Table 2, and the sieving results of the polyethylene product are shown in Table 3.

[0160] Example 16

[0161] 1. Carrier preparation: ZSM-5 molecular sieve microspheres were prepared as carriers according to the method in patent 201210073742.8. The average particle size, specific surface area, pore volume, and the proportion of micropores, mesopores, and macropores in the microspheres are shown in Table 1.

[0162] 2. Catalyst synthesis: Same as in Example 1. The aluminum and zirconium contents in the catalyst are shown in Table 2.

[0163] 3. Polymerization: Same as in Example 1. The polymerization results are shown in Table 2, and the sieving results of the polyethylene product are shown in Table 3.

[0164] Table 1. Structural parameters of microsphere carriers

[0165]

[0166] Table 2. Aggregation Results

[0167]

[0168] Table 3. Sieving results of polymer powder

[0169]

[0170] As can be seen from the above embodiments, the metallocene catalyst obtained using the hierarchical porous silica prepared by this invention as a support exhibits high polymerization yield and activity, as well as high apparent density and narrow molecular weight distribution of the polymer powder. This is because the hierarchical porous silica contains a certain proportion of micropores, mesopores, and macropores, and the proportion of macropores is reasonably controlled, allowing molecules with chain segment sizes larger than the pore size to efficiently contact the catalyst center, thus significantly improving the activity of the olefin polymerization catalyst (see Examples 1 and 13); adjusting the micropore ratio shortens the residence time of small molecules inside the micropore channels, reducing the probability of side reactions, while suppressing the formation of fine powder with a particle size greater than 120 mesh, resulting in high apparent density and low fine powder content of the polymerization product, and superior product particle morphology (see Examples 5 and 14). The catalyst provided by this invention is particularly suitable for the homopolymerization of ethylene or the copolymerization reaction of ethylene with α-olefin CH2=CHR (where R is hydrogen or an alkyl or aryl group with 1 to 6 carbons).

[0171] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing a silica-supported metallocene polyethylene catalyst, characterized in that, include: A. Preparation of emulsion system (101) Dissolve 100 parts of acrylate monomers and 2-100 parts of silicon precursor in 5-200 parts of organic hydrocarbon diluent to form a homogeneous solution; (102) Add 0.5-10 parts of silane coupling agent to the solution in step (101); the silane coupling agent is chloropropyl-terminated polydiethylsiloxane, vinyl-terminated polymethylphenylsiloxane, amino-terminated polydimethylsiloxane or methacryloxy-terminated polydimethylsiloxane. (103) Add 0.5-10 parts of polymerization initiator to the solution obtained in step (102) to obtain a mixed solution as the oil phase; (104) Mix the oil phase obtained in step (103) with water in a certain proportion and stir; (105) While stirring, add a certain amount of surfactant to the microemulsion obtained in step (104) to form an oil-in-water microemulsion; (106) Heat the oil-in-water emulsion prepared in step (105) to 60-90°C and maintain the reaction for 1-10 hours to polymerize the acrylate monomers and obtain polyacrylate microspheres loaded with silicon precursors. (107) The polyacrylate particles loaded with silicon precursor obtained in step (106) are immersed in a hydrolysate composed of acid, alcohol and water and stirred for 2-20 hours to allow the silicon precursor to undergo a sol-gel process to generate silicon dioxide, thus obtaining polyacrylate / silicon dioxide hybrid particles. (108) The polyacrylate / silica hybrid particles obtained in step (107) are calcined at 400-1200℃ for 2-10 hours to completely decompose the polyacrylate and obtain a hierarchical porous silica microsphere carrier. B. Preparation of spherical catalysts (201) Transfer the hierarchical porous silica microspheres to a reactor that has been fully purged with nitrogen, add toluene and methylaluminoxane, stir at 25-80℃ for 1-10 hours, wash with hexane after completion, and finally dry the solid with nitrogen to obtain hierarchical porous silica microspheres loaded with methylaluminoxane. (202) Under nitrogen protection, multi-level porous silica microspheres loaded with methylaluminoxane were added to the reactor, toluene was added, and the mixture was stirred into a slurry; A zirconium-centered metallocene compound was dissolved in a container purged with nitrogen to prepare a solution. The metallocene compound solution was slowly added dropwise to the reactor under stirring at 25-80°C. The reaction was stirred for 0.3-2 hours. After the reaction was completed, the mixture was allowed to stand, the liquid was filtered out, washed with toluene and hexane, and dried with nitrogen to obtain a silica-supported metallocene polyethylene catalyst.

2. The method according to claim 1, characterized in that, The acrylate monomers are ester compounds formed by acrylic acid or its homologues with fatty alcohols or aromatic alcohols.

3. The method according to claim 1, characterized in that, The acrylate monomers are methyl acrylate, methyl 2-methacrylate, ethyl acrylate, or ethyl 2-methacrylate.

4. The method according to claim 1, characterized in that, The silicon precursor is a silicate and silicate compound that can form silicon dioxide through hydrolysis / condensation processes.

5. The method according to claim 4, characterized in that, The silicon precursors mentioned are sodium silicate, potassium silicate, methyl orthosilicate, and ethyl orthosilicate.

6. The method according to claim 1, characterized in that, The polymerization initiator is an ester, alkane, or acyl substance with a peroxy group.

7. The method according to claim 6, characterized in that, The polymerization initiator is benzoyl peroxide, lauroyl peroxide, tert-butyl peroxide, dicumyl peroxide, tert-amyl peroxide acetate, or 1,1-bis(tert-amylperoxy)cyclohexane.

8. The method according to claim 1, characterized in that, The surfactant is anionic surfactant, cationic surfactant, amphoteric surfactant, or nonionic surfactant.

9. The method according to claim 8, characterized in that, The surfactant is sorbitol fatty acid ester, partially hydrolyzed polyvinyl alcohol, polyoxyethylene fatty acid ester, polyoxyethylene ether, polyoxyethylene amine, polyoxyethylene amide, or polypropylene glycol.

10. The method according to claim 1, characterized in that, The proportions of each component are as follows: 100 parts by mass of acrylate monomers, 60 parts by mass of organic hydrocarbon diluent, 40 parts by mass of silicon precursor, 3 parts by mass of silane coupling agent, and 2 parts by mass of polymerization initiator.

11. The method according to claim 1, characterized in that, The interaction temperature of each component in steps (101)-(105) is 0℃-50℃.

12. The method of claim 11, characterized in that, The interaction temperature of each component in steps (101)-(105) is 15℃-35℃.

13. The method according to claim 1, characterized in that, The acid contained in the hydrolysate in step (107) is an organic acid or inorganic acid that does not dissolve silica.

14. The method of claim 13, characterized in that, The hydrolysate composed of acid, alcohol and water in step (107) contains one or a mixture of hydrochloric acid, nitric acid, sulfuric acid, chloric acid, formic acid, acetic acid, and benzoic acid.

15. The method according to claim 1, characterized in that, The alcohol in the hydrolysate composed of acid, alcohol and water in step (107) includes one or a mixture of two or more of methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, 2-methylpentanol, 2-ethylbutanol, heptanol, 2-ethylhexanol, octanol and decanol.

16. The application of the silica-supported metallocene polyethylene catalyst prepared by the method according to any one of claims 1-15 in the homopolymerization reaction of ethylene.

17. The homopolymerization of ethylene, characterized in that, The silica-supported metallocene polyethylene catalyst is prepared using the method described in any one of claims 1-15.

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