Composite carrier supported polyolefin catalyst, its preparation method and application

Abstract

The present application relates to a kind of composite carrier loaded polyolefin catalyst and its preparation method and application, catalyst is with metal organic framework modified cellulose composite material as carrier, in situ load metallocene compound as catalytically active component;Preparation method includes the following steps: (1) with cellulose powder, metallocene compound, metal salt and organic ligand as raw material, preparation is obtained metallocene@MOFs / cellulose;(2) metallocene@MOFs / cellulose is dispersed in solvent, methylaluminoxane solution is added to carry out reaction, and the composite carrier loaded polyolefin catalyst of the present application is obtained.Compared with prior art, the preparation process of the present application is simple and fast, and the ash content in the polymer powder produced by the polymerization reaction using the catalyst of the present application is reduced by 75% compared with the existing silica gel carrier.

Description

Technical Field

[0001] This invention relates to the field of polyolefin catalyst technology, specifically to a polyolefin catalyst supported on a composite support, its preparation method, and its application. Background Technology

[0002] To meet the requirements of existing olefin polymerization processes and industrial production facilities, industrial metallocene polyolefin catalysts typically require the main catalyst (metallocene compound) and the co-catalyst (alkylaluminoxane) to be supported on a morphologically uniform, structurally stable, and appropriately sized support. Currently, silica gel is the primary support for metallocene polyolefin catalysts, maintaining excellent catalytic activity and controlling the polymer morphology after loading into the metallocene catalytic system. However, silica gel supports are costly to produce and involve complex processes. When used in the loading process, they require high-temperature calcination in an inert gas atmosphere and consume large quantities of expensive alkylaluminoxanes, resulting in high energy and reagent costs. Furthermore, silica gel supports introduce inorganic impurities that cannot be easily removed into the product, causing it to fail to meet the application requirements in fields such as medical and health applications, high-performance fibers, and high-end membrane materials.

[0003] Cellulose, as a natural organic polymer material, has many advantages such as wide availability and low cost. It can be compounded with polyethylene or polypropylene to prepare polyolefin fiber reinforcements for many high-end application fields such as new energy and biomedicine. However, cellulose, which contains many polar groups in its molecules, has poor compatibility with polyolefin resins, and the products prepared by directly mixing them by physical methods have poor performance. Summary of the Invention

[0004] The purpose of this invention is to provide a polyolefin catalyst supported on a composite support, its preparation method and application, which has excellent catalytic activity and does not introduce excessive inorganic impurities into the product.

[0005] The objective of this invention can be achieved through the following technical solution: a polyolefin catalyst supported on a composite support, using a cellulose composite material modified with metal-organic frameworks (MOFs) as the support and in-situ supported metallocene compounds as the catalytically active components.

[0006] Preferably, the polyolefin catalyst supported on the composite support is treated with methylaluminoxane.

[0007] A method for preparing a polyolefin catalyst supported on the above-mentioned composite support includes the following steps:

[0008] (1) Metallocene@MOFs / cellulose were prepared using cellulose powder, metallocene compounds, metal salts and organic ligands as raw materials;

[0009] (2) Disperse metallocene@MOFs / cellulose in a solvent, add methylaluminoxane solution to react, and obtain the polyolefin catalyst supported on the composite support.

[0010] In this invention, a supported metallocene catalyst is prepared by using MOF-modified cellulose composite material as a support and metallocene compounds in situ loaded during the synthesis of the support as active components, followed by a one-step activation treatment.

[0011] Preferably, the cellulose powder in step (1) contains lignin and hemicellulose.

[0012] Preferably, the particle size of the cellulose powder in step (1) is 10-50 μm.

[0013] Preferably, the cellulose powder in step (1) has not been chemically modified beforehand.

[0014] Preferably, the metallocene compound in step (1) is a metallocene complex catalyst with polyolefin catalytic ability.

[0015] More preferably, the metallocene compound in step (1) specifically includes Cp2ZrCl2.

[0016] Preferably, the metal salt in step (1) includes one or more of zirconium n-propoxide, zirconium isopropoxide, zirconium n-butoxide, zirconium acetate, and zirconium chloride.

[0017] Preferably, the organic ligand in step (1) includes one or more of terephthalic acid and biphenyl acid.

[0018] Preferably, in the raw materials described in step (1), the mass ratio of metal salt to organic ligand is (1:1) to (6:1).

[0019] Preferably, in the metallocene@MOFs / cellulose in step (1), the mass ratio of metal salt to cellulose is (1:3) to (2:1), and the mass ratio of metallocene compound to cellulose is (1:6) to (1:1).

[0020] Preferably, step (1) specifically includes the following steps: under gas protection, dry cellulose powder, metallocene compound, metal salt, organic ligand, solvent and grinding beads are added to a centrifuge tube, the reaction is shaken by a vortex mixer, toluene and / or n-hexane are added to wash the solid product, and finally the product is dried under vacuum at 40-60°C to obtain metallocene@MOFs / cellulose.

[0021] More preferably, in step (1), cellulose powder, metal salt and organic ligand are first added to the centrifuge tube, then solvent and grinding beads are added to the centrifuge tube, and then the centrifuge tube is placed on a vortex mixer and shaken for 4 to 6 minutes. Finally, metallocene compound is added and shaken for 22 to 28 minutes.

[0022] More preferably, in step (1), 3 to 5 mL of solvent is added to a 50 mL centrifuge tube.

[0023] More preferably, the oscillation frequency of the vortex mixer in step (1) is 500 to 2500 rpm.

[0024] More preferably, the oscillation reaction temperature in step (1) is room temperature.

[0025] More preferably, step (1) is finally vacuum dried at 50°C for 24 hours to obtain metallocene@MOFs / cellulose.

[0026] More preferably, the solvent in step (1) includes one or more of methanol and N,N-dicarboxymethylformamide (DMF).

[0027] More preferably, the gas in step (1) is nitrogen.

[0028] Preferably, the reaction conditions for the treatment of metallocene@MOFs / cellulose with methylaluminoxane in step (2) are: 0-60°C and stirring time 1-24h.

[0029] More preferably, step (2) specifically includes the following steps: under gas protection, the metallocene@MOFs / cellulose prepared in step (1) is added to toluene, and a methylaluminoxane toluene solution is added under stirring. The reaction is carried out at 0-60°C for 1-12 hours. Finally, the solvent is removed by vacuum distillation of the obtained solution to obtain the polyolefin catalyst supported by the composite support.

[0030] More preferably, the gas in step (2) is nitrogen.

[0031] Preferably, the mass ratio of methylaluminoxane to metallocene@MOFs / cellulose in step (2) is (1:10) to (1:5).

[0032] Application of a polyolefin catalyst supported on the above-mentioned composite support in gas-phase polymerization or slurry polymerization.

[0033] This invention relates to a metallocene catalyst supported on a cellulose composite support modified with a metal-organic framework (MOF). Cellulose, primarily derived from plant-based raw materials, is inexpensive and abundant. When used as a support for polyolefin catalysts, it significantly reduces production costs and does not introduce additional ash into the product. However, its small particle surface area and limited pore structure hinder the loading of active components and control of product morphology. This invention addresses these issues by modifying cellulose with MOFs, which possess ultra-high specific surface area and abundant pore structure, while simultaneously supporting metallocene compounds in situ. Since metal-organic frameworks (MOFs) are crystalline porous materials with a periodic, multidimensional framework structure, formed by the coordination of inorganic units of metal ions or metal clusters with organic ligands, the composite support prepared using MOFs and cellulose exhibits high specific surface area and a rich pore structure. Using this composite support to prepare metallocene polyolefin catalysts results in excellent catalytic activity without introducing excessive inorganic impurities into the product, thus significantly reducing ash content in high-end polyolefin products.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The catalyst of this invention has a simple preparation process, is quick and easy to prepare, has low equipment requirements, and low production cost;

[0036] 2. In this invention, metallocene compounds are in situ loaded onto the composite support and then activated in one step, which can rapidly complete the preparation of metallocene polyolefin catalysts;

[0037] 3. The metal-organic framework modified cellulose composite support for supporting metallocene catalysts of the present invention can be used in both gas-phase polymerization and slurry polymerization processes, thus meeting the needs of different polymerization processes;

[0038] 4. The ash content of the polymer powder produced by polymerization using the catalyst of this invention is reduced by 75% compared with that produced using existing silica gel carriers;

[0039] 5. This invention uses MOFs materials with ultra-high specific surface area to modify cellulose, which can provide more channels for catalytic active centers to be used for immobilization while maintaining the advantages of the original cellulose support. The specific surface area of ​​the prepared catalyst is also significantly improved, which is beneficial to improving the catalytic activity of the catalyst.

[0040] 6. The preparation method of this invention avoids the disadvantages of conventional MOF preparation methods, such as high temperature, large amount of solvent, long time, and inability to support metallocene catalysts in situ. The preparation process of the composite support is simple and quick, does not generate a large amount of solvent, and can support metallocene compounds in situ within the MOF channels without leaching during subsequent processing. It also eliminates the need for high concentrations of metallocene compounds for loading, thereby improving the utilization rate of metallocene compounds and simplifying the preparation process of metallocene catalyst loading. Detailed Implementation

[0041] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0042] A method for preparing a polyolefin catalyst supported on a composite support includes the following steps: First, under nitrogen protection, dry cellulose powder, metallocene compounds, metal salts, organic ligands, a small amount of solvent, and grinding beads are added to a centrifuge tube. After vortexing the reaction, toluene and / or n-hexane are added to wash the solid product, and finally, vacuum drying is performed to obtain metallocene@MOFs / cellulose. Subsequently, under nitrogen protection, the obtained metallocene@MOFs / cellulose is dispersed in toluene, and then a methylaluminoxane solution is added to react. Afterward, vacuum distillation is performed under nitrogen protection to remove residual toluene, thereby obtaining the metallocene polyolefin catalyst supported on the MOFs / cellulose composite support.

[0043] The following detailed description is based on specific embodiments.

[0044] Example 1

[0045] Under nitrogen protection, 0.3 g of dried cellulose with a particle size of 10 μm, 0.3 g of zirconium propoxide, and 0.1 g of terephthalic acid were weighed and added to a 50 mL centrifuge tube. Then, 5 mL of methanol and grinding beads were added to the tube, and the centrifuge tube was placed on a vortex mixer and shaken at 2000 rpm for 5 minutes. Subsequently, 0.05 g of the metallocene compound Cp₂ZrCl₂ was added to the centrifuge tube, and the mixture was shaken for another 25 minutes. The solid was obtained by washing with toluene and n-hexane, respectively, and then dried under vacuum at 50 °C for 24 h to obtain metallocene@UiO-66(Zr) / cellulose-1.

[0046] Under nitrogen protection, 1 g of the metallocene@UiO-66(Zr) / cellulose-1 prepared in step (1) was weighed and added to 10 mL of toluene. Then, 10 g of a 10% (w / w) methylaluminoxane toluene solution was added to the above solution with stirring. The reaction was carried out at 40 °C for 6 hours with stirring. Afterwards, the residual solvent was removed by vacuum distillation under air-free conditions to obtain the metallocene catalyst supported on the UiO-66(Zr) / cellulose composite support. ICP characterization showed that the Al content in the catalyst was 12.87% (w / w).

[0047] After purging the 2L high-pressure reactor with nitrogen, 1L of n-hexane was added. After removing impurities with triethylaluminum, 100mg of the metallocene catalyst prepared in step (2) was added. Ethylene was introduced until the pressure in the reactor reached 1.0MPa, and the reaction was carried out at 80℃ for 1 hour. The catalyst activity and molecular weight distribution are shown in Table 1.

[0048] Example 2

[0049] (1) Following step (1) of Example 1, 0.6 g of zirconium isopropoxide was used instead of zirconium n-propoxide, and the other operation steps were the same, to obtain metallocene@UiO-66(Zr) / cellulose-2.

[0050] (2) Weigh 1 g of the metallocene@UiO-66(Zr) / cellulose-2 prepared in step (1) and add it to 10 mL of toluene. Under stirring, add 10 g of a 10% (w / w) methylaluminoxane toluene solution to the above solution and stir the reaction at 40 °C for 6 hours. Then, remove the residual solvent by vacuum distillation under air-free conditions to obtain the metallocene catalyst supported on the UiO-66(Zr) / cellulose composite support. ICP characterization showed that the Al content in the catalyst was 14.97% (w / w).

[0051] (3) Polymerization evaluation tests were conducted according to the steps in Example 1. Catalyst activity and molecular weight distribution are shown in Table 1.

[0052] Example 3

[0053] (1) Following step (1) of Example 1, 0.6 g of zirconium butoxide was used instead of zirconium propoxide, and the other operation steps were the same, to obtain metallocene@UiO-66(Zr) / cellulose-3.

[0054] (2) Weigh 1 g of the metallocene@UiO-66(Zr) / cellulose-3 prepared in step (1) and add it to 10 mL of toluene. Under stirring, add 10 g of a 10% (w / w) methylaluminoxane toluene solution to the above solution and stir the reaction at 40 °C for 6 hours. Then, remove the residual solvent by vacuum distillation under air-free conditions to obtain the metallocene catalyst supported on the UiO-66(Zr) / cellulose composite support. ICP characterization showed that the Al content in the catalyst was 11.88% (w / w).

[0055] (3) Polymerization evaluation tests were conducted according to the steps in Example 1. Catalyst activity and molecular weight distribution are shown in Table 1.

[0056] Example 4

[0057] (1) Following step (1) of Example 1, 0.1g of zirconium acetate was used to replace zirconium propoxide, the oscillation frequency was changed to 2500rpm, and the other operation steps were the same, to obtain metallocene@UiO-66(Zr) / cellulose-4.

[0058] (2) Weigh 1 g of the metallocene@UiO-66(Zr) / cellulose-4 prepared in step (1) and add it to 10 mL of toluene. Under stirring, add 10 g of a 10% (w / w) methylaluminoxane toluene solution to the above solution and stir the reaction at 60 °C for 1 hour. Then, remove the residual solvent by vacuum distillation under air-free conditions to obtain the metallocene catalyst supported on the UiO-66(Zr) / cellulose composite support. ICP characterization showed that the Al content in the catalyst was 12.18% (w / w).

[0059] (3) Polymerization evaluation tests were conducted according to the steps in Example 1. Catalyst activity and molecular weight distribution are shown in Table 1.

[0060] Example 5

[0061] (1) Following step (1) of Example 1, 0.2g of zirconium chloride was used to replace zirconium propoxide, the oscillation frequency was changed to 1500rpm, and the other operation steps were the same, to obtain metallocene@UiO-66(Zr) / cellulose-5.

[0062] (2) Weigh 1 g of the metallocene@UiO-66(Zr) / cellulose-5 prepared in step (1) and add it to 10 mL of toluene. Under stirring, add 10 g of a 10% (w / w) methylaluminoxane toluene solution to the above solution and stir the reaction at 30 °C for 12 hours. Then, remove the residual solvent by vacuum distillation under air-free conditions to obtain the metallocene catalyst supported on the UiO-66(Zr) / cellulose composite support. ICP characterization showed that the Al content in the catalyst was 10.73% (w / w).

[0063] (3) Polymerization evaluation tests were conducted according to the steps in Example 1. Catalyst activity and molecular weight distribution are shown in Table 1.

[0064] Example 6

[0065] (1) Following step (1) of Example 1, cellulose with a particle size of 30 μm was used instead of cellulose with a particle size of 10 μm, the amount of metallocene compound Cp2ZrCl2 added was changed to 0.1 g, the oscillation frequency was changed to 1500 rpm, and other operation steps were the same, to obtain metallocene@UiO-66(Zr) / cellulose-6.

[0066] (2) Weigh 1 g of the metallocene@UiO-66(Zr) / cellulose-6 prepared in step (1) and add it to 10 mL of toluene. Under stirring, add 50 g of a 10% (w / w) methylaluminoxane toluene solution to the above solution and stir the reaction at 10 °C for 20 hours. Then, remove the residual solvent by vacuum distillation under air-free conditions to obtain the metallocene catalyst supported on the UiO-66(Zr) / cellulose composite support. ICP characterization showed that the Al content in the catalyst was 14.27% (w / w).

[0067] (3) Polymerization evaluation tests were conducted according to the steps in Example 1. Catalyst activity and molecular weight distribution are shown in Table 1.

[0068] Example 7

[0069] (1) Following step (1) of Example 1, cellulose with a particle size of 40 μm was used instead of cellulose with a particle size of 10 μm, the amount of metallocene compound Cp2ZrCl2 added was changed to 0.3 g, the shaking frequency was changed to 1000 rpm, and other operating steps were the same, to obtain metallocene@UiO-66(Zr) / cellulose-7.

[0070] (2) Weigh 1 g of the metallocene@UiO-66(Zr) / cellulose-6 prepared in step (1) and add it to 10 mL of toluene. Under stirring, add 30 g of a 10% (w / w) methylaluminoxane toluene solution to the above solution and stir the reaction at 10 °C for 20 hours. Then, remove the residual solvent by vacuum distillation under air-free conditions to obtain the metallocene catalyst supported on the UiO-66(Zr) / cellulose composite support. ICP characterization showed that the Al content in the catalyst was 12.33% (w / w).

[0071] (3) Polymerization evaluation tests were conducted according to the steps in Example 1. Catalyst activity and molecular weight distribution are shown in Table 1.

[0072] Example 8

[0073] (1) Under nitrogen protection, 0.3 g of dried cellulose with a particle size of 50 μm, 0.2 g of zirconium propoxide, and 0.1 g of biphenyl dicarboxylic acid were weighed and added to a 50 mL centrifuge tube. Then, 3 mL of DMF and grinding beads were added to the tube, and the centrifuge tube was placed on a vortex mixer and shaken at a frequency of 500 rpm for 5 minutes. Subsequently, 0.3 g of the metallocene compound Cp2ZrCl2 was added to the centrifuge tube, and the mixture was shaken for another 25 min. The solid was obtained by washing with toluene and n-hexane, respectively, and then dried under vacuum at 50 °C for 24 h to obtain metallocene@UiO-67(Zr) / cellulose-1.

[0074] (2) Under nitrogen protection, 1 g of the metallocene@UiO-67(Zr) / cellulose-1 prepared in step (1) was weighed and added to 10 mL of toluene. Under stirring, 1 g of a 10% (w / w) methylaluminoxane toluene solution was added to the above solution, and the reaction was carried out at 30 °C for 12 hours. Afterwards, the residual solvent was removed by vacuum distillation under air-free conditions to obtain the metallocene catalyst supported on the UiO-67(Zr) / cellulose composite support. ICP characterization showed that the Al content in the catalyst was 5.10% (w / w).

[0075] (3) Polymerization evaluation tests were conducted according to the steps in Example 1. Catalyst activity and molecular weight distribution are shown in Table 1.

[0076] Example 9

[0077] (4) Following step (1) of Example 8, cellulose with a particle size of 30 μm was used instead of cellulose with a particle size of 50 μm, the amount of zirconium propoxide added was changed to 0.1 g, the amount of metallocene compound Cp2ZrCl2 added was changed to 0.05 g, the oscillation frequency was changed to 800 rpm, and the other operation steps were the same, to obtain metallocene@UiO-66(Zr) / cellulose-7.

[0078] (5) Weigh 1 g of the metallocene@UiO-66(Zr) / cellulose-7 prepared in step (1) and add it to 10 mL of toluene. Under stirring, add 10 g of a 10% (w / w) methylaluminoxane toluene solution to the above solution and stir the reaction at 0 °C for 24 hours. Then, remove the residual solvent by vacuum distillation under air-free conditions to obtain the metallocene catalyst supported on the UiO-66(Zr) / cellulose composite support. ICP characterization showed that the Al content in the catalyst was 9.93% (w / w).

[0079] (6) Polymerization evaluation tests were conducted according to the steps in Example 1. Catalyst activity and molecular weight distribution are shown in Table 1.

[0080] Comparative Example 1

[0081] (1) Under nitrogen protection, 0.3 g of dried cellulose with a particle size of 10 μm, 0.2 g of zinc nitrate, and 0.1 g of terephthalic acid were weighed and added to a 50 mL centrifuge tube. Then, 5 mL of methanol and grinding beads were added to the tube. The centrifuge tube was placed on a vortex mixer and vortexed at a frequency of 2000 rpm for 5 minutes. Subsequently, 0.1 g of Cp2ZrCl2 was added to the centrifuge tube, and the mixture was vortexed for another 25 minutes. The product was washed with toluene and n-hexane, respectively, and then dried under vacuum at 50 °C for 24 h to obtain a white solid A.

[0082] (2) Under nitrogen protection, 1 g of white solid A was weighed and added to 10 mL of toluene. Then, 10 g of a 10% (w / w) methylaluminoxane toluene solution was added to the above solution with stirring. The mixture was stirred and reacted at 50 °C for 4 hours. Afterwards, the mixture was distilled under reduced pressure in the absence of air to obtain the metallocene catalyst XA. ICP characterization showed that the Al content in the catalyst was 6.39% by mass.

[0083] (3) Polymerization evaluation tests were conducted according to the steps in Example 1. Catalyst activity and molecular weight distribution are shown in Table 1.

[0084] Comparative Example 2

[0085] (1) Under nitrogen protection, 0.3 g of dried cellulose with a particle size of 10 μm, 0.3 g of zirconium propoxide and 0.1 g of 2-methylimidazole were weighed and added to a 50 mL centrifuge tube. Then, 5 mL of methanol and grinding beads were added to the tube. The centrifuge tube was placed on a vortex mixer and vortexed at a frequency of 2000 rpm for 5 minutes. Subsequently, 0.1 g of Cp2ZrCl2 was added to the centrifuge tube and the mixture was vortexed for another 25 minutes. The product was washed with toluene and n-hexane, respectively, and dried under vacuum at 50 °C for 24 h to obtain a white solid B.

[0086] (2) Under nitrogen protection, 1 g of white solid B was weighed and added to 10 mL of toluene. Then, 10 g of a 10% (w / w) methylaluminoxane toluene solution was added to the solution with stirring. The mixture was stirred and reacted at 40 °C for 6 hours. Afterwards, the mixture was distilled under reduced pressure in the absence of air to obtain the metallocene catalyst XB. ICP characterization showed that the Al content in the catalyst was 5.39% by mass.

[0087] (3) Polymerization evaluation tests were conducted according to the steps in Example 1. Catalyst activity and molecular weight distribution are shown in Table 1.

[0088] Comparative Example 3

[0089] (1) Under nitrogen protection, 0.3 g of dried cellulose with a particle size of 10 μm, 0.3 g of zirconium propoxide, and 0.1 g of terephthalic acid were weighed and added to a 50 mL centrifuge tube. Then, 5 mL of toluene and grinding beads were added to the tube. The centrifuge tube was placed on a vortex mixer and vortexed at a frequency of 2000 rpm for 5 minutes. Subsequently, 0.1 g of Cp2ZrCl2 was added to the centrifuge tube, and the mixture was vortexed for another 25 minutes. The product was washed with toluene and n-hexane, respectively, and then dried under vacuum at 50 °C for 24 h to obtain a white solid C.

[0090] (2) Under nitrogen protection, 1 g of white solid C was weighed and added to 10 mL of toluene. Then, 10 g of a 10% (w / w) methylaluminoxane toluene solution was added to the solution with stirring. The mixture was stirred and reacted at 40 °C for 6 hours. Afterwards, the mixture was distilled under reduced pressure in the absence of air to obtain the metallocene catalyst XC. ICP characterization showed that the Al content in the catalyst was 5.82% (w / w).

[0091] (3) Polymerization evaluation tests were conducted according to the steps in Example 1. Catalyst activity and molecular weight distribution are shown in Table 1.

[0092] Comparative Example 4

[0093] (1) Under nitrogen protection, 1 g of Grace Davison 955 silica support was weighed and added to 10 mL of toluene. While stirring, 10 g of a 10% (w / w) methylaluminoxane toluene solution was added to the above solution, and the mixture was stirred at 50 °C for 1 hour. Subsequently, 0.1 g of Cp₂ZrCl₂ was added to the above suspension, and the mixture was heated and stirred for another hour. After settling, the mixture was distilled under reduced pressure in the absence of air to obtain the metallocene catalyst XD. ICP characterization showed that the Al content in the catalyst was 8.73% by mass.

[0094] (3) Polymerization evaluation tests were conducted according to the steps in Example 1. Catalyst activity and molecular weight distribution are shown in Table 1.

[0095] Comparative Example 5

[0096] Under nitrogen protection, 0.3 g of dried cellulose with a particle size of 10 μm, 0.3 g of zirconium propoxide, and 0.1 g of terephthalic acid were weighed and added to a 50 mL centrifuge tube. Then, 5 mL of methanol and grinding beads were added to the tube. The centrifuge tube was placed on a vortex mixer and vortexed at 2000 rpm for 5 minutes. The mixture was then vortexed for another 25 minutes, and the solid was obtained by washing with toluene and n-hexane. The solid was then dried under vacuum at 50 °C for 24 h to obtain the UiO-66(Zr) / cellulose composite carrier. 0.05 g of the metallocene compound Cp₂ZrCl₂ was dissolved in 20 mL of toluene. The dried composite carrier was dispersed in the solution and stirred for 30 minutes. The solid was obtained by washing with toluene and n-hexane, and then dried under vacuum at 50 °C for 24 h to obtain a white solid D.

[0097] Under nitrogen protection, 1 g of the white solid D prepared in step (1) was weighed and added to 10 mL of toluene. Then, 10 g of a 10% (w / w) methylaluminoxane toluene solution was added to the above solution with stirring. The mixture was stirred and reacted at 40 °C for 6 hours. Afterwards, the residual solvent was removed by vacuum distillation under air-free conditions to obtain the metallocene catalyst XE. ICP characterization showed that the Al content in the catalyst was 7.29% (w / w).

[0098] After purging the 2L high-pressure reactor with nitrogen, 1L of n-hexane was added. After removing impurities with triethylaluminum, 100mg of the metallocene catalyst prepared in step (2) was added. Ethylene was introduced until the pressure in the reactor reached 1.0MPa, and the reaction was carried out at 80℃ for 1 hour. The catalyst activity and molecular weight distribution are shown in Table 1.

[0099] Table 1 Catalyst activity and polymer molecular weight distribution

[0100] No. <![CDATA[Active g PE / g Cat ·h]]> Ash content ppm Example 1 562 76 Example 2 806 53 Example 3 523 81 Example 4 544 78 Example 5 423 98 Example 6 689 62 Example 7 508 84 Example 8 259 94 Example 9 386 101 Comparative Example 1 136 89 Comparative Example 2 118 98 Comparative Example 3 106 114 Comparative Example 4 396 209 Comparative Example 5 132 128

[0101] As can be seen from the comparison between Comparative Example 1 and Example 1, the metal salt used in the example is zirconium propoxide, while that used in the comparative example is zinc nitrate. These two metal salts have different chemical properties and coordination abilities, which affects the preparation of the MOFs / cellulose composite support, thus significantly affecting the loading of the metallocene catalyst and its activity in the reaction. Consequently, the activity of the metallocene catalyst obtained in Comparative Example 1 is lower than that in Example 1.

[0102] A comparison of Comparative Example 2 and Example 1 shows that the organic ligand used in Example 1 is terephthalic acid, while that used in Comparative Example 2 is 2-methylimidazole. These two organic ligands have completely different chemical properties, coordination abilities, and functional groups involved in coordination. This affects the modification of cellulose particles by MOFs, thereby affecting the structure and properties of the composite support, and also affecting the preparation of the metallocene catalyst. Consequently, the activity of the supported metallocene catalyst obtained in Comparative Example 2 is lower than that in Example 1.

[0103] As can be seen from the comparison between Comparative Example 3 and Example 1, the solvent used in step (1) of Example 1 is methanol, while the solvent used in Comparative Example 2 is toluene. These two mixed solvents have different solubilizing and activating abilities for organic ligands, which will affect the structure and properties of the MOF-modified cellulose composite support, and thus affect the preparation of the supported metallocene catalyst, resulting in the activity of the supported metallocene catalyst obtained in Comparative Example 3 being lower than that in Example 1.

[0104] As can be seen from the comparison between Comparative Example 4 and Example 1, the comparative example used Davison 955 silica instead of MOF-modified cellulose composite support for supporting the metallocene catalyst. After polymerization using the prepared metallocene catalyst, more inorganic impurities were introduced into the product, resulting in a higher ash content in the polymer product of the supported metallocene catalyst obtained in Comparative Example 4 compared to Example 1.

[0105] The comparison between Comparative Example 5 and Example 1 shows that the stepwise loading of metallocene compounds in the comparative example resulted in a significantly reduced activity of the supported metallocene catalyst compared to the in-situ loading method in Example 1, and the ash content in the polymerization product was higher than that in Example 1.

[0106] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A polyolefin catalyst supported on a composite support, characterized in that, A cellulose composite material modified with a metal-organic framework was used as a carrier, and metallocene compounds were loaded in situ as the catalytically active components.

2. A method for preparing a polyolefin catalyst supported on a composite support as described in claim 1, characterized in that, Includes the following steps: (1) Metallocene@MOFs / cellulose were prepared using cellulose powder, metallocene compounds, metal salts and organic ligands as raw materials; (2) Disperse metallocene@MOFs / cellulose in a solvent, add methylaluminoxane solution to react, and obtain the polyolefin catalyst supported on the composite support.

3. The method for preparing the polyolefin catalyst supported on the composite support according to claim 2, characterized in that, The cellulose powder in step (1) contains lignin and hemicellulose; the particle size of the cellulose powder is 10-50 μm.

4. The method for preparing the polyolefin catalyst supported on the composite support according to claim 2, characterized in that, The metallocene compound mentioned in step (1) is a metallocene complex catalyst with polyolefin catalytic ability.

5. The method for preparing the polyolefin catalyst supported on the composite support according to claim 2, characterized in that, The metal salt in step (1) includes one or more of zirconium n-propoxide, zirconium isopropoxide, zirconium n-butoxide, zirconium acetate, and zirconium chloride; The organic ligands in step (1) include one or more of terephthalic acid and biphenyl acid.

6. The method for preparing the polyolefin catalyst supported on the composite support according to claim 2, characterized in that, In the raw materials described in step (1), the mass ratio of metal salt to organic ligand is (1:1) to (6:1); In step (1), the mass ratio of metal salt to cellulose in the metallocene@MOFs / cellulose is (1:3) to (2:1), and the mass ratio of metallocene compound to cellulose is (1:6) to (1:1).

7. The method for preparing the polyolefin catalyst supported on the composite support according to claim 2, characterized in that, Step (1) specifically includes the following steps: Under gas protection, dry cellulose powder, metallocene compound, metal salt, organic ligand, solvent and grinding beads are added to a centrifuge tube. After the reaction is shaken by a vortex mixer, toluene and / or n-hexane are added to wash the solid product. Finally, the product is dried under vacuum at 40-60°C to obtain metallocene@MOFs / cellulose. The solvent in step (1) includes one or more of methanol and N,N-dicarboxylic acid formamide.

8. The method for preparing the polyolefin catalyst supported on the composite support according to claim 2, characterized in that, Step (2) specifically includes the following steps: Under gas protection, the metallocene@MOFs / cellulose prepared in step (1) is added to toluene, and a methylaluminoxane toluene solution is added under stirring. The reaction is carried out at 0-60°C for 1-12 hours. Finally, the solvent is removed by vacuum distillation of the obtained solution to obtain the polyolefin catalyst supported by the composite support.

9. The method for preparing the polyolefin catalyst supported on the composite support according to claim 8, characterized in that, The mass ratio of methylaluminoxane to metallocene@MOFs / cellulose in step (2) is (1:10) to (1:5).

10. The application of a polyolefin catalyst supported on a composite support as described in claim 1 in gas-phase polymerization or slurry polymerization.