A supported metallocene catalyst suitable for the production of polyethylene and a process for its preparation and use

Abstract

This invention relates to a supported metallocene catalyst suitable for polyethylene production, its preparation method, and its applications. The supported metallocene catalyst is prepared by loading a metallocene active component onto a modified silica composite support obtained through stepwise modification of silica gel with alkylaluminum and benzoic acid-boron compounds. The metallocene active component includes one or more of bridged metallocenes, non-bridged metallocenes, and mono-metallocenes. Compared with existing technologies, this invention optimizes the silica gel modification process and performs composite modification with the reaction products of benzoic acid and boron compounds to form a high-performance composite support. The resulting catalyst exhibits higher catalytic activity and more uniform dispersion of active centers. The resulting polyolefin product has regular particles, high bulk density, and superior mechanical properties, and can be widely used in the homopolymerization of ethylene and the copolymerization of ethylene with α-olefins to prepare polyolefins, especially suitable for the industrial production of medium- and high-density polyethylene.

Description

Technical Field

[0001] This invention relates to the field of polyolefin catalyst technology, and in particular to a supported metallocene catalyst suitable for the production of polyethylene, its preparation method, and its application. Background Technology

[0002] Metallocene catalysts, due to their single active center, produce polyolefin products with regular molecular chains and uniform distribution of comonomers. They possess unparalleled advantages in terms of mechanical strength and optical properties compared to traditional Ziegler-Natta catalysts, making them the core catalysts for the production of high-end polyolefins.

[0003] Supported loading is a key prerequisite for the industrial application of metallocene catalysts. Traditional loading methods mainly fall into two categories: one is to co-load methylaluminoxane (MAO) and metallocene onto inorganic supports such as silica gel and MgCl2; the other is to solidify MAO into methylaluminoxane particles (sMAO) to achieve self-loading of metallocene. However, existing loading technologies still have many shortcomings: when MAO and metallocene are directly co-loaded onto silica gel, the bonding force between MAO and the silica gel surface is weak, making desorption easy. This results in poor dispersion of the active sites of metallocene, low catalyst activity, and the product is prone to sticking to the reactor. Although sMAO alone self-loads metallocene with high catalytic activity, the mechanical stability of sMAO particles is poor, making them easy to break during polymerization. This leads to a high content of fine powder and a low bulk density in the product, which is not conducive to industrial collection and transportation.

[0004] Silica gel is a commonly used support for polyolefin catalysts, with advantages such as controllable particle size, large specific surface area, and good mechanical stability. However, this type of support still has problems such as poor MAO curing effect, insufficient electronic environment regulation, and difficulty in further improving catalytic efficiency and product performance. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a supported metallocene catalyst suitable for the production of polyethylene, its preparation method and application, specifically relating to a method for preparing a benzoic acid-boron compound composite modified silica gel supported metallocene catalyst, and the application of this catalyst in ethylene homopolymerization and ethylene-α-olefin copolymerization.

[0006] The objective of this invention can be achieved through the following technical solutions: One of the technical solutions of the present invention is to provide a supported metallocene catalyst suitable for the production of polyethylene. Specifically, it provides a metallocene catalyst with higher catalytic activity, more uniform dispersion of active centers, and excellent mechanical stability. The catalyst uses silica-supported modified methylaluminoxane modified with benzoic acid-boron compound composite products as a composite support, which can effectively solve the technical problems of insufficient MAO bonding strength, poor dispersion of active centers, and low product bulk density of traditional single modified supported metallocene catalysts.

[0007] Furthermore, the supported metallocene catalyst comprises a silica-supported modified methylaluminoxane composite support and a metallocene active component supported on the silica-supported modified methylaluminoxane composite support.

[0008] Furthermore, the silica-supported modified methylaluminoxane composite carrier is prepared by reacting silica gel sequentially with alkylaluminum and benzoic acid-boron compound composite products.

[0009] Furthermore, the preparation method of the silica-supported modified methylaluminoxane composite carrier specifically includes the following steps: (1) Add silica gel to an organic solvent and disperse it by ultrasonication to obtain a silica gel suspension; (2) Under the protection of an inert gas, alkyl aluminum is added dropwise to the silica gel suspension obtained in step (1) and reacted to obtain an alkyl aluminum modified silica gel system; (3) Add the benzoic acid-boron compound composite product to the alkyl aluminum modified silica gel system obtained in step (2) and react in steps with controlled temperature to generate and solidify the modified methyl aluminum oxane in situ on the silica gel surface to obtain the silica gel-supported modified methyl aluminum oxane system. (4) The silica-supported modified methylaluminoxane system obtained in step (3) is filtered, washed and dried to obtain a silica-supported modified methylaluminoxane composite carrier.

[0010] Furthermore, the benzoic acid-boron compound complex product is prepared by reacting benzoic acid and boron compounds.

[0011] Furthermore, the boron compound is selected from one or more of boric acid, borane, and borate esters.

[0012] More preferably, the boron compound is boric acid.

[0013] Furthermore, the molar ratio of benzoic acid to boron compounds is (0.01~100):1.

[0014] Furthermore, the molar ratio of the benzoic acid-boron compound composite product to silica gel is (0.01~50):1.

[0015] Furthermore, the silica gel is dehydrated and activated silica gel with an average particle size of 10-100 micrometers and a specific surface area of ​​200-800 m². 2 / g, pore volume 0.5~2.0cm 3 / g.

[0016] Furthermore, the dehydration and activation treatment of the silica gel is carried out under the protection of inert gases such as nitrogen or argon, with gradient fluidized drying at 100~600℃ and constant temperature at 100℃ for 2~4 hours, which can effectively remove physical water and molecular water on the surface of the silica gel and improve the bonding force between the silica gel and alkyl aluminum.

[0017] Furthermore, the alkylaluminum is selected from one or more of trimethylaluminum, triethylaluminum, and triisobutylaluminum.

[0018] More preferably, the alkylaluminum is trimethylaluminum.

[0019] Furthermore, the molar ratio of the alkyl aluminum to the silica gel is (0.01~50):1.

[0020] Furthermore, the molar ratio of the benzoic acid-boron compound composite product to alkyl aluminum is (0.01~10):1.

[0021] Further, the metallocene active component is a metallocene compound with the general formula CpxMAy, where x≥1; M is a transition metal of group IVB, VB or VIB; Cp represents an unsubstituted or substituted cyclopentadienyl ligand, indene ligand, fluorenyl ligand, benzo[a]indene ligand, dibenzo[a]fluorenyl ligand or benzo[a]fluorenyl ligand; A is one or more of amines, ethers, carboxylic acids, dienes, phosphines, halogens, hydrogen atoms, and alkyl groups; (x+y) equals the valence of M.

[0022] More preferably, x=2.

[0023] More preferably, M is Ti, Zr, or Ha.

[0024] Furthermore, the metallocene active component includes one or more of bridged metallocene compounds, non-bridged metallocene compounds, and monometallocene compounds.

[0025] Furthermore, the metallocene active component includes one or more of bridged metallocene compounds, non-bridged metallocene compounds, and monometallocene compounds.

[0026] Furthermore, the bridging metallocene compound is selected from one or more of rac-ethylenebis(1-indenyl)zirconia, rac-dimethylsilylbis(2-methylindenyl)zirconia, and isopropylidenecyclopentadienylfluorenylzirconia.

[0027] Furthermore, the non-bridged metallocene compound is selected from one or more of zirconium dichloride, titanium dichloride, bis(n-butylcyclopentadienyl)zirconia, and bis(pentamethylcyclopentadienyl)zirconia.

[0028] Furthermore, the monoclonal metallocene compound is selected from one or more of cyclopentadienyl zirconium trichloride, cyclopentadienyl titanium trichloride, and pentamethylcyclopentadienyltriethoxyzirconium.

[0029] Furthermore, the loading of the metallocene active component is 0.01~5.0 wt% of the mass of the silica-supported modified methylaluminoxane composite support, preferably 0.05~3.0 wt%. This loading ensures that the active centers are fully dispersed, avoids the aggregation of active centers due to excessive loading, and at the same time ensures the high catalytic efficiency of the catalyst.

[0030] The second technical solution of the present invention provides a method for preparing a supported metallocene catalyst suitable for the production of polyethylene. This method has simple steps and mild reaction conditions. It draws on the preparation idea of ​​methylaluminoxane and achieves in-situ generation and composite modification of modified methylaluminoxane on the surface of silica gel through an innovative stepwise composite modification process, thereby achieving efficient loading of metallocene and making it suitable for industrial scale-up production.

[0031] Furthermore, the preparation method includes the following steps: (1) Add silica gel (dehydrated and activated silica gel) to an organic solvent and disperse it by ultrasonication to obtain a silica gel suspension; (2) Under the protection of an inert gas, alkyl aluminum is added dropwise to the silica gel suspension obtained in step (1), and the reaction is carried out at a set temperature to obtain an alkyl aluminum modified silica gel system; (3) Add the benzoic acid-boron compound composite product to the alkyl aluminum modified silica gel system obtained in step (2) and react in steps with controlled temperature to generate and solidify the modified methyl aluminum oxane in situ on the silica gel surface to obtain the silica gel-supported modified methyl aluminum oxane system. (4) The silica-supported modified methylaluminoxane system obtained in step (3) is filtered, washed and dried to obtain a silica-supported modified methylaluminoxane composite carrier. (5) Disperse the silica-supported modified methylaluminoxane composite carrier obtained in step (4) in an organic solvent, add the metallocene active component, stir and impregnate at a set temperature, so that the metallocene active component is loaded on the silica-supported modified methylaluminoxane composite carrier, and obtain the product to be treated. (6) The product to be treated obtained in step (5) is filtered, washed with solvent to remove excess metallocene active components, and dried to obtain metallocene catalyst product.

[0032] Furthermore, the preparation of the benzoic acid-boron compound complex product includes the following process: Benzoic acid and boron compounds were reacted in an organic solvent to prepare a benzoic acid-boron compound composite product.

[0033] Furthermore, the reaction temperature of benzoic acid with boron compounds in organic solvents is -20 to 60°C, and the reaction time is 0.5 to 3 hours.

[0034] Furthermore, the reaction of benzoic acid with boron compounds in an organic solvent is a stirred reaction at a stirring speed of 100-200 rpm. After the reaction is completed, the alkylaluminum modified silica gel system is directly added without separation. The organic solvent is selected from one or more of toluene, xylene, n-hexane, kerosene, and dichlorobenzene, with toluene being preferred.

[0035] Further, in step (1), the organic solvent is selected from one or more of toluene, xylene, n-hexane, kerosene, and dichlorobenzene, with toluene being preferred.

[0036] Furthermore, in step (2), the reaction temperature is -50~100℃, the reaction time is 1~4h, and stirring is carried out during the reaction at a speed of 100~300rpm.

[0037] Further, in step (3), the stepwise temperature-controlled reaction is as follows: first, the reaction is carried out at -15~-20℃ for 0.5~2h, then the temperature is raised to 60~80℃ for 24~32h, and finally the temperature is raised to 90~110℃ for 8~16h.

[0038] Further, in step (3), after the stepwise temperature-controlled reaction is completed, n-hexane is added to the reaction system to precipitate, the volume ratio of n-hexane to the reaction system is (3~6):1, and the temperature at which n-hexane is added is 20~50℃.

[0039] Furthermore, in step (4), the washing solvent is n-hexane, the drying treatment is vacuum drying, the drying temperature is 40~80℃, and the drying time is 4~8h.

[0040] Furthermore, in step (5), the impregnation reaction temperature is -50~100℃, the reaction time is 2~8h, and the stirring speed is 150~400rpm.

[0041] Furthermore, in step (5), the organic solvent is selected from one or more of toluene, xylene, n-hexane, kerosene, and dichlorobenzene, with toluene being preferred.

[0042] Further, in step (6), the solvent is n-hexane, the drying process is vacuum drying, the drying temperature is 40~80℃, and the drying time is 4~12h.

[0043] The third technical solution of this invention provides an application of a supported metallocene catalyst suitable for the production of polyethylene, which is used in the polymerization of olefins to produce polyolefins. This catalyst can be used for the homopolymerization of ethylene and the copolymerization of ethylene with α-olefins, exhibiting high catalytic efficiency, uniform particle size and high bulk density of the polymerization product, no significant sticking to the reactor, and excellent mechanical properties.

[0044] Furthermore, the olefin polymerization is ethylene homopolymerization, or copolymerization of ethylene with C3~C10 α-olefins.

[0045] Furthermore, the α-olefin is selected from one or more of propylene, 1-butene, 1-hexene, and 1-octene, preferably 1-hexene.

[0046] Optionally, when the olefin polymerization is ethylene homopolymerization, the process of producing polyolefin by olefin polymerization includes: adding solvent, ethylene, supported metallocene catalyst and co-catalyst to a reactor to carry out a polymerization reaction to obtain polyolefin product.

[0047] Optionally, when the olefin polymerization is a copolymerization of ethylene and C3~C10 α-olefin, the process of olefin polymerization to produce polyolefin includes: adding solvent, ethylene, α-olefin, supported metallocene catalyst and co-catalyst to a reactor to carry out a polymerization reaction to obtain polyolefin product.

[0048] Furthermore, the molar ratio of the α-olefin to ethylene is (0.01~0.5):1.

[0049] Furthermore, the amount of supported metallocene catalyst added is such that the concentration of supported metallocene catalyst in the entire polymerization system is 0.01~50 ppm.

[0050] Furthermore, the amount of co-catalyst added is such that the concentration of co-catalyst in the entire polymerization system is 5~300ppm; Furthermore, the co-catalyst is selected from one or more of triethylaluminum, triisobutylaluminum, and diethylaluminum chloride, with triethylaluminum being preferred.

[0051] Furthermore, the polymerization reaction adopts a slurry reactor, slurry loop, or solution polymerization process, preferably slurry reactor polymerization or slurry loop polymerization.

[0052] Furthermore, the reaction pressure of the slurry reactor polymerization is 0.1~5MPa, and the reaction temperature is 40~100℃, preferably 60~90℃.

[0053] Furthermore, the reaction pressure for slurry loop polymerization is 0.5~6MPa, and the reaction temperature is 50~100℃, preferably 60~90℃.

[0054] Furthermore, the polymerization reaction time is 1-4 hours. After the reaction is completed, the reaction is terminated with an acidic ethanol solution, and the product is obtained by drying.

[0055] Furthermore, the obtained polyolefin product is a polyethylene or ethylene-α-olefin copolymer with a bulk density of 0.30~0.48 g / cm³. 3 The catalyst has a polymerization efficiency of ≥10000gPE / g·h, produces no obvious fine powder, and has excellent mechanical properties, which are superior to the polymerization product performance of existing single modified silica-supported metallocene catalysts.

[0056] The technical concept of this invention includes: A silica-based composite modification process was designed, first reacting silica with alkyl aluminum, then modifying it with the composite reaction product of benzoic acid and boron compounds. The curing synergistic effect of benzoic acid promotes strong bonding and in-situ curing of modified methylaluminoxane on the silica surface, while the coordination electron regulation effect of boron compounds optimizes the electronic environment of the silica surface. This achieves a dual improvement in MAO curing strength and active center dispersion, forming a high-performance silica-supported modified MAO composite carrier. This composite carrier retains the mechanical stability of silica, preventing carrier breakage during polymerization, while achieving strong bonding between MAO and silica and high dispersion of metallocene active centers through composite modification, significantly improving the catalytic activity, stability, and performance of the polymerization product.

[0057] Compared with the prior art, the present invention has the following beneficial effects: 1) This invention provides a supported metallocene catalyst suitable for the production of polyethylene, its preparation method and application. The supported metallocene catalyst uses silica-modified MAO modified with benzoic acid-boron compound composite products as a composite support, taking into account the mechanical stability of silica, the high-efficiency loading characteristics of modified MAO, and the synergistic modification effect of benzoic acid and boron compounds. The catalyst has high catalytic activity, uniformly dispersed active centers, and a polymerization efficiency ≥10000gPE / g·h, which is much higher than that of traditional silica co-supported metallocene catalysts, and is also superior to existing supported metallocene catalysts modified with single benzoic acid or boron compounds.

[0058] 2) This invention provides a supported metallocene catalyst suitable for the production of polyethylene, its preparation method and application. The preparation method draws on the preparation idea of ​​methylaluminoxane, optimizes the silica gel modification process, and achieves in-situ generation and composite modification of modified MAO on the silica gel surface through the stepwise reaction of alkylaluminum-benzoic acid-boron compound composite products, avoiding MAO desorption and MAO agglomeration. Moreover, the composite products are directly added to the reaction system after one-step preparation, simplifying the process steps. The reaction conditions are mild and suitable for industrial scale-up production.

[0059] 3) This invention provides a supported metallocene catalyst suitable for polyethylene production, its preparation method, and its application. When used in olefin polymerization, the catalyst exhibits no significant sticking to the reactor, and the resulting polyolefin product has uniform particles and a high bulk density (0.30~0.48 g / cm³). 3 It has a low content of fine powder, which makes it easy to collect and transport industrially. The product has regular molecular chains, uniform distribution of comonomers, and excellent mechanical properties. Detailed Implementation

[0060] The present invention will now be described in detail with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Component models, material names, connection structures, control methods, and other features not explicitly stated in this technical solution are considered to be common technical features disclosed in the prior art.

[0061] This invention relates to a composite modified silica-supported metallocene catalyst suitable for the production of polyolefins, its preparation method, and its applications. The catalyst is prepared by loading a metallocene active component onto a modified silica composite support obtained through stepwise modification of silica with alkylaluminum and benzoic acid-boron compounds. The metallocene active component includes one or more of bridged metallocenes, non-bridged metallocenes, and mono-metallocenes. This invention optimizes the silica modification process by performing composite modification with the reaction products of benzoic acid and boron compounds to form a high-performance composite support. The resulting catalyst exhibits higher catalytic activity and more uniform dispersion of active centers. The resulting polyolefin products have regular particle size, high bulk density, and superior mechanical properties. It can be widely used in the homopolymerization of ethylene and the copolymerization of ethylene with α-olefins to prepare polyolefins, and is particularly suitable for the industrial production of medium- and high-density polyethylene.

[0062] Unless otherwise specified, the reagents used in the following examples and comparative examples are commercially available products, and the methods used are those known in the art.

[0063] The performance indicators of each polymer in the following examples and comparative examples were determined using the following methods: 1. Polymerization efficiency: Measured by the mass of polyethylene produced per unit mass of catalyst per hour, expressed in gPE / g·h; 2. Product particle size D50: Measured using a laser particle size analyzer, unit is micrometer; 3. Bulk density: Measured according to ASTM-D1895 standard, unit is g / cm³. 3 ; 4. Melt flow index: Measured according to ASTM D1238 standard (2.16 kg load, 190 °C), unit is g / 10 min.

[0064] Example 1 This embodiment provides a method for preparing and applying a supported metallocene catalyst (specifically, a metallocene catalyst with bridged metallocene as the active component) suitable for polyethylene production, comprising the following steps: 1. Dehydration and activation of silica gel: Take silica gel with an average particle size of 35 micrometers and a specific surface area of ​​400 m². 2 / g of silica gel was subjected to gradient fluidized drying at 100~600℃ under nitrogen protection, with a constant temperature of 100℃ for 3h per 100℃, and then sealed with nitrogen after cooling to room temperature to obtain dehydrated activated silica gel. 2. Alkyl aluminum modification: Take 10g of dehydrated activated silica gel, add it to 100mL of toluene solvent and sonicate for 20min to obtain silica gel suspension; under nitrogen protection, add trimethylaluminum (molar ratio of trimethylaluminum to dehydrated activated silica gel 2:1) at a dropping rate of 1mL / min, and stir at 200rpm at 30℃ for 2h to obtain trimethylaluminum modified silica gel system. 3. Preparation and composite modification of benzoic acid-boric acid composite products: Benzoic acid and boric acid were added to 50 mL of toluene solvent at a molar ratio of 1:1 and stirred at 150 rpm for 1 h at 40 °C to obtain benzoic acid-boric acid composite products. The benzoic acid-boric acid composite product system was directly added to the above alkyl aluminum modified silica gel system and reacted at 25 °C for 1 h, then heated to 70 °C for 28 h, and then heated to 100 °C for 12 h. The molar ratio of benzoic acid-boron compound composite products to alkyl aluminum was 5:1. After cooling to 30 °C, 400 mL of n-hexane was added, and precipitation was obtained to obtain silica gel supported modified sMAO system. 4. Preparation of composite support: The above silica-supported modified sMAO system was filtered, washed four times with n-hexane, and dried under vacuum at 60°C for 6 hours to obtain silica-supported modified sMAO composite support. 5. Metallocene support: Take 5g of silica gel-supported modified sMAO composite support, add it to 50mL of toluene for dispersion, add rac-ethylene bis(1-indenyl)zirconium dichloride (loading 1.0wt%), stir and impregnate at 250rpm at 50℃ for 4h, filter, wash 4 times with n-hexane, and vacuum dry at 60℃ for 8h to obtain metallocene catalyst Cat-1. 6. Ethylene polymerization: In a 2L steel pressure-resistant water-circulating temperature-controlled reactor, a slurry reactor polymerization process was adopted. The reactor was purged with vacuum and nitrogen at 95℃ for 3 hours. Then, 1L of n-hexane, 50mg Cat-1, and 2mL of triethylaluminum (co-catalyst concentration 200ppm) were added. After ethylene purging 4 times, 1.0MPa of ethylene was added, and the polymerization was carried out at 70℃ for 2 hours. The reaction was terminated with acidic ethanol, and the product was dried to obtain polyethylene.

[0065] Test results: The polymerization efficiency of this catalyst is 11280 gPE / g·h, and the bulk density is 0.36 g / cm³. 3 The melt flow index is 1.32 g / 10 min.

[0066] Example 2 This embodiment provides a method for preparing and applying a supported metallocene catalyst (specifically, a metallocene catalyst with a non-bridged metallocene as the active component) suitable for the production of polyethylene, including the following steps: 1. Dehydration and activation of silica gel, and modification with alkyl aluminum: Same as in Example 1; 2. Preparation and composite modification of benzoic acid-boric acid composite products: The molar ratio of benzoic acid to boric acid is 1.2:1, and the remaining steps are the same as in Example 1; 3. Preparation of the composite carrier: Same as in Example 1; 4. Metallocene support: Take 5g of composite support, add it to 50mL of toluene for dispersion, add bis(pentamethylcyclopentadienyl)zirconium dichloride (loading 1.5wt%), stir and impregnate at 300rpm at 60℃ for 3h, filter, wash 4 times with n-hexane, and vacuum dry at 60℃ for 8h to obtain metallocene catalyst Cat-2. 5. Ethylene-1-hexene copolymerization: In a 2L steel pressure-resistant water-circulating temperature-controlled reactor, vacuum-nitrogen purging was carried out at 95℃ for 3 hours. Then, 1L of n-hexane, 50mg of Cat-2, and 2mL of triisobutylaluminum (co-catalyst concentration 150ppm) were added. After purging 4 times with a mixed gas of ethylene and 1-hexene (molar ratio 10:1), a mixed gas of 1.2MPa was added, and polymerization was carried out at 80℃ for 2 hours. The reaction was terminated with acidic ethanol, and the product was dried to obtain the ethylene-1-hexene copolymer.

[0067] Test results: The polymerization efficiency of this catalyst is 10860 gPE / g·h, and the bulk density is 0.33 g / cm³. 3 The melt flow index is 1.05 g / 10 min.

[0068] Example 3 This embodiment provides a method for preparing and applying a supported metallocene catalyst (specifically, a metallocene catalyst with a single metallocene as the active component) suitable for the production of polyethylene, including the following steps: 1. Dehydration and activation of silica gel, and modification with alkyl aluminum: Same as in Example 1; 2. Preparation and composite modification of benzoic acid-boric acid composite products: The molar ratio of benzoic acid to boric acid is 0.8:1, and the remaining steps are the same as in Example 1; 3. Preparation of the composite carrier: Same as in Example 1; 4. Metallocene support: Take 5g of composite support, add it to 50mL of toluene for dispersion, add cyclopentadienyl zirconium trichloride (loading amount 0.8wt%), stir and impregnate at 200rpm at 40℃ for 6h, filter, wash 4 times with n-hexane, and vacuum dry at 60℃ for 8h to obtain metallocene catalyst Cat-3. 5. Ethylene polymerization: The polymerization conditions are the same as in Example 1, and polyethylene product is obtained.

[0069] Test results: The polymerization efficiency of this catalyst is 10520 gPE / g·h, and the bulk density is 0.34 g / cm³. 3 The melt flow index is 1.38 g / 10 min.

[0070] Example 4 This embodiment provides a method for preparing and applying a supported metallocene catalyst (specifically, a composite modified metallocene catalyst of different boron compounds) suitable for the production of polyethylene, including the following steps: 1. Dehydration and activation of silica gel, and modification with alkyl aluminum: Same as in Example 1; 2. Preparation and composite modification of benzoic acid-trimethyl borate composite product: Benzoic acid and trimethyl borate were combined in a molar ratio of 1:1, and the remaining steps were the same as in Example 1; 3. Preparation of composite support and catalyst: Same as in Example 1, metallocene catalyst Cat-4 was obtained; 4. Ethylene polymerization: The polymerization conditions are the same as in Example 1.

[0071] Test results: The polymerization efficiency of this catalyst is 10680 gPE / g·h, and the bulk density is 0.32 g / cm³. 3 The melt flow index is 1.23 g / 10 min.

[0072] Comparative Example 1 This comparative example provides a method for preparing and applying a supported metallocene catalyst (specifically a conventional silica gel co-supported metallocene catalyst) suitable for polyethylene production, including the following steps: 1. Take 10g of the dehydrated activated silica gel from Example 1 and add it to 100mL of toluene and ultrasonically disperse for 20min; 2. Add methylaluminoxane (MAO to dehydrated activated silica gel mass ratio 1:1), stir and react at 30℃ for 2h, then add rac-ethylenebis(1-indenyl)zirconium dichloride (loading 1.0wt%), stir and impregnate at 50℃ for 4h; 3. After filtration and washing with n-hexane four times, the product was dried under vacuum at 60°C for 8 hours to obtain the conventional silica gel co-supported metallocene catalyst Cat-D1. 4. The polymerization conditions are the same as in Example 1.

[0073] Test results: The polymerization efficiency of this catalyst is 3250 gPE / g·h, the D50 of the polyethylene product is 40 micrometers, and the bulk density is 0.28 g / cm³. 3 There was a slight sticking phenomenon in the vessel.

[0074] Comparative Example 2 This comparative example provides a method for preparing and applying a supported metallocene catalyst (specifically, a single boric acid-modified silica gel supported metallocene catalyst) suitable for the production of polyethylene, including the following steps: 1. Dehydration and activation of silica gel, and modification with alkyl aluminum: Same as in Example 1; 2. Boric acid modification: Boric acid (molar ratio of trimethylaluminum 1:1) was added directly, and the remaining modification, support and catalyst preparation steps were the same as in Example 1 to obtain catalyst Cat-D2; 3. The polymerization conditions are the same as in Example 1.

[0075] Test results: The polymerization efficiency of this catalyst is 7560 gPE / g·h, and the bulk density is 0.29 g / cm³. 3 There was no sticking to the vessel.

[0076] Comparative Example 3 This comparative example provides a method for preparing and applying a supported metallocene catalyst (specifically, a single benzoic acid-modified silica gel supported metallocene catalyst) suitable for the production of polyethylene, including the following steps: 1. Dehydration and activation of silica gel, and modification with alkyl aluminum: Same as in Example 1; 2. Benzoic acid modification: Benzoic acid (molar ratio of trimethylaluminum 1:1) was added directly, and the remaining modification, support and catalyst preparation steps were the same as in Example 1 to obtain catalyst Cat-D3; 3. The polymerization conditions are the same as in Example 1.

[0077] Test results: The polymerization efficiency of this catalyst is 8820 gPE / g·h, and the bulk density is 0.31 g / cm³. 3 There was no sticking to the vessel.

[0078] Comparative Example 4 This comparative example provides a method for preparing and applying a supported metallocene catalyst (specifically a high-load metallocene catalyst) suitable for polyethylene production, including the following steps: 1. Dehydration and activation of silica gel, and modification with alkyl aluminum: Same as in Example 1; 2. Preparation and composite modification of benzoic acid-boric acid composite products: The molar ratio of benzoic acid to boric acid is 0.8:1, and the remaining steps are the same as in Example 1; 3. Preparation of the composite carrier: Same as in Example 1; 4. Metallocene support: The loading of rac-ethylene bis(1-indenyl)zirconia dichloride was 6.0 wt%, yielding the metallocene catalyst Cat-D4; 5. Ethylene polymerization: The polymerization conditions are the same as in Example 1, and polyethylene product is obtained.

[0079] Test results: The polymerization efficiency of this catalyst is 7562 gPE / g·h, and the bulk density is 0.28 g / cm³.3 There was a slight sticking phenomenon.

[0080] Comparative Example 5 This comparative example provides a method for preparing and applying a supported metallocene catalyst (specifically, a single alkylaluminum modified silica gel supported metallocene catalyst) suitable for the production of polyethylene, including the following steps: 1. Dehydration and activation of silica gel, and modification with alkyl aluminum: Same as in Example 1, to obtain catalyst Cat-D5; 2. Ethylene polymerization: The polymerization conditions are the same as in Example 1, and polyethylene product is obtained.

[0081] Test results: The polymerization efficiency of this catalyst is 6890 gPE / g·h, and the bulk density is 0.29 g / cm³. 3 There is a sticking phenomenon in the vessel.

[0082] Comparative Example 6 This comparative example provides a method for preparing and applying a supported metallocene catalyst (specifically, a benzoic acid and boric acid modified silica gel supported metallocene catalyst) suitable for the production of polyethylene, including the following steps: 1. Dehydration and activation of silica gel, and modification with alkyl aluminum: Same as in Example 1; 2. Preparation and composite modification of benzoic acid-boric acid composite products: Benzoic acid and boric acid do not react, but are directly added to the alkylaluminum modified silica gel system. The remaining steps and conditions are the same as in Example 1. 3. Preparation of the composite carrier: Same as in Example 1; 4. Metallocene support: Same as in Example 1, to obtain the metallocene catalyst Cat-D6; 5. Ethylene polymerization: The polymerization conditions are the same as in Example 1, and polyethylene product is obtained.

[0083] Test results: The polymerization efficiency of this catalyst is 7120 gPE / g·h, and the bulk density is 0.28 g / cm³. 3 There was no sticking to the vessel.

[0084] Table 1 shows a performance comparison between the examples and the comparative examples.

[0085] Table 1. Performance Comparison of Examples and Comparative Examples As can be seen from Example 1 and Comparative Example 1 in Table 1, the polymerization efficiency of Cat-1 in Example 1 is much higher than that of Cat-D1 in Comparative Example 1, and the bulk density of Cat-1 in Example 1 is also significantly greater than that of Cat-D1 in Comparative Example 1. In addition, Cat-D1 in Comparative Example 1 also exhibits sticking phenomenon. This indicates that alkyl aluminum modification can optimize key performance indicators such as polymerization efficiency and product bulk density.

[0086] As can be seen from Example 1 and Comparative Example 2 in Table 1, the polymerization efficiency of Cat-1 in Example 1 is much higher than that of Cat-D2 in Comparative Example 2, and the bulk density of Cat-1 in Example 1 is also significantly greater than that of Cat-D2 in Comparative Example 2. Compared with single boric acid modification, the benzoic acid-boron compound composite product can optimize key performance indicators such as polymerization efficiency and product bulk density.

[0087] As can be seen from Example 1 and Comparative Example 3 in Table 1, the polymerization efficiency of Cat-1 in Example 1 is much higher than that of Cat-D3 in Comparative Example 3, and the bulk density of Cat-1 in Example 1 is also significantly greater than that of Cat-D3 in Comparative Example 3. Compared with the modification of benzoic acid alone, the benzoic acid-boron compound composite product can optimize key performance indicators such as polymerization efficiency and product bulk density.

[0088] As can be seen from Example 1 and Comparative Example 4 in Table 1, the polymerization efficiency of Cat-1 in Example 1 is much higher than that of Cat-D4 in Comparative Example 4, and the bulk density of Cat-1 in Example 1 is also significantly greater than that of Cat-D4 in Comparative Example 4. This indicates that excessive loading will lead to the aggregation of active centers, which in turn leads to a decrease in polymerization efficiency and bulk density.

[0089] As can be seen from Example 1 and Comparative Example 5 in Table 1, the polymerization efficiency of Cat-1 in Example 1 is much higher than that of Cat-D5 in Comparative Example 5, and the bulk density of Cat-1 in Example 1 is also significantly greater than that of Cat-D5 in Comparative Example 5. The addition of benzoic acid-boron compound composite products can optimize key performance indicators such as polymerization efficiency and product bulk density.

[0090] As can be seen from Example 1 and Comparative Example 6 in Table 1, the polymerization efficiency of Cat-1 in Example 1 is much higher than that of Cat-D6 in Comparative Example 6, and the bulk density of Cat-1 in Example 1 is also significantly greater than that of Cat-D6 in Comparative Example 6. Compared with the addition of benzoic acid and boric acid alone, the benzoic acid-boron compound composite product can optimize key performance indicators such as polymerization efficiency and product bulk density.

[0091] The comparison results above show that the composite modified catalyst of the present invention is significantly superior to traditional catalysts and single modified catalysts in terms of key performance indicators such as polymerization efficiency and product bulk density, fully demonstrating the synergistic effect of benzoic acid and boron compounds, and is more suitable for industrial application.

[0092] 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 supported metallocene catalyst suitable for the production of polyethylene, characterized in that, The supported metallocene catalyst comprises a silica-supported modified methylaluminoxane composite support and a metallocene active component supported on the silica-supported modified methylaluminoxane composite support; The loading amount of the metallocene active component is 0.01~5.0 wt% of the mass of the silica-supported modified methylaluminoxane composite carrier.

2. The supported metallocene catalyst suitable for producing polyethylene according to claim 1, characterized in that, The silica-supported modified methylaluminoxane composite carrier is prepared by reacting silica gel sequentially with alkylaluminum and benzoic acid-boron compound composite products, specifically including the following steps: (1) Add silica gel to an organic solvent and disperse it by ultrasonication to obtain a silica gel suspension; (2) Under the protection of an inert gas, alkyl aluminum is added dropwise to the silica gel suspension obtained in step (1) and reacted to obtain an alkyl aluminum modified silica gel system; (3) Add the benzoic acid-boron compound composite product to the alkyl aluminum modified silica gel system obtained in step (2) and react in steps with controlled temperature to generate and solidify the modified methyl aluminum oxane in situ on the silica gel surface to obtain the silica gel-supported modified methyl aluminum oxane system. (4) The silica-supported modified methylaluminoxane system obtained in step (3) is filtered, washed and dried to obtain a silica-supported modified methylaluminoxane composite carrier.

3. The supported metallocene catalyst suitable for producing polyethylene according to claim 2, characterized in that, In step (1), the organic solvent is selected from one or more of toluene, xylene, n-hexane, kerosene, and dichlorobenzene; In step (2), the reaction temperature is -50~100℃, the reaction time is 1~4h, and the reaction is stirred at a speed of 100~300rpm. In step (3), the stepwise temperature-controlled reaction is as follows: first, the reaction is carried out at -15~-20℃ for 0.5~2h, then the temperature is raised to 60~80℃ for 24~32h, and finally the temperature is raised to 90~110℃ for 8~16h. In step (3), after the stepwise temperature-controlled reaction is completed, n-hexane is added to the reaction system to precipitate. The volume ratio of n-hexane to the reaction system is (3~6):1, and the temperature at which n-hexane is added is 20~50℃. In step (4), the washing solvent is n-hexane, the drying treatment is vacuum drying, the drying temperature is 40~80℃, and the drying time is 4~8h.

4. A supported metallocene catalyst suitable for producing polyethylene according to claim 2, characterized in that, The benzoic acid-boron compound complex product is prepared by reacting benzoic acid and boron compounds; The preparation of the benzoic acid-boron compound complex product includes the following process: Benzoic acid and boron compounds were reacted in an organic solvent to prepare a benzoic acid-boron compound composite product; The reaction temperature of benzoic acid with boron compounds in organic solvents is -20~60℃, and the reaction time is 0.5~3h. The reaction of benzoic acid with boron compounds in an organic solvent is a stirred reaction at a stirring speed of 100-200 rpm. After the reaction is complete, the alkylaluminum modified silica gel system is directly added without separation. In the preparation of the benzoic acid-boron compound composite product, the organic solvent is selected from one or more of toluene, xylene, n-hexane, kerosene, and dichlorobenzene; The boron compounds are selected from one or more of boric acid, borane, and borate esters; The molar ratio of benzoic acid to boron compounds is (0.01~100):1; The molar ratio of the benzoic acid-boron compound composite product to silica gel is (0.01~50):

1.

5. A supported metallocene catalyst suitable for producing polyethylene according to claim 2, characterized in that, The silica gel is dehydrated and activated silica gel with an average particle size of 10-100 micrometers and a specific surface area of ​​200-800 m². 2 / g, pore volume 0.5~2.0cm 3 / g; The dehydration and activation treatment of the silica gel is carried out under inert gas protection by gradient fluidized drying at 100~600℃, with a constant temperature of 100℃ for 2~4 hours. The alkylaluminum is selected from one or more of trimethylaluminum, triethylaluminum, and triisobutylaluminum; The molar ratio of the alkylaluminum to the silica gel is (0.01~50):1; The molar ratio of the benzoic acid-boron compound composite product to alkyl aluminum is (0.01~10):

1.

6. A supported metallocene catalyst suitable for producing polyethylene according to claim 1, characterized in that, The metallocene active component is a metallocene compound with the general formula CpxMAy, where x≥1; M is a transition metal of group IVB, VB, or VIB; Cp represents an unsubstituted or substituted cyclopentadienyl ligand, indene ligand, fluorenyl ligand, benzo[a]indene ligand, dibenzo[a]fluorenyl ligand, or benzo[a]fluorenyl ligand; A is one or more of amines, ethers, carboxylic acids, dienes, phosphines, halogens, hydrogen atoms, and alkyl groups; (x+y) equals the valence of M. The metallocene active component includes one or more of bridged metallocene compounds, non-bridged metallocene compounds, and mono-metallocene compounds. The metallocene active component includes one or more of bridged metallocene compounds, non-bridged metallocene compounds, and mono-metallocene compounds. The bridged metallocene compound is selected from one or more of rac-ethylenebis(1-indenyl)zirconia, rac-dimethylsilylbis(2-methylindenyl)zirconia, and isopropylidenecyclopentadienylfluorenylzirconia. The non-bridged metallocene compound is selected from one or more of zirconium dichloride, titanium dichloride, bis(n-butylcyclopentadienyl)zirconia, and bis(pentamethylcyclopentadienyl)zirconia. The monoclonal metallocene compound is selected from one or more of cyclopentadienyl zirconium trichloride, cyclopentadienyl titanium trichloride, and pentamethylcyclopentadienyltriethoxyzirconium.

7. A method for preparing a supported metallocene catalyst suitable for producing polyethylene as described in any one of claims 1-6, characterized in that, Includes the following steps: The silica-supported modified methylaluminoxane composite carrier was dispersed in an organic solvent, and the metallocene active component was added. The mixture was stirred and impregnated to load the metallocene active component onto the silica-supported modified methylaluminoxane composite carrier, thus obtaining the product to be treated. The obtained product was filtered, washed with solvent to remove excess metallocene active components, and dried to obtain the metallocene catalyst product.

8. The method for preparing a supported metallocene catalyst suitable for producing polyethylene according to claim 7, characterized in that, The impregnation reaction temperature is -50~100℃, the reaction time is 2~8h, and the stirring speed is 150~400rpm; The organic solvent is selected from one or more of toluene, xylene, n-hexane, kerosene, and dichlorobenzene; The solvent is n-hexane, and the drying process is vacuum drying at a temperature of 40-80°C for 4-12 hours.

9. The application of a supported metallocene catalyst suitable for the production of polyethylene as described in any one of claims 1-6, characterized in that, The supported metallocene catalyst was used for olefin polymerization to produce polyolefins. The olefin polymerization is ethylene homopolymerization, or copolymerization of ethylene with C3~C10 α-olefins; The α-olefin is selected from one or more of propylene, 1-butene, 1-hexene, and 1-octene.

10. The method for applying a supported metallocene catalyst suitable for the production of polyethylene according to claim 9, characterized in that, When the olefin is polymerized into ethylene homopolymer, the process of producing polyolefin by olefin polymerization includes: adding solvent, ethylene, supported metallocene catalyst and co-catalyst to a reactor to carry out a polymerization reaction and obtain polyolefin product; When the olefin polymerization is a copolymerization of ethylene and C3~C10 α-olefin, the process of olefin polymerization to produce polyolefin includes: adding solvent, ethylene, α-olefin, supported metallocene catalyst and co-catalyst to a reactor to carry out a polymerization reaction to obtain polyolefin product; The molar ratio of the α-olefin to ethylene is (0.01~0.5):1; The amount of supported metallocene catalyst added is such that the concentration of supported metallocene catalyst in the entire polymerization system is 0.01~50 ppm, and the amount of co-catalyst added is such that the concentration of co-catalyst in the entire polymerization system is 5~300 ppm. The co-catalyst is selected from one or more of triethylaluminum, triisobutylaluminum, and diethylaluminum chloride; The polymerization reaction is carried out using slurry autoclave, slurry loop, or solution polymerization processes. The bulk density of the obtained polyolefin product is 0.30~0.48 g / cm³. 3 The catalyst polymerization efficiency is ≥10000gPE / g·h.

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