Bimetal active center catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of olefin polymerization catalysts, and particularly discloses a bimetallic active center catalyst as well as a preparation method and application thereof. The bimetallic active center catalyst comprises a Z-N catalyst and a metallocene catalyst loaded on the Z-N catalyst; the Z-N catalyst comprises a titanium metal active center catalyst and an olefin prepolymer coated on the surface of the titanium metal active center catalyst. According to the invention, titanium metal and metallocene are taken as double active centers, and the catalyst with the titanium metal active center is coated with the olefin prepolymer, so that when the catalyst is used for catalyzing olefin polymerization, the polymerization activity release is more uniform, and the prepared olefin polymer has similar bimodal molecular weight distribution, wide molecular weight distribution, high melt-flow ratio and high molecular weight distribution. The processing performance and the mechanical performance are excellent, and the high market application value is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of olefin polymerization catalysts, and in particular to a bimetallic active center catalyst and a preparation method and application thereof. Background Art

[0002] The molecular weight and molecular weight distribution of olefin polymers significantly influence the rheological properties of their melts and the mechanical properties of the final product, such as toughness, strength, and environmental stress cracking resistance. These properties are enhanced at higher molecular weights. However, the processing properties of olefin polymers (resins) generally decrease with increasing molecular weight. Olefin polymers with broad or bimodal molecular weight distributions (referred to as broad / bimodal olefin polymers) impart excellent melt flow at high shear rates, enabling improved blow molding and extrusion performance.

[0003] At present, the main ways to control the molecular weight and distribution of olefin polymers are: (1) adding a post-reactor or using the resin melt blending method. However, this method not only increases the cost, but also makes it difficult to make the resin completely and evenly blended. It usually contains a high content of gel, which affects the performance of the resin; (2) using multi-stage reactor segmented polymerization. This method can evenly mix in the reactor and has greater flexibility in operation adjustment. It can solve the above-mentioned gel problem, but the process efficiency is low and the production cost is very high; (3) using bimetallic or multimetallic active component catalysts in a single reactor, taking advantage of the different polymerization behaviors of different active components, and directly producing bimodal wide-distribution olefin polymers in a single reactor. Theoretically, this method is optimal, but in practice, it is very difficult to achieve the coordination and unification of multiple polymerization behaviors. In actual applications, the inventors found that when Ziegler-Natta catalysts (ZN catalysts for short) or single-active-site catalysts are used for olefin polymerization, the molecular weight distribution of the generated olefin polymers is relatively narrow, making it impossible to prepare wide / bimodal olefin polymers in a single reactor. When catalysts containing two or more different active components are used for olefin polymer production in a single reactor, what is actually produced is a polyolefin mixture with very different molecular weight distributions, and its production and processing performance is very poor, making it difficult to meet the requirements of high-quality resin products. Summary of the Invention

[0004] In response to the above problems, the present invention provides a bimetallic active center catalyst, a preparation method and application thereof, with titanium metal and metallocene as dual active centers, and an olefin prepolymer is used to coat the titanium metal active center catalyst, so that when the bimetallic active center catalyst catalyzes olefin polymerization, the polymerization activity is released more evenly, and the obtained olefin polymer has a molecular weight distribution similar to a bimodal distribution, a wide molecular weight distribution, a high melt flow ratio, and excellent processing performance and mechanical properties.

[0005] In order to solve the above technical problems, the technical solution provided by the present invention is: In a first aspect, the present invention provides a bimetallic active center catalyst, comprising: a ZN catalyst and a metallocene catalyst supported on the ZN catalyst; The ZN catalyst comprises: a titanium metal active center catalyst and an olefin prepolymer coated on the surface of the titanium metal active center catalyst; The structural formula of the active component of the titanium metal active center catalyst is shown in Formula 1: TiX 1 a-1 (OR 1 ) 4-a Formula 1 In formula 1 and formula 2, a represents 2, 3 or 4, R 1 represents a C1~C20 alkyl group, X 1 Represents halogen.

[0006] Compared to the prior art, the bimetallic active site catalyst provided by the present invention, the ZN catalyst containing a titanium metal active site, can catalyze the polymerization to produce olefin polymers with relatively high molecular weights, while the metallocene catalyst can catalyze the polymerization to produce olefin polymers with relatively low molecular weights and narrow molecular weight distributions. The inventors, through extensive experiments, have found that if the release rate of polymerization activity from the ZN catalyst is too rapid, the amount of high molecular weight olefin polymer produced is large, which is out of balance with the low molecular weight olefin polymer produced by the metallocene active site, thus preventing the formation of a uniform bimodal distribution. By coating an olefin prepolymer on the surface of the titanium metal active site catalyst, the present invention ensures a more uniform and stable release of polymerization activity during the subsequent olefin polymerization reaction (i.e., the use of the bimetallic active site catalyst), thereby adjusting the ratio of high and low molecular weight olefin polymers to achieve a uniform distribution, thereby improving the overall performance of the olefin polymers and achieving the production of olefin polymers with a broad, bimodal molecular weight distribution in a single reactor.

[0007] The bimetallic active center catalyst provided by the present invention has high activity and is suitable for polymerization reactions of various olefins. Because the titanium metal active center and the metallocene active center are evenly loaded on the bimetallic active center catalyst, high molecular weight olefin polymer chains and low molecular weight olefin polymer chains can be evenly distributed in the olefin polymer particles, forming a bimodal molecular weight distribution. The resulting olefin polymer has a broad molecular weight distribution, a high melt flow ratio, and excellent processing and mechanical properties. It is particularly suitable for the production of polyethylene pipes and has high market application value.

[0008] Preferably, the titanium metal active center catalyst is prepared by the following method: Alkoxymagnesium is used as a carrier, a titanium compound is first loaded, and then a titanium metal active center catalyst is formed under the action of an organic aluminum compound.

[0009] In the present invention, a titanium compound can be supported on an alkoxymagnesium via a titanium loading reaction, forming a porous structure with numerous macropores. Metallocene catalysts are difficult to load due to their relatively large steric hindrance. However, ZN catalysts prepared using an alkoxymagnesium support have advantages such as high activity, good hydrogen adjustment, low fines content, high bulk density, and high porosity, making them easy to load. An organoaluminum compound, acting as a cocatalyst, can reduce the tetravalent titanium in the titanium compound to trivalent titanium (as shown in Formula 1) and a small amount of divalent titanium (as shown in Formula 7). The trivalent titanium has a highly active center, forming a titanium metal active center catalyst. Finally, a metallocene catalyst is introduced to increase the metallocene active center, forming a bimetallic active center catalyst with both titanium and metallocene as active centers.

[0010] TiX 1 a-2 (OR 1 ) 4-a Formula 7 In formula 7, a represents 2, 3 or 4, R 1 represents a C1~C20 alkyl group, X 1 Represents halogen.

[0011] Further preferably, the chemical formula of the magnesium alkoxide is as shown in Formula 2: Mg(OR 2 ) b (OR 3 ) 2-b Formula 2 In formula 2, b represents 0, 1 or 2, R 2 、R 3 Each independently represents a C1 to C10 alkyl group.

[0012] More preferably, in Formula 2, R 2 、R 3 Each independently represents a C1 to C5 alkyl group.

[0013] More preferably, the alkoxymagnesium includes at least one of dimethoxymagnesium, diethoxymagnesium, dipropoxymagnesium, diisopropoxymagnesium, dibutoxymagnesium, diisobutoxymagnesium, methoxyethoxymagnesium, methoxypropoxymagnesium, ethoxypropoxymagnesium, ethoxyisopropoxymagnesium, ethoxybutoxymagnesium or ethoxyisobutoxymagnesium.

[0014] Most preferably, the magnesium alkoxide includes at least one of diethoxymagnesium, dipropoxymagnesium, diisopropoxymagnesium or dibutoxymagnesium.

[0015] Further preferably, the chemical formula of the titanium compound is as shown in Formula 3: TiX 1 a (OR 1 ) 4-a Formula 3 In formula 3, a represents 2, 3 or 4, R 1 represents a C1~C20 alkyl group, X 1 Represents halogen.

[0016] More preferably, in Formula 1, Formula 3 and Formula 7, R 1 It represents a C1 to C5 alkyl group.

[0017] More preferably, the titanium compound includes at least one of titanium halide, titanium alkoxide halide or titanium alkoxide.

[0018] For example, the titanium halide includes at least one of titanium tetrachloride, titanium tetrabromide or titanium tetraiodide.

[0019] For example, the alkoxy titanium halide includes at least one of methoxytitanium trichloride, ethoxytitanium trichloride, propoxytitanium trichloride, n-butoxytitanium trichloride, dimethoxytitanium dichloride, diethoxytitanium dichloride, dipropoxytitanium dichloride, di-n-butoxytitanium dichloride, trimethoxytitanium chloride, triethoxytitanium chloride, tripropoxytitanium chloride, triisopropoxytitanium chloride or tri-n-butoxytitanium chloride.

[0020] For example, the titanium alkoxide is at least one of tetraethoxytitanium, tetrapropoxytitanium or tetrabutoxytitanium.

[0021] Further preferably, the chemical formula of the organoaluminum compound is as shown in Formula 4: AYR 4 c X 2 3-c Formula 4 In formula 4, c represents 1, 2 or 3, R 4 represents a C1~C20 alkyl group, X 2 Represents halogen.

[0022] More preferably, in Formula 4, R 4 It represents a C1~C10 alkyl group.

[0023] More preferably, the organoaluminum compound comprises at least one of an alkylaluminum or an alkylaluminum halide.

[0024] For example, the alkylaluminum includes at least one of triethylaluminum, tributylaluminum, triisobutylaluminum, tri-n-hexylaluminum or tri-n-octylaluminum.

[0025] For example, the alkylaluminum halide includes at least one of diethylaluminum monochloride, ethylaluminum dichloride, or ethylaluminum sesquichloride.

[0026] Further preferably, the chemical formula of the olefin monomer used in the olefin prepolymer is as shown in Formula 5: CH2=CHR 5 Formula 5 In formula 5, R 5 It represents hydrogen or a C1-C12 alkyl group.

[0027] More preferably, in Formula 5, R 5 It represents hydrogen or a C1-C8 straight-chain alkyl group.

[0028] More preferably, the olefin monomer includes at least one of ethylene, propylene, 1-butene, 1-hexene or 1-octene.

[0029] Most preferably, the olefin monomer comprises ethylene or propylene.

[0030] Further preferably, the raw material of the metallocene catalyst includes a metallocene compound, and the chemical formula of the metallocene compound is shown in Formula 6: A 1 A 2 MR 6 R 7 Formula 6 In formula 6, A 1 、A 2 Each independently represents a cyclopentadienyl group, a cyclopentadienyl group substituted by a C1-C8 alkyl group, a cyclopentadienyl group bridged with an ethyl group, or a cyclopentadienyl group bridged with a dimethylsilyl group, M represents Ti, Zr or Hf, R 6 、R 7 Each independently represents a halogen atom, a C1~C4 alkyl group or a C1~C4 alkoxy group.

[0031] More preferably, in Formula 6, A 1 、A 2 Each independently represents a cyclopentadienyl group or a cyclopentadienyl group substituted by a C1 to C4 alkyl group, R 6 、R 7 Each independently represents a halogen atom, a C1~C2 alkyl group or a C1~C2 alkoxy group.

[0032] More preferably, the metallocene compound includes Cp2ZrCl2, Cp2TiCl2, Cp2HfCl2, Cp2TiMeCl, Cp2ZrMe2, Cp2TiMe2, (n-PrCp)2ZrCl2, (n-BuCp)2ZrCl2, (n-PrCp)2ZrMe2, (n-BuCp)2ZrMe2, [Et(Ind)2]ZrCl2, [Et(Ind)2]HfCl2, [Et(2,4,7 -Me3Ind)2]ZrCl2, [Et(IndH4)2]ZrCl2, [Ph2CEt(Ind)(Cp)]ZrCl2, [Me2CEt(Ind)(Cp)]ZrCl2, [Me2CEt(Ind)(3-MeCp)]ZrCl2, [Ph2C(Flu)(Cp)]ZrCl2, [Me2C(Flu)(Cp)]ZrCl2 or at least one of [Me2C(Flu)(Cp)]HfCl2.

[0033] Preferably, organoaluminoxane is also added when the metallocene compound is supported.

[0034] In the present invention, adding the metallocene compound after adding the organoaluminoxane can improve the activity of the metallocene catalyst, and at the same time, the metallocene catalyst can be more firmly combined with the ZN catalyst, thereby improving the stability of the release of the metallocene catalyst activity.

[0035] More preferably, the organoaluminoxane includes at least one of methylaluminoxane and modified methylaluminoxane.

[0036] More preferably, the molar ratio of the magnesium alkoxide, the titanium compound, the organoaluminum compound, the olefin monomer, the organoaluminoxane and the metallocene compound is 1:(0.1-100):(0.1-100):(0.01-100):(0.1-100):(0.01-10).

[0037] More preferably, the molar ratio of the magnesium alkoxide, the titanium compound, the organoaluminum compound, the olefin monomer, the organoaluminoxane and the metallocene compound is 1:(0.1-20):(0.01-50):(0.1-50):(0.1-20):(0.01-5).

[0038] More preferably, the molar ratio of the magnesium alkoxide, the titanium compound, the organoaluminum compound, the olefin monomer, the organoaluminoxane and the metallocene compound is 1:(0.1-5):(0.01-30):(0.1-30):(0.1-5):(0.01-1).

[0039] Most preferably, the molar ratio of the magnesium alkoxide, the titanium compound, the organoaluminum compound, the olefin monomer, the organoaluminoxane and the metallocene compound is 1:(0.5-5):(0.5-8):(10-25):(0.1-5):(0.01-0.3).

[0040] In a second aspect, the present invention provides a method for preparing the bimetallic active center catalyst, comprising the following steps: S1. Under an inert atmosphere, adding magnesium alkoxide and a titanium compound to a solvent to carry out a titanium-supporting reaction to obtain a catalyst precursor; S2. Under an inert atmosphere, the catalyst precursor and the organoaluminum compound are added to a solvent, and after a reduction reaction, an olefin monomer is added to carry out a prepolymerization reaction to obtain a ZN catalyst; S3. Under an inert atmosphere, the ZN catalyst, the organoaluminoxane and the metallocene compound are sequentially added into a solvent to carry out a metallocene loading reaction to obtain a bimetallic active center catalyst.

[0041] The present invention provides a method for preparing a bimetallic active center catalyst. First, a titanium compound is loaded onto an alkoxymagnesium support through a titanium loading reaction. Then, tetravalent titanium is reduced to trivalent titanium (and a small amount of divalent titanium) using an organoaluminum oxide. A prepolymerization reaction is then performed to produce a ZN catalyst coated with an olefin prepolymer. Finally, a metallocene compound is loaded onto the catalyst to form a titanium metal / metallocene bimetallic active center catalyst. The preparation method is simple and suitable for large-scale production.

[0042] It should be noted that if the metallocene is loaded first and then the titanium compound is loaded, the metallocene will become ineffective and a bimetallic active center catalyst cannot be formed.

[0043] Preferably, the inert atmosphere comprises a nitrogen atmosphere.

[0044] Preferably, the solvent includes at least one of an aromatic hydrocarbon solvent or an alkane solvent.

[0045] Further preferably, the aromatic hydrocarbon solvent includes at least one of benzene, toluene, xylene, ethylbenzene, propylbenzene, trimethylbenzene or chlorobenzene.

[0046] Further preferably, the alkane solvent includes at least one of hexane, heptane, decane or cyclohexane.

[0047] The present invention does not make any special requirements on the amount of solvent used, and the conventional amount used in the art can be used. For example, the material-liquid ratio in S1 to S3 can be 1 g: (5 to 20) mL.

[0048] Preferably, in S1, the temperature of the titanium loading reaction is -20°C to 150°C.

[0049] Further preferably, in S1, the temperature of the titanium loading reaction is 0°C to 100°C (more preferably 80°C to 100°C), and the time of the titanium loading reaction is 0.5h to 2h.

[0050] For example, in S1, after the titanium loading reaction is completed, the process further includes solid-liquid separation and washing to obtain a catalyst precursor. The above operations can remove impurities such as excess reactants and by-products on the catalyst precursor, which is beneficial to the subsequent reaction.

[0051] For example, in S2, the organoaluminum compound can be directly added to the reaction system, or can be prepared into a solution with a solvent and then added to the reaction system.

[0052] Preferably, in S2, the temperature of the reduction reaction is -20°C to 50°C.

[0053] Further preferably, in S2, the temperature of the reduction reaction is 10° C. to 30° C., and the time of the reduction reaction is 0.5 h to 1.5 h.

[0054] Preferably, in S2, the temperature of the prepolymerization reaction is -20°C to 50°C, and the pressure of the prepolymerization reaction is 0 to 0.05 MPa.

[0055] Further preferably, in S2, the temperature of the prepolymerization reaction is 10° C. to 30° C., the pressure of the prepolymerization reaction is 0 to 0.01 MPa, and the time of the prepolymerization reaction is 15 min to 2 h.

[0056] The temperature and pressure of the prepolymerization reaction in the present invention are relatively low, the polymerization speed of the olefin monomer is relatively slow, and under the action of a small amount of organic aluminum compound, a ZN catalyst uniformly coated with an olefin prepolymer protective film can be formed.

[0057] For example, in S2, after the prepolymerization reaction is completed, the process further includes solid-liquid separation, washing, and drying to obtain the ZN catalyst. The above operations can remove impurities such as excess reactants and by-products on the ZN catalyst, which is beneficial for the subsequent reaction.

[0058] For example, in S3, the organoaluminoxane can be directly added to the reaction system, or can be prepared into a solution with a solvent and then added to the reaction system.

[0059] Preferably, in S3, the temperature of the metallocene loading reaction is -20°C to 100°C.

[0060] More preferably, in S3, the temperature of the metallocene loading reaction is 0°C to 50°C (more preferably 15°C to 40°C), and the time of the metallocene loading reaction is 2h to 4h.

[0061] For example, in S3, after the metallocene loading reaction is completed, the steps further include: solid-liquid separation, washing, and drying to obtain the bimetallic active center catalyst. The drying method may be vacuum drying or nitrogen drying.

[0062] In a third aspect, the present invention provides an application of the bimetallic active center catalyst in the preparation of olefin polymers.

[0063] While polyolefin catalysts prepared using magnesium alkoxides as supports offer numerous advantages, the molecular weight distribution of olefin polymers produced using existing catalysts is relatively narrow. In actual production, a dual-reactor or triple-reactor system with various polymerization process conditions must be employed to achieve the goal of producing olefin polymers with a broad molecular weight. The present invention utilizes a bimetallic active site catalyst to produce polyolefins with a broad, bimodal molecular weight distribution in a single reactor.

[0064] Preferably, the method for preparing an olefin polymer comprises the following steps: Under an inert atmosphere, a bimetallic active center catalyst and an organoaluminum compound are added to a solvent to carry out a pre-complexation reaction to obtain an activated catalyst; The polymerization reaction of olefin monomers is carried out under the action of the activated catalyst and hydrogen to obtain olefin polymers.

[0065] The method for preparing olefin polymers provided by the present invention involves pre-complexing a bimetallic active-center catalyst with an organoaluminum compound. This activates the bimetallic active-center catalyst and eliminates highly active sites on the catalyst surface (i.e., the highly active sites undergo a pre-complexation reaction with the organoaluminum compound), thereby reducing its initial activity and ensuring smooth subsequent polymerization. Hydrogen, acting as a chain transfer agent, can control the molecular weight of the olefin polymer; the more hydrogen introduced, the lower the molecular weight of the olefin polymer.

[0066] Further preferably, the molar ratio of titanium in the bimetallic active center catalyst to aluminum in the organoaluminum compound is 1:(100-200).

[0067] In the present invention, the organoaluminum compound in the pre-complexation reaction may be the same as or different from the organoaluminum compound in the bimetallic active center catalyst raw material.

[0068] More preferably, the temperature of the pre-complexation reaction is 20° C. to 30° C., and the time of the pre-complexation reaction is 0.01 h to 1 h.

[0069] More preferably, the olefin monomer includes at least one of C1-C14 linear olefins, C4-C8 branched olefins or C2-C8 diolefins.

[0070] More preferably, the C1-C14 linear olefin includes at least one of propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene or 1-decene.

[0071] More preferably, the C4-C8 branched olefin includes at least one of 3-methyl-1-butene or 4-methyl-1-pentene.

[0072] More preferably, the C2-C8 diene comprises at least one of butadiene, vinylcyclopentene or vinylcyclohexene.

[0073] More preferably, the polymerization reaction temperature is 30° C. to 180° C. (more preferably 60° C. to 120° C.), the polymerization reaction pressure is 0.6 MPa to 0.8 MPa, and the polymerization reaction time is 0.5 h to 2 h. DETAILED DESCRIPTION

[0074] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0075] In the present invention, unless otherwise specified, all materials are commercially available products or homemade products with reference to existing technologies.

[0076] Example 1 This embodiment provides a bimetallic active center catalyst, including a ZN catalyst and a metallocene catalyst supported on the ZN catalyst, wherein the ZN catalyst includes a titanium metal active center catalyst (active components are TiCl3 and TiCl2OEt) and an olefin prepolymer coated on the surface of the titanium metal active center catalyst.

[0077] The bimetallic active center catalyst includes the following raw materials: magnesium alkoxide (diethoxymagnesium), a titanium compound (titanium tetrachloride), an organoaluminum compound (triisobutylaluminum), an olefin monomer (ethylene), an organoaluminoxane (methylaluminoxane), and a metallocene compound (Cp2ZrCl2). The molar ratio of magnesium alkoxide, titanium compound, organoaluminum compound, olefin monomer, organoaluminoxane, and metallocene compound is 1:2.5:0.9:25.2:0.71:0.012.

[0078] The preparation method of the above-mentioned bimetallic active center catalyst comprises the following steps: S1. In a five-necked flask with stirring and sufficient nitrogen replacement, add 200 mL of dehydrated and deoxygenated toluene and 20 g of diethoxymagnesium with an average particle size of 18 μm, cool to 0°C, slowly add 48 mL of titanium tetrachloride dropwise, and raise the temperature to 100°C after addition to carry out titanium loading reaction. After keeping warm for 1 hour, separate the solid and liquid, wash the solid matter, and obtain a catalyst precursor.

[0079] S2. Add the catalyst precursor and 500 mL of hexane into a stirred five-necked flask that has been fully replaced with nitrogen, add 78.7 mL of a hexane solution containing 2 mol / L triisobutylaluminum at room temperature, and stir at a constant temperature to carry out a reduction reaction. After keeping the temperature for 0.5 h, slowly introduce ethylene. After the addition is completed, continue stirring at room temperature for 0.5 h, separate the solid and liquid, wash the solid, and dry it to obtain a ZN catalyst.

[0080] S3. In a five-necked flask with stirring and fully replaced with nitrogen, 80 mL of dehydrated and deoxygenated toluene, 10 g of ZN catalyst, 30 g of a toluene solution containing 10 wt% methylaluminoxane, and 0.26 g of Cp2ZrCl2 were added in sequence at room temperature. The metallocene loading reaction was carried out at 35°C. After keeping the temperature for 2 h, the solid-liquid separation was carried out, and the solid was washed and dried to obtain 11.5 g of a bimetallic active center catalyst.

[0081] Example 2 This embodiment provides a bimetallic active center catalyst, including a ZN catalyst and a metallocene catalyst supported on the ZN catalyst, wherein the ZN catalyst includes a titanium metal active center catalyst (active components are TiCl3 and TiCl2OPr) and an olefin prepolymer coated on the surface of the titanium metal active center catalyst.

[0082] The bimetallic active center catalyst includes the following raw materials: magnesium alkoxide (dipropoxymagnesium), a titanium compound (ethoxytitanium trichloride), an organoaluminum compound (triethylaluminum), an olefin monomer (propylene), an organoaluminoxane (modified methylaluminoxane), and a metallocene compound ((n-PrCp)2ZrCl2). The molar ratio of the magnesium alkoxide, titanium compound, organoaluminum compound, olefin monomer, organoaluminoxane, and metallocene compound is 1:1:1:20:2:0.05.

[0083] The preparation method of the above-mentioned bimetallic active center catalyst comprises the following steps: S1. In a five-necked flask with stirring and sufficient nitrogen replacement, add 200 mL of dehydrated and deoxygenated xylene and 20 g of dipropoxymagnesium with an average particle size of 18 μm, cool to 0°C, slowly add 27.6 g of ethoxytitanium trichloride dropwise, and raise the temperature to 90°C after the addition to carry out titanium loading reaction. After keeping the temperature for 1.5 hours, separate the solid and liquid, wash the solid, and obtain a catalyst precursor.

[0084] S2. Add the catalyst precursor and 500 mL of heptane into a stirred five-necked flask that has been fully replaced with nitrogen, add 70.3 mL of a heptane solution containing 2 mol / L triethylaluminum at room temperature, and stir at a constant temperature to carry out a reduction reaction. After keeping the temperature for 1 hour, slowly introduce propylene. After the addition is completed, continue stirring at room temperature for 0.5 hour, separate the solid and liquid, wash the solid, and dry it to obtain a ZN catalyst.

[0085] S3. In a five-necked flask with stirring and fully replaced with nitrogen, 80 mL of dehydrated and deoxygenated xylene, 10 g of ZN catalyst, 68.1 g of a toluene solution containing 10 wt% of modified methylaluminoxane, and 1.1 g of (n-PrCp)2ZrCl2 were added in sequence at room temperature, and a metallocene loading reaction was carried out at 30°C. After keeping the temperature for 3 h, the solid-liquid separation was carried out, and the solid was washed and dried to obtain a bimetallic active center catalyst.

[0086] Example 3 This embodiment provides a bimetallic active center catalyst, including a ZN catalyst and a metallocene catalyst supported on the ZN catalyst, wherein the ZN catalyst includes a titanium metal active center catalyst (active components are TiCl3 and TiCl2(Oi-Pr)) and an olefin prepolymer coated on the surface of the titanium metal active center catalyst.

[0087] The bimetallic active center catalyst includes the following raw materials: magnesium alkoxide (diisopropoxymagnesium), a titanium compound (titanium tetrachloride), an organoaluminum compound (tributylaluminum), an olefin monomer (propylene), an organoaluminoxane (methylaluminoxane), and a metallocene compound ((n-BuCp)2ZrCl2). The molar ratio of magnesium alkoxide, titanium compound, organoaluminum compound, olefin monomer, organoaluminoxane, and metallocene compound is 1:3:0.75:16:3:0.04.

[0088] The preparation method of the above-mentioned bimetallic active center catalyst comprises the following steps: S1. In a five-necked flask with stirring and sufficient nitrogen replacement, add 200 mL of dehydrated and deoxygenated ethylbenzene and 20 g of diisopropoxymagnesium with an average particle size of 18 μm, cool to 0°C, slowly add 46.3 mL of titanium tetrachloride dropwise, and raise the temperature to 80°C after addition to carry out titanium loading reaction. After keeping warm for 2 hours, separate the solid and liquid, wash the solid matter, and obtain a catalyst precursor.

[0089] S2. Add the catalyst precursor and 500 mL of decane into a stirred five-necked flask that has been fully replaced with nitrogen, add 52.8 mL of a decane solution containing 2 mol / L tributylaluminum at room temperature, and stir at a constant temperature to carry out a reduction reaction. After keeping the temperature for 1 hour, introduce propylene under normal pressure. After the addition is completed, continue stirring at room temperature for 1 hour, separate the solid and liquid, wash the solid, and dry it to obtain a ZN catalyst.

[0090] S3. In a five-necked flask with stirring and fully replaced with nitrogen, 80 mL of dehydrated and deoxygenated trimethylbenzene, 10 g of ZN catalyst, 102.1 g of trimethylbenzene solution containing 10 wt% methylaluminoxane and 0.95 g of (n-BuCp)2ZrCl2 were added in sequence at room temperature, and the metallocene loading reaction was carried out at 40°C. After keeping the temperature for 3.5 hours, the solid-liquid separation was carried out, and the solid was washed and dried to obtain a bimetallic active center catalyst.

[0091] Example 4 This embodiment provides a bimetallic active center catalyst, including a ZN catalyst and a metallocene catalyst supported on the ZN catalyst, wherein the ZN catalyst includes a titanium metal active center catalyst (active components are TiCl3, TiCl2OBu and TiCl2OPr) and an olefin prepolymer coated on the surface of the titanium metal active center catalyst.

[0092] The bimetallic active-center catalyst comprises the following raw materials: magnesium alkoxide (dibutoxymagnesium), a titanium compound (propoxytitanium trichloride), an organoaluminum compound (tri-n-hexylaluminum), an olefin monomer (1-butene), an organoaluminoxane (modified methylaluminoxane), and a metallocene compound (Cp2TiCl2). The molar ratio of magnesium alkoxide, titanium compound, organoaluminum compound, olefin monomer, organoaluminoxane, and metallocene compound is 1:0.5:2:15:0.5:0.1.

[0093] The preparation method of the above-mentioned bimetallic active center catalyst comprises the following steps: S1. In a five-necked flask with stirring and sufficient nitrogen replacement, add 200 mL of dehydrated and deoxygenated chlorobenzene and 20 g of dibutoxymagnesium with an average particle size of 18 μm, cool to 0°C, slowly add 13.12 g of propoxytitanium trichloride dropwise, and raise the temperature to 100°C after addition to carry out titanium loading reaction. After keeping warm for 1 hour, separate the solid and liquid, wash the solid matter, and obtain a catalyst precursor.

[0094] S2. Add the catalyst precursor and 500 mL of cyclohexane into a stirred five-necked flask that has been fully replaced with nitrogen, add 125 mL of cyclohexane solution containing 2 mol / L tri-n-hexyl aluminum at room temperature, and stir at a constant temperature to carry out a reduction reaction. After keeping warm for 0.5 h, slowly add 1-butene under normal pressure. After the addition is completed, continue stirring at room temperature for 0.5 h, separate the solid and liquid, wash the solid, and dry it to obtain a ZN catalyst.

[0095] S3. In a five-necked flask with stirring and fully replaced with nitrogen, 80 mL of dehydrated and deoxygenated propylbenzene, 10 g of ZN catalyst, 18.5 g of propylbenzene solution containing 10 wt% modified methylaluminoxane, and 1.29 g of Cp2TiCl2 were added in sequence at room temperature, and the metallocene loading reaction was carried out at 25°C. After keeping the temperature for 2 h, the solid-liquid separation was carried out, and the solid was washed and dried to obtain a bimetallic active center catalyst.

[0096] Example 5 This embodiment provides a bimetallic active center catalyst, including a ZN catalyst and a metallocene catalyst supported on the ZN catalyst, wherein the ZN catalyst includes a titanium metal active center catalyst (active components are TiCl3 and TiCl2OEt) and an olefin prepolymer coated on the surface of the titanium metal active center catalyst.

[0097] The bimetallic active center catalyst includes the following raw materials: magnesium alkoxide (diethoxymagnesium), a titanium compound (titanium tetrachloride), an organoaluminum compound (tri-n-octylaluminum), an olefin monomer (ethylene), an organoaluminoxane (methylaluminoxane), and a metallocene compound (Cp2HfCl2). The molar ratio of magnesium alkoxide, titanium compound, organoaluminum compound, olefin monomer, organoaluminoxane, and metallocene compound is 1:5:1.25:20:5:0.15.

[0098] The preparation method of the above-mentioned bimetallic active center catalyst comprises the following steps: S1. In a five-necked flask with stirring and sufficient nitrogen replacement, add 200 mL of dehydrated and deoxygenated hexane and 20 g of diethoxymagnesium with an average particle size of 18 μm, cool to 0°C, slowly add 96 mL of titanium tetrachloride dropwise, and raise the temperature to 120°C after addition to carry out titanium loading reaction. After keeping warm for 0.5 h, separate the solid and liquid, wash the solid, and obtain a catalyst precursor.

[0099] S2. Add the catalyst precursor and 500 mL of hexane into a stirred five-necked flask that has been fully replaced with nitrogen, add 109.4 mL of a hexane solution containing 2 mol / L tri-n-octylaluminum at room temperature, and stir at a constant temperature to carry out a reduction reaction. After keeping the temperature for 1.5 hours, slowly introduce ethylene. After the addition is completed, continue stirring at room temperature for 1.5 hours, separate the solid and liquid, wash the solid, and dry it to obtain a ZN catalyst.

[0100] S3. In a five-necked flask with stirring and fully replaced with nitrogen, 80 mL of dehydrated and deoxygenated toluene heptane, 10 g of ZN catalyst, 211 g of a toluene solution containing 10 wt% methylaluminoxane, and 4.15 g of Cp2HfCl2 were added in sequence at room temperature, and a metallocene loading reaction was carried out at 50°C. After keeping the temperature for 4 h, the solid-liquid separation was carried out, and the solid was washed and dried to obtain a bimetallic active center catalyst.

[0101] Example 6 This embodiment provides a bimetallic active center catalyst, including a ZN catalyst and a metallocene catalyst supported on the ZN catalyst, wherein the ZN catalyst includes a titanium metal active center catalyst (active component is TiCl 3、 The bimetallic active-center catalyst comprises a magnesium alkoxide (methoxyethoxymagnesium), a titanium compound (titanium tetrachloride), an organoaluminum compound (diethylaluminum monochloride), an olefin monomer (propylene), an organoaluminoxane (modified methylaluminoxane), and a metallocene compound ((n-PrCp)2ZrCl2). The molar ratio of the magnesium alkoxide, titanium compound, organoaluminum compound, olefin monomer, organoaluminoxane, and metallocene compound is 1:2:0.5:15:1:0.05.

[0102] The preparation method of the above-mentioned bimetallic active center catalyst comprises the following steps: S1. In a five-necked flask with stirring and sufficient nitrogen replacement, add 200 mL of dehydrated and deoxygenated decane and 20 g of methoxyethoxymagnesium with an average particle size of 18 μm, cool to 0°C, slowly add 43.9 mL of titanium tetrachloride dropwise, and raise the temperature to 90°C after addition to carry out titanium loading reaction. After keeping warm for 1.5 hours, separate the solid and liquid, wash the solid, and obtain a catalyst precursor.

[0103] S2. Add the catalyst precursor and 500 mL of heptane into a five-necked flask with stirring that has been fully replaced with nitrogen, add 50 mL of a heptane solution containing 2 mol / L diethylaluminum monochloride at room temperature, and stir at a constant temperature to carry out a reduction reaction. After keeping the temperature for 1 hour, slowly introduce propylene. After the addition is completed, continue stirring at room temperature for 1 hour, separate the solid and liquid, wash the solid, and dry it to obtain a ZN catalyst.

[0104] S3. In a stirred five-necked flask fully substituted with nitrogen, 80 mL of dehydrated and deoxygenated cyclohexane), 10 g of ZN catalyst, 48.3 g of a toluene solution containing 10 wt% modified methylaluminoxane, and 1.57 g of (n-PrCp)2ZrCl2 were added in sequence at room temperature. The metallocene-supported reaction was carried out at 45°C. After keeping the temperature for 3 h, the solid-liquid separation was performed, and the solid was washed and dried to obtain a bimetallic active center catalyst.

[0105] Example 7 This embodiment provides a bimetallic active center catalyst, including a ZN catalyst and a metallocene catalyst supported on the ZN catalyst, wherein the ZN catalyst includes a titanium metal active center catalyst (active component is TiCl 3、TiCl2OEt and TiCl2OPr) and olefin prepolymers coated on the surface of titanium metal active center catalyst.

[0106] The bimetallic active-center catalyst comprises the following raw materials: a magnesium alkoxide (ethoxypropoxymagnesium), a titanium compound (titanium tetrachloride), an organoaluminum compound (triisobutylaluminum), an olefin monomer (propylene), an organoaluminoxane (methylaluminoxane), and a metallocene compound ([Et(Ind)2]ZrCl2). The molar ratio of the magnesium alkoxide, titanium compound, organoaluminum compound, olefin monomer, organoaluminoxane, and metallocene compound is 1:0.5:1:15:0.2:0.01.

[0107] The preparation method of the above-mentioned bimetallic active center catalyst comprises the following steps: S1. In a five-necked flask with stirring and sufficient nitrogen replacement, add 200 mL of dehydrated and deoxygenated cyclohexane and 20 g of ethoxypropoxymagnesium with an average particle size of 18 μm, cool to 0°C, slowly add 8.6 mL of titanium tetrachloride dropwise, and raise the temperature to 105°C after addition to carry out titanium loading reaction. After keeping warm for 1 hour, separate the solid and liquid, wash the solid matter, and obtain a catalyst precursor.

[0108] S2. Add the catalyst precursor and 500 mL of cyclohexane into a stirred five-necked flask that has been fully replaced with nitrogen, add 78 mL of a cyclohexane solution containing 2 mol / L triisobutylaluminum at room temperature, and stir at a constant temperature to carry out a reduction reaction. After keeping the temperature for 0.5 h, slowly introduce propylene. After the addition is completed, continue stirring at room temperature for 0.5 h, separate the solid and liquid, wash the solid, and dry it to obtain a titanium-containing ZN catalyst.

[0109] S3. In a five-necked flask with stirring and fully replaced with nitrogen, 80 mL of dehydrated and deoxygenated decane, 10 g of ZN catalyst, 48.3 g of decane solution containing 10 wt% methylaluminoxane, and 0.27 g of [Et(Ind)2]ZrCl2 were added in sequence at room temperature, and a metallocene loading reaction was carried out at 30°C. After keeping the temperature for 2 h, the solid-liquid separation was carried out, and the solid was washed and dried to obtain a bimetallic active center catalyst.

[0110] Comparative Example 1 This comparative example provides a metallocene catalyst. Compared with Example 1, its raw materials do not include alkoxymagnesium (replaced with activated silica gel of equal mass), titanium compound, organoaluminum compound and olefin monomer.

[0111] The preparation method of the above-mentioned metallocene catalyst comprises the following steps: In a five-necked flask with stirring and sufficient nitrogen replacement, 80 mL of dehydrated and deoxygenated toluene, 10 g of silica gel (activated at 300 ° C for 2 h before addition), 30 g of a toluene solution containing 10 wt% methylaluminoxane (methylaluminoxane) and 0.26 g of Cp2ZrCl2 were added in sequence at room temperature. The metallocene loading reaction was carried out at 35 ° C. After keeping warm for 2 h, the solid-liquid separation was carried out, and the solid was washed and dried to obtain 12.7 g of metallocene catalyst.

[0112] Comparative Example 2 This comparative example provides a bimetallic active center catalyst. Compared with Example 1, its raw materials do not include olefin monomers.

[0113] The preparation method of the above-mentioned bimetallic active center catalyst comprises the following steps: S1. Same as Example 1, no further details will be given.

[0114] S2. Add the catalyst precursor and 500 mL of hexane into a five-necked flask with stirring that has been fully replaced with nitrogen, add 315 mL of a hexane solution containing 2 mol / L triisobutylaluminum at room temperature, and stir at a constant temperature to carry out a reduction reaction. After keeping the temperature for 0.5 h, separate the solid and liquid, wash and dry the solid, and obtain a titanium metal active center catalyst.

[0115] S3. In a five-necked flask with stirring that has been fully replaced with nitrogen, 80 mL of dehydrated and deoxygenated toluene, 10 g of a titanium metal active center catalyst, 30 g of a toluene solution containing 10 wt% methylaluminoxane, and 0.26 g of Cp2ZrCl2 were added in sequence at room temperature, and a metallocene loading reaction was carried out at 35°C. After keeping the temperature for 2 hours, the solid-liquid separation was performed, and the solid was washed and dried to obtain a bimetallic active center catalyst.

[0116] Comparative Example 3 This comparative example provides a bimetallic active center catalyst. Compared with Example 1, its raw materials do not include an organoaluminum compound and an olefin monomer.

[0117] The preparation method of the above-mentioned bimetallic active center catalyst comprises the following steps: S1. Same as Example 1, no further details will be given.

[0118] S2. In a five-necked flask with stirring and fully replaced with nitrogen, 80 mL of dehydrated and deoxygenated toluene, 10 g of catalyst precursor, 30 g of a toluene solution containing 10 wt% methylaluminoxane, and 0.26 g of Cp2ZrCl2 were added in sequence at room temperature, and a metallocene loading reaction was carried out at 35°C. After keeping the temperature for 2 h, the solid-liquid separation was performed, and the solid was washed and dried to obtain a bimetallic active center catalyst.

[0119] Comparative Example 4 This comparative example provides a bimetallic active center catalyst, which is similar to Example 1, except that the alkoxy magnesium is replaced by a magnesium chloride solution.

[0120] The preparation method of the above-mentioned bimetallic active center catalyst comprises the following steps: S1. In a five-necked flask with stirring and sufficient nitrogen replacement, add 8g MgCl2, 100mL toluene, 12mL ethanol, 5.6mL tributyl phosphate and 5.0mL epichlorohydrin, and stir until MgCl2 is completely dissolved; cool to 0°C, slowly add 48mL titanium tetrachloride dropwise, and raise the temperature to 100°C after addition to carry out titanium loading reaction. After keeping warm for 1h, separate the solid and liquid, wash the solid, and obtain the catalyst precursor.

[0121] S2~S3 are the same as S2~S3 in Example 1 and will not be described in detail.

[0122] Application Example 1 This application example provides a method for preparing an olefin polymer, comprising the following steps: After the stainless steel reactor was fully purged with nitrogen, 1 L of n-hexane, 4 mL of 0.5 mol / L triethylaluminum hexane solution, 4 mL of 0.5 mol / L triisobutylaluminum hexane solution, and 160 mg of the bimetallic active center catalyst of Example 1 were added in sequence, and the mixture was stirred at room temperature for a pre-complexation reaction. After keeping the temperature for 5 minutes, an activated catalyst was obtained; The temperature was raised to 70°C, and hydrogen was introduced into the stainless steel reactor to fully replace the pressure. When the pressure in the reactor reached 0.05 MPa, the introduction of hydrogen was stopped. Then ethylene was introduced to make the total pressure in the reactor reach 0.73 MPa. After the polymerization reaction was carried out at 80°C for 2 hours, the reactor was cooled and stirring was stopped, and the reaction product, polyethylene, was discharged.

[0123] Application Examples 2~7 Application Examples 2-7 each provide a method for preparing an olefin polymer, similar to Application Example 1, except that the bimetallic active center catalyst is replaced with the bimetallic active center catalyst of Examples 2-7. The remaining conditions and procedures are the same as those of Application Example 1 and are not further described.

[0124] Comparative Application Example 1 This comparative example provides a method for preparing an olefin polymer, which is similar to that of Example 1, except that the bimetallic active center catalyst is replaced with the metallocene catalyst of Comparative Example 1, and hydrogen is not added. Ethylene alone is introduced to a total pressure of 0.73 MPa in the reactor. The specific method comprises the following steps: After the stainless steel reactor was fully purged with nitrogen, 1 L of n-hexane, 4 mL of 0.5 mol / L triethylaluminum hexane solution, 4 mL of 0.5 mol / L triisobutylaluminum hexane solution, and 160 mg of the bimetallic active center catalyst of Comparative Example 1 were added in sequence, and the mixture was stirred at room temperature for a pre-complexation reaction. After keeping the temperature for 5 minutes, an activated catalyst was obtained; The temperature was raised to 70°C, and ethylene was introduced into the stainless steel reactor to fully replace the reaction mixture. Ethylene was then introduced to a total pressure of 0.73 MPa. The polymerization reaction was carried out at 80°C for 2 hours, and the reactor was cooled and stirring was stopped. The reaction product, polyethylene, was discharged.

[0125] Application Comparative Examples 2 to 4 Comparative Examples 2 to 4 each provide a method for preparing an olefin polymer, which is similar to Example 1, except that the bimetallic active center catalyst is replaced with the bimetallic active center catalyst of Comparative Examples 2 to 4, respectively. The remaining conditions and operations are the same as those of Example 1 and are not further described.

[0126] Comparative Application Example 5 This comparative example provides a method for preparing an olefin polymer, similar to that of Example 1, except that the bimetallic active center catalyst is replaced with the catalyst precursor of Example 1 and the reactor pressure is set to 0.10 MPa when hydrogen flow is stopped, yielding a polymer with a similar MI (0.3 g / 10 min). The remaining conditions and procedures are the same as those of Example 1 and are not further described.

[0127] Performance Testing The chemical composition and particle size distribution of the catalysts provided in Examples 1 to 7 and Comparative Examples 1 to 4 were tested, and the test results are shown in Table 1. The catalyst performance and molecular weight distribution of polyethylene corresponding to Examples 1 to 7 and Comparative Examples 1 to 5 were tested, and the test results are shown in Table 2.

[0128] Chemical composition of the catalyst: The metal elements in the catalyst were determined by spectrophotometry, the halogen was determined by silver nitrate titration, and the alkoxy was determined by gas chromatography.

[0129] Particle size distribution of polymer: refer to standard ASTM E1187.

[0130] Melt index (MI): refer to ASTM D1238.

[0131] Bulk density (BD) of polymer: refer to DIN53194.

[0132] Polymer molecular weight (Mw, Mn) and molecular weight distribution coefficient (Mw / Mn): Molecular weight and molecular weight distribution were determined by gel permeation chromatography (GPC) using a Waters Alliance GPCV 2000 instrument. The solvent was 1,2,4-trichlorobenzene, the sample concentration was 1 mg / mL, and the solvent flow rate was 1.0 mL / min. The measurement temperature was 150°C. Each sample was measured three times, and the average value was calculated.

[0133] Table 1 Test results of catalysts of Examples and Comparative Examples

[0134] Table 2 Test results of catalytic performance of application examples and comparative examples

[0135] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A bimetallic active center catalyst, characterized in that: include: A ZN catalyst and a metallocene catalyst supported on the ZN catalyst; The ZN catalyst comprises: a titanium metal active center catalyst and an olefin prepolymer coated on the surface of the titanium metal active center catalyst; The structural formula of the active component of the titanium metal active center catalyst is shown in Formula 1: TiX 1 a-1 (OR 1 ) 4-a Formula 1 In formula 1, a represents 2, 3 or 4, R 1 represents a C1~C20 alkyl group, X 1 Represents halogen.

2. The bimetallic active site catalyst according to claim 1, characterized in that The titanium metal active center catalyst is prepared by the following method: Alkoxymagnesium is used as a carrier, a titanium compound is first loaded, and then a titanium metal active center catalyst is formed under the action of an organic aluminum compound.

3. The bimetallic active site catalyst according to claim 2, characterized in that The chemical formula of the magnesium alkoxide is shown in Formula 2: Mg(OR 2 ) b (OR 3 ) 2-b Formula 2 In formula 2, b represents 0, 1 or 2, R 2 、R 3 Each independently represents a C1~C10 alkyl group; The chemical formula of the titanium compound is shown in Formula 3: TiX 1 a (OR 1 ) 4-a Formula 3 In formula 3, a represents 2, 3 or 4, R 1 represents a C1~C20 alkyl group, X 1 represents halogen; The chemical formula of the organoaluminum compound is shown in Formula 4: AlR 4 c X 2 3-c Formula 4 In formula 4, c represents 1, 2 or 3, R 4 represents a C1~C20 alkyl group, X 2 represents halogen; The chemical formula of the olefin monomer used in the olefin prepolymer is shown in Formula 5: CH2=CHR 5 Formula 5 In formula 5, R 5 represents hydrogen or a C1~C12 alkyl group; The raw material of the metallocene catalyst includes a metallocene compound, and the chemical formula of the metallocene compound is shown in Formula 6: A 1 A 2 MR 6 R 7 Formula 6 In formula 6, A 1 、A 2 Each independently represents a cyclopentadienyl group, a cyclopentadienyl group substituted by a C1-C8 alkyl group, a cyclopentadienyl group bridged with an ethyl group, or a cyclopentadienyl group bridged with a dimethylsilyl group, M represents Ti, Zr or Hf, R 6 、R 7 Each independently represents a halogen atom, a C1~C4 alkyl group or a C1~C4 alkoxy group.

4. The bimetallic active site catalyst according to claim 3, characterized in that When the metallocene compound is supported, an organoaluminoxane needs to be added.

5. The bimetallic active site catalyst according to claim 4, characterized in that The molar ratio of the magnesium alkoxide, the titanium compound, the organoaluminum compound, the olefin monomer, the organoaluminoxane and the metallocene compound is 1:(0.1-100):(0.1-100):(0.01-100):(0.1-100):(0.01-10); The organoaluminoxane includes at least one of methylaluminoxane and modified methylaluminoxane.

6. The bimetallic active site catalyst according to claim 3, characterized in that In formula 1 and formula 3, R 1 represents a C1~C5 alkyl group; In formula 2, R 2 、R 3 Each independently represents a C1~C5 alkyl group; In formula 4, R 4 represents a C1~C10 alkyl group; In formula 5, R 5 represents hydrogen or a C1~C8 straight-chain alkyl group; In formula 6, A 1 、A 2 Each independently represents a cyclopentadienyl group or a cyclopentadienyl group substituted by a C1 to C4 alkyl group, R 6 、R 7 Each independently represents a halogen atom, a C1~C2 alkyl group or a C1~C2 alkoxy group.

7. The bimetallic active site catalyst according to claim 6, characterized in that The alkoxy magnesium includes at least one of dimethoxy magnesium, diethoxy magnesium, dipropoxy magnesium, diisopropoxy magnesium, dibutoxy magnesium, diisobutoxy magnesium, methoxyethoxy magnesium, methoxypropoxy magnesium, ethoxypropoxy magnesium, ethoxyisopropoxy magnesium, ethoxybutoxy magnesium or ethoxyisobutoxy magnesium; The titanium compound includes at least one of titanium tetrachloride, titanium tetrabromide, titanium tetraiodide, methoxytitanium trichloride, ethoxytitanium trichloride, propoxytitanium trichloride, n-butoxytitanium trichloride, dimethoxytitanium dichloride, diethoxytitanium dichloride, dipropoxytitanium dichloride, di-n-butoxytitanium dichloride, trimethoxytitanium chloride, triethoxytitanium chloride, tripropoxytitanium chloride, triisopropoxytitanium chloride, tri-n-butoxytitanium chloride, tetraethoxytitanium, tetrapropoxytitanium or tetrabutoxytitanium; The organoaluminum compound includes at least one of triethylaluminum, tributylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, diethylaluminum monochloride, ethylaluminum dichloride or sesquiethylaluminum; The olefin monomer comprises at least one of ethylene, propylene, 1-butene, 1-hexene or 1-octene; The metallocene compounds include Cp2ZrCl2, Cp2TiCl2, Cp2HfCl2, Cp2TiMeCl, Cp2ZrMe2, Cp2TiMe2, (n-PrCp)2ZrCl2, (n-BuCp)2ZrCl2, (n-PrCp)2ZrMe2, (n-BuCp)2ZrMe2, [Et(Ind)2]ZrCl2, [Et(Ind)2]HfCl2, [Et(2,4,7-Me3 At least one of [Et(IndH4)2]ZrCl2, [Ph2CEt(Ind)(Cp)]ZrCl2, [Me2CEt(Ind)(Cp)]ZrCl2, [Me2CEt(Ind)(3-MeCp)]ZrCl2, [Ph2C(Flu)(Cp)]ZrCl2, [Me2C(Flu)(Cp)]ZrCl2 or [Me2C(Flu)(Cp)]HfCl2.

8. The method for preparing a bimetallic active center catalyst according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Under an inert atmosphere, adding magnesium alkoxide and a titanium compound to a solvent to carry out a titanium-supporting reaction to obtain a catalyst precursor; S2. Under an inert atmosphere, the catalyst precursor and the organoaluminum compound are added to a solvent, and after a reduction reaction, an olefin monomer is added to carry out a prepolymerization reaction to obtain a ZN catalyst; S3. Under an inert atmosphere, the ZN catalyst, the organoaluminoxane and the metallocene compound are sequentially added into a solvent to carry out a metallocene loading reaction to obtain a bimetallic active center catalyst.

9. The method for preparing a bimetallic active center catalyst according to claim 8, wherein: In S1, the temperature of the titanium loading reaction is -20°C to 150°C; In S2, the temperature of the reduction reaction is -20°C to 50°C; In S2, the temperature of the prepolymerization reaction is -20°C to 50°C, and the pressure of the prepolymerization reaction is 0 to 0.05 MPa; In S3, the temperature of the metallocene loading reaction is -20°C to 100°C.

10. Use of the bimetallic active center catalyst according to any one of claims 1 to 7 or the bimetallic active center catalyst prepared by the preparation method of the bimetallic active center catalyst according to any one of claims 8 to 9 in the preparation of olefin polymers.

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