Solid methylaluminoxane catalyst embedded in situ with metallocene and its preparation method and application

Abstract

The application belongs to the technical field of olefin polymerization, and particularly relates to a solid methylaluminoxane catalyst in-situ embedding a metallocene and a preparation method and application thereof. The preparation method comprises the following steps: (1) reacting trimethylaluminum and an unsaturated double bond-containing oxygen-containing organic compound in a toluene solvent to obtain a homogeneous methylaluminoxane precursor solution, and then performing a first heating reaction to obtain a first reaction liquid; (2) dissolving a metallocene compound in toluene to obtain a metallocene solution, and then adding the metallocene solution into the first reaction liquid and performing a second heating reaction to obtain a second reaction liquid; and (3) cooling the second reaction liquid, adding a poor solvent, and performing post-treatment to obtain the solid methylaluminoxane catalyst. The obtained solid methylaluminoxane catalyst is mainly used for olefin polymerization. The method effectively reduces the ash content of the polymer and inhibits the shedding of active components and the fouling of the reactor in the polymerization process.

Description

Technical Field

[0001] This invention belongs to the field of olefin polymerization technology, specifically relating to an in-situ embedded metallocene solid methylaluminoxane catalyst, its preparation method, and its application. Background Technology

[0002] Metallocene catalysts, due to their single active site characteristic, can be used to prepare polyolefin products with controllable microstructure and narrow molecular weight distribution, but they require the use of a co-catalyst (such as methylaluminoxane MAO). Traditional methods involve dissolving the main catalyst (metallocene compound) and the co-catalyst MAO in a solvent before use, but the resulting polymerization products have poor morphology and tend to stick to the reactor. Therefore, in industrial applications, homogeneous metallocene catalysts are generally supported.

[0003] Commonly used supported catalysts are inert solid inorganic supports such as silica, alumina, and magnesium chloride. These supports primarily bond with metallocenes and MAO through surface hydroxyl groups; however, this method significantly weakens the overall polymerization activity of the catalyst. To address this, researchers have developed solid methylaluminoxane (sMAO), a substance that can simultaneously act as a support and co-catalyst, derived from a supported catalytic system. CN102239187A discloses a method for preparing a solid polymethylaluminoxane composition, using trimethylaluminum as a raw material to prepare a homogeneous MAO solution, followed by heating and aging reactions, and post-treatment to obtain sMAO. This sMAO, when compounded with transition metal compounds, can be used for olefin polymerization catalysis.

[0004] However, the two-step method described above, which involves first preparing the sMAO support and then adsorbing the metallocene, suffers from several adverse consequences. Firstly, during polymerization, the sMAO particles possess a stable, dense cross-linked network with narrow pores, making it difficult for metallocene molecules to penetrate the particles. This results in the active components being physically adsorbed onto the particle surface. Secondly, the particle surface experiences intense expansion pressure as the polymer chains grow, causing the surface-loaded active centers to easily detach from the support and enter the solvent or gas phase, inducing severe reactor scaling and leading to low polymer bulk density and high fine powder content. Thirdly, the sMAO particle utilization rate is low, resulting in a small metallocene compound loading. The support contains a large amount of unbound sMAO, which lacks catalytic activity and agglomerates in the polymerization product, forming crystal points and causing inorganic ash residue in the polymer. Summary of the Invention

[0005] This invention provides a method for preparing a solid methylaluminoxane catalyst with in-situ embedded metallocene. First, trimethylaluminum and an oxygen-containing organic compound with unsaturated double bonds are heated once to generate a MAO precursor with double-bonded side chains. Then, metallocene is added and heated a second time to complete pre-activation. Finally, the mixture is cooled and a poor solvent is added to precipitate sMAO while simultaneously embedding the metallocene in situ to obtain a solid catalyst. This method eliminates the need for an external support and effectively solves the problem of active component detachment.

[0006] This invention proposes a method for preparing a solid methylaluminoxane catalyst with in-situ embedded metallocene, comprising the following steps:

[0007] (1) Under a protective atmosphere, trimethylaluminum and an oxygen-containing organic compound with unsaturated double bonds react in toluene solvent to obtain a homogeneous methylaluminoxane precursor solution, and then carry out a first heating reaction to obtain a first reaction solution. (2) Dissolve the metallocene compound in toluene to obtain a metallocene solution, add it to the first reaction solution above, and carry out a second heating reaction to obtain a second reaction solution; (3) After cooling the second reaction solution, add a poor solvent to induce the precipitation of solid methylaluminoxane particles. The metallocene compound is simultaneously embedded in the solid methylaluminoxane. After post-processing, the solid methylaluminoxane catalyst with metallocene embedded in situ is obtained.

[0008] Furthermore, in step (1), the general structural formula of the oxygen-containing organic compound containing unsaturated double bonds is R. 1 R 2 C=CR 3 –L–X; where R 1 R 2 and R 3 Each is independently selected from hydrogen atoms and C1–C6 straight-chain or branched alkyl groups; L is C1–C6. 12 The linking group of a straight-chain or branched alkylene group; X is selected from hydroxyl, carboxyl, or carbonyl –C(=O)R 4 , where R 4 It is a C1–C6 alkyl group; Preferably, the oxygen-containing organic compound containing an unsaturated double bond is selected from at least one of 4-penten-1-ol, 5-hexen-1-ol, 7-octen-1-ol, 5-hexenoic acid, and dimethyloctenone.

[0009] Further, in step (1), the molar ratio of aluminum atoms in trimethylaluminum to oxygen atoms in the oxygen-containing organic compound is 1.1~5 : 1; and / or, In step (1), trimethylaluminum and an oxygen-containing organic compound with unsaturated double bonds react in toluene solvent, specifically including: adding trimethylaluminum to toluene, cooling to 15°C, adding the oxygen-containing organic compound with unsaturated double bonds dropwise, controlling the system temperature not to exceed 15°C, mixing, and heating to room temperature for 10~30 min; and / or, In step (1), the temperature of the first heating reaction is 40-80℃, and the time of the first heating reaction is 16-48 hours.

[0010] Further, in step (2), the general structural formula of the metallocene compound is Cp′X n Cp"MQ2; where Cp′ and Cp" are unsubstituted or substituted cyclopentadienyl, indenyl or fluorenyl, X is a bridging group connecting Cp′ and Cp" and the bridging group is selected from C1-C4 carbon bridges or silicon bridges; n=0 or 1; M is zirconium (Zr) or hafnium (Hf); Q is halogen, alkyl or alkoxy.

[0011] Further, in step (2), the molar ratio of aluminum to transition metal in the metallocene compound in the methylaluminoxane precursor solution is (10-2000):1; and / or, In step (2), the temperature of the second heating reaction is 80-110℃, and the time of the second heating reaction is 8-24 hours.

[0012] Further, in step (3), the undesirable solvent is an aliphatic solvent; preferably, the aliphatic solvent is selected from at least one of n-hexane, pentane, cyclohexane, methylcyclohexane, heptane, or isoalkanes; and / or, In step (3), the amount of the undesirable solvent added is 2 to 6 times the total volume of the second reaction solution.

[0013] In step (3), the second reaction solution is cooled to 0-60°C, and the temperature does not exceed the boiling point of the unsuitable solvent.

[0014] The present invention also proposes an in-situ embedded metallocene solid methylaluminoxane catalyst prepared by any of the above preparation methods.

[0015] The present invention also proposes a method for olefin polymerization, comprising the following steps: Solvent, alkyl aluminum, and any of the above-described in-situ embedded metallocene solid methylaluminoxane catalysts are added to a polymerization reactor. After heating to the reaction temperature, ethylene is introduced to adjust the pressure, and then reactants are introduced to carry out the reaction and obtain the product.

[0016] Furthermore, the solvent includes at least one selected from n-hexane, cyclohexane, toluene, and dichloromethane; and / or, Alkyl aluminum includes at least one of triethylaluminum, trimethylaluminum, and triisobutylaluminum; and / or, The ratio of solid methylaluminoxane catalyst, solvent, and alkylaluminum used in in-situ embedded metallocene is 10-50 mg : 300-1000 mL : 1-5 mL; and / or, The reaction temperature is 50–90 °C, and the reaction time is 1–5 h; and / or, Adjust the pressure to 0.5~6 MPa.

[0017] Further, the olefin polymerization reaction includes ethylene homopolymerization or copolymerization of ethylene with C3-C10 α-olefins; and / or, The reaction raw materials include at least one of ethylene and α-olefin; and / or, The α-olefin is selected from at least one of propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or 1-decene.

[0018] This invention has the following advantages: This invention proposes a method for preparing a solid methylaluminoxane catalyst with in-situ embedded metallocene. The method employs an integrated in-situ embedding process. First, a low-molecular-weight MAO precursor with double-bonded side chains is prepared by reacting trimethylaluminum with an oxygen-containing organic compound containing unsaturated double bonds. A first heating reaction causes the precursor to undergo demethanization and crosslinking, forming a loose and porous oligomeric MAO network framework. Then, a metallocene compound is added, followed by a second heating reaction for pre-activation. Finally, a poor solvent is added at a lower temperature to precipitate solid methylaluminoxane, achieving simultaneous in-situ embedding of the metallocene. The oxygen-containing organic compound can assist in constructing the aluminoxane framework through oxygen-containing groups, rely on long aliphatic hydrocarbon chains to support the pores and prevent pore shrinkage, and utilize the double bonds to copolymerize with olefins during polymerization to achieve uniform and controllable disintegration of the support. This invention abandons the traditional two-step post-loading process of sMAO, requires no additional inorganic support, and effectively solves the problems of easy detachment of active components, low embedding rate, poor catalytic activity, and inorganic ash content in polymers associated with traditional catalysts. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a scanning electron microscope (SEM) image at 8000x magnification of the solid methylaluminoxane catalyst with in-situ embedded metallocene obtained in Example 1 of the present invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0022] This invention provides a method for preparing an in-situ embedded metallocene solid methylaluminoxane catalyst, comprising the following steps: (1) Under a protective atmosphere, trimethylaluminum and an oxygen-containing organic compound with unsaturated double bonds react in toluene solvent to obtain a homogeneous methylaluminoxane precursor solution, and then carry out a first heating reaction to obtain a first reaction solution. (2) Dissolve the metallocene compound in toluene to obtain a metallocene solution, add it to the first reaction solution above, and carry out a second heating reaction to obtain a second reaction solution; (3) After cooling the second reaction solution, add a poor solvent to induce the precipitation of solid methylaluminoxane particles. The metallocene compound is simultaneously embedded in the solid methylaluminoxane. After post-processing, the solid methylaluminoxane catalyst with metallocene embedded in situ is obtained.

[0023] The method for preparing a solid methylaluminoxane catalyst with in-situ metallocene encapsulation proposed in this invention involves the following steps: First, trimethylaluminum reacts with an oxygen-containing organic compound containing unsaturated double bonds to obtain a low-molecular-weight MAO precursor with double-bonded side chains. Then, through a first heating reaction, the precursor molecules undergo continuous demethylation and cross-linking to generate oligomeric MAO oligomers, forming a loose and porous aluminoxane molecular network that provides a skeletal basis for subsequent uniform encapsulation of the metallocene. Next, a metallocene compound is added, and a second heating reaction is performed to pre-activate the metallocene with MAO. Finally, cooling and the addition of a poor solvent cause the solid methylaluminoxane to precipitate, simultaneously encapsulating the metallocene in situ, thus obtaining the target solid catalyst.

[0024] In this reaction, oxygen-containing organic compounds with unsaturated double bonds play a key role. First, the oxygen-containing groups can promote the hydrolysis of trimethylaluminum. Second, the long aliphatic hydrocarbon chains of oxygen-containing organic compounds can act as supports, interspersed between aluminum oxide molecules, to prevent significant shrinkage of pores during subsequent cross-linking processes. Third, in the catalytic polymerization of olefins, the unsaturated double bonds can also act as anchoring sites, copolymerizing with olefins and promoting a uniform and controllable disintegration process of the support.

[0025] This method breaks away from the traditional approach of two-step loading of sMAO and metallocene compounds. It introduces oxygen-containing organic compounds with unsaturated double bonds and constructs an aluminum oxane three-dimensional framework with the metallocene active center embedded inside the solid methylaluminoxane through an in-situ integrated embedding preparation process. No additional inorganic support is required, which effectively solves key technical problems such as easy detachment of active components, high ash content, low catalytic activity, and poor embedding rate.

[0026] In step (1) of the present invention, trimethylaluminum and an oxygen-containing organic compound containing unsaturated double bonds undergo an intermolecular demethanization addition reaction to obtain a low molecular weight MAO precursor with double bond side chains. After heating and polycondensation, a reaction solution containing oligomeric MAO oligomers is obtained.

[0027] In one embodiment of the present invention, in step (1), the protective gas includes at least one of nitrogen, argon, and helium.

[0028] In one embodiment of the present invention, in step (1), the general structural formula of the oxygen-containing organic compound containing unsaturated double bonds is R. 1 R 2 C=CR 3 –L–X; where R 1 R 2 and R 3 Each is independently selected from hydrogen atoms and C1–C6 straight-chain or branched alkyl groups; L is C1–C6. 12 The linking group of a straight-chain or branched alkylene group; X is selected from hydroxyl (–OH), carboxyl (–COOH) or carbonyl –C(=O)R 4 , where R 4 It is a C1–C6 alkyl group.

[0029] In a preferred embodiment of the present invention, in step (1), the oxygen-containing organic compound containing unsaturated double bonds is selected from at least one of 4-penten-1-ol, 5-hexen-1-ol, 7-octen-1-ol, 5-hexenoic acid, and dimethyloctenone.

[0030] In a preferred embodiment of the present invention, in step (1), the molar ratio of aluminum atoms in trimethylaluminum to oxygen atoms in oxygen-containing organic compounds is 1.1~5:1.

[0031] In a preferred embodiment of the present invention, in step (1), trimethylaluminum and an oxygen-containing organic compound containing unsaturated double bonds react in toluene solvent, specifically including: adding trimethylaluminum to toluene, cooling to 15°C, adding an oxygen-containing organic compound containing unsaturated double bonds dropwise, controlling the system temperature not to exceed 15°C, mixing, and heating to room temperature for 10~30 min.

[0032] Preferably, the ratio of trimethylaluminum to toluene is 4~7g : 50g.

[0033] In a preferred embodiment of the present invention, in step (1), the temperature of the first heating reaction is 40-80°C and the time of the first heating reaction is 16-48 hours.

[0034] In step (2) of this embodiment, a metallocene compound is added to the reaction solution containing oligomeric MAO, and the MAO is pre-activated by a second heating reaction.

[0035] In one embodiment of the present invention, in step (2), the general structural formula of the metallocene compound is Cp′X. n Cp"MQ2; where Cp′ and Cp" are unsubstituted or substituted cyclopentadienyl, indenyl or fluorenyl, X is a bridging group connecting Cp′ and Cp" and the bridging group is selected from C1-C4 carbon bridges or silicon bridges, preferably ethylene bridges; n=0 or 1; M is a group IVB transition metal element, preferably Zr; Q is a halogen, alkyl or alkoxy, preferably chlorine.

[0036] In one embodiment of the present invention, in step (2), the molar ratio n(Al:Zr) of aluminum element in the methylaluminoxane precursor solution to transition metal element in the metallocene compound is (10-2000):1; preferably (30-500):1.

[0037] The ratio of transition metal elements to toluene in metallocene compounds is 0.5~1 mmol: 10~80 ml.

[0038] In one embodiment of the present invention, in step (2), the temperature of the second heating reaction is 80-110°C, and the time of the second heating reaction is 8-24 hours.

[0039] In step (3) of the present invention, the temperature is lowered and a poor solvent is added, and solid particles are simultaneously precipitated from the aluminum oxane crosslinking network. The metallocene ions are embedded in the pore framework in situ. After post-treatment (such as washing and drying), a self-supported sMAO metallocene solid catalyst with uniform internal loading and not easy to fall off is obtained.

[0040] In one embodiment of the present invention, in step (3), the undesirable solvent is an aliphatic solvent.

[0041] Preferably, in step (3), the aliphatic solvent is selected from at least one of n-hexane, pentane, cyclohexane, methylcyclohexane, heptane, or isoalkanes.

[0042] In one embodiment of the present invention, in step (3), the amount of the undesirable solvent added is 2 to 6 times the total volume of the second reaction solution.

[0043] In one embodiment of the present invention, in step (3), the second reaction solution is cooled to 0-60°C, and the temperature does not exceed the boiling point of the undesirable solvent.

[0044] In one embodiment of the present invention, the post-processing in step (3) specifically includes: filtering and separating the solid particles precipitated in step (3), washing, and vacuum drying to obtain the catalyst.

[0045] In one embodiment of the present invention, in step (3), the encapsulation rate of the metallocene active component zirconium in the in-situ encapsulated metallocene solid methylaluminoxane catalyst is ≥90%.

[0046] This invention also proposes in-situ embedded metallocene solid methylaluminoxane catalysts prepared by any of the above preparation methods.

[0047] This invention also provides a method for olefin polymerization, comprising the following steps: Solvent, alkyl aluminum, and in-situ embedded metallocene solid methylaluminoxane catalyst are added to a polymerization reactor. After heating to the reaction temperature, ethylene is introduced to adjust the pressure, and then reactants are introduced to carry out the reaction and obtain the product.

[0048] The polymerization process proposed in this invention not only significantly suppresses the problems of active component shedding and reactor scaling during polymerization and completely eliminates polymer ash, but also greatly improves catalyst activity. Furthermore, the resulting catalyst particles have regular morphology, more uniform active centers, and higher catalyst loading.

[0049] In one embodiment of the present invention, the solvent includes at least one selected from n-hexane, cyclohexane, toluene, and dichloromethane.

[0050] In one embodiment of the present invention, the alkylaluminum includes at least one selected from triethylaluminum, trimethylaluminum, and triisobutylaluminum. In this embodiment of the present invention, the role of adding alkylaluminum in the above-mentioned olefin polymerization reaction is to eliminate impurities in the system, synergistically activate and stabilize the cationic active centers.

[0051] In one embodiment of the present invention, the ratio of the in-situ embedded metallocene solid methylaluminoxane catalyst, solvent, and alkylaluminum is 10~50mg:300~1000mL:1~5ml.

[0052] In one embodiment of the present invention, the reaction temperature is 50~90 °C. The reaction time is 1~5 h.

[0053] In one embodiment of the present invention, the pressure is adjusted to 0.5~6 MPa.

[0054] In one embodiment of the present invention, the olefin polymerization reaction includes ethylene homopolymerization or copolymerization of ethylene with C3-C10 α-olefins.

[0055] In one embodiment of the present invention, the reaction raw materials include at least one of ethylene and α-olefin.

[0056] In one embodiment of the present invention, the α-olefin is selected from at least one of propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or 1-decene.

[0057] The present invention will now be described in detail with reference to the embodiments.

[0058] Example 1 (1) Under nitrogen protection, 6 g of trimethylaluminum (containing 83.3 mmol Al) and 50 g of toluene were added to the purged glass reactor, and the temperature was lowered to 15 °C. Under stirring, 10.3 ml of 4-penten-1-ol (the molar ratio of oxygen atoms in trimethylaluminum to 4-penten-1-ol was 1.2) was slowly added dropwise over 30 min, controlling the dropping rate to keep the system temperature below 15 °C. After the addition was complete, the mixture appeared as a white suspension. It was heated to room temperature and stirred for 20 min until the system was converted into a colorless, transparent, homogeneous methylaluminoxane precursor solution; then the temperature was slowly raised to 80 °C and heated for 28 h to obtain the first reaction solution. The Al content in the methylaluminoxane precursor solution was 0.52 wt%. (2) Dissolve 360 ​​mg of bis(1-n-butyl-3-methylcyclopentadienyl)zirconium dichloride (containing 0.833 mmol of zirconium), wherein the molar ratio of aluminum to transition metal in the methylaluminoxane precursor solution n(Al:Zr) = 100, in 30 ml of toluene to obtain a metallocene solution. Add the solution to the homogeneous solution after the reaction in step (1), and then heat to 100 °C for 8 h. The system remains homogeneous. (3) Cool the homogeneous solution after the reaction in step (2) to 20°C naturally, and slowly add 350 ml of n-hexane to it to form a pale yellow solid precipitate; filter to separate the precipitated solid particles, wash with 30 ml of n-hexane 3 times, filter, dry, and obtain 2.6 g of solid powder, which is the in-situ embedded metallocene solid methylaluminoxane catalyst.

[0059] Example 2 Same as Example 1, except that in step (2), 350 mg of rac-vinylbis(1-indenyl)zirconia (containing 0.833 mmol of zirconium) was weighed to replace 360 ​​mg of bis(1-n-butyl-3-methylcyclopentadienyl)zirconia (containing 0.833 mmol of zirconium), n(Al:Zr)=100, and it was dissolved in 50 ml of toluene and then added to the system.

[0060] Example 3 Same as Example 1, except that in step (2), 356 mg of rac-vinylbis(4,5,6,7-tetrahydro-1-indenyl)zirconia (containing 0.833 mmol of zirconium) was weighed to replace 360 ​​mg of bis(1-n-butyl-3-methylcyclopentadienyl)zirconia (containing 0.833 mmol of zirconium), n(Al:Zr)=100, and it was dissolved in 50 ml of toluene and then added to the system.

[0061] Examples 4-6 Similar to Example 1, except that the molar ratio n(Al:Zr) of aluminum in the homogeneous methylaluminoxane precursor solution to transition metal in the metallocene compound is controlled to be 200, 300, and 500, respectively.

[0062] Comparative Example 1 A supported metallocene catalyst Using an unsaturated double-bonded organic compound as the oxygen source, a solid methylaluminoxane support is first prepared, followed by loading a metallocene compound. The process includes the following steps: Preparation of methylaluminoxane support (free of metallocene compounds): Under nitrogen protection, 6 g of trimethylaluminum (containing 83.3 mmol Al) and 50 g of toluene were added to a purged glass reactor and cooled to 15 °C. 10.3 mL of 4-penten-1-ol (the molar ratio of oxygen atoms in trimethylaluminum to 4-penten-1-ol was 1.2) was slowly added dropwise with stirring, ensuring the system temperature did not exceed 15 °C. After stirring at room temperature for 20 min, the temperature was slowly increased to 80 °C and heated for 28 h, then heated at 100 °C for 8 h. After the reaction was complete, the system was naturally cooled to 20 °C. 350 mL of n-hexane was added to the homogeneous solution to induce the formation of a white solid precipitate. The precipitate was separated by filtration, washed with hexane, and dried under vacuum to obtain the solid methylaluminoxane support. The Al content in the solid methylaluminoxane support was 42.0 wt%.

[0063] Metallocene compound post-loading: 2.6 g of solid methylaluminoxane support was added to a three-necked flask and pre-dispersed in 30 ml of toluene; 175 mg of bis(1-n-butyl-3-methylcyclopentadienyl)zirconia dichloride dissolved in 30 ml of toluene was injected using a disposable syringe, n(Al:Zr)=100, and the reaction was mechanically stirred at room temperature for 2 hours. After the reaction was completed, the mixture was allowed to stand and separate into layers. The supernatant was exported and washed three times with n-hexane. Finally, the solid powder catalyst was obtained by vacuum drying.

[0064] Comparative Example 2 A supported metallocene catalyst Using benzoic acid as an oxygen source, metallocene compounds are in-situ embedded, including the following steps: Same as Example 1, except that 6.01g of benzoic acid (containing 99.96mmol O) was used instead of 4-penten-1-ol.

[0065] Comparative Example 3 A supported metallocene catalyst Using benzoic acid as the oxygen source, a solid methylaluminoxane support was first prepared, followed by loading a metallocene compound, including the following steps: Similar to Comparative Example 1, except that 6.01 g of benzoic acid (containing 99.96 mmol O) was used instead of 4-penten-1-ol in the reaction with trimethylaluminum solution.

[0066] Comparative Example 4 A supported metallocene catalyst The method involves loading metallocene compounds onto inorganic silica gel modified with MAO, including the following steps: 20 g of activated silica gel carrier (model 955, manufactured by Grace Company, USA) that has been calcined at 200 °C for 2 h and 600 °C for 4 h in a muffle furnace was added to a glass reactor purged with nitrogen. 30 ml of toluene was added, the system was heated to 50 °C, and 11 g of MAO (10 wt% toluene solution) was added dropwise. The mixture was stirred and impregnated for 4 hours. After filtration, the mixture was washed 3 times with 30 ml of toluene and then 2 times with hexane. The mixture was then dried to obtain a white carrier with good flowability.

[0067] Add 2g of the above-prepared carrier to a three-necked flask purged with nitrogen, add 20ml of toluene for dispersion, start stirring, add 46mg of bis(1-n-butyl-3-methylcyclopentadienyl)zirconium dichloride dissolved in 50ml of toluene at room temperature, n(Al:Zr)=100, mechanically stir the reaction for 2 hours, after the reaction is completed, let it stand to separate into layers, export the supernatant, add n-hexane for washing, repeat 3 times, vacuum dry to obtain solid powder catalyst.

[0068] Experimental Example 1 Slurry polymerization experiment The solid catalysts obtained in the examples and comparative examples were subjected to slurry polymerization reactions, respectively. In a 1-liter glass reactor, a vacuum and nitrogen-filling process was performed, repeated three to four times. Under nitrogen purging, 500 ml of n-hexane and 3 ml of triethylaluminum were sequentially injected into the reactor. After stirring for 5 minutes, 20 mg of solid catalyst was injected. The venting valve was opened to purge the residual nitrogen in the reactor. All valves were closed, and the temperature was raised to 80°C. Ethylene gas was then introduced to 1.0 MPa. After reacting for 1 hour, the ethylene supply was stopped. The product was then cooled, settled, filtered, and vacuum dried to obtain polyethylene.

[0069] Test Example 1 (1) Product Characterization Figure 1 This is a scanning electron microscope (SEM) image at 8000x magnification of the solid methylaluminoxane catalyst sample with in-situ embedded metallocene obtained in Example 1 of this application.

[0070] (2) Catalytic activity determination The catalytic activity of different catalysts in Experiment Example 1 above was tested. The catalytic activity was calculated as the mass of polyethylene produced per gram of catalyst per hour. The results are shown in Table 1.

[0071] (3) Inductively Coupled Plasma Mass Spectrometry (ICP-MS) Analysis The weight percentage of metals in the supported metallocene catalyst was quantitatively determined. A Thermo Fisher iCAPQ inductively coupled plasma mass spectrometer was used for the analysis, and the results are shown in Table 1.

[0072] (4) Determination of zirconium encapsulation rate Multiply the total mass of the obtained solid catalyst by the zirconium mass percentage detected by ICP to obtain the actual total mass of zirconium element loaded. Divide this by 100% of the theoretical total mass of zirconium element initially added to calculate the specific encapsulation rate.

[0073] Encapsulation rate = (mass of obtained solid catalyst × mass percentage of zirconium in solid catalyst) / total mass of zirconium element input × 100%. The results are shown in Table 1.

[0074] (5) Characterization of polymer molecular weight distribution Molecular weight distribution (Mw / Mn) was determined by high-temperature gel permeation chromatography (GPC) using an Agilent PL220 instrument. The mobile phase was 1,2,4-trichlorobenzene, the test temperature was 150 ℃, the sample concentration was 1.0 mg / mL, and the flow rate was 1.0 mL / min. The results are shown in Table 1.

[0075] Table 1 shows the aggregation results data for each embodiment and comparative example. serial number Zirconium content in catalyst (wt%) Encapsulation rate (%) <![CDATA[catalytic activity gPE·(gcat) -1 > Mw / Mn Example 1 2.70 92.5 2500 2.3 Example 2 2.68 94.8 3200 3.2 Example 3 2.73 92.4 2836 3.0 Example 4 1.40 95.2 2305 2.3 Example 5 0.94 95.9 1855 2.2 Example 6 0.56 97.4 1581 2.3 Comparative Example 1 0.85 35.6 1326 2.3 Comparative Example 2 0.60 22.5 1121 2.3 Comparative Example 3 0.52 15.0 1030 2.2 Comparative Example 4 0.35 42.5 800 2.6 As can be seen from the table, when using traditional post-loading methods, traditional oxygen sources, or inorganic silica supports (such as Comparative Examples 1-4), the lack of flexible aliphatic hydrocarbon chains to support the precipitation process of the support network leads to a tendency for the framework structure to shrink and collapse. Furthermore, the significant diffusion resistance in the post-loading process severely limits the loading and encapsulation efficiency of metallocenes, resulting in a substantial decrease in catalytic activity. For inorganic silica support systems, the activity is low, and silica easily introduces inorganic ash residues. This invention, by introducing long-chain double-bonded compounds to maintain the openness of the framework network and combining this with an in-situ synchronous co-precipitation mechanism, improves the encapsulation efficiency and catalytic activity of metallocenes, while avoiding the introduction of ash due to the addition of an inorganic support, demonstrating promising application prospects.

[0076] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a solid methylaluminoxane catalyst with in-situ embedded metallocene, characterized in that, Includes the following steps: (1) Under a protective atmosphere, trimethylaluminum and an oxygen-containing organic compound with unsaturated double bonds react in toluene solvent to obtain a homogeneous methylaluminoxane precursor solution, and then carry out a first heating reaction to obtain a first reaction solution. (2) Dissolve the metallocene compound in toluene to obtain a metallocene solution, add it to the first reaction solution above, and carry out a second heating reaction to obtain a second reaction solution; (3) After cooling the second reaction solution, add a poor solvent to induce the precipitation of solid methylaluminoxane particles. The metallocene compound is simultaneously embedded in the solid methylaluminoxane. After post-processing, the solid methylaluminoxane catalyst with metallocene embedded in situ is obtained.

2. The preparation method according to claim 1, characterized in that, In step (1), the general structural formula of oxygen-containing organic compounds containing unsaturated double bonds is R. 1 R 2 C=CR 3 –L–X; where R 1 R 2 and R 3 Each is independently selected from hydrogen atoms and C1–C6 straight-chain or branched alkyl groups; L is C1–C6. 12 The linking group of a straight-chain or branched alkylene group; X is selected from hydroxyl, carboxyl, or carbonyl –C(=O)R 4 , where R 4 It is a C1–C6 alkyl group; Preferably, the oxygen-containing organic compound containing an unsaturated double bond is selected from at least one of 4-penten-1-ol, 5-hexen-1-ol, 7-octen-1-ol, 5-hexenoic acid, and dimethyloctenone.

3. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of aluminum atoms in trimethylaluminum to oxygen atoms in the oxygen-containing organic compound is 1.1~5 : 1; and / or, In step (1), trimethylaluminum and an oxygen-containing organic compound with unsaturated double bonds react in toluene solvent, specifically including: adding trimethylaluminum to toluene, cooling to 15°C, adding the oxygen-containing organic compound with unsaturated double bonds dropwise, controlling the system temperature not to exceed 15°C, mixing, and heating to room temperature for 10~30 min; and / or, In step (1), the temperature of the first heating reaction is 40-80℃, and the time of the first heating reaction is 16-48 hours.

4. The preparation method according to claim 1, characterized in that, In step (2), the general structural formula of the metallocene compound is Cp′X n Cp"MQ2; where Cp′ and Cp" are unsubstituted or substituted cyclopentadienyl, indenyl or fluorenyl, X is a bridging group connecting Cp′ and Cp" and the bridging group is selected from C1-C4 carbon bridges or silicon bridges; n=0 or 1; M is zirconium or hafnium; Q is halogen, alkyl or alkoxy.

5. The preparation method according to claim 1, characterized in that, In step (2), the molar ratio of aluminum to transition metal in the metallocene compound in the methylaluminoxane precursor solution is (10-2000):1; and / or, In step (2), the temperature of the second heating reaction is 80-110℃, and the time of the second heating reaction is 8-24 hours.

6. The preparation method according to claim 1, characterized in that, In step (3), the undesirable solvent is an aliphatic solvent; preferably, the aliphatic solvent is selected from at least one of n-hexane, pentane, cyclohexane, methylcyclohexane, heptane, or isoalkanes; and / or, In step (3), the second reaction solution is cooled to 0-60°C, and the temperature does not exceed the boiling point of the unsuitable solvent.

7. The in-situ embedded metallocene solid methylaluminoxane catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. A method for olefin polymerization, characterized in that, Includes the following steps: Solvent, alkyl aluminum, and the in-situ embedded metallocene solid methylaluminoxane catalyst prepared according to claim 7 are added to a polymerization reactor. After heating to the reaction temperature, ethylene is introduced to adjust the pressure, and then reactants are introduced to carry out the reaction and obtain the product.

9. The method according to claim 8, characterized in that, Solvents include at least one of n-hexane, cyclohexane, toluene, and dichloromethane; and / or, Alkyl aluminum includes at least one of triethylaluminum, trimethylaluminum, and triisobutylaluminum; and / or, The ratio of solid methylaluminoxane catalyst, solvent, and alkylaluminum used in in-situ embedded metallocene is 10-50 mg : 300-1000 mL : 1-5 mL; and / or, The reaction temperature is 50–90 °C, and the reaction time is 1–5 h; and / or, Adjust the pressure to 0.5~6 MPa.

10. The method according to claim 8, characterized in that, The olefin polymerization reaction includes ethylene homopolymerization or copolymerization of ethylene with C3-C10 α-olefins; and / or, The reaction raw materials include at least one of ethylene and α-olefin; and / or, The α-olefin is selected from at least one of propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or 1-decene.

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