A process for the preparation of a gel-resistant solution of methylaluminoxane

Abstract

The application relates to a preparation method of a gel-resistant methylaluminoxane solution and belongs to the technical field of olefin coordination polymerization catalysts. Steps are as follows: 1) preparing crude trimethylaluminum: methylaluminum sesquichloride is prepared by the reaction of an initiator-promoted aluminum powder and chloromethane; after nuclear magnetic quantitative determination, molten sodium is added, 70% to 99% of the methylaluminum sesquichloride is controlled to be reduced into trimethylaluminum, and a crude liquid is obtained; 2) low-temperature hydrolysis polymerization: the crude liquid is added with an organic solvent, oxygen-carrying water vapor inert gas is passed, and hydrolysis polymerization is carried out at-20 DEG C to 10 DEG C; the methylaluminum sesquichloride is partially reacted, and the unreacted state and the product thereof are mixed to be used as a stabilizer; and the product is obtained after treatment. The application breaks through the technical prejudice that the less the impurities are, the better the product is, uses the dual mechanisms of the original state and the derived state to inhibit gel, and solves the problems of unstable storage of the existing methylaluminoxane solution, high storage and transportation cost, and the like.

Description

Technical Field

[0001] This invention belongs to the technical field of olefin coordination polymerization catalysts in chemical products, specifically a method for preparing an anti-gelling methylaluminoxane solution. Background Technology

[0002] Polyolefin materials possess excellent comprehensive properties and have extremely high commercial and scientific research value. Therefore, research on metallocene catalysts used in olefin polymerization has been continuously advancing both domestically and internationally. Currently, the core research direction for metallocene catalysts focuses on improving catalytic efficiency and stereoselectivity, aiming to prepare high-performance polyolefin products with excellent mechanical properties, chemical stability, and thermal stability through low-concentration catalytic systems. Methylaluminoxane is an indispensable and crucial cocatalyst in metallocene catalytic systems. Existing methylaluminoxane preparation processes are mainly divided into two types: direct water preparation processes and indirect water preparation processes.

[0003] However, existing preparation processes have significant technical flaws. Regardless of the process used, the methylaluminoxane solution exhibits poor storage stability. After two weeks of storage, colorless, transparent microparticles and gels form inside the solution, some suspended in the solution system and others adhering to the inner wall of the container. Even with low-temperature storage, the inhibition of gel formation remains limited. After more than four weeks of storage, particle and gel precipitation inevitably occurs, severely impacting the performance and storage life of the methylaluminoxane solution.

[0004] The precipitation of microparticles and gels in methylaluminoxane solutions can have adverse effects in several ways, hindering the industrial application of the product. Firstly, the formation of gels and solid particles significantly reduces the catalytic activity of methylaluminoxane in olefin polymerization, while also causing uneven solute dispersion and decreased overall fluidity within the solution. This directly impacts the quality and production stability of polyolefin products, reduces production capacity, and leads to significant economic losses for enterprises. Secondly, suppressing gel formation requires low-temperature transportation and storage conditions, significantly increasing product storage and transportation costs. Furthermore, the methylaluminoxane material adhering to the inner walls of storage tanks cannot be properly removed, making subsequent equipment cleaning difficult and cumbersome, resulting in material waste, product loss, and further increasing production and maintenance costs. Summary of the Invention

[0005] In view of the above-mentioned problems in the prior art, the purpose of this invention is to design a technical solution for preparing an anti-gelling methylaluminoxane solution, which improves the long-term storage stability of methylaluminoxane by controlling the residual amount of methyl sesquialuminum in the preparation stage of trimethylaluminum, while maintaining excellent catalytic activity.

[0006] The method for preparing an anti-gelling methylaluminoxane solution is characterized by comprising the following steps: 1) Preparation of crude trimethylaluminum by initiating reaction: Using an initiator as a reaction aid, aluminum powder reacts with chloromethane to generate methyl sesquialuminum. The content of methyl sesquialuminum in the system is determined by chemical titration. Based on this, the theoretical amount of sodium metal to be fed is calculated. Molten sodium metal is added dropwise, and the reducing property of sodium metal is used to reduce 70% to 99% of the methyl sesquialuminum in the system to trimethylaluminum. The unreduced methyl sesquialuminum remains in the system. Impurities and organic solvents are removed by distillation to obtain a trimethylaluminum organic solution containing a small amount of methyl sesquialuminum. The methyl sesquialuminum is dimethylaluminum monochloro and / or dimethylaluminum dichloro, and the molar ratio of aluminum content of methyl sesquialuminum to trimethylaluminum in the organic solution is 0.2 to 20: 70 to 100. 2) Low-temperature preparation of methylaluminoxane solution: Add organic solvent to the trimethylaluminum organic crude liquid containing a small amount of methyl sesquialuminum obtained in step 1), and stir until the system is uniformly mixed; continuously pass an inert gas carrying deoxygenated deionized water or distilled water vapor, and carry out a hydrolysis polymerization reaction at -25℃ to 10℃. The methyl sesquialuminum partially participates in the hydrolysis polymerization reaction, and remains in the system as an anti-gelling stabilizer in the form of the remaining unreacted form and the mixture of its reaction products, thus synthesizing crude methylaluminoxane; after the reaction is completed, the system is successively filtered and subjected to vacuum distillation to remove residual impurities and some organic solvent, and finally obtains a methylaluminoxane solution with anti-gelling properties; wherein, the molar ratio of the mixture as an anti-gelling stabilizer to the aluminum content of the methylaluminoxane structural unit is 0.1 to 30:100.

[0007] The method for preparing an anti-gelling methylaluminoxane solution is characterized in that, in step 1): chemical titration is performed, assuming that dimethylaluminum chloride and dimethylaluminum chloride are a mol and b mol respectively, the total aluminum content is determined by EDTA back titration, and the chloride ion content is determined by silver nitrate titration. ， Calculate the molar amounts of monochlorodimethylaluminum and dichloromonomethylaluminum, and then calculate the mass of sodium metal required to reduce a specified proportion of methylsesquialuminum to trimethylaluminum according to the stoichiometric relationship.

[0008] The method for preparing an anti-gelling methylaluminoxane solution is characterized in that, in step 1), 90% to 98% of the methyl sesquialuminum in the system is reduced to trimethylaluminum.

[0009] The method for preparing an anti-gelling methylaluminoxane solution is characterized in that, in step 1), the initiator is iodoethane or iodomethane; and the reaction temperature of the aluminum powder with chloromethane is 100℃~160℃, preferably 120℃~140℃.

[0010] The method for preparing an anti-gelling methylaluminoxane solution is characterized in that, in step 2), the organic solvent is at least one of C6-C20 saturated alkanes, cycloalkanes, and aromatic hydrocarbons, preferably at least one of hexane, heptane, cyclohexane, toluene, and decane.

[0011] The method for preparing an anti-gelling methylaluminoxane solution is characterized in that, in step 2), the molar ratio of trimethylaluminum to water is 3:1 to 1:2.

[0012] The method for preparing an anti-gelling methylaluminoxane solution is characterized in that, in step 2), the inert gas is nitrogen or argon, and the inert gas flow rate is 0.2 mL / min to 4 mL / min, preferably 1 mL / min to 2 mL / min; the hydrolysis reaction rate is controlled by adjusting the amount of water carried by the inert gas.

[0013] The method for preparing an anti-gelling methylaluminoxane solution is characterized in that, in step 2), the temperature of the hydrolysis polymerization reaction is controlled at -20℃ to 0℃, preferably -15℃ to -5℃, and the reaction time is 3-5h; the concentration of the trimethylaluminum organic crude liquid in the organic solvent after preparation is 1-5mol / L, preferably 2-3mol / L.

[0014] The method for preparing an anti-gelling methylaluminoxane solution is characterized in that, in step 2), the molar ratio of the mixture used as an anti-gelling stabilizer to the aluminum content of the methylaluminoxane structural unit is 1-15:100, preferably 2-5:100.

[0015] The method for preparing an anti-gelling methylaluminoxane solution is characterized in that: the prepared methylaluminoxane solution does not precipitate gel after being stored at 25°C in the dark for 8 weeks, or only has trace amounts of insoluble particles, and its catalytic activity for olefin polymerization after 8 weeks of storage remains at more than 90% of that of a fresh sample.

[0016] In the hydrolysis polymerization process of step 2) of this invention, the small amount of methyl sesquialuminum contained in the trimethylaluminum organic solution obtained in step 1) exhibits different reaction characteristics from trimethylaluminum. Specifically, some methyl sesquialuminum undergoes hydrolysis under low temperature and trace water conditions to generate an intermediate containing Al–O-Al bonds and residual Al–Cl bonds. This intermediate further undergoes co-condensation with the hydrolysis products of trimethylaluminum, changing the MAO polymerization pathway and forming chlorinated aluminum oxygen structural units embedded in the methylaluminoxane molecular chain. At the same time, some methyl sesquialuminum remains in its original chemical form due to being in a local low water concentration environment or not being sufficiently exposed to water vapor, and does not participate in the hydrolysis polymerization reaction.

[0017] Therefore, in the final methylaluminoxane solution, the actual anti-gelling stabilizer is the mixture of unreacted pristine methyl sesquialuminum molecules and the methyl sesquialuminum reaction products. The pristine methyl sesquialuminum molecules preferentially passivate trace active hydroxyl groups in the system by providing Lewis acid centers and coordination unsaturated sites, and coordinate or react with the active aluminum centers at the ends of MAO oligomer chains, blocking excessive bridging polymerization between MAO oligomers. Meanwhile, the chlorinated aluminum oxide structural units inhibit the three-dimensional cross-linking of aluminum oxide segments through steric hindrance and charge regulation. This dual stabilization mechanism of the pristine and derived states enables the product of this invention to exhibit significantly superior anti-gelling performance compared to traditional processes during long-term storage.

[0018] This invention achieves the following unexpected technical effects by deliberately retaining 70%–99% reduced methyl sesquialuminum in the trimethylaluminum preparation process and utilizing the aforementioned dual stabilization mechanism: 1) Steric hindrance effect: The Cl atom in the reaction product of methyl sesquialuminum introduces aluminum oxide segments, which have greater steric hindrance than pure methyl aluminum oxide segments. This can disrupt the regular chain or cage-like arrangement of MAO, increase the flexibility and disorder of molecular chains, and hinder the excessive cross-linking and aggregation between aluminum oxide segments, thereby kinetically inhibiting the formation of a three-dimensional network gel structure.

[0019] 2) Charge balance regulation: The electron-withdrawing effect of Cl atoms can reduce the Lewis acidity of local aluminum centers, reduce the tendency of self-association between aluminum centers, and improve the thermodynamic stability of the system.

[0020] 3) Impurity anchoring effect: Unreacted virgin methyl sesquialuminum can preferentially coordinate with trace amounts of water and hydroxyl impurities in the system, preventing these impurities from initiating irreversible cross-linking reactions of methyl aluminum oxane.

[0021] 4) Overcoming Technical Bias: This invention overcomes the technical bias in the field that fewer impurities are always better, and for the first time clearly defines the stabilizing role of methyl sesquialuminum in the methylaluminoxane system. Experiments show that when the reduction degree is controlled within the range of 90% to 95%, the catalytic activity of the fresh sample is even slightly higher than that of the sample with completely removed impurities. This is because an appropriate amount of Cl atoms can help activate the active centers of the metallocene main catalyst. While ensuring catalytic activity, this invention extends the gel induction period of methylaluminoxane from the conventional 2 weeks to more than 8 weeks, and the catalytic activity remains above 94% of that of the fresh sample after 8 weeks, far superior to the comparative example with completely removed sesquialuminum (only 52% of the activity was retained after 8 weeks). Detailed Implementation

[0022] The present invention will be further described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0023] 1) In a decane solvent system, at 120°C, 2g of iodoethane was added to 100g of aluminum powder, and sufficient chloromethane was introduced. The content of methyl sesquialuminum in the reaction system was accurately determined by nuclear magnetic resonance detection, and the amount of metallic sodium was accurately calculated accordingly, so that 90% of the aluminum component in the methyl sesquialuminum system was reduced to trimethylaluminum. After the reaction was completed, the impurities and decane solvent in the system were removed by a 130°C distillation process to obtain a trimethylaluminum solution containing the methyl sesquialuminum component. 2) Accurately weigh 72g of the above-mentioned trimethylaluminum solution containing methyl sesquialuminum and prepare a homogeneous mixture in 450g of toluene solvent. Transfer the resulting mixture to the second reaction vessel. Set the stirring speed in the reaction vessel to 800r / min and the initial temperature to -10℃. Slowly introduce 11.4g of distilled water into the reaction vessel system with nitrogen gas. By adjusting the nitrogen gas flow rate to 2L / min in real time, strictly control the temperature of the reaction system to never exceed 0℃. After all the distilled water has been introduced into the system and has fully reacted with the trimethylaluminum toluene solution, close the nitrogen gas valve and continue to keep the reaction at a constant temperature for 4h to synthesize crude methylaluminoxane. After the reaction, filter the resulting system and remove some of the solvent by vacuum distillation to finally obtain a methylaluminoxane solution with excellent anti-gelling properties. Example 2

[0024] 1) In a decane solvent system, at 130°C, 4g of iodoethane was added to 100g of aluminum powder, and sufficient chloromethane was introduced. The content of methyl sesquialuminum in the reaction system was accurately determined by nuclear magnetic resonance detection, and the amount of metallic sodium was accurately calculated accordingly, so that 93% of the aluminum component in the methyl sesquialuminum system was reduced to trimethylaluminum. After the reaction was completed, impurities and decane solvent in the system were removed by distillation at 150°C to obtain a trimethylaluminum solution containing the methyl sesquialuminum component. 2) Accurately weigh 72g of the above-mentioned trimethylaluminum solution containing methyl sesquialuminum and prepare a homogeneous mixture in 400g of toluene solvent. Transfer the resulting mixture to the second reactor. Set the stirring speed in the reactor to 1000r / min and the initial temperature to -15℃. Slowly introduce 11g of distilled water into the reactor system with nitrogen gas. By adjusting the nitrogen gas flow rate to 3L / min in real time, strictly control the temperature of the reaction system to never exceed -5℃. After all the distilled water has been introduced into the system and has fully reacted with the trimethylaluminum toluene solution, close the nitrogen gas valve and continue to keep the reaction at a constant temperature for 2h to synthesize crude methylaluminoxane. After the reaction, filter the resulting system and remove some of the solvent by vacuum distillation to finally obtain a methylaluminoxane solution with excellent anti-gelling properties. Example 3

[0025] 1) In a decane solvent system, at 150°C, 3g of iodoethane was added to 100g of aluminum powder, and sufficient chloromethane was introduced. The content of methyl sesquialuminum in the reaction system was accurately determined by nuclear magnetic resonance detection, and the amount of metallic sodium was accurately calculated accordingly, so that 95% of the aluminum component in the methyl sesquialuminum system was reduced to trimethylaluminum. After the reaction was completed, impurities and decane solvent in the system were removed by a 150°C distillation process to obtain a trimethylaluminum solution containing the methyl sesquialuminum component. 2) Accurately weigh 72g of the above-mentioned trimethylaluminum solution containing methyl sesquialuminum and prepare a homogeneous mixture in 428g of toluene solvent. Transfer the resulting mixture to the second reaction vessel. Set the stirring speed in the reaction vessel to 1200r / min and the initial temperature to -5℃. Slowly introduce 10.3g of distilled water into the reaction vessel system with nitrogen gas. By adjusting the nitrogen gas flow rate to 1.5L / min in real time, strictly control the temperature of the reaction system to never exceed 5℃. After all the distilled water has been introduced into the system and has fully reacted with the trimethylaluminum toluene solution, close the nitrogen gas valve and continue to keep the reaction at a constant temperature for 5h to synthesize crude methylaluminoxane. After the reaction, filter the resulting system and remove some of the solvent by vacuum distillation to finally obtain a methylaluminoxane solution with excellent anti-gelling properties. Example 4

[0026] 1) In a decane solvent system, at 120°C, 5g of iodoethane was added to 100g of aluminum powder, and sufficient chloromethane was introduced. The content of methyl sesquialuminum in the reaction system was accurately determined by nuclear magnetic resonance detection, and the amount of metallic sodium was accurately calculated accordingly, so that 98% of the aluminum component in the methyl sesquialuminum system was reduced to trimethylaluminum. After the reaction was completed, impurities and decane solvent in the system were removed by distillation at 135°C to obtain a trimethylaluminum solution containing the methyl sesquialuminum component. 2) Accurately weigh 72g of the above-mentioned trimethylaluminum solution containing methyl sesquialuminum and prepare a homogeneous mixture in 500g of toluene solvent. Transfer the resulting mixture to the second reaction vessel. Set the stirring speed in the reaction vessel to 1500r / min and the initial temperature to -20℃. Slowly introduce 13.3g of distilled water into the reaction vessel system with nitrogen gas. By adjusting the nitrogen gas flow rate to 4L / min in real time, strictly control the temperature of the reaction system to never exceed -5℃. After all the distilled water has been introduced into the system and has fully reacted with the trimethylaluminum toluene solution, close the nitrogen gas valve and continue to keep the reaction at a constant temperature for 4h to synthesize crude methylaluminoxane. After the reaction, filter the resulting system and remove some of the solvent by vacuum distillation to finally obtain a methylaluminoxane solution with excellent anti-gelling properties.

[0027] Comparative Example 1) In a decane solvent system, at 130°C, 3g of iodoethane was added to 100g of aluminum powder, sufficient chloromethane was introduced, and 260g of molten sodium was added dropwise to reduce methyl sesquialuminum to trimethylaluminum. After the reaction was completed, impurities and decane solvent in the system were removed by distillation at 130°C to obtain trimethylaluminum.

[0028] 2) Accurately weigh 72g of the above-mentioned trimethylaluminum and 430g of toluene solvent to prepare a homogeneous mixed solution, and transfer the obtained mixed solution to the second reaction vessel; set the stirring speed in the reaction vessel to 1000r / min, the initial temperature to -10℃, and slowly introduce 14.4g of distilled water into the reaction vessel system with nitrogen gas. By adjusting the nitrogen gas flow rate to 2.5L / min in real time, strictly control the temperature of the reaction system to never exceed 0℃; after all the distilled water has been introduced into the system and fully reacted with the trimethylaluminum toluene solution, close the nitrogen gas valve and continue to keep the reaction at a constant temperature for 4h; after the reaction is completed, filter the obtained system and remove some of the solvent by vacuum distillation to finally obtain a methylaluminoxane solution.

[0029] Application Example 1 Using 5.5 g of 10% wt methylaluminoxane solution prepared in Examples 1-4 and the comparative example as a co-catalyst, and 10 mg of pentamethylcyclopentadienyl titanium trichloride as the main catalyst, the polymerization reaction was carried out with 50 mL of styrene for 2 hours under a nitrogen atmosphere and at an experimental temperature of 60 °C to obtain isotropic polystyrene.

[0030] Application Example 2 After storing the 10%wt methylaluminoxane solution prepared in Examples 1-4 and the comparative examples at room temperature for two weeks, 5.5g of the solution was used as a co-catalyst, and 8mg of pentamethylcyclopentadienyl titanium trichloride was used as the main catalyst. The solution was polymerized with 50mL of styrene under a nitrogen atmosphere and at an experimental temperature of 40℃ for 4 hours to obtain isotropic polystyrene.

[0031] Application Example 3 After storing the 10%wt methylaluminoxane solution prepared in Examples 1-4 and the comparative examples at room temperature for four weeks, 5.5g of the solution was used as a co-catalyst, and 8.5mg of pentamethylcyclopentadienyl titanium trichloride was used as the main catalyst. The solution was polymerized with 50mL of styrene under a nitrogen atmosphere at an experimental temperature of 55℃ for 3 hours to obtain isotropic polystyrene.

[0032] Application Example 4 After storing the 10%wt methylaluminoxane solution prepared in Examples 1-4 and the comparative examples at room temperature for six weeks, 5.5g of the solution was used as a co-catalyst, and 12mg of pentamethylcyclopentadienyl titanium trichloride was used as the main catalyst. The solution was polymerized with 50mL of styrene under a nitrogen atmosphere and at an experimental temperature of 45℃ for 4 hours to obtain isotropic polystyrene.

[0033] Application Example 5 After storing the 10%wt methylaluminoxane solution prepared in Examples 1-4 and the comparative examples at room temperature for eight weeks, 5.5g of the solution was used as a co-catalyst, and 10mg of pentamethylcyclopentadienyl titanium trichloride was used as the main catalyst. The solution was polymerized with 50mL of styrene under a nitrogen atmosphere at an experimental temperature of 50℃ for 3 hours to obtain isotropic polystyrene.

[0034] The following experimental data further demonstrates the beneficial effects of the present invention.

[0035] Experiment 1: The polymerization activity and yield of olefins prepared by the samples of Examples 1-4 and the comparative examples are shown in Table 1.

[0036] Table 1. Comparison of polymerization activity and yield in olefin preparation of Examples 1-4 and comparative examples.

[0037] As can be seen from Application Example 1 in Table 1, the presence of a portion of methyl sesquialuminum and its intermediates does not significantly affect the polymerization of olefins. Table 1 shows that, within 0-8 weeks, the polymerization activity and yield of methylaluminoxane solutions containing methyl sesquialuminum and its hydrolysis intermediates remained relatively stable over time during olefin preparation. This was particularly true for methylaluminoxane solutions prepared by hydrolysis of 93%–95% methyl sesquialuminum after reduction to trimethylaluminum. While methylaluminoxane solutions prepared by hydrolysis of 100% methyl sesquialuminum after reduction to trimethylaluminum initially exhibited the best polymerization activity and yield for olefin preparation, these decreased slightly in the second week, and the decrease became more pronounced after the third week. This indicates that a small amount of sesquialuminum in the methylaluminoxane solution has almost no impact on the polymerization activity and yield of olefins; on the contrary, it effectively extends the storage time, maintaining the polymerization activity and yield of olefins without significant changes.

[0038] Experiment 2: Gelation Time Test Take the 10wt% methylaluminoxane solutions prepared in Examples 1-4 and the comparative examples, place them at 25°C in a dark environment, and observe the time for gel formation. The results are shown in Table 2 below: Table 2. Gelation time test results for 10 wt% methylaluminoxane solutions prepared in Examples 1-4 and Comparative Examples.

[0039] Table 2 shows that the comparative methylaluminoxane solution gelled after 14 days of storage at room temperature, and by 8 weeks, a large amount of gel had formed and the fluidity had been lost. In contrast, the gelation time for Examples 1-4 was extended to 56-68 days, and by 8 weeks, no macroscopic gel had formed, with only trace amounts of insoluble particles present. This indicates that by controlling the reduction of sesquialuminum to 70%-99% during the trimethylaluminum synthesis stage, methylsesquialuminum remains in the final system as a mixed stabilizer, kinetically inhibiting the three-dimensional cross-linking of aluminum oxide segments can be effectively achieved. This extends the gelation induction period of methylaluminoxane from the conventional 2 weeks to more than 8 weeks, demonstrating a significant anti-gelling effect.

[0040] Experiment 3: Effect of different reduction degrees on catalytic activity. Using pentamethylcyclopentadienyl titanium trichloride as the main catalyst, the fresh catalytic activity of methylaluminoxanes prepared with different reduction degrees was investigated. The results are shown in Table 3 below: Table 3. Fresh catalytic activity test results of methylaluminoxanes prepared with different reduction degrees.

[0041] Table 3 shows that when the reduction degree of methyl sesquialuminum is controlled within the range of 70% to 99%, the fresh catalytic activity of the obtained methylaluminoxane is 94.5% to 99.3% of that of the comparative example (100% reduction); especially in the reduction degree range of 90% to 98%, the catalytic activity is comparable to or even slightly improved compared to the pure product. This indicates that the long-standing technical bias in the field that lower sesquialuminum impurities are always better is not valid. An appropriate amount of residual methyl sesquialuminum not only does not impair catalytic performance, but the chlorine atoms therein can also help activate the active centers of metallocene catalysts, achieving a synergistic improvement in anti-gelling performance and catalytic activity.

[0042] Experiment 4: Verification of Low-Temperature Storage Stability The samples from Example 3 and the comparative example were stored in a refrigerator at 4°C for 12 weeks. After observation, the comparative example showed obvious gel clumps, and its catalytic activity decreased to 41% of that of the fresh sample. Example 3 showed only a very small amount of insoluble matter, and its catalytic activity remained at 92% of that of the fresh sample. The technical effects described in this invention can also be obtained by storing the samples from Examples 1, 2, and 4 at low temperatures.

[0043] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing an anti-gelling methylaluminoxane solution, characterized in that... Includes the following steps: 1) Preparation of crude trimethylaluminum by initiating reaction: Using an initiator as a reaction aid, aluminum powder reacts with chloromethane to generate methyl sesquialuminum. The content of methyl sesquialuminum in the system is determined by chemical titration. Based on this, the theoretical amount of sodium metal to be fed is calculated. Molten sodium metal is added dropwise, and the reducing property of sodium metal is used to reduce 70% to 99% of the methyl sesquialuminum in the system to trimethylaluminum. The unreduced methyl sesquialuminum remains in the system. Impurities and organic solvents are removed by distillation to obtain a trimethylaluminum organic solution containing a small amount of methyl sesquialuminum. The methyl sesquialuminum is dimethylaluminum monochloro and / or dimethylaluminum dichloro, and the molar ratio of aluminum content of methyl sesquialuminum to trimethylaluminum in the organic solution is 0.2 to 20: 70 to 100. 2) Low-temperature preparation of methylaluminoxane solution: Add organic solvent to the trimethylaluminum organic crude liquid containing a small amount of methyl sesquialuminum obtained in step 1), and stir until the system is uniformly mixed; continuously pass an inert gas carrying deoxygenated deionized water or distilled water vapor, and carry out a hydrolysis polymerization reaction at -25℃ to 10℃. The methyl sesquialuminum partially participates in the hydrolysis polymerization reaction, and remains in the system as an anti-gelling stabilizer in the form of the remaining unreacted form and the mixture of its reaction products, thus synthesizing crude methylaluminoxane; after the reaction is completed, the system is successively filtered and subjected to vacuum distillation to remove residual impurities and some organic solvent, and finally obtains a methylaluminoxane solution with anti-gelling properties; wherein, the molar ratio of the mixture as an anti-gelling stabilizer to the aluminum content of the methylaluminoxane structural unit is 0.1 to 30:

100.

2. The method for preparing an anti-gelling methylaluminoxane solution as described in claim 1, characterized in that... In step 1): Chemical titration detection, assuming that dimethylaluminum chloride and dimethylaluminum chloride are a mol and b mol respectively, the total aluminum content is determined by EDTA back titration, and the chloride ion content is determined by silver nitrate titration. ， ， Calculate the molar amounts of dimethylaluminum monochloro and dimethylaluminum dichloro, and then calculate the mass of sodium metal required to reduce a specified proportion of methylsesquialuminum to trimethylaluminum according to stoichiometry.

3. The method for preparing an anti-gelling methylaluminoxane solution as described in claim 1, characterized in that... In step 1), 90%–98% of the methyl sesquialuminum in the system is reduced to trimethylaluminum.

4. The method for preparing an anti-gelling methylaluminoxane solution as described in claim 1, characterized in that... In step 1): the initiator is iodoethane or iodomethane; the reaction temperature of the aluminum powder and chloromethane is 100℃~160℃, preferably 120℃~140℃.

5. The method for preparing an anti-gelling methylaluminoxane solution as described in claim 1, characterized in that... In step 2), the organic solvent is at least one of saturated alkanes, cycloalkanes, and aromatic hydrocarbons of C6 to C20, preferably at least one of hexane, heptane, cyclohexane, toluene, and decane.

6. The method for preparing an anti-gelling methylaluminoxane solution as described in claim 1, characterized in that... In step 2), the molar ratio of trimethylaluminum to water is 3:1 to 1:

2.

7. The method for preparing an anti-gelling methylaluminoxane solution as described in claim 1, characterized in that... In step 2): the inert gas is nitrogen or argon, and the inert gas flow rate is 0.2 mL / min to 4 mL / min, preferably 1 mL / min to 2 mL / min; the hydrolysis reaction rate is controlled by adjusting the amount of water carried by the inert gas.

8. The method for preparing an anti-gelling methylaluminoxane solution as described in claim 1, characterized in that... In step 2): the temperature of the hydrolysis polymerization reaction is controlled at -20℃ to 0℃, preferably -15℃ to -5℃, and the reaction time is 3-5h; the concentration of the trimethylaluminum organic crude liquid in the organic solvent after preparation is 1-5mol / L, preferably 2-3mol / L.

9. The method for preparing an anti-gelling methylaluminoxane solution as described in claim 1, characterized in that... In step 2): the molar ratio of the mixture as an anti-gelling stabilizer to the aluminum content of the methylaluminoxane structural unit is 1-15:100, preferably 2-5:

100.

10. The method for preparing an anti-gelling methylaluminoxane solution as described in claim 1, characterized in that: The prepared methylaluminoxane solution showed no gel precipitation or only trace amounts of insoluble particles when stored at 25°C in the dark for 8 weeks. After 8 weeks of storage, its catalytic activity for olefin polymerization remained at more than 90% of that of the fresh sample.

Images