A process for the preparation of an alkylaluminoxane solution

Abstract

The application discloses a preparation method of an alkyl aluminoxane solution and belongs to the field of alkyl aluminoxane preparation. First, aluminum hydroxide solid is vacuum dried at high temperature to remove adsorbed water; then, the aluminum hydroxide is dispersed in anhydrous hydrocarbon solvent under anhydrous and oxygen-free conditions, a hydrocarbon solution of trimethylaluminum is added, and an alkyl aluminoxane base is prepared through a metathesis reaction between the aluminum hydroxide and the trimethylaluminum; then, alkyl aluminum and inorganic salt hydrate are added into the alkyl aluminoxane base respectively, and the reaction is carried out at a set temperature; after the reaction is completed, inorganic salt by-products are removed through filtration to obtain the alkyl aluminoxane solution. The method has the advantages of mild reaction, high yield and few by-products.

Description

Technical Field

[0001] This invention belongs to the field of alkylaluminoxane preparation, and more specifically, relates to a method for preparing an alkylaluminoxane solution. Background Technology

[0002] Alkyl aluminum oxanes are an important class of alkyl aluminum derivatives that can efficiently activate Ziegler-Natta catalysts, metallocene catalysts, and non-metallocene transition metal catalysts, and are widely used in the field of olefin polymerization.

[0003] Traditional methods for preparing alkylaluminoxanes mainly include direct hydrolysis and indirect hydrolysis. Direct hydrolysis involves the direct reaction of alkylaluminum with water, resulting in a fast reaction rate and high product yield, making it very suitable for large-scale production (US 3242099, US4730071, US 4730072, US 4772736, US4908463, US 4924018, US 5041584, CN 100413870C, CN 102190678 B, CN 111004265 A). However, the degree of reaction is difficult to control, and the reaction process is highly exothermic, making process safety difficult to guarantee. It also places high demands on production equipment and incurs significant investment costs.

[0004] Indirect hydrolysis introduces water into the reaction system by slowly releasing water of crystallization from the hydrate, allowing it to react with alkylaluminum in solution (US 4544762, US 4404344, US 4665208, US 5041583, US 5099050, US5147137, CN1309724C). The advantages of this method are its slower reaction rate and safer, more controllable production process. However, the yield is generally lower than that of direct hydrolysis, typically only around 50%, and the inorganic salts carrying the water of crystallization need to be separated, resulting in complex post-processing. Therefore, a milder and more efficient production process needs to be developed. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a method for preparing an alkylaluminoxane solution. The method first prepares an alkylaluminoxane substrate using aluminum hydroxide and excess trimethylaluminum as raw materials, and then hydrolyzes the alkylaluminum via an indirect hydrolysis method to assemble the alkylaluminoxane sheet structure to form an alkylaluminoxane solution. This method has the advantages of mild reaction, high yield, and few byproducts.

[0006] To achieve the above objectives, the present invention provides a method for preparing an alkylaluminoxane solution, the method comprising:

[0007] 1) Solid aluminum hydroxide is vacuum dried at high temperature to remove the adsorbed moisture;

[0008] 2) Under anhydrous and oxygen-free conditions, the aluminum hydroxide treated in step 1) is dispersed in anhydrous hydrocarbon solvent. At a certain temperature, an appropriate amount of trimethylaluminum hydrocarbon solution is added, and alkylaluminoxane substrate is prepared by metathesis reaction of aluminum hydroxide and trimethylaluminum.

[0009] 3) Add appropriate amounts of alkyl aluminum and inorganic salt hydrate respectively. After the reaction is completed at a certain temperature, remove the inorganic salt byproduct by filtration to obtain an alkyl aluminum oxane solution.

[0010] As a preferred embodiment, in step 1), the temperature for vacuum drying of aluminum hydroxide is 30~200℃, preferably 100-150℃, and the water content of aluminum hydroxide after vacuum drying is 0.01wt%~1wt%, preferably 0.01wt%~0.1wt%.

[0011] As a preferred embodiment, the hydrocarbon solvent used in step 2) is selected from one or a mixture thereof, such as n-pentane, isopentane, n-hexane, cyclohexane, isopentane, n-heptane, isopentane, methylcyclohexane, n-octane, isopentane, n-nonane, isopentane, n-dodecane, isopentane, n-tetradecane, isopentane, n-hexadecane, isopentane, benzene, toluene, xylene, trimethylbenzene, 1,2-dichloroethane, and 1,1,2,2-tetrachloroethane.

[0012] As a preferred embodiment, the temperature in step 2) is 100-160℃; the mass ratio of aluminum hydroxide to trimethylaluminum is 1:2.

[0013] As a preferred embodiment, the alkylaluminum in step 3) is one or a mixture of several of trimethylaluminum, triethylaluminum, triisobutylaluminum and trioctylaluminum.

[0014] As a preferred embodiment, the inorganic salt hydrate in step 3) is one or a mixture of several of aluminum sulfate hexadecahydrate, aluminum sulfate octadecahydrate, aluminum nitrate nonahydrate, ferric sulfate heptahydrate, and copper sulfate pentahydrate.

[0015] As a preferred embodiment, the mass ratio of alkyl aluminum to aluminum hydroxide in step 3) is 0.5 to 5, and the mass ratio of inorganic salt hydrate to aluminum hydroxide is 0.3 to 3.

[0016] As a preferred option, the reaction temperature in step 3) is -20~150℃, preferably 100~130℃.

[0017] The method for preparing alkylaluminoxane solution provided by the present invention uses aluminum hydroxide and excess trimethylaluminum as raw materials to prepare alkylaluminoxane substrate, and then hydrolyzes alkylaluminum by indirect hydrolysis and assembles alkylaluminoxane sheet structure to form alkylaluminoxane solution. It has the advantages of mild reaction, high yield and few by-products. Detailed Implementation

[0018] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0019] The preparation principle of this invention is as follows: Vacuum-dried aluminum hydroxide is first uniformly mixed with a certain amount of trimethylaluminum. Through metathesis reaction and self-assembly process, an alkylaluminoxane substrate composed of 7 Al(OAlMe2)3 structural units is formed. Then, the R2AlOAlR2 units formed by the hydrolysis of alkylaluminum are further assembled into an alkylaluminoxane plate-like structure. The specific reaction formula is as follows:

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026] .

[0027] Typically, but not limited to, the method for preparing the alkylaluminoxane solution of the present invention includes:

[0028] 1) Solid aluminum hydroxide is vacuum dried at high temperature to remove the adsorbed moisture; wherein, the vacuum drying temperature of aluminum hydroxide is 30~200℃, preferably 100-150℃, and the water content of aluminum hydroxide after vacuum drying is 0.01wt%~1wt%, preferably 0.01wt%~0.1wt%.

[0029] 2) Under anhydrous and oxygen-free conditions, the aluminum hydroxide treated in step 1) is dispersed in anhydrous hydrocarbon solvent. At a certain temperature, an appropriate amount of trimethylaluminum hydrocarbon solution is added, and alkylaluminoxane substrate is prepared by metathesis reaction of aluminum hydroxide and trimethylaluminum.

[0030] In step 2), the hydrocarbon solvent used is selected from one or a mixture of the following: n-pentane, isopentane, n-hexane, cyclohexane, isopentane, n-heptane, isopentane, methylcyclohexane, n-octane, isopentane, n-nonane, isopentane, n-dodecane, isopentane, n-tetradecane, isopentane, n-hexadecane, isopentane, benzene, toluene, xylene, trimethylbenzene, 1,2-dichloroethane, and 1,1,2,2-tetrachloroethane. The temperature in this step is 100-160℃, and the reaction time is 12-48 hours. The amount of aluminum hydroxide used in step 2) is 4-11 parts (by weight), the amount of trimethylaluminum is 8-22 parts, and the amount of anhydrous hydrocarbon solvent used to disperse the aluminum hydroxide is 60-90 parts.

[0031] 3) Add appropriate amounts of alkyl aluminum and inorganic salt hydrate respectively. After the reaction is completed at a certain temperature, remove the inorganic salt byproduct by filtration to obtain an alkyl aluminum oxane solution.

[0032] In step 3), the alkylaluminum is one or a mixture of several of trimethylaluminum, triethylaluminum, triisobutylaluminum, and trioctylaluminum, and the inorganic salt hydrate is one or a mixture of several of aluminum sulfate hexadecylhydrate, aluminum sulfate octadecylhydrate, aluminum nitrate nonahydrate, ferric sulfate heptahydrate, and copper sulfate pentahydrate. Similarly, based on the aforementioned steps, the amount of aluminum hydroxide used is 4-11 parts by weight, the amount of inorganic salt hydrate is 3-9 parts, and the amount of alkylaluminum is 6-18 parts. The reaction temperature in step 3) is -20 to 150°C, preferably 100-130°C, and the reaction time is 6-24 hours.

[0033] This invention utilizes the slow and precise addition of alkylaluminum solution and accurate control of reaction temperature to construct the sheet-like structure of alkylaluminoxanes by replacing most of the hydrolyzed trimethylaluminum with the reaction product of aluminum hydroxide and trimethylaluminum. The sheet-like alkylaluminoxane is then further assembled by the partial hydrolysis unit of trialkylaluminum. The reaction process is exothermic and mild, and the byproducts are reduced by about 60% compared with the indirect hydrolysis method, thereby achieving the goal of efficient preparation of alkylaluminoxanes.

[0034] The present invention discloses a method for preparing an alkylaluminoxane solution. Products with different alkylaluminum compositions can be applied to different olefin polymerization processes, mainly including ethylene polymerization and copolymerization.

[0035] Example 1

[0036] 1) Weigh 41.6g of aluminum hydroxide solid (which has been vacuum dried at 150℃ to remove adsorbed moisture until the water content is ≤0.1%).

[0037] 2) Under anhydrous and oxygen-free conditions, dried aluminum hydroxide was dispersed in 500 mL of methylcyclohexane. At room temperature, 460 mL of a methylcyclohexane solution of trimethylaluminum (trimethylaluminum content was 82.3 g) was added. The solution was then transferred to a sealed container and heated to 140 °C for 24 h to prepare an alkylaluminoxane substrate through the metathesis reaction of aluminum hydroxide and trimethylaluminum.

[0038] 3) Slowly add 127.63 g of triisobutylaluminum to the obtained alkylaluminoxane substrate, mix well, and then slowly add 27.1 g of aluminum sulfate hexahydrate powder through a solid feeder. After reacting at 80 °C for 12 h, remove the inorganic salt byproducts by filtration to obtain an alkylaluminoxane solution.

[0039] Example 2

[0040] The steps in this embodiment are the same as those in Embodiment 1, except that the methylcyclohexane solvent in step 2) is replaced with toluene, and the triisobutylaluminum in step 3) is replaced with trimethylaluminum, with a dosage of 52.1g.

[0041] Example 3

[0042] The steps in this embodiment are the same as those in Example 1, except that the methylcyclohexane solvent in step 2) is replaced with n-hexane, and the amount of triisobutylaluminum used in step 3) is 140.4g.

[0043] Example 4

[0044] The steps in this embodiment are the same as those in Embodiment 1, except that the temperature in step 1) is 150°C and the temperature in step 3) is 100°C.

[0045] Example 5

[0046] The steps in this embodiment are the same as those in Embodiment 1, except that the temperature in step 2) is 110°C and the reaction time is 12h; and the temperature in step 3) is 50°C.

[0047] Example 6

[0048] The steps in this embodiment are the same as those in Example 1, except that the volume of methylcyclohexane in step 2) is 300 mL.

[0049] Example 7

[0050] The steps in this embodiment are the same as those in embodiment 2, except that the temperature in step 2) is 120°C and the temperature in step 3) is 120°C.

[0051] Example 8

[0052] The steps in this embodiment are the same as those in embodiment 2, except that the temperature in step 2) is 130°C and the temperature in step 3) is 130°C.

[0053] Example 9

[0054] The steps in this embodiment are the same as those in Example 1, except that the methylcyclohexane solvent in step 2) is replaced with n-heptane, and the triisobutylaluminum in step 3) is replaced with trioctylaluminum, with a dosage of 231.8g.

[0055] Example 10

[0056] The steps in this embodiment are the same as those in Example 9, except that the n-heptane solvent in step 2) is replaced with IsoparE, and the amount of trioctylaluminum in step 3) is 252.3g.

[0057] Example 11

[0058] The steps in this embodiment are the same as those in embodiment 9, except that the temperature in step 1) is 140°C and the temperature in step 3) is 80°C.

[0059] Comparative Example 1

[0060] Alkyl aluminum oxane solution was prepared by indirect hydrolysis:

[0061] 1) Under anhydrous and oxygen-free conditions, 776.9 g of aluminum sulfate hexahydrate was dispersed in 500 ml of toluene;

[0062] 2) 161.6 g of trimethylaluminum was dissolved in 460 mL of toluene;

[0063] 3) Under stirring conditions at 20°C, the aluminum sulfate hexahydrate dispersion was slowly added to the trimethylaluminum solution. After the addition was complete, the mixture was kept warm and stirred for another 30 hours. The aluminum sulfate byproduct was removed by filtration to obtain an alkylaluminoxane solution.

[0064] Comparative Example 2

[0065] Alkyl aluminum oxane solution was prepared by reacting 218.4 g of triisobutylaluminum with 82.3 g of trimethylaluminum and 776.9 g of aluminum sulfate hexadecylhydrate at 20 °C. After the reaction was completed, inorganic salt byproducts were removed by filtration to obtain the alkyl aluminum oxane solution.

[0066] Triisobutylaluminum and trimethylaluminum were added to a solvent and mixed evenly. Aluminum sulfate hexadecylhydrate was dispersed in the solvent and slowly added to the alkylaluminum mixed solution at 20°C. After the addition was complete, the reaction was stirred for 12 hours. After filtering to remove the aluminum sulfate byproduct, an alkylaluminoxane solution was obtained.

[0067] Comparative Example 3

[0068] The steps in this embodiment are the same as in embodiment 1, except that the reaction in step 3) is not performed.

[0069] Comparative Example 4

[0070] The steps in this embodiment are the same as in Example 1, except that the amount of aluminum hydroxide used is less, only 31.2g of aluminum hydroxide is used, and the amounts of trimethylaluminum, triisobutylaluminum and aluminum sulfate hexadecylhydrate are the same as in Example 1.

[0071] Test Example 1: Conditions for Ethylene Oligomerization

[0072] A 500 mL autoclave was heated to a vacuum state and evacuated for 2 hours. After several nitrogen purgings, ethylene was introduced, and the autoclave was cooled to a predetermined temperature. Then, 200 mL of dehydrated methylcyclohexane, 0.8 mL of alkylaluminoxane synthesized in each example and comparative example, 0.75 mg of PNP ligand as shown in Formula I, and 0.56 mg of chromium acetylacetone were added. The oligomerization reaction was carried out at 60 °C, 0.2 MPa hydrogen partial pressure, and 4 MPa ethylene pressure. After 30 min of reaction, the autoclave was cooled with condensate, depressurized, and the product was discharged and analyzed. The oligomerization activity and product distribution are shown in Table 1.

[0073]

[0074] Table 1 - Comparison of carbon number distribution of ethylene oligomers

[0075]

[0076] a It refers to 1-C6 in C6 = The percentage of mass content. b It refers to 1-C8 in C8 = The percentage of mass content.

[0077] As can be seen from Table 1, the MMAO prepared in this invention has a better catalytic activation effect than the comparative example, and there is no significant difference in the distribution of α-olefin products.

[0078] Test Example 2: Conditions for Ethylene-α-olefin copolymerization

[0079] A 500 mL autoclave was heated to a vacuum state and evacuated for 2 hours. After several purgings with nitrogen, ethylene was introduced, and the autoclave was cooled to a predetermined temperature. Then, 200 mL of dehydrated isoparE, 25 mL of 1-octene, 0.6 mL of the alkylaluminoxane synthesized in Examples 9, 10, and 11, and 2 μmol of CGC catalyst as shown in Formula II were added. The ethylene-octene copolymerization reaction was carried out at 130 °C and 3 MPa. After 10 min, the pressure was released, the product was discharged, and analyzed. The copolymerization activity and basic physical parameters of the product are shown in Table 2.

[0080]

[0081] Table 2 Activity and basic physical parameters of ethylene-octene copolymerization products

[0082]

[0083] As can be seen from Table 2, the MMAO prepared by the present invention has the ability to activate metallocene catalysts to prepare ethylene-α-olefin copolymerization.

[0084] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing an alkylaluminoxane solution, characterized in that, The method includes the following steps: 1) Dry the solid aluminum hydroxide under vacuum at high temperature to remove the adsorbed moisture; 2) Under anhydrous and oxygen-free conditions, the aluminum hydroxide treated in step 1) is dispersed in an anhydrous hydrocarbon solvent. At a set temperature, a hydrocarbon solution of trimethylaluminum is added, and an alkylaluminoxane substrate is prepared through the metathesis reaction of aluminum hydroxide and trimethylaluminum. The temperature mentioned in step 2) is 100-160℃; the reaction time is 12-48h; and the molar ratio of aluminum hydroxide to trimethylaluminum is 0.5-5. 3) Add alkyl aluminum and inorganic salt hydrate to the alkylaluminoxane substrate in step 2), and react at a set temperature. After the reaction is complete, remove the inorganic salt byproduct by filtration to obtain an alkylaluminoxane solution. The molar ratio of alkyl aluminum to aluminum hydroxide is 0.5~5, and the mass ratio of inorganic salt hydrate to aluminum hydroxide is 0.3~3. The reaction temperature in step 3) is -20~150℃, and the reaction time is 6-24h. The alkyl aluminum is one or a mixture of several of trimethylaluminum, triethylaluminum, triisobutylaluminum, and trioctylaluminum. The inorganic salt hydrate is one or a mixture of several of aluminum sulfate hexadecylhydrate, aluminum sulfate octadecylhydrate, aluminum nitrate nonahydrate, ferric sulfate heptahydrate, and copper sulfate pentahydrate.

2. The preparation method according to claim 1, characterized in that, In step 1), the temperature for vacuum drying of aluminum hydroxide is 100-150℃, and the water content of aluminum hydroxide after vacuum drying is 0.01wt%~1wt%.

3. The preparation method according to claim 1, characterized in that, Step 2) The hydrocarbon solvent used is selected from one or a mixture of n-pentane, n-hexane, cyclohexane, n-heptane, methylcyclohexane, n-octane, n-nonane, n-dodecane, n-tetradecane, n-hexadecane, benzene, toluene, xylene, and trimethylbenzene.

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