A method for preparing modified methylaluminoxane and its uses

Abstract

This invention discloses a method for preparing modified methylaluminoxane and its uses. The method includes: (1) reacting trimethylaluminum with (meth)acrylate as shown in Formula 1 under heating in the presence of an inert organic solvent to prepare methylaluminoxane; (2) mixing the methylaluminoxane obtained in step (1) with long-chain alkylaluminum and reacting under heating to obtain modified methylaluminoxane. The method of this invention is simple to operate, safe and controllable, and yields a high amount of modified methylaluminoxane; and requires no complex post-processing. The method of this invention can operate under mild reaction conditions, and compared with reactions involving other alcohols or water, it has a higher yield, higher conversion rate, and fewer byproducts.

Description

Technical Field

[0001] This invention relates to a method for synthesizing a catalyst, and more particularly to a method for preparing modified methylaluminoxane and its uses. Background Technology

[0002] Alkyl aluminum oxanes can be used as cocatalysts for the polymerization of metallocene and post-transition metal olefins. Methyl aluminum oxane (MAO) is commonly used in industry as a cocatalyst for olefin polymerization.

[0003] The synthesis methods of methylaluminoxane (MAO) are basically divided into two types. One is the hydrolysis method, which can be summarized into direct hydrolysis and indirect hydrolysis processes depending on the different ways water is added to the reaction. Direct hydrolysis processes include: static mixer method, atomized water method, film deposition method, T-reactor method, ice method, and ultrasonic dispersion method. The indirect hydrolysis process mainly uses trimethylaluminum to react with inorganic salt hydrates to prepare MAO. The direct hydrolysis process, which adds water to a trimethylaluminum toluene solution, can achieve a high reaction yield, but due to the extremely high risk of the reaction between trimethylaluminum and water, this process has very high requirements for equipment quality. The indirect hydrolysis process has a lower reaction yield of the target product MAO due to the limitations of the feeding process itself. The other type is the non-hydrolysis method, which mainly uses trimethylaluminum to react with carbon dioxide, alcohols, aldehydes, and organic acid compounds, and then obtains MAO through pyrolysis. However, using carbon dioxide as the oxygen source requires the reaction to proceed under certain pressure; using liquid aldehydes as the oxygen source makes the reaction difficult to control due to their high concentration; and using organic acids and alcohols as the oxygen source results in overly vigorous reactions that are difficult to control and pose certain risks. None of these methods are suitable for the large-scale production of methylaluminoxanes. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for preparing modified methylaluminoxane, the method comprising:

[0005] (1) In the presence of an inert organic solvent, trimethylaluminum is heated and reacted with (meth)acrylate as shown in Formula 1 to prepare methylaluminoxane;

[0006]

[0007] R1, R2, R3, or R4 may be the same or different, and are independently selected from C. 1-10 alkyl;

[0008] (2) The methylaluminoxane obtained in step (1) is mixed with long-chain alkyl aluminum and heated to react, thereby obtaining modified methylaluminoxane.

[0009] According to an embodiment of the present invention, in step (1), R1, R2, R3 or R4 may be the same or different, and are independently selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, etc.

[0010] According to an embodiment of the present invention, in step (1), the inert organic solvent is any organic hydrocarbon solvent known to those skilled in the art that does not react with trimethylaluminum compounds. Examples include alkanes (e.g., heptane, hexane) or aromatic hydrocarbons (e.g., toluene, xylene, ethylbenzene, isopropylbenzene, mesitylene). Toluene is preferred as the solvent. For inert solvents, it is desirable to also exclude solvents that can complex with aluminum-containing reactants, examples of which are solvents containing oxygen or nitrogen atoms, such as ethers like tetrahydrofuran.

[0011] According to an embodiment of the present invention, in step (1), the molar ratio of the methylaluminum to the (meth)acrylate shown in Formula 1 is 1:0.1-0.9, preferably 1:0.3-0.8, and more preferably 1:0.5-0.7.

[0012] According to an embodiment of the present invention, in step (1), the mass ratio of trimethylaluminum in an inert organic solvent is 5-50 wt%, preferably 10-30 wt%.

[0013] According to an embodiment of the present invention, in step (1), the temperature of the reaction is 0-80°C, preferably 10-60°C, for example 10°C, 20°C, 30°C, 40°C, 50°C or 60°C; the reaction time is 5-30h.

[0014] According to an embodiment of the present invention, in step (2), the long-chain alkyl aluminum is an alkyl aluminum with a chain carbon number of not less than 4, for example, selected from at least one of triisobutylaluminum, tributylaluminum, tri-n-octylaluminum, triisooctylaluminum, di-n-octylaluminum chloride, di-n-octylaluminum bromide, etc.

[0015] According to an embodiment of the present invention, in step (2), the molar ratio of trimethylaluminum to long-chain alkylaluminum is 1-8:1.

[0016] According to an embodiment of the present invention, in step (2), the reaction temperature of methylaluminoxane with long-chain alkylaluminum is 60-170°C, and the reaction time is 2-10h.

[0017] The present invention also provides modified methylaluminoxane prepared by the above method.

[0018] The present invention also provides the use of the above-described modified methylaluminoxane as a catalyst component in catalysts used in olefin polymerization or oligomerization methods.

[0019] The beneficial effects of this invention are:

[0020] 1. This method is simple to operate, safe and controllable, and has a high yield of modified methylaluminoxane; and it does not require complicated post-processing.

[0021] 2. The method of the present invention can achieve higher yield, higher conversion rate and fewer by-products under mild reaction conditions compared with other alcohol or water reactions.

[0022] 3. The modified methylaluminoxane prepared by this method can be used as a co-catalyst to catalyze olefin polymerization with high polymerization activity. Detailed Implementation

[0023] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0024] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0025] Example 1

[0026] Preparation method of modified methylaluminoxane

[0027] (1) 7.2 mL of toluene and 0.72 g (10 mmol) of trimethylaluminum (from AkzoNobel) were placed in a 100 mL reaction flask equipped with a magnetic stir bar. 0.94 g (5 mmol) of (meth)acrylate of Formula 1 (wherein R1, R2, R3 and R4 are all methyl) was slowly added to the solution, wherein the molar ratio of methylaluminum to (meth)acrylate of Formula 1 was 1:0.5, and the mass ratio of the trimethylaluminum in the inert organic solvent was 10 wt%. The reaction was carried out at room temperature for 19 h to obtain methylaluminoxane.

[0028] (2) The methylaluminoxane obtained in step (1) was mixed with 0.6 g (3 mmol) of tributylaluminum and reacted at 100 °C for 8 h under magnetic stirring to obtain modified methylaluminoxane; the yield of modified methylaluminoxane was 56%.

[0029] Therefore, using a modified methylaluminoxane toluene solution as a co-catalyst, and with the metallocene catalyst ethyl di(indenyl)zirconia (Et(Ind)2ZrCl2) as the main catalyst, ethylene polymerization is catalyzed. The specific process is as follows:

[0030] Ethylene polymerization was carried out under anhydrous and oxygen-free conditions. To the reaction system, 50 ml of toluene, 4.0 ml of modified methylaluminoxane, the main catalyst (Al / Ti = 1720), and 1 atm of ethylene were added sequentially. The reaction was carried out at 25°C for 1 hour, and the reaction was terminated with an ethanol solution containing a small amount of hydrochloric acid. The resulting product was filtered, washed several times with ethanol, and dried under vacuum at 40°C for 12 hours to obtain polyethylene. The polymerization activity was 1.78 × 10⁻⁶. 7 g polymer per mole of metallocene catalyst per hour.

[0031] Example 2

[0032] A method for preparing modified methylaluminoxane

[0033] (1) 7.2 mL of toluene and 0.72 g (10 mmol) of trimethylaluminum (from AkzoNobel) were placed in a 100 mL reaction flask equipped with a magnetic stir bar. 1.36 g (6 mmol) of (meth)acrylate of Formula 1 (wherein R1 and R2 are both methyl, R3 is hexyl, and R4 is propyl) was slowly added to the solution, wherein the molar ratio of methylaluminum to (meth)acrylate of Formula 1 was 1:0.6, and the mass ratio of the trimethylaluminum in the inert organic solvent was 10 wt%; the reaction was carried out at 40 °C for 18 h to obtain methylaluminoxane.

[0034] (2) The methylaluminoxane obtained in step (1) was mixed with 0.4 g (2 mmol) of tributylaluminum and reacted at 80 °C for 10 h under magnetic stirring to obtain modified methylaluminoxane; the yield of modified methylaluminoxane was 63%.

[0035] Therefore, the modified methylaluminoxane toluene solution was used as a co-catalyst, and the metallocene catalyst Et(Ind)₂ZrCl₂ was used as the main catalyst to catalyze the polymerization of ethylene. The ethylene polymerization process was the same as in Example 1, and the polymerization activity was 1.95 × 10⁻⁶. 7 g polymer per mole of metallocene catalyst per hour.

[0036] The embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing modified methylaluminoxane, characterized in that, The method includes: (1) In the presence of an inert organic solvent, trimethylaluminum is heated and reacted with (meth)acrylate as shown in Formula 1 to prepare methylaluminoxane; R1, R2, R3, or R4 may be the same or different, and are independently selected from C. 1-10 alkyl; (2) The methylaluminoxane obtained in step (1) is mixed with long-chain alkyl aluminum and heated to react, thereby obtaining modified methylaluminoxane.

2. The method according to claim 1, characterized in that, In step (1), R1, R2, R3 or R4 may be the same or different, and are independently selected from methyl, ethyl, propyl, butyl, pentyl or hexyl.

3. The method according to claim 1, characterized in that, In step (1), the inert organic solvent is at least one of heptane, hexane, toluene, xylene, ethylbenzene, isopropylbenzene, and mesitylene.

4. The method according to claim 1, characterized in that, In step (1), the molar ratio of the methylaluminum to the (meth)acrylate shown in Formula 1 is 1:0.1-0.

9.

5. The method according to claim 1, characterized in that, In step (1), the mass ratio of trimethylaluminum in the inert organic solvent is 5-50 wt%.

6. The method according to claim 1, characterized in that, In step (1), the reaction temperature is 0-80℃ and the reaction time is 5-30h.

7. The method according to claim 1, characterized in that, In step (2), the long-chain alkyl aluminum is selected from at least one of triisobutylaluminum, tributylaluminum, tri-n-octylaluminum, triisooctylaluminum, di-n-octylaluminum chloride, and di-n-octylaluminum bromide.

8. The method according to claim 1, characterized in that, In step (2), the molar ratio of trimethylaluminum to long-chain alkylaluminum is 1-8:1; The reaction temperature of methylaluminoxane with long-chain alkylaluminum is 60-170℃, and the reaction time is 2-10h.

9. The modified methylaluminoxane prepared by the method according to any one of claims 1-8.

10. Use of the modified methylaluminoxane of claim 9 as a catalyst component in a catalyst for olefin polymerization or oligomerization methods.

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