Method and reaction device for preparing methylaluminoxane by directly hydrolyzing trimethyl aluminum

Abstract

The invention discloses a method for preparing methylaluminoxane by directly hydrolyzing trimethyl aluminum and a reaction device, and belongs to the technical field of chemical products. Comprising the following steps: introducing low-temperature methane gas containing gas-phase water into a trimethylaluminum organic solution, carrying out hydrolysis reaction under the dual effects of ultrasonic vibration and mechanical stirring and mixing, and filtering to remove solid substances after the reaction is completed, so as to obtain a methylaluminoxane solution. According to the method for preparing methylaluminoxane through direct hydrolysis of trimethyl aluminum, the hydrolysis quality of methylaluminoxane can be guaranteed, generation of gels such as aluminum hydroxide is effectively controlled, and the product yield is greatly increased; and the byproduct methane is high in purity, can be recycled and is free of environmental pollution and energy waste, so that the production cost is remarkably reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical products, and specifically relates to a method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum and a reaction device. Background Art

[0002] Methyl aluminoxane, MAO (methyl aluminoxane), is a polymer composed of [OAl (CH3)] units with a complex structure and an indeterminate degree of polymerization. Its structural formula is: .

[0003] Methylaluminoxane (MAO) is a highly efficient co-catalyst in metallocene olefin polymerization catalysts with high catalytic activity. It is required as a co-catalyst in metallocene polyolefins (PE / PP), metallocene polyolefin elastomers (POE), metallocene polyolefin lubricants (PAO), metallocene polyolefin waxes, new materials cyclic polyolefins (COC / COP), and other metallocene catalysts used in the synthesis of new materials.

[0004] The reduction of metallocene polyolefin costs, improvement of quality and expansion of its application range depend on the improvement, optimization and large-scale industrial production of metallocene catalysts and methylaluminoxane co-catalysts, and on improving the efficiency of catalytic polymerization, high-quality and low-cost catalysts, stable quality and sufficient supply.

[0005] There are many methods for synthesizing methylaluminoxane using trimethylaluminum hydration, primarily categorized into direct hydrolysis and indirect hydrolysis. Direct hydrolysis methods include those described in CN113292587A and CN1597685A. Indirect hydrolysis methods, such as those described in CN102286012A and CN200910090468, use inorganic salts containing crystalline water, such as CuSO₄.5H₂O and Al₂(SO₄)₃.16H₂O, to prepare organic solutions of methylaluminoxane.

[0006] Since water reacts with trimethylaluminum very quickly, it is difficult to avoid the methylaluminoxane generated during the reaction from reacting with water for the second time to form aluminum hydroxide solid. The methylaluminoxane organic solution obtained by direct hydrolysis often contains gel or small particles of aluminum hydroxide solid. These small particles are also easy to aggregate to form gel after standing still. Even after filtering the gel and small particles, the methylaluminoxane solution will form gel again after two or three weeks.

[0007] The indirect hydrolysis method uses water of crystallization of inorganic salts or water adsorbed by other substances. These inorganic substances cannot be well soluble or effectively dispersed with trimethylaluminum solution, resulting in the phenomenon of local over-hydrolysis to generate aluminum hydroxide. Although the generated aluminum hydroxide can be filtered out when filtering the inorganic salts, due to the continued local over-hydrolysis, gel will still precipitate after the solution has been stationary for a period of time.

[0008] If gel is produced during the preparation of methylaluminoxane solution, the content of methylaluminoxane in the solution is reduced, affecting the product quality of methylaluminoxane. At the same time, the yield is reduced, resulting in great economic losses. Summary of the Invention

[0009] In response to the above-mentioned problems existing in the prior art, the present invention aims to provide a method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum and a technical solution for a reaction apparatus. This method prevents excessive hydrolysis, ensures the quality of methylaluminoxane hydrolysis, effectively controls the production of gels such as aluminum hydroxide, and significantly improves product yield. In addition, the by-product methane is of high purity and recyclable, without environmental pollution or energy waste, thereby significantly reducing production costs.

[0010] The method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum is characterized by comprising the following steps: 1) Methane gas is introduced into a low-temperature aqueous solution at -30°C to 25°C to produce low-temperature methane gas containing gaseous water; 2) Passing low-temperature methane gas containing gaseous water into the trimethylaluminum organic solution at a methane gas flow rate of 0.2-5 L / min and a trimethylaluminum organic solution concentration of 15-50wt%; 3) The hydrolysis reaction is carried out under the dual effects of ultrasonic vibration and mechanical stirring. The power of the ultrasonic vibrator is 15kHz-40kHz, the mechanical stirring speed is 500-1000 rpm, and the hydrolysis temperature is -30℃ to 50℃; 4) After the reaction is completed, the solid matter is filtered out to obtain a methylaluminoxane solution.

[0011] The method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum is characterized in that in step 1), the temperature of the low-temperature aqueous solution is -20°C to 10°C, preferably -10°C to 0°C; and the low-temperature aqueous solution is a calcium chloride aqueous solution or an ethylene glycol aqueous solution.

[0012] The method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum is characterized in that in step 2), the methane flow rate is 0.5-3 L / min.

[0013] The method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum is characterized in that in step 2), the trimethylaluminum organic solution is a trimethylaluminum benzene solution or a trimethylaluminum toluene solution, and the concentration of the trimethylaluminum organic solution is 20-40wt%, preferably 25-30wt%.

[0014] The method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum is characterized in that in step 3), the power of the ultrasonic vibrator is 20kHz-30kHz, and the mechanical stirring speed is 600-800 rpm.

[0015] The method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum is characterized in that in step 3), the hydrolysis temperature is -15°C to 30°C, preferably -5°C to 5°C.

[0016] The method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum is characterized in that in step 3), the pressure of the hydrolysis reaction is 0.05-1.0 MPa, preferably 0.1-0.8 MPa, and more preferably 0.3-0.5 MPa.

[0017] The reaction device used in the method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum is characterized by comprising a system device consisting of a methane storage tank, a methane circulation compressor, a low-temperature brine tank, and a hydrolysis kettle connected in sequence with pipelines. An ultrasonic vibrator and a mechanical stirrer are installed in the hydrolysis kettle for ultrasonic vibration and mechanical stirring. The gas phase outlet of the hydrolysis kettle is connected to the methane storage tank through a methane recovery pipeline.

[0018] The ultrasonic vibrator used in the present invention converts 50-60Hz alternating current into 15kHz-40kHz high-frequency power and supplies it to the transducer. The transducer converts the high-frequency electrical energy into mechanical vibration energy, achieving micron-level vibration and mixing. The mechanical stirrer used in the present invention should have the function of re-inhaling the gas above the liquid surface, the function of turning the liquid phase upside down, and the function of quickly breaking and dispersing the methane bubbles in the feed with water. The ultrasonic vibrator and mechanical stirrer used in the present invention can be purchased directly on the market. The methane at the gas phase outlet of the hydrolysis kettle of the present invention is returned to the storage tank and compressed by the compressor and then brought back into the hydrolysis kettle with water to continue the hydrolysis reaction.

[0019] The reaction device is characterized by being equipped with an automatic exhaust valve, a pressure relief valve, and a safety valve on the external piping of the methane storage tank. The by-product methane of the present invention is of high purity, and the methane storage tank is connected to the gas furnace or storage tank via the external piping to achieve energy recovery and utilization.

[0020] In the present invention, a hydrolysis kettle, a methane storage tank, a methane circulation compressor, and a low-temperature brine tank system are connected and purged, cleaned, dried, tested, and replaced with nitrogen according to chemical requirements to meet chemical material feeding requirements. A low-temperature aqueous solution is injected into a brine tank, a trimethylaluminum organic solution is added to the hydrolysis tank, and methane is added to the methane storage tank. The system pressure, the brine tank temperature, and the hydrolysis tank temperature are controlled, a stirrer and an ultrasonic vibrator of the hydrolysis tank are turned on, and the methane circulation compressor is started to slowly feed water-carrying methane into the hydrolysis tank, and a low-temperature hydrolysis reaction is carried out under pressure. After the reaction is completed, the solution is filtered to remove solid matter to obtain a clear and transparent methylaluminoxane solution.

[0021] The above-mentioned method and reaction device for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum have the following beneficial effects: First, a methane-water circulation reaction is selected because methane and trimethylaluminum solution have good compatibility. Water-containing methane disperses quickly and well in the trimethylaluminum organic solution, avoiding local over-hydrolysis reaction. The by-product methane is of high purity and can be recycled and used, without environmental pollution or energy waste. Second, an ultrasonic vibrator is used to break the bubbles of methane gas in the solution to quickly disperse the reaction at the micron level, further avoiding local over-hydrolysis. Third, the water inlet rate can be controlled by adjusting the circulating gas volume, which regulates the reaction speed, prevents excessive hydrolysis, ensures the quality of methylaluminoxane hydrolysis, effectively controls the production of gels such as aluminum hydroxide, and greatly improves the product yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure of the system device of the present invention; In the figure: 1-methane storage tank, 2-methane circulation compressor, 3-low-temperature brine tank, 4-hydrolysis kettle, 5-ultrasonic vibrator, 6-mechanical agitator, 7-methane recovery pipeline, 8-automatic exhaust valve, 9-pressure discharge valve, 10-safety valve. DETAILED DESCRIPTION

[0023] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and drawings. Those skilled in the art should understand that the following specific description is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention. Example 1

[0024] The methylaluminoxane system was prepared by ultrasonic hydrolysis, such as Figure 1 As shown, the system needs to be vacuumed and nitrogen-filled multiple times, 2.0L of calcium chloride aqueous solution (25%) that has been boiled at high temperature to remove dissolved oxygen is injected into the brine tank, 2.0L of trimethylaluminum toluene solution (18%) is injected into the hydrolysis kettle, methane is injected into the methane storage tank to a pressure of 0.4MPa, chilled water is passed through the brine tank and the hydrolysis kettle until the liquid phase temperature of the brine tank and the hydrolysis kettle reaches -20℃, the hydrolysis kettle is turned on and stirred at 1000 rpm, and the ultrasonic vibrator of the hydrolysis kettle is turned on. To 3KW, start the compressor to pass methane into the brine tank at a flow rate of 3L / min, and the methane carrying low-temperature water vapor enters the hydrolysis kettle. By controlling the methane flow rate and the flow rate of the chilled brine entering the hydrolysis kettle, the liquid phase temperature of the hydrolysis kettle is controlled to be -20±2°C. When the weight of the water passed into the hydrolysis kettle is 98% of the theoretical water amount, the hydrolysis reaction is stopped. The reaction time is about 20.5 hours. The reaction liquid is filtered to obtain a toluene solution of methylaluminoxane. The yield of methylaluminoxane is 85.6wt%. Example 2

[0025] Other processes were the same as in Example 1, except that the calcium chloride aqueous solution (25 wt %) was replaced with an ethylene glycol aqueous solution (40 wt %). The yield of methylaluminoxane was 87.2 wt %. Example 3

[0026] Other conditions are the same as those in Example 1. The effects of different concentrations of trimethylaluminum toluene solution on the yield of methylaluminoxane are shown in Table 1.

[0027] Table 1 Effect of different concentrations of trimethylaluminum toluene solution on the yield of methylaluminoxane Serial number Trimethylaluminum toluene solution concentration wt% Methylaluminoxane yield wt% 1 15 85.8 2 20 85.2 3 30 82.5 The data in Table 1 show that as the concentration of trimethylaluminum toluene solution increases, the yield of methylaluminoxane decreases significantly. Example 4

[0028] Other conditions are the same as those in Example 1. The effects of different hydrolysis pressures on the yield of methylaluminoxane are shown in Table 2.

[0029] Table 2 Effect of different hydrolysis pressures on the yield of methylaluminoxane Serial number Hydrolysis gas phase pressure (MPa) Methylaluminoxane yield wt% 1 0.05 86.6 2 0.8 85.8 3 1.0 85.3 The data in Table 2 show that the gas phase pressure of hydrolysis has no significant effect on the yield of methylaluminoxane. Example 5

[0030] Other conditions are the same as those in Example 1. The effects of different hydrolysis temperatures on the yield of methylaluminoxane are shown in Table 3.

[0031] Table 3 Effect of different hydrolysis temperatures on the yield of methylaluminoxane Serial number Hydrolysis temperature (℃) Methylaluminoxane yield wt% 1 -20 86.8 2 10 80.5 3 30 65.3 The data in Table 3 show that the increase in hydrolysis temperature has a great influence on the yield of methylaluminoxane. The higher the hydrolysis temperature, the lower the yield of methylaluminoxane. Example 6

[0032] Other conditions were the same as those in Example 1. The effects of the stirring speed of the hydrolysis kettle and the power of the ultrasonic vibrator on the yield of methylaluminoxane are shown in Table 4.

[0033] Table 4 Effect of stirring speed of hydrolysis kettle and power of ultrasonic vibrator on yield of methylaluminoxane Serial number Stirring speed (rpm) Ultrasonic vibrator power (KW) Methylaluminoxane yield wt% 1 200 2.0 65.3 2 500 2.5 72.8 3 1000 3.0 85.6 The data in Table 4 show that increasing the stirring speed and the power of the ultrasonic vibrator are very helpful in increasing the yield of methylaluminoxane. Example 7

[0034] Other conditions were the same as those in Example 1. The effects of the brine tank temperature and the amount of methane gas on the yield of methylaluminoxane are shown in Table 5.

[0035] Table 5 Effect of brine tank temperature and methane gas volume on methylaluminoxane yield

[0036] The data in Table 5 show that under the conditions of a stirring speed of 1000 rpm and an ultrasonic vibrator power of 3 kW, lowering the brine tank temperature results in a low water content in methane, a slow hydrolysis rate of trimethylaluminum, and a high yield of methylaluminoxane; lowering the methane flow rate results in a low amount of water, a slow hydrolysis rate of trimethylaluminum, and a high yield of methylaluminoxane.

[0037] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum, characterized in that The following steps are involved: 1) Methane gas is introduced into a low-temperature aqueous solution at -30°C to 25°C to produce low-temperature methane gas containing gaseous water; 2) Passing low-temperature methane gas containing gaseous water into the trimethylaluminum organic solution at a methane gas flow rate of 0.2-5 L / min and a trimethylaluminum organic solution concentration of 15-50 wt%; 3) The hydrolysis reaction is carried out under the dual action of an ultrasonic vibrator and mechanical stirring. The power of the ultrasonic vibrator is 15kHz-40kHz, the mechanical stirring speed is 500-1000 rpm, and the hydrolysis temperature is -30°C to 50°C. 4) After the reaction is completed, the solid matter is filtered out to obtain a methylaluminoxane solution.

2. The method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum as claimed in claim 1, characterized in that In step 1), the temperature of the low-temperature aqueous solution is -20°C to 10°C, preferably -10°C to 0°C; the low-temperature aqueous solution is a calcium chloride aqueous solution or an ethylene glycol aqueous solution.

3. The method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum as claimed in claim 1, characterized in that In step 2), the methane flow rate is 0.5-3 L / min.

4. The method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum as claimed in claim 1, characterized in that In step 2), the trimethylaluminum organic solution is a trimethylaluminum benzene solution or a trimethylaluminum toluene solution, and the concentration of the trimethylaluminum organic solution is 20-40 wt%, preferably 25-30 wt%.

5. The method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum as claimed in claim 1, characterized in that In step 3), the power of the ultrasonic vibrator is 20 kHz to 30 kHz, and the mechanical stirring speed is 600 to 800 rpm.

6. The method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum as claimed in claim 1, characterized in that In step 3), the hydrolysis temperature is -15°C to 30°C, preferably -5°C to 5°C.

7. The method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum as claimed in claim 1, characterized in that In step 3), the pressure of the hydrolysis reaction is 0.05-1.0 MPa, preferably 0.1-0.8 MPa, more preferably 0.3-0.5 MPa.

8. The reaction device used in the method for preparing methylaluminoxane by direct hydrolysis of trimethylaluminum as claimed in claim 1 is characterized in that The system device comprises a methane storage tank (1), a methane circulation compressor (2), a low-temperature brine tank (3), and a hydrolysis kettle (4) connected in sequence with pipelines. An ultrasonic vibrator (5) and a mechanical stirrer (6) are installed in the hydrolysis kettle (4) for ultrasonic vibration and mechanical stirring. The gas phase outlet of the hydrolysis kettle (4) is connected to the methane storage tank (1) through a methane recovery pipeline (7).

9. The reaction device according to claim 8, characterized in that An automatic exhaust valve (8), a pressure discharge valve (9), and a safety valve (10) are provided on the external pipe of the methane storage tank (1).

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