Preparation method of aluminoxane, polyethylene catalyst and application

Abstract

The invention provides a preparation method of aluminoxane, a polyethylene catalyst and application. The preparation method of the aluminoxane comprises the following steps that a raw material system containing aluminum alkyl and a first material are subjected to a first reaction, the first material comprises one or more of furyl diol, furyl dialdehyde and furyl dicarboxylic acid, and an intermediate mixed solution is obtained; and introducing carbon dioxide into the intermediate mixed solution, and carrying out a second reaction at 0-120 DEG C to obtain the aluminoxane. According to the invention, the content of free alkyl aluminum in aluminoxane can be reduced.

Description

Technical Field

[0001] This invention relates to the field of aluminum oxane preparation technology, specifically to a method for preparing aluminum oxane, a polyethylene catalyst, and its applications. Background Technology

[0002] Aluminoxanes are commonly used cocatalysts in the field of olefin polymerization, playing important roles in catalyst activation and system purification. They have wide applications in the production of polyolefin elastomers (POE), metallocene polypropylene (mPP), metallocene polyethylene (mPE), cyclic olefin copolymers (COC), polymethylpentene (PMP), and ethylene oligomers.

[0003] Common methods for preparing aluminum oxanes include: 1. Direct reaction of alkyl aluminum with free water to generate aluminum oxanes; 2. Reaction of alkyl aluminum with the water of crystallization of inorganic salts to generate aluminum oxanes; 3. Reaction of alkyl aluminum with other substances containing active oxygen to generate aluminum oxanes. Common reaction processes are as follows:

[0004]

[0005] 3Me3Al+CO2→Me2AlOAlMe2+Me2AlOC(Me)3

[0006] For example, US patents US 5831109 and US 5728855 report a non-hydrolysis method for preparing alkylaluminoxanes. This method uses alkylaluminum as a raw material, reacts it with substances containing C=O structures or CO2 to generate intermediate products, and then heats them at 60-120°C for 1-24 hours to convert these intermediate products into alkylaluminoxanes. However, during the thermal decomposition process, about 1 / 3 of the Al equivalent enters the product solution as free alkylaluminum. Chinese patent CN 111004265A reports a hydrolysis method for preparing alkylaluminoxanes. This method divides the alkylaluminum solution, water, and inert solvent into n (n≥4) streams in a stream mixer. These streams are mixed and reacted to obtain alkylaluminoxanes. However, the aluminum oxane product solution prepared by this direct hydrolysis method often contains 5% or even higher levels of free alkylaluminum.

[0007] Under the action of a catalyst, an excessively high content of free alkyl aluminum in the aluminoxane solution will lead to the generation of a large amount of polyethylene wax during the ethylene oligomerization process, which will have an extremely adverse effect on the continuity of the reaction and the scale-up of engineering.

[0008] Therefore, how to reduce the content of free alkyl aluminum in aluminoxane products is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0009] This invention provides a method for preparing aluminoxane, a polyethylene catalyst, and its application, which can reduce the content of free alkyl aluminum in aluminoxane.

[0010] This invention provides a method for preparing aluminum oxane, comprising the following steps: subjecting a raw material system including alkyl aluminum and a first material to a first reaction, wherein the first material includes one or more of furanyl diol, furanyl dialdehyde, and furanyl dicarboxylic acid, to obtain an intermediate mixed solution; and introducing carbon dioxide into the intermediate mixed solution to carry out a second reaction, thereby obtaining the aluminum oxane.

[0011] Optionally, the alkylaluminum has the structure shown in Formula 1.

[0012]

[0013] In Formula 1, R1 is selected from alkyl groups having 1 to 20 carbon atoms. Preferably, R1 can be selected from methyl, ethyl, propyl, butyl, isobutyl, hexyl, octyl, isooctyl or decyl. More preferably, R1 can be selected from methyl, ethyl, isobutyl, hexyl, octyl or decyl.

[0014] Optionally, the alkyl aluminum in the raw material system has a mass percentage of 1% to 100%, preferably 10% to 70%, more preferably 15% to 50%; and / or, the molar ratio of the alkyl aluminum to the first material is 0.1 to 15.0, preferably 1.0 to 10.0, more preferably 1.0 to 5.0, and even more preferably 2.0 to 3.0; and / or, the raw material system further includes a solvent, the solvent including aromatic hydrocarbons and / or aliphatic hydrocarbons; and / or, the temperature of the first reaction is -40 to 220°C, preferably 0 to 190°C, more preferably 20 to 140°C; the time of the first reaction is 0.5 to 48 h, preferably 1 to 36 h, more preferably 1 to 12 h.

[0015] Optionally, the temperature of the second reaction is 0–120°C, preferably 20–100°C; and / or, the process of introducing carbon dioxide into the intermediate mixed solution to carry out the second reaction and obtain the aluminum oxane includes: introducing carbon dioxide into the intermediate mixed solution at a rate of 20–200 mL / min for a time of 22–225 min, carrying out the second reaction at 0–120°C to obtain the aluminum oxane; and / or, the process of introducing carbon dioxide into the intermediate mixed solution to carry out the second reaction and obtain the aluminum oxane includes: introducing carbon dioxide into the intermediate mixed solution at a rate of 20–200 mL / min, stopping the introduction of carbon dioxide after the pressure of the reaction system reaches 1–3 MPa, carrying out the second reaction at 0–120°C to obtain the aluminum oxane.

[0016] Optionally, the molar ratio of carbon dioxide to alkyl aluminum is greater than 0.1, preferably 0.2 to 3.0.

[0017] Optionally, the structure of the aluminum oxane is as shown in Formula 2 or Formula 3.

[0018]

[0019] In Formulas 2 and 3, R2, R3, R4, and R5 are each independently selected from alkyl groups having 1 to 20 carbon atoms, R1 is selected from alkyl groups having 1 to 20 carbon atoms, and n is 2 to 100.

[0020] Optionally, the preparation process of the aluminoxane is carried out in a reactor, which includes one or more of the following: a batch reactor, a tubular reactor, a tower reactor, a microchannel reactor, and a low-temperature plasma reactor.

[0021] Optionally, after the second reaction is completed, the product of the second reaction is post-processed. The post-processing method includes one or more of aging, filtration, sedimentation, distillation, and condensation to obtain the aluminum oxide.

[0022] The present invention also provides a polyethylene catalyst comprising obtaining the aluminoxane according to the preparation method described above.

[0023] The present invention also provides a method for preparing polyethylene, comprising polymerizing ethylene under the catalytic action of a polyethylene catalyst as described above, to obtain the polyethylene.

[0024] This invention provides a method for preparing aluminoxane, a polyethylene catalyst, and its application. It can reduce the content of free alkyl aluminum in aluminoxane, and the aluminoxane can be used in ethylene oligomerization reaction. It has high co-catalytic activity, and the polyethylene produced has a low amount of polyethylene wax, which improves the quality of polyethylene products, has high production efficiency, and the production process is safe and controllable. Attached Figure Description

[0025] Figure 1 The image shows the 1H NMR spectrum of the aluminum oxane from Example 1. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0027] This invention provides a method for preparing aluminum oxane, comprising the following steps: subjecting a raw material system including alkyl aluminum and a first material to a first reaction, wherein the first material includes one or more of furanyl diol, furanyl dialdehyde, and furanyl dicarboxylic acid, to obtain an intermediate mixed solution; and introducing carbon dioxide into the intermediate mixed solution to carry out a second reaction, thereby obtaining the aforementioned aluminum oxane (furanyl aluminum oxane).

[0028] According to the inventor's research and analysis: In the above-mentioned process of preparing aluminoxane (modified aluminoxane or a solution containing aluminoxane), the use of carbon dioxide can effectively remove free alkyl aluminum in the intermediate mixed solution, thereby removing free alkyl aluminum in the aluminoxane. This avoids the participation of high content of free alkyl aluminum in the above-mentioned aluminoxane-catalyzed ethylene oligomerization reaction, reduces the amount of polyethylene wax generated in the ethylene oligomerization reaction, improves the quality of the ethylene oligomerization reaction product, and also improves the catalytic activity of the above-mentioned aluminoxane in ethylene oligomerization reaction. Its catalytic activity is higher than that of methylaluminoxane. At the same time, due to the reduction in the amount of polyethylene wax generated, the safety risks and hidden dangers caused by frequent pipe unclogging can be reduced, the continuous production time can be extended, which is conducive to improving the production efficiency of the ethylene oligomerization reaction and reducing production costs.

[0029] In some embodiments, the structure of the alkyl aluminum described above is as shown in Formula 1.

[0030]

[0031] In Formula 1, R1 is selected from alkyl groups having 1 to 20 carbon atoms. For example, the number of carbon atoms in the alkyl group can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, or 20.

[0032] Preferably, R1 can be selected from methyl, ethyl, propyl, butyl, isobutyl, hexyl, octyl, isooctyl or decyl.

[0033] More preferably, R1 can be selected from methyl, ethyl, isobutyl, hexyl, octyl or decyl.

[0034] The mass percentage (mass fraction) of the aforementioned alkyl aluminum in the raw material system can be 1% to 100%, for example, 1%, 5%, 10%, 25%, 35%, 55%, 60%, 70%, 80%, 90%, 100%, or any combination thereof, preferably 10% to 70%, more preferably 15% to 50%. That is, the aforementioned raw material system including alkyl aluminum can be alkyl aluminum or a mixture including alkyl aluminum.

[0035] In some embodiments, the above-described feedstock system further includes a solvent, which comprises aromatic hydrocarbons and / or aliphatic hydrocarbons. Specifically, the solvent may include one or more of benzene, toluene, xylene, hexane, heptane, cyclohexane, methylcyclohexane, and isoalkanes.

[0036] In the first material, furanyl diol may include furanyl diethanol, furanyl dialdehyde may include furanyl dicarboxaldehyde, and furanyl dicarboxylic acid may include furanyl dicarboxylic acid.

[0037] The molar ratio of the alkylaluminum and the first material can be 0.1 to 15.0, for example, 0.1, 0.5, 1.0, 3.0, 5.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0 or any combination thereof, preferably 1.0 to 10.0, more preferably 1.0 to 5.0, and even more preferably 2.0 to 3.0.

[0038] In some embodiments, the temperature of the first reaction is -40 to 220°C, for example, a range of -40°C, -30°C, -20°C, -10°C, 0°C, 20°C, 50°C, 60°C, 100°C, 140°C, 150°C, 190°C, 200°C, 220°C, or any combination thereof, preferably 0 to 190°C, more preferably 20 to 140°C.

[0039] In some embodiments, the time for the first reaction is 0.5 to 48 hours, for example, a range of 0.5 hours, 1 hour, 5 hours, 10 hours, 12 hours, 20 hours, 30 hours, 36 hours, 40 hours, 48 ​​hours or any combination thereof, preferably 1 to 36 hours, more preferably 1 to 12 hours.

[0040] The temperature of the second reaction described above can be 0–120°C, for example, 0°C, 10°C, 20°C, 50°C, 60°C, 80°C, 100°C, 110°C, 120°C, or any combination thereof, preferably 20–100°C. This facilitates the complete reaction of free alkyl aluminum, improves the removal degree of free alkyl aluminum, ensures that the content of free alkyl aluminum in the aluminoxane is not higher than 0.5% (0–0.5%), and avoids the digestion of aluminoxane, thereby improving the ethylene oligomerization activity of the aluminoxane solution and reducing the content of polyethylene wax in the reaction solution catalyzing the ethylene oligomerization.

[0041] In some embodiments, the process of introducing carbon dioxide into an intermediate mixed solution and carrying out a second reaction at 0–120°C to obtain aluminum oxane includes: introducing carbon dioxide into the intermediate mixed solution at a rate of 20–200 mL / min for a duration of 22–225 min, and carrying out the second reaction at 0–120°C to obtain aluminum oxane. It is understood that the above-mentioned second reaction is carried out under normal pressure, and the carbon dioxide introduction time is the time of the second reaction. In specific implementations, the time of the second reaction can be controlled by adjusting the carbon dioxide introduction time. For example, the carbon dioxide introduction rate can be a range of 20 mL / min, 50 mL / min, 100 mL / min, 150 mL / min, 200 mL / min, or any combination thereof; the carbon dioxide introduction time can be a range of 22 min, 50 min, 100 min, 150 min, 200 min, 225 min, or any combination thereof.

[0042] In some embodiments, the process of introducing carbon dioxide into an intermediate mixed solution and carrying out a second reaction at 0–120°C to obtain aluminum oxane includes: introducing carbon dioxide into the intermediate mixed solution at a rate of 20–200 mL / min, stopping the introduction of carbon dioxide after the pressure of the reaction system reaches 1–3 MPa, and carrying out the second reaction at 0–120°C to obtain aluminum oxane. The above-described second reaction process can be carried out under high pressure. Exemplarily, the pressure can be a range of 1 MPa, 2 MPa, 3 MPa, or any combination thereof.

[0043] The molar ratio of carbon dioxide to alkyl aluminum can be greater than 0.1, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 1.0, 1.5, 2.0, 2.5, 3.0 or any combination thereof, preferably 0.2 to 3.0.

[0044] After the second reaction is completed, the product can be post-processed. Post-processing methods include one or more of aging, filtration, sedimentation, distillation, and condensation to obtain aluminum oxane. This aluminum oxane can be stored and sold externally or used directly in downstream ethylene oligomerization reactions.

[0045] In practice, the preparation process of the aforementioned aluminoxane can be carried out in a reactor, which includes one or more of the following: a batch reactor, a tubular reactor, a tower reactor, a microchannel reactor, and a low-temperature plasma reactor.

[0046] The structure of the aluminum oxane in the embodiments of the present invention is shown in Formula 2 or Formula 3.

[0047]

[0048] In Formulas 2 and 3, R2, R3, R4, and R5 can each be independently selected from alkyl groups having 1 to 20 carbon atoms, and R1 can be selected from alkyl groups having 1 to 20 carbon atoms. For example, the number of carbon atoms in the alkyl groups R1, R2, R3, R4, and R5 can each be independently selected from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, and 20; n can be 2 to 100.

[0049] Preferably, R2, R3, R4, and R5 can each be independently selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, octyl, or decyl. More preferably, R2, R3, R4, and R5 can each be independently selected from methyl, ethyl, isobutyl, tert-butyl, hexyl, octyl, or decyl.

[0050] This invention also provides a polyethylene catalyst, comprising aluminum oxane prepared according to the above preparation method.

[0051] Understandably, the aforementioned polyethylene catalyst also includes a main catalyst. This invention does not specifically limit the main catalyst; any polyethylene main catalyst commonly used in the art can be used, such as the main catalyst shown in Formula 4.

[0052]

[0053] The main catalyst shown in Formula 4 above can be synthesized according to the method described in the specific embodiment of Chinese patent document CN 117563674A. The materials and reagents used in the synthesis of the main catalyst can be obtained commercially.

[0054] In specific implementation, the ratio of the aluminoxane (or a solution containing alkylaluminum) and the main catalyst shown in Formula 4 in the embodiments of the present invention can be adjusted according to an Al / Cr (molar ratio) of 90 to 110, for example, 90, 100, 110 or any combination thereof.

[0055] This invention also provides a method for preparing polyethylene, comprising polymerizing ethylene under the catalytic action of the above-mentioned polyethylene catalyst to obtain polyethylene.

[0056] The process of polymerizing ethylene under the catalysis of the above-mentioned polyethylene catalyst to obtain polyethylene includes: mixing the main catalyst, the above-mentioned alkyl aluminum (or a solution containing alkyl aluminum) and solvent, then introducing hydrogen gas to raise the pressure to 0.3-0.7 MPa, for example 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa or any combination thereof, and then continuously introducing ethylene to maintain the system pressure at 4-6 MPa, for example 4 MPa, 5 MPa, 6 MPa or any combination thereof, and carrying out the polymerization reaction at a temperature of 38-42°C, for example 38°C, 39°C, 40°C, 41°C, 42°C or any combination thereof, and after the polymerization reaction is completed, cooling and depressurizing to obtain polyethylene (ethylene oligomer).

[0057] The ratio of the main catalyst to the volume can be (0.08 to 0.12) mmol:1L, for example, 0.08 mmol:1L, 0.1 mmol:1L, 0.12 mmol:1L or any combination thereof.

[0058] The aforementioned volume may include dehydrated and deoxygenated methylcyclohexane.

[0059] During the mixing of the main catalyst, the aforementioned alkylaluminum (or a solution containing alkylaluminum), and the solvent, the temperature of the mixture can be maintained in advance at 38–42°C, for example, 38°C, 39°C, 40°C, 41°C, 42°C, or any combination thereof (i.e., the polymerization reaction temperature). Furthermore, to further improve the efficiency of the polymerization reaction, stirring can be performed during the polymerization process; after the polymerization reaction is completed, an ice-water bath can be used for cooling.

[0060] The polymerization reaction time can be 18 to 22 minutes, for example, 18 minutes, 19 minutes, 20 minutes, 21 minutes, 22 minutes or any combination thereof.

[0061] In practice, the polymerization reaction can be carried out in a reactor. This embodiment of the invention does not impose a particular limitation on the volume of the reactor; for example, the volume of the reactor can be 2L. Understandably, before carrying out the polymerization reaction, oxygen and moisture in the reactor must be removed. For example, the reactor can be heated to 130–140°C, then evacuated to 20–22 MPa and maintained for 2–2.2 hours. Then, nitrogen gas can be used to purge the reactor 3–4 times. After the nitrogen purging is completed, the reactor should be restored to normal pressure and cooled to room temperature before carrying out the polymerization reaction.

[0062] After obtaining polyethylene (an oligomer of ethylene), the polyethylene wax can be removed by filtration. The yield of polyethylene wax can be obtained by weighing the polyethylene wax. At the same time, the yield of 1-hexene and 1-octene can be obtained by gas chromatography analysis of the filtrate. The above weighing and gas chromatography analysis processes can be performed according to conventional methods in this field.

[0063] The present invention will now be described in more detail through specific embodiments.

[0064] The raw materials used in the various embodiments and comparative examples of this invention can all be purchased through ordinary commercial channels, and no additional purification treatment has been performed unless otherwise specified.

[0065] Example 1

[0066] This embodiment provides a method for preparing modified alkylaluminoxanes, including the following steps:

[0067] 300g of a 10% (w / w) trimethylaluminum toluene solution and 325g of furanyl dicarboxylic acid were reacted at -30℃ for 36 hours to obtain an intermediate mixed solution.

[0068] The intermediate mixture was then heated to 20°C, and carbon dioxide was introduced into it at a rate of 100 mL / min for 22 minutes. The second reaction was carried out at 20°C for the same duration as the carbon dioxide introduction time (22 minutes). After the second reaction was complete, the product was filtered to obtain a solution containing aluminum oxane (which also contained toluene). A small amount of the aluminum oxane-containing solution was dissolved in deuterated benzene and subjected to NMR. 1 ¹H spectroscopy was used to calculate the free alkyl aluminum content. For detailed testing methods, please refer to Macromolecules 1990, 23, 4489-4491.

[0069] This embodiment also provides a method for preparing polyethylene, including the following steps:

[0070] 1 L of dehydrated and deoxygenated methylcyclohexane, 0.1 mmol of the main catalyst shown in Formula 4, and the solution containing aluminum oxane prepared in this example were mixed and heated to 40 °C. The amount of aluminum oxane solution added was adjusted according to Al / Cr (molar ratio) = 100. Stirring was started, and hydrogen gas was introduced into the above mixture to increase the pressure to 0.5 MPa. Then, ethylene was continuously introduced to maintain the pressure of the mixture at 5 MPa. The polymerization reaction was carried out at 40 °C for 20 min. Then, the ethylene was stopped, and the reactor was quickly cooled using an ice-water bath. The pressure was slowly released to atmospheric pressure to obtain α-olefin and polyethylene wax (ethylene oligomer).

[0071] Comparative Example 2

[0072] A 30% MAO toluene solution produced by Grace Company was selected as a control, and other conditions were basically the same as in the examples.

[0073] Referring to Example 1, the preparation of aluminum oxane and polyethylene in Examples 2-31 and Comparative Example 1 was carried out. The raw material system, first material, molar ratio of alkyl aluminum to first material, temperature and time of the first reaction, carbon dioxide introduction rate, introduction time or pressure at the end of introduction, temperature and time of the second reaction, and molar ratio of carbon dioxide to alkyl aluminum for each example and comparative example are summarized in Table 1; other conditions are consistent with those in Example 1.

[0074] Table 1

[0075]

[0076]

[0077] Test case

[0078] 1. The following parameters of the above embodiments and comparative examples were tested:

[0079] 1) Content of free alkyl aluminum in aluminoxane: Free alkyl aluminum has a distinct characteristic peak in the range of -0.2 to 1.0 ppm in the NMR 1H spectrum. If this characteristic peak is not detected, it indicates that the content of free alkyl aluminum is 0. The specific results are shown in Table 2.

[0080] 2) Content of polyethylene wax (PE) in polyethylene: The polyethylene (ethylene oligomer product) was filtered to remove the polyethylene wax in the polyethylene. The removed polyethylene wax was weighed to obtain the content of polyethylene wax in the polyethylene. The specific results are shown in Table 2.

[0081] The selectivity of aluminoxane in ethylene polymerization was evaluated. The specific process included gas chromatography analysis of the filtered filtrate to obtain the yields of 1-hexene (1-C6), 1-octene (1-C8) and other small molecule olefin monomers. The specific results are shown in Table 2.

[0082] 3) Catalytic activity (co-catalytic activity) of aluminoxane in the preparation of polyethylene: The test method is referred to the patent document CN117563674A, page 6, paragraph

[0041] , and the specific results are shown in Table 2;

[0083] 4) Measure the 1H NMR spectrum (¹H NMR) of the aluminum oxane from Example 1, such as... Figure 1 As shown;

[0084] 5) Molecular weight of aluminum oxane: For detailed test methods, refer to Macromolecules 1990, 23, 4489-4491.

[0085] 2. Test Results

[0086] Table 2

[0087]

[0088]

[0089] Data Analysis:

[0090] The aluminoxane solution prepared in the embodiments of the present invention has high ethylene oligomerization activity, while the polyethylene wax content in the reaction solution is extremely low. In addition, the molecular weight of the aluminoxane prepared in the embodiments of the present invention can be 7000-15000 g / mol.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for the preparation of aluminoxane characterized in that, The method comprises the following steps: carrying out a first reaction on a raw material system comprising alkyl aluminum and a first material, the first material comprising one or more of furan-based diols, furan-based dials, furan-based dicarboxylic acids, to obtain an intermediate mixed solution; introducing carbon dioxide into the intermediate mixed solution to carry out a second reaction, to obtain the aluminoxane.

2. The process for the preparation of aluminoxane according to claim 1, characterized in that, The structure of the alkyl aluminum is shown in Formula 1, in Formula 1, R1 is selected from alkyl groups with 1-20 carbon atoms, preferably, R1 can be selected from methyl, ethyl, propyl, butyl, isobutyl, hexyl, octyl, isooctyl or decyl; more preferably, R1 can be selected from methyl, ethyl, isobutyl, hexyl, octyl or decyl.

3. The method for preparing aluminoxane according to claim 1, wherein, the mass percentage of the alkyl aluminum in the raw material system is 1%-100%, preferably 10%-70%, more preferably 15%-50%; and / or, the molar ratio of the alkyl aluminum to the first material is 0.1-15.0, preferably 1.0-10.0, more preferably 1.0-5.0, further preferably 2.0-3.0; and / or, the raw material system further comprises a solvent, and the solvent comprises aromatic hydrocarbons and / or aliphatic hydrocarbons; and / or, the temperature of the first reaction is -40-220℃, preferably 0-190℃, more preferably 20-140℃; the time of the first reaction is 0.5-48h, preferably 1-36h, more preferably 1-12h.

4. The method for preparing aluminoxane according to claim 1, wherein, the temperature of the second reaction is 0-120℃, preferably 20-100℃; and / or, the process of introducing the carbon dioxide into the intermediate mixed solution to carry out the second reaction to obtain the aluminoxane comprises: introducing the carbon dioxide into the intermediate mixed solution at a flow rate of 20-200 mL / min, the carbon dioxide is introduced for 22-225 min, the second reaction is carried out at 0-120℃ to obtain the aluminoxane; and / or, the process of introducing the carbon dioxide into the intermediate mixed solution to carry out the second reaction to obtain the aluminoxane comprises: introducing the carbon dioxide into the intermediate mixed solution at a flow rate of 20-200 mL / min, the reaction system is pressurized to 1-3 MPa, then the introduction of the carbon dioxide is stopped, the second reaction is carried out at 0-120℃ to obtain the aluminoxane.

5. The method for preparing aluminoxane according to any one of claims 1-4, wherein, the molar ratio of the carbon dioxide to the alkyl aluminum is greater than 0.1, preferably 0.2-3.

0.

6. The method for preparing aluminoxane according to any one of claims 1-4, wherein, the structure of the aluminoxane is shown in Formula 2 or Formula 3, in Formula 2 and Formula 3, R2, R3, R4 and R5 are each independently selected from alkyl groups with 1-20 carbon atoms, R1 is selected from alkyl groups with 1-20 carbon atoms, and n is 2-100.

7. The process for the preparation of aluminoxane according to any one of claims 1 to 4, characterized in that, The preparation process of the aluminoxane is carried out in a reactor, and the reactor comprises one or more of a kettle reactor, a tubular reactor, a tower reactor, a micro-channel reactor, and a low-temperature plasma reactor.

8. The process for the preparation of aluminoxane according to any one of claims 1 to 4, characterized in that, After the second reaction is completed, the product of the second reaction is subjected to post-treatment, and the post-treatment method comprises one or more of aging, filtration, sedimentation, distillation, and condensation, to obtain the aluminoxane.

9. A polyethylene catalyst characterized in that, The aluminoxane is obtained by the preparation method according to any one of claims 1-8.

10. A process for the preparation of polyethylene, characterized in that, The polyethylene is prepared by subjecting ethylene to polymerization under the catalysis of the polyethylene catalyst according to claim 9.

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