Method for synthesizing alkylaluminoxane from paraformaldehyde and preparation method of modified alkylaluminoxane

Abstract

The invention discloses a method for synthesizing alkylaluminoxane from paraformaldehyde and a preparation method of modified alkylaluminoxane. The method for synthesizing alkylaluminoxane comprises the following steps: step 1, reacting paraformaldehyde with trialkyl aluminum to prepare an alkylaluminoxane precursor solution; and 2, pyrolyzing the obtained alkyl aluminoxane precursor to prepare the alkyl aluminoxane. The invention also provides a method for preparing modified alkylaluminoxane by using the alkylaluminoxane. The method provided by the invention can effectively avoid the defects that the existing reaction needs high pressure, is difficult to quantify and cannot realize large-scale production, is more beneficial to the realization of industrial large-scale production requirements, and improves the production speed and safety of methylaluminoxane at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of fine chemical synthesis, and particularly relates to a method for synthesizing alkylaluminoxane from paraformaldehyde and a method for preparing modified alkylaluminoxane. Background Art

[0002] Methylaluminoxane, as the core cocatalyst of the metallocene catalyst system, has very important uses in the field of olefin polymerization. This methylaluminoxane has a cage-like structure that can effectively disperse negative charges to make it a non-coordinating charge balance body of the metallocene cation active center, showing unique properties in olefin polymerization. The use of methylaluminoxane-based cocatalysts can greatly improve the activity of the catalyst.

[0003] The synthesis methods of methylaluminoxane are basically divided into two types. The first is the hydrolysis method, which can be summarized as a direct hydrolysis process and an indirect hydrolysis process according to different feeding methods of the water participating in the reaction. The direct water process takes the way of adding water to the trimethylaluminum toluene solution, and a relatively high reaction yield can be obtained. However, due to the extremely high danger of the reaction between trimethylaluminum and water, this process has very high requirements for the quality of the equipment. The indirect water process has a low reaction yield of the target product MAO due to the limitations of the feeding process itself. There is also a non-hydrolysis method, which mainly uses trimethylaluminum to react with carbon dioxide, alcohols, organic acid compounds, and then obtains MAO through pyrolysis (such as patents US 5831109, US 5728855). However, when using carbon dioxide as the oxygen source reagent, in order to ensure the progress of the reaction, it needs to be carried out under a certain pressure. If the reactants accumulate, it is easy to suddenly trigger and cause production accidents; when using organic acids and alcohols as the oxygen source reagents, the reaction is too intense and difficult to control. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for synthesizing alkylaluminoxane from paraformaldehyde and a method for preparing modified alkylaluminoxane, with milder reaction conditions and a safer and more controllable production process.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A method for synthesizing alkylaluminoxane from paraformaldehyde, comprising the following steps:

[0007] Step 1: React paraformaldehyde with trialkylaluminum at a reaction temperature to prepare an alkylaluminoxane precursor solution.

[0008] Step 2: Pyrolyze the obtained alkylaluminoxane precursor to prepare alkylaluminoxane.

[0009] In the present invention, the alkyl in the alkylaluminoxane is an alkyl with C1-C8, preferably methylaluminoxane.

[0010] In the present invention, the alkyl group in the trialkylaluminum is an alkyl group with 1 - 8 carbon atoms, and trimethylaluminum is preferred.

[0011] In the present invention, in step one, the degree of polymerization of paraformaldehyde is 2 - 300, preferably 5 - 150, and more preferably 10 - 30.

[0012] In the present invention, in step one, the molar ratio of trialkylaluminum to formaldehyde monomer in paraformaldehyde is 1:0.1 - 1:10, preferably 1:0.5 - 1:1.5.

[0013] In the present invention, the reaction temperature in step one is -20 - 100 °C, preferably 0 - 50 °C.

[0014] In the present invention, in step one, the reaction of paraformaldehyde with trialkylaluminum is carried out in a solvent, and the solvent can be one or a mixture of several of any liquid alkanes and aromatic hydrocarbons, and toluene or heptane is preferred.

[0015] In the present invention, in step two, the pyrolysis temperature is 80 - 200 °C, preferably 100 - 150 °C.

[0016] The present invention also provides a preparation method of a modified alkylaluminoxane: Mix and react the alkylaluminoxane prepared by the preparation method of the present invention with a modified alkylaluminum to obtain a modified alkylaluminoxane.

[0017] In the present invention, the structure of the modified alkylaluminum is AlR 3 , where R is any alkyl group other than methyl, and the modified alkylaluminum is preferably triethylaluminum, triisobutylaluminum, trihexylaluminum, or trioctylaluminum.

[0018] In the present invention, the molar ratio of the trialkylaluminum to the modified alkylaluminum is 1:0.1 - 1:10, preferably 1:0.3 - 1:3.

[0019] In the present invention, the reaction temperature of the alkylaluminoxane and the modified alkylaluminum is 20 - 150 °C, preferably 60 - 100 °C.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] If liquid aldehyde is used as the oxygen source in practice, the excellent reaction is too fast, the reaction is not easy to control, safety accidents are likely to occur, and large-scale production cannot be carried out. In this application, solid paraformaldehyde is used as the oxygen source reagent to synthesize alkylaluminoxane and modified alkylaluminoxane. The reaction conditions are mild, and the time required for the synthesis and decomposition of the intermediate is usually more than 8 hours; high pressure operation is not required, and there are no safety problems caused by sudden accumulation of reactants. It has high economic advantages, can effectively avoid the disadvantages of the existing reaction that cannot be produced on a large scale, is more conducive to meeting the requirements of large-scale industrial production, and at the same time improves the production speed and safety of alkylaluminoxane and modified alkylaluminoxane.

[0022] When the methylaluminoxane or modified methylaluminoxane prepared by the method of the present invention is used in the olefin polymerization reaction, under the same conditions of the main catalyst, the co-catalytic activity is higher. Detailed implementation mode

[0023] In order to make the purpose, technical solution and advantages of the present invention clearer, the following further details the present invention with reference to the embodiments. It should be understood that the present invention is not limited to the listed embodiments, but should also include any other well-known changes within the scope of the rights required by the present invention.

[0024] The raw materials used in the embodiments and comparative examples of the present invention can all be obtained through ordinary commercial channels. Among them, low-polymerization paraformaldehyde is prepared by the methods described in Examples 1-6 and Comparative Examples 1-2 of Chinese Patent CN101845130A; the sample prepared by the method described in Comparative Example 2 is stored in a sealed manner. As the storage time increases, the degree of polymerization increases. After 8 days of storage, the degree of polymerization is 78; after 13 days of storage, the degree of polymerization is 149; after 42 days of storage, the degree of polymerization is 261; after 47 days of storage, the degree of polymerization is 295. The principle of this increase in the degree of polymerization is well known in the industry. For example, it is described in detail in "Research on the Preparation Process of Paraformaldehyde and Its Auxiliaries, Journal of Nanjing University of Technology, 2004, vol26".

[0025] In the embodiments of the present invention, methylaluminoxane can be prepared or further modified methylaluminoxane can be prepared. The obtained methylaluminoxane or modified methylaluminoxane can be used as a co-catalyst to catalyze the copolymerization of ethylene and α-olefin to test its co-catalytic activity.

[0026] In the polymerization experiment, the main catalyst is a compound shown in formula (VII). This compound is synthesized according to the method described in Example 19 of Patent CN111943977A, X is Me, and the materials, reagents, etc. used can all be obtained through commercial channels.

[0027]

[0028] Ethylene and octene copolymerization reaction: 0.8 L of dried n-hexane solvent was added to a 2 L stainless steel autoclave, and the temperature was raised to 170 °C. After stirring for 30 min, the autoclave was cleaned. After the cleaning was completed, it was cooled to room temperature and the solvent was discharged. Then the temperature was raised to 160 °C and evacuated and dried for 60 min. During this period, nitrogen replacement was carried out 10 - 15 times. The autoclave was cooled to below 80 °C, 0.8 L of n-hexane and 0.2 L of 1-octene were added to the autoclave, 1 μmol of the metal compound shown in formula (VII) was added, and then a certain amount of MAO or MMAO was added according to Al / M = 500. After raising the temperature to the set temperature (polymerization temperature), 3 MPa of ethylene was introduced to start the polymerization reaction, and the reaction was carried out for 6 min. Then the ethylene was vented, the reaction solution was put into ethanol, the precipitated solid was collected, and it was dried to constant weight in a vacuum drying oven at 60 °C and then weighed.

[0029] Example 1

[0030] (1) 5 g of paraformaldehyde (prepared by the method of Example 6 of Patent CN101845130A, degree of polymerization 8) and 100 mL of heptane were added to a 250 mL jacketed flask. The temperature of the flask was controlled at 20 °C using an oil bath, and 12.9 g of trimethylaluminum was slowly added under continuous stirring. (The molar ratio of trimethylaluminum to paraformaldehyde monomer was 1.0). The obtained solution was stirred at 20 °C for 12 hours to prepare a methylaluminoxane precursor.

[0031] (2) The methylaluminoxane precursor prepared in step (1) was heated to 120 °C and stirred and pyrolyzed for 12 h to release the generated gas, obtaining a methylaluminoxane solution. The prepared MAO was used for the copolymerization of ethylene and octene, and the overall polymerization activity was 2.1×10 9 g (polymer) / mol (catalyst)·h.

[0032] Example 2

[0033] (1) 7 g of paraformaldehyde (prepared by the method of Example 1 of Patent CN101845130A, degree of polymerization 10) and 100 mL of hexane were added to a 250 mL jacketed flask. The temperature of the flask was controlled at -20 °C using an oil bath, and 3.6 g of trimethylaluminum was slowly added under continuous stirring. (The molar ratio of trimethylaluminum to paraformaldehyde monomer was 0.2). The obtained solution was stirred at -20 °C for 24 hours to prepare a methylaluminoxane precursor.

[0034] (2) The methylaluminoxane precursor prepared in step (1) was heated to 80 °C and stirred and pyrolyzed for 24 h to release the generated gas, obtaining a methylaluminoxane solution. The prepared MAO was used for the copolymerization of ethylene and octene, and the overall polymerization activity was 1.9×10 9 g (polymer) / mol (catalyst)·h.

[0035] Example 3

[0036] (1) Add 9 g of paraformaldehyde (prepared by the method of Comparative Example 2 of Patent CN101845130A, with a degree of polymerization of 47) and 100 mL of toluene to a 250 mL jacketed flask. Control the temperature of the flask at 0 °C using an oil bath, and slowly add 46.3 g of trimethylaluminum with continuous stirring (the molar ratio of trimethylaluminum to paraformaldehyde monomer is 2). The resulting solution is stirred at 0 °C for 17 hours to obtain a methylaluminoxane precursor.

[0037] (2) Heat the methylaluminoxane precursor prepared in step (1) to 100 °C, stir and pyrolyze for 16 h, and release the generated gas to obtain a methylaluminoxane solution. The prepared MAO is used for the copolymerization of ethylene and octene, and the overall polymerization activity is 2.5×10 9 g (polymer) / mol (catalyst)·h.

[0038] Example 4

[0039] (1) Add 6 g of paraformaldehyde (prepared by the method of Comparative Example 2 of Patent CN101845130A, stored for another 8 days, with a degree of polymerization of 78) and 100 mL of methylcyclohexane to a 250 mL jacketed flask. Control the temperature of the flask at 40 °C using an oil bath, and slowly add 61.7 g of trimethylaluminum with continuous stirring (the molar ratio of trimethylaluminum to paraformaldehyde monomer is 4). The resulting solution is stirred at 40 °C for 10 hours to obtain a methylaluminoxane precursor.

[0040] (2) Heat the methylaluminoxane precursor prepared in step (1) to 140 °C, stir and pyrolyze for 10 h, and release the generated gas to obtain a methylaluminoxane solution. The prepared MAO is used for the copolymerization of ethylene and octene, and the overall polymerization activity is 2.2×10 9 g (polymer) / mol (catalyst)·h.

[0041] Example 5

[0042] (1) Add 4 g of paraformaldehyde (prepared by the method of Comparative Example 2 of Patent CN101845130A, stored for another 13 days, with a degree of polymerization of 149) and 100 mL of cyclohexane to a 250 mL jacketed flask. Control the temperature of the flask at 60 °C using an oil bath, and slowly add 61.6 g of trimethylaluminum with continuous stirring (the molar ratio of trimethylaluminum to paraformaldehyde monomer is 6). The resulting solution is stirred at 60 °C for 8 hours to obtain a methylaluminoxane precursor.

[0043] (2) Heat the methylaluminoxane precursor prepared in step (1) to 160 °C, stir and pyrolyze for 8 h, and release the generated gas to obtain a methylaluminoxane solution. The prepared MAO is used for the copolymerization of ethylene and octene, and the overall polymerization activity is 2.0×10 9g (polymer) / mol (catalyst)·h.

[0044] Example 6

[0045] (1) 8 g of paraformaldehyde (prepared by the method of Comparative Example 2 of Patent CN101845130A, stored for another 42 days, degree of polymerization 261) and 100 mL of cyclohexyltoluene were added to a 250 mL jacketed flask. The temperature of the flask was controlled at 80 °C using an oil bath. 164.6 g of trimethylaluminum was slowly added under continuous stirring (the molar ratio of trimethylaluminum to paraformaldehyde monomer was 8). The resulting solution was stirred at 80 °C for 6 hours to obtain a methylaluminoxane precursor.

[0046] (2) The methylaluminoxane precursor prepared in step (1) was heated to 180 °C and pyrolyzed with stirring for 6 h, and the generated gas was released to obtain a methylaluminoxane solution. The prepared MAO was used for the copolymerization of ethylene and octene, and the overall polymerization activity was 1.8×10 9 g (polymer) / mol (catalyst)·h.

[0047] Example 7

[0048] (1) 3 g of paraformaldehyde (prepared by the method of Comparative Example 2 of Patent CN101845130A, stored for another 47 days, degree of polymerization 295) and 100 mL of heptane were added to a 250 mL jacketed flask. The temperature of the flask was controlled at 100 °C using an oil bath. 77.1 g of trimethylaluminum was slowly added under continuous stirring (the molar ratio of trimethylaluminum to paraformaldehyde monomer was 10). The resulting solution was stirred at 100 °C for 3 hours to obtain a methylaluminoxane precursor.

[0049] (2) The methylaluminoxane precursor prepared in step (1) was heated to 200 °C and pyrolyzed with stirring for 4 h, and the generated gas was released to obtain a methylaluminoxane solution. The prepared MAO was used for the copolymerization of ethylene and octene, and the overall polymerization activity was 1.7×10 9 g (polymer) / mol (catalyst)·h.

[0050] Example 8

[0051] Steps (1) and (2) refer to Example 3. In step (3), triethylaluminum was added to the MAO solution prepared in (2) (the molar ratio of trimethylaluminum to triethylaluminum was 0.1). The resulting mixture was heated and stirred at 20 °C for 6 hours to obtain a transparent modified methylaluminoxane solution. The prepared MMAO was used for the copolymerization of ethylene and octene, and the overall polymerization activity was 2.8×10 9 g (polymer) / mol (catalyst)·h.

[0052] Example 9

[0053] Steps (1) and (2) refer to Example 3. In step (3), triisobutylaluminum (the molar ratio of trimethylaluminum to triisobutylaluminum is 1) is added to the MAO solution prepared in (2). The resulting mixture is heated and stirred at 60 °C for 6 hours to obtain a transparent modified methylaluminoxane solution. The prepared MMAO is used for the copolymerization of ethylene and octene, and the overall polymerization activity is 3.1×10 9 g (polymer) / mol (catalyst)·h.

[0054] Example 10

[0055] Steps (1) and (2) refer to Example 3. In step (3), trihexylaluminum (the molar ratio of trimethylaluminum to trihexylaluminum is 5) is added to the MAO solution prepared in (2). The resulting mixture is heated and stirred at 100 °C for 6 hours to obtain a transparent modified methylaluminoxane solution. The prepared MMAO is used for the copolymerization of ethylene and octene, and the overall polymerization activity is 3.5×10 9 g (polymer) / mol (catalyst)·h.

[0056] Example 11

[0057] Steps (1) and (2) refer to Example 3. In step (3), trioctylaluminum (the molar ratio of trimethylaluminum to trioctylaluminum is 10) is added to the MAO solution prepared in (2). The resulting mixture is heated and stirred at 150 °C for 6 hours to obtain a transparent modified methylaluminoxane solution. The prepared MMAO is used for the copolymerization of ethylene and octene, and the overall polymerization activity is 4.2×10 9 g (polymer) / mol (catalyst)·h.

[0058] Comparative Example 1

[0059] A 10% MAO toluene solution produced by Grace Company is used as a cocatalyst for the copolymerization of ethylene and octene. Under the same polymerization conditions as the above examples, the activity is 1×10 8 g (polymer) / mol (catalyst)·h.

[0060] Comparative Example 2

[0061] An MMAO hexane solution produced by Tosoh Corporation of Japan is used as a cocatalyst for the copolymerization of ethylene and octene. Under the same polymerization conditions as the above examples, the activity is 3×10 8 g (polymer) / mol (catalyst)·h.

[0062] Comparative Example 3

[0063] Referring to the method described in Reference Example 1, in Step 1, 5 g of paraformaldehyde was changed to 5.1 g of formaldehyde, and the reaction temperature in the flask rapidly increased to over 150 °C within 2 minutes, and the color of the reaction solution significantly darkened. The finally prepared MAO was used for the copolymerization of ethylene and octene, and the activity was 1.0×10 7 g (polymer) / mol (catalyst)·h.

[0064] The above are only the preferred embodiments of the present invention. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent.

Claims

1. A method for synthesizing alkylaluminoxane from paraformaldehyde, characterized in that, it comprises the following steps: Step 1, reacting paraformaldehyde with trialkylaluminum to prepare an alkylaluminoxane precursor solution; Step 2, pyrolyzing the obtained alkylaluminoxane precursor to prepare alkylaluminoxane.

2. The method according to claim 1, characterized in that, the alkyl group in the alkylaluminoxane is an alkyl group of C1-C6, preferably methylaluminoxane; preferably, the alkyl group in the trialkylaluminum is an alkyl group of C1-C6, preferably trimethylaluminum.

3. The method according to claim 1 or 2, characterized in that, in Step 1, the degree of polymerization of paraformaldehyde is 2-300, preferably 5-150, more preferably 10-30; preferably, in Step 1, the molar ratio of trialkylaluminum to formaldehyde monomer in paraformaldehyde is 1:0.1-1:10, preferably 1:0.5-1:1.

5.

4. The method according to any one of claims 1-3, characterized in that, the reaction temperature in Step 1 is -20-100°C, preferably 0-50°C; preferably, in Step 1, the reaction of paraformaldehyde with trialkylaluminum is carried out in a solvent, and the solvent is one or more mixtures of liquid alkanes and aromatic hydrocarbons, preferably toluene or heptane.

5. The method according to any one of claims 1-4, characterized in that, in Step 2, the pyrolysis temperature is 80-200°C, preferably 100-150°C.

6. A method for preparing a modified alkylaluminoxane, characterized in that, mixing and reacting the alkylaluminoxane prepared by the preparation method according to any one of claims 1-5 with a modified alkylaluminum to obtain a modified alkylaluminoxane.

7. The preparation method according to claim 6, characterized in that, the alkylaluminoxane is methylaluminoxane.

8. The preparation method according to claim 6 or 7, characterized in that, The structure of the modified alkylaluminum is AlR 3 , where R is any alkyl group other than methyl, and the modified alkylaluminum is preferably triethylaluminum, triisobutylaluminum, trihexylaluminum, or trioctylaluminum.

9. The preparation method according to any one of claims 6-8, characterized in that, the molar ratio of trialkylaluminum to modified alkylaluminum is 1:0.1-1:10, preferably 1:0.3-1:

3.

10. The preparation method according to any one of claims 6-9, characterized in that, the reaction temperature of alkylaluminoxane and modified alkylaluminum is 20-150°C, preferably 60-100°C.

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