A process for the preparation of a metallocene polyethylene having a broad molecular weight distribution

Abstract

The present application relates to a kind of preparation method of metallocene polyethylene of wide molecular weight distribution, belong to olefin polymerization catalysis technical field.The preparation method of metallocene polyethylene of wide molecular weight distribution provided by the present application includes the following steps: (1) mixed metallocene catalyst, organic aluminum compound and mixed solvent, heating, and into ethylene is carried out polymerization reaction;The mixed solvent includes organic solvent A and organic solvent B, the organic solvent A is inert alkane or aromatic hydrocarbon, and the organic solvent B is the organic solvent containing polar functional group;(2) after reaction, quenching agent is added to terminate the reaction, washing, filtration, drying, it is finished.The present application uses mixed solvent system, and the use amount and the ratio of two components of mixed solvent are adjusted to realize the adjustment of metallocene polyethylene molecular weight distribution, greatly reduce the requirement of complex bifunctional catalyst, catalyst cost is low, polymerization process is simple, product performance is flexible, and application prospect is wide.

Description

Technical Field

[0001] This invention belongs to the field of olefin polymerization catalysis technology, specifically relating to a method for preparing metallocene polyethylene with a wide molecular weight distribution. Background Technology

[0002] The molecular weight and molecular weight distribution of polyethylene have a significant impact on the mechanical and processing properties of the product. For example, in the application of polyethylene pipes, not only is a high molecular weight required to provide good mechanical properties, but a wide molecular weight distribution is also needed for good processing performance. In recent years, metallocene polyethylene has attracted widespread attention due to its advantages such as high stereoregularity and uniform distribution of short branches. Preparing metallocene polyethylene products with a wide molecular weight distribution may yield high-performance products that combine multiple advantages. Therefore, the synthesis of metallocene polyethylene with a wide molecular weight distribution has always been a research hotspot in the field of olefin polymerization.

[0003] The existing methods for preparing polyethylene products with a wide molecular weight distribution mainly include: (1) segmented polymerization in different reactors. This method can achieve uniform mixing in the reactor and has great flexibility in operation adjustment, but the production efficiency is low and the production cost is high; (2) using bimetallic or multimetallic active component catalysts in a single reactor and utilizing their different polymerization behaviors to directly produce polyethylene products with a wide molecular weight distribution in a single reactor. However, this method requires comprehensive consideration of multiple polymerization behaviors, which is quite difficult.

[0004] Currently, the publicly disclosed methods for producing metallocene polyethylene with a wide molecular weight distribution mainly include: Patent WO9526369 discloses a method using a bimetallic composite catalyst with magnesium chloride supporting Ti(OBu)Cl3 and Cp2ZrCl2 bimetallic active centers to catalyze the synthesis of metallocene polyethylene with a wide molecular weight distribution; CN1258682A provides a composite catalyst that, based on existing catalysts composed of metallocene compounds, transition metal halides from Groups III-VI of the periodic table, and magnesium halides, introduces an activity promoter, an organic alcohol, during the catalyst preparation process, thereby improving the polymerization activity and obtaining polyethylene with a wide molecular weight distribution; CN1247875A discloses a composite metallocene catalyst using methylaluminoxane as a co-catalyst to produce short-branched metallocene polyethylene products with a wide molecular weight distribution.

[0005] As can be seen from the above technologies, the current mainstream approach to preparing metallocene polyethylene products with a wide molecular weight distribution focuses on catalyst modulation, achieving product preparation by selecting different catalytic systems. In addition, there are technologies for preparing wide molecular weight polyethylene products using non-metallocene catalytic systems, which also largely focus on catalyst structure modulation. Technologies for achieving wide molecular weight polyethylene products from the perspective of process conditions are almost non-reported. Solution polymerization, with its advantages of good heat transfer, easy control of polymerization temperature, low polymer concentration, and easy adjustment of molecular weight distribution, plays an important role in polyethylene production. Therefore, developing a method for preparing wide molecular weight polyethylene from a process perspective is of great significance. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems existing in the prior art and provide a simple and easy method for preparing metallocene polyethylene with a wide molecular weight distribution by adjusting the polymerization process rather than using a catalyst.

[0007] This invention is achieved through the following technical solution:

[0008] This invention provides a method for preparing metallocene polyethylene with a wide molecular weight distribution, comprising the following steps:

[0009] (1) A metallocene catalyst, an organoaluminum compound, and a mixed solvent are mixed, heated, and ethylene is introduced to carry out a polymerization reaction; the mixed solvent includes organic solvent A and organic solvent B, wherein organic solvent A is an inert alkane or an aromatic hydrocarbon, and organic solvent B is an organic solvent containing polar functional groups.

[0010] (2) After the reaction is complete, add a quencher to terminate the reaction, wash, filter, and dry to obtain the product.

[0011] Solvents, as the primary polymerization reaction medium, significantly influence the polymerization rate, polymer solution stability, system viscosity, intrinsic viscosity, molecular weight and molecular weight distribution, and glass transition temperature of solution polymerization. This invention, using a conventional metallocene catalyst, employs a mixed solvent system. An organic solvent B containing polar functional groups is introduced into the existing conventional single organic solvent A system. The combination of these two solvents has a unique effect of broadening the molecular weight distribution of metallocene polyethylene. The molecular weight distribution of metallocene polyethylene can be adjusted by regulating the amounts and ratios of the two components in the mixed solvent, greatly reducing the requirements for complex bifunctional catalysts, saving production costs, and requiring minimal changes to the overall process, making it easy to operate. The catalyst prepared by this invention is low-cost, using conventional metallocene catalysts, and the polymerization process is simple, offering flexible product performance tuning and broad application prospects.

[0012] In a preferred embodiment of the method for preparing metallocene polyethylene with a wide molecular weight distribution according to the present invention, in step (1), the metallocene catalyst is a catalyst containing group IVB metals.

[0013] Preferably, in step (1), the group IVB metal in the metallocene catalyst is titanium, zirconium, or hafnium.

[0014] The preparation method of this invention can utilize metallocene catalysts containing group IVB metals, preferably metallocene catalysts containing titanium, zirconium, and hafnium, such as ethylene-bridged bis(indene)zirconium dichloride, tert-butylaminotetramethylcyclopentadiene titanium dichloride, and bis(3-propyl)cyclopentadiene hafnium dichloride. This method avoids the use of expensive multi-component metallocene catalysts to achieve a broad distribution of polymetallocene polyethylene products, significantly reducing production costs.

[0015] In a preferred embodiment of the method for preparing metallocene polyethylene with a wide molecular weight distribution according to the present invention, in step (1), the organoaluminum compound is at least one of trimethylaluminum, triethylaluminum, triisobutylaluminum, and methylaluminoxane.

[0016] In a preferred embodiment of the method for preparing metallocene polyethylene with a wide molecular weight distribution according to the present invention, in step (1), the temperature of the polymerization reaction is 50℃-150℃ and the pressure of the polymerization reaction is 0.1MPa-10MPa.

[0017] Preferably, the polymerization reaction temperature is 60℃-90℃ and the polymerization reaction pressure is 0.5MPa-3MPa.

[0018] In a preferred embodiment of the method for preparing metallocene polyethylene with a wide molecular weight distribution according to the present invention, in step (1), the volume ratio of organic solvent A and organic solvent B in the mixed solvent is (1-100):1.

[0019] Preferably, in step (1), the volume ratio of organic solvent A to organic solvent B in the mixed solvent is (2-20):1. This invention has found that this volume ratio of mixed solvent can more effectively control the molecular weight distribution of metallocene polyethylene.

[0020] In a preferred embodiment of the method for preparing metallocene polyethylene with a wide molecular weight distribution according to the present invention, in step (1), the organic solvent A is at least one of n-pentane, cyclopentane, n-hexane, cyclohexane, methylcyclopentane, n-heptane, benzene, toluene, xylene, and trimethylbenzene; and the organic solvent B is at least one of diethyl ether, tetrahydrofuran, methylcyclopentane ether, n-butyl ether, isopropyl ether, methyl tert-butyl ether, dichloroethane, and dichloromethane.

[0021] Preferably, the organic solvent A is one of n-hexane, cyclohexane, and toluene; and the organic solvent B is one of diethyl ether, tetrahydrofuran, and dichloromethane.

[0022] In a preferred embodiment of the method for preparing metallocene polyethylene with a wide molecular weight distribution according to the present invention, in step (2), the quenching agent is an alcohol-ketone compound.

[0023] Preferably, the quenching agent is at least one selected from methanol, ethanol, isopropanol, and acetone.

[0024] The metallocene polyethylene product prepared by the method of the present invention has a molecular weight distribution range of 2-20, preferably between 3-16, and a weight-average molecular weight of 50,000-500,000, preferably between 60,000-200,000. The metallocene polyethylene obtained by the present invention has a molecular weight distribution range covering 2-20, and the product performance is fully adjustable.

[0025] The present invention has the following beneficial effects:

[0026] 1. Cost advantage of metallocene catalysts. Metallocene catalysts are inherently expensive, and multifunctional, multi-component metallocene catalysts are even more difficult to prepare and obtain. The preparation method of this invention achieves the regulation of the molecular weight distribution of metallocene polyethylene using conventional metallocene catalysts.

[0027] 2. Cost Advantages. The preparation method of this invention uses a mixed solvent system instead of the original single solvent system, eliminating the need for additional adjustments to the process flow. This results in low operating costs and excellent implementation effects.

[0028] 3. Advantages of the polymerization process. The preparation method of this invention uses a mixed solvent system. By adjusting the ratio of different solvents, the viscosity of the polymer solution can be effectively controlled. The solubility parameters and polarities of different solvents are utilized to adjust the polymer's solubility in the solvent, thereby increasing the polymerization rate. When the solubility parameters and polarity of the solvent are close to those of the polymer product, the polymer chains can fully extend in the solvent, and the chain growth ends can be exposed, which is conducive to the diffusion and collision of monomer molecules, allowing for sufficient contact and polymerization. Conversely, when the polymer chains are coiled into clusters, the chain growth ends are embedded in the clusters, hindering their contact with monomer molecules and thus reducing the polymerization rate.

[0029] 4. Product Advantages. The preparation method of this invention can adjust the molecular weight distribution by changing the types and ratios of the two solvent components, covering a molecular weight distribution range of 2-20, thus achieving fully adjustable product performance. Attached Figure Description

[0030] Figure 1 This is a gel permeation chromatography (GPC) chromatogram of the metallocene polyethylene product in Example 3. Detailed Implementation

[0031] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0032] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0033] Example 1

[0034] A method for preparing metallocene polyethylene with a wide molecular weight distribution includes the following steps:

[0035] (1) First, evacuate the 500mL polymerization reactor and heat it to 110℃ for baking. Then, replace the gas with high-purity nitrogen three times and cool it to room temperature. Prepare a 1g / L n-hexane solution with the metallocene catalyst ethylene-bridged bis(indene)zirconia and a 100g / L n-hexane solution with triisobutylaluminum. Then, under nitrogen protection, add 188mL of organic solvent A (n-hexane), 100mL of organic solvent B (dichloromethane), and 10mL of triisobutylaluminum solution to the polymerization reactor in sequence. Stir at 400rpm for 10min. Then, under nitrogen protection, add 2mL of metallocene catalyst solution to the polymerization reactor. Heat the polymerization reactor to the set polymerization reaction temperature of 80℃. Introduce ethylene into the polymerization reactor and adjust the ethylene to the set polymerization reaction pressure of 1.0MPa. During the reaction, keep the ethylene supply continuously. After reacting at 80℃ for 2h, stop the introduction of ethylene gas and cool the polymerization reactor to room temperature. Slowly release the ethylene gas in the polymerization reactor to release pressure to atmospheric pressure.

[0036] (2) Add 50 mL of quenching agent ethanol to terminate the reaction, open the polymerization reactor, add 100 mL of n-hexane, then wash, filter, vacuum dry and weigh the polymer solution to obtain 22 g of polymer. The catalytic activity of the metallocene catalyst is calculated to be 11000 g / g cat. Further characterize the physicochemical properties of the polymer. The characterization data are shown in Table 1.

[0037] Example 2

[0038] In this embodiment, the organic solvent A added in Example 1 was replaced with 238 mL of n-hexane, and the organic solvent B was replaced with 50 mL of dichloromethane. Other conditions remained unchanged, and 32 g of polymer was obtained. The catalytic activity of the metallocene catalyst was calculated to be 16000 g / g cat. The physicochemical properties of the polymer were further characterized, and the characterization data are shown in Table 1.

[0039] Example 3

[0040] In this embodiment, the organic solvent A added in Example 1 was replaced with 273 mL of n-hexane, and the organic solvent B was replaced with 15 mL of dichloromethane. Other conditions remained unchanged, yielding 45 g of polymer. The catalytic activity of the metallocene catalyst was calculated to be 22500 g / g cat. Further characterization of the polymer's physicochemical properties was performed; the characterization data are shown in Table 1, and the GPC spectrum is attached. Figure 1 .

[0041] Example 4

[0042] In this embodiment, the organic solvent B added in Example 1 was replaced with 100 mL of diethyl ether, while other conditions remained unchanged. 14 g of polymer was obtained, and the catalytic activity of the metallocene catalyst was calculated to be 7000 g / g cat. The physicochemical properties of the polymer were further characterized, and the characterization data are shown in Table 1.

[0043] Example 5

[0044] In this embodiment, the organic solvent A added in Example 1 was replaced with 238 mL of n-hexane, and the organic solvent B was replaced with 50 mL of diethyl ether. Other conditions remained unchanged, and 17 g of polymer was obtained. The catalytic activity of the metallocene catalyst was calculated to be 8500 g / g cat. The physicochemical properties of the polymer were further characterized, and the characterization data are shown in Table 1.

[0045] Example 6

[0046] In this embodiment, the organic solvent A added in Example 1 was replaced with 273 mL of n-hexane, and the organic solvent B was replaced with 15 mL of diethyl ether. Other conditions remained unchanged, and 17 g of polymer was obtained. The catalytic activity of the metallocene catalyst was calculated to be 8500 g / g cat. The physicochemical properties of the polymer were further characterized, and the characterization data are shown in Table 1.

[0047] Example 7

[0048] In this embodiment, the organic solvent B added in Example 1 was replaced with 100 mL of tetrahydrofuran, while other conditions remained unchanged. 8 g of polymer was obtained, and the catalytic activity of the metallocene catalyst was calculated to be 4000 g / g cat. The physicochemical properties of the polymer were further characterized, and the characterization data are shown in Table 1.

[0049] Example 8

[0050] In this embodiment, the organic solvent A added in Example 1 was replaced with 238 mL of n-hexane, and the organic solvent B was replaced with 50 mL of tetrahydrofuran. Other conditions remained unchanged, and 13 g of polymer was obtained. The catalytic activity of the metallocene catalyst was calculated to be 6500 g / g cat. The physicochemical properties of the polymer were further characterized, and the characterization data are shown in Table 1.

[0051] Example 9

[0052] In this embodiment, the organic solvent A added in Example 1 was replaced with 273 mL of n-hexane, and the organic solvent B added was replaced with 15 mL of tetrahydrofuran. Other conditions remained unchanged, and 17 g of polymer was obtained. The catalytic activity of the metallocene catalyst was calculated to be 8000 g / g cat. The physicochemical properties of the polymer were further characterized, and the characterization data are shown in Table 1.

[0053] Example 10

[0054] In this embodiment, the n-hexane used in Example 1 was replaced with cyclohexane, the added organic solvent A was replaced with 273 mL of cyclohexane, and the added organic solvent B was replaced with 15 mL of dichloromethane. Other conditions remained unchanged, and 39 g of polymer was obtained. The catalytic activity of the metallocene catalyst was calculated to be 19500 g / g cat. The physicochemical properties of the polymer were further characterized, and the characterization data are shown in Table 1.

[0055] Example 11

[0056] In this embodiment, the hexane used in Example 1 was replaced with toluene, the added organic solvent A was replaced with 273 mL of toluene, and the added organic solvent B was replaced with 15 mL of dichloromethane. Other conditions remained unchanged, and 28 g of polymer was obtained. The catalytic activity of the metallocene catalyst was calculated to be 14000 g / g cat. The physicochemical properties of the polymer were further characterized, and the characterization data are shown in Table 1.

[0057] Example 12

[0058] A method for preparing metallocene polyethylene with a wide molecular weight distribution includes the following steps:

[0059] (1) First, evacuate the 500mL polymerization reactor and heat it to 110℃ for baking. Then, replace the gas with high-purity nitrogen three times and cool it down to room temperature. Prepare the metallocene catalyst dichlorozirconia to a 1g / L hexane solution and the triisobutylaluminum to a 100g / L hexane solution. Then, under nitrogen protection, add 273mL of organic solvent A (hexane), 15mL of organic solvent B (dichloromethane), and 10mL of triisobutylaluminum solution to the polymerization reactor in sequence. Stir at 400rpm for 10min. Then, under nitrogen protection, add 2mL of metallocene catalyst solution to the polymerization reactor. Heat the polymerization reactor to the set polymerization reaction temperature of 80℃. Introduce ethylene into the polymerization reactor and adjust the ethylene to the set polymerization reaction pressure of 1.0MPa. During the reaction, keep the ethylene supply continuously. After reacting at 80℃ for 2h, stop the introduction of ethylene gas and cool the polymerization reactor to room temperature. Slowly release the ethylene gas in the polymerization reactor to release pressure to atmospheric pressure.

[0060] (2) Add 50 mL of quencher ethanol to terminate the reaction, open the polymerization reactor, add 100 mL of n-hexane, then wash, filter, vacuum dry and weigh the polymer solution to obtain 32 g of polymer. The catalytic activity of the metallocene catalyst is calculated to be 16000 g / g cat.

[0061] Example 13

[0062] In this embodiment, the metallocene catalyst dichlorozirconia in Example 12 was replaced with tert-butylaminotetramethylcyclopentadiene titanium dichloride, while other conditions remained unchanged. 75g of polymer was obtained, and the catalytic activity of the metallocene catalyst was calculated to be 37500g / g cat.

[0063] Example 14

[0064] In this embodiment, the metallocene catalyst dichlorozirconia in Example 12 was replaced with bis(3-propyl)cyclopentadiene hafnium dichloride, while other conditions remained unchanged. 28g of polymer was obtained, and the catalytic activity of the metallocene catalyst was calculated to be 14000g / g cat.

[0065] Example 15

[0066] In this embodiment, the ethylene pressure in Example 12 was set to 1.5 MPa, and other conditions remained unchanged. 42 g of polymer was obtained, and the catalytic activity of the metallocene catalyst was calculated to be 21000 g / g cat.

[0067] Example 16

[0068] In this embodiment, the ethylene pressure in Example 12 was set to 2.5 MPa, and other conditions remained unchanged. 50 g of polymer was obtained, and the catalytic activity of the metallocene catalyst was calculated to be 25000 g / g cat.

[0069] Example 17

[0070] In this embodiment, the polymerization reaction temperature in Example 12 was set to 75°C, and other conditions remained unchanged. 33g of polymer was obtained, and the catalytic activity of the metallocene catalyst was calculated to be 16500g / g cat.

[0071] Example 18

[0072] In this embodiment, the polymerization reaction temperature in Example 12 was set to 85°C, and other conditions remained unchanged. 13g of polymer was obtained, and the catalytic activity of the metallocene catalyst was calculated to be 6500g / g cat.

[0073] Example 19

[0074] In this embodiment, the preparation method changed triisobutylaluminum in Example 12 to triethylaluminum, while keeping other conditions unchanged, and 28g of polymer was obtained. The catalytic activity of the metallocene catalyst was calculated to be 14000g / g cat.

[0075] Comparative Example 1

[0076] A method for preparing metallocene polyethylene with a wide molecular weight distribution includes the following steps:

[0077] (1) First, evacuate the 500mL polymerization reactor and heat it to 110℃ for baking. Then, replace the gas with high-purity nitrogen three times and cool it to room temperature. Prepare a 1g / L hexane solution with the metallocene catalyst ethylene-bridged bis-indene dizirconia and a 100g / L hexane solution with triisobutylaluminum. Then, under nitrogen protection, add 288mL of organic solvent A hexane and 10mL of triisobutylaluminum solution to the polymerization reactor and stir at 400rpm for 10min. Then, under nitrogen protection, add 2mL of metallocene catalyst solution to the polymerization reactor and heat the polymerization reactor to the set polymerization reaction temperature of 80℃. Introduce ethylene into the polymerization reactor and adjust the ethylene to the set polymerization reaction pressure of 1.0MPa. During the reaction, keep the ethylene supply continuously. After reacting at 80℃ for 2h, stop the introduction of ethylene gas and cool the polymerization reactor to room temperature. Slowly release the ethylene gas in the polymerization reactor to release the pressure to atmospheric pressure.

[0078] (2) Add 50 mL of quenching agent ethanol to terminate the reaction, open the polymerization reactor, add 100 mL of n-hexane, then wash, filter, vacuum dry and weigh the polymer solution to obtain 25 g of polymer. The catalytic activity of the metallocene catalyst is calculated to be 12500 g / g cat. Further characterize the physicochemical properties of the polymer. The characterization data are shown in Table 1.

[0079] Comparative Example 2

[0080] In this comparative preparation method, the addition of 288 mL of n-hexane in Comparative Example 1 was changed to 188 mL of n-hexane, while other conditions remained unchanged. 26 g of polymer was obtained, and the catalytic activity of the metallocene catalyst was calculated to be 13000 g / g cat. The physicochemical properties of the polymer were further characterized, and the characterization data are shown in Table 1.

[0081] Comparative Example 3

[0082] In this comparative preparation method, n-hexane in Comparative Example 1 was replaced with cyclohexane, and other conditions remained unchanged. 18g of polymer was obtained, and the catalytic activity of the metallocene catalyst was calculated to be 9000g / g cat. The physicochemical properties of the polymer were further characterized, and the characterization data are shown in Table 1.

[0083] Comparative Example 4

[0084] In this comparative preparation method, hexane in Comparative Example 1 was replaced with toluene, and other conditions remained unchanged. 21g of polymer was obtained, and the catalytic activity of the metallocene catalyst was calculated to be 10500g / g cat. The physicochemical properties of the polymer were further characterized, and the characterization data are shown in Table 1.

[0085] Comparative Example 5

[0086] In this comparative preparation method, hexane in Comparative Example 1 was replaced with tetrahydrofuran, and other conditions remained unchanged. 6g of polymer was obtained, and the catalytic activity of the metallocene catalyst was calculated to be 3000g / g cat. The physicochemical properties of the polymer were further characterized, and the characterization data are shown in Table 1.

[0087] Comparative Example 6

[0088] In this comparative preparation method, hexane in Comparative Example 1 was replaced with diethyl ether, and other conditions remained unchanged. 11g of polymer was obtained, and the catalytic activity of the metallocene catalyst was calculated to be 5500g / g cat. The physicochemical properties of the polymer were further characterized, and the characterization data are shown in Table 1.

[0089] Comparative Example 7

[0090] In this comparative preparation method, hexane in Comparative Example 1 was replaced with dichloromethane, and other conditions remained unchanged. 15g of polymer was obtained, and the catalytic activity of the metallocene catalyst was calculated to be 7500g / g cat. The physicochemical properties of the polymer were further characterized, and the characterization data are shown in Table 1.

[0091] The key polymerization process parameters and polymer characterization data of Examples 1-11 and Comparative Examples 1-7 are shown in Table 1.

[0092] Table 1 Key polymerization process parameters and polymer characterization data for Examples 1-11 and Comparative Examples 1-7

[0093]

[0094] As can be seen from Table 1, by adjusting the volume ratio of organic solvent A and organic solvent B, metallocene polyethylene products with different molecular weight distributions were obtained in Examples 1-3, 4-6, and 7-9. This shows that the preparation method of the present invention achieves controllable adjustment of the molecular weight distribution of metallocene polyethylene by using a mixed solvent system and adjusting the volume ratio of the two solvents, and can obtain metallocene polyethylene with a wide molecular weight distribution.

[0095] This invention has discovered that introducing an organic solvent B containing polar functional groups into a solvent system has a special effect of broadening the molecular weight distribution of metallocene polyethylene. Comparing Example 1 and Comparative Example 1, it can be seen that, with the same solvent volume, introducing 100 mL of dichloromethane in Example 1 increased the molecular weight distribution of metallocene polyethylene from 2.7 to 8.2, indicating that the mixed solvent system prepared by the present invention can significantly improve the molecular weight distribution of metallocene polyethylene.

[0096] The difference between Comparative Example 1 and Comparative Example 2 lies in the amount of hexane added, but both yielded the same molecular weight distribution of metallocene polyethylene, indicating that the volume of the organic solvent does not affect the molecular weight distribution of metallocene polyethylene, and the molecular weight distribution of metallocene polyethylene prepared under a single solvent system remains essentially unchanged. Comparative Examples 5-7 all used a single organic solvent B. Under this single solvent system, the polymerization reaction suffers from limitations such as low polymerization activity or narrow molecular weight distribution. The preparation method of this invention, by changing the single solvent system to a mixed solvent system, can improve the molecular weight distribution of metallocene polyethylene. Furthermore, by adjusting the volume ratio of the two solvents, the molecular weight distribution of metallocene polyethylene can be controllably adjusted.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing metallocene polyethylene with a wide molecular weight distribution, characterized in that, Includes the following steps: (1) A metallocene catalyst, an organoaluminum compound, and a mixed solvent are mixed, heated, and ethylene is introduced to carry out a polymerization reaction; the mixed solvent includes organic solvent A and organic solvent B, wherein organic solvent A is an inert alkane or an aromatic hydrocarbon, and organic solvent B is an organic solvent containing polar functional groups. (2) After the reaction is complete, add a quencher to terminate the reaction, wash, filter, and dry to obtain the product; In step (1), the volume ratio of organic solvent A to organic solvent B in the mixed solvent is (2-20):1; in step (1), organic solvent A is at least one of n-hexane, cyclohexane, and toluene; and organic solvent B is at least one of diethyl ether, tetrahydrofuran, and dichloromethane.

2. The method for preparing metallocene polyethylene with a wide molecular weight distribution according to claim 1, characterized in that, In step (1), the metallocene catalyst is a catalyst containing group IVB metals.

3. The method for preparing metallocene polyethylene with a wide molecular weight distribution according to claim 2, characterized in that, In step (1), the group IVB metal in the metallocene catalyst is titanium, zirconium, or hafnium.

4. The method for preparing metallocene polyethylene with a wide molecular weight distribution according to claim 1, characterized in that, In step (1), the organoaluminum compound is at least one of trimethylaluminum, triethylaluminum, triisobutylaluminum, and methylaluminoxane.

5. The method for preparing metallocene polyethylene with a wide molecular weight distribution according to claim 1, characterized in that, In step (1), the temperature of the polymerization reaction is 50℃-150℃, and the pressure of the polymerization reaction is 0.1MPa-10MPa.

6. The method for preparing metallocene polyethylene with a wide molecular weight distribution according to claim 5, characterized in that, In step (1), the temperature of the polymerization reaction is 60℃-90℃, and the pressure of the polymerization reaction is 0.5MPa-3MPa.

7. The method for preparing metallocene polyethylene with a wide molecular weight distribution according to claim 1, characterized in that, In step (2), the quenching agent is an alcohol-ketone compound.

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