Modified MgCl2 supported polyethylene catalyst and preparation method thereof

Abstract

The invention discloses a modified MgCl2 supported Ziegler-Natta catalyst for ethylene polymerization and a preparation method of the modified MgCl2 supported Ziegler-Natta catalyst. According to the catalyst, titanium is adsorbed on an MgCl2 carrier, the MgCl2 carrier is X element doped modified MgCl2, the modified MgCl2 carrier comprises an MgCl2 system in which part of Cl element is substituted by the X element, the MgCl2 carrier comprises the following components in percentage by weight: 10-25% of magnesium, 1-15% of titanium, 35-60% of halogen and 1-10% of non-metallic element X, X is any one of N, P, O, S, Se, F, Br and I, and the molar ratio of titanium to magnesium is 1: 1-1: 2000. Modified MgCl2 is adopted as a catalyst carrier, when the synthesized spherical catalyst is used for ethylene polymerization, the ultrahigh polymerization activity of the catalyst is maintained, a polyethylene product has higher molecular weight and narrower molecular distribution, and the tensile strength and bending modulus of polyethylene are remarkably improved.

Description

Technical Field

[0001] The present invention relates to a supported polyethylene catalyst and a preparation method thereof, in particular to a modified MgCl2 supported Ziegler-Natta catalyst for ethylene polymerization and a preparation method thereof. Background Art

[0002] Currently, over 150 million tons of polyethylene and polypropylene are produced annually worldwide using improved Ziegler-Natta catalysts. Since their discovery, Ziegler-Natta catalysts have continuously improved their activity and stereoselectivity, resulting in six generations of catalysts, based on their performance improvements. The third generation of Ziegler-Natta catalysts began using titanium compounds supported on high-surface-area supports to improve polymerization efficiency. Research has found that MgCl2 and TiCl3 crystals have similar structures and can form a cocrystal, facilitating the loading of TiCl3 on the MgCl2 surface, making MgCl2 the most suitable support for Ziegler-Natta catalysts. Further research has shown that the addition of appropriate benzoate electron donor compounds can enhance the directional nature of propylene polymerization. Subsequent generations of Ziegler-Natta catalysts all contain a ternary mixture of MgCl2 / electron donor / TiCl4, where the electron donation enhances catalyst activity and stereoselectivity. MgCl2-supported Ziegler-Natta catalysts have significantly simplified olefin polymerization and production processes, revolutionizing the production of commercial linear polyethylene and isotactic polypropylene.

[0003] For ethylene polymerization, TiCl4 has the best activity when supported on MgCl2. The dramatic increase in supported catalyst activity is due to the increase in chain growth rate and the number of active centers. TiCl4 dispersed on the high surface area of ​​MgCl2 increases the number of active centers and reacts with the co-catalyst AlEt3 to form the activated catalyst TiCl2Et. 2+ The smaller electropositivity of the ion increases the active center Ti 3+ The ionic charge density stabilizes the π-bonds on the olefin monomers that coordinate with the active centers, accelerating the monomer insertion reaction and increasing the chain growth rate. MgCl2 can only be loaded with TiCl4 after being activated by chemical or mechanical milling. Chemical activation involves the formation of a complex between MgCl2 and an alcohol, or the reaction of magnesium ethoxide with TiCl4. Mechanical milling involves grinding MgCl2 and TiCl4 in a ball mill for a long time to activate the support and load the catalyst. The activated MgCl2 forms a disordered amorphous structure, providing abundant sites for TiCl4 loading.

[0004] The modification of ethylene polymerization catalysts can improve the properties of polyethylene. Patent CN202411073431.0 prepares a catalyst by synthesizing a MgCl2-AlCl3 composite support, loading a TiCl4 active component on the composite support, and performing heat treatment and post-treatment on the catalyst. This catalyst can produce polyethylene products with higher activity and a broader product molecular weight distribution. Patent CN202111680277.X provides a Ziegler-Natta type catalyst system for ethylene polymerization, its preparation method and application. The catalyst system includes a solid component and a cocatalyst. The solid component includes a porous organic polymer support modified with a magnesium compound and a titanium compound. Through the design and preparation at the support level, the Ziegler-Natta type catalyst for olefins is obtained in this invention. No additional internal electron donor needs to be added during the preparation process, and the catalyst can produce ultra-high molecular weight polyethylene with a viscosity-average molecular weight reaching 7 million. The differences in the microenvironment of the loading sites in the support lead to different catalytic performances of the catalyst active centers after loading, thus affecting the distribution and properties of polymer components. The performance of ethylene polymerization catalysts can be improved by modifying and decorating the MgCl2 support. Summary of the Invention

[0005] The object of the present invention is to provide a catalyst that can have a higher molecular weight and a narrower molecular weight distribution in polyethylene polymerization. Another object of the present invention is to provide a preparation method of this catalyst.

[0006] A catalyst for polyethylene polymerization, in which titanium is adsorbed on a MgCl2 support. The MgCl^2 support is MgCl2 doped and modified with element X. The modified MgCl2 support contains a MgCl2 system in which part of the Cl element is replaced by element X. In the MgCl2 support, by weight percentage, it consists of 10%-25% magnesium, 1%-15% titanium, 35%-60% halogen, and 1%-10% non-metal element X. X is any one of the elements N, P, O, S, Se, F, Br, and I. The molar ratio of titanium to magnesium is 1:1 to 1:2000.

[0007] Preferably, in the catalyst of the present invention, the magnesium particle size distribution is 50-250 μm, which is provided by a magnesium halide alcoholate with the structural general formula Mg(OR1) m Y (2-m) ·n(R2OH). In the general formula, R1 is an alkyl group, aralkyl group or aryl group with C1-C 20 ; Y is a halogen; m is an integer of 0≦m<2; n is a decimal or integer of 0<n<5; R2 is an alkyl group, aralkyl group or aryl group with C1-C 20 ; and the magnesium halide is one of magnesium chloride, magnesium bromide, chloromethoxy magnesium or chloroethoxy magnesium.

[0008] More preferably, the magnesium halide in the magnesium halide alcoholate of the catalyst of the present invention is magnesium chloride, and the molar ratio of titanium to magnesium is 1:1 to 1:50.

[0009] The preparation method of the X-element-doped modified MgCl2 catalyst of the present invention is as follows: 1) Under the protection of inert gas, magnesium halide, Mg m X n or NaX p After heating and melting with alcohol and methyl silicone oil, a cooling medium is added, and the mixture is sprayed into a high-speed stirring molding kettle, so that the dispersed X-element doped MgCl2 alcoholate melt droplets are rapidly cooled and solidified into spherical particles, thereby preparing a spherical X-element doped modified MgCl2 carrier. The alcohol used is any one of methanol, ethanol, propanol, isopropanol, butanol or isobutanol. The Mg m X n is any one of Mg3N2, Mg3P2, MgO, MgS, MgSe, MgF2, MgBr2 and MgI2, wherein the NaX k Where k = 1-3, X is any one of N, P, O, S, Se, F, Br and I, and the cooling medium used is hexane at -30 to 0°C; 2) adding the prepared X-element-doped modified MgCl2 spherical support to a titanium halide at -20°C under anhydrous and oxygen-free conditions, reacting for 1 hour, gradually raising the temperature to 120°C, continuing the reaction for 1 hour, filtering, washing, and drying to obtain a modified MgCl2 supported catalyst, wherein the titanium halide is any one of tetraethoxytitanium, tetrabutoxytitanium, chlorotrialkoxytitanium, dichlorodialkoxytitanium, trichloroalkoxytitanium, titanium tetrachloride, or titanium tetrabromide.

[0010] Preferably, the alcohol used in the catalyst preparation method of the present invention is ethanol, and the titanium halide used is titanium tetrachloride.

[0011] More preferably, the catalyst preparation method of the present invention is: 1) Under nitrogen, 0.5 mol of anhydrous MgCl₂, 0.05 mol of MgBr₂, 1.5 mol of anhydrous ethanol, and 500 mL of methyl silicone oil were placed in a reactor and heated to 80°C for 3 h. Simultaneously, 2 L of hexane was added to the reactor and cooled to –20°C. After the reaction was complete, the mixture was sprayed into the rapidly stirred reactor at a constant flow rate, causing the dispersed Br-doped MgCl₂ alcoholate melt droplets to rapidly cool and solidify into spherical particles. Finally, after washing with anhydrous hexane six times, the mixture was transferred to a round-bottom flask, vacuum-evacuated, and filled with nitrogen to obtain Br-doped MgCl₂ spherical supports. 2) Under anhydrous and oxygen-free conditions, 5.0 g of Br-doped MgCl₂ spherical support was added to 30 mL of titanium tetrachloride liquid at -20°C. After reacting for 1 hour, the temperature was gradually raised to 120°C for another hour and filtered. The catalyst was then washed five times with 20 mL of hexane at 60°C and once with 10 mL of hexane at room temperature. The catalyst was then dried under vacuum to obtain the modified MgCl₂ supported catalyst.

[0012] In the modified MgCl2 species of the present invention, the X element is evenly distributed throughout the MgCl2, replacing some of the Cl element in the MgCl2. When the Ti active species is loaded onto the carrier, the Ti atoms interact not only with the Cl element but also with the X element on the surface. The Cl and X elements interact differently with the Ti active centers, thereby regulating the ethylene polymerization performance of the Ti active centers. This results in polyethylene products with higher molecular weights and narrower molecular weight distributions.

[0013] Compared with the prior art, the positive effects of the present invention are: Compared to the prior art, the modified MgCl2 in this invention contains an additional non-metallic element, X. When the Ti active species is loaded onto the carrier, the Ti atoms can interact not only with the Cl element but also with the X element on the surface. Cl and X interact differently with the Ti active centers, thereby regulating the ethylene polymerization performance of the Ti active centers. This results in polyethylene products with higher molecular weights and narrower molecular weight distributions. Furthermore, the modified MgCl2 carrier is easily prepared through a one-step reaction, highlighting the application advantages of this modified MgCl2.

[0014] The present invention adopts modified MgCl2 as a catalyst carrier. When the synthesized spherical catalyst is used for ethylene polymerization, it not only maintains the ultra-high polymerization activity of the catalyst, but also has a polyethylene product with a higher molecular weight and a narrower molecular distribution, significantly improving the tensile strength and flexural modulus of the polyethylene. DETAILED DESCRIPTION

[0015] The following are specific embodiments of the present invention. Example 1

[0016] (1) Preparation of MgBr2-doped MgCl2 carrier Under nitrogen, 0.5 mol of anhydrous MgCl₂, 0.05 mol of MgBr₂, 1.5 mol of anhydrous ethanol, and 500 mL of methyl silicone oil were placed in a reactor and heated to 80°C for 3 h to melt. Simultaneously, 2 L of hexane was added to the reactor and cooled to –20°C. After the reaction was complete, the mixture was sprayed into the high-speed stirring reactor at a constant flow rate, causing the dispersed Br-doped MgCl₂ alcoholate melt droplets to rapidly cool and solidify into spherical particles. Finally, after washing with anhydrous hexane six times, the material was transferred to a round-bottom flask, vacuum-evacuated, and filled with nitrogen to obtain Br-doped MgCl₂ spherical supports.

[0017] The physical properties of the modified MgCl2 carrier are shown in Table 1 (2) Preparation of supported catalyst Under anhydrous and oxygen-free conditions, 5.0 g of a microspherical Br-doped MgCl2 support was added to 30 mL of titanium tetrachloride at -20°C. After one hour of reaction, the temperature was gradually raised to 120°C, followed by one hour of reaction and filtration. The catalyst was then washed five times with 20 mL of hexane at 60°C and once with 10 mL of hexane at room temperature. The catalyst was then dried under vacuum to obtain the modified MgCl2 supported catalyst.

[0018] The contents of the various components in the catalyst are shown in Table 2.

[0019] (3) Ethylene slurry polymerization In a 10-liter vacuum-dried reaction flask thoroughly purged with nitrogen and ethylene, 0.2 kg of hexane was first added, followed by 50 mg of the supported catalyst (the molar ratio of titanium in the supported catalyst to aluminum in the co-catalyst was 1:100), and 5 ml of triethylaluminum. Ethylene was then continuously introduced, with the reaction pressure controlled at 0.8 MPa. The reactor temperature was raised to 70°C, and polymerization was allowed to proceed for 1 hour. Unreacted ethylene was then vented to yield ultrahigh molecular weight polyethylene.

[0020] The relevant data of the aggregation are listed in Table 3. Example 2

[0021] (1) Preparation of MgS-doped MgCl2 carrier: Under nitrogen, 0.5 mol of anhydrous MgCl₂, 0.03 mol of Na₂S, 1.5 mol of anhydrous methanol, and 500 mL of methyl silicone oil were placed in a reactor and heated to 80°C for 3 h to melt. Simultaneously, 2 L of hexane was added to the molding vessel and cooled to –20°C. After the reaction was complete, the mixture was sprayed into the rapidly stirred molding vessel at a constant flow rate, causing the dispersed S-doped MgCl₂ alcoholate melt droplets to rapidly cool and solidify into spherical particles. Finally, after washing six times with anhydrous hexane, the material was transferred to a round-bottom flask, vacuum-evacuated, and filled with nitrogen to obtain the S-doped MgCl₂ spherical support.

[0022] The physical properties of the modified MgCl2 carrier are shown in Table 1 (2) Preparation of supported catalyst: Same as Example 1. The contents of the components in the catalyst are shown in Table 2.

[0023] (3) Ethylene slurry polymerization: Same as Example 1. The polymerization data are listed in Table 3. Example 3

[0024] (1) Preparation of MgI2-doped MgCl2 carrier: Under nitrogen, 0.5 mol of anhydrous MgCl₂, 0.06 mol of MgI₂, 1.5 mol of anhydrous propanol, and 500 mL of methyl silicone oil were placed in a reactor and heated to 80°C for 3 h. Simultaneously, 2 L of hexane was added to the reactor and cooled to –20°C. After the reaction was complete, the mixture was sprayed into the high-speed stirring reactor at a constant flow rate, causing the dispersed I-doped MgCl₂ alcoholate melt droplets to rapidly cool and solidify into spherical particles. Finally, after washing six times with anhydrous hexane, the material was transferred to a round-bottom flask, vacuum-evacuated, and filled with nitrogen to obtain I-doped MgCl₂ spherical supports.

[0025] The physical properties of the modified MgCl2 carrier are shown in Table 1 (2) Preparation of supported catalyst: Same as Example 1. The contents of the components in the catalyst are shown in Table 2.

[0026] (3) Ethylene slurry polymerization: Same as Example 1. The polymerization data are listed in Table 3. Example 4

[0027] (1) Preparation of MgF2-doped MgCl2 carrier: Under nitrogen, 0.5 mol of anhydrous MgCl₂, 0.08 mol of NaF, 1.5 mol of anhydrous ethanol, and 500 mL of methyl silicone oil were placed in a reactor and heated to 80°C for 3 h to melt. Simultaneously, 2 L of hexane was added to the molding vessel and cooled to –20°C. After the reaction was complete, the mixture was sprayed into the rapidly stirred molding vessel at a constant flow rate, causing the dispersed F-doped MgCl₂ alcoholate melt droplets to rapidly cool and solidify into spherical particles. Finally, after washing six times with anhydrous hexane, the material was transferred to a round-bottom flask, vacuum-evacuated, and filled with nitrogen to obtain the F-doped MgCl₂ spherical support.

[0028] The physical properties of the modified MgCl2 carrier are shown in Table 1 (2) Preparation of supported catalyst: Same as Example 1. The contents of the components in the catalyst are shown in Table 2.

[0029] (3) Ethylene slurry polymerization: Same as Example 1. The polymerization data are listed in Table 3. Example 5

[0030] (1) Preparation of MgSe-doped MgCl2 carrier: Under nitrogen, 0.5 mol of anhydrous MgCl₂, 0.02 mol of Na₂Se, 1.5 mol of anhydrous ethanol, and 500 mL of methyl silicone oil were placed in a reactor and heated to 80°C for 3 h to melt. Simultaneously, 2 L of hexane was added to the reactor and cooled to –20°C. After the reaction was complete, the mixture was sprayed into the high-speed stirring reactor at a constant flow rate, causing the dispersed Se-doped MgCl₂ alcoholate melt droplets to rapidly cool and solidify into spherical particles. Finally, after washing six times with anhydrous hexane, the material was transferred to a round-bottom flask, vacuum-evacuated, and filled with nitrogen to obtain Se-doped MgCl₂ spherical supports.

[0031] The physical properties of the modified MgCl2 support are shown in Table 1.

[0032] (2) Preparation of supported catalyst: Same as Example 1. The contents of the components in the catalyst are shown in Table 2.

[0033] (3) Ethylene slurry polymerization: Same as Example 1. The polymerization data are listed in Table 3. Comparative Example

[0034] (1) Preparation of MgCl2 carrier: Under nitrogen, 0.5 mol of anhydrous MgCl₂, 1.5 mol of anhydrous ethanol, and 500 mL of methyl silicone oil were placed in a reactor and heated to 80°C for 3 h. Simultaneously, 2 L of hexane was added to the molding vessel and cooled to –20°C. After the reaction was complete, the mixture was sprayed into the rapidly stirred molding vessel at a constant flow rate, causing the dispersed MgCl₂ alcoholate melt droplets to rapidly cool and solidify into spherical particles. Finally, after washing six times with anhydrous hexane, the material was transferred to a round-bottom flask, vacuum-evacuated, and filled with nitrogen to obtain a spherical MgCl₂ support.

[0035] The physical properties of MgCl2 carrier are shown in Table 1 (2) Preparation of supported catalyst: Same as Example 1. The contents of the components in the catalyst are shown in Table 2.

[0036] (3) Ethylene slurry polymerization: Same as Example 1. The polymerization data are listed in Table 3.

[0037]

Claims

1. Modified MgCl2 supported polyethylene catalyst, titanium adsorbed on MgCl2 support, characterized in that The MgCl2 carrier is X-element-doped modified MgCl2, which contains a MgCl2 system in which part of the Cl element is replaced by the X element. The MgCl2 carrier is composed of 10%-25% magnesium, 1%-15% titanium, 35%-60% halogen, and 1%-10% non-metallic element X by weight, where X is any one of N, P, O, S, Se, F, Br, and I, and the molar ratio of titanium to magnesium is 1:1 to 1:2000.

2. The catalyst according to claim 1, characterized in that The magnesium has a particle size distribution of 50 to 250 μm and is provided by a magnesium halide alcoholate having a structural general formula of Mg(OR1) m Y (2-m) ·n(R2OH). In the general formula, R1 is an alkyl group, aralkyl group or aryl group having 1 to 20 carbon atoms; Y is a halogen; m is an integer satisfying 0 ≦ m < 2; n is a decimal or integer satisfying 0 < n < 5; R2 is an alkyl group, aralkyl group or aryl group having 1 to 20 carbon atoms, and the magnesium halide is one of magnesium chloride, magnesium bromide, chloromethoxymagnesium or chloroethoxymagnesium.

3. The catalyst according to claim 2, characterized in that The magnesium halide in the magnesium halide alcoholate is magnesium chloride, and the molar ratio of titanium to magnesium is 1:1 to 1:

500.

4. The method for preparing the catalyst according to claim 1, wherein: 1) Under the protection of inert gas, magnesium halide, Mg m X n or NaX p After heating and melting with alcohol and methyl silicone oil, a cooling medium is added, and the mixture is sprayed into a high-speed stirring molding kettle, so that the dispersed X-element doped MgCl2 alcoholate melt droplets are rapidly cooled and solidified into spherical particles, thereby preparing a spherical X-element doped modified MgCl2 carrier. The alcohol used is any one of methanol, ethanol, propanol, isopropanol, butanol or isobutanol. The Mg m X n is any one of Mg3N2, Mg3P2, MgO, MgS, MgSe, MgF2, MgBr2 and MgI2, wherein the NaX k Where k = 1-3, X is any one of N, P, O, S, Se, F, Br and I, and the cooling medium used is hexane at -30 to 0°C; 2) adding the prepared X-element-doped modified MgCl2 spherical support to a titanium halide at -20°C under anhydrous and oxygen-free conditions, reacting for 1 hour, gradually raising the temperature to 120°C, continuing the reaction for 1 hour, filtering, washing, and drying to obtain a modified MgCl2 supported catalyst, wherein the titanium halide is any one of tetraethoxytitanium, tetrabutoxytitanium, chlorotrialkoxytitanium, dichlorodialkoxytitanium, trichloroalkoxytitanium, titanium tetrachloride, or titanium tetrabromide.

5. The method for preparing the catalyst according to claim 4, wherein: The alcohol used is ethanol, and the titanium halide used is titanium tetrachloride.

6. The method for preparing a catalyst according to claim 5, wherein: 1) Under nitrogen, 0.5 mol of anhydrous MgCl₂, 0.05 mol of MgBr₂, 1.5 mol of anhydrous ethanol, and 500 mL of methyl silicone oil were placed in a reactor and heated to 80°C for 3 h. Simultaneously, 2 L of hexane was added to the reactor and cooled to –20°C. After the reaction was complete, the mixture was sprayed into the rapidly stirred reactor at a constant flow rate, causing the dispersed Br-doped MgCl₂ alcoholate melt droplets to rapidly cool and solidify into spherical particles. Finally, after washing six times with anhydrous hexane, the mixture was transferred to a round-bottom flask, vacuum-evacuated, and filled with nitrogen to obtain Br-doped MgCl₂ spherical supports. 2) Under anhydrous and oxygen-free conditions, 5.0 g of Br-doped MgCl₂ spherical support was added to 30 mL of titanium tetrachloride liquid at -20°C. After one hour of reaction, the temperature was gradually raised to 120°C, the reaction continued for another hour, and the mixture was filtered. The catalyst was then washed five times with 20 mL of hexane at 60°C and once with 10 mL of hexane at room temperature. The catalyst was then dried under vacuum to obtain the modified MgCl₂ supported catalyst.

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