Bimodal polyethylene catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the field of olefin polymerization catalysts, and particularly relates to a bimodal polyethylene catalyst as well as a preparation method and application thereof, and the bimodal polyethylene catalyst comprises a solid catalyst taking a large-particle carrier and a self-formed small-particle carrier as a carrier together; in the solid catalyst, titanium active centers are uniformly dispersed on a large-particle carrier and a self-formed small-particle carrier; the self-forming small-particle carrier comprises an alcohol magnesium compound. Compared with the prior art, the invention overcomes the defect that the performance (activity, hydrogen regulation sensitivity and copolymerization performance) of a Ziegler-Natta type bimodal polyethylene catalyst in the prior art still needs to be improved, and provides a novel bimodal polyethylene catalyst. The bulk density and the copolymerization unit content of polymerized powder prepared by adopting the catalyst system are greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of olefin polymerization catalysts, and in particular relates to a bimodal polyethylene catalyst, its preparation method, and its application. Background Technology

[0002] Polyolefins are the most produced and widely used polymer materials, serving as fundamental materials in numerous fields such as petrochemicals, aerospace, and advanced manufacturing. They are a pillar industry vital to the national economy and people's livelihoods. my country is the world's largest importer and consumer of polyolefins, but its production capacity still cannot meet consumer demand, especially for high-end polyolefin products, which are heavily reliant on imports. This has exacerbated the structural and contradictory nature of the polyolefin industry, with severe homogenization of low-end products. This is mainly due to the late start of domestic catalyst preparation technology, which has been subject to foreign technological blockades, severely limiting the development of high-value-added products from production facilities.

[0003] Typically, the development of high-end polyolefin products involves improving polymerization processes and developing new catalyst systems. This allows for control over the distribution of comonomers within the polymer molecular chain, enabling more precise control over polymer crystallization. For example, bimodal polyethylene (BPE), with its bimodal molecular weight distribution, is a widely used general-purpose resin. Compared to ordinary polyethylene, BPE not only possesses superior mechanical properties but also excellent processing performance, making it widely used in films, building materials, pipes, and blow molding materials. It is a high-value-added polyethylene product. BPE has a significant market prospect both domestically and internationally, with demand increasing year by year. Currently, most domestic polyethylene producers have weak technological R&D capabilities, and almost all BPE production processes are patented by foreign companies. Therefore, high-value-added BPE products still largely rely on imports. Thus, accelerating the development of domestic BPE catalyst technology and equipment is beneficial for adjusting product structure, enhancing market competitiveness, and increasing economic benefits.

[0004] Typically, the production processes for bimodal polyethylene include slurry method, gas phase method, and solution method. The reactor types are mainly divided into loop reactor, stirred tank reactor, and gas phase fluidized bed reactor. Combining two or more of these reactors can yield bimodal products.

[0005] As for bimodal polyethylene catalysts, such as patent CN1279069C, which uses dibutylmagnesium as the magnesium source, the catalyst is finally obtained through alcoholysis, silica gel loading, titanium washing, and alkylation. However, this catalyst is only suitable for the development of high value-added products using the process of Borealis. Moreover, the high price of dibutylmagnesium and its dependence on imports result in high raw material costs for the catalyst product and relatively low economic benefits.

[0006] Developing a Ziegler-Natta bimodal polyethylene catalyst with significantly superior performance compared to the well-known Ziegler-Natta catalysts in the field, characterized by high activity, excellent hydrogen sensitivity, and good copolymerization properties, would be of great value. Summary of the Invention

[0007] The purpose of this invention is to provide a bimodal polyethylene catalyst, its preparation method, and its application in order to solve at least one of the above-mentioned problems. This invention addresses the shortcomings of existing Ziegler-Natta type bimodal polyethylene catalysts, whose performance (activity, hydrogen sensitivity, and copolymerization performance) still needs improvement. This solution provides a novel bimodal polyethylene catalyst, and the bulk density and copolymer unit content of the polymer powder prepared using this catalyst system are greatly improved.

[0008] The inventors discovered that: (1) the catalyst product is prepared by using two types of carriers. The self-formed small particle carrier loaded with titanium can be used to produce high molecular weight polyethylene products and improve the impact resistance of polyethylene; the large particle carrier loaded with titanium can be used to produce linear low-density or high-density products, ensuring that the catalyst has good hydrogen regulation performance and can produce polymers with lower molecular weight; (2) the self-formed small particles are mixed with the large particle carrier to carry out titaniumization together, so that the two types of carriers can carry out titaniumization tests at the same time, ensuring the uniform dispersion of the titanium active center of the catalyst, while the conventional active component and the modified active component center play their respective roles and do not exclude each other.

[0009] Based on the above findings, this invention is proposed.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] The first aspect of this invention discloses a bimodal polyethylene catalyst, comprising a solid catalyst supported by both large particulate support and self-formed small particulate support.

[0012] In the solid catalyst, titanium active centers are uniformly dispersed on large particle supports and self-formed small particle supports;

[0013] The self-forming small particle carrier includes magnesium alkoxide compounds.

[0014] Preferably, the self-forming small particle carrier is magnesium ethoxylate;

[0015] The large-particle carriers include activated carbon, diatomaceous earth, kaolin, montmorillonite, alumina, and silica. Large-particle carriers refer to carrier materials with a large specific surface area and pore volume.

[0016] More preferably, the large particle carrier is silicon dioxide.

[0017] A second aspect of this invention discloses a method for preparing the bimodal polyethylene catalyst as described above, comprising the following steps:

[0018] (1) Preparation of self-forming small particle carriers:

[0019] Magnesium compounds and alcohols are co-dispersed in an electron donor to react, and then a multi-electron donor is added to continue the reaction. The precipitated particles are self-forming small particle carriers.

[0020] (2) Activation of large particle carriers:

[0021] Large particle carriers were purged under a nitrogen atmosphere;

[0022] Large particulate support purged with nitrogen was reacted with pentane and triethylaluminum, and dried to obtain alkylated large particulate support.

[0023] (3) Preparation of magnesium-titanium composite:

[0024] Magnesium chloride, an electron donor, and a titanium compound are mixed and reacted to obtain a magnesium-titanium complex.

[0025] (4) Preparation of titanium-modified solid catalysts:

[0026] The alkylated large-particle carrier obtained in (2) is added to the solution in (1) and dispersed evenly to form a mixed carrier solution;

[0027] The magnesium-titanium composite obtained in (3) was added dropwise to the mixed support solution, heated to react, and then dried to obtain a titanium-modified solid catalyst.

[0028] (5) Preparation of bimodal polyethylene catalyst:

[0029] Triethylaluminum was mixed with the obtained titanium-modified solid catalyst to obtain the bimodal polyethylene catalyst.

[0030] Preferably, in (1):

[0031] The magnesium compound mentioned is magnesium chloride;

[0032] The alcohols mentioned include methanol, ethanol, ethylene glycol, glycerol, 1,4-butanediol, propanol, isopropanol, butanol, isobutanol, tert-butanol, hexanol, cyclohexanol, octanol, isooctanol, decanol, benzyl alcohol, and phenethyl alcohol.

[0033] The electron donors include organic compounds containing lone pairs of electrons;

[0034] The aforementioned multi-electron donors include propylene glycol, 1,3-butanediol, 1,4-butanediol, pentanediol, and isomers of pentanediol;

[0035] The molar ratio of the magnesium compound, alcohol compound, and multi-electron donor is 1:

[0036] (0.1-1.5): (0.5-2.5);

[0037] The reaction temperature is 45-80℃, preferably 65℃, and the reaction time is 2-8h, preferably 3.5h;

[0038] The continued reaction is carried out at a temperature of 50-80℃, preferably 65℃, for a time of 2 hours.

[0039] More preferably, the alcohol compound is at least one of ethanol and isooctyl alcohol.

[0040] More preferably, the multi-electron donor is at least one of propylene glycol and 1,4-butanediol.

[0041] Preferably, in (3):

[0042] The electron donors include organic compounds containing lone pairs of electrons;

[0043] The titanium compounds mentioned include TiCl4, TiBr4, TiI4, Ti(OC2H5)Cl3, Ti(OCH3)Cl3, Ti(OC4H9)Cl3, Ti(OC2H5)Br3, Ti(OC2H5)2Cl2, Ti(OCH3)2Cl2, Ti(OCH3)2I2, Ti(OC2H5)3Cl, Ti(OCH3)3Cl, and Ti(OC2H5)3I;

[0044] The molar ratio of magnesium chloride to titanium compound is 1:(0.01-0.25);

[0045] The reaction was carried out at a temperature of 70°C for 6 hours.

[0046] More preferably, the titanium compound is at least one selected from TiCl4, Ti(OC2H5)Cl3, Ti(OCH3)Cl3 and Ti(OC4H9)Cl3.

[0047] More preferably, the titanium compound is TiCl4.

[0048] Preferably, the elements containing lone pairs of electrons include oxygen, nitrogen, and sulfur.

[0049] More preferably, the electron donor is tetrahydrofuran, which also serves as a solvent.

[0050] Preferably, in (2):

[0051] The purging temperature is 600℃, and the time is 4-18 hours;

[0052] The reaction was carried out at a temperature of 60°C for 1 hour.

[0053] Preferably, in (4):

[0054] The heating reaction was carried out at a temperature of 70°C for 2 hours.

[0055] The drying temperature is 80°C.

[0056] Preferably, in (5):

[0057] The aluminum-titanium molar ratio of the triethylaluminum to the titanium-modified solid catalyst is 500.

[0058] The third aspect of this invention discloses the application of a bimodal polyethylene catalyst as described above in the preparation of bimodal polyethylene.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] The catalyst for olefin polymerization of the present invention employs a self-forming small-particle magnesium alkoxide compound (a self-forming small-particle support, specifically magnesium ethoxylate) and a large-particle support as a common support for the catalyst. The two are blended and then supported with titanium for joint titanization. This allows the two types of supports to undergo titanization experiments simultaneously, ensuring that the titanium active centers in the catalyst are uniformly dispersed on different supports. At the same time, the conventional active component and the modified active component centers can each play their roles without mutual exclusion, thereby improving the catalyst's activity, hydrogen sensitivity, and copolymerization performance.

[0061] In addition, the bulk density and copolymer unit content of the polymer powder prepared using the catalyst system of the present invention are greatly improved. Detailed Implementation

[0062] The present invention will now be described in detail with reference to specific embodiments, but these are by no means limitations on the present invention.

[0063] Unless otherwise specified, the reagents used in the following description are commercially available products, and the methods used are those known in the art.

[0064] The bulk component (titanium-modified solid catalyst) of the bimodal polyethylene catalyst for olefin polymerization is prepared by the following method:

[0065] (1) Preparation of self-forming small particle carriers

[0066] Magnesium compounds and alcohols are dispersed in an electron donor and reacted at a certain temperature to form a transparent solution. Then, a multi-electron donor is added and the reaction continues for a period of time to precipitate white particulate matter.

[0067] (2) Activation of large particle carriers

[0068] Large particulate supports were continuously heated to 600°C under nitrogen flow and maintained for 4-18 hours, then gradually cooled to room temperature for later use. A certain amount of the heat-treated large particulate supports was added to pentane and triethylaluminum, reacted at 60°C for 1 hour, and then dried to obtain alkylated large particulate supports.

[0069] (3) Preparation of titanium compounds

[0070] A certain amount of magnesium chloride, an electron donor, and a titanium compound were reacted at 70°C for 3.5 h to form a magnesium-titanium complex.

[0071] (4) Titanium plating and drying

[0072] Add the dried large-particle support (2) to the solution of (1) and stir and mix at room temperature for 30 min to disperse the two supports evenly. Then slowly add the magnesium-titanium composite in (3) dropwise (dropping rate 0.2-0.5 mL / min to achieve uniform dispersion) to the mixed support solution of the two evenly mixed supports. After the dropwise addition is completed, continue to heat to 70℃ and react for 2 h. Then heat to 80℃ for drying to obtain the main component of the catalyst (titanium-modified solid catalyst).

[0073] in:

[0074] The magnesium compound is magnesium chloride.

[0075] The electron donor is selected from organic compounds containing lone pairs of electrons, including O, N, and S. Tetrahydrofuran is preferred as the electron donor, and it also functions as a solvent.

[0076] The alcohol compound can be any alcohol compound conventionally used in the art, preferably at least one of methanol, ethanol, ethylene glycol, glycerol, 1,4-butanediol, propanol, isopropanol, butanol, isobutanol, tert-butanol, hexanol, cyclohexanol, octanol, isooctanol, decanol, benzyl alcohol, and phenethyl alcohol. More preferably, at least one of ethanol and isooctanol.

[0077] The multiple electron donor is not limited to propylene glycol, 1,3-butanediol, 1,4-butanediol, pentanediol and their various isomers, but is preferably at least one of propylene glycol and 1,4-butanediol.

[0078] The titanium compound may be selected from at least one of TiCl4, TiBr4, TiI4, Ti(OC2H5)Cl3, Ti(OCH3)Cl3, Ti(OC4H9)Cl3, Ti(OC2H5)Br3, Ti(OC2H5)2Cl2, Ti(OCH3)2Cl2, Ti(OCH3)2I2, Ti(OC2H5)3Cl, Ti(OCH3)3Cl, and Ti(OC2H5)3I. Preferably, it is selected from at least one of TiCl4, Ti(OC2H5)Cl3, Ti(OCH3)Cl3, and Ti(OC4H9)Cl3. More preferably, the titanium compound is TiCl4.

[0079] Large-particle carriers are carrier materials with large specific surface area and pore volume, such as activated carbon, diatomaceous earth, kaolin, montmorillonite, alumina, and silica. Silica is preferred, specifically commercially available PQ ES70W grade silica.

[0080] Example 1

[0081] (1) Add 60 mL of tetrahydrofuran, 3 g of magnesium chloride and 1.25 mL of ethanol to a 250 mL three-necked glass reaction flask and react at 65 °C for 3.5 h. Continue to add 4 mL of 1,4-butanediol to the reaction flask. After the addition is complete, continue to react for 2 h. White solid particles (ethoxymagnesium) precipitate out.

[0082] (2) Select silicon dioxide, purge with nitrogen at 600°C for 4.5 hours, cool naturally to room temperature under nitrogen atmosphere, then add pentane and triethylaluminum, heat to 60°C and stir thoroughly for 1 hour, then evaporate the solvent to obtain thermally activated silicon dioxide.

[0083] (3) Add 60 mL of tetrahydrofuran to another 250 mL three-necked flask, then add 2 g of anhydrous magnesium chloride and 0.5 g of titanium trichloride. While stirring, add 2 mL of ethanol, heat to 70 °C, and react for 3.5 hours to obtain the magnesium-titanium complex.

[0084] (4) Add the dried silica from (2) to the reaction flask from (1) and stir and mix at room temperature for 30 min to disperse the two supports evenly. Then, react the magnesium-titanium composite from (3) with the mixed supports, keep the temperature in the flask at 70°C and continue the reaction for 2 h, and then heat to 80°C to dry to obtain a solid catalyst component with good flowability (titanium-modified solid catalyst).

[0085] Titanium catalyst components: Mg m Ti n Cl 2m+3n Al 0.3n (OR) 2.5m (m = 0 to 2, n = 0 to 4, and neither m nor n is 0);

[0086] Titanium-based catalyst composition: Mg: 4.65 wt%; Ti: 0.89 wt%; Al: 1.3 wt%; Cl: 15.23 wt%.

[0087] Application examples

[0088] Homopolymerization: In a 2L stainless steel reactor, after complete purging with high-purity nitrogen, 1.2L of hexane, 1.0mL of triethylaluminum, and 0.030g of the solid catalyst (titanium-treated solid catalyst) prepared in Example 1 were added. The temperature was raised to 70°C, and hydrogen was introduced to bring the pressure inside the reactor to 0.2MPa. After the temperature reached 75°C, ethylene was introduced to bring the total pressure inside the reactor to 0.8MPa. Polymerization was carried out at 80°C for 2 hours. The catalyst activity was 4952kgPE / kgCat, the bulk density was 0.35g / mL, and the molecular weight distribution (MWD) was 8.9.

[0089] Example 2

[0090] The other steps are the same as in Example 1, except that:

[0091] (3) Add 60 mL of tetrahydrofuran to another 250 mL three-necked flask, then add 2 g of anhydrous magnesium chloride and 0.5 g of titanium trichloride. While stirring, add 1 mL of ethanol, heat to 70 °C, and react for 3.5 hours to obtain the magnesium-titanium complex.

[0092] The laboratory evaluation conditions for the catalyst were the same: catalyst activity 4708 kgPE / kgCat, bulk density: 0.30 g / mL, molecular weight distribution (MWD): 8.3.

[0093] Comparative Example 1

[0094] The carrier activation steps are the same as in Example 1, except that:

[0095] (1) Under nitrogen protection, 60 mL of tetrahydrofuran was added to a 250 mL three-necked flask, followed by 2 g of anhydrous magnesium chloride and 0.5 g of titanium trichloride. Under stirring, 2 mL of ethanol was added, and the mixture was heated to 70 °C and reacted for 3.5 hours to obtain a magnesium-titanium complex.

[0096] (2) Add activated silica to (1) and stir for 2 hours. Then heat to 80°C and dry to obtain a solid catalyst (titanium-modified solid catalyst) component with good flowability.

[0097] The laboratory evaluation conditions for the catalyst were the same: catalyst activity 3154 kgPE / kgCat, bulk density: 0.34 g / mL, molecular weight distribution (MWD): 6.5.

[0098] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A bimodal polyethylene catalyst, characterized in that, Solid catalysts that use both large-particle supports and self-forming small-particle supports as carriers; In the solid catalyst, titanium active centers are uniformly dispersed on large particle supports and self-formed small particle supports; The self-forming small particle carrier includes magnesium alkoxide compounds.

2. The bimodal polyethylene catalyst according to claim 1, characterized in that, The self-forming small particle carrier is magnesium ethoxylate; The large-particle carriers include activated carbon, diatomaceous earth, kaolin, montmorillonite, alumina, and silica.

3. A method for preparing a bimodal polyethylene catalyst as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Preparation of self-forming small particle carriers: Magnesium compounds and alcohols are co-dispersed in an electron donor to react, and then a multi-electron donor is added to continue the reaction. The precipitated particles are self-forming small particle carriers. (2) Activation of large particle carriers: Large particle carriers were purged under a nitrogen atmosphere; Large particulate support purged with nitrogen was reacted with pentane and triethylaluminum, and dried to obtain alkylated large particulate support. (3) Preparation of magnesium-titanium composite: Magnesium chloride, an electron donor, and a titanium compound are mixed and reacted to obtain a magnesium-titanium complex. (4) Preparation of titanium-modified solid catalysts: The alkylated large-particle carrier obtained in (2) is added to the solution in (1) and dispersed evenly to form a mixed carrier solution; The magnesium-titanium composite obtained in (3) was added dropwise to the mixed support solution, heated to react, and then dried to obtain a titanium-modified solid catalyst. (5) Preparation of bimodal polyethylene catalyst: Triethylaluminum was mixed with the obtained titanium-modified solid catalyst to obtain the bimodal polyethylene catalyst.

4. The method for preparing a bimodal polyethylene catalyst according to claim 3, characterized in that, (1) The magnesium compound mentioned is magnesium chloride; The alcohols mentioned include methanol, ethanol, ethylene glycol, glycerol, 1,4-butanediol, propanol, isopropanol, butanol, isobutanol, tert-butanol, hexanol, cyclohexanol, octanol, isooctanol, decanol, benzyl alcohol, and phenethyl alcohol. The electron donors include organic compounds containing lone pairs of electrons; The aforementioned multi-electron donors include propylene glycol, 1,3-butanediol, 1,4-butanediol, pentanediol, and isomers of pentanediol; The molar ratio of the magnesium compound, alcohol compound, and multi-electron donor is 1: (0.1-1.5)：(0.5-2.5)； The reaction is carried out at a temperature of 45-80℃ for 2-8 hours. The continued reaction was carried out at a temperature of 50-80℃ for 2 hours.

5. The method for preparing a bimodal polyethylene catalyst according to claim 3, characterized in that, (3) The electron donors include organic compounds containing lone pairs of electrons; The titanium compounds mentioned include TiCl4, TiBr4, TiI4, Ti(OC2H5)Cl3, Ti(OCH3)Cl3, Ti(OC4H9)Cl3, Ti(OC2H5)Br3, Ti(OC2H5)2Cl2, Ti(OCH3)2Cl2, Ti(OCH3)2I2, Ti(OC2H5)3Cl, Ti(OCH3)3Cl, and Ti(OC2H5)3I; The molar ratio of magnesium chloride to titanium compound is 1:(0.01-0.25); The reaction was carried out at a temperature of 70°C for 6 hours.

6. A method for preparing a bimodal polyethylene catalyst according to claim 4 or 5, characterized in that, The elements containing lone pairs of electrons include oxygen, nitrogen, and sulfur.

7. The method for preparing a bimodal polyethylene catalyst according to claim 3, characterized in that, (2) The purging temperature is 600℃, and the time is 4-18 hours; The reaction was carried out at a temperature of 60°C for 1 hour.

8. The method for preparing a bimodal polyethylene catalyst according to claim 3, characterized in that, (4) The heating reaction was carried out at a temperature of 70°C for 2 hours. The drying temperature is 80°C.

9. The method for preparing a bimodal polyethylene catalyst according to claim 3, characterized in that, (5) The aluminum-titanium molar ratio of the triethylaluminum to the titanium-modified solid catalyst is 500.

10. The use of a bimodal polyethylene catalyst as described in claim 1 or 2 in the preparation of bimodal polyethylene.