Ziegler-Natta catalysts for ethylene polymerization or copolymerization and their applications

Abstract

This invention relates to a Ziegler-Natta catalyst for ethylene polymerization or copolymerization, characterized in that the catalyst contains titanium and vanadium, wherein the molar ratio of titanium to vanadium is 1 to 10:1. The Ziegler-Natta catalyst for ethylene polymerization or copolymerization is used in homopolymerization of ethylene or copolymerization of ethylene with other α-olefins. Compared with existing catalysts, this catalyst has the advantages of near-spherical particle shape, narrow particle size distribution, less fine powder, good copolymerization performance, and good hydrogen regulation sensitivity, which can more effectively regulate the molecular weight distribution of the polymer and the distribution of comonomers on the polymer molecular chain. Furthermore, the production process is simple and the production cost is low.

Description

Technical Field

[0001] This invention relates to a Ziegler-Natta catalyst for the polymerization or copolymerization of ethylene, wherein the Ziegler-Natta catalyst is used for homopolymerization of ethylene or copolymerization of ethylene with other α-olefins. Background Technology

[0002] High-density polyethylene (HDPE) has good mechanical strength at high temperatures, but poor resistance to long-term creep. In recent years, significant progress has been made in the study of the relationship between the molecular structure and properties of polyethylene. By improving the polymerization process and developing new catalyst systems, it is possible to control the distribution of comonomers in the polymer molecular chain and more accurately control the crystallization of the polymer, making it possible for polyethylene to have both good high-temperature resistance and resistance to long-term creep.

[0003] The preparation method of highly efficient titanium-based Ziegler-Natta catalysts for ethylene polymerization is well known, mainly consisting of titanium halides supported by MgCl2 or SiO2. For example, the preparation method of ethylene polymerization and copolymerization catalysts disclosed in JP 4951378 involves reacting ground magnesium chloride with ethanol to generate a MgCl2·6C2H5OH alcohol slurry, followed by esterification with diethylaluminum chloride to obtain a complex, and finally reacting with TiCl4 to obtain a titanium-based Ziegler-Natta catalyst supported by MgCl2. This catalyst preparation method is simple, the reaction conditions are mild, and the catalyst exhibits high activity during ethylene polymerization. However, this preparation method suffers from drawbacks: the magnesium chloride support only swells in mineral oil and cannot dissolve; the magnesium chloride in the slurry reaction system contains irregular flaky particles generated during the original grinding process, resulting in poor particle morphology, low bulk density, and uneven particle size in the obtained solid catalyst. Consequently, the polymer morphology is also poor, with a high content of fine powder, which easily generates static electricity and clogs pipes. Furthermore, the high oligomer content in the solvent during polymerization causes significant problems for post-processing.

[0004] Patent CN1229092 discloses a catalyst system for ethylene polymerization and copolymerization. This catalyst system comprises: (1) a Ti-containing solid catalyst component; and (2) an alkylaluminum compound. The Ti-containing solid catalyst component is formed by dissolving magnesium halide in an organic epoxy compound and an organic phosphorus compound to form a homogeneous solution. Ethanol is added to treat the dissolved magnesium halide, and then the solution is mixed with titanium tetrahalide. In the presence of precipitating agents such as organic anhydrides, organic acids, ethers, and ketones, a solid is precipitated to obtain a solid catalyst. When this catalyst system is used for ethylene polymerization, the resulting polymer has a high content of fine powder, low catalyst activity, and poor hydrogen regulation performance. It is not suitable for preparing bimodal polymers and is difficult to replace the existing highly active Ziegler-Natta catalyst for ethylene slurry polymerization. Simultaneously, the bulk density of the polymer is also slightly lower than that of existing catalysts.

[0005] Patent CN1112373 discloses a solid titanium catalyst composition and its preparation process. It mainly uses low-carbon alcohols to dissolve magnesium halides, adds alkane diluents and silane electron-donating compounds, and then reacts with titanium halides to precipitate a solid catalyst. Although this catalyst can produce ethylene polymers with excellent particulate properties when used in ethylene polymerization, it suffers from problems such as long induction time, large fluctuations in catalytic activity, and low oligomer content.

[0006] To address the problems of the aforementioned technologies, patents CN1180712 and CN1752116A disclose a catalyst for ethylene polymerization or copolymerization and its preparation method. In this method, at least one unsaturated fatty acid ester containing one or more ester groups and / or at least one water-in-oil nonionic surfactant are added during the reaction of magnesium compounds and organic alcohols to form an alcohol slurry. This allows magnesium halide and alcohol to form a swollen alcohol slurry in a diluent at a lower temperature, eliminating the need to dissolve the magnesium halide at high temperatures. This also yields a catalyst with a particulate morphology and reduces the amount of alcohol used in forming the alcohol slurry. The catalyst preparation process is simple, easy to operate, and cost-effective. However, when used for ethylene polymerization, this catalyst still suffers from drawbacks such as insensitivity to hydrogen regulation, poor polymer particle morphology, and a high proportion of fine powder. This is detrimental to producing polymers with a wide molecular weight distribution using a single catalyst.

[0007] Patents CN101245115A, CN102272172A, and CN1112373A disclose a solid titanium catalyst composition and its preparation process. This method primarily uses low-carbon alcohols to dissolve magnesium halides, adding alkane diluents and silane-based electron-donating compounds or organoboron compounds, which then react with the titanium halide to precipitate a solid catalyst. Although this catalyst exhibits high catalytic activity and produces ethylene polymers with excellent particulate properties during ethylene polymerization, its hydrogen regulation performance and oligomer content remain unsatisfactory. Patent CN1471541A discloses a method for preparing a solid titanium complex catalyst for ethylene polymerization. This involves reacting a magnesium halide compound with an alcohol to prepare a magnesium solution, then reacting it with an ester compound with at least one hydroxyl group and a boron compound with at least one alkoxy group, followed by reaction with a mixture of titanium compounds and haloalkane compounds, followed by recrystallization to produce a solid catalyst. This catalyst exhibits advantages such as high catalytic activity, high polymer packing density, and narrow particle size distribution; however, its hydrogen regulation performance and oligomer content also remain unsatisfactory.

[0008] Based on the above analysis, in the preparation method of Ziegler-Natta catalysts for ethylene polymerization, researchers can control the particle size, morphology, and distribution of the catalyst through emulsification technology, and regulate the catalyst activity through the catalyst composition and electron-donating compounds. However, controlling the copolymerization performance, hydrogen sensitivity, and oligomer formation of the catalyst has always been a challenge, which is crucial for developing polyethylene products with bimodal distributions.

[0009] The resin for heat-resistant polyethylene pipes must first and foremost exhibit a bimodal or multimodal molecular weight distribution. The high molecular weight fraction provides superior resistance to environmental stress cracking, slow crack growth, high creep resistance, high tensile strength, and high impact strength. The low molecular weight fraction effectively reduces melt viscosity at high shear rates, improves flowability during processing, and ensures high crystallinity, resulting in good rigidity. Only when the high and low molecular weight fractions are in a certain proportion can the final strength and service life of the pipe be improved while simultaneously considering its processing performance.

[0010] Dow Chemical Company first developed PE-RT resin for pipes using a solution polymerization process (WOP 03 / 020821 Al, USP 2007 / 0112160 Al, USP 7250473 B2, USP 2010 / 0003439 Al) through copolymerization of ethylene and octene. In 1991, they developed DOWLEX 2344 resin, a type I PE-RT resin, a copolymer of ethylene and octene with a density of 0.933 g / mL. In 2001, the company launched another grade, Dowlex 2388 (type II PE-RT), which is also a copolymer of ethylene and 1-octene. Patents CN101796085 A and CN 102325810A disclose heat-resistant polyethylene copolymers prepared by metallocene-catalyzed copolymerization of ethylene and 1-hexene, exhibiting high zero-shear viscosity and good processability. Patent CN1906220A discloses an ethylene-1-hexene copolymer for non-crosslinked water supply pipes, featuring a high comonomer content and a more uniform comonomer distribution, exhibiting a bimodal or broad molecular weight distribution, and demonstrating excellent processability, resistance to internal pressure creep at high temperatures, and resistance to environmental stress cracking. This copolymer is prepared using a supported metallocene catalyst. LyondellBasell (US 2010 / 0076136 A1, CN 101400933A, CN 1162453C, CN 102712715 A, CN 102325811A, CN 102282182 A) utilizes a three-reactor tandem process to produce PE-RT (ethylene-butene copolymer), controlling the amount of comonomer and catalyst added in different reactors to regulate the molecular structure of polyethylene. The production process involves producing low-molecular-weight polyethylene in the first reactor, and adding comonomers in the second and third reactors to control the distribution of the copolymer, resulting in pressure- and heat-resistant polyethylene pipe materials. CN 101353387A provides a method for preparing highly branched copolymers by copolymerizing ethylene with α-olefins. This method uses a mixed modifier composed of conjugated diene and alkoxysilane to improve the insertion rate and distribution uniformity of the comonomers. CN 101472950A discloses a process and equipment for polymerizing ethylene with comonomers under high pressure, employing a free radical polymerization mechanism. Yangzi Petrochemical (CN 101654494A) discloses an ethylene copolymer manufactured using a specific supported non-metallocene catalyst, and a method for manufacturing this ethylene copolymer. This copolymer is mainly used to manufacture peroxide-crosslinked heat-resistant polyethylene pipes. CN 101688033A reports a process for preparing multi-peak polyethylene copolymer resin compositions using metallocene or Ziegler-Natta catalysts via fluidized bed and moving bed methods.Patent CN201210445946.X discloses a method for preparing ethylene copolymers by tandem polymerization. By continuously using two salicylaldehyde-imine metal catalysts with different catalytic properties to co-catalyze the ethylene polymerization reaction, ethylene copolymers can be obtained using a single ethylene monomer. Its advantage is that it eliminates the step of adding external comonomers and can directly synthesize ethylene copolymers, but the heat resistance of the product is poor.

[0011] Existing methods for preparing heat-resistant polyethylene copolymers typically suffer from one or more of the following drawbacks: (1) Polyethylene prepared using metallocene catalysts has a narrow molecular weight distribution and poor processability. (2) The reaction steps involved in two- or multiple-reactor series polymerization are numerous, making process condition control difficult. (3) The thermal and mechanical properties of the polyethylene copolymers cannot meet the long-term high-temperature performance requirements of hot water pipes. Summary of the Invention

[0012] The purpose of this invention is to prepare a Ziegler-Natta catalyst with better catalytic performance and a more reasonable preparation process.

[0013] As one aspect of the invention, a Ziegler-Natta catalyst for ethylene polymerization or copolymerization is provided, the catalyst containing titanium and vanadium in a molar ratio of titanium to vanadium of 1 to 10:1.

[0014] In at least one possible embodiment, the catalyst further contains magnesium, and the molar ratio of the total molar amount of titanium and vanadium to the molar amount of magnesium is 1:1.0 to 15.0.

[0015] In at least one possible embodiment, the catalyst is prepared from the following components:

[0016] (1) Microemulsions of magnesium compounds;

[0017] (2) Triethylene glycol methyl ether borate triester;

[0018] (3) A mixture of liquid titanium compounds and liquid vanadium compounds;

[0019] in,

[0020] The magnesium compound microemulsion is a microemulsion formed by a magnesium halide-organic alcohol-dispersant dissolution system; such microemulsions can remain stable for a long time under static conditions.

[0021] The triethylene glycol methyl ether borate triester is an organoboron compound without active hydrogen.

[0022] The general formula of the titanium compound is Ti(OR). a X b In the formula, R represents C1 to C2.10 The aliphatic hydrocarbon group or aryl group, where X is a halogen, a is 0, 1, 2 or 3; b is an integer from 1 to 4, and a + b = 3 or 4;

[0023] The general formula for the vanadium compound mentioned above is V(OR). a X b In the formula, R represents C1 to C2. 10 The aliphatic hydrocarbon group or aryl group, where X is a halogen, a is 0, 1, 2 or 3; b is an integer from 1 to 4, and a + b = 3 or 4;

[0024] In the mixture of liquid titanium compound and liquid vanadium compound, the molar ratio of titanium to vanadium is 1 to 10:1;

[0025] The molar ratio of the mixture of liquid titanium compound and liquid vanadium compound to magnesium compound is 1:1.0 to 15.0.

[0026] In at least one possible embodiment, the magnesium compound microemulsion contains, based on 1 mol of magnesium halide, 0.1 to 10.0 mol of organic alcohol, 0.20 to 0.25 mol of triethylene glycol methyl ether borate, and 0.1 to 10.0 mol of dispersant.

[0027] In at least one possible embodiment, the magnesium halide is a magnesium dihalide, or a derivative in which one halogen atom in a magnesium dihalide molecule is replaced by a hydrocarbon group or a hydrocarbon oxygen group, or a mixture thereof.

[0028] In at least one possible embodiment, the organic alcohol is selected from straight-chain or branched alkyl alcohols, cycloalkanols, and aromatic alcohols or aryl alcohols having 1 to 10 carbon atoms, as well as halogenated derivatives of the above organic alcohols.

[0029] In at least one possible embodiment, the molar ratio of the organic alcohol to the magnesium compound is 1 to 10:1.

[0030] In at least one possible embodiment, the molar ratio of the organic alcohol to the magnesium compound is 3 to 4:1.

[0031] As another aspect of the invention, there is a Ziegler-Natta catalyst composition for ethylene polymerization or copolymerization, the composition comprising the above-described catalyst and an organoaluminum compound having the general formula AlR n X 3-n In the formula, R is an alkyl group, X is a halogen, and n is an integer 1 ≤ n ≤ 3.

[0032] In at least one possible embodiment, the molar ratio of aluminum to titanium is 10 to 200:1. In this invention, an excess of organoaluminum compound needs to be added during the reaction process to remove impurities such as water from the reaction system; therefore, the aluminum content in the final polymerization product will be significantly higher.

[0033] In at least one possible embodiment, the organoaluminum compound is one or a mixture of triethylaluminum, triisobutylaluminum, dichlorodiethylaluminum, dichloroethylaluminum, sesquiethylaluminum, or the like.

[0034] As another aspect of the invention, it relates to the use of the above-described catalyst or composition in the homopolymerization of ethylene or the copolymerization of ethylene with higher α-olefins.

[0035] As another aspect of the invention, it relates to the homopolymerization of ethylene or the copolymerization of ethylene with higher α-olefins, using the above-described catalyst or the above-described composition.

[0036] As another aspect of the invention, there is a connection to an ethylene homopolymer or ethylene copolymer containing titanium and vanadium, wherein the molar ratio of titanium to vanadium is 1 to 10:1.

[0037] In a specific embodiment of this invention, a multifunctional borate ester compound is added as a modifier during the dissolution of magnesium chloride, allowing it to interact with the diluent and solvent to form a magnesium chloride microemulsion system. This system is then reacted with a mixture of liquid titanium and liquid vanadium compounds, and a spherical ethylene polymerization solid Ziegler-Natta catalyst is prepared by precipitation. This overcomes the shortcomings of existing technologies and provides a Ziegler-Natta catalyst highly suitable for ethylene slurry polymerization, particularly for producing polymers with a wide relative molecular mass distribution. Compared with existing catalysts, this catalyst has advantages such as spherical particles, narrow particle size distribution, less fine powder, good copolymerization performance, and good hydrogen sensitivity, allowing for more effective adjustment of the polymer's molecular weight distribution and the distribution of comonomers on the polymer molecular chain. Furthermore, the production process is simple and the production cost is low. This invention also provides a multi-peak structure HDPE copolymer and its preparation method to solve the problems of complex processes, difficulty in controlling polymer molecular structure and properties, and poor processing performance in existing technologies.

[0038] The preparation process of the Ziegler-Natta catalyst provided by this invention is summarized as follows:

[0039] The catalyst is prepared from the following components:

[0040] (1) Microemulsions of magnesium compounds;

[0041] (2) Triethylene glycol methyl ether borate triester;

[0042] (3) A mixture of liquid titanium compounds and liquid vanadium compounds;

[0043] in,

[0044] The magnesium compound microemulsion is a microemulsion formed by a magnesium halide-organic alcohol-dispersant dissolution system; this microemulsion can remain stable for a long time under static conditions.

[0045] The triethylene glycol methyl ether borate triester is an organoboron compound without active hydrogen.

[0046] The general formula of the titanium compound is Ti(OR). a X b In the formula, R represents C1 to C2. 10 The aliphatic hydrocarbon group or aryl group, where X is a halogen, a is 0, 1, 2 or 3; b is an integer from 1 to 4, and a + b = 3 or 4;

[0047] The general formula for the vanadium compound mentioned above is V(OR). a X b In the formula, R represents C1 to C2. 10 The aliphatic hydrocarbon group or aryl group, where X is a halogen, a is 0, 1, 2 or 3; b is an integer from 1 to 4, and a + b = 3 or 4;

[0048] In the mixture of liquid titanium compound and liquid vanadium compound, the molar ratio of titanium to vanadium is 1 to 10:1.

[0049] The molar ratio of the mixture of liquid titanium compound and liquid vanadium compound to magnesium compound is 1.0 to 15.0.

[0050] (1) Preparation of magnesium compound microemulsion

[0051] Magnesium halide is dissolved in an alcohol solvent system, and an inert diluent is added to the preferred solvent system to form a uniform microemulsion. The preferred dissolution temperature is 50–150°C. An organoboron compound without active hydrogen atoms is added during or after the solution is formed.

[0052] (2) Preparation of solid catalysts

[0053] The above solution is reacted with a mixture of titanium and vanadium compounds. An organoboron compound without active hydrogen atoms can also be added when the solution in step (1) reacts with the titanium and vanadium compounds. The mixture is slowly heated to 50-120°C. The solid gradually precipitates and forms particles. After a certain reaction time, the unreacted substances and solvent are removed, and the mixture is washed with an inert diluent to obtain the catalyst component of the present invention.

[0054] The catalyst prepared above (component A) is used in combination with an organoaluminum compound (component B) to catalyze the homopolymerization of ethylene and the copolymerization of ethylene with other α-olefins. The organoaluminum compound has the general formula AlR. n X 3-n In the formula, R is an alkyl group, X is a halogen, and n is an integer 1 ≤ n ≤ 3.

[0055] The catalyst composed of components A and B of this invention is suitable for the homopolymerization of ethylene and the copolymerization of ethylene with other α-olefins. The polymerization methods can include slurry polymerization, gas-phase polymerization, solution polymerization, etc., with slurry polymerization being the preferred method. The aforementioned α-olefins can be propylene, butene, pentene, hexene, octene, 4-methylpentene-1, etc. This catalyst comprises the catalyst components of this invention and a catalyst with the general formula AlR. n X 3-n The reaction product of the organoaluminum compound, wherein R can be a hydrocarbon group with 1 to 20 carbon atoms, especially alkyl, aralkyl, and aryl; X is a halogen, especially chlorine and bromine; and n is a number where 0 ≤ n ≤ 3. Specific compounds include alkylaluminum halides such as trimethylaluminum, triethylaluminum, triisobutylaluminum, trioctylaluminum, diethylaluminum chloride, diisobutylaluminum chloride, sesquiethylaluminum chloride, and dichloroethylaluminum, with trialkylaluminum compounds being preferred, especially triethylaluminum and triisobutylaluminum. The molar ratio of aluminum to titanium is 5 to 500, preferably 20 to 200.

[0056] Polymerization can be carried out using solution polymerization, slurry polymerization, or gas-phase polymerization. Slurry polymerization media include inert solvents such as propane, isobutane, hexane, heptane, cyclohexane, naphtha, raffinate, hydrogenated gasoline, kerosene, benzene, toluene, xylene, and other saturated aliphatic or aromatic hydrocarbons.

[0057] The polymerization can be carried out in batch, semi-continuous, or continuous processes, in single-reactor or multi-reactor series polymerization. The polymerization temperature is 0–150℃, with 40–100℃ being preferred. To adjust the molecular weight and comonomer distribution of the final polymer, hydrogen is used as a molecular weight regulator, and C4–C12 aliphatic α-olefins are used as comonomers.

[0058] This invention proposes a multi-peak HDPE copolymer and its preparation method, characterized by using the above-mentioned solid Ziegler-Natta catalyst for ethylene polymerization or copolymerization, and carrying out ethylene homopolymerization and multi-stage copolymerization reactions in a single reactor under hydrogen regulation, including the following steps:

[0059] a) Inject an organic solvent into the reactor, add solid catalyst component A and component B to the organic solvent, add a certain amount of hydrogen, and the ethylene homopolymerization reaction temperature is between 50 and 100°C, the pressure is 0.5 to 1.0 MPa, and the reaction is carried out for 0.1 to 5 hours to obtain ethylene homopolymer. Then, reduce the reactor temperature to 20 to 30°C, vent the reactor, and replace the reactor with nitrogen.

[0060] b) Add a certain amount of hydrogen to the reaction vessel containing the suspension solution of polyethylene homopolymer and organic solvent obtained in step a, and pass a mixture of ethylene and C4-C12 aliphatic α-olefin at 50-100°C, maintain the pressure at 0.1-0.5 MPa, react for 0.1-2 hours to obtain polyethylene copolymer, lower the temperature of the reaction vessel to 20-30°C, vent the reaction vessel, and replace the reaction vessel with nitrogen;

[0061] c) Add a small amount of hydrogen to the reaction vessel containing the suspension of polyethylene copolymer and organic solvent obtained in step b, and pass a mixture of ethylene and C4-C12 aliphatic α-olefin at 50-100°C, maintaining a pressure of 0.1-0.5 MPa, and react for 0.1-2 hours to obtain the polyethylene copolymer product.

[0062] The prepared polymer products have the following characteristics: density 0.940–0.955 g / cm³, melt index (190℃, 5 kg) 0.1–1.0 g / 10 min, branching degree 2.5–4.5 / 1000 carbon atoms, multi-peak molecular weight distribution, Mw / Mn 12–20, weight-average molecular weight <50,000, mass content 40–50%, crystallinity 65–75%, and crystal thickness 35–45 nm; weight-average molecular weight 50–1,000,000, mass content 50–60%, crystallinity 45–55%, and crystal thickness 20–30 nm; weight-average molecular weight >1,000,000, mass content 0–5%, crystallinity 30–40%, and crystal thickness 10–20 nm.

[0063] The organic solvent is one or more inert solvents such as toluene, isopentane, n-hexane, cyclohexane, or heptane.

[0064] In step a, the amount of hydrogen added is such that the hydrogen / ethylene pressure ratio is 1 to 10.

[0065] In step b, the amount of hydrogen used is such that the partial pressure ratio of hydrogen / ethylene-α-olefin mixture is 0 to 1.

[0066] In step c, the amount of hydrogen used is such that the partial pressure ratio of hydrogen / ethylene-α-olefin mixture is 0 to 0.2.

[0067] In step b, the partial pressure ratio of the C4-C12 aliphatic α-olefin gas to the ethylene gas is 0.01 to 1.0.

[0068] In step c, the partial pressure ratio of the C4-C12 aliphatic α-olefin gas to the ethylene gas is 0.01 to 1.0.

[0069] The prepared multi-peak HDPE copolymer has excellent heat and pressure resistance properties and is suitable for extrusion molding as a heat-resistant pipe material.

[0070] Furthermore, the present invention proposes a polyethylene copolymer pipe made from the aforementioned polyethylene copolymer.

[0071] Specifically, in the method for preparing heat-resistant polyethylene described in this invention, the polymerization reaction is carried out in an inert organic solvent, and the solvent can be alkanes, aromatics, or halogenated hydrocarbons. Typical solvents include one or a mixture of several inert hydrocarbons such as toluene, isopentane, n-hexane, cyclohexane, or heptane.

[0072] The method for preparing heat-resistant polyethylene according to the present invention uses a solid Ziegler-Natta catalyst system for the polymerization or copolymerization of the above-mentioned ethylene.

[0073] Catalyst components A and B are typically dispersed in an inert solvent. The usual amount of the main catalyst in the reactor is 0.001 to 0.06 millimoles of titanium per liter of diluent, and the amount of the co-catalyst is usually 0.02 to 10 millimoles of aluminum per liter of diluent.

[0074] A certain amount of hydrogen gas is added to the reactor, with a hydrogen / ethylene pressure ratio of 1–10, preferably 3–6. The ethylene homopolymerization reaction is carried out at a temperature between 50–100°C, preferably 70–90°C, at a pressure of 0.5–1.0 MPa, for 0.1–5 hours to obtain an ethylene homopolymer with high density and a high MI value. The reactor temperature is then reduced to 20–30°C, the reactor is vented, and nitrogen is used to purge the reactor.

[0075] In a reactor containing ethylene homopolymer and an organic solvent suspension, a certain amount of hydrogen is added, with a hydrogen / ethylene-α-olefin mixed gas partial pressure ratio of 0 to 1, preferably 0.1 to 0.5. The reaction temperature is 50 to 100°C. A mixed gas of ethylene and C4 to C12 aliphatic α-olefins is introduced, preferably one or a mixture of two of 1-butene, 1-hexene, or 1-octene. The partial pressure ratio of C4 to C12 aliphatic α-olefin gas to ethylene gas is 0.01 to 1.0, preferably 0.01 to 0.5. The reaction pressure is 0.1 to 0.5 MPa, preferably 0.2 to 0.4 MPa. The reaction is carried out for 0.1 to 2 hours to obtain a low-density polyethylene copolymer with a low MI value. The reactor temperature is then reduced to 20 to 30°C, the reactor is vented, and the reactor is purged with nitrogen.

[0076] In a reactor containing a suspension of polyethylene copolymer and organic solvent, a small amount of hydrogen is added, with a hydrogen / ethylene-α-olefin partial pressure ratio of 0–0.2, preferably 0.01–0.1. The reaction temperature is 50–100°C. A mixture of ethylene and C4–C12 aliphatic α-olefins is introduced, preferably one or a mixture of two of 1-butene, 1-hexene, or 1-octene. The partial pressure ratio of the C4–C12 aliphatic α-olefin gas to the ethylene gas is 0.01–1.0, preferably 0.01–0.5. The pressure is maintained at 0.1–0.5 MPa, preferably 0.1–0.3 MPa, and the reaction is carried out for 0.1–2 hours to obtain a polyethylene copolymer.

[0077] The polymer product prepared by this invention has a density of 0.940–0.955 g / cm³. 3 The polymer exhibits a melt index (190℃, 5Kg) of 0.1-1.0 g / 10min, a branching degree of 2.5-4.5 / 1000 carbon atoms, a multimodal molecular weight distribution, a Mw / Mn ratio of 12-20, and a mass content of 40-50% for weight-average molecular weight <50,000, a crystallinity of 65-75%, and a wafer thickness of 35-45 nm. For weight-average molecular weights of 50-1,000,000, the mass content is 50-60%, the crystallinity is 45-55%, and the wafer thickness is 20-30 nm. For weight-average molecular weights >1,000,000, the mass content is 0-5%, the crystallinity is 30-40%, and the wafer thickness is 10-20 nm. This wide molecular weight distribution helps maintain good strength and processability, making it suitable for extrusion molding into pipes. The low molecular weight fraction provides a higher crystal thickness, which is beneficial to improving the mechanical properties and heat distortion temperature of the polymer. The high molecular weight fraction has a suitable crystal thickness, indicating that it can contribute to some mechanical properties and also contains a certain amount of tethered molecular chain structure to resist crack propagation. The ultra-high molecular weight fraction has a thinner crystal thickness, indicating that it has more branched structure, which can form a large number of tethered molecules to resist crack propagation and improve melt strength. The copolymer can be used for heat-resistant pipes.

[0078] Compared with the prior art, the present invention has the following advantages:

[0079] This invention provides a catalyst and its preparation method that are highly suitable for ethylene slurry polymerization processes, particularly for single-reactor or multi-reactor tandem polymerization to produce polyethylene with a wide relative molecular mass distribution and tunable comonomer distribution. Because the magnesium compound is made into a microemulsion state during catalyst preparation, spherical catalyst particles are easily precipitated. The non-active hydrogen organoboron compound not only acts as a precipitant and precipitation aid, but its addition also improves the particle morphology of the catalyst, further improving the particle morphology of the polymer. Furthermore, triethylene glycol methyl ether borate triester participates in the coordination of the active center, affecting the chemical environment of the active center and giving the catalyst good hydrogen-tunable sensitivity. The addition of liquid vanadium compound forms a second active center in the catalyst. The main characteristics of the vanadium active component are the high molecular weight of its ethylene polymerization product and the high amount of comonomer insertion. Utilizing these characteristics, the molecular weight and molecular weight distribution of the polymer product, as well as the content and distribution of short branches, can be effectively improved, thereby improving the comonomer distribution and long-chain branched structure of high-density polyethylene.

[0080] This invention provides a method for copolymerizing ethylene with low-cost α-olefins using a solid Ziegler-Natta catalyst (either through polymerization or copolymerization) under mild conditions in a single reactor. By adjusting the polymerization process, the polymer molecular weight can be made to exhibit a multi-peak distribution. This method features a short process flow, flexible operation, and easily controllable product performance and structure. The prepared copolymer has a wide molecular weight distribution and exhibits a multi-peak distribution. Different molecular weight components and copolymers correspond to different material properties, thus meeting the performance requirements of heat-resistant polyethylene pipe materials. It is suitable for extrusion molding as a heat-resistant pipe material. Detailed Implementation

[0081] The present invention is further described below with reference to embodiments, but the scope of the invention is not limited to these embodiments. The scope of the invention is set forth in the claims.

[0082] Polymer density was determined in accordance with standard GB / T 1033-86.

[0083] The polymer melt flow rate was determined in accordance with standard GB / T 3682-2000.

[0084] Melting point and crystallinity were determined using differential scanning calorimetry in accordance with standard ASTM D 3418-03.

[0085] Molecular weight and its distribution were determined by high-temperature gel permeation chromatography (GPC). A PL220 GPC column packed with a mix-B column was used. The sample was prepared by dissolving 10 mg of resin in 10 mL of 1,2,4-trichlorobenzene. The nominal flow rate of the mobile phase was 1.0 mL / min, and the temperature was 155 °C. Molecular weight was calculated using a narrow-distribution polystyrene calibration curve.

[0086] Branching degree was tested according to JY / T007-1996. 50–100 mg of sample was weighed into a 5 mm diameter NMR tube, 0.5 mL of deuterated o-dichlorobenzene was added, the sample was heated to dissolve and air bubbles were removed, and the carbon NMR spectrum of the sample was measured at 120 °C. 13 C-NMR). Spectral width 22123.895 Hz, pulse width 45°, sampling time 0.741 s, decoupling method was combined pulse decoupling, pulse interval was 3 s, and calibration was performed using an isolated methylene peak with a chemical shift of 30.00.

[0087] Example 1

[0088] (1) Preparation of catalyst components: Under nitrogen protection, 4.76 g (50 mmol) of anhydrous magnesium chloride, 75 mL of decane, and 16.3 g (125 mmol) of isooctanol were heated to 130 °C and stirred for 3 hours to obtain a homogeneous magnesium compound microemulsion. 2.5 mmol of triethylene glycol methyl ether borate was added to the microemulsion and stirred at 50 °C for 2 hours to dissolve it in the solution. The obtained microemulsion was cooled to room temperature and then added dropwise over 1 hour with stirring to a mixture of 150 mL of titanium tetrachloride and vanadium tetrachloride, maintained at 0 °C, wherein the molar ratio of titanium to vanadium was 3:1. After the addition was complete, the mixture was kept at 0 °C for 1 hour, and then the temperature was increased to 120 °C over 2 hours with stirring and maintained at this temperature for 2 hours. After the 2-hour reaction was completed, the resulting solid was separated by hot filtration. The solid catalyst was thoroughly washed with decane and hexane until no precipitated titanium and vanadium compounds were detected in the washing solution. After drying, a solid catalyst component was obtained.

[0089] (2) Ethylene polymerization: In a 5L polymerization reactor, 2.5L of n-hexane, 5mmol of triethylaluminum, and 20mg of the catalyst prepared above were added sequentially. The temperature was raised to 70°C, hydrogen gas was added at 0.48MPa, the temperature was raised to 85°C, ethylene was introduced, and the pressure was maintained at 0.8MPa. The reaction was carried out for 3 hours. Then, the reactor temperature was lowered to 30°C, vented, and purged with nitrogen. The temperature was raised to 70°C, hydrogen gas was added at 0.06MPa, and a 1-butene / ethylene mixture was introduced at 80°C. The 1-butene / ethylene gas partial pressure ratio was 0.3, and the pressure was maintained at 0.35MPa. The reaction was carried out for 1 hour. The reaction temperature was lowered to 30°C, vented, and purged with nitrogen. The temperature was raised to 70°C, hydrogen gas was added at 0.01MPa, and a 1-butene / ethylene mixture was introduced at 75°C. The 1-butene / ethylene gas partial pressure ratio was 0.02, and the pressure was maintained at 0.25MPa. The reaction was carried out for 0.5 hours to obtain the ethylene copolymer. The polymerization activity, polymer bulk density, and particle size distribution results are shown in Table 1. The polymer performance test results are shown in Table 2.

[0090] Example 2

[0091] (1) Preparation of the catalyst component: 4.76 g (50 mmol) of anhydrous magnesium chloride, 75 mL of decane, and 16.3 g (125 mmol) of isooctanol were heated to 130 °C and reacted for 3 hours to obtain a microemulsion of a magnesium compound. The obtained magnesium compound microemulsion was cooled to room temperature and then added dropwise over 1 hour with stirring to a mixture of 150 mL of titanium tetrachloride and vanadium tetrachloride, with a molar ratio of titanium to vanadium of 5:1, maintained at 0 °C. After the addition was complete, the mixture was maintained at 0 °C for 1 hour, and then 2.5 mmol of triethylene glycol methyl ether borate was added to the solution, and the mixture was maintained for 1 hour to allow the triethylene glycol methyl ether borate to dissolve in the solution system. Then, the temperature was raised to 120 °C with stirring over 2 hours and maintained at this temperature for 2 hours. After the 2-hour reaction was completed, the resulting solid was separated by hot filtration. The solid catalyst was thoroughly washed with hexane and decane until no precipitated titanium compounds were detected in the washing solution. After drying, a solid titanium catalyst component was obtained.

[0092] (2) Ethylene polymerization: In a 5L polymerization reactor, 2.5L of n-hexane, 5mmol of triethylaluminum, and 20mg of the catalyst prepared above were added sequentially. The temperature was raised to 70°C, hydrogen gas was added at 0.48MPa, the temperature was raised to 85°C, ethylene was introduced, and the pressure was maintained at 0.8MPa. The reaction was carried out for 3 hours. Then, the reactor temperature was lowered to 30°C, vented, and purged with nitrogen. The temperature was raised to 70°C, hydrogen gas was added at 0.06MPa, and a 1-butene / ethylene mixture was introduced at 80°C. The 1-butene / ethylene gas partial pressure ratio was 0.3, and the pressure was maintained at 0.35MPa. The reaction was carried out for 1 hour. The reaction temperature was lowered to 30°C, vented, and purged with nitrogen. The temperature was raised to 70°C, hydrogen gas was added at 0.01MPa, and a 1-butene / ethylene mixture was introduced at 75°C. The 1-butene / ethylene gas partial pressure ratio was 0.02, and the pressure was maintained at 0.25MPa. The reaction was carried out for 0.5 hours to obtain the ethylene copolymer. The polymerization activity, polymer bulk density, and particle size distribution results are shown in Table 1. The polymer performance test results are shown in Table 2.

[0093] Example 3

[0094] Similar to Example 1, except that 5.0 mmol of triethylene glycol methyl ether borate, a mixture of titanium tetrachloride and vanadium tetrachloride were added, wherein the molar ratio of titanium to vanadium was 1:1. The polymerization activity, polymer bulk density, and particle size distribution results are shown in Table 1. The polymer performance test results are shown in Table 2.

[0095] Example 4

[0096] Similar to Example 2, except that the added organoboron compound without active hydrogen is triethylene glycol methyl ether borate triester, added in an amount of 5.0 mmol, in a mixture of titanium tetrachloride and vanadium tetrachloride, wherein the molar ratio of metallic titanium to vanadium is 10:1. The polymerization activity, polymer bulk density, and particle size distribution results are shown in Table 1. The polymer performance test results are shown in Table 2.

[0097] Example 5

[0098] The catalyst preparation was the same as in Example 1, except for the ethylene polymerization.

[0099] Ethylene polymerization: In a 5L polymerization reactor, 2.5L of n-hexane, 5mmol of triethylaluminum, and 20mg of magnesium chloride-supported TiC14 Ziegler-Natta catalyst were added sequentially. The temperature was raised to 70°C, hydrogen gas was added at 0.6MPa, the temperature was raised to 85°C, ethylene was introduced, and the pressure was maintained at 0.8MPa. The reaction was carried out for 3 hours. The reactor temperature was then lowered to 30°C, vented, and purged with nitrogen. The temperature was then raised to 70°C, and 0.12 MPa of hydrogen was added. A 1-butene / ethylene mixture was introduced at 80°C, with a 1-butene / ethylene partial pressure ratio of 0.7, maintaining a pressure of 0.35 MPa. The reaction was carried out for 1 hour. The reaction temperature was then lowered to 30°C, vented, and purged with nitrogen. The temperature was then raised to 70°C, and 0.005 MPa of hydrogen was added. A 1-butene / ethylene mixture was introduced at 75°C, with a 1-butene / ethylene partial pressure ratio of 0.1, maintaining a pressure of 0.25 MPa, and the reaction was carried out for 0.5 hours to obtain the ethylene copolymer. The polymer performance test results are shown in Table 1.

[0100] Example 6

[0101] The catalyst preparation is the same as in Example 2, except for the ethylene polymerization.

[0102] Ethylene polymerization: In a 5L polymerization reactor, 2.5L of n-hexane, 5mmol of triethylaluminum, and 20mg of magnesium chloride-supported TiC14 Ziegler-Natta catalyst were added sequentially. The temperature was raised to 70°C, hydrogen gas was added at 0.48MPa, the temperature was raised to 85°C, ethylene was introduced, and the pressure was maintained at 0.8MPa. The reaction was carried out for 3 hours. The reactor temperature was then lowered to 30°C, vented, and purged with nitrogen. The temperature was then raised to 70°C, and 0.06 MPa of hydrogen was added. A 1-butene / ethylene mixture was introduced at 80°C, with a 1-butene / ethylene partial pressure ratio of 0.1, maintaining a pressure of 0.35 MPa. The reaction was carried out for 1 hour. The reaction temperature was then lowered to 30°C, vented, and purged with nitrogen. The temperature was then raised to 70°C, and 0.01 MPa of hydrogen was added. A 1-butene / ethylene mixture was introduced at 75°C, with a 1-butene / ethylene partial pressure ratio of 0.01, maintaining a pressure of 0.25 MPa, and the reaction was carried out for 0.5 hours to obtain the ethylene copolymer. The polymerization activity, polymer bulk density, and particle size distribution results are shown in Table 1. The polymer performance test results are shown in Table 2.

[0103] Comparative Example 1

[0104] Same as Example 1. The difference is that a microemulsion of magnesium compound was added dropwise to 150 mL of titanium tetrachloride, without vanadium tetrachloride. The polymerization activity, polymer bulk density, and particle size distribution results are shown in Table 1. The polymer performance test results are shown in Table 2.

[0105] Comparative Example 2

[0106] Same as Example 1. The difference is that no organoboron compound without active hydrogen was added. The ethylene polymerization evaluation was as in Example 1, and the polymerization activity, polymer bulk density, and particle size distribution results are shown in Table 1. The polymer performance test results are shown in Table 2.

[0107] Comparative Example 3

[0108] The catalyst was prepared according to the method described in Example 1 of CN1229092.

[0109] In a reactor fully purged with high-purity nitrogen, 0.042 mol anhydrous MgCl2 (approximately 4 g), 60 mL toluene, 0.032 mol epichlorohydrin, 0.022 mol tributyl phosphate, and 0.017 mol ethanol were added sequentially. The mixture was stirred and heated to 80 °C, and maintained for 15 minutes until the solids were completely dissolved, forming a homogeneous solution. Then, 0.0074 mol phthalic anhydride was added, and the mixture was maintained for another hour. The solution was then cooled to -25 °C, and 0.5 mol titanium tetrachloride (approximately 55 mL) was added dropwise. The mixture was then slowly heated to 80 °C and reacted for 3 hours. After filtration, the solution was washed three times with toluene and hexane, and then dried under vacuum to obtain a solid catalyst.

[0110] The ethylene polymerization evaluation was as described in Example 1. The polymerization activity, polymer bulk density, and particle size distribution results are shown in Table 1. The polymer performance test results are shown in Table 2.

[0111] Comparative Example 4

[0112] The catalyst was prepared according to the method described in Example JP4951378.

[0113] In a reactor fully purged with high-purity nitrogen, 10 mol of commercially available anhydrous MgCl2 was added, suspended in 10 L of hexane. At room temperature, 60 mol of ethanol was added dropwise, and the mixture was stirred for 30 minutes. While maintaining the system temperature below 40°C, 31 mol of diethylaluminum chloride was added dropwise, and the mixture was stirred for 30 minutes. Then, 5 mol of TiCl4 was added, and the system was maintained at 60°C with stirring for 6 hours. After filtration and washing with hexane, a solid catalyst was obtained.

[0114] The ethylene polymerization evaluation is as in Example 1. The polymerization activity, polymer bulk density, and particle size distribution results are shown in Table 1, and the polymer performance test results are shown in Table 2.

[0115] Table 1 Results of polymerization activity, polymer bulk density, and particle size distribution

[0116]

[0117]

[0118] As can be seen from Tables 1 and 2, compared with existing olefin catalysts, the catalyst component A used in this invention has higher polymerization activity, higher bulk density of the polymer, more concentrated particle size distribution, and concentrated molecular weight distribution in the medium to high molecular weight region, resulting in better mechanical and heat resistance properties.

[0119] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes should all fall within the protection scope of the claims of the present invention.

Claims

1. A Ziegler-Natta catalyst composition for ethylene polymerization or copolymerization, characterized in that, The composition includes a catalyst and an organoaluminum compound with the general formula AlR. n X 3-n In the formula, R is an alkyl group, X is a halogen, and n is an integer 1 ≤ n ≤ 3; The catalyst contains titanium and vanadium, wherein the molar ratio of titanium to vanadium is 1 to 10:1; the catalyst also contains magnesium, wherein the molar ratio of the total molar amount of titanium and vanadium to the molar amount of magnesium is 1:1.0 to 15.0; the catalyst is prepared from the following components: (1) Microemulsions of magnesium compounds; (2) Triethylene glycol methyl ether borate triester; (3) A mixture of liquid titanium compounds and liquid vanadium compounds; The magnesium compound microemulsion is formed from a magnesium halide-organic alcohol-dispersant dissolution system; the titanium compound has the general formula Ti(OR). a X b In the formula, R represents C1 to C2. 10 The vanadium compound is an aliphatic hydrocarbon group or an aryl group, where X is a halogen, a is 0, 1, 2 or 3; b is an integer from 1 to 4, and a + b = 3 or 4; wherein the general formula of the vanadium compound is V(OR). a X b In the formula, R represents C1 to C2. 10 The aliphatic hydrocarbon group or aryl group, X is a halogen, a is 0, 1, 2 or 3; b is an integer from 1 to 4, a+b=3 or 4; wherein the mixture of liquid titanium compound and liquid vanadium compound has a molar ratio of titanium to vanadium of 1 to 10:1; the molar ratio of the mixture of liquid titanium compound and liquid vanadium compound to magnesium compound is 1:1.0 to 15.

0. The catalyst preparation method includes: adding a multifunctional borate ester compound as a modifier during the dissolution of magnesium chloride, allowing it to interact with a diluent and solvent to form a magnesium chloride microemulsion system, which is then reacted with a mixture composed of liquid titanium compound and liquid vanadium compound, and finally preparing an ethylene polymerization solid Ziegler-Natta catalyst by precipitation.

2. The Ziegler-Natta catalyst composition for ethylene polymerization or copolymerization according to claim 1, characterized in that, In the microemulsion of the magnesium compound, based on 1 mol of magnesium halide, the amount of organic alcohol is 0.1 to 10.0 mol, the amount of triethylene glycol methyl ether borate triester is 0.20 to 0.25 mol, and the amount of dispersant is 0.1 to 10.0 mol.

3. The Ziegler-Natta catalyst composition for ethylene polymerization or copolymerization according to claim 1, characterized in that, The magnesium halide is a magnesium dihalide, or a derivative in which one halogen atom in a magnesium dihalide molecule is replaced by a hydrocarbon group or a hydrocarbon oxygen group, or a mixture thereof.

4. The Ziegler-Natta catalyst composition for ethylene polymerization or copolymerization according to claim 1, characterized in that, The organic alcohol is selected from straight-chain and branched alkyl alcohols, cycloalkanols with 1 to 10 carbon atoms, and aromatic alcohols or aryl alcohols with 6 to 20 carbon atoms, as well as halogenated derivatives of the above organic alcohols.

5. The Ziegler-Natta catalyst composition for ethylene polymerization or copolymerization according to claim 1, characterized in that, The molar ratio of the organic alcohol to the magnesium compound is 1 to 10:

1.

6. The Ziegler-Natta catalyst composition for ethylene polymerization or copolymerization according to claim 5, characterized in that, The molar ratio of the organic alcohol to the magnesium compound is 3 to 4:

1.

7. The Ziegler-Natta catalyst composition for ethylene polymerization or copolymerization as described in claim 1, characterized in that, The molar ratio of aluminum to titanium is 10 to 200:

1.

8. The Ziegler-Natta catalyst composition for ethylene polymerization or copolymerization according to claim 1, characterized in that, The organoaluminum compound is one or a mixture of triethylaluminum, triisobutylaluminum, dichlorodiethylaluminum, dichloroethylaluminum, sesquiethylaluminum, or the like.

9. The use of the Ziegler-Natta catalyst composition for ethylene polymerization or copolymerization according to any one of claims 1-8 in the homopolymerization of ethylene or the copolymerization of ethylene with higher α-olefins.

10. Homopolymerization of ethylene or copolymerization of ethylene with higher α-olefins, characterized in that, Use the Ziegler-Natta catalyst composition for ethylene polymerization or copolymerization as described in any one of claims 1-8.

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