Process for the preparation of bimodal polyethylene resins and the resulting bimodal polyethylene resins and pipe material articles

Abstract

The present invention provides a method for preparing a bimodal polyethylene resin, and the bimodal polyethylene resin and pipe material product obtained. The method comprises producing the bimodal polyethylene resin in a process of at least two reactors in series in the presence of a Ziegler-Natta catalyst system containing titanium. The polyethylene resin obtained has a bimodal molecular weight distribution, a resin density of 0.943-0.963 g / cm 3 , and a melt index of 0.10-0.40 g / 10 min under a load of 5 kg. The bimodal polyethylene resin has good tensile properties, impact resistance, and excellent resistance to thermal degradation. The bimodal polyethylene resin is suitable for preparing high-performance, large-diameter bimodal polyethylene pipe material products.

Description

Technical Field

[0001] This invention relates to the field of polyethylene, and more specifically, to a method for preparing bimodal polyethylene resin using a Ziegler-Natta catalyst, and the resulting bimodal polyethylene resin and pipe material products. Background Technology

[0002] Polyethylene (PE) is a highly crystalline, non-polar thermoplastic resin. In its natural state, PE is milky white, and in thin sections, it is somewhat translucent. PE exhibits excellent resistance to most household and industrial chemicals. It possesses excellent electrical properties, particularly high dielectric strength, making it well-suited for wires and cables. Medium to high molecular weight PE grades exhibit excellent impact resistance, even at temperatures as low as -40°F for polyethylene pipes. PE is characterized by high strength, good toughness, high rigidity, and resistance to both heat and cold, while also possessing good molding and processing properties and low cost, making it widely used in the manufacture of various plastic products.

[0003] Polyethylene plastic pipes are mainly divided into two categories: high-density polyethylene (HDPE) (low-pressure polyethylene) and low-density polyethylene (LDPE) (high-pressure polyethylene). Polyethylene materials have a wide range of applications, and pipes are just one important aspect of its applications. Due to differences in physical properties, HDPE and LDPE are used in different pipe applications: Low-density polyethylene (LDPE) has good flexibility. However, its compressive strength is relatively low, so it can only be used for low-pressure, small-diameter pipes. It is often made into coils for rural water improvement and some non-long-term use applications. High-density polyethylene (HDPE), on the other hand, has better compressive strength and is widely used in pressure pipe applications (such as PE80 and PE100). PE80, simply put, means that the pipe material can withstand continuous pressure at 20℃ for 50 years without damage, and the minimum required strength of the pipe wall is 80 MPa, and so on. In the early stages of plastic pipe development, the use of polyethylene pressure pipes was far less than that of polyvinyl chloride (PVC) pipes. With the emergence of new HDPE materials and technologies, this cost (weight) difference has changed significantly. With the advent of second-generation polyethylene pipe materials (equivalent to PE80) and third-generation polyethylene pipe materials (equivalent to PE100), under the same diameter (200mm), pressure rating, and conditions, the weight of polyethylene pipes of the same length is only 93% of that of UPVC pipes. Therefore, second- and third-generation polyethylene pipe materials not only significantly improve the minimum required strength of PE but also enhance the material's resistance to environmental stress cracking, exhibiting significant resistance to rapid crack growth. More importantly, they allow for reduced wall thickness and increased transport cross-sections under the same operating pressure. Furthermore, they increase the pressure required and improve transport capacity with the same wall thickness (for example, when transporting natural gas with the same wall thickness, PE100 polyethylene pipes can reach a pressure of 10 bar, while PE80 polyethylene pipes can only reach 8 bar). With the improvement of polyethylene technology, the economic benefits are significant. Recent reports indicate that the fourth-generation polyethylene pipe material, PE125, has been successfully developed, suggesting that larger diameter and more economical polyethylene pressure pipelines will have a wide range of applications.

[0004] Currently, the more mature bimodal pipe material products on the market use imported catalysts to produce PE100 pipe materials. These catalysts improve the fine powder content of the polymer and extend the operating cycle of the equipment, but they do not fundamentally solve the long-standing problems of excessive fine powder, high oligomer content, and short operating cycles in slurry processes. Imported catalysts have the problem of high oligomer content, resulting in an operating cycle of approximately one month, and requiring shutdown for cooking after five months of operation. Therefore, developing a superior domestic slurry polyethylene catalyst with low fine powder and oligomer content will have significant economic and social benefits, and will also bring my country's technology in this field to international standards. Strengthening research on high-performance slurry catalysts in my country is both urgent and necessary, directly impacting my country's technological progress and substantial economic benefits, particularly in this field. Summary of the Invention

[0005] Therefore, addressing the problems existing in the prior art, this invention provides a method for direct catalytic polymerization using a titanium-containing Ziegler-Natta catalyst in multiple reactors connected in series. Furthermore, by combining different chain transfer agents, hydrogen amounts, and comonomer amounts in the reaction, bimodal polyethylene resin with specific melt index, molecular weight, and molecular weight distribution can be prepared. The bimodal polyethylene resin prepared by this invention does not exhibit the problems found in low molecular weight analysis and possesses high resistance to environmental stress cracking and good tensile properties, making it highly suitable for the production of high-performance bimodal polyethylene pipe material resins.

[0006] One objective of this invention is to provide a method for preparing bimodal polyethylene resin, comprising producing the bimodal polyethylene resin by using at least two reactors in series in the presence of a titanium-containing Ziegler-Natta catalyst system.

[0007] The method for preparing bimodal polyethylene resin according to the present invention comprises a series of ethylene homopolymerization and ethylene copolymerization reactions in the presence of a titanium-containing Ziegler-Natta catalyst system. Preferably, the method of the present invention is carried out in two or more reactors operating in series.

[0008] The tandem ethylene homopolymerization and ethylene copolymerization reactions may include two or more reaction stages; wherein both the ethylene homopolymerization and ethylene copolymerization reactions may be carried out in one or more stages; preferably, the ethylene homopolymerization reaction is carried out in one stage, and the ethylene copolymerization reaction is carried out in one or two stages; more preferably, the tandem ethylene homopolymerization and ethylene copolymerization reactions include one ethylene homopolymerization reaction stage and a subsequent ethylene copolymerization reaction stage.

[0009] According to a preferred embodiment of the technical solution of the present invention, the method for preparing the bimodal polyethylene resin includes the following steps:

[0010] The first-stage ethylene homopolymerization reaction includes ethylene homopolymerization in the presence or absence of hydrogen, using a Ziegler-Natta catalyst system containing titanium, to obtain a stream containing ethylene homopolymer. Preferably, the melt index of the obtained first-stage ethylene homopolymer is greater than or equal to 60 g / 10 min at a load of 1.2 kg, more preferably greater than or equal to 65 g / 10 min; the density of the ethylene homopolymer obtained from the first-stage ethylene homopolymerization reaction is ≥0.963 g / cm³. 3 The preferred value is 0.963–0.980 g / cm³. 3 More preferably, it is 0.965–0.975 g / cm³. 3 .

[0011] The second stage is the ethylene copolymerization reaction. In the presence or absence of hydrogen, the stream containing ethylene homopolymer obtained in the previous stage is copolymerized with ethylene monomers and comonomers to produce a bimodal polyethylene resin that is a mixture of homopolymer and copolymer.

[0012] The phrase "in the presence or absence of hydrogen" means that hydrogen may or may not be added, depending on the actual reaction conditions.

[0013] The preparation method described above includes a series of ethylene homopolymerization and ethylene copolymerization reactions. By controlling the hydrogen-to-ethylene ratio and the ethylene copolymerization conditions, a molecular weight distribution structure containing two parts (homopolymerization part) and a high molecular weight part (copolymerization part) is obtained, thereby obtaining the bimodal polyethylene resin.

[0014] More specifically, the preparation method described in this invention:

[0015] The reaction temperature of the first stage ethylene homopolymerization reaction is 60-100℃, preferably 70-90℃; the reaction pressure is 0.1-3.0MPa, preferably 0.5-2MPa.

[0016] The reaction temperature of the second-stage ethylene copolymerization reaction is 60–100°C, preferably 70–90°C; the reaction pressure is 0.01–3.0 MPa, preferably 0.05–2 MPa.

[0017] Preferably, the first stage of ethylene homopolymerization is carried out in the presence of hydrogen, and the molar ratio (% / %) of hydrogen to ethylene in the ethylene homopolymerization stage is 4.5 to 7.5, preferably 5.5 to 6.5, for example, specifically 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5. The molar ratio (% / %) of hydrogen to ethylene described in this invention is the ratio of the molar percentage concentration of hydrogen (mol%) to the molar percentage concentration of ethylene (mol%) in actual production.

[0018] Preferably, the second-stage ethylene copolymerization reaction is carried out in the presence of hydrogen, and the hydrogen to ethylene ratio (%) in the ethylene copolymerization reaction stage is 0.01 to 0.3, preferably 0.05 to 0.2, for example, specifically 0.01, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, or 0.3. The hydrogen to ethylene molar ratio (%) described in this invention is the ratio of the molar percentage concentration of hydrogen (mol%) to the molar percentage concentration of ethylene (mol%) in actual production.

[0019] Preferably, the molar ratio (% / %) of the comonomer to ethylene in the second-stage ethylene copolymerization reaction is 0.01–0.2, more preferably 0.03–0.1, and specifically can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, or 0.2. The molar ratio (% / %) of the comonomer to ethylene described in this invention is the ratio of the actual molar percentage concentration (mol%) of the comonomer to the molar percentage concentration (mol%) of ethylene in production.

[0020] The preferred comonomer structure is CH2=CHR; wherein R is preferably a linear or branched alkane having 1 to 10 carbon atoms; the comonomer is more preferably at least one of propylene, butene-1, pentene-1, hexene-1, octene-1, and decene-1, and the most preferred comonomer is at least one of hexene-1, butene-1, and octene-1.

[0021] The packing material of the catalyst, the flow rate of each stage, or the range of reaction time are routinely adjusted and selected according to the actual reactor load.

[0022] In the method for preparing bimodal polyethylene resin according to the present invention, the same catalyst system is used for both the first-stage homopolymerization reaction and the second-stage copolymerization reaction. Specifically, the reactor for the two-stage reaction only needs to inject the catalyst during the first-stage homopolymerization reaction, and it is not necessary to re-inject the catalyst during the second-stage copolymerization reaction.

[0023] The titanium-containing Ziegler-Natta catalyst system used in the preparation method of bimodal polyethylene resin of this invention can be any existing titanium-containing Ziegler-Natta catalyst system. Specific examples of the titanium-containing Ziegler-Natta catalyst system of this invention can be found in patent documents CN1958620A, CN1958622A, CN102344514A, CN102344515A, CN102875708A, CN103772536A, CN102875709A, CN102993344A, CN102875707A, etc. The entire contents of these patent documents are incorporated herein by reference.

[0024] Preferably, in the preparation method of the bimodal polyethylene resin of the present invention, the titanium-containing Ziegler-Natta catalyst system includes the following components: (1) magnesium-containing compound; (2) organophosphorus compound; (3) organoalcohol compound; (4) organoepoxide compound; (5) silicon-containing compound; (6) titanium-containing compound; and (7) aluminum-containing compound.

[0025] The titanium-containing Ziegler-Natta catalyst system of this invention is formed by forming a magnesium complex from a magnesium-containing compound in a solvent system containing organophosphorus compounds, organoepoxide compounds, and organoalcohol compounds. Typically, this magnesium complex is a homogeneous and transparent solution. The magnesium complex is then reacted with silicon-containing compounds, titanium-containing compounds, and aluminum-containing compounds to form the catalyst system.

[0026] The components of the titanium-containing Ziegler-Natta catalyst system include:

[0027] The magnesium-containing compound preferably has the general formula Mg(OR) 6 ) p X 1 2-p Magnesium-containing compounds. In the formula R 6 C1~C 20 Saturated or unsaturated straight-chain or branched hydrocarbon groups or C3-C6 groups 20 Cyclic hydrocarbon group; X 1 It is a halogen, preferably chlorine, where p is an integer and 0 ≤ p ≤ 2.

[0028] Further, the magnesium-containing compound is preferably selected from at least one of magnesium chloride, magnesium bromide, magnesium chloromethoxy, magnesium chloroethoxy, magnesium chloroisopropoxy, magnesium chlorobutoxy, magnesium chlorooctoxy, magnesium diethoxy, magnesium dipropoxy, magnesium dibutoxy, magnesium dioctoxy, magnesium isopropoxy, magnesium butoxy, magnesium n-octoxy, and magnesium 2-ethylhexyloxy; more preferably selected from at least one of magnesium chloride, magnesium diethoxy, magnesium dipropoxy, magnesium dibutoxy, and magnesium dioctoxy; and most preferably selected from magnesium chloride and / or magnesium diethoxy.

[0029] The organophosphorus compound is preferably selected from at least one of the following: a hydrocarbon ester of orthophosphoric acid, a hydrocarbon ester of phosphorous acid, a halohydrocarbon ester of orthophosphoric acid, and a halohydrocarbon ester of phosphorous acid; more preferably selected from at least one of the following: triethyl phosphate, tributyl phosphate, triisooctyl phosphate, triphenyl phosphate, triethyl phosphite, tributyl phosphite, and di-n-butyl phosphite.

[0030] The organic epoxy compound is preferably selected from at least one of C2-C8 aliphatic olefins, C2-C8 aliphatic dienes, C2-C8 halogenated aliphatic olefins, oxides of C2-C8 halogenated aliphatic dienes, glycidyl ethers, and internal ethers; preferably selected from at least one of ethylene oxide, propylene oxide, butane oxide, butadiene oxide, butadiene dioxide, epichlorohydrin, tetrahydrofuran, methyl glycidyl ether, and diglycidyl ether; most preferably epichlorohydrin and / or tetrahydrofuran.

[0031] The organic alcohol compound is preferably a straight-chain, branched, or cycloalkyl alcohol with 1 to 10 carbon atoms or an aryl alcohol with 6 to 20 carbon atoms, wherein the hydrogen atoms in the organic alcohol compound may optionally be replaced by halogen atoms; more preferably, the organic alcohol compound is selected from at least one of ethanol, propanol, butanol, 2-ethylhexanol, and glycerol; most preferably, it is selected from at least one of ethanol and 2-ethylhexanol.

[0032] The solvent system for the magnesium complex may optionally contain an inert diluent, typically an aromatic or alkane compound. Aromatic compounds include benzene, toluene, xylene, monochlorobenzene, dichlorobenzene, trichlorobenzene, monochlorotoluene, and their derivatives. Alkanes include one or a mixture of straight-chain alkanes, branched alkanes, or cycloalkanes with 3 to 20 carbon atoms, such as butane, pentane, hexane, cyclohexane, heptane, etc., as long as they facilitate the dissolution of magnesium halides. The aforementioned inert diluents may be used alone or in combination.

[0033] The silicon-containing compound is preferably an organosilicon compound without active hydrogen atoms, and its general formula is R. 1 x R 2 ySi(OR 3 ) Z , where R 1 R 2 R 3 Same or different, R 1 and R 2 These are hydrocarbon groups or halogens with 1 to 10 carbon atoms, respectively, R 3 It is a hydrocarbon group with 1 to 10 carbon atoms, where x, y, and z are positive integers, 0≤x≤2, 0≤y≤2, 0≤z≤4, and x+y+z=4.

[0034] The silicon-containing compound is more preferably selected from silicon tetrachloride, silicon tetrabromide, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tetra(2-ethylhexyloxy)silane, ethyltrimethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, n-propyltriethoxysilane, n-propyltrimethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, cyclopentyltrimethoxysilane, cyclopentyltriethoxysilane, 2-methylcyclo... Pentyltrimethoxysilane, 2,3-dimethylcyclopentyltrimethoxysilane, cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, tert-butyltriethoxysilane, n-butyltrimethoxysilane, n-butyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, cyclohexyltriethoxysilane, cyclohexyltrimethoxysilane Phenylacetoxysilane, phenyltrimethoxysilane, monochlorotrimethoxysilane, monochlorotriethoxysilane, ethyltriisopropoxysilane, vinyltributoxysilane, trimethylphenoxysilane, methyltrienylpropoxysilane, vinyltriacetylsilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diisopropyldimethoxysilane, diisopropyldiethoxysilane, tert-butylmethyldimethoxysilane, tert-butylmethyldiethoxysilane, tert-pentylmethyldiethoxysilane At least one of dicyclopentyldimethoxysilane, dicyclopentyldiethoxysilane, methylcyclopentyldiethoxysilane, methylcyclopentyldimethoxysilane, trimethylmethoxysilane, trimethylethoxysilane, tricyclopentylmethoxysilane, tricyclopentylethoxysilane, dicyclopentylmethylmethoxysilane, and cyclopentyldimethylmethoxysilane; most preferably at least one of tetraethoxysilane, tetramethoxysilane, and tetrabutoxysilane; most preferably selected from tetraethoxysilane and / or silicon tetrachloride.

[0035] The titanium-containing compound preferably has the general formula Ti(OR) 5 ) a X 2 b Titanium-containing compounds, where R 5X is an aliphatic or aromatic hydrocarbon group with 1 to 14 carbon atoms. 2 The compound is a halogen, a is 0, 1 or 2, b is an integer from 0 to 4, and a+b=3 or 4; the titanium-containing compound is more preferably selected from at least one of titanium tetrachloride, titanium tetrabromide, titanium tetraiodide, titanium tetrabutoxy, titanium tetraethoxy, titanium monochlorotriethoxy, titanium trichloride, titanium dichlorodiethoxy, and titanium trichloromonoethoxy, most preferably selected from at least one of titanium tetrachloride, titanium tetraethoxy, and titanium tetrabutoxy; and most preferably titanium tetrachloride.

[0036] The aluminum-containing compound is preferably of the general formula AlR. 4 n X 3 3-n Organoaluminum compounds, where R 4 X is a hydrogen or hydrocarbon group with 1 to 20 carbon atoms. 3 The halogen is n, where n is an integer from 0 to n ≤ 3; the aluminum-containing compound is more preferably selected from at least one of triethylaluminum, diethylaluminum monochloro, diethylaluminum monochloro, sesquiethylaluminum, diisobutylaluminum monochloro, triisobutylaluminum monochloro, diisopropylaluminum monochloro, methyl-n-propylaluminum monochloro, and diphenylaluminum monochloro; most preferably, at least one of diethylaluminum monochloro, diethylaluminum monochloro, and triethylaluminum.

[0037] The components of the titanium-containing Ziegler-Natta catalyst system of the present invention, based on the amount of magnesium compound per mole in the magnesium complex, are as follows: silicon compound: 0.05-1 mole, preferably 0.1-0.5 mole, for example, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 mole; aluminum compound: 0-5 mole, preferably 0.01-3 mole, for example, 0, 0.01, 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 mole; titanium compound: 1-15 mole, preferably 2-10 mole, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 mole.

[0038] In the solvent system for forming the magnesium complex in the titanium-containing Ziegler-Natta catalyst system of the present invention, the organic epoxy compound is 0.2 to 10 moles, preferably 0.3 to 4 moles, for example, 0.2, 0.3, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 moles per mole of magnesium compound; the organic phosphorus compound is 0.1 to 10 moles, preferably 0.2 to 4 moles, for example, 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 moles per mole; and the organic alcohol compound is 0.1 to 10 moles, preferably 1 to 4 moles, for example, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 moles per mole.

[0039] Preferably, the titanium-containing Ziegler-Natta catalyst system of the present invention is prepared by a method comprising the following steps:

[0040] (1) Under inert gas protection, the magnesium-containing compound is dissolved in a solvent system containing the organic epoxy compound and the organic phosphorus compound to form a homogeneous solution of the magnesium complex at a dissolution temperature of 50–90°C; the organic alcohol compound is added during or after the solution is formed to obtain a magnesium complex reaction solution. The reaction should be allowed to proceed until it is complete, generally for 0.5–6 hours, preferably 1–6 hours.

[0041] (2) The above reaction solution is brought into contact with the titanium-containing compound at a temperature of -40℃ to 20℃. The silicon-containing compound and aluminum-containing compound are introduced before, after, or during the reaction to carry out the reaction. The mixture is then slowly heated to 60 to 110℃, and the solid gradually precipitates out and forms particles. The reaction is allowed to proceed until it is complete, generally for 0.5 to 10 hours, preferably 0.5 to 6 hours.

[0042] The process may then include: (3) removing unreacted material and solvent from the mixture (i.e., the product after the reaction in step (2)) to obtain the titanium-containing Ziegler-Natta catalyst system.

[0043] Unreacted materials and solvents can be removed using conventional methods in the prior art, such as filtration. Furthermore, it is preferable to wash the reaction products with an inert diluent, such as hexane, to obtain the titanium-containing Ziegler-Natta catalyst system.

[0044] The bimodal polyethylene resin of the present invention uses a titanium-containing Ziegler-Natta catalyst system. During the polymerization reaction, a co-catalyst commonly used in ethylene polymerization reactions, such as an organoaluminum co-catalyst, can also be added in the usual amount.

[0045] The method for preparing bimodal polyethylene resin of the present invention employs slurry polymerization, wherein ethylene polymerization is carried out in at least two slurry reactors connected in series. The series-connected reactors yield high-molecular-weight polyethylene (i.e., the ethylene copolymer portion) and low-molecular-weight polyethylene (i.e., the ethylene homopolymer portion) with different molecular weights, allowing for good reaction mixing of polyethylenes of different molecular weights within the reactors.

[0046] The slurry polymerization medium can be any common slurry polymerization medium, including at least one of the following: isobutane, hexane, heptane, cyclohexane, naphtha, raffinate, hydrogenated gasoline, kerosene, benzene, toluene, xylene, and other saturated aliphatic hydrocarbons or aromatic hydrocarbons, etc.

[0047] Hydrogen is typically used as a molecular weight regulator to adjust the molecular weight of the final polymer.

[0048] The second objective of this invention is to provide a bimodal polyethylene resin obtained by the aforementioned preparation method.

[0049] The bimodal polyethylene resin of the present invention comprises a low molecular weight portion (homopolymer unit) and a high molecular weight portion (copolymer unit), that is, it has a bimodal molecular weight distribution.

[0050] Furthermore,

[0051] The melt index of the bimodal polyethylene resin of the present invention is 0.10-0.40 g / 10 min under a 5 kg load, preferably 0.15-0.35 g / 10 min.

[0052] The density range of the bimodal polyethylene resin described in this invention is 0.943–0.963 g / cm³. 3 The preferred value is 0.945–0.955 g / cm³. 3 .

[0053] According to one aspect of the technical solution of the present invention, the homopolymer unit portion of the bimodal polyethylene resin has a density range of ≥0.963 g / cm³. 3 The preferred concentration is 0.963–0.980 g / cm³. 3 A more preferred range is 0.965–0.975 g / cm³. 3 The melt index of the homopolymer unit portion of the bimodal polyethylene resin is greater than or equal to 60 g / min under a load of 1.2 kg, preferably greater than or equal to 65 g / 10 min.

[0054] According to one aspect of the present invention, the bimodal polyethylene resin contains copolymer units derived from comonomers copolymerized with ethylene. The comonomers of the copolymer units include α-olefin monomers.

[0055] Further, the comonomer is preferably CH2=CHR; wherein R is preferably a linear or branched alkane having 1 to 10 carbon atoms; the comonomer is more preferably at least one of propylene, butene-1, pentene-1, hexene-1, octene-1, and decene-1, and most preferably at least one of hexene-1, butene-1, and octene-1.

[0056] The comonomer content of the copolymer unit in the bimodal polyethylene resin is greater than 0 and less than or equal to 1.0 wt%, preferably 0.001 to 0.8 wt%, specifically, for example, 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.20 wt%, 0.25 wt%, 0.30 wt%, 0.35 wt%, 0.40 wt%, 0.45 wt%, 0.5 wt%, 0.55 wt%, 0.60 wt%, 0.65 wt%, 0.70 wt%, 0.75 wt%, 0.80 wt%, 0.85 wt%, 0.90 wt%, 0.95 wt%, and 1.0 wt%.

[0057] Preferably, the melt index of the copolymer unit portion of the bimodal polyethylene resin is 0.2 to 0.35 g / 10 min under a 5 kg load.

[0058] According to one aspect of the technical solution of the present invention, the bimodal polyethylene resin of the present invention has good tensile properties, less low molecular weight wax precipitation and good processing properties.

[0059] The nominal tensile strain at break of the bimodal polyethylene resin described in this invention is greater than or equal to 500%.

[0060] The tensile yield stress of the bimodal polyethylene resin described in this invention is greater than or equal to 20 MPa.

[0061] The bimodal polyethylene resin of this invention has a notched impact strength of 20 kJ / m² in a simply supported beam at 23°C. 2 .

[0062] A third objective of this invention is to provide pipe materials made from the aforementioned bimodal polyethylene resin. In specific applications, various existing extrusion processes and molding methods in the art can be used to obtain bimodal polyethylene pipe materials, such as cable materials and natural gas pipelines.

[0063] The bimodal polyethylene resin obtained by this invention can be applied to pipe materials. It is prepared using a titanium-containing Ziegler-Natta catalyst system in multiple reactors connected in series. This catalyst system has advantages such as controllable particle size distribution, narrow particle size distribution, high catalytic activity, good hydrogen sensitivity, and high comonomer content. The bimodal polyethylene resin prepared by the titanium-based catalyst of this invention has the characteristics of adjustable molecular weight, low oligomer formation, and outstanding mechanical properties, environmental stress resistance, and thermal degradation resistance. Using the titanium-containing Ziegler-Natta catalyst system described in this invention in a multi-reactor process solves the long-standing problems of excessive fine powder, high oligomer content, and short equipment operation cycles in slurry processes. The mechanical properties and weather resistance of the resin are significantly improved, resulting in considerable economic benefits.

[0064] The bimodal polyethylene resin prepared using the titanium-containing Ziegler-Natta catalyst system described in this invention exhibits good particle morphology, concentrated particle size distribution, and low content of large particles and fine powder, resulting in good flowability and facilitating processing. Furthermore, the bimodal polyethylene resin of this invention has low oligomer content, and its molecular weight and molecular weight distribution are controllable, leading to excellent processing performance. Moreover, the bimodal polyethylene resin of this invention does not contain low-molecular-weight precipitates. The unique resin structure of the bimodal polyethylene resin of this invention makes the polyethylene pipe materials prepared from it resistant to environmental stress cracking and possess excellent mechanical properties. The bimodal polyethylene resin of this invention has a melt index of 0.10–0.40 g / 10 min (5 kg), preferably 0.15–0.35 g / 10 min, and a density of 0.943–0.963 g / cm³. 3 The preferred value is 0.945–0.955 g / cm³. 3 It is ideal for high-performance, large-diameter pipe materials. Detailed Implementation

[0065] The present invention will be further described below through specific embodiments, but these do not constitute any limitation on the present invention.

[0066] The polymer-related data in the examples were obtained using the following test methods:

[0067] (1) Resin tensile properties: determined according to the method described in GB / T 1040.2-2006, with a test speed of 50 mm / min.

[0068] (2) Melt mass flow rate (also known as melt index, MI): determined according to the method described in ASTM D1238-2038. A CEAST 7026 melt indexer was used at 190°C. The melt index of the resin after the ethylene homopolymerization reaction was measured under a load of 1.2 kg, and the melt index of the resin after the ethylene copolymerization reaction was measured under a load of 5 kg. A normal die with a diameter of 2.095 mm was used for the measurement.

[0069] (3) Notched impact strength of simply supported beam: determined according to the method described in GB / T 1043.1.

[0070] (4) Resin density: Determined according to the method described in GB / T 1033.2-2010. The extruded sample used for testing melt flow rate was used as the sample for density determination. The sample surface was smooth, without voids or burrs. After the sample was cut, it was placed on a cold metal plate, and then immersed in a beaker containing distilled water. The beaker was covered and boiled in 200 ml of boiling distilled water for 30 min for annealing. Then the beaker was placed in the laboratory environment to cool to room temperature, and the test was carried out within 24 hours.

[0071] (5) Content of comonomers in bimodal polyethylene resin: determined by nuclear magnetic resonance (NMR). A Bruker Avance III 400MHz NMR spectrometer with a 10mm probe was used. The solvent was deuterated o-dichlorobenzene; approximately 250 mg of sample was placed in 2.5 ml of deuterated solvent and heated in an oil bath at 140°C to dissolve the sample and form a homogeneous solution. 13C-NMR was collected at a probe temperature of 125°C, using a 90° pulse, a sampling time AQ of 5 seconds, a delay time D1 of 10 seconds, and more than 5000 scans.

[0072] (6) Particle size distribution of resin powder: The particle size distribution of resin powder was investigated by using a German Retsch sieve analyzer.

[0073] (7) Oxidation induction time: Determined according to the method described in GB / T19466.6-2009. The plastic sample and an inert reference (e.g., alumina) are placed in a differential thermal analyzer, and the inert gas (e.g., nitrogen) in the sample chamber is rapidly replaced with oxygen at a certain temperature. The change in the DTA curve (differential thermal spectrum) caused by sample oxidation is measured, and the oxidation induction period (OIT) (min) is obtained to evaluate the heat aging resistance of the plastic.

[0074] (8) Flexural modulus: Determined by the method described in the test standard GB / T 9341-2008.

[0075] The raw materials used in the embodiments and comparative examples of this invention are all commercially available.

[0076] Example 1

[0077] (1) Preparation of the titanium-containing Ziegler-Natta catalyst system:

[0078] The preparation method of the solid catalyst is the same as that in patent ZL200510117428.5 (CN1958620A). In a reactor thoroughly purged with high-purity nitrogen, 4.0 g of magnesium dichloride, 50 ml of toluene, 4.0 ml of epichlorohydrin, 4.0 ml of tributyl phosphate, and 6.4 ml of ethanol were added sequentially. The mixture was heated to 70°C with stirring, and the reaction was continued for 1 hour after the solid had completely dissolved to form a homogeneous solution. The system was then cooled to -5°C, and 40 ml of titanium tetrachloride was slowly added dropwise. Then, 3 ml of tetraethoxysilane was added, and the reaction was continued for 1 hour. The temperature was slowly increased to 80°C, and the reaction was continued for 2 hours. Stirring was stopped, and the mixture was allowed to stand. The suspension quickly separated into layers. The supernatant was removed, and the mixture was washed twice with toluene and four times with hexane. The mixture was then dried with high-purity nitrogen to obtain a solid titanium-containing Ziegler-Natta catalyst system with good flowability and a narrow particle size distribution.

[0079] (2) Polymerization reaction:

[0080] The polymerization reaction is carried out in two slurry reactors connected in series.

[0081] The titanium-containing Ziegler-Natta catalyst system and co-catalyst (triethylaluminum) obtained above were continuously fed into the first reactor through a catalyst storage tank to complete the first stage of ethylene homopolymerization. The polymerization temperature in the first reactor was 84℃, and the reaction pressure was 0.78MPa. Hydrogen was added to the feed of the first reactor as a molecular weight regulator, and hexane was added as a diluent. The hydrogen addition rate was 22 kg / h, with a hydrogen / ethylene molar ratio (%) of 6.0, yielding ethylene homopolymer. The ethylene homopolymer prepared in the first reactor had a melt index of 85 g / 10 min and a density of 0.9692 g / cm³. 3 .

[0082] The ethylene-containing homopolymer stream from the first reactor enters the second reactor. The polymerization temperature in the second reactor is 78℃, and the reaction pressure is 0.24 MPa. The feed to the second reactor includes 1.79 kg / h of hydrogen and 565 kg / h of butene comonomer. The hydrogen / ethylene molar ratio (%) is 0.117, and the butene / ethylene molar ratio (%) is 0.045. The bimodal polyethylene resin obtained from the second reactor has a melt index of 0.23 g / 10 min and a density of 0.949 g / cm³. 3 After the reaction in the second reactor was completed, the melt flow index of the bimodal polyethylene resin granules obtained was 0.22 g / 10 min; the density was 0.949 g / cm³. 3 The comonomer content of the bimodal polyethylene resin is 0.067% (wt). Specific test data for the basic and mechanical properties of the resin are shown in Tables 1-5.

[0083] The obtained bimodal polyethylene resin was used to prepare pipe materials using existing processes. The resin exhibited excellent processing performance and did not have the problem of low-molecular-weight precipitates. The unique resin structure of the bimodal polyethylene resin of this invention improved the environmental stress cracking resistance and rapid crack propagation resistance of the prepared polyethylene pipe materials.

[0084] Comparative Example 1

[0085] Bimodal polyethylene pipe material resin was prepared using the TH series catalyst transferred from Lyondellbasell.

[0086] After activation, the solid catalyst components are continuously fed into the first reactor through a catalyst storage tank to complete the first stage of ethylene polymerization. The polymerization temperature in the first reactor is 85℃, and the reaction pressure is 0.78 MPa. The hydrogen addition rate is 25 kg / h, with a hydrogen / ethylene molar ratio (%) of 6.5, yielding ethylene homopolymer. The ethylene homopolymer prepared in the first reactor has a melt index of 102 g / 10 min and a density of 0.9694 g / cm³. 3 .

[0087] The ethylene-containing homopolymer stream from the first reactor enters the second reactor. The polymerization temperature in the second reactor is 82℃, and the reaction pressure is 0.24 MPa. The butene feed rate to the second reactor is 639 kg / h, with a butene / ethylene molar ratio of 0.051 and a hydrogen / ethylene molar ratio of 0.290. The melt index of the bimodal polyethylene resin obtained from the second reactor is 0.23 g / 10 min, and its density is 0.949 g / cm³. 3 After the reaction in the second reactor was completed, the melt index of the resulting bimodal polyethylene resin granules was 0.22 g / 10 min, and the density was 0.949 g / cm³. 3 The comonomer content of the bimodal polyethylene resin is 0.061% wt. Specific test data for the basic and mechanical properties of the resin are shown in Tables 1-5.

[0088] Comparative Example 2

[0089] Bimodal polyethylene pipe material resin was prepared using imported Z501 series catalysts.

[0090] After activation, the solid catalyst components are continuously fed into the first reactor through a catalyst storage tank to complete the first stage of ethylene polymerization. The polymerization temperature in the first reactor is 84℃, and the reaction pressure is 0.78 MPa. The hydrogen addition rate is 12.5 kg / h, with a hydrogen / ethylene molar ratio (%) of 3.23, yielding ethylene homopolymer. The ethylene homopolymer prepared in the first reactor has a melt index of 103 g / 10 min and a density of 0.9697 g / cm³. 3 .

[0091] The ethylene-containing homopolymer stream from the first reactor enters the second reactor. The polymerization temperature in the second reactor is 78℃, and the reaction pressure is 0.24 MPa. The butene feed rate to the second reactor is 645 kg / h, with a butene / ethylene molar ratio of 0.052 and a hydrogen / ethylene molar ratio of 0.006. The melt index of the bimodal polyethylene resin obtained from the second reactor is 0.28 g / 10 min, and its density is 0.949 g / cm³. 3 After the reaction in the second reactor was completed, the melt index of the resulting bimodal polyethylene resin granules was 0.25 g / 10 min; the density was 0.949 g / cm³. 3 The comonomer content of the bimodal polyethylene resin is 0.060% wt. Specific test data for the basic and mechanical properties of the resin are shown in Tables 1-5.

[0092] Table 1. Particle size distribution of resin powder and catalyst activity

[0093]

[0094] As can be seen from the data in Table 1, the titanium-containing Ziegler-Natta catalyst prepared by the method provided in this invention can produce bimodal polyethylene resin with good particle morphology, fewer large and small particles, and good flowability when used in ethylene polymerization in two or more reactions connected in series. This is beneficial to the stable operation of the feed system and improves the production load of the unit. Comparative Example 1 has a higher content of fine powder, while Comparative Example 2 has a higher content of large particles.

[0095] Table 2. Hydrogen-to-ethylene ratio in polymerization reactor and polymer powder density

[0096]

[0097] Table 3. Melt index of polymer powder in polymerization reactor

[0098]

[0099] As can be seen from Tables 2 and 3, when producing bimodal polyethylene resin with a specific density and melt index, the titanium-containing Ziegler-Natta catalyst prepared by the method provided by this invention can carry out ethylene polymerization in two or more reactions connected in series. The hydrogen-to-ethylene ratio in the first reactor can meet the production requirements under low conditions; the amount of hydrogen added to the second reactor is easy to control, the production is stable, and the resin products produced meet the required indicators.

[0100] Table 4. Butene-to-ethylene ratio in polymerization reactor and comonomer content in polymer powder

[0101]

[0102] As can be seen from Table 4, the titanium-containing Ziegler-Natta catalyst prepared by the method provided by the present invention can significantly increase the content of polymer comonomers when ethylene polymerization is carried out in two or more reactions connected in series, even with a small amount of butene added, which is beneficial to improving the mechanical properties of the resin.

[0103] Table 5 Mechanical properties of the resin

[0104]

[0105] As can be seen from the data in Table 5, the titanium-containing Ziegler-Natta catalyst prepared by the method provided by this invention can carry out ethylene polymerization in two or more reactions connected in series. The bimodal polyethylene resin prepared by the method provided by this patent has higher tensile strength, higher impact strength, better toughness and better thermal degradation resistance than the polyethylene resin in the comparative example, and is suitable for preparing large-diameter bimodal polyethylene pipe materials.

Claims

1. A method for preparing bimodal polyethylene resin, characterized in that: The bimodal polyethylene resin is produced using a process involving at least two reactors connected in series in the presence of a titanium-containing Ziegler-Natta catalyst system, wherein the titanium-containing Ziegler-Natta catalyst system comprises the following components: (1) a magnesium-containing compound; (2) an organophosphorus compound; (3) an organoalcohol compound; (4) an organoepoxide compound; (5) a silicon-containing compound; (6) a titanium-containing compound; and (7) an aluminum-containing compound; the bimodal polyethylene resin is used in pipe material products. The method specifically includes the following steps: The first stage of ethylene homopolymerization reaction includes ethylene homopolymerization in the presence of hydrogen in the presence of a titanium-containing Ziegler-Natta catalyst system to obtain a stream containing ethylene homopolymer, wherein the molar ratio of hydrogen to ethylene is 4.5~7.

5. The second stage of ethylene copolymerization: In the presence of hydrogen, the stream containing ethylene homopolymer obtained in the previous stage is copolymerized with ethylene monomer and comonomer to obtain the bimodal polyethylene resin, wherein the molar ratio of hydrogen to ethylene is 0.11~0.

3.

2. The method for preparing bimodal polyethylene resin according to claim 1, characterized in that: The reaction temperature for the first stage of ethylene homopolymerization is 60~100℃; the reaction pressure is 0.1~3.0MPa; and / or, The molar ratio of hydrogen to ethylene is 5.5 to 6.

5.

3. The method for preparing bimodal polyethylene resin according to claim 2, characterized in that: The reaction temperature of the first stage ethylene homopolymerization reaction is 70~90℃; the reaction pressure is 0.5~2.0MPa.

4. The method for preparing bimodal polyethylene resin according to claim 1, characterized in that: The melt index of the ethylene homopolymer obtained from the first-stage ethylene homopolymerization reaction is greater than or equal to 60 g / 10 min at a load of 1.2 kg; and / or, The density of the ethylene homopolymer obtained from the first stage of ethylene homopolymerization is greater than or equal to 0.963 g / cm³. 3 .

5. The method for preparing bimodal polyethylene resin according to claim 4, characterized in that: The melt index of the ethylene homopolymer obtained from the first-stage ethylene homopolymerization reaction is greater than or equal to 65 g / 10 min at a load of 1.2 kg; and / or, The density of the ethylene homopolymer obtained from the first stage of ethylene homopolymerization reaction is 0.963~0.980 g / cm³. 3 .

6. The method for preparing bimodal polyethylene resin according to claim 5, characterized in that: The density of the ethylene homopolymer obtained from the first stage of ethylene homopolymerization reaction is 0.965~0.975 g / cm³. 3 .

7. The method for preparing bimodal polyethylene resin according to claim 1, characterized in that: The reaction temperature for the second-stage ethylene copolymerization reaction is 60~100℃; the reaction pressure is 0.01~3.0MPa; and / or, The second-stage ethylene copolymerization reaction is carried out in the presence of hydrogen, wherein the molar ratio of hydrogen to ethylene is 0.11~0.2; and / or, In the second stage of ethylene copolymerization, the molar ratio of the comonomer to ethylene is 0.01 to 0.

20.

8. The method for preparing bimodal polyethylene resin according to claim 7, characterized in that: The reaction temperature for the second-stage ethylene copolymerization reaction is 70~90℃; the reaction pressure is 0.05~2.0MPa; and / or, In the second stage of the ethylene copolymerization reaction, the molar ratio of the comonomer to ethylene is 0.03 to 0.

10.

9. The method for preparing bimodal polyethylene resin according to claim 1, characterized in that: The comonomer has the following structural formula: CH2=CHR, where R is a linear or branched alkane with 1 to 10 carbon atoms.

10. The method for preparing bimodal polyethylene resin according to claim 9, characterized in that: The comonomer is at least one of propylene, butene-1, pentene-1, hexene-1, octene-1, and decene-1.

11. The method for preparing bimodal polyethylene resin according to claim 1, characterized in that: The titanium-containing Ziegler-Natta catalyst system is formed by reacting a magnesium-containing compound with a solvent system containing an organophosphorus compound, an organic epoxy compound, and an organic alcohol compound to form a magnesium complex; and then reacting the magnesium complex with a silicon-containing compound, a titanium-containing compound, and an aluminum-containing compound to form the catalyst system.

12. The method for preparing bimodal polyethylene resin according to claim 1, characterized in that... The components of the titanium-containing Ziegler-Natta catalyst system include: The magnesium-containing compound is selected from the general formula Mg(OR) 6 ) p X 1 2-p Magnesium-containing compounds; where R 6 C1~C 20 Saturated or unsaturated straight-chain or branched hydrocarbon groups, or C3~C 20 Cyclic hydrocarbon group; X 1 For halogens, p is an integer and 0 ≤ p ≤ 2; and / or, The organophosphorus compound is selected from at least one of the following: alkyl esters of orthophosphoric acid, alkyl esters of phosphorous acid, haloalkyl esters of orthophosphoric acid, and haloalkyl esters of phosphorous acid; and / or, The organic epoxy compound is selected from at least one of C2-C8 aliphatic olefins, C2-C8 aliphatic dienes, C2-C8 haloaliphatic olefins, oxides of C2-C8 haloaliphatic dienes, glycidyl ethers, and internal ethers; and / or, The organic alcohol compound is a straight-chain, branched, or cycloalkyl alcohol with 1 to 10 carbon atoms, or an alcohol containing an aryl group with 6 to 20 carbon atoms, wherein the hydrogen atoms in the organic alcohol compound may optionally be substituted with halogen atoms; and / or, The silicon-containing compound is an organosilicon compound without active hydrogen atoms, and its general formula is R. 1 x R 2 y Si(OR 3 ) Z , where R 1 R 2 R 3 Same or different, R 1 and R 2 Each can be a hydrocarbon group or a halogen with 1 to 10 carbon atoms, R 3 For hydrocarbon groups with 1 to 10 carbon atoms, where x, y, and z are positive integers, 0 ≤ x ≤ 2, 0 ≤ y ≤ 2, 0 ≤ z ≤ 4, and x + y + z = 4; and / or, The general formula of the titanium-containing compound is Ti(OR). 5 ) a X 2 b Titanium-containing compounds, where R 5 It is an aliphatic or aromatic hydrocarbon group with 1 to 14 carbon atoms, X 2 For halogens, a is 0, 1, or 2, b is an integer from 0 to 4, a + b = 3 or 4; and / or, The aluminum-containing compound has the general formula AlR. 4 n X 3 3-n Organoaluminum compounds, where R 4 X is a hydrogen or hydrocarbon group with 1 to 20 carbon atoms. 3 For halogens, n is an integer where 0 < n ≤ 3.

13. The method for preparing bimodal polyethylene resin according to claim 12, characterized in that: The magnesium-containing compound is selected from the general formula Mg(OR) 6 ) p X 1 2-p Magnesium-containing compounds, where X 1 For chlorine; and / or, The organophosphorus compound is selected from at least one of triethyl phosphate, tributyl phosphate, triisooctyl phosphate, triphenyl phosphate, triethyl phosphite, tributyl phosphite, and di-n-butyl phosphite; and / or, The organic epoxy compound is selected from at least one of ethylene oxide, propylene oxide, butane oxide, butadiene oxide, butadiene dioxide, epichlorohydrin, tetrahydrofuran, methyl glycidyl ether, and diglycidyl ether; and / or, The organic alcohol compound is selected from at least one of ethanol, propanol, butanol, 2-ethylhexanol, and glycerol; and / or, The silicon-containing compound is selected from silicon tetrachloride and / or tetraethoxysilane; and / or, The titanium-containing compound is selected from at least one of titanium tetrachloride, titanium tetrabromide, titanium tetraiodide, titanium tetrabutoxy, titanium tetraethoxy, titanium monochlorotriethoxy, titanium trichloride, titanium dichlorodiethoxy, and titanium trichloromonoethoxy; and / or, The aluminum-containing compound is selected from at least one of triethylaluminum, diethylaluminum chloride, diethylaluminum chloride, sesquiethylaluminum, diisobutylaluminum chloride, triisobutylaluminum chloride, diisopropylaluminum chloride, methylpropylaluminum chloride, and diphenylaluminum chloride.

14. The method for preparing bimodal polyethylene resin according to claim 13, characterized in that: The magnesium-containing compound is selected from at least one of magnesium chloride, magnesium bromide, magnesium chloromethoxy, magnesium chloroethoxy, magnesium chloroisopropoxy, magnesium chlorobutoxy, magnesium chlorooctoxy, magnesium diethoxy, magnesium diepropoxy, magnesium diebutoxy, magnesium dieoctoxy, magnesium isopropoxy, magnesium butoxy, magnesium n-octoxy, and magnesium 2-ethylhexyloxy.

15. The method for preparing bimodal polyethylene resin according to claim 11, characterized in that: The components of the titanium-containing Ziegler-Natta catalyst system, based on the mole of magnesium compound in the magnesium complex, are: silicon compound 0.05–1 mole; aluminum compound 0–5 moles; titanium compound 1–15 moles; and / or, In the solvent system in which the magnesium complex is formed in the titanium-containing Ziegler-Natta catalyst system, the organic alcohol compound is 0.1 to 10 moles per mole of magnesium compound. The amount of organic epoxy compounds is 0.2 to 10 moles; the amount of organic phosphorus compounds is 0.1 to 10 moles.

16. The method for preparing bimodal polyethylene resin according to claim 15, characterized in that: The components of the titanium-containing Ziegler-Natta catalyst system, based on the mole of magnesium compound in the magnesium complex, are: silicon compound 0.1–0.5 mol; aluminum compound 0.01–3 mol; titanium compound 2–10 mol; and / or, In the solvent system for forming the magnesium complex in the titanium-containing Ziegler-Natta catalyst system, the organic alcohol compound is 1-4 moles, the organic epoxy compound is 0.3-4 moles, and the organic phosphorus compound is 0.2-4 moles per mole of magnesium compound.

17. The preparation method according to claim 11, characterized in that: The titanium-containing Ziegler-Natta catalyst system is prepared by a method comprising the following steps: (1) Under the protection of an inert gas, the magnesium-containing compound is dissolved in a solvent system containing an organic epoxy compound and an organic phosphorus compound to form a homogeneous solution of magnesium complex at a dissolution temperature of 50~90℃; an organic alcohol compound is added during or after the solution is formed to obtain a magnesium complex reaction solution. (2) The above reaction solution is contacted with the titanium-containing compound at a temperature of -40℃ to 20℃. The silicon-containing compound and aluminum-containing compound are introduced before, after or during the reaction to carry out the reaction. The mixture is then slowly heated to 60 to 110℃ to obtain the Ziegler-Natta catalyst system.

18. The bimodal polyethylene resin obtained by the preparation method according to any one of claims 1 to 17.

19. The bimodal polyethylene resin according to claim 18, characterized in that: The melt flow index of the bimodal polyethylene resin is 0.10~0.40 g / 10 min under a 5 kg load; the density of the bimodal polyethylene resin is 0.943~0.963 g / cm³. 3 ; and / or, The melt index of the homopolymer unit portion of the bimodal polyethylene resin is greater than or equal to 60 g / 10 min under a load of 1.2 kg, and the melt index of the copolymer unit portion of the bimodal polyethylene resin is 0.2~0.35 g / 10 min under a load of 5 kg.

20. The bimodal polyethylene resin according to claim 19, characterized in that: The melt flow index of the bimodal polyethylene resin is 0.15~0.35 g / 10 min under a 5 kg load; the density of the bimodal polyethylene resin is 0.945~0.955 g / cm³. 3 .

21. The bimodal polyethylene resin according to claim 18, characterized in that: The nominal tensile strain at break of the bimodal polyethylene resin is greater than or equal to 500%; and / or, The tensile yield stress of the bimodal polyethylene resin is greater than or equal to 20 MPa; and / or, The bimodal polyethylene resin has a notched impact strength of 20 kJ / m² in a simply supported beam at 23°C. 2 .

22. Pipe material articles prepared from bimodal polyethylene resin according to any one of claims 18 to 21.

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