Bimodal polyethylene and its applications

Abstract

The application provides a bimodal polyethylene and application thereof. The bimodal polyethylene is obtained by gas phase polymerization of monomers under catalysis of a catalyst; the monomers include ethylene or ethylene and alpha-olefins; and the catalyst includes a chromium-titanium bimetallic catalyst, which includes a carrier and a chromium active component and a titanium active component supported on the carrier, a precursor of the chromium active component includes a chromium metallocene compound, and a precursor of the titanium active component includes a titanium metallocene compound. The application also provides application of the bimodal polyethylene. The bimodal polyethylene has a wide molecular weight distribution and a bimodal molecular weight distribution.

Description

Technical Field

[0001] This invention relates to the field of polyethylene technology, and more particularly to a bimodal polyethylene and its applications. Background Technology

[0002] Polyethylene is the most widely used plastic in the world, accounting for 39% of the most common thermoplastics and 62% of polyolefins. In the 1930s, Imperial Chemical Industries (ICI) achieved the first commercial application of polyethylene by producing low-density polyethylene (LDPE) using free radical polymerization. However, the product's weak mechanical properties limited its application in various fields. In the early 1950s, Hogan and Banks of Phillips Corporation developed an inorganic chromium catalyst (Phillips catalyst), which significantly improved the various properties of polyethylene, leading to its wider application. Subsequently, in 1953, Karl Ziegler developed another catalyst with titanium as the active center, the Ziegler-Natta catalyst. The polyethylene produced by this catalyst had different characteristics from that produced by the Phillips catalyst, meeting the needs of different fields. In the following decades, various high-performance polyethylenes were continuously developed and produced, applied in daily life, medical, and military fields. Currently, polyethylene is mainly divided into low-density polyethylene, high-density polyethylene (HDPE), and linear low-density polyethylene (LLDPE). Among them, HDPE, due to its excellent mechanical properties and processing rheological characteristics, has wide applications in packaging films, blow-molded containers, and extruded pipes, accounting for more than 50% of the polyethylene market share. Over the past 20-30 years, bimodal polyethylene has developed rapidly as a high-performance polymer product, becoming the fastest-growing type of high-density polyethylene. Currently, bimodal polyethylene is mainly produced through a two-reactor series process. In one reactor, a catalyst is used to synthesize a higher molecular weight ethylene / α-olefin copolymer, while in another reactor, a chain transfer agent, such as hydrogen, is introduced to synthesize a lower molecular weight ethylene homopolymer. This production process requires two reactors, resulting in high equipment investment and energy consumption, and is also quite complex to operate. Summary of the Invention

[0003] To address the aforementioned problems, the present invention aims to provide a bimodal polyethylene that can be synthesized in a single reactor and its applications. This bimodal polyethylene has a broad molecular weight distribution and exhibits a bimodal molecular weight distribution.

[0004] To achieve the above objectives, the present invention provides a bimodal polyethylene, which is obtained by gas-phase polymerization of monomers under the action of a catalyst.

[0005] The monomer includes ethylene or ethylene and α-olefin;

[0006] The catalyst includes a chromium-titanium dual-center catalyst, which includes a support and chromium active components and titanium active components supported on the support. The precursor of the chromium active component includes a chromium dicerocene compound, and the precursor of the titanium active component includes a titanocene compound.

[0007] In the above-mentioned chromium-titanium dual-center catalyst, the weight of Cr in the chromium active component is generally 0.1-5 wt% of the weight of the chromium-titanium dual-center catalyst (i.e., the total weight of the chromium active component, titanium active component, and support), and the weight of Ti in the titanium active component is 0.1-5 wt% of the weight of the chromium-titanium dual-center catalyst.

[0008] In a specific embodiment of the present invention, when the monomer is ethylene, homopolymerization reaction is carried out; when the monomers are ethylene and α-olefin, copolymerization reaction can be carried out.

[0009] The chromium-titanium dual-center catalyst used in this invention is a supported catalyst. By loading the chromium and titanium active components onto a support, the independent catalytic characteristics of the two metal centers can be maintained. When applied to the gas-phase polymerization of ethylene, this catalyst can effectively regulate the structural properties of polyethylene products through the active centers, resulting in polymer products with a wide molecular weight distribution and a bimodal distribution.

[0010] In the above-mentioned chromium-titanium dual-center catalyst, the structure of the chromium-dicenocene compound is shown in the following formula:

[0011] Cp1-Cr-Cp2,

[0012] Wherein, Cp1 and / or Cp2 include one of cyclopentadienyl, indenyl, and fluorenyl, that is, Cp1 and / or Cp2 are one of the following structures:

[0013] In specific implementation schemes, the structures of Cp1 and Cp2 can be the same or different, without any special restrictions.

[0014] According to a specific embodiment of the present invention, the precursor of the chromium active component may be selected from the following structures:

[0015]

[0016] In the above-mentioned chromium-titanium dual-center catalyst, the structure of the titanium cadmium compound is shown in the following formula:

[0017]

[0018] Cp can be one of cyclopentadienyl, indenyl, and fluorenyl, and R1, R2, and R3 each include H or a hydrocarbon group having 1-8 carbon atoms.

[0019] In a specific implementation, the hydrocarbon group having 1-8 carbon atoms may include one or more combinations of methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, isobutyl, pentyl, isopentyl, hexyl, isohexyl, phenyl, benzyl, and benzyl.

[0020] According to a specific embodiment of the present invention, the precursor of the titanium active component may include the following structure:

[0021]

[0022] In the aforementioned chromium-titanium dual-center catalyst, the support generally comprises a porous inorganic support. Specifically, the porous inorganic support may include one or more of the following: silica, alumina, aluminosilicates, inorganic clay, titanium dioxide, zirconium oxide, magnesium oxide, iron oxide, tin oxide, and zinc oxide. The inorganic clay may include montmorillonite, and the silica may include amorphous porous silica gel.

[0023] According to a specific embodiment of the present invention, the specific surface area of ​​the porous inorganic carrier is generally 100-1000 m². 2 / g.

[0024] According to a specific embodiment of the present invention, the pore volume of the porous inorganic carrier is generally 0.3-5.0 cm³. 3 / g (i.e., pore volume is generally 0.3-5.0cm³) 3 / g).

[0025] According to a specific embodiment of the present invention, the average pore size of the porous inorganic carrier is generally 5-50 nm.

[0026] In specific embodiments of the present invention, an organometallic co-catalyst may be further added to the above-mentioned catalyst to activate it as needed. The organometallic co-catalyst may include one or more of organoaluminum compounds, organolithium compounds, organoboron compounds, etc.

[0027] Specifically, the organoaluminum compound may include one or more combinations of trialkylaluminum Al(R)3, alkylaluminoxane MAO, dialkylalkoxyaluminum Al(R)2OR, dialkylaluminum halide Al(R)2X, ethyl sesquialuminum chloride, etc., wherein R is an alkyl group, which may be an alkyl group having 1-12 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-dodecyl, etc.; X is a halogen, such as fluorine, chlorine, bromine, and iodine, preferably chlorine. Preferably, the organoaluminum compound may include one or more combinations of triethylaluminum, triisobutylaluminum, and alkylaluminoxane, etc.

[0028] In a specific embodiment of the present invention, the molar ratio of the organometallic co-catalyst to Cr in the catalyst is 10-2000:1, preferably 50-400:1.

[0029] The preparation method of the above-mentioned chromium-titanium dual-center catalyst may include: calcining the support, then impregnating the calcined support in a precursor of chromium active component, a precursor of titanium active component and an inert solvent, and drying it to obtain the catalyst.

[0030] In the above-mentioned preparation method of chromium-titanium dual-center catalyst, the calcination process can remove physical water and some hydroxyl groups from the surface of the support, and expose more active sites on the surface of the support that can bind with the active component precursor, thereby improving the loading effect of chromium and titanium as active centers in the support.

[0031] In the above-mentioned preparation method of chromium-titanium dual-center catalyst, if the calcination temperature is too low, the removal of physical water and hydroxyl groups on the support surface will be insufficient, resulting in poor binding effect between the active component precursor and the support; while if the calcination temperature is too high, the microporous structure in the support will be destroyed. This invention has found that controlling the calcination temperature to 300-900℃, for example, 300-600℃, is beneficial to improving the binding effect between the active component precursor and the support.

[0032] In the above-mentioned method for preparing chromium-titanium dual-center catalysts, the calcination time is generally controlled to be 1-10 h, for example, 2-4 h.

[0033] In the above-mentioned method for preparing chromium-titanium dual-center catalysts, the calcination is generally carried out in a dry, inert atmosphere, such as nitrogen or argon, to prevent contamination of the catalyst by air, water, or other components.

[0034] In the above-described method for preparing the chromium-titanium dual-center catalyst, the process of impregnating the calcined support with the precursors of the chromium and titanium active components allows the precursors of the chromium and titanium active components to be loaded onto the support. In a specific embodiment of the present invention, the precursors of the chromium and titanium active components can impregnate the support in any order, or simultaneously.

[0035] In the above-mentioned preparation method of chromium-titanium dual-center catalyst, the impregnation temperature is generally controlled at 20-180℃, for example, 45-120℃.

[0036] In the above-mentioned preparation method of chromium-titanium dual-center catalyst, the impregnation time is generally controlled to be 1-24h, for example, 4-12h.

[0037] According to a specific embodiment of the present invention, the inert solvent serves as the medium for the impregnation process of the carrier. Specifically, the inert solvent may include one or a combination of two or more of benzene, toluene, and xylene. The inert solvent preferably includes toluene.

[0038] In the above-described method for preparing the chromium-titanium dual-center catalyst, the drying process removes the inert solvent from the system. Specifically, the drying temperature is generally controlled at 60-150°C, for example, 80-130°C.

[0039] In the above-mentioned method for preparing chromium-titanium dual-center catalysts, the drying time is generally controlled to be 2-24 hours, for example, 6-16 hours.

[0040] According to a specific embodiment of the present invention, the reaction temperature of the gas-phase polymerization is generally controlled at 70-120°C.

[0041] According to a specific embodiment of the present invention, the reaction pressure of the gas-phase polymerization is generally controlled at 1900-2200 kPa.

[0042] According to a specific embodiment of the present invention, in the gas-phase polymerization reaction system (generally a system formed by mixing reaction gases), the sum of the molar concentrations of water and oxygen is generally less than 5 ppm.

[0043] According to a specific embodiment of the present invention, the above-described gas-phase polymerization process can be carried out in a gas-phase fluidized bed.

[0044] According to a specific embodiment of the present invention, in the reaction gas of gas-phase polymerization, with the total molar number of all gases being 100%, the molar percentage of nitrogen is 20-80%, the molar percentage of ethylene is 20-60%, and the molar ratio of α-olefin to ethylene is 0-0.1:1 (i.e., when the monomer includes α-olefin and ethylene, the molar ratio of the two is less than 0.1:1).

[0045] According to a specific embodiment of the present invention, the reactant gas may further include a molecular weight regulator. The molar ratio of the molecular weight regulator to ethylene can be controlled to be 0.2:1 or less (i.e., the molar ratio of the molecular weight regulator to ethylene is 0-0.2:1). In a specific embodiment, the molecular weight regulator may be hydrogen or the like.

[0046] According to a specific embodiment of the present invention, the α-olefin generally includes one or more combinations of propylene, 1-butene, 1-hexene and 1-octene.

[0047] According to a specific embodiment of the present invention, compared with existing polyethylene, the above-mentioned polyethylene product has a wider molecular weight distribution, generally above 40, and the molecular weight distribution trend chart ( Figure 1As can be seen from the figure, the polyethylene product prepared by the present invention has a bimodal structure.

[0048] According to a specific embodiment of the present invention, the melt flow rate of the bimodal polyethylene is generally 0.01-5.0 g / 10 min (measured using a 5 kg weight).

[0049] According to a specific embodiment of the present invention, the density of the bimodal polyethylene is generally 0.940-0.960 g / cm³. 3 .

[0050] This invention also provides applications of the above-mentioned bimodal polyethylene in pipe manufacturing, film manufacturing, and hollow pipe manufacturing.

[0051] The beneficial effects of this invention are as follows:

[0052] The bimodal polyethylene provided by this invention can be prepared by gas-phase method through homopolymerization of ethylene or copolymerization of ethylene and α-olefins. Based on the hydrogen-sensitive nature of the active center of this catalyst, the melt flow rate of bimodal polyethylene can be adjusted by the hydrogen concentration; for example, the melt flow rate of bimodal polyethylene can be increased by increasing the hydrogen flow rate. Based on the difference in copolymerization performance of the active center, comonomers can be effectively inserted into the high molecular weight portion to form a wider molecular weight distribution with a bimodal structure, which helps to improve the long-term mechanical properties of bimodal polyethylene products. Attached Figure Description

[0053] Figure 1 The molecular weight distribution results are for the polymers prepared in Examples 1 to 7. Figure 1 In the examples, a to g correspond to Examples 1 to 7, respectively. Detailed Implementation

[0054] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0055] The various polymer properties in the examples and comparative examples were measured according to the following methods:

[0056] 1. High-temperature gel permeation chromatography (HT-GPC)

[0057] Weight-average molecular weight and molecular weight distribution were determined by high-temperature gel permeation chromatography: A PL-220 high-temperature gel permeation chromatograph (Polymer Laboratories) was used to determine the molecular weight and molecular weight distribution of polyethylene. 1,2,4-trichlorobenzene was used as the solvent, and the determination was performed at 160℃. A universal correction method using narrow-distribution polystyrene as the standard was employed to process the data.

[0058] 2. 13C High-Temperature Nuclear Magnetic Resonance Spectroscopy (HT-13C NMR)

[0059] The short-chain content of the polymer was determined by high-temperature carbon NMR spectroscopy: In this experiment, a Bruker Avance III 500 NMR spectrometer was used to determine the short-chain content of polyethylene. Deuterated p-dichlorobenzene was used as the solvent, and the measurement was performed at 110℃. The carbon signal (shift within 30.00 ppm) on the polyethylene main chain was used as an internal standard to calculate the short-chain content.

[0060] 3. Melt flow rate and density shall be determined in accordance with GB / T3682 "Melt Flow Rate Determination Method" and GB / T1033 "Plastics - Determination of Density of Non-Foamed Plastics".

[0061] 4. Polymerization activity: The ratio of the mass of the polymerized product obtained to the mass of the catalyst added is the polymerization activity.

[0062] The chromium-titanium dual-center catalysts used in Examples 1-9 below were prepared by the following method:

[0063] 1 kg of SiO2 support (specific surface area 500 m²) 2 / g, pore volume 1.8cm 3 SiO2 (with a pore size of 21 nm) was placed in a fluidized bed and calcined at high temperature under a nitrogen atmosphere at 600 °C for 4 hours. After calcination, heating was stopped, and the SiO2 was allowed to cool naturally to room temperature before being collected and stored under nitrogen protection. The calcined support was then impregnated with a toluene solution of precursors for chromium and titanium active components (toluene was the sole solvent). The amount of precursors added was calculated based on 1 wt% of Cr and 1 wt% of Ti relative to the total catalyst weight. After continuous stirring at 80 °C for 4 hours, the catalyst was washed three times with 200 mL of toluene at room temperature and then dried at 130 °C for 4 hours under a nitrogen atmosphere to obtain a chromium-titanium dual-center catalyst. The dried chromium-titanium dual-center catalyst was then transferred and stored under nitrogen protection.

[0064] In the above experiments, three catalysts were prepared: chromium-titanium dual-center catalyst a, chromium-titanium dual-center catalyst b, and chromium-titanium dual-center catalyst c. However, the preparation was not limited to these three catalysts. The chromium active component precursor and the titanium active component precursor used in each catalyst were all commercially available. Their specific structures are shown below:

[0065]

[0066] Example 1

[0067] This embodiment provides a bimodal polyethylene, which is obtained by gas-phase polymerization of olefin monomers. The raw materials for producing this bimodal polyethylene are:

[0068] 1. Polymer-grade ethylene gas, with a feed rate of 15 kg / hour, has the following composition:

[0069] Component Name unit Control Indicators ethylene % (vol) ≥99.95 (methane + ethane) <![CDATA[(mL / m 3 )]]> ≤500 C3 and higher components <![CDATA[(mL / m 3 )]]> ≤20 Acetylene <![CDATA[(mL / m 3 )]]> ≤5 carbon monoxide <![CDATA[(mL / m 3 )]]> ≤2 carbon dioxide <![CDATA[(mL / m 3 )]]> ≤2 oxygen <![CDATA[(mL / m 3 )]]> ≤2 water (mg / kg) ≤5 <![CDATA[Sulfur (calculated as H2S)]]> <![CDATA[(mL / m 3 )]]> ≤1

[0070] 2. Chromium-titanium dual-center catalyst a, added at a rate of 10 g / hour;

[0071] 3. Polymer-grade hydrogen gas, added at a rate of 20 grams per hour, with the following composition:

[0072] Component Name unit Control Indicators hydrogen % (vol) ≥99.99 oxygen <![CDATA[(mL / m 3 )]]> ≤5 water <![CDATA[(mL / m 3 )]]> ≤3 Nitrogen <![CDATA[(mL / m 3 )]]> ≤50 CO <![CDATA[(mL / m 3 )]]> ≤1 <![CDATA[CO2]]> <![CDATA[(mL / m 3 )]]> ≤1 methane <![CDATA[(mL / m 3 )]]> ≤10

[0073] 4. Nitrogen and ethane are both inert components and do not participate in the reaction.

[0074] The volume ratio of the gas mixture is:

[0075] Ethylene 20.0-30.0

[0076] Hydrogen gas 1.0-2.0

[0077] Nitrogen gas 60.0-70.0.

[0078] A mixture of ethylene, nitrogen, and hydrogen is added to a gas-phase fluidized bed and kept in circulation. A chromium-titanium dual-center catalyst a is added, and the reaction temperature in the reactor is adjusted to 95-100℃ and the reaction pressure to 2000-2200kPa to obtain ethylene homopolymer base resin.

[0079] Example 2

[0080] This embodiment provides a bimodal polyethylene, which is obtained by gas-phase polymerization of olefin monomers. The raw materials for producing this bimodal polyethylene are:

[0081] 1. Polymer-grade ethylene gas, with a feed rate of 25 kg / hour, has the following composition:

[0082] Component Name unit Control Indicators ethylene % (vol) ≥99.95 (methane + ethane) <![CDATA[(mL / m 3 )]]> ≤500 C3 and higher components <![CDATA[(mL / m 3 )]]> ≤20 Acetylene <![CDATA[(mL / m 3 )]]> ≤5 carbon monoxide <![CDATA[(mL / m 3 )]]> ≤2 carbon dioxide <![CDATA[(mL / m 3 )]]> ≤2 oxygen <![CDATA[(mL / m 3 )]]> ≤2 water (mg / kg) ≤5 <![CDATA[Sulfur (calculated as H2S)]]> <![CDATA[(mL / m 3 )]]> ≤1

[0083] 2. Chromium-titanium dual-center catalyst a, added at a rate of 10 g / hour;

[0084] 3. Polymer-grade hydrogen gas, added at a rate of 20 grams per hour, with the following composition:

[0085] Component Name unit Control Indicators hydrogen % (vol) ≥99.99 oxygen <![CDATA[(mL / m 3 )]]> ≤5 water <![CDATA[(mL / m 3 )]]> ≤3 Nitrogen <![CDATA[(mL / m 3 )]]> ≤50 CO <![CDATA[(mL / m 3 )]]> ≤1 <![CDATA[CO2]]> <![CDATA[(mL / m 3 )]]> ≤1 methane <![CDATA[(mL / m 3 )]]> ≤10

[0086] 4. Nitrogen and ethane are both inert components and do not participate in the reaction.

[0087] The volume ratio of the gas mixture is:

[0088] Ethylene 30.0-40.0

[0089] Hydrogen gas 1.0-2.0

[0090] Nitrogen gas 45.0-55.0.

[0091] A mixture of ethylene, nitrogen, and hydrogen is added to a gas-phase fluidized bed and kept in circulation. A chromium-titanium dual-center catalyst a is added, and the reaction temperature in the reactor is adjusted to 95-100℃ and the reaction pressure to 2000-2200kPa to obtain ethylene homopolymer base resin.

[0092] Example 3

[0093] This embodiment provides a bimodal polyethylene, which is obtained by gas-phase polymerization of olefin monomers. The raw materials for producing this bimodal polyethylene are:

[0094] 1. Polymer-grade ethylene gas, with a feed rate of 35 kg / hour, has the following composition:

[0095] Component Name unit Control Indicators ethylene % (vol) ≥99.95 (methane + ethane) <![CDATA[(mL / m 3 )]]> ≤500 C3 and higher components <![CDATA[(mL / m 3 )]]> ≤20 Acetylene <![CDATA[(mL / m 3 )]]> ≤5 carbon monoxide <![CDATA[(mL / m 3 )]]> ≤2 carbon dioxide <![CDATA[(mL / m 3 )]]> ≤2 oxygen <![CDATA[(mL / m 3 )]]> ≤2 water (mg / kg) ≤5 <![CDATA[Sulfur (calculated as H2S)]]> <![CDATA[(mL / m 3 )]]> ≤1

[0096] 2. Chromium-titanium dual-center catalyst a, added at a rate of 10 g / hour;

[0097] 3. Polymer-grade hydrogen gas, added at a rate of 20 grams per hour, with the following composition:

[0098] Component Name unit Control Indicators hydrogen % (vol) ≥99.99 oxygen <![CDATA[(mL / m 3 )]]> ≤5 water <![CDATA[(mL / m 3 )]]> ≤3 Nitrogen <![CDATA[(mL / m 3 )]]> ≤50 CO <![CDATA[(mL / m 3 )]]> ≤1 <![CDATA[CO2]]> <![CDATA[(mL / m 3 )]]> ≤1 methane <![CDATA[(mL / m 3 )]]> ≤10

[0099] 4. Nitrogen and ethane are both inert components and do not participate in the reaction.

[0100] The volume ratio of the gas mixture is:

[0101] Ethylene 40.0-45.0

[0102] Hydrogen gas 1.0-2.0

[0103] Nitrogen gas 40.0-45.0.

[0104] A mixture of ethylene, nitrogen, and hydrogen is added to a gas-phase fluidized bed and kept in circulation. A chromium-titanium dual-center catalyst a is added, and the reaction temperature in the reactor is adjusted to 95-100℃ and the reaction pressure to 2000-2200kPa to obtain ethylene homopolymer base resin.

[0105] Example 4

[0106] This embodiment provides a bimodal polyethylene, which is obtained by gas-phase polymerization of olefin monomers. The raw materials for producing this bimodal polyethylene are:

[0107] 1. Polymer-grade ethylene gas, with a feed rate of 25 kg / hour, has the following composition:

[0108]

[0109]

[0110] 2. Chromium-titanium dual-center catalyst a, added at a rate of 10 g / hour;

[0111] 3. Polymer-grade hydrogen gas, added at a rate of 20 grams per hour, with the following composition:

[0112] Component Name unit Control Indicators hydrogen % (vol) ≥99.99 oxygen <![CDATA[(mL / m 3 )]]> ≤5 water <![CDATA[(mL / m 3 )]]> ≤3 Nitrogen <![CDATA[(mL / m 3 )]]> ≤50 CO <![CDATA[(mL / m 3 )]]> ≤1 <![CDATA[CO2]]> <![CDATA[(mL / m 3 )]]> ≤1 methane <![CDATA[(mL / m 3 )]]> ≤10

[0113] 4. Polymer-grade 1-hexene gas, added at a rate of 40 g / hour, with the following composition:

[0114] Component Name unit Control Indicators 1-Hexene % (wt) ≥99.0 Total n-α-olefins % (wt) ≥99.0 Total branched olefins % (wt) ≤1.0 <![CDATA[C4 and lower carbon]]> % (wt) ≤0.5 <![CDATA[C8 and higher carbon]]> % (wt) ≤0.1 Total alkanes % (wt) ≤0.05 peroxide mg / kg ≤1.0 water mg / kg ≤25 Color Platinum-Cobalt ≤10

[0115] 5. Nitrogen and ethane are both inert components and do not participate in the reaction.

[0116] The volume ratio of the gas mixture is:

[0117] Ethylene 30.0-40.0

[0118] Hydrogen gas 1.0-2.0

[0119] Nitrogen gas 45.0-55.0.

[0120] A mixture of ethylene, nitrogen, and hydrogen is added to a gas-phase fluidized bed and kept in a circulating state. A chromium-titanium dual-center catalyst a and a comonomer 1-hexene are added. The reaction temperature in the reactor is adjusted to 95-100℃ and the reaction pressure is 2000-2200kPa to obtain a basic resin formed by the polymerization of ethylene and comonomer.

[0121] Example 5

[0122] This embodiment provides a bimodal polyethylene, which is obtained by gas-phase polymerization of olefin monomers. The raw materials for producing this bimodal polyethylene are:

[0123] 1. Polymer-grade ethylene gas, with a feed rate of 25 kg / hour, has the following composition:

[0124] Component Name unit Control Indicators ethylene % (vol) ≥99.95 (methane + ethane) <![CDATA[(mL / m 3 )]]> ≤500 C3 and higher components <![CDATA[(mL / m 3 )]]> ≤20 Acetylene <![CDATA[(mL / m 3 )]]> ≤5 carbon monoxide <![CDATA[(mL / m 3 )]]> ≤2 carbon dioxide <![CDATA[(mL / m 3 )]]> ≤2 oxygen <![CDATA[(mL / m 3 )]]> ≤2 water (mg / kg) ≤5 <![CDATA[Sulfur (calculated as H2S)]]> <![CDATA[(mL / m 3 )]]> ≤1

[0125] 2. Chromium-titanium dual-center catalyst a, added at a rate of 10 g / hour;

[0126] 3. Polymer-grade hydrogen gas, added at a rate of 20 grams per hour, with the following composition:

[0127] Component Name unit Control Indicators hydrogen % (vol) ≥99.99 oxygen <![CDATA[(mL / m 3 )]]> ≤5 water <![CDATA[(mL / m 3 )]]> ≤3 Nitrogen <![CDATA[(mL / m 3 )]]> ≤50 CO <![CDATA[(mL / m 3 )]]> ≤1 <![CDATA[CO2]]> <![CDATA[(mL / m 3 )]]> ≤1 methane <![CDATA[(mL / m 3 )]]> ≤10

[0128] 4. Polymer-grade 1-hexene gas, added at a rate of 60 g / hour, with the following composition:

[0129]

[0130]

[0131] 5. Nitrogen and ethane are both inert components and do not participate in the reaction.

[0132] The volume ratio of the gas mixture is:

[0133] Ethylene 30.0-40.0

[0134] Hydrogen gas 1.0-2.0

[0135] Nitrogen gas 45.0-55.0.

[0136] A mixture of ethylene, nitrogen, and hydrogen gases is added to a gas-phase fluidized bed and kept in a continuous circulation state. A chromium-titanium dual-center catalyst a and a comonomer 1-hexene are added. The reaction temperature in the reactor is adjusted to 95-100℃ and the reaction pressure is 2000-2200kPa to obtain a basic resin formed by the polymerization of ethylene and the comonomer.

[0137] Example 6

[0138] This embodiment provides a bimodal polyethylene, which is obtained by gas-phase polymerization of olefin monomers. The raw materials for producing this bimodal polyethylene are:

[0139] 1. Polymer-grade ethylene gas, with a feed rate of 25 kg / hour, has the following composition:

[0140] Component Name unit Control Indicators ethylene % (vol) ≥99.95 (methane + ethane) <![CDATA[(mL / m 3 )]]> ≤500 C3 and higher components <![CDATA[(mL / m 3 )]]> ≤20 Acetylene <![CDATA[(mL / m 3 )]]> ≤5 carbon monoxide <![CDATA[(mL / m 3 )]]> ≤2 carbon dioxide <![CDATA[(mL / m 3 )]]> ≤2 oxygen <![CDATA[(mL / m 3 )]]> ≤2 water (mg / kg) ≤5 <![CDATA[Sulfur (calculated as H2S)]]> <![CDATA[(mL / m 3 )]]> ≤1

[0141] 2. Chromium-titanium dual-center catalyst a, added at a rate of 10 g / hour;

[0142] 3. Polymer-grade hydrogen gas, added at a rate of 20 grams per hour, with the following composition:

[0143]

[0144]

[0145] 4. Polymer-grade 1-hexene gas, added at a rate of 80 g / hour, with the following composition:

[0146] Component Name unit Control Indicators 1-Hexene % (wt) ≥99.0 Total n-α-olefins % (wt) ≥99.0 Total branched olefins % (wt) ≤1.0 <![CDATA[C4 and lower carbon]]> % (wt) ≤0.5 <![CDATA[C8 and higher carbon]]> % (wt) ≤0.1 Total alkanes % (wt) ≤0.05 peroxide mg / kg ≤1.0 water mg / kg ≤25 Color Platinum-Cobalt ≤10

[0147] 5. Nitrogen and ethane are both inert components and do not participate in the reaction.

[0148] The volume ratio of the gas mixture is:

[0149] Ethylene 30.0-40.0

[0150] Hydrogen gas 1.0-2.0

[0151] Nitrogen gas 45.0-55.0.

[0152] A mixture of ethylene, nitrogen, and hydrogen is added to a gas-phase fluidized bed and kept in a circulating state. A chromium-titanium dual-center catalyst a and a comonomer 1-hexene are added. The reaction temperature in the reactor is adjusted to 95-100℃ and the reaction pressure is 2000-2200kPa to obtain a basic resin formed by the polymerization of ethylene and comonomer.

[0153] Example 7

[0154] This embodiment provides a bimodal polyethylene, which is obtained by gas-phase polymerization of olefin monomers. The raw materials for producing this bimodal polyethylene are:

[0155] 1. Polymer-grade ethylene gas, with a feed rate of 25 kg / hour, has the following composition:

[0156]

[0157]

[0158] 2. Chromium-titanium dual-center catalyst a, added at a rate of 10 g / hour;

[0159] 3. Polymer-grade hydrogen gas, added at a rate of 15 grams per hour, with the following composition:

[0160] Component Name unit Control Indicators hydrogen % (vol) ≥99.99 oxygen <![CDATA[(mL / m 3 )]]> ≤5 water <![CDATA[(mL / m 3 )]]> ≤3 Nitrogen <![CDATA[(mL / m 3 )]]> ≤50 CO <![CDATA[(mL / m 3 )]]> ≤1 <![CDATA[CO2]]> <![CDATA[(mL / m 3 )]]> ≤1 methane <![CDATA[(mL / m 3 )]]> ≤10

[0161] 4. Polymer-grade 1-hexene gas, added at a rate of 60 g / hour, with the following composition:

[0162] Component Name unit Control Indicators 1-Hexene % (wt) ≥99.0 Total n-α-olefins % (wt) ≥99.0 Total branched olefins % (wt) ≤1.0 <![CDATA[C4 and lower carbon]]> % (wt) ≤0.5 <![CDATA[C8 and higher carbon]]> % (wt) ≤0.1 Total alkanes % (wt) ≤0.05 peroxide mg / kg ≤1.0 water mg / kg ≤25 Color Platinum-Cobalt ≤10

[0163] 5. Nitrogen and ethane are both inert components and do not participate in the reaction.

[0164] The volume ratio of the gas mixture is:

[0165] Ethylene 30.0-40.0

[0166] Hydrogen gas 1.0-2.0

[0167] Nitrogen gas 45.0-55.0.

[0168] A mixture of ethylene, nitrogen, and hydrogen is added to a gas-phase fluidized bed and kept in a circulating state. A chromium-titanium dual-center catalyst a and a comonomer 1-hexene are added. The reaction temperature in the reactor is adjusted to 95-100℃ and the reaction pressure is 2000-2200kPa to obtain a basic resin formed by the polymerization of ethylene and comonomer.

[0169] Example 8

[0170] This embodiment provides a bimodal polyethylene, which is obtained by gas-phase polymerization of olefin monomers. The raw materials for producing this bimodal polyethylene are:

[0171] 1. Polymer-grade ethylene gas, with a feed rate of 25 kg / hour, has the following composition:

[0172] Component Name unit Control Indicators ethylene % (vol) ≥99.95 (methane + ethane) <![CDATA[(mL / m 3 )]]> ≤500 C3 and higher components <![CDATA[(mL / m 3 )]]> ≤20 Acetylene <![CDATA[(mL / m 3 )]]> ≤5 carbon monoxide <![CDATA[(mL / m 3 )]]> ≤2 carbon dioxide <![CDATA[(mL / m 3 )]]> ≤2 oxygen <![CDATA[(mL / m 3 )]]> ≤2 water (mg / kg) ≤5 <![CDATA[Sulfur (calculated as H2S)]]> <![CDATA[(mL / m 3 )]]> ≤1

[0173] 2. Chromium-titanium dual-center catalyst a, added at a rate of 10 g / hour;

[0174] 3. Polymer-grade hydrogen gas, added at a rate of 35 grams per hour, with the following composition:

[0175] Component Name unit Control Indicators hydrogen % (vol) ≥99.99 oxygen <![CDATA[(mL / m 3 )]]> ≤5 water <![CDATA[(mL / m 3 )]]> ≤3 Nitrogen <![CDATA[(mL / m 3 )]]> ≤50 CO <![CDATA[(mL / m 3 )]]> ≤1 <![CDATA[CO2]]> <![CDATA[(mL / m 3 )]]> ≤1 methane <![CDATA[(mL / m 3 )]]> ≤10

[0176] 4. Polymer-grade 1-hexene gas, added at a rate of 60 g / hour, with the following composition:

[0177]

[0178]

[0179] 5. Nitrogen and ethane are both inert components and do not participate in the reaction.

[0180] The volume ratio of the gas mixture is:

[0181] Ethylene 30.0-40.0

[0182] Hydrogen gas 1.0-2.0

[0183] Nitrogen gas 45.0-55.0.

[0184] A mixture of ethylene, nitrogen, and hydrogen is added to a gas-phase fluidized bed and kept in a circulating state. A chromium-titanium dual-center catalyst a and a comonomer 1-hexene are added. The reaction temperature in the reactor is adjusted to 95-100℃ and the reaction pressure is 2000-2200kPa to obtain a basic resin formed by the polymerization of ethylene and comonomer.

[0185] Example 9

[0186] This embodiment provides a bimodal polyethylene, which is obtained by gas-phase polymerization of olefin monomers. The raw materials for producing this bimodal polyethylene are:

[0187] 1. Polymer-grade ethylene gas, with a feed rate of 25 kg / hour, has the following composition:

[0188] Component Name unit Control Indicators ethylene % (vol) ≥99.95 (methane + ethane) <![CDATA[(mL / m 3 )]]> ≤500 C3 and higher components <![CDATA[(mL / m 3 )]]> ≤20 Acetylene <![CDATA[(mL / m 3 )]]> ≤5 carbon monoxide <![CDATA[(mL / m 3 )]]> ≤2 carbon dioxide <![CDATA[(mL / m 3 )]]> ≤2 oxygen <![CDATA[(mL / m 3 )]]> ≤2 water (mg / kg) ≤5 <![CDATA[Sulfur (calculated as H2S)]]> <![CDATA[(mL / m 3 )]]> ≤1

[0189] 2. Chromium-titanium dual-center catalyst a, added at a rate of 10 g / hour;

[0190] 3. Polymer-grade hydrogen gas, added at a rate of 50 grams per hour, with the following composition:

[0191]

[0192]

[0193] 4. Polymer-grade 1-hexene gas, added at a rate of 60 g / hour, with the following composition:

[0194] Component Name unit Control Indicators 1-Hexene % (wt) ≥99.0 Total n-α-olefins % (wt) ≥99.0 Total branched olefins % (wt) ≤1.0 <![CDATA[C4 and lower carbon]]> % (wt) ≤0.5 <![CDATA[C8 and higher carbon]]> % (wt) ≤0.1 Total alkanes % (wt) ≤0.05 peroxide mg / kg ≤1.0 water mg / kg ≤25 Color Platinum-Cobalt ≤10

[0195] 5. Nitrogen and ethane are both inert components and do not participate in the reaction.

[0196] The volume ratio of the gas mixture is:

[0197] Ethylene 30.0-40.0

[0198] Hydrogen gas 1.0-2.0

[0199] Nitrogen gas 45.0-55.0.

[0200] A mixture of ethylene, nitrogen, and hydrogen is added to a gas-phase fluidized bed and kept in a circulating state. A chromium-titanium dual-center catalyst a and a comonomer 1-hexene are added. The reaction temperature in the reactor is adjusted to 95-100℃ and the reaction pressure is 2000-2200kPa to obtain a basic resin formed by the polymerization of ethylene and comonomer.

[0201] The preparation method of the chromium-centered catalyst used in the following comparative examples is as follows:

[0202] 1 kg of SiO2 support (specific surface area 500 m²) 2 SiO2 (containing a pore volume of 1.8 ml / g and a pore size of 21 nm) was placed in a fluidized bed for high-temperature calcination under a nitrogen atmosphere at 600°C for 4 hours. After calcination, heating was stopped, and the SiO2 was allowed to cool naturally to room temperature. The SiO2 was then collected and stored under nitrogen protection. The calcined support was then impregnated with a precursor of the chromium active component. In a toluene solution, the amount of the chromium active component precursor added was calculated as 1 wt% of the weight of Cr relative to the total weight of the catalyst. After continuous stirring at 80 °C for 4 h, the catalyst was washed three times with 200 mL of toluene at room temperature, and then dried at 130 °C for 4 h under nitrogen atmosphere to obtain the chromium-centered catalyst. The dried chromium-centered catalyst was transferred and stored under nitrogen protection.

[0203] Comparative Example 1

[0204] This comparative example provides a polyethylene obtained by gas-phase polymerization of olefin monomers. The raw materials for producing this polyethylene are:

[0205] 1. Polymer-grade ethylene gas, with a feed rate of 25 kg / hour, has the following composition:

[0206] Component Name unit Control Indicators ethylene % (vol) ≥99.95 (methane + ethane) <![CDATA[(mL / m 3 )]]> ≤500 C3 and higher components <![CDATA[(mL / m 3 )]]> ≤20 Acetylene <![CDATA[(mL / m 3 )]]> ≤5 carbon monoxide <![CDATA[(mL / m 3 )]]> ≤2 carbon dioxide <![CDATA[(mL / m 3 )]]> ≤2 oxygen <![CDATA[(mL / m 3 )]]> ≤2 water (mg / kg) ≤5 <![CDATA[Sulfur (calculated as H2S)]]> <![CDATA[(mL / m 3 )]]> ≤1

[0207] 2. Chromium-centered catalyst, added at a rate of 10 g / hour;

[0208] 3. Polymer-grade hydrogen gas, added at a rate of 15 grams per hour, with the following composition:

[0209] Component Name unit Control Indicators hydrogen % (vol) ≥99.99 oxygen <![CDATA[(mL / m 3 )]]> ≤5 water <![CDATA[(mL / m 3 )]]> ≤3 Nitrogen <![CDATA[(mL / m 3 )]]> ≤50 CO <![CDATA[(mL / m 3 )]]> ≤1 <![CDATA[CO2]]> <![CDATA[(mL / m 3 )]]> ≤1 methane <![CDATA[(mL / m 3 )]]> ≤10

[0210] 4. Nitrogen and ethane are both inert components and do not participate in the reaction.

[0211] The volume ratio of the gas mixture is:

[0212] Ethylene 30.0-40.0

[0213] Hydrogen gas 1.0-2.0

[0214] Nitrogen gas 45.0-55.0.

[0215] A mixture of ethylene, nitrogen, and hydrogen is added to a gas-phase fluidized bed and kept in a continuous circulation state. A chromium-centered catalyst is added, and the reaction temperature in the reactor is adjusted to 95-100℃ and the reaction pressure to 2000-2200kPa to obtain a basic resin formed by the polymerization of ethylene and comonomers.

[0216] Comparative Example 2

[0217] This comparative example provides a polyethylene obtained by gas-phase polymerization of olefin monomers. The raw materials for producing this polyethylene are:

[0218] 1. Polymer-grade ethylene gas, with a feed rate of 25 kg / hour, has the following composition:

[0219] Component Name unit Control Indicators ethylene % (vol) ≥99.95 (methane + ethane) <![CDATA[(mL / m 3 )]]> ≤500 C3 and higher components <![CDATA[(mL / m 3 )]]> ≤20 Acetylene <![CDATA[(mL / m 3 )]]> ≤5 carbon monoxide <![CDATA[(mL / m 3 )]]> ≤2 carbon dioxide <![CDATA[(mL / m 3 )]]> ≤2 oxygen <![CDATA[(mL / m 3 )]]> ≤2 water (mg / kg) ≤5 <![CDATA[Sulfur (calculated as H2S)]]> <![CDATA[(mL / m 3 )]]> ≤1

[0220] 2. Chromium-centered catalyst, added at a rate of 10 g / hour;

[0221] 3. Polymer-grade hydrogen gas, added at a rate of 35 grams per hour, with the following composition:

[0222] Component Name unit Control Indicators hydrogen % (vol) ≥99.99 oxygen <![CDATA[(mL / m 3 )]]> ≤5 water <![CDATA[(mL / m 3 )]]> ≤3 Nitrogen <![CDATA[(mL / m 3 )]]> ≤50 CO <![CDATA[(mL / m 3 )]]> ≤1 <![CDATA[CO2]]> <![CDATA[(mL / m 3 )]]> ≤1 methane <![CDATA[(mL / m 3 )]]> ≤10

[0223] 4. Nitrogen and ethane are both inert components and do not participate in the reaction.

[0224] The air-fuel mixture ratio is:

[0225] Ethylene 30.0-40.0

[0226] Hydrogen gas 1.0-2.0

[0227] Nitrogen gas 45.0-55.0.

[0228] A mixture of ethylene, nitrogen, and hydrogen is added to a gas-phase fluidized bed and kept in a continuous circulation state. A chromium-centered catalyst is added, and the reaction temperature in the reactor is adjusted to 95-100℃ and the reaction pressure to 2000-2200kPa to obtain a basic resin formed by the polymerization of ethylene and comonomers.

[0229] Comparative Example 3

[0230] This comparative example provides a polyethylene obtained by gas-phase polymerization of olefin monomers. The raw materials for producing this polyethylene are:

[0231] 1. Polymer-grade ethylene gas, with a feed rate of 25 kg / hour, has the following composition:

[0232] Component Name unit Control Indicators ethylene % (vol) ≥99.95 (methane + ethane) <![CDATA[(mL / m 3 )]]> ≤500 C3 and higher components <![CDATA[(mL / m 3 )]]> ≤20 Acetylene <![CDATA[(mL / m 3 )]]> ≤5 carbon monoxide <![CDATA[(mL / m 3 )]]> ≤2 carbon dioxide <![CDATA[(mL / m 3 )]]> ≤2 oxygen <![CDATA[(mL / m 3 )]]> ≤2 water (mg / kg) ≤5 <![CDATA[Sulfur (calculated as H2S)]]> <![CDATA[(mL / m 3 )]]> ≤1

[0233] 2. Chromium-centered catalyst, added at a rate of 10 g / hour;

[0234] 3. Polymer-grade hydrogen gas, added at a rate of 20 grams per hour, with the following composition:

[0235]

[0236]

[0237] 4. Polymer-grade 1-hexene gas, added at a rate of 40 g / hour, with the following composition:

[0238] Component Name unit Control Indicators 1-Hexene % (wt) ≥99.0 Total n-α-olefins % (wt) ≥99.0 Total branched olefins % (wt) ≤1.0 <![CDATA[C4 and lower carbon]]> % (wt) ≤0.5 <![CDATA[C8 and higher carbon]]> % (wt) ≤0.1 Total alkanes % (wt) ≤0.05 peroxide mg / kg ≤1.0 water mg / kg ≤25 Color Platinum-Cobalt ≤10

[0239] 5. Nitrogen and ethane are both inert components and do not participate in the reaction.

[0240] The volume ratio of the gas mixture is:

[0241] Ethylene 30.0-40.0

[0242] Hydrogen gas 1.0-2.0

[0243] Nitrogen gas 45.0-55.0.

[0244] A mixture of ethylene, nitrogen, and hydrogen is added to a gas-phase fluidized bed and kept in circulation. A chromium-titanium dual-center catalyst and the comonomer 1-hexene are added. The reaction temperature in the reactor is adjusted to 95-100℃ and the reaction pressure is 2000-2200kPa to obtain a basic resin formed by the polymerization of ethylene and the comonomer.

[0245] Comparative Example 4

[0246] This comparative example provides a polyethylene obtained by gas-phase polymerization of olefin monomers. The raw materials for producing this polyethylene are:

[0247] The raw materials for producing polyethylene resin are the following substances:

[0248] 1. Polymer-grade ethylene gas, with a feed rate of 25 kg / hour, has the following composition:

[0249]

[0250]

[0251] 2. Chromium-titanium dual-center catalyst, added at a rate of 10 g / hour;

[0252] 3. Polymer-grade hydrogen gas, added at a rate of 20 grams per hour, with the following composition:

[0253] Component Name unit Control Indicators hydrogen % (vol) ≥99.99 oxygen <![CDATA[(mL / m 3 )]]> ≤5 water <![CDATA[(mL / m 3 )]]> ≤3 Nitrogen <![CDATA[(mL / m 3 )]]> ≤50 CO <![CDATA[(mL / m 3 )]]> ≤1 <![CDATA[CO2]]> <![CDATA[(mL / m 3 )]]> ≤1 methane <![CDATA[(mL / m 3 )]]> ≤10

[0254] 4. Polymer-grade 1-hexene gas, added at a rate of 80 g / hour, with the following composition:

[0255] Component Name unit Control Indicators 1-Hexene % (wt) ≥99.0 Total n-α-olefins % (wt) ≥99.0 Total branched olefins % (wt) ≤1.0 <![CDATA[C4 and lower carbon]]> % (wt) ≤0.5 <![CDATA[C8 and higher carbon]]> % (wt) ≤0.1 Total alkanes % (wt) ≤0.05 peroxide mg / kg ≤1.0 water mg / kg ≤25 Color Platinum-Cobalt ≤10

[0256] 5. Nitrogen and ethane are both inert components and do not participate in the reaction.

[0257] The volume ratio of the gas mixture is:

[0258] Ethylene 30.0-40.0

[0259] Hydrogen gas 1.0-2.0

[0260] Nitrogen gas 45.0-55.0.

[0261] A mixture of ethylene, nitrogen, and hydrogen is added to a gas-phase fluidized bed and kept in circulation. A chromium-titanium dual-center catalyst and the comonomer 1-hexene are added. The reaction temperature in the reactor is adjusted to 95-100℃ and the reaction pressure is 2000-2200kPa to obtain a basic resin formed by the polymerization of ethylene and the comonomer.

[0262] Table 1 shows the analysis results of polyethylene in Examples 1 to 9 and Comparative Examples 1 to 4.

[0263] Table 1

[0264]

[0265] As shown in Table 1, the chromium-titanium dual-center catalyst used in this invention exhibits high polymerization activity and copolymerization performance. Compared to single-active-center catalysts, the polyethylene melt flow rate prepared by the dual-active-center catalyst in this invention is significantly improved, reaching 0.1-0.25 g / 10 min. Figure 1 The molecular weight distribution of the polymers in Examples 1 to 7 is shown below. Figure 1 It can be seen that polyethylene prepared by chromium-titanium dual-center catalyst has a wider molecular weight distribution, reaching over 40, and exhibits a bimodal distribution.

[0266] This invention can be described in other specific forms that do not depart from the spirit or main features of this invention. The above embodiments of this invention are only illustrative and not limiting. Any minor modifications, equivalent changes and alterations made to the above embodiments based on the essential technology of this invention shall fall within the scope of the technical solution of this invention.

Claims

1. A bimodal polyethylene, wherein, The bimodal polyethylene is obtained by gas-phase polymerization of monomers under the catalysis of a catalyst; the molecular weight distribution of the bimodal polyethylene is above 40. The monomer includes ethylene or ethylene and α-olefin; The catalyst includes a chromium-titanium dual-center catalyst, which includes a support and chromium active components and titanium active components supported on the support. The precursor of the chromium active component includes a chromium dicerocene compound, and the precursor of the titanium active component includes a titanium cerocene compound. In the chromium-titanium dual-center catalyst, the structure of the chromium-dicenocene compound is shown in the following formula: Cp1-Cr-Cp2, Wherein, Cp1 and / or Cp2 include one of cyclopentadienyl, indenyl, and fluorenyl; Cp includes one of cyclopentadienyl, indole, and fluorenyl, and R1, R2, and R3 each include H or a hydrocarbon group having 1-8 carbon atoms.

2. The bimodal polyethylene according to claim 1, wherein, In the chromium-titanium dual-center catalyst, the weight of Cr in the chromium active component is 0.1-5 wt% of the weight of the chromium-titanium dual-center catalyst, and the weight of Ti in the titanium active component is 0.1-5 wt% of the weight of the chromium-titanium dual-center catalyst.

3. The bimodal polyethylene according to claim 1, wherein, The hydrocarbon group having 1-8 carbon atoms includes one or more combinations of methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, isobutyl, pentyl, isopentyl, hexyl, isohexyl, phenyl, benzyl, and benzyl.

4. The bimodal polyethylene according to claim 1, wherein, In the chromium-titanium dual-center catalyst, the support comprises a porous inorganic support.

5. The bimodal polyethylene according to claim 4, wherein, The porous inorganic carrier includes one or more of the following: silicon oxide, aluminum oxide, aluminosilicate, inorganic clay, titanium oxide, zirconium oxide, magnesium oxide, iron oxide, tin oxide, and zinc oxide.

6. The bimodal polyethylene according to claim 5, wherein, The inorganic clay includes montmorillonite, and the silica includes amorphous porous silica gel.

7. The bimodal polyethylene according to claim 4, wherein, The specific surface area of ​​the porous inorganic carrier is 100-1000 m². 2 / g, pore volume 0.3-5.0cm³ 3 / g, with an average pore size of 5-50nm.

8. The bimodal polyethylene according to claim 1, wherein, The chromium-titanium dual-center catalyst further includes an organometallic co-catalyst.

9. The bimodal polyethylene according to claim 8, wherein, The organometallic cocatalyst includes one or more of organoaluminum compounds, organolithium compounds, and organoboron compounds.

10. The bimodal polyethylene according to claim 8, wherein, The molar ratio of Cr in the organometallic co-catalyst and the chromium-titanium dual-center catalyst is 10-2000:

1.

11. The bimodal polyethylene according to claim 8, wherein, The molar ratio of Cr in the organometallic co-catalyst and the chromium-titanium dual-center catalyst is 50-400:

1.

12. The bimodal polyethylene according to claim 9, wherein, The organoaluminum compounds include one or more of the following: trialkylaluminum Al(R)3, alkylaluminoxane MAO, dialkylalkoxyaluminum Al(R)2OR, dialkylaluminum halide Al(R)2X, and ethyl sesquialuminum chloride, wherein X is a halogen and R is an alkyl group.

13. The bimodal polyethylene according to claim 12, wherein, R is an alkyl group having 1-12 carbon atoms.

14. The bimodal polyethylene according to claim 12, wherein, R is one or a combination of two or more of the following: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, and n-dodecyl.

15. The bimodal polyethylene according to claim 12, wherein, The organoaluminum compounds include one or more of triethylaluminum, triisobutylaluminum, and alkylaluminoxanes.

16. The bimodal polyethylene according to claim 1, wherein, The preparation method of the chromium-titanium dual-center catalyst includes calcining the support, then impregnating the calcined support in a precursor of chromium active component, a precursor of titanium active component and an inert solvent, and drying it to obtain the catalyst.

17. The bimodal polyethylene according to claim 16, wherein, The roasting temperature is 300-900℃.

18. The bimodal polyethylene according to claim 16, wherein, The roasting temperature is 300-600℃.

19. The bimodal polyethylene according to claim 16, wherein, The roasting time is 1-10 hours.

20. The bimodal polyethylene according to claim 16, wherein, The roasting time is 2-4 hours.

21. The bimodal polyethylene according to claim 16, wherein, The immersion temperature is 20-180℃; the immersion time is 1-24h.

22. The bimodal polyethylene according to claim 16, wherein, The impregnation temperature is 45-120℃.

23. The bimodal polyethylene according to claim 16, wherein, The soaking time is 4-12 hours.

24. The bimodal polyethylene according to claim 16, wherein, The inert solvent includes one or more of benzene, toluene, and xylene.

25. The bimodal polyethylene according to claim 24, wherein, The inert solvent includes toluene.

26. The bimodal polyethylene according to claim 1, wherein, The reaction temperature for the gas-phase polymerization is 70-120℃, and the reaction pressure is 1900-2200kPa.

27. The bimodal polyethylene according to claim 1, wherein, In the gas-phase polymerization reaction system, the sum of the molar concentrations of water and oxygen is less than 5 ppm.

28. The bimodal polyethylene according to claim 1, wherein, In the reaction gases of gas-phase polymerization, with the total molar number of all gases being 100%, the molar percentage of nitrogen is 20-80%, the molar percentage of ethylene is 20-60%, and the molar ratio of α-olefin to ethylene is 0-0.1:

1.

29. The bimodal polyethylene according to claim 28, wherein, The reactant gas also includes a molecular weight regulator.

30. The bimodal polyethylene according to claim 29, wherein, The molar ratio of the molecular weight regulator to ethylene is less than 0.2:

1.

31. The bimodal polyethylene according to claim 1, wherein, The α-olefin includes one or more of propylene, 1-butene, 1-hexene, and 1-octene.

32. The bimodal polyethylene according to claim 1, wherein, The bimodal polyethylene has a melt flow rate of 0.01-5.0 g / 10 min and a density of 0.940-0.960 g / cm³. 3 .

33. The application of bimodal polyethylene according to any one of claims 1-32 in pipe manufacturing, film manufacturing, and hollow pipe manufacturing.

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