A zirconium-based double-active-center catalyst and its preparation method and application

Abstract

The present invention belongs to the technical field of polyethylene catalysts, and particularly relates to a zirconium-based dual-active-site catalyst, its preparation method, and application. This zirconium-based dual-active-site catalyst uses iron- or zirconium-ion-exchanged clay and ligand raw materials as reactants. A heterogeneous catalyst, in which iron and zirconium ions are successfully fixed between clay layers, is successfully prepared via a one-pot process. These reactants are then mixed to form a zirconium-based dual-active-site catalyst. This zirconium-based dual-active-site catalyst exhibits high catalytic activity and can be used for the production of bimodal polyethylene in a single pot.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyethylene catalysts, and in particular relates to a zirconium-based double-active-center catalyst and a preparation method and application thereof. Background Art

[0002] Polyethylene is the most widely used plastic in the world, accounting for 39% of the most common thermoplastics and 62% of polyolefins. Currently, polyethylene is primarily categorized into low-density polyethylene (LDPE), high-density polyethylene (HDPE), and linear low-density polyethylene (LLDPE). HDPE, due to its strength, rigidity, and ease of processing, is widely used in packaging films, blow-molded containers, and extruded pipes, accounting for over 50% of the polyethylene market. Over the past 20-30 years, bimodal polyethylene (BPE), a high-performance polymer, has rapidly developed and has become the fastest-growing HDPE product. Bimodal polyethylene, with its excellent processing and mechanical properties, holds a significant position in the polyethylene market, attracting significant market attention and generating significant added value.

[0003] Currently, the main methods for producing bimodal polyethylene include melt blending, tandem reactors, and single reactors. The melt blending method uses parallel reactors to produce polymers with higher and lower molecular weights, respectively, and then melt blends the two polymers proportionally to obtain bimodal polyethylene. However, this method makes it difficult to ensure uniform polymer mixing. The tandem reactor method connects two reactors in series and controls the polymerization reaction conditions in each reactor to produce polyethylene with a bimodal molecular weight distribution. The tandem reactor method is the predominant polymerization process currently used, but it is relatively complex and expensive. The single reactor method uses a composite catalyst. One metal center in the bimetallic catalyst has a lower chain transfer rate and better copolymerization performance, allowing the synthesis of high-molecular-weight ethylene / α-olefin copolymers, while the other metal center has a faster chain transfer rate and poorer copolymerization performance, allowing the synthesis of lower-molecular-weight ethylene homopolymers. This allows the synthesis of polyethylene products with a bimodal molecular weight distribution using only a single reactor. Compared with the melt blending method and the series reactor method, the single reactor method has a simple polymerization process, lower process equipment investment and energy consumption, easier operation, good product uniformity, and greater production potential. Therefore, it is becoming a hot topic of research at home and abroad, and is gradually moving towards industrial application. Summary of the Invention

[0004] In response to the above problems, the present invention proposes a zirconium-based dual-active center catalyst and its preparation method and application, which provide more possibilities for the single-reactor synthesis of bimodal polyethylene.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a zirconium-based dual-active-site catalyst, comprising a zirconium-based catalyst and an iron-based catalyst, wherein the mass ratio of the zirconium-based catalyst to the iron-based catalyst is 1:(0.3-1.8).

[0007] In a second aspect, the present invention provides a method for preparing the zirconium-based dual-active-site catalyst, comprising the following steps: S1, preparing zirconium-based clay and iron-based clay by ion exchange method respectively; S2, combining the zirconium-based clay and iron-based clay with corresponding ligands to prepare a zirconium-based catalyst and an iron-based catalyst respectively; S3, uniformly mixing the zirconium-based catalyst and the iron-based catalyst to obtain a zirconium-based dual-active-site catalyst.

[0008] Furthermore, the specific preparation method of the zirconium-based clay in S1 is: slowly adding sodium-based clay to zirconium tetrachloride solution under stirring, stirring and reacting until the sodium ion concentration in the reaction solution no longer increases significantly, filtering, stirring and washing the filter cake with deionized water multiple times, and drying to obtain zirconium-based clay; the dosage ratio of the sodium-based clay to the zirconium tetrachloride solution is (1-1.5) g: (10-25) mL; the zirconium concentration in the zirconium tetrachloride solution is 0.3-0.5 mol / L; the reaction temperature is 50-80°C, the drying temperature is 80-100°C, and the stirring speed is 100-300 r / min.

[0009] Furthermore, the specific preparation method of the iron-based clay in S1 is: slowly adding sodium-based clay to ferric chloride solution under stirring, stirring and reacting until the sodium ion concentration in the reaction solution no longer increases significantly, filtering, stirring and washing the filter cake with deionized water for multiple times, and drying to obtain iron-based clay; the dosage ratio of sodium-based clay to ferric chloride solution is (1-1.5) g: (15-30) mL; the iron concentration in the ferric chloride solution is 0.4-0.8 mol / L, the reaction temperature is 50-80°C, the drying temperature is 80-100°C, and the stirring speed is 100-300 r / min.

[0010] Furthermore, the sodium-based clay in S1 is one of sodium-based montmorillonite, sodium-based saponite, and sodium mica.

[0011] Furthermore, the specific preparation method of the zirconium-based catalyst in S2 is: under a nitrogen atmosphere, zirconium-based clay, acenaphthenequinone, and 8-aminoquinoline are added to a solvent, heated to react for 100-120 hours, filtered, the filter cake is washed, and dried to obtain a zirconium-based catalyst; the amount ratio of the zirconium-based clay, acenaphthenequinone, 8-aminoquinoline and solvent is (1-1.5) g: (2-2.5) mmol: (4-5) mmol: (10-20) mL.

[0012] Furthermore, the specific preparation method of the iron-based catalyst in S2 is: under a nitrogen atmosphere, iron-based clay, acenaphthenequinone, and 8-aminoquinoline are added to a solvent, heated to react for 100-120 hours, filtered, the filter cake is washed, and dried to obtain an iron-based catalyst; the amount ratio of the iron-based clay, 2,6-diacetylpyridine, 2,4,6-trimethylaniline and solvent is (1-1.5) g: (1.8-2.2) mmol: (3.6-4.4) mmol: (10-20) mL.

[0013] Furthermore, the solvents are ethanol or acetonitrile.

[0014] Furthermore, before the S2 operation, both the zirconium-based clay and the iron-based clay are activated at 200-250° C. for 4-8 hours.

[0015] In a third aspect, the present invention provides the use of the zirconium-based dual-active-site catalyst for producing bimodal polyethylene in a single reactor.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention obtains bimodal polyethylene by polymerizing ethylene in a single reactor using a mixed catalyst consisting of two heterogeneous catalysts of zirconium and iron complexes fixed between layered clay mineral layers. The bimodal polyethylene is a mixture of linear low-density polyethylene produced by a zirconium-based catalyst and high-density polyethylene produced by an iron-based catalyst.

[0018] The present invention utilizes a one-pot method, with clay exchanged with iron ions and zirconium ions and ligand raw materials as reactants, to successfully prepare a heterogeneous catalyst that successfully fixes metal ions between clay layers. After mixing them to prepare a zirconium-based dual-active center catalyst, it is used to prepare single-pot bimodal polyethylene, and the catalyst has high activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A preparation roadmap for zirconium-based dual-active-site catalysts;

[0020] Figure 2 is the XRD pattern of the catalyst prepared in Example 3;

[0021] Figure 3 DCS curves of polyethylene prepared by different methods, among which (a) is polyethylene prepared by iron-based catalyst, (b) is polyethylene prepared by zirconium-based catalyst; (c) is polyethylene prepared by zirconium-based dual-active center catalyst; (d) is P-mix-PE; (e) is M-mix-PE. DETAILED DESCRIPTION

[0022] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0023] Example 1

[0024] A zirconium-based dual-active-site catalyst comprises a zirconium-based catalyst and an iron-based catalyst; the mass ratio of the zirconium-based clay catalyst to the iron-based clay catalyst is 1:0.3.

[0025] The method for preparing the zirconium-based dual-active-site catalyst comprises the following steps:

[0026] S1.1. Preparation of zirconium-based clay: Slowly add 1 g of sodium-based clay (sodium montmorillonite) to 10 mL of a 0.3 mol / L zirconium tetrachloride solution while stirring at 100 rpm. Heat to 50°C and continue stirring until the sodium ion concentration in the reaction solution no longer increases significantly. Filter, wash the filter cake with deionized water several times, and dry at 80°C to obtain zirconium-based clay.

[0027] S1.2. Prepare iron-based clay: Slowly add 1 g of sodium-based clay (sodium-based saponite) to 15 mL of a 0.4 mol / L zirconium tetrachloride solution while stirring at 100 rpm. Raise the temperature to 50°C and continue stirring until the sodium ion concentration in the reaction solution no longer increases significantly. Filter, wash the filter cake several times with deionized water, and dry at 80°C to obtain zirconium-based clay.

[0028] S2.1, preparing a zirconium-based catalyst: Under a nitrogen atmosphere, zirconium-based clay was vacuum-calcined at 200°C for 4 hours and then cooled to room temperature; the activated zirconium-based clay, acenaphthenequinone, and 8-aminoquinoline were added to ethanol solvent, reacted at 70°C for 100 hours, filtered, and the filter cake was washed with the reaction solvent, toluene, and hexane in sequence, and dried at 80°C to obtain the zirconium-based catalyst; the amount ratio of the zirconium-based clay, acenaphthenequinone, 8-aminoquinoline, and solvent was 1 g:2 mmol:4 mmol:10 mL;

[0029] S2.2, preparing an iron-based catalyst: under a nitrogen atmosphere, calcining an iron-based clay in vacuum at 200°C for 4 hours, and then cooling to room temperature; adding the activated iron-based clay, 2,6-diacetylpyridine, and 2,4,6-trimethylaniline to ethanol solvent, reacting at 70°C for 100 hours, filtering, washing the filter cake, and drying to obtain an iron-based catalyst; the amount ratio of the iron-based clay, 2,6-diacetylpyridine, 2,4,6-trimethylaniline, and solvent is 1 g:1.8 mmol:3.6 mmol:10 mL;

[0030] S3, preparing a zirconium-based dual-active-center catalyst: grinding and mixing the zirconium-based catalyst and the iron-based catalyst to obtain a zirconium-based dual-active-center catalyst.

[0031] Example 2

[0032] A zirconium-based dual-active-site catalyst comprises a zirconium-based catalyst and an iron-based catalyst; the mass ratio of the zirconium-based clay catalyst to the iron-based clay catalyst is 1:0.8.

[0033] The method for preparing the zirconium-based dual-active-site catalyst comprises the following steps:

[0034] S1.1. Prepare zirconium-based clay: Slowly add 1.1 g of sodium-based clay (sodium-based saponite) to 14 mL of a 0.4 mol / L zirconium tetrachloride solution while stirring at 150 rpm. Raise the temperature to 55°C and continue stirring until the sodium ion concentration in the reaction solution no longer increases significantly. Filter, wash the filter cake several times with deionized water, and dry at 85°C to obtain zirconium-based clay.

[0035] S1.2. Prepare iron-based clay: Slowly add 1.1 g of sodium-based clay (sodium-based saponite) to 18 mL of a 0.5 mol / L zirconium tetrachloride solution while stirring at 150 rpm. Raise the temperature to 55°C and continue stirring until the sodium ion concentration in the reaction solution no longer increases significantly. Filter, wash the filter cake several times with deionized water, and dry at 85°C to obtain zirconium-based clay.

[0036] S2.1, preparing a zirconium-based catalyst: Under a nitrogen atmosphere, zirconium-based clay was vacuum-calcined at 210°C for 5 hours, and then cooled to room temperature; the activated zirconium-based clay, acenaphthenequinone, and 8-aminoquinoline were added to ethanol solvent, reacted at 72°C for 100 hours, filtered, and the filter cake was washed with the reaction solvent, toluene, and hexane, and dried at 85°C to obtain the zirconium-based catalyst; the amount ratio of the zirconium-based clay, acenaphthenequinone, 8-aminoquinoline, and solvent was 1.1 g:2.1 mmol:4.2 mmol:12 mL;

[0037] S2.2, preparing an iron-based catalyst: under a nitrogen atmosphere, calcining an iron-based clay in a vacuum at 210°C for 5 hours, and then cooling to room temperature; adding the activated iron-based clay, 2,6-diacetylpyridine, and 2,4,6-trimethylaniline to ethanol solvent, reacting at 72°C for 100 hours, filtering, washing the filter cake, and drying to obtain an iron-based catalyst; the amount ratio of the iron-based clay, 2,6-diacetylpyridine, 2,4,6-trimethylaniline, and solvent is 1.1 g:1.9 mmol:3.8 mmol:12 mL;

[0038] S3, preparing a zirconium-based dual-active-center catalyst: grinding and mixing the zirconium-based catalyst and the iron-based catalyst to obtain a zirconium-based dual-active-center catalyst.

[0039] Example 3

[0040] A zirconium-based dual-active-site catalyst comprises a zirconium-based catalyst and an iron-based catalyst; the mass ratio of the zirconium-based clay catalyst to the iron-based clay catalyst is 1:1.

[0041] The preparation method of a zirconium-based dual-active center catalyst (such as Figure 1 ), including the following steps:

[0042] S1.1. Preparation of zirconium-based clay: Slowly add 1.3 g of sodium-based clay (sodium mica) to 18 mL of a 0.4 mol / L zirconium tetrachloride solution while stirring at 200 r / min. Raise the temperature to 65°C and continue stirring until the sodium ion concentration in the reaction solution no longer increases significantly. Filter, wash the filter cake several times with deionized water, and dry at 90°C to obtain zirconium-based clay.

[0043] S1.2. Prepare iron-based clay: Slowly add 1.3 g of sodium-based clay (sodium mica) to 22 mL of a 0.6 mol / L zirconium tetrachloride solution while stirring at 200 rpm. Raise the temperature to 65°C and continue stirring until the sodium ion concentration in the reaction solution no longer increases significantly. Filter, wash the filter cake several times with deionized water, and dry at 90°C to obtain zirconium-based clay.

[0044] S2.1, preparation of a zirconium-based catalyst: zirconium-based clay was activated by vacuum calcining at 225°C for 6 hours under a nitrogen atmosphere, and then cooled to room temperature; the activated zirconium-based clay, acenaphthenequinone, and 8-aminoquinoline were added to acetonitrile solvent, reacted at 75°C for 110 hours, filtered, and the filter cake was washed with the reaction solvent, toluene, and hexane in sequence, and dried at 100°C to obtain the zirconium-based catalyst; the amount ratio of the zirconium-based clay, acenaphthenequinone, 8-aminoquinoline, and solvent was 1.2 g:2.3 mmol:4.6 mmol:15 mL;

[0045] S2.2, preparing an iron-based catalyst: under a nitrogen atmosphere, calcining an iron-based clay in a vacuum at 225°C for 6 hours, and then cooling to room temperature; adding the activated iron-based clay, 2,6-diacetylpyridine, and 2,4,6-trimethylaniline to acetonitrile, reacting at 75°C for 110 hours, filtering, washing the filter cake, and drying to obtain an iron-based catalyst; the amount ratio of the iron-based clay, 2,6-diacetylpyridine, 2,4,6-trimethylaniline, and solvent is 1.2 g:2 mmol:4 mmol:15 mL;

[0046] S3, preparing a zirconium-based dual-active-center catalyst: grinding and mixing the zirconium-based catalyst and the iron-based catalyst to obtain a zirconium-based dual-active-center catalyst.

[0047] X-ray fluorescence spectroscopy was performed on the prepared iron- and zirconium-based clays, and the exchange capacity of iron and zirconium ions was calculated. The results showed that the exchange capacity of zirconium ions was 0.52 mmol / g and the exchange capacity of iron ions was 0.48 mmol / g. This indicates that zirconium and iron ions were successfully exchanged between the sodium-based clay layers, achieving the replacement of interlayer cations and providing a foundation for the subsequent preparation of zirconium- and iron-based catalysts.

[0048] Figure 2 The XRD pattern of the prepared catalyst is shown in Figure 2. Figure 2 It can be seen that compared with the iron-based clay and zirconium-based clay without ligand insertion, the spectra of the iron-based catalyst and the zirconium-based catalyst show a low-angle side shift and increased peak intensity. Calculated from the diffraction angle of the bottom reflection peak, the bottom surface spacing of the zirconium-based catalyst is 1.40nm, and the bottom surface spacing of the iron-based catalyst is 1.45nm. This is because the iron-based and zirconium-based ligands are inserted between the clay layers, which expands the interlayer spacing and causes the bottom surface reflection peak to shift to the low-angle side. The stacking regularity of the layers is improved, which increases the peak intensity, indicating that the target catalyst has been successfully prepared.

[0049] The specific surface areas of sodium-based clay, prepared iron-based clay and zirconium-based clay were measured. The results showed that the specific surface area of sodium-based clay was 1.6m 2 / g, the specific surface area of sodium-based clay of zirconium-based clay is 3.5m 2 / g, the specific surface area of sodium-based clay of zirconium-based clay is 2.9m 2 / g. Although the specific surface area increased after cation exchange, the increase was small. This indicates that the cation exchange process did not cause significant damage to the crystal structure of the sodium-based clay.

[0050] Example 4

[0051] A zirconium-based dual-active-site catalyst comprises a zirconium-based catalyst and an iron-based catalyst; the mass ratio of the zirconium-based clay catalyst to the iron-based clay catalyst is 1:1.5.

[0052] The method for preparing the zirconium-based dual-active-site catalyst comprises the following steps:

[0053] S1.1. Preparation of zirconium-based clay: Slowly add 1.4 g of sodium-based clay (sodium-based saponite) to 22 mL of a 0.5 mol / L zirconium tetrachloride solution while stirring at 250 rpm. Heat to 70°C and continue stirring until the sodium ion concentration in the reaction solution no longer increases significantly. Filter, wash the filter cake with deionized water several times, and dry at 95°C to obtain zirconium-based clay.

[0054] S1.2. Prepare iron-based clay: Slowly add 1.4 g of sodium-based clay (sodium-based saponite) to 26 mL of a 0.7 mol / L zirconium tetrachloride solution while stirring at 250 rpm. Raise the temperature to 70°C and continue stirring until the sodium ion concentration in the reaction solution no longer increases significantly. Filter, wash the filter cake several times with deionized water, and dry at 95°C to obtain zirconium-based clay.

[0055] S2.1, preparation of a zirconium-based catalyst: zirconium-based clay was activated by vacuum calcining at 240°C for 7 hours under a nitrogen atmosphere, and then cooled to room temperature; the activated zirconium-based clay, acenaphthenequinone, and 8-aminoquinoline were added to acetonitrile, reacted at 75°C for 115 hours, filtered, and the filter cake was washed sequentially with the reaction solvent, toluene, and hexane, and dried at 110°C to obtain the zirconium-based catalyst; the amount ratio of the zirconium-based clay, acenaphthenequinone, 8-aminoquinoline, and solvent was 1.3 g:2.4 mmol:4.8 mmol:18 mL;

[0056] S2.2, preparing an iron-based catalyst: under a nitrogen atmosphere, calcining an iron-based clay in a vacuum at 240°C for 7 hours, and then cooling to room temperature; adding the activated iron-based clay, 2,6-diacetylpyridine, and 2,4,6-trimethylaniline to acetonitrile, reacting at 75°C for 115 hours, filtering, washing the filter cake, and drying to obtain an iron-based catalyst; the amount ratio of the iron-based clay, 2,6-diacetylpyridine, 2,4,6-trimethylaniline, and solvent is 1.3 g:2.1 mmol:4.2 mmmol:18 mL;

[0057] S3, preparing a zirconium-based dual-active-center catalyst: grinding and mixing the zirconium-based catalyst and the iron-based catalyst to obtain a zirconium-based dual-active-center catalyst.

[0058] Example 5

[0059] A zirconium-based dual-active-site catalyst comprises a zirconium-based catalyst and an iron-based catalyst; the mass ratio of the zirconium-based clay catalyst to the iron-based clay catalyst is 1:1.8.

[0060] The method for preparing the zirconium-based dual-active-site catalyst comprises the following steps:

[0061] S1.1. Preparation of zirconium-based clay: Slowly add 1.5 g of sodium-based clay (sodium montmorillonite) to 25 mL of a 0.5 mol / L zirconium tetrachloride solution while stirring at 300 r / min. Raise the temperature to 80°C and continue stirring until the sodium ion concentration in the reaction solution no longer increases significantly. Filter, wash the filter cake several times with deionized water, and dry at 100°C to obtain zirconium-based clay.

[0062] S1.2. Preparation of iron-based clay: Slowly add 1.5 g of sodium-based clay (sodium montmorillonite) to 30 mL of a 0.8 mol / L zirconium tetrachloride solution while stirring at 300 rpm. Raise the temperature to 80°C and continue stirring until the sodium ion concentration in the reaction solution no longer increases significantly. Filter, wash the filter cake several times with deionized water, and dry at 100°C to obtain zirconium-based clay.

[0063] S2.1, preparing a zirconium-based catalyst: Under a nitrogen atmosphere, zirconium-based clay was vacuum-calcined at 250°C for 8 hours, and then cooled to room temperature; the activated zirconium-based clay, acenaphthenequinone, and 8-aminoquinoline were added to ethanol solvent, reacted at 78°C for 120 hours, filtered, and the filter cake was washed with the reaction solvent, toluene, and hexane in sequence, and dried at 120°C to obtain the zirconium-based catalyst; the amount ratio of the zirconium-based clay, acenaphthenequinone, 8-aminoquinoline, and solvent was 1.5 g:2.5 mmol:5 mmol:20 mL;

[0064] S2.2, preparing an iron-based catalyst: under a nitrogen atmosphere, calcining an iron-based clay in a vacuum at 250°C for 8 hours, and then cooling to room temperature; adding the activated iron-based clay, 2,6-diacetylpyridine, and 2,4,6-trimethylaniline to ethanol solvent, reacting at 78°C for 120 hours, filtering, washing the filter cake, and drying to obtain an iron-based catalyst; the amount ratio of the iron-based clay, 2,6-diacetylpyridine, 2,4,6-trimethylaniline, and solvent is 1.5 g:2.2 mmol:4.4 mmol:20 mL;

[0065] S3, preparing a zirconium-based dual-active-center catalyst: grinding and mixing the zirconium-based catalyst and the iron-based catalyst to obtain a zirconium-based dual-active-center catalyst.

[0066] Polyethylene preparation:

[0067] Seven groups of experiments were set up, and the catalysts were: 1 mg of the zirconium-based dual-active center catalyst prepared in Examples 1 to 5, 1 mg of the iron-based catalyst prepared in Example 3, and 1 mg of the zirconium-based catalyst prepared in Example 3. The catalysts were then added to 2 mL of toluene to prepare a toluene suspension.

[0068] The specific preparation process of polyethylene is as follows: in a 120mL autoclave, nitrogen is first introduced to completely expel the air from the autoclave, 50mL of n-hexane, 1mL of a 0.2mol / L triethylaluminum activator in toluene, and 2mL of a toluene suspension containing the catalyst are added. The gas in the system is then replaced with ethylene, the ethylene pressure is adjusted to 0.8MPa, the temperature is raised to 55°C, and the polymerization reaction is carried out for 60min. After the reaction is completed, the ethylene is cut off to stop the reaction. The mixture in the autoclave is then poured into 10% hydrochloric acid-ethanol to precipitate the product. The polymer is filtered and washed three times alternately with water and ethanol, and then vacuum dried at 60°C to constant weight to obtain a solid polymer, namely polyethylene. The prepared polyethylene was tested and analyzed, and the results are shown in Table 1.

[0069] Table 1. Polyethylene test results

[0070]

[0071] As can be seen from Table 1, compared with single-site zirconium-based catalysts and iron-based catalysts, the zirconium-based dual-active site catalyst used in the present invention has higher polymerization activity, the molecular weight distribution of the prepared polyethylene is wider, and the melt flow rate is also significantly improved.

[0072] The polyethylenes obtained by the iron-based catalyst and the zirconium-based catalyst were physically mixed and melt-mixed to obtain P-mix-PE and M-mix-PE, respectively. Then, the polyethylene prepared in Example 3, the polyethylene prepared by the zirconium-based catalyst, the polyethylene prepared by the iron-based catalyst, P-mix-PE, and M-mix-PE were subjected to a differential scanning calorimeter to obtain DCS curves. The results are shown in FIG. Figure 3 shown.

[0073] from Figure 3As can be seen, polyethylene prepared using a zirconium-based catalyst alone exhibits a melting peak at 114°C due to the formation of methyl branches caused by "chain walking," along with a shoulder peak around 107°C. Polyethylene prepared using an iron-based catalyst exhibits a high-density polyethylene melting peak at 135°C, indicating that the two catalysts produce polyethylene with different structures and melting points. The DSC curve of polyethylene prepared using a zirconium-based dual-site catalyst exhibits melting point peaks corresponding to the PE obtained from the two individual catalysts, as well as a new peak at 125°C. Comparing the DSC curves of P-mix-PE and M-mix-PE reveals that the physically mixed polyethylene exhibits only the melting point peaks of each individual polyethylene, while the melted mixed polyethylene exhibits a new peak at 126°C, in addition to the low-melting-point peak. This shows that when the polyethylene prepared by the zirconium-based dual-active center catalyst is melted for the first time, the two partially melted polyethylenes are mixed at the microscopic level. After cooling, polyethylene crystals with different physical properties from the single polyethylene crystals are formed, resulting in the appearance of a new peak at 125°C, indicating that the polyethylene prepared has unique microstructure and thermal properties. Combined with the molecular weight and molecular weight distribution, the prepared polyethylene is bimodal polyethylene.

[0074] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A zirconium-based dual-active-site catalyst, characterized in that: The invention comprises a zirconium-based catalyst and an iron-based catalyst, wherein the mass ratio of the zirconium-based catalyst to the iron-based catalyst is 1:(0.3-1.8); the zirconium-based dual-active-center catalyst is prepared by the following steps: S1, using sodium-based clay and zirconium tetrachloride to prepare zirconium-based clay by an ion exchange method, and using sodium-based clay and ferric chloride to prepare iron-based clay by an ion exchange method; the sodium-based clay is one of sodium-based montmorillonite, sodium-based saponite, and sodium mica; S2, combining the zirconium-based clay and the iron-based clay with corresponding ligands to prepare the zirconium-based catalyst and the iron-based catalyst respectively; S3, uniformly mixing the zirconium-based catalyst and the iron-based catalyst to obtain the zirconium-based dual-active-center catalyst; the corresponding ligand of the zirconium-based clay is ; The corresponding ligands of iron-based clay are .

2. A method for preparing a zirconium-based dual-active-site catalyst according to claim 1, characterized in that: The specific preparation method of the zirconium-based clay in S1 is as follows: slowly adding sodium-based clay to a zirconium tetrachloride solution under stirring, stirring and reacting until the sodium ion concentration in the reaction solution no longer increases significantly, filtering, washing the filter cake with deionized water with stirring multiple times, and drying to obtain the zirconium-based clay; the dosage ratio of the sodium-based clay to the zirconium tetrachloride solution is (1-1.5) g: (10-25) mL; the zirconium concentration in the zirconium tetrachloride solution is 0.3-0.5 mol / L; the reaction temperature is 50-80°C, the drying temperature is 80-100°C, and the stirring speed is 100-300 r / min.

3. The method for preparing a zirconium-based dual-active-site catalyst according to claim 2, characterized in that: The specific preparation method of the iron-based clay in S1 is as follows: slowly adding sodium-based clay to a ferric chloride solution under stirring, stirring and reacting until the sodium ion concentration in the reaction solution no longer increases significantly, filtering, washing the filter cake with deionized water by stirring multiple times, and drying to obtain the iron-based clay; the dosage ratio of sodium-based clay to ferric chloride solution is (1-1.5) g: (15-30) mL; the iron concentration in the ferric chloride solution is 0.4-0.8 mol / L, the reaction temperature is 50-80°C, the drying temperature is 80-100°C, and the stirring speed is 100-300 r / min.

4. The method for preparing a zirconium-based dual-active-site catalyst according to claim 3, characterized in that: The specific preparation method of the zirconium-based catalyst in S2 is: under a nitrogen atmosphere, zirconium-based clay, acenaphthenequinone, and 8-aminoquinoline are added to a solvent, heated to react for 100-120 hours, filtered, the filter cake is washed, and dried to obtain the zirconium-based catalyst; the dosage ratio of the zirconium-based clay, acenaphthenequinone, 8-aminoquinoline, and solvent is (1-1.5) g: (2-2.5) mmol: (4-5) mmol: (10-20) mL.

5. The method for preparing a zirconium-based dual-active-site catalyst according to claim 4, characterized in that: The specific preparation method of the iron-based catalyst in S2 is: under a nitrogen atmosphere, iron-based clay, 2,6-diacetylpyridine, and 2,4,6-trimethylaniline are added to a solvent, heated to react for 100-120 hours, filtered, the filter cake is washed, and dried to obtain the iron-based catalyst; the amount ratio of the iron-based clay, 2,6-diacetylpyridine, 2,4,6-trimethylaniline and solvent is (1-1.5) g: (1.8-2.2) mmol: (3.6-4.4) mmol: (10-20) mL.

6. The method for preparing a zirconium-based dual-active-site catalyst according to claim 5, characterized in that: The solvents are all ethanol or acetonitrile.

7. The method for preparing a zirconium-based dual-active-site catalyst according to claim 6, characterized in that: Before the S2 operation, both the zirconium-based clay and the iron-based clay were activated at 200-250° C. for 4-8 h.

8. Use of the zirconium-based dual-active-site catalyst according to claim 1, characterized in that: Used for single-reactor production of bimodal polyethylene.

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