High-activity chromium polyethylene catalyst and preparation method thereof

Abstract

The invention relates to a high-activity chromium polyethylene catalyst and a preparation method thereof, and the high-activity chromium polyethylene catalyst comprises an inorganic carrier modified by alkyl aluminum and / or alkoxy aluminum, and a chromium element and a titanium element which are sequentially loaded on the modified inorganic carrier, the preparation method comprises the following steps: (1) inorganic carrier modification: modifying an inorganic carrier by using alkyl aluminum and / or alkoxy aluminum; (2) chromium loading; (3) titanium loading; and (4) high-temperature roasting: further roasting the modified inorganic carrier powder simultaneously loaded with the chromium element and the titanium element in a dry non-reducing gas environment at the roasting temperature of 300-950 DEG C for 0.5-48 hours to obtain the chromium polyethylene catalyst. Compared with the prior art, the activity of the prepared chromium-based catalyst is improved by more than 10 times, the production cost of a chromium-based polyethylene product is greatly reduced, the impurity content of the product is reduced, and the quality of the product is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of polyethylene catalysts, and particularly relates to a highly active chromium-based polyethylene catalyst and a preparation method thereof. Background Art

[0002] Chromium-based polyethylene catalysts are one of the most important catalysts in the industrial production of polyethylene, and among them, Phillips catalyst is the most representative. This type of catalyst usually uses hexavalent chromium as the active component, which is supported on carriers such as porous silica gel or modified silica gel, and has significant advantages such as high catalytic activity, simple process, and no need for cocatalysts. J. P Hogan and R. L. Bank reported a silica-supported chromium oxide catalyst in the patent US2825721, which is the first-generation Phillips catalyst well-known to people later. Some patents such as US4294724, US4295997, US4528338, US5401820, US6388017, etc. have carried out modification research on such supported chromium oxide catalysts and developed Phillips catalysts.

[0003] Chromium-based catalysts can produce polyethylene products with relatively high molecular weight and wide molecular weight distribution, which makes the final products have excellent mechanical properties and processing properties, and are widely used in high-performance product fields such as pipes and hollow products. However, this type of catalyst also has some limitations, such as relatively low utilization rate of the active component, difficult molecular weight regulation, limited copolymer monomer adaptability, etc. In addition, due to the presence of hexavalent chromium, special attention needs to be paid to environmental protection requirements during use. Low-activity catalysts will result in a large amount of catalyst residues in the raw materials, deteriorating the properties of the raw materials and limiting the application fields.

[0004] In recent years, the research on chromium-based catalysts has mainly focused on aspects such as carrier modification technology, development of new cocatalysts, optimization of active center structure, and product performance regulation. By means of developing new carrier materials, improving the structure of the active component, and increasing the catalytic efficiency, researchers are committed to developing a new generation of more efficient and more environmentally friendly chromium-based catalysts to meet the growing market demand. These research progress not only promote the improvement of catalyst performance, but also provide a new direction for the sustainable development of the polyethylene industry.

[0005] Currently, aiming at the problem of relatively low utilization rate of the active component, Chinese patent CN112409514A uses ultrasonic technology in the catalyst loading stage to reduce carrier fragmentation and increase loading uniformity to improve activity. Chinese patent CN103159875A improves the polymerization activity of the catalyst through a new catalyst preparation process. Chinese patent CN108976322A modifies by introducing vanadium and chromium simultaneously on a porous inorganic carrier to improve the activity of the catalyst.

[0006] However, the above methods can only increase the catalyst activity to within 500 gPE / gCAT / h. Summary of the Invention

[0007] The object of the present invention is to provide a highly active chromium-based polyethylene catalyst and a preparation method thereof to improve the catalyst activity.

[0008] The object of the present invention can be achieved by the following technical solutions: A highly active chromium-based polyethylene catalyst includes an inorganic carrier modified by alkylaluminum and / or alkoxyaluminum, and chromium and titanium elements sequentially loaded on the modified inorganic carrier.

[0009] Preferably, the mass ratio of the alkylaluminum and / or alkoxyaluminum to the inorganic carrier is (0.1~10):100.

[0010] Preferably, the content of the chromium element accounts for 0.1~5.0% of the mass of the modified inorganic carrier.

[0011] More preferably, the content of the chromium element accounts for 3~5% of the mass of the modified inorganic carrier.

[0012] Preferably, the content of the titanium element accounts for 0.1~10% of the mass of the modified inorganic carrier loaded with the chromium element.

[0013] Preferably, the inorganic carrier is selected from at least one of silica, aluminum oxide, silica gel, aluminum phosphate, titanium dioxide, zirconium oxide, magnesium oxide, calcium oxide, and inorganic clay.

[0014] More preferably, the inorganic clay includes kaolin and montmorillonite.

[0015] Preferably, the average particle size of the inorganic carrier is 0.1 micrometer to 100 micrometers, the pore volume is 0.2 cm 3 / g to 10.0 cm 3 / g, and the specific surface area is 15 m 2 / g to 1000 m 2 / g.

[0016] Preferably, the alkylaluminum and / or alkoxyaluminum is selected from at least one of triisobutylaluminum, tri-n-hexylaluminum, triisopropylaluminum, methyldiethylaluminum, trimethylaluminum, diethylaluminum ethoxide, diethylaluminum methoxide, dimethylaluminum ethoxide, diisopropylaluminum ethoxide, diethylaluminum propoxide, diisobutylaluminum ethoxide, and methylethylaluminum ethoxide.

[0017] A preparation method of the above highly active chromium-based polyethylene catalyst includes the following steps: (1)Inorganic support modification: Modify the inorganic support with alkylaluminum and / or alkoxyaluminum to obtain the modified inorganic support; (2)Chromium loading: Prepare a solution of chromium salt with a solvent, mix it with the above-mentioned modified inorganic support, heat and let stand after thorough mixing until dry to obtain the modified inorganic support powder loaded with chromium element; (3)Titanium loading: Further mix the modified inorganic support powder loaded with chromium element with an organotitanium compound solution and a cocatalyst, let stand after thorough mixing, and then raise the temperature until dry to obtain the modified inorganic support powder loaded with both chromium element and titanium element; (4)High-temperature calcination: Further calcine the modified inorganic support powder loaded with both chromium element and titanium element in a dry non-reducing gas environment at a calcination temperature of 300-950 °C and a calcination time of 0.5-48 hours to obtain the chromium-based polyethylene catalyst.

[0018] Preferably, in step (1), the impregnation method is used for blending modification.

[0019] Preferably, in step (2), heat and let stand at 50 °C to 110 °C.

[0020] Preferably, the chromium salt in step (2) is one or more of chromium acetate, dichromate, chromate, chromium nitrate or chromium oxide.

[0021] Preferably, the content of chromium element in the chromium salt in step (2) accounts for 0.1-5.0% of the mass of the modified inorganic support.

[0022] Preferably, the solvent in step (2) is water, an alcohol solvent or a ketone solvent.

[0023] More preferably, the alcohol solvent is methanol, ethanol or propanol.

[0024] More preferably, the ketone solvent is acetone or butanone.

[0025] Preferably, after thorough mixing in step (3), let stand at 0-50 °C for 0-4 hours, and then raise the temperature to 60-80 °C until dry.

[0026] Preferably, the organotitanium compound in step (3) is at least one of tetra-isopropyl titanate, tetra-ethyl titanate, tetra-butyl titanate, tetra-isooctyl titanate or n-butyl titanate.

[0027] Preferably, the cocatalyst in step (3) is at least one of triethylaluminum, triisobutylaluminum or diethylaluminum chloride.

[0028] Preferably, the solvent of the organotitanium compound solution in step (3) is water, an alcohol solvent or a ketone solvent.

[0029] More preferably, the alcohol solvent is methanol, ethanol or propanol.

[0030] More preferably, the ketone solvent is acetone or butanone.

[0031] Preferably, the content of titanium in the organic titanium compound in step (3) accounts for 0.1-10% of the mass of the modified inorganic carrier loaded with chromium.

[0032] Preferably, in step (3), the mass ratio of the co-catalyst to the modified inorganic carrier loaded with chromium element is (0.1-5):100.

[0033] The present invention has found through research that the catalyst obtained by successively loading a chromium-containing compound and a titanium-containing compound on an inorganic carrier modified by alkyl aluminum and / or alkoxy aluminum and then calcining the catalyst at high temperature can produce a higher activity in the polymerization reaction under the synergistic effect of titanium, chromium and aluminum, and can increase the polymerization activity to more than 3000 gPE / gCAT / h.

[0034] Furthermore, the catalyst using the specific treatment method of the present invention can greatly stimulate the reaction activity of the loaded chromium under the synergistic effect of titanium, chromium and aluminum in a specific ratio, so that the polymerization reaction produces extremely high activity, and the polymerization activity can be increased to 8000~20000 gPE / gCAT / h.

[0035] At the same time, the present invention also found that when the effective concentration of chromium element loading reaches more than 3wt%, the polymerization activity is greatly improved. In order to make the chromium element effectively loaded at a high concentration and play a good role as an active center point, it is necessary to first use alkyl aluminum and / or alkoxy aluminum to treat the carrier, and then load the titanium compound from outside the system again after loading the chromium element. If it is only dependent on the carrier to carry aluminum, titanium and other elements, or there are differences in the carrier treatment steps, or other means are used to introduce aluminum, titanium and other elements, even if a large amount of chromium salts are loaded, it cannot effectively play a good role as an active center point, and it cannot improve the polymerization activity.

[0036] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention provides a highly active chromium-based polyethylene and a preparation method thereof, which greatly improves the polymerization activity of the chromium-based polyethylene, reduces production costs, and improves product cleanliness; 2. The present invention provides a highly active chromium catalyst, which can reduce the polymerization cost of chromium polyethylene resin and reduce the content of impurities introduced by the catalyst in the resin product; 3. The activity of the chromium-based catalyst prepared by the present invention is increased by more than 10 times, which greatly reduces the production cost of chromium-based polyethylene products, reduces the impurity content of the products, and improves the product quality; 4. Compared with other current methods for preparing chromium-based polyethylene catalysts, the catalyst preparation method of the present invention is simple and has industrial potential. The activity of the prepared catalyst is greatly improved and has good market prospects. 5. The present invention can greatly stimulate the reaction activity of the loaded chromium through the synergistic effect of titanium, chromium and aluminum, so that the polymerization reaction produces extremely high activity, and the polymerization activity can be improved; 6. The present invention adopts the steps of inorganic carrier alkyl aluminum and / or alkoxy aluminum modification, chromium loading, titanium loading and high temperature calcination to effectively load the chromium element at a high concentration and play a good role as an active center point, thereby improving the polymerization activity. DETAILED DESCRIPTION

[0037] The embodiments of the present invention are described in detail below. The following embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0038] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0039] A method for preparing a chromium-based high-activity polyethylene catalyst comprises the following steps: (1) Support modification: using alkyl aluminum and / or alkoxy aluminum to modify the inorganic support; (2) Chromium loading: using a solvent to prepare a chromium salt solution, mixing it with the modified carrier, and after fully mixing, heating and standing at 50°C to 110°C until dry to obtain a chromium-loaded modified carrier powder; (3) Titanium loading: The modified carrier loaded with chromium is further mixed with the organic titanium compound solution and the co-catalyst, and after being fully mixed, the mixture is allowed to stand at 0 to 50° C. for 0 to 4 hours, and then the mixture is heated to 60 to 80° C. until it is dried, thereby obtaining a modified carrier powder loaded with chromium and titanium at the same time; (4) High-temperature calcination: The modified dry carrier is further calcined in a dry non-reducing gas environment at a calcination temperature of 300 to 950° C. for a calcination time of 0.5 to 48 hours to obtain a chromium-based polyethylene catalyst.

[0040] The following describes it in detail with reference to specific embodiments.

[0041] Catalyst evaluation method: The ethylene pressurized polymerization reaction device is a 2L stainless steel reactor equipped with water circulation temperature control. Nitrogen is charged, and 1L of n-hexane and the catalyst are added under a nitrogen atmosphere. Then, nitrogen is replaced with ethylene three times. The ethylene inlet valve is adjusted to keep the ethylene pressure constant at 1 Mpa, and the polymerization reaction is carried out at 90 °C. After the reaction is completed, it is dried to a constant weight and weighed to obtain the polyethylene product, and the catalyst activity is calculated.

[0042] The catalyst activity is represented by the weight of polyethylene produced per gram of catalyst per hour (gPE / gCAT / h).

[0043] In the examples or comparative examples, the silica gels used are silica gel 3020 and 955 produced by GRACE Company, and the specific properties are as follows: Silica gel 3020: Particle size: 20 - 45 μm, specific surface area: 300 m² / g, pore volume: 1.6 mL / g, pore diameter: 15 - 20 nm.

[0044] Silica gel 955: Particle size: 35 - 70 μm, specific surface area: 280 - 300 m² / g, pore volume: 1.65 mL / g.

[0045] The specific properties of K10 montmorillonite and K30 montmorillonite used in the examples are as follows: K10 montmorillonite: Particle size: <2 μm, specific surface area: 220 - 270 m² / g, pore volume: 0.3 - 0.4 mL / g.

[0046] K30 montmorillonite: Particle size: <2 μm, specific surface area: 200 - 240 m² / g, pore volume: 0.25 - 0.35 mL / g.

[0047] The specific properties of the clay inorganic carriers in the examples are as follows: Kaolin: Particle size: 0.1 - 4 μm, specific surface area: 15 - 30 m² / g, pore volume: 0.2 - 0.3 mL / g.

[0048] Example 1 Triisobutylaluminum and silica gel 3020 are blended and modified at a mass ratio of 0.1:100. Ethanol and potassium dichromate are mixed at a mass ratio of 5:1 and then blended with the modified carrier. The chromium content in potassium dichromate is 0.1% of the mass of the modified carrier. After the above mixture is heated and allowed to stand at 50 °C for 10 hours, the mixture presents a dry powder state.

[0049] Mix the above powder with titanium tetraisopropoxide, ethanol, and triethylaluminum. The content of titanium in titanium tetraisopropoxide accounts for 0.1% of the powder mass, triethylaluminum accounts for 1% of the powder mass, and the powder mass accounts for 10% of the solvent. Let the above mixture stand at 0 °C for 4 hours, then heat it to 80 °C and keep it for 1 hour, presenting a dry powder state.

[0050] Calcine the above dry powder at 300 °C for 48 hours to obtain a chromium-based polyethylene catalyst. After polymerization evaluation, the polymerization activity of this catalyst can reach 3000 gPE / gCAT / h.

[0051] Example 2 Blend and modify tri-n-hexylaluminum and silica gel 955 at a mass ratio of 1:100. Mix ethanol and potassium dichromate at a mass ratio of 5:1 and then blend with the modified carrier. The content of chromium in potassium dichromate is 1% of the mass of the modified carrier. Let the above mixture heat and stand at 60 °C for 6 hours, and the mixture presents a dry powder state.

[0052] Mix the above powder with tetra-isooctyl titanate, propanol, and triethylaluminum. The content of titanium in tetra-isopropyl titanate accounts for 4% of the powder mass, triethylaluminum accounts for 1% of the powder mass, and the powder mass accounts for 10% of the solvent. Let the above mixture stand at 30 °C for 2 hours, then heat it to 80 °C and keep it for 1 hour, presenting a dry powder state.

[0053] Calcine the above dry powder at 500 °C for 8 hours to obtain a chromium-based polyethylene catalyst. After polymerization evaluation, the polymerization activity of this catalyst can reach 3500 gPE / gCAT / h.

[0054] Example 3 Blend and modify ethoxydiethylaluminum and K10 montmorillonite at a mass ratio of 10:100. Mix ethanol and potassium dichromate at a mass ratio of 5:1 and then blend with the modified carrier. The content of chromium in potassium dichromate is 5% of the mass of the modified carrier. Let the above mixture heat and stand at 110 °C for 1 hour, and the mixture presents a dry powder state.

[0055] Mix the above powder with tetrabutyltitanium, acetone, and triethylaluminum. The content of titanium in tetra-isopropyl titanate accounts for 1% of the powder mass, triethylaluminum accounts for 2% of the powder mass, and the powder mass accounts for 10% of the solvent. Let the above mixture stand at 10 °C for 2 hours, then heat it to 80 °C and keep it for 1 hour, presenting a dry powder state.

[0056] Calcine the above dry powder at 400 °C for 6 hours to obtain a chromium-based polyethylene catalyst. After polymerization evaluation, the polymerization activity of this catalyst can reach 5500 gPE / gCAT / h.

[0057] Example 4 Ethoxydimethylaluminum and K30 montmorillonite were blended and modified at a mass ratio of 3:100. Ethanol and chromium acetate were mixed at a mass ratio of 3:1 and then blended with the modified carrier. The chromium content in potassium dichromate was 2% of the mass of the modified carrier. After heating and standing the above mixture at 100 °C for 2 hours, the mixture presented a dry powder state.

[0058] The above powder was blended with tetrabutyltitanium, methyl ethyl ketone, and triethylaluminum. The titanium content in tetra-isopropyltitanium accounted for 1% of the powder mass, triethylaluminum accounted for 2% of the powder mass, and the powder mass accounted for 10% of the solvent. The above blend was allowed to stand at 20 °C for 3 hours, then heated to 80 °C and held for 1 hour, presenting a dry powder state.

[0059] The above dry powder was calcined at 950 °C for 6 hours to obtain a chromium-based polyethylene catalyst. After polymerization evaluation, the polymerization activity of this catalyst could reach 4000 gPE / gCAT / h.

[0060] Example 5 A mixture of ethoxydiisobutylaluminum and ethoxymethylethylaluminum was blended and modified with kaolin. The mass ratio of ethoxydiisobutylaluminum to ethoxymethylethylaluminum was 1:1, and the blend accounted for 5% of the kaolin mass. Acetone and chromium nitrate were mixed at a mass ratio of 3:1 and then blended with the modified carrier. The chromium content in potassium dichromate was 2% of the mass of the modified carrier. After heating and standing the above mixture at 100 °C for 2 hours, the mixture presented a dry powder state.

[0061] Tetra-isooctyl titanate and n-butyl titanate were configured into a blend at a mass ratio of 1:1. The above powder was blended with the titanium-containing blend, methyl ethyl ketone, and triethylaluminum. The titanium content in the titanium-containing blend accounted for 2% of the powder mass, triethylaluminum accounted for 5% of the powder mass, and the powder mass accounted for 10% of the solvent. The above blend was allowed to stand at 20 °C for 1 hour, then heated to 80 °C and held for 2 hours, presenting a dry powder state.

[0062] The above dry powder was calcined at 500 °C for 5 hours to obtain a chromium-based polyethylene catalyst. After polymerization evaluation, the polymerization activity of this catalyst could reach 5000 gPE / gCAT / h.

[0063] Comparative Example 1 The same carrier modification, chromium loading, and calcination methods as in Example 1 were used, but titanium loading was not carried out. The other preparation conditions were the same as in Example 1 to obtain a catalyst. The activity obtained from the evaluation of the resulting catalyst was 350 gPE / gCAT / h.

[0064] Comparative Example 2 In Example 1, titanium loading was carried out first on the basis of carrier modification, then chromium loading was carried out, and then high-temperature calcination was carried out. The other preparation conditions were the same as those in Example 1. The obtained catalyst had no activity after polymerization evaluation.

[0065] Comparative Example 3 The carrier was not modified with alkylaluminum. The other preparation conditions were the same as those in Example 1. The obtained catalyst had an activity of 200 gPE / gCAT / h after polymerization evaluation.

[0066] Comparative Example 4 In Example 1, the carrier was not modified with alkylaluminum first. After mixing ethanol and potassium dichromate in a mass ratio of 5:1 and blending with the modified carrier, then triisobutylaluminum and the blend were blended and modified in a mass ratio of 0.1:600. The other preparation conditions were the same as those in Example 1. The obtained catalyst had no activity after polymerization evaluation.

[0067] Table 1 Key parameters and performance data of each example and comparative example

[0068] It can be found from the above table that modifying the carrier with alkylaluminum and alkoxyaluminum (such as triisobutylaluminum, diethylaluminum ethoxide, etc.) can significantly improve the catalyst activity. The selection and loading sequence of chromium source and titanium source have important effects on the catalyst activity. Not carrying out titanium loading (Comparative Example 1) or not modifying the carrier (Comparative Example 3) will lead to a significant decrease in catalyst activity. Carrying out titanium loading first and then chromium loading (Comparative Example 2) will lead to complete inactivation of the catalyst.

[0069] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. Those skilled in the art can obviously make various modifications to these embodiments easily and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A highly active chromium-based polyethylene catalyst, characterized in that, It includes an inorganic support modified by alkylaluminum and / or alkoxyaluminum, and chromium element and titanium element sequentially supported on the modified inorganic support.

2. The highly active chromium-based polyethylene catalyst according to claim 1, characterized in that, The mass ratio of the alkylaluminum and / or alkoxyaluminum to the inorganic support is (0.1~10):

100. The content of the chromium element accounts for 0.1~5.0% of the mass of the modified inorganic support, and the content of the titanium element accounts for 0.1~10% of the mass of the modified inorganic support loaded with the chromium element.

3. The highly active chromium-based polyethylene catalyst according to claim 1, wherein The inorganic support is selected from at least one of silica, alumina, silica gel, aluminum phosphate, titanium dioxide, zirconia, magnesia, calcium oxide, and inorganic clay.

4. The highly active chromium-based polyethylene catalyst according to claim 1, wherein, The average particle size of the inorganic carrier is 0.1 micrometers to 100 micrometers, the pore volume is 0.2 cm 3 / g to 10.0 cm 3 / g, and the specific surface area is 15 m 2 / g to 1000 m 2 / g.

5. The highly active chromium-based polyethylene catalyst according to claim 1, wherein The alkylaluminum and / or alkoxyaluminum is selected from at least one of triisobutylaluminum, tri-n-hexylaluminum, triisopropylaluminum, methyldiethylaluminum, trimethylaluminum, diethylaluminum ethoxide, diethylaluminum methoxide, dimethylaluminum ethoxide, diisopropylaluminum ethoxide, diethylaluminum propoxide, diisobutylaluminum ethoxide, and methylethylaluminum ethoxide.

6. A method for preparing the highly active chromium-based polyethylene catalyst according to any one of claims 1 to 5, characterized in that, It includes the following steps: (1) Inorganic support modification: The inorganic support is modified with alkylaluminum and / or alkoxyaluminum to obtain a modified inorganic support. (2) Chromium loading: A chromium salt is formulated into a solution with a solvent and mixed with the above-mentioned modified inorganic support. After thorough mixing, it is heated and allowed to stand until dry to obtain a modified inorganic support powder loaded with chromium element. (3) Titanium loading: The modified inorganic support powder loaded with chromium element is further mixed with an organotitanium compound solution and a cocatalyst. After thorough mixing, it is allowed to stand, and then heated until dry to obtain a modified inorganic support powder loaded with both chromium element and titanium element. (4) High-temperature calcination: The modified inorganic support powder loaded with both chromium element and titanium element is further calcined in a dry non-reducing gas environment at a calcination temperature of 300~950 °C and a calcination time of 0.5~48 hours to obtain the chromium-based polyethylene catalyst.

7. The preparation method of the highly active chromium-based polyethylene catalyst according to claim 6, characterized in that, In step (2), it is heated and allowed to stand at 50 °C~110 °C. In step (3), after thorough mixing, it is allowed to stand at 0~50 °C for 0~4 hours, and then heated to 60~80 °C until dry.

8. The preparation method of the highly active chromium-based polyethylene catalyst according to claim 6, characterized in that, The chromium salt in step (2) is one or more of chromium acetate, dichromate, chromate, chromium nitrate, or chromium oxide. The solvent in step (2) is water, an alcohol solvent, or a ketone solvent.

9. The preparation method of the highly active chromium-based polyethylene catalyst according to claim 6, characterized in that, The organotitanium compound in step (3) is at least one of tetraisopropyltitanium, tetraethyltitanium, tetrabutyltitanium, tetraisooctyl titanate, or n-butyl titanate. The cocatalyst in step (3) is at least one of triethylaluminum, triisobutylaluminum, or diethylaluminum chloride. The solvent of the organotitanium compound solution in step (3) is water, an alcohol solvent, or a ketone solvent.

10. The preparation method of the highly active chromium-based polyethylene catalyst according to claim 6, characterized in that the content of the chromium element in the chromium salt in step (2) accounts for 0.1~5.0% of the mass of the modified inorganic support; the content of the titanium element in the organotitanium compound in step (3) accounts for 0.1~10% of the mass of the modified inorganic support loaded with the chromium element; the mass ratio of the cocatalyst to the modified inorganic support loaded with the chromium element in step (3) is (0.1~5):100.

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