Catalyst composition and preparation method therefor, and preparation method for high melt strength polyethylene

Abstract

The present invention provides a catalyst composition and a preparation method therefor, and a preparation method for high melt strength polyethylene. The catalyst composition comprises a main catalyst and a co-catalyst; the co-catalyst comprises an alkylaluminum compound and a pyridine compound; and the main catalyst is prepared by reacting a magnesium compound, a silicon compound and a titanium compound in a molar ratio of 1:0.1-10:0.05-3. When catalyzing ethylene polymerization, the catalyst composition of the present invention can significantly improve the melt strength of a polymerization product.

Description

Catalyst Composition, Preparation Method Thereof, and Preparation Method of High Melt Strength Polyethylene

[0001] Cross - reference Information

[0002] This application claims the priority of a Chinese patent application with the application number 202411515564.9, titled "Catalyst Composition, Preparation Method Thereof, and Preparation Method of High Melt Strength Polyethylene", filed with the Chinese Patent Office on October 28, 2024. The entire content of which is incorporated herein by reference. Technical Field

[0003] The present invention relates to the technical field of ethylene polymerization catalysts, and specifically to a catalyst composition, a preparation method thereof, and a preparation method of high melt strength polyethylene. Background Art

[0004] Since the successful development of high - efficiency polyethylene catalysts, the polyethylene industry has undergone a huge change. In recent years, along with the development of ethylene polymerization processes, catalysts compatible with the polymerization processes have also made great progress. Among them, high - efficiency catalysts still play an important role in the field of polyethylene catalysts due to their excellent polymerization performance and mature application technologies. After years of exploration and research, many high - efficiency Ziegler - Natta catalysts have been prepared, and many of these catalysts are used to produce high - density polyethylene.

[0005] High - density polyethylene (HDPE) has a high density, good balance between rigidity and toughness, excellent chemical resistance, is not hygroscopic and has good waterproof properties. It can be used to produce various hollow containers such as large - scale shipping containers, automobile fuel tanks, and fruit milk bottles. At present, high - density polyethylene large - hollow container products have been widely used in the packaging of various hazardous and non - hazardous chemicals, oils, and other liquids, and are gradually replacing metal containers, becoming the main form of liquid packaging in some industries.

[0006] High - density polyethylene used for hollow container products is mainly produced using chromium - based catalysts. Chromium - based catalysts can produce high - density polyethylene with a wide relative molecular mass distribution. Such polyethylene contains a certain amount of high - relative - molecular - mass components, thus meeting the requirements for melt strength during the blow - molding process of hollow containers and the requirements for environmental stress cracking resistance (ESCR) of products. In addition, during the catalytic ethylene polymerization process of chromium - based catalysts, a small amount of long - chain branches can be formed online. The presence of these long - chain branches is beneficial to both the blow - molding process of hollow containers and the final mechanical properties of products. At present, polyethylene manufacturers basically use chromium - based catalysts to produce special materials for large - hollow containers.

[0007] Compared to chromium-based catalysts, titanium-based catalysts cannot produce polyethylene with a wide molecular weight distribution. To achieve a wider molecular weight distribution, a two-reactor series reactor approach is generally used for the production of bimodal polyethylene. The low molecular weight fraction is produced in the first reactor, while the high molecular weight fraction is produced in the second reactor, thus meeting the requirement for a wide molecular weight distribution in hollow containers. However, polyethylene produced by titanium-based catalysts typically has lower melt strength and insufficient melt tensile strength, making it unsuitable for blow molding processes in the production of hollow blow-molded products. Summary of the Invention

[0008] To solve the above-mentioned technical problems, the present invention aims to provide a catalyst composition and its preparation method, as well as a method for preparing high melt strength polyethylene, which catalyzes the preparation of high melt strength polyethylene through a specific combination of catalysts.

[0009] To achieve the above objectives, the present invention provides a catalyst composition comprising a main catalyst and a co-catalyst, wherein the co-catalyst comprises an alkylaluminum compound and a pyridine compound, and the main catalyst is prepared by reacting a magnesium compound, a silicon compound, and a titanium compound in a molar ratio of 1:0.1-10:0.05-3; the molar ratio of the alkylaluminum compound to the titanium compound in the main catalyst is 10-200:1, and the molar ratio of the alkylaluminum compound to the pyridine compound is 1:1-10;

[0010] The magnesium compounds include those with the general formula Mg(OR) 1 One or more combinations of compounds of type 2, R 1 Selected from saturated or unsaturated C2-C 20 hydrocarbon group;

[0011] The silicon compound includes those with the general formula Si(OR) 2 ) m Cl 2-m One or more combinations of compounds, R 2 Selected from saturated or unsaturated C2-C 20 Hydrocarbon group, 0 < m ≤ 2;

[0012] The titanium compound includes those with the general formula Ti(OR) 3 ) n Cl 4-n One or more combinations of compounds, R 3 Selected from saturated or unsaturated C2-C 20 Hydrocarbon group, 0 ≤ n < 4.

[0013] During their research, the inventors unexpectedly discovered a Ziegler-Natta type titanium-based main catalytic system. This main catalytic system, combined with a co-catalyst composed of alkylaluminum and pyridine compounds, has a significant effect on improving the melt strength of the polymerization product during ethylene polymerization.

[0014] According to a specific embodiment of the present invention, preferably, R 1 R 2 R 3 Each is independently selected from straight-chain hydrocarbon groups, branched hydrocarbon groups, or cyclic hydrocarbon groups, and each is independently selected from C2-C. 20 Aliphatic hydrocarbons.

[0015] According to a specific embodiment of the present invention, preferably, R 1 R 2 R 3 Each is independently selected from C2-C 20 Alkyl, more preferably C2-C 10 alkyl.

[0016] According to a specific embodiment of the present invention, preferably, R 1 R 2 R 3 Each is independently selected from ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, or isooctyl.

[0017] According to a specific embodiment of the present invention, preferably, the molar ratio of magnesium compound, silicon compound and titanium compound is 1:0.5-5:0.1-2.

[0018] According to a specific embodiment of the present invention, preferably, the magnesium compound includes alkoxy magnesium, which includes one or more of diethoxy magnesium, dibutoxy magnesium, and dipropoxy magnesium.

[0019] According to a specific embodiment of the present invention, preferably, the magnesium compound is in the form of particles with a particle size of 2-20 micrometers, more preferably 5-15 micrometers.

[0020] According to a specific embodiment of the present invention, preferably, the silicon compound comprises silicon tetrachloride and C2-C 20 A mixture of reaction products of fatty alcohols; reaction conditions include: C2-C 20 The molar ratio of fatty alcohol to silicon tetrachloride is 1-4:1, the reaction temperature is 20-50℃, and the reaction time is 0.5-5h.

[0021] According to a specific embodiment of the present invention, preferably, the titanium compound comprises titanium tetrachloride and / or a mixture of the reaction products of titanium tetrachloride and fatty alcohols; the reaction conditions include: C2-C 20The molar ratio of fatty alcohol to titanium tetrachloride is 0-4:1, the reaction temperature is 20-100℃, and the reaction time is 0.5-5h.

[0022] According to a specific embodiment of the present invention, preferably, the alkyl group in the alkylaluminum compound has 1-20 carbon atoms.

[0023] According to a specific embodiment of the present invention, preferably, the alkylaluminum compound includes one or more of triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, and tri-n-octylaluminum.

[0024] According to a specific embodiment of the present invention, preferably, the pyridine compound includes one or more combinations of pyridine, 2-methylpyridine, 2-ethylpyridine, 2-isopropylpyridine, 2,4-dimethylpyridine, 2,6-dimethylpyridine, 2-methyl-6-ethylpyridine, 2,6-diethylpyridine, 2-chloro-6-methylpyridine, 2,6-dichloropyridine, 2,4,6-trimethylpyridine, 2,4,6-triethylpyridine, 2,4,6-trichloropyridine, and 2,4,6-triisopropylpyridine.

[0025] The present invention also provides a method for preparing the above-mentioned catalyst composition, which includes the following steps:

[0026] Preparation of the main catalyst: A particulate magnesium compound is dispersed in an organic solvent, and then a silicon compound and a titanium compound are slowly added at low temperature to carry out a chlorination reaction, followed by aging. The resulting particles are the main catalyst. The addition temperature of the silicon compound is -10℃ to 100℃, and the addition temperature of the titanium compound is -10℃ to 20℃. The addition rates of the silicon compound and the titanium compound are respectively not more than 2L / min, preferably 0.01-2L / min.

[0027] An alkylaluminum compound and a pyridine compound are provided to form the catalyst composition with the main catalyst.

[0028] In the preparation method of the above catalyst composition, preferably, the aging reaction temperature is 80℃-100℃ and the reaction time is 0.5-15h, more preferably 2-5h.

[0029] According to a specific embodiment of the present invention, an inert dispersant may be added to ensure the complete reaction of the solid magnesium compound. The inert dispersant does not participate in the reaction process; its purpose is merely to increase the dispersion effect of the solid component. Preferably, the reaction process for preparing the main catalyst is carried out in an inert dispersant, which includes one or more of hexane, heptane, octane, toluene, xylene, 1,2-dichloroethane, chlorocyclohexane, chlorobenzene, and other hydrocarbons or halogenated hydrocarbons, more preferably one or more of pentane, hexane, heptane, and toluene.

[0030] In the preparation method of the aforementioned main catalyst, the order of addition of the silane and titanium compounds in the step of reacting the solid magnesium compound with the silane compound and titanium compound is not particularly required; the silane compound can be added first, followed by the titanium compound, or vice versa. This step mainly involves the chlorination of the solid magnesium compound, simultaneously removing other substituent groups. Experiments have shown that the feeding temperature and rate of the silane and titanium compounds are crucial for controlling the morphology of the solid particles. Higher feeding temperatures and faster feeding rates will damage the particle morphology of the solid magnesium compound. Therefore, in this step, the reaction temperature of the silane compound is selected to be between -10℃ and 100℃, and the addition time is between 30 minutes and 5 hours. Similarly, the reaction process of the titanium compound also needs precise control. Typically, the titanium compound is added at a temperature between -10°C and 20°C over a period of 30 minutes to 5 hours. After addition, the system temperature is preferably raised to 80-100°C using a slow heating rate of 0.5-2°C / min, followed by stirring and reaction for a period of time. This reaction is called catalyst maturation. Maturization is beneficial to the catalyst particle shape, narrowing the particle size distribution and increasing particle strength, thereby reducing particle breakage during ethylene polymerization. The maturation temperature is generally equal to or higher than the titanium compound addition temperature, and the maturation time can be controlled between 0.5 and 15 hours, preferably 2 to 5 hours.

[0031] After the aging reaction, the aged catalyst suspension is typically washed to remove excess reactants and byproducts formed during the preparation process. Any inert solvent can be used for this washing step, such as one or a combination of isobutane, pentane, hexane, heptane, or cyclohexane, with hexane usually chosen as the inert solvent. After washing, the main catalyst suspension needs to undergo a drying step to obtain a solid main catalyst. This drying step can be completed by purging the catalyst suspension with hot nitrogen gas under heating conditions.

[0032] In the catalyst composition of the present invention, the alkyl aluminum compound and the pyridine compound can be mixed with the main catalyst sequentially, or they can be premixed and then mixed with the main catalyst. Preferably, the alkyl aluminum compound and the pyridine compound are premixed before use. More preferably, the mixing temperature is 25-80°C and the mixing time is 0.5-3 hours.

[0033] This invention also provides a method for preparing high melt strength polyethylene, which includes the following steps:

[0034] The above catalyst composition is uniformly dispersed in the reaction solvent, heated to the reaction temperature, and then ethylene is introduced to carry out the polymerization reaction to obtain the high melt strength polyethylene.

[0035] In the above-mentioned method for preparing high melt strength polyethylene, preferably, when dispersing the catalyst composition in the reaction solvent, the alkyl aluminum compound and pyridine compound are first added to the reaction solvent and mixed evenly, and then the main catalyst is added and dispersed evenly.

[0036] In the above-mentioned method for preparing high melt strength polyethylene, preferably, the polymerization reaction temperature is 80°C and the reaction time is 2 hours; the pressure of ethylene in the reaction system is maintained at 1 MPa.

[0037] In the above-mentioned method for preparing high melt strength polyethylene, preferably, the reaction solvent includes one or more combinations of propane, isobutane, isopentane, and hexane.

[0038] The technical solution provided by this invention has the following beneficial effects:

[0039] The present invention uses magnesium compounds, silicon compounds and titanium compounds to prepare the main catalyst, and combines it with two co-catalysts, alkyl aluminum compounds and pyridine compounds. This combination can significantly improve the melt strength of the polymerization product when catalyzing ethylene polymerization, and is suitable for the preparation of hollow containers. Detailed Implementation

[0040] 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.

[0041] Melt strength test

[0042] The experimental setup for melt strength testing consists of a single-screw extruder equipped with a capillary tube and a melt strength tester. First, the polyethylene resin melt to be tested is extruded from the extruder die. Then, the resulting extruded melt bundle is pulled by two rollers moving in opposite directions on a balance beam. The rollers accelerate uniformly until the melt bundle breaks. The force experienced when the melt bundle breaks is defined as the melt strength.

[0043] Example 1

[0044] This embodiment provides a method for preparing polyethylene, as detailed below:

[0045] (1) Preparation of the main component of the catalyst

[0046] A 500 mL reactor was dried and fully purged with nitrogen. Then, 200 mL of anhydrous hexane and 10 g of magnesium dibutoxylate were added. The reactor temperature was raised to 50 °C. Next, a mixture of silicon tetrachloride and ethanol (molar ratio of silicon tetrachloride to ethanol: 1:2) was added, and the mixture was stirred at 50 °C for 0.5 hours. Then, 20 mL of titanium tetrachloride was added, and the reaction was continued for 0.5 hours. Finally, the temperature was raised to 100 °C, and the mixture was stirred for 1 hour. After the reaction was complete, stirring was stopped, and the supernatant was pressed out after the solid particles settled. Another 200 mL of anhydrous hexane was added, and the mixture was stirred for 0.5 hours. The mixture was allowed to stand, and the supernatant was pressed out after the solid particles settled. This process was repeated three times. Finally, the mixture was heated to 80 °C under vacuum to dry the catalyst powder, obtaining the main catalyst. The titanium content was tested, and the titanium content in the main catalyst of this embodiment was found to be 5.4 wt%.

[0047] (2) Catalytic ethylene polymerization reaction

[0048] Triethylaluminum solution (concentration 15-25wt%) and pyridine were mixed at a molar ratio of 1:1 to obtain a co-catalyst solution. Based on the determination of titanium content in the main catalyst and the molar ratio (aluminum-titanium ratio) of alkylaluminum compound to titanium compound in the main catalyst being 10-200:1, the amount of co-catalyst solution required to add 10mg of main catalyst was determined. In a 2L polymerization reactor, 1L of hexane and the predetermined amount of co-catalyst solution were added, followed by 10mg of main catalyst powder. The temperature was raised to 80℃, and ethylene was continuously introduced to carry out the polymerization reaction of ethylene. The total polymerization pressure was maintained at 1.0MPa. After the polymerization reaction was carried out for 2 hours, the temperature was lowered, the pressure was released, the material was discharged, dried, and polyethylene powder was obtained and weighed.

[0049] Example 2

[0050] This embodiment provides a method for preparing polyethylene, which differs from Example 1 only in that: in step (1), "10 mL of a mixture of silicon tetrachloride and ethanol (molar ratio of silicon tetrachloride to ethanol is 1:2)" is replaced with: 12 mL of a mixture of silicon tetrachloride and ethanol (molar ratio of silicon tetrachloride to ethanol is 1:3); other conditions are the same as in Example 1. The titanium content in the main catalyst obtained in step (1) of this embodiment is 5.1 wt%.

[0051] Example 3

[0052] This embodiment provides a method for preparing polyethylene, which differs from Example 1 only in that the amount of titanium tetrachloride used in step (1) is adjusted from 20 mL to 10 mL; other conditions are the same as in Example 1. The titanium content in the main catalyst obtained in step (1) of this embodiment is 6.1 wt%.

[0053] Example 4

[0054] This embodiment provides a method for preparing polyethylene, which differs from Example 1 only in that: the amount of titanium tetrachloride in step (1) is adjusted from 20 mL to 30 mL, and the mixture of 10 mL of silicon tetrachloride and ethanol (the molar ratio of silicon tetrachloride and ethanol is 1:2) is adjusted to a mixture of 10 mL of silicon tetrachloride and isopropanol in a molar ratio of 1:3; other conditions are the same as in Example 1. The titanium content in the main catalyst obtained in step (1) of this embodiment is 7.2 wt%.

[0055] Example 5

[0056] This embodiment provides a method for preparing polyethylene, which differs from Example 1 only in that the co-catalyst solution in step (2) is prepared by mixing triethylaluminum solution and 2,6-dimethylpyridine in a molar ratio of 1:2. Other conditions are the same as in Example 1. The titanium content in the main catalyst obtained in step (1) of this embodiment is 5.9 wt%.

[0057] Example 6

[0058] The preparation conditions for the main catalyst are the same as in Example 1.

[0059] This embodiment provides a method for preparing polyethylene, which differs from Example 1 only in that: the co-catalyst solution in step (2) is prepared by mixing triethylaluminum solution and 2,6-dichloropyridine in a molar ratio of 1:5; other conditions are the same as in Example 1. The titanium content in the main catalyst obtained in step (1) of this embodiment is 6.3 wt%.

[0060] Example 7

[0061] This embodiment provides a method for preparing polyethylene, which differs from Example 1 only in that: the co-catalyst solution in step (2) is prepared by mixing triethylaluminum solution and 2,4,6-trimethylpyridine in a molar ratio of 1:10; other conditions are the same as in Example 1. The titanium content in the main catalyst obtained in step (1) of this embodiment is 4.9 wt%.

[0062] Example 8

[0063] The preparation conditions for the main catalyst are the same as in Example 1.

[0064] This embodiment provides a method for preparing polyethylene, which differs from Example 1 only in that: the co-catalyst solution in step (2) is prepared by mixing triethylaluminum solution and 2-ethylpyridine in a molar ratio of 1:6, while other conditions are the same as in Example 1. The titanium content in the main catalyst obtained in step (1) of this embodiment is 6.5 wt%.

[0065] Example 9

[0066] This embodiment provides a method for preparing polyethylene, which differs from Example 1 only in that: the co-catalyst solution in step (2) is prepared by mixing triethylaluminum solution and 2-chloro-6-methylpyridine in a molar ratio of 1:7; other conditions are the same as in Example 1. The titanium content in the main catalyst obtained in step (1) of this embodiment is 5.9 wt%.

[0067] Example 10

[0068] This embodiment provides a method for preparing polyethylene, which differs from Example 1 only in that: the co-catalyst solution in step (2) is prepared by mixing triethylaluminum solution and 2,4,6-triethylpyridine in a molar ratio of 1:3; other conditions are the same as in Example 1. The titanium content in the main catalyst obtained in step (1) of this embodiment is 6.3 wt%.

[0069] Example 11

[0070] This embodiment provides a method for preparing polyethylene, which differs from Example 1 only in that: the co-catalyst solution in step (2) is prepared by mixing triethylaluminum solution and 2-isopropylpyridine in a molar ratio of 1:4; other conditions are the same as in Example 1. The titanium content in the main catalyst obtained in step (1) of this embodiment is 7.1 wt%.

[0071] Comparative Example 1

[0072] This comparative example provides a method for preparing polyethylene, wherein the main catalyst is based on the method disclosed in patent CN201210402234, as follows:

[0073] (1) Preparation of the main catalyst

[0074] A 500 mL reactor was dried and fully purged with nitrogen. Then, 4.0 g of magnesium chloride, 50 mL of toluene, 2.0 mL of epichlorohydrin, and 3.0 mL of tributyl phosphate were added sequentially. The mixture was heated to 50 °C with stirring and maintained at this temperature for 15 minutes. Next, 6.0 mL of ethanol was added, and the reaction was continued with stirring for another 15 minutes. The solution was then cooled to -5 °C to 0 °C, and 30 mL of titanium tetrachloride was added dropwise. Then, 10 mL of 1,2-dichlorohexane was added, and the solution was heated to 80 °C. The mother liquor was removed. Finally, 40 mL of 1,2-dichlorohexane was added, and the reaction was carried out at 60 °C for 30 minutes. The mixture was filtered, washed four times with hexane, and dried under vacuum to obtain the main catalyst. The titanium content in the main catalyst prepared in this comparative example was 5.7 wt%.

[0075] (2) Catalytic ethylene polymerization reaction: Same as in Example 1.

[0076] Comparative Example 2

[0077] This comparative example provides a method for preparing polyethylene, wherein the main catalyst is based on the method disclosed in patent US20090203857, as follows:

[0078] (1) Preparation of the main catalyst

[0079] A 500 mL reactor was dried and fully purged with nitrogen. Then, 150 g of magnesium ethoxylate, 350 mL of hexane, 4.9 mL of silicon tetrachloride, and 4.9 mL of isopropanol were added sequentially. The mixture was heated to 70 °C with stirring and maintained for 2 hours. Next, 36 mL of titanium tetrachloride was added dropwise, and the reaction was continued for 6 hours. After filtration, the catalyst was washed four times with hexane and dried under vacuum to obtain the main catalyst. The titanium content in the main catalyst prepared in this comparative example was 6.7 wt%.

[0080] (2) Catalytic ethylene polymerization reaction: Same as in Example 1.

[0081] Comparative Example 3

[0082] This comparative example provides a method for preparing polyethylene, which differs from Example 1 only in that the co-catalyst solution in step (2) is a triethylaluminum solution (concentration of 1M); other conditions are the same as in Example 1. The titanium content in the main catalyst prepared in this comparative example is 7.7 wt%.

[0083] Comparative Example 4

[0084] (1) Preparation of the main component of the catalyst

[0085] A 500 mL reactor was dried and fully purged with nitrogen. Then, 200 mL of anhydrous hexane and 10 g of magnesium dibutoxylate were added. The reactor temperature was raised to 50 °C, followed by the addition of 20 mL of titanium tetrachloride. The reaction was allowed to proceed for 0.5 hours. Finally, the temperature was raised to 100 °C, and the reaction was stirred for 1 hour. After the reaction was complete, stirring was stopped, and the supernatant was pressed out after the solid particles settled. Another 200 mL of anhydrous hexane was added, and the mixture was stirred for 0.5 hours. The mixture was allowed to stand, and the supernatant was pressed out after the solid particles settled. This process was repeated three times. Finally, the mixture was heated to 80 °C under vacuum to dry the catalyst powder, yielding the main catalyst. The titanium content in the main catalyst prepared in this comparative example was 6.8 wt%.

[0086] (2) Catalytic ethylene polymerization reaction: Same as in Example 1.

[0087] The catalyst activity was calculated for the reactions of the above examples and comparative examples, and the melt strength and melt index of the polymer powder were tested. The results are shown in Table 1.

[0088] Table 1

[0089] As can be seen from the data in the table, the catalytic system composed of the main catalyst and the co-catalyst of the present invention produces polyethylene with significantly higher melt strength, making it more suitable for polyethylene processing methods such as blow molding.

[0090] Comparative studies have revealed that other main catalyst systems, when combined with co-catalysts composed of pyridine compounds and alkylaluminum compounds, do not produce the same results.

Claims

1. A catalyst composition comprising a main catalyst and a co-catalyst, the co-catalyst comprising an alkylaluminum compound and a pyridine compound, wherein the main catalyst is prepared by reacting a magnesium compound, a silicon compound, and a titanium compound in a molar ratio of 1:0.1-10:0.05-3; the molar ratio of the alkylaluminum compound to the titanium compound in the main catalyst is 10-200:1, and the molar ratio of the alkylaluminum compound to the pyridine compound is 1:1-10; The magnesium compounds include those with the general formula Mg(OR) 1 One or more combinations of compounds of type 2, R 1 Selected from saturated or unsaturated C2-C 20 hydrocarbon group; The silicon compound includes those with the general formula Si(OR) 2 ) m Cl 2-m One or more combinations of compounds, R 2 Selected from saturated or unsaturated C2-C 20 Hydrocarbon group, 0 < m ≤ 2; The titanium compound includes those with the general formula Ti(OR) 3 ) n Cl 4-n One or more combinations of compounds, R 3 Selected from saturated or unsaturated C2-C 20 Hydrocarbon group, 0 ≤ n < 4.

2. The catalyst composition according to claim 1, wherein, R 1 R 2 R 3 Each is independently selected from straight-chain hydrocarbon groups, branched hydrocarbon groups, or cyclic hydrocarbon groups, and each is independently selected from C2-C. 20 Aliphatic hydrocarbons.

3. The catalyst composition according to claim 1, wherein, R 1 R 2 R 3 Each is independently selected from C2-C 20 alkyl.

4. The catalyst composition according to claim 1, wherein, R 1 R 2 R 3 Each is independently selected from C2-C 10 alkyl.

5. The catalyst composition according to claim 1, wherein, R 1 R 2 R 3 Each is independently selected from ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, or isooctyl.

6. The catalyst composition according to claim 1, wherein, The molar ratio of magnesium compounds, silicon compounds, and titanium compounds is 1:0.5-5:0.1-2.

7. The catalyst composition according to claim 1, wherein, The magnesium compound includes alkoxy magnesium, which includes one or more of diethoxy magnesium, dibutoxy magnesium, and dipropoxy magnesium.

8. The catalyst composition according to claim 1, wherein, The magnesium compound is in particulate form with a particle size of 2-20 micrometers.

9. The catalyst composition according to claim 1, wherein, The silicon compound includes silicon tetrachloride and C2-C. 20 A mixture of reaction products of fatty alcohols; reaction conditions include: C2-C 20 The molar ratio of fatty alcohol to silicon tetrachloride is 1-4:1, the reaction temperature is 20-50℃, and the reaction time is 0.5-5h.

10. The catalyst composition according to claim 1, wherein, The titanium compound comprises titanium tetrachloride and / or a mixture of the reaction products of titanium tetrachloride and fatty alcohols; the reaction conditions include: C2-C 20 The molar ratio of fatty alcohol to titanium tetrachloride is 0-4:1, the reaction temperature is 20-100℃, and the reaction time is 0.5-5h.

11. The catalyst composition according to claim 1, wherein, The alkyl group in the alkylaluminum compound has 1-20 carbon atoms.

12. The catalyst composition according to claim 11, wherein, The alkylaluminum compound includes one or more of triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, and tri-n-octylaluminum.

13. The catalyst composition according to claim 1, wherein, The pyridine compounds include one or more combinations of pyridine, 2-methylpyridine, 2-ethylpyridine, 2-isopropylpyridine, 2,4-dimethylpyridine, 2,6-dimethylpyridine, 2-methyl-6-ethylpyridine, 2,6-diethylpyridine, 2-chloro-6-methylpyridine, 2,6-dichloropyridine, 2,4,6-trimethylpyridine, 2,4,6-triethylpyridine, 2,4,6-trichloropyridine, and 2,4,6-triisopropylpyridine.

14. A method for preparing the catalyst composition according to any one of claims 1-13, comprising the following steps: Preparation of the main catalyst: A particulate magnesium compound is dispersed in an organic solvent, and then a silicon compound and a titanium compound are slowly added at low temperature to carry out a chlorination reaction, followed by aging. The resulting particles are the main catalyst. in, The feeding temperature for silicon compounds is -10℃ to 100℃, and the feeding temperature for titanium compounds is -10℃ to 20℃; the feeding rate for silicon compounds and titanium compounds shall not exceed 2L / min respectively. An alkylaluminum compound and a pyridine compound are provided to form the catalyst composition with the main catalyst.

15. The method for preparing the catalyst composition according to claim 14, wherein, The ripening reaction temperature is 80℃-100℃, and the reaction time is 0.5-15h.

16. The method for preparing the catalyst composition according to claim 14, wherein, The reaction process for preparing the main catalyst is carried out in an inert dispersant, which includes one or more of hexane, heptane, octane, toluene, xylene, 1,2-dichloroethane, chlorocyclohexane, and chlorobenzene.

17. A method for preparing high melt strength polyethylene, comprising the following steps: The catalyst composition according to any one of claims 1-13 is uniformly dispersed in a reaction solvent, heated to the reaction temperature, and then ethylene is introduced to carry out a polymerization reaction to obtain the high melt strength polyethylene.

18. The method for preparing high melt strength polyethylene according to claim 17, wherein, When dispersing the catalyst composition in the reaction solvent, the alkylaluminum compound and pyridine compound are first added to the reaction solvent and mixed evenly, and then the main catalyst is added and dispersed evenly.

19. The method for preparing high melt strength polyethylene according to claim 17, wherein, The reaction solvent includes one or more of propane, isobutane, isopentane, and hexane.

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