Catalyst for gas phase system polyethylene as well as preparation method and application of catalyst

Abstract

The preparation method comprises the following steps: mixing an ether electron donor main solvent, an active titanium source, an active magnesium source and an alcohol electron donor auxiliary solvent, carrying out a reaction to obtain an active component complex, mixing the active component complex with surface-treated fine silica gel, carrying out adsorption and thickening to obtain homogeneous slurry, and drying the homogeneous slurry to obtain the gas phase system polyethylene catalyst. The components of the catalyst are (TiCl3-4) (MgCl2) 2.5-5 (R1OR2 + R3OH) 7-10 (SiO2) 1.5-2.5, R1 to R3 are alkyl groups, the carbon atom number of the ether electron donor main solvent is 2-6, the carbon atom number of the alcohol electron donor auxiliary solvent is 2-16, and the molar ratio of the ether electron donor main solvent to the alcohol electron donor auxiliary solvent is 1: (0.0824-0.391). Compared with the prior art, the catalyst has higher catalytic activity and better responsiveness to hydrogen and comonomers.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and relates to a catalyst for gas-phase polyethylene, its preparation method, and its application. Background Technology

[0002] Polyethylene (PE) polymers are widely used in industry and daily life, such as packaging, agriculture, construction, industrial applications, and wires and cables. The smoothness of the polyethylene synthesis process and the quality of its performance largely depend on the formulation and preparation method of the catalyst.

[0003] Unlike other polyethylene processing technologies, polymerization catalysts have a greater impact on gas-phase fluidized bed polyethylene processes. The diffusion factors in the gas-solid reaction impose requirements on parameters such as the pore structure, diameter, and specific surface area of ​​catalyst particles, reflecting a high degree of correlation with the catalyst forming process and carrier characteristics. Chain reactions during polymerization are always accompanied by the continuous splitting of catalyst particles and the exposure of active centers, thus requiring continuous adjustment and optimization of catalyst formulation and preparation processes to meet the needs of downstream polymerization. Furthermore, polymer performance is closely related to catalyst characteristics. The apparent properties of polyethylene, such as particle size, particle size distribution, fine powder content, bulk density, whiteness, and morphology, are highly correlated with the catalyst's particle size and distribution, crushing strength, initial activity (kinetic behavior), yield, and morphological reproducibility. The polymer's melt index and density are highly correlated with the catalyst's hydrogen responsiveness and comonomer responsiveness. The polymer's molecular weight distribution (MWD) is determined by the type and model of the catalyst. The long-term stable operation of the polymer synthesis process and the total monomer consumption are also closely related to the catalyst. Therefore, in order to obtain polymer products with stable downstream polymerization reaction and excellent performance, it is necessary to first explore the formulation technology of catalysts and the preparation process technology.

[0004] Patent CN103524643A discloses a method for preparing a polyethylene catalyst, which employs a spray-processing technique. The method involves first reacting anhydrous magnesium halide with general formula compounds ROX and NR. 1 3. Perform preprocessing, where R and R in the general formula 1 The reaction mixture consists of a C1-10 hydrocarbon group, X is a halogen, the reaction temperature is -50 to 50 °C, the reaction time is 0.5 to 10 h, and anhydrous magnesium halide, ROX, and NR are used. 1The molar ratio of 3 is 1:(1~5):(1~5); then the pretreated magnesium halide support is prepared into a mother liquor with titanium compounds and electron donors; then it is mixed with an appropriate amount of inorganic filler, spray-formed, and then contacted with the active component of titanium compounds to obtain a catalyst. However, this patent emphasizes that the magnesium halide must be modified and pretreated, dried, and then prepared into a mother liquor with titanium compounds and electron donors. This not only results in more time-consuming, energy-intensive, wasteful, and costly processes, but also uses the modified magnesium halide as a support, which only improves its crystal morphology, without changing the active center of the catalyst or enhancing its activity.

[0005] Patent CN102492062A discloses a method for preparing self-forming ethylene polymerization catalyst particles. This method includes the following steps: preparation of dry powder from a slurry catalyst in a gas-phase fluidized bed polyethylene process; secondary spray forming, adding recovered catalyst fine powder and organic solvent to a stirred tank, heating to 40-120 °C, then adding magnesium halide, titanium halide, and alkyl aluminum, stirring for 1-6 h, then adding a thickener, stirring for 3-6 h, then adding the slurry dry powder collected in a bag filter to the stirred tank, stirring at low speed for 3-6 h to obtain a secondary spray slurry, atomizing the secondary spray slurry in an atomizer, drying in a drying tower, and then separating it in a cyclone separator to obtain the secondary spray-formed slurry catalyst dry powder. However, this patent mainly relates to the reuse of fine powder waste collected in a dust collector during the primary spray drying and forming process of the catalyst, which is a method to reduce solid waste and increase product yield, but it does not enhance the activity of the catalyst.

[0006] Patent CN107759718A discloses a catalyst for homopolymerization or copolymerization of ethylene and its preparation method. The catalyst comprises: a titanium-containing active component and an activator component. The titanium-containing active component includes: a fuming oxide, magnesium dihalide, titanium halide, an electron donor compound, a modifier, and a structural modifier. The active component is AlR. n X 3-n The patent describes an organoaluminum compound, where R is a hydrocarbon group with 1-20 carbon atoms, X is a halogen, and n is a number where 1 < n ≤ 3, specifically one of triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, or diethylaluminum chloride; the modifier is tetra-n-butoxysilane; and the structural modifier is anhydrous ethanol. However, this patent emphasizes the addition of modifiers and structural modifiers. Tetra-n-butoxysilane is a high-boiling-point liquid, and its presence in catalyst particles results in low catalyst particle strength, making them prone to deformation and breakage, which is detrimental to the long-term stable operation of downstream polymerization reactors. Ethanol also improves the crystal morphology of magnesium halides but does not enhance their activity. Summary of the Invention

[0007] The purpose of this invention is to overcome at least one defect of the prior art by providing a catalyst for gas-phase polyethylene, its preparation method, and its application. This invention has higher catalytic activity and better responsiveness to hydrogen and comonomers.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] One technical solution of the present invention is to provide a catalyst for a gas-phase polyethylene system, comprising mixing an ether-based electron-donating main solvent, an active titanium source, an active magnesium source, and an alcohol-based electron-donating secondary solvent; mixing the resulting active component complex with surface-treated fine silica gel; adsorbing and thickening the resulting homogeneous slurry; and drying the slurry to obtain the gas-phase polyethylene catalyst. The catalyst composition is (TiCl... 3~4 (MgCl2) 2.5~5 (R 1 OR 2 +R 3 OH) 7~10 ·(SiO2) 1.5~2.5 R 1 To R 3 All are hydrocarbon-based. The number of carbon atoms in the ether-based electron-donating main solvent is 2 to 6, and the number of carbon atoms in the alcohol-based electron-donating secondary solvent is 2 to 16. The molar ratio of the ether-based electron-donating main solvent to the alcohol-based electron-donating secondary solvent is 1:(0.0824 to 0.391).

[0010] As a preferred technical solution, the molar ratio of titanium to magnesium in the catalyst is 1:(2.9~4.6).

[0011] As a preferred technical solution, the molar ratio of the ether-based electron donor main solvent to the alcohol-based electron donor secondary solvent is 1:(0.164~0.276).

[0012] As a preferred technical solution, the active titanium source of tetravalent titanium, after reduction treatment, forms a catalyst containing two types of active metal centers: trivalent titanium and tetravalent titanium, with a ratio of trivalent titanium to tetravalent titanium of (3.5~6.5):1.

[0013] As a preferred technical solution, taking into account both particle strength and diffusion limitation of gas-solid reaction in fluidized bed, the responsiveness of the catalyst to hydrogen and comonomers (especially to higher α-olefins) is improved, and the average particle size of the catalyst is 10~40 μm (dry basis).

[0014] As a preferred technical solution, the average particle size of the catalyst is 20~30 μm (dry basis).

[0015] As a preferred technical solution, the catalyst has a titanium content of 1.8~2.8%wt, a magnesium content of 5~6.8%wt, a main solvent content of 18~27%wt, and a secondary solvent content of 2~10%wt.

[0016] As a preferred technical solution, the catalyst has a titanium content of 2~2.6%wt, a magnesium content of 5.5~6.3%wt, a main solvent content of 23~26%wt, and a secondary solvent content of 2~6%wt.

[0017] As a preferred technical solution, the two electron-donating solvents of the catalyst exist as coordinating groups of the catalyst active center complex, and their proportion does not exceed 35%wt; otherwise, the catalyst particles are easily broken.

[0018] Furthermore, the primary solvent of the ether electron donor is selected from one or more cyclic ethers such as tetrahydrofuran and 1,4-dioxane, and the secondary solvent of the alcohol electron donor is selected from one or more primary alcohols such as ethanol, propanol, butanol, hexanol, 2-methylpentanol, n-heptanol, isooctanol, and n-octanol.

[0019] Furthermore, the active titanium source is selected from one or more titanium chlorides, namely titanium trichloride and titanium tetrachloride, and the active magnesium source is selected from one or more magnesium chlorides, namely active magnesium chloride and nascent magnesium chloride.

[0020] As a preferred technical solution, the newly formed magnesium chloride accounts for 5-25% of the total magnesium chloride.

[0021] Furthermore, the average particle size of the active magnesium chloride is 100~170 μm;

[0022] The newly formed magnesium chloride is prepared by mixing it with an active titanium source via a two-step or one-step method:

[0023] The two-step method includes the following steps:

[0024] Under inert gas protection, magnesium powder and chloroalkanes react, dry, remove excess chloroalkanes, and the resulting nascent magnesium chloride is mixed with solvent and active titanium source for the next step of preparation.

[0025] Chlorinated alkanes are selected from one or more of chloropropane, chloron-butane, and chloroisobutane;

[0026] The reaction temperature is 55~75 ℃, and the time is 3~5 h.

[0027] The drying process uses evaporation drying, which takes 8-12 hours.

[0028] The one-step method includes the following steps:

[0029] Under inert gas protection, titanium tetrachloride and magnesium powder react without drying to produce titanium trichloride and newly formed magnesium chloride. Solvent is added, and active magnesium chloride is added according to the stoichiometric ratio of the catalyst to proceed to the next step of preparation.

[0030] The reaction temperature is 50~70 ℃ and the time is 2~4 h. The temperature of the in-situ reaction of magnesium powder should be limited, otherwise the temperature rise will exceed 90 ℃ due to excessive heat release, which will aggravate the side reactions.

[0031] As a preferred technical solution, the inert gas is selected from nitrogen or argon.

[0032] Furthermore, the surface-treated fine silicone is micron-sized aerosol silicon dioxide with a hydrophobic surface treatment.

[0033] As a preferred technical solution, porous microparticle catalysts contain very few free and weakly loaded titanium ions, which are difficult to detect and are beneficial to stable polymerization reaction and uniform polymer quality and good flowability.

[0034] One of the technical solutions of the present invention is to provide a method for preparing a catalyst for a gas-phase polyethylene system, the method comprising the following steps:

[0035] S1. First, mix the ether-based electron donor solvent, the active titanium source, and the active magnesium source, and perform a complexation reaction to obtain a solution of the primary active component complex.

[0036] Then, a secondary solvent is added to modify the reaction, resulting in a complex solution of the composite active components.

[0037] S2. First, add surface-treated fine silica gel to a portion of the complex solution of composite active components, then add the remaining complex solution of composite active components. The mixture will adsorb, thicken, and fuse into a homogeneous phase to obtain a homogeneous slurry.

[0038] S3. Drying the homogeneous slurry removes excess solvent, achieving "morphological reconstruction" of the particulate catalyst and obtaining a catalyst for the gas-phase polyethylene system.

[0039] Furthermore, in step S1, the temperature of the complexation reaction and the modification reaction are both 55~75 ℃, and the time is both 2~5 h;

[0040] In step S2, surface-treated fine silica gel is first added to a 10-30% complex solution of composite active components. The adsorption and thickening temperature is 55-75 ℃, and the formation time is 2-5 h. The ratio of surface-treated fine silica gel to the complex solution of composite active components and the slurry temperature maintained will affect the particle size and strength of the catalyst particles formed later. These factors must be strictly controlled and adjusted according to the morphology and particle size distribution of the particles.

[0041] Furthermore, the drying process in step S3 adopts spray drying at a temperature of 145~170 ℃ for 13~16 h.

[0042] As a preferred technical solution, in step S3, the spray head rotation speed is 20000~22000 rpm, the slurry feed rate is 33~35 L / h, and the catalyst accounts for 88~96%wt% of the homogeneous slurry.

[0043] One of the technical solutions of the present invention is to provide the application of the catalyst of the gas-phase polyethylene system described above in the homopolymerization, copolymerization or hydrogenation of ethylene in the gas-phase fluidized bed polyethylene process.

[0044] Furthermore, in order to facilitate protection, storage, and feeding, the catalyst is impregnated and mixed with white oil to form a uniform slurry, wherein the proportion of catalyst in the slurry is 4~35%wt;

[0045] Further activation, alkylation, and polarization of the slurry using organometallic compounds gradually enhance catalyst activity and allow for stable and controllable release of activity. The organometallic compounds are selected from one or more Lewis acid organometallic compounds with polarization capabilities, such as dichloroethylaluminum, dichlorodiethylaluminum, triethylaluminum, triisobutylaluminum, and tri-n-hexylaluminum, to polarize the active center and enhance the catalyst's responsiveness to comonomers.

[0046] As a preferred technical solution, the catalyst in the slurry accounts for 5~32%wt.

[0047] As a preferred technical solution, the types of these organometallic compounds are varied to enable the catalyst to synthesize polymers covering the entire density range.

[0048] As a preferred technical solution, this series of organometallic compounds for activating the catalyst should be used in order of increasing activity to gradually improve the catalyst's activity and stabilize its performance.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] (1) The present invention adopts electronic environment modification of catalyst active center, “tailoring” and control of catalyst particle structure, and adjustment of different functional components to adapt to different polymerization conditions, so as to achieve the purpose of catalyst efficiency and control of polymerization stability and polymer performance, and adapt to gas phase fluidized bed polyethylene process operation and synthesis of polymers with desired performance.

[0051] (2) The two electron-donating solvents of the present invention contribute cyclooxygen groups and alkoxy groups to the active center respectively. Since the structures and amounts of these two groups complexed in the active center are different, this asymmetry and the electronic structure of the two groups make the active center not only more responsive to different polymer monomers, but also stimulate the active center to maintain a high activity state, especially for higher α-olefins.

[0052] (3) Unlike traditional carrier-type catalysts that directly adsorb the formula mother liquor onto amorphous silica gel, this invention integrates the active component complex with the surface-treated fine silica gel, and then uses a special drying method to remove excess solvent and carry out catalyst morphology reconstruction, thus realizing the transformation of catalyst preparation from "surface loading" to "bulk phase fusion".

[0053] (4) The present invention adopts a "bulk phase fusion" catalyst preparation method that mixes and thickens the active component complex with the surface-treated fine silica gel, so that the active component is loaded into the silica. This method can break through the upper limit of adsorption and loading of active components on the traditional amorphous silica gel as a carrier, and load several times the amount of active component complex, thereby obtaining higher and more stable activity.

[0054] (5) The present invention adopts a catalyst preparation method of “morphological reconstruction” to control the total content of main and secondary solvents in catalyst particles, which can perfectly take into account the appearance of the catalyst and continue to play the morphological replication effect in fluidized bed polyethylene production. The catalyst has better particle strength, reduces the generation of fragments and fine powders, and greatly improves the flow properties of polymer.

[0055] (6) Since slurry materials are easy to measure and feed evenly, the present invention mixes the obtained particulate catalyst with a large proportion of white oil to make a fluid slurry; at the same time, an oil film is coated on the catalyst particles, which not only better protects the catalyst, but also creates a "hysteresis" effect because the reactants must pass through the oil film first during the polymerization process. This helps to eliminate the violent initial activity burst, avoid the potential risk of runaway reaction and excessive fine powder caused by the catalyst particles breaking too quickly, and realize the "tailoring" and adjustment of catalyst performance. Detailed Implementation

[0056] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0057] Unless otherwise specified, the equipment used in the following embodiments is conventional equipment in the art; unless otherwise specified, the reagents used are commercially available products or prepared by conventional methods in the art. In the following embodiments, unless otherwise described in detail, conventional experimental methods in the art can be used.

[0058] Unless otherwise specified, the following procedures are generally performed at room temperature and atmospheric pressure.

[0059] Example:

[0060] A catalyst for a gas-phase polyethylene system and its preparation method, the specific steps of which are as follows:

[0061] S1. First, add titanium tetrachloride and magnesium powder to a nitrogen-sealed reactor at 60 ℃ and react for 2 h to generate titanium trichloride and newly generated magnesium chloride. Add tetrahydrofuran and add active magnesium chloride with an average particle size of 140 μm according to the stoichiometric ratio of the catalyst. Then, perform a complexation reaction at 65 ℃ for 3 h to obtain a complex solution of the primary active component.

[0062] Ethanol was then added to the same reactor at 65 °C, and the modification reaction was carried out for 3 h to obtain a complex solution of the composite active components.

[0063] The complex of the composite active components contains two active metal centers, trivalent titanium and tetravalent titanium, with a ratio of trivalent titanium to tetravalent titanium of 5.92:1;

[0064] S2. First, add 20% composite active component complex solution to a 65 ℃ stirred tank. While stirring, add aerosol silica with an average particle size of 10 μm that has been hydrophobically treated. Then add the remaining composite active component complex solution. Adsorb and thicken, and form for 3 h to fuse into a homogeneous phase to obtain a homogeneous slurry.

[0065] S3. The nitrogen-sealed spray drying loop system is purged with high-purity nitrogen. The circulating fan is turned on and the temperature is raised to 160 ℃ for circulation preparation. Tetrahydrofuran is injected to establish circulation and parameter balance. Nitrogen is removed and the entire process of feeding, spraying, evaporation, filtration and backflushing, condensation, recovery and non-condensable gas return to circulation is balanced. Slurry is introduced, parameters are adjusted, spray drying is carried out, particles are collected, samples are collected, circulation is maintained and loop stability is maintained. The system is run continuously for 14 h at a spray head speed of 21000 rpm and a slurry feed rate of 34 L / h. Finally, the powder particles produced from the bottom of the cyclone separator account for 93% wt of the input material, and the catalyst of the gas phase system polyethylene is obtained.

[0066] The catalyst's composition is (TiCl) 3.1 (MgCl2) 4.5 (C4H8O+C2H5OH) 7.3·(SiO2) 2.1 The molar ratio of the main solvent to the auxiliary solvent is 1:0.172, the average particle size of the catalyst is 22 μm (dry basis), the titanium content is 2.59%wt, the magnesium content is 5.87%wt, the main solvent content is 24.5%wt, and the auxiliary solvent content is 2.7%wt.

[0067] Comparative Example 1:

[0068] A catalyst for a gas-phase polyethylene system and its preparation method are basically the same as those in the examples, except that in step S1, only an equal amount of active titanium source titanium trichloride and an equal amount of active magnesium source active magnesium chloride are added to tetrahydrofuran in equal amounts of total solvent amount, instead of first adding titanium trichloride and newly generated magnesium chloride generated by the reaction of titanium tetrachloride and magnesium powder, the remaining titanium tetrachloride and the added active magnesium chloride to tetrahydrofuran for complexation reaction, and then adding ethanol for modification reaction.

[0069] The catalyst consists of (TiCl3)(MgCl2). 4.5 (C4H8O) 7.3 ·(SiO2) 2.1 The catalyst has an average particle size of 23 μm (dry basis), a titanium content of 2.51% wt, a magnesium content of 5.76% wt, and a solvent content of 28.2% wt.

[0070] Comparative Example 2:

[0071] A catalyst for a gas-phase polyethylene system and its preparation method are basically the same as those in the examples, except that in step S1, only an equal amount of active titanium source titanium chloride and an equal amount of active magnesium source active magnesium chloride are added to tetrahydrofuran in equal amounts of total solvent amount, instead of first adding titanium trichloride and newly generated magnesium chloride generated by the reaction of titanium tetrachloride and magnesium powder, the remaining titanium tetrachloride and the added active magnesium chloride to tetrahydrofuran for complexation reaction, and then adding ethanol for modification reaction.

[0072] The catalyst consists of (TiCl4)(MgCl2). 4.5 (C4H8O) 7.3 ·(SiO2) 2.1 The catalyst has an average particle size of 22 μm (dry basis), a titanium content of 2.55% wt, a magnesium content of 5.81% wt, and a solvent content of 27.6% wt.

[0073] Comparative Example 3:

[0074] A catalyst for a gas-phase polyethylene system and its preparation method are basically the same as those in the examples, except that in step S1, only titanium tetrachloride and magnesium powder generated by the reaction of titanium tetrachloride and magnesium powder, the remaining titanium tetrachloride, and the added active magnesium chloride are added to tetrahydrofuran in equal amounts of total solvent, instead of first complexing in tetrahydrofuran and then adding ethanol for modification.

[0075] The catalyst's composition is (TiCl) 3.1 (MgCl2) 4.5 (C4H8O) 7.3 ·(SiO2) 2.1 The catalyst has an average particle size of 25 μm (dry basis), a titanium content of 2.56%wt, a magnesium content of 5.91%wt, and a solvent content of 28.3%wt.

[0076] Based on the fact that the performance of some catalysts, such as activity and responsiveness to hydrogen and comonomers, in gas-phase fluidized bed polyethylene processes is highly similar to their performance in slurry polymerization, the following applications focus on testing the catalysts in slurry polymerization.

[0077] The specific steps for applying the above catalyst in slurry polymerization of ethylene homopolymer are as follows:

[0078] TS1. Under nitrogen protection, the catalyst is impregnated and mixed with white oil at a mass ratio of 1:9 to form a uniform slurry;

[0079] TS2, The polymerization stirred tank is purged with high-purity nitrogen and passes the test;

[0080] TS3, prepare a hexane diluent containing 10% wt diethylaluminum monochloro (DEAC) and a hexane diluent containing 10% wt triethylaluminum (TEAL);

[0081] TS4. Inject 3 L of purified hexane solvent into the polymerization stirred tank;

[0082] TS5: After pretreating the slurry with 0.14 mL of hexane dilution containing 10% wt diethylaluminum chloride, allow it to set for 3 hours.

[0083] TS6. Use 1.5 mL of hexane dilution containing 10% wt triethylaluminum to pretreat the hexane solvent in the polymerization stirred tank for 20 min, and heat to 60 °C;

[0084] TS7-1. Inject 0.23 g of pretreated slurry into the polymerization stirred tank, and simultaneously introduce high-purity ethylene to maintain the tank pressure at 0.6 MPa.

[0085] After TS8 polymerization for 2 hours, the ethylene feed into the polymerization reactor was stopped, the hexane solvent was evaporated, and dry polyethylene powder was obtained. The powder was weighed, bagged, and labeled.

[0086] The specific steps for applying the above catalyst in slurry polymerization of ethylene copolymerization are as follows:

[0087] Steps TS1 to TS6 are the same as those for ethylene homopolymerization;

[0088] TS7-2. Inject 30 g of purified 1-butene into the polymerization stirred tank;

[0089] 0.21 g of pretreated slurry was injected into the polymerization stirred tank, and high-purity ethylene was introduced at the same time to maintain the tank pressure at 0.6 MPa;

[0090] After TS8 polymerization for 2 hours, the ethylene feed into the polymerization reactor was stopped, the hexane solvent was evaporated, and dry polyethylene powder was obtained. The powder was weighed, bagged, and labeled.

[0091] The specific steps for applying the above catalyst in the hydrogenation of slurry-polymerized ethylene are as follows:

[0092] Steps TS1 to TS6 are the same as those for ethylene homopolymerization;

[0093] TS7-3. Introduce purified hydrogen gas into the polymerization stirred tank to pressurize it to 0.1 MPa;

[0094] 0.24 g of pretreated slurry was injected into the polymerization stirred tank, and high-purity ethylene was introduced at the same time to maintain the tank pressure at 0.6 MPa;

[0095] After TS8 polymerization for 2 hours, the ethylene feed into the polymerization reactor was stopped, the hexane solvent was evaporated, and dry polyethylene powder was obtained. The powder was weighed, bagged, and labeled.

[0096] Among them, the polymerization stirred tank is 5 L, 1 MPa pressure resistant, and is equipped with a stirrer (paddle type, adjustable speed, up to 800 rpm), temperature measuring port, pressure measuring port, and outer jacket.

[0097] Ethylene, polymerization grade, comes from pipelines and undergoes deoxygenation, carbon monoxide removal, and dehydration before use, at a pressure of 0.8 MPa.

[0098] Hydrogen, cracked hydrogen, dehydrated before use, 1 MPa pressure;

[0099] Hexane, polymerization grade, in drums, further dehydrated by molecular sieve before use;

[0100] 1-Butene, polymer grade, bottled in steel cylinders, further dehydrated by molecular sieve before use.

[0101] The catalyst was subjected to the following tests or experiments, and the results were then analyzed.

[0102] Experimental example:

[0103] The activity, polymer melt index, and density of the above catalysts were tested, and the test results are shown in Table 1.

[0104] Table 1. Small-scale evaluation results of ethylene homopolymerization, copolymerization, or hydrogenation in the examples and comparative examples.

[0105] As shown in Table 1, unlike Comparative Examples 1 and 2 which all used active magnesium chloride, Comparative Example 3 and the examples, although the in-situ synthesized nascent magnesium chloride accounted for only 9.8% of the total magnesium chloride, and the in-situ synthesized trivalent titanium accounted for 85.5% of the total titanium, the nascent magnesium chloride had high purity and the magnesium and titanium ions had similar radii and intercalated with each other. The active center of the complex generated in situ prevented the intrusion and contamination of other poisons and impurities, thus significantly improving the catalyst activity and the response performance to hydrogen and comonomers. Under the same hydrogen concentration, the melt index of the polymer increased significantly, and under the same comonomer concentration, the polymer density decreased significantly. Moreover, the temperature rise during polymerization was significantly faster, indicating that the catalyst in Comparative Example 3 and the examples showed significant changes in kinetic behavior, with rapid initial activity release and high overall activity.

[0106] Meanwhile, the embodiments employed a combination of electron-donating main and secondary solvents. Compared with the single main solvent in Comparative Example 3, two different complementary groups were introduced into the active center of the complex, further optimizing the coordination of the active center. The asymmetric electron distribution of the epoxy and alkoxy groups exposed more active sites, significantly improving the activity and response performance of the catalyst.

[0107] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A catalyst for a gas-phase polyethylene system, characterized in that, A mixture of a mixed ether-based electron-donating main solvent, an active titanium source, an active magnesium source, and an alcohol-based electron-donating secondary solvent is reacted to obtain an active component complex, which is then mixed with surface-treated fine silica gel. The resulting homogeneous slurry is adsorbed, thickened, and dried to obtain a gas-phase polyethylene catalyst. The catalyst's composition is (TiCl...). 3~4 (MgCl2) 2.5~5 (R 1 OR 2 +R 3 OH) 7~10 ·(SiO2) 1.5~2.5 R 1 To R 3 All are hydrocarbon-based. The number of carbon atoms in the ether-based electron-donating main solvent is 2 to 6, and the number of carbon atoms in the alcohol-based electron-donating secondary solvent is 2 to 16. The molar ratio of the ether-based electron-donating main solvent to the alcohol-based electron-donating secondary solvent is 1:(0.0824 to 0.391).

2. The catalyst for a gas-phase polyethylene system according to claim 1, characterized in that, The primary solvent of the ether electron donor is selected from one or more cyclic ethers such as tetrahydrofuran and 1,4-dioxane, and the secondary solvent of the alcohol electron donor is selected from one or more primary alcohols such as ethanol, propanol, butanol, hexanol, 2-methylpentanol, n-heptanol, isooctanol, and n-octanol.

3. The catalyst for a gas-phase polyethylene system according to claim 1, characterized in that, The active titanium source is selected from one or more titanium chlorides, including titanium trichloride and titanium tetrachloride, and the active magnesium source is selected from one or more magnesium chlorides, including active magnesium chloride and newly formed magnesium chloride.

4. The catalyst for a gas-phase polyethylene system according to claim 3, characterized in that, The average particle size of the active magnesium chloride is 100~170 μm; The newly formed magnesium chloride is prepared by mixing it with an active titanium source via a two-step or one-step method: The two-step method includes the following steps: Magnesium powder reacts with chloroalkanes, is dried, and the resulting nascent magnesium chloride is mixed with solvent and active titanium source; Chlorinated alkanes are selected from one or more of chloropropane, chloron-butane, and chloroisobutane; The reaction temperature is 55~75 ℃, and the time is 3~5 h. The drying process uses evaporation drying, which takes 8-12 hours. The one-step method includes the following steps: Titanium tetrachloride reacts with magnesium powder to produce titanium trichloride and newly formed magnesium chloride. Solvent is added, and active magnesium chloride is added according to the stoichiometric ratio of the catalyst. The reaction temperature is 50~70 ℃ and the time is 2~4 h.

5. The catalyst for a gas-phase polyethylene system according to claim 1, characterized in that, The surface-treated fine silicone is micron-sized aerosol silicon dioxide with a hydrophobic surface treatment.

6. A method for preparing a catalyst for a gas-phase polyethylene system as described in any one of claims 1 to 5, characterized in that, The method includes the following steps: S1. First, mix the ether-based electron donor solvent, the active titanium source, and the active magnesium source, and perform a complexation reaction to obtain a solution of the primary active component complex. Then, a secondary solvent is added to modify the reaction, resulting in a complex solution of the composite active components. S2. First, add surface-treated fine silica gel to a portion of the complex solution of composite active components, then add the remaining complex solution of composite active components. Adsorption and thickening are then performed to obtain a homogeneous slurry. S3. Dry the homogeneous slurry to obtain a catalyst for the gas-phase polyethylene system.

7. The method for preparing a catalyst for a gas-phase polyethylene system according to claim 6, characterized in that, In step S1, the temperature for both the complexation reaction and the modification reaction is 55~75 ℃, and the time is 2~5 h. In step S2, surface-treated fine silica gel is first added to a 10-30% complex solution of composite active components. The adsorption and thickening temperature is 55-75 °C, and the formation time is 2-5 h.

8. The method for preparing a catalyst for a gas-phase polyethylene system according to claim 6, characterized in that, The drying process in step S3 is spray drying, with a temperature of 145~170 ℃ and a time of 13~16 h.

9. The use of a catalyst for gas-phase polyethylene as described in any one of claims 1 to 5 in the homopolymerization, copolymerization or hydrogenation of ethylene in a gas-phase fluidized bed polyethylene process.

10. The application of the catalyst for a gas-phase polyethylene system according to claim 9, characterized in that, The catalyst is mixed with white oil to form a slurry, wherein the catalyst accounts for 4-35% wt% of the slurry; The slurry is further activated, alkylated, and polarized using organometallic compounds selected from one or more Lewis acid organometallic compounds with polarizing capabilities, such as dichloroethylaluminum, dichlorodiethylaluminum, triethylaluminum, triisobutylaluminum, and tri-n-hexylaluminum.

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