A preparation method of ethoxymagnesium microspheres and a preparation method of polyethylene catalyst

Abstract

The present invention belongs to the technical field of polyolefin catalysts, and more specifically, relates to a method for preparing ethoxymagnesium microspheres and a polyethylene catalyst. The method comprises stirring and dissolving an initiator, a modifier, and anhydrous ethanol. Magnesium powder, the remainder of anhydrous ethanol, and the modifier are then added under stirring. After the reaction is complete, the ethoxymagnesium microspheres are filtered, washed, and dried to obtain more regular particles with an average particle size adjustable within a range of 5 to 20 μm. The polyethylene catalyst prepared using the ethoxymagnesium microspheres as a carrier exhibits high activity and high hydrogen sensitivity. The resulting polyethylene product exhibits good morphology, high bulk density, and low fines content.

Description

Technical Field

[0001] The invention belongs to the technical field of polyolefin catalysts, and more particularly relates to a method for preparing ethoxymagnesium microspheres and a method for preparing a polyethylene catalyst. Background Art

[0002] Since the successful development of high-efficiency polyethylene catalysts in the 1970s, catalyst preparation technology has made significant progress. A variety of high-efficiency polyethylene catalysts have been successfully developed, driving the development of a number of high-performance polyethylene products and reducing the production costs of polyethylene products. The core of polyethylene catalyst research is to control the polymerization activity, hydrogen sensitivity, copolymerization performance, and polymer particle morphology and particle size distribution of the catalyst based on matching different production process conditions. In particular, the slurry polyethylene production process requires not only a very high catalyst activity but also the control of the polymer particle morphology, molecular weight, and distribution. This is mainly because in the slurry polyethylene production process, polyethylene products with good particle morphology can reduce the slurry concentration in the reactor and reduce fine powder adhesion to the pipe wall during powder transportation, preventing polyethylene powder from clogging the pipe.

[0003] Catalysts used in the slurry polyethylene production process are mainly divided into anhydrous magnesium chloride-based and alkoxymagnesium-based catalysts based on the source of the carrier. The preparation route of magnesium chloride-based catalysts generally involves first dissolving magnesium chloride in a Lewis base solution, which is then precipitated under the action of a titanium-containing compound to form a catalyst. Magnesium chloride-based catalysts generally have advantages such as high polymerization activity, concentrated particle size distribution, and a wide particle size adjustment range. However, they generally have poor hydrogen sensitivity and low polymerization activity under high hydrogen conditions. The technical routes for preparing alkoxymagnesium-based catalysts can be roughly divided into two categories. One is to first prepare alkyl magnesium into particles, and then react the alkyl magnesium particles with a titanium compound in an inert solvent to form a catalyst. The other is to dissolve alkoxymagnesium and alkoxytitanium to form a solution containing alkoxymagnesium and alkoxytitanium, and then precipitate the solution under the action of a chlorination agent / alkylaluminum to form a catalyst. Alkoxymagnesium-based catalysts generally have the advantages of high activity, high hydrogen sensitivity and copolymerization performance, and are particularly suitable for the development and production of bimodal resin products. However, they usually have poor particle morphology, poor resin powder fluidity, and the bulk density of the resin powder still needs to be further improved. In addition, the fine powder content is relatively high. These defects affect the increase in production load and easily lead to blockage of the discharge pipeline.

[0004] CN201410743733.4 discloses a catalyst for ethylene polymerization and a preparation method. The activity of the catalyst prepared by this invention is insufficient and needs to be further improved; CN201811330321.2 discloses an alkoxymagnesium composite microsphere particle and a solid polyethylene catalyst prepared therefrom. The preparation process of the catalyst of this invention is complicated, the preparation cycle is long, the catalyst activity needs to be improved, and the polyethylene fine powder content needs to be further reduced; CN202310568649.2 discloses a catalyst component based on an alkoxymagnesium carrier for ethylene polymerization or copolymerization, a preparation method and its application. A large amount of alkyl aluminum compound is required in the preparation process of the catalyst of this invention, and the production cost of the catalyst is relatively high. At the same time, the preparation method of small-particle alkoxymagnesium is not disclosed. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a method for preparing ethoxy magnesium microspheres and a method for preparing a polyethylene catalyst. The present invention adds citrate and / or alcohol ether modifiers, as well as alkanes and / or silicone oil modifiers, to the reaction between alcohol and magnesium powder under the action of an initiator. The ethoxy magnesium microsphere particles prepared are more regular, with an average particle size adjustable within the range of 5 to 20 μm. The ester or ether groups therein can also act as a modified carrier, thereby improving the activity of the subsequently prepared polyethylene catalyst. In the process of preparing the polyethylene catalyst, a combination of silanes, diethers, and succinate compounds is used as an internal electron donor, which improves the activity and high hydrogen sensitivity of the prepared polyethylene catalyst. The resulting polyethylene product has a good morphology, high bulk density, and low fine powder content.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention is to provide a method for preparing ethoxy magnesium microspheres, comprising the following steps:

[0008] The product is obtained by reacting anhydrous ethanol and magnesium powder as raw materials under the action of an initiator, a modifier and a modifier.

[0009] Furthermore, the initiator includes iodine and / or magnesium chloride, preferably magnesium chloride.

[0010] Furthermore, the modifying agent includes alkanes and / or silicone oils.

[0011] Preferably, the alkane includes at least one of pentane, n-hexane, cyclohexane, n-heptane, n-decane and toluene, more preferably n-hexane.

[0012] Preferably, the silicone oil includes at least one of methyl silicone oil, ethyl silicone oil, phenyl silicone oil, methyl hydrogen silicone oil, methylphenyl silicone oil, methylchlorophenyl silicone oil, methylethoxy silicone oil, methyltrifluoropropyl silicone oil, methylvinyl silicone oil, methylhydroxy silicone oil, ethyl hydrogen silicone oil, hydroxy hydrogen silicone oil and cyanide silicone oil, more preferably methyl silicone oil.

[0013] Furthermore, the modifier includes a citrate compound and / or an alcohol ether compound.

[0014] Preferably, the citrate compound includes at least one of trimethyl citrate, triethyl citrate and tributyl citrate, more preferably tributyl citrate.

[0015] Preferably, the alcohol ether compound includes at least one of ethylene glycol monomethyl ether, glycerol dimethyl ether, triethylene glycol monoethyl ether, diethylene glycol monomethyl ether and polytetrahydrofuran, more preferably ethylene glycol monomethyl ether and / or polytetrahydrofuran.

[0016] Furthermore, the volume ratio of the anhydrous ethanol, the modifier and the finishing agent is 1:0.8-2.5:0.3-2.5, and the preferred volume ratio is 1:1.8-2.2:1.5-2.5.

[0017] Furthermore, the mass ratio of the magnesium powder to anhydrous ethanol is 1:9-20, and the preferred mass ratio is 1:15.

[0018] Furthermore, the molar ratio of the initiator to the magnesium powder is 0.001 to 0.01:1, and the preferred molar ratio is 0.005:1.

[0019] Furthermore, the particle size of the magnesium powder is 20 to 75 μm.

[0020] Furthermore, the specific steps of the reaction are:

[0021] Stir and dissolve the initiator, modifier and 20% to 40% of the total amount of anhydrous ethanol to obtain solution A;

[0022] Under stirring conditions, magnesium powder, the remaining anhydrous ethanol and the modifier are added to the solution A for reaction. After the reaction is completed, the solution is filtered, washed and dried to obtain the ethoxy magnesium microspheres.

[0023] Preferably, the reaction is carried out under the protection of an inert gas at a reaction temperature of 50 to 80°C, preferably 60 to 75°C.

[0024] Preferably, the washing is performed using anhydrous ethanol.

[0025] Preferably, the drying is vacuum drying at 60°C.

[0026] Preferably, the magnesium powder, the remaining anhydrous ethanol and the modifier can also be added in batches, the number of batch additions is 2 to 20 times, the time interval between batches is 5 to 40 minutes, preferably the number of batch additions is 4 times, and the time interval between batches is 20 minutes.

[0027] The second technical solution of the present invention is to provide ethoxymagnesium microspheres prepared by the above preparation method.

[0028] The third technical solution of the present invention is to provide an application of the above-mentioned ethoxymagnesium microspheres as a carrier in the preparation of a polyolefin catalyst.

[0029] The fourth technical solution of the present invention is to provide a polyethylene catalyst, the raw materials of which include the above-mentioned ethoxymagnesium microspheres.

[0030] A fifth technical solution of the present invention is to provide a method for preparing the above-mentioned polyethylene catalyst, comprising the following steps:

[0031] The polyethylene catalyst is obtained by reacting ethoxymagnesium microspheres as a carrier and titanium tetrachloride as an active component precursor under the action of an internal electron donor compound.

[0032] Furthermore, the molar ratio of the internal electron donor compound to the magnesium in the ethoxymagnesium microspheres is 0.05 to 0.2:1.

[0033] Furthermore, the internal electron donor compound comprises a silane compound, a diether compound and a succinate compound in a molar ratio of 1:0.2-0.8:0.1-0.6.

[0034] Preferably, the structural formula of the silane compound is shown in Formula 1 below:

[0035]

[0036] Wherein, R1 and R2 are independently selected from C1-C6 hydrocarbon group, piperidinyl group, alkoxy group, pyrrolyl group, glycidyl ether group, thiocyanate group, isocyanate group; R3 and R4 are independently selected from C1-C6 hydrocarbon group, alkoxy group, amino group.

[0037] More preferably, the silane compound includes at least one of butyltriethoxysilane, tetrabutoxysilane, methyltriethoxysilane, methyltriacetoxysilane and tetraethoxysilane (ethyl orthosilicate).

[0038] Preferably, the structural formula of the diether compound is shown in Formula 2 below:

[0039]

[0040] Wherein, R1 and R2 are independently selected from C3 to C6 hydrocarbon groups.

[0041] More preferably, the diether compound includes 2,2-diisopropyl-1,3-dimethoxypropane and / or 2,2-diisobutyl-1,3-dimethoxypropane.

[0042] Preferably, the structural formula of the succinate compound is shown in Formula 3 or Formula 4 below:

[0043]

[0044] Wherein, in formula 3, R1 and R2 are independently selected from hydrogen groups and C1 to C8 hydrocarbon groups, and R3 and R4 are independently selected from C1 to C6 hydrocarbon groups; in formula 4, R1 and R2 are independently selected from C1 to C6 hydrocarbon groups.

[0045] More preferably, the succinate compound includes at least one of diethyl 2,3-diisopropylsuccinate, diethyl 2,3-diisobutylsuccinate and spiro-substituted butyl succinate.

[0046] Furthermore, the mass percentage of titanium in the polyethylene catalyst is 3 to 8%.

[0047] Furthermore, the specific steps of the reaction are as follows:

[0048] S1. Under the protection of inert gas, the first portion of n-hexane and ethoxymagnesium microspheres are mixed and cooled to -15 to 0°C to obtain a mixed solution;

[0049] S2. Add the first portion of titanium tetrachloride dropwise to the mixed solution, and react at a temperature below 0° C. for 30 minutes to obtain a reaction solution;

[0050] S3, heating the reaction solution to 50° C., adding the internal electron donor compound and reacting for 1 hour, then heating to 100-120° C. and reacting for 2 hours, and obtaining a solid product by sedimentation and filtration;

[0051] S4. Add a second portion of n-hexane and a second portion of titanium tetrachloride to the solid product and heat to 100-120° C. to react for 2 hours. After sedimentation, filtration, washing and drying, the polyethylene catalyst is obtained.

[0052] Preferably, the volume / mass ratio of the first portion of n-hexane to the ethoxymagnesium microspheres is 6-15 mL / g, more preferably 10 mL / g.

[0053] Preferably, the amount of the first portion of titanium tetrachloride added is 1 / 7 to 1 / 3 of the volume of the first portion of n-hexane, preferably 1 / 5.

[0054] Preferably, the dropping time is 60 to 90 minutes.

[0055] Preferably, the heating rate of the heating in step S3 and step S4 is 1° C. / 3 min.

[0056] Preferably, the volume ratio of the second portion of n-hexane to the second portion of titanium tetrachloride is 3 to 6:1, more preferably 5:1.

[0057] Preferably, the washing is performed using n-hexane at 60° C. for 4 to 5 times.

[0058] Technical solution six of the present invention: provides an application of a polyethylene catalyst in slurry polyethylene production.

[0059] The inert gas in the present invention is one of helium, neon, argon, krypton, xenon and nitrogen.

[0060] It can be seen from the above technical solution that compared with the existing technology, it has the following beneficial effects:

[0061] According to the present invention, when alcohol reacts with magnesium powder under the action of an initiator, citrate esters and / or alcohol ether modifiers, as well as alkanes and / or silicone oil modifiers, are added. This allows the prepared ethoxy magnesium microspheres to have more regular particles. The average particle size of the ethoxy magnesium microspheres is adjustable within the range of 5-20 μm. Furthermore, groups such as ester groups and ether groups also have a modifying effect on the carrier, thereby improving the activity of a subsequently prepared polyethylene catalyst. Furthermore, in the present invention, titanium tetrachloride is added in batches, thereby effectively improving the uniformity of titanium loading, effectively dissolving alkoxy titanium, and increasing the effective titanium content.

[0062] The present invention adopts a compound of silanes, succinates and diether compounds as internal electron donors to prepare an alkoxy magnesium support type polyethylene catalyst in the catalyst preparation process. The electron donor improves the microscopic chemical environment around the active center through its electron-donating property. The addition of three electron donors in this application can effectively complement each other, which is more conducive to improving the chemical environment around the active center, thereby improving the catalyst activity and sensitivity to hydrogen. The polyethylene product prepared by the catalyst prepared by the present invention has good morphology, high bulk density and low fine powder content. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0064] Figure 1 This is an electron microscope photograph of the ethoxymagnesium microspheres prepared in Example 1.

[0065] Figure 2 This is an electron microscope photograph of the ethoxymagnesium microspheres prepared in Comparative Example 1.

[0066] Figure 3 This is an electron microscope photograph of the ethoxymagnesium microspheres prepared in Example 5.

[0067] Figure 4 This is an electron microscope photograph of the ethoxymagnesium microspheres prepared in Example 7. DETAILED DESCRIPTION

[0068] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0069] The compositions of the catalysts in the examples and comparative examples of the present invention were determined by the following method:

[0070] (1) The catalyst sample was extracted with heptane and sulfuric acid solution. The obtained extract was filtered and the aqueous layer was used for Ti determination, wherein the Ti content was analyzed by absorbance method;

[0071] (2) The particle size and particle size distribution of the catalyst were measured using a MAS-TERSIZE2000 particle size distribution analyzer produced by Malvern, UK. N-hexane was used as a dispersant and the measurement range was 0.02 to 2,000.00 μm. The particle size distribution of the catalyst was measured using SPAN = (D 90 -D 10 ) / D 50 express.

[0072] The performance indicators of each polymer in the examples or comparative examples were measured according to the following methods.

[0073] Determination of polymer particle size distribution: Determined in accordance with ASTM E1187;

[0074] Determination of polymer bulk density: Determined in accordance with GB / T 1636-2008.

[0075] The particle size of the magnesium powder used in the present invention is between 20 and 75 μm.

[0076] Example 1

[0077] Preparation of ethoxymagnesium microspheres:

[0078] (1) Under the protection of inert gas (argon), start stirring and add 32 mL of anhydrous ethanol, 0.24 g of magnesium chloride (initiator), and 390 mL of n-hexane (modifier) to the reactor in sequence. Heat the mixture to 70°C to dissolve the magnesium chloride to obtain solution A.

[0079] (2) Then, 3.0 g of magnesium powder, 32 mL of anhydrous ethanol, and 33.7 mL of ethylene glycol monomethyl ether (modifier) were added to solution A and reacted at 70 °C for 20 min.

[0080] (3) Repeat step (2) three times, then add 68 mL of ethanol and react at 70°C for 6 h until the color turns white and no hydrogen is generated in the bubbler (reaction is complete);

[0081] (4) After the reaction, the product was settled, filtered, and then vacuum dried at 60°C for 3 h to obtain ethoxymagnesium microspheres with an average particle size of 9.87 μm.

[0082] Examples 2 to 8 are the preparation of ethoxymagnesium microspheres. Compared with Example 1, the difference is that the types and amounts of the modifiers and modifiers used are different. The other condition parameters are consistent with the example, as shown in Table 1.

[0083] Table 1

[0084]

[0085] Comparative Example 1

[0086] Preparation of ethoxymagnesium microspheres:

[0087] (1) Under the protection of inert gas (argon), start stirring and add 32 mL of anhydrous ethanol and 0.24 g of magnesium chloride (initiator) to the reactor in sequence. Raise the temperature to 70°C to dissolve the magnesium chloride to obtain solution A.

[0088] (2) Then, 3.0 g of magnesium powder and 32 mL of anhydrous ethanol were added to solution A and reacted at 70 °C for 20 min;

[0089] (3) Repeat step (2) three times, then add 68 mL of ethanol and react at 70°C for 6 h until the color turns white and no hydrogen is generated in the bubbler (reaction is complete);

[0090] (4) After the reaction, the product was settled, filtered, and then vacuum dried at 60°C for 3 h to obtain ethoxymagnesium microspheres with an average particle size of 22.3 μm.

[0091] Comparative Example 2

[0092] Compared with Example 8, the only difference is that no modifier is added, and the average particle size of the obtained ethoxy magnesium microspheres is 15.8 μm.

[0093] Comparative Example 3

[0094] Compared with Example 1, the only difference is that no modifier is added, and the average particle size of the obtained ethoxy magnesium microspheres is 18.6 μm.

[0095] Comparative Example 4

[0096] Compared with Example 6, the only difference is that no modifier is added, and the average particle size of the obtained ethoxy magnesium microspheres is 20.4 μm.

[0097] From the average particle size of the ethoxy magnesium microspheres prepared in Examples 1 to 8 and Comparative Example 1, it can be seen that the addition of modifiers such as citrates and / or alcohol ethers, as well as alkanes and / or silicone oil modifiers in the preparation of ethoxy magnesium microspheres can effectively reduce the particle size of the microspheres, and through the changes in the modifiers and modifiers added in Examples 1 to 8, it can be seen that by regulating the type and amount of the modifiers and modifiers added, ethoxy magnesium microspheres of different particle sizes can be obtained, so that the particle size of the ethoxy magnesium microspheres is adjustable in the range of 5-20 μm.

[0098] The comparison of the average particle size of the ethoxy magnesium microspheres prepared in Example 8 and Comparative Example 2, the comparison of the average particle size of the ethoxy magnesium microspheres prepared in Example 1 and Comparative Example 3, and the comparison of the average particle size of the ethoxy magnesium microspheres prepared in Example 6 and Comparative Example 4 further proves that the addition of modifiers and modifiers can regulate the average particle size of the ethoxy magnesium microspheres.

[0099] The data of the average particle size of the ethoxymagnesium microspheres in Comparative Example 1, Comparative Example 2 and Example 8, the data of the average particle size of the ethoxymagnesium microspheres in Comparative Example 1, Comparative Example 3 and Example 1, and the data of the average particle size of the ethoxymagnesium microspheres in Comparative Example 1, Comparative Example 4 and Example 6, can further prove that the modifier and the modifier used in the present invention have a synergistic effect on the regulation of the average particle size of the ethoxymagnesium microspheres.

[0100] Example 9

[0101] Preparation of polyethylene catalyst:

[0102] S1. Under the protection of inert gas (argon), 100 mL of n-hexane and 10 g of the ethoxymagnesium microsphere carrier prepared in Example 1 were added to the reactor, and then the temperature was lowered to -15°C to obtain a mixed solution;

[0103] S2. Add 20 mL of titanium tetrachloride solution dropwise to the mixed solution for 90 min, and react at -10°C for 30 min to obtain a reaction solution;

[0104] S3, heating the reaction solution to 50°C at a rate of 1°C / 3min, adding 0.005 mol of ethyl orthosilicate, 0.001 mol of 2,2-diisopropyl-1,3-dimethoxypropane and 0.003 mol of diethyl 2,3-diisopropylsuccinate, and reacting at 50°C for 1 hour, then heating to 110°C at a rate of 1°C / 3min, and reacting at 110°C for 2 hours, and obtaining a solid product by sedimentation and filtration;

[0105] S4. Add 100 mL of n-hexane and 20 mL of titanium tetrachloride to the solid product, raise the temperature to 110°C at a rate of 1°C / 3 min, react at 110°C for 2 h, settle, filter, and wash 5 times with 60°C n-hexane solution and then dry to obtain a polyethylene catalyst. The mass percentage of titanium is 6.2% and the SPAN is 1.20.

[0106] Examples 10 to 15 are preparations of polyethylene catalysts. Compared with Example 9, the difference is that the composition and amount of the internal electron donor compound are different. The condition parameters are consistent with the example, see Table 2 for details.

[0107] Table 2

[0108]

[0109]

[0110] Example 16

[0111] Preparation of polyethylene catalyst:

[0112] Compared with Example 9, the only difference is that the ethoxymagnesium microsphere carrier prepared in Example 2 is used in step S1, the mass percentage of titanium in the prepared polyethylene catalyst is 7.2%, and the SPAN is 1.25.

[0113] Example 17

[0114] Preparation of polyethylene catalyst:

[0115] Compared with Example 9, the only difference is that the ethoxymagnesium microsphere carrier prepared in Example 6 is used in step S1, the mass percentage of titanium in the prepared polyethylene catalyst is 4.0%, and the SPAN is 1.15.

[0116] Example 18

[0117] Preparation of polyethylene catalyst:

[0118] Compared with Example 9, the only difference is that the ethoxymagnesium microsphere carrier prepared in Example 7 is used in step S1, the mass percentage of titanium in the prepared polyethylene catalyst is 4.8%, and the SPAN is 1.09.

[0119] Comparative Example 5

[0120] Preparation of polyethylene catalyst:

[0121] Compared with Example 9, the only difference is that the ethoxymagnesium microsphere carrier prepared in Comparative Example 1 is used in step S1, the mass percentage of titanium in the prepared polyethylene catalyst is 7.0, and the SPAN is 1.38.

[0122] Comparative Example 6

[0123] Compared with Example 9, the only difference is that during the catalyst preparation process, the electron donor is 0.008 mol 2,2-diisopropyl-1,3-dimethoxypropane, and the mass percentages of the components in the catalyst are Ti=6.4% and SPAN=1.26.

[0124] Comparative Example 7

[0125] Compared with Example 9, the only difference is that the electron donor in the catalyst preparation process is 0.008 mol ethyl orthosilicate, and the mass percentage of each component in the catalyst is Ti = 6.9%, SPAN = 1.24.

[0126] Comparative Example 8

[0127] Compared with Example 9, the only difference is that during the catalyst preparation process, the electron donor is 0.008 mol 2,3-diisopropyl succinate, and the mass percentages of the components in the catalyst are Ti=6.7% and SPAN=1.27.

[0128] Comparative Example 9

[0129] Compared with Example 9, the only difference is that during the catalyst preparation process, the electron donors are 0.005 mol ethyl orthosilicate and 0.003 mol 2,3-diisopropylsuccinate, and the mass percentages of the components in the catalyst are Ti = 5.8% and SPAN = 1.18.

[0130] Comparative Example 10

[0131] Compared with Example 9, the only difference is that during the catalyst preparation process, the electron donor is 0.005 mol ethyl orthosilicate and 0.003 mol 2,2-diisopropyl-1,3-dimethoxypropane, and the mass percentage of each component in the catalyst is Ti = 5.6% and SPAN = 1.20.

[0132] Comparative Example 11

[0133] Compared with Example 9, the only difference is that the carrier prepared in Comparative Example 3 is used in the catalyst preparation process, and the mass percentage of each component in the catalyst is Ti=7.1%, and SPAN=1.32.

[0134] Test example

[0135] The polyethylene catalysts prepared in Examples 9 to 18 and Comparative Examples 5 to 11 were used in polyethylene preparation. The specific preparation methods are as follows:

[0136] Evaluation of ethylene slurry polymerization: In a 2 L stainless steel reactor, after nitrogen replacement, 1.0 L of n-hexane previously dehydrated with molecular sieves, 0.25 mmol of triethylaluminum, and 0.005 mmol (in terms of titanium atoms) of the solid catalyst prepared above were added in sequence. The temperature of the system was then raised to 70°C, and hydrogen was introduced to a reactor pressure of 0.28 MPa (gauge pressure). Ethylene was then continuously introduced to maintain the reactor pressure at 1.0 MPa (gauge pressure) during the polymerization reaction time. After polymerization for 2 hours at 80°C and 1.0 MPa, the temperature was lowered and the reaction mixture was discharged. The polymerization results are shown in Table 3.

[0137] Table 3

[0138]

[0139]

[0140] From the data of Example 9 and Comparative Example 11 in Table 3, it can be seen that the modifier acts as an electron donor, affecting the activity of the catalyst.

[0141] The addition of three electron donors effectively improves the catalyst activity, thereby affecting the morphology distribution of polyethylene particles; small particle size carriers are more conducive to increasing the packing density of polyethylene particles.

[0142] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0143] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for regulating the average particle size of ethoxymagnesium microspheres, characterized in that the steps include: It is obtained by reacting anhydrous ethanol and magnesium powder as raw materials under the action of initiator, modifier and modifier; The initiator includes iodine and / or magnesium chloride; The modifying agent includes n-hexane and / or methyl silicone oil; The modifier includes ethylene glycol monomethyl ether, tributyl citrate or polytetrahydrofuran; The volume ratio of the anhydrous ethanol, the modifier and the finishing agent is 1:0.8-2.5:0.3-2.5; the mass ratio of the magnesium powder and anhydrous ethanol is 1:9-20; the molar ratio of the initiator and the magnesium powder is 0.001-0.01:1; and the particle size of the magnesium powder is 20-75 μm.

2. The method according to claim 1, characterized in that The reaction is carried out under the protection of inert gas at a temperature of 50-80°C.

3. Ethoxy magnesium microspheres prepared by the method according to claim 1 or 2.

4. Use of the ethoxymagnesium microspheres as claimed in claim 3 as a carrier in improving the catalytic performance of a polyolefin catalyst in producing polyethylene.

5. A polyethylene catalyst, characterized in that The raw materials include the ethoxy magnesium microspheres according to claim 3.

6. A method for preparing a polyethylene catalyst as claimed in claim 5, characterized in that the steps include: The polyethylene catalyst is obtained by reacting ethoxymagnesium microspheres as a carrier and titanium tetrachloride as an active ingredient precursor under the action of an internal electron donor compound; The internal electron donor compound comprises a silane compound, a diether compound and a succinate compound, and the molar ratio is 1:0.2-0.8:0.1-0.

6.

7. The preparation method according to claim 6, characterized in that The molar ratio of the internal electron donor compound to the magnesium in the ethoxymagnesium microspheres is 0.05-0.2:

1.

8. The preparation method according to claim 6, characterized in that The mass percentage of titanium in the polyethylene catalyst is 3-8%.

9. Use of the polyethylene catalyst according to claim 5 in slurry polyethylene production.

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