CN108623723B

CN108623723B - Ethylene polymerization process and polyethylene

Info

Publication number: CN108623723B
Application number: CN201710166700.1A
Authority: CN
Inventors: 亢宇; 张明森; 吕新平; 周俊岭; 徐世媛; 张志会
Original assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petroleum and Chemical Corp
Current assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petroleum and Chemical Corp
Priority date: 2017-03-20
Filing date: 2017-03-20
Publication date: 2020-10-23
Anticipated expiration: 2037-03-20
Also published as: CN108623723A

Abstract

The invention relates to the field of polymerization reaction, and discloses an ethylene polymerization method and polyethylene prepared by the method, wherein under the condition of polymerization reaction, ethylene is subjected to polymerization reaction in the presence of a catalyst, wherein the catalyst contains a spherical mesoporous composite material and a magnesium salt and/or a titanium salt loaded on the spherical mesoporous composite material, the average particle size of the spherical mesoporous composite material is 20-30 micrometers, the specific surface area is 100-300 square meters per gram, the pore volume is 0.5-1.8 milliliters per gram, the pore diameter is in bimodal distribution, and the most probable pore diameters corresponding to the two peaks are 1-10 nanometers and 20-55 nanometers respectively. The method uses a supported catalyst with stable mesoporous structure, and can obtain polyethylene products with lower bulk density and melt index and difficult breakage.

Description

Ethylene polymerization process and polyethylene

Technical Field

The invention relates to the field of polymerization reaction, in particular to a method for polymerizing ethylene and polyethylene prepared by the method.

Background

Since the synthesis of a regular mesoporous material with highly ordered pore channels by the company Mobile in 1992, the application of the mesoporous material in the fields of catalysis, separation, medicine and the like has attracted much attention due to the high specific surface, the regular pore channel structure and the narrow pore size distribution. Zhao Dong Yuan et al (1998) synthesizedA novel material, mesoporous material SBA-15, has highly ordered pore diameter (6-30nm), large pore volume (1.0 cm)³,/g), thicker pore walls (4-6nm), maintained high mechanical strength and good catalytic adsorption performance (see D.Y.ZHao, J.L.Feng, Q.S.Huo, et al Science 279(1998) 548-550). CN1341553A discloses a preparation method of a mesoporous molecular sieve carrier material, and the mesoporous material prepared by the method is used as a heterogeneous reaction catalyst carrier, so that the separation of a catalyst and a product is easy to realize.

However, the conventional ordered mesoporous material SBA-15 has a rod-like microscopic morphology, the flowability of the material is poor, and the high specific surface area and the high pore volume of the material cause the material to have strong water and moisture absorption capacity, so that the agglomeration of the ordered mesoporous material is further aggravated, and the storage, transportation, post-processing and application of the ordered mesoporous material are limited.

The development and application of polyethylene catalysts is a major breakthrough in the field of olefin polymerization catalysts after traditional Ziegler-Natta catalysts, which makes the research of polyethylene catalysts enter a rapidly developing stage. The homogeneous phase polyethylene catalyst has high activity, needs large catalyst consumption and high production cost, and the obtained polymer has no granular shape and cannot be used in a polymerization process of a slurry method or a gas phase method which is widely applied. An effective method for overcoming the above problems is to carry out a supporting treatment of the soluble polyethylene catalyst. At present, a great number of researches on the loading of polyethylene catalysts are reported. In order to develop new support/catalyst/cocatalyst systems in depth, it is necessary to develop different supports to drive the further development of the supported catalyst and polyolefin industries.

The mesoporous material of the supported polyethylene catalyst reported in the previous literature is MCM-41, and the catalytic activity of the MCM-41 which is treated by MAO and then supported by the polyethylene catalyst after ethylene polymerization is 10⁶gPE/(mol Zr h). The reason that the mesoporous material MCM-41 is low in ethylene polymerization activity after loading a catalyst is mainly that the thermal stability and the hydrothermal stability of a pore wall structure of the MCM-41 are low, partial collapse of the pore wall is caused in the loading process, the loading effect is influenced, and the catalytic activity is influenced.

Therefore, it is still a technical problem to be solved urgently to find a mesoporous material with a stable mesoporous structure, and a supported catalyst which can still maintain an ordered mesoporous structure after an active component is supported and has high catalytic activity.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide an ethylene polymerization method and polyethylene, wherein a supported catalyst with stable mesoporous structure is used in the method, and a polyethylene product with low bulk density and melt index and difficult breakage can be obtained.

In order to achieve the above object, the present invention provides a method for polymerizing ethylene, wherein ethylene is polymerized in the presence of a catalyst under polymerization conditions, wherein the catalyst comprises a spherical mesoporous composite material and a magnesium salt and/or a titanium salt supported on the spherical mesoporous composite material, wherein the spherical mesoporous composite material has an average particle size of 20-30 μm, a specific surface area of 100-300 m/g, a pore volume of 0.5-1.8 ml/g, a pore diameter in a bimodal distribution, and two peaks respectively correspond to a maximum pore diameter of 1-10 nm and a maximum pore diameter of 20-55 nm.

The invention also provides polyethylene prepared by the method.

The invention adopts the secondary ball milling technology and the cyclone separation technology in the spray drying technology, the secondary ball milling technology enables the obtained slurry to be more exquisite, the spherical particles obtained after spray drying have stable structure, can be repeatedly used as a catalyst carrier, have high strength and are not easy to break, and the preparation of the spherical mesoporous composite material does not need to use a binder, so that the structure of a sample can be prevented from being damaged in the process of removing the binder at high temperature. The obtained spherical mesoporous composite material has small particle size, uniform particle size distribution and narrow particle size distribution curve by adopting a cyclone separation technology, can avoid the agglomeration of the ordered mesoporous material in the use process, improves the fluidity of the ordered mesoporous material, and brings convenience to the storage, transportation, post-processing and application of the ordered mesoporous material.

In addition, the mesoporous structure of the spherical mesoporous composite material provided by the invention is stable, the ordered mesoporous structure can be still maintained after the active component is loaded, and the supported catalyst prepared from the mesoporous composite material has good fluidity. When the supported catalyst is used for ethylene polymerization reaction, a polyethylene product which has low bulk density and melt index and is not easy to break can be obtained, and specifically, the bulk density of the prepared polyethylene product is less than 0.4g/mL, the melt index is less than 0.5g/10min, and the breaking rate is less than 3 weight percent.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 is an X-ray diffraction pattern (XRD spectrum) of the spherical mesoporous composite material of example 1, with 2 θ on the abscissa and intensity on the ordinate;

FIG. 2 is a Scanning Electron Micrograph (SEM) of the spherical mesoporous composite material of example 1;

FIG. 3 is a graph showing a particle size distribution of the spherical mesoporous composite material according to example 1;

fig. 4 is a pore size distribution diagram of the spherical mesoporous composite material in example 1.

Detailed Description

The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

The present invention provides a process for the polymerization of ethylene, the process comprising: under the condition of polymerization reaction, ethylene is subjected to polymerization reaction in the presence of a catalyst, wherein the catalyst comprises a spherical mesoporous composite material and a magnesium salt and/or a titanium salt loaded on the spherical mesoporous composite material, the average particle size of the spherical mesoporous composite material is 20-30 micrometers, the specific surface area is 100-300 square meters per gram, the pore volume is 0.5-1.8 milliliters per gram, the pore diameters are in bimodal distribution, and the most probable pore diameters corresponding to the two modes are 1-10 nanometers and 20-55 nanometers respectively.

According to a preferred embodiment of the present invention, the average particle diameter of the spherical mesoporous composite material is 21-29 μm, the specific surface area is 210-290 square meters/g, the pore volume is 0.8-1.8 ml/g, the pore diameters are distributed in two peaks, and the two peaks respectively correspond to the most probable pore diameters of 1-8 nm and 30-52 nm.

According to a more preferred embodiment of the present invention, the average particle diameter of the spherical mesoporous composite material is 22-28 μm, the specific surface area is 220-280 square meters/g, the pore volume is 1-1.7 ml/g, the pore diameters are distributed in two peaks, and the most probable pore diameters corresponding to the two peaks are 1-5 nm and 40-50 nm, respectively.

In the invention, the average particle size of the spherical mesoporous composite material is measured by a laser particle size distribution instrument, the specific surface area, the pore volume and the most probable pore diameter are measured by a nitrogen adsorption method, and the surface morphology of the spherical mesoporous composite material is measured by a Scanning Electron Microscope (SEM). In the present invention, the average particle diameter is an average particle diameter.

According to the present invention, in the catalyst, the contents of the spherical mesoporous composite material and the magnesium salt and/or titanium salt supported on the spherical mesoporous composite material are not particularly limited, and may be determined according to a supported catalyst that is conventional in the art. For example, the spherical mesoporous composite may be included in an amount of 90 to 99 wt%, and the sum of the contents of the magnesium salt and the titanium salt, in terms of magnesium element and titanium element, respectively, may be 1 to 10 wt%, based on the total weight of the catalyst. Preferably, the content of the spherical mesoporous composite material is 90.5-98.5 wt%, and the sum of the contents of the magnesium salt and the titanium salt calculated by the magnesium element and the titanium element respectively can be 1.5-9.5 wt%. More preferably, the content of the spherical mesoporous composite material is 91-96 wt%, and the sum of the contents of the magnesium salt and the titanium salt calculated by the magnesium element and the titanium element respectively is 4-9 wt%.

In the present invention, the kind of the magnesium salt and the titanium salt is not particularly limited, and may be conventionally selected in the art. For example, the magnesium salt may be one or more of magnesium chloride, magnesium sulfate, magnesium nitrate and magnesium bromide, preferably magnesium chloride; the titanium salt may be titanium tetrachloride and/or titanium trichloride.

In the invention, the content of each element in the catalyst component can be measured by adopting an X-ray fluorescence spectrum analysis method.

In the present invention, the catalyst may be prepared according to various methods conventionally used in the art, as long as a magnesium salt and/or a titanium salt is supported on the spherical mesoporous composite.

In a preferred case, the preparation method of the catalyst may include: in the presence of inert gas, the spherical mesoporous composite material is contacted with mother liquor containing magnesium salt and/or titanium salt.

Preferably, the conditions of the contacting include: the temperature is 25-100 ℃, preferably 40-60 ℃; the time is 0.1 to 5 hours, preferably 1 to 3 hours.

The mother liquor containing magnesium salt and/or titanium salt can be an organic solvent containing magnesium salt and/or titanium salt, the organic solvent can be isopropanol and tetrahydrofuran, and the volume ratio of tetrahydrofuran to isopropanol can be 1: 1-3, preferably 1: 1-1.5.

During the preparation of the catalyst, the magnesium salt and/or the titanium salt is preferably used in an excess amount with respect to the spherical mesoporous composite material. More preferably, the magnesium salt, the titanium salt and the spherical mesoporous composite material are used in such amounts that the sum of the contents of the magnesium salt and the titanium salt, respectively, in terms of magnesium element and titanium element, in the prepared supported catalyst, is 1-10 wt% and the content of the spherical mesoporous composite material is 90-99 wt%, based on the total weight of the catalyst. Preferably, the sum of the contents of the magnesium salt and the titanium salt calculated by magnesium element and titanium element respectively is 1.5-9.5 wt%, and the content of the spherical mesoporous composite material is 90.5-98.5 wt%. More preferably, the sum of the contents of the magnesium salt and the titanium salt calculated by magnesium element and titanium element respectively is 4-9 wt%, and the content of the spherical mesoporous composite material is 91-96 wt%.

In a preferred embodiment of the present invention, the magnesium salt and the titanium salt may be used in a weight ratio of 1: 0.1 to 2, preferably 1: 0.5-2.

In the present invention, the preparation method of the catalyst further comprises: after the spherical mesoporous composite material is contacted with the mother solution containing magnesium salt and/or titanium salt, the composite material loaded with the magnesium salt and/or titanium salt is filtered and dried. The drying conditions are not particularly limited and may be drying means and conditions which are conventional in the art. Preferably, the preparation of the catalyst further comprises a washing process after filtration and before drying, and/or a milling process after drying. The washing and milling conditions can be selected by the person skilled in the art according to the practical circumstances and will not be described in detail here.

In the present invention, the inert gas is a gas which does not react with the raw materials and the product, and may be, for example, nitrogen gas or at least one of group zero element gases in the periodic table, preferably nitrogen gas, which is conventional in the art.

In the present invention, the spherical mesoporous composite may further contain silica introduced through silica gel. The term "silica introduced through silica gel" refers to a silica component which is brought into the finally prepared spherical mesoporous composite material by using silica gel as a preparation raw material during the preparation of the spherical mesoporous composite material. In the spherical mesoporous composite material, the content of the silica introduced through the silica gel may be 1 to 200 parts by weight, preferably 20 to 180 parts by weight, and more preferably 50 to 150 parts by weight, with respect to 100 parts by weight of the spherical mesoporous molecular sieve material.

In the present invention, the spherical mesoporous composite does not contain a binder such as polyvinyl alcohol or polyethylene glycol, etc. In addition, the term "the crushing rate of the spherical mesoporous composite material is less than 3 wt%" means that when the supported catalyst prepared by using the spherical mesoporous composite material is used for preparing polyethylene, the crushing rate of the obtained polyethylene product is less than 3 wt%.

According to the present invention, the preparation method of the spherical mesoporous composite material may comprise the steps of:

(1) providing a mesoporous molecular sieve material or preparing a filter cake of the mesoporous molecular sieve material as a component a;

(2) providing silica gel or preparing a filter cake of silica gel as component b;

(3) mixing the component a and the component b, performing first ball milling, mixing the obtained first ball milling slurry with water for pulping, performing second ball milling to obtain second ball milling slurry, performing spray drying on the second ball milling slurry, and screening by adopting a cyclone separation technology;

the average particle size of the spherical mesoporous composite material is 20-30 microns, the specific surface area is 100-300 square meters/g, the pore volume is 0.5-1.8 ml/g, the pore diameters are in bimodal distribution, and the most probable pore diameters corresponding to the two peaks are 1-10 nanometers and 20-55 nanometers respectively.

In the present invention, by controlling the particle size of the spherical mesoporous composite material within the above range, it can be ensured that the spherical mesoporous composite material is not easily agglomerated, and the supported catalyst prepared by using it as a carrier can improve the conversion rate of reaction raw materials in the ethylene polymerization process.

In the preparation process of the spherical mesoporous composite material, the pore size distribution of the spherical mesoporous composite material is controlled to be bimodal distribution mainly by controlling the composition of a mesoporous material filter cake (component a), and the microscopic morphology of the spherical mesoporous composite material is controlled to be spherical mainly by controlling a forming method (namely, firstly, the component a and the component b are mixed and subjected to first ball milling, the obtained first ball milling slurry is mixed with water for pulping, then, second ball milling is carried out to obtain second ball milling slurry, and the second ball milling slurry is subjected to spray drying).

According to the present invention, in the step (1), the process of preparing the filter cake of the mesoporous molecular sieve material may include: and carrying out first mixing contact on the template agent, the acid agent and the silicon source, and crystallizing and filtering the obtained mixture. The order of the first mixing and contacting is not particularly limited, and the template agent, the acid agent and the silicon source may be mixed at the same time, or any two of them may be mixed, and the other components may be added and mixed uniformly. According to a preferred embodiment, the templating agent and the acid agent are first mixed together, followed by the addition of the silicon source.

In the present invention, the template agent is preferably Cetyl Trimethyl Ammonium Bromide (CTAB) and polyethylene glycol octyl phenyl ether, and the acid agent is hydrochloric acid.

According to the present invention, the silicon source is not particularly limited, and various silicon sources conventionally used in the art may be used. For example, the silicon source may be at least one of ethyl orthosilicate, methyl orthosilicate, propyl orthosilicate, sodium orthosilicate, and silica sol, and is preferably ethyl orthosilicate.

In the present invention, the amounts of the templating agent, silicon source, and acid agent may vary over a wide range. For example, the molar ratio of silicon source: polyethylene glycol octyl phenyl ether: cetyl trimethylammonium bromide (CTAB): hydrogen chloride: water 1: 0.1-0.5: 0.1-0.6: 5-50: 100-500, preferably 1: 0.2-0.5: 0.2-0.4: 10-20: 200-300. Wherein, the mole number of the polyethylene glycol octyl phenyl ether is calculated according to the average molecular weight of the polyethylene glycol octyl phenyl ether.

The polyethylene glycol octyl phenyl ether can be various polyethylene glycol octyl phenyl ethers which can be used as a template agent, such as triton X-100. In addition, since Triton X-100 is usually a liquid, it can be measured by volume. For example, the volume of the polyethylene glycol octylphenyl ether (pure triton X-100) may be 72 to 179ml with respect to 1mol of the silicon source.

In the present invention, the conditions of the first mixing contact are not particularly limited, and for example, the conditions of the first mixing contact include: the temperature can be 10-60 ℃, preferably 25-60 ℃; the time can be 10 to 72 hours, preferably 10 to 30 hours; the pH may be from 1 to 7, preferably from 3 to 6. In order to further facilitate uniform mixing between the substances, the first mixing contact is preferably carried out under stirring conditions.

According to a preferred embodiment of the present invention, the first mixing contact comprises: (1) cetyl Trimethyl Ammonium Bromide (CTAB), polyethylene glycol octyl phenyl ether (triton X-100) and hydrochloric acid are stirred at the temperature of 25-60 ℃ until being dissolved; (2) stirring the solution obtained in the step (1) and silicate ester at the temperature of 25-60 ℃ for 10-72 hours, and standing for 10-72 hours.

In the present invention, the crystallization conditions are not particularly limited and may be conventionally selected in the art. For example, the crystallization conditions include: the temperature can be 25-60 ℃, preferably 30-50 ℃; the time may be 10 to 40 hours, preferably 15 to 35 hours. According to a preferred embodiment, the crystallization is carried out by hydrothermal crystallization.

In the present invention, in the above-mentioned process of preparing a filter cake of the mesoporous molecular sieve material, the process of obtaining the filter cake by filtration may include: after filtration, repeated washing with deionized water (washing times may be 2 to 10) and suction filtration.

In the step (1), "providing the mesoporous molecular sieve material" may be directly weighing or selecting the mesoporous molecular sieve material, or may be preparing the mesoporous molecular sieve material. The preparation method of the mesoporous molecular sieve material can be carried out according to a conventional method, and for example, the preparation method can comprise the following steps: a filter cake of the mesoporous molecular sieve material is prepared according to the above method and the resulting filter cake is then dried.

According to the present invention, in the step (2), the process for preparing the filter cake of silica gel comprises: and carrying out second mixing contact on the water glass, the polyhydric alcohol and the inorganic acid, and filtering the obtained mixture.

In the present invention, the conditions of the second mixing contact are not particularly limited and may be appropriately determined according to a conventional process for preparing silica gel. For example, the conditions of the second mixing contact include: the temperature can be 10-60 ℃, preferably 20-40 ℃; the time may be 1 to 5 hours, preferably 1 to 3 hours; the pH value is 2-4. In order to facilitate uniform mixing of the substances, the second mixing contact reaction process is preferably performed under stirring conditions.

In the present invention, the amounts of the water glass, the mineral acid and the polyol may vary within a wide range. For example, the weight ratio of water glass, mineral acid and polyol may be 1 to 8: 0.1-5: 1, preferably 3 to 6: 0.5-4: 1, more preferably 3 to 6: 1-3: 1.

in the present invention, the water glass is an aqueous solution of sodium silicate, and the concentration thereof may be 3 to 20% by weight, preferably 10 to 20% by weight. The inorganic acid may be various inorganic acids conventionally used in the art, and may be, for example, one or more of sulfuric acid, nitric acid, and hydrochloric acid. The inorganic acids can be used in pure form or in the form of their aqueous solutions, preferably in the form of 3 to 20% by weight aqueous solutions. The inorganic acid is preferably used in such an amount that the pH of the contact reaction system of the water glass and the inorganic acid is 2 to 4.

In the present invention, the kind of the polyol is not particularly limited, and for example, it may be glycerin and/or ethylene glycol.

According to the invention, in the step (2), "providing silica gel" may be directly weighing or selecting the silica gel product, or preparing silica gel. The method for preparing silica gel may be carried out according to conventional methods, and may include, for example: a filter cake of silica gel was prepared according to the above method and the resulting filter cake was then dried.

In the above process for preparing a filter cake of silica gel, the process for obtaining the filter cake by filtration may include: after filtration, washing is carried out until the content of sodium ions is 0.2 wt% or less, preferably 0.01 to 0.03 wt%, and then suction filtration is carried out. The washing method is a routine choice in the field, and can be water washing and/or alcohol washing, and the specific conditions are well known to those skilled in the art and are not described in detail herein.

According to the invention, in step (3), the amounts of component a and component b can vary within wide limits. For example, the component b may be used in an amount of 1 to 200 parts by weight, preferably 20 to 180 parts by weight, and more preferably 50 to 150 parts by weight, relative to 100 parts by weight of the component a.

The invention is realized by a secondary ball milling method of slurry in order to improve the strength of the carrier.

According to the present invention, in the step (3), the first ball milling and the second ball milling may be performed in a ball mill in which the inner wall of a ball milling jar is preferably an agate inner liner, and the diameter of the milling balls in the ball mill may be 2-3 mm; the number of the grinding balls can be reasonably selected according to the size of the ball milling tank, and for the ball milling tank with the size of 50-150mL, 1 grinding ball can be generally used; the material of the grinding ball can be agate, polytetrafluoroethylene and the like, and agate is preferred. The conditions of the first ball milling and the second ball milling can be the same or different, and the conditions of the first ball milling and the second ball milling respectively and independently comprise: the rotation speed of the grinding ball can be 200-; preferably, the rotation speed of the grinding balls is 300-.

According to the present invention, in the step (3), the temperature for mixing the obtained first ball-milling slurry with water for pulping may be 25 to 60 ℃, preferably 25 to 50 ℃; the weight ratio of the first ball-milling slurry to the amount of water may be 1: 0.1 to 5, preferably 1: 0.5-3.5.

According to the present invention, in the step (3), the spray drying may be performed according to a conventional manner, and may be selected from at least one of a pressure spray drying method, a centrifugal spray drying method, and a pneumatic spray drying method. According to a preferred embodiment of the present invention, the spray drying is a centrifugal spray drying method. The spray drying may be carried out in an atomizer. The conditions of the spray drying may include: the temperature is 150-; preferably, the spray drying conditions include: the temperature is 150-250 ℃, and the rotating speed is 11000-13000 r/min.

According to the present invention, the step of screening the second ball-milling slurry by using a cyclone separation technique after spray-drying may include: : and carrying out spray drying on the second ball-milling slurry, and carrying out cyclone separation on the discharged gas containing the powder particles so as to collect the powder particles. Specifically, the cyclone separation technology is adopted to separate the powder particles contained in the discharged gas, the recovered powder particles fall into the powder collecting cylinder, the waste gas is delivered to the centrifugal fan from the outlet of the separator, the butterfly valve is installed at the lower part of the cyclone separator, and when the cyclone separator works, the butterfly valve is opened, and the obtained sample has uniformly distributed particle sizes.

According to the present invention, in the step (3), when the component a is a filter cake of a mesoporous molecular sieve material and the component b is a filter cake of silica gel, that is, when the step (1) is a process for preparing a filter cake of a mesoporous molecular sieve material and the step (2) is a process for preparing a filter cake of silica gel, the preparation method of the carrier may further include: after the spray drying process of step (3), the templating agent is removed from the powder particles collected by cyclone separation. The conditions for removing the template agent comprise: the temperature can be 250-800 ℃, preferably 300-600 ℃; the time may be 10 to 40 hours, preferably 20 to 30 hours.

According to the present invention, the conditions of the polymerization reaction may be those conventional in the art. For example, the polymerization reaction is carried out in the presence of an inert gas under conditions comprising: the temperature can be 10-100 ℃, the time can be 0.5-5h, and the pressure can be 0.1-2 MPa; preferably, the temperature is 20-95 ℃, the time is 1-4h, and the pressure is 0.5-1.5 MPa; further preferably, the temperature is 70-85 ℃, the time is 1-2h, and the pressure is 1-1.5 MPa.

The pressure referred to herein is gauge pressure.

In the present invention, the polymerization reaction may be carried out in the presence of a solvent, and the solvent used in the polymerization reaction is not particularly limited, and may be, for example, hexane.

According to the present invention, in a preferred aspect, a process for the polymerization of ethylene comprises: under the condition of polymerization reaction, in the presence of catalyst and adjuvant making ethylene undergo the process of polymerization reaction; preferably, the adjuvant is an alkyl aluminium compound.

In the present invention, the alkyl aluminum compound has a structure represented by formula I:

AlR_nX⁵ _(3-n)formula I

In the formula I, R may be each C₁-C₅Alkyl groups of (a); x⁵May each be one of the halogen groups, preferably-Cl; n is 0, 1, 2 or 3.

Preferably, said C₁-C₅The alkyl group of (a) may be one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl and neopentyl.

In the present invention, specific examples of the alkyl aluminum compound include, but are not limited to: trimethylaluminum, dimethylaluminum chloride, triethylaluminum, diethylaluminum chloride, tri-n-propylaluminum, di-n-propylaluminum chloride, tri-n-butylaluminum, tri-sec-butylaluminum, tri-tert-butylaluminum, di-n-butylaluminum chloride and diisobutylaluminum chloride. Most preferably, the alkyl aluminium compound is triethyl aluminium.

In the present invention, the amount of the alkyl aluminum compound may also be selected conventionally in the art, and in general, the mass ratio of the alkyl aluminum compound to the amount of the catalyst may be 1: 0.1 to 10; preferably, the mass ratio of the alkyl aluminum compound to the catalyst is 1: 0.2 to 8; more preferably 1: 0.4-4.

In the invention, the ethylene polymerization method can further comprise the step of performing suction filtration separation on the final reaction mixture after the polymerization reaction is finished, so as to obtain the polyethylene granular powder.

The invention also provides polyethylene prepared by the method.

The present invention will be described in detail below by way of examples.

In the following examples and comparative examples, cetyltrimethylammonium bromide (CTAB) was purchased from carbofuran (J & K), average molecular weight 364, CAS: 57-09-0; polyoxyethylene octyl phenyl ether (Triton X-100) was purchased from Shanghai Biotechnology engineering Co., Ltd, cat # TB 0198.

In the following examples and comparative examples, X-ray diffraction analysis was carried out on an X-ray diffractometer, model D8Advance, available from Bruker AXS, Germany; scanning electron microscopy analysis was performed on a scanning electron microscope, model XL-30, available from FEI, USA; pore structure parameter analysis was performed on a nitrogen desorption apparatus model Autosorb-1 available from corna, usa, wherein the sample was degassed at 200 ℃ for 4 hours before testing; the X-ray fluorescence analysis is carried out on an X-ray fluorescence analyzer with the model of Axios-Advanced of the Netherlands company; the particle size distribution curve was measured by a malvern laser particle sizer.

The bulk density of the polyolefin powder was determined by the method specified in GB/T1636-2008.

Polymer melt index: measured according to ASTM D1238-99.

Crushing rate of polyethylene granular powder: and (3) screening and measuring by using a 800-mesh screen, specifically, passing the polyethylene granular powder through the 800-mesh screen, wherein the crushing rate is the percentage of the weight of the polyethylene granular powder which passes through the 800-mesh screen to the weight of the polyethylene granular powder to be tested.

Example 1

This example serves to illustrate the ethylene polymerization process and the resulting polyethylene of the present invention.

(1) Preparation of spherical mesoporous composite material

Adding 1.5 g CTAB (cetyl trimethyl ammonium bromide) and 1.5ml polyethylene glycol octyl phenyl ether (Triton-X100) into 29.6 g hydrochloric acid consisting of 37 wt% concentrated hydrochloric acid and 75 g water, mixing and stirring at 40 ℃ until CTAB is completely dissolved; adding 4.35 g of tetraethoxysilane into the solution, stirring for 15 hours at the temperature of 40 ℃ and the mechanical stirring speed of 340r/min, and standing for 24 hours at the temperature of 40 ℃; transferring the obtained solution into a reaction kettle with a polytetrafluoroethylene lining, crystallizing at 50 ℃ for 24 hours, and filtering and washing to obtain a mesoporous material filter cake A1.

Mixing 15 wt% of water glass, 12 wt% of sulfuric acid solution and glycerol in a weight ratio of 5: 1: 1 at 30 ℃ for 1.5 hours, followed by adjustment of the pH to 3 with 98% strength by weight sulfuric acid, suction filtration of the resulting reaction mass and washing with distilled water to a sodium ion content of 0.02% by weight, to give a filter cake of silica gel B1.

And (3) putting the prepared 20g of filter cake A1 and 10g of filter cake B1 into a 100mL ball milling tank together, wherein the ball milling tank is made of agate, the grinding balls are made of agate, the diameter of each grinding ball is 3mm, the number of the grinding balls is 1, and the rotating speed is 400 r/min. And sealing the ball milling tank, and carrying out first ball milling in the ball milling tank at the temperature of 25 ℃ for 5 hours. The obtained first ball-milled slurry was mixed with 15g of water at 25 ℃ for pulping, followed by second ball milling at 25 ℃ for 5 hours. And (3) spray-drying the obtained second ball-milling slurry at 200 ℃ at the rotating speed of 12000r/min, then screening by adopting a cyclone separation technology, calcining the screened product in a muffle furnace at 550 ℃ for 10h, and removing the template agent to obtain the spherical mesoporous composite material C1.

The spherical mesoporous composite material C1 is characterized by XRD, a scanning electron microscope and a nitrogen adsorption instrument.

Fig. 1 is an X-ray diffraction pattern, and it can be seen that the spherical mesoporous composite material C1 has a mesoporous structure specific to a mesoporous material.

FIG. 2 is a SEM image of the spherical mesoporous composite C1, which shows that the spherical mesoporous composite C1 is microspheres with a particle size of 20-30 μm and has good dispersibility.

FIG. 3 is a graph showing the particle size distribution of the spherical mesoporous composite C1, and it can be seen that the spherical mesoporous composite C1 has a uniform particle size distribution.

Fig. 4 is a pore size distribution diagram of the spherical mesoporous composite material C1, and it can be seen from the diagram that the spherical mesoporous composite material C1 has a double-pore structure distribution and uniform pore channels.

The pore structure parameters of the spherical mesoporous composite material C1 are shown in table 1 below.

TABLE 1

The first most probable aperture and the second most probable aperture are separated by a comma: the comma is preceded by a first most probable aperture and the comma is followed by a second most probable aperture.

(2) Preparation of the catalyst

0.1g of magnesium chloride and 0.1g of titanium tetrachloride were dissolved in 10mL of a composite solvent of tetrahydrofuran and isopropanol (the volume ratio of tetrahydrofuran to isopropanol was 1: 1.2) to form a catalyst mother liquor. 1g of the spherical mesoporous composite material C1 was added to the mother liquor at 45 ℃ for immersion for 1h, then filtered, and washed with n-hexane for 4 times, dried at 75 ℃ and ground to obtain the catalyst D1.

As a result of X-ray fluorescence analysis, in the catalyst D1 described in this example, the content of magnesium element was 7.5% by weight and the content of titanium element was 2% by weight in terms of element.

(3) Ethylene polymerization

In a 2L stainless steel high pressure polymerization reactor, nitrogen and ethylene were each replaced three times, then 200mL of hexane was added, the reactor was warmed to 80 ℃ and 800mL of hexane was added, 2mL of a 1mol/L Triethylaluminum (TEA) solution in hexane was added with the addition of hexane, then 0.5g of catalyst component D1 was added, ethylene gas was introduced, the pressure was raised to 1.0MPa and maintained at 1.0MPa, and after 1 hour of reaction at 70 ℃, separation by suction filtration was carried out to obtain a polyethylene pellet powder. Bulk Density (BD) and melt index MI of the obtained polyethylene granular powder_2.16The pulverization rates and the catalyst efficiencies are shown in Table 8.

Example 2

(1) Preparation of spherical mesoporous composite material

1.125 g CTAB (cetyl trimethyl ammonium bromide) and 3.75ml polyethylene glycol octyl phenyl ether (Triton-X100) were added to 20.6 g hydrochloric acid consisting of 37 wt% concentrated hydrochloric acid and 62.2 g water, mixed and stirred at 40 ℃ until CTAB was completely dissolved; then 4.35 g of tetraethoxysilane is added into the solution, and after crystallization is carried out for 35 hours at the temperature of 30 ℃, filtration and washing are carried out to obtain a mesoporous material filter cake A2.

Mixing 20 wt% of water glass, 12 wt% of sulfuric acid solution and glycerol in a weight ratio of 3: 2: 1, and then the reaction mixture was subjected to a contact reaction at 40 ℃ for 3 hours, followed by adjusting the pH to 4 with sulfuric acid having a concentration of 98% by weight, and then the resulting reaction mass was subjected to suction filtration and washed with distilled water until the sodium ion content was 0.02% by weight, to obtain a silica gel cake B2.

And putting 10g of the prepared filter cake A2 and 10g of the prepared filter cake B2 into a 100mL ball milling tank together, wherein the ball milling tank is made of agate, the grinding balls are made of agate, the diameter of each grinding ball is 3mm, the number of the grinding balls is 1, and the rotating speed is 500 r/min. And sealing the ball milling tank, and carrying out first ball milling in the ball milling tank at the temperature of 35 ℃ for 20 hours. The obtained first ball-milled slurry was mixed with 20g of water at 35 ℃ for pulping, followed by second ball milling at 25 ℃ for 10 hours. And (3) spray-drying the obtained second ball-milling slurry at the rotation speed of 13000r/min at the temperature of 150 ℃, then screening by adopting a cyclone separation technology, calcining the screened product in a muffle furnace at the temperature of 600 ℃ for 15h, and removing the template agent to obtain the spherical mesoporous composite material C2.

The pore structure parameters of the spherical mesoporous composite material C2 are shown in table 2 below.

TABLE 2

(2) Preparation of the catalyst

0.1g of magnesium chloride and 0.2g of titanium tetrachloride were dissolved in 10mL of a composite solvent of tetrahydrofuran and isopropanol (the volume ratio of tetrahydrofuran to isopropanol was 1: 1.5) to form a catalyst mother liquor. 1g of spherical mesoporous composite material C2 was added to the mother liquor at 60 ℃ for immersion for 1h, then filtered, and washed with n-hexane for 4 times, dried at 75 ℃ and ground to obtain catalyst D2.

As a result of X-ray fluorescence analysis, in the catalyst D2 described in this example, the content of magnesium element was 7.0% by weight and the content of titanium element was 0.8% by weight in terms of element.

(3) Ethylene polymerization

In a 2L stainless steel high pressure polymerization reactor, nitrogen and ethylene were each replaced three times, then 200mL of hexane was added, the reactor was warmed to 75 ℃ and 900mL of hexane was added, 2mL of a 1mol/L Triethylaluminum (TEA) solution in hexane was added with the addition of hexane, then 0.1g of catalyst component D2 was added, ethylene gas was introduced, the pressure was raised to 1MPa and maintained at 1MPa, and after 1.5 hours of reaction at 75 ℃ the reaction solution was separated by suction filtration to obtain polyethylene pellet powder. Bulk Density (BD) and melt index MI of the obtained polyethylene granular powder_2.16The pulverization rates and the catalyst efficiencies are shown in Table 8.

Example 3

(1) Preparation of spherical mesoporous composite material

0.75 g CTAB (cetyl trimethyl ammonium bromide) and 2.25ml polyethylene glycol octyl phenyl ether (Triton-X100) were added to 41.2 g of hydrochloric acid consisting of 37% by weight of concentrated hydrochloric acid and 93.3 g of water, and mixed and stirred at 60 ℃ until CTAB was completely dissolved; adding 4.35 g of tetraethoxysilane into the solution, stirring for 10 hours at the temperature of 60 ℃ and the mechanical stirring speed of 340r/min, and standing for 20 hours at the temperature of 60 ℃; transferring the obtained solution into a reaction kettle with a polytetrafluoroethylene lining, crystallizing at 40 ℃ for 30 hours, and filtering and washing to obtain a mesoporous material filter cake A3.

Mixing 10 wt% of water glass, 12 wt% of sulfuric acid solution and ethylene glycol in a weight ratio of 6: 3: 1 at 45 ℃ and then adjusted to a pH of 2 with sulfuric acid having a concentration of 98% by weight, the reaction mass obtained is filtered off with suction and washed with distilled water to a sodium ion content of 0.02% by weight, giving a silica gel cake B3.

And putting 10g of the prepared filter cake A3 and 15g of the prepared filter cake B3 into a 100mL ball milling tank together, wherein the ball milling tank is made of agate, the grinding balls are made of agate, the diameter of each grinding ball is 3mm, the number of the grinding balls is 1, and the rotating speed is 300 r/min. And sealing the ball milling tank, and carrying out first ball milling in the ball milling tank at the temperature of 50 ℃ for 10 hours. The resulting first ball-milled slurry was mixed with 87.5g of water at 50 ℃ for slurrying, followed by second ball milling at 40 ℃ for 5 hours. And (3) spray-drying the obtained second ball-milling slurry at 250 ℃ at the rotating speed of 11000r/min, then screening by adopting a cyclone separation technology, calcining the screened product in a muffle furnace at 400 ℃ for 24 hours, and removing the template agent to obtain the spherical mesoporous composite material C3.

The pore structure parameters of the obtained spherical mesoporous composite material C3 are shown in table 3 below.

TABLE 3

(2) Preparation of the catalyst

0.2g of magnesium chloride and 0.1g of titanium tetrachloride were dissolved in 10mL of a composite solvent of tetrahydrofuran and isopropanol (the volume ratio of tetrahydrofuran to isopropanol was 1: 1) to form a catalyst mother liquor. 1g of the spherical mesoporous composite material C3 was added to the mother liquor at 40 ℃ for immersion for 3h, then filtered, and washed with n-hexane for 4 times, dried at 75 ℃ and ground to obtain the catalyst D3.

As a result of X-ray fluorescence analysis, in the catalyst D3 described in this example, the content of magnesium element was 6.6% by weight and the content of titanium element was 1.2% by weight in terms of element.

(3) Ethylene polymerization

In a 2L stainless steel high-pressure polymerization kettleNitrogen and ethylene were each replaced three times, then 200mL of hexane were added, the kettle was warmed to 85 ℃ and 700mL of hexane were added, along with the addition of hexane, 2mL of a 1mol/L solution of Triethylaluminum (TEA) in hexane was added, then 1g of catalyst component D3 was added, ethylene gas was introduced, the pressure was raised to 1MPa and maintained at 1MPa, and after reacting at 85 ℃ for 2 hours, separation by suction filtration was carried out to obtain polyethylene pellet powder. Bulk Density (BD) and melt index MI of the obtained polyethylene granular powder_2.16The pulverization rates and the catalyst efficiencies are shown in Table 8.

Example 4

A spherical mesoporous composite and a supported catalyst were prepared in the same manner as in example 1, except that glycerol was not added in the preparation of the filter cake of silica gel, to obtain a spherical mesoporous composite C4 and a catalyst D4.

The pore structure parameters of the spherical mesoporous composite material C4 are shown in table 4 below.

TABLE 4

The catalyst D4 according to this example contained 6.2 wt% of magnesium and 0.8 wt% of titanium, calculated as elements, by X-ray fluorescence analysis.

(3) Ethylene polymerization

Polymerization of ethylene was carried out in accordance with the procedure of Experimental example 1, except that the same parts by weight of the catalyst D4 prepared in example 4 was used in place of the catalyst D1 prepared in example 1. Bulk Density (BD) and melt index MI of the obtained polyethylene granular powder_2.16The pulverization rates and the catalyst efficiencies are shown in Table 8.

Comparative example 1

This comparative example serves to illustrate a reference ethylene polymerization process and polyethylene

Commercially available ES955 silica Gel (GRACE) was calcined under nitrogen at 400 deg.C for 10h to remove hydroxyl groups and residual moisture, thereby obtaining heat-activated ES955 silica gel.

A catalyst was prepared according to the procedure of step (2) of example 1, except that the same parts by weight of the above-mentioned activated ES955 silica gel was used in place of the spherical mesoporous composite C1, thereby preparing a comparative catalyst DD 1.

(3) Ethylene polymerization

Polymerization of ethylene was carried out in accordance with the procedure of Experimental example 1, except that the catalyst D1 prepared in example 1 was replaced with the same parts by weight of comparative catalyst DD1, respectively. Bulk Density (BD) and melt index MI of the obtained polyethylene granular powder_2.16The pulverization rates and the catalyst efficiencies are shown in Table 8.

Comparative example 2

The spherical mesoporous composite and the supported catalyst were prepared according to the method of example 1. Except that only the first ball milling was performed, and the second ball milling was not performed. Specifically, 10g of the cake A1 prepared above and 10g of the cake B1 were put together in a 100mL ball mill pot. And sealing the ball milling tank, and carrying out first ball milling in the ball milling tank at the temperature of 25 ℃ for 5 hours. The first ball-milled slurry obtained was mixed with 40g of water at 25 ℃ for slurrying, and the slurry obtained was spray-dried at 200 ℃ at 12000 r/min. The spherical mesoporous composite material DC2 and the supported catalyst DD2 are prepared.

The pore structure parameters of the spherical mesoporous composite material DC2 are shown in table 5 below.

TABLE 5

According to X fluorescence analysis, in the catalyst DD2, the content of magnesium element is 6.8 wt% and the content of titanium element is 1.1 wt% calculated by element.

(3) Ethylene polymerization

Polymerization of ethylene was carried out in accordance with the procedure of experimental example 1 except that the catalyst D1 prepared in example 1 was replaced with the same parts by weight of the catalyst DD2, respectively. Bulk Density (BD) and melt index MI of the obtained polyethylene granular powder_2.16The pulverization rates and the catalyst efficiencies are shown in Table 8.

Comparative example 3

The spherical mesoporous composite and the supported catalyst were prepared according to the method of example 1. The difference is that the screening is not carried out by adopting a cyclone separation technology, specifically, the obtained second ball-milling slurry is subjected to spray drying at the temperature of 200 ℃ and the rotating speed of 12000r/min, then a product obtained after the spray drying is calcined for 10 hours at the temperature of 550 ℃ in a muffle furnace, and a template agent is removed, so that the spherical mesoporous composite material DC3 and the supported catalyst DD3 are obtained.

The pore structure parameters of the spherical mesoporous composite material DC3 are shown in table 6 below.

TABLE 6

According to X fluorescence analysis, in the catalyst DD3, the content of magnesium element is 6.0 wt% and the content of titanium element is 0.8 wt% calculated by element.

(3) Ethylene polymerization

Polymerization of ethylene was carried out in accordance with the procedure of experimental example 1 except that the catalyst D1 prepared in example 1 was replaced with the same parts by weight of the catalyst DD3, respectively. Bulk Density (BD) and melt index MI of the obtained polyethylene granular powder_2.16The pulverization rates and the catalyst efficiencies are shown in Table 8.

Comparative example 4

The spherical mesoporous composite and the supported catalyst were prepared according to the method of example 1.

The difference is that only the first ball milling is carried out, the second ball milling is not carried out, and the cyclone separation technology is not adopted for screening. Specifically, 10g of the cake A1 prepared above and 10g of the cake B1 were put together in a 100mL ball mill pot. And sealing the ball milling tank, and carrying out first ball milling in the ball milling tank at the temperature of 25 ℃ for 5 hours. And mixing the obtained first ball-milling slurry with 40g of water at 25 ℃ for pulping, spray-drying the obtained slurry at 200 ℃ at the rotating speed of 12000r/min, calcining the spray-dried product in a muffle furnace at 550 ℃ for 10h, and removing a template agent to obtain the spherical mesoporous composite material DC4 and the supported catalyst DD 4.

The pore structure parameters of the spherical mesoporous composite material DC4 are shown in table 7 below.

TABLE 7

According to X fluorescence analysis, in the catalyst DD4, the content of magnesium element is 5.4 wt% and the content of titanium element is 1.0 wt% calculated by element.

(3) Ethylene polymerization

Polymerization of ethylene was carried out in accordance with the procedure of experimental example 1 except that the catalyst D1 prepared in example 1 was replaced with the same parts by weight of the catalyst DD4, respectively. Bulk Density (BD) and melt index MI of the obtained polyethylene granular powder_2.16The pulverization rates and the catalyst efficiencies are shown in Table 8.

TABLE 8

As can be seen from the results of comparing the above experimental examples 1 to 4 with the experimental comparative examples 1 to 4, when the spherical mesoporous composite material and the supported catalyst provided by the present invention are used in an ethylene polymerization reaction, the catalyst has high catalytic activity, and a polyethylene product with low bulk density and melt index and being not easy to break can be obtained, specifically, the bulk density of the prepared polyethylene product is below 0.5g/mL, the melt index is below 0.5g/10min, and the crushing rate is less than 3 wt%. The polyethylene products which are not obtained by the method of the invention have the crushing rate of more than 5 weight percent.

The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.

It should be noted that the various features described in the above embodiments may be combined in any suitable manner without departing from the scope of the invention. The invention is not described in detail in order to avoid unnecessary repetition.

In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.

Claims

1. A process for the polymerization of ethylene, the process comprising: under the condition of polymerization reaction, in the presence of a catalyst, performing polymerization reaction on ethylene, wherein the catalyst contains a spherical mesoporous composite material and a magnesium salt and/or a titanium salt loaded on the spherical mesoporous composite material, wherein the average particle size of the spherical mesoporous composite material is 20-30 microns, the specific surface area is 100-300 square meters per gram, the pore volume is 0.5-1.8 milliliters per gram, the pore diameters are in bimodal distribution, and the most probable pore diameters corresponding to the two peaks are 1-10 nanometers and 20-55 nanometers respectively;

the preparation method of the spherical mesoporous composite material comprises the following steps:

(3) and mixing the component a and the component b, carrying out first ball milling, mixing the obtained first ball milling slurry with water for pulping, carrying out second ball milling to obtain second ball milling slurry, carrying out spray drying on the second ball milling slurry, and screening by adopting a cyclone separation technology.

2. The method of claim 1, wherein the spherical mesoporous composite material is present in an amount of 90 to 99 wt%, and the sum of the amounts of the magnesium salt and the titanium salt, calculated as magnesium and titanium, is 1 to 10 wt%, based on the total weight of the catalyst.

3. The method of claim 1, wherein the catalyst is prepared by contacting the spherical mesoporous composite with a mother liquor comprising a magnesium salt and/or a titanium salt in the presence of an inert gas.

4. The method of claim 3, wherein the conditions of the contacting comprise: the temperature is 25-100 ℃ and the time is 0.1-5 h.

5. The method according to claim 1, wherein the spherical mesoporous composite does not contain a binder and has a pulverization rate of less than 3 wt%.

6. The method according to claim 1, wherein, in the step (3), the component b is used in an amount of 1 to 200 parts by weight, relative to 100 parts by weight of the component a.

7. The method according to claim 6, wherein, in the step (3), the component b is used in an amount of 20-180 parts by weight with respect to 100 parts by weight of the component a.

8. The method according to claim 6, wherein, in the step (3), the component b is used in an amount of 50 to 150 parts by weight with respect to 100 parts by weight of the component a.

9. The method of claim 5, wherein, in step (1), the process of preparing a filter cake of mesoporous molecular sieve material comprises: and carrying out first mixing contact on the template agent, the acid agent and the silicon source, and crystallizing and filtering the obtained mixture.

10. The method of claim 9, wherein the templating agent is cetyl trimethylammonium bromide and polyethylene glycol octylphenyl ether, the acid agent is hydrochloric acid, and the silicon source is at least one of ethyl orthosilicate, methyl orthosilicate, propyl orthosilicate, sodium orthosilicate, and silica sol.

11. The method of claim 9, wherein the ratio of silicon source: polyethylene glycol octyl phenyl ether: cetyl trimethylammonium bromide: hydrogen chloride: water 1: 0.01-0.5: 0.1-0.6: 5-50: 100-500.

12. The method of claim 9, wherein the conditions of the first mixing contact comprise: the temperature is 10-60 ℃, the time is 10-72 hours, and the pH value is 1-7; the crystallization conditions include: the temperature is 25-60 ℃ and the time is 10-72 hours.

13. The method of claim 1, wherein, in the step (2), the process of preparing the filter cake of silica gel comprises: and carrying out second mixing contact on the water glass, the polyhydric alcohol and the inorganic acid, and filtering the obtained mixture.

14. The method of claim 13, wherein the conditions of the second mixing contact comprise: the temperature is 10-60 deg.C, the time is 1-5 hr, and the pH value is 2-4.

15. The method of claim 13, wherein the weight ratio of the water glass, the inorganic acid, and the polyol is 1-8: 0.1-5: 1.

16. the method of claim 13, wherein the inorganic acid is one or more of sulfuric acid, nitric acid, and hydrochloric acid; the polyalcohol is glycerol and/or ethylene glycol.

17. The method of any one of claims 1 to 16, wherein in step (3), the conditions of the first ball mill and the second ball mill are the same or different, and each of the conditions of the first ball mill and the second ball mill independently comprises: the rotation speed of the grinding ball is 200-800r/min, the temperature in the ball milling tank is 15-100 ℃, and the ball milling time is 0.1-100 hours.

18. The method of claim 17, wherein the first ball-milled slurry is used in an amount of 1: 0.1-5 ℃, and the temperature for mixing the first ball-milling slurry and water for pulping is 25-60 ℃.

19. The method of claim 17, wherein the conditions of the spray drying comprise: the temperature is 150-600 ℃, and the rotating speed is 10000-15000 r/min.

20. The method of claim 17, wherein the step of screening the second ball-milled slurry using a cyclone technique after spray drying comprises: and carrying out spray drying on the second ball-milling slurry, and carrying out cyclone separation on the discharged gas containing the powder particles so as to collect the powder particles.

21. The method of claim 17, wherein component a is a filter cake of mesoporous molecular sieve material and component b is a filter cake of silica gel; the method further comprises the following steps: after the spray drying process of step (3), the templating agent is removed from the powder particles collected by cyclone separation.

22. The method of claim 21, wherein the conditions for removing the templating agent comprise: the temperature is 250 ℃ and 800 ℃, and the time is 10-40 hours.

23. The process of claim 1, wherein the polymerization reaction is carried out in the presence of an inert gas, and the conditions of the polymerization reaction include: the temperature is 10-100 ℃, the time is 0.5-5h, and the pressure is 0.1-2 MPa.

24. The polyethylene produced by the process of any one of claims 1-23, wherein the polyethylene has a bulk density of 0.5g/mL or less, a melt index of 0.5g/10min or less, and a pulverization rate of less than 3 wt%.