CN108727522B

CN108727522B - Process for the polymerization of ethylene and polyethylene

Info

Publication number: CN108727522B
Application number: CN201710260727.7A
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: 2017-04-20
Filing date: 2017-04-20
Publication date: 2020-10-23
Anticipated expiration: 2037-04-20
Also published as: CN108727522A

Abstract

The invention relates to the field of polymerization reaction, and discloses an ethylene polymerization method and polyethylene prepared by the method. The method for polymerizing ethylene comprises the step of polymerizing ethylene in the presence of a catalyst under polymerization reaction conditions, 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, and the spherical mesoporous composite material is prepared by a preparation method comprising the following steps of: (1) preparing a mesoporous material filter cake; (2) preparing a silica gel filter cake; (3) and respectively or after mixing, carrying out ball milling on the mesoporous material filter cake and the silica gel filter cake, washing a ball-milled product by using a ceramic membrane filter, and then carrying out spray drying to obtain the spherical mesoporous composite material. The method uses a supported catalyst with high activity, and can obtain polyethylene products with lower bulk density and melt index.

Description

Process for the polymerization of ethylene 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 1992, the mesoporous material has high specific surface, regular pore channel structure and narrow pore size distribution, so that the mesoporous material is catalyzed to be preparedApplications in the fields of chemistry, separation, medicine and the like have attracted much attention. A novel mesoporous material SBA-15 is synthesized by Zhao Dongyuan et al in 1998, which has highly ordered pore diameter (6-30nm) and 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.

At present, common catalyst carriers are mesoporous materials and silica gel carriers. Among them, the mesoporous material has not high enough catalytic activity after loading the polyethylene catalyst, and there is a need to develop a catalyst carrier capable of improving activity to promote further development of the carrier catalyst and polyolefin industry.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide an ethylene polymerization method and polyethylene, wherein the supported catalyst used in the method has high catalytic efficiency, and polyethylene products with lower bulk density and melt index can be obtained.

At present, silica gel and mesoporous materials are usually removed by using a plate-and-frame filter press, but the catalytic activity of a carrier obtained by using the method after loading a catalyst is low, possibly because the removal of impurities is not thorough. In addition, the plate and frame filter press still has a lot of shortcomings, for example, plate and frame filter press area is great, simultaneously, because the plate and frame filter press is discontinuous operation, inefficiency, the operation room environment is relatively poor, has secondary pollution, and in addition, because use filter cloth, it is relatively poor to get rid of the impurity effect, and waste water can not recycle, wastes the water source very much in the washing process, simultaneously because the exhaust waste water can't be handled, causes environmental pollution and secondary waste again. After intensive research, the inventor of the invention finds that when the ceramic membrane is used for washing the three-dimensional cubic mesoporous composite material, the obtained three-dimensional cubic mesoporous composite material has higher catalytic activity after loading a polyethylene catalyst, and the obtained polyethylene product has lower bulk density and melt index. The present inventors have completed the present invention based on the above findings.

In order to achieve the above object, the present invention provides a method for polymerizing ethylene, comprising: polymerizing ethylene in the presence of a catalyst under a polymerization reaction condition, wherein the catalyst comprises a three-dimensional cubic mesoporous composite material and a magnesium salt and/or a titanium salt loaded on the three-dimensional cubic mesoporous composite material, and the three-dimensional cubic mesoporous composite material is prepared by a preparation method comprising the following steps of: (1) carrying out first mixing contact on a template agent, butanol, ethyl orthosilicate and an acid agent, and crystallizing and filtering the obtained mixture to obtain a mesoporous material filter cake; (2) carrying out second mixing contact on water glass and inorganic acid, and filtering a mixture obtained after the contact to obtain a silica gel filter cake; (3) respectively or after mixing the mesoporous material filter cake and the silica gel filter cake, washing the mixture by using a ceramic membrane filter, and then carrying out ball milling and spray drying to obtain a three-dimensional cubic mesoporous composite material; or respectively or after mixing, ball-milling the mesoporous material filter cake and the silica gel filter cake, and then washing and spray-drying by using a ceramic membrane filter to obtain the three-dimensional cubic mesoporous composite material.

The invention also provides polyethylene prepared by the method.

The carrier of the three-dimensional cubic mesoporous composite material prepared by the ceramic membrane filtration method has the following advantages: (1) the separation process is simple, the separation efficiency is high, the number of matched devices is small, the energy consumption is low, and the operation is simple and convenient; (2) the template agent is directly removed by ceramic membrane filtration, and compared with the prior art, the step of removing the template agent by calcination is omitted; (3) the cross-flow filtration is adopted, and the higher membrane surface flow rate is used, so that the accumulation of pollutants on the membrane surface is reduced, and the membrane flux is improved; (4) the ceramic membrane has good chemical stability, acid resistance, alkali resistance, organic solvent resistance and strong regeneration capability, and can be suitable for the preparation process of the carrier; (5) the production of waste liquid is obviously reduced, and the method is green and environment-friendly.

The carrier prepared by the method has large aperture and high specific surface area, and is beneficial to the loading of catalytic components; in addition, the carrier has a spherical geometric shape, and the shape has obvious advantages in the aspects of reducing powder agglomeration, improving fluidity and the like. The supported catalyst prepared by adopting the carrier prepared by the invention has higher catalytic activity in the process of catalyzing ethylene polymerization reaction, and can obtain a polyethylene product with lower bulk density and melt index, and the obtained polyethylene product is spherical and has uniform particle size.

Drawings

FIG. 1 is an X-ray diffraction pattern of a three-dimensional cubic mesoporous composite material C1 in example 1;

FIG. 2 is an SEM scanning electron micrograph of a three-dimensional cubic mesoporous composite material C1 in example 1;

fig. 3 is a pore size distribution diagram of the three-dimensional cubic mesoporous composite material C1 in example 1.

Detailed Description

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: polymerizing ethylene in the presence of a catalyst under a polymerization reaction condition, wherein the catalyst comprises a three-dimensional cubic mesoporous composite material and a magnesium salt and/or a titanium salt loaded on the three-dimensional cubic mesoporous composite material, and the three-dimensional cubic mesoporous composite material is prepared by a preparation method comprising the following steps of:

(1) carrying out first mixing contact on a template agent, butanol, ethyl orthosilicate and an acid agent, and crystallizing and filtering the obtained mixture to obtain a mesoporous material filter cake;

(2) carrying out second mixing contact on water glass and inorganic acid, and filtering a mixture obtained after the contact to obtain a silica gel filter cake;

(3) respectively or after mixing the mesoporous material filter cake and the silica gel filter cake, washing the mixture by using a ceramic membrane filter, and then carrying out ball milling and spray drying to obtain a three-dimensional cubic mesoporous composite material; or respectively or after mixing the mesoporous material filter cake and the silica gel filter cake, ball-milling, washing by using a ceramic membrane filter, and spray-drying to obtain the three-dimensional cubic mesoporous composite material

In the present invention, the template may be any template that is conventional in the art, as long as the pore structure of the obtained three-dimensional cubic mesoporous composite material can meet the requirements. For example, the templating agent may be a triblock copolymer polyoxyethylene-polyoxypropylene-polyoxyethylene. Wherein the templating agent is commercially available (e.g., from Aldrich under the trade name P123, formula EO)₂₀PO₇₀EO₂₀And Mn of 5800) or can be prepared by various conventional methods. When in useWhen the template agent is polyoxyethylene-polyoxypropylene-polyoxyethylene, the mole number of the template agent is calculated according to the number average molecular weight of polyoxyethylene-polyoxypropylene-polyoxyethylene.

According to the present invention, the acid agent may be any of various substances or mixtures (e.g., solution) that can be conventionally used for adjusting pH, and preferably, the acid agent is hydrochloric acid. Hydrochloric acid as an acid agent is preferably used in the form of an aqueous solution. The pH of the aqueous hydrochloric acid solution may be 1-6.

According to the invention, the butanol is preferably n-butanol.

According to the present invention, the molar ratio of the template, butanol and tetraethoxysilane may vary within a wide range as long as a mesoporous molecular sieve material cake having a three-dimensional cubic pore structure may be formed, and generally, the molar ratio of the amounts of the template, butanol and tetraethoxysilane may be 1: 10-100: 10-90, preferably 1: 60-90: 50-75.

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, according to a preferred embodiment of the invention, the first mixing contact is carried out under stirring conditions.

The crystallization conditions are not particularly limited in the present invention, and may be selected conventionally in the art, for example, the crystallization conditions may include: the temperature is 30-150 ℃ and the time is 10-72 hours. Preferably, the crystallization conditions include: the temperature is 40-100 ℃ and the time is 20-40 hours. The crystallization is carried out by a hydrothermal crystallization method.

According to the present invention, in the step (2), the weight ratio of the amount of the water glass to the inorganic acid is not particularly limited and may be appropriately determined according to a conventional process for preparing silica gel. Preferably, the weight ratio of the water glass to the inorganic acid may be 3-6: 1. The weight of the water glass includes the water content therein. When the inorganic acid is used in the form of a solution, the weight of the inorganic acid includes the amount of water therein.

In the present invention, the conditions of the second mixing contact are not particularly limited and may be appropriately determined according to the conventional processes for preparing silica gel. Preferably, 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 1.5 to 3 hours; the pH value is 2-4. In order to further facilitate uniform mixing between the substances, the second mixing contact is preferably carried out under stirring conditions.

The water glass is an aqueous solution of sodium silicate, and the concentration thereof may be 10 to 50% by weight, preferably 12 to 30% by weight.

According to the present invention, the inorganic acid may be various inorganic acids conventionally used in the art, and for example, may be at least one of sulfuric acid, nitric acid and hydrochloric acid. The inorganic acid may be used in a pure form or in the form of an aqueous solution thereof. 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 invention, the ceramic filter is a gas, liquid and solid separation and purification device which integrates filtration, slag discharge, cleaning and regeneration and takes a ceramic membrane element as a core. The ceramic membrane filter may include a ceramic membrane module and a ceramic membrane element, and the ceramic membrane element may be an inorganic ceramic membrane element (inorganic ceramic membrane for short). The inorganic ceramic membrane is a precise ceramic filter material with a porous structure, which is usually formed by sintering alumina, titanium oxide, zirconium oxide and the like at high temperature, a porous supporting layer, a transition layer and a microporous membrane layer are asymmetrically distributed, and the filtering precision covers micro-filtration, ultra-filtration and nano-filtration. Ceramic membrane filtration is a form of "cross-flow filtration" of fluid separation process: the raw material liquid flows at high speed in the membrane tube, the clarified penetrating fluid containing small molecular components penetrates through the membrane outwards along the direction vertical to the clear penetrating fluid under the drive of pressure, and the turbid concentrated solution containing large molecular components is intercepted by the membrane, so that the purposes of separating, concentrating and purifying the fluid are achieved. The ceramic membrane can be obtained commercially, for example, an inorganic ceramic membrane element obtained from york jiugu high-tech co. The ceramic membrane module may be determined according to the particular circumstances of the ceramic membrane element and the sample to be treated.

According to a specific embodiment, the parameters of the inorganic ceramic membrane elements used in the present invention include: the membrane is made of alumina, and has a shape of multi-channel cylindrical, the number of channels is 19, the diameter of the channel is 4mm, the length is 1016mm, the outer diameter (diameter) is 30mm, and the effective membrane area is 0.24m²。

In the present invention, the conditions for the washing treatment using the ceramic membrane filter include: the operating pressure can be from 2.5 to 3.9bar, preferably from 3 to 3.5 bar; the membrane pressure on the side of the circulation may be from 3 to 5bar, preferably from 3.5 to 4.5 bar; the pressure of the membrane at the circulating side can be 2-2.8bar, preferably 2.2-2.6 bar; the flow rate of the circulating side membrane surface can be 4-5m/s, and is preferably 4-4.5 m/s; the pressure of the permeation side is 0.3-0.5 bar; the temperature may be 10-60 ℃. Wherein the operating pressure is the average of the cycle side membrane inlet pressure and the cycle side membrane outlet pressure.

According to a specific embodiment, in the step (3), the mesoporous material filter cake and the silica gel filter cake are respectively washed by using a ceramic membrane filter, and then are mixed, ball-milled and spray-dried to obtain the three-dimensional cubic mesoporous composite material.

According to a specific embodiment, in the step (3), the mesoporous material filter cake and the silica gel filter cake are respectively washed by using a ceramic membrane filter, then are respectively subjected to ball milling, are mixed and are subjected to spray drying, so as to obtain the three-dimensional cubic mesoporous composite material.

According to a specific embodiment, in the step (3), the mesoporous material filter cake and the silica gel filter cake are mixed and then washed by using a ceramic membrane filter, and then ball-milling and spray-drying are performed to obtain the three-dimensional cubic mesoporous composite material.

According to a specific implementation mode, in the step (3), the mesoporous material filter cake and the silica gel filter cake are respectively ball-milled, then the two ball-milled products are respectively washed by using a ceramic membrane filter, and the washed products are mixed and then spray-dried to obtain the three-dimensional cubic mesoporous composite material.

According to a specific embodiment, in the step (3), the mesoporous material filter cake and the silica gel filter cake are respectively ball-milled, and then the ball-milled products are mixed and then are subjected to washing treatment and spray drying by using a ceramic membrane filter, so as to obtain the three-dimensional cubic mesoporous composite material.

According to a specific embodiment, in the step (3), the mesoporous material filter cake and the silica gel filter cake are mixed and then ball-milled, and then the ball-milled product is subjected to washing treatment and spray drying by using a ceramic membrane filter, so as to obtain the three-dimensional cubic mesoporous composite material.

The washing treatment may be performed using water and/or an alcohol (e.g., ethanol). According to a preferred embodiment of the present invention, when the content of sodium ions in the washing liquid of the ceramic membrane filter is detected to be 0.02 wt% or less and the content of the template agent is detected to be less than 1 wt%, the filtration is stopped to obtain a filter cake.

According to the present invention, in step (3), the amount of the mesoporous material filter cake and the silica gel filter cake may vary within a wide range, and for example, the silica gel filter cake 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 mesoporous material filter cake.

According to the present invention, in the step (3), the conditions and the specific operation method of the ball milling are not particularly limited and may be conventionally selected in the art. For example, the ball milling may be carried out in a ball mill in which the inner walls of the milling bowl are preferably lined with polytetrafluoroethylene and the grinding balls in the ball mill may have a diameter of 2-3 mm; the number of the grinding balls can be reasonably selected according to the size of the ball milling tank, and 1 grinding ball can be generally used for the ball milling tank with the size of 50-150 ml; the material of the grinding ball can be agate, polytetrafluoroethylene and the like, and agate is preferred. The ball milling conditions may include: the rotation speed of the grinding ball can be 300-500r/min, the temperature in the ball milling tank can be 15-100 ℃, and the ball milling time can be 0.1-100 hours.

According to the present invention, in step (3), the spray drying may be carried out according to a conventional method. May be at least one selected from the group consisting 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 100-300 ℃, and the rotating speed is 10000-15000 r/min; preferably, the spray drying conditions include: the temperature is 150-250 ℃, and the rotating speed is 11000-13000 r/min.

The preparation method of the three-dimensional cubic mesoporous composite material in the prior art usually further comprises a step of removing the template agent after spray drying, for example, removing the template agent by a calcination method. Because the method of the invention adopts the ceramic membrane for washing treatment, the method for preparing the three-dimensional cubic mesoporous composite material of the invention can not comprise the step of calcining to remove the template agent.

In the invention, the average particle diameter of the three-dimensional cubic mesoporous composite material is 30-60 mu m, and the specific surface area is 150-600m²The pore volume is 1-2mL/g, the pore diameter is in bimodal distribution, and the most probable pore diameters corresponding to the two peaks are 4-10 nanometers and 20-60 nanometers respectively;

preferably, the average particle diameter of the three-dimensional cubic mesoporous composite material is 40-55 μm, and the specific surface area is 300-400m²The pore volume is 1.2-1.8mL/g, the pore diameter is in bimodal distribution, and the most probable pore diameters corresponding to the two modes are 5-10 nanometers and 40-55 nanometers respectively.

In the present invention, the specific surface area, pore volume and pore diameter are measured by a nitrogen adsorption method, and the average particle diameter is measured by a laser particle size distribution instrument. The average particle diameter is the average particle diameter.

According to the invention, the content of the three-dimensional cubic mesoporous composite material in the supported catalyst and the content of the magnesium salt and/or the titanium salt supported on the three-dimensional cubic mesoporous composite material can be changed in a large range. For example, the content of the three-dimensional cubic mesoporous composite may be 50 to 99% by weight, and the sum of the contents of the magnesium salt and the titanium salt, respectively, in terms of magnesium element and titanium element, may be 1 to 50% by weight, based on the total weight of the catalyst. Preferably, the content of the three-dimensional cubic mesoporous composite material is 85-99 wt% based on the total weight of the catalyst, and the sum of the contents of the magnesium salt and the titanium salt calculated by magnesium element and titanium element respectively is 1-15 wt%.

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

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 supported 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 three-dimensional cubic mesoporous composite.

According to a preferred embodiment, the method for preparing the supported catalyst comprises: in the presence of inert gas, the three-dimensional cubic mesoporous composite material is contacted with mother liquor containing magnesium salt and/or titanium salt.

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

In the preparation process of the catalyst, the magnesium salt and the titanium salt are preferably used in an excess amount relative to the three-dimensional cubic mesoporous composite material. For example, the magnesium salt, the titanium salt and the three-dimensional cubic mesoporous composite material are used in amounts such that the content of the three-dimensional cubic mesoporous composite material in the prepared supported catalyst is 50-99 wt%, and the sum of the contents of the magnesium salt and the titanium salt, calculated as magnesium element and titanium element, respectively, is 1-50 wt%; preferably, the content of the three-dimensional cubic mesoporous composite material is 85-99 wt% based on the total weight of the catalyst, and the sum of the contents of the magnesium salt and the titanium salt calculated by magnesium element and titanium element respectively is 1-15 wt%.

Preferably, the conditions for contacting the three-dimensional cubic mesoporous composite material with the mother liquor containing magnesium salt and/or titanium salt comprise: the temperature is 25-100 ℃, preferably 40-75 ℃; the time is 0.1-5h, preferably 1-4 h.

In the present invention, the preparation method of the supported catalyst further comprises: after the three-dimensional cubic mesoporous composite material is contacted with a mother solution containing magnesium salt and/or titanium salt, filtering and drying the three-dimensional cubic mesoporous composite material loaded with the magnesium salt and/or titanium salt. 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 supported catalyst also 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.

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,

polyoxyethylene-polyoxypropylene-polyoxyethylene, available from Aldrich, abbreviated as P123, having the formula EO₂₀PO₇₀EO₂₀The substance having a number average molecular weight Mn of 5800 is registered with the American chemical Abstract under the accession number 9003-11-6.

The ceramic membrane filter used was an inorganic ceramic membrane element of JWCM19 x 30, available from Kyosu Jiuwu high-tech Co., Ltd., and a packing membrane area of 0.5m²The ceramic membrane module of (a); the parameters of the inorganic ceramic membrane element include: the shape is a multi-channel cylinder, the number of channels is 19, the diameter of the channels is 4mm, the length is 1016mm, and the outer diameter (diameter) is 30 mm.

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.

Example 1

This example serves to illustrate the process for the polymerization of ethylene according to the invention and the polyethylene obtained

(1) Preparation of three-dimensional cubic mesoporous composite material

6g (0.001mol) of triblock copolymer P123 is dissolved in a solution formed by 10mL of hydrochloric acid aqueous solution with the pH value of 4 and 220mL of deionized water, the solution is stirred for 4h at 15 ℃ until the P123 is dissolved to form a transparent solution, 6g (0.08mol) of n-butanol is added into the transparent solution and stirred for 1h, then the transparent solution is placed in a water bath with the temperature of 30 ℃, 12.9g (0.062mol) of ethyl orthosilicate is slowly dripped into the solution (1g/min), the temperature is kept at about 30 ℃ and stirred for 24h, then the solution is subjected to hydrothermal treatment at the temperature of 100 ℃ for 24h, and the mesoporous material filter cake A1 is obtained through suction filtration.

Mixing 15 wt% water glass and 12 wt% sulfuric acid solution according to the weight ratio of water glass to sulfuric acid of 5: 1, stirring and reacting for 2 hours at 30 ℃, adjusting the pH of the obtained reaction product to 3 by using sulfuric acid with the concentration of 98 weight percent, and then carrying out suction filtration on the reaction material to obtain a silica gel filter cake B1.

Mixing 10g of the filter cake A1 and 10g of the filter cake B1, and washing the mixture by using a ceramic membrane filter until the content of sodium ions is 0.02 wt% and the content of a template agent is less than 1 wt%, thereby obtaining the three-dimensional cubic mesoporous composite filter cake. Wherein the operating pressure of the membrane module is 3.3bar, the pressure of the membrane at the circulating side is 4bar, the pressure of the membrane at the circulating side is 2.5bar, the flow rate of the membrane surface at the circulating side is 4m/s, the pressure of the permeation side is 0.3bar, and the temperature is 20 ℃.3 parts by weight of water is consumed for preparing one part by weight of the filter cake of the three-dimensional cubic mesoporous composite material.

And (3) putting the three-dimensional cubic mesoporous composite filter cake into a 100mL ball milling tank, wherein the ball milling tank is made of agate, 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 (3) sealing the ball milling tank, carrying out ball milling for 5h at the temperature of 60 ℃ in the ball milling tank, and carrying out spray drying on the ball-milled slurry at the temperature of 200 ℃ at the rotating speed of 12000r/min to obtain the three-dimensional cubic mesoporous composite material C1.

And characterizing the three-dimensional cubic mesoporous composite material C1 by using an XRD (X-ray diffraction), a scanning electron microscope and a nitrogen adsorption instrument.

FIG. 1 is an X-ray diffraction pattern with 2 θ on the abscissa and intensity on the ordinate. As can be seen from the figure, the diffraction peaks of the XRD spectrogram are well preserved, which shows that the pore canal of the three-dimensional cubic mesoporous composite material C1 has a cubic structure and good orderliness.

FIG. 2 is an SEM image. As can be seen from the figure, the microscopic morphology of the three-dimensional cubic mesoporous composite material C1 is a spherical structure with the grain diameter of 30-60 μm, and the dispersion performance is good.

Fig. 3 is a pore size distribution diagram of the three-dimensional cubic mesoporous composite material C1. As can be seen from the figure, the three-dimensional cubic mesoporous composite material C1 has a double-pore structure distribution and uniform pore channels.

The pore structure parameters of the three-dimensional cubic 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 first most probable aperture and the second most probable aperture are arranged in the order from left to right.

(2) Preparation of Supported catalysts

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 three-dimensional cubic mesoporous composite material C1 was added to the mother liquor at 45 ℃ and immersed 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, the catalyst D1 obtained in this example had a magnesium element content of 2.7 wt% and a titanium element content of 0.8 wt%, calculated as elements.

(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_2.16And the catalyst efficiencies are listed in table 4.

Example 2

(1) Preparation of three-dimensional cubic mesoporous composite material

6g (0.001mol) of triblock copolymer P123 is dissolved in a solution formed by 10mL of hydrochloric acid aqueous solution with the pH value of 5 and 220mL of deionized water, the solution is stirred for 4h at 15 ℃ until the P123 is dissolved to form a transparent solution, 4.5g (0.06mol) of n-butanol is added into the transparent solution and stirred for 1h, then the transparent solution is placed in a water bath at 60 ℃, 10.4g (0.05mol) of ethyl orthosilicate is slowly dripped into the solution, the solution is stirred for 48h under the condition that the temperature is kept at about 60 ℃ and the pH value is 5.5, then the solution is subjected to hydrothermal treatment for 20h at 80 ℃, and the mesoporous material filter cake A2 is obtained by suction filtration.

Mixing 15 wt% water glass and 12 wt% sulfuric acid solution according to the weight ratio of water glass to sulfuric acid of 4: 1, stirring and reacting for 1.5 hours at 40 ℃, adjusting the pH of the obtained reaction product to 2 by using sulfuric acid with the concentration of 98 weight percent, and then carrying out suction filtration on the reaction material to obtain a silica gel filter cake B2.

And (3) mixing the prepared 20 g of filter cake A2 with 30 g of filter cake B2, and washing the mixture by using a ceramic membrane filter until the content of sodium ions is 0.02 wt% and the content of a template agent is less than 1 wt%, thereby obtaining the three-dimensional cubic mesoporous composite filter cake. Wherein the operating pressure of the membrane module is 3bar, the pressure of the membrane at the circulating side is 3.5bar, the pressure of the membrane at the circulating side is 2.5bar, the flow rate of the membrane surface at the circulating side is 4.5m/s, the pressure of the permeation side is 0.4bar, and the temperature is 60 ℃.

And (3) putting the three-dimensional cubic mesoporous composite filter cake into a 100mL ball milling tank, wherein the ball milling tank is made of agate, 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 (3) sealing the ball milling tank, ball milling for 0.5h in the ball milling tank at the temperature of 80 ℃, and spray drying the ball milled slurry at the temperature of 250 ℃ at the rotating speed of 11000r/min to obtain the three-dimensional cubic mesoporous composite material C2.

The pore structure parameters of the three-dimensional cubic mesoporous composite material C2 are shown in table 2 below.

TABLE 2

(2) Preparation of Supported catalysts

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 the three-dimensional cubic mesoporous composite material C2 was added to the mother liquor at 60 ℃ and immersed for 1h, then filtered, and washed with n-hexane for 4 times, dried at 75 ℃ and ground to obtain the catalyst D2.

As a result of X-ray fluorescence analysis, the catalyst D2 obtained in this example had a magnesium element content of 2.1 wt% and a titanium element content of 0.6 wt%, calculated as elements.

(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_2.16And the catalyst efficiencies are listed in table 4.

Example 3

This example illustrates the ethylene polymerization process and the polyethylene obtained according to the invention

(1) Preparation of three-dimensional cubic mesoporous composite material

Dissolving 6g (0.001mol) of triblock copolymer P123 in a solution formed by 10mL of hydrochloric acid with the pH value of 3 and 220mL of deionized water, stirring for 4h until the P123 is dissolved to form a transparent solution, adding 6.75g (0.09mol) of n-butyl alcohol into the transparent solution, stirring for 1h, then placing the solution in a water bath at 15 ℃, slowly dripping 15.6g (0.075mol) of ethyl orthosilicate into the solution, stirring for 72h under the condition that the temperature is kept at about 15 ℃ and the pH value is 3.5, then carrying out hydrothermal treatment at 40 ℃ for 40h, and carrying out suction filtration to obtain a mesoporous material filter cake A3;

mixing 15 wt% water glass and 12 wt% sulfuric acid solution according to the weight ratio of water glass to sulfuric acid of 6:1, stirring and reacting at 20 ℃ for 3 hours, adjusting the pH to 4 by using 98 wt% sulfuric acid, and performing suction filtration on the obtained reaction material to obtain a silica gel filter cake B3.

And (3) mixing the prepared 20 g of filter cake A3 with 10g of filter cake B3, and washing the mixture by using a ceramic membrane filter until the content of sodium ions is 0.02 wt% and the content of a template agent is less than 1 wt%, thereby obtaining the three-dimensional cubic mesoporous composite filter cake. Wherein the operating pressure of the membrane module is 3.4bar, the pressure of the membrane at the circulating side is 4.5bar, the pressure of the membrane at the circulating side is 2.3bar, the flow rate of the membrane surface at the circulating side is 4.2m/s, the pressure of the permeate side is 0.5bar, and the temperature is 40 ℃.

And (2) putting the three-dimensional cubic mesoporous composite filter cake into a 100mL ball milling tank (wherein the ball milling tank is made of polytetrafluoroethylene, grinding balls are made of agate, the diameter of the grinding balls is 3mm, the number of the grinding balls is 1, the rotating speed is 500r/min), sealing the ball milling tank, carrying out ball milling for 10 hours at the temperature of 40 ℃ in the ball milling tank, and carrying out spray drying on the slurry subjected to ball milling at the temperature of 150 ℃ at the rotating speed of 13000r/min to obtain the three-dimensional cubic mesoporous composite C3.

The pore structure parameters of the three-dimensional cubic mesoporous composite material C3 are shown in table 3 below.

TABLE 3

(2) Preparation of Supported catalysts

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 three-dimensional cubic mesoporous composite material C3 was added to the mother liquor at 40 ℃ to be immersed for 1 hour, 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, the catalyst D3 obtained in this example had a magnesium element content of 2.2 wt% and a titanium element content of 0.7 wt%, calculated as elements.

(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 85 ℃ and 700mL of hexane was added, 2mL of a 1mol/L Triethylaluminum (TEA) solution in hexane was added with the addition of hexane, 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, a polyethylene pellet powder was obtained. Bulk Density (BD) and melt index MI of the obtained polyethylene granular powder_2.16And the catalyst efficiencies are listed in table 4.

Comparative example 1

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

(1) Preparation of the support

Mixing 15 wt% water glass and 12 wt% sulfuric acid solution in the weight ratio of 5: 1 at 20 c, followed by adjustment of the pH to 3 with 98% by weight sulfuric acid, and then treatment of the resulting reaction mass with a plate and frame filter press, followed by washing with water to a sodium ion content of 0.02% by weight, to give a silica gel filter cake. Eleven parts by weight of water were consumed to prepare one part by weight of the silica gel filter cake.

And (3) putting 10g of the silica gel filter cake into a 100ml ball milling tank, wherein the ball milling tank is made of polytetrafluoroethylene, 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 (3) sealing the ball milling tank, carrying out ball milling for 5h at the temperature of 60 ℃ in the ball milling tank, carrying out spray drying on the ball-milled slurry at the temperature of 200 ℃ at the rotating speed of 12000r/min, and calcining the spray-dried product in a muffle furnace at the temperature of 400 ℃ for 10h in a nitrogen atmosphere to remove hydroxyl and residual moisture, thereby obtaining the silica gel carrier DA 1.

(2) Preparation of Supported catalysts

The procedure was followed as in example 1, except that the three-dimensional cubic mesoporous composite material C1 was replaced with the above silica gel carrier DA1 to obtain a supported catalyst DD 1.

As a result of X-ray fluorescence analysis, the obtained catalyst DD1 contained 1.1 wt% of magnesium, 1.7 wt% of titanium, and 18.32 wt% of chlorine.

(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 supported catalyst DD1 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 4.

Comparative example 2

(1) Preparation of the support

The procedure of example 1 was followed, except that the mixture of the mesoporous material cake and the silica gel cake was washed with distilled water without using a ceramic membrane filter, and the three-dimensional cubic mesoporous composite cake was obtained by mixing distilled water with the above mixture, followed by suction filtration, and repeating the washing until the sodium ion content was 0.02% by weight. Eleven parts by weight of water consumed by preparing one part by weight of the three-dimensional cubic mesoporous composite filter cake. And then ball milling and spray drying are carried out according to the method of example 1, so as to obtain the three-dimensional cubic mesoporous composite material DC 1.

(2) Preparation of Supported catalysts

The procedure was followed as in example 1, except that the three-dimensional cubic mesoporous composite material C1 was replaced with the three-dimensional cubic mesoporous composite material DC1 described above, to obtain the supported catalyst DD 2.

(3) Ethylene polymerization

Polymerization of ethylene was conducted in accordance with the procedure of Experimental example 1, except that the same parts by weight of the supported catalyst DD2 was used in place of the catalyst DD prepared in example 1Catalyst D1. 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 4.

Comparative example 3

(1) The preparation of the support and supported catalyst was carried out according to the method of comparative example 2, except that the following steps were added after spray drying: and calcining the spray-dried product in a muffle furnace at 400 ℃ for 24h in a nitrogen atmosphere, and removing the template agent to obtain the three-dimensional cubic mesoporous composite material DC2 and the supported catalyst DD 3.

(2) 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 supported catalyst DD3 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 4.

TABLE 4

From the results of examples 1-3 and comparative examples 1-3, it can be seen that the polyethylene catalyst prepared by using the three-dimensional cubic mesoporous composite material prepared by the method of the present invention as the carrier has high catalytic activity, and can obtain spherical polyethylene products with low bulk density and low melt index.

In addition, the carrier of the supported catalyst prepared by the method of the invention has less water consumption and less generated waste water. The catalyst can be directly loaded after spray drying without calcining, thereby simplifying the preparation process.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims

1. A process for the polymerization of ethylene, the process comprising: the preparation method is characterized in that the catalyst contains a three-dimensional cubic mesoporous composite material and magnesium salt and/or titanium salt loaded on the three-dimensional cubic mesoporous composite material, wherein the three-dimensional cubic mesoporous composite material is obtained by a preparation method comprising the following steps:

(3) respectively or after mixing the mesoporous material filter cake and the silica gel filter cake, washing the mixture by using a ceramic membrane filter, and then carrying out ball milling and spray drying to obtain a three-dimensional cubic mesoporous composite material; or respectively or after mixing, ball-milling the mesoporous material filter cake and the silica gel filter cake, and then washing and spray-drying by using a ceramic membrane filter to obtain the three-dimensional cubic mesoporous composite material.

2. The method according to claim 1, wherein the washing treatment using the ceramic membrane filter comprises: the operating pressure is 2.5-3.9bar, the pressure of the circulating side inlet membrane is 3-5bar, the pressure of the circulating side outlet membrane is 2-2.8bar, and the flow rate of the circulating side membrane surface is 4-5 m/s; the pressure of the permeation side is 0.3-0.5 bar; the temperature is 10-60 ℃.

3. The method according to claim 1, wherein the silica gel cake is used in an amount of 1 to 200 parts by weight with respect to 100 parts by weight of the mesoporous material cake.

4. The method according to claim 3, wherein the silica gel cake is used in an amount of 20 to 180 parts by weight with respect to 100 parts by weight of the mesoporous material cake.

5. The method according to claim 3, wherein the amount of the silica gel filter cake is 50 to 150 parts by weight based on 100 parts by weight of the mesoporous material filter cake.

6. The method according to claim 1, wherein, in step (1), the template agent is a triblock copolymer polyethylene oxide-polypropylene oxide-polyethylene oxide, and the acid agent is hydrochloric acid.

7. The method of claim 1, wherein the molar ratio of templating agent, butanol, and ethyl orthosilicate is from 1: 10-100: 10-90.

8. The method of claim 7, wherein the molar ratio of the templating agent, butanol, and ethyl orthosilicate is from 1: 60-90: 50-75.

9. The method of claim 1, 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 30-150 ℃ and the time is 10-72 hours.

10. The method of claim 1, 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.

11. The method according to claim 1, wherein the weight ratio of the water glass to the inorganic acid is 3-6: 1; the inorganic acid is one or more of sulfuric acid, nitric acid and hydrochloric acid.

12. The method of claim 1, wherein the ball milling conditions comprise: 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.

13. The method of claim 1, wherein the conditions of the spray drying comprise: the temperature is 150-600 ℃, and the rotating speed is 10000-15000 r/min.

14. The method as claimed in any one of claims 1 to 13, wherein the three-dimensional cubic mesoporous composite has an average particle diameter of 30 to 60 μm and a specific surface area of 150-600m²The pore volume is 1-2mL/g, the pore diameter is in bimodal distribution, and the most probable pore diameters corresponding to the two modes are 4-10 nanometers and 20-60 nanometers respectively.

15. The method as claimed in claim 14, wherein the three-dimensional cubic mesoporous composite has an average particle diameter of 40-55 μm and a specific surface area of 300-400m²The pore volume is 1.2-1.8mL/g, the pore diameter is in bimodal distribution, and the most probable pore diameters corresponding to the two modes are 5-10 nanometers and 40-55 nanometers respectively.

16. The method according to claim 1, wherein the content of the three-dimensional cubic mesoporous composite is 50 to 99% by weight, and the sum of the contents of the magnesium salt and the titanium salt, calculated as magnesium element and titanium element, respectively, is 1 to 50% by weight, based on the total weight of the catalyst.

17. The method of claim 16, wherein the three-dimensional cubic mesoporous composite is present in an amount of 85 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 15 wt%, based on the total weight of the catalyst.

18. The method of claim 1, wherein the catalyst is prepared by a method comprising: in the presence of inert gas, the three-dimensional cubic mesoporous composite material is contacted with mother liquor containing magnesium salt and/or titanium salt.

19. The method of claim 18, wherein the conditions of the contacting comprise: the temperature is 25-100 ℃ and the time is 0.1-5 h.

20. 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.

21. A polyethylene prepared by the process of any one of claims 1 to 20, wherein the polyethylene has a bulk density of 0.4g/mL and a melt index MI_2.16Is 0.41g/10 min;

or the polyethylene has a bulk density of 0.41g/mL and a melt index MI_2.16Is 0.4g/10 min;

or the polyethylene has a bulk density of 0.39g/mL and a melt index MI_2.16It was 0.4g/10 min.