CN108948239B

CN108948239B - Polyolefin catalyst and polyolefin and preparation method thereof

Info

Publication number: CN108948239B
Application number: CN201710390063.6A
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: 2017-05-27
Filing date: 2017-05-27
Publication date: 2020-10-20
Anticipated expiration: 2037-05-27
Also published as: CN108948239A

Abstract

The invention relates to the field of catalysts, and discloses a polyolefin catalyst, polyolefin and preparation methods thereof. The method for preparing a polyolefin catalyst comprises the steps of: (1) in the presence of a template agent, contacting a silicon source with an ammonia water solution to obtain a mesoporous material; (2) mixing the mesoporous material with silica gel and montmorillonite, and then sequentially carrying out filtration washing, ball milling, pulping and spray drying on the mixed material to obtain a spherical double mesoporous montmorillonite composite carrier; (3) in the presence of inert gas, the spherical double mesoporous montmorillonite composite carrier is impregnated in catalyst mother liquor containing magnesium salt and/or titanium salt, and then the filtration and the drying are sequentially carried out; wherein, the filtration and washing in the step (2) are carried out in a ceramic membrane filter, and the content of sodium ions in the mixed material after filtration and washing is not higher than 0.2 percent by weight and the content of the template agent is not higher than 1 percent by weight calculated by sodium element. The method is efficient, simple, energy-saving and environment-friendly.

Description

Polyolefin catalyst and polyolefin and preparation method thereof

Technical Field

The present invention relates to a homogeneous catalysis olefin polymerization reaction technology, and specifically relates to a method for preparing a polyolefin catalyst, a polyolefin catalyst prepared by the method, a method for olefin polymerization, and a polyolefin prepared by the method.

Background

The development and application of polyolefin catalysts is a major breakthrough in the field of olefin polymerization catalysts after traditional Ziegler-Natta catalysts, which makes the research of polyolefin catalysts enter a rapidly developing stage. Because the homogeneous polyolefin catalyst needs a large amount of catalyst to reach high activity, the production cost is high, and the obtained polymer has no granular shape and cannot be used in the polymerization process of a slurry method or a gas phase method which is widely applied, the method for effectively overcoming the problems is to carry out loading treatment on the soluble polyolefin catalyst.

However, the conventional carrier used for the supported polyolefin catalyst often adopts a means of filtering by using a plate and frame filter press in the purification process to remove impurities, but the plate and frame filter press occupies a large area, and meanwhile, the plate and frame filter press runs discontinuously, so that the efficiency is low, the environment of an operation room is poor, secondary pollution is generated, in addition, because the plate and frame filter press needs to use filter cloth, the effect of removing impurities is poor, the waste liquid after washing cannot be recycled, a water source is wasted greatly in the washing process, and simultaneously, the discharged waste water cannot be treated, so that the environmental pollution and the secondary waste are caused. In order to investigate the synthesis of silica gel in depth, it is necessary to try different methods of purification of the support in order to drive the further development of supported catalysts and olefin polymerization processes.

Disclosure of Invention

The invention aims to overcome the defects that the existing method for preparing a supported polyolefin catalyst carrier is low in purification efficiency, poor in effect, complex to operate, large in water consumption and environment-polluted, and further causes the low loading rate of the existing supported polyolefin catalyst carrier and the poor catalytic activity of the supported polyolefin catalyst prepared by the existing supported polyolefin catalyst carrier, and provides a preparation method of the supported polyolefin catalyst, the polyolefin catalyst prepared by the method, an olefin polymerization method and polyolefin prepared by the method.

In order to achieve the above object, the inventors of the present invention found, after research, that in a method for preparing a spherical double mesoporous montmorillonite composite carrier, a ceramic membrane filter is used to purify the spherical double mesoporous montmorillonite composite carrier, the purification efficiency is high, the effect is good, a template agent can be removed without calcination, the operation is simple, the water consumption is small, the environment is friendly, and a supported polyolefin catalyst prepared from the spherical double mesoporous montmorillonite composite carrier has high loading rate and good catalytic activity, so that the supported polyolefin catalyst prepared from the spherical double mesoporous montmorillonite composite carrier can obtain a significantly improved reaction raw material conversion rate when used in olefin polymerization, thereby completing the present invention.

In one aspect, the present invention provides a method for preparing a polyolefin catalyst, the method comprising the steps of:

(1) in the presence of a template agent, contacting a silicon source with an ammonia water solution to obtain a mesoporous material;

(2) mixing the mesoporous material with silica gel and montmorillonite, and then sequentially carrying out filtration washing, ball milling, pulping and spray drying on the mixed material to obtain a spherical double mesoporous montmorillonite composite carrier;

(3) in the presence of inert gas, the spherical double mesoporous montmorillonite composite carrier is impregnated in catalyst mother liquor containing magnesium salt and/or titanium salt, and then the filtration and the drying are sequentially carried out;

wherein, the filtration and washing in the step (2) are carried out in a ceramic membrane filter, and the content of sodium ions in the mixed material after filtration and washing is not higher than 0.2 percent by weight and the content of the template agent is not higher than 1 percent by weight calculated by sodium element.

In a second aspect, the invention provides a polyolefin catalyst prepared by the process provided herein.

In a third aspect, the present invention provides a process for the polymerisation of olefins, said process comprising: and (2) carrying out polymerization reaction on olefin monomers under the polymerization reaction condition in the presence of a catalyst, wherein the catalyst is the polyolefin catalyst provided by the invention and/or the polyolefin catalyst prepared by the method provided by the invention.

In a fourth aspect, the present invention provides a polyolefin prepared by the olefin polymerization process provided by the present invention.

According to the method for preparing the polyolefin catalyst, the ceramic membrane filter is used for filtering and washing, cross-flow filtration is adopted, the membrane surface flow rate is high in the filtering process, the accumulation of pollutants on the surface of the membrane can be reduced, the membrane flux is high, the mesoporous material and the silica gel which are prepared in the early stage are directly mixed with the montmorillonite in a mobile phase state for washing and filtering, the separation efficiency is high, the separation process is simple, the template agent is removed without calcination in the later stage, the prepared spherical double-mesoporous montmorillonite composite carrier can be guaranteed to have a stable mesoporous structure and a high load rate, and the supported olefin catalyst prepared from the spherical double-mesoporous montmorillonite composite carrier is further guaranteed to have high catalytic activity and selectivity.

The invention adopts the ball milling technology and the spray drying technology to lead the obtained slurry to be more exquisite, and the spherical particles obtained after the spray drying have stable structure, can be repeatedly used as the catalyst carrier, and have high strength and are not easy to break. By adopting the spray drying technology, the obtained spherical porous mesoporous composite material has small particle size, uniform particle size distribution and narrow particle size distribution curve, 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.

The mesoporous structure of the carrier in the polyolefin catalyst prepared by the method provided by the invention is stable, the ordered mesoporous structure can be still maintained after the active component is loaded, the efficiency of the supported catalyst prepared by the supported catalyst and the property of the prepared polyolefin product are obviously improved, the catalytic efficiency is high when the supported catalyst is used for olefin monomer polymerization reaction, and the polyolefin product with lower bulk density and melt index can be obtained, specifically, in the olefin polymerization reaction carried out by using the supported olefin catalyst, the catalyst efficiency can reach 2453g PE/gcat h, the bulk density of the prepared polyolefin is below 0.45g/mL, and the melt index is not more than 0.5g/10 min.

In addition, the method for preparing the polyolefin catalyst provided by the invention has the advantages of simple preparation process, energy consumption saving, low preparation cost and good economy.

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 of the spherical mesoporous montmorillonite composite carrier of example 1;

FIG. 2 is an SEM scanning electron micrograph of the spherical mesoporous montmorillonite composite support of example 1;

FIG. 3 is a pore size distribution curve of the spherical mesoporous montmorillonite composite support of 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 method for preparing a polyolefin catalyst, comprising the steps of:

According to the invention, the ceramic membrane filter is a set of precise super-filtration purification equipment which can be widely applied to various fields, the core component of the ceramic membrane filter is a microporous ceramic membrane filter tube, the ceramic membrane filter tube is formed by scientifically mixing various raw materials such as kaolin, zirconia and the like through the processes of biscuiting, crushing, grading, forming, pore forming, membrane making and the like, and the ceramic membrane filter tube has excellent thermal stability and pore stability, has high strength and chemical corrosion resistance, is suitable for precise filtration of various media, has good cleaning and regeneration performance, has double advantages of high-efficiency filtration and precise filtration, and can filter at the filtration rate of 5-10 m/s.

According to the invention, the filtration washing in step (2) is carried out in a ceramic membrane filter, said filtration washing being a fluid separation process in the form of "cross-flow filtration", in particular comprising: directly mixing the mesoporous material prepared in the step (1) with liquid silica gel and montmorillonite in a liquid form, enabling the mixed raw material liquid to flow in a membrane tube at a high speed, taking the pressure difference on two sides of the membrane as a driving force and the membrane as a filtering medium according to different penetration material molecular diameters and different penetration rates in a certain membrane aperture range, and obtaining clear penetrating fluid (water, inorganic salt Na) containing small molecular components under the driving action of certain pressure by taking the pressure difference on two sides of the membrane as a driving force and taking the membrane as a filtering medium⁺Small molecular liquid substances such as template agent and the like) outwards permeate the membrane along the vertical direction, turbid concentrated solution containing macromolecular components (suspended substances, macromolecular substances such as glue, microorganisms and the like) is blocked on the outer surface or the inner surface of the membrane in a mechanical filtration, adsorption and other modes, the filtration resistance is increased along with the extension of the filtration time, and when the pressure difference reaches the preset back flushing pressure difference, the motor transmission and each corresponding valve in the back flushing mechanismStarting, operating according to a program switch, and backwashing can be completed by adopting compressed air or water or purified liquid or solvent, so that the purposes of separating, concentrating and purifying the fluid are finally achieved. In the invention, the filtration washing process is carried out at a filtration rate of 5-10m/s, the washing process needs to be supplemented continuously, the washing mode can be water washing and/or alcohol washing, for example, deionized water can be used for repeated washing and backwashing, then ethanol is used for repeated washing and backwashing, so as to reduce the sticky accumulation of pollutants on the surface of a membrane, improve the membrane flux, the respective washing times and backwashing times can be selected according to the actual experimental effect until the content of sodium ions in sodium element in the mixed material after filtration washing in a membrane tube is not higher than 0.2 wt%, preferably 0.01-0.03 wt%, and the content of a template agent is not higher than 1 wt%, and finally the mixed material in the membrane tube is collected for subsequent treatment, so that the prepared spherical double-mesoporous montmorillonite composite carrier can be directly used for preparing a polyolefin catalyst without carrying out subsequent calcination treatment to remove the template agent, simple operation and energy consumption saving. And when the ceramic membrane filter is adopted for filtering and washing, manual online operation is not needed, and time and labor are saved.

According to the invention, in the step (3), the ball milling object is a mixed material in the ceramic filter membrane tube which is filtered and washed by the ceramic membrane filter until the content of sodium ions calculated by sodium element is not higher than 0.2 wt%, preferably 0.01-0.03 wt%, and the content of the template agent is not higher than 1 wt%, and the specific operation method and conditions of the ball milling are not particularly limited, so as to ensure that the structure of the mesoporous material is not damaged or not basically damaged, and silica gel and montmorillonite enter the pore channels of the mesoporous material. One skilled in the art can select various suitable conditions to implement the present invention based on the above principles. Specifically, the ball milling may be performed in a ball mill, wherein 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 ball milling conditions 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 specific operating methods and conditions of the spray drying are conventional in the art. Specifically, slurry prepared from the ball-milled product and water is added into an atomizer to rotate at a high speed so as to realize spray drying. Wherein the spray drying conditions comprise: the temperature can be 100-300 ℃, and the rotating speed can be 10000-15000 r/min; preferably, the spray drying conditions include: the temperature is 150-250 ℃, and the rotating speed is 11000-13000 r/min; most preferably, the spray drying conditions include: the temperature is 200 ℃, and the rotating speed is 12000 r/min.

According to the present invention, in step (1), the conditions under which the silicon source is contacted with the aqueous ammonia solution are not particularly limited, and for example, the conditions under which the silicon source is contacted with the aqueous ammonia solution may include: the temperature is 25-100 ℃, and the time is 10-72 hours; preferably, the conditions for contacting the silicon source and the aqueous ammonia solution may include: the temperature is 30-150 ℃ and the time is 10-72 hours.

According to the present invention, in the step (1), the amount of each substance used in the preparation of the mesoporous material can be selected and adjusted within a wide range. For example, the silicon source, the template agent, and the ammonia and water in the ammonia water are used in a molar ratio of 1: 0.1-1: 0.1-5: 100-200, preferably 1: 0.2-0.5: 1.5-3.5: 120-180.

According to the present invention, in the step (1), the kind of the template is not particularly limited, and may be various templates conventionally used in the art as long as the obtained spherical mesoporous dimononite composite support can have the above-mentioned pore structure, and preferably, the template may be cetyltrimethylammonium bromide (CTAB).

According to the present invention, in step (1), the kind of the silicon source is not particularly limited, and may be various conventional silicon sources, and the silicon source may include at least one of tetraethoxysilane, methyl orthosilicate, propyl orthosilicate, sodium orthosilicate and silica sol, and preferably, the silicon source is tetraethoxysilane.

According to the present invention, in step (2), the preparation method of the silica gel is not particularly limited, and may be a method for preparing a silica gel that is conventional in the art, for example, the method includes: the water glass is contacted with an inorganic acid solution.

Preferably, the conditions for contacting the water glass with the inorganic acid include: the temperature can be 10-60 ℃, preferably 20-40 ℃; the time may be 1 to 5 hours, preferably 1.5 to 3 hours, and the pH value is 2 to 4. In order to further facilitate uniform mixing between the substances, the contact of the water glass with the mineral acid is preferably carried out under stirring conditions.

According to the invention, the water glass is an aqueous solution of sodium silicate conventional in the art, and its concentration may be 10 to 50% by weight, preferably 12 to 30% by weight.

According to the present invention, the kind of the inorganic acid may be conventionally selected in the art, and for example, may be one or more 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 reaction system has a pH of 2 to 4 under the contact conditions of the water glass and the inorganic acid.

According to the present invention, in the step (2), the amount of the mesoporous material, the silica gel and the montmorillonite can be selected according to the components of the spherical mesoporous and mesoporous montmorillonite composite carrier to be expected, and preferably, the amount of the silica gel is 1 to 200 parts by weight and the amount of the montmorillonite is 1 to 50 parts by weight based on 100 parts by weight of the mesoporous material.

More preferably, the amount of the silica gel is 50 to 150 parts by weight based on 100 parts by weight of the mesoporous material; the dosage of the montmorillonite is 20-50 parts by weight.

According to the present invention, in the step (3), 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.

According to the present invention, in step (3), the impregnation conditions may include: the dipping temperature is 25-100 ℃, and preferably 40-60 ℃; the impregnation time is from 0.5 to 1 hour, preferably from 1 to 3 hours.

The invention also provides a polyolefin catalyst prepared by the method.

According to the invention, the polyolefin catalyst prepared by the method contains a spherical double-mesoporous montmorillonite composite carrier and a magnesium salt and/or a titanium salt loaded on the composite carrier, wherein the spherical double-mesoporous montmorillonite composite carrier contains montmorillonite, silica and a mesoporous molecular sieve material with two-dimensional hexagonal pore channel distribution, the average particle size of the spherical double-mesoporous montmorillonite composite carrier is 20-50 mu m, and the specific surface area of the spherical double-mesoporous montmorillonite composite carrier is 200-650m²The pore volume is 0.5-1.5mL/g, the pore size distribution is bimodal, and the most probable pore sizes corresponding to the bimodal are 2-10nm and 15-45nm respectively.

According to the invention, the spherical double mesoporous montmorillonite composite carrier has a special one-dimensional and two-dimensional hexagonal pore canal diplopore distribution structure, the average particle size of the particles is measured by adopting a laser particle size distribution instrument, and the specific surface area, the pore volume and the most probable pore diameter are measured according to a nitrogen adsorption method. In the present invention, the particle size refers to the particle size of the raw material particles, and is expressed by the diameter of the sphere when the raw material particles are spherical, by the side length of the cube when the raw material particles are cubic, and by the mesh size of the screen that can sieve out the raw material particles when the raw material particles are irregularly shaped.

According to the invention, the spherical double-mesoporous montmorillonite composite carrier can ensure that the spherical double-mesoporous montmorillonite composite carrier is not easy to agglomerate by controlling the particle size of the spherical double-mesoporous montmorillonite composite carrier within the range, and the conversion rate of reaction raw materials in the olefin polymerization reaction process can be improved by using the spherical double-mesoporous montmorillonite composite carrier as a supported catalyst prepared by using the spherical double-mesoporous montmorillonite composite carrier as a carrier. When the specific surface area of the spherical double mesoporous montmorillonite composite carrier is less than 200m²When the volume/g and/or pore volume is less than 0.5mL/g, the catalytic activity of the supported catalyst prepared by using the supported catalyst is remarkably reduced; when the spherical double mediumThe specific surface area of the porous montmorillonite composite carrier is more than 650m²When the pore volume is more than 1.5mL/g, the supported catalyst prepared by using it as a carrier is liable to undergo agglomeration during the olefin polymerization reaction, thereby affecting the catalyst efficiency during the olefin reaction and the flowability of the polyolefin product to be produced.

Preferably, the average particle diameter of the spherical double mesoporous montmorillonite composite carrier is 35-55 μm, and the specific surface area is 250-450m²The pore volume is 0.8-1.4mL/g, the pore size distribution is bimodal, and the most probable pore sizes corresponding to the bimodal are 5-8nm and 20-30nm respectively.

According to the present invention, in the polyolefin catalyst, the content of the spherical mesoporous montmorillonite composite support is 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, is 1 to 10 wt% with respect to 100 parts by weight of the polyolefin catalyst;

according to 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 polyolefin catalyst component can be measured by adopting an X-ray fluorescence spectrum analysis method.

According to the present invention, in the polyolefin catalyst, the contents of the spherical mesoporous montmorillonite composite carrier and the magnesium salt and/or titanium salt supported on the spherical mesoporous montmorillonite composite carrier are not particularly limited and may be determined according to a supported catalyst that is conventional in the art. For example, the spherical mesoporous montmorillonite composite support may be contained 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 polyolefin catalyst. Preferably, the content of the spherical double mesoporous montmorillonite composite carrier can be 90.5-98.5 wt%, and the sum of the contents of the magnesium salt and the titanium salt calculated by magnesium element and titanium element respectively can be 1.5-9.5 wt%. More preferably, the content of the spherical double mesoporous montmorillonite composite carrier can be 91-96 wt%, and 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%.

Preferably, the polyolefin catalyst has an average particle diameter of 20 to 50 μm and a specific surface area of 250-450m²The pore volume is 0.6-1.1mL/g, the pore diameter distribution is bimodal, and the most probable pore diameters corresponding to the bimodal are 2-10nm and 20-30nm respectively.

According to the present invention, in the spherical double mesoporous montmorillonite composite carrier, the content of the silica is 1 to 200 parts by weight, preferably 50 to 150 parts by weight, with respect to 100 parts by weight of the mesoporous molecular sieve material having a two-dimensional hexagonal pore distribution; the content of the montmorillonite is 1-50 parts by weight, and preferably 20-50 parts by weight.

According to the present invention, the mesoporous molecular sieve material having a two-dimensional hexagonal pore distribution structure may be a mesoporous molecular sieve material conventionally used in the art, and may be prepared according to a conventional method.

The present invention also provides a process for the polymerization of olefins, the process comprising: and under the condition of polymerization reaction, in the presence of a catalyst, carrying out polymerization reaction on olefin monomers, wherein the catalyst is the polyolefin catalyst provided by the invention or the polyolefin catalyst prepared by the method provided by the invention.

According to the present invention, the reaction conditions of the polymerization reaction are not particularly limited and may be olefin polymerization reaction conditions conventional in the art, for example, the reaction may be carried out in the presence of an inert gas, and the polymerization reaction conditions may include: the temperature is 10-100 ℃, the time is 0.5-5h, and the pressure is 0.1-2 MPa; preferably, the conditions of the polymerization reaction may include: 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.

In a specific embodiment, the supported polyolefin catalyst can be a supported polyethylene catalyst, the polymerization reaction is an ethylene polymerization reaction, and the ethylene polymerization process comprises: under the condition of ethylene 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, filtration washing was performed in an alumina ceramic membrane filter available from kyoto corporation, south of Jiangsu;

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 an ASAP2020-M + C type adsorber, available from Micromeritics, USA, and BET method was used for the specific surface area and pore volume calculation of the sample; the particle size distribution of the sample is carried out on a Malvern laser particle sizer; the rotary evaporator is produced by German IKA company, and the model is RV10 digital; the active component loading of the propane dehydrogenation catalyst was measured on a wavelength dispersive X-ray fluorescence spectrometer, model Axios-Advanced, available from parnacco, netherlands; analysis of the reaction product composition was performed on a gas chromatograph available from Agilent under model 7890A;

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

The melt index of polyolefins is determined using the method specified in ASTM D1238-99.

Example 1

(1) Preparation of polyolefin catalyst

Adding hexadecyl trimethyl ammonium bromide and ethyl orthosilicate into an ammonia water solution with the concentration of 25 weight percent at the temperature of 80 ℃, and then adding deionized water, wherein the adding amount of the ethyl orthosilicate is 1g, and the mol ratio of ammonia to water in the ethyl orthosilicate, the hexadecyl trimethyl ammonium bromide and the ammonia water is 1: 0.37: 2.8: 142 and stirred at the temperature of 80 ℃ for 4 hours to obtain a mesoporous molecular sieve material A1 with two-dimensional hexagonal pore channel distribution.

Water glass with a concentration of 15 wt% and a sulfuric acid solution with a concentration of 12 wt% were mixed in a weight ratio of 5:1 and were brought into contact for reaction at 30 ℃ for 1.5h, followed by adjustment of the pH to 3 with sulfuric acid with a concentration of 98 wt% to give a reaction product, silica gel B1.

Stirring and mixing 10g of the prepared mesoporous material A1, 10g of silica gel B1 and 10g of montmorillonite, introducing the mixture into a ceramic membrane filtering system, filtering and washing the mixture by using deionized water and ethanol until the content of sodium ions in the mixture is 0.02 wt% calculated by sodium element and the content of hexadecyl trimethyl ammonium bromide is 0.5 wt%, collecting the mixture in a ceramic membrane tube, and putting the mixture 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, and the rotating speed is 400 r/min. Sealing the ball milling tank, and carrying out ball milling for 1 hour in the ball milling tank at the temperature of 60 ℃ to obtain 30g of solid powder; the solid powder is dissolved in 30g of deionized water to prepare slurry, and then spray drying is carried out at 200 ℃ and at the rotating speed of 12000r/min, so as to obtain 30g of spherical double mesoporous montmorillonite composite carrier C1 with a two-dimensional hexagonal pore distribution structure.

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. Adding 1g of spherical double-mesoporous montmorillonite composite carrier C1 into the mother liquor at 45 ℃, soaking for 1h, then filtering, washing with n-hexane for 4 times, drying at 75 ℃, and grinding to obtain the catalyst Cat-1.

The spherical double mesoporous montmorillonite composite carrier C1 and the polyethylene catalyst Cat-1 are characterized by an XRD, a scanning electron microscope and an ASAP2020-M + C type adsorption instrument.

In the polyethylene catalyst Cat-1 obtained in this example, the content of magnesium was 6.1% by weight, the content of titanium was 3% by weight, and the content of chlorine was 11% by weight, in terms of elements.

FIG. 1 is an X-ray diffraction pattern in which the abscissa is 2. theta. and the ordinate is intensity, and the XRD pattern of a spherical double mesoporous montmorillonite composite carrier C1 has a hexagonal pore structure of 2D specific to a mesoporous material, as can be seen from the small-angle peaks appearing in the XRD pattern;

FIG. 2 is an SEM (scanning electron microscope) image, and it can be seen that the microscopic morphology of the spherical double mesoporous montmorillonite composite carrier C1 is mesoporous spheres with a particle size of 20-50 μm, and the spherical double mesoporous montmorillonite composite carrier has good dispersibility.

Fig. 3 is a particle size distribution curve of the spherical mesoporous montmorillonite composite carrier C1, and it can be seen from the graph that the spherical mesoporous montmorillonite composite carrier C1 has a uniform particle size distribution.

Table 1 shows the pore structure parameters of the spherical double mesoporous montmorillonite composite carrier C1 and the polyethylene catalyst Cat-1.

TABLE 1

Sample (I)	Specific surface area (m)²/g)	Pore volume (mL/g)	Most probable aperture^*(nm)	Particle size (. mu.m)
					Composite carrier C1	292	1.3	7，29	20-50
Catalyst Cat-1	253	1.1	6，25.5	20-50

*: 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.

As can be seen from the data in table 1, the specific surface area and the pore volume of the spherical double mesoporous montmorillonite composite carrier are reduced after the main active components of magnesium salt and titanium salt are loaded, which indicates that the active components of magnesium salt and sodium salt enter the interior of the spherical double mesoporous montmorillonite composite carrier during the loading reaction.

(2) 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 solution of Triethylaluminum (TEA) in hexane was added with the addition of hexane, then 0.5g of catalyst Cat-1 was added, ethylene gas was introduced, the pressure was raised to 1MPa and maintained at 1MPa, and after 1 hour of reaction at 70 ℃, 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_2.16And the catalyst efficiencies are listed in table 4.

Example 2

(1) Preparation of polyolefin catalyst

Adding hexadecyl trimethyl ammonium bromide and ethyl orthosilicate into an ammonia water solution with the concentration of 25 weight percent at 50 ℃, and adding deionized water, wherein the adding amount of the ethyl orthosilicate is 1g, and the mol ratio of ammonia to water in the ethyl orthosilicate, the hexadecyl trimethyl ammonium bromide and the ammonia water is 1: 0.5: 1.5: 180 ℃ and stirring at the temperature of 50 ℃ for 7 hours to obtain a mesoporous molecular sieve material A2 with two-dimensional hexagonal pore channel distribution.

Water glass with a concentration of 15 wt% and a sulfuric acid solution with a concentration of 12 wt% were mixed in a weight ratio of 4:1 and were brought into contact for reaction at 40 ℃ for 2 hours, followed by adjustment of the pH to 2 with sulfuric acid with a concentration of 98 wt% to give a reaction product, silica gel B2.

Stirring and mixing 20g of the prepared mesoporous material A2, 10g of silica gel B2 and 8g of montmorillonite, introducing the mixture into a ceramic membrane filtering system, filtering and washing the mixture by using deionized water and ethanol until the content of sodium ions in the mixture is 0.02 wt% calculated by sodium element and the content of hexadecyl trimethyl ammonium bromide is 0.3 wt%, collecting the mixture in a ceramic membrane tube, and putting the mixture 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, and the rotating speed is 400 r/min. Sealing the ball milling tank, and carrying out ball milling for 0.5 hour in the ball milling tank at the temperature of 80 ℃ to obtain 38g of solid powder; the solid powder is dissolved in 33 g of deionized water to prepare slurry, and then spray drying is carried out at 250 ℃ and the rotating speed of 11000r/min, thus obtaining 35g of spherical double mesoporous montmorillonite composite carrier C2 with a two-dimensional hexagonal pore distribution structure.

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. Adding 1g of spherical double-mesoporous montmorillonite composite carrier C2 into the mother liquor at 60 ℃, soaking for 1h, then filtering, washing with n-hexane for 4 times, drying at 75 ℃, and grinding to obtain the catalyst Cat-2.

The spherical double mesoporous montmorillonite composite carrier C2 and the polyethylene catalyst Cat-2 are characterized by an XRD, a scanning electron microscope and an ASAP2020-M + C type adsorption instrument.

In the polyethylene catalyst Cat-2 obtained in this example, the content of magnesium was 6.9% by weight, the content of titanium was 2.7% by weight, and the content of chlorine was 9.1% by weight, in terms of elements.

Table 2 shows the pore structure parameters of the spherical double mesoporous montmorillonite composite carrier C2 and the polyethylene catalyst Cat-2.

TABLE 2

Sample (I)	Specific surface area (m)²/g)	Pore volume (mL/g)	Most probable aperture^*(nm)	Particle size (. mu.m)
					Composite carrier C2	262	1.1	6，28	25-45
Catalyst Cat-2	237	0.9	5，22	25-45

As can be seen from the data in table 2, the specific surface area and the pore volume of the spherical double mesoporous montmorillonite composite carrier are reduced after the main active components of magnesium salt and titanium salt are loaded, which indicates that the active components of magnesium salt and sodium salt enter the interior of the spherical double mesoporous montmorillonite composite carrier during the loading reaction.

(2) Ethylene polymerization

In a 2L stainless steel high pressure polymerization kettle, nitrogen and ethylene are replaced by three times respectively, then 200mL hexane is added, the kettle is heated to 75 ℃, 900mL hexane is added, 2mL of 1mol/L triethyl aluminum (TEA) hexane solution is added along with the addition of the hexane, 0.1g of catalyst Cat-2 is added, ethylene gas is introduced, the pressure is increased to 1MPa and maintained at 1MPa, and the mixture is reacted for 1.5 hours at 75 ℃ and then is filtered and separated to obtain polyethylene particle powder. The resulting polymerBulk Density (BD) and melt index MI of ethylene granular powder_2.16And the catalyst efficiencies are listed in table 4.

Example 3

(1) Preparation of polyolefin catalyst

Adding hexadecyl trimethyl ammonium bromide and ethyl orthosilicate into an ammonia water solution with the concentration of 25 weight percent at 90 ℃, and adding deionized water, wherein the adding amount of the ethyl orthosilicate is 1g, and the mol ratio of ammonia to water in the ethyl orthosilicate, the hexadecyl trimethyl ammonium bromide and the ammonia water is 1: 0.2: 3.5: 120 and stirred at the temperature of 90 ℃ for 3 hours to obtain a mesoporous molecular sieve material A3 with two-dimensional hexagonal pore channel distribution.

Mixing 15 wt% water glass and 12 wt% sulfuric acid solution in the weight ratio of 6:1, contacting at 20 deg.c for 3 hr, and regulating the pH value to 4 with 98 wt% sulfuric acid to obtain silica gel B3 as the reaction product.

Stirring and mixing 20g of the prepared mesoporous material A3, 30g of silica gel B3 and 12g of montmorillonite, introducing the mixture into a ceramic membrane filtering system, filtering and washing the mixture by using deionized water and ethanol until the content of sodium ions in the mixture is 0.02 wt% calculated by sodium element and the content of hexadecyl trimethyl ammonium bromide is 0.4 wt%, collecting the mixture in a ceramic membrane tube, and putting the mixture 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, and the rotating speed is 550 r/min. Sealing the ball milling tank, and carrying out ball milling for 10 hours in the ball milling tank at the temperature of 40 ℃ to obtain 55g of solid powder; the solid powder is dissolved in 30g of deionized water to prepare slurry, and then spray drying is carried out at 250 ℃ and at the rotating speed of 13000r/min, so as to obtain 53g of spherical double mesoporous montmorillonite composite carrier C3 with a two-dimensional hexagonal pore distribution structure.

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. Adding 1g of spherical double-mesoporous montmorillonite composite carrier C3 into the mother liquor at 40 ℃, soaking for 1h, then filtering, washing with n-hexane for 4 times, drying at 75 ℃, and grinding to obtain the catalyst Cat-3.

The spherical double mesoporous montmorillonite composite carrier C3 and the polyethylene catalyst Cat-3 are characterized by an XRD, a scanning electron microscope and an ASAP2020-M + C type adsorption instrument.

In the polyethylene catalyst Cat-3 obtained in this example, the content of magnesium was 6.6% by weight, the content of titanium was 2.3% by weight, and the content of chlorine was 9.2% by weight, in terms of elements.

Table 3 shows the pore structure parameters of the spherical double mesoporous montmorillonite composite carrier C3 and the polyethylene catalyst Cat-3.

TABLE 3

Sample (I)	Specific surface area (m)²/g)	Pore volume (mL/g)	Most probable aperture^*(nm)	Particle size (. mu.m)
					Composite carrier C3	303	1.2	8，26	30-50
Catalyst Cat-3	262	1	6，22	30-50

(2) Ethylene polymerization

In a 2L stainless steel high pressure polymerization kettle, nitrogen and ethylene are replaced by three times respectively, then 200mL hexane is added, the kettle is heated to 75 ℃, 900mL hexane is added, 2mL of 1mol/L triethyl aluminum (TEA) hexane solution is added along with the addition of the hexane, 0.1g of catalyst Cat-2 is added, ethylene gas is introduced, the pressure is increased to 1MPa and maintained at 1MPa, and the mixture is reacted for 1.5 hours at 75 ℃ and then is filtered and separated to obtain polyethylene particle powder. 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

(1) Preparation of polyolefin catalyst

Preparing a spherical double-mesoporous montmorillonite composite carrier according to the method of example 1, except that in the step (1), the mesoporous molecular sieve material solution with two-dimensional hexagonal pore distribution is required to be subjected to suction filtration and washed with deionized water four times to obtain a filter cake DA1 of the mesoporous molecular sieve material with two-dimensional hexagonal pore distribution; in the step (2), the obtained silica gel needs to be subjected to suction filtration, and is washed by deionized water until the content of sodium ions in terms of sodium element is 0.02 wt%, so that a filter cake DB1 of the silica gel is obtained; and then stirring and mixing the filter cake DA1 of the mesoporous material, the filter cake DB1 of the silica gel and the montmorillonite, filtering and washing the mixture without a ceramic filter membrane filter, and directly putting the mixture into a ball milling tank for ball milling. And sequentially pulping and spray-drying the solid powder obtained by ball milling, calcining the product obtained by spray-drying in a muffle furnace at 600 ℃ for 15h, and removing cetyl trimethyl ammonium bromide (template agent) to obtain the spherical double-mesoporous montmorillonite composite carrier D1. Thereafter, a polyolefin catalyst was prepared according to the method of example 1, except that the spherical mesoporous montmorillonite composite carrier D1 was used in place of the spherical mesoporous montmorillonite composite carrier C1 in the same weight part, thereby obtaining a comparative polyolefin catalyst Cat-D-1.

As a result of X-ray fluorescence analysis, in the catalyst Cat-D-1 obtained in this example, the content of magnesium was 2.2% by weight, the content of titanium was 1.7% by weight, and the content of chlorine was 12.5% by weight, in terms of elements.

(2) Ethylene polymerization

Polymerization of ethylene was conducted in accordance with the procedure of example 1, except that the catalyst Cat-1 prepared in example 1 was replaced with the same parts by weight of comparative catalyst Cat-D-1, respectively. 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 2

(1) Preparation of polyolefin catalyst

Silica gel was prepared according to the method in example 1, and the obtained silica gel was filtered using a plate and frame filter press, and then the silica gel obtained by filtering with the plate and frame filter press was calcined at 400 ℃ for 10 hours under nitrogen protection to remove hydroxyl groups and residual moisture, thereby obtaining a silica gel support D2 prepared by a heat-activated plate and frame filter press. In the preparation process, eleven tons of water are consumed to obtain one ton of the silica gel carrier. Then, a catalyst was prepared according to the method of example 1, except that the same parts by weight of the above silica gel carrier D2 was used instead of the spherical mesoporous montmorillonite composite carrier C1, thereby obtaining a comparative catalyst Cat-D-2.

As a result of X-ray fluorescence analysis, in the catalyst Cat-D-2 obtained in this example, the content of magnesium was 1.1% by weight, the content of titanium was 1.6% by weight, and the content of chlorine was 18.63% by weight, in terms of the elements.

(2) Ethylene polymerization

Polymerization of ethylene was conducted in accordance with the procedure of example 1, except that the catalyst Cat-1 prepared in example 1 was replaced with the same parts by weight of comparative catalyst Cat-D-2, respectively. Bulk Density (BD) and melt index MI of the obtained polyethylene granular powder_2.16And the catalyst efficiencies are listed in table 4.

TABLE 4

From the results of comparing the above examples 1-3 with the comparative examples 1-2, it can be seen that the polyolefin catalyst and the spherical mesoporous montmorillonite composite carrier prepared by the method of the present invention have high catalytic efficiency when used for olefin polymerization reaction, and can obtain polyolefin products with low bulk density and melt index, specifically, when the spherical mesoporous montmorillonite composite carrier and the supported catalyst prepared by the method of the present invention are used for ethylene polymerization reaction, the catalytic efficiency can reach 2453g PE/gcat h, the bulk density of the prepared polyethylene product can reach below 0.45g/mL, and the melt index does not exceed 0.5g/10 min. The catalyst which is not obtained by the method has lower catalytic efficiency, and when the catalyst is used for catalyzing ethylene polymerization, the obtained polyethylene product has higher bulk density and poorer flowability.

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 preparing a polyolefin catalyst, comprising the steps of:

wherein, the filtration and washing in the step (2) are carried out in a ceramic membrane filter, and the content of sodium ions in the mixed material after filtration and washing is not higher than 0.2 percent by weight and the content of the template agent is not higher than 1 percent by weight calculated by sodium element;

wherein the template agent is cetyl trimethyl ammonium bromide; the silicon source comprises at least one of tetraethoxysilane, methyl orthosilicate, propyl orthosilicate, sodium orthosilicate and silica sol;

in the step (1), the molar ratio of the silicon source, the template agent, the ammonia in the ammonia water and the water is 1: 0.1-1: 0.1-5: 100-;

in the step (2), the amount of the silica gel is 1 to 200 parts by weight based on 100 parts by weight of the mesoporous material; the dosage of the montmorillonite is 1-50 parts by weight.

2. The method of claim 1, wherein, in step (1), the conditions of the contacting comprise: the temperature is 25-100 ℃ and the time is 1-10 h.

3. The method of claim 1, wherein, in step (1), the silicon source is tetraethoxysilane.

4. The method according to claim 1, wherein, in the step (2), the preparation method of the silica gel comprises: the water glass is contacted with an inorganic acid solution.

5. The method of claim 4, wherein in step (2), the conditions of the contacting comprise: the temperature is 10-60 deg.C, the time is 1-5h, and the pH value is 2-4.

6. The method according to claim 4, wherein, in the step (2), the inorganic acid solution is an aqueous solution of at least one of sulfuric acid, nitric acid and hydrochloric acid.

7. The method according to claim 1, wherein, in the step (2), the silica gel is used in an amount of 50 to 150 parts by weight, based on 100 parts by weight of the mesoporous material; the dosage of the montmorillonite is 20-50 parts by weight.

8. The method of claim 1, wherein, in step (3), the impregnation conditions include: the dipping temperature is 25-100 ℃; the dipping time is 0.5-1 h.

9. The method of claim 1, wherein, in step (3), the impregnation conditions include: the dipping temperature is 40-60 ℃; the dipping time is 1-3 h.

10. A polyolefin catalyst prepared by the process of any one of claims 1-9.

11. The polyolefin catalyst according to claim 10, wherein the polyolefin catalyst comprises a spherical mesoporous double-mesoporous montmorillonite composite carrier and a magnesium salt and/or a titanium salt loaded on the composite carrier, the spherical mesoporous double-mesoporous montmorillonite composite carrier comprises montmorillonite, silica and a mesoporous molecular sieve material with a two-dimensional hexagonal pore channel distribution, and the average particle diameter of the spherical mesoporous double-mesoporous montmorillonite composite carrier is 20-50 μm, and the specific surface area is 200-650 m-²The pore volume is 0.5-1.5mL/g, the pore size distribution is bimodal, and the most probable pore sizes corresponding to the bimodal are 2-10nm and 15-45nm respectively.

12. The polyolefin catalyst according to claim 11, wherein the spherical mesoporous montmorillonite composite support is contained in an amount of 90 to 99% by weight and the sum of the contents of the magnesium salt and the titanium salt in terms of magnesium element and titanium element, respectively, is 1 to 10% by weight with respect to 100 parts by weight of the polyolefin catalyst.

13. The polyolefin catalyst according to claim 10 or 11, wherein the polyolefin catalyst has an average particle diameter of 20 to 50 μm and a specific surface area of 250-450m²The pore volume is 0.6-1.1mL/g, the pore diameter distribution is bimodal, and the most probable pore diameters corresponding to the bimodal are 2-10nm and 20-30nm respectively.

14. The polyolefin catalyst according to claim 11, wherein the silica is contained in an amount of 1-200 parts by weight, relative to 100 parts by weight of the mesoporous molecular sieve material having a two-dimensional hexagonal pore distribution; the content of the montmorillonite is 1-50 parts by weight.

15. The polyolefin catalyst according to claim 11, wherein the silica is contained in an amount of 50-150 parts by weight, relative to 100 parts by weight of the mesoporous molecular sieve material having a two-dimensional hexagonal pore distribution; the content of the montmorillonite is 20-50 parts by weight.

16. A process for the polymerization of olefins, the process comprising: a process for polymerizing an olefin monomer under polymerization conditions in the presence of a catalyst, wherein the catalyst is a polyolefin catalyst according to any one of claims 10 to 15.

17. The process of claim 16, wherein the polymerization reaction is carried out in the presence of an inert gas, and the conditions of the polymerization reaction comprise: the temperature is 10-100 ℃, the time is 0.5-5h, and the pressure is 0.1-2 MPa.