CN107417832B

CN107417832B - Ethylene polymerization method and polyethylene

Info

Publication number: CN107417832B
Application number: CN201610349201.1A
Authority: CN
Inventors: 亢宇; 张明森; 周俊领; 吕新平; 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: 2016-05-24
Filing date: 2016-05-24
Publication date: 2020-05-12
Anticipated expiration: 2036-05-24
Also published as: CN107417832A

Abstract

The invention relates to the field of polymerization reaction, in particular to an ethylene polymerization method and polyethylene prepared by the method. The invention discloses a method for polymerizing ethylene, which comprises the following steps: polymerizing ethylene in the presence of a catalyst under a polymerization reaction condition, wherein the catalyst comprises a spherical composite material and a magnesium salt and/or a titanium salt loaded on the spherical composite material, and the spherical composite material comprises a mesoporous molecular sieve material with a three-dimensional cubic cage-shaped structure and silica gel. The invention also discloses polyethylene prepared by the method. The ethylene polymerization method provided by the invention can be used for obtaining a polyethylene product with low bulk density and melt index and low possibility of breakage.

Description

Ethylene polymerization method and polyethylene

Technical Field

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

Background

Polyethylene is a polymer produced by polymerization using ethylene as a monomer. The polyethylene has the advantages of excellent low temperature resistance, good chemical stability and the like, and is widely applied to the field of chemical industry. In the process of preparing polyethylene, the use of a polyethylene catalyst is one of the key factors affecting the yield and quality of polyethylene products.

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.

Since the synthesis of a regular mesoporous material with highly ordered pore channels by the company Mobile in 1992, the application of the mesoporous material in the fields of catalysis, separation, medicine and the like has attracted much attention due to the high specific surface, the regular pore channel structure and the narrow pore size distribution. 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 mesoporous material of the supported polyethylene catalyst reported in the previous literature is MCM-41, and the catalytic activity of the MCM-41 which is treated by MAO and then supported by the polyethylene catalyst after ethylene polymerization is 10⁶gPE/(mol Zr h). The reason that the mesoporous material MCM-41 is loaded with the catalyst and then has lower ethylene polymerization activity is mainly the pore wall of the MCM-41The structure thermal stability and the hydrothermal stability are poor, and the pore wall is partially collapsed in the loading process, so that the loading effect is influenced, and the catalytic activity is influenced. Therefore, there is a need to find a mesoporous material which has a stable mesoporous structure and can maintain order after loading a catalyst, so as to improve catalytic activity and polyethylene product performance.

Disclosure of Invention

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

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 spherical composite material and a magnesium salt and/or a titanium salt loaded on the spherical composite material, the spherical composite material comprises a mesoporous molecular sieve material with a three-dimensional cubic cage structure and silica gel, the pore volume of the spherical composite material is 0.5-1.8mL/g, and the specific surface area is 200-²The average particle size is 20-60 mu m, the pore diameters are distributed in a bimodal mode, the two modes correspond to a first most probable pore diameter and a second most probable pore diameter respectively, the first most probable pore diameter is smaller than the second most probable pore diameter, the first most probable pore diameter is 1-10nm, and the second most probable pore diameter is 10-50 nm.

The invention also provides polyethylene prepared by the method.

In the ethylene polymerization method provided by the invention, the used spherical composite material has a stable mesoporous structure, can still maintain an ordered mesoporous structure after an active component is loaded, the supported polyethylene catalyst prepared by the spherical composite material has high catalytic activity when used for ethylene polymerization reaction, and simultaneously, a polyethylene product which has low bulk density and melt index and is not easy to break can be obtained, specifically, the bulk density of the prepared polyethylene product is less than 0.42g/mL, the melt index is less than 0.7g/10min, and the powder breaking rate is less than 3%.

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 spherical composite C1 according to example 1 of the present invention;

FIG. 2 is an X-ray diffraction pattern of catalyst D1 according to example 1 of the present invention;

FIG. 3 is an SEM scanning electron micrograph of the micro-morphology of spherical composite material C1 according to example 1 of the present invention;

FIG. 4 is a pore size distribution diagram of spherical composite material C1 according to example 1 of the present invention.

Detailed Description

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

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

The present invention provides a process for the polymerization of ethylene, the process comprising: polymerizing ethylene in the presence of a catalyst under a polymerization reaction condition, wherein the catalyst comprises a spherical composite material and a magnesium salt and/or a titanium salt loaded on the spherical composite material, the spherical composite material comprises a mesoporous molecular sieve material with a three-dimensional cubic cage-shaped structure and silica gel, and the spherical composite materialThe pore volume of (A) is 0.5-1.8mL/g, the specific surface area is 200-650m²The average particle size is 20-60 mu m, the pore diameters are distributed in a bimodal mode, the two modes correspond to a first most probable pore diameter and a second most probable pore diameter respectively, the first most probable pore diameter is smaller than the second most probable pore diameter, the first most probable pore diameter is 1-10nm, and the second most probable pore diameter is 10-50 nm.

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

According to the method of the present invention, by controlling the particle size of the spherical composite material within the above range, it can be ensured that the spherical composite material is not easily agglomerated, and the conversion rate of the reaction raw material during the ethylene polymerization can be improved by using it as a supported catalyst made of a carrier. When the specific surface area of the spherical composite material 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 specific surface area of the spherical composite material is more than 650m²When the volume/g and/or pore volume is more than 1.8mL/g, the supported catalyst prepared by using the supported catalyst as a carrier is easy to agglomerate in the ethylene polymerization process, thereby influencing the monomer conversion rate in the ethylene polymerization process.

Preferably, the pore volume of the spherical composite material is 0.6-1.6mL/g, and the specific surface area is 200-450m²(iv) g, an average particle diameter of 30 to 55 μm, a first mode pore diameter of 3 to 8nm, and a second mode pore diameter of 20 to 45 nm.

Further preferably, the pore volume of the spherical composite material is 1.0-1.2mL/g, and the specific surface area is 200-300m²(iv) g, an average particle diameter of 50 to 55 μm, a first mode pore diameter of 6 to 8nm, and a second mode pore diameter of 25 to 42 nm.

The content of the molecular sieve material having a three-dimensional cubic cage-like structure and the silica gel in the spherical composite material in the present invention is not particularly limited as long as the microscopic size of the spherical composite material satisfies the above conditions. In a preferred case, the silica gel may be contained in an amount of 1 to 200 parts by weight with respect to 100 parts by weight of the mesoporous molecular sieve material having a three-dimensional cubic cage structure, and more preferably, the silica gel is contained in an amount of 50 to 200 parts by weight with respect to 100 parts by weight of the mesoporous molecular sieve material having a three-dimensional cubic cage structure, from the viewpoint of further improving the properties of the polyethylene product.

In the present invention, the contents of the molecular sieve material having a three-dimensional cubic cage-like structure and the silica gel may be determined according to the amounts of both used in preparing the spherical composite material.

The present invention does not particularly limit the preparation method of the spherical composite material as long as it contains a mesoporous molecular sieve material having a three-dimensional cubic cage structure and silica gel and has the above-mentioned microscopic size, and in order to further improve the performance of the polyethylene product, it is preferable that the preparation method of the spherical composite material comprises the steps of:

(1) providing a mesoporous molecular sieve material with a three-dimensional cubic cage-like structure or preparing a filter cake of the mesoporous molecular sieve material with the three-dimensional cubic cage-like structure as a component a;

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

(3) and mixing and ball-milling the component a, the component b and the binder, pulping solid powder obtained after ball-milling by using water, and then spray-drying the obtained slurry.

In the step (1), the process of preparing a filter cake of the mesoporous molecular sieve material having a three-dimensional cubic cage-like structure may include: in an acidic aqueous solution, in the presence of potassium sulfate, a template agent is contacted with a silicon source, and a mixture obtained after the contact is crystallized and filtered.

The amount of the potassium sulfate may be 100-800 mol, preferably 200-400 mol, relative to 1mol of the template; the silicon source may be used in an amount of 20 to 200 moles, preferably 100 to 200 moles.

In the present invention, the templating agent may be various templating agents conventionally used in the art. Most preferablyPreferably, the templating agent is a triblock copolymer polyoxyethylene-polyoxypropylene-polyoxyethylene, which is commercially available (e.g., from Fuka corporation under the trade name

F108, molecular formula EO₁₃₂PO₆₀EO₁₃₂And Mn is 14600), or can be prepared by a conventional method. When the template is polyoxyethylene-polyoxypropylene-polyoxyethylene, the number of moles of the template is calculated from the average molecular weight of polyoxyethylene-polyoxypropylene-polyoxyethylene.

In the present invention, the silicon source may be various silicon sources conventionally used in the art, preferably the silicon source is at least one of tetraethoxysilane, methyl orthosilicate, propyl orthosilicate, sodium orthosilicate and silica sol, and most preferably tetraethoxysilane.

In the present invention, the acidic aqueous solution may be various acidic aqueous solutions conventionally used in the art, and for example, may be at least one aqueous solution of hydrochloric acid, sulfuric acid, nitric acid, and hydrobromic acid, and preferably an aqueous hydrochloric acid solution.

In the present invention, the conditions for contacting the templating agent with the silicon source may include: the temperature is 25-60 ℃, the time is 10-72 hours, the pH value is 1-7, and preferably, the conditions of the template agent and the silicon source contact can comprise: the temperature is 35-45 deg.C, and the time is 20-30 hr. In order to further facilitate uniform mixing between the substances, the contacting of the templating agent and the silicon source is preferably performed under stirring conditions. The dosage of the acidic aqueous solution is preferably such that the pH value of the contact reaction system of the template agent and the silicon source is 1-7.

The crystallization conditions may include: the temperature is 90-150 ℃, and the time is 10-40 hours; preferably, the temperature is 90-120 ℃ and the time is 20-30 hours. Further preferably, the crystallization is performed by a hydrothermal crystallization method.

In the above process of preparing a filter cake of a mesoporous molecular sieve material having a three-dimensional cubic cage structure, the process of obtaining the filter cake by filtration may include: after filtration, repeated washing with deionized water (washing times may be 2 to 10) and suction filtration.

In the step (1), "providing the mesoporous molecular sieve material having a three-dimensional cubic cage structure" may be a product obtained by directly weighing or selecting the mesoporous molecular sieve material having a three-dimensional cubic cage structure, or may be a product obtained by preparing the mesoporous molecular sieve material having a three-dimensional cubic cage structure. The preparation method of the mesoporous molecular sieve material having a three-dimensional cubic cage structure may be performed according to a conventional method, and for example, the preparation method may include: a filter cake of a mesoporous molecular sieve material having a three-dimensional cubic cage-like structure is prepared according to the above method, and the resulting filter cake is then dried.

In the step (2), the process of preparing the filter cake of silica gel may include: the water glass is contacted with the polyhydric alcohol in the presence of the mineral acid, and the mixture obtained after the contact is filtered.

In the present invention, the polyol is not particularly limited, and is preferably at least one of ethylene glycol, propylene glycol and glycerin, preferably ethylene glycol and/or glycerin, and more preferably glycerin.

The conditions for contacting the water glass with the polyol are not particularly limited and may be appropriately determined according to the conventional process for preparing silica gel. Preferably, the contacting conditions include: the temperature is 10-60 ℃, preferably 30-45 ℃; for a period of 1 to 5 hours, preferably 1 to 3 hours; the pH value is 2-4, preferably 2.5-3.5.

In order to facilitate the uniform mixing of the materials, the contact reaction of the water glass and the polyol is preferably carried out under stirring.

Preferably, the weight ratio of the water glass, the inorganic acid and the polyhydric alcohol is 3-6: 2-3: 1; more preferably 3 to 5: 1: 1.

the water glass is an aqueous solution of sodium silicate, and the concentration thereof may be 3 to 20% by weight, preferably 10 to 20% by weight.

The inorganic acid may be various inorganic acids conventionally used in the art, and 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 water glass and a polyhydric alcohol is 2 to 4.

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

According to the present invention, in step (3), the amount and type of the binder are not particularly limited, and in order to improve the strength of the spherical composite material and further improve the performance of the polyethylene product, the amount of the component b may be 1 to 200 parts by weight and the amount of the binder may be 1 to 10 parts by weight, relative to 100 parts by weight of the component a; preferably, the component b is used in an amount of 50 to 200 parts by weight, and the binder is used in an amount of 2 to 8 parts by weight. More preferably, the binder is polyvinyl alcohol and/or polyethylene glycol, most preferably polyvinyl alcohol.

In the step (3), the ball milling may be performed in a ball mill, the inner wall of a ball milling pot in the ball mill is preferably agate lining, and the diameter of the milling balls in the ball mill may be 2-3 mm; the number of the grinding balls can be reasonably selected according to the size of the ball milling tank, and for the ball milling tank with the size of 50-150mL, 1 grinding ball can be generally used; the material of the grinding ball can be agate, polytetrafluoroethylene and the like, and agate is preferred. The ball milling conditions may include: the rotation speed of the grinding ball is 200-; preferably, the rotation speed of the grinding balls is 300-.

In the step (3), the process of slurrying the solid powder obtained after ball milling with water may be performed at 25 to 60 ℃. The weight ratio of solid powder to water used in the pulping process may be 1:0.1-5, preferably 1: 0.5-3.5.

In step (3), the spray drying may be carried out according to conventional means, for example in an atomizer. The conditions of the spray drying may include: the temperature is 150-; preferably, the spray drying conditions include: the temperature is 150-250 ℃, and the rotating speed is 11000-13000 r/min.

In the step (3), when the component a is a filter cake of a mesoporous molecular sieve material having a three-dimensional cubic cage structure and the component b is a filter cake of silica gel, that is, when the step (1) is a process of preparing a filter cake of a mesoporous molecular sieve material having a three-dimensional cubic cage structure and the step (2) is a process of preparing a filter cake of silica gel, the preparation method of the spherical composite material may further include: after the spray-drying process of step (3), the template is removed from the spray-dried product. Preferably, the conditions for removing the template agent include: the temperature is 90-600 ℃, and the temperature is more preferably 400-600 ℃; the time is 10 to 80 hours, and more preferably 10 to 24 hours.

According to the present invention, in the catalyst, the content of the magnesium salt and/or the titanium salt is not particularly limited, and may be suitably determined according to a supported catalyst which is conventional in the art, and preferably, the content of the carrier is 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, based on the total weight of the catalyst; more preferably, the content of the carrier is 94 to 96% by weight, the sum of the contents of the magnesium salt and the titanium salt in terms of magnesium element and titanium element, respectively, is 4 to 6% by weight, and most preferably, the content of the carrier is 94.5 to 95% 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 5 to 5.5% by weight.

In the present invention, the catalyst may be prepared according to various methods conventionally used in the art as long as a magnesium salt and/or a titanium salt is supported on the spherical composite material, and preferably, the preparation method of the catalyst includes: the spherical composite material is impregnated in a mother liquor containing magnesium salt and/or titanium salt in the presence of inert gas, and then sequentially filtered and dried, wherein preferably, the impregnation conditions comprise: the temperature is 25-100 ℃ and the time is 0.1-5h, and further preferably, the impregnation conditions comprise: the temperature is 40-60 ℃ and the time is 1-3 h.

In the present invention, the magnesium salt may be various magnesium salts conventionally used in the art, for example, may be one or more of magnesium chloride, magnesium sulfate, magnesium nitrate and magnesium bromide, and is preferably magnesium chloride.

In the present invention, the titanium salt may be various titanium salts conventionally used in the art, and for example, titanium tetrachloride and/or titanium trichloride may be mentioned.

In the present invention, the amount of the magnesium salt and the titanium salt is not particularly limited, and preferably, the amount of the carrier, the magnesium salt and the titanium salt is such that the content of the carrier 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% in the prepared supported polyethylene catalyst, based on the total weight of the catalyst; more preferably, the content of the carrier is 94 to 96% by weight, the sum of the contents of the magnesium salt and the titanium salt in terms of magnesium element and titanium element, respectively, is 4 to 6% by weight, and most preferably, the content of the carrier is 94.5 to 95% 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 5 to 5.5% by weight.

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

The mother liquor may preferably further contain an organic solvent for dissolving the magnesium salt and the titanium salt, and the organic solvent is not particularly limited in the present invention as long as the magnesium salt and the titanium salt can be dissolved, and for example, isopropanol and tetrahydrofuran may be contained, and the volume ratio of isopropanol to tetrahydrofuran may be 1: 1-3, preferably 1: 1-1.5.

In the present invention, the drying conditions for the preparation of the catalyst in the present invention are not particularly limited, and may be various conditions commonly used in the art; preferably, the preparation of the 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.

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 is 10-100 ℃, the time is 0.5-5h, and the pressure is 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.

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, which is conventional in the art, and is preferably nitrogen gas.

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 order to further increase the conversion of ethylene, the polymerization is carried out in the presence of an alkylaluminum compound having the structure represented by formula I:

AlR_nX⁵ _(3-n)formula I

In the formula I, n R may be C₁-C₅Alkyl groups of (a); 3-n X⁵May each be one of the halogen groups, preferably-Cl; n is 0, 1, 2 or 3.

Said C is₁-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.

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.

The amount of the aluminum alkyl compound may also be chosen as is conventional in the art, and in general, the mass ratio of the aluminum alkyl 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.

The ethylene polymerization method can also comprise the step of carrying out suction filtration and separation on the final reaction mixture after the polymerization reaction is finished, so as to prepare 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 was obtained from Fuka under the trade name

F108, molecular formula EO₁₃₂PO₆₀EO₁₃₂Abbreviated as F108, and an average molecular weight Mn of 14600.

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

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.

Polyethylene pulverization rate: determined by sieving through a 800 mesh screen.

Example 1

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

(1) Preparation of spherical composite Material

1.46g (0.0001mol) of template F108 and 5.24g (0.03mol) of K₂SO₄Stirring with 60g hydrochloric acid solution with equivalent concentration of 2 at 38 ℃ until F108 is completely dissolved;

4.2g (0.02mol) of tetraethyl orthosilicate was added to the above solution, stirred at 38 ℃ for 15 minutes, and left to stand at 38 ℃ for 24 hours;

then the mixture is transferred into a reaction kettle with an agate inner lining, crystallized for 24 hours at the temperature of 100 ℃, filtered and washed for 4 times by deionized water, and then filtered by suction to obtain a filter cake A1 of the mesoporous molecular sieve material with the three-dimensional cage-shaped structure.

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

And (3) putting 10g of the prepared filter cake A1, 10g of the prepared filter cake B1 and 0.5g of polyvinyl alcohol into a 100mL ball milling tank together, wherein the ball milling tank is made of agate, the grinding balls are made of agate, the diameter of each grinding ball is 3mm, the number of the grinding balls is 1, and the rotating speed is 400 r/min. Sealing the ball milling tank, and ball milling for 5 hours in the ball milling tank at the temperature of 25 ℃ to obtain solid powder; dissolving the solid powder in 25g of deionized water, and spray-drying at 200 ℃ at a rotating speed of 12000 r/min; and calcining the product obtained after spray drying in a muffle furnace at 550 ℃ for 10 hours to remove F108 (template) to obtain the spherical composite material C1.

The spherical composite material C1 was characterized by XRD, scanning electron microscope and nitrogen adsorption apparatus.

Fig. 1 is an X-ray diffraction pattern, and it can be seen from the figure that the spherical composite material C1 has a three-dimensional cubic cage-like structure unique to mesoporous materials.

Fig. 2 is an X-ray diffraction pattern, and it can be seen that the supported polyethylene catalyst D1 has a three-dimensional cubic cage-like structure unique to a mesoporous material.

FIG. 3 is a SEM image of the spherical composite C1, which shows that the spherical composite C1 is microspheres with a particle size of 20-60 μm and has good dispersibility.

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

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

TABLE 1

Sample (I)	Specific surface area (m)²/g)	Pore volume (mL/g)	Pore size of the most probable pore (nm)	Average particle diameter (μm)
					C1	230	1.2	8，40	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.

(2) Preparation of the catalyst

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

The catalyst D1 according to this example contained 4 wt% of magnesium and 1.3 wt% of titanium, calculated as elements, by X-ray fluorescence analysis.

(3) Preparation of polyethylene

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. The polyethylene granular powder was measured to have a Bulk Density (BD) of 0.38g/mL and a melt index MI_2.16The powder grinding rate is less than 3 percent when the powder is 0.5g/10 min. The efficiency of the catalyst is determined by calculation to be 2300gPE/gcat h.

Comparative example 1

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

A catalyst was prepared by following the procedure of step (2) of example 1, except that the same parts by weight of ES955 silica gel was used in place of the spherical composite material C1. Thus, comparative catalyst DD1 was obtained.

As a result of X-ray fluorescence analysis, in comparative catalyst DD1, the content of magnesium was 3% by weight and the content of titanium was 1.2% by weight in terms of the element.

Polymerization of ethylene was carried out in accordance with the procedure in step (3) of example 1, except that the same part by weight of comparative catalyst DD1 was used in place of catalyst D1 prepared in example 1. The Bulk Density (BD) of the obtained polyethylene granular powder is 0.4g/mL, the melt index MI2.16 is 0.87g/10min, and the powder crushing rate is more than 8%. The efficiency of the catalyst was found by calculation to be 1767gPE/gcat.

Comparative example 2

Spherical composites, preparation of catalyst and preparation of polyethylene were prepared in the same manner as in example 1, except that, in the preparation of the spherical composites in step (1), 10g of the filter cake a1 and 10g of the filter cake B1 were put together in a 100mL ball mill pot, that is, polyvinyl alcohol was not added as a binder. Thus, comparative catalyst DD2 was obtained.

It was found by X-ray fluorescence analysis that, in comparative catalyst DD2, the content of magnesium was 2.3% by weight and the content of titanium was 0.7% by weight, in terms of element.

Polymerization of ethylene was carried out in accordance with the procedure in step (3) of example 1, except that the same part by weight of comparative catalyst DD2 was used in place of catalyst D1 prepared in example 1. The Bulk Density (BD) of the obtained polyethylene granular powder was 0.69g/mL, and the melt index MI was_2.16When the powder is equal to 0.77g/10min, the crushing rate is more than 8 percent. The efficiency of the catalyst was determined by calculation to be 1300gPE/gcat h.

Example 2

(1) Preparation of spherical composite Material

1.46g (0.0001mol) of template F108 and 6.96g (0.04mol) of K₂SO₄Stirring with 60g hydrochloric acid solution with equivalent concentration of 2 at 38 ℃ until F108 is completely dissolved;

adding 3.1g (0.015mol) of tetraethoxysilane into the solution, stirring for 15min at 45 ℃, and standing for 30h at 45 ℃;

then transferring the mixture into an agate-lined reaction kettle, crystallizing the mixture for 30 hours at 120 ℃, then filtering the mixture, washing the mixture for 4 times by using deionized water, and performing suction filtration to obtain a filter cake A2 of the mesoporous molecular sieve material with the three-dimensional cage-shaped structure.

Mixing 20 wt% of water glass, 12 wt% of sulfuric acid solution and propylene glycol in a weight ratio of 4: 1: 1 at 40 ℃ for 3 hours, followed by adjustment of the pH to 4 with 98% strength by weight sulfuric acid, suction filtration of the reaction mass obtained and washing with distilled water to a sodium ion content of 0.02% by weight, a filter cake of silica gel B2 was obtained.

10g of the filter cake A2, 5g of the filter cake B2 and 0.2g of polyvinyl alcohol are placed into a 100mL ball milling tank together, wherein the ball milling tank is made of agate, the grinding balls are made of agate, the diameter of each grinding ball is 3mm, the number of the grinding balls is 1, and the rotating speed is 500 r/min. Sealing the ball milling tank, and ball milling for 10 hours in the ball milling tank at the temperature of 30 ℃ to obtain solid powder; dissolving the solid powder in 100g of deionized water, and spray-drying at 150 ℃ at the rotating speed of 13000 r/min; calcining the product obtained after spray drying in a muffle furnace at 600 ℃ for 15 hours, and removing F108 (template) to obtain the spherical composite material C2.

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

TABLE 2

Sample (I)	Specific surface area (m)²/g)	Pore volume (mL/g)	Pore size of the most probable pore (nm)	Average particle diameter (μm)
					C2	299	1.0	7，41	50

(2) Preparation of the catalyst

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

The catalyst D2 according to this example contained 3.4 wt% of magnesium and 2 wt% of titanium, calculated as elements, by X-ray fluorescence analysis.

(3) Preparation of polyethylene

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. The polyethylene granular powder obtained had a Bulk Density (BD) of 0.2g/mL and a melt index MI_2.16The powder grinding rate is less than 3 percent when the powder is 0.7g/10 min. The efficiency of the catalyst was determined by calculation to be 2100g PE/gcat h.

Example 3

(1) Preparation of spherical composite Material

1.46g (0.0001mol) of template F108 and 3.48g (0.02mol) of K₂SO₄Stirring with 60g hydrochloric acid solution with equivalent concentration of 2 at 38 ℃ until F108 is completely dissolved;

adding 2.1g (0.01mol) of tetraethoxysilane into the solution, stirring at 35 ℃ for 15min, and standing at 35 ℃ for 20 hours;

then transferring the mixture into a reaction kettle with an agate inner lining, crystallizing the mixture for 20 hours at 90 ℃, then filtering the mixture, washing the mixture for 4 times by using deionized water, and then carrying out suction filtration to obtain a filter cake A3 of the mesoporous molecular sieve material with the three-dimensional cage-shaped structure.

Mixing water glass with the concentration of 10 weight percent, sulfuric acid solution with the concentration of 12 weight percent and ethylene glycol according to the weight ratio of 3: 1: 1, then adjusting the pH value to 2 with sulfuric acid with the concentration of 98 weight percent, then carrying out suction filtration on the obtained reaction material, and washing the reaction material with distilled water until the content of sodium ions is 0.02 weight percent to obtain a filter cake B3 of silica gel.

And (3) putting 10g of the prepared filter cake A3, 20g of the prepared filter cake B3 and 0.8g of polyethylene glycol into a 100mL ball milling tank together, wherein the ball milling tank is made of agate, the grinding balls are made of agate, the diameter of each grinding ball is 3mm, the number of the grinding balls is 1, and the rotating speed is 300 r/min. Sealing the ball milling tank, and carrying out ball milling for 20 hours in the ball milling tank at the temperature of 50 ℃ to obtain solid powder; dissolving the solid powder in 50g of deionized water, and spray-drying at 250 ℃ at the rotating speed of 11000 r/min; and calcining the product obtained after spray drying in a muffle furnace at 400 ℃ for 24h, and removing F108 (template) to obtain the spherical composite material C3.

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

TABLE 3

Sample (I)	Specific surface area (m)²/g)	Pore volume (mL/g)	Pore size of the most probable pore (nm)	Average particle diameter (μm)
					C3	203	1.1	6，42	50

(2) Preparation of the catalyst

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

The catalyst D3 according to this example contained 3.1 wt% of magnesium and 1.9 wt% of titanium, calculated as elements, by X-ray fluorescence analysis.

(3) Preparation of polyethylene

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. The polyethylene granular powder obtained had a Bulk Density (BD) of 0.4g/mL and a melt index MI_2.16The powder grinding rate is less than 2 percent when the powder is 0.5g/10 min. The efficiency of the catalyst was found by calculation to be 2050g PE/gcat h.

Example 4

Spherical composites, a catalyst and polyethylene were prepared in the same manner as in example 1, except that glycerol was not added during the preparation of the silica gel cake in the preparation of the spherical composites in step (1). Obtaining the spherical composite material C4, the catalyst D4 and polyethylene particle powder.

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

TABLE 4

Sample (I)	Specific surface area (m)²/g)	Pore volume (mL/g)	Pore size of the most probable pore (nm)	Average particle diameter (μm)
					C4	260	1.2	7，25	54

The catalyst D4 according to this example contained 3.5 wt% of magnesium and 1.8 wt% of titanium, calculated as elements, by X-ray fluorescence analysis.

Determination of polyethylene granular powder, pile of polyethylene granular powderA density (BD) of 0.42g/mL and a melt index MI_2.16When the powder is equal to 0.33g/10min, the crushing rate is less than 3 percent. The efficiency of the catalyst was determined by calculation to be 1950g PE/gcat h.

As can be seen from the results of comparing examples 1-4 with comparative examples 1-2, the catalyst of the method for ethylene polymerization provided by the invention has higher catalytic activity, and can obtain polyethylene products with lower bulk density and melt index and difficult breakage, specifically, the bulk density of the prepared polyethylene products is less than 0.42g/mL, the melt index is less than 0.7g/10min, and the powder breaking rate is less than 3%.

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

It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.

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

Claims

1. A process for the polymerization of ethylene, the process comprising: polymerizing ethylene in the presence of a catalyst under a polymerization reaction condition, and is characterized in that the catalyst contains a spherical composite material and a magnesium salt and/or a titanium salt loaded on the spherical composite material, wherein the spherical composite material contains a mesoporous molecular sieve material with a three-dimensional cubic cage structure and silica gel, the pore volume of the spherical composite material is 0.5-1.8mL/g, and the specific surface area is 200-²The average particle diameter is 20-60 μm, the pore diameters are distributed in a bimodal mode, the bimodal mode corresponds to a first most probable pore diameter and a second most probable pore diameter respectively, and the first most probable pore diameterThe diameter is smaller than the second most probable pore diameter, the first most probable pore diameter is 1-10nm, and the second most probable pore diameter is 10-50 nm;

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

(3) mixing and ball-milling the component a, the component b and a binder, pulping solid powder obtained after ball-milling with water, and then spray-drying the obtained slurry;

in the step (3), the component a and the component b are used in such amounts that the component b is used in an amount of 1 to 200 parts by weight and the binder is used in an amount of 1 to 10 parts by weight, relative to 100 parts by weight of the component a.

2. The method of claim 1, wherein the catalyst is prepared by a method comprising: the spherical composite material is impregnated in a mother liquor containing magnesium salt and/or titanium salt in the presence of inert gas, and then sequentially filtered and dried.

3. The method of claim 2, wherein the conditions of the impregnation comprise: the temperature is 25-100 ℃ and the time is 0.1-5 h.

4. The process according to claim 2, wherein the amount of the magnesium salt and/or the titanium salt is such that the content of the magnesium salt and/or the titanium salt in terms of magnesium element is 1 to 10% by weight based on the total weight of the catalyst.

5. The method according to claim 1, wherein the silica gel is contained in an amount of 1-200 parts by weight with respect to 100 parts by weight of the mesoporous molecular sieve material having a three-dimensional cubic cage structure.

6. The method according to claim 1, wherein the silica gel is contained in an amount of 50-200 parts by weight with respect to 100 parts by weight of the mesoporous molecular sieve material having a three-dimensional cubic cage structure.

7. The method according to claim 1, wherein, in the step (3), the components a and b are used in such amounts that the component b is used in an amount of 50 to 200 parts by weight and the binder is used in an amount of 2 to 8 parts by weight, relative to 100 parts by weight of the component a.

8. The method of claim 1, wherein the binder is polyvinyl alcohol and/or polyethylene glycol.

9. The method of claim 1, wherein the binder is polyvinyl alcohol.

10. The method of claim 1, wherein, in step (1), the process of preparing a filter cake of mesoporous molecular sieve material having a three-dimensional cubic cage structure comprises: in an acidic aqueous solution, in the presence of potassium sulfate, a template agent is contacted with a silicon source, and a mixture obtained after the contact is crystallized and filtered.

11. The method as claimed in claim 10, wherein the amount of potassium sulfate is 100-800 moles and the amount of silicon source is 20-200 moles with respect to 1 mole of the template.

12. The method of claim 10, wherein the templating agent is a triblock copolymer polyoxyethylene-polyoxypropylene-polyoxyethylene; the silicon source is at least one of ethyl orthosilicate, methyl orthosilicate, propyl orthosilicate, sodium orthosilicate and silica sol; the acidic aqueous solution is at least one aqueous solution of hydrochloric acid, sulfuric acid, nitric acid and hydrobromic acid.

13. The method of claim 10, wherein the conditions of the contacting comprise: the temperature is 25-60 ℃, the time is 10-72 hours, and the pH value is 1-7; the crystallization conditions include: the temperature is 90-150 ℃ and the time is 10-40 hours.

14. The method of claim 1, wherein, in the step (2), the process of preparing the filter cake of silica gel comprises: the water glass is contacted with the polyhydric alcohol in the presence of the mineral acid, and the mixture obtained after the contact is filtered.

15. The method of claim 14, wherein in step (2), the polyol is at least one of ethylene glycol, propylene glycol, and glycerol.

16. The method according to claim 14, wherein, in step (2), the polyol is ethylene glycol and/or glycerol.

17. The method of claim 14, wherein the weight ratio of the water glass, the inorganic acid, and the polyol is 3-6: 2-3: 1.

18. the method of claim 14, wherein in step (2), the conditions of the contacting comprise: the temperature is 10-60 ℃, the time is 1-5 hours, and the pH value is 2-4; the inorganic acid is at least one of sulfuric acid, nitric acid and hydrochloric acid.

19. The method of claim 1, wherein, in step (3), the ball milling conditions comprise: the rotation speed of the grinding ball is 300-; the conditions of the spray drying include: the temperature is 150-600 ℃, and the rotating speed is 10000-15000 r/min.

20. The method of any of claims 1-19, wherein component a is a filter cake of a mesoporous molecular sieve material having a three-dimensional cubic cage structure and component b is a filter cake of silica gel, the method further comprising: after the spray-drying process of step (3), the template is removed from the spray-dried product.

21. The method of claim 20, wherein the conditions for removing the templating agent comprise: the temperature is 90-600 ℃, and the time is 10-80 hours.

22. 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.

23. The process of claim 1, wherein the polymerization reaction is carried out in the presence of an inert gas, and the conditions of the polymerization reaction include: the temperature is 20-95 ℃, the time is 1-4h, and the pressure is 0.5-1.5 MPa.

24. A polyethylene produced by the process of any one of claims 1 to 23.