A ziegler-natta catalyst for producing high molecular weight polyethylene with a narrow molecular weight distribution and a method for producing the same

Abstract

The present application provides a kind of Ziegler-Natta catalyst for preparing high molecular weight polyethylene with narrow molecular weight distribution, porous polymer microspheres are used as carrier, load the Ziegler-Natta catalyst doped with trace metallocene, the doping amount of metallocene is 0.01-2wt% of the amount of Ziegler-Natta catalyst.The preparation method includes the reaction of porous polymer microspheres with alkyl magnesium chloride, then with aluminoxane compound, then the product is reacted with titanium tetrachloride, finally, add metallocene to the product to obtain Ziegler-Natta catalyst.The present application uses porous polymer microspheres as carrier, dopes trace metallocene in Ziegler-Natta catalyst, and the composite catalyst prepared is used for the synthesis of high molecular weight polyethylene, and high molecular weight polyethylene with narrow molecular weight distribution can be obtained, which can meet the application needs of lithium ion battery separator materials.

Description

Technical Field

[0001] This invention relates to the field of polyethylene preparation technology, and more particularly to a Ziegler-Natta catalyst for preparing high molecular weight polyethylene with a narrow molecular weight distribution. Background Technology

[0002] High molecular weight polyethylene (HMWPE) is a linear thermoplastic engineering plastic with excellent comprehensive properties. While the molecular weight of ordinary polyethylene is generally between 40,000 and 120,000, that of HMWPE can reach 1 million to 4 million. With the significant increase in molecular weight, some properties of the resin undergo abrupt changes, such as excellent wear resistance; strong impact resistance, maintaining a high impact strength even at low temperatures; and good self-lubricating properties. HMWPE can and is replacing carbon steel, stainless steel, bronze, etc., and is widely used in textiles, papermaking, food machinery, transportation, ceramics, coal mining, and other fields.

[0003] High molecular weight polyethylene (HMWPE) includes ultra-high molecular weight polyethylene (UHMWPE) and extra-high molecular weight polyethylene (UHMWPE). UHMWPE generally refers to linear polyethylene with a viscosity-average molecular weight (MAM) ranging from 300,000 to 1.5 million, while UHMWPE is linear polyethylene with a MAM greater than 1.5 million. The applications of HMWPE vary depending on its molecular weight. For example, HMWPE resin with a MAM > 4 million is mainly used for fiber production; HMWPE resin with a MAM between 2 million and 4 million is mainly used for pipe production; and HMWPE resin with a MAM between 500,000 and 1.5 million is mainly used for lithium-ion battery separators.

[0004] Generally, the relative molecular weight distribution, particle morphology, and particle size distribution of high molecular weight polyethylene (HMWPE) powder are affected by factors such as catalysts and polymerization processes. These performance parameters, in turn, affect the processability of the polymer powder, thus impacting product performance. In existing technologies, conventional Ziegler-Natta catalysts can only prepare HMWPE with a broad molecular weight distribution. Metallocene catalysts can prepare HMWPE with a narrow molecular weight distribution, but the resulting polyethylene has insufficient molecular weight. Chinese patent CN1729206A reports that some components of the Ziegler-Natta catalyst system are toxic to the metallocene catalyst system; that is, it is generally believed that mixing the two reduces the catalyst's effectiveness. Chinese patent CN1413222A reports the use of a Ziegler-Natta / metallocene hybrid catalyst for preparing bimodal polyolefins with a broad molecular weight distribution.

[0005] Therefore, researching novel Ziegler-Natta catalysts to prepare high molecular weight polyethylene with narrow molecular weight distribution has important practical value. Summary of the Invention

[0006] The present invention aims to provide a Ziegler-Natta catalyst for preparing high molecular weight polyethylene with a narrow molecular weight distribution and a method thereof, so as to solve the above-mentioned defects in the prior art.

[0007] This invention is achieved through the following technical solution:

[0008] A Ziegler-Natta catalyst for preparing high molecular weight polyethylene with a narrow molecular weight distribution is provided, which uses porous polymer microspheres as a support and supports a Ziegler-Natta catalyst doped with trace amounts of metallocene, wherein the amount of metallocene doping is 0.01-2 wt% of the amount of Ziegler-Natta catalyst used.

[0009] The porous polymer microspheres are copolymers of polystyrene, divinylbenzene, and acrylonitrile. There are many methods for preparing porous polymer microspheres, such as suspension polymerization, dispersion polymerization, seed swelling polymerization, and SPG membrane emulsification. Among these, microspheres prepared by seed swelling polymerization have uniform particle size, strong scalability, and broad application prospects, as illustrated in patents CN1927899A, CN101045755A, CN1644606A, and CN101434673A. This application preferably uses the following method to prepare porous polymer microspheres. The specific preparation method is as follows:

[0010] 1) Preparation of linear polystyrene seed microspheres

[0011] Styrene, ethanol, ethylene glycol monomethyl ether, azobisisobutyronitrile, and polyvinylpyrrolidone (PVPK-30) in a weight ratio of 10:44:44:0.1:2 were added to a four-necked reactor equipped with a mechanical stirrer, reflux condenser, nitrogen conduit, and temperature detection device. The mixture was stirred at a speed of 60–120 rpm and polymerized in a water bath at 60–80 °C for 12–24 h under nitrogen protection. After the reaction was completed, the reaction solution was centrifuged to remove the supernatant. The precipitate was washed with ethanol and water, and then dried in a vacuum drying oven to obtain linear polystyrene seed microspheres with uniform particle size.

[0012] 2) Two-step seed swelling polymerization to prepare porous polymer microspheres

[0013] (1) Prepare an ethanol aqueous solution of 0.25wt% sodium dodecyl sulfonate to obtain a dispersion; the ethanol aqueous solution is a solvent and is composed of ethanol:water in a mass ratio of 5:1.

[0014] (2) Disperse polystyrene seeds with a dispersion liquid, wherein the mass ratio of polystyrene seeds to dispersion liquid is 0.5:10-30, and ultrasonically disperse for 5-20 min to obtain a seed emulsion;

[0015] (3) Disperse 1-chlorododecane swelling agent with a dispersion liquid, wherein the mass ratio of 1-chlorododecane swelling agent to dispersion liquid is 0.5:20-40, and ultrasonically disperse for 10-60 min to obtain a swelling agent emulsion;

[0016] (4) Mix the well dispersed seed emulsion and the well dispersed swelling agent emulsion, place them in a four-port reactor equipped with mechanical stirring, reflux condenser, nitrogen conduit and temperature detection device, and swell at 25-35℃ and 80-120rpm for 8-24h to carry out the first step of swelling and obtain activated seed emulsion.

[0017] (5) Disperse the mixed monomers, initiator, and porogen in a dispersion liquid; wherein the mass ratio of the mixed monomers, initiator, porogen, and dispersion liquid is 10:0.1:10:30-60, the mixed monomers are composed of styrene, divinylbenzene, and acrylonitrile, and the proportion of each monomer is not limited; the initiator is benzoyl peroxide; the porogen is toluene, n-heptane, or other inert solvents, and the proportion of each porogen is not limited, and ultrasonically disperse for 10-60 min to obtain an emulsion of mixed monomers, initiator, and porogen; the other inert solvents include organic acids, alcohols, esters, aromatic solvents, or optionally substituted aliphatic hydrocarbons with 12 carbon atoms;

[0018] (6) After the first swelling step is completed, the well dispersed mixed monomer, initiator and pore-forming agent emulsion is added to the activated seed emulsion and swollen at 25-35℃ and 80-120rpm for 8-24h to carry out the second swelling step to obtain the swollen microsphere emulsion.

[0019] (7) Prepare a 5wt% PVPK-30 aqueous solution to obtain a stabilizer solution;

[0020] (8) After the second swelling step is completed, the swollen microsphere emulsion is transferred to a separatory funnel and allowed to stand for separation. The unswollen residual monomers are removed. The separated swollen microsphere emulsion is transferred to a four-hole reactor. 5wt% PVPK-30 stabilizer solution is added at a mass ratio of stabilizer solution to separated swollen microsphere emulsion of 2:1. Polymerization is carried out in a water bath at 60-80℃ for 12-24 hours under nitrogen protection. After the reaction is completed, the reaction liquid is centrifuged and the upper liquid is removed. The precipitate is washed with ethanol and water respectively, extracted with dichloromethane, and dried under vacuum to obtain porous polymer microspheres.

[0021] The average pore size of the porous polymer microspheres is 10-20 nm; the size of the porous polymer microspheres is 3-5 μm.

[0022] This invention further provides a method for preparing the above-mentioned Ziegler-Natta catalyst, comprising the following steps:

[0023] Step 1: React porous polymer microspheres with alkyl magnesium chloride in a solvent at 45-50℃ for 10-15 hours, wherein the weight ratio of the porous polymer microspheres to alkyl magnesium nitride is 1:2-25.

[0024] Step 2: React the product from Step 1 with the aluminoxane compound in a solvent at 45-50°C for 10-12 hours, wherein the weight ratio of the porous polymer microspheres to the aluminoxane compound is 20:1-3.

[0025] Step 3: React the product from Step 2 with titanium tetrachloride in a solvent at 45-65°C for 3-6 hours, wherein the weight ratio of the porous polymer microspheres to titanium tetrachloride is 1:3-5.

[0026] Step four: Add metallocene to the product of step three, and react at 45-50℃ for 10-12 h to obtain the porous polymer microsphere-supported metallocene-doped Ziegler-Natta composite catalyst.

[0027] The metallocenes mentioned in this invention refer to organometallic coordination compounds formed by the linkage of transition metals with cyclopentadiene, such as cyclopentadienyl titanium trichloride (CAS: 1270-98-0), bis(cyclopentadienyl) titanium dichloride (CAS: 1271-19-8), bis(cyclopentadiene) zirconium dichloride (CAS: 1291-32-3), bis(pentamethylcyclopentadiene) zirconium dichloride (CAS: 54039-38-2), etc., preferably cyclopentadienyl titanium trichloride or bis(cyclopentadienyl) titanium dichloride.

[0028] The preferred doping amount of metallocene is 0.05-0.1 wt% of the amount of Ziegler-Natta catalyst.

[0029] The alkyl magnesium chloride described in this invention can be a commonly used component in the art, such as methyl magnesium chloride, ethyl magnesium chloride, or butyl magnesium chloride.

[0030] The aluminum oxane compound described in this invention may use components commonly used in the art, such as methylaluminoxane or modified methylaluminoxane.

[0031] The applicant unexpectedly discovered that by using porous polymer microspheres as a carrier and doping a trace amount of metallocene into a Ziegler-Natta catalyst, a composite catalyst was prepared for the synthesis of high molecular weight polyethylene, unexpectedly yielding high molecular weight polyethylene with a narrow molecular weight distribution. Based on the above discovery, this invention was completed.

[0032] The Ziegler-Natta catalyst may further include internal and / or external electron donors. The roles of internal and external electron donors are well known in the art, and their components and amounts can be increased, decreased, or adjusted according to the actual needs of the polyethylene product. For example, internal electron donors may be ethers or esters, including but not limited to cyclobutyl-1,1-diethanol dimethyl ether, 1,3-diethers, 1,3-propanediol dimethyl ether, 2,2-diisobutyl-1,3-propanediol dimethyl ether, cyclopentyl-1,1-diethanol dimethyl ether, 1,3-diol esters, di-n-butyl phthalate, diisobutyl phthalate, ethyl benzoate, dibutyl phthalate, etc.; external electron donors may be alkoxysiloxane compounds.

[0033] The Ziegler-Natta catalyst of this invention is used to prepare high molecular weight polyethylene, which has excellent processing performance and a narrow molecular weight distribution compared with conventional high molecular weight polyethylene, and can meet the application requirements of lithium-ion battery separator materials. Detailed Implementation

[0034] The following description is provided to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples and are not intended to limit the scope of the invention; other obvious variations will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0035] Unless otherwise specified, all instruments and reagents used in the embodiments of this invention are conventional commercial instruments or reagents. The molecular weight distribution was determined by high-temperature gel permeation chromatography to measure the weight-average molecular weight Mw and number-average molecular weight Mn of the polymer, and then the molecular weight distribution index was calculated as Mw / Mn.

[0036] Example 1

[0037] Preparation of Ziegler-Natta catalysts:

[0038] 1) 20g of porous polymer microspheres (polystyrene, divinylbenzene and acrylonitrile copolymer, with an average pore size of 23.8nm and a microsphere size of 4.5um) were reacted with 360g of methylmagnesium chloride in hexane solvent at 50℃ for 12h;

[0039] 2) Continue adding 1g of methylaluminoxane and react at 50℃ for 12h;

[0040] 3) Continue adding 100g of titanium tetrachloride and react at 65℃ for 5 hours;

[0041] 4) Finally, add 0.2 g of bis(cyclopentadienyl)titanium dichloride and react at 50 °C for 10 h to obtain the Ziegler-Natta catalyst.

[0042] Example 2

[0043] Preparation of high molecular weight polyethylene:

[0044] 1) Ethylene is injected into the ethylene refining unit, and impurities and moisture are removed by desulfurization and dechlorination towers, CO removal towers, deoxygenation towers and drying towers to obtain refined ethylene;

[0045] 2) The porous polymer microspheres prepared in Example 1, loaded with metallocene-doped Ziegler-Natta composite catalyst and triethylaluminum co-catalyst, were injected into the catalyst pre-fabrication unit and thoroughly mixed to obtain a catalyst composition with an Al / Ti molar ratio of 75 / 1.

[0046] 3) The refined ethylene and catalyst composition were injected into the gas-phase fluidized bed reactor respectively to carry out the polymerization reaction. The polymerization temperature was controlled at 95℃±5℃, the pressure was 3.0MPa±0.3MPa, the gas flow rate was controlled at 0.8m / s±0.2m / s, and the residence time was 1h.

[0047] 4) The polymer material is discharged into the slurry reactor, where the polymerization reaction continues in the presence of solvent. The polymerization temperature is controlled at 90℃±5℃, the pressure at 0.6MPa±0.1MPa, the material residence time at 70min, and the material level at 55%±5%.

[0048] 5) The discharged powder enters a degassing tower and a drying tower to remove unreacted monomers. It then enters a processing unit where it is treated with nitrogen gas containing a small amount of water vapor to fully remove the activity of any unconsumed co-catalyst, finally obtaining the high molecular weight polyethylene powder. The product has a weight-average molecular weight of 2.33 million and a molecular weight distribution index of 2.05.

[0049] Comparative Example

[0050] High molecular weight polyethylene was prepared using a conventional Ziegler-Natta catalyst (undoped metallocene).

[0051] 1) Ethylene is injected into the ethylene refining unit, and impurities and moisture are removed by desulfurization and dechlorination towers, CO removal towers, deoxygenation towers and drying towers to obtain refined ethylene;

[0052] 2) The Ziegler-Natta catalyst and the triethylaluminum co-catalyst were injected into the catalyst pre-preparation unit and thoroughly mixed to obtain a catalyst composition with an Al / Ti molar ratio of 75 / 1;

[0053] 3) The refined ethylene and catalyst composition were injected into the gas-phase fluidized bed reactor respectively to carry out the polymerization reaction. The polymerization temperature was controlled at 95℃±5℃, the pressure was 3.0MPa±0.3MPa, the gas flow rate was controlled at 0.8m / s±0.2m / s, and the residence time was 1h.

[0054] 4) The polymer material is discharged into the slurry reactor, where the polymerization reaction continues in the presence of solvent. The polymerization temperature is controlled at 90℃±5℃, the pressure at 0.6MPa±0.1MPa, the material residence time at 70min, and the material level at 55%±5%.

[0055] 5) The discharged powder enters a degassing tower and a drying tower to remove unreacted monomers. It then enters a processing unit where it is treated with nitrogen gas containing a small amount of water vapor to fully remove the activity of any unconsumed co-catalyst, finally yielding high molecular weight polyethylene powder. The product has a weight-average molecular weight of 2.29 million and a molecular weight distribution index of 3.32.

[0056] The high molecular weight polyethylene prepared using the Ziegler-Natta catalyst of this invention has a molecular weight distribution index that is 40% lower than that prepared using conventional Ziegler-Natta catalysts, and has the advantage of a narrow molecular weight distribution, which can meet the application requirements of materials for lithium-ion battery separators.

[0057] Those skilled in the art should understand that the above embodiments are merely examples and do not limit the invention. The objectives of the invention have been fully and effectively achieved. The functions and principles of the invention have been shown and explained in the embodiments, and any variations or modifications can be made to the implementation of the invention without departing from the stated principles.

Claims

1. A Ziegler-Natta catalyst for the preparation of high molecular weight polyethylene with a narrow molecular weight distribution, characterized in that, The application discloses a porous polymer microsphere as a carrier, which is loaded with a Ziegler-Natta catalyst doped with a trace amount of a metallocene, wherein the metallocene is cyclopentadienyl titanium trichloride or bis(cyclopentadienyl) titanium dichloride, and the doping amount of the metallocene is 0.05-0.1wt% of the amount of the Ziegler-Natta catalyst; the porous polymer microsphere is a polystyrene, divinylbenzene and acrylonitrile copolymer; and the porous polymer microsphere is prepared by the following method. 1) Preparation of linear polystyrene seed microspheres In a four-port reactor provided with a mechanical stirrer, a reflux condenser, a nitrogen inlet pipe and a temperature detection device, 10 parts by weight of styrene, 44 parts by weight of ethanol, 44 parts by weight of ethylene glycol monomethyl ether, 0.1 parts by weight of azobisisobutyronitrile and 2 parts by weight of polyvinylpyrrolidone PVP K-30 are stirred at a speed of 60-120 rpm under the protection of nitrogen at a water bath temperature of 60-80 ℃ for 12-24 hours; after the reaction is completed, the reaction solution is centrifuged to remove the upper liquid, and the precipitate is washed with ethanol and water and dried in a vacuum drying box to obtain linear polystyrene seed microspheres with uniform particle size; 2) Preparation of porous polymer microspheres by two-step seed swelling polymerization (1) an ethanol aqueous solution containing 0.25wt% of sodium dodecyl sulfonate is prepared to obtain a dispersion liquid; the ethanol aqueous solution is a solvent and is composed of 5 parts by weight of ethanol and 1 part by weight of water; (2) the polystyrene seed is dispersed in the dispersion liquid, and the mass ratio of the polystyrene seed to the dispersion liquid is 0.5:10-30; ultrasonic dispersion is performed for 5-20 minutes to obtain a seed emulsion; (3) 1-chlorododecane is used as a swelling aid and is dispersed in the dispersion liquid, and the mass ratio of the 1-chlorododecane swelling aid to the dispersion liquid is 0.5:20-40; ultrasonic dispersion is performed for 10-60 minutes to obtain a swelling aid emulsion; (4) the dispersed seed emulsion and the dispersed swelling aid emulsion are mixed and placed in a four-port reactor provided with a mechanical stirrer, a reflux condenser, a nitrogen inlet pipe and a temperature detection device, and are swelled at 25-35 ℃ and at a speed of 80-120 rpm for 8-24 hours to perform the first-step swelling, thereby obtaining an activated seed emulsion; (5) a mixed monomer, an initiator and a porogen are dispersed in the dispersion liquid, and the mass ratio of the mixed monomer, the initiator, the porogen and the dispersion liquid is 10:0.1:10:30-60; the mixed monomer is composed of styrene, divinylbenzene and acrylonitrile, and the proportions of the monomers are not limited; the initiator is dibenzoyl peroxide; the porogen is toluene, n-heptane or other inert solvents, and the proportions of the porogens are not limited; ultrasonic dispersion is performed for 10-60 minutes to obtain a mixed monomer, initiator and porogen emulsion; the other inert solvents include organic acids, alcohols, esters, aromatic solvents or optionally substituted aliphatic hydrocarbons with 12 carbons; (6) after the first-step swelling is completed, the dispersed mixed monomer, initiator and porogen emulsion is added to the activated seed emulsion, and is swelled at 25-35 ℃ and at a speed of 80-120 rpm for 8-24 hours to perform the second-step swelling, thereby obtaining a swelled microsphere emulsion; (7) a 5wt% PVP K-30 aqueous solution is prepared to obtain a stabilizer solution; (8) After the second swelling step, the swollen microsphere emulsion is transferred to a separatory funnel and allowed to separate into layers, and the residual monomer that has not swelled is removed. The separated swollen microsphere emulsion is transferred to a four-necked reactor, 5 wt% PVP K-30 stabilizer solution is added at a mass ratio of 2:1, and the solution is polymerized under nitrogen protection at 60-80°C in a water bath for 12-24 hours. After the reaction is completed, the reaction solution is centrifuged and the precipitate is washed with ethanol and water, extracted with dichloromethane, and dried in a vacuum to obtain the porous polymer microspheres; The Ziegler-Natta catalyst further comprises an internal electron donor and / or an external electron donor, the internal electron donor is selected from ether or ester compounds, and the external electron donor is selected from alkoxysiloxane compounds; The preparation method of the Ziegler-Natta catalyst, characterized in that it comprises the following steps: Step one, the porous polymer microspheres and alkyl magnesium chloride are reacted in a solvent at 45-50°C for 10-15 hours, and the weight ratio of the porous polymer microspheres to alkyl magnesium chloride is 1:2-25; Step two, the product of step one and aluminoxane compound are reacted in a solvent at 45-50°C for 10-12 hours, and the weight ratio of the porous polymer microspheres to aluminoxane compound is 20:1-3; Step three, the product of step two and titanium tetrachloride are reacted in a solvent at 45-65°C for 3-6 hours, and the weight ratio of the porous polymer microspheres to titanium tetrachloride is 1:3-5; Step four, metallocene is added to the product of step three, and the mixture is reacted at 45-50°C for 10-12 hours to obtain the Ziegler-Natta catalyst.

2. The Ziegler-Natta catalyst for the production of high molecular weight polyethylene with a narrow molecular weight distribution according to claim 1, characterized in that, The average pore size of the porous polymer microspheres is 10-20 nm, and the size of the porous polymer microspheres is 3-5 μm.

3. The Ziegler-Natta catalyst for the production of high molecular weight polyethylene with a narrow molecular weight distribution according to claim 1, characterized in that, The alkyl magnesium chloride is at least one selected from methyl magnesium chloride, ethyl magnesium chloride, or butyl magnesium chloride.

4. The Ziegler-Natta catalyst for the production of high molecular weight polyethylene with a narrow molecular weight distribution according to claim 1, characterized in that, The aluminoxane compound is methyl aluminoxane or modified methyl aluminoxane.