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CN-121991266-A - Powdery high-melt-index ethylene homopolymer and preparation method thereof

CN121991266ACN 121991266 ACN121991266 ACN 121991266ACN-121991266-A

Abstract

The invention relates to a powdery high-melt-index ethylene homopolymer, which has a melt index of 600-2500g/10min under a load of 2.16kg and a temperature of 190 ℃, has a molecular mass distribution of 3.0-10.0, a melting point of 115-135 ℃, a true density of 0.950-0.980g/cm 3 , a crystallinity of 70-95%, a bulk density of 0.30-0.55g/cm 3 and an average particle size of 50-500mm, and is prepared by a preparation method of ethylene kettle-type homopolymerization under the conditions of 2.0-7.0:1 of a molar ratio of hydrogen to ethylene in a gas phase of a reaction kettle under the conditions of 2.0-100 ℃ and a temperature of 2.0-7.0:1 by using a Ziegler-type catalyst and a Ziegler-Natta catalyst main catalyst and alkyl aluminum or halogenated alkyl aluminum as cocatalysts, and using straight chain alkane, branched alkane, cycloalkane and branched cycloalkane as polymerization solvents.

Inventors

  • LI CHUANFENG
  • WANG WENRUI
  • JING KUN

Assignees

  • 中国石油化工股份有限公司
  • 中国石化扬子石油化工有限公司

Dates

Publication Date
20260508
Application Date
20241108

Claims (10)

  1. 1. A powdered high melt index ethylene homopolymer characterized by having a melt index of 600-2500g/10min under a load of 2.16kg at 190 ℃, a molecular mass distribution of 3.0-10.0, a melting point of 115-135 ℃, a true density of 0.950-0.980g/cm 3 , a crystallinity of 70-95%, a bulk density of 0.30-0.55g/cm 3 , and an average particle size of 50-500mm.
  2. 2. The powder high melt index ethylene homopolymer of claim 2, wherein the powder high melt index ethylene homopolymer has a melt index of 1000 to 2000g/10min at 190 ℃ under a load of 2.16kg, a molecular mass distribution of 4.0 to 8.0, a melting point of 122 to 132 ℃, a true density of 0.952 to 0.970g/cm 3 , a crystallinity of 75 to 90%, a bulk density of 0.33 to 0.50g/cm 3 , and an average particle size of 100 to 300mm.
  3. 3. The process for preparing a powdery high melt index ethylene homopolymer as claimed in claim 1 or 2, characterized in that under the condition of the ethylene kettle-type slurry polymerization, the kettle-type slurry polymerization is carried out in a batch or continuous mode with a molar ratio of hydrogen to ethylene of 2.0 to 7.0:1, a polymerization activity of more than 1 kgPE/gCat.h and a polymerization time of 1 to 10h by using a Ziegler-type catalyst and/or a Ziegler-Natta type catalyst as a main catalyst and using alkylaluminum and/or haloalkylaluminum as a cocatalyst and one or more of a linear alkane, a branched alkane, a cycloalkane and a branched cycloalkane as a polymerization solvent at a polymerization temperature of 70 to 100 ℃ and a polymerization pressure of 1.0 to 4.2 MPa.
  4. 4. The process for preparing a powdery high melt index ethylene homopolymer according to claim 3, wherein under the condition of an ethylene tank type slurry polymerization, a Ziegler type catalyst or a Ziegler-Natta type catalyst is used as a main catalyst, aluminum alkyl is used as a cocatalyst, linear alkane and cycloalkane are used as polymerization solvents, the polymerization temperature is 80-95 ℃, the polymerization pressure is 1.5-3.6MPa, the molar ratio of hydrogen to ethylene is 3.0-6.0:1, the polymerization activity is more than 1.5kg PE/gCat.h, and the polymerization time is 3-8h.
  5. 5. The method for producing a powdery high melt index ethylene homopolymer as claimed in claim 4, wherein the polymerization solvent is at least one selected from the group consisting of n-hexane, cyclohexane, n-pentane, isopentane, neopentane, n-heptane, isoheptane and methylcyclohexane.
  6. 6. The method for producing a powdery high melt index ethylene homopolymer as claimed in claim 5, wherein the polymerization solvent is at least one selected from the group consisting of n-hexane, n-pentane and n-heptane.
  7. 7. The method for producing a powdery high melt index ethylene homopolymer as claimed in claim 4, wherein the cocatalyst is at least one selected from triethylaluminum, triisobutylaluminum and tri-n-hexylaluminum.
  8. 8. The process for preparing a powdery high melt index ethylene homopolymer according to claim 3, wherein the active metal element of the main catalyst is selected from the group consisting of group IVB metal elements, and the molar ratio of aluminum to active metal is 10 to 250:1 based on the total aluminum element in the cocatalyst and the active metal element in the main catalyst.
  9. 9. The process for preparing a powdery high melt index ethylene homopolymer according to claim 8, wherein the molar ratio of aluminum to active metal is 20 to 100:1 based on the total aluminum element in the cocatalyst and the active metal element in the main catalyst.
  10. 10. The method for producing a powdery high melt index ethylene homopolymer according to claim 8, wherein the active metal element of the main catalyst is titanium element.

Description

Powdery high-melt-index ethylene homopolymer and preparation method thereof Technical Field The invention belongs to the technical field of petrochemical industry, and particularly relates to a powdery high-melt-index ethylene homopolymer and a preparation method thereof. Background The high melt index polyethylene is low molecular weight polyethylene, the molecular weight is generally 1.5-5.0 ́ -10 4 g/mol, the chemical stability is good, the polyethylene is colorless, odorless and nontoxic, the chemical composition, saponification value, electrical property, density and the like are similar to those of polyethylene wax and paraffin wax, the polyethylene wax is completely insoluble in water and all aqueous solutions, the acid and alkali resistance and chemical corrosion resistance are realized, the polyethylene wax can be used for processing lubricants of ultra-high molecular weight polyethylene, and the mechanical properties of the final product can be better maintained while the processing properties are improved and improved. In the industrial production of polyethylene, melt index (melt mass flow rate) is an important product index to reflect the molecular weight of polyethylene. The method is used for controlling the quality of products and dividing polyethylene products with different brands in industry, reflects the melt flow characteristic and the molecular weight, is a key index in the field of product processing application, can better adapt the selected raw materials to the requirements of the processing technology, and improves the reliability and the quality of the products in the aspect of molding. The high melt index polyethylene is used to make the injection molding product easy to mold and process, reduce injection defect and rejection rate, reduce the processing temperature, injection pressure, mold clamping force, etc. during the product processing and production, reduce energy consumption, shorten the product molding period, raise product yield, and simplify the injection molding process and reduce the use cost of material. Therefore, the production of the special material for high-melt-index polyethylene injection molding is one of important directions of polyethylene development, and has good comprehensive performance and wide market prospect. The current common method in industry is to adjust the melt index of polyethylene products by partial pressure of hydrogen, comonomer and ethylene, and the catalyst activity is very low (polymerization activity is less than 1 kgPE/gCat.h) under the existence of high partial pressure of hydrogen and comonomer, the production efficiency is low, the melting point of polyethylene products is low, ash content is high, the morphology is poor, and powdery polyethylene with the melt index higher than 500g/10min is difficult to obtain, and the prior art only carries out polymerization production in a first kettle or a second kettle in a serial polymerization mode and can not provide powdery products. Chinese patent CN112574340a discloses a process for preparing high melt index polyethylene using a catalyst system comprising a catalyst comprising titanium element and a catalyst system comprising an alkyl aluminum and a multi-element external electron donor under hydrogen as a regulator, and provides polyethylene preparation examples having a melt index of not more than 50g/10 min. Chinese patent CN114507311a discloses a process for preparing ethylene polymers using ziegler-natta catalysts, where comonomers must be present in the gas phase of the reactor, whereby the process for preparing polyethylene is complicated in applications involving storage, refining, transport, separation, recycling, etc. of the comonomers. Under the condition of ethylene solution polymerization with high hydrogen-ethylene mole ratio, metallocene catalyst is adopted to obtain high melt index polyethylene wax with narrow molecular weight distribution, but the polymerization cost is higher, the catalyst and the polymer are completely dissolved in a polymerization solvent, the catalyst and the polymer belong to a uniform solution system, and the polymer after post treatment is in a molten state and can not directly provide powdery products. Disclosure of Invention Based on the prior art, the inventor creatively discovers that by adopting Ziegler type catalyst, ziegler-Natta type catalyst or the mixture of the catalysts as a main catalyst and alkyl aluminum or halogenated alkyl aluminum as a cocatalyst, in the presence of ethylene and alkane polymerization solvent or mixed alkane solvent, the powdery high-melt-index ethylene homopolymer with excellent morphology is obtained through batch or continuous kettle type ethylene slurry homopolymerization. Specifically, the present invention provides a powdery high melt index ethylene homopolymer having a melt index of 600 to 2500g/10min, preferably 1000 to 2000g/10min, a molecular mass distribution of 3.0 to 10.0, preferably 4.0 to 8.0, a m