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CN-121991265-A - Powdery high-melt-index polyethylene and preparation method thereof

CN121991265ACN 121991265 ACN121991265 ACN 121991265ACN-121991265-A

Abstract

The invention relates to a powdery high-melt-index polyethylene, which has a melt index of 600-2500g/10min under a load of 2.16kg and a temperature of 190 ℃, a molecular mass distribution of 1.2-1.8, a melting point of 90-135 ℃, a crystallinity of 50-90%, a true density of 0.930-0.970g/cm 3 , a branching degree of 0-1.0mol%, a bulk density of 0.30-0.55g/cm 3 and an average particle size of 200-1000mm. And a process for preparing the same by polymerizing a raw material comprising ethylene, hydrogen and/or a comonomer in a kettle-type slurry at a polymerization temperature of 70 to 100 ℃ and a temperature difference in the kettle of less than 2.0 ℃ and a polymerization pressure of 1.0 to 4.2MPa by using an alkane solvent having a boiling point of 5 to 55 ℃ or a mixed alkane solvent having a saturated vapor pressure of 20 to 150KPa at 20 ℃ as a polymerization solvent, using a single-site catalyst as a main catalyst, and aluminoxane, a modified aluminoxane, an alkylaluminum or a haloalkylaluminum as a cocatalyst. The preparation method is simple and easy to control, the obtained powdery polyethylene has high melt index, adjustable and controllable average particle size, true density, melting point, crystallinity and the like, and the particle size distribution is narrow.

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 polyethylene characterized by a melt index of 600-2500g/10min under a load of 2.16kg and 190 ℃, a molecular mass distribution of 1.2-1.8, a melting point of 90-135 ℃, a crystallinity of 50-90%, a true density of 0.930-0.970g/cm 3 , a branching degree of 0-1.0mol%, a bulk density of 0.30-0.55g/cm 3 , and an average particle size of 200-1000mm.
  2. 2. The powdered high melt index polyethylene according to claim 2, wherein the powdered high melt index polyethylene has a melt index of 1000-2000g/10min at 190 ℃ under a load of 2.16kg, a melting point of 100-125 ℃, a crystallinity of 60-85%, a true density of 0.935-0.960g/cm 3 , a branching degree of 0-0.5mol%, a bulk density of 0.33-0.50g/cm 3 , and an average particle size of 300-700mm.
  3. 3. The process for preparing a powdery high melt index polyethylene according to claim 1 or 2, characterized in that it comprises carrying out a pot slurry polymerization of aluminoxane, modified aluminoxane, alkylaluminum, haloalkylaluminum or a mixture thereof as a cocatalyst under a pot slurry polymerization condition of ethylene with a single site catalyst as a main catalyst, an alkane solvent having a boiling point of 0 to 90 ℃ or a mixed alkane solvent having a saturated vapor pressure of 4 to 200KPa at 20 ℃ as a polymerization solvent, a polymerization temperature of 70 to 100 ℃, a temperature difference in the pot of less than 2.0 ℃, a polymerization pressure of 1.0 to 4.2MPa, a molar ratio of hydrogen to ethylene in a reactor gas phase of 0.5 to 5.0:1, a molar ratio of comonomer to ethylene of 0 to 0.5:1, and a polymerization time of 1 to 10 hours, and a pot slurry polymerization of 50 to 250g of polyethylene/L polymerization solvent with a polymerization activity of more than 1.5×10 5 g pe/molM ·h per unit hour.
  4. 4. The process for preparing polyethylene with high melt index as claimed in claim 3, wherein the main catalyst is a supported metallocene catalyst or a supported non-metallocene catalyst, the cocatalyst is a modified aluminoxane or an alkylaluminum, the polymerization solvent is an alkane solvent with a boiling point of 25-82 ℃ or a mixed alkane solvent with a saturated vapor pressure of 30-160KPa at 20 ℃, the polymerization temperature is 80-95 ℃, the temperature difference in the reactor is less than 1.5 ℃, the polymerization pressure is 1.5-3.6MPa, the molar ratio of hydrogen to ethylene is 1.0-4.0:1, the molar ratio of comonomer to ethylene is 0-0.25:1, the polymerization time is 2-6h, the slurry concentration in the reactor is 100-200g of polyethylene/L polymerization solvent, and the polymerization activity per unit hour is greater than 1.8X10 5 g PE/molM. H.
  5. 5. The process for preparing a pulverulent high melt index polyethylene according to claim 4, wherein the polymerization solvent is selected from n-hexane, cyclohexane, n-pentane, isopentane, neopentane, n-heptane, isoheptane, preferably n-hexane and n-pentane.
  6. 6. A process for the preparation of a powdered high melt index polyethylene according to claim 3, wherein said comonomer is selected from the group consisting of C 3 -C 10 a-olefins.
  7. 7. A process for preparing a pulverulent high-melt-index polyethylene according to claim 6, wherein the comonomer is one or more of propylene, 1-butene, 1-hexene, 1-octene, preferably propylene, 1-butene or 1-hexene.
  8. 8. A process for the preparation of a powdered high melt index polyethylene according to claim 3, wherein said main catalyst active metal element is selected from the group consisting of group IVB metal elements, preferably zirconium and titanium elements.
  9. 9. A process for the preparation of a powdered high melt index polyethylene according to claim 3, wherein said cocatalyst is selected from methylaluminoxane, triisobutylaluminum modified methylaluminoxane, triethylaluminum, triisobutylaluminum or tri-n-hexylaluminum.
  10. 10. A process for the preparation of a pulverulent high melt index polyethylene according to claim 3, characterized in that the molar ratio of aluminium to active metal is from 10 to 500:1, preferably from 50 to 250:1, based on the total aluminium element in the cocatalyst and on the active metal element in the main catalyst.

Description

Powdery high-melt-index polyethylene and preparation method thereof Technical Field The invention belongs to the technical field of petrochemical industry, and particularly relates to powdery high-melt-index polyethylene 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, the melt index (melt mass flow rate) is an important product index, is commonly used in industry to control the quality of products and divide polyethylene products of different brands, reflects the melt flow characteristic and the molecular weight, is a key index in the application field of product processing, can better adapt to the requirements of processing technology by using the selected raw materials, and improves the reliability and quality of the product in molding. The additive is used as high melt index polyethylene, so that the injection molding product is easy to mold and process, injection defects and rejection rate are reduced, processing temperature, injection pressure, mold clamping force and the like can be reduced in the process of processing and producing the product, thus reducing energy consumption, shortening the molding cycle of the product, improving the product yield, and the injection molding process can be simplified by using the additive to mold thin-wall products with complex structures and produce parts with complex design parameters or longer flow length, and the use cost of raw materials is reduced. 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 and ethylene, and under the conditions of high hydrogen partial pressure and high copolymerization, the catalyst activity is extremely low, the polymerization time is long, the production efficiency is low, the melting point of polymer products is low, the ash content is high, the morphology is poor, polyethylene with the melt index higher than 500g/10min is difficult to obtain, the existing large-scale application technology only carries out copolymerization in a first kettle or a second kettle in a series polymerization mode, and powdery products cannot be provided. Chinese patent CN112574340a discloses a process for preparing high melt index polyethylene using 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. The high melt index ethylene polymer with narrow relative molecular mass distribution is more beneficial to improving the application performance when used as an additive, can effectively maintain the overall mechanical property of the product and improve the processing performance of the product, or can be added with a smaller amount when maintaining the mechanical property and the processing performance of the existing product. Chinese patents CN114621379a and CN114524893a disclose ethylene polymers prepared with low molar ratios of hydrogen to ethylene in ethylene slurries using metallocene catalysts and non-metallocene catalysts, respectively, with broad molecular weight distributions of ethylene polymers. 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. Therefore, according to the current practical application demands, there is still a need to develop and invent a high melt index polyethylene with good particle morphology, narrow relative molecular mass distribution and adjustable and controllable properties, which