Polypropylene or propylene-ethylene copolymer preparation method

Abstract

The invention relates to the field of propylene homopolymerisation or random copolymerization and discloses a polypropylene or propylene-ethylene copolymer preparation method. The preparation method comprises the steps: (1) performing propylene prepolymerization on liquid-phase propylene carrying a polymerization catalyst to obtain raw material slurry containing propylene prepolymer, wherein a prepolymerization temperature is 40 to 45 DEG C, prepolymerization pressure is 3.2 to 3.9 MPaG, and the olefin polymerization catalyst is 0.04 to 0.06 weight% of the liquid-phase propylene; (2) mixing the raw material slurry, recycled liquid-phase propylene and recycled circulation hydrogen into a liquid-phase polymerization raw material; (3a) performing propylene liquid-phase homopolymerization andpropylene gas-phase homopolymerization on the liquid-phase polymerization raw material to obtain a product containing propylene homopolymer; or (3b) performing liquid-phase random copolymerization andgas-phase random copolymerization on the liquid-phase polymerization raw material and ethylene to obtain a product containing propylene ethylene random copolymer and performing gas-solid separation on the product to separate polymer out and recycle propylene and hydrogen, wherein the ethylene feeding quantity is 5 weight% or less of the liquid-phase propylene. The method can reduce unit product energy consumption and propylene loss in propylene polymerization.

Description

technical field [0001] The invention relates to the field of propylene polymerization industrialization, in particular to a method for preparing polypropylene or propylene-ethylene copolymers in a three-stage process. Background technique [0002] Polypropylene is a polymer polymerized from propylene as a monomer. It is a very important variety of general-purpose plastics. It has the characteristics of abundant raw materials, low price, easy processing and molding, and non-toxicity. It can also be used through copolymerization, blending, It has a very broad application field, and it is the second largest plastic after polyethylene among polyolefin resins. And propylene can also be copolymerized with ethylene to prepare propylene-ethylene random copolymer. [0003] At present, the domestic and foreign production technologies of polypropylene mainly include: liquid phase bulk method, gas phase bulk method and polymerization method in which liquid phase bulk and gas phase bulk...

AI Technical Summary

Problems solved by technology

Its advantages include high heat removal efficiency of the reactor, stable production operation, uniform residence time of materials during the reaction period, wide range of melting index of the products produced, and low energy consumption; its disadvantages are that hot spots and plasticized blocks are easily generated in the reactor, and the reactor High processing difficulty, key equipment needs to be imported, high investment

[0010] Hypol process of Mitsui, Japan: the combination process of liquid phase body and gas phase body produces polypropylene. The first two reactors are vertical stirring tanks, and the latter two are vertical gas fluidized bed polymerization tanks; its advantages can produce random copolymerization and Block copolymerization products; its disadvantages are long process, low equipment efficiency, fully mixed gas phase reaction, uneven product quality, poor catalyst adaptability, and small device scale; there are no new Hypol process devices in China in recent years

[0011] However, in the process of industrialization of the above-mentioned various processes, there are defects of high energy consumption per unit of propylene polymer production, which in turn affects the quality and stability of polymer products, as well as the safety of device operation, and increases the investment in project industrialization. Affects the economics of the project

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