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[Chemical Knowledge]：Production and manufacturing method and process of polyethylene

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The manufacturing method
of polyethylene
1. Introduction

Polyethylene is a widely used plastic material with excellent chemical resistance, electrical insulation and processing properties, so it has an important position in the field of chemical production raw materials. This article will introduce the manufacturing methods of polyethylene, including high pressure method, low pressure method and gas phase method.

2. high-pressure method

high-pressure method is the earliest method of producing polyethylene, and it is also one of the methods still in use. In this method, ethylene monomer is polymerized under high pressure (150-300MPa) and high temperature (180-200 ° C.) using an initiator such as oxygen or peroxide to produce polyethylene. The specific steps are as follows:

1. Ethylene monomer, initiator and regulator are added to a high-pressure polymerization kettle.
2. Heat the polymerization kettle to the desired temperature while pressurizing to the desired pressure.
3. Maintain time and temperature to polymerize ethylene monomer to form polyethylene.
4. Reduce the temperature and pressure, and remove the polymer from the polymerization kettle.
Polyethylene produced
high-pressure method has low molecular weight, wide molecular weight distribution, more branched chains and low crystallinity, so it has better flexibility and processability. However, this method has high energy consumption and low production efficiency, and is gradually replaced by the low-pressure method.

3. low pressure method

low pressure method is the main method of production of polyethylene, including solution method, suspension method and gas phase method. These processes are carried out under the conditions of low pressure (0.1-1.0MPa) and relatively low temperature (70-90 ° C.), using a catalyst such as a Ziegler-Natta catalyst or a chromium-based catalyst to initiate the polymerization of ethylene monomers to produce polyethylene. The specific steps are as follows:

1. Ethylene monomer, catalyst and other additives are added to the polymerization reactor.
2. At a certain temperature and pressure, the ethylene monomer is polymerized to produce polyethylene.
3. Through flash evaporation, extrusion granulation and other processes, the polymer is separated from the unreacted monomer and catalyst to obtain the polyethylene product.
Polyethylene produced
low-pressure method has higher molecular weight, narrower molecular weight distribution, fewer branches and higher crystallinity, so it has better mechanical properties and heat resistance. This method has low energy consumption and high production efficiency, and has become the main method for the production of polyethylene.

4. gas phase method

gas phase method is a new method for the production of polyethylene developed in recent years. The method is to add ethylene monomer and catalyst together into the fluidized bed reactor, under the condition of low pressure (0.1-0.5MPa) and high temperature (80-100 ℃), the ethylene monomer is polymerized to produce polyethylene. The specific steps are as follows:

1. Add the catalyst to the fluidized bed reactor and heat to the desired temperature.
2. Ethylene monomer is introduced to polymerize into polyethylene under the action of a catalyst.
3. By controlling the reaction conditions and the type and amount of catalyst, polyethylene with different molecular weight and molecular structure can be obtained.
4. Through cooling, separation and other processes, the polymer is separated from the unreacted monomer and catalyst to obtain the polyethylene product.
Polyethylene produced
gas phase method has the advantages of high molecular weight, narrow molecular weight distribution, few branches, high crystallinity, and the advantages of low energy consumption, high production efficiency and good product quality, so it has been widely used in polyethylene production.

5. conclusion

polyethylene is an important raw material for chemical production, and its manufacturing methods include high pressure method, low pressure method and gas phase method. Polyethylene obtained by different methods is different in molecular structure, performance and application. With the continuous advancement of technology and the continuous improvement of application requirements, the manufacturing methods of polyethylene are constantly developing and improving.

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