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

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Polyethylene is an important material widely used in all kinds of plastic products, textiles and other industries. Its production process is complex, need to go through multiple links of processing to finally make. This article will introduce the production process and preparation method of polyethylene in detail. Pre-preparation for the production of

1. polyethylene
ethylene monomer needs to be used in the production process of
polyethylene, so storage, transportation and purification should be carried out before production to ensure its quality meets the production requirements. At the same time, it is also necessary to prepare some additives, such as hydrogen peroxide, ultraviolet absorbers, stabilizers, etc., to maintain the stability of the production process and the quality of polyethylene.

2. Polyethylene Production Process

Polyethylene Production Process There are two main types: free radical polymerization and anionic polymerization. This paper mainly introduces the process of free radical polymerization.

1. Feeding

ethylene monomer, stabilizer, hydrogen peroxide, antioxidant, ultraviolet absorber and other raw materials are added to the reactor in turn, and a certain amount of solvent is added, such as cyclohexane, n-heptane, etc.

2. Oxidation

The ethylene monomer in the reaction kettle is oxidized, hydrogen peroxide is added to the reaction kettle, and it is evenly dispersed by stirring, and then heated to a certain temperature to decompose it into free radicals to initiate polymerization. At the same time, the flow of oxygen needs to be maintained during the reaction to maintain the oxygen concentration.

3. Polymerization

When the free radical concentration in the reaction solution reaches a certain value, the polymerization reaction of ethylene monomer occurs to produce polyethylene. At this time, it is necessary to gradually increase the reaction temperature in order to promote the progress of the polymerization reaction.

4. Washing

After completion of the polymerization reaction, impurities and unreacted monomers in the reaction need to be removed by washing. Under normal circumstances, the use of water washing and acid washing and other methods to remove impurities. In the washing process, it is necessary to add a surfactant, so that the polymer can easily escape from the solvent and form a particulate material.

5. drying

after washing polyethylene particles contain a lot of water, need to be removed by dehydration drying. Methods such as high temperature drying or vacuum drying are usually used. The synthesis reaction mechanism of

3. polyethylene The synthesis reaction of

polyethylene is a free radical polymerization reaction, which is mainly divided into the following steps:

1. Oxidative decomposition: Hydrogen peroxide decomposes into two radicals under the action of high temperature: hydroxyl radical and peroxy radical.

2. Chain transfer reaction: hydroxyl radicals attack vinyl monomers to form β-site radicals. At this time, β-site radicals can continue to attack other monomer molecules to form chain transfer reactions.