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[Chemical Knowledge]：Manufacturing method and process flow of PX (paraxylene)

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The manufacturing method
of PX (p-xylene)
PX, that is, p-xylene, is an important raw material for chemical production, mainly used for the production of PTA (purified terephthalic acid) and BDO(1,4-butanediol). With the increasing demand for chemical products such as polyester fibers and plastics, the manufacturing methods of PX have also attracted much attention. This article will introduce the manufacturing method of PX, including raw material preparation, reaction process, separation and purification steps.

1. raw material preparation

PX manufacturing raw materials are mainly naphtha and coal tar, of which naphtha is the main source. Naphtha is a light petroleum product, mainly composed of hydrocarbons, which can be used to make PX by catalytic reforming or steam cracking to obtain aromatic hydrocarbons.

2. reaction process

1. Alkylation reaction

Alkanes and olefins in naphtha can generate aromatics through alkylation reaction, which is an important step in the manufacture of PX. Commonly used alkylation catalysts are acidic catalysts and fluorination catalysts. In the presence of acidic catalysts, alkanes and olefins can be alkylated with aromatics to produce aromatic products such as p-xylene.

2. Dehydrogenation reaction

dehydrogenation reaction is a reaction in which hydrogen atoms in hydrocarbon compounds are removed to generate corresponding olefins or aromatic hydrocarbons. In naphtha, alkanes and naphthenes can generate aromatics through dehydrogenation reaction, which further improves the yield of PX.

3. Isomerization Reaction

An isomerization reaction is a reaction in which one isomer of a hydrocarbon compound is converted into another isomer. In the process of producing PX, the generated m-xylene and p-xylene can be converted into each other by an isomerization reaction to improve the purity of p-xylene.

3. separation and purification

After the reaction process, the mixture needs to be separated and purified to obtain high-purity PX. Commonly used separation methods are distillation, extraction, crystallization and so on. Among them, distillation is a common separation method, which separates the different components of the mixture by heating and condensing. In the manufacturing process of PX, the mixture is gradually separated and purified by multi-column distillation, and finally a high-purity PX product is obtained.

4. Environmental Protection and Safety
The manufacturing process of
PX involves a variety of chemical reactions and operations such as high temperature and high pressure, so it is necessary to pay attention to environmental protection and safety issues. In the production process, it is necessary to strengthen the treatment and emission control of waste gas, waste water and other pollutants to avoid harm to the environment and human body. At the same time, it is necessary to strengthen equipment maintenance and operation management to prevent accidents.

In short, the manufacturing method of PX involves multiple links and steps, and it is necessary to strictly control the quality of raw materials, reaction conditions, separation and purification and other process parameters to ensure product quality and production safety. With the continuous progress and application of technology, it is believed that the manufacturing method of PX will be more efficient, environmentally friendly and safe in the future.

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