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

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PX (p-xylene) is an important chemical raw material, widely used in the production of plastics, fibers and resins. The following are several common PX manufacturing methods:

method 1: catalytic reforming method

catalytic reforming method is a naphtha as raw material, through catalytic reforming reaction, the generation of aromatic hydrocarbon mixture, and then separated from the PX method. The specific steps are as follows:

1. Naphtha pretreatment: Naphtha usually contains impurities such as sulfur and nitrogen, and pretreatment such as desulfurization and denitrification is required to protect the activity of the catalyst.
2. Catalytic reforming reaction: under the action of the catalyst, the alkanes and cycloalkanes in the naphtha undergo dehydrogenation, cyclization and other reactions to generate aromatic mixtures.
3. Aromatic separation: PX in the aromatic mixture is separated by distillation, extraction and other separation methods.

this method has the advantages of easy availability of raw materials and low production cost, the activity and selectivity of the catalyst have a great influence on the yield and purity of PX.

method two: toluene disproportionation method

The toluene disproportionation method is a method that uses toluene as a raw material, undergoes a disproportionation reaction, generates a mixture of benzene and xylene, and then separates PX from it. The specific steps are as follows:

1. Pretreatment of toluene: Toluene usually contains impurities such as moisture and sulfur, and pretreatment such as drying and desulfurization is required to protect the activity of the catalyst.
2. disproportionation reaction: under the action of catalyst, toluene disproportionation reaction occurs to produce benzene and xylene mixture.
3. Product separation: PX in the mixture of benzene and xylene is separated by a separation method such as distillation.

this method has the advantages of easy availability of raw materials and mild reaction conditions, it needs to consume a large amount of hydrogen and steam, and the production cost is high.

Method III: Toluene Oxidation Method

Toluene oxidation method is a method of directly generating PX by using toluene as raw material through oxidation reaction. The specific steps are as follows:

1. Pretreatment of toluene: Toluene usually contains impurities such as moisture and sulfur, and pretreatment such as drying and desulfurization is required to protect the activity of the catalyst.
2. oxidation reaction: under the action of catalyst, toluene and oxygen oxidation reaction, PX and benzoic acid and other products.
3. Product isolation: PX is isolated from the reaction mixture by distillation, crystallization and other separation methods.

this method has the advantages of simple steps and high product purity, the activity and selectivity of the catalyst have a great influence on the yield and purity of PX, and the reaction conditions need to be strictly controlled to prevent the formation of by-products.

The above three methods are common PX manufacturing methods, and each has its own advantages and disadvantages. Which method to choose needs to be determined according to specific production conditions and needs. At the same time, in order to ensure the production efficiency and product quality of PX, it is necessary to strictly control the operating conditions of each production link to ensure the stability and reliability of the production process.

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