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

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Xylene is an important organic compound, which is widely used in fine chemical industry, such as chemical production, organic synthesis and coating manufacturing. In the preparation of xylene, there are many different processes and methods to choose from. In this article, we will discuss the production process and preparation method of xylene.

1. Production process

production of xylene mainly uses two processes: TDP method and TDP-HDA method.

TDP method (Toluene Disproportion Alkylation) Introduction: This method uses a mixture of toluene and benzene for crude separation, and then uses methylbenzene and benzene to alkylate in the presence of a catalyst to produce xylene. The catalyst of the TDP method is phosphotungstic acid and alumina, and the reaction needs to be carried out at high temperature and high pressure.

TDP-HDA method (Toluene Disproportion Alkylation-combined with Hydro-Dealkylation) Introduction: This method is an improved version on the basis of TDP method, using hydrodealkylation reaction. The catalyst for this process is aluminum chloride, and the reaction can be carried out at relatively low temperatures and pressures.

2. Preparation Methods There are many methods for the preparation of xylene from

, including chemical synthesis, coal tar fractionation and acid distillation.

chemical synthesis: chemical synthesis is obtained by oxidation of benzene and toluene in clean air. In this reaction, toluene first reacts with oxygen in the air to form toluene peroxide, and then reacts with benzene to form xylene. The process requires the use of yttrium peroxide as a catalyst and the reaction at higher temperatures and pressures.

Coal tar fractionation: Coal tar is a by-product produced in the coking process, which can be fractionated to obtain benzene and toluene, and then used to prepare xylene by the TDP method or the TDP-HDA method.

acid distillation method: this method is the coal tar after heating distillation to obtain benzene and toluene, and then use acid catalyst to promote the aromatization reaction of xylene. This method uses some organic acids or inorganic acids as catalysts, and the reaction needs to be carried out under high temperature and high pressure.

Xylene is a very important organic compound, and there are many options for its preparation. The methods described above can all be used for the preparation of xylene, and each has its advantages and disadvantages. The specific method used depends on actual needs and economic considerations. In the future, with the continuous progress of technology, the preparation method of xylene will also have more improvement and optimization.