Preparation method of PMDA CAS 89-32-7 Pyromellitic Dianhydride

There can be many methods to produce Pyromellitic Dianhydride PMDA. The raw materials used can be xylene, trimethylene, tetratoluene or anthracene. The oxidation methods include liquid phase method and gas phase method. 1. Gas phase oxidation of mesitylene. This method is characterized by simple process, can omit the dehydration to anhydride process, does not need other oxidants except air (such as nitric acid, permanganate, chromic acid, etc.), and does not need the catalyst separation process necessary for the liquid phase. It can be produced continuously and is easy to realize automatic operation. It is the main method developed abroad. Starting from 1,2,4-trimethylbenzene, the raw material can be alkylated with propylene in the presence of catalyst to produce 1,2,4-trimethyl-5-propyl benzene, and then the pyromellitic dianhydride can be obtained by gas-phase air catalytic oxidation. 2. It is obtained by chloromethylation, oxidation and cyclization of xylene (p-xylene or m-xylene). The industrial pyromellitic dianhydride is white to light yellow green crystal. The melting point of the first grade product is 284-287 ℃, and the melting point of the second grade product is 283.5-287 ℃. When 1,2,4-trimethylbenzene is produced by oxidation method, 3000kg of 1,2,4-trimethylbenzene and 1200kg of propylene are consumed per ton of product.

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