Pyromellitic acid dianhydride by tetralkyl - benzene air oxidation

摘要

Pyromellitic acid dianhydride (PMDA), useful in production of heat-resistant electrically insulating polyimides or polyimidazopyrrolones by polycondensation with aromatic di- or tetraamines, in made by air vapour-phase oxidation of at least one 1,2,4,5-tetraalkyl-benzene. PMDA is separated from oxidation product gas mixture by keeping latter at 150-230 degrees C under exclusion of surrounding atmosphere until most PMDA present has crystallised (pref. for over 15 secs. in a collecting vessel at 170-200 degrees C.).