Pyromellitic Dianhydride

With continued growth in demand for high-purity pyromellitic dianhydride (PMDA) for the manufacture of polyimides, there is a need for an improved process. In this review, we evaluate a process for PMDA manufacture from durene (1,2,4,5-tetramethyl benzene) that promises higher yields, a simpler recovery scheme, and higher product purity, which is important for making high-quality polyimides. We evaluate a process for the vapor-phase oxidation of durene to PMDA based on recent Nippon Shokubai patents that describe improved catalysts and a one-step process for the recovery of high-purity PMDA from the reaction vapor.