Method for isolation of an aromatic dianhydride and aromatic dianhydrides prepared by the method

A method for producing an aromatic dianhydride, the method comprising:

• reacting an aromatic diimide with a substituted or unsubstituted phthalic anhydride in an aqueous medium in the presence of an amine exchange catalyst at a reaction temperature of 140 to 250° C. and a reaction pressure of 150 to 300 psig, to provide an aqueous reaction mixture comprising an N-substituted phthalimide, an aromatic tetraacid salt, and at least one of an aromatic triacid salt and an aromatic imide diacid salt;
• removing the phthalimide from the aqueous reaction mixture by extracting the aqueous reaction mixture with an organic solvent using a single extraction column, wherein the extraction column is a sieve tray extraction column;
• and
• converting the aromatic tetraacid salt to the corresponding aromatic dianhydride.