Patent ID: 6696604
Filing Date: 2004-02-24
Classification: C07C,C07D

Abstract:
A method for making trimellitic anhydride comprising:a) oxidizing pseudocumene in the presence of a solvent and a catalyst comprising multivalent metals to produce trimellitic acid; b) crystallizing and filtering said trimellitic acid to produce a crude trimellitic acid cake having impurities comprising said multivalent metals; c) dehydrating said crude trimellitic cake to form crude trimellitic anhydride; and d) distilling said crude trimellitic anhydride in a fractionation column to separate the crude trimellitic anhydride into a low boiling point fraction and a less volatile bottoms fraction; wherein a viscosity reducer comprising an alkali or alkali earth metal salt of a mineral acid selected from the group consisting of sulfuric acid, nitric acid, boric acid, phosphoric acid hydrobromic acid, and mixtures thereof is added after step a) but before step d) so that said viscosity reducer is present in said bottoms fraction.