Patent ID: 7897808

Claim:
In a process for producing a terephthalic acid that employs recycling of a mother liquor and/or a wash liquor to an oxidation section of said process, the improvement comprising: (a) introducing at least a portion of said mother liquor and/or wash liquor into a purge section of said process as a purge feed stream, wherein said purge feed stream comprises impurities from said oxidation step and one or more catalyst components, wherein said impurities comprise mono-functional impurities and non-mono-functional impurities; (b) separating said purge feed stream into a (i) mono-functional impurity depleted stream, wherein said mono-functional impurity depleted stream comprises IPA, PA, trimellitic acid, 2,5,4′-tricarboxybiphenyl, 2,5,4′-tricarboxybenzophenone, 4-carboxybenzaldehyde (4-CBA), naphthalene dicarboxylic acid, monocarboxyfluorenones, and/or dicarboxyfluorenones; (ii) and a catalyst and mono-functional impurity rich mother liquor; and (c) separating said catalyst and mono-functional impurity rich mother liquor into (ii-1) a catalyst rich stream and a (ii-2) mono-functional impurity rich stream wherein a portion of said (i) mono-functional impurity depleted stream is subsequently combined with at least one stream containing terephthalic acid obtained after completion of all liquid phase oxidation to form a combined stream.