Patent ID: 7956215

Claim:
In a process for producing terephthalic acid (TPA) obtained by oxidizing para-xylene via at least one liquid phase oxidation step that employs a recycled liquid, wherein said recycled liquid comprises at least a portion of a recovered mother liquor that has been recovered downstream of said liquid phase oxidation step, the improvement comprising: (a) introducing at least a portion of said recovered mother liquor into a purge treatment zone as a purge feed stream, wherein said purge feed stream comprises oxidation byproducts from said liquid phase oxidation step, wherein said oxidation byproducts include benzoic acid (BA) and non-BA byproducts comprising isophthalic acid, phthalic acid (PA), trimellitic acid, 2,5,4′-tricarboxybiphenyl, 2,5,4′-tricarboxybenzophenone, naphthalene dicarboxylic acid, and/or dicarboxyfluorenones; and (b) separating at least a portion of said purge feed stream into a BA rich stream and a non-BA byproduct rich stream, wherein the concentration of said BA in said BA rich stream is at least about 1.5 times the concentration of said BA in said purge feed stream on a weight basis, wherein the concentration of said non-BA byproducts in said non-BA byproduct rich stream is at least about 1.5 times of the concentration of said non-BA byproducts in said purge feed stream on a weight basis; wherein a portion of said non-BA byproducts is subsequently combined with a TPA product stream to form a combined stream.