Patent ID: 7902395

Claim:
A process for producing terephthalic acid and/or isophthalic acid via at least one liquid phase oxidation step of a xylene isomer, 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, comprising: (a) introducing at least a portion of said recovered mother liquor into a purge treatment zone as, wherein said purge feed stream comprises oxidation byproducts from said liquid phase oxidation step and one or more catalyst components, wherein said oxidation byproducts include benzoic acid (BA) and non-BA byproducts; wherein said non-BA byproducts comprise IPA, PA, trimellitic acid, 2,5,4′-tricarboxybiphenyl, 2,5,4′-tricarboxybenzophenone, para-toluic acid (p-TAc), 4-carboxybenzaldehyde (4-CBA), naphthalene dicarboxylic acid, monocarboxyfluorenones, monocarboxyfluorenes, and/or dicarboxyfluorenones; (b) separating at least a portion of said purge feed stream into (i) a non-BA byproduct rich stream comprising non-BA byproducts and (ii) a catalyst and BA rich stream, wherein the concentration of said non-BA byproducts in said non-BA byproduct rich stream is at least about 1.5 times the concentration of said non-BA byproducts in said purge feed stream on a weight basis, wherein the cumulative concentration of all of said catalyst components in said catalyst and BA rich stream is at least about 1.5 times the cumulative concentration of all of said catalyst components in said purge feed stream on a weight basis, and wherein the concentration of BA in said catalyst and BA rich stream is at least about 1.5 times the concentration of BA in said purge feed stream on a weight basis; and (c) separating at least a portion of said (ii) catalyst and BA rich stream into a catalyst rich stream and a BA rich stream, wherein the cumulative concentration of all of said catalyst components in said catalyst rich stream is at least about 1.5 times the cumulative concentration of all of said catalyst components in said purge feed stream on a weight basis, wherein the concentration of BA in said BA rich stream is at least about 1.5 times the concentration of BA in said purge feed stream on a weight basis; wherein a portion of said non-BA byproducts rich stream is subsequently combined with at least one stream containing terephthalic acid and/or isophthalic acid obtained after completion of all liquid phase oxidation to form a combined stream.