Abstract: A process for producing terephthalic acid by the catalytic liquid phase oxidation of para-xylene with either molecular oxygen or a gas containing molecular oxygen and recovering terephthalic acid from the liquid phase oxidation reaction product; characterized in that (1) the recovery of terephthalic acid is performed at a temperature (T.sub.2) which satisfies the following equation[(T.sub.1 - 150).sup.1.9 /150] + 150 .ltoreq. T.sub.2 .ltoreq. T.sub.1wherein (T.sub.1) is the temperature of the above liquid phase oxidation, and (2) a part or whole of the catalyst-containing mother liquor remaining after the recovery of terephthalic acid is recycled to the catalytic liquid phase oxidation while maintaining it at a temperature (T.sub.3) which satisfies the following equationT.sub.2 .ltoreq. T.sub.3 .ltoreq. T.sub.1wherein (T.sub.2) is the temperature employed in the recovery of terephthalic acid.

Abstract: An improved process for continuously preparing terephthalic acid by a catalytic liquid-phase oxidation which comprises recycling a part of the mother liquor of the oxidation product to the catalytic liquid-phase oxidation zone either as such or after concentration, concentrating the remainder of the mother liquor, until the amount of acetic acid in the resulting bottoms becomes not more than 5% by weight based on the weight of the residual bottoms and the amount of benzoic acid bottoms becomes not less than 15% by weight based on the weight based on the weight of the residual bottoms, contacting the bottoms in the hot and molten state with 2 to 5 times their weight of water, and rapidly cooling the bottom to a temperature of not more than 50.degree.C., separating an aqueous solution containing the catalyst from the resulting granular solid mixture and recycling the aqueous solution to the catalytic liquid-phase oxidation zone.