Terephthalic Acid → 4-Formylbenzoic acid

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A process for the production of high purity terephthalic acid comprising the steps of dissolving a crude terephthalic acid in a solvent consisting essentially of water to form an aqueous solution of crude terephthalic acid having a content of 4-carboxybenzaldehyde of at least 1,000 ppm, said crude terephthalic acid being obtained by the oxidation of a paradialkylbenzene, subjecting said aqueous solution of crude terephthalic acid having a content of 4-carboxybenzaldehyde of at least 1,000 ppm to oxidation at a temperature of from 230° to 300° C. and a pressure of 30-100 Kg/cm2 by an oxygen-containing gas at a feed rate of 0.4-10 moles of oxygen per mole of 4-carboxybenzaldehyde contained in the crude terephthalic acid, said oxidation being conducted in the presence of a fixed bed catalyst, to obtain a resultant solution, said aqueous solution of crude terephthalic acid having a concentration of 100-700 g of terephthalic acid per liter of aqueous solution, and subjecting the resultant solution to hydrogenation by hydrogen at a temperature in the range of 270°-300° C. and a hydrogen partial pressure of 5-15 Kg/cm2 in the presence of a catalyst to obtain a high purity terephthalic acid.

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