Process for the production of a high purity terephthalic acid

In a process for the production of a high purity terephthalic acid by a liquid phase oxidation reaction of para-xylene by means of molecular oxygen or a molecular oxygen-containing gas in an aliphatic monocarboxylic acid solvent in the presence of a cobalt-manganese-bromine catalyst system, the improvement wherein in the liquid phase oxidation reaction, there are used acetaldehyde in an amount of 0.05 to 0.60 mole per mole of para-xylene and as the cobalt-manganese-bromine catalyst system (A) at least one cobalt compound selected from the group consisting of cobalt acetate, cobalt propionate, cobalt butyrate, cobalt naphthenate, cobalt carbonate, cobalt benzoate, cobalt bromoacetate, cobalt bromide and hydrates thereof, (B) at least one manganese compound selected from the group consisting of manganese acetate, manganese propionate, manganese butyrate, manganese naphthenate, manganese carbonate, manganese benzoate, manganese bromoacetate, manganese bromide and hydrates thereof and (C) at least one bromine compound selected from the group consisting of hydrogen bromide, cobalt bromide and hydrates thereof, manganese bromide and hydrates thereof, bromoacetic acid, cobalt bromoacetate and a hydrate thereof, manganese bromoacetate and a hydrate thereof, aralkyl bromides and alkane bromides, in amount such as will provide a cobalt atom concentration of 0.01 to 0.05% by weight based on the aliphatic monocarboxylic acid solvent, a manganese atom concentration of 35 to 100% by weight based on the cobalt atom and a bromine atom concentration of 0.10 to 0.40% by weight based on the aliphatic monocarboxylic acid solvent, and the liquid phase oxidation reaction is effected at a temperature of 170.degree. to 190.degree. C. under an elevated pressure while maintaining the water concentration in the reaction system at a level of 3 to 9% by weight based on the aliphatic monocarboxylic acid, followed by separation and recovery of terephthalic acid crystals from the reaction mixture.