Process for continuous production of high purity terephthalic acid

A process for continuously producing high purity terephthalic acid, in particular, useful for direct polymerization, which comprises continuously introducing p-dialkylbenzene as a feed material together with a solvent and an oxidation catalyst into a reactor, subjecting the p-dialkylbenzene to a liquid phase oxidation with oxygen in the reactor to produce terephthalic acid, continuously or intermittently introducing the reaction mixture containing terephthalic acid thus produced into a stabilizer, and oxidizing the reaction mixture in the stabilizer for an extended period of time with a molecular oxygen containing gas of a low oxygen concentration at a temperature and pressure the same as or lower than those in the oxidation reaction while keeping the volume change of the contents in the stabilizer below about 30% by volume of the contents of the stabilizer.