Process for continuous production of high purity terephthalic acid

In a process of continuously producing high purity terephthalic acid by continuously introducing one or more p-dialkylbenzenes into an oxidation reactor together with a solvent and an oxidation catalyst, subjecting the raw material to a liquid phase oxidation with molecular oxygen or molecular oxygen containing gas, and separating and recovering terephthalic acid formed from the reaction mixture, the improvement which comprises continuously or intermittently introducing the oxidation reaction product from the oxidation reactor into a stabilizer which can retain the oxidation reaction product from the oxidation reactor for 10 to 200 minutes and also can keep the volume change of the contents below 27% by volume even while oxidation reaction product is being introduced and oxidatively treating the oxidation reaction product in the stabilizer, to completely oxidize oxidizable materials selected from the group consisting of unreacted feed materials, reaction intermediate products and active compounds, for about 10 to 200 minutes at a temperature and pressure the same as or lower than those employed in the preceding oxidation reaction by continuously introducing a molecular oxygen containing gas selected from the group consisting of an off-gas exhausted from the oxidation reactor and a mixture thereof with air, said molecular oxygen containing gas having an oxygen concentration of 2 to 15 volume % so that the oxygen concentration in the reaction system does not exceed the explosive limit during said treatment and while maintaining the volume change of the contents in the stabilizer below about 27% by volume, by controlling the amount of the oxidation reaction product introduced from the oxidation reactor to the stabilizer and the amount of the oxidation reaction product discharged from the stabilizer, thereby to maintain the volume change of the contents below about 27% by volume.