PURPOSE: To obtain high-purity terephthalic acid, by oxidizing p-xylene with molecular oxygen, additionally oxidizing the resultant product at a lower temperature as necessary, additionally oxidizing the product at a high temperature and feeding molecular oxygen into a feed line for feeding the reaction mixture to the first crystallizer.
CONSTITUTION: ≥95wt%, preferably ≥98wt% p-xylene is oxidized into terephthalic acid with molecular oxygen at 180W230°C, preferably 190W210°C in the presence of a catalyst consisting of a heavy metal and bromine in acetic acid solvent and, as necessary, preliminary additional oxidation is carried out using molecular oxygen at a temperature 20W30°C lower than the above- mentioned temperature and further additional oxidation is performed at 235W290°C using molecular oxygen. Molecular oxygen is then fed into a feed line for feeding the resultant reaction mixture to the first crystallizer to afford the titled substance.
EFFECT: The terephthalic acid obtained by the above-mentioned method can be directly reacted with a glycol component to produce a polyester.
IZUMISAWA YOSHIAKI
FUKUDA KATSUNORI
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