PROCESS AND APPARATUS FOR PREPARING TEREPHTHALIC ACID BY AIR OXIDATION OF PARA-XYLENE

Disclosed are a process and an apparatus for preparing terephthalic acid by air oxidation of para-xylene. Said process is: in a reaction system with oxidation reactor and crystallizer connecting in series, para-xylene with dissolved metalloporphyrins or mixed catalyst of metalloporphyrins and metal salt, and air, oxygen-poor air, oxygen-rich air or carbon-dioxide-containing air are fed into the oxidation reactor which stay in the reactor for 70-180 minutes at 140-200 °C. The oxidation mixture crystallizes by flooding or being pumped into crystallizer. Para-xylene, para-toluic acid and para-methyl benzyl alcohol obtained by separation are fed into oxidation reactor, mixed with para-xylene containing metalloporphyrins catalyst for the second oxidation, and the crystals are purified to obtain purified terephthalic acid. In the present invention para-xylene is oxidized directly into terephthalic acid, the energy consumption is low, the production efficiency is high, and the conversion of para-xylene and the yield of terephthalic acid are above 95%.