PROCESS FOR PRODUCING TEREPHTHALIC ACID SUITABLE FOR USE IN DIRECT POLYMERIZATION

摘要

A process for producing terephthalic acid suitable for use in direct polymerization, which comprises oxidizing p-xylene with molecular oxygen in an acetic acid solvent in the presence of a heavy metal compound and a bromine compound, wherein after a main reaction step of oxidizing at least 90 mole% of p-xylene fed has been performed, 1) a first purifying step of feeding a gas containing molecular oxygen to the oxidation reaction mixture obtained from the main reaction step in such a proportion that the concentration of oxygen in the off-gas becomes at least 0.5% by volume and smashing the oxidation reaction mixture at a temperature of 140 to 230.degree.C to decrease the average particle diameter of terephthalic acid by at least 20% from its average particle diameter before smashing, and 2) a second purifying step of feeding a gas containing molecular oxygen to the slurry from the first purifying step in such a proportion that the concentration of oxygen in the off gas becomes 0.05 to 5% by volume, and contacting the slurry with the molecular oxygen-containing gas at a temperature at least 13.degree.C higher than in the first purifying step and within the range of 180 to 300.degree.C, are performed successively, and the resulting purified slurry is subjected to solid liquid separation to recover terephthalic acid.