| 摘要 |
PURPOSE:To obtain high-purity terephthalic acid in a high yield by purifying an aqueous solution of crude terephthalic acid obtained by the oxidizing reaction of p-xylene in the presence of a platinum group metal. CONSTITUTION:p-Xylene is oxidized to provide crude terephthalic acid, which is then completely dissolved in water at 220-320 deg.C, preferably 260-300 deg.C. The resultant aqueous solution is then brought into contact with a platinum group metal (palladium supported on active carbon is preferably used as a fixed bed) and purified. The obtained aqueous solution is subsequently cooled to 70-180 deg.C, preferably 110-170 deg.C and the first crystal of the terephthalic acid is recovered. The mother liquid is further cooled to a temperature within the range of 20-130 deg.C, preferably 30-50 deg.C which is lower than the depositing temperature of the first crystal by >=20 deg.C to deposit the second crystal. At least a part of the resultant second crystal is circulated to the purifying step. The crystallization ratio in recovering the first crystal is within the range of usually 90-99.5%, preferably 92-99%. |
