PRODUCTION OF HIGH-PURITY TEREPHTHALIC ACID

摘要

PURPOSE:To obtain terephthalic acid having high purity by increasing the terephthalic acid concentration in a mixture to be supplied to a high-temperature post-oxidization process in the terephthalic acid production process comprising the oxidization of p-xylene and subsequent low-temperature post-oxidization and high-temperature post-oxidization. CONSTITUTION:p-Xylene is oxidized with molecular oxygen in acetic acid solvent at 180-230 deg.C in the presence of a catalyst consisting of a heavy metal and bromine until >=95wt.% of the p-xylene is oxidized to terephthalic acid. The reaction system is subjected to low-temperature post-oxidization with molecular oxygen at a temperature lower than the temperature of the 1st oxidizing reaction by 0-50 deg.C (preferably 2-30 deg.C). A part of condensed liquid generated by condensing the oxidization exhaust gas of the reactor in the above oxidization reaction is purged from the reaction system to increase the terephthalic acid concentration in the mixture by >=2wt.% (preferably 5-10wt.%) and the mixture is supplied to a high-temperature post-oxidization stage and subjected to the high-temperature post-oxidization at 235-290 deg.C. The obtained mixture is crystallized to recover terephthalic acid crystals.