METHOD FOR PRODUCING TEREPHTHALIC ACID BY SEQUENTIAL OXIDATION OF n-XYLENE WITH MANGANESE DIOXIDE AND POTASSIUM PERMANGANATE UNDER MILD CONDITIONS
A method for producing terephthalic acid from p-xylene has been developed. The metod allows the product to be synthesized under mild conditions, namely at atmospheric pressure and temperatures no higher than 90 °С. The process consists of two stages: by the first p-xylene is oxidized by manganese dioxide in a mixture of 35-60% sulfuric acid and 10-30% perchloric acid and then obtained intermediates are oxidized by potassium permanganate in an alkaline medium. The temperature range from 75 °C to 90 °C is optimal for the first stage of the synthesis. Regime of the first stage was selected based on the results of its thermochemical study by differential scanning calorimetry. The high efficiency of using of mixture of acids as a promoter of p-xylene oxidation in a wide range of their concentrations was confirmed. It was found that oxidation of the first stage products with potassium permanganate provides high-purity terephthalic acid (up to 99,9 %) with an output up to 86 % at the second stage. This method of synthesis of terephthalic acid can compete with currently used technologies for its production based on catalytic oxidation of p-xylene with by molecular oxygen under harsh conditions with using an organic solvent