A strategy for total recovery of residue from terephthalic acid production process

Abstract

Terephthalic acid is generally produced via oxidation of p-xylene. In this process, a large quantity of residue is produced containing cobalt, manganese, and bromine catalysts as well as by-products such as benzoic acid. Our purpose is to totally recover this residue. Extraction by water has been used as an efficient method to recover catalyst from this residue. In this study, the best condition for extraction was obtained at water/residue dilution ratio of 6 : 1, extraction temperature of 45°C and extraction time of 40 min. Efficiency of catalyst recovery was 92 wt % at these conditions. The catalyst containing extracted solution can be reused in the oxidation process after being concentrated by an evaporator. The benzoic acid content of the residue is also recovered by recrystallization. The best condition for recrystallization was achieved at water/residue dilution ratio of 4: 1 and dissolution and crystallization temperatures of 95 and 25°C, respectively. Recovery efficiency and purity of benzoic acid were 85 and 97 wt %, respectively, at these conditions. The recovered benzoic acid can be used in many applications. Once catalysts and benzoic acid were recovered from residue, whatever remained was terephthalic acid which was recovered by up to 98 wt % with a purity of 95% and can be recycled to the purity unit.