METHOD OF PRODUCING PURIFIED TEREPHTHALIC ACID Russian patent published in 1998 - IPC

FIELD: industrial organic synthesis. SUBSTANCE: invention aims at producing purified terephthalic acid with p-toluic acid content equal or below 200 ppm. To this end, aqueous solution is pretreated by hydrogen and resultant water slurry containing purified terephthalic acid crystals and p- toluic acid, dissolved and within terephthalic acid crystals, is introduced into filter cell or a set of filter cells in the filtration zone operating within temperature range from about 38 to about 205 C and pressure from atmospheric to 1620 kPa. Filter cell or a set of filter cells is arranged in such a way as to enable formation of filtration cake on each cell. Each cell is then displaced from filtration zone into washing zone, where each cell receives water stream to provide water reservoir over filtration cake. Water stream pressure is at least by 3.45 kN/sq.m superior to that in washing zone and its temperature ranges from about 38 to 205 C. Cake is washed for a time long enough to reduce concentration of p-toluic acid to 200 ppm or lower. Further, each cell is displaced into decompression zone where pressure drops to a value from atmospheric to about 620-55 kN/sq.m thereby cooling cake to a temperature as high as 166 C. Crystals of purified terephthalic acid are finally discharged. EFFECT: increased purity of product. 12 cl, 1 tbl