Process for the purification of terephthalic acid

A process for the purification of a crude terephthalic acid product contaminated with up to about 5% by weight (50,000 ppm) of p-toluic acid and up to about 2.5% by weight (25,000 ppm) of 4-carboxybenzaldehyde to produce fiber-grade terephthalic acid, which process comprises the steps of:

• (a) dissolving from about 10 to 30 parts by weight of said crude product in 100 parts of water at a temperature between about 247.degree. and 275.degree. C., to produce a first solution;
• (b) cooling the resulting first solution down to a temperature between about 190.degree. and 240.degree. C., to precipitate crystals;
• (c) recovering the precipitated crystals by solid-liquid separation at the temperature ultimately reached in the colling step;
• (d) washing the recovered crystals by contacting with water at the same temperature as in the recovery step;
• (e) dissolving from about 10 to 30 parts by weight of the washed crystals in 100 parts of water at a temperature between about 247.degree. and 275.degree. C., to produce a second solution;
• (f) recooling the resulting second solution down to a temperature between about 190.degree. and 240.degree. C. to reprecipitate crystals;
• (g) recovering the reprecipitated crystals by solid-liquid separation at the temperature ultimately reached in said re-cooling step;
• and
• (h) washing the reprecipitated crystals by contacting with water at the same temperature as in the recovery step (g).