Purification of terephthalic acid by crystal aging

The rate of removal of 4-carboxybenzaldehyde (4-CBA) from terephthalic acid (TPA) crystals during crystal aging was determined in both aqueous solution and 90% acetic acid (10% water by volume). It was found experimentally that over 50% of the 4-CBA could be removed from TPA crystals aged 2 h at 493 K in 90% acetic acid. It was also found that purification occurs more rapidly in 90% acetic acid than in water at the same aging conditions. A crystal aging and purification mechanism based on the oxidation of 4-CBA to TPA in the solution and periodic growth and dissolution due to temperature fluctuations was developed and used to estimate the purification rate. Estimated purification levels were within the experimental error of 15% in most cases