Patent ID: 7692039

Claim:
A process for preparing purified terephthalic acid (PTA), comprising the steps: i) dissolving crude terephthalic acid (CTA) in an aqueous medium in a reactor; ii) hydrogenating CTA to convert an impurity of 4-carboxybenzaldehyde at a temperature of about 260-320° C. and a pressure of about 1100-1300 psig using an hydrogenation catalyst; iii) crystallizing terephthalic acid in the reactor by lowering the temperature without depressurization of the hydrogenated CTA in the aqueous medium to about 160° C. and then, optionally, depressurizing the reactor to 100 psi by release of hydrogen gas; iv) transferring the content of the reactor to a filtration unit; v) filtrating the content at a temperature of about 140-160° C. and a pressure of about 40-100 psig to obtain a filter cake; vi) washing the filter cake obtained with water having a temperature of about 140-160° C. in the filtration unit; vii) drying the filter cake wherein, in the alternative: a) in step iii) lowering the temperature at a rate of about 1° C./min or b) in step iii) lowering the temperature by passing coolant through coolant circulation coils disposed at and/or in the reactor or c) after step iii) depressurizing the reactor by evaporations to a pressure of about 100 psig after the temperature of about 160° C. has been reached or d) after step iii) maintaining the temperature after the temperature of about 160° C. has been reached.