Patent ID: 6245939
Filing Date: 2001-06-12
Classification: C07C

Abstract:
In a process for producing highly pure aromatic carboxylic acid from an impure solid acid intermediate product which includes the steps of:(a) hydrogenating a solution of the impure product at elevated temperature and pressure in the presence of a hydrogenation catalyst;(b) optionally separating the solution from the catalyst; and(c) cooling the solution to precipitate pure aromatic carboxylic acid crystals; the improvement comprising the steps of:(d) metering the impure solid acid intermediate product into a holding tank containing said solvent in response to a feedback signal thereby forming a slurry of impure acid crystals at a temperature in the range of 95.degree. C. to 100.degree. C. and having a concentration in the range of 28% to 30% w/w while continuously agitating the slurry as it is formed;(e) removing the slurry from the holding tank through a retaining screen whereby solid particles of undissolved impure product which are too large to pass through said screen are retained in said holding tank;(f) measuring the density of the slurry downstream of the holding tank and converting the measurement to a feedback signal;(g) communicating the feedback signal to step (d); and simultaneously therewith or thereafter(h) heating the slurry to thereby further dissolve the slurry particles.