Crystallization method for production of purified aromatic dicarboxylic acids

摘要

Disclosed is a method for the recovery of crystalline terephthalic acid containing less than about 150 ppmw p-toluic acid by subjecting a solution of terephthalic acid containing minor amounts of p-toluic acid to crystallization in a crystallization zone comprising a plurality of series-connected crystallizers wherein the solution is subjected to rate-controlled evaporative cooling by sequential reduction in pressure and temperature to cause crystallization of terephthalic acid, wherein the pressure of the solution at the end of the crystallization zone is about ambient pressure or less. Solvent which is evaporated from the crystallizers is collected and condensed and the condensed solvent is returned to the crystallization zone at a point subsequent to the crystallizer from which it was obtained.