METHODS AND APPARATUS FOR ISOLATING DICARBOXYLIC ACID

摘要

Disclosed is a method for purifying aromatic dicarboxylic acid such as isophthalic acid or terephthalic acid. The process treats a crude carboxylic acid (CCA) composition by: A. feeding a CCA composition comprising a liquid and a solid, said liquid comprising an organic solvent and said solids comprising dicarboxylic acid (DCA), to a filter cake formation zone to form: (i) a CCA wet cake composition comprising said DCA solids and a portion of said organic solvent, said CCA wet cake composition having a first liquid level; and (ii) a first mother liquor stream; B. dewatering said CCA wet cake composition to form: (i) a dewatered CCA wet cake composition having a second liquid level that is lower than the first liquid level or having no liquid level; and (ii) a second mother liquor stream; and C. washing the dewatered CCA wet cake composition with a wash stream in a wash zone to form: (i) a washed CCA wet cake composition; and (ii) a wash liquor stream; wherein step B is performed before step C. By dewatering before a final wash stage is performed, the amount of cobalt metal in the final wet cake product is reduced. The process is flexible in that it allows one to use less wash solvent to obtain an equivalent reduction of cobalt metal in the wet cake composition. Optionally, one may obtain a low moisture wet cake without employing a separate drying step.