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Abstract

The invention makes available an improved process for the crystallization and purification of a water-insoluble aromatic dicarboxylic acid, such as 2,6-naphthalenedicarboxylic acid. The process involves steps of contacting the insoluble acid with aqueous base to make a water-soluble di salt of the acid, removal of insoluble impurities to obtain a clear solution of the di salt, partial acidification of the solution by adding a water-soluble acid, holding the thus-obtained slurry of the insoluble acid and its salt for a time sufficient to allow dissolution of the initially-formed small particles of the insoluble acid and the formation of large well-formed crystals, then acidifying the slurry further to convert remaining salts to the insoluble acid, and recovering this acid. The crystallization can be accelerated by recycling product and by adding surfactants, and can be operated in a continuous mode. 2,6-Naphthalenedicarboxylic acid thus crystallized is readily dried, non-sticky, non-dusty, and of high purity.

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First Claim