Production of large crystals with a narrow crystal size distribution by a novel WWDJ batch crystallizer

Abstract

A novel batch crystallizer has been developed and used for the crystallization of l-aspartic acid, resulting in large product crystals with a narrow crystal size distribution. The batch crystallizer was equipped with a slurry sprinkler fixed on the shaft of an impeller, and a double-deck jacket. The slurry sprinkler, known as Wall Wetter, is specially designed for agitating the slurry and sprinkling it on the wall of the crystallizer headspace which is covered by the upper jacket. It was expected that by setting the upper jacket temperature at an appropriate high temperature, fine crystals could be dissolved during the fall of slurry along the wall, and consequently the crystal size distribution would shift to the large side. l-aspartic acid was chosen as an example to demonstrate this process. l-aspartic acid was crystallized at an initial supersaturation ratio ( C/ C s) of 1.7 with no seeds. The classification exponent n and characteristic size D e of product crystals, which were evaluated by the Rosin Rammler Sperling Bennet (RRSB) distribution function, were 3.9 and 302 μm, respectively, compared with 2.2 and 237 μm, respectively, in a control crystallization experiment not using the Wall Wetter.