*3.2. Continuous Crystallization in DTB Crystallizer*

Based on the results of the multi-stage discontinuous crystallization trials, the final heat and mass balance, as well as the crystallizer design, were defined, to serve as a basis for the continuous crystallization tests. Due to the negative impact of the present impurities on the crystal shape, and due to the required product purity, the concentration factor within the continuous crystallization was limited to 2.5 for the continuous tests.

The major parameters to be confirmed are the achievement of the crystal size, crystal size distribution and the purity of the final product.

The purity of the crystalline product (after washing with 15% water based on the solid amount) on a dry basis was analyzed to be above 99.7%. This is in accordance with the limit of 99.3% purity on a dry basis, which was defined by the customer.

Three major product aspects were observed for the product from the continuous laboratory-scale DTB crystallizer, which are as follows:


**Figure 8.** (**a**) Crystals after 1.5h of continuous crystallization in bench scale DTB (d´ = 956μm); (**b**) crystals after 6h (d´= 1149 μm); (**c**) crystals after 10h (d´= 1435 μm).
