Managing Impurities in An Integrated Crystallization System
Special Symposium - EPIC-1: European Process Intensification Conference - 1
EPIC-1: Multifunctionality (MF-2)
Keywords: Crystallization, Impurity incorporation, Washing, Process development
Crystallization is widely used for separation as well as purification of various products, ranging from commodity chemicals such as mineral salts to specialty chemicals and active pharmaceutical ingredients. Despite the fact that it is thermodynamically possible to crystallize pure substances, impurities may still be incorporated into the final product through different mechanisms. Mother liquor that contains impurities can be trapped inside the crystals during growth, adsorbed on crystal surface, or imperfectly removed from the voids among the crystals during solid-liquid separation. Therefore, in order to achieve the target product purity, post-crystallization steps such as filtration, washing, deliquoring, and recrystallization must be designed properly along with the crystallization process itself as an integrated system.
This presentation discusses a workflow for managing the impurity content in the product of a crystallization process in consideration of the entire train of crystallization and post-crystallization steps. The workflow is illustrated using a case study on the purification of Vitamin C (ascorbic acid). Experiments are performed to determine the dependence of the impurity inclusion on several key factors such as growth rate, solvent concentration, and the yield of crystallization. The impurity concentration profile within the crystals is also investigated to determine whether the impurity content can be minimized by controlling the crystal size or by partially dissolving the crystals. Next, the effect of washing and deliquoring on the amount of surface impurities are evaluated. Semi-empirical models based on fundamental knowledge about the physical phenomena involved are used to correlate the performance of washing and deliquoring steps to the target product purity. In this way, the specifications for a suitable solid/liquid separation unit, such as a rotary filter, a belt filter, or a centrifuge, which also performs washing and deliquoring functions in the same equipment, can be determined.
Presented Thursday 20, 12:00 to 12:20, in session EPIC-1: Multifunctionality (MF-2).
