(241e) On the Fines Removal in a Continuous Plug Flow Crystallizer: Optimal Spatial Temperature Profile With Dissolution

Fine crystals from a crystallizer can cause reduction of the efficiency of the downstream processes as well as final product quality. In this work, a systematic study is performed for obtaining the optimal temperature profile for the reduction of fines in a continuous plug flow crystallizer (PFC). The PFC consists of multiple modules or segments where the temperature of the each segment can be controlled separately. An optimization problem is formulated for a target crystal size distribution (CSD) (without fines) with the temperature of the PFC segments as decision variables. It is found that for the crystallization kinetics considered here, the optimal temperature profile also introduces dissolution steps so that the crystal fines due to secondary nucleation can be reduced significantly. A systematic study on the growth and dissolution kinetics is also performed. This study suggests that the key factor that determines whether the dissolution steps will be successful in reducing fines (without compromising the final size of the crystals from seed) is the size dependence of the growth and dissolution kinetics. If kinetics of the system is such that the larger crystals grow faster than the smaller ones and the smaller crystals dissolve faster than the larger ones, best results for fines removal is achieved. On the other hand, when both the growth and dissolution kinetics are independent of crystal size, fines removal found to be ineffective by temperature cycling.