How cooling surface affect nucleation and impurity migration behavior during layer melt crystallization: A case study of 2′,4′-dichloro-5′-fluoroacetophenone

As a green and efficient purification technology, layer melt crystallization is widely used in chemical separation industry. However, during the melt crystallization process, how surface properties and cooling rate affect the metastable zone width (MSZW) and how MSZW affects the impurity migration in the cooling stage and sweating stage are rare explored. In this paper, 2',4'-dichloro-5'-fluoroacetophenone is taken as a case study to explore this problem. Firstly, our results indicate that MSZW increases with increasing surface energy of the cooling surface. Importantly, we propose a new model to predict that ΔT/T0/T1 has a linear relationship with ln (R/T0/ΔT), which is validated by MSZW experiments. Secondly, the separation effect of the cooling surface with low surface energy is better than that of the surface with high surface energy. The purity of the crystal layer during sweating is limited by the cooling stage's separation effect. Finally, by employing mass balance, we predict that the impurity distribution coefficient of the crystal layer before and after sweating is linear, and this relationship is unaffected by the cooling surface and cooling rate, which is successfully verified by experiments.