Study on the nucleation kinetics of DL-methionine based on the metastable zone width of unseeded batch crystallization

Abstract

The metastable zone width (MSZW) of DL-methionine aqueous solution for unseeded batch crystallization was measured by turbidity method. The spontaneous nucleation curves at different stirring rates (250 rpm, 350 rpm and 450 rpm) and cooling rates (18.0 K/h, 30.0 K/h and 42.0 K/h) were obtained by measuring the nucleation temperatures of solutions with saturation temperatures from 304.3 K to 341.9 K. The results show that the increase in saturation temperature and stirring rate makes the MSZW narrower. This is mainly because the enhanced mass transfer makes solute molecules more likely to collide and thus facilitate nucleation. Also the increase in cooling rate widen the MSZW for there is a time lag between nucleation and turbidity is detected. These data provide the operating boundary of crystallization and are important in production to obtain the desired crystal quality. Meanwhile, the nucleation kinetics is studied based on the MSZW data by five semi-empirical models in this work. And the interfacial energy between DL-methionine and water was determined, which decreases from 1.88 mJ·m2 to 0.99 mJ·m2 when temperature increases from 304.3 K to 341.9 K.