(351av) Ultrasound-Assisted Intensified Crystallization of L-Glutamic Acid: Crystal Nucleation and Polymorph Transformation

Solution crystallization is an important and energy-efficient separation process for crystalline material production. In the past few years, several external fields were introduced to optimize the crystal product, in which the ultrasonic irradiation was proved to be one of the most effective technologies to tune crystal properties and intensify the crystallization process. In this work, the crystallization of L-glutamic acid with ultrasound applied was explored in detail, including the process of nucleation, polymorphic control and polymorphic transformation (Fig. 1). The induction time and metastable zone widths (MSZWs) were measured with and without ultrasound during the nucleation process. The induction time and MSZWs were decreased by ultrasound and the induction time was further decreased by higher ultrasonic power. The calculated nucleation parameters (such as interfacial energy, critical nucleus size and critical Gibbs energy) showed an obvious decrease in the presence of ultrasound, indicating that the nucleation was enhanced with ultrasound applied. By adjusting the ultrasonic power in the quench cooling process, the difference in nucleation temperatures would determine the distribution of polymorphs. In further, the polymorphic transformation was investigated quantitively, and to the best of our knowledge, it was the first time to study the transformation kinetics with ultrasound using Avrami-Erofeev model. In the transformation process, the crystallization mechanism of the stable form was modified by ultrasound. The ultrasound eliminated the nucleation element in the rate-limiting step and facilitated the crystal growth of stable form. Thus, the ultrasound has a profound influence on L-glutamic acid crystallization.