Probing into Nucleation Mechanisms of Cooling Crystallization of Sodium Chlorate in a Stirred Tank Crystallizer and an Oscillatory Baffled Crystallizer

• Published in: Crystal growth & design Vol. 12; no. 5; pp. 2525 - 2532
• Main Authors: Callahan, Craig J, Ni, Xiong-Wei
• Format: Journal Article
• Language: English
• Published: Washington,DC American Chemical Society 02.05.2012
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; General studies of phase transitions; Materials science; Methods of crystal growth; physics of crystal growth; Nucleation; Physics; Solid-solid transitions; Specific phase transitions; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation; Monocrystals; Nucleation; Model compound; Crystallization; Growth mechanism; Sodium chlorates; Crystal seeds; Secondary nucleation; Heat treatments; Stirred crystallizer
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg300135w

In this paper we report our recent studies into why different nucleation behaviors in cooling crystallizations were observed in a stirred tank crystallizer (STC) and an oscillatory baffled crystallizer (OBC). Using sodium chlorate as the model compound and setting up a number of hypotheses, we identified and verified different nucleation mechanisms for the above two systems: while under the same operational conditions, secondary nucleation occurred exclusively in the STC where the product crystals bore the same handedness as the seeds; a combination of primary and secondary nucleation was displayed in the OBC where a mixture of left- and right-handed crystals coexisted when a single-handedness crystal was seeded. Through further hypothesis, we established the vital link between the nucleation mechanisms and the ways mixing is generated in the two systems and discovered that the scraping action between the baffle edge and the wall of the crystallizer could be the main culprit for the unexpected primary nucleation generated. All of our data in this paper confirm that the fluid mechanical environment in crystallizers plays a profound role on nucleation and subsequent growth.