Raman and ATR FTIR spectroscopy in reactive crystallization: Simultaneous monitoring of solute concentration and polymorphic state of the crystals

• Published in: Journal of crystal growth Vol. 311; no. 13; pp. 3466 - 3475
• Main Authors: Qu, Haiyan, Alatalo, Hannu, Hatakka, Henry, Kohonen, Jarno, Louhi-Kultanen, Marjatta, Reinikainen, Satu-Pia, Kallas, Juha
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.06.2009; Elsevier
• Subjects: A1. Polymorphism; A2. Industrial crystallization; A2. Precipitation; B3. ATR FTIR spectroscopy; B3. In-line monitoring; B3. Raman spectroscopy; Condensed matter: structure, mechanical and thermal properties; Crystalline state (including molecular motions in solids); Crystallographic aspects of phase transformations; pressure effects; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; General studies of phase transitions; Nucleation; Physics; Solid-solid transitions; Specific phase transitions; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; 82.80.Gk; A1. Polymorphism; B3. Raman spectroscopy; A2. Industrial crystallization; A2. Precipitation; B3. In-line monitoring; 81.10.Dn; B3. ATR FTIR spectroscopy; Glutamic acid; Fourier transform spectroscopy; Nucleation; Chemical precipitation; Process control; Crystallization; Crystallizer; Raman spectroscopy; Optimization; Attenuated total reflection; Polymorphism; Crystal structure
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2009.04.018

Batch-reactive crystallization of the two polymorphs of l-glutamic acid was studied using in-line Raman and ATR FTIR spectroscopy. It was observed that the barrier to the nucleation of the stable β-form was higher, and thus the occurrence of β-form nucleation requires a higher supersaturation level. The local supersaturation level inside the reactive crystallizer is significantly affected by the feeding manner of the reactant. When the reactant was fed to a poorly mixed zone, such as the surface of the liquid, a high local supersaturation level was generated near the feeding point. This high local supersaturation level drastically increased with the increase in the concentrations of the reactants. As a consequence, the fraction of the β-form increased with the increase in reactants concentrations. On the other hand, feeding the reactant to a well-mixed zone near the impeller can avoid the occurrence of high local supersaturation, and therefore the dependence of the polymorphic composition of the final product on the concentration of the reactants can be reduced. The information obtained from the spectroscopy leads to improved understanding of the precipitation process and offers great potential for process optimization and control of crystalline quality.