Closed-Loop Control of Reactive Crystallization PART II: Polymorphism Control of L-Glutamic Acid by Sonocrystallization and Seeding

• Published in: Chemical engineering & technology Vol. 33; no. 5; pp. 751 - 756
• Main Authors: Hatakka, H., Alatalo, H., Louhi-Kultanen, M., Lassila, I., Hæggström, E.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.05.2010; WILEY‐VCH Verlag
• Subjects: Crystallization; Polymorphism; Seed crystals; Ultrasound
• ISSN: 0930-7516; 1521-4125
• DOI: 10.1002/ceat.200900577

The impact of different nucleation methods with controlled supersaturation on the polymorphism of L‐glutamic acid crystals was studied in a 50 dm3 semi‐batch crystallizer, in which 1.5 M H2SO4 was fed into a 1.5 M monosodium glutamate solution. Supersaturation was controlled by a feedback loop based on measured ATR‐FTIR spectra and on a thermodynamic model developed in house. Ultrasound‐initiated nucleation produced pure α‐polymorph (over 99.5 wt %) in the end product crystals at 1 mol/dm3 supersaturation. Seeded crystallization also produced almost pure α‐polymorph crystals (over 93 wt %), whereas spontaneous nucleation produced a polymorph mixture (from 30–70 wt %) under the same operating conditions. This indicates that supersaturation‐controlled sonocrystallization can be used to control polymorphism in crystals. The novelty herein is the simplicity of the method directing the generation of a desired polymorph. Attempts are made to control the mass fraction of the α‐polymorph of L‐glutamic acid in a semi‐batch process during a controlled supersaturation. The impact of different nucleation methods is studied and results indicate that supersaturation‐controlled sonocrystallization or supersaturation‐controlled seeding can be used to control polymorphism. The novelty herein is the simplicity of the method directing the generation of a desired polymorph.