Ways of manipulating the polymorphism of glycine during supercritical fluid crystallisation

Publication Type:

Journal Article

Source:

Journal of Supercritical Fluids, Volume 44, Number 3, pp. 422-432 (2008)

ISBN:

0896-8446

DOI Name (links to online publication)

10.1016/j.supflu.2007.09.016

Keywords:

polymorphism; aqueous solution; solute concentration; anti-solvent; carbon-dioxide; beta-glycine; liquid-equilibrium; aqueous-solutions; crystal-structure; alpha-glycine; gamma-glycine; molecular-crystals; elevated pressures; particle formation

Abstract:

The precipitation of glycine from aqueous solution was studied using a mixture of supercritical carbon dioxide and ethanol as drying medium and as anti-solvent. Glycine. which has three polymorphs, was precipitated by a direct spraying process using a coaxial nozzle under high pressure. By simple manipulation of the solute concentration, the process could be tuned to selectively precipitate either pure alpha or beta-glycine, as determined by X-ray powder diffraction. When decreasing the solute concentration or increasing the ethanol fraction in the system, the precipitation of the metastable beta-glycine was preferred over the precipitation of alpha-glycine. Modelling of the mass transfer around a drop showed that the ethanol fraction inside the drop can reach significant values, and that the evaporation occurs in less than a second, leaving little space for recrystallisation. Even though the crystal growth rate was extreme (up to 800 mu m/s), the product was crystalline. (C) 2007 Published by Elsevier B.V.

28/10/2009