(390a) Determination of Metastable Zone Width for Anti-Solvent Crystallization of Glycine

The Metastable Zone Width (MSZW) is defined as the area between the saturation curve and the labile zone where nucleation occurs spontaneously.  The metastability limit can thus be defined as the supersaturation at which the onset of nucleation can be detected when the supersaturation steadily increases under isothermal conditions. It is extremely important to determine the MSZW for a crystallization process as it reflects the nucleation characteristics of a system and determines the operating window for the process. The MSZW unlike solubility is not a thermodynamic property and must be determined experimentally for a given crystallization process. The MSZW can be determined by looking at changes in solution or solid phase properties upon onset of nucleation and several techniques have been proposed that exploit these properties for determination of the MSZW.

This work investigates the suitability of a simple optical probe consisting of a laser source, a light-dependent resistance, and a simple processing circuit for determination of MSZW of an anti-solvent crystallization process. The isothermal crystallization of glycine from glycine-water solution using ethanol as anti-solvent is used to measure the performance of the proposed measurement system.