Optimizing the Crystal Habit of Glycine by Using an Additive for Impinging Jet Crystallization

Additives selectively inhibit or enhance the growth of crystal faces and effectively change crystal morphology. This paper demonstrates the first use of potassium chloride as additive during impinging jet crystallization of glycine, and also describes the optimization of this process by means of a full factorial design. The structural evaluation of powder particles was carried out by i.a. X-ray powder diffraction, differential scanning calorimetry, scanning electron microscopy with energy dispersive X-ray spectroscopy, headspace gas chromatography and flame atomic absorption spectrometry. It was observed that even a minor amount of KCl had a significant effect on the roundness, and reduced the particle size significantly compared to the samples without additive, despite of the extremely rapid nature of the crystallization process. This method resulted in the α-polymorph of glycine with an appropriate low residual additive content and a minimal residual organic solvent content. Based on the elemental maps of the samples, the arrangement and the optimal concentration of the additive were determined.