Continuous Production of Spherical Multicrystals by Extractive Crystallization in a Droplet Based Fluidic Device

A novel continuous fluidic method based on extractive crystallization for producing monodisperse spherical crystal aggregates with potential use in pharmaceutical engineering is presented. A model system of aqueous solution containing KCl as the precursor dispersed phase and 1-hexanol as the continuous extraction phase was investigated experimentally. Monodisperse droplets of the aqueous phase were generated by a fluidic T-junction in the stable dripping regime. Supersaturation was achieved by extraction of the aqueous phase into the organic phase. The effect of extraction rate on the size, morphology, and internal pore structure of the resulting spherical crystal aggregates was systematically investigated. It was shown that nearly monodisperse particles with a tunable size can be produced by adjusting the initial solute concentration. The dissolution rates of the resulting spherical aggregates were measured and compared with single cubic crystals of identical mass. It was shown that a four- to five-fold improvement in the dissolution rate constant can be obtained due to the internal porosity of the multicrystals, compared to single cubic crystals of identical size.