Is spherical crystallization without additives possible?

The quasi-emulsion solvent diffusion method of spherical crystallization consists in producing in one step crystallization and agglomeration of small crystals in droplets of an emulsion. Additives are generally used to stabilize the emulsion before crystallization. The aim of this study is to investigate the feasibility of spherical crystallization without surfactant. Experiments were performed in an automated batch laboratory scale crystallization process to study the influence of the process operating conditions on the structure of the particles obtained. The results clearly show that, for the experiments performed two types of particles are formed: primary spherical particles and secondary agglomerates. The pattern of the primary particles, observed under scanning electron microscopy, suggests that these particles results from a spherulitic crystal growth mechanism inside the droplet. The secondary agglomerates results of the agglomeration of the spherical particles. In addition, a set of experiments were performed with carefully selected solvents to study the influence of the crystallization solution/water interfacial tension, at constant hydrodynamic conditions and supersaturation level. The results of these experiments demonstrate that the interfacial tension is not a key parameter for designing such a process.