Concomitant crystallization for in situ encapsulation of organic materials

Concomitant crystallization leads to process intensification through the synergistic combination of the partial processes of particle formation and encapsulation within a single process step. Both cooling and electrospray crystallization in multi-component solutions were used to create (sub-)micron sized particles of different crystalline materials. Concentrations were varied to control core and shell material. Depending on the relative initial concentrations used, concomitant electrospray crystallization of isonicotinamide and caffeine leads to encapsulated particles. Only limited encapsulation was achieved during concomitant cooling crystallization. Concomitant cooling crystallization of cyclotrimethylenetrinitramine (RDX)–2,4,6-trinitrotoluene (TNT) resulted in separate RDX and TNT particles. Using electrospray crystallization, spherical nano-particles were produced, for which the component distribution within the particles could not be determined. Whereas crystallization from bulk solvent starts with a nucleus that grows gradually outward, whereby heterogeneous growth of a coating material on this core particle is not guaranteed, it appears that crystallization from evaporating solvent droplets starts at the surface of the droplets, and moves gradually inward. The resulting RDX–TNT powders have been tested for impact and friction sensitivity. The impact sensitivity has decreased compared to the raw materials, and the friction sensitivity did not change.