Spraying Effect On Particle Size and Morphology in Recrystallization of RDX Using Supercritical Carbon Dioxide Anti-Solvent

Supercritical fluid processes have gained great attention as a new and environmentally-benign method of preparing the micro-particles of energetic materials like explosives and propellants. In this work, RDX (cyclotrimethylenetrinitramine) was selected as a target explosive. The micro-particles formation of RDX using supercritical carbon dioxide (CO₂) anti-solvent recrystallization process was performed and the effect of spraying method on the size and morphology of prepared particles was observed. N,N-Dimethylformamide was used as an organic solvent for dissolving the RDX. A spraying tube tip nozzle with an inside diameter of 0.0006 inches and a length of 10 ~ 20 mm was installed into the end of a feed line of RDX solution in order to make a pressure difference between the RDX solution phase and the CO₂ phase during spraying the RDX solution into the CO₂ phase. The pressure difference was controlled in the range of 0 to 100 bar by changing the length of the spraying nozzle. In our experiments, other operating conditions were kept constant at 40 ^oC, 100 bar, and 20 wt. % of RDX concentration in feed solution, 25 ml/min of CO₂ feed flow rate, and 25 ml/min of RDX solution feed flow rate. A big pressure difference generated between CO₂ phase and solvent phase during the spraying of RDX solution into CO₂ phase could produce the RDX particles with better quality. Specifically, the RDX particles of uniform and spherical shape with the average size of less than 5 µm were obtained at the pressure difference of about 100 bar.