Melting point depression by using supercritical CO2 for a novel melt dispersion micronization process

The melting point of solid substances can be depressed considerably by using supercritical fluids that are highly dissolvable in the molten substance. This fact can be used in micronization processes where thermo-labile materials are liquefied at a temperature lower than their normal melting point in order to produce fine particles. In the present study, the melting points of four different materials under various pressures applied by CO2 were determined visually with the first melting point method: phenanthrene, beta-sitosterol, an insecticide, and a pharmaceutical active. The aqueous suspensions of all materials except phenanthrene were also studied. Thus, it was possible to determine the solid-liquid-vapor equilibrium lines of these materials on a temperature-pressure plane. Finally, a thermodynamic model for describing the phase equilibria of such binary systems was developed implementing the Peng-Robinson equation of state and two different approaches concerning the fugacity of the solid phase.