Analysis of the supercritical antisolvent mechanisms governing particles precipitation and morphology by in situ laser scattering techniques

A general description of the mechanisms governing the supercritical (sc) antisolvent (SAS) process is given. It simplifies the complex interactions of phase equilibria, jet fluid dynamics and mass transfer by two characteristic and competing times. One of them characterizes the time for the disappearance of the interface between the liquid and the fluid phase (liquid/fluid interface) where the fluid phase is represented either by a liquid or by a sc fluid phase depending on the pressure and the mixture composition. The second one is the time for particle precipitation. This description is experimentally supported by the investigation of the SAS process at various process conditions using in situ light scattering measurements which allow the access to both, to the liquid/fluid (droplets) and to the solid/fluid (particles) interface. SAS experiments were conducted by injecting the solution – yttrium acetate dissolved in dimetylsulfoxide – into the antisolvent carbon dioxide with different flow rates at a constant carbon dioxide molar fraction. The variation of the liquid flow rate did not affect the morphology of the precipitate. As a consequence, the occurrence of nano particles, micro particles and expanded micro particles can be assigned to the precipitation of the particles from a single-phase mixture, a two-phase mixture of short lifetime and a two-phase mixture of long lifetime, respectively. These particular precipitation regimes have been experimentally attained by varying either the pressure or the solute concentration.

► Time scale model to describe the SAS process.
► Model is based on experimental investigations.
► Experimental investigations performed in situ via in house established optical technique.
► The model qualifies to explain the occurrence of particular particle morphologies.
► Particular particle morphologies can be specifically precipitated at particular process conditions.