Process performances and characteristics of powders produced using supercritical CO2 as solvent and antisolvent

A carbon dioxide (CO2) soluble compound (cholesterol) was successfully precipitated either by rapid expansion of SCCO2 solutions (RESS process, acronym for Rapid Expansion of Supercritical Solution), or from methylene chloride solutions by antisolvent precipitation (SAS-process, acronym for Supercritical Antisolvent process). The same fluid was thus used either as a solvent or as an antisolvent to precipitate cholesterol. Performances of RESS and SAS were compared through the analysis of the particle characteristics and production rates. Differences were related to supersaturation and time scale of nucleation/growth involved in both processes. Polydispersity, large size and elongated shape were characteristics of particles produced by SAS, especially when experiments were performed under conditions of total miscibility of CO2 and organic solvent. Conditions where vapor-liquid equilibrium exists promoted a confinement of the growth that consequently reduced the final particle size. RESS, by comparison, produced smaller and monodispersed particles. Production of small particles is a key advantage for RESS, but lower production rates and yield might be disadvantages. The combination of the two processes offers the opportunity of tunable sizing of powder, switching from a large production of particles ranging from 10 to 100 mum, to a limited production of fine crystals below 10 mum. (C) 2004 Elsevier B.V. All rights reserved.