Recrystallization Powerful method precipitation

The application of supercritical fluids as anti-solvents is an alternative recrystallization technique for processing solids that are insoluble in SCF. This method exploits the ability of gases to dissolve in organic liquids and to lower the solvent power of the liquid for the compounds in solution, thus causing the solids to precipitate. 

Supercritical anti-solvent and related processes (GAS/SAS/ASES/SEDS) In these processes, the SCE is used as an antisolvent that causes precipitation of the substrate(s) dissolved initially in a liquid solvent. This general concept consists of decreasing the solvent power of a polar liquid solvent in which the substrate is dissolved, by saturating it with carbon dioxide in supercritical conditions, causing the substrate precipitation or recrystallization. Depending on the desired solid morphology, various methods of implementation are available ... 

On this basic concept different practical ways of performing the recrystallization process can be used. In the first method, to the solution is simply added the dense carbon dioxide. The volume of the solution increases several-fold in the presence of the antisolvent due to the decrease in density. This causes a concurrent decrease in solvent power the solutitm becomes supersaturated, and the solute precipitates, often as crystalline microparticles. This essentially batch process is normally termed gas antisolvent (GAS) [32]. 

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