Formation of Particles from Gas Saturated Solution PGSS

2 Formation of Particles from Gas Saturated Solution (PGSS) 

PGSS is a new process about which little information is available, because most is covered by patents [16]. PGSS has been applied successfully to the micronisation of glycerides [17] and polyethyleneglycols [16]. 

This technique takes advantage of the fact that the solubility of gases in HCs (either liquid or solid) can lower significantly the melting temperature of the HC. 

In a PGSS experiment, the SCF is first dissolved in the HC by increasing the pressure until a melt is obtained. The gas-saturated solution is then expanded through a nozzle where it is cooled simultaneously by evaporation and Joule-Thompson effects. In this way supersaturation conditions are reached, and solid particles are formed. Again, the product is completely free of organic solvents. The amount of SCF needed is low, between 0.2 and 0.6 kg per kilogram of HC. 

Operating pressures are between 100 and 200 bar, and temperatures around 373 K or more are usually needed. 

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Both the nucleation of supercritical anti-solvent bubbles in a polymer+organic solvent-rich phase in the supercritical anti-solvent process (SAS) (or, equivalently, precipitation with a compressed antisolvent PCA) (e.g., [76]) and the nucleation of bubbles of a dissolved supercritical fluid from a saturated and nozzle-expanded solution containing a solute to be precipitated, in the formation of particles from gas-saturated solutions (PGSS) [77] are bubble nucleation problems, to which the above ideas apply. In the latter case, the nucleation of bubbles occurs simultaneously with that of solid particles within the bulk supersaturated solution. 

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