specialists in production of supercritical fluids systems.

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Processes like RESS and PGSS are using CO2 as a solvent to solubilize the active ingredients contained in raw material subjected to extraction.



RESS process is consisting of two steps; (a) dissolving the solid substance in a SCF and (b) formation of particles due to supersaturation. In the RESS process, at first SCF-CO2 is pumped at desired pressure and temperature to extraction chamber containing solid substance(s) through heat exchanger. The supercritical solution expands rapidly in the precipitator causing a collapse of  pressure and temperature, which favors the formation of drops and particles.

The SCF percolates and dissolves the solid substance(s) in the extractor and then the resulted solution is depressurized through a heated nozzle or capillary at supersonic speed into a low pressure chamber. The supercritical solution is expanded adiabatically in the chamber, which leads to a rapid drop in temperature and pressure and spontaneous formation of droplets/particles. During the rapid expansion of the supercritical solution, the density and solvent power decrease significantly, resulting in super saturation of the solution and consequently precipitation of desire particles free of a residual solvent

The RESS process advantages are its simplicity, effectiveness and the absence of organic solvents.

There is also a variation of the traditional RESS that uses a solid cosolvent (RESS-SC). This concept is widely used in the field of extraction with SCF and is called co-extraction. Generally, the RESS process is batch type, but there is also a continuous RESS process, which allows to obtain micro-particles in a constant and continuous way.





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The PGSS process is quite similar to the RESS process with one important difference: in PGSS process, the polymer(s) are first melted or suspended in solvent at a given temperature in an autoclave and then solubilizing SCF-CO2 in above melted or liquid suspended substance(s), leading to a so called gas saturated solution or suspension that is further depressurized through a nozzle with the formation of droplets or solid particles.
Unlike to RESS technique, the principle governing PGSS process involves both the pressure and temperature- and solvent-induced phase separation. This technique avoids the low solubility in SC-CO2 of many molecules of pharmaceutical interest such as proteins and peptides that would be too difficult to treat with RESS.

Advantages of PGSS process are; a) substance need not be soluble in SCF-CO2, b) simplicity of this process, leading to low processing cost and wide range of application, c) can be used with suspensions of active ingredient(s) in polymer(s) or other carrier substance leading to composite particles, d) can be applied to process inorganic powders to pharmaceutical compounds, and e) low solvent gas usage and pressure than RESS process as operational condition.





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