Liquid extraction, also known as liquid-liquid extraction or solvent extraction, is a separation process that uses two immiscible liquids to separate dissolved compounds based on their differing solubilities. 

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This can also be applied to extract specific compounds from solids, like the extraction of astaxanthins from dried algae.  In this particular example the extraction is mostly done by Super-Critical CO2 extraction (SCE).  SCE has become popular over the last years due to it’s green character: unlike organic solvents, SCE does not leave traces of solvents in the final product.

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CO2 becomes super-critical above 31 deg C and 74 bar.  Adjustment of pressures from 74 up to 1,000 bar and temperatures from 34 to several hundreds or degrees C allow modification of the CO2 polarity and extraction strength.

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Some more examples of SC applications:

• removal of caffeine from coffee

• SC particle formation of homogenous sub-micron active ingredients

• SC Fractionation to separate several organic compounds

• aerogel drying