Supercritical Fluid Extraction

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Supercritical Fluid Extraction
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Supercritical Fluid Extraction

• SF combines desirable properties of gases and
  liquids
• Solubility of liquids
• Penetration power of gases
• Process flexibility Density of SF and solubility
  of a solute in it can be changed in a continuous
  manner by change of pressure
• Environmental perspective Innocuous substances
  such as water and carbon dioxide can be used as
  extracting solvents instead of organics

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Applications of SFE

• Separation and purification of oils, flavours and
  medicinal components
• Removal of grease and other fouling material
• Removal of impurities from chemical products
• Breaking of azeotropes
• Fractionation and purification of polymers e.g.
  removal of unchanged monomers from polymers
• Food and beverage processing e.g. production of
  decaf coffee, alcohol free beer

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SFE Solute solubility

• Density of a SF increases with pressure i.e. more
  solvent molecules per unit volume
• Pressure packs the solvent molecules closer and
  facilitates the entrapment of more solute
  molecules
• Dependence of solubility on pressure can be
  utilized to fine-tune the SFE process

Solubility of solute in SF Mass/volume
Pressure
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SFE Enhanced penetration

• Diffusivity of solvent molecules in a SF approach
  gaseous state diffusivity
• Solute diffusivity within a SF approaches that
  shown in gaseous phase

Solvent (SF)
Solute
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Density of SF
TR 0.8
TR 1.0
TR 0.9
TR 1.1
?R
1
TR 1.2
1
PR
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SFE Types

• Liquid-SF extraction
• Similar to liquid-liquid extraction
• Examples
• Increasing ethanol concentration in aqueous
  solution
• Removal of alcohol from beer
• Solid-SF extraction
• Similar to solid-liquid extraction (leaching)
• Examples
• Removal of caffeine from coffee beans
• Polymer fractionation
• Extraction of flavours from rose petals

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Liquid-SF extraction Ethanol enrichment by
supercritical CO2
Ethanol
Supercritical carbon dioxide
Water
Probably not the best extracting fluid for
ethanol enrichment!
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Production of supercritical fluid
Adiabatic compression
Adiabatic compression heating
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Enrichment of ethanol using supercritical CO2
Pressure reduction valve
Separator
Ethanol water mixture
Recycled carbon dioxide
Extractor
Ethanol
Carbon dioxide
Compressor
Raffinate
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SFE using membrane

• Efficient segregation of streams
• Compactness of apparatus
• Large interfacial area
• Constant interfacial area which is independent of
  the fluid velocity

Feed
Raffinate
SF
Extract
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Solid-SF extraction
Pressure reduction valve
Separator
Coffee beans
Recycled carbon dioxide
Extractor
Caffeine
Carbon dioxide
Compressor
Raffinate