mass transfer, supercritical fluid, extraction, high pressure extraction, supercritical fluid extraction, separation process

1. Megha Rajasekhar(1RV14CH022)
Shri Lakshmi S B(1RV14CH041)
Supercritical Fluid Extraction
MASS TRANSFER –II SELF STUDY

2. Supercritical Fluid
 Supercritical fluid is a substance which exists at a
temperature and pressure beyond the critical point
 It has the properties of both a gas and a liquid
 It dissolves substances like a liquid and diffuses through
solids like a gas
 Hence making it suitable for extraction

3. Supercritical Fluid Extraction
 Supercritical CO2 is most widely used solvent
 In food industry for decaffeination of coffee, extraction
of essential oils, etc.
 Extraction of antioxidants from fruits and vegetables in
cosmetic industry

4. CO2 as solvent
 Carbon dioxide has relatively low critical pressure (74 bar)
and temperature (32°C) .
 CO2 is relatively non-toxic, non-flammable, available in
high purity at relatively low cost.
 CO2 can be easily removed from the extract.
 Protects samples against any oxidative degradation.
 The main drawback of CO2 is its lack of polarity for the
extraction of polar analytes . This can be countered by the
addition of modifiers.

5. CO2 as solvent
 For a wide range of solutes, CO2 gives better yields
compared to organic solvents like ethane, propane,
ethylene, dimethyl ether in sub and supercritical conditions
 Better substitute for polluting organic solvents
 For the extraction of oils, supercritical CO2, second to N2O,
fares better than supercritical trifluoromethane and SF6

7. Alternate solvents
 NO2 was considered better suited for polar compounds
because of its permanent dipole moment. This fluid has
been shown to cause violent explosions when used for
samples having high organic content and is therefore used
only when absolutely necessary.
 SF6 is a non-polar molecule and as a supercritical fluid, it
has been shown to selectively extract aliphatic
hydrocarbons from a mixture containing both aliphatic and
aromatic hydrocarbons.
 Freons, especially CHClF2 (Freon-22), has on several

8. Advantages
 Low temperature processing reduces degradation of
temperature and oxygen-sensitive components.
 Extract and raffinate are free of solvent and can be
used in food.
 Volatile components are not lost as in other methods
 Replace harmful organic solvents

9. Disadvantages
 Relatively high pressures are required. High initial capital
cost of high-pressure equipment
 Hazards of high pressure and the use of inflammable
solvents are unfavorable

10. Process
 The system consists of a pump, a pressure cell to contain
the sample and a collecting vessel.
 The supercritical fluid diffuses into the matrix
 The analyte gets dissolved into the supercritical fluid
 The dissolved material is swept from the extraction cell into
a separator at lower pressure and the extracted material
settles out.
 The CO2 can be cooled and recycled or discharged to
atmosphere.
 The pressure requirement is at least 74 bars. Most

12. Effect of matrix on SFE
 Different factors such as the particle size, shape, surface
area, porosity, moisture, level of extractable solutes and
the nature of the matrix will affect the supercritical fluid
extraction results.
 Decreasing the particle size of solid matrices leads to a
higher surface area, making extraction more efficient. Yet,
excessive grinding may hinder the extraction due to
readsorption of the analytes onto matrix surfaces. This
could be avoided by increasing the flow rate

13. Effect of Pressure and Temperature
 Four parameters decide the solute behavior in supercritical
media
 The miscibility or threshold pressure, which corresponds to
the pressure at which the solute partitions into the
supercritical fluid
 The pressure at which the solute reaches its maximum
solubility
 The fractionation pressure range, which is the pressure
region between the miscibility and solubility maximum
pressures

14. Effect of Pressure and Temperature
 An elevation of pressure at a given temperature results in
an increase in the fluid density, which means an enhanced
solubility of the solutes.
 But, the higher the extraction pressure, the smaller is the
volume of fluid necessary for a given extraction.
 Increase in temperature, decreases the density of the
solvent but increases the volatility of solute.
 For a non-volatile solute increase in temperature increases
extraction

16. Effect of flow rate
 The speed of the supercritical fluid flowing through the cell
has a strong influence on the extraction efficiencies.
 The slower the fluid velocity, the deeper it penetrates the
matrix and becomes saturated with the solute in the vessel
 But larger fluid velocities are required to prevent re-
absorption of solute into matrix
 For a given extraction cell, the flow rate can be easily
changed by using a new restrictor with a different inside
diameter.

17. Effect of modifiers
 Modifiers are added to the primary fluid to enhance
extraction efficiency.
 The nature of the modifier depends on the nature of the
solute to be extracted
 Modifier must be a good solvent in its liquid state for the
target analyte.
 Polar modifiers increase the extraction efficiency of polar
analytes e.g. water and methanol are used with CO2

18. Effect of time
 Maximize the contact of the supercritical fluid solvent with
the sample material in order to enhance the efficiency
 10–20 min static extraction prior to dynamic extraction
improved the extract recoveries
 Increased dynamic extraction time enhance the extraction

19. Effect of water
 Water opens pores, swells the matrix, thereby allowing the
fluid better access to analytes, and aid in flow through the
matrix.
 Increase the polarity of the fluid
 Highly water soluble analyte will prefer to partition into the
aqueous phase in case of excess water

20. Collection methods
 Solvent collection
 CO2–analyte mixture is depressurized directly in contact
with the solvent OR
 CO2–analyte mixture is first depressurized to gas phase in
a glass transfer tube before contacting the solvent
 Solid trapping - CO2 and the analytes are depressursied
and the analytes are collected directly onto silica gel, or
bonded phase packing or onto glass or stainless steel
beads

21. Collection methods

23. Decaffeination of Coffee
 Caffeine is chemically bound in an acid structure
present in the coffee bean
 Thus large amounts of CO2 are required for extraction
 Water somehow acts as a chemical agent, freeing
caffeine from its bound form in the coffee matrix
 The amount of CO2 required can be theoretically
calculated. The solubility of caffeine is about 0.2 wt% at
60°C and 300 bar. If the caffeine content of coffee is
about 1 wt%, 5 times the amount of CO2 is required for

24. Summary
 Better extraction solubility, higher purity products,
environmentally friendly
 Quicker process due to faster diffusion
 Requires maintenance of high pressures and
temperature
 Widely used for lab analysis than in industries

25. References
 Supercritical Fluid Extraction of Fungal Oil Using CO 2, N20,
CHF 3 and SF 6 - Keiji Sakaki, Toshihiro Yokochi, Osamu
Suzuki and Toshikatsu Hakuta
 Supercritical Fluid Extraction - S. S. H. Rizvi, Institute of Food
Science, Cornell University
 Supercritical fluid extraction in plant essential and volatile oil
analysis - Seied Mahdi Pourmortazavi, Seiedeh Somayyeh
Hajimirsadeghi
 Supercritical Fluid Extraction (SFE) for the Removal of Lipid and
Interfering Compounds Prior to Radiocarbon Dating of
Archaeological Artifacts - Jerry W. King, Jenny Phomakay,