Extraction Of Liquid Mixture Using Supercritical Dense Carbon Dioxide

1. Extraction Of Liquid Mixture Using
Supercritical Dense Carbon Dioxide
Ruchita M. Joshi
Saurabh S. Naik

2. Introduction
 Supercritical fluids are substances having temperature and
pressure conditions above their respective critical values
and distinct liquid and gas phases does not exist
 Supercritical Fluid Extraction is a process that uses gases at
high pressures as solvents to extract valuable materials
 Process begins with CO2 in vapour form

3.  First category - fractionation of edible oil
components and derivatives is perhaps the
furthermost explored area followed by the
determination of essential oils
 Second category - removal of ethanol and
separation of the aromas from alcoholic beverages
 Third category - aqueous mixture is the
dealcoholisation of alcoholic beverages and, to a
more limited extent

4. Methodology
 Supercritical fluids (SCFs) are increasingly
replacing the organic solvents that are used in
industrial purification and recrystalization
operations
 SCF-based processes has helped to eliminate the
use of hexane and methylene chloride as solvents
 SCF processes are used in polymers,
pharmaceuticals, fine chemicals industries
 Characterized by physical and thermal properties
between those of pure liquid and gas

5. Properties of Supercritical Fluid
 Supercritical fluids are highly compressed gases,
which combine properties of gases and liquids in
an intriguing manner
 Supercritical fluids can lead to reactions, which
are difficult to achieve in conventional solvents
 Supercritical fluids have solvent power similar to
light hydrocarbons
 Solubility increases with increasing density (that
is with increasing pressure)

6. Characteristics of a supercritical fluid
 Critical Temperature (Tc): highest temperature at
which a gas can be converted to a liquid by an
increasing pressure.
 Critical pressure (Pc): highest pressure at which
liquid converted to traditional gas by an increasing
temperature.
 Triple point (Tp): point at which the gas, liquid
and solid phases all exist in equilibrium.

8. Model of SFE
 Two essential steps to SFE, transport from with
solid particles to surface, and dissolution in
supercritical fluid
 Extraction is initially rapid, until concentration at
surface drops to zero, and rate becomes much
slower
 Relative rates of diffusion and dissolution are
illustrated where dissolution is fast relative to
diffusion

9. SFE LOOP

10. Optimization
 The optimum will depend on the purpose of the
extraction
 For an analytical extraction to determine,
antioxidant content of a polymer, then essential
factors are complete extraction in the shortest
time
 Production of an essential oil extract from a plant,
then quantity of CO2 used will be a significant
cost, and "complete" extraction

11. Maximizing diffusion
 Achieved by increasing the temperature, swelling
the matrix, or reducing the particle size.
 swelling can sometimes be increased by
increasing pressure of solvent, and by adding
modifiers to the solvent.

12. Maximizing solubility
 Higher pressure will increase solubility
 Effect of temperature is less certain, as close to
the critical point, increasing temperature
causes decreases in density, and dissolving
power
 Addition of low levels of modifiers such as
methanol and ethanol, can also significantly
increase solubility, particularly of more polar
compounds

13. Optimizing flow rate
 Density of CO2 changes to temperature
 Maximize rate of extraction, flow rate should be
high enough for extraction to be completely
diffusion limited
 Minimize amount of solvent used, extraction should
be completely solubility limited
 Flow rate must be determined depending on
competing factors of time and solvent costs

14. Modes of operation of packed columns and
applications
 Three different modes of operation in CC-
SFF in packed columns: stripping mode,
reflux mode, and batch or semi-batch
modes.
 major areas of research; edible oil
components and derivatives, essential oils
and alcoholic beverages

15. Stripping mode
 Stripping mode of operation is achieved when
liquid mixture is fed from top of column and dense
gas is fed at the bottom of column causing the
counter current flow
 Extract is recovered by expansion of loaded CO2
in the separator
 In this operation there is no partial reflux of the
extract slight variations of the stripping mode

16. Reflux mode
 In reflux mode of operation liquid feed is
introduced in middle section of column and extract
is partially returned to top of column to achieve
counter current flow
 Partial reflux of extract is done in order to obtain
an extract richer in light components

17. Semi-batch contacting equipment
 Semi-batch contacting can achieved in columns
with continuous flow of CO2 through a portion of
liquid held in bottom of column
 Extract is recovered by pressure reduction in a
separator at controlled temperature and pressure
 This mode of operation is a much less common
technique than stripping and reflux modes of
operation

18. Membrane contactors
 Use of membrane contactors to fractionate liquid
mixtures using dense CO2
 Liquid fractionation with supercritical fluids in a
separation device containing a porous membrane
 One fluid phase is on one side of membrane
occupying pores on other side of membrane
 Pressure of fluid phase 1 must be equal to or
greater than the pressure of second fluid phase

19. Mixer-settler process and components
 Role of mixing devices (e.g., static mixers and
nozzles) in each case of main applications,
findings, developments, and future directions is
provided
 Separation process consists of two steps: first
mixes solvent and solution with solute(s) of
interest, that together follow to a second step
where a latent settling takes place allowing phases
to separate by gravity

20. Spray processes
 High-pressure spray processes are a group of five
similar technologies that have in common
atomization of the mixture (liquid + CO2) or
suspension in an empty column or recipient
 A simplified schematic flow diagram of the five
processes: Rapid Expansion of Supercritical
Solutions, Particles from Gas-Saturated Solutions
Spray drying of gas loaded liquids, Spray
Extraction.

21. Phase equilibrium and relevant physicochemical
properties
 Separation processes are based on phase
equilibrium of adjacent fluid or fluid-solid
phases
 Presence of an inter phase is essential for mass
transfer of the desired solute
 Rate of mass transfer is dependent on both,
equilibrium and hydrodynamic conditions

22. Density and viscosity
 Density and viscosity of loaded supercritical fluids
and expanded liquid phases in three areas
 Densities and viscosities of coexisting phases of
lipid-type mixtures with CO2 such as Anhydrous
Milk Fat (AMF) fatty acids and derivatives, cocoa
butter, fish oil fatty acid ethyl esters, minor
components of edible oils such as tocopherol and
carotene, and capsaicin are predominant

23. Interfacial tension and contact angle
 Effect of density and viscosity of coexisting phases
in operation of separation equipment
 IFT and contact angles on technical surfaces
involved in process
 In spray columns and other processes which make
use of large exchange area of small liquid drops

24. Advantages
 Selectivity
 Speed
 Environmental improvement and reduced
product contamination

25. Limitations
 High pressures increases cost compared to
conventional liquid extraction, so SFE will only be
used where there are significant advantages
 Carbon dioxide itself is non-polar, and limited
dissolving power, so cannot always be used as a
solvent on its own, particularly for polar solutes
 Use of modifiers increases the range of materials
which can be extracted
 Food grade modifiers such as ethanol can used, and
can in collection of extracted material, but reduces
some benefits of using a solvent which is gaseous at
room temperature

26. Concluding Remarks
 SFE fully developed in five areas : General rugged
extraction methods, Ease of use, Automation, Cost
effectiveness, ability to interface with existing lab
and computer systems
 Static mixer and settler systems have potential to be
used for measuring equilibrium solubility of single
components in fluid phase and of fluid phase in
liquid
 Pump hydrodynamics for a compressed gas cyclone
constructed satisfactorily performed its function as a
separator

27. References
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