SUPERCRITICAL FLUID EXTRACTION

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2. CONTENTS
INTRODUCTION
SUPERCRITICAL FLUID (SCF)
PROPERTIES OF SCF
SUPERCRITICAL FLUID EXTRACTION
(SFE) PROCESSES
INSTRUMENTATION &EXTRACTION
PROCESSES
EQUIPMENT DEVELOPMENT
ADVANTAGES
DISADVANTAGES
APPLICATIONS 2

3. INTRODUCTION
In the last century, an increasing interest has been paid to
supercritical fluids as alternate solvents for the extraction of
natural bioactive molecules from plants. The main reason for
the interest in supercritical fluid extraction (SFE) was the
possibility of carrying out extractions at temperature near to
ambient, thus preventing the substance of interest from
incurring in thermal denaturation.
1980s the fundamentals of this new extraction process were
already understood, but the design criteria for large-scale
application of SFE were still missing. After twenty years of
research and development, SFE is currently a well-
established unit operation for extraction and separation. It
can profitably be applied in the extraction of medicinal and
aromatic plants (MAPs).
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4. SUPERCRITICAL
FLUID
What is supercritical fluid?
A fluid is termed as supercritical fluid when the
temperature & pressure are higher than the
corresponding critical values . Above the critical
temperature there is no phase transition. Its
physical & chemical properties are between those of
pure liquid & gas. The diffusivity of SF is much
higher than for a liquid .
SUPERCRITICAL FLUID readily penetrates
porous & fibrous solids & also has good catalytic
properties.
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5. The critical temperature is the temperature
above with a distinct liquid phase cannot
exist, regardless of pressure. The vapor
pressure of a substance at its critical
temperature is its critical pressure. Carbon
dioxide is known to be the most stable and
an excellent solvent compound.
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6. PROPERTIES OF
SCF
 liquid-like density
 gas-like viscosity
 less surface tension
 Low heat of vaporization
 High diffusivity
E.g. carbon dioxide
Critical temperature=31.1
Critical pressure=73.8 bar /
72.83 atm/1070.37 psi
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7. Reasons for using co2 as solvent:
1. Easily attains the supercritical state
2. it is non-toxic and non-flammable
3. inexpensive
According to CHARSTIL
The possibility of using SF as extraction
Solvent depends on their density (1)
Where,
S= solute solubility
ρ = solvent density
a ,b,c are correlation parameter
When a fluid approaches the critical conditions, its density gets closer to liquid
state
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Disappearance of phase boundary
(meniscus)
on heating from below critical point (top
left)
to above critical conditions (bottom right)
S=ρa exp ( b/T+c)

8.  Density of SF increases with pressure i.e. more solvent
molecules per unit volume
 Pressure packs the solvent molecule closer and facilitate the
entrapment of more solute molecule
 Solubility of solutes depends on parameters a,b,c
 In case of co2 the solubility of solute of interest of medicinal
and aromatic plants applications is at best in range of 1 to
1000 by weight this is because co2 is a poor solvent even at
supercritical conditions only for non-polar substances as it
does not dissolves polar solvent . it is good solvent only for low
molecular weight solutes.
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9. FUGACITY COEFFICIENT
According to the iso-fugacity criterion applied to the substance to be
extracted,
Between the two phases at equilibrium (the condensed one – either solid or
Liquid – and the supercritical one), we have:
Yi =psat/p Ei (2)
Ei = ϕi o,v exp vs/l P – psat (3)
ϕi v RT
Where yi is the mole fraction of i in the supercritical phase, ϕi o,v and ϕi v
are
The fugacity coefficients of i in the standard state and in the mixture,
respectively,
At the process conditions, psat is the solute saturation (or sublimation)
Partial pressure (i.e. The component volatility), and v s/l is the molar
volume
Of the condensed phase (either solid or liquid). T is the absolute
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10. .
Ei is the so-called enhancement Factor, which accounts for the increasing
solubility due to system nonidealities with respect of the ideal behaviour
From Eq. 1 or Eqs. 2-3, the solubility is only one of two fundamental
pieces of information that must be known in order to assess the feasibility
of an SFE process for MAPs.
The second one is selectivity, which is defined as the ratio of the solubility
of the substance i of interest with respect to a reference substance j:
αij =si/sj (4)
Co2 is rather non-selective: when it is able to dissolve a group of similar
substances (For example, in terms of carbon atoms), all of them are
extracted to a similar extent, provided they have similar polarities.
Therefore, it can be stated that co2 alone is not as selective as a good and
pure solvent. It is also noteworthy that CO2 capacity and selectivity may be
improved by using an organic solvent as the entrainer, also called the co-
solvent, with the function of modifying chemical interactions between CO2
and the substance to be dissolved in it.
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11. SFE PROCESSES
 Principle
Feed material comes in contact with SCF the volatile substances
present will partition into supercritical phase. After the dissolution of
soluble material the SCF containing dissolved substances is removed
from feed material . The extract is separated from SCF by means of
temp&/ pressure change. The SCF is recycled.
 Theory
Extraction of soluble solutes from solid matrix takes place by three
mechanisms
1. swelling of solid phase by solvent accompanied by extraction of
entrapped solute
2. reactive extraction where insoluble solutes interacts with solvent
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12.  3. based on interactions
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a. If there is no
interaction between
solute & solid phase
Process is simple
dissolution of solute in a
solvent that does not
dissolve solid matrix
b. If there is extraction
then the process is
desorption.

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14. 1.FLUID SOURCE ( tank of carbon dioxide)
2.SYRINGE PUMP (pressure of 400
atm/709.27 bar/10 287.16 psi)
3.Valve to control the flow of critical fluid
4.Exit valve
5.Flow restrictor (depressurizes the scf)
6.Collection device
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15. FEED VALVE
SFE
VESSEL
PUMP
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SCF
COLLECTI
ON
VESSEL

16. 1. The feed (containing solute)indicated by A comes in contact with
supercritical co2 at suitable temperature & pressure.
2. COMPONENT A is selectively extracted & is recovered from
supercritical solution by increasing temperature , product is
recovered from separation section & supercritical fluid is recycled.
Separation is achieved by two ways:
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Temperature is constant Pressure is constant
In this case product
separation is achieved by
depressurization &
mechanical energy has to
be provide to raise co2
pressure.
In this case the
temperature is increased
& circulation of solvent
can be done.

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19. Multiple extractor, single separator scheme
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20.  Amount of substance of interest extracted with respect to total
amount initially contained in the solid is plotted against
extraction time.
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21. In order to design and develop an SFE process for MAPs with
CO2 (possibly assisted by ethanol or water as entrainer), we
need to know and optimize:
1. The solubility of the substance of interest
2. The selectivity of this substance with respect to others that
are extracted simultaneously
3. The extraction profiles
4. The way to separate the substance of interest from the total
extract
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22. 1. A liquid CO2 storage tank
2. A pump for liquid CO2
3. A cooler to prevent CO2 from evaporating in the pump
4. A heat exchanger to control the temperature of CO2
entering the extractor
5. An extraction vessel
6. A heat exchanger to control the CO2 plus solute mixture
entering the separator
7. A separation vessel
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24. SFE of MAPs is mostly an extraction operation from solid
materials, which is carried out in batch or semi batch mode.
Therefore, extraction vessels need to be pressurized,
depressurized, opened, filled, and closed again several times per
day. In order to ensure fast and safe operation procedures and
reliable seals, gaskets like O-rings are useful and closure
devices have been specifically designed.
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25. 1. Environmental improvement and reduced product
contamination
SFE is an alternative to liquid extraction using solvents
such as hexane or dichloromethane. There will always be
some residual solvent left in the extract and matrix, and
there is always some level of environmental contamination
from their use. In contrast, carbon dioxide is easy to
remove simply by reducing the pressure, leaving almost no
trace.
2. Selectivity
The properties of a supercritical fluid can be altered by
varying the pressure and temperature, allowing selective
extraction.
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26. 3. Speed
Extraction is a diffusion -based process, with the solvent
required to diffuse into the matrix, and the extracted
material to diffuse out of the matrix into the solvent.
Diffusivities are much faster in supercritical fluids than in
liquids, and therefore extraction can occur faster. Both the
higher diffusivity and lower viscosity significantly increase
the speed of the extraction
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27.  The requirement for high pressures increases the cost
compared to conventional liquid extraction, so SFE will only be
used where there are significant advantages.
 Carbon dioxide itself is non-polar, and has somewhat limited
dissolving power, so cannot always be used as a solvent on its
own, particularly for polar solutes.
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28.  A large number of MAPs has been considered for possible
extraction by supercritical CO2. The most recent developments
suitable to have industrial relevance are listed below.
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29.  RECRYSTALLIZATION OF PHARMACEUTICALS
 Separation of oils, flavours& medicinal components
 Removal of impurities from chemical products
 Fractionation &purification of polymers
 Supercritical fluid extraction has also been applied to
environmental remediation such as the extraction of PCBs and
other organics from water and soil.
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30. CONCLUSION
 Low operating temperature preserves all natural properties of
products & organic solvent free products are obtained
 The obvious unappealing aspect of dealing with supercritical
fluids is the relatively high-pressure conditions that must be
used. However, this problem has been circumvented by the use
of flow reactors
 Hence, one can no longer claim that reactions in supercritical
fluids are either too dangerous and/or expensive to carry out.
Improvements in both areas have allowed the improvement of
present technology.
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31. THANK YOU
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