extraction kak
TRANSCRIPT
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Chapter-3
LIQUID EXTRACTION(Solvent Extraction)
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Separation of components ofa liquid solution by contactingwith another insoluble liquid in
one of the feed components.
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Separation of solution of acetic acid in waterwith ethyl acetate.
in single stage, multistage countercurrent,continuous contact with or without reflux.
Feed Solution to be extracted.Solvent Liquid with which the feed is contacted.
Extract
Solvent rich product of the operation.Raffinate Residual liquid from which solute has
been removed.More complicated processes may use two
solvents.Ex: Separation of a mixture of p- and o-nitrobenzoic acids using insoluble liquidschloroform and water. Double-solvent orfractionalextraction
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Fields of usefulnessa) In competition with other mass-transfer operations
- distillation, evaporation (direct separation methods)- latent heat- thermal decomposition (long chain fatty acids fromvegetable oils with propane)- Tantalum and niobium
b) As a substitute for chemical methods- disposal problems- metal separations U-V, Hf-Zr, W-Mo
c) In separations not possible by other methods
- vapor pressures,- separation of aromatic and paraffinic hydrocarbonsof nearly same mol wt by extraction with a numberof solvents. Extractive distillation liquid extraction.
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Analogy between Distillation and Extraction
Distillation Extraction
Addition of heat Addition of solvent
Reboiler Solvent Mixer
Removal of heat Removal of solvent
Condenser Solvent separator
Mixture of liquid and vapor Two-phase liquid mixture
Relative volatility Selectivity
Distillate Extract product
Residue Raffinate
More volatile component Solute to be extracted
Less volatile component Carrier component from which
solute is to be extracted
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NotationA, B, C
Same letter for quantity of a solutionor mixture.E, R, Bmass per time
Solvent-free (B-free) quantities areindicated by primed letters. Thus
x= weight fraction C in the solvent-lean (A-rich), or raffinate , liquids
y= weight fraction C in the solvent-
rich (B-rich), or extract, liquids
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E
E
x = x/(1-x) = mass C/ mass non-C in the raffinateliquid.
y = y/(1-y) = mass C/ mass non-C in the extractliquid.
X = weight fraction C in the raffinate liquids on a B-free basis, mass of C/mass of (A + C)
Y = weight fraction C in the extract liquid on a B-free basis, mass of C/mass of (C + A)
N= weight fraction B on a B-free basis, mass of
B/mass of (A + C)= mass of B-free solution/time
E= /(1+ )EN
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Coordinates of Ternary liquid
Equilibrium (TLE)Equilateral triangular coordinates
Rectangular coordinates
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RM
ME
xx
xx
RM
ME
E
R
line
line
Equilateral Triangular Coordinates
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Types of Liquid systems in
Extraction1) Systems of three liquids with onepair partially soluble.
2) Systems of three liquids with twopairs partially soluble.
3) Systems of two partially solubleliquids with one solid.
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Systems of three liquids with one pair partially solubleEx: 1) Water-chloroform-acetone
2) Benzene-water-acetic acid
Binodal solubility curve
P plait point
y*
/x = distribution coefficient
Solutropic
tie line
horizontal
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Effect of temperature on solubility
Effect of pressure on liquid equilibrium isvery small.
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Systems of three liquids with two pairs partially soluble
(A-B and B-C partially miscible)
Ex;1) Chlorobenzene(A)-Water(B)-Methylethylketone(C)
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Effect of temperature
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Systems of two partially soluble liquids with one solid
(A-B are partially miscible)
Ex; 1) Aniline(A)-Isooctane(B)-naphthalene (C)
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To expand one concentration scale relative to
another.Unequal scales can be used.
Other coordinates
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Fig. 10.10 Rectangularcoordinates, solvent-freebasis, for a system of two
partly miscible liquid pairs
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Ex: Distribution of formic andacetic acids between partially
soluble water and CCl4.
Multicomponent systems
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Choice of solvent1. Selectivity
2. Distribution coefficient (y*/x, neednot be 1)
3. Insolubility of solvent4. Recoverability5. Density
6. Interfacial tension (high for coalescence)7. Chemical reactivity8. Viscosity, vapor pressure, freezing point9. Nontoxic, nonflammable, low cost.
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EQUIPMENT AND FLOWSHEETSSTAGEWISE CONTACTSingle-stage Extraction
F + S1 = M1 = E1 + R1
FxF+ S1ys = M1xM1
(10.6)
(10.7)
(10.8)
Min and Max -
solvent
11
1111
111111
1
11
)(
xy
xxME
xMxRyE
yxxx
FS
M
M
SM
MF
S l t f b i
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Solvent-free basis
Balance for C and B
Figure 10.13: Single-stage extraction, solvent-free
coordinates.
)1(
)1(
)(
1
'
11
1
'
11
11
11
'
1'
1
1
'
11
'
11
'
1
''
1
'
11
'
11
'
1
''
'
1
'
1
'
1
''
R
E
M
REMSF
MSF
NRR
NEE
XY
XXME
NRNENMNXNF
XRYEXMYSXF
REMSF
(10.9)
(10.10)
(10.11)
(10.12)
(10.13)
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If the solvent is pure B,NS= , these equations still apply, with the
simplification that S= 0, YS= 0, SNS=B, andF
=M1. Minimum and
maximum amounts of solvent correspond to puttingM1 atD andKon the
figure, as before.
Equations (10.9) and (10.10) lead to
(10.14)11
11
'
1
'
1
XX
XY
E
R
M
M
Analogy with distillation?
If solvent is pure, operating line passes through the 45oline
atXF.
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Multistage cross-current Extraction
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Total balance : (10.15)
C Balance: (10.16)
For the solvent-free coordinates,
A + C balance : (10.17)
C balance : (10.18)
B balance : (10.19)nnnn
n
RnEnMnSnRn
nnnnMnSnnn
nnnnn
nnnnMnnSnnn
nnnnn
NRNENMNSNR
XRYEXMYSXR
REMSR
xRyExMySxR
REMSR
'''''
1
''''
1
'
1
''1''1
11
1
1
For any stage n
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Wherex = x/(1-x) andy = y/(1-y)
Figure 10.16: Crosscurrent extraction with an insoluble
solvent
Insoluble liquids:
(10.20)
(10.21)''
1
''
''''
1
nn
nS
n
nnnSnn
xxyy
BA
AxyByBAx
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Countercurrent multistage extraction
material balance about the entire plant is
(10.22)
Point M can be located on line FS through a balance for substance C,
(10.23)
(10.24)
Equation(10.22) indicates that M must lie on line RNpE1, as shown.
Rearrangement of Eq. (10.22) provides
(10.25)RN
SFM
MNNSF
N
EFSR
SF
SyFx
x
MxxRyESyFx
MRESF
P
PP
P
1
11
1
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A material balance for stagess throughNp is
(10.26)
(10.27)RssN
sNs
ERSR
ERSR
p
p
1
1
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Minimum solvent for countercurrent extraction
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When the number of stages is very large
I l bl li id
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Insoluble liquids
When the liquids A and B are insoluble over the range of solute
concentrations encountered,
(10.35)
or (10.36)
Which is the equation of a straight line, the operating line, of slope A/B,through points . For stages 1 through s, similarly
(10.37)
),(),,( ''''1 pNSF xyxy
''
'
1
'
1
''
''
1
'1
'''
sF
s
NF
S
NFS
xx
yy
B
A
xx
yy
B
A
ByAxAxBy
p
p
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For the special case where the equillibrium curve is of constant slope
Eq. (5.50) applies,
Where is the extraction factor. This can be used in
conjunction with Fig. 5.16, with as
ordinate and as parameter.
1)/(
/)/(
/1'
'1'
'''
''
p
pp
N
N
SF
NF
ABm
ABmABm
myx
xx
''' / xym
ABm /'
)//()/( '''''' myxmyx SFSNp
ABm /'
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Continuous counter-current extraction with reflux
Feed introduced at feed stage f(and not at one end of thecascade).
Solvent removed from extract E1to produce solvent freestream Epart of which is removed as product and part
returned as reflux.
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Murphree Stage efficiency
For extract EME
=
For raffinate EMR =
The overall stage efficiency Eoof the cascade is the ratio of number oftheoretical stages to the number of actual stages required to bring
about a given concentration change.
1
*
1
mm
mm
yy
yy
*
1
1
mm
mm
xx
xx
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Solute Carrier Solvent
Acetic Acid Water Ethyl acetate
Acetic Acid Water Isopropyl acetate
Benzoic acid Water Benzene
Penicillin Broth Butyl acetate
Vanilla Oxidized liquors Toluene
Vitamin A Fish-liver oil Propane
Vitamin E Vegetable oil Propane
Representative Industrial Liquid-Liquid Extraction
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Emulsions
Emulsiona mixture of two immiscible liquids.
Stability (or permanence) of the emulsion is of utmost
importance in extraction.
Stable emulsionsthe ones which do not coalesce and settle
rapidly - should be avoided.
An emulsion should break or separate into two phases;
sedimentation and coalescence of dispersed phase must occur.
The sedimentation is more rapid if the size of the droplets and
the density difference of the liquids are large and the viscosity of
the continuous phase (?) is small.
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Stable emulsionswhich settle over long periods of time
should be avoided (droplets 1 to 1.5 m). Higher the interfacial tensionmore rapid coalescence. Higher mutual solubility leads to lower interfacial tension.
High viscosity of continuous phase reduces the rate at which the
residual film between the drops is removedhinders
coalescence. Dust particles at the interface between two liquids also hinder
coalescence.
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Staged-type extractors
Two major types
Single stage mixer-settlers and multistage cascades
constructed from them
Sieve tray multistage towers
Mixerstwo types
Flow mixers or line mixers
Mixing vessels
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Gravity Settlers
a) Simpleb) & c) with
coalescer
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Mixer-settler Cascades
Flow sheet of three-stage countercurrent mixer settler cascade
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KerrMcGee uranium extractor
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Box-type mixer settler cascade
Si ( f )
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Sieve-tray (perforated plate) towers
Very effective with respect to liquid-
handling capacity and extraction
efficiency, particularly for systems of
low interfacial tension (?).
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pilot Khni column
There are several types of such columnsthat are commercially available,e.g. the Scheibel, Oldshue, Rushton,Khni columns and the rotating-disk contactors.
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Flow configuration (gravitational field)
Feed heavier (denser) Solvent heavier (denser)
Solvent lighter Feed lighter
FeedSolvent
Feed Solvent
Counterflow in centrifugal field.
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Design (Differential or continuous-contact extractors)
One of the liquids can be pumped at any rate.
The maximum rate for the other liquid will depend, inter alia,upon the density difference of the liquids.
At flow rates more than this, one of the liquids will be rejected
flooding.
Flooding velocities of extractors are much lower.
Large diameter and more open cross-section will ensure that
flooding velocities are not reached.
Internal structures will help in flooding.
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Effect of axial mixing
Axial mixing severely reduces the extraction rates.
Pe = Ul/D
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Towers filled with same random packings used
for used for gas-liquid contact , also used for
liquid extractors.
Packing serves to reduce axial mixingsomewhat.
The position of the interface can be adjusted by
a control valve for pressure in the bottom outlet
pipe.
Packed towers
Packed extraction tower, light
liquid dispersed
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The nature of the liquid flow requires that the choice of
packing and arrangement of dispersed phase behaviorbe given careful attention.
If the dispersed phase preferentially wets the packing, it will
pass as rivulets, and not as droplets, and the interfacial area
produced will be small.
For this reason, the packing material should be preferentially
wetted by the continuous phase.
Usually, ceramics are preferentially wet by aqueous liquids,
and carbon and plastics by organic liquids.
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Mixco Lightnin CMContactor (Oldshue-
Rushton extractor)
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Rotating disc contactor (RDC)
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Scheibel extractor
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Pulsed column
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Centrifugal extractor
Useful for
Small density differences
Very short residence times
are essential e.g., extraction
of penicillin from nutrientbroth
Advantages and Disadvantages of Different Extraction Equipment
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Class of Equipment Advantages Disadvantages
Mixer settlers Good contacting
Handles wide flow
ratio
Low headroom
High efficiencyMany stages available
Reliable scale-up
Large Holdup
High power costs
High investment
Large floor space
Interstage pumpingmay be required
Continuous,
counterflow
contactors (nomechanical drive)
Low initial cost
Low operating cost
Simple construction
Limited throughput
with small density
difference
Cannot handle high
flow ratio
High headroom
Difficult scaleup
Advantages and Disadvantages of Different Extraction Equipment
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Class of Equipment Advantages Disadvantages
Continuous,
counterflow contactors
(mechanical agitation)
Good dispersion
Reasonable cost
Many stages possible
Relatively easy scale-
up
Limited throughput
with small density
difference
Cannot handle
emulsifying systems
Cannot handle high
flow ratio
Centrifugal extractors Handles low density
difference between
phases
Low holdup volume
Short holdup volumeLow space
requirements
Small inventory of
solvent
High initial costs
High operating cost
High maintenance cost
Limited number of
stages in a single unit
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Always 1raffinate entry, extract exit
2extract entry, raffinate exit
1
2
1
1ln
2
1
))(1(
)1(
)1(
))(1(
)1(
))(1(
)1(
1
2
1
2
1
2
1
2
x
x
xx
dx
xxx
dxxN
xak
R
aF
RH
NHxxx
dxxH
xxxaF
dxxRZ
x
x i
x
x i
iMtR
iMRR
tR
tRtR
x
x i
iMiR
x
x iR
iM
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Where xi = interface concentration of solute
FR, kR = transfer coefficients for raffinate phase
HtR = raffinate height of transfer unitNtR= number of raffinate transfer units
(1-x)iM= logarithmic mean of1-xand 1-xi
The interface concentration corresponding to any bulk raffinate
concentration x if found through Eq. (5.21) adapted to the presentsituation
(10.102)
R
EF
F
i
i
y
y
x
x
1
1
1
1
NHNHZ OEOEOROR (10 103)
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)1()1()1(
)]1/()1ln[()1()1()1(
1
1ln
2
1
))(1(
)1(
1
1ln
2
1
))(1(
)1(
)1(
)1(
2
1
1
2
1
2
1
2
1
2
1
2
yy
yyy
xxxxx
y
y
yy
dy
yyy
dyyN
x
x
xx
dx
xxx
dxxN
yaK
E
aF
EH
xaK
R
aF
RH
NHNHZ
M
M
y
y
y
y
MtOE
x
x
x
x
MtOR
MEOE
tOE
MROE
tOR
tOEtOEtORtOR (10.103)
(10.104)
(10.105)
(10.106)
(10.107)
(10.108)
(10.109)
If x and y are expressed in weight fractions
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Ifx andy are expressed in weight fractions,
(10.110)
(10.111)
Where ris the ratio of molecular weights of non-solute to thesolute, for weight ratio concentrations,
(10.112)
(10.113)'
2
'
1
''
'
'
1
'
2
''
'
2
1
2
1
1
2
1
2
1
1ln
2
1
1
1ln
2
1
1)1(
1)1(ln
2
1
1
1ln
2
1
1)1(
1)1(ln
2
1
1
1ln
2
1
'1
'2
'1
'2
1
2
1
2
ry
ry
yy
dyN
rx
rx
xx
dxN
ry
ry
y
y
yy
dyN
rx
rx
x
x
xx
dxN
y
y
tOE
x
x
tOR
y
y
tOE
x
x
tOR
Dil t l ti
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Dilute solutions
(10.114), (10.116) and (10.117) can be used in terms of
weight fractions
RmE
R
mE
R
mE
mxy
mxy
N
mER
mE
R
mE
R
myx
myx
N
yyaZKxxaZKyyExxR
yy
yyN
xx
xxN
tOE
tOR
MEMR
M
tOE
M
tOR
/1
1ln
/1
1/
/
ln
)()()()(
)(,
)(
11
12
22
21
2121
2121
(10.114)
Equivalent expressions in terms of mass transfer coefficients are
(10.115)
In addition the equivalent of Henrys laws applies
(10.116)
(10.117)
U f i li d fl id
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Use of specialized fluids
For separation of complex mixtures into their components, it has been
necessary to develop fluids with highly selective characteristics.
Metallurgical, nuclear, biotechnology and food industries are major users
of this technique.
Supercritical fluidscan be highly selective and their solvent power can be
controlled by the adjustment of the operating pressure. With SCF such as CO2 there is no residual contamination of the product as
the solvent evaporates completely at the end of operation.
S percritical fl ids
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Supercritical fluids
A substance that exists above its critical point (?).
Many materials dont decompose before reaching the supercritical region. Two most popular and inexpensive fluidswater, CO2nontoxic and
nonflammable.
Other SCFsethane, ethylene, propane, ammonia.
Densities of these fluids change considerably with changes in T and P.
Therefore, density dependent property such as solubility can bemanipulated(?).
Advantages of SCFsviscosities are less than those of typical liquids anddiffusivities of solutes are closer to those of gases.
SCFs combine the advantages of gases (diffusivities) and liquids (solvent
power). Commercial applicationdecaffeination of tea and coffee.
Extraction of spices, flavors, range of natural products, includingpharmaceutical compounds, health supplements and fragrances.
Fractionation of coal by use of high
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Fractionation of coal by use of high
temperature solvent extraction
For separation of coal (corresponding to the refining of petroleum)
Solvent extraction method extracts coal using a flowing stream of
non-polar solvent such as tetralin or 1-methylnaphthalene under
10 MPa at temperatures lower than 350 C.
To increase the extraction yield strong polar solvents such as
pyridine
Design of optimal solvent for extraction of bio-
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g p
active ingredients from mulberry leaves
Recent studies on exploiting natural compounds for
medicine and cosmetics have drawn much attention to theeffective extraction of the desired bio-active ingredientsfrom natural products.
Typically, various solvents of water, alcohols, acetone andether, etc. are used to extract bio-active substances from
natural products due to their broad solubility propensity onsolvents.
Water is generally applied to extract high polar ingredients,such as carbohydrates, glycosides, and amino acids, whileether is used to extract low polar ingredients, such as
aromatic compounds. Thereby, alcoholwater mixtures are used to extract out
various ingredients having broad range of solubilitypropensity for the investigation of the specific functionalityof the molecular compounds from extracted ingredients.
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To develop a method for determining the optimal solvent conditions anddesigning a solvent for the optimal extraction of bio-active ingredientsfrom mulberry leaf known to contain the active ingredients for anti-
oxidation and anti-hyperpigmentation. Since the extraction of specific ingredients from natural resources
depends on the polarity of the solvent, the extraction efficiency of thesolvent for bio-active ingredients is investigated, along with the variationin the polarity of the solvent according to the species and composition of abinary alcoholwater solvent.
Methanol, ethanol, n-propanol, and iso-propanol are used as the alcoholspecies for the binary mixture. Plus, ethylene glycol and acetone are usedto design model solvents to confirm the relationship between theextraction of bio-active ingredients and the solvent polarity.
Based on the extraction of mulberry leaf, activities of ingredients specific
to anti-oxidation and anti-hyperpigmentation are used as references toevaluate the extraction efficiency of the solvent
Soxhlet extractor
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Soxhlet extractor
It was originally designed for the extraction
of a lipid from a solid material.
However, a Soxhlet extractor is not limited
to the extraction of lipids.
Typically, a Soxhlet extraction is onlyrequired where the desired compound has
only a limited solubility in a solvent, and the
impurity is insoluble in that solvent