Extraction KAK

7/28/2019 Extraction KAK

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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

Extraction KAK

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