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7/30/2019 2. Liquid Liquid Extraction
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ByRakibul IslamI Shafiul Alam I Shefaul Islam I Nadia Munsef I Masudul Huda Khan I Abdullah al Faruk
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Liquid-liquid extraction is a
reliable process of extracting
a targeted compound from a
solution, with the help of
another solvent which is
immiscible with the former,
but has higher affinity to the
targeted compound.
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The solute should be soluble in both solvents.
The solute must have higher affinity for the 2nd solvent
The solvents should be immiscible.
The solution should be diluted.
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Fasterextraction
process
Simpleinstrument
s are used
Smallamount ofsolvent isrequired
Easierthan otherextractionprocesses
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Liquid-Liquid Extraction
Solution (Feed phase)
After extraction
Raffinate
2nd Solvent (Solvent phase)
After extraction
Extract
The simplified principle of liquid-liquid
extraction is given bellow :
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Nernsts distribution law :
Kp = Partition coefficient/distribution constant
Co= Concentration of the analyte present in the organic
phase
Caq = Concentration of the analyte present in the aqueousphase
Kp = Co/Caq
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Only applicable tovery dilute solutions
Does not hold goodwhen the disturbing
substancesencounters
association ordistribution in either
phases
The Nernst distribution law possessesfollowing limitations:
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4. Isolation of the targetedcompound
3.Separation
of twophases
2. Gentleagitation
toincrease
thesurfacearea
1.Addition
of 2ndsolvent in
thesolution in
a
separatory funnel
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Volumes are measured
initially and it is used in
calculation.
The phase is separated
and diluted to a knownvolume.
Marker substances can be
used
The effectiveness of an
extraction is solely depend
upon the volume of the
solvents. It can be calculated
by appropriate partition co-efficient.
Error due to volume change: Effectiveness of an extraction:
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Miscibility
Density
Solubility
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: Factors responsible for slow-coalescence :
1. Finelydivided
powders ofalumina,
gelatin, acaciaetc
2. Surfactantswhich can
stabilize theemulsion.
3. Ionic
species mayget absorbed
andaccumulatearound thedroplets.
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Gentle andcautiousagitation,
Large
contactsurfacebetween
thesolvent,
finely
dividedcompounds should
beremoved,
emulsifying
agentsshould beremoved
byadsorbent
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Mechanical means,
Centrifugation,
Addition of monovalent and divalent ions,
Ethanol or higher alcohol,
Silicone-defoaming agent,
Thermal shock,
Altering the ratio of the solvents,
Thin-bed of an adsorbent
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Effect of PH
Effect oftemperature
Liquid-Liquid Extraction