2. liquid liquid extraction

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

2. liquid liquid extraction

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