Extraction Is A Terminology Used in The Mass Transfer Operations When A Desired Solute Is
Extraction Is A Terminology Used in The Mass Transfer Operations When A Desired Solute Is
Extraction Is A Terminology Used in The Mass Transfer Operations When A Desired Solute Is
selectively removed from rest of inerts or non desired materials by use of a liquid solvent. If the
solute desired is present in another liquid mixture then the operation is termed as Liquid-liquid
extraction and if the solute is present in a solid phase the operation is termed as leaching.
Liquid-liquid extraction is a mass transfer operation in which a solute dispersed or dissolved in a
liquid media is separated in by use of a solvent which has differential solubiliies with media and
solute and has a phase characteristics. The substance i.e. solute when dissolved in a medium can
be taken into another liquid which is insoluble with the medium but has a higher solubility with
solute. Due to the insolubility there will be two separate phases, one in which the solvent with a
higher percentage of solute called as Extract and the other being the original medium in which
the solute of lower percentage called as Raffinate.
SOLVENT C
B+C Rich in B
EXRACT A %
Let F = kgs of feed.
E = kgs of Extract.
R = kgs of Raffinate.
B = solvent.
C = solute.
A = the media in which C is dissolved.
Then if Y is the mole fraction in the Extract
Y=
kg C
Kg A+kg B+kg C
If X is the weight of C in the raffinate then,
X=
kg C
Kg A+kg B+kg C
__ (1)
__ (2)
We can define X' and Y' which will be the ratios of mass of C to mass of A + B in raffinate
and extract.
X' = X
, Y' = Y
1X
1-Y
We can also define X = weight fraction of C on a B free basis.
i.e.
X = Mass C
in raffinate Y = Mass C
in Extract
Mass A + B
Mass A + C
And
N = Mass C
Mass A + C
Then NF, NR, NE will be the values o B/A+C in feed. Raffinate and Extract.
i.e.
equilibrium stage. The two liquid phases are accordingly called as Extract (solvent rich
phase) and Raffinate (diluent rich phase). If the operations are carried out in such a manner
that if the fresh solvent is added to raffinate phase then the operation is termed as crosscurrent operations.
1.
2.
3.
4.
ADVANTAGES:
Low cost.
Low energy consumption.
Variety of solvents is available.
Easy to scale-up.
DISADVANTAGES:
Emulsification may occur.
1. Effluent must be treated.
APPLICATIONS:
Solvent extraction is used 1. In nuclear reprocessing and ore processing.
2. In the production of fine organic compounds.
3. In the processing of perfumes.