Batch extraction

1
Batch extraction

• A batch of feed is contacted with a batch of
  extracting solvent
• System is allowed to attain equilibrium
• Phases are separated
• Attributes
• Conceptually simple
• Uses simple equipment
• Process calculation is easy
• Solute transfer is constrained by equilibrium
• Batch extraction is unattractive for large scale
  processes

2
Extraction of antibiotic
Aqueouspenicillin G solution
Butyl acetate
Organic extract
AcidicpH
Neutral aqueous solution
Organic raffinate
Aqueous raffinate
Aqueous extract
3
Mixer settler unit
Must generate high interfacial area Must provide
high mass transfer coefficient Low entrainment of
air bubbles
Low aspect ratio, i.e. of flat geometry Must
allow coalescence and phase separation Must allow
easy collection of phases
4
Batch extraction calculationImmiscible solvents

• Equilibrium relationship
• y f (x)
• Usually y K x
• Solute material balance
• Solute in (feed extracting solvent)
• solute in (extract raffinate)
• Extraction factor
• E K (L/H)

5
Batch extraction calculationImmiscible solvents

• Analytical solution
• When y K x
• y (K x0)/(1 E)
• x x0/(1E)
• p E/(1 E)
• Graphical solution
• When y non-linear function of x
• Equilibrium line y f (x)
• Operating line y (H/L) (x0 x)

6
Single stage continuous extractionImmiscible
solvents
Must generate high interfacial area Must provide
high mass transfer coefficient Low entrainment of
air bubbles
Low aspect ratio, i.e. of flat geometry Must
allow coalescence and phase separation before exit
7
Single stage continuous extractionImmiscible
solvents

• Analytical solution
• When y K x
• y (K x0)/(1 E)
• x x0/(1E)
• p E/(1 E)
• Graphical solution
• When y non-linear function of x
• Equilibrium line y f (x)
• Operating line y (QH/QL) (x0 x)

8
Batch extractionPartially miscible solvent
A
F
M
R1
E1
R2
E2
B
S
N
9
Cross-current extraction
y2
yn-1
yn
y1
n
n-1
2
1
QH x0
QH xn
QL,n-1
QL,2
QL,n
QL,1