Separation processes

1
Batch extraction

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

2
Single stage continuous extraction

• Analytical solution
• When y K x
• y (K x0)/(1 ?)
• x x0/(1?)
• f ?/(1 ?)
• Graphical solution
• When y non-linear function of x
• Equilibrium line y f (x)
• Operating line y (QR/QE) (x0 x)

3
Staged counter-current extraction
y2
yn-2
QE, y0 0
QE yn
yn-1
y1
n
1
2
n-1
QR x0
QR x1
xn
x2
x3
xn-1
4
Analytical solution

• Basic assumptions
• The rafinnate and extract streams from each stage
  are in equilibrium
• There is negligible entrainment of the other
  phase with each exit stream
• The same equilibrium relationship holds good for
  all the stages, i.e. the value of K is
  independent of solute concentration

5
Graphical solution
y
Equilibrium line
Operating line
y2
Stage no. 2
y1
Stage no. 1
x
x3
x1
x2
6
Differential extraction

• Continuous process
• Feed and extracting solvent flow past one another
• One phase is dispersed in the other
• Contacting and phase separation takes place
  within one unit
• Phases are not in equilibrium except locally i.e
  at the interface

Extract
Feed
Extracting solvent
Raffinate
7
Supercritical Fluid Extraction
8
Applications of SFE

• Separation and purification of oils, flavours and
  medicinal components
• Breaking of azeotropes
• Food and beverage processing e.g. production of
  decaf coffee, alcohol free beer

9
Supercritical fluid extraction
Pressure reduction valve
Separator
Feed
Recycled SF
Extractor
Extract
SF top-up
Compressor
Raffinate