Approximate analysis of packed bed adsorption

1

• Limitations with exact analysis of packed bed
  adsorption
• For highly diffusible molecules value of E needs
  to be known
• Exact analysis requires a priory knowledge of
  breakthrough or exhaustion times

2
Approximate analysis of packed bed adsorption

• Approximate analysis is based on the following
  assumptions and approximations
• At any point within the packed bed, q is in
  equilibrium with y, i.e. no mass transfer
  limitations
• Unbound solute concentration profile remains
  unaltered as it passes through the packed bed
• The solute concentration profile is approximated
  with a straight line

3
Approximate analysis
yF
tE
y
tB
0
Equilibrium zone
l
Adsorption zone
0
Bed length
4
Problems with packed beds

• High pressure drop
• Inability to handle feed with particulate
  material
• Need to use low flow rates
• Radial dispersion problems

Solutions
Stack of porous membranes
Feed
Feed
Membrane adsorber
Fluidised bed adsorber
5
Gas adsorption

• Relies on diffusion of gas molecules to adsorbent
  
• Involves the interplay of pressure and volume
• Solute concentration in gas adsorption is
  expressed in terms of relative pressure or
  partial pressure.

Langmuir adsorption isotherm
BET isotherm
Freundlich isotherm
6
BET Isotherms
Type V
Type III
Type I
Type IV
Type II
Temperature and pressure swing adsorption
T1
T2
T1 gt T2
Bound concentration
P2
P1
Adsorbate partial pressure