Page 100 - Adsorption Technology & Design, Elsevier (1998)

Processes and cycles 97

entrance. Once the adsorbent in this region becomes saturated with the
adsorbate molecules, the zone in which the mass transfer occurs moves
progressively through the bed towards the exit, as shown schematically in
Figure 5.1. When breakthrough of the adsorbate begins to occur it is
necessary to take the bed off-line so that the adsorbent can be regenerated.
At any instant in time in the adsorption step it is clear from Figure 5.1 that
the adsorbent particles upstream and downstream of the mass transfer zone
(MTZ) do not participate in the mass transfer processes. Upstream of the

Feed

Saturated
adsorbent I

I MTZ
1
Regenerated CF '
adsorbent __
MTZ,
- lr-

., . ~
co

Concentration
of adsorbate
in bed effluent
gh
curve

Time

Figure 5.1 Sketch showing the concentration profile, mass transfer and break-
through curve in packed bed adsorption (redrawn from Crittenden 1992,
p. 4.19).