Adsorption - Principles of Chemical Separations with Environmental Applications - page 181

7

Adsorption

There is a continual exchange of ideas between all minds of a generation.
- AUGUSTE RODIN (1911)

7.1 Objectives

1 Define the concepts of mass transfer zone, breakthrough, and exhaustion.
2 Use the scale-up approach and the kinetic approach to design fixed-bed adsorption
columns based on laboratory or pilot column data.

7.2 Background

Adsorption is a process whereby a substance (adsorbate, or sorbate) is accumulated on the
surface of a solid (adsorbent, or sorbent). The adsorbate can be in a gas or liquid phase. The
driving force for adsorption is unsaturated forces at the solid surface which can form bonds
with the adsorbate. These forces are typically electrostatic or van der Waals interactions
(reversible). Stronger interactions involve direct electron transfer between the sorbate and
the sorbent (irreversible). The strength of this interaction dictates the relative ease or
difficulty in removing (desorbing) the adsorbate for adsorbent regeneration and adsorbate
recovery. The selective nature of the adsorbent is primarily due to the relative access and
strength of the surface interaction for one component in a feed mixture. The solid is the
mass-separating agent and the separating mechanism is the partitioning between the fluid
and solid phases. An energy-separating agent, typically a pressure or temperature change,
is used to reverse the process and regenerate the sorbent.