Page 7 - Adsorption Technology & Design, Elsevier (1998)

4 The development of adsorption technology

to percolate through a carbon bed. The method of water treatment depended
on both the extent and form of contamination. The spent carbonaceous
adsorbents were usually regenerated by steaming in a secondary plant.
Activated carbons were in general use during the first three decades of the
twentieth century for the purification of air and for recovering solvents from
vapour streams. The carbon adsorbents were activated prior to use as an
adsorbent by treatment with hot air, carbon dioxide or steam. The plants for
solvent recovery and air purification were among the first to employ
multibed arrangements which enabled regeneration of the carbon adsorbent
(usually by means of hot air or steam) while other beds were operating as
adsorbers. Thus the concept of cyclic operation began to be adopted and
applied to other operations on a broader basis.
The dehumidification of moisture-laden air and the dehydration of gases
were, and still are, achieved by means of silica gel as an adsorbent. In 1927,
for example, an adsorption unit containing silica gel was installed to
dehumidify iron blast furnace gases at a factory near Glasgow. It has been
pointed out (Wolochow 1942) that this plant was the first known plant using
a solid adsorbent for dehumidifying blast furnace gases. Six silica gel units
treated one million cubic metres of air per second. Five of the units acted as
adsorbers while the sixth unit was being regenerated. An arrangement of
piping and valves enabled each adsorber to be switched sequentially into use
as an adsorber, thus providing for a continuous flow of dehumidified gas.
This unit is an example of one of the earlier thermal swing processes in
operation.

1.3 MODERN PRACTICE

Thermal swing adsorption (TSA) processes gradually became dominant for
a variety of purposes by the end of the first quarter of the twentieth century.
But it was not until the advent of adsorbents possessing molecular sieving
properties when processes for the separation of gaseous mixtures de-
veloped. Naturally occurring and synthesized alumina-silica minerals
(discussed in Chapter 2) have unique crystalline structures, the micro-
porosity of which is precisely determined by the configuration of silica
-alumina cages linked by four- or six-membered oxygen rings. Such
structures admit and retain molecules of certain dimensions to the exclusion
of others, and are therefore excellent separating agents. Barrer (1978)
extensively researched and reviewed the adsorptive properties of these
materials which are referred to as zeolites. Walker et al. (1966a, 1966b), on
the other hand, thoroughly investigated the adsorptive properties of
microporous carbons and laid many of the foundations for the development