Page 18 - Adsorption Technology & Design, Elsevier (1998)

Adsorbents 15

Figure 2.6 Sketch showing the molecular sieving effect for normal and iso-paraffins
in a 5A zeolite (redrawn from Gioffre 1989).

personnel protection, solvent recovery, volatile organic compound control,
hydrogen purification, and water treatment.
Activated carbons comprise elementary microcrystallites stacked in
random orientation and are made by the thermal decomposition of various
carbonaceous materials followed by an activation process. Raw materials
include hard and soft woods, rice hulls, refinery residuals, peat, lignin, coals,
coal tars, pitches, carbon black and nutshells, such as coconut. There are
two types of manufacturing process, involving gas activation or chemical
activation. The gas activation process first involves heating in the absence of
air at 400-500~ to drive off volatile materials and to form small pores.
Activation is then carried out with, for example, steam at between 800 and
1000~ Other gases such as carbon dioxide or flue gases can be used instead.
Chemical activation (Keller et al. 1987) can be carried out using, for
example, zinc chloride or phosphoric acid to produce an activated carbon