Page 123 - Adsorbents fundamentals and applications

108 ACTIVATED CARBON

1200

Influent
1000
Concentration of TCE [ppb] 600
800

400
Ce
C0
200 Effluent C0 GAC(FS400)
ACF(FT15)
Ce
0
0 100 200 300 400
Flow volume (I/g Carbon)
Figure 5.20. Breakthrough curves of trichloroethylene in contaminated ground water in packed
beds of GAC (Filtrasorb 400) and ACF (phenolic resin-based, FT 15) (from Suzuki, 1990, with
permission).

of graphite (1.38 m -cm). The electrical resistivities of ACF clothes and fabrics
are, however, substantially higher. Subrenat et al. (2001) measured the electrical
resistivities of fabrics of a number of rayon-based ACFs and reported values as
high as 600 m -cm. The electrical resistivity of a ACF composite monolith was
130 m -cm. Comparing different ACF-clothes, the electrical resistivity increased
with surface area due to higher void fraction (Subrenat et al., 2001).
The high conductivity enables sorbent regeneration by resistance heating of
the beds, which has been referred to as electrothermal desorption. Electrother-
mal desorption has been studied by a number of groups (Petrovska et al., 1991;
Burchell et al., 1997; Lordgooei et al., 1998; Sullivan et al., 2001; Subrenat et al.,
2001). This approach is particularly promising for purification such as removal
of VOCs, as demonstrated by Lordgooei et al. (1998) by using a fiber-cloth
adsorber.
The graphitic nature also makes ACFs heat resistant, so they are inflammable
◦
up to 1000 C. Lack of dust/fines from the ACF has also been claimed as
an advantage.
The high tensile strength of the activated carbon fibers gives ACF the versa-
tility to be formed into a large variety of different types of cloths, fabrics, papers,
felts, and composites. Combined with high adsorption capacities and rates, these
different materials are excellent candidates for fabricating low-volume, high-
throughput adsorption devices. For example, a rotor-type adsorber (with counter-
current thermal regeneration) made from corrugated ACF has been demonstrated
for solvent removal from air (Suzuki, 1994). This type of adsorber, or monolithic
wheel, has been discussed in some detail by Humphrey and Keller (1997).