Environmental Engineering Reference
In-Depth Information
table 21.2
Comparisons of
q
e
via various raw and modified CNts
Adsorbent
modification
q
e
(mg g
-1
)
Conditions
References
CNT
ApTS
43.3
C
in
:15%
[38]
T
: 20°C
114.0
C
in
: 50%
[38]
T
: 20°C
SWCNT
—
87.0
C
in
: 99%
[39]
T
: 35°C
SWCNT
pEI
72.0
C
in
: 100%
[51]
T
: 75°C
CNT
TEpA
130.6
C
in
: 02%
[49]
T
: 25°C
mWCNT
514.8
C
in
: 100%
[54]
T
: 25°C
P
: 11 bar
90
80
70
60
50
40
30
20
10
0
1
10
20
Cyclic adsorption (
n
)
30
40
fiGure 21.18
Cyclic CO
2
adsorption on CNT(ApTS) via a thermal/vacuum desorption (
C
in
= 15%,
T
ad
= 50°C,
T
desorption
= 130°C,
P
= 0.03 atm). Adapted from
http://ehs.epa.gov.tw/DocList/Downloadpublication/2722.
21.3.1.3 Adsorbent Regenerability
The regenerability of reactivation of adsorbents is another important parameter for
lengthy operations. If the regeneration of CNTs is not carried out, the practical use of CNTs in the field is not possible. If the
regeneration of CNTs is performed, they should be successfully regenerated and reused through a number of cycles and then
they can be possibly accepted as cost-effective adsorbents for capturing CO
2
from flue gas. A comparison of the energy con-
sumption between CNT(ApTS) and the traditional 30% mEA adsorption mixture reveals a remarkably lower energy input for
the regeneration process, with 111.1 kJ mol
-1
and 2.010 kJ mol
-1
for CNT(ApTS) and 30% mEA, respectively.
Some authors have reported results from the cyclic adsorption/desorption process and found an excellent behavior. The
regeneration of CNT(ApTS) via vacuum temperature swing adsorption (VTSA) achieves only 7.7% attrition after 40 cycles
(Fig. 21.18).
Although CNT(ApTS) shows good performance in CO
2
adsorption, the unit cost of the employed CNTs is approximately
US$5 g
-1
, which is much higher than the typical cost of GAC at US$1 kg
-1
. Although the use of CNTs for large-scale CO
2
sequestration is impractical at this moment, a lightweight reusable absorption system offers a potential solution in closed
systems such as spacecraft and orbiting space stations as well as in submarines.
