Chemistry Reference
In-Depth Information
4.4 Capture and Separation of Carbon Dioxide with POFs
Accelerated by the worldwide economic growth and industrial development, the
demand for fossil fuels (such as coal, oil, and natural gas, etc.) is projected to
continue to increase in the future. One of the most severe environment concerns
of our age is the escalating level of atmospheric greenhouse gases (mainly CO
2
)
because of the increasing carbon dioxide emission. Subsequent environmental
degeneration and adverse climate change sharply affect our civilization today.
Flue gas emissions of power plants are responsible for roughly 30 % of total
CO
2
emissions. Nitrogen is a main component (>70 %) of flue gas, whereas the
major impurity is CO
2
(10-15 %); separating CO
2
from N
2
is highly demanded
[
52
,
53
]. Thus, it requires the development of new technologies for capture and
sequestration of CO
2
(CCS). The proposed alternative strategies for CCS have
been developed so far: (1) chemisorption using aqueous solutions of amines [
54
];
(2) physical adsorption by porous materials. In the library of solid adsorbents [
52
,
53
], zeolites, carbons, mesoporous silica-supported amines, and metal organic
frameworks, have exhibited good performances for practical CCS implementation.
As a steadily developing porous material, porous organic frameworks (POFs)
have attracted much attention thanks to their distinctive advantages such as high
thermal and chemical stability, tunable pore surface, high surface areas, etc.
Therefore, POFs is an excellent candidate for CO
2
capture. Typical postcombusion
flue gas mainly contains N
2
(73-77 %), and CO
2
concentration is relatively high
(15-16 %) compared to other minor components, such as H
2
O, O
2
, CO, NOx, and
SOx. Facing such complicated gas composition of flue gas, an ideal adsorbent for
capturing CO
2
from post-combustion flue gas would display corresponding fea-
tures: (1) high CO
2
loading capacity; (2) high selectivity for CO
2
over the other
flue gas components; (3) long-term stability under rigorous conditions, especially
water stability; (4) minimal energy penalty for regeneration; (5) cost for synthesis
of POFs, etc.
Table
4.4
lists the CO
2
uptake of some representative POFs under low and high
pressure, respectively. Under high pressure, the CO
2
uptake capacity is related to
the surface area of POF materials. But under low pressure, the CO
2
uptake capac-
ity is independent of the surface area of POF materials, and the reason is compli-
cated. We introduce some typical strategies to enhance the CO
2
adsorption ability.
4.4.1 Porosity of POFs Controlled by Original
Building Units
In 2011, Cooper et al. reported that a series of conjugated microporous polymer
(CMP) networks were constructed using the Sonogashira-Hagihara cross-cou-
pling reaction of 1,3,5-triethynylbenzene with different reactive -Br contained
compounds [
55
]. Thus, a range of chemical functional groups including carbox-
ylic acids, amines, hydroxyl groups, and methyl groups have been successfully
