Adsorption - Introduction to Carbon Capture and Sequestration - page 260

Section 5
Novel materials for carbon
capture
Finding novel materials for carbon capture is a very active area of
research. For a detailed description of the state of the art, we refer to
many of the excellent review articles that have appeared over the last few
years [6.8-6.12]. In this section, we give a short review of the materials
that are currently being considered. This review is far from complete and
is most likely biased by our own research interests. Adsorption is at pre-
sent used for several commercial gas separations, and the materials that
are used are the usual suspects: micro- or mesoporous inorganic and
organic adsorbents like zeolites, silica gels, aluminas, or activated car-
bons. The applications for these materials include the separation of bulk
CO 2 from a gas mixture (CO 2 from natural gas or from hydrogen) and the
removal of trace CO 2 from a contaminated gas [6.13]. Because of this
established practical experience with these materials in related gas sepa-
rations they are the fi rst candidates to be tested for carbon capture. More
advanced materials include metal-organic frameworks (MOFs).
Physisorbents
Zeolites
We introduced zeolites previously. One of the practical limitations of zeo-
lite research is that only a limited number of the 200 known zeolite struc-
tures are readily available. The selectivity of these structures is not
suffi ciently high for the all-silica structures to be attractive for carbon
capture. The selectivity can be enhanced, however, by synthesizing zeo-
lites in which some of the Si 4+ atoms are replaced with Al 3+ atoms and
the charge defi cit is compensated with a cation. With these cations the
selectivity is greatly enhanced, along with the unfortunate tendency to
have a strong affi nity for water. As water is an important component in
fl ue gasses, the adsorption of water limits the capacity of these materials.
Zeolites are very stable materials, however, and thus are relatively easy