Page 21 - Adsorbents - fundamentals and applications

6 INTRODUCTORY REMARKS

and purifications accomplished by chromatography in the pharmaceutical and
food industries.

1.3. NEW SORBENTS AND FUTURE APPLICATIONS
In the development of new energy technologies, such as fuel cells, adsorption can
play a key enabling role. A breakthrough in sorbent development is needed to
solve the critical problem of hydrogen storage for hydrogen fuel cells. The best
fuel for fuel cells is gasoline (because of its high-energy density, ready availabil-
ity, and safety in handling). However, to avoid poisoning of the Pt catalyst in the
fuel cell, the sulfur content in gasoline needs to be reduced from the present level
of ∼350 ppm to <1 ppm. These challenges cannot be met with the sorbents that
are currently available.
Future needs for a clean environment will lead to increasingly higher standards
for air and water pollutants. These challenges require better sorbents that are not
commercially available. Traditionally, sorbents were developed based on empiri-
cism. To meet the new challenges, tailored sorbents need to be developed based
on fundamental principles. Theoretical tools, such as ab initio molecular orbital
theory and Monte Carlo simulations can be used to speed up the sorbent design. It
is one of the goals of this book to help put sorbent design on a more rational basis.
Some of the most challenging problems in separation and purification that
require new sorbents are given in Table 1.2. New sorbents that can solve these
problems are also given. Details of these new sorbents are discussed in Chap-
ter 10. Further innovations are needed for meeting these and many more future
challenges.

Table 1.2. Some future separation and purification applications by new sorbents

Application Sorbent and Notes
CH 4 storage for on-board vehicular Super-activated carbon and activated carbon
storage fibers
Near or meeting DOE target storage
capacity
H 2 storage for on-board vehicular Carbon nanotubes Possible candidate (?)
storage
N 2 /CH 4 separation for natural gas Clinoptilolite, Sr-ETS-4 by kinetic
upgrading separation
Sulfur removal from transportation fuels π-complexation sorbents such as Cu(I)Y,
(gasoline, diesel and jet fuels) AgY
CO removal from H 2 to <1 ppm for fuel π-complexation sorbents such as
cell applications CuCl/γ -Al 2 O 3 , CuY, and AgY
NO x removal Fe-Mn-Ti oxides, Fe-Mn-Zr oxides, Cu-Mn
oxides
Removal of dienes from olefins (to π-complexation sorbents such as Cu(I)Y,
<1 ppm) AgY