(491f) Hot Reformate Gas Desulfurization Using Regenerable Cerium and Lanthanum Oxide Sorbents

Desulfurization of hot reformate gas, which is
produced by catalytic partial oxidation (CPOX) or autothermal reforming of
heavy fuels, such as JP-8, is required prior to using the gas in a solid oxide
fuel cell (SOFC). This requires development of sorbent materials with favorable
sulfidation equilibria, good kinetics, and high structural stability and
regenerability at the SOFC operating temperature (650-800^oC) to
avoid heat exchanger penalties. Sorbent performance stability in cyclic
operation of sulfidation and regeneration at such high temperatures imposes
major constraints on the choice of suitable materials.

Cerium and lanthanum oxide-based materials have been
developed in our lab as high-temperature regenerable sorbents for the removal
of H₂S upstream of the SOFC anode.^1,2  A major
finding of our research is that H₂S can be reversibly
adsorbed onto the cerium and lanthanum oxide surfaces at temperatures as high
as 800 ^oC, on both fresh or pre-sulfided sorbents.  The
adsorption and desorption processes are very fast;  thus, removal of H₂S
to sub parts per million levels is achieved at very short (millisecond) contact
times. Any type of sulfur-free gas, including water vapor, can be used to
regenerate the sorbent surface. Preferably, the anode off-gas stream is used to
sweep the desorbed H₂S to a burner¹.

Detailed studies of cyclic sorbent
sulfidation/regeneration under different operating conditions will be
presented. H₂S-TPD results suggest that reversible H₂S
adsorption/desorption would be possible with lanthana, ceria and their mixtures
at temperatures as low as 350 ^oC. Therefore, this type of sorbent
and desulfurization method may be used for polishing reformate gas streams for
any use, including low-temperature PEM fuel cells. H₂S adsorption uptakes
and kinetics of adsorption will be reported in this presentation.

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References

1 M.
Flytzani-Stephanopoulos; M Sakbodin; Z. Wang, Science 2006,  in
press

2. Z. Wang ; M.
Flytzani-Stephanopoulos, Energy and Fuels, 2005, 19 (5),
2089 ¨C2097