(119h) Cerium and Lanthanum Oxide-Based Sorbents for Regenerative Hot Reformate Gas Desulfurization

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
feeding 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.

Lanthanum
or copper oxide doped cerium oxides are being studied in our lab as
high-temperature regenerable sorbents for the removal of H₂S upstream
of the SOFC anode.^{1, 2} An major finding of our research is that at
high temperatures (>650^oC) and at high sulfidation space velocity
(> 20,000 h^-1), sulfidation can be limited onto the surface of
the sorbent. This surface adsorption is reversible, and thus the sulfided
sorbents can be fully regenerated.

Detailed
studies of cyclic sorbent sulfidation/regeneration under different operating
conditions have been carried out in our lab. We have shown that under oxidative
regeneration conditions, high regeneration space velocities (> 80,000h^-1)
can be used to suppress sulfate formation and shorten the total time required
for complete sorbent regeneration, and this creates new opportunities for
sorber/regenerator reactor designs to meet the requirements of solid oxide fuel
cell systems at any scale. Alternatively, other gas mixtures, such as the anode
exhaust gas can be used for complete regeneration. To prevent re-adsorption of
the desorbed H₂S onto the sorbent bed, cyclic sulfidation/
regeneration tests were carried out with pre-sulfided sorbents. The surface
sulfur capacity of the sorbents remained unaffected. Characterization of fresh,
sulfided and regenerated samples supports the observation of full sorbent
regenerability.

References

1.     
M.
Flytzani-Stephanopoulos, Z. Wang and M.Sakbodin, Removal of Hydrogen Sulfide
from Hot Reformate Gas using CeO₂-based sorbents, Proceedings of
Collaborative Technology Alliances Conference, Power and Energy, CTAC 2005,
Crystal City, VA, June 1-3, 2005

2.     
Z.
Wang and M.Flytzani-Stephanopoulos, Cerium Oxide-Based Sorbents for
Regenerative Hot Reformate Gas Desulfurization, Energy and Fuels, web
release date: 16-Jun-2005; (Article) DOI: 10.1021/ef049664a