Type of Document Dissertation Author Yi, Kwang Bok Author's Email Address email@example.com URN etd-01062004-164031 Title Ceria-Zirconia Oxide High Temperature Desulfurization Sorbent Degree Doctor of Philosophy (Ph.D.) Department Chemical Engineering Advisory Committee
Advisor Name Title Douglas P. Harrison Committee Chair Elizabeth J. Podlaha Committee Member Karsten E. Thompson Committee Member Louis J. Thibodeaux Committee Member Edward B. Overton Dean's Representative Keywords
- nonstoichiometric cerium oxide
Date of Defense 2003-12-11 Availability unrestricted AbstractHigh temperature desulfurization of highly reducing coal-derived gases using ceria and ceria-zirconia sorbents is the primary object of this dissertation research. If H2S concentration is reduced to less than 1 ppmv the product gas may be used with fuel cells and downstream catalytic process.
CeO2 is reduced to a non-stoichiometric oxide, which is superior to CeO2 in removing H2S. Moreover, ZrO2 addition to CeO2 to form a solid solution, Ce1-xZrxO2, increases the reducibility of CeO2. This should also result in improved desulfurization performance.
Pure CeO2 and sorbents, both commercially available and prepared at LSU, were tested. XRD analysis indicated that all sorbents containing ceria and zirconia formed a single phase. TGA analysis showed that overall reducibility of Ce1-xZrxO2 sorbents was better than pure CeO2. BET surface area measurements were also made to further characterize the sorbents.
In the early stages of this research, commercially available sorbents were used for sulfidation tests. Experimental results were very promising. However, these commercially available sorbents were obtained from different sources and the differences in chemical and structural properties overwhelmed the possible effect of ZrO2 addition.
Experimental results using LSU sorbents prepared using a coprecipitation method also produced favorable desulfurization results. H2S concentration in the product gas was reduced to less than 1 ppmv during the prebreakthrough phase of sulfidation tests with feed rates corresponding to about 3.8 second reactor residence time at temperatures in the range of 600 to 750oC. Addition of ZrO2 did not result in significant reduction of the H2S concentration during prebreakthrough, but did increase the duration of the prebreakthrough period. Addition of CO2, an oxygen source, to the feed gas decreased the prebreakthrough duration, but did not alter the sorbentís ability to achieve sub-ppmv H2S concentrations level during prebreakthrough.
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