HIGH EFFICIENCY DESULFURIZATION OF SYNTHESIS GAS
Mixed metal oxides containing CeO{sub 2} and ZrO{sub 2} are being studied as high temperature desulfurization sorbents capable of achieving the DOE Vision 21 target of 1 ppmv or less H{sub 2}S. The research is justified by recent results in this laboratory that showed that reduced CeO{sub 2}, designated CeOn (1.5 < n < 2.0), is capable of achieving the 1 ppmv target in highly reducing gas atmospheres. The addition of ZrO{sub 2} has improved the performance of oxidation catalysts and three-way automotive catalysts containing CeO{sub 2}, and should have similar beneficial effects on CeO{sub 2} desulfurization sorbents. An electrochemical method for synthesizing CeO{sub 2}-ZrO{sub 2} was developed and the products were characterized by XRD and TEM during year 01. Nanocrystalline particles having a diameter of about 5 nm and containing from approximately 10 mol% to 80 mol% ZrO{sub 2} were prepared. XRD analysis showed the product to be a solid solution at low ZrO{sub 2} contents with a separate ZrO{sub 2} phase emerging at higher ZrO{sub 2} levels. Unfortunately, the quantity of CeO{sub 2}-ZrO{sub 2} that could be prepared electrochemically was too small to permit full desulfurization testing. Also during year 01 a laboratory-scale fixed-bed reactor was constructed for desulfurization testing. All components of the reactor and analytical systems that may be exposed to low concentrations of H{sub 2}S are constructed of quartz, Teflon, or silcosteel. Reactor product gas composition as a function of time is determined using a Varian 3800 gas chromatograph equipped with a pulsed flame photometric detector (PFPD) for measuring low H{sub 2}S concentrations (<{approx}10 ppmv) and a thermal conductivity detector (TCD) for higher concentrations of H{sub 2}S. Larger quantities of CeO{sub 2}-ZrO{sub 2} mixtures from other sources, including mixtures prepared in this laboratory using a coprecipitation procedure, have been obtained. Much of the work during year 02 consisted of characterization and desulfurization testing of materials obtained from commercial sources. To properly evaluate the effect of ZrO{sub 2} addition on desulfurization capability, the physical properties of the sorbent must be similar. That is, a CeO{sub 2}-ZrO{sub 2} mixture from source A would not necessarily be superior to pure CeO{sub 2} from source B if the properties were dissimilar. Therefore, research during year 03 concentrated CeO{sub 2} and CeO{sub 2}-ZrO{sub 2} mixtures prepared in this laboratory using the coprecipitation procedure. The structure of these sorbents is similar and the effect of ZrO{sub 2} addition can better be separated from other effects. X-ray diffraction tests of the sorbents prepared in house have confirmed the existence of a solid solution of ZrO{sub 2} in CeO{sub 2}. Reduction tests using an electrobalance reactor have confirmed that CeO{sub 2}-ZrO{sub 2} mixtures are more easily reduced than pure CeO{sub 2}. Reduction of CeO{sub 2}-ZrO{sub 2} begins at a lower temperature and the final value of n in CeO{sub n} (1.5 < n < 2.0) is smaller in CeO{sub 2}-ZrO{sub 2} than in pure CeO{sub 2}. Desulfurization tests have shown that both CeO{sub 2} and CeO{sub 2}-ZrO{sub 2} sorbents are capable of reaching the target sub-ppmv H{sub 2}S level in highly reducing gases. Both CeO{sub 2} and CeO{sub 2}-ZrO{sub 2} sorbents have successfully removed H{sub 2}S to the minimum detectable limit of the PFPD detector, approximately 100 ppbv.
- Research Organization:
- Louisiana Sate University (US)
- Sponsoring Organization:
- (US)
- DOE Contract Number:
- FG26-00NT40813
- OSTI ID:
- 823018
- Resource Relation:
- Other Information: PBD: 1 Nov 2003
- Country of Publication:
- United States
- Language:
- English
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