X-ray Absorption Spectroscopic Study of the Reactions, Dispersion, and Degradation of the CA and K Catalytic Species in Coal Gasification. Annual Report January-December 1986

摘要

EXAFS spectroscopy, supplemented by other techniques, is being used to investigate the behavior and reaction of alkali and alkaline earth catalysts in various chars derived from lignite and other carbonaceous materials. In the current year, in-situ EXAFS techniques have been successfully developed and demonstrated for Ca and K in lignites and chars under pyrolysis and gasification conditions to 600 C. The in-situ EXAFS investigation revealed only minor changes the state of Ca in chars under pyrolysis and O2 gasification to 500 C. For K-loaded chars, however, similar minor changes were observed during pyrolysis but K2CO3 was formed under O2 gasification. In addition, a reexamination of Ca in freshly prepared rapidly and slowly prepared chars was undertaken. In contrast to earlier work on aged chars, EXAFS revealed that slowly pyrolyzed chars do contain significant CaO; however, Ca in rapidly pyrolyzed chars remains highly disordered as no evidence for CaO or other phase was found. The authors attribe the lack of CaO in the aged chars to hydrolysis and reaction of CaO to Ca(OH)2 and CaCO3. Both ambient and in-situ EXAFS examinations of Rb-loaded materials are as yet somewhat inconclusive because of experimental problems and the similarities exhibited in spectra of key compounds.