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TitleSynchrotron-based X-ray absorption spectroscopy study of vanadium redox speciation during petroleum coke combustion and gasification
AuthorDuchesne, M AORCID logo; Nakano, J; Hu, Y; MacLennan, A; Bennett, J; Nakano, A; Hughes, R WORCID logo
SourceFuel vol. 227, 2018 p. 279-288, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20220126
PublisherElsevier BV
Mediapaper; digital; on-line
File formatpdf
Subjectsfossil fuels; vanadium; vanadium geochemistry; spectroscopy; spectroscopic analyses; absorption; petroleum; coke; slag; ash
Illustrationsphotographs; tables; graphs
ProgramClean Fossil Fuels
Released2018 05 22
AbstractVanadium in petroleum coke can have environmental and technological impacts in gasification and combustion processes. The multitude of vanadium oxidation and coordination states has made it difficult to characterize vanadium-rich materials, particularly for materials where the vanadium is associated with an amorphous state and cannot be characterized by X-ray diffraction. This study presents two methods whereby vanadium is characterized by synchrotron-based X-ray absorption spectroscopy, which applies to both crystalline and amorphous phases. The first method, comparison of main edge energies, is relatively straightforward but presents multiple limitations. The other method, linear combination fitting, overcomes many of these limitations but relies on the availability of suitable reference materials. These methods, applied to pilot plant gasification and combustion samples, indicate various trends in vanadium speciation, such as higher oxidation states for combustion samples relative to gasification samples. Analysis of synthetic pseudo-binary materials, which is important for the development of thermodynamic equilibrium models, indicated that V5+ is stable with high oxygen partial pressures encountered during combustion. With a lower oxygen partial pressure, representative of gasification conditions, V5+ is stable if there is enough calcium present; otherwise, V3+ is stable.
Summary(Plain Language Summary, not published)
Vanadium is found in various by-products of metal refinement and fossil fuel combustion/gasification. The oxidation state of vanadium in the by-products has technological and environmental implications. For example, the oxidation state may affect refractory wear inside reactors, as well as leachability and toxicity of industrial by-products. The vanadium can be found in either crystalline or amorphous phases. Determination of vanadium's oxidation state in crystalline phases can be achieved via the widely adopted X-ray diffraction (XRD) technique. However, this technique does not provide information on vanadium in amorphous phases. This study determined the oxidation state of crystalline and amorphous vanadium in various industrial and laboratory samples using X-ray absorption spectroscopy (XAS) in a collaborative effort involving Natural Resources Canada, the United States Department of Energy and Canadian Light Source.

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