This talk will focus on the study of two heteroatoms commonly found in fossil fuel materials: sulfur and nitrogen. The chemical structures of these elements often reveal a wealth of important information, such as depositional environments, and lead us to understand the complex chemical processes during maturation. Moreover, knowledge of the chemical structures of the heteroatoms could address some of the major issues in the production of oil and gas, as well as problems in environmental pollution during utilization of the fossil-fuel resources. X-ray absorption Near-Edge Spectroscopy (XANES) using synchrotron radiation is one of the best methods to identify and quantify the different chemical structures of these elements. This method is direct, non-destructive, and the usage of powerful synchrotron radiation makes the identification of the different chemical structures of the elements very effective. Sulfur XANES can be explained with a simple atomic picture, while a molecular approach is needed for nitrogen XANES analysis. In the case of sulfur, the characteristic resonances between the signature peaks in the absorption spectra shift to higher photon energies with an increase of formal oxidation number. For nitrogen, the signature 1s to π* and/or 1s to σ resonances for different chemical structures are distinctly different. Coals, petroleum asphaltenes, kerogens, bitumens, and shale rocks have been extensively studied using XANES, and the heteroatom chemistry shows consistent trends between samples from different depositional environments and maturity stages. Overall, the heteroatom chemistry follows the carbon chemistry quite closely; immature samples show a higher aliphatic to aromatic ratios, and more oxygen-rich structures than the relatively more mature samples. For instance, Type I kerogen and lower ranked coals show more sulfidic than thiophenic structures than the more mature Type II kerogens and higher rank coals. In addition, inorganic sulfur forms are found in coals and kerogens, but not in asphaltenes. Nitrogen forms in all the carbonaceous materials studied are found to be aromatic. The experimental details as well as the results will be discussed, and commonalities between the general trends of the chemical structures of these elements will be highlighted.<br/>

Overview of heteroatom chemistry in fossil fuels

255th National Meeting (2018)

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