Characterization of sulfur in asphaltenes by sulfur K- and L-edge XANES spectroscopy (original) (raw)
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Geochimica et Cosmochimica Acta, 1999
Asphaltene samples extracted from archeological and geological bitumens from the Middle East, France, and Spain were studied by sulfur K-and L-edge X-ray absorption near-edge structure (XANES) spectroscopy in combination with isotopic analyses (␦ 13 C and ␦D). Within each series, the samples were genetically related by their ␦ 13 C values. The gross and elemental composition and the ␦D values were used to characterize the weathering state of the samples. Sulfur K-and L-edge XANES results show that in all the samples, dibenzothiophenes are the dominant forms of sulfur. In the least oxidized asphaltenes, minor species include disulfides, alkyl and aryl sulfides, and sulfoxides. With increasing alteration the proportion of oxidized sulfur (sulfoxides, sulfones, sulfonates and sulfates) increases, whereas the disulfide and sulfide content decreases. This evolution is observed in all the series, regardless of the origin of the asphaltenes. This work illustrates the advantages of XANES spectroscopy as a selective probe for determining sulfur speciation in natural samples. It also shows that S K-and L-edge XANES spectroscopy are complementary for identifying the oxidized and reduced forms of sulfur, respectively.
… et Cosmochimica Acta, 1999
Asphaltene samples extracted from archeological and geological bitumens from the Middle East, France, and Spain were studied by sulfur K-and L-edge X-ray absorption near-edge structure (XANES) spectroscopy in combination with isotopic analyses (␦ 13 C and ␦D). Within each series, the samples were genetically related by their ␦ 13 C values. The gross and elemental composition and the ␦D values were used to characterize the weathering state of the samples. Sulfur K-and L-edge XANES results show that in all the samples, dibenzothiophenes are the dominant forms of sulfur. In the least oxidized asphaltenes, minor species include disulfides, alkyl and aryl sulfides, and sulfoxides. With increasing alteration the proportion of oxidized sulfur (sulfoxides, sulfones, sulfonates and sulfates) increases, whereas the disulfide and sulfide content decreases. This evolution is observed in all the series, regardless of the origin of the asphaltenes. This work illustrates the advantages of XANES spectroscopy as a selective probe for determining sulfur speciation in natural samples. It also shows that S K-and L-edge XANES spectroscopy are complementary for identifying the oxidized and reduced forms of sulfur, respectively.
XANES measurements of sulfur chemistry during asphalt oxidation
Fuel, 2015
Sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy is used to measure how the speciation of sulfur compounds evolves within a warm-mix asphalt as a consequence of the Rolling Thin-Film Oven (RTFO) and Pressure Aging Vessel (PAV) oxidative aging procedures. Identifying the types of sulfur compounds present is important for quantifying the growth in polar sulfur-containing species that can alter the asphalt's mechanical properties over time. Elemental analysis indicates that the sulfur content of the asphalt holds constant at 5% during aging. XANES analysis indicates that thiophenic sulfur compounds are most prevalent (62%), followed by sulfide and elemental sulfur compounds. RTFO and PAV aging cause smaller and larger shifts from sulfide to sulfoxide. The amount of unreacted sulfide remains larger than the amount of sulfoxide, even with PAV aging. The XANES spectra lack features that would be expected if engine oil additives indicative of recycled engine oil bottoms were present. The results indicate the importance of including thiophene, sulfide, and sulfoxide chemistries within molecular asphalt models.
Sulphur speciation in bitumens and asphaltenes by X-ray absorption fine structure spectroscopy
Geochimica et Cosmochimica Acta, 1994
The S Ledge and K-edge XANES spectra were collected on bitumen and asphaltene samples as well as model compounds in order to determine the feasibility of monitoring transformations of organic sulphur in bitumen during genesis, processing, and upgrading. Using the spectra of model compounds as fingerprints, it was possible to speciate the sulphur forms in bitumen and asphaltene. The reduced form of sulphur such as thiophenes are the predominant form of sulphur in the bitumen and asphaltene samples analyzed. No significant amounts of oxidized sulphur forms could be detected. Spectra collected using total electron yield and fluorescence yield were identical, confirming that there is no preferential partitioning at the bitumen/air interface, or oxidation during sample handling. Also important was the finding that bitumen could be analyzed at moderately high vacuum (lo-* torr). Thus XANES represents a rapid, nondestructive mean of characterizing specific classes of compounds in complex matrices, such as bitumen.
Fuel, 2019
Argentinian crude oil samples from different origins have been processed to separate in the four fractions Saturates, Aromatics, Resins, and Asphaltenes (SARA). Asphaltene and resin fractions were extracted using npentane and n-heptane as precipitating solvents. Sulphur contents of the samples were determined by elemental analysis and X-ray Absorption Spectroscopy at the Sulphur K-edge was used to perform sulphur speciation for resin and asphaltene fractions. Reduce sulphur as sulphides, disulphides and thiophenes dominate the spectra of asphaltenes, resins I and crude oils samples. A higher abundance of sulfoxide forms were found in the resin II fraction. In addition, it was found that the asphaltenes are more enriched in aromatic sulphur (thiophene) when the n-heptane solvent is employed. From the sulphur speciation determination it was possible to incorporate different sulphur forms in the hypothetical average molecular structures for the Argentinian asphaltenes.
Sulfur Chemistry of Asphaltenes from a Highly Compositionally Graded Oil Column
Energy & Fuels, 2013
Hydrocarbons in subsurface reservoirs are generally found to be compositionally graded, with fluids deeper in connected and equilibrated reservoirs being relatively enriched in asphaltenes. These gradients result from effects such as gravity, entropy, and solubility. However, it is unclear if those same effects lead to gradients in the detailed molecular composition of asphaltenes. Here, we investigate the sulfur chemistry of asphaltenes from a reservoir with a large gradient in asphaltene content. Measurements of the sulfur content from combustion as well as measurements of sulfur speciation from K-edge X-ray absorption near edge structure (XANES) spectroscopy find no significant difference in the composition of the asphaltenes. Thus, different locations within this reservoir contain oils with different asphaltene concentrations, but the asphaltenes from throughout the reservoir all have the same sulfur chemistry. This result suggests that gradients in asphaltene content can be successfully modeled with the simplifying assumption that the asphaltene molecular composition is not graded in connected and equilibrated reservoirs.
Sulfur and Nitrogen Chemical Speciation in Crude Oils and Related Carbonaceous Materials
Applying Nanotechnology to the Desulfurization Process in Petroleum Engineering
This chapter gives an overview of sulfur x-ray absorption near edge spectroscopy (XANES) studies performed on some carbonaceous materials, viz. crude oil and related materials (asphaltenes, kerogens, bitumens, and resins), and coals. Thiophene, sulfide, sulfoxide, sulfone, pyrite, and sulfate are found in varying amounts in these materials. In source rock bitumens, sulfoxide is more abundant than in the kerogens, while within the kerogens, the less aromatic Type I samples show a smaller ratio of thiophenic/ sulfidic sulfur than in Type II samples. Petroleum asphaltenes have a similar sulfur chemistry, regardless of the source or the burial depth. Resins and oil fractions retain the polar sulfoxide species of the parent oil similar to the more polar asphaltenes fractions. More aromatic sulfur species also dominate in the more matured coals than in the younger coals. Studies of nitrogen XANES also reveal that aromatic forms of nitrogen prevail in samples with increased aromatic carbon.
Sulfur characterization in asphaltene, resin and oils fractions of two crude oils
Sulfur chemical species have been determ ined for asphaltenes, resins, and oil fractions of crude oils by using X-ray absorption nearedge structure (XANES) spectroscop y. The prevalent sulfur species are thiophene, sul® de, and sulfoxide. The asphaltene of one crude oil was known to have a very high sulfoxide content; the issue addressed here is whether the sulfoxide polar group is also dominant for sulfur in the resin and the (typically nonpolar) oil fractions of the same cru de oil. Results from this study show that large sulfoxide fractions are obtained for all components of this oil. Another crude oil, lower in oxygen, also shows sim ilar sulfur composition in all three fractions; nevertheless, the oil fractions of both crudes tend to have somewhat larger sul® de fractions.