Analysis of Sulfur X-ray Absorption Near-edge Spectroscopy in Asphaltenes, Resins, and Maltenes of Two Different Crude Oils

Sulfur chemical structures present in crude oil products such as petroleum asphaltenes, resins, and maltenes obtained from two different oils have been determined using X-ray absorption nearedge structure (XANES) spectroscopy. Maltenes are pentane soluble portions, resins are pentane insoluble and heptane soluble portions, and asphaltenes are heptane insoluble portions of crude oil. The sulfur forms in these six fossil fuel samples are predominately organic; of them thiophene, sulfide and sulfoxide are the main contributors. One of the crude oils is known to have a high sulfoxide content; results from this study showed that there is a considerable amount of sulfoxide present in its asphaltene, resin, and maltene fractions. In spite of the fact that asphaltenes are known to be more polar than the other two fractions, and also that sulfoxide is a very polar chemical moiety, this structure is present in considerable amounts also in the resin and the maltene fractions of this particular crude oil. The second oil, lower in oxygen content, showed consistently less amount of sulfoxide in all its asphaltene, resin, and maltene fractions. Furthermore, no evidence for higher oxides such as sulfones, sulfonates, and sulfates are found in the three fractions of either of the crude oils.