Study on the relationship between sulfur functionalities and the characteristics of THAR asphaltene

The asphaltenes contain a lot of hetero-atoms, such as sulfur, nitrogen and oxygen, which play an important role on the polarity and association characteristics of asphaltenes. The n-heptane asphaltene was derived from the Tahe atmospheric residue (THAR). In addition, THAR n-heptane asphaltene was divided into three sub-fractions by difference of the polarities. The mean dipole moments of asphaltene sub-fractions were investigated. All of these asphaltene sub-fractions were measured by ¹H-NMR spectrometry. From the spectra, the average structural parameters could be obtained in order to analyze the association characteristics. The structures of sulfur functional groups were analyzed by X-ray absorption near edge structure (XANES) to study the influence of sulfur atoms upon the characterization of asphaltene. The results showed that as the polarity increased, the ratio of H/C atom decreased and association increased. For all sub-fractions samples, thiophene was the most dominant functional group of the reduced sulfur and followed by sulfide. The oxidized form of sulfur was present predominantly as sulphoxide, sulfone and sulfonate. Thiophene, sulfone and sulfonate influenced the characteristics of asphaltenes, but did not determine the polarity and association of asphaltenes. Thus, the sulphur atoms were not the decisive factors to determine the polarity and association of asphaltenes.