Longli Zhang

Study on Colloidal Model of Petroleum Residues through the Attraction Potential between Colloids.

The samples of DaGang atmospheric residue (DG-AR), Middle East atmospheric residue (ME-AR), TaHe atmospheric residue (TH-AR), and their thermal reaction samples were chosen for study. All the samples were fractioned into six components separately, including saturates plus light aromatics, heavy aromatics, light resins, middle resins, heavy resins, and asphaltenes. The dielectric permittivity of the solutions of these components was measured, and the dielectric permittivity values of the components can be determined by extrapolation, which increased steadily from saturates plus light aromatics to asphaltenes. Moreover, the Hamaker constants of the components were calculated from their dielectric permittivity values. The Van der Waals attractive potential energy between colloids corresponding to various models could be calculated from the fractional composition and the Hamaker constants of every component. It was assumed that the cores of colloidal particles were formed by asphaltenes and heavy resins mainly; the other fractions acted as dispersion medium. For the three serials of thermal reaction samples, the Van der Waals attraction potential energy between colloids for this kind of model was calculated. For TH-AR thermal reaction samples, the Van der Waals attraction potential energy presented the maximum as thermal reaction is going on, which was near to the end of coke induction period.

Speciation and quantification of sulfur compounds in petroleum asphaltenes by derivative XANES spectra

Abstract The XANES spectrum is employed to study the sulfur functional groups in asphaltenes. Since the asphaltenes are complicated mixture, it is difficult to distinguish different classes of sulfur compounds in asphaltenes. Therefore, the higher order derivative spectra of sulfur XANES were introduced in order to improve sulfur XANES resolution and to qualitatively analysis sulfur functional groups in asphaltenes. Sulfur XANES spectra were deconvoluted by using of several Gaussian and arctangent functions to quantify the sulfur species. In order to convert peak area percentages to atomic percentages, the relative 1 s →3 p transition probabilities of different sulfur classes must be considered. The areas of the different Gaussian peaks were calculated and revised for their oxidation state-dependent absorption cross-section. The contribution of sulfur species to total sulfur was calculated by the corrected peak areas. The result showed that sulfur species in asphaltenes of atmospheric and vacuum residue were mainly in form of thiophene, sulfoxide, thiophene sulfone and sulfate, while hardly contained sulfide.

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

Abstract 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 asphaltenes. 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.