Chemical speciation of Sulphur in petroleum asphaltenes using XANES spectroscopies

BAVA, Y. B.; GERONÉS, M.; ANDRINI, L.; GIOVANETTI LISANDRO; ERBEN, M. F.

Campinas

Congreso; LNLS 27th Annual Users' Meeting (RAU); 2017

CNPEM

Asphalthenes are complex mixture of heteroatom rich aromatic hydrocarbons that arepresent as a solid suspension in crude oils. The asphalthenes are the fraction of oilinsoluble in heptane (or pentane) but soluble in toluene. All asphaltene chemicalproprieties, excepting elemental composition, had been the subject of debate, speciallytheir molecular weight and structure. The most probable composition of asphaltenes area complex mixtures of polycyclic aromatic hydrocarbons groups (PAHs) of seven fusedaromatic rings (7FAR) with a width of three to ten fused aromatic rings (3FAR-10FAR)with substituted alkyl chains with heteroatoms functional groups. Sulphur is the mostabundant heteroatom in the oil, present in the heavier fractions: asphaltenes (about 0.5 to7 wt%,) and resins. Thus, the knowledge of the sulphur chemistry in petroleum helps inthe mitigation of sulphur induced problems in resource utilization. Sulfur speciationvaries greatly in asphaltenes from different locations representing different source andreservoir rocks. Besides sulfur is a good marker of the alteration of oils because it is verysensitive to oxidation, and exhibits a range of oxidation states from -2 to +6. [1, 2] TheXANES spectroscopy is an appropriated technique for the speciation of chemical speciesand provide qualitative and quantitative information about the sulphur chemistry inasphaltenes. [3, 4]Three samples of asphaltenes were extracted from different Argentinian crude oils byprecipitation with n-pentane, n-hexane and n-heptane, using a solvent to the bitumen ratioof 40:1 volume/weight. The precipitated asphaltenes were separated from malthenes byfiltration and then the resins coprecipitated were removed with a Soxhlet extraction withthe respective n-alkane. The XANES measurements were performed in the SXS beamlineat LNLS. The commercial standard models used for the experiment were sodium sulfide,pyrite, dibenzyl sulfide, dibenzyl disulfide, diphenyl disulfide, dibenzothiophene,dibenzothiophene sulfona, thianthrene, tetraphenylthiophene, dimethyl sulfone, diphenylsulfoxide, diphenyl sulfone, and potassium sulfate.The spectra of asphalthenes can be describe in terms of three different sulfur structuresas sulfide, thiophene and sulfate. It has been possible to observe a major contribution ofsulfide structure in asphalthenes coprecipitated with resins compare to the spectra ofasphantenes. It is well know that the precipitation in n-heptano is selective forasphalthenes of highest molecular weight, and in this case, the XANES spectra show adifferent shape according to the solvent. An increase in the contribution of more oxidatedsulphur form as thiophenic and sulfone group were observed.[1] Mullins, O. C.; Sheu, E. Y.; Hammami, A.; Marshall, A. G. Asphaltenes, Heavy Oils, andPetroleomics; 2007.[2] Mullins, O. C. Annu. Rev. Anal. Chem. 2011, 4, 393?418.[3] Pomerantz, A. E.; Bake, K. D.; Craddock, P. R.; Kurzenhauser, K. W.; Kodalen, B. G.; Mitra-kirtley,S.; Bolin, T. B. Org. Geochem. 2014, 68, 5?12.