Identification of sulphur, oxygen and nitrogen species in heavy oils by X-ray photoelectron spectroscopy.
Résumé
The removal of heteroelements issued from petroleum products is an important problematic in the developments of the refining processes, in particular for the refining of the unconventional oils for which it is necessary to better understand and quantify the chem. environments of those heteroelements. The aim of this work was to evaluate how the speciation of sulfur, nitrogen and oxygen in oils with the XPS in the "cold" mode could be the appropriate technique. The characterization of liqs. and solids with low m.p., has been possible thanks to the use of the liq. nitrogen cooling system, for which the temp. can reach -135 °C on the sample holder in the anal. chamber. The S 2p high resoln. spectra recorded for the sulfur org. compds. has allowed establishing a valuable database for sulfur environments where six classes can be distinguished. The methodol. developed in this work has been applied to the anal. of a straight run atm. residue for which thiol and thiophenic/sulfide environment has been identified. The relative concn. of those two chem. classes has been evaluated. 70% of the whole sulfur is present in thiophenic/sulfide group whereas the rest is thiol chem. class. The analyses performed on hydrotreated effluents highlight larger reactivity of the thiol compds. But, we are facing a quite high detection limit of the XPS technique estd. at 0.1 at.% not permitting the detection of sulfur in the highly desulphurised effluents. This is still a main limitation for deep hydrotreatment applications but this technique can be used to investigate visbreaking, deasphalting or combustion processes where the heteroelement removing is less severe. Developments on the XPS technique have to be continued in order to reduce its detection limit. The whole quant. anal. must be considered carefully as hydrogen is not detected by XPS. However, the S/C, N/C and O/C at. ratio of the ref. samples are relatively consistent with combustion techniques.