Separation And Characterization Of Large-molecular Sulfur Compounds In The Crude Oil

Conventional sulfur compounds can be analyzed by chromatographic technique.However,the composition of large-molecular sulfur compounds is complex,which is difficult to be separated by chromatography,or even impossibly to be passed by gas chromatography column.A methylation/demethylation method developed by the State Key Laboratory of Heavy Oil was used to isolate highly purified thiophenic fraction and sulfidic fraction from crude oil in Bohai Bay.The detailed characterization of large-molecular sulfur compounds was carried out at molecular level by gas chromatography-mass spectrometry?GC-MS?and Fourier transform ion cyclotron resonance mass spectrometry?FT-ICR MS?.According to FT-ICR MS,the carbon number of the sample oil ranges from 10 to55,and the equivalent double bond number?DBE?is 0-20,it was proved that large-molecular sulfur compounds are indeed existed.Based on GC-MS structure results of the conventional sulfur compounds,and correlated to FT-ICR MS results of large-molecular sulfur compounds,the chemical structures of large-molecular sulfur compounds were inferred.The chemical structures of large-molecular sulfidic fraction are mainly monocyclic sulfides,steranes and hopanoids,The chemical structures of large-molecular thiophenic fraction are dominated by conventional thiophene structures,but sterane structure coexists in some specific carbon number spots.The highly abundant C₄₀ sulfur compounds found in the crude oil possibly has carotene skeleton structure,which is mainly formed by the interaction of algal organic matters??-carotene?in salt-lake sediments with reduced inorganic S during long-term hypoxia,and can be used as a biomarker reflecting the sedimentary environment.The results of this study broaden the awareness of organic sulfur compounds in crude oil and have crucial geochemical significance for the discovery and discussion of C₄₀ sulfur compounds.