Molecular Structure Characterization And Geochemical Significance Of Sulfur Compounds In Crude Oils

Organic sulfur compounds in crude oil are of rich types and various structures,which are one of the important objects in petroleum processing and geochemistry research.High resolution mass spectrometry can be used to characterize sulfur compounds at the molecular level,and the further structural analysis on the basis of molecular characterization can help accurately grasp the impact of sulfur compounds on petroleum processing and provide significant clues for geochemistry research from the perspective of the origin of sulfur compounds.In this study,a new method for the rapid separation of sulfidic compounds from the crude oil is developed,the scheme for the analyses of molecular structures of sulfur compounds in crude oil is developed,a series of novel sulfur compounds are identified,and the origin mechanism of sulfides is explained.A novel approach for the separation of sulfidic compounds in petroleum is established.Sulfidic compounds and non-polar hydrocarbons in crude oil are firstly enriched on the alumina column,consequently removing the majority of aromatic hydrocarbons and thiophenes as well as strongly polar nitrogen compounds.Then the sulfide-rich fraction is transferred to silica gel column chromatography,and the non-polar hydrocarbons are eluted with a non-polar solvent,before the sulfidic fraction is eluted with a solvent of a certain polarity.The separation process was investigated by high resolution mass spectrometry and chromatography,and the results show that the separated sulfidic sulfur fraction can meet the requirements of chromatographic instruments for the direct analysis of sulfidic compounds.This method is simple,efficient and suitable for the routine analysis of sulfidic compounds in crude oils,distillates and petroleum products.A solution of molecular composition and structure analysis of sulfur compounds in crude oil is proposed.Firstly,the sulfide-rich fraction is obtained from crude oil by methylation-demethylation or the alumina and silica adsorption method.Then the thiophenic sulfur fraction is further separated with an alumina column to obtain thiophenes with different aryl rings,eliminating the interference between different series.Part of the sulfidic sulfur fraction is desulfurized by Raney nickel,during which sulfidic compounds with various isomers can be reduced to their original hydrocarbon skeletons.Finally,the separated and desulfurized fractions were analyzed by Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS)and gas chromatography-mass spectrometry(GC-MS)to obtain detailed molecular composition and structure information of the sulfur compounds.Based on the scheme for the analysis of molecular structures of sulfur compounds in crude oils,a series of novel sulfur compounds have been identified in a Bohai crude oil,and the composition and distribution of organic sulfur compounds have been systematically analyzed in an Iraq crude oil of high sulfur content.These novel sulfur compounds are a series of cyclic sulfides with skeleton structures of squalene,lexene and?-carotene bio-precursors,and the majority of these sulfur compounds possess a thiane ring or a thiolane ring with a quaternary carbon atom which may be an important obstacle for these compounds to further aromatize into thiophenes in this crude oil.The structural analysis of sulfur compounds in Middle East crude oil is carried out according to different fractions.Mercaptans,sulfides and thiophenes with carbon numbers less than C₁₀ are predominant in the naphtha fraction,the intermediate fraction is dominated by thiophenes,cyclic sulfides and thiadiamondoids with carbon numbers of C₁₀-C₂₅.The thiophene and thioether isolated from the residue accounted for less than half of the total sulfur content,sulfide carbon number as high as more than C₆₀.The sulfur compounds in representative crude oil samples from different geological sources in Tarim Basin Junggar Basin and Bohai Bay basin are separated and analyzed and the structural distribution of sulfides and saturated hydrocarbons in each crude oil is investigated.Conversion to saturated hydrocarbons and sulfides are important ways to preserve the characteristic carbon skeleton of active biological precursors at the early stage of deposition and diagenesis These compounds protect the carbon skeleton of the precursors and can be used as biomarkers to study the origin mechanism and evolutionary path of petroleum.