Molecular Characterization Method And Large Scale Preparation Of Sulfur-containing Compounds In Petroleum

Sulfur-containing compounds(SCCs)are the most abundant heteroatom compounds in petroleum.Molecular composition of SCCs is of great significance to petroleum exploitation and utilization.It is one of the most effective methods for analyzing SCCs by chemically derivatizing.Sulfides and thiophenes can be converted into corresponding sulfonium salts and analyzed their molecular composition using electrospray high resolution mass spectrometry.The sulfonium salt can be further separated and demethylated,sulfides and thiophene compounds can also be separated.Methyl derivatization is a key step in the analysis and separation of SCCs.However,the process is complicated,the reaction time is too long and the repeatability is poor,which seriously affects the application of the method.In this paper,starting from the mechanism of methylation reaction,a new method of methyl derivatization is developed and the large scale preparation of sulfides and thiophenes is realized.In this paper,AgSbF₆ is used to replace the traditional methylation reagent Ag BF₄,which solves the problems of slow methylation reaction and low conversion rate.The new method reduces the reaction time from the original 12-48h to 20min and the conversion rate is as high as 95%.Not only does it greatly save the reaction time,but also does not have any discriminatory effect on some SCC_S with complex structure and large steric hindrance.This method has been successfully applied to high-sulfur crude oil and low-sulfur distillate oil,while making up for the defect that Ag BF₄ cannot characterize the molecular composition of low-sulfur distillate oil.Taking VGO as an example,a new method for characterizing SCC_S in petroleum was standardized by rapid methylation combined with positive ion electrospray ionization source(ESI)electrostatic field orbitrap mass spectrometry(Orbitrap MS)(pretreatment reaction and high resolution mass spectrometry).The experiment proves that the method has good stability and repeatability.Combine rapid methylation with demethylation(selective separation of SCC_S)and use gradient methylation/demethylation to separate SCC_S in crude oil to obtain different sulfur-containing fractions.According to gas chromatography-mass spectrometry(GC-MS)and Orbitrap MS characterization results finds that secondary methylation using AgSbF₆can quickly convert the SCC_S that Ag BF₄ failed to convert to obtain a higher yield of sulfide and thiophene.It is successfully used in the separation and large scale preparation of SCC_S.Taking crude oil as an example,by the method of methylation/demethylation to preparate large scale SCC_S in crude oil.Combined with multiple SCC_S preparation experiments,the conversion rate of methylation reaction of SCC_S during the experiment,the separation of the methylsulfonium salt phase and the unreacted oil phase,the reduction reaction conversion rate of sulfides and thiophenes,and the separation of(reduced)SCC_S after demethylation is optimized.Finally,a set of practical solutions for large scale separation and preparation of SCC_S were established for the subsequent preparation of mixed model SCC_S.