Molecular Characterization And Thermal Evolution Features Of Shale Oil Composition And Structure

Constantly variation of oil price has brought industrialized society depending on the oil with much more uncertainty factors.Many countries are seeking for energy such as oil shale,biomass and oil sand which can replace petroleum resources.Oil shale reserves are abundant in China.Shale oil can be produced by retorting of oil shale,which is similar but different from crude oil.The study of molecular characterization and thermal evolution behavior of shale oil composition and structure are of great significance.This study focused on the scientific problem of the influence of retorting temperature on the molecular composition and structure of shale oil.In additon,based on the fine separation method of shale oil and advanced molecular characterization method,the similarities and differences of composition and structure of shale oils from six representative areas of China(Huadian,Wangqing,Fushun,Longkou,Maoming and Yaojie)were analyzed comparatively.In this study,the influence of final retorting temperature on the composition and structure of Huadian shale oil and the transformation of heteroatom compounds in Huadian shale oil produced at different temperatures were studied.Furthermore,the relationship between the composition of shale oil and the pyrolysis reactivity of oil shale was revealed from chemical bond formation and fracture.In this study,the similarities and differences of basic characteristics of shale oil from different locations were analyzed comparatively.A new method for shale oil separation based on distillation separation,acidic-basic extraction and column chromatography of neutral fraction was developed.Hence,the acidic,basic and neutral sub-fractions of<300? fractions and>300? fractions of six different shale oils were obtained,and the molecular structure was characterized by the most suitable analysis method,respectively.The results showed that phenols and carboxylic acids were dominant in acidic fractions and the relative content of lower phenols was obvious higher than that of higher phenols.Moreover,basic nitrogen compounds were dominant in basci fractions of<300? fractions in shale oils.The relative content of pyridine and quinoline compounds in Yaojie shale oil was obviously higher than those that in shale oils from other locations.In addition,aliphatic hydrocarbons,aromatic hydrocarbons,aliphatic ketones,aliphatic nitriles and other different types of compounds were separated by using preparative chromatography with cyclohexane,cyclohexane/toluene,toluene/dichloromethane,dichloromethane,ether/methanol and methanol as the mobile phase.The basic research on the extraction of high value-added chemicals from shale oil was carried out systematically.Finally,a new method of shale oil separation was formed,which included distillation separation,acidic-basic extraction and column chromatography.Molecular structure of shale oil>300? fractions from six locations was characterized by 1H,13C NMR and FT-IR.The average molecular structure parameters and the relative content and distribution information of various functional groups were also calculated.The results showed that Huadian shale oil>300? fraction had the highest alkyl carbon ratio,average carbon number of substituents,the ratio of-CH2-to-CH3 and the lowest degree of alkane branching,which indicated that average carbon chain of the compounds of Huadian shale oil>300? fraction was the longest.Moreover,because Maoming and Longkou oil shales are associated with coal,the aromatic carbon ratio of shale oil fractions>300? was relatively high.]H,13C NMR and FT-IR can be effectively applied to the molecular level research of heavy oils.The experimental results can complement and verify each other.It provides a new way to characterize the molecular structure of heavy fractions of shale oil.The influence of final retorting temperature on the composition and structure of Huadian shale oil was studied by GC×GC-TOF/MS and NMR methods relatively in order to grasp the pyrolysis behavior of oil shale and provide basic data for the study of pyrolysis mechanism of oil shale.The results showed that GC×GC-TOF/MS analysis has a very high peak capacity compared with one-dimensional GC-MS analysis.The number of detected compounds was at least one order of magnitude higher,which greatly reduced the overlap of chromatographic peaks.Furthermore,the aromatization reaction of naphthenes was intensified and the degree of alkane branching was reduced with the increase of the final retorting temperature.However,the short-chain aliphatic hydrocarbons in<300? gradually increased while the long-chain aliphatic hydrocarbons decreased with the increase of the final retorting temperature.It provides important basic data for the study of pyrolysis mechanism of oil shale,and also opens up a new way for the analysis of complex shale oil.Based on the selective ionization characteristics of different types of polar heteroatom compounds in shale oil in positive and negative ESI conditions,the qualitative analysis of different types of heteroatom compounds was carried out by FT-ICR MS,and the relative abundance was calculated.The similarities and differences of composition of heteroatomic compounds in Huadian shale oil produced at five different temperatures were explored at molecular level.The results showed that polycondensation at higher retorting temperature points increased thiophene sulfur content and the relative abundance of pyrrole containing neutral nitrogen compounds.However,the cracking reaction at higher retorting temperature points decreases the amount of aliphatic carboxylic acid compounds with DBE value of 1 in Huadian shale oil,and resulted in the molecular structure of basic nitrogen heteroatom compounds in oil shale more closer to that of N1 compounds,which enriched the heteroatom compounds in shale oil to those with low DBE values.This provides a new way to study the occurrence and variation of heteroatom compounds.In summary,based on the advanced analytical and testing methods,a molecular characterization method for the composition and structure of different fractions of shale oil had been established.The evolution of shale oil composition and structure with the final retorting temperature was investigated at the molecular level.Furthermore,the influence of secondary cracking and polymerization on abundance and distribution of heteroatom compounds at higher temperatures were revealed from the chemical bond formation and fracture.This study also provides a basis for the regulation of oil shale retorting conditions and the development of shale oil hydrogenation catalysts,and provides an important reference for the theoretical study of molecular structure and pyrolysis mechanism of oil shale.