Research On The Structual Characteristics Of Functional Groups In Oil Shale And Their Kerogen

In face of the shortage of petroleum resource and large reserve of oil shale in china,developing high quality of oil shale rationally will be a great supplement.Oil shale is a sedimentary rock composed with inorganic minerals and organic,which especially contains a large amount of inorganic mineral.Currently,researchers from all of the world take the kerogen instead of oil shale using acid treatment when they study the structural characteristics of oil shale.But this process also changed the structure of oil shale.In this paper,The purpose of this study is to better understand the chemical structures of oil shales and kerogens,the change of chemical structures of oil shales during the acid treatment and the he hydrocarbon-generating ability of oil shales.The chemical composition and structure of oil shales(Huadian and YaoJie)and the kerogens isolated from them were determined by solid-state 13 C NMR and Fourier transform infrared(FT-IR)spectroscopies.Moreover,functional group and chemical transformations were also carried out by treating the raw oil shales with hydrochloric acid(HCl)and hydrofluoric acid(HF).The FT-IR and 13 C NMR results indicate that the oil shales and kerogens are mainly composed of aliphatic hydrocarbons(above 55%)containing mainly the methylene group,mostly forming long straight chains and a small amount of branched chains.The FT-IR analysis showed that the hydrogen bonding in the structure mainly involves OH–OH and OH–O bonds,more than 65%.The HCl and HF treatments caused chemical transformation.Compared to the long-chain aliphatic structures in the kerogens,oil shales showed a higher amount of branching in the structures.The acid treatments improved the ability of kerogens for hydrocarbon generation.Furthermore,the acid treatments slightly affected the content of aliphatic hydrogens and hydroxyl groups;but significantly affected the content of oxygen-containing functional groups and aromatic structures in the oil shales.Particularly for aliphatic hydrogens,the intensity of C–H stretching vibration decreased,whereas the intensities of other vibrations slightly increased.The OH–N,OH–O,and ring hydrogen bonding are slightly destroyed.The oxygen-containing groups in the oil shales are mainly the C–OH group,followed by the C–O,O=C–O,and C=O(O–C–O)groups in the descending order.After the acid treatment,the main oxygen-containing groups were the C–OH and C–O groups,because hydrolysis,substitution,and ion exchange occurred.The main aromatic hydrocarbon structure in the oil shales showed three adjacent H deformation,whereas kerogens showed the two and three adjacent H deformation.The chemical structure of five selected oil shales were studied by Fourier transform infrared(FTIR)spectroscopies with curve-fitting analysis,and the hydrocarbon-generating ability were also investigated.The result shows that FTIR is a useful method for quantitative characterization of hydrocarbon-generating ability.The FTIR analysis indicates that aliphatic hydrocarbons mainly contain the methylene group(?55%),mostly forming long straight chains and a small amount of branched chains.The higher hydrocarbon~generating ability means that the oil shale has longer straight chains,higher gas-generating capacitiy,lower content of aromatic structures and more content of oxygen-containing group.In addition,there has good correlation between fa,Hal/Har and H/C atomic ratio.The higher content in H/C means the lower content in fa and higher content in Hal/Har.