Molecular Simulation Of Three Dimensional Structural Characteristics Of Oil Shale Kerogen

Oil shale is a type of sedimentary rock embedded with solid organic matter.It can be used for direct combustion or retorting to obtain oil supplemental shale oil.The main organic component of kerogen in oil shale is an organic macromolecule polymer that undergoes complex physical and chemical changes during the pyrolysis process.A single experimental technique research method has been difficult to improve the existing comprehensive development and utilization technology of oil shale..Therefore,the molecular structure of oil shale kerogen must be studied in-depth.With the development of science and technology,the deepening of molecular chemistry research and the improvement of computer processing data,molecular simulation is playing an increasingly important role in the study of the molecular structure of oil shale kerogen.Based on¹³C NMR,XPS and elemental analysis data of Fushun and Maoming oil shale kerogens,this paper constructed two-dimensional average molecular structure model of kerogen in Fushun and Maoming oil shale in China.The structural model of Fushun and Maoming oil shale kerogen was optimized and refined through physical density and chemical bond concentration.The physical density and chemical bond concentration of the kerogen structure model were well matched with the experiment.The model was verified from the perspective of physical density and chemical bonding.The accuracy and rationality.Molecular dynamics simulations of energy optimization of two-dimensional structural models of Fushun and Maoming oil shale kerogen were conducted by MS?Materials Studio2017?,and their initial optimized structures were obtained.Based on this,molecular dynamics annealing simulations were performed.A global energy optimal configuration is obtained,namely a three-dimensional structural model of oil shale kerogen.Based on the three-dimensional structural model of kerogen,the quantum mechanical parameters such as bond length,bond level,and electrostatic potential based on the density functional theory were calculated to analyze the active site of kerogen pyrolysis in the early stage of chemical reaction;Molecular structure and quantum mechanical calculations were performed to analyze the stability of C-C and C-O bonds under different functional groups,free radicals,and different attachment modes.The chemical reactivity of the small molecule structure was used to study the chemical reaction of carbon skeleton in the middle and late stages of kerogen pyrolysis.In the process,the microscopic chemical evolution mechanism in the pyrolysis process is obtained and the overall pyrolysis reaction sequence of kerogen is predicted.The pyrolysis of oil shale kerogen is mainly due to the adjustment of macromolecular structure and the breakage and recombination of chemical bonds.Therefore,it is necessary to study the energy characteristics and various types of chemical bond properties for maintaining the stability of kerogen structure.In this paper,based on the three-dimensional structural model of oil shale kerogen of self-constructed and nine different metamorphic degrees in the literature,the relationship between the degree of metamorphism of kerogen in oil shale and the concentration of various chemical bonds and energy density is studied.The results showed that with the increase of oil shale kerogen,the concentration of chemical bonds formed by aromatic carbon and aromatic carbon,aliphatic carbon,and hydrogen atoms increased,and the concentration of chemical bonds formed by fatty carbon,aliphatic carbon,and hydrogen atoms decreased.Among them,the concentration of chemical bonds between aromatic carbons,fatty carbons,and hydrogen atoms changes most significantly.The valence electron energy density and the non-bond energy density of the kerogen potential energy of the oil shale composition generally increase with the increase of the kerogen metamorphic degree,becoming a stable chemical energy that composes the oil shale kerogen.