Chemical structure characteristics and multidimensional model construction of Fushun oil shale kerogen: An experimental and simulation study

• FT-IR was applied to obtain quantitative information of functional groups and substituted positions of aromatic rings of Fushun kerogen. • The number of condensed rings of aromatic structure and alicyclic were taken into account in molecular construction. • A new calculation method for the average chain length and branching degree was proposed. Solid state 13 C nuclear magnetic resonance ( 13 C NMR), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) were carried out to characterize the chemical structure characteristics and to establish the average molecular structure of kerogen extracted from Fushun oil shale. NMR predictor was used to calculate the chemical shift of carbon atoms to verify the rationality of the constructed model. And the stability of 3D model was studied by molecular dynamics (MD) simulations. 13 C NMR results demonstrate that Fushun kerogen consists of 76.98% of aliphatic structure dominated by long linear methylene and 21.6% of aromatic structure (mainly protonated aromatic carbon). Functional groups observed in 13 C NMR spectra were also detected in FT-IR spectra at wavenumber range of 1800-1000 cm −1 . XPS analysis indicates that nitrogen-containing groups were pyrrole, pyridine and primary amines, and sulfur existed as sulfoxides, thiophenes and mercaptans. By comparing the calculated 13 C NMR and experimental 13 C NMR, it was found that the aromatic structure condensed in two aromatic rings and the aliphatic structure without alicyclic and epoxy ether were more rational for the chemical structure model of Fushun kerogen. A new method to evaluate the average methylene chain length was proposed. Finally, a relatively rational 2D molecular structure with a molecular formula of C 228 H 350 O 10 N 6 S 3 was constructed. The most stable 3D periodic structure (20 optimized molecules, 48.44 × 49.63 × 50.28 Å 3 ) with the lowest total potential energy was obtained by MD simulation and density of it was 0.943 g/cm 3 .