Three-dimensional molecular modeling of Dachengzi oil shale kerogen

Abstract

A three-dimensional (3D) molecular model of Dachengzi oil shale kerogen was constructed using quantitative 13C direct polarization/magic angle spinning solid-state nuclear magnetic resonance (DP/MAS SSNMR) data and accurate quantum chemistry methods. The heteroatom-containing functional groups were carefully identified using X-ray photoelectron spectroscopy (XPS) and pyrolysis experimental data. A large portion of C487H778O43N8S5 was selected for the model to introduce more types of functional groups and make the model representative. The carbon unit fractions, structural parameters and atomic ratios of the model well matched with the experimental data. The equilibrium structure was obtained by geometry optimization using the density functional theory (DFT) method at the B3LYP/STO-3G level of theory and validated by frequency calculations at the same level. The final geometry is an incompact structure containing a large number of branches, which well reflects the cross-linked molecular structure of the kerogen. The simulated 13C NMR spectrum was generated using quantum chemical calculations at the B3LYP/6-31G(d) level. The simulated spectrum is in good agreement with the experimental spectrum, indicating the validity and reliability of the model.

Keywords

• dachengzi oil shale
• kerogen
• molecular modeling
• quantum chemistry
• simulated 13c nmr.