Chemical Composition and Structural Characteristics of Oil Shales and Their Kerogens Using Fourier Transform Infrared (FTIR) Spectroscopy and Solid-State 13C Nuclear Magnetic Resonance (NMR)

The chemical composition and chemical structure of selected oil shales and the kerogens isolated from them were studied by solid-state C-13 nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy with curve-fitting analysis, and the changes during the removal of the inorganic matrix were also investigated. The C-13 NMR results indicate that the oil shales and kerogens are mainly composed of aliphatic carbon (>= 55%). FTIR analysis indicates that aliphatic hydrocarbons mainly contain the methylene group, mostly forming long straight chains and a small amount of branched chains, and the hydroxy groups mainly contain OH-OH and OH-O bonds (>= 65%). Both the C-13 NMR and FTIR analyses show that the acid treatment improved the hydrocarbon-generating ability in kerogen. Furthermore, the curve-fitting analysis indicates that the HCl and HF treatments slightly affected the aliphatic and hydroxyl structures, but significantly affected the oxygen-containing and aromatic structures in the oil shales. 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 groups, in descending order. After the acid treatment, the main oxygen-containing groups were the C-OH and C-O groups; because of the hydrolysis, substitution, and ion exchange. The C-13 NMR results indicate that the acid treatment not only decreased the extent of aromatic ring condensation (fused aromatic rings), but also decreased the number of condensed aromatic rings.