Investigation of Behavior of Sulfur in Oil Fractions During Oil Shale Pyrolysis

In this study, the theoretical and experimental basis for the examination of sulfur-containing compounds during the pyrolysis of oil shale, involving 19 sulfur compound models and 34 corresponding reaction pathways, is discussed. In addition, the types of sulfur compounds in shale oils at different pyrolysis temperatures were determined by flash pyrolysis–gas chromatography–mass spectrometry and a gas chromatography–sulfur chemiluminescence detector. The reaction pathway for the sulfur-containing model provided reliable results for the conversion behavior of sulfur, which was consistent with the experimental values. With increasing temperature, the content of Cn-thiophene continuously decreased. In contrast, the Cn-benzothiophene concentration generally increased with increasing temperature. The S═O double bond affected the C–S bond order, and the bond order was reduced due to the effect of oxygen atoms. Calculation results revealed that the alkyl side-chain group tends to form an aromatic ring structure, leading to the increase in the relative content of Cn-thiophene/benzothiophene. Meanwhile, the Mulliken atomic charge, bond dissociation energy, bond length, and Mayer bond order of thioether and sulfoxide compounds were estimated. Quantum chemistry was successfully employed to analyze the chemical reactions, which provided a basis for promoting the understanding of the kerogen pyrolysis mechanism at the molecular level.