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In this study, structural parameters of Longkou oil shale kerogen were examined and identified by the combination of pyrolysis–gas chromatography–mass spectrometry, Fourier transform infrared spectroscopy, 13C nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy. Based on the experimental data, a three-dimensional kerogen model was generated using quantum chemistry and molecular dynamics methods. The optimized molecular configuration was discussed, which showed good agreement with the experimental results in terms of structural characteristics. Electron density analysis was performed to examine the bonding characteristics of kerogen, and the bond length distribution of the Longkou kerogen model was analyzed, revealing that the S atom exhibits higher affinity for the H atom compared to the aliphatic carbon from the comparison of the electron density of the C–S and S–H bonding regions. Mulliken charge analysis was carried out to evaluate the partial atomic charges of heteroatoms. The charges on the cyclic structure tended to be equally distributed because of the presence of conjugated π bond, leading to the loss of charges on the N atoms. Besides, the HOMO–LUMO properties of Longkou kerogen were calculated, and a detailed picture of the frontier orbitals of kerogen for the inter- or intramolecular chemical reactions was obtained. This study validated that polycyclic aromatic structures in kerogen play a crucial role in the reactive sites for bond cleavage during the deformation of kerogen.

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In this paper, the Thermogravimetric Analysis-Fourier Transform Infrared Spectroscopy (TG-FTIR) technique is used to analyze the pyrolysis behavior of kerogen of two different oil shales at different heating rates. The pyrolysis reaction mechanism of kerogen and the regularity of change in the composition of its pyrolysis products are discussed. Furthermore, the apparent activation energy (E) and the frequency factor (k 0) are determined through the distributed activation energy model (DAEM), and the relationships between E and the kerogen chemical structure, conversion rate, frequency factor, and the amount of kerogen pyrolysis products generated are established. The results show that the kerogen structure is similar to that of aliphatic chains, its pyrolysis takes place mostly in the range of 350-520 °C, and the post-pyrolysis semicoke residue accounts for less than 32.5%. In the kerogen pyrolysis process, first the precipitation of free water takes place, followed by depolymerization and decarboxylation, so that the main alkyl side chains are constantly parting and cycling, and the oxygencontaining group gradually breaks up and produces substances such as alkanes, carboxylic acids, alcohols, and aldehydes until a more stable graphite-like structure of kerogen is formed. In the products of kerogen pyrolysis, the concentrations of released lightweight noncondensable volatiles (CH 4 , CO, CO 2) are lower than those of liberated condensable volatiles containing macromolecules (e.g., CH x , C=O groups) that show the Gaussian-like distribution. The apparent activation energy in the two kinds of kerogen varies in the range of 100-495 kJ•mol-1. At the same time, during the entire pyrolysis system, the apparent activation energy and logarithm values of the frequency factor (lnk 0) exhibit a good linear relationship. The study reveals the pyrolysis reaction mechanism of oil shale in terms of the

Various analytical techniques were used to study the molecular composition and structure of heteroatom compounds in Huadian (HD) shale oil. On the basis of the results obtained from gas chromatography−nitrogen chemiluminescence detection and gas chromatography−sulfur chemiluminescence detection, the composition of nitrogen-and sulfur-containing compounds was estimated. Molecular composition and structural information of heteroatom compounds were characterized on the basis of their type (double-bond equivalence (DBE)), class (number of oxygen, nitrogen, and sulfur heteroatoms), and carbon number distribution using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). In the positive-ion ESI FT-ICR MS mode, a total of 14 different basic species were detected for basic nitrogen compounds. N 1 class compounds dominated followed by N 1 O 1 and N 2 class compounds. The DBE value of N 1 O X compounds having high relative abundance values increased with the increase in the number of oxygen atoms. In the negative-ion ESI FT-ICR MS mode, a total of 12 classes of compounds were detected for neutral nitrogen compounds and acidic compounds of HD shale oil. O 2 class species were dominant, followed by N 1 and O 1 class compounds. N 1 class species with DBE values of 9, 12, and 15 were carbazoles, benzocarbazoles, and dibenzocarbazoles, respectively.