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
X-ray photoelectron spectroscopy (XPS) was used to investigate changes in nitrogen functionalities present in Chinese Huadian (HD), Maoming (MM) and Yaojie (YJ) oil shales during pyrolysis. Throughout the process (T ≤ 600 °C), most of the nitrogen contained in raw oil shale samples was retained in their semi-cokes. Five peaks of nitrogen functionalities (N 1s) appeared in the XPS spectra of raw HD, MM and YJ oil shale samples and their semi-cokes: N-6 (pyridine), N-A (amino), N-5 (pyridone), N-Q (quaternary nitrogen) and N-X1 (pyridine N-oxide). To obtain an acceptable fit, an additional peak at 404 (±0.5) eV (N-X2) was required in the N 1s spectra of the samples. N-5 could either represent pyridone or a mixture of pyridone and pyrrolic nitrogen forms, the most abundant ones in all samples. At a relatively low temperature (300 °C) the desorption reaction occurred and the amount of chemisorbed oxygen associated nitrogen (N-X2) decreased significantly. As the pyrolysis temperature increased from 300 to 500 °C, pyridine N-oxide was converted to pyridone, and, simultaneously, the latter was converted to pyridine and pyridine structures associated with oxygenquaternary nitrogen. In the semi-cokes of Huadian and Maoming oil shale samples at 600 °C, most of the pyridone was converted into pyridine and quaternary nitrogen. At this temperature, especially the condensation reaction of pyridine into quaternary nitrogen occurred in the semi-coke of Yaojie oil shale sample, while quaternary nitrogen represented the nitrogen atoms in the interior of precursors of the graphene layers.
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