Three oil shale samples from different areas in Huadian have been non-isothermally pyrolysed using thermogravimetric analyzer (TGA). The analyses were performed at different heating rates (10, 20, 40, 50, 100 K min -1 ) up to 900 °C with nitrogen as purge gas. The weight loss curve showed that pyrolysis of oil shale took place mainly in the range of 200-600 °C. It was attributed to decomposition of hydrocarbonaceous material. At higher temperatures, the weight lessens due to decomposition of carbonates. On the basis of experimental data a model of pyrolysis kinetics was proposed. Kinetic parameters -activation energy (E) and frequency factor (A) -were determined by two methods: the direct Arrhenius plot method and the integral method. There was no clear relationship between activation energy and heating rate. The integral method of analysis gave lower values of activation energy than the direct Arrhenius plot method.
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.
In this study, the geochemistry data of 162 coal measure tight gas samples (77) samples from Ordos Basin, 85 samples from Sichuan Basin) is collected. Then, the carbon isotope evolution of coal measure tight sandstone gas is investigated. The result indicates that three features in carbon isotope evolution of coal measure tight gas appear. (1) The coal measure tight gas has a same feature as shale gas, that the carbon isotope of heavy gas would show a rollover with the decreasing wetness of gases. The corresponding range of gas wetness is about 2.5%~5% at which the carbon isotope of ethane begin to rollover. (2) The carbon isotope series of coal measure tight gas presents successively positive sequence, partial reversal and full reversal with increasing maturity of source rock. (3) The maturity ranges corresponding to of coal measure tight gas with the positive sequence, partial reverse and full reverse of carbon isotope are R o <2.0 %, R o =1.75~3.0% and R o >3.0% of in-situ source rock, respectively. On the bases of pyrolysis experiment of a I type of organic matter, the authors propose that the mixing between primary and cracking gas could just only cause the carbon isotope rollover of heavy hydrocarbon gases, but not cause the carbon isotopic reversal of hydrocarbon. Finally, a conclusion is suggested that carbon isotope reversal of coal measure gas has a close relationship with demethylation happening at the maturity above 3.0% R o according to published data about coal chemical structure measurement. The isotopic fractionation during the process of heavy gases formation by linkage of methyl from demethylation is one of capital factors of carbon isotopic reversal.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.