Characteristics of Estonian Oil Shale Kerogen and Its Pyrolysates with Thermal Bitumen as a Pyrolytic Intermediate
2017
Shi, Jian | Ma, Yue | Li, Shuyuan | Wu, Jianxun | Zhu, Yukai | Teng, Jinsheng
Preparation and collection of thermal bitumen, a pyrolytic intermediate, are key factors in elucidating the mechanism of oil shale pyrolysis. Electron paramagnetic resonance (EPR), gas chromatography, Fourier transform infrared spectrophotometry, nuclear magnetic resonance (NMR) spectrometry, distortionless enhancement by polarization transfer (DEPT), and X-ray photoelectron spectroscopy were employed to investigate the thermochemical transformation in oil shale pyrolysis. Results showed that thermal bitumen was continuously generated and decomposed during the pyrolysis process. The maximum yield of thermal bitumen at 380 °C was 11.17%. EPR analysis showed that the g factor of kerogen and the pyrolysates was slightly higher than 2 and increased as pyrolysis progressed because of the aromatization of saturates and decarboxylation. CO₂ and CO were mainly generated at temperatures lower than 340 °C, and less was obtained in the subsequent pyrolysis process. In contrast, C₂–C₅ organic gases were mainly generated at temperatures higher than 340 °C. NMR and DEPT analyses indicated that kerogen, thermal bitumen, and shale oil were mainly composed of aliphatic structures. During the pyrolysis process, aliphatic structures were constantly transformed into aromatic compounds, which were easily retained in shale oil and semi-coke. Pyrrolic, pyridinic, and quaternary compounds constituted 80% of the nitrogen compounds in kerogen and the pyrolysates. The sulfoxide content of thermal bitumen and semi-coke was considerably higher than that of kerogen, indicating that sulfoxide compounds present better thermostability during the pyrolysis process.
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