Two-step pyrolysis degradation mechanism of oil shale through comprehensive analysis of pyrolysis semi-cokes and pyrolytic gases

Despite kerogen's importance as organic matter produced from oil shale, its pyrolytic degradation mechanism remains unexplored. As the potential demand for oil shale utilization increases, identifying the physical relationship between pyrolysis degradation and temperature for kerogen becomes all the more important. Here, we determine the variation in the pyrolysis degradation of the Huadian oil shale through comprehensive analysis using terahertz spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, infrared spectroscopy, and mass spectroscopy. Through the hybrid detection of pyrolysis semi-cokes and pyrolytic gases, we provide a detailed pyrolysis model for oil shale and show that it can be used to predict the essential characteristics that are amenable to experimental validation. Kerogen in oil shale was first depolymerized into asphalt monomer. The macromolecular organic matter (OM) began to decompose and produce CO2, but the OM did not decompose into low-carbon oil and gas. As the temperature continued to rise, the asphalt monomer decomposed into shale oil and shale gas. The OM in the oil shale generated a large amount of oil and gas. Consequently, these results demonstrate the two-step pyrolysis degradation of oil shale, which provides theoretical support for underground in-situ pyrolysis technology and underground oil shale development.