An optical mechanism for detecting the whole pyrolysis process of oil shale

Pyrolysis is one of the most widely applied method for oil shale. Although an accurate exploration of the pyrolysis mechanism of oil shale is of utmost importance to optimize the pyrolysis parameters and decrease energy cost, the typically used pyrolysis techniques fail to provide comprehensive information of entire pyrolysis process. Terahertz time-domain spectroscopy (THz-TDS), a new optical method with different sensitivities to oil, water, gas, and minerals, was used to characterize the physical properties of oil shale’s pyrolysis products The confirmed collected tendency combined with the obvious turning points indicated the four stages during the pyrolysis of oil shale, which solves the acknowledgeable difficulty in identifying the organic decomposition and the mineral reaction. Water and kerogen, which highly absorbed THz waves, were volatized and then decomposed due to the continuous increasing of THz transmittance with THz signal varying by 27.9% and 18.6% from room temperature (∼22 °C) to 500 °C. In particular, the THz signal then decreased by 153%, indicating that the more sensitive calcium oxide crystals in THz range were obtained due to the decomposition of calcite. The THz results were validated by the combination of the material analysis techniques, including thermogravimetric analysis, mass spectrometry, scanning electron microscopy, and energy-dispersive spectrometry. The results proved the ability of this spectroscopic technique to be applied in the key detection of oil shale in the petroleum industry.