Pyrolysis characteristics analysis of Chang-7 oil shale using thermal analysis and pyrolysis-gas chromatograph-mass spectrometry

摘要

There are vast resources of oil shale in the Chang-7 section of the Upper Triasic Yanchang Formation, Ordos Basin, China. They would provide secure access to transportation fuels, if utilized in an effective, economic and environmental manner. A Chang-7 oil shale sample containing pyrite has been pyrolysed in a thermogravimetric analyzer at constant heating rates of 5, 10, 20 degrees C/min up to 1150 degrees C with nitrogen as purge gas. Meanwhile, the pyrolysis-gas chromatographmass spectrometry experiments were performed on parallel samples of Chang-7 oil shale sample at 20 degrees C/min in the four temperature sections, ranging from 100 to 700 degrees C to understand the decomposition mechanism. The initial decomposition temperature and the final decomposition temperature of hydrocarbonaceous material were about 367 degrees C and 521 degrees C (average values), respectively, which raised with the increase of heating rate. The decomposition of pyrite began to take place over 500 degrees C, and the pyrolysates involving sulfur compounds are harmful to the environment and corrode the equipment. Thus, we recommended that the final temperature of Chang-7 oil shale pyrolysis was best not to exceed 550 degrees C considering the heating rate to avoid environmental pollution and damage of the instruments. Chang-7 oil shale exhibited a single stage decomposition in the range of about 367-521 degrees C, representing the rearrangement of kerogen molecules in the temperature range of 100-350 degrees C. The activation energies of kerogen decomposition were calculated using Coats-Redfern method at different heating rate. We found that both activation energy and pre-exponential factor increased with an increasing heating rate. Finally, the DTA curves of Chang-7 oil shale verified the reliability of the calculated activation energies.