Abstract
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℃/min up to 1150℃ with nitrogen as purge gas. Meanwhile, the pyrolysis-gas chromatograph-mass spectrometry experiments were performed on parallel samples of Chang-7 oil shale sample at 20℃/min in the four temperature sections, ranging from 100 to 700℃ to understand the decomposition mechanism. The initial decomposition temperature and the final decomposition temperature of hydrocarbonaceous material were about 367℃ and 521℃ (average values), respectively, which raised with the increase of heating rate. The decomposition of pyrite began to take place over 500℃, 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℃ 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℃, representing the rearrangement of kerogen molecules in the temperature range of 100–350℃. 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.
Highlights
With the decline in new discoveries of conventional reservoirs and the shortage of conventional energy resources, searching potential petroleum alternative energy has been the focus of many countries
According to the the weight loss (TG) and differential thermogravimetric (DTG) data, the decomposition temperature scale of C7 oil shale was divided into four sections, A1 (100–387C), A2 (387–472C), A3 (472–536C) and A4 (536–700C)
The pyrolysis mechanism of C7 oil shale was identified through Thermogravimetric analysis (TGA) and Py-GC-mass spectrometry (MS) experiments
Summary
With the decline in new discoveries of conventional reservoirs and the shortage of conventional energy resources, searching potential petroleum alternative energy has been the focus of many countries. Chang-7 section oil shale sample of Ordos Basin, was pyrolysed in a TGA in relation to heating rate and temperature. Based on the pyrolysis experiment, we analyzed the influence of heating rate and pyrolysis temperature on the Chang-7 section oil shale and investigated the composition of pyrolysates using pyrolysis-gas chromatograph-mass spectrometry (Py-GC-MS) apparatus in four temperature sections (100–387C, 387–472C, 472–536C and 536–700C) at constant heating rate (20C/min). After the pyrolysates were swept into the GC injector with He as carrier gas (1.2 ml/min) for GC–MS system analyzing, the sample cup was pulled out of the quartz tube to await pyrolysis at the step to avoid further degradation of samples while the GC–MS analysis is underway. The measurement methods and conditions were similar to the first step but the heating temperature ranges were 387–472C, 472–536C, 536–700C, respectively
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