Studies on the co-pyrolysis characteristics of oil shale and spent oil shale

Co-pyrolysis of oil shale from different regions with spent oil shale from subcritical water extraction experiments is experimentally conducted using thermogravimetric analysis (TG). The mixture samples (oil shale/spent oil shale in blending ratio of 1:1) are heated from 30 up to 850 °C with heating rate of 5, 10 and 30 °C min−1, nitrogen flow rate of 30 mL min−1. Three different stages are identified based on TG curves of the mixture samples. The second stage which is due to the release of volatile matter is the primary reaction stage, and the mass loss discrepancies of the experimental and calculated TG profiles in the second stage are considered as a measurement of the interactions extent during the co-pyrolysis. The experimental mass loss of Nong’an and Fushun oil shale/spent oil shale mixture samples is higher than the calculated data, and the experimental mass loss of Huadian and Mudanjiang oil shale/spent oil shale mixture samples is lower than the calculated data. It is concluded that the interaction effect obviously occurred during the co-pyrolysis of oil shale and spent oil shale. In addition, the effect of kaoline and montmorillonite on the cracking of the kerogen is discussed according to the co-pyrolysis of kerogen and inorganic mineral. The release index of the kerogen, kerogen/kaolinite and kerogen/montmorillonite is 2.06 × 107, 4.58 × 107 and 1.89 × 107 % K−3 min−1, respectively. And the kinetic parameters of the samples are obtained by Kissinger–Akahira–Sunose method based on the thermogravimetric data, and the apparent activation energy of the kerogen, kerogen/kaolinite and kerogen/montmorillonite is 58.4, 25.7 and 95.9 kJ mol−1, respectively. According to the release index and the kinetic parameters of the samples, we can conclude that the kaolinite is helpful for the pyrolysis of kerogen and the montmorillonite inhibits the pyrolysis of kerogen.