Non-isothermal thermogravimetric analysis of pyrolysis kinetics of four oil shales using Sestak-Berggren method

In this study, the non-isothermal pyrolysis method was used to investigate the pyrolysis characteristics of oil shale from four areas: namely Nongan, Fuyu, Mongolia, and North Korea, with special emphasis on Fuyu oil shale. X-ray diffraction was performed to determine the mineral composition of the oil shale. The pyrolysis behaviours of the oil shale at different heating rates were determined by thermogravimetric analysis and differential thermogravimetric analysis. During pyrolysis, as the heating rate increased, the oil shale reaction zone moved to a higher temperature due to thermal hysteresis. The activation energies of the oil shale samples from four areas were obtained by the Flynn-Wall-Ozawa (FWO), Starink, and Friedman methods. The results showed that the activation energy was not stable throughout the conversion stage, and the overall trend showed an increase with an increase in temperature. The average activation energy in the second stage was 304, 307, and 342kJmol(-1) for Fuyu oil shale; 328, 333, and 348kJmol(-1) for Nongan oil shale; 341, 347, and 422kJmol(-1) for North Korea oil shale; and 362, 363, and 379kJmol(-1) for Mongolia oil shale by the FWO, Starink, and Friedman methods, respectively. The fluctuation of activation energy showed that thermal degradation in oil shale was a complicated multistep reaction, regardless of the area. The quality and characteristics of organic matter and mineral impacted the pyrolysis process and kinetic characteristics. The Sestak-Berggren method was used to fit the data from oil shale pyrolysis. The results indicated that the main mass loss phase of oil shale pyrolysis was controlled by a nucleation mechanism.