Practices for modeling oil shale pyrolysis and kinetics

Oil shale is one of the largest, relatively undeveloped natural fossil fuel resources in the world and so an important potential source of energy. The organic matter of oil shale is present as a complex combination of carbon, hydrogen, sulfur and oxygen named kerogen. Pyrolysis-gas chromatography-mass spectroscopy affords the opportunity to chemically characterize the main structural skeleton in this kerogen and is a favorable method to study the structural characteristics of kerogen at a molecular level. The thermal degradation of oil shale kerogen is a complex chemical process, accompanied by the wide variety of products obtained, which poses difficulties in the determination of the kinetics and mechanism of pyrolysis. Understanding the kinetics of kerogen decomposition to oil is critical to design a viable retorting process. Comprehensive kinetic data are also essential for accurate mathematical modeling of various oil shale processes. Classic graphical methods cannot unambiguously measure and estimate kinetic parameters due to the mathematical complexity. Advanced isoconversion methods would be appropriate for the calculation of the distribution of activation energies for multiple reactions involved in the decomposition of complex material such as kerogen to products. The range of variability in the principal activation energy is from about 200 to 242 kJ mol(-1), with most samples being in the middle half of that range, while the range of frequency factors most likely in the 10(12)-10(16) s(-1) range, with most values within the middle half of that range. The review presents the complexity of the oil shale pyrolysis mechanism and pyrolysis kinetics along with the challenges in experimental procedures and modeling of oil shale pyrolysis kinetics.