Type I kerogen-rich oil shale from the Democratic Republic of the Congo: mineralogical description and pyrolysis kinetics

Abstract

Abstract The Democratic Republic of the Congo holds important reserves of oil shale which is still under geological status. Herein, the characterization and pyrolysis kinetics of type I kerogen-rich oil shale of the western Central Kongo (CK) were investigated. X-ray diffraction, Fourier-transform infrared spectroscopy and thermal analysis (TG/DTA) showed that CK oil shale exhibits a siliceous mineral matrix with a consistent organic matter rich in aliphatic chains. The pyrolysis behavior of kerogen revealed the presence of a single mass loss between 300 and 550 °C, estimated at 12.5% and attributed to the oil production stage. Non-isothermal kinetics was performed by determining the activation energy using the iterative isoconversional model-free methods and exhibits a constant value with E = 211.5 ± 4.7 kJ mol−1. The most probable kinetic model describing the kerogen pyrolysis mechanism was obtained using the Coats–Redfern and Arrhenius plot methods. The results showed a unique kinetic triplet confirming the nature of kerogen, predominantly type I and reinforcing the previously reported geochemical characteristics of the CK oil shale. Besides, the calculation of thermodynamic parameters (ΔH*, ΔS* and ΔG*) corresponding to the pyrolysis of type I kerogen revealed that the process is non-spontaneous, in agreement with DTA experiments.