Free radical transformations in the Irati oil shale due to diabase intrusion

Electron spin resonance (ESR) spectroscopy was used to evaluate the effect of a diabase intrusion on the production and decomposition of free radicals in the Irati oil shale (Paraná Basin, Brazil). Free radical concentration measurements on the stratigraphic column CERI-2 indicated that the ratio between the extent of thermal alteration on sedimentary organic matter and the intrusive thickness was 1.14. Kinetics of free radical transformation obtained from laboratory pyrolysis of Irati oil shale can be described by first-order production and decomposition reactions of distinct species. Although these species present different kinetic parameters, they are not resolved and lie inside the envelope of the “single line” ESR spectrum. The activation energies for parallel first-order production reactions of two main species of free radicals, in the temperature range of 360–420°C, were found to be 54 ± 2 kcal mol−1 and 36 ± 9 kcal mol−1.