D.c. electrical conductivity of Green River oil shales

Abstract

The recent interest in the kinetics and mechanistic aspects of the thermal decomposition of oil shale kerogen¹ derives largely from its importance as an alternative energy source to petroleum. In spite of considerable research effort, how oil shale kerogen decomposes to gaseous and liquid hydrocarbon fuels is still not fully understood¹. The present study considers the d.c. electrical conduction behaviour of Green River oil shales. The observed trends in the electrical behaviour of these materials are correlated with a two-step decomposition model in which the rate-determining processes are shown to be (1) breakdown of an outershell polar bridge structure with an activation energy of 15 ± 2 kcal mol^–1 (180–350°C) and (2) cleavage of an inner core naphthenic structure also involving polar groups with an activation energy of 35 ± 3 kcal mol^–1 (350–500°C). These structural changes are shown to correspond to the chemical transformation of kerogen to liquid and gaseous hydrocarbons through a bitumen intermediate. Although the present data pertain to Green River oil shales in particular, the observed trend of charge transfer mechanisms in the thermal decomposition behaviour of thermally unstable materials may be indicative of how thermal and electrical properties of all solid materials in general are closely coupled. The common mechanistic origin identified in the present study for the processes of thermal decomposition and electrical conduction, offers the possibility of improving the thermal stability characteristics of a solid by appropriate changes in the electric field surrounding it.