Laboratory models for aromatization and isomerization of hydrocarbons in sedimentary basins

Abstract

With increasing depth in the Earth's crust, changes take place in the sedimentary distributions of aromatic steroid hydrocarbons and of stereoisomers of certain types of alkanes1,2. The changes occur before and during the early stages of hydrocarbon generation and have been interpreted as resulting from aromatization and configurational isomerization reactions respectively3. We have now brought about an aromatization reaction and an isomerization reaction in the laboratory under free radical conditions, sulphur being chosen as a convenient source of radicals, and have extracted rate constants from the absolute concentration–time functions of the organic substrates. The activation energies and pre-exponential factors were then deduced from the temperature dependence of the rate coefficients. The values of these activation parameters show that, in the laboratory, the aromatization is more temperature dependent than the isomerization reaction, as suggested previously from the distributions of steroidal compounds in sedimentary basins3–5.