Thermal and clay catalysed cracking in the formation of natural gas

Abstract

The rates of formation and isotopic compositions of the gaseous hydrocarbons produced by the pyrolysis at 400(DEGREES)C and 500(DEGREES)C of n-octadecane both alone and in the presence of several natural clay catalysts have been studied to investigate the mechanisms of hydrocarbon cracking, and assess the importance of clay catalysis in natural gas formation. In the thermal cracking of octadecane, the carbon isotopic fractionation, compared to the starting material, of the gaseous hydrocarbons decreased with increasing hydrocarbon size. However, this effect could not be explained by dilution of a uniform carbon-carbon bond cleavage isotope effect, by carbon atoms in ethane and higher hydrocarbons not involved in bond cleavage. An explanation has been proposed for the fact that the isotope effect for carbon bond cleavage, in fact, decreases with the size of the hydrocarbon being cleaved from the starting material. ...