Thermal cracking of n-octodecane and its geochemical significance.

The mechanism of carbon isotopic fractionation for gaseous hydrocarbons is revealed by investigating the residual liquid hydrocarbons in laboratory pyrolysates of n-octodecane. The results indicate that cracking and polymerization in the relatively low temperatures and disproportionation reactions leading to light hydrocarbons and polyaromatic hydrocarbons at high temperatures are probably causes for the carbon isotope reversal of gaseous hydrocarbons that is commonly observed in pyrolysis experiments. This study provides significant insight for quantitative modeling of natural gas Δ13C values and aid in the identification and assessment of natural gases derived from oil cracking. [ABSTRACT FROM AUTHOR]