Temperature and pressure dependence of n-hexadecane cracking

The rates and product compositions of hexadecane cracking are reported for temperatures ranging from 300 to 370°C and pressures of 150 to 600 bar. The overall apparent activation energy at an intermediate pressure of 300–350 bar is about 74 kcal/mol. This is higher than the overall 60 kcal/mol energy consistent with higher temperature measurements, even though the rates from our highest temperatures overlap with those from earlier reports. The product composition is consistent with a free radical mechanism in which alkene intermediates react with primary and secondary radicals to form branched and normal liquid products both smaller and larger than the starting material. Pressure has a retarding effect on the rate of reaction, but the dependence is not measured precisely enough to say more than that the survival of oil is likely to vary by a factor of two or so under typical geologic conditions. A simple kinetic model having five first-order reactions is presented that predicts the lumped kinetic species of C1, C2–C4, C5–C9, C10–C15, C16, and C16+. The gas is depleted in methane compared to most natural gas.