Behaviour of model substrates in catalytic hydropyrolysis to investigate preservation of biomarkers released from kerogens and asphaltenes

To study the extent of cracking and isomerization undergone by n-alkanes and steranes upon formation from specific functionalities, a series of hydropyrolysis tests were conducted on stearic acid, oleic acid, and 5-β cholanic acid, together with cholesterol bound to a phenolic group via an ether link. Selectivities for hydrogenating aliphatic carboxylic acids to the corresponding alkanes were extremely high with > 90% being achieved for stearic acid 5-β cholanic acid. Hydrocracking and isomerization were negligible for single functionalized steranes. However, complex formation with surface oxygen functional groups for both the carboxylic acids and asphaltenes was a contributory factor to not achieving higher conversions until temperatures in excess of 500°C. Ether bonds did not start to cleave until 350°C indicating that biomarkers released at lower temperatures from S-rich kerogens arise from cleaving sulfides only.