Composition and origin of the aliphatic extractable hydrocarbons in the Puertollano (Spain) oil shale

Abstract

The composition of the saturated aliphatic fraction extractable from the Puertollano oil shale, the most important deposit of this material in the Iberian Peninsula, has been studied by GC and GC-MS. This fraction contained mainly n-alkanes, n-alkylcyclohexanes, and n-alkylmethylcycohexanes. The cyclohexanes showed a distribution very similar to that of n-alkanes suggesting a common origin. Contributions from higher plant derived material (mainly conifers) were apparent, based on the presence of diterpenoid compounds. An angiosperm contribution was evidenced by the presence of des-A-triterpenoid hydrocarbons, derived from oleanane and ursane skeletons. Hopanes, 8,14- secohopanes, ring-D aromatized 8,14- secohopanes, benzohopanes, a C 24 17,21- secohopane and a C 31 hexacyclic saturated hopane were found in the extracts, showing the influence of microorganisms. Different pathways are suggested for the formation of benzohopanes, and the C 31 hexacyclic hopanoid found in the extracts.