Additional structural details on Athabasca asphaltene and their ramifications

After some general comments on the concept of asphaltene, outstanding probl ems relating to the molecular structure of Athabasca asphaltene are discuss ed in light of new results on aromatic-attached appendages derived from rut henium-ions-catalyzed oxidation (RICO). Detected were homologous series of or-branched C-1-C-4 n-alkyl side chains up to C-30-C-40 in an aggregate amo unt of similar to 10% of the n-alkyl side chains, C-15-C-20 regular isopren oids, C-20-C-28 cheilanthanes, C-27-C-32 hopanes, C-27-C-29 steranes, C-21- C-24 pregnanes, and a number of branched hydrocarbons giving hydroxy carbox ylic acids. The nature and distribution of these aromatic-attached biomarke rs are similar but not identical to those reported to be attached to the as phaltene via a sulfide bridge. They may have originated from secondary biot ic sources and became incorporated into the asphaltene via a Friedel-Crafts -type reaction. Additional, previously not considered reactions in the RICO of asphaltene are described, and aspects of the analytical procedures are reviewed. Also, a new protocol minimizing losses due to separations and vol atility is discussed. Further structural elements of the asphaltene molecul e were identified in the polar fraction of the asphaltene pyrolysis oil, in cluding alkylpyridines and -quinolines, n-alkanoic/alkenoic acids, n-alkyla mides (tentative), and n-alcohols. All straight-chain species were dominate d by even carbon members. It is shown that contrary to recent erroneous sug gestions in the literature, pericondensed aromatic units play a very minor role in the molecular structure of petroleum asphaltene.