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After some general comments on the concept of asphaltene, outstanding problems relating to the molecular structure of Athabasca asphaltene are discussed in light of new results on aromaticattached appendages derived from ruthenium-ions-catalyzed oxidation (RICO). Detected were homologous series of R-branched C 1 -C 4 n-alkyl side chains up to C 30 -C 40 in an aggregate amount of ∼10% of the n-alkyl side chains, C 15 -C 20 regular isoprenoids, 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 carboxylic acids. The nature and distribution of these aromatic-attached biomarkers are similar but not identical to those reported to be attached to the asphaltene via a sulfide bridge. They may have originated from secondary biotic 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 volatility is discussed. Further structural elements of the asphaltene molecule were identified in the polar fraction of the asphaltene pyrolysis oil, including alkylpyridines and -quinolines, n-alkanoic/alkenoic acids, n-alkylamides (tentative), and n-alcohols. All straight-chain species were dominated by even carbon members. It is shown that contrary to recent erroneous suggestions in the literature, pericondensed aromatic units play a very minor role in the molecular structure of petroleum asphaltene.

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The molecular structural units of Boscan and Duri asphaltenes have been investigated in ruthenium-ion-catalyzed oxidation (RICO) and pyrolysis. From the RICO reactions, homologous series of n-alkanoic acids (C1−C31), representing aromatic-attached n-alkyl side chains, α,ω-di-n-alkanoic acids (C4−C26), representing polymethylene bridges connecting two aromatic units, and benzenecarboxylic acids, indicating the major modes of aromatic condensations in the asphaltene molecules and the minor role of pericondensed aromatic structures in them, were detected and measured. The RICO reaction also yielded a nondistillable oxidized residue. Pyrolysis of this material after methylation yielded a homologous series of n-alkanes and n-alk-1-enes, n-alkanoic and n-alkenoic acid methyl esters, and free n-alkanoic acids with strong even-to-odd carbon preference. These products prove the presence of naphthenic-attached n-alkyl side chains and bridges, polymethylene bridges connecting aromatic to naphthenic systems, and n-alkanoic acid ester/n-alkanol ether side chains attached to naphthenic carbons in the asphaltene. Among the pyrolysis products of the whole asphaltene identified were homologous series of α- and α,α-n-alkyl-substituted thiolanes and thianes, a series of dicyclic terpenoid sulfides, along with a homologous series of 1-n-alkyldibenzothiophenes. In general, the nature of the products identified were the same as those found in the asphaltenes from Alberta tar sand, carbonate bitumens, heavy oils, and some immature oils from China, but their distributions showed some variance, reflecting differences in biotic source materials, source rocks, depositional environment, and diagenetic and thermal history.

Relying on experimental and theoretical data available from the literature, it is shown that the conclusions derived from measurements of fluorescence decay and depolarization kinetic times as reported in a series of papers over the past decade (Ralston, et al. and references therein) are egregiously wrong. To start with, the decay time measurements were done with inappropriate instrumentation which resulted in misleading results. Misinterpretation of the results led to the mistaken conclusion that bichromophoric type molecules are absent from petroleum asphaltene and therefore the architecture of the asphaltene molecule features a single condensed cyclic core spiked with some alkyl chains, in spite of irrefutable chemical evidence to the contrary. It was further concluded that if the asphaltene core is a single condensed ring, then the fluorescence depolarization with rotational correlation time method is applicable for the molecular weight determination of asphaltene. This is definitely not so, since, regardless of any other considerations, asphaltene is a mixture of a plethora of different, unknown components, with unknown concentrations along with innumerable different, unknown and some known chromophores portraying widely different absorption coefficients, fluorescence quantum yields, and kinetic decay times. Consequently, asphaltene fluorescence is a highly complex function of the above attributes and as such it is a totally unsuitable property for its molecular weight determination. The injection of an incorrect, single condensed ring core architecture for asphaltene has caused some confusion in asphaltene chemistry that has now hopefully been settled.