Elizabeth M. Lown

The molecular structure of asphaltene: an unfolding story

Abstract From detailed chemical and thermal degradation studies, a host of structural units have been identified in Alberta asphaltenes. It has been shown that the extent of aromatic condensation is low and that highly condensed pericyclic aromatic structures are present in very low concentrations. From the available data reported to date, it is concluded that petroleum asphaltenes were mainly derived through the catalytic cyclization, aromatization and condensation of n -alkanoic, probably fatty acids, precursors.

Rate Constants for Silylene Reactions

It is only since 1985 that the absolute rate constanss have been measured for some reactions of divalent silylene species. In this article the absolute rate constant data reported to date for the reactions of SiH2, SiMe2, SiMePh, SiHCl, SiCl2, SiF2 and SiBr2 are reviewed and, where possible, mechanistic pathways discussed. The reactivity of silylenes is, in general, much higher than had previously been estimated on the basis of relative rate studies.

Structural features of Athabasca bitumen related to upgrading performance

Using a combination of instrumental and chemical methods, many new classes of compounds appearing as homologous series have been detected in Athabasca oil sand bitumen and in the chemical and thermal degradative products of asphaltene and the heavy ends of maltene. In general, the volatile portion of the maltene is rich in cyclic terpenoid structures and devoid in aliphatic compounds or normal alkane-derived cyclic molecules while the asphaltene fraction and heavy ends of maltene are abundant in normal alkyl-substituted aromatics, thianes, thiolanes, thiophenes, benzo- and dibenzothiophenes. This paper reports that Ru(VIII)-catalyzed oxidation permitted the quantitative estimation of the n-alkyl groups attached to aromatic carbons and of n-alkyl bridges between two aromatic units and their concentration distribution according to chain length. It also showed the presence of a large naphthenic core containing cyclic sulfides, which, during oxidation, were converted to their sulfones.