Aromatic Structure in Asphalt Fractions

The Effect of Asphaltenes on Asphalt Viscosity

“…Greater degrees of aggregation lead to more compact shapes since, to a first approximation, only the stack height keeps increasing but not its diameter. The shape of stacks containing six aromatic sheets, which seem to be common (Yen et al, 1961(Yen et al, , 1967Ferris et al, 1967), approaches that of a sphere, as is also shown in Figure 3. Larger molecules would thus contribute increasingly less to the viscosity, and the asphaltene curve in Figure 2 would remain flat if it were not for another effect.…”

“…Rodlike or platelet structures have higher rotational friction and thus higher intrinsic viscosities than random coils of the same molecular weight. Yen et al (1961), Dickie and Yen (1967), Ferris et al (1967), and Altgelt (1970), produced evidence that asphaltenes of low molecular weight (up to about 1000) consist of single sheets of condensed aromatic and naphthenic rings to which some relatively short side chains are attached. The sheets have a diameter of about 15 A and a thickness of 3.5 A, the latter depending on the saturated hydrocarbon content.…”

“…We interpret this behavior in terms of intramolecular aggregation. Larger asphaltenes consist of several sheets of condensed ring systems connected with each other by relatively short chains or bridges (Yen et al, 1961;Ferris et al, 1967;. The nature of these bridges is uncertain and, in this context, unimportant.…”

“…Larger molecules would thus contribute increasingly less to the viscosity, and the asphaltene curve in Figure 2 would remain flat if it were not for another effect. Asphaltenes with four or more condensed ring systems are believed to aggregate in several stacks rather than just one (Dickie and Yen, 1967;Ferris et al, 1967).…”

Catalogue of Plausible Molecular Models for the Molecular Dynamics of Asphaltenes and Resins Obtained from Quantitative Molecular Representation

“…Reported molecular weights of petroleum asphaltenes range anywhere from 400 Da to 10 000 Da, although most current estimates are closer to the 800 -1500 Da average value. 27,28,29,30,31,32 In context, the larger values contributed to the proposal of molecular pictures of large asphaltenes, such as those provided by INTEVEP-Petróleos de Venezuela S. A. and investigated by researchers from the Venezuelan Institute of Scientific Research (IVIC). These were models of a "continental" morphology (similar to "island" motifs, but with a much larger PAH core).…”