Molecular Size and Structure of Asphaltenes from Various Sources

TLDR

Fluorescence depolarization was employed to measure the sizes of asphaltene and model compounds. Asphaltenes exhibit mean molecular weights of ~750 amu (range 500–1000 amu), with size correlated to fused ring count (typically one or two rings), showing subtle variations among crude oil and vacuum resid sources, smaller sizes for coal-derived asphaltenes, and a continuous size distribution overlapping resins.

Abstract

Fluorescence depolarization measurements are used to determine the size of asphaltene molecules and of model compounds for comparison. Mean molecular weights of roughly 750 amu with a range of roughly 500−1000 amu are found for petroleum asphaltenes. A strong correlation is established between the size of an individual fused ring system in an asphaltene molecule and the overall size of this corresponding molecule, showing that asphaltene molecules have one or perhaps two fused ring systems per molecule. Subtle differences in molecular size are found for different virgin crude oil asphaltenes and for a vacuum resid asphaltene. Coal asphaltene molecules are found to be much smaller than petroleum asphaltenes. The molecular sizes of resins and asphaltenes are found to form a continuous distribution.