Molecular size and structure of asphaltenes from various sources

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 f or petroleum asphaltenes. A strong correlation is established between the s ize of an individual fused ring system in an asphaltene molecule and the ov erall size of this corresponding molecule, showing that asphaltene molecule s have one or perhaps two fused ring systems per molecule. Subtle differenc es in molecular size are found for different virgin crude oil asphaltenes a nd 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.