Molecular Size and Structure of Asphaltenes

Fluorescence depolarization measurements are used to determine the size of asphaltene molecules and of model compounds for comparison. Mean molecular weights of 750 amu have been found for petroleum asphaltenes. A strong correlation is established between the size of fused rings in asphaltene molecules and the overall size of these molecules, showing that asphaltenes have one or perhaps two fused ring systems per molecule. Coal asphaltene molecules are found to be much smaller than petroleum asphaltenes.