Estimation of the Structural Parameter Distribution of Asphaltene Using a Preparative GPC Technique

Abstract

Vacuum residues of three kinds of asphaltenes, Iranian Light, Khafji, and Maya, were separated into 5 fractions by a preparative GPC, followed by an average structural analysis to estimate the structural parameter distribution. The H/C atomic ratio increased and carbon aromaticity (fa) decreased as the molecular weight (MW) increased up to MW of 1700 and was nearly constant at MW above 1700, while H/C + fa was constant throughout the range of MW. The parameters on the numbers of total and aromatic rings, N/C and S/C were nearly constant. The estimated formula weight of a unit was between 400 and 1200. The results suggest that asphaltene molecules can be classified into 3 types according to MW: (1) low MW molecules, consisting of a single unit, (2) moderate MW molecules, consisting of 1-2 units, and (3) high MW molecules, consisting of several units with no further enlargement of a unit size, size, which suggests polymerization or aggregation of the units.