Temperature and Solvent Effect on the Molecular Size and Shape of Heavy Oil Fractions

Abstract

Two kinds of heavy oil were fractionated into eight fractions by liquid–solid adsorption chromatography. The viscosity curves of relative viscosity versus concentration for dilute solutions of heavy oil fractions were determined, using the isovolume viscosity determination method. The intrinsic viscosity was obtained according to the Einstein law, and subsequently, the equivalent sphere hydrodynamic diameter was calculated. The results show that the equivalent sphere hydrodynamic diameters of heavy oil fractions are 1.1–4.0 nm under the experimental condition, while the molecular size of asphaltene is much larger than that of other fractions. The molecular size is not only related to the molecular weight but also affected by the spatial configuration of the heavy oil molecule. Different temperature and solvent conditions lead to various spatial configurations of heavy oil molecules, which results in different molecular sizes.