COLLOIDAL NATURE OF VACUUM RESIDUE

Vacuum residues from Duri, Alaska North Slope, Ratawi, Oriente and Merey crude oils are observed to be colloidal dispersions of the asphaltenes (heptane insolubles) in the other molecules that make up the vacuum residue. It is suggested that molecules in the heptane-insoluble portion self-associate, and form solid-like particles that can be distinguished from the other molecules in vacuum residue by rheological measurements. Intrinsic viscosities are measured for these colloidal particles (7-9 at 93-degrees-C). The differences in intrinsic viscosities for the various asphaltenes are small in spite of significant differences in their heteroatom content. This suggests that the heteroatoms are buried inside the colloidal particles, and therefore have only a small influence on the hydrodynamic disturbance caused by the particles in the suspending fluid.