An electron spin resonance probe method for the understanding of petroleumasphaltene macrostructure

Molecularly, petroleum asphaltenes are induced dipoles, which agglomerate i nto nanometer-sized colloids of different aggregation states. The electron spin resonance (ESR) vanadyl probe method is used to investigate the asphal tene macrostructures under different temperatures and microwave powers. Oxo vanadium complexes native to an asphaltene isolated from Boscan crude oil, Venezuela, function as tracers to examine the behavior of micelle agglomera tes when subjected to a microwave field. Both mobile and bounded oxovanadiu m compounds in colloidal asphaltene solution are in a state of equilibrium. It is noted that a greater amount of mobile vanadyl complexes can be stabi lized in a dispersing medium (single-aromatic ring solvent series) with a h igher-valued Hansen hydrogen bonding solubility parameter. We found that co nversion of ESR vanadyl hyperfine lines occurs from anisotropic to isotropi c as the temperature of a 4% Boscan asphaltene solution in o-xylene increas ed from 25 degrees C to 100 degrees C. Free tumbling of total vanadyl compl exes in organic solvent signifies dissociation of micelles at packing imper fections prior to their release from aromatic hosts. Coupling of petroleum asphaltenes with microwave power can overcome charge transfer and charge ba lance interactions within micelle agglomerates. The relative content of mob ile to bounded vanadyl complexes in 4% Boscan asphaltene solution of o-xyle ne was found to increase with microwave power at 45 degrees C. Microwave en ergy will enable effective dispersion of colloidal asphaltene in heavy oil refining and upgrading. (C) 2000 Elsevier Science B.V. All rights reserved.