Depolarized Light Scattering for Study of Heavy Oil and Mesophase Formation Mechanisms

Mesophase formation in heavy oil fractions during thermal cracking was studied by a depolarized light scattering technique using a high temperature/high pressure stirred hot-stage reactor. The advantage of this technique relies on its ability to track the ordering of components at the molecular and nanoscale prior to the onset of observable mesophase. A mechanism for mesophase formation in pitches has been suggested based on the evaluation of the previous models for mesophase formation with the scattering results. The results suggest that mesophase formation does not follow a typical phase separation or nucleation process but instead is a result of the homogeneous self-assembly of planar aromatic molecules into clusters and finally spherical submicrometer domains that coalesce to form the final texture of micrometer-scale mesophase spheres. The scattering behavior of asphaltenes suggests that this material is more aggregated than the maltenes, at temperatures up to 350 degrees C. This new technique can be used in conjunction with traditional hot-stage microscopy to study the mechanisms of mesophase formation and predict the onset of mesophase formation during the cracking of heavy oil.