Mesophase Formation in Heavy Oil

  • Author / Creator
    Bagheri, Seyed Reza
  • Coke formation is a major problem in the petroleum industry because of its effect on liquid yield, catalyst deactivation, and fouling of reactor internals and downstream vessels. Carbonaceous mesophase is a liquid crystalline phase which forms during cracking of heavy oil, as a subset of coke. A novel hot-stage reactor was designed and built to allow the in situ observation of mesophase formation at operating conditions of industrial reactors. The reactor was equipped with a magnetic stirrer to allow the addition of catalyst particles. The effect of cooling and depressurization on the formation and growth of carbonaceous mesophase in petroleum vacuum residue was studied using this reactor. The results showed that cooling below the cracking temperature at constant pressure can stop the formation and growth of mesophase by stopping chemical reactions. On the other hand, depressurization to atmospheric pressure, while maintaining reaction temperature, can promote the formation and growth of mesophase. The effect of stirring on mesophase formation was also investigated. Stirring can result in a bimodal distribution of size of mesophase domains in which very large mesophase regions coexist with a large number of small mesophase domains. Catalyst gives a delay in the onset of mesophase formation by its chemical activity, and a decrease in the amount of bulk mesophase regions by suppressing the coalescence of smaller mesophase domains as a physical effect. The results showed catalyst is less effective at higher catalyst concentrations due to the agglomeration of its particles. Mesophase formation was studied by a depolarized light scattering technique. 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 is a not a phase separation or nucleation process, but the homogeneous self-assembly of planer aromatic molecules into clusters and finally spherical submicron domains that coalesce to form the final micron-scale mesophase spheres. The role of asphaltenes in mesophase formation suggests that asphaltenes are a more aggregated phase in comparison to maltenes at high temperatures.

  • Subjects / Keywords
  • Graduation date
    Fall 2012
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.