Probing the Molecular Interactions of Asphaltenes in Organic Solvents Using a Surface Forces Apparatus

  • Author / Creator
    Natarajan, Anand
  • A fundamental understanding of the stability of water-in-bitumen emulsions stabilized by surface active agents requires a good description of the molecular interactions between the different materials in contact. Of these surface active agents, asphaltenes and oil contaminated fine solids are major contributors to a stable emulsion. In this thesis, the molecular interactions of asphaltene surfaces in model oils, toluene and heptane, were measured using a surface forces apparatus. Adsorption of asphaltenes on mica surfaces was studied to understand the interactions that can occur between crude oil components and oil-contaminated fine solids during the extraction process. The repulsive force measured between two asphaltene surfaces in toluene is attributed to steric repulsion, whereas the weak attractive force measured in heptane can be described by van der Waals forces. By fitting the measured force-distance profiles with theoretical models, the presence of secondary structures of asphaltenes in toluene was observed, stemming from the polydispersity/complexity of asphaltene molecules/aggregates. The adsorption results show that asphaltene adsorption onto mica is highly dependent on adsorption time and concentration of the solution. The adsorption process was identified to be controlled by diffusion of asphaltenes from the bulk solution to the mica surface. Ethyl Cellulose (EC) is an effective demulsifier for water-in-bitumen emulsions. The interactions between asphaltenes, mica and EC were measured to understand the molecular mechanisms involved in destabilizing water-in-bitumen emulsions. Both EC and asphaltenes were observed to irreversibly adsorb on mica surface. The repulsive interaction forces measured during approach between EC and asphaltene surfaces in toluene were shown to have a steric nature, while the adhesive force measured between them during separation are attributed to attractive bridging forces between mica surfaces. Asphaltenes were observed to physisorb on EC coated surfaces and contribute to bridging adhesion. On the other hand, EC molecules were observed to gradually displace the irreversibly coated asphaltene films from mica surface, in which the asphaltenes are pushed into globule structures or nanoaggregates. The above results provide an insight into the basic interaction mechanisms of asphaltenes in organic media and hence in crude oil and bitumen production.

  • Subjects / Keywords
  • Graduation date
    Spring 2014
  • 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.