Colloidal Phenomena in Relation to Non-Aqueous Bitumen Extraction

• Author / Creator

  Mirmontazeri, Leylisadat

• The non-aqueous extraction process involves dilution of mined oil sand with an organic solvent (the “diluent”), followed by separation of unwanted materials (clays, silica sand, connate water, etc.) from the diluted bitumen. The main focus of this research is on the removal of fines solids from organic liquids, with particular emphasis on the interfacial science behind the process. Two possible scenarios were proposed for the removal of the solids: (a) through aggregation of the solids with one another (i.e. homo-aggregation), and (b) through attachment of the solids to water droplets (i.e. hetero-aggregation); both mechanism are to occur in non-aqueous environments. The study of homo-aggregation was conducted on both macroscopic and microscopic length scales; the methods of investigation were, respectively, sedimentation test and the micropipette technique. It was discovered that the inter-particle forces were strongly dependent on the aromatic content of the diluent. This, we speculate, was due to the conformations of the bituminous molecules that were adsorbed on the solid surfaces. In particular, when in an aromatic environment, the adsorbed molecules are highly extended, thus forming steric barriers which prevent aggregation of the solids (via van der Waals attraction). It was also discovered that the rate of settling of the solids was strongly correlated with the adhesive force between the particles; the latter was measured using a micro-cantilever technique that was developed for this research. For example, in a purely aromatic diluent, the inter-particle force was zero; the fine solids were stabilized and settled as individual particles. Thus, aromatic diluents are detrimental to homo-aggregation. In the study of hetero-aggregation (i.e. attachment of solids to water droplets in non-aqueous liquids), the opposite was observed: it was the aliphatic diluent that created suppression of aggregation. The reason, which we discovered in this research, was due to a “rigid skin” that was created at the oil-water interface (i.e. the water droplet surface); this was likely due to the accumulation of colloidal asphaltene precipitates at the interface. We further demonstrated that addition of sodium naphthenates (SN), a class of surfactants indigenous to bitumen, could prevent formation of the rigid skin. However, SN had also the effect of significantly lowering the oil-water interfacial tension, which in turn weakened the solid-water attachment force. We have also examined the role of aliphatic solvents in particle sedimentation. It was discovered that, although the precipitation of asphaltenes would suppress homo-aggregation of the unwanted solids, the “network” of precipitates was capable of trapping the particles, which led to their separation — albeit at a slower rate compared to that by homo-aggregation. (This study provided the first mechanistic insight into the so-called “paraffinic froth treatment” process that is widely employed in the oil sands industry.)

• Subjects / Keywords

  • Surfactants
  • Oil sands
  • Interfacial tension
  • Force measurement

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3XG9FK3X

• 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.