Behavior of Bitumen-coated Fine Solids in Organic Media from Non-aqueous Extraction of Oil Sands

  • Author / Creator
    Jing Liu
  • The non-aqueous extraction (NAE) technique for recovering bitumen from oil sands ore has been proposed as a potential substitute to the conventional water-based extraction method in order to reduce the environmental and carbon footprint of extracting this natural resource. In the NAE process, bitumen was dissolved and liberated from raw oil sands ore by organic solvent. Due to high bitumen recovery and good applicability for all kinds of oil sands ores, as well as the generation of dry stackable extraction tailings, NAE has gained increasing attention from both the industry and academia. However, the fact that considerable amounts of fine solids are found in the produced bitumen makes the NAE bitumen unsuitable for the downstream operations, impeding the industrial application of NAE. Therefore, understanding the behavior of the fine solids in organic media is of fundamental and practical importance to solve the challenging issue inherent to the NAE process. It has been found that the indigenous fine solids are mainly composed of quartz and clays with the surface adhering layer of bitumen coatings. The presence of bitumen coatings renders the fine solids more hydrophobic and oleophilic, increasing the difficulty in removing the fine solids in oil media.
    In this work, surface properties of the fine solids collected from Athabasca oil sands have been systematically characterized, which shows that the bitumen coatings are heterogeneously distributed over the solid surface. Bitumen domains and mineral regions have been distinguished on the solid surface via analyzing nano-mechanical and hydrophobicity properties of sample surface. To unravel the stabilization mechanisms of fine solids with bitumen coatings, interfacial interactions between fine solids in organic solvent have been then quantitatively analyzed using the colloidal probe AFM technique, and behaviors of bitumen adsorption to silica surface in organic solvent have been analyzed using the quartz crystal microbalance with dissipation monitoring (QCM-D), respectively. It was found that bitumen coatings would fully extend and swell in cyclohexane, giving rise to the steric repulsion between the fine solids. With addition of heptane, the steric repulsion could be notably weakened by causing the shrink and collapse of the bitumen layer. Meanwhile, the adsorbed mass of bitumen coatings could be enhanced by slightly decreasing volume fraction of cyclohexane (φc) in bulk solution but could be inversely reduced if φc became smaller than the asphaltene precipitation onset. Sedimentation tests showed that the effectiveness of settling bitumen-coated silica particles was strongly associated with the interfacial interactions of fine solids and behavior of bitumen adsorption in organic media. Furthermore, a two-step agglomeration strategy has been developed to facilitate settling of the bitumen-coated silica particles by modifying their surface wettability using an amphiphilic polymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG-PEG) and introducing a small amount of water to trigger the agglomeration of the particles. The results showed that the two-step method can achieve high initial settling rate (ISR) and low content of residual solids in the supernatant simultaneously. The study of underlying interaction mechanisms revealed that PEG-PPG-PEG can favorably adsorb to the bitumen-coated silica surfaces in cyclohexane to make the surfaces more less hydrophobic, thereby altering the interactions between the particle surfaces and water drops from repulsion to attraction.
    This research work has developed useful methodologies for studying the behavior of bitumen-coated fine solids suspended in organic media and has explored a feasible strategy to destabilize such fine solids. Our results have improved the fundamental understanding of the interaction mechanisms among fine solids, bitumen, water drops and polymer additives in oil media, with important implications on developing more effective and economical strategies of removing fine solids from the NAE bitumen.

  • Subjects / Keywords
  • Graduation date
    Fall 2019
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
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