Demulsification Mechanism of Asphaltene Model Compounds- or Bitumen- Stabilized Emulsions by EO-PO Copolymers

• Author / Creator

  Niu, Zhen

• The formation of stable water-in-oil (W/O) emulsions in the oil sands industry is highly undesirable because it poses great threats to the downstream operations, such as downstream upgrader corrosion, catalyst fouling, increased pumping cost, etc. To break the stable emulsions and to assist the separation of water from diluted bitumen, ethylene oxide-propylene oxide (EO-PO) polymeric demulsifiers are widely used. Understanding factors that affect emulsion stability and the role played by the demulsifiers in demulsification is of considerable importance to the oil industry. However, studying molecular mechanisms of stabilizing or destabilizing water-in-heavy oil emulsions is challenging due to the non-transparent nature of crude oil or bitumen even in diluted systems, as most measurements are based on visualization of the experimental systems. In comparison, measurement of interfacial properties using the oil-in-water (O/W) system is much easier, which is often practiced.
  We aim to uncover the relationship between the measured interfacial properties of W/O and O/W systems using asphaltene model compounds C5Pe or C5PeC11, as their solutions have better optical transparency. The measured interfacial tension of the W/O system was always lower than that of the O/W system, indicating a larger amount of surface-active components adsorbed at the oil−water interface in W/O systems. The different amount of surface-active components adsorbed due to the reservoir effect (more C5Pe molecules are available for adsorption when oil is used as the continuous phase) affected the arrangement of molecules at the interface and hence the measured crumpling ratio, dilatational rheology, and coalescence time that could not be observed using flat oil−water interfaces. Although similar trends were observed in most situations, the O/W configuration could only give qualitative results for the W/O system.
  The features of the W/O and O/W systems were also investigated when demulsifier is introduced. Specifically, the effect of the EO-PO demulsifier on the interfacial properties of the asphaltene model compounds C5Pe or C5PeC11 in xylene solution−water interface was studied, with the aim to understand the demulsification mechanism and investigate whether the EO-PO demulsifier could work similarly through adsorption replacement (the W/O system) and competitive adsorption (the O/W system). It was found the surface active EO-PO molecules could decrease the interfacial tension and interfacial film rigidity of the C5Pe/C5PeC11−water interface for both W/O and O/W systems. Interfacial pressure-area isotherm, AFM imaging, and shear rheology measurements were also carried out using diffusion (simulating adsorption displacement in the W/O system) and spreading (simulating competitive adsorption in the O/W system) protocols. The results confirmed that C5Pe molecules were responsible for the high interfacial film rigidity and the EO-PO demulsifier was able to destroy or avoid the formation of the C5Pe network interfacial film. Molecular dynamics simulation revealed that EO-PO molecules were more competitive for the interface and could replace most of the adsorbed C5Pe molecules, which made the interfacial film unstable. In addition, the adsorbed EO-PO molecules could form a new barrier at the interface, which inhibited the adsorption of the C5Pe molecules.
  The demulsification performance of the EO-PO demulsifier on the water-in-diluted bitumen emulsions at elevated temperatures was investigated, while the reversed O/W emulsion systems were used for characterizing interfacial properties. Generally, better demulsification efficiency of the W/O emulsions by EO-PO copolymers was achieved at higher temperatures. As indicated by the interfacial tension results of the O/W system, the adsorption of the EO-PO molecules at the oil−water interface was enhanced at elevated temperatures. The droplet contraction experiment of the interfacial film using the O/W system revealed that EO-PO copolymers could significantly soften the interfacial film formed at the oil−water interface, especially at elevated temperatures. The breakage of the interfacial film was observed with Brewster angle microscopy. Overall, the enhanced EO-PO adsorption could greatly soften and even break the interfacial diluted bitumen film at the oil−water interface at high temperatures, therefore promoting the coalescence of water droplets for efficient emulsion breakup.

• Subjects / Keywords

  • EO-PO Copolymers
  • Asphaltene Model Compound
  • W/O and O/W Emulsions
  • High Temperature Demulsification

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-a5a4-kv92

• License

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