Extending Depletion Flocculation Phase Behavior Models to Partially Soluble and Aggregating Colloids—Asphaltenes

• Author / Creator

  Pouralhosseini, Sayyid S

• Mixtures of colloids + non-adsorbing polymers + good solvents are well known to exhibit multiphase behaviors that are driven by the depletion flocculation mechanism where one phase, designated a colloid gas, is largely comprised of polymer and solvent, while the other phase, designated a colloid (liquid or solid), comprises largely solvent + colloid. Qualitative aspects of this behavior are well-understood and quantitative models for the phase behavior of mono-dispersed hard-sphere particles + mono-dispersed non-adsorbing polymers in good solvents, such as the Fleer–Tuinier1 model are well established. In this work, a generalization of the Fleer–Tuinier model for cases where the fraction of colloid that is soluble in a solvent and the size distribution of colloid particles both vary with global composition is described. The impacts of temperature variation, and mean polymer size, on phase diagrams are also treated theoretically and validated experimentally. By incorporating the Ostwald–Freundlich equation, which links the size of nanoparticles to their solubility in the parameterization of the modified Fleer–Tuinier model, the number of parameters that must be identified by fitting experimental data is minimized. Envisioned applications and illustrations are drawn from the hydrocarbon energy sector where, for example, self-assembled nano-aggregates, known as asphaltenes, pose production, pipelining, and refining challenges. The solubility, mean size and size distribution of these self-assembling species are well known to be dependent on global composition. Quantitative fits to measured phase diagrams for Maya2 and Athabasca asphaltenes + polystyrene (non-adsorbing polymer) + toluene (good solvent) at 298 K at fixed polymer mean molar mass are obtained for both mixtures. Variations of the two-phase to single-phase boundaries, critical points, and tie lines with changes in temperature at fixed polymer size and with polymer mean size at fixed temperature are then predicted and the outcomes compared with data. The modeling approach, data fitting procedure, and the quality of the predictions, for these illustrative examples, are presented. The importance of these results with respect to the broader development of depletion flocculation models for applications where partially soluble and aggregating colloids arise is discussed.

• Subjects / Keywords

  • Asphaltenes
  • Flocculation
  • Non-adsorbing
  • Delpletion
  • Polymers

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3XS5JN63

• 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.