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Effects of Diluent Addition and Mixing Conditions on Solvent Deasphalting of Bitumen Emulsions

  • Author / Creator
    Alili, Aligulu

  • Unconventional oil reserves, such as Canada’s oil sands, must replace dwindling conventional oil supplies to meet the globally increasing energy demands. Canada is home to the third largest oil reserves, primarily in the form of bitumen deposits. Unlike conventional oil, bitumen has some unique characteristics that render its extraction more challenging. As a consequence of its high asphaltene content, bitumen is substantially denser and more viscous than conventional oil, and thus, it gives rise to challenges in the forms of sedimentation, deposition, precipitation, fouling, coke formation, and catalyst deactivation in both upstream and downstream processes. By studying the effects of the solvent-to-bitumen ratio (S/B) and mixing conditions on the solvent deasphalting (SDA) of the steam-assisted gravity drainage (SAGD) extracted bitumen emulsion, the goal of this project is to support the design of a solvent deasphalting process to enhance the bitumen production and treatment processes in bitumen extraction sites. The particular objective of this study is to determine the effectiveness of the SDA process applied to bitumen emulsions produced during the SAGD process.
    The experiments of this study were performed in a bench-scale windowed reactor, in which both mixing and settling were conducted. Both batch and semi-batch experiments were performed to assess the feasibility of the process for scale-up to a larger scale continuous process. Operating temperature and pressure were kept constant at 164 ℃ and 40 bars. The effects of S/B ratio (0.9 – 2.2), mixing intensity (0.1 – 0.5 W/kg), and mixing energy (0.1 – 1.6 kJ/kg) on asphaltene precipitation and deasphalted oil (DAO) quality were studied.
    The effects of the S/B ratio on the solvent deasphalting of bitumen emulsion vary depending upon the value of the S/B ratio. Below the onset of asphaltene precipitation, no asphaltene precipitation was detected and the addition of solvent merely diluted the bitumen and slightly reduced its density and viscosity. However, above the onset value, a substantial increase in asphaltene precipitation was observed with the addition of more solvent. For the studied solvent blends, the onset of the asphaltene precipitation was found to be below 0.9 and for the S/B ratio range studied here, the optimum S/B ratio for a commercial SDA process was determined to be about 1.8.
    Almost no literature data is available regarding the impact of mixing parameters on asphaltene precipitation from bitumen emulsion upon treatment with paraffinic solvents. In the studied range of mixing intensity and mixing energy, it was revealed that the impact of changing mixing conditions on solvent deasphalting of bitumen emulsion is insignificant. Provided that a well-mixed bitumen emulsion and solvent stream has been achieved, the amount of mixing energy and mixing intensity does not perceptibly change the asphaltene precipitation yield and the deasphalted oil quality, at least for the conditions studied here.
    It was proven that settling time has a substantial impact on the asphaltene content of deasphalted oil and higher quality oil can be obtained with longer settling times. This indicates that aggregates with a wide range of diameters and densities exist in the system. Nevertheless, after the first 10 minutes of the settling process, asphaltene aggregates settling significantly drops and the change in asphaltene content of DAO samples becomes less noticeable.
    Finally, it was determined that from the perspective of a commercial-scale bitumen emulsion upgrading plant, a multistage SDA process is more favourable than a single-stage SDA with a high S/B ratio. The residence time in mixers and settlers can be significantly reduced to increase production rate and improve process economics.

  • Subjects / Keywords
  • Graduation date
    Fall 2020
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-snww-ey68
  • License
    Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.