Fundamental Understanding of Sodium Citrate in Bitumen Liberation

• Author / Creator

  Xiang, Bailin

• In the traditional water-based extraction process, sodium hydroxide (NaOH) is a commonly used chemical aid to improve bitumen recovery from oil sands. Recently, sodium citrate (Na3Cit) was applied as a secondary process aid together with NaOH by Syncrude Canada Ltd. in the water-based extraction process. The combined addition of Na3Cit and NaOH was found significantly enhanced bitumen recovery compared to applying NaOH individually. The underlying mechanism of such enhancement remains to be further understood. As one of the essential steps in the water-based extraction process, bitumen liberation is believed to be influenced by the addition of Na3Cit, thereby contributed to the enhanced bitumen recovery. In this thesis, the roles of Na3Cit in the bitumen liberation and its effect on solid wettability alternation were investigated. Theoretical models were applied to describe the bitumen recession process in the presence of Na3Cit and calcium ions (Ca2+) in alkaline solutions.
  In contrast to the visualization techniques used in the previous research, bitumen liberation was quantified for the first time using a quartz crystal microbalance with dissipation (QCM-D). Bitumen was spin-coated on the silica sensors to simulate the oil sands and then exposed to aqueous solution for bitumen liberation. The effects of various operation conditions (such as solid wettability, solution pH, and temperature) on bitumen liberation were analyzed by QCM-D, which proved the feasibility of studying bitumen liberation through QCM-D. The synergetic effect of Na3Cit and NaOH on the bitumen liberation process was investigated using QCM-D in the presence of Na3Cit and NaOH, respectively and in combination. The highest degree of bitumen liberation (DBL) was observed with the combined addition of Na3Cit and NaOH.
  Bitumen recession from quartz surfaces was studied in the presence and absence of Ca2+ and Na3Cit. The dynamic displacements of bitumen from quartz surfaces were recorded by the video camera and analyzed by hydrodynamic and molecular kinetic models. At pH 8.5 and 45 ºC, the addition of Ca2+ slowed down the three-phase contact line (TPCL) movement. Model fittings suggested that the viscous resistance and contact line friction increased in the presence of Ca2+. In contrast, the presence of Na3Cit accelerated the bitumen displacement rate and generated smaller static water contact angles on the quartz surfaces. Both viscous resistance and contact line friction decreased with increasing the concentration of Na3Cit.
  The effect of Na3Cit on solid wettability alternation was investigated through QCM-D and contact angle measurements. The alumina sensors were applied to simulate the alumina components contained in clay minerals from oil sands. It was found that adsorption of naphthenic acids (nature surfactants from bitumen) on alumina surfaces induced an increase of surface hydrophobicity. However, the addition of Na3Cit prevented the adsorption of naphthenic acids in both cases with and without Ca2+. Therefore, the alumina surfaces remained hydrophilic in the presence of Na3Cit.
  The benefits of Na3Cit in the bitumen liberation process and the solid wettability were attributed to its ability to modify the interfacial properties, including zeta potential and interfacial tension in this complex system. Increased negative charges were observed not only on bitumen surfaces but also on silica and alumina surfaces in the presence of Na3Cit under alkaline conditions, which led to stronger repulsions between bitumen and those solids. Moreover, adding Na3Cit decreased the adhesive force between bitumen and silica, as indicated by atomic force microscope measurement. On the other hand, the bitumen-water interfacial tension was slightly reduced by Na3Cit, which promoted the bitumen detachment processes. Due to a strong affinity of Na3Cit to alumina surfaces, Na3Cit preferably adsorbed on alumina surfaces and prevented the adsorption of naphthenic acids. Besides, Ca2+ was chelated by Na3Cit, which reduced Ca2+ concentration and counterbalanced its detrimental effects on bitumen liberation.

• Subjects / Keywords

  • QCM-D
  • Sodium citrate
  • Bitumen liberation

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-2p1f-s661

• 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.