UBC Theses and Dissertations
The dispersing action of polysaccharides in oil sand slurries Arinaitwe, Esau
Six carboxymethyl celluloses (CMC) of different degrees of substitution, molecular weights, and molecular weight distributions (MWDs) were researched as dispersants of oil sand slurries. The molecular weights and MWDs were determined by analytical ultracentrifugation. Viscometric studies on dilute solutions indicated semi-flexible, random coiling behavior of the polymers assuming an extended conformation in distilled water and coiled conformation in a dilute sodium chloride solution. It was found that the ionic strength, rather than pH or temperature, had the strongest effect on the intrinsic viscosity and conformation of CMC. Calculations of the persistence length and expansion factors of the polymers showed that the lowest molecular weight CMC was most flexible among the tested samples. As rheological and sedimentation tests showed, addition of CMC stabilized oil sand slurries towards aggregation and settling. All the polymers dispersed oil sand slurries by adsorbing on the solid particles and preventing mineral–mineral interactions. The molecular weight of the polymers was a more important factor than the degree of substitution in dispersing the slurries. The role of CMC was also to enhance the liberation of bitumen from solids. This role was analyzed through contact angle measurements in which it was demonstrated that all the CMC samples accelerated bitumen displacement and detachment from the illite surface. The CMC sample of the lowest molecular weight was found to be most effective in promoting bitumen displacement from the illite surface, and this action was attributed to the small effective size and high flexibility of the chain, which allowed the polymer to very closely approach the three-phase point of contact between the mineral, water, and bitumen. Wettability studies also revealed that CMC interacted very weakly with bitumen and did not permanently change the natural hydrophobicity of bitumen. Since a good rheological dispersant should not render bitumen hydrophilic and prevent bitumen extraction, the weak wetting action of CMC at the bitumen-solution interface is actually highly desirable. Overall, this dissertation demonstrated that CMC could play a significant role in improving the processability of low-grade oil sand ores, particularly since the polymer was also shown to be effective at neutral pH and low temperature.
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