Water-mediated adhesion of oil sands on solid surfaces at low temperature and possible solutions to mitigate adhesion
Creators: Yang, Qimeng
Publisher: name: University of Alberta Library
Year: 2022

<p>Adhesion of frozen granular materials on solid surfaces creates various problems for surface cleaning, reduces the carrying capacity of vehicles, and increases energy consumption for inland transportation. Here in the first part of this thesis, water content demonstrates to determine the adhesion strength of oil sands (a complex granular matter) on solid surfaces at temperature of -2.5 ◦C to -20 ◦C. Measurements by X-ray micro-computed tomography revealed that water formed capillary bridges between the sand particles and the solid substrate and more air gaps at the interface between oil sands and the substrate are filled with interstitial water at a higher content. The minimal force required to push the frozen oil sands off the substrate was experimentally measured and the adhesion strength was identified to increase linearly with water content from 4 to 14 wt% on both rubber and steel substrate. For short freezing time at a fixed water content, lowering the temperature increased the adhesion strength on the steel substrate. Fouling from a layer of bitumen or asphaltenes aggravated the adhesion of oil sands on steel. A theoretical model was proposed to rationalize the linear relationship between water content and the adhesion strength, based on the contact area between ice and the substrate.</p>

<p>In the second main part of this thesis, the adhesion behavior of oil sands under more complicated conditions was studied. The dependence of the adhesion of oil sands on hydrophobicity and softness of the substrates was found to follow the same trend as the ice adhesion strength on both hard and soft substrates. The adhesion strength of oil sands was directly proportional to the ice adhesion strength on the substrate, confirming the significance of ice to the adhesion of frozen granular matrix. Furthermore, the adhesion of oilsands on the substrate was found to increase with the load on the oilsands up to a plateau. The increase of adhesion strength with the load was attributed to the increase in water/ice contact area with the substrate under a higher load, and the plateau in adhesion strength may be explained by the fact that the void space in the oil sands granular matrix was limited by the packing mode.</p>

<p>Finally, the performance of various types of liquids including aqueous ethylene glycol solution as anti-freezing liquid by spraying each liquid on a target substrate was evaluated. We first established a simple method to spray coat a little amount of pure ethylene glycol on the substrate to dramatically decrease the oil sands adhesion strength. More types of the anti-freezing liquids were tested after we found the strategy worked well in reducing the oil sands adhesion. Also, the sprayed droplets were found to stay stable with time and under shearing force. The strategy of spraying anti-freezing liquids was proven to be applicable for the industrial scale as well. The approach proposed in this thesis work may reduce the energy consumption in transport and processing of wet granular materials, and potentially save manpower and the cost from cleaning in industrial operations. The insight from this thesis work may have wide applicability to many natural and industrial processes, such as soil formation, food processing and storage, and porous structures in ice crystal-templating nanomaterials synthesis by freezing-drying.</p>