Water-mediated adhesion of oil sands on solid surfaces at low temperature

Abstract

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 in-land transportation. Here we report that water content determines the adhesion strength of oil sands on solid surfaces at temperature of -2.5 ◦C to -20 ◦C. Our measurements by X-ray micro-computed tomography revealed that water forms 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. We experimentally measured the minimal force required to push the frozen oil sands off the substrate and identified that the adhesion strength increased linearly with water content from 4% to 14% 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. We also found an effective method to reduce the adhesion of oil sands by spraying a little amount of anti-freezing liquid on the substrate. Our approach 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 our work may have wide applicability to many natural/industrial processes, such as soil formation, food processing, and porous structures in ice crystal-templating nanomaterials synthesis by freezing-drying.

General mechanism and mitigation for strong adhesion of frozen oil sands on solid substrates

“…Oil sands sample (Imperial Oil, Canada) was homogenized under ambient condition and stored in sealed plastic bags at -18 • C, as reported in our previous work. 18 The oil sands samples used in this study naturally contained 4 wt% of water, 13 wt% of bitumen and 83 wt% of solids. 18 To prevent evaporation of water, the vessel containing the homogenized oil sands were sealed with paraffin films till the samples were fully unfrozen before each measurements.…”

“…18 The oil sands samples used in this study naturally contained 4 wt% of water, 13 wt% of bitumen and 83 wt% of solids. 18 To prevent evaporation of water, the vessel containing the homogenized oil sands were sealed with paraffin films till the samples were fully unfrozen before each measurements.…”

“…The fabrication of oil sands with C w higher than 4 wt% was described in our previous work. 18 After removing the excess oil sands not touching the substrate, the coated substrate was placed in a freezer at a temperature of -10 • C for 1 hr. To avoid contamination and eliminate the variation in water content of the oil sands layer, the coated substrate was wrapped in a paraffin film before being placed in the freezer.…”

“…16,17 We recently showed that at temperatures below the freezing point of water, the adhesion of oil sands increases rapidly, and the adhesion strength of oil sands is strongly correlated to the water content. 18 However, the effects from substrate properties and from the load sustained by the oil sands on the adhesion strength on solid substrates remain unclear.…”

“…22 The volume of the void space depends on the water contents, which can reach 25 v% for oil sands with 4 wt% of water under 0.06 M P a of load. 18 With increasing load, the volume of the void spaces in the matrix would be lower. 21,23 In this work, we show that the adhesion of oil sands resembles the adhesion behavior of ice on the same kind of substrates, for both hard substrates (with Young's modulus on the order of GP a) and soft substrates (Young's modulus on the order of M P a).…”