Multi-scale evaluation of surfactant effects on asphalt desorption behavior from oil sand surfaces

Abstract

This study created a hydrophobic oil sand model to investigate the impact of surfactants on the desorption behavior of asphalt from solid surface. Cationic surfactant cetyl trimethyl ammonium bromide (CTAB) and anionic surfactant sodium dodecyl benzene sulfonate (SDBS) were used to soak the model to observe the effect of surfactants on asphalt desorption. The effect of surfactant pretreatment on the wettability of the substrate was evaluated by measuring the contact angle of ultrapure water on the substrate and observing the morphological changes of the solid surface by atomic force microscopy. The results show that the contact angle of the model treated with SDBS decreases to 10° after 3 days, which significantly improves the wettability of the substrate surface and promotes the desorption of asphalt. However, CTAB has no obvious effect on asphalt desorption. The standard deviation of the gray value of the sand surface image is significantly reduced to 38.693 after the SDBS treatment, which can be seen by binarizing the image. This suggests that the asphalt and solution are evenly distributed and that there is hardly any discernible boundary. Nevertheless, neither of the two surfactants can improve the water-based extraction efficiency of oil sands after soaking treatment. The asphalt yield is <5 % after 30 days of pretreatment with CTAB solution, while only 45 % asphalt yield is obtained after 30 days of pretreatment with SDBS solution. Despite these variations, the quality of asphalt foam remains relatively the same. This may be related to the failure of surfactants to improve the surface wettability of hydrophobic sand. Therefore, the surface wettability of the sand is considered to be a key factor affecting the asphalt desorption and final yield. This study can provide a scientific basis for oil sand recovery to a certain extent.