The interfacial activity of asphaltenes, naphthenic acids, and naphthenates has been amply studied in the literature, as they are involved in the formation and stabilization of bitumen and heavy crude oil emulsions. While most of the literature evaluates one component at a time, in this work these bitumen components were separated one at a time from Athabasca bitumen, and the surface activity of the resulting fraction was evaluated as a function of pH, solvent aromaticity (heptane/toluene mixtures, known as heptol, at volume ratios 50/50 and 80/20), and temperature for selected systems. The interfacial activity was evaluated in two ways: via dynamic interfacial tension during adsorption on a bitumen drop of constant volume, and via dynamic interfacial tension during drop volume cycling. The adsorption data were interpreted using a model that combined multicomponent adsorption kinetics inspired by Langmuir-Freundlich kinetics with the Fainerman surface equation of state. The volume cycling experiments were interpreted using the compression relaxation model, which segregates adsorption/relaxation effects from elastic phenomena at interfaces. Overall, the adsorption data confirmed that naphthenic acids are the fastest adsorbing species that tend to dominate the interface, but that asphaltenes adsorb, almost irreversibly, at longer time scales and likely forming a sublayer previously proposed in the literature. The dilatational elasticity of the interface seems to be highly influenced by that asphaltene sublayer, which softens at high pH at room temperature, or at 80 C independently of the pH of the system. 642 J Surfact Deterg J Surfact Deterg (2020) 23: 641-659 643 J Surfact Deterg J Surfact Deterg (2020) 23: 641-659 N.C., not calculated; N.O., not observed. Green to red is a desirable to non-desirable scale. 646 J Surfact Deterg J Surfact Deterg (2020) 23: 641-659
Bitumen froth is a water-in-bitumen emulsion (∼30 wt % water, 60 wt % bitumen, and 10 wt % of solids) stream obtained during the water-based extraction process of mined oil sands. The separation of water (to 2 wt % or less) and solids (to 0.5 wt % or less) from the froth is necessary to prevent corrosion, catalyst deactivation, and fouling in downstream processes. In naphthenic froth treatment (NFT), aromatic naphtha is added to reduce the density and viscosity of bitumen to aid in this separation, which often requires the addition of demulsifiers and centrifugation. This work looks at simulating the dewatering of froth using a bench-scale mixer and heptol 80/20 (80 vol % heptane; 20 vol % toluene) as a simulated naphtha solvent. Power dissipation during mixing, water contents, image analysis of micrographs, and acoustic spectroscopy were used to examine the dewatering process as a function of time for three froth samples with different compositions. Gravity drainage, in the absence of additives, led to a residual water content, after 2 h, ranging from 1.7 to 3.7 wt % for the three different samples, consistent with the typical residual water reported for these systems. Micrographs of the diluted froth show the eventual disappearance of large water drops and the prevalence of smaller emulsified drops (<10 μm) in the residual water. An examination of this residual water using acoustic spectroscopy showed that up to 0.8 wt % water is in the form of ∼0.3 μm submicron drops that cannot be removed by gravity or centrifugation. A dewatering model using an initial drop size distribution (DSD) of water drops also supports the existence of a substantial amount of submicron drops. A low-shear dewatering test suggests that most of this submicron water was in the froth before simulated froth treatment, formed potentially during bitumen extraction and transportation, prior to solvent dilution and dewatering. Cryo-SEM imaging further supports this hypothesis. Studies of water solubilization in toluene–asphaltene and toluene–naphthenic acid systems suggest that up to 0.5 wt % of this submicron water could be originated from water–asphaltene association. The presence of high solid contents in the froth correlated with high residual water and submicron water contents, pointing to the potential role of solids in the formation of submicron drops.
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