Solids Associated with the Asphaltene Fraction of Oil Sands Bitumen

Bitumen separated from Athabasca oil sands by the hot water extraction process (HWEP) contains residual salty water and inorganic solids. Because of their strong interaction with bitumen, the solids fraction has been designated bitumen associated solids, abbreviated as BS. The major constituent of BS is ultrafine, aluminosilicate, clay crystallites. There is a minor contribution from sulfur- and titanium-bearing minerals. The surfaces of BS particles are rendered asphaltene-like owing to the adsorption of polar, aromatic, toluene-insoluble organics. Most of these solids are removed when asphaltenes are precipitated during treatment of bitumen with solvents less polar in nature than the naphtha in current use. Owing to their bi-wettable surface characteristics, the BS are likely to occur in association with water droplets in the bitumen phase. These droplets, or clusters, have an asphaltene-like exterior and exist as a stable colloidal dispersion in the maltene component of bitumen. These factors explain the intractable nature of the water and solids remaining with bitumen after conventional froth treatment by dilution with aromatic naphtha followed by centrifugation. During fluid, or delayed coking of bitumen, most of the BS are removed with the coke. However, deposition of the carbon-rich solids may also contribute to fouling in reactor systems and catalyst deactivation in catalytic hydroprocessing. Also, ultrafine BS and salt particles may themselves become entrained in the volatile overhead liquids and cause corrosion and fouling in downstream process units. Dilution of bitumen froth with a less polar solvent than naphtha reduces the overall stability of asphaltene micelles in the maltene component of bitumen. Asphaltene then co-precipitates with the inorganic particles and water to form a “rag layer”. This process yields bitumen of excellent quality, in terms of solids and water content. However, in some cases, the product losses are unacceptable relative to the conventional froth treatment approach using centrifugation. It is expected that bitumen recovery can be improved by identifying a solvent, or solvent blend, capable of selective flocculation and precipitation of the clay−water clusters while precipitating only a minor amount of asphaltene. Preliminary results show that this approach is a realistic proposition.