Solids associated with the asphaltene fraction of oil sands bitumen

Bitumen separated from Athabasca oil sands by the hot water extraction proc ess (HWEP) contains residual salty water and inorganic solids. Because of t heir strong interaction with bitumen, the solids fraction has been designat ed bitumen associated solids, abbreviated as BS. The major constituent of B S is ultrafine, aluminosilicate, clay crystallites. There is a minor contri bution from sulfur- and titanium-bearing minerals. The surfaces of BS parti cles are rendered asphaltene-like owing to the adsorption of polar, aromati c, toluene-insoluble organics. Most of these solids are removed when asphal tenes are precipitated during treatment of bitumen with solvents less polar in nature than the naphtha in current use. Owing to their bi-wettable surf ace characteristics, the BS are likely to occur in association with water d roplets in the bitumen phase. These droplets, or clusters, have an asphalte ne-like exterior and exist as a stable colloidal dispersion in the maltene component of bitumen. These factors explain the intractable nature of the w ater and solids remaining with bitumen after conventional froth treatment b y dilution with aromatic naphtha followed by centrifugation. During fluid, or delayed coking of bitumen, most of the BS are removed with the coke. How ever, deposition of the carbon-rich solids may also contribute to fouling i n reactor systems and catalyst deactivation in catalytic hydroprocessing. A lso, ultrafine BS and salt particles may themselves become entrained in the volatile overhead liquids and cause corrosion and fouling in downstream pr ocess units. Dilution of bitumen froth with a less polar solvent than napht ha reduces the overall stability of asphaltene micelles in the maltene comp onent of bitumen. Asphaltene then co-precipitates with the inorganic partic les and water to form a "rag layer". This process yields bitumen of excelle nt quality, in terms of solids and water content. However, in some cases, t he product losses are unacceptable relative to the conventional froth treat ment approach using centrifugation. It is expected that bitumen recovery ca n be improved by identifying a solvent, or solvent blend, capable of select ive flocculation and precipitation of the clay-water clusters while precipi tating only a minor amount of asphaltene. Preliminary results show that thi s approach. is a realistic proposition.