Hot or warm water processes are used to extract bitumen from Canadian oil or tar sands. The application of these methods to the processing of tar sand deposits found in the Western United States, notably Utah, has not been commercially successful, however, because of the consolidated nature of the deposits and the high viscosity of the bitumen. It is demonstrated here that a previously developed method employing ionic liquids (ILs) together with a nonpolar solvent such as toluene can effect a separation at ambient temperatures (∼25 °C), although with greater difficulty than Canadian oil sands. Essentially, a multiphase system consisting of a sand and clay slurry, an ionic liquid layer, and an organic layer containing the bitumen can be formed by simply mixing the components. More than 90% of the bitumen is released from the sand, but only in successive extractions. Water is not used in this stage of the separation, but relatively small amounts are used to separate entrained IL from the sand and clays.
Previous work in this laboratory has shown that bitumen and oil can be readily separated from sand, using ionic liquids at ambient temperatures. To probe the mechanism underlying the relative ease of separation, atomic force microscopy (AFM) has been used to study interaction forces and adhesion between bitumen surfaces and a silica probe in the presence of liquid media. The energy of adhesion between bitumen samples obtained from both Canadian and U.S. oil sands are approximately an order of magnitude smaller in an ionic liquid medium than in aqueous solution. This behavior was traced to the ability of ionic liquids to form layered charge structures on surfaces. Although interactions between the silica probe and an aged crude oil sample could not be determined, because the probe adhesion to the oil film exceeded the force capacity of the AFM, thermodynamic considerations indicate that the energy of separation of silica from aged oil is also significantly smaller in an ionic liquid medium than in aqueous solution.
Athabasca oil sands are complex and heterogeneous, consisting of sand, fines (mainly clays, defined as particles less than 44 μm in size), bitumen, and water. High-grade ores usually have higher bitumen contents and lower fines contents than low-grade ores and are more easily processed to give a high yield of bitumen, although factors such as weathering and oxidation are also important. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]
It is demonstrated that bitumen can be separated from "water-wet" Alberta oil sands and "oil-wet" Utah oil sands using a so-called analogue ionic liquid (IL) based on deep eutectic mixtures of choline chloride and urea (ChCl/U) together with a diluent such as naphtha. Unlike conventional ILs, these eutectics are relatively cheap and environmentally friendly. The process is straightforward and involves simply mixing the components at ambient temperatures followed by standard solid/liquid and liquid/liquid separation steps. The ChCl/U mixture appears to reduce the adhesion of bitumen to sand, facilitating separation. It is also immiscible with hydrocarbons such as bitumen or oil. Coupled with a large density difference, this results in a sharp phase separation of hydrocarbons from the ChCl/U mixture. The ChCl/U deep eutectic essentially acts as a separating fluid, keeping the naphtha-diluted bitumen and extracted sand apart, facilitating subsequent separations and solvent recovery steps. However, ChCl/U mixtures are highly viscous at ambient temperatures, but high concentrations of this deep eutectic in water also work well. Initial scale-up work suggests that this approach may form the basis for a viable large-scale process.
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