Review on Applications of Ionic Liquids (ILs) for Bitumen Recovery: Mechanisms, Challenges, and Perspectives

Water- and solvent-based ex situ extraction processes have been employed to extract bitumen from mineable oil sands. On the other hand, bitumen is recovered in situ from deeper deposits most efficiently by injecting steam to reduce viscosity and increasing production flow to the surface. However, the water-based process with or without solvent (including steam injection) is not sustainable due to various challenges including water requirement and treatment, high energy consumption, and related environmental pollution problems emanating from high volatility of solvents. Ionic liquids (ILs) have become desirable in several industrial applications due to many unique properties including low volatility compared with traditional organic solvents. The potential for application of ILs for bitumen extraction is reviewed in this work, with a focus on the mechanistic aspect. Depending on the properties and/or functionality, the ILs can be used in bitumen extraction (with or without organic solvents) with minimal clay fines contamination and lower water and energy requirements. In the solvent-assisted IL recovery system, the IL-clay interaction is responsible for reducing the adhesive force between bitumen and the sand, which subsequently facilitates separation. Conversely, considering the types of ILs explored in the absence of solvent, the IL-bitumen interaction plays an additional role. Hitherto, applications of ILs in bitumen recovery are at a very preliminary stage. Apart from understanding the mechanisms, the major impediment lies in the high cost and environmental impact due to toxicity. Therefore, to make ILs more attractive for bitumen recovery, concerted efforts should be intensified to reduce the cost of producing ILs, ameliorate environmental impacts, and facilitate field scale applications through technoeconomic analysis of the process.