Imidazoles and imidazole-amine hybrids are unique classes of organic solvents that feature properties similar to aqueous amine solvents and ionic liquids (ILs), both of which have received a great deal of attention for CO2 capture applications. However, to date, the utility of the imidazole platform has not been considered, despite its potential advantages over both ILs and aqueous amine solvents. Imidazole-based solvents possess many desirable features for CO2 capture processes including low viscosities (< 5 cP), very low vapor pressures (<< 1 mm Hg at ambient temperature), high CO2 capacities (> 100 g/L), and a much lower cost relative to ILs. When used in combination with an amine, the inherent basicity (H+ accepting capability) of the imidazole platform allows the entire solvent volume to be reactive toward CO2, producing a highly effective solvent is obtained that can be used under the low partial pressures found in post-combustion flue gas (2 psia). Imidazole-amine hybrids are able to exceed the 1:2 (mol:mol) stochiometric limitations of CO2-amine chemistry in a non-aqueous solvent, and are found to absorb up to 1:1 (mol:mol) CO2 per amine, while maintaining viscosities as low as 10 cP in a highly CO2-rich state. Because these solvents exhibit very low volatility under both CO2-lean and CO2-rich conditions, solvent regeneration energy can be minimized (i.e. minimal losses due to latent heat).
At the benchscale, we have demonstrated the viability of imidazoles and imidazole-amine hybrids for CO2 capture. By systematically varying the structures of the imidazole and/or amine components, we have characterized the key physical (viscosity, density), thermodynamic (vapor-liquid equilibrium and heat of reaction) and chemical properties needed to model solvent performance within CO2 capture processes, and have developed structure-property relationships for selecting imidazoles and imidazole-amine hybrid solvents likely to have the greatest utility.
The discussion will focus on our work relating to solvent chemistry, characterization of physical and thermodynamic properties, structure-property relationships, and our associated modeling efforts. Consideration will be given to how these solvents might be scaled from the lab to the field with an emphasis on potential impacts of water, SO2 and other flue gas contaminants as well as process improvements that might be achieved through modification of the conventional absorber-stripper process design for a non-aqueous solvent.
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