Abstract:
The CO2 capture efficiency of nine newly synthesized ionic liquids (ILs), both in their pure states as well as in binary and ternary systems with water and amines, was investigated. The study encompassed ILs with fluorinated and tricyanomethanide anions as well as ILs that interact chemically with CO2 such as those with amino acid and acetate anions. Compared to amines, some of the novel ILs exhibited a majority of important advantages for CO2 capture such as enhanced chemical and thermal stabilities and negligible vapor pressure; the previous features counterbalance the disadvantages of lower CO2 absorption capacity and rate, making these ILs promising CO2 absorbents that could partially or totally replace amines in industrial scale processes. In addition to their ability to capture CO2, important issues including corrosivity and ecotoxicity were also examined. A thorough investigation of the capture efficiency and corrosion properties of several solvent formulations proved that some of the new ILs encourage future commercial-scale applications for appropriate conditions. ILs with a tricyanomethanide anion confirmed a beneficial effect of water addition on the CO2 absorption rate (ca. 10-fold) and capacity (ca. 4-fold) and high efficiency for corrosion inhibition, in contrast with the negative effect of water on the CO2 absorption capacity of ILs with the acetate anion. ILs with a fluorinated anion showed high corrosivity and an almost neutral effect of water on their efficiency as CO2 absorbents. ILs having amino acid anions presented a reduced toxicity and high potential to completely replace amines in solutions with water but, in parallel, showed thermal instability and degradation during CO2 capture. Tricyanomethanide anion-based ILs had a beneficial effect on the capture efficiency, toxicity, and corrosiveness of the standard amine solutions. As a consolidated output, we propose solvent formulations containing the tricyanomethanide anion-based ILs and less than 10 vol % of primary or secondary amines. These solvents exhibited the same CO2 capture performance as the 20-25 vol % standard amine solutions. The synergetic mechanisms in the capture efficiency, induced by the presence of the examined ILs, were elucidated, and the results obtained can be used as guidance for the design and development of new ILs for more efficient CO2 capture. © 2014 American Chemical Society.
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