CO2 adsorption from simulated flue-gas onto nanoporous activated carbons functionalized with ionic liquids

The increasing level of atmospheric CO2 has driven research efforts to the development of high-performance processes for CO2 capture from flue-gases in order to mitigate global warming effects mainly deriving from fossil fuels combustion. Post-combustion CO2 capture adopting ionic liquids (ILs) appears a promising route due to the tuneable chemico-physical properties and extremely low vapour pressure of ILs. A very challenging application of ILs is the inclusion in porous solids to increase their CO2 affinity and to overcome the limits of the industrial-scale application of ILs for CO2 capture, i.e. their high cost and viscosity. In this work CO2 removal performances of 1-hexyl-3-methylimidazolium tetrafluoroborate [Hmim][BF4] and 1-ethyl-3-methylimidazolium glycine [Emim][Gly] ILs supported on Filtrasorb 400 and Nuchar RGC30 nanoporous activated carbons (ACs) are investigated. The sorbents preparation was performed by excess solution impregnation of each substrate with [Hmim][BF4] (two ethyl acetate solutions with IL concentrations C°=5.6×10-3 and 2.2×10-2 M) and [Emim][Gly] (one methanol solution C°=5.6×10-3 M) followed by solution filtration and residual solvent evaporation. Porosimetric characterization of functionalized ACs by means of N2 adsorption at 77 K revealed that investigated ILs preferentially adsorb in micropores. CO2 adsorption tests onto [Hmim][BF4] functionalized ACs were conducted in a fixed bed reactor at 303, 323 and 353 K and for simulated flue-gas streams (CO2 1-30% by vol., balance N2). Preliminary adsorption experiments for [Emim][Gly] functionalized carbons were performed under 15% CO2 streams at 303 and 353 K. Results highlighted that the use of [Hmim][BF4] for the functionalization of highly microporous ACs appears as not suitable for flue-gas treatment because pore blocking induced by this IL determines a worsening of the parent carbons CO2 adsorption capacity mostly at lower temperatures. On the contrary, the more-chemically CO2 affine amino acid-based [Emim][Gly] IL was effective in ameliorating the parent carbons sorptive performances towards CO2 at 353 K, hence confirming the interest of ACs functionalization by ILs in the field of CO2 capture.