Application of activated carbons incorporating [Emim][Gly] ionic liquid for post-combustion CO2 capture

As long as the use of fossil fuels plays a crucial role in worldwide energy production, CO2 capture and storage (CCS) is a key strategy for mitigating global climate change commonly related to greenhouse gas emissions. Among CCS technological pathways, post-combustion CO2 capture from flue-gases is considered a prompt solution to mitigate CO2 environmental impacts because treatment units can be retrofitted to existing power plants. In this scenario, the investigation of ionic liquids (ILs) as innovative solvents for CO2 capture appears an attractive option for the development of efficient post-combustion purification systems due to the unique characteristics of this class of compounds, such as negligible vapour pressure, high thermo-chemical stability and tuneable chemico-physical properties. Notwithstanding many scientific papers investigate different ILs in CCS field, there is scarce information concerning the effect of confining ILs into porous substrates on CO2 capture performances. This application can be considered very promising for ILs use optimization due to their generally high market costs and for the expected improvement of CO2 adsorption capacity. This work investigates CO2 capture capacity of Filtrasorb 400 and Nuchar RGC30 activated carbons (ACs) functionalized with 1-ethyl-3-methylimidazolium glycine [Emim][Gly] IL. The adsorbents were prepared by impregnating each AC at two levels of IL concentration C°=5.6×10-3 and 2.2×10-2 M in methanol, followed by solution filtration and residual solvent evaporation. N2 porosimetric characterization at 77 K of raw and functionalized ACs revealed that [Emim][Gly] preferentially adsorbs in micropores for both ACs and in general the higher the IL loading, the greater the micropore occlusion. CO2 adsorption tests on functionalized ACs were performed in a fixed bed column at 303 and 353 K with simulated flue-gas (CO2 1-30% by vol., balance N2). Results showed that, for both ACs pores blocking induced by the presence of the IL is the prevailing effect at 303 K which determines a worsening of CO2 capture performances of each functionalized material with respect to the parent one. For both Filtrasorb 400 and Nuchar RGC30 impregnated with [Emim][Gly] at C°=5.6×10-3 M the active phase was able to ameliorate the parent AC capture performances at 353 K thanks to a good compromise between IL loading and pore accessibility (i.e. a low pore volume reduction). Results obtained in this work encourage future research efforts in the field of porous substrates functionalization with amine-based ILs as a potential route to improve their CO2 capture performances, in particular at high temperatures at which the parent material performances are quite scarce to allow a cost-effective treatment of a real flue-gas.