The effect of water on CO2 adsorption by a supported amino acid ionic liquid

The adoption of ionic liquids (IL) for the selective removal of CO2 from industrial flue-gases represents a promising route to cut down the emissions of this greenhouse gas in the power sector. The dispersion of IL onto high-surface area substrates can promote a faster CO2 capture dynamics with respect to their use as liquid absorbents, with associated economic benefits for the purification process. This scientific contribution aims at elucidating the role of water on CO2 adsorption under realistic flue-gas conditions by a supported amino acid ionic liquid, a topic poorly investigated in the pertinent literature. Three supported ionic liquid sorbents (SILP) were prepared via wet impregnation of a mesoporous alumina with 1-ethyl-3-methylimidazolium glycinate [Emim][Gly] IL at 5, 9 and 16% wt. active phase loadings. CO2 capture tests on both raw and functionalized sorbents were performed in a fixed-bed adsorber at 303, 323 and 353 K under both dry and wet conditions (CO2 15% vol., H2O 0, 3.3 and 6.3% vol., balance N2). Results demonstrated superior capture performances of SILP sorbents with respect to the parent substrate, and the presence of water in the model flue-gas promoted CO2 capture on all the investigated sorbents. The sorbent with the highest IL loading exhibited at 323 and 353 K a non-monotonic effect of water content on CO2 adsorption capacity, possibly due to a more marked competition between CO2 and H2O for the sorbent active sites occurring at higher water concentration (Figure 1). SILP sorbents tested under wet conditions also displayed slower saturation dynamics (mainly at 303 K) likely ascribable to a greater number of active sites available for CO2 molecules. The obtained outcomes are encouraging for the potential application of the produced SILP sorbents for CO2 removal from humid flue-gases, e.g. deriving from wet scrubbers for SO2 emissions control.