Search

The development of high-efficiency and cost-effective purification processes for CO2 capture from flue-gas is today considered mandatory to mitigate energy-related emissions. The use of ionic liquids (ILs) for post-combustion CO2 capture is a very attractive option to circumvent amine-based absorbents drawbacks. Recent literature studies suggest the use of ILs supported onto porous substrates for CO2 capture, when dealing with ILs exhibiting high viscosities and as a strategy to minimize their utilization costs. Nevertheless, most of the adsorption studies are generally performed in pure CO2 streams, not representative of a real flue-gas. This work investigates the CO2 capture of a mesoporous alumina functionalized with 1-ethyl-3-methylimidazolium glycinate ([Emim][Gly]) IL. Two sorbents were prepared by impregnation of the substrate with [Emim][Gly] in ethanol solution at two concentration values of active phase (1.08×10–2 and 2.01×10–2 kg L–1), followed by solvent evaporation. N2 pore size analysis of sorbents showed that the impregnation treatment did not significantly affect the pore size distribution of the raw support. CO2 adsorption runs on either raw or [Emim][Gly]-functionalized alumina were performed in a fixed-bed column at 303, 323, 353 and 373 K and for mimicking flue-gas streams (CO2 15% vol., balance N2). Results testified the effectiveness of the functionalization treatment with [Emim][Gly] IL which determined an increase in the parent sorbent CO2 capture capacity, mainly at lower temperatures. At 303 K, the adsorption capacity values derived for sorbents loaded with 5 and 9% wt. IL were about 35 and 60% greater than the figure obtained for raw alumina, respectively (Figure 1). Dynamic tests showed that functionalized sorbents were characterized by slower saturation kinetics. Moreover, an increase in the operating temperature determined a reduction of the saturation time, likely due to a reduction of the IL viscosity promoting faster CO2 diffusion rates within the IL film confined into the sorbent pores.

The development of high-performance depuration processes for CO2 removal from flue-gases deriving from fossil-fueled power plants represents one of the most stimulating scientific and technological challenges of the third millennium, to face the global climate change. Post-combustion CO2 capture by means of ionic liquids (IL) supported onto porous substrates is a promising strategy to cope with the main issues associated with IL, and related to their generally high viscosity and market costs. Despite the great scientific interest for IL properties, such as high thermo-chemical stability and selectivity for CO2 when containing basic functional groups, few studies investigated the effect of the support textural properties on the CO2 capture efficiency of IL confined in nanospaces, under typical flue-gas conditions. This work analyses the CO2 capture performances of two mesoporous substrates, namely γ-Al2O3 (termed as Al-raw) and Amberlite XAD1180N (termed as Amb-raw), both raw and functionalized with 1-ethyl-3-methylimidazolium glycinate [Emim][Gly] IL. The functionalized sorbents were prepared by wet impregnation of each substrate with [Emim][Gly] in ethanol solutions, at different active phase concentrations (i.e. C0=7.8, 14.3 and 25.0 g L-1) followed by solvent evaporation. Functionalized sorbents were termed as Al-[Emim][Gly]5%, Amb-[Emim][Gly]5%, Al-[Emim][Gly]9%, Amb-[Emim][Gly]9%, Al-[Emim][Gly]16% and Amb-[Emim][Gly]14%, where 5, 9, 14 and 16% represent the IL mass fractions effectively dispersed onto the support, as determined by thermogravimetric analysis. CO2 adsorption tests on the selected sorbents were performed in a fixed-bed column at 303, 323, 353 and 373 K and for mimicking flue-gas effluents (CO2 15% vol., balance N2). Experimental results highlighted a monotonic enhancement of the CO2 capture performances with the IL loading for both the parent substrates, mainly at lower process temperatures. For example, at 303 K Amb-[Emim][Gly]14% displayed a value of the adsorption capacity nearly 5-times greater than the one obtained for Amb-raw. In the case of Al-[Emim][Gly]16% tested at 303 K, the capture capacity increased by a factor 3 with respect to Al-raw. Dynamic adsorption tests testified slower saturation kinetics of each functionalized sorbent when compared to its unsupported counterpart, likely due to a partial pore clogging effect determined by the active phase. Faster adsorption dynamics and a greater IL utilization factor were observed for sorbents belonging to the Amb-[Emim][Gly] series at each impregnation condition. These experimental evidences are possibly ascribable to a greater mean pore diameter and surface area values retrieved for the Amberlite support ensuring a greater dispersion of the IL film and faster CO2 diffusion rates within the pores network. In general, the obtained results are very encouraging to quicken the applicability of supported ionic liquid sorbents in post-combustion CO2 capture systems.