Enhancement of post-combustion CO2 capture capacity by incorporation of task-specific ionic liquid into ZIF-8

Abstract In this present work, two task specific ionic liquids (TSILs) were encapsulated into the framework of a Zeolite imidazolate framework-8 (ZIF-8) to enhance its CO2 capture capacity and CO2/N2 selectivity at post-combustion conditions. 1-Ethyl-3-methylimidazolium amino-acetate {[EMIM][glycine (Gly)]} and 1-Ethyl-3-methylimidazolium (S)-2-aminopropionate {[EMIM][alanine (Ala)]} were selected as TSILs. TSIL@ZIF-8 composites sorbents were prepared by varying the loading of TSIL, and properties such as sorbent thermal stability, porous structure and crystal nature of the composite were investigated. Incorporation of TSIL into ZIF-8 led to a dramatic rise in CO2 uptake particularly at pressures lower than 1.0 bar. At this low-pressure range, CO2 uptake was greater than in pristine ZIF-8 for all TSIL loadings and TSIL@ZIF-8 composites with 30 wt% [Emim][Gly] reached a CO2 uptake capacity of 0.76 mmol·g−1 solid at 0.1 bar, and 0.88 mmol/g-solid at 0.2 bar at 303 K. These values were 13 and 7 times higher that CO2 uptake in pristine ZIF-8 at identical conditions. TSIL functionalized composites also exhibited much higher selectivity than pristine ZIF-8 at all pressures. For instance, at 30 wt% [EMIM][Gly] loading, CO2/N2 ideal selectivities at 313 K were 28 and 19 at 0.1 and 0.2 bar, respectively. This synthesized composite sorbent, with significantly high CO2 uptake, better CO2/N2 selectivity at the low-pressure region (