(112e) Enhanced CO2 Uptake and Selectivity upon Incorporation of Task-Specific Ionic Liquids into Highly Porous MOF-177 at Post-Combustion Capture Condition

Recently, Metal-organic-frameworks (MOFs) have gained tremendous attraction for application in CO₂ capture and storage due to an exceptional surface area, pore volume and for their tunability. Although some of the MOFs have shown excellent CO₂ uptake at high pressure, lower uptake at post combustion condition (partial pressure of CO₂ is 0.15 bar) is a major hindrance for widespread application in CO₂ capture operations. Researchers have deployed various strategies to enhance CO₂ uptake such as grafting amines functionalities covalently to the ligands, impregnating amines or ionic liquids (ILs). Post-synthesis modification of pores of solid sorbents by impregnation of amino functionalized ionic liquid also known as task-specific ionic liquid (TSILs) to enhance CO₂ capture capacity has shown promising results.

In this study, 1-ethyl-3-methylimidazolium [Emim] cations with Glycine [Gly] and Alanine [Ala] as reactive Amino Acid (AA) anions forming [Emim][Gly] and [Emim][Ala] as TSILs were immobilized into the pores of MOF-177 through the incipient wetness technique. TSIL@MOF-177 composites sorbents were prepared for three different loadings (10, 20 and 30) wt.% of TSIL and the developed composites were characterized and investigated from the engineering perspective in terms of CO₂ capture capacity, selectivity, and enthalpy of adsorption. CO₂ adsorption isotherms were measured at three different temperatures (303, 313 and 323 K) in the pressure range varying from (0.1 to 10) bar. In addition, N₂ adsorption isotherms were also measured for all composites and the pristine MOF-177 from which CO₂/N₂ ideal selectivities were calculated. In addition, experimental adsorption isotherms were modelled using the Freundlich model and the isosteric heats of adsorption were calculated and compared to those of the pristine MOF-177.

Impregnation of TSILs into the highly porous metal organic frameworks (MOF-177) had a remarkable impact on CO₂ capture and selectivity. The highest CO₂ uptake achieved by [Emim][Gly]@MOF-177 composite was 0.45 mmol/g-solid and 0.42 mmol/g-solid at 0.2 bar, 303 K for [Emim][Ala]@MOF-177 composite which were 3 and 2.8 times higher than the pristine MOF-177 at the same conditions, respectively. It was also observed that the optimum loading of TSIL was 20 wt.% as further increase to a loading to 30 wt.% did not results in any incremental CO₂ uptake. CO₂ selectivity over N₂ was also enhanced from 5 for the pristine MOF-177 to 13 and 11 for [Emim][Gly] and [Emim][Ala], respectively, at 0.2 bar and 313 K. This significant improvement of both CO₂ uptake and selectivity can be attributed to the chemisorption interaction between CO₂ and -NH₂ functional group present in the amino acid anion in TSIL which was also reflected in the increase in the isosteric heat of adsorption (Q_st) values from the value of the pristine MOF. Significantly high CO₂ uptake and CO₂/N₂ selectivity at the low pressure region (<1.0 bar) makes these functionalized MOFs promising candidates for the post-combustion CO₂ capture operation.