Novel Inverse Supported Ionic Liquid Absorbents for Acidic Gas Removal from Flue Gas

This work reports on the astonishing high capacity of inverse supported ionic liquid absorbents, hereinafter denoted as “inverse SILPs” to remove acidic gases (SO₂ and CO₂) from flue gas streams. These nonconventional SILPs are easily prepared in the form of flowing powder via a phase inversion technique and consist of tiny ionic liquid (IL) droplets enclosed into an ultrathin, porous solid sleeve of pyrogenic silica nanoparticles. The CO₂/N₂ and SO₂/CO₂ separation performance and regeneration efficiency of inverse SILPs developed from six different ILs and two IL/chitosan ionogels was examined via gravimetric CO₂, N₂ absorption isotherms and via SO₂, CO₂, O₂ breakthrough curves from gas mixtures in fixed beds. The involved ILs varied from chemisorbing ones, composed of alkyl- or alkanol-ammonium cations and amino acid anions, to physisorbing ones including ether functionalized anions and 1-alkyl-3-methylimidazolium cations. It is noteworthy that the best performing inverse SILP consisted of a very common IL, the 1-butyl-3-methylimidazolium chloride [BMIM]­[Cl], the absorption capacity of which was slightly enhanced by dissolving 5 wt % of chitosan to form the respective ionogel. The material’s performance was stable in repeated cycles of absorption and regeneration at 60 °C under helium flow, exhibiting SO₂/CO₂ selectivity of above 300, while the SO₂ and CO₂ absorption capacity was 1.6 and 0.6 mmol/g respectively at 25 °C, in a gas stream of 1 bar composed of 0.13 vol % SO₂, 13 vol % CO₂, 11.5 vol % O₂ and N₂ (balance).