Multiple-Site SO2-Capture Ionic Liquids with Nearly Uniform Site Performance

We propose a series of azolium poly(azolyl)borate ionic liquids (ILs) for reversible SO2 capture. Density functional calculations demonstrate that the designed borate anions can strongly bond to SO2 at multiple sites with nearly uniform binding energies. Thus, as well as high overall uptakes, the ILs can achieve much higher effective uptakes (the uptake difference between absorption and desorption conditions) than existing SO2-capture reagents. The larger size of the borate anions, the evenly distributed negative charge among the azolyl rings, and the blocking of the conjugation by the tetrahedral boron concertedly reduce absorbate-absorbate repulsion, which leads to a large disparity among binding sites in other multiple-site SO2 sorbents.