Reversible SO₂ Removal from Simulated Flue Gas by Ion Exchange Membranes Using the Humidity-Swing

An ion exchange membrane (IEM) loaded with CO₃²⁻ ions was developed for reversible SO₂ removal by humidity-swing based on the hydrolysis of CO₃²⁻ and SO₃²⁻ ions. The dry environment promotes the hydrolysis of CO₃²⁻ in IEM to generate OH⁻ which binds SO2 to form HSO₃⁻ and HCO₃⁻ that react with SO2 to form HSO₃⁻ and CO₂. The absorbent can be regenerated with a HSO₃⁻-to-SO₃²⁻ transformation in a humid environment at room temperature. The SO₃²⁻ ions in IEM are able to be hydrolyzed again into HSO₃⁻ ions and OH⁻ ions for SO₂ absorption when the surroundings are dry, and the absorbed SO₂ will be released when wet. The transformation between SO₃²⁻ ions and HSO₃⁻/OH⁻ ions driven by humidity-swing was verified by quantum chemical calculations. The SO₂ absorption capacity of IEM reached 1.76 mmol/g. Besides, the effect of SO₂ concentration on the desulfuration performance was experimentally studied and the results showed that the absorption rate and quantity increased significantly with the initial SO₂ concentration ranging from 500 to 4000 ppm. The present work represents a new approach for SO₂ removal and sheds light on more gas separation applications by humidityswing. Copyright © 2019 American Chemical Society.