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

An ion exchange membrane (IEM) loaded with CO3 2− ions was developed for reversible SO2 removal by humidity-swing based on the hydrolysis of CO3 2− and SO3 2− ions. The dry environment promotes the hydrolysis of CO3 2− 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-SO3 2− transformation in a humid environment at room temperature. The SO3 2− 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 SO3 2− 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. 1.