Sulfur dioxide absorption characteristics of aqueous amino acid solutions

The SO₂ absorption/desorption performances of 14 aqueous amino acid solutions were evaluated to identify efficient absorbents to remove SO₂ from coal-powered plant emissions. SO₂ absorption/desorption experiments were conducted at 298.15 and 373.15 K, respectively, using 600 ppmv SO₂ (N₂ balance) and N₂ purging. Thereafter, the absorption/desorption loadings and rates of the solutions, as well as their net cyclic capacities, were compared. The SO₂ absorption mechanisms were explored via ¹³C NMR, ¹H NMR, and UV–Vis analyses, and the relationship between the pKa values and absorption performances of the 14 aqueous amino acid solutions was investigated. Furthermore, the effects of absorption temperature, absorbent concentration, and inlet SO₂ concentration on the SO₂ absorption performances of the solutions were explored. 5-Aminovaleric acid, 4-aminobutyric acid, β-alanine, and histidine were identified as suitable SO₂ absorbents based on their absorption/desorption performances and their net cyclic capacities. Furthermore, the net cyclic capacities of these four absorbents were similar or superior to those of previously reported deep eutectic solvents and ionic liquids. The results of this study provide a strategy for preparing eco-friendly SO₂ absorbents.