Reversible and Efficient Absorption of SO2 with Natural Amino Acid Aqueous Solutions: Performance and Mechanism

In previous research, we have found and reported for the first time that β-alanine aqueous solution could be employed to efficiently separate SO2 from flue gas. However, the performance of most natural amino acids (AAs) on SO2 absorption and their interaction mechanisms are not fully understood. In this work, the performance of 20 natural AA aqueous solutions on SO2 absorption from flue gas was systematically studied. The experimental data showed that monoamino AAs (MAAs) exhibited good absorption performance, especially glycine, of which the saturation uptake of SO2 reached 0.461 g/g. All the MAAs showed excellent regeneration performance, while the polyamino AAs of lysine, arginine, and histidine performed poorly. Based on the characterization and analysis using Fourier transform infrared spectroscopy, Raman spectroscopy, 13C-nuclear magnetic resonance, and the density-functional theory simulation, it was found that the interaction mechanism between MAA aqueous solutions represented by glycine and SO2 is complex, including the hydrolysis of SO2 and the protonation of MAAs, the formation of hydrogen bonds between cationic MAAs and HSO3–, and the interaction between zwitterionic MAAs and SO2. In addition, cationic glycine could form a carboxylic acid dimer, which further interacted with HSO3– through hydrogen bonds.