SO2 Capture Using pH-Buffered Aqueous Solutions of Protic Triamine-Based Ionic Liquid

In this work, a kind of aqueous solution of novel protic triamine-based ionic liquid was proposed for efficient SO2 capture. The mixed absorbents were prepared by blending 1,1,4,7,7-pentaethyldiethylene (PEDETA) with sulfuric acid and water, and their physicochemical properties were studied by various methods. Remarkably, the viscosities of the mixed absorbents are in the range of 1.44–1.85 mPa s at 293.2 K, which is as low as water. Detailed SO2 absorption experiments were carried out to investigate the influence of some important factors, including temperature (298.2, 313.2, and 328.2 K), SO2 partial pressure (0–1 bar), and sulfuric acid proportion. It is worth noting that the mixed absorbents showed excellent absorption capacity, especially at a low partial pressure. All absorbed SO2 could be released easily and completely by the method of heating reflux. More importantly, the absorbent could be reused for at least 5 cycles without noticeable changes in both absorption performance and chemical structure. A thermogravimetric analysis further confirmed its good thermal stability. The detailed absorption mechanism was proposed and demonstrated by an infrared spectrum. In the end, the pKa values and reaction enthalpy of the protonation reaction of PEDETA were determined by acid titration and parameter analysis based on the reaction equilibrium model. In summary, the mixed absorbents, which possess low viscosities, good resistance to sulfuric acid, excellent capacity, and reusability, may have a good perspective in industrial SO2 capture.