The absorption of SO₂ by morpholine cyclic amines with sulfolane as the solvent for flue gas

The absorption properties of N-(2-hydroxyethyl) morpholine (HEM), morpholine (MP) and N-(2-aminoethyl) morpholine (AEM) for SO₂ were studied using sulfolane (SUL) as solvent in this work. Among these solvent combinations, HEM/SUL shows the best cyclic absorption performance, and the capacity of HEM-SUL-40 (40 wt% of HEM and 60 wt% of SUL) to absorb 8580 mg/m³ SO₂ (the remainder is N₂) is 192.18 mg/g at 293.15 K. The absorption capacity of the second cycle is 97.5% of the first absorption cycle, which is higher than 70% of the Cansolv amine solution in a commercial application with similar experimental conditions. However, MP/SUL is difficult to desorb at high temperature, and the absorption capacity of AEM/SUL is much lower than HEM/SUL and MP/SUL. According to the FTIR, ¹H NMR and ¹³C NMR, all three cyclic amines have charge transfer effects with SO₂. The structure of HEM/SUL can be recovered after heating, but MP cannot be recovered. Δ_rG_m° in the reaction against HEM with SO₂ increases significantly with increasing temperature. The Δ_rG_m° of HEM-SO₂ and MP-SO₂ at 353.15 K is -12.56 kJ/mol and -16.29 kJ/mol, respectively, which further explains the easy desorption of HEM-SO₂ and the difficult desorption of MP-SO₂ at high temperature.