Absorption and desorption of SO2 in aqueous solutions of diamine-based molten salts

Desorption of CO2, SO2, and NH3 in the vacuum evaporation of desulfurization wastewater

Mechanical vapor compression and multi-effect evaporation have been widely used in achieving zero discharge of desulfurization wastewater as they are energy-saving and efficient technologies. Solubilized weak ions, such as CO₃^2-, SO₃^2-, and NH₄⁺, in the desulfurization wastewater are partly converted into CO₂, SO_2, and NH₃, respectively, during the vacuum evaporation process, thus affecting the heat exchange and compressor performance. In this study, the migration and coupling mechanism of CO₂, SO₂, and NH₃ desorption in desulfurized wastewater under vacuum evaporation were analyzed. The effects of temperature, pressure, reaction time, and other factors on the migration process were discussed. The hydrolysis and electrolytic equilibrium constants of the related ions were obtained for temperatures between 70 and 90 °C. The results demonstrate the relationship between the desorption capacities of CO₂, SO₂, and NH₃ and the hydrolysis constants of their respective ions. The desorption of CO₂ and NH₃ increased significantly when CO₃^2- and NH₄⁺ coexisted, whereas the SO₂ desorption capacity remained low under the same experimental conditions. The experimental results indicate that the desorption of CO₂, SO₂, and NH₃ is controlled by chemical reactions and can be described by first-order reaction kinetics.

Hydrotalcite-based CeNiAl mixed oxides for SO2 adsorption and oxidation

The impact of Ce on SO₂ adsoption and oxidation was studied over a series of flower-like hydrotalcite-based CeNiAl mixed oxides. Combined with XRD, BET, pyridine chemisorption, CO₂-TPD, XPS and H₂-TPR results, it revealed that introduction of Ce into NiAlO generates new centres for oxygen storage and release, promotes the enhancement of Lewis acid strength, increases weakly and strongly alkaline sites, and increases ability for SO₂ adsorption and oxidation. Furthermore, in situ Fourier transform infrared spectroscopy revealed that adsorbed SO₂ molecules formed surface bidentate binuclear sulfate. Taken together, we propose that the addition of Ce⁴⁺ to NiAlO acts to improve this compound as major adsorbent for SO₂.

Liquid-liquid phase-change absorption of SO2 using N, N-dimethylcyclohexylamine as absorbent and liquid paraffin as solvent

In the present work, liquid-liquid phase-change absorption of SO₂ was investigated using N, N-dimethylcyclohexylamine (DMCHA) as an absorbent, and high boiling liquid paraffin (LP) as a solvent to reduce volatilization of the absorbent. The homogenous solution was split into two immiscible phases upon SO₂ loading. The phase-change mechanism was attributed to the polarity variation of DMCHA before and after absorption by forming the charge-transfer complex DMCHA·SO₂. The viscosity of the lower phase reached a maximum value of 24.5 mPa s at the absorption capacity of 1 mol SO₂/mol DMCHA, and the viscosity of the corresponding upper phase was 46.4 mPa s. Both are lower than the reported viscosity of most ionic liquids. This solution exhibited extremely high mass selectivity of SO₂/CO₂ with a value of 626. The mass absorption capacity was founded to be 1.19 g SO₂/g DMCHA at 1 atm, which is comparable with the highest reported mass absorption capacity. At low partial pressure, the absorption capacity still reached 0.78 g/g at 0.1 atm, 0.43 g/g at 0.02 atm and 0.27 g/g at 0.001 atm. Furthermore, DMCHA could be completely regenerated in 10 min via microwave heating. All the results indicated this phase-change solution is a promising candidate for SO₂ capture.

Amine-Functionalized Covalent Organic Framework for Efficient SO2 Capture with High Reversibility

Removing sulfur dioxide (SO2) from exhaust flue gases of fossil fuel power plants is an important issue given the toxicity of SO2 and subsequent environmental problems. To address this issue, we successfully developed a new series of imide-linked covalent organic frameworks (COFs) that have high mesoporosity with large surface areas to support gas flowing through channels; furthermore, we incorporated 4-[(dimethylamino)methyl]aniline (DMMA) as the modulator to the imide-linked COF. We observed that the functionalized COFs serving as SO2 adsorbents exhibit outstanding molar SO2 sorption capacity, i.e., PI-COF-m10 record 6.30 mmol SO2 g-1 (40 wt%). To our knowledge, it is firstly reported COF as SO2 sorbent to date. We also observed that the adsorbed SO2 is completely desorbed in a short time period with remarkable reversibility. These results suggest that channel-wall functional engineering could be a facile and powerful strategy for developing mesoporous COFs for high-performance reproducible gas storage and separation.