Highly Efficient and Reversible Capture of Low Partial Pressure SO₂ by Functional Deep Eutectic Solvents

Abstract

Deep eutectic solvents (DESs) have been seen as promising absorbents for SO2 capture in recent years. In this work, a series of DESs based on imidazole derivatives were synthesized to investigate the low pressure SO2 absorption. The physical properties were determined, and the DESs exhibited low viscosities and high stability. Effects of composition, operating temperature and pressure, and water content on SO2 absorption capacity were investigated. It was demonstrated that the 1-butyl-3-methyl­imidazolium chloride (BmimCl):​4-methyl­imidazole (4CH3-Im) (1:2) could absorb 1.42 and 0.189 gSO2 /gDES at 101.3 and 1 kPa SO2 partial pressure, respectively, which were higher than most reports to date under this condition. The absorbed SO2 could be released easily under mild condition, and there was no change in absorption performance after 5 cycles. Furthermore, the absorption mechanism studied by FTIR and NMR indicated that the high SO2 absorption capacity originated from the synergistic interaction of BmimCl and 4CH3-Im on SO2. This work opens opportunity for low partial pressure SO2 capture and insight into the formation mechanism of DESs for further investigation.

Highly efficient and reversible absorption of SO2 by hydroxyl ammonium ionic liquids at low partial pressure

“…(a), a new characteristic absorption peak appeared in the spectrum of ILs at 966 cm −1 after the absorption of SO 2 , which was attributed to stretching vibrations of the SO group. This peak disappeared in the spectrum of recycled ILs after the desorption process . Likewise, a peak at 1720 cm −1 , due to the stretching vibrations of CO of carboxylic acid, was observed only in the spectra of absorbed ILs, and not in the case of recycled ILs or ILs before the absorption process.…”

“…Actual flue gas contains 10–15% H 2 O vapour along with SO 2 and reports suggest that presence of H 2 O greatly reduces SO 2 absorption capacity . Figure shows clearly that addition of H 2 O reduced the SO 2 absorption capacity of hydroxyl ammonium ILs.…”

“…S2. Moreover, the newly formed chemical bond, NS, was unstable at higher temperature, which induced the desorption process from ILs . These results suggest that low temperature was favorable for high absorption, whereas high temperature was beneficial for releasing SO 2 and regeneration of ILs.…”

“…When the temperature increased from 25 °C to 60 °C, the molar absorption capacities of SO 2 decreased by about 30.9%, 37.8% and 37.3% for [TEOA][CA], [TEOA][LA] and [TEOA][AC], respectively. The effect of temperature on absorption of SO 2 could be explained on the basis of exothermic reactions between ILs and SO 2 molecules . Released heat could increase the temperature of ILs rapidly when the thermostat was turned off, as shown in Fig.…”

“…The effect of temperature on absorption of SO 2 could be explained on the basis of exothermic reactions between ILs and SO 2 molecules. 14,[33][34][35][36] Released heat could increase the temperature of ILs rapidly when the thermostat was turned off, as shown in Fig. S2.…”