Behaviors of SO2 absorption in [BMIm][OAc] as an absorbent to recover SO2 in thermochemical processes to produce hydrogen

The solubility behavior of SO2 in 1-butyl-3-methylimidazolium acetate ([BMIm][OAc]) was investigated. The solubility of SO2 in [BMIm][OAc] was measured to be 0.6 in mole fraction at 50 °C in a stream of SO2 gas. The desorption of SO2 from [BMIm][OAc] was never completed, until the temperature was raised to 170 °C in a stream of N2, indicating that the absorption of SO2 is irreversible at the experimental condition. An in-situ IR study showed that acetate anion in [BMIm][OAc] transformed into acetic acid during the SO2 absorption. After removing acetic acid at 170 °C by evacuation, the bands at 1210, 1045 and 850 cm−1 appeared in IR spectra. The bands at 1210 and 1047 cm−1 were assigned to S–O stretching mode of HOSO2− (an isomer of HSO3−) and the band at 885 cm−1 was assigned to the symmetric stretching mode of HO–S. FT-IR study suggested that acetic acid and most plausibly [BMIm][HOSO2] were generated from the interactions of [BMIm][OAc] with SO2 and adventitious water in feed gas and/or [BMIm][OAc] during absorption–desorption process. [BMIm][HOSO2] recovered after removing acetic acid was found to be a new and reversible SO2 absorbent with the SO2 absorption capacity of 0.55 in mole fraction.