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To explore environmentally benign solvents for the absorption of NO and NO2, a series of caprolactam tetrabutyl ammonium halide ionic liquids were synthesized. The solubility of NO and NO2 was measured at temperatures ranging from 298.2 to 363.2 K and atmospheric pressure, and the following trend in the solubility of NO and NO2 in ionic liquids with various halide anions was observed, respectively: F > Br > Cl and Br > Cl > F. Moreover, as the temperature increased from 308.15 to 363.15 K and the mole ratio of caprolactam increased from 2:1 to 6:1, the solubility of NO increased. Alternatively, the solubility of NO2 decreased as the temperature increased from 298.15 to 363.15 K, and the mole ratio of caprolactam increased from 2:1 to 6:1. The absorption and desorption of NO and NO2 was practically reversible in the ionic liquids, which was characterized by nuclear magnetic resonance. The method, which is at least partially reversible, offers interesting possibilities for the removal of NO and NO2.

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To explore environmentally benign solvents for absorbing and using H2S, a series of caprolactam tetrabutyl ammonium bromide ionic liquids were synthesized, the solubilities of H2S in which were measured at 303.2−363.2 K and atmospheric pressure. The solubility of H2S in the ionic liquid (1:1 mole ratio) was 5.40% at 303.2 K and ambient pressure, decreased sharply as temperature increased, and increased with the increasing mole ratio of caprolactam. The absorption and desorption of H2S were practically reversible in the ionic liquids, which was characterized by nuclear magnetic resonance. Using air, hydrogen sulfide could be oxidized to elemental S in the ionic liquids, which makes it easier to recycle hydrogen sulfide. Caprolactam tetrabutyl ammonium bromide ionic liquids would be useful for removing and reusing H2S in pollution control and could be regarded as the most potential absorbent and recoverer of H2S.

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