Theoretical and experimental investigation on the capture of H2S in a series of ionic liquids.

H2S absorptions in ionic liquids (ILs), including tetramethyl guanidinelactate (TMGL), 4-bis(2-hydroxypropyl)-1,1,3,3-tetramethyl guanidinium tetrafluoroborate ([TMGHPO2][BF4]) and 1-butyl-3-methylimidazolium cation ([BMIM](+)) with the anions chloride ([Cl](-)), tetrafluoroborate ([BF4](-)), hexafluorophosphate ([PF6](-)), triflate ([TfO](-)), bis-(trifluoromethyl) sulfonylimide ([Tf2N](-)), were studied in experiment and computational methods. [TMGHPO2][BF4] showed the best H2S absorption capacity among the seven ILs. Density functional theory (DFT) calculations were applied to reveal the absorption mechanisms. Interaction energy results were consistent with absorptivities (molar ratio of H2S in IL) measured in experiment. As the best candidate absorbent, [TMGHPO2][BF4] was chosen as an example to characterize the hydrogen bonds and orbital interactions between H2S and [TMGHPO2][BF4] in atoms in molecules (AIM) and natural bond orbital (NBO) methods, respectively. IR spectrums obtained in both experimental and computational method were used to characterize the features of absorption process. The results indicated that H2S was physically absorbed by ILs, in which hydrogen bond was the driving force.