Molecular dynamic insight into solubility of H2S in ionic liquids [emim][BF4], [emim][OTf] and [emim][Tf2N

Abstract

Natural gas sweetening is one of the important processes in petroleum industry. Ionic liquids (ILs) as a new class of compounds are an alternative to conventional solvents to achieve this goal. In this study, the solubility of H2S gas in ionic liquids 1-Ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]), 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate ([emim][OTf]) and 1-Ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl)imide was calculated based on the excess chemical potential energy by molecular dynamics free energy perturbation (FEP) technique. In this regard, validation was carried out for force fields of gas and ILs. Two force fields, All-Atom (A-A) and United-Atom (U-A), were compared to calculate the H2S solubility in the ILs. The performance of A-A force field was better for [emim][BF4] and [emim][OTf]; whereas, that of U-A force field for [emim][Tf2N]. The calculated Henry’s constant and chemical potential energy were in a good agreement with experimental data. The results showed that higher negative potential energy resulted in higher molar fraction and the ionic liquid [emim][BF4] had the best performance for H2S removal from a gas stream.