Highly efficient and selective absorption of H2S in phenolic ionic liquids: A cooperative result of anionic strong basicity and cationic hydrogen-bond donation

Abstract

A series of phenolic ILs containing different cations were synthesized and investigated for the absorption of H2S and CO2 in this work. It is interestingly found that the solubilities of H2S in these phenolic ILs are comparably high because of the strong interaction of basic phenolate anion with acidic H2S, while the solubilities of CO2 decrease significantly with the increase of cationic hydrogen-bond donation. Tetramethylguanidinium phenolate ([TMGH][PhO]), which is constructed with anion of strong basicity and cation of strong hydrogen-bond donating ability, is thus highlighted with both high solubilities of H2S (0.56mol/mol at 313.2K and 0.1bar, and 0.85mol/mol at 313.2K and 1bar) and high selectivities of H2S/CO2 (6.2 for the ratio of H2S solubility at 313.2K and 0.1bar vs. CO2 solubility at 313.2K and 1bar, and 9.4 for the ratio of H2S solubility at 313.2K and 1barvs. CO2 solubility at 313.2K and 1bar). Owing to the small molecular size of [TMGH][PhO], the absolute solubilities of H2S in it (2.68mol/kg at 313.2K and 0.1bar, and 4.08mol/kg at 313.2K and 1bar) are particularly fascinating, and much higher than other absorbents reported in the literature. Furthermore, [TMGH][PhO] is cost-effective in comparison with other functionalized ILs specifically designed for H2S capture, since it can be facilely synthesized from the one-step neutralization of readily available 1,1,3,3-tetramethylguanidine and phenol. The results obtained in this work indicate that [TMGH][PhO] is a promising candidate for the selective sweetening of natural gas.