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 H 2 S and CO 2 in this work. It is interestingly found that the solubilities of H 2 S in these phenolic ILs are comparably high because of the strong interaction of basic phenolate anion with acidic H 2 S, while the solubilities of CO 2 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 H 2 S (0.56 mol/mol at 313.2 K and 0.1 bar, and 0.85 mol/mol at 313.2 K and 1 bar) and high selectivities of H 2 S/CO 2 (6.2 for the ratio of H 2 S solubility at 313.2 K and 0.1 bar vs. CO 2 solubility at 313.2 K and 1 bar, and 9.4 for the ratio of H 2 S solubility at 313.2 K and 1 bar vs. CO 2 solubility at 313.2 K and 1 bar). Owing to the small molecular size of [TMGH][PhO], the absolute solubilities of H 2 S in it (2.68 mol/kg at 313.2 K and 0.1 bar, and 4.08 mol/kg at 313.2 K and 1 bar) 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 H 2 S 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.