Engineering highly reversible hydrogen bonding interaction in pebax/deep eutectic solvent blended membranes for efficient separation of H2S from CO2 and CH4

Removal of H2S and CO2 is a key step for natural gas upgrading. However, further separating H2S/CO2 remains challenging as they are both acid gas with similar kinetic diameters, incurring complex processes and high cost for recovering H2S as sulfur resource. Herein we reported for the first time the introduction of highly reversible hydrogen bonding into Pebax/deep eutectic solvent (DES) blended membranes comprising 1-ethyl-3-methylimidazolium chloride ([Emim]Cl)-based DESs for selectively separating H2S from CO2 and CH4. The successful fabrication of Pebax/DES membranes was confirmed by various characterizations. Benefitting from the highly reversible DES–H2S hydrogen bonding interaction, the H2S permeability, H2S/CO2 and H2S/CH4 selectivity for single gas tests are high up to 1829 Barrer, 14.35 and 242.0, respectively. Based on solution-diffusion data, the acidic [Emim]Cl/levulinic acid (Lev) DESs are found to be the most efficient owing to the moderate DES–H2S hydrogen bonding interaction and thus fast H2S diffusion, which was also confirmed by quantum chemical calculations coupled with visual study of weak interactions. Permeation test of mixed gas shows that Pebax/DES blended membranes can steadily and efficiently separate H2S/CO2/CH4 (3/3/94 vol.%) ternary gas, with 1450 Barrer of H2S permeability, 34.5 of H2S/CO2 selectivity and 160 of H2S/CH4 selectivity obtained, which may indicates the applicability of these materials in desufuration of natural gas. To summarize, this work demonstrated the vital role of DES–H2S hydrogen bonding interaction in dominating H2S permeation, which may provide an easy but effective way for fabricating high-performance H2S sepration membranes.