Rational Design of Porous Ionic Liquids for Coupling Natural Gas Purification with Waste Gas Conversion

Removal of trace impurities for natural gas purification coupled with waste gas conversion is highly desired in industry. We here report a type of porous ionic liquids (PILs) that can realize the continuous flow separation of CH₄ /CO₂ /H₂ S and the conversion of the captured H₂ S to useful products. The PILs are synthesized through a step-by-step surface modification of ionic liquids (ILs) onto UiO-66-OH nanocrystals. The introduction of free tertiary amine groups on the nanocrystal surface endows these PILs with an exceptional ability to enrich H₂ S from CO₂ and CH₄ with impressive selectivity, while the permanent pores of UiO-66-OH act as containers to store an exceptionally higher amount of the selectively captured H₂ S than the corresponding nonporous ILs. Simultaneously, the tertiary amines as dual functional moieties offer effective catalytic sites for the conversion of the H₂ S stored in PILs into 3-mercaptoisobutyric acid, a key intermediate required for the synthesis of Captopril (an antihypertensive drug). Molecular dynamics, density functional theory calculations and Grand Canonical Monte Carlo simulations help understand both the mechanisms of separation and catalysis performance, confirming that the tertiary amines as well as the permanent pores in UiO-66-OH play vital roles in the whole procedure.