Enhanced separation of CO2/CH4 with tetramethylammonium ionic liquids modified by ethylene glycol through hydrogen bond synergy

Efficient CO₂/CH₄ separation is crucial for the value-added utilization of natural gas, shale gas, and biomethane. This work developed a series of tetramethylammonium-based ionic liquids (ILs) containing ethylene glycol (EG) as high-performance absorbents. Among them, the [N₁₁₁₁][1,2,4-Tz]/EG (1:1) system exhibited a high CO₂ capacity of 0.205 g/g at 40 °C and 100 kPa, together with exceptional CO₂/CH₄ selectivity (574). The separation performance was finely tuned by varying the EG content, which regulated the hydrogen-bond network within the hybrid system, leading to a remarkably low regeneration energy of 1.13 GJ·t −1 CO₂, superior to conventional ILs and amine solvents. Mechanistic studies unveiled that the hydrogen bonds between EG and IL anions not only promoted CO₂ activation but also directed the reaction pathway toward the formation of thermodynamically stable carbonate species (RCO₃ − ) rather than carbamates, thus facilitating the low-energy regeneration process. This study demonstrates that hydrogen bond modulation in EG-IL systems provides a sustainable and efficient strategy for CO₂ capture.