Immobilization of Ionic Liquids with a New Cellulose Ester Containing Imidazolium Cation for High-Performance CO₂ Separation Membranes

CO₂ gas separation is of significant importance to protect the environment and utilize the carbon resource. In this work, two kinds of new cellulose esters containing imidazolium cation, cellulose acetate (CA) 1-butyl-3-methylimidazolium chloride and CA 1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide (CA-BmimTf₂ N), are designed and synthesized. The resultant cationized cellulose esters effectively lock various ionic liquids (ILs) via electrostatic interactions. Due to the strong attraction interactions, the obtained cellulose ester/ILs composite membranes are uniform, smooth, and highly transparent. Moreover, the added ILs with a long alkyl chain in the cation and a bis(trifluoromethane sulfonyl)imide anion remarkably improve the CO₂ permeability of the cellulose ester/ILs membranes, because of the dramatic increase of the CO₂ diffusion rate. The CA-BmimTf₂ N/C₁₀ mimTf₂ N membranes exhibit the highest CO₂ permeability, which is 3800% higher than that of CA membrane and 1700% higher than that of CA-BmimTf₂ N membrane. More importantly, the CA-BmimTf₂ N/C₁₀ mimTf₂ N membranes have good mechanical properties and thermal stability. Such high-performance CO₂ separation membranes with high CO₂ permeability, high transparency, and good mechanical property have a huge potential in the practical utilization for gas separation.