Ether-functionalized ionic liquid based composite membranes for carbon dioxide separation

Abstract

The efficient separation of CO₂ from other light gases has received growing attentions due to its importance in reducing greenhouse gas emissions and applications in gas purification. In this work, we developed a series of composite membranes composed of ether-functionalized pyridinium-based ionic liquids ([E_nPy][NTf₂]) and cellulose acetate (CA) polymer matrices to improve CO₂ separation performance. CA + [E_nPy][NTf₂] and CA + [C_nPy][NTf₂] composite membranes were fabricated by a casting method. The CO₂, N₂ and CH₄ permeabilities of the CA + IL composite membranes were measured, and the CO₂/N₂ and CO₂/CH₄ permselectivities were further calculated. The results showed that the CA + 40 wt% [E₁Py][NTf₂] composite membrane exhibits approximately a seven-fold increase in CO₂ permeability with CO₂/N₂ and CO₂/CH₄ permselectivities of 32 and 24, respectively. The characterization results showed that the mechanical properties and thermal stabilities of the CA + [E₁Py][NTf₂] composite membranes are affected by both plasticizing effect and affinity of the ILs for the gases, which also lead to the changes in the CO₂/N₂ and CO₂/CH₄ permselectivities. Compared with membranes containing the non-functionalized analogues [C_nPy][NTf₂], the addition of [E_nPy][NTf₂] improves the ideal permselectivities of CA + IL composite membranes, whereas it decreases slightly the gas permeabilities.