Application of Protic Ionic Liquids to CO2 Separation in a Sulfonated Polyimide-Derived Ion Gel Membrane

Abstract

It is of great interest to determine whether a relatively easily prepared and inexpensive protic ionic liquid (PIL) could be used in place of an aprotic ionic liquid (AIL) in a composite membrane for CO2 separation. We prepared mechanically reliable sulfonated polyimide (SPI) composite membranes with a PIL, [N124][NTf2] (N,N,N-butylethylmethylammonium bis(trifluoromethylsulfonyl)amide) by a solution casting method, and their mechanical, thermal, and gas separation (CO2 and N2) properties were compared with those of membranes incorporating an isomeric AIL, [N1123][NTf2] ([N1123]+, N,N,N,N-ethyldimethylpropylammonium). We discussed the influence of the presence or absence of active protons in the ILs on CO2 separation characteristics and the applicability of the PIL to a CO2 separation membrane. The SPI/PIL membrane exhibited a slightly lower selectivity, but higher permeability, than the SPI/AIL membrane. It is supposed that these differences originate from the difference in membrane structure and CO2 inte...