Ionic liquid-based semi-interpenetrating polymer network (sIPN) membranes for CO₂ separation

This work explores the preparation of ionic liquid (IL)-based semi-interpenetrating polymer network (sIPN) membranes composed of poly(ethylene oxide) (PEO) network and linear nitrile butadiene rubber (NBR), incorporating up to 66 wt% of three ILs with a common cation ([C2mim]+) and different anions ([C(CN)3]–, [NTf2]– and [FSI]–). All sIPN/IL membranes were characterized by Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and puncture tests. Ideal CO2/N2 and CO2/H2 separation performances of the prepared sIPN/IL membranes were investigated at T = 20 °C and 35 °C, respectively, and 1 bar of feed pressure. The incorporation of both [C2mim][NTf2] and [C2mim][FSI] ILs allowed to obtain sIPN/IL membranes with higher IL contents (66 wt%) compared to previously reported PIL–IL membranes with similar IL structures (40 wt%). The membranes containing [NTf2]– and [C(CN)3]– anions showed improved thermal stability compared to the neat PEO/NBR sIPN, being thermally stable up to 300 °C. Although sIPN/IL membrane mechanical properties were affected by the incorporation of IL, all membranes revealed high elongation properties (elongation upon puncture = 68–170%), mainly due to the presence of NBR component in the sIPN structure. The highest CO2/N2 permselectivity was obtained for the sIPN/66 wt% [C2mim][C(CN)3] membrane, while the sIPN/66 wt% [C2mim][FSI] membrane revealed the highest CO2 and N2 permeabilities. The incorporation of 66 wt% of [C2mim][FSI] into the sIPN also showed superior CO2/H2 separation performance, with a CO2 permeability of 727 Barrer and a CO2/H2 permselectivity of 10.9.