Synthesis of Imidazolium based PILs and Investigation of Their Blend Membranes for Gas Separation

Abstract

Polymeric (ionic liquid) (PIL) copolymers bearing cationic imidazolium pendants and polar acrylic acid groups (P(VBCImY-co-AAx)), which both favor the interaction with CO2 molecules, have been synthesized and blended with film forming, high glass transition temperature aromatic polyether-based pyridinium PILs (PILPyr). The blend membranes based on the above combination have been prepared and characterized in respect to their thermal and morphological behavior as well as to their gas separation properties. The used copolymers and blends showed a wide range of glass transition temperatures from 32 to 286 °C, while blends exhibited two phase morphology despite the presence of polar groups in the blend components that could participate in specific interactions. Finally, the membranes were studied in terms of their gas separation behavior. It revealed that blend composition, counter anion type and acrylic acid molar percentage affect the gas separation properties. In particular, PILPyr-TFSI/P(VBCImTFSI-co-AA20) blend with 80/20 composition shows CO2 permeability of 7.00 Barrer and quite high selectivity of 103 for the CO2/CH4 gas pair. Even higher CO2/CH4. selectivity of 154 was achieved for PILPyr-BF4/P(VBCImBF4-co-AA10) blend with composition 70/30.

Poly(ethylene oxide)-Based Copolymer-IL Composite Membranes for CO2 Separation

“…For instance, the composite membrane containing 30 wt% IL1-[EMIM][TFSI] has a T g value of 15.4 °C, while an increase in IL1 content (40 wt%) is followed by a further T g decrease to −7.3 °C. This is due to the plasticization effect, resulting in flexible and soft membrane structures [ 18 ] with increased free volume and, consequently, lower T g , as already reported [ 35 , 38 ]. Regarding the effect of the anion’s chemical structure on T g , the comparison of composite membranes containing the same IL content (40 wt%) but ILs with different counter anions (TFSI - and C(CN) 3 - ), reveals that the T g of composite membranes containing IL2-[EMIM][C(CN) 3 ] is higher (4 °C) than the corresponding of composite membranes with IL1.…”

“…Regarding the precursor spectrum, the peak signal at 2868 cm −1 is assigned to methylene group vibrations of the PEO units [ 8 , 34 ]. In addition, the doublet peak at 1487 and 1471 cm −1 and the peak signal at 1583 cm −1 correspond to the C=C/C=N vibrations of the pyridine ring [ 8 , 35 ]. Considering that all ILs used in this work for the preparation of polymer-IL composite membranes contain a common imidazolium cation, the characteristic peak at 1574 cm −1 assigned to the imidazolium ring in plane symmetric/asymmetric stretch and –CH 2 (N)/-CH 3 (N)CN could not be observed in all composite membrane spectra due to overlapping with the peak at 1583 cm −1 .…”