Novel pyrrolidinium-based polymeric ionic liquids with cyano counter-anions: High performance membrane materials for post-combustion CO2 separation

• Pyrrolidinium-based PILs containing cyano counter-anions were synthesized.
• The membrane forming ability of PIL–IL composites was evaluated.
• CO2 and N2 permeation properties were determined by the time-lag method.
• The best CO2/N2 separation performances were achieved for C(CN)3-based membranes.
• The first PIL-membrane outperforming the current CO2/N2 upper bound is reported.

Polymeric ionic liquids (PILs) are blossoming as a new generation of materials at the interface of many areas leading to a renaissance of the field of ionic polymers. Although PILs are interesting membranes materials for CO2 separation, additional research is still required to realize their full potential. In this work, pyrrolidinium-based polymers containing different cyano-functionalized counter-anions were synthesized by straightforward anion exchange reactions and characterized. Their film forming ability blended with different amounts of free ionic liquid (IL) was evaluated and the CO2 and N2 permeation properties through the prepared composites were determined. The results show that increasing the IL content in the composites not only increased CO2 permeability but also boosted the CO2/N2 permselectivity, leading to improved separation performances. The best performance was achieved for the C(CN)3-based membrane containing 60 wt% of IL, which overcomes the Robeson 2008 upper bound, with CO2 permeability of 439.3 Barrer and CO2/N2 permselectivity of 64.4. Therefore, the pyrrolidinium-based PIL combined with the [C(CN)3]− as counter-anion has potential for efficient post-combustion CO2 separation, suggesting the preparation of high performance membranes for industrial applications.

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