MOF-based Cellulose Acetate MMMs For an Advanced Propene/Propane Separation

Introduction.

The separation of propene/propane is among the most energy-intensive industrial processes because of the massive scale and the high energy demanded by the traditional cryogenic distillation method [1]. In this work, we report the preparation of MMMs consisting of cellulose acetate, 30% wt. [BMIM]⁺[Tf₂N]^‑, and 20% wt. of a series of ZIFs (ZIF-8, ZIF-67, and ZIF-8-67). The aim is to surpass the current state-of-the-art by incorporating bimetallic ZIF-8-67, supported by an ionic liquid as both a compatibiliser and a promoter of permeability.

Experimental/methodology.

Thin film composites were fabricated by spin-coating on PAN support. X-Ray diffraction, FT-IR, and SEM were performed. Single-gas and mixed-gas permeation measurements were applied [2].

Results and discussion.

The addition of 30%[BMIM]⁺[Tf₂N]^‑, by showing the trade-off behaviour, led to an increase in Propene permeability, compared to the neat CA membrane. The contribution of a series of ZIFs in ZIF/IL-CA MMMs increased the C₃H₆/C₃H₈ selectivity as well as the C₃H₆ permeability, with ZIF-8-67 outperforming its parent ZIFs. C₃H₆/C₃H₈ Mixed-gas measurements confirmed a selective performance of ZIF-8-67/IL-CA MMM.

Conclusion

Overall, this study highlights the significant role of bimetallic ZIF-8-67 in enhancing gas separation performance when incorporated into IL-CA membranes. The synergistic properties of Zn²⁺ and Co²⁺ in ZIF-8-67, combined with the role of [BMIM]⁺[Tf₂N]^- in addressing interfacial inconsistency, contributed to its superior gas transport properties and selectivity.

[1] A.C.C. Campos, et al., Ind. Eng. Chem. Res. 2018, 57, 10071–10085.

[2] S. C. Fraga, et al., J. Membr. Sci. 2018, 561, 39.