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Open AccessArticle

Role of Cation Structure in CO2 Separation by Ionic Liquid/Sulfonated Polyimide Composite Membrane

1
Department of Chemistry and Biotechnology, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan
2
Research Center for Computational Design of Advanced Functional Materials (CD-FMat), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
*
Author to whom correspondence should be addressed.
Present address: Department of Materials and Life Sciences, Faculty of Science and Technology, Sophia University, 7-1 Kioicho, Chiyoda-ku, Tokyo 102-8554, Japan.
Membranes 2019, 9(7), 81; https://doi.org/10.3390/membranes9070081
Received: 9 May 2019 / Revised: 26 June 2019 / Accepted: 3 July 2019 / Published: 4 July 2019
The development of suitable separation technologies for the separation of carbon dioxide is a pressing technological requirement. The application of ion gel membranes for this purpose continues to stimulate a great deal of research, and in this study we focus on the chemical structure of the ionic liquid component in the ion gel, and its interactions with the sulfonated polyimide polymer. Whilst such membranes are known to give promising carbon dioxide separation properties together with mechanical strength and thin-film-processability, we further elaborate on how changing the cation of the ionic liquid from a typical imidazolium cation to a protic variant effects the physicochemical, thermal, and structural properties of the membranes, and how these changes further influence the carbon dioxide separation properties. We compare and contrast our findings with our earlier study on protic and aprotic ammonium-based ionic liquids, and highlight that for CO2 absorption behavior in the imidazolium systems, the importance of directionality of interactions (ion pairs exhibit a large energy stabilization only for a specific geometrical arrangement of cation and anion, e.g., hydrogen bonding rather than Coulombic interaction) between cation and anion applies not only to the protic system, but also to the nominally aprotic cation. Finally, we demonstrate that the phase separation behavior in the ion gels is an important factor in determining the carbon dioxide separation behavior. View Full-Text
Keywords: carbon dioxide separation membrane; protic ionic liquid; sulfonated polyimide carbon dioxide separation membrane; protic ionic liquid; sulfonated polyimide
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MDPI and ACS Style

Hayashi, E.; Hashimoto, K.; L. Thomas, M.; Tsuzuki, S.; Watanabe, M. Role of Cation Structure in CO2 Separation by Ionic Liquid/Sulfonated Polyimide Composite Membrane. Membranes 2019, 9, 81.

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